Despite significant advancements in therapeutic approaches to triple-negative breast cancer, treatments remain relatively ineffective once metastasis occurs. The introduction of immunotherapy has revolutionized oncological therapies, yet significant hurdles remain before its full potential can be realized. In this review, we examine immune escape mechanisms shared between pregnancy (the 'fetal allograft') and cancer. We discuss the use of abortion-inducing agents in the context of cancer immunotherapy, and we also provide rationale and preliminary data on FloraStilbene™, a combination of the polyphenol antioxidant pterostilbene and the glucocorticoid receptor antagonist mifepristone, for the stimulation of anticancer immunity.

Keywords: triple-negative breast cancer, metastasis, cancer immunotherapy, immune escape mechanisms, fetal allograft, pregnancy and cancer parallels, abortion-inducing agents, florastilbene™, immune modulation.

Breast cancer is the most prevalent oncological condition in females and represents a significant medical problem.¹ According to a 2022 estimate by the American Cancer Society, there were 287,850 newly diagnosed cases of breast cancer with invasive properties. From 1989 to 2019, the mortality rate from breast cancer was reported to be 41% higher in black women compared to white women, presumably due to later diagnoses.² It is widely accepted that about 10% of breast cancers are associated with mutations, such as alterations in BRCA1 and BRCA2.³ Breast cancer is typically categorized based on the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), with cells lacking all three—referred to as 'triple-negative'- considered the most invasive.⁴

The treatment of early-stage breast cancer typically involves a combination of surgery,⁵ radiation therapy,⁶ and systemic therapy (such as chemotherapy, hormonal therapy, or targeted therapy).⁷ The specific treatment plan depends on various factors, including the size and location of the tumor, its spread to the lymph nodes, and the patient’s overall health condition and preferences. The most common surgical options are lumpectomy or mastectomy. Radiation therapy is often recommended after surgery to help eradicate any remaining cancer cells and reduce the risk of recurrence, using high-energy radiation to target the affected area of the breast. Systemic therapy may also be recommended for some patients with early breast cancer, particularly if the cancer is hormone receptor-positive or HER2-positive.

As the disease progresses, the primary goal of treating advanced breast cancer shifts towards controlling the spread of the cancer, managing symptoms, and improving the patient’s quality of life.⁸ Common treatments for advanced breast cancer include: systemic therapy- such as chemotherapy, hormone therapy, targeted therapy, and immunotherapy-designed to attack cancer cells throughout the body; surgery to remove or debulk the primary tumor or large metastases, or to alleviate symptoms such as pain or dyspnea; radiation therapy, which may be used to shrink tumors and relieve symptoms like pain, neurological symptoms, or dyspnea; and palliative care, focusing on providing support to patients and families by managing symptoms, maintaining quality of life, engaging in goals-of-care discussions, and addressing the emotional and psychological effects of the disease. Treatment for advanced breast cancer is typically focused on managing the disease rather than curing it, and thus may be ongoing and change over time depending on the cancer’s response to therapy.

Historically, cancer immunotherapy has focused on melanoma and renal cancers, with the possibility of immunotherapy for breast cancer being relatively understudied.⁹ Due to the higher incidences of immunologically mediated spontaneous remissions in these two cancers, they have traditionally been viewed as 'immunogenic'.^10–15 This review will discuss more recent findings suggesting that immune responses in breast cancer may exist and can be therapeutically leveraged.¹⁶

Immunotherapy offers the ability to specifically target and kill tumor cells without some of the toxicity associated with traditional oncological therapies such as radiation and chemotherapy. Despite initial controversies regarding the natural role of the immune system in controlling cancer development, a theory known as 'immunosurveillance',¹⁷ it is now widely accepted that the immune system not only keeps cancer at bay but also that that proper immune stimulation can be used as a therapy for cancer.¹⁸ Initial clinical approvals of immunotherapy began with immunogenic tumors such as melanoma and kidney cancer.¹⁹ but it eventually expanded to other cancers, including breast cancer.²⁰

This expansion is underscored by the recognition of tumor immunogenicity, which is determined partly by whether immune cells infiltrate the cancer and whether this correlates with a better or worse prognosis. Melanoma, for instance, was identified as immunogenic through studies demonstrating that 'tumor-infiltrating lymphocytes' (TILs) were associated with enhanced survival.²¹ The active role of TILs in suppressing the tumor was demonstrated in reports where TILs were extracted from patients, expanded outside the body—free from the tumor's immunosuppressive pressures—and then re-infused into the same patients.²² In three consecutive clinical trials using TILs, objective response rates between 49% and 72% were observed in advanced melanoma.²³ Furthermore, it was shown that the re-infused cells homed back to the tumor,^24,25 leading to the discovery of the first tumor-specific antigens, the melanoma-associated antigen (MAGE) family.²⁶

Similarly, in breast cancer, numerous studies have demonstrated a correlation between TILs and improved survival. Ren et al. examined 68 patients with triple-negative breast cancer and found a strong correlation between tumor infiltration by T cells, specifically CD3 and CD8, and longer progression-free survival.²⁷ Similar findings have been reported by other independent researchers.^28,29 An increased number of TILs is associated with a better response to therapy.³⁰ It is believed that TILs control the tumor through direct killing, primarily by CD8 cytotoxic lymphocytes,³¹ as well as by suppressing tumor growth and angiogenesis, mediated by the production of cytokines such as interferon-gamma.³² The secretion of perforin and granzyme B by CD8 T cells, known mechanisms of cellular destruction, logically correlates with improved survival, a finding that has indeed been demonstrated.³³

Building on the role of specific immune cells, T cells are known to eradicate cancer by recognizing molecular signatures on tumors known as “tumor-associated antigens.” Cancerous cells, to gain an advantage over normal cells, often start producing new proteins that are not typically found in the adult body, usually mutated versions of existing proteins. When cancer begins producing these proteins, T cells recognize and attempt to eliminate the tumor.

T cells are considered part of the adaptive immune system, because of their ability to create immunological memory. Innate immune system cells, such as natural killer (NK) cells, are another mechanism of protection from neoplasia. Unlike T cells, which recognize peptides presented on HLA molecules, NK cells eliminate cells that lack HLA molecules. HLA molecules serve as a 'negative signal' that prevents NK cell activation; a mechanism central to the 'missing self' hypothesis.³⁴ Originally thought of as the immune system’s 'backup' when cancer cells down regulate HLA to evade T cell-mediated killing, NK cells also target cells expressing proteins indicative of 'cellular stress.' Given that cancer cells produce proteins at a much faster rate than normal cells, they express these 'danger proteins,' which activate NK cells.³⁵ Studies have demonstrated that breast cancer patients with higher levels of NK cell activity tend to live longer than those with lower levels.³⁶

If the body has such potent means of protecting itself against cancer, why do tumors arise and progress? One of the main reasons is that cancer effectively leverages components of the immune system that down regulate immunity after immune recognition. One such immune regulatory mechanism involves T regulatory (Treg) cells. These cells have been demonstrated to protect the body against autoimmunity,³⁷ transplant rejection,³⁸ and immunologically mediated miscarriages.³⁹ Importantly, this mechanism is co-opted by cancer cells to escape immune destruction.

One example of this is a study by Bates et al. who assessed the numbers of Treg cells (identified by FOXP3 expression) in tissue microarray cores from pure ductal carcinoma in situ (DCIS), invasive breast cancer, or from comparable areas of normal terminal duct lobular breast tissue. Treg cell numbers were significantly higher in samples from in situ and invasive breast carcinomas than in normal breast tissue. Importantly, high numbers of FOXP3-positive Treg cells identified patients with DCIS at increased risk of relapse and patients with invasive tumors with both shorter relapse-free and overall survival. Another important finding in the same study was that high numbers of FOXP3-positive Treg cells can identify patients at risk of relapse after 5 years.⁴⁰ The correlation between Treg numbers and poor prognosis has been reported by other studies.^41–43 Interestingly, some drugs used in breast cancer, such as estrogen blockers, may reduce Treg numbers.⁴⁴

Besides being associated with poor prognosis Tregs also play a role in response to therapy. In a clinical study, 93 patients with breast cancer diagnosed by core-needle biopsy (CNB) and treated with primary systemic chemotherapy (PSC) were examined. CNB and surgically resected specimens were stained with a FOXP3 mouse monoclonal antibody to compare the numbers of FOXP3- positive cells in the tumors before and after PSC. A median cut-off value of >16.3/high power field (HPF) and >6.6/HPF defined high numbers of Tregs in CNB and in surgical specimens, respectively. The patients were assigned into four groups (HH, high number of FOXP3-positive cells in both CNB and surgical specimen; LL, low number in both specimens; HL, high in CNB and low in the surgical specimen; LH, low in CNB and high in surgical specimen). Lymph vessel invasion-positive, clinically non-responder and ER-negative tumors contained significantly more FOXP3- positive cells after PSC. Prognosis was better among patients with low numbers than high numbers of FOXP3-positive cells both in CNB and in surgically resected specimens. In multivariate analysis, the LL group demonstrated significantly better recurrence-free survival than the non-LL group (LH, HL, and HH). These findings suggest that the number of FOXP3-positive cells identified during PSC represents a promising predictive factor that might also be an important therapeutic target for breast cancer.⁴²

In another study, it was shown that pathologic complete responses (pCR) to chemotherapy in breast cancer patients were associated with decreases of intratumor Tregs. High CD8 infiltration and no Foxp3 infiltration on final histologic specimens were independently associated with pCR. This study suggests that Treg cells may be suppressing the activity of effector cells that otherwise could be capable of killing the tumor.⁴⁵

In the search novel immune stimulators researchers have exampled biological situations that may resemble the growth and progression of neoplasia. Correlations between cancer and pregnancy have previously been made based on shared characteristics such as angiogenesis, cellular trafficking, and immune modulation.⁴⁶ The process of immunologically mediated miscarriage is associated with similar types of immune responses as those seen in tumors regressing from immunotherapy, specifically, activation and infiltration of NK cells,^47–51 macrophages,^52–54 and CD8 cytotoxic T cells.⁵⁵ Given these similarities, the authors questioned whether agents that terminate pregnancy might also have effects against cancer. Abortogenic agents have been shown to possess anticancer properties; these include agents that suppress indoleamine 2,3-dioxygenase,^56–61 myeloid-derived suppressor cells,^62–67 and Treg,^68–71 as well as checkpoint inhibitors.⁷² Furthermore, cancer and pregnancy share numerous means of immune evasion, including over-expression of Fas ligand,^73–76 hCG,^77–83 HLA-G,⁸⁴ PD-L1,^85–93 TIM-3,^72,94,95 arginase,^96–99 and VISTA.^100–102

RU-486, now known as mifepristone, was originally synthesized by Georges Teutsch based on experiments aimed at developing artificial steroids. The name originates from the name of the company that developed it, Roussel-Uclaf (RU), and it was compound number 38486, shortened from RU-38486 to RU-486. This compound was first noted for its potent binding to the glucocorticoid receptor and for blocking glucocorticoid biological activities in tissue culture. Subsequently, it was found to block progesterone receptor activity only in the presence of progesterone. This finding led to studies on its abortifacient effects, which are associated with erosion of the endometrium, detachment of the chorion from the decidua basalis, atrophy of the corpus luteum, enhanced uterine contractibility, cervical softening and dilatation, and eventual expulsion of the embryo and endometrium.¹⁰³ Although the abortifacient effects have been ascribed to progesterone receptor antagonism, there is increasing evidence that immunological mechanisms such as suppression of Treg cell activity play a significant role in its action.¹⁰⁴ Given the fundamental role of Treg cell activity in cancer’s escape from the immune response, if RU486 can reduce the number or activity of these cells, it may have a potential role as a cancer therapeutic.

One suggestion that RU-486 may induce abortion in part through immune modulation came from Mao et al., who showed that progesterone increases the numbers of Treg cells as well as augmenting their immune suppressive activity. Blocking progesterone signaling with RU-486 resulted in a loss of Treg number and activity, which correlated with immunological cell infiltration, inflammatory cytokine secretion, and eventual fetal loss.¹⁰⁵ A direct cause-and-effect relationship between Treg loss and fetal death was illustrated in a publication in which RU-486 was administered to pregnant mice, resulting in impaired Treg functional competence, increased cytotoxic CD8 T cells, and fetal loss. Importantly, adoptive transfer of Treg cells- but not conventional T cells- alleviated fetal loss.¹⁰⁴ Essentially, this shows that depletion of Treg cells is a mechanism of action, as the transfer of healthy Treg cells prevented abortion.

Besides inducing immunity by reducing Treg cells, RU-486 also augments the maturation of dendritic cells. These cells, classically known as 'professional antigen-presenting cells' for their unique ability to activate naïve T cells,¹⁰⁶ promote the generation of Treg cells and a healthy pregnancy when in an immature state.^107,108 Conversely, when dendritic cells are mature, they no longer induce the generation of Treg cells but instead lead to immune activation.¹⁰⁹ Just as Treg cells allow for cancers to escape immune killing, immature dendritic cells have been shown to provide means of tumor immune evasion through the induction of energy in tumor-reactive T cells or conversion to Treg cells.^110,111

Yinghua et al., conducted a series of experiments to assess the ability of RU-486 to alter immunity by DC manipulation.¹¹² They showed that the drug promoted the expression of the DC maturation markers CD80, CD86, and ICAM-1 while decreasing the cancer-associated immune suppressive molecules indoleamine 2,3-dioxygenase^113–115 and TGF-beta.¹¹⁶ Importantly, when Tregs were cultured with RU486-cultured DC, the Tregs lost suppressive activity. These experiments suggest that RU486 possesses a direct maturation-inducing effect on DC, which blocks Treg generation through modulating the upstream cytokine TGF-beta.

It appears that some parallels may exist between the process of RU-486 induction of immunological reactions against the 'fetal allograft' and immune-mediated tumor rejection. If this is the case, then it is important to provide an overview of existing work evaluating this abortogen in the context of oncology.

The mechanisms of cancer immunity induced by RU-486 could involve the reduction of Tregs, which is associated with immune suppression in numerous cancers, inhibition of glucocorticoid signaling, and suppression of transforming growth factor beta (TGF-beta) activity. In one series of experiments, BALB/c-green fluorescent protein (GFP)+ bone marrow (BM) cells were transplanted into immune deficient NSG mice to generate an immune competent NSG/BM-GFP+ (NSG-R) mouse model. Treatment with RU-486 inhibited the growth of 59-2-HI tumors and caused alterations in the tumor microenvironment similar to those observed in fetal loss. Tumors in RU-486-treated immune competent mice showed increased infiltration of F4/80+ macrophages, natural killer, and CD8 T cells, displaying a central memory phenotype. Mechanistically, RU-486 induced immunogenic cell death both in vitro and in vivo, as depicted by the expression and subcellular localization of the alarmins calreticulin and HMGB-1, and the induction of a gene program characteristic of immunogenic cell death. Moreover, RU-486-treated tumor cells efficiently activated immature DC, evidenced by enhanced expression of MHC-II and CD86, and induced a memory T-cell response, attenuating tumor onset and growth after re-challenge. Of relevance to current clinical oncology, RU-486 treatment increased the sensitivity of tumors to inhibition of the PD-L1 checkpoint.¹¹⁷

To demonstrate that RU-486 induces anticancer immunity through immune stimulation and not necessarily progesterone inhibition, a series of experiments were conducted using several human prostate cancer cell lines in murine immune deficient and immune competent hosts. The experiments assessed effects of RU-486 alone or in combination with IL-12 adenoviral gene therapy. Treatment of human PC3 prostate xenograft (androgen independent) or TRAMP-C1 tumors (androgen receptor positive) with the combination Ad5IL-12 vector and RU-486 produced significantly better therapeutic efficacy compared to controls. Additionally, combination therapy increased the capacity of tumor sentinel lymph node lymphocytes to produce Granzyme B in response to tumor cell targets. Finally, combination therapy tended towards a decrease in CD4+/FoxP3+ T regulatory cell populations in the draining lymph nodes. These experiments provide in vivo support for the hypothesis that RU-486 directly acts as an immune stimulator.¹¹⁸

In addition to its immune modulating anticancer effects, RU-486 has been reported to directly suppress neoplasia in several animal models. For example, in one study, sixty-one mice developing spontaneous leukemia were treated with RU-486 and 33 controls with olive oil. Quality of life was determined by body conditioning score (BCS). Treatment was initiated when the mice were 6 months old. Within 2 weeks of therapy, 11.4% of the RU-486 treated mice died compared to a 50% mortality in the control group. The BCS was 5 (highest quality) in 82% of treated mice vs. 11% of controls after 2 weeks of therapy.¹¹⁹ Similar therapeutic responses were seen in a lung cancer model where mice received RU-486 at 0.3 mg three times weekly from 8 weeks compared to olive oil in the controls. The survival at one year for mice treated with mifepristone was 57.6% vs. 26.6% for controls.¹²⁰

Clinical signals exist suggesting the potential utility of RU-486 in oncology. In one report, RU-486 was administered at 200 mg per day orally to two patients with stage IV colon cancer suffering from extensive metastases. This regimen was well-tolerated, and both patients not only survived far longer than expected but also experienced marked improvements in quality of life and increased energy upon initiating RU-486. Though the metastatic lesions did not disappear, no new ones appeared for a substantial time, and the existing ones did not grow.¹²¹

In contrast to many therapeutic interventions, RU-486 appears not to be limited by the blood-brain barrier. A 43-year-old male with end-stage stage IV glioblastoma multiforme was treated exclusively with RU-486 at 200 mg orally daily. The patient exhibited definite palliative effects for several weeks and lived significantly longer than predicted before treatment.¹²²

Additionally, two case reports describe the administration of mifepristone monotherapy daily at 200 mg to a moribund woman with never-treated metastatic lung cancer and a male with bilateral renal cell carcinoma who had undergone only a unilateral hemi nephrectomy. Both patients experienced long-term high-quality survival- 5 years for the patient with lung cancer, with complete remission of all lung lesions, and 12 years for the male patient with kidney cancer. Neither patient reported any treatment-associated adverse effects.¹²³

Interestingly, RU-486 may also show activity in patients where other treatments have failed. A 68-year-old woman suffering from metastatic non-small cell lung cancer progressed despite treatment with a checkpoint inhibitor (nivolumab) and three rounds of multi-agent chemotherapy. After 1.5 years of treatment with single-agent mifepristone, her cancer remained stable, with some tumor regression reported.¹²⁴ Similar therapeutic outcomes were published for cases of pancreatic cancer,¹²⁵ leukemia, and osteosarcoma.¹²⁶

The therapeutic potential of RU-486 has not been restricted to solid tumors alone. In one report, an 81-year-old woman with chronic lymphocytic leukemia, which had progressed to an acute rapidly progressing stage, was treated with only 200 mg of mifepristone daily. The patient showed dramatic improvement upon initiation of therapy and maintained remission until the time of publication, which was 12 months.¹²⁷

Res Nova Biologics Inc has screened various compounds for augmentation of RU-486's immune modulatory efficacy. The naturally derived compound pterostilbene was identified as possessing the strongest ability to enhance multiple cancer inhibitory biological activities of RU-486. This compound is a naturally derived analogue of resveratrol¹²⁸ and has been shown to possess therapeutic activity in a wide variety of conditions, including diabetes, aging, depression, and brain injury.¹²⁹

Mechanistically, pterostilbene exhibits several interesting biological functions, including activation of NRF2, which mediates numerous anti-apoptotic activities,^130,131 suppression of NF-kappa,¹³² and inhibition of p38 MAP kinase,¹³³ both potent mediators of inflammation. Interestingly, the effects of pterostilbene on cancer can be considered paradoxical; it appears to have anti-apoptotic effects in non-malignant cells,¹³⁴ while inducing death in transformed cells both in vitro^135,136 and in vivo.¹³⁷

In the context of immunotherapy, pterostilbene possesses numerous interesting properties. According to United States Patent #9682047B2, administration of pterostilbene was capable of enhancing the therapeutic effects of interleukin-2 in a murine model of melanoma. The immune stimulatory activities of pterostilbene appear to function through the suppression of feedback inhibition loops. For example, immune activation using agents such as interleukin-2 or toll-like receptor activators stimulates the immune suppressive enzyme cyclo-oxygenase 2 (COX-2),^138,139 which produces prostaglandin E2, a known promoter of Treg cell generation dependent on COX-2 activity.¹⁴⁰

Another mechanism by which pterostilbene stimulates antitumor immunity is by down regulating oxidative stress and neutrophil activity, which are associated with numerous tumors and the suppression of T cell immunity through cleavage of the TCR-zeta chain.¹⁴¹ Pterostilbene has been shown to suppress neutrophil activation in various systems, including a melanoma model of metastasis,¹⁴² a cardiac ischemic reperfusion model,¹⁴³ and an arthritis model.¹⁴⁴ Mechanistically, pterostilbene induces accelerated apoptosis of activated neutrophils through a caspase-3 dependent mechanism and suppresses the production of oxidative radicals at a pre-apoptotic stage.¹⁴⁵

Additionally, augmentation of tumor sensitivity to NK cell-mediated killing by pterostilbene has been reported. Yulin et al reported that pterostilbene treatment enhanced the expression of NK group 2 member D (NKG2D) ligands- major histocompatibility complex class I chain-related proteins A and B (MICA/B) on prostate cancer cells. These molecules are typically seen as activators of NK natural cytotoxicity towards cancer cells. The authors found that inhibition of miR-20a by pterostilbene was occurring, which normally silences expression of the 3' untranslated region (UTR) of MICA/B. Blocking expression of miR-20a by pterostilbene results in up regulation of MICA/B, making prostate cancer cells significantly more sensitive to NK-mediated killing.¹⁴⁶ Given that RU-486 enhances NK activity, a potent synergy is anticipated between these two agents. Accordingly, we initiated a series of experiments to assess this hypothesis.

In order to assess whether FloraStilbene possesses ability to suppress tumor growth, the classical triple negative 4T1 model was utilized. 4T1 cells were grown in RPMI 1640 media in a fully humidified atmosphere with 5% carbon dioxide. 4T1 triple-negative murine breast cancer cells were administered to female BALB/c mice at a concentration of 500,000 cells per mouse in the mammary pad. Mice were treated with either a) saline; b) pterostilbene at 2 mg/kg; c) RU-486 at 3 mg/kg; or d) a combination of pterostilbene and RU-486. Each treatment group consisted of 10 mice. As shown in Figure 1 below, significant synergy was observed in the regression of this model of breast cancer.

Figure 1 Suppression of 4T1 growth by FloraStilbene.

FloraStilbene™ increases NK cell activity. Tumor-bearing mice treated as described above were sacrificed at the indicated times, and NK activity was assessed using the MTT cytotoxicity assay against labeled 4T1 cells. It is known that MTT readings correspond to the number of cells present in the exponential growth phase. To utilize the MTT assay, MTT liquid was made at (10µl MTT solution in each 100µl media) added to each well and the plates were then incubated at 37°C for 5 hours. Subsequently, the remaining MTT solution was discarded DMSO was added to each well to dissolve the formazan crystals. The plates were shaken for 5 minutes on a plate shaker to ensure adequate solubility. Absorbance readings of each well was performed at 540 nm (single wavelength) using a multi scan plate reader.

NK cells were extracted from spleens using Magnetic Activated Cell Sorting (MACS) by Miltenyi Biotec, according to the manufacturer's instructions. NK cells were plated at a 10 to 1 ratio. As seen in Figure 2 below, an increase in NK cell activity was observed with FloraStilbene™ treatment.

Figure 2 FloraStilbene increases NK activity.

In order to mechanistically assess the immuno modulatory activity of FloraStilbene, the expression of the TCR zeta chain was assessed. Erythrocyte depleted samples were examined by flow cytometry using intracellular cytokine staining. Briefly, 2 mm monensin was added to T cells for 4 h. Cells were fixed with 2% PFA and permeabilized with FACS buffer (PBS supplemented with 5% FBS and 0.1% sodium azide) containing 0.1% saponin. An anti-TCR zeta chain antibody, was used for indirect staining prior to a secondary goat antimouse R-phycoerythrin-conjugated antibody. Protection from loss of TCR-zeta was observed, suggesting a possible mechanism of immune-preservation/immune stimulation by FloraStilbene.

Clinical uses of FloraStilbene

Stimulation of immunity to cancer is major unrealized goal. Preliminary data presented supports the possible use of combinations of pterostilbene and RU486. These studies have limitations, however early clinical responses have been observed which will be the subject of future publications.

We believe that increasing the activity of NK cells could enhance the efficacy of drugs already on the market for the treatment of breast cancer. For example, trastuzumab (Herceptin) represents a significant therapeutic modality whose efficacy is influenced by NK activity. In one study, immunological responses were assessed in 26 patients receiving trastuzumab monotherapy as maintenance management after chemotherapy (8 mg/kg load and then standard doses of 6 mg/kg every 3 weeks). Cytotoxic activity against the MHC class I-negative standard NK target K562 cell line and HER2-specific ADCC against a trastuzumab-coated HER2-positive SKBR3 cell line were assessed in peripheral blood mononuclear cells (PBMC) harvested after the first standard dose. After six months, seventeen patients were scored as responders and nine as non-responders according to the RECIST criteria, while progression-free survival (PFS) was calculated during a 12-month follow-up. It was shown that the responders had significantly higher levels of both NK and ADCC activities that were not different from those of eleven normal controls. The NK activity of the non-responders was significantly lower than that of the normal controls. At twelve months, there was a marked correlation between PFS and NK activity only. PFS was significantly longer in patients with high levels of NK activity, whereas its pattern was unrelated to high or low ADCC activity.¹⁴⁷

Based on the direct and indirect cancer inhibiting properties of RU486 and pterostilbene, as well as our pilot data, we conclude that the FloraStilbene product being developed by Res Nova Biologics possesses promising potential as a monotherapy or as an adjuvant to existing immunotherapies.

None.

The authors declare that there is no conflicts of interest.

1. Sung H, et al. Global cancer statistics 2020: Globocan estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2021;71(3):209–249.
2. Breast cancer research highlights.
3. Kuchenbaecker KB, Hopper JL, Barnes DR, et al. Risks of breast, ovarian, and contralateral breast cancer for BRCA1 and BRCA2 mutation carriers. JAMA. 2017;317(23):2402–2416.
4. Szulc A, Wozniak M. Targeting pivotal hallmarks of cancer for enhanced therapeutic strategies in triple–negative breast cancer treatment–in vitro, in vivo and clinical trials literature review. Cancers (Basel). 2024;16(8):1483.
5. Lagendijk M, Maaren MC, Saadatmand S, et al. Breast conserving therapy and mastectomy revisited: breast cancer-specific survival and the influence of prognostic factors in 129,692 patients. Int J Cancer. 2018;142(1):165–175.
6. Rajan KK, Fairhurst K, Birkbeck B, et al. Overall survival after mastectomy versus breast–conserving surgery with adjuvant radiotherapy for early–stage breast cancer: meta–analysis. BJS Open. 2024;8(3):zrae040.
7. Brett JO, Mayer EL. new developments in systemic management for high–risk early–stage hormone–receptor–positive, HER2–negative breast cancer. Curr Treat Options Oncol. 2023;24(6):594–610.
8. Premji SK, O'Sullivan CC. Standard–of–care treatment for HER2+ metastatic breast cancer and emerging therapeutic options. Breast Cancer (Auckl). 2024;18:11782234241234418.
9. Bayraktar S, Batoo S, Okuno S, et al. Immunotherapy in breast cancer. J Carcinog. 2019;18:2.
10. Cervinkova M, Kucerova P, Cizkova J. Spontaneous regression of malignant melanoma – is it based on the interplay between host immune system and melanoma antigens? Anticancer Drugs. 2017;28(8):819–830.
11. Gray A, Grushchak S, Mudaliar K, et al. The microenvironment in primary cutaneous melanoma with associated spontaneous tumor regression: evaluation for T–regulatory cells and the presence of an immunosuppressive microenvironment. Melanoma Res. 2017;27(2):104–109.
12. Saleh F, Renno W, Klepacek I, et al. Direct evidence on the immune–mediated spontaneous regression of human cancer: an incentive for pharmaceutical companies to develop a novel anti–cancer vaccine. Curr Pharm Des. 2005;11(27):3531–3543.
13. Cole WH. Spontaneous regression of cancer and the importance of finding its cause. Natl Cancer Inst Monogr. 1976;44:5–9.
14. Crisci A, Corsale I, Abrami F, et al. Spontaneous regression of lung metastases from renal cell carcinoma: the importance of immunogenetic factors and a review of the literature. Minerva Urol Nefrol. 2008;60(2):123–135.
15. Malik M, Michalak M, Sigorski D, et al. Spontaneous regression of metastatic renal cell carcinoma after cytoreductive nephrectomy followed by relapse at 3 years. Pol Arch Intern Med. 2024;134(3):16681.
16. D'Alessandris N, Santoro A, Arciuolo D, et al. What can trigger spontaneous regression of breast cancer? Diagnostics (Basel). 2023;13(7):1224.
17. Prehn RT. Immuno surveillance, regeneration and oncogenesis. Prog Exp Tumor Res. 1971;14:1–24.
18. Michaels E, Chen N, Nanda R. The role of immunotherapy in triple–negative breast cancer (TNBC). Clin Breast Cancer. 2024;24(4):263–270.
19. Mishra AK, Ali A, Dutta S, et al. Emerging trends in immunotherapy for cancer. Diseases. 2022;10(3):60.
20. Wong RS, Ong RJ, Lim JS. Immune checkpoint inhibitors in breast cancer: development, mechanisms of resistance and potential management strategies. Cancer Drug Resist. 2023;6(4):768–787.
21. Elder D. Tumor progression, early diagnosis and prognosis of melanoma. Acta Oncol. 1999;38(5):535–547.
22. Chiou SH, Sheu BC, Chang WC, et al. Current concepts of tumor–infiltrating lymphocytes in human malignancies. J Reprod Immunol. 2005;67(1–2):35–50.
23. Rosenberg SA, Dudley ME. Adoptive cell therapy for the treatment of patients with metastatic melanoma. Curr Opin Immunol. 2009;21(2):233–240.
24. Prins RM, Shu CJ, Radu CG, et al. Anti–tumor activity and trafficking of self, tumor–specific T cells against tumors located in the brain. Cancer Immunol Immunother. 2008;57(9):1279–1289.
25. Burke KP, Markson SC, Sharpe AH. Tracking tumor–specific CD8(+) T cell responses. Trends Immunol. 2023;44(5):326–328.
26. Boon T, Cerottini JC, Eynde BV, et al. Tumor antigens recognized by T lymphocytes. Annu Rev Immunol. 1994;12:337–365.
27. Ren X, Song Y, Pang J, et al. Prognostic value of various immune cells and immunoscore in triple–negative breast cancer. Front Immunol. 2023;14:1137561.
28. Sun GY, Zhang J, Wang BZ, et al. The prognostic value of tumour–infiltrating lymphocytes, programmed cell death protein–1 and programmed cell death ligand–1 in Stage I–III triple–negative breast cancer. Br J Cancer. 2023;128(11):2044–2053.
29. Sun YP, Ke YL, Li X. Prognostic value of CD8(+) tumor–infiltrating T cells in patients with breast cancer: a systematic review and meta–analysis. Oncol Lett. 2023;25(1):39.
30. Agarwal G, Chanthar KMMV, Katiyar S, et al. Predictive and prognostic role of tumor–infiltrating lymphocytes in patients with advanced breast cancer treated with primary systemic therapy. World J Surg. 2023;47(5):1238–1246.
31. Yannelli JR, Hyatt C, McConnell S, et al. Growth of tumor–infiltrating lymphocytes from human solid cancers: summary of a 5–year experience. Int J Cancer. 1996;65(4):413–421.
32. Oshi M, Newman S, Tokumaru Y, et al. Intra–tumoral angiogenesis is associated with inflammation, immune reaction and metastatic recurrence in breast cancer. Int J Mol Sci. 2020;21(18).
33. Li CH, Kuo WH, Chang WC, et al. Activation of regulatory T cells instigates functional down–regulation of cytotoxic T lymphocytes in human breast cancer. Immunol Res. 2011;51(1):71–79.
34. Ljunggren HG, Karre K. In search of the 'missing self': MHC molecules and NK cell recognition. Immunol Today. 1990;11(7):237–244.
35. Santara SS, Lee DJ, Crespo A, et al. The NK cell receptor NKp46 recognizes ecto–calreticulin on ER–stressed cells. Nature. 2023;616(7956):348–356.
36. Mamessier E, Bertucci F, Sabatier R, et al. "Stealth" tumors: breast cancer cells shun NK–cells anti–tumor immunity. Oncoimmunology. 2012;1(3):366–368.
37. Goswami TK, et al. Regulatory T cells (Tregs) and their therapeutic potential against autoimmune disorders -advances and challenges. Hum Vaccin Immunother. 2022;18(1):2035117.
38. Salazar EKA, Hernández AC, Cruz SA, et al. Induced regulatory T cells as immunotherapy in allotransplantation and autoimmunity: challenges and opportunities. J Leukoc Biol. 2024;116(2):947–965.
39. Woidacki K, Meyer N, Schumacher A, et al. Transfer of regulatory T cells into abortion–prone mice promotes the expansion of uterine mast cells and normalizes early pregnancy angiogenesis. Sci Rep. 2015;5:13938.
40. Bates GJ, Fox SB, Han C, et al, Quantification of regulatory T cells enables the identification of high–risk breast cancer patients and those at risk of late relapse. J Clin Oncol. 2006;24(34):5373–5380.
41. Gupta S, Joshi K, Wig JD, et al. Intratumoral FOXP3 expression in infiltrating breast carcinoma: Its association with clinic pathologic parameters and angiogenesis. Acta Oncol. 2007;46(6):792–797.
42. Aruga T, Suzuki E, Saji S, et al. A low number of tumor–infiltrating FOXP3–positive cells during primary systemic chemotherapy correlates with favorable anti–tumor response in patients with breast cancer. Oncol Rep. 2009;22(2):273–278.
43. Kruijf EM, Nes JGH, Sajet A, et al. The predictive value of HLA class I tumor cell expression and presence of intratumoral tregs for chemotherapy in patients with early breast cancer. Clin Cancer Res. 2010;16(4):1272–1280.
44. Generali D, Bates G, Berruti A, et al. Immunomodulation of FOXP3+ regulatory T cells by the aromatase inhibitor letrozole in breast cancer patients. Clin Cancer Res. 2009;15(3):1046–1051.
45. Ladoire S, Arnould L, Apetoh L, et al. Pathologic complete response to neoadjuvant chemotherapy of breast carcinoma is associated with the disappearance of tumor–infiltrating foxp3+ regulatory T cells. Clin Cancer Res. 2008;4(8):2413–2420.
46. Ichim TE, Li S, Ma H, et al. Induction of tumor inhibitory anti–angiogenic response through immunization with interferon gamma primed placental endothelial cells: ValloVax. J Transl Med. 2015;13:90.
47. Sotnikova N, Voronin D, Antsiferova Y, et al. Interaction of decidual CD56+ NK with trophoblast cells during normal pregnancy and recurrent spontaneous abortion at early term of gestation. Scand J Immunol. 2014;80(3):198–208.
48. Emmer PM, Nelen WL, Steegers EA, et al. Peripheral natural killer cytotoxicity and CD56 (pos) CD16 (pos) cells increase during early pregnancy in women with a history of recurrent spontaneous abortion. Hum Reprod. 2000;15(5):1163–1169.
49. Gao Y, Wang PL. Increased CD56(+) NK cells and enhanced Th1 responses in human unexplained recurrent spontaneous abortion. Genet Mol Res. 2015;14(4):18103–18109.
50. Taima A, Fukui A, Yamaya A, et al. A semen–based stimulation method to analyze cytokine production by uterine CD56 (bright) natural killer cells in women with recurrent pregnancy loss. J Reprod Immunol. 2020;142:103206.
51. Dons'koi BV, Baksheev SM, Sudoma IO, et al. A blinded investigation: accentuated NK lymphocyte CD335 (NKp46) expression predicts pregnancy failures. Diagnostics (Basel). 2023;13(11):1845.
52. Yang HL, Lai JJ, Shi JW, et al. A defective lysophosphatidic acid–autophagy axis increases miscarriage risk by restricting decidual macrophage residence. Autophagy. 2022;18(10):2459–2480.
53. Lea RG, McIntyre S, Baird JD, et al. Tumor necrosis factor–alpha mRNA–positive cells in spontaneous resorption in rodents. Am J Reprod Immunol. 1998;39(1):50–57.
54. Kang X, Zhang X, Zhao A. Macrophage depletion and TNF–alpha inhibition prevent resorption in CBA/J x DBA/2 model of CpG–induced abortion. Biochem Biophys Res Commun. 2016;469(3):704–710.
55. Gulan G, Podack ER, Rukavina D, et al. Perforin–expressing lymphocytes in peripheral blood and decidua of human first–trimester pathological pregnancies. Am J Reprod Immunol. 1997;38(1):9–18.
56. Mellor AL, Chandler P, Lee GK, et al. Indoleamine 2,3–dioxygenase, immunosuppression and pregnancy. J Reprod Immunol. 2002;57(1–2):143–150.
57. Uyttenhove C, et al. Evidence for a tumoral immune resistance mechanism based on tryptophan degradation by indoleamine 2,3–dioxygenase. Nat Med. 2003;9(10):1269–1274.
58. Lob S, Konigsrainer A. Is IDO a key enzyme bridging the gap between tumor escape and tolerance induction? Langenbecks Arch Surg. 2008;393(6):995–1003.
59. Trabanelli S, Ocadlikova D, Evangelisti C, et al. Induction of regulatory T cells by dendritic cells through indoleamine 2,3–dioxygenase: a potent mechanism of acquired peripheral tolerance. Curr Med Chem. 2011;18(15):2234–2239.
60. Johnson TS, Munn DH. Host indoleamine 2,3–dioxygenase: contribution to systemic acquired tumor tolerance. Immunol Invest. 2012;41(6–7):765–797.
61. Durr S, Kindler V. Implication of indolamine 2,3 dioxygenase in the tolerance toward fetuses, tumors, and allografts. J Leukoc Biol. 2013;93(5):681–687.
62. Kang X, Zhang X, Liu Z, et al. Granulocytic myeloid–derived suppressor cells maintain feto–maternal tolerance by inducing Foxp3 expression in CD4+CD25–T cells by activation of the TGF–beta/beta–catenin pathway. Mol Hum Reprod. 2016;22(7):499–511.
63. Jou E, Chaudhury N, Nasim F. Novel therapeutic strategies targeting myeloid–derived suppressor cell immunosuppressive mechanisms for cancer treatment. Explor Target Antitumor Ther. 2024;5(1):187–207.
64. Bazargan S, Bunch B, Ojwang' AME, et al. Targeting myeloid–derived suppressor cells with gemcitabine to enhance efficacy of adoptive cell therapy in bladder cancer. Front Immunol. 2023;14:1275375.
65. Ren J, Zeng W, Tian F, et al. Myeloid–derived suppressor cells depletion may cause pregnancy loss via upregulating the cytotoxicity of decidual natural killer cells. Am J Reprod Immunol. 2019;81(4):e13099.
66. Ostrand–Rosenberg S, Sinha P, Figley C, et al. Frontline Science: Myeloid–derived suppressor cells (MDSCs) facilitate maternal–fetal tolerance in mice. J Leukoc Biol. 2017;101(5):1091–1101.
67. Pan T, Liu Y, Zhong LM, et al. Myeloid–derived suppressor cells are essential for maintaining feto–maternal immunotolerance via STAT3 signaling in mice. J Leukoc Biol. 2016;100(3):499–511.
68. Chen T, Darrasse-Jèze G, Bergot A-S, et al. Self–specific memory regulatory T cells protect embryos at implantation in mice. J Immunol. 2013;191(5):2273–2281.
69. Alijotas–Reig J, Llurba E, Gris JM. Potentiating maternal immune tolerance in pregnancy: a new challenging role for regulatory T cells. Placenta. 2014;35(4):241–248.
70. Namdar A, Mirzaei R, Memarnejadian A, et al. Prophylactic DNA vaccine targeting Foxp3(+) regulatory T cells depletes myeloid–derived suppressor cells and improves anti–melanoma immune responses in a murine model. Cancer Immunol Immunother. 2018;67(3):367–379.
71. Li M, Sun F, Xu Y, et al. Tim–3(+) decidual Mphis induced Th2 and Treg bias in decidual CD4(+)T cells and promoted pregnancy maintenance via CD132. Cell Death Dis. 2022;13(5):454.
72. Wang S, Cao C, Piao H, et al. Tim–3 protects decidual stromal cells from toll–like receptor–mediated apoptosis and inflammatory reactions and promotes Th2 bias at the maternal–fetal interface. Sci Rep. 2015;5:9013.
73. Uckan D, Steele A, Wang BY, et al. Trophoblasts express Fas ligand: a proposed mechanism for immune privilege in placenta and maternal invasion. Mol Hum Reprod. 1997;3(8):655–62.
74. Bamberger AM, Schulte HM, Thuneke I, et al. Expression of the apoptosis–inducing Fas ligand (FasL) in human first and third trimester placenta and choriocarcinoma cells. J Clin Endocrinol Metab. 1997;82(9):3173–3175.
75. Pongcharoen S, Searle RF, Bulmer JN. Placental Fas and Fas ligand expression in normal early, term and molar pregnancy. Placenta. 2004;25(4):321–330.
76. Vacchio MS, Hodes RJ. Fetal expression of Fas ligand is necessary and sufficient for induction of CD8 T cell tolerance to the fetal antigen H–Y during pregnancy. J Immunol. 2005;174(8):4657–4661.
77. Talwar GP, Gupta JC, Shankar NV. Immunological approaches against human chorionic gonadotropin for control of fertility and therapy of advanced–stage cancers expressing hCG/subunits. Am J Reprod Immunol. 2011;66(1):26–39.
78. Cole LA. Biological functions of hCG and hCG–related molecules. Reprod Biol Endocrinol. 2010;8:102.
79. Cai S, Lin R, Liu S, et al. Intrauterine infusion of human chorionic gonadotropin improves the endometrial FoxP3(+) Tregs level and pregnancy outcomes in patients with lower endometrial FoxP3(+) Tregs. J Reprod Immunol. 2022;153:103678.
80. Khare P, Bose A, Singh P, et al. Gonadotropin and tumorigenesis: Direct and indirect effects on inflammatory and immunosuppressive mediators and invasion. Mol Carcinog. 2017;56(2):359–370.
81. Poloski E, Oettel A, Ehrentraut S, et al. JEG–3 trophoblast cells producing human chorionic gonadotropin promote conversion of human CD4+FOXP3– T cells into CD4+FOXP3+ regulatory T cells and foster T cell suppressive activity. Biol Reprod. 2016;94(5):106.
82. Schumacher A, Heinze K, Witte J, et al. Human chorionic gonadotropin as a central regulator of pregnancy immune tolerance. J Immunol. 2013;190(6):2650–2658.
83. Varghese GR, Patra D, Sunil Jaikumar V, et al. βhCG mediates immune suppression through upregulation of CD11b(+) Gr1(+) myeloid derived suppressor cells, CD206(+) M2 macrophages, and CD4(+) FOXP3(+) regulatory T–cells in BRCA1 deficient breast cancers. Immunology. 2023;170(2):270–285.
84. Morandi F, Airoldi I. HLA–G and other immune checkpoint molecules as targets for novel combined immunotherapies. Int J Mol Sci. 2022;23(6):2925.
85. Gu YZ, Xu Q, Chen YJ, et al. Different roles of PD–L1 and FasL in immunomodulation mediated by human placenta–derived mesenchymal stem cells. Hum Immunol. 2013;74(3):267–276.
86. Acs B, Madaras L, Tőkés AM, et al. PD–1, PD–L1 and CTLA–4 in pregnancy–related – and in early–onset breast cancer: A comparative study. Breast. 2017;35:69–77.
87. Zhang Y, Ma L, Hu X, et al. The role of the PD–1/PD–L1 axis in macrophage differentiation and function during pregnancy. Hum Reprod. 2019;34(1):25–36.
88. Meggyes M, Miko E, Szigeti B, et al. The importance of the PD–1/PD–L1 pathway at the maternal–fetal interface. BMC Pregnancy Childbirth. 2019;19(1):74.
89. Zeng W, Qin S, Wang R, et al. PDL1 blockage increases fetal resorption and Tfr cells but does not affect Tfh/Tfr ratio and B–cell maturation during allogeneic pregnancy. Cell Death Dis. 2020;11(2):119.
90. Wang WJ, Salazar Garcia MD, Deutsch G, et al. PD–1 and PD–L1 expression on T–cell subsets in women with unexplained recurrent pregnancy losses. Am J Reprod Immunol. 2020;83(5):e13230.
91. Zhang T, Zhu W, Zhao Y, et al. Early transient suppression of immune checkpoint proteins T–cell immunoglobulin mucin–3 and programmed cell death–1 in peripheral blood lymphocytes after blastocyst transfer is associated with successful implantation. Fertil Steril. 2020;114(2):426–435.
92. Liu X, Aneas I, Sakabe N, et al. Single cell profiling at the maternal–fetal interface reveals a deficiency of PD–L1(+) non–immune cells in human spontaneous preterm labor. Sci Rep. 2023;13(1):7903.
93. Zhang Y, et al. Decidual macrophages derived NO downregulates PD–L1 in trophoblasts leading to decreased treg cells in recurrent miscarriage. Front Immunol. 2023;14:1180154.
94. Chabtini L, Mfarrej B, Mounayar M, et al. TIM–3 regulates innate immune cells to induce fetomaternal tolerance. J Immunol. 2013;190(1):88–96.
95. Greenbaum S, Averbukh I, Soon E, et al. A spatially resolved timeline of the human maternal–fetal interface. Nature. 2023;619(7970):595–605.
96. Delyea C, Bozorgmehr N, Koleva P, et al. CD71(+) erythroid suppressor cells promote fetomaternal tolerance through arginase–2 and PDL–1. J Immunol. 2018;200(12):4044–4058.
97. Yu HR, Kuo HC, Huang LT, et al., L–Arginine modulates neonatal lymphocyte proliferation through an interleukin–2 independent pathway. Immunology. 2014;143(2):184–192.
98. Kropf P, et al. Arginase activity mediates reversible T cell hypo responsiveness in human pregnancy. Eur J Immunol. 2007;37(4):935–945.
99. Bronte V, Zanovello P. Regulation of immune responses by L–arginine metabolism. Nat Rev Immunol. 2005;5(8):641–654.
100. Zhao SJ, Muyayalo KP, Luo J, et al. Next generation of immune checkpoint molecules in maternal–fetal immunity. Immunol Rev. 2022;308(1):40–54.
101. Ahmed J, Nishizaki D, Miyashita H, et al. TIM–3 transcriptomic landscape with clinical and immunomic correlates in cancer. Am J Cancer Res. 2024;14(5):2493–2506.
102. Olbromski M, Mrozowska M, Piotrowska A, et al. The VISTA/VSIG3/PSGL–1 axis: crosstalk between immune effector cells and cancer cells in invasive ductal breast carcinoma. Cancer Immunol Immunother. 2024;73(8):136.
103. Ulmann A, Teutsch G, Philibert D. Ru 486. Sci Am. 1990;262(6):42–48.
104. Green ES, Moldenhauer LM, Groome HM, et al. Regulatory T cells are paramount effectors in progesterone regulation of embryo implantation and fetal growth. JCI Insight. 2023;8(11):e162995.
105. Mao G, Wang J, Kang Y, et al. Progesterone increases systemic and local uterine proportions of CD4+CD25+ Treg cells during midterm pregnancy in mice. Endocrinology. 2010;151(11):5477–5488.
106. Yin X, Chen S, Eisenbarth SC. Dendritic cell regulation of T helper cells. Annu Rev Immunol. 2021;39:759–790.
107. Pletinckx K, Döhler A, Pavlovic V, et al. Role of dendritic cell maturity/costimulation for generation, homeostasis, and suppressive activity of regulatory T cells. Front Immunol. 2011;2:39.
108. Ichim TE, Zhong R, Min WP. Prevention of allograft rejection by in vitro generated tolerogenic dendritic cells. Transpl Immunol. 2003;11(3–4):295–306.
109. Takashima A, Kitajima T. T cell–mediated terminal maturation of dendritic cells, a critical transition into fully potent antigen presenting cells. Pathol Biol (Paris). 1998;46(1):53–60.
110. Gabrilovich D, Ishida T, Oyama T, et al. Vascular endothelial growth factor inhibits the development of dendritic cells and dramatically affects the differentiation of multiple hematopoietic lineages in vivo. Blood. 1998;92(11):4150–4166.
111. Awad RM, Vlaeminck YD, Maebe J, et al. Turn back the TIMe: targeting tumor infiltrating myeloid cells to revert cancer progression. Front Immunol. 2018;9:1977.
112. Li Y, Cao L, Qian Z, et al. Mifepristone regulates Tregs function mediated by dendritic cells through suppressing the expression of TGF–beta. Immunopharmacol Immunotoxicol. 2021;43(1):85–93.
113. Zheng X, Koropatnick J, Chen D, et al. Silencing IDO in dendritic cells: a novel approach to enhance cancer immunotherapy in a murine breast cancer model. Int J Cancer. 2013;132(4):967–977.
114. Fujiwara Y, Kato S, Nesline MK, et al. Indoleamine 2,3–dioxygenase (IDO) inhibitors and cancer immunotherapy. Cancer Treat Rev. 2022;110:102461.
115. Amobi A, Qian F, Lugade AA, et al. Tryptophan catabolism and cancer immunotherapy targeting IDO mediated immune suppression. Adv Exp Med Biol. 2017;1036:129–144.
116. Beck C, Schreiber H, Rowley D. Role of TGF–beta in immune–evasion of cancer. Microsc Res Tech. 2001;52(4):387–395.
117. Sequeira GR, Sahores A, Moreno TD, et al. Enhanced antitumor immunity via endocrine therapy prevents mammary tumor relapse and increases immune checkpoint blockade sensitivity. Cancer Res. 2021;81(5):1375–1387.
118. Gabaglia CR, DeLaney A, Gee J, et al. Treatment combining RU486 and Ad5IL–12 vector attenuates the growth of experimentally formed prostate tumors and induces changes in the sentinel lymph nodes of mice. J Transl Med. 2010;8:98.
119. Check JH, Sansoucie L, Chern J, et al. Mifepristone treatment improves length and quality of survival of mice with spontaneous leukemia. Anticancer Res. 2009;29(8):2977–2980.
120. Check JH, Sansoucie L, Chern J, et al. Mifepristone treatment improves length and quality of survival of mice with spontaneous lung cancer. Anticancer Res. 2010;30(1):119–122.
121. Check JH, Dix E, Sansoucie L, et al. Mifepristone may halt progression of extensively metastatic human adenocarcinoma of the colon -case report. Anticancer Res. 2009;29(5):1611–1613.
122. Check JH, Wilson C, Cohen R, et al. Evidence that Mifepristone, a progesterone receptor antagonist, can cross the blood brain barrier and provide palliative benefits for glioblastoma multiforme grade IV. Anticancer Res. 2014;34(5):2385–2388.
123. Check JH, Check D, Wilson C, et al. Long–term high–quality survival with single–agent mifepristone treatment despite advanced cancer. Anticancer Res. 2016;36(12):6511–6513.
124. Check JH, Check D, Poretta T. Mifepristone extends both length and quality of life in a patient with advanced non–small cell lung cancer that has progressed despite chemotherapy and a check–point inhibitor. Anticancer Res. 2019;39(4):1923–1926.
125. Check JH, Check D, Srivastava MD, et al. Treatment with mifepristone allows a patient with end–stage pancreatic cancer in hospice on a morphine drip to restore a decent quality of life. Anticancer Res. 2020;40(12):6997–7001.
126. Check JH, Check D, Poretta T, et al. Palliative benefits of oral mifepristone for the treatment of metastatic fibroblastic osteosarcoma. Anticancer Res. 2021;41(4):2111–2115.
127. Check JH, et al. Mifepristone causing complete remission of rapidly advancing leukemia with measurement of progesterone–induced blocking factor. Anticancer Res. 2014;34(5):2413–2416.
128. Duta–Bratu CG, Nitulescu GM, Mihai DP, et al. Resveratrol and other natural oligomeric stilbenoid compounds and their therapeutic applications. Plants (Basel). 2023;12(16):2935.
129. Nagarajan S, Mohandas S, Ganesan K, et al. New insights into dietary pterostilbene: sources, metabolism, and health promotion effects. Molecules. 2022;27(19):6316.
130. Kosuru R, Rai U, Prakash S, et al. Promising therapeutic potential of pterostilbene and its mechanistic insight based on preclinical evidence. Eur J Pharmacol. 2016;789:229–243.
131. Mendonca E, Xavier JA, Fragoso MBT, et al. E–stilbenes: general chemical and biological aspects, potential pharmacological activity based on the Nrf2 pathway. Pharmaceuticals (Basel). 2024;17(2):232.
132. Mamun, AA, Shao C, Geng P, et al. Polyphenols targeting NF–kappa B pathway in neurological disorders: what we know so far? Int J Biol Sci. 2024;20(4):1332–1355.
133. Wu J, Li M, He J, et al. Protective effect of pterostilbene on concanavalin A–induced acute liver injury. Food Funct. 2019;10(11):7308–7314.
134. Abd–Elmawla MA, Abdelalim E, Ahmed KA, et al. The neuroprotective effect of pterostilbene on oxaliplatin–induced peripheral neuropathy via its anti–inflammatory, anti–oxidative and anti–apoptotic effects: comparative study with celecoxib. Life Sci. 2023;315:121364.
135. Khalil MI, Agamy AF, Elshewemi SA, et al. Pterostilbene induces apoptosis in hepatocellular carcinoma cells: biochemical, pathological, and molecular markers. Saudi J Biol Sci. 2023;30(8):103717.
136. Wang Z, Wang T, Chen X, et al. Pterostilbene regulates cell proliferation and apoptosis in non–small–cell lung cancer via targeting COX–2. Biotechnol Appl Biochem. 2023;70(1):106–119.
137. Obrador E, Palmer RS, Jebbar AJ, et al. Pterostilbene in cancer therapy. Antioxidants (Basel). 2021;10(3):492.
138. Eisenthal A. Indomethacin up–regulates the generation of lymphokine–activated killer–cell activity and antibody–dependent cellular cytotoxicity mediated by interleukin–2. Cancer Immunol Immunother. 1990;31(6):342–348.
139. Bryn T, Yaqub S, Mahic M, et al. LPS–activated monocytes suppress T–cell immune responses and induce FOXP3+ T cells through a COX–2–PGE2–dependent mechanism. Int Immunol. 2008;20(2):235–245.
140. Sharma S, Yang SC, Zhu L, et al. Tumor cyclooxygenase–2/prostaglandin E2–dependent promotion of FOXP3 expression and CD4+ CD25+ T regulatory cell activities in lung cancer. Cancer Res. 2005;65(12):5211–5220.
141. Schmielau J, Finn OJ. Activated granulocytes and granulocyte–derived hydrogen peroxide are the underlying mechanism of suppression of t–cell function in advanced cancer patients. Cancer Res. 2001;61(12):4756–4760.
142. Su D, Xu S, Ji K, et al. Pterostilbene supresses inflammation–induced melanoma metastasis by impeding neutrophil elastase–mediated thrombospondin–1 degradation. Chin Herb Med. 2023;15(1):94–101.
143. Lv M, Liu K, Fu S, et al. Pterostilbene attenuates the inflammatory reaction induced by ischemia/reperfusion in rat heart. Mol Med Rep. 2015;11(1):724–728.
144. Jancinova V, Perečko T, Harmatha J, et al. Decreased activity and accelerated apoptosis of neutrophils in the presence of natural polyphenols. Interdiscip Toxicol. 2012;5(2):59–64.
145. Perecko T, Drábiková K, Nosáľ R, et al. Involvement of caspase–3 in stilbene derivatives induced apoptosis of human neutrophils in vitro. Interdiscip Toxicol. 2012;5(2):76–80.
146. Youlin K, Simin L, Jian K, et al. Inhibition of miR–20a by pterostilbene facilitates prostate cancer cells killed by NK cells via up–regulation of NKG2D ligands and TGF–beta1down–regulation. Heliyon. 2023;9(4):e14957.
147. Beano A, Signorino E, Evangelista A, et al. Correlation between NK function and response to trastuzumab in metastatic breast cancer patients. J Transl Med. 2008;6:25.