Minnelide suppresses GVHD and enhances survival while maintaining GVT responses

Allogeneic hematopoietic stem cell transplantation (aHSCT) can cure patients with otherwise fatal leukemias and lymphomas. However, the benefits of aHSCT are limited by graft-versus-host disease (GVHD). Minnelide, a water-soluble analog of triptolide, has demonstrated potent anti-inflammatory and anti-tumor activity in several pre-clinical models and has proven both safe and efficacious in clinical trials for advanced gastro-intestinal malignancies. Here, we tested the effectiveness of Minnelide in preventing acute GVHD as compared to cyclophosphamide post-aHSCT (PTCy). Strikingly, we found Minnelide improved survival, weight loss and clinical scores in an MHC-mismatched model of aHSCT. These benefits were also apparent in minor MHC-matched aHSCT and xenogeneic HSCT models. Minnelide was comparable to PTCy in terms of survival, GVHD clinical score and colonic length. Notably, in addition to decreased donor T cell infiltration early post-HSCT, several regulatory cell populations including Tregs, ILC2s and MDSCs in the colon were increased which together may account for Minnelide's GVHD suppression post-HSCT. Importantly, Minnelide GVHD prevention was accompanied by preservation of graft-versus-tumor (GVT) activity. As Minnelide possesses anti-AML activity and is being applied in clinical trials, together with the present findings, we conclude that this compound might provide a new approach for AML patients undergoing aHSCT.

The soluble guanylyl cyclase pathway is inhibited to evade androgen deprivation-induced senescence and enable progression to castration resistance

Castration-resistant prostate cancer (CRPC) is fatal and therapeutically under-served. We describe a novel CRPC-restraining role for the vasodilatory soluble guanylyl cyclase (sGC) pathway. We discovered that sGC subunits are dysregulated during CRPC progression and its catalytic product, cyclic GMP (cGMP), is lowered in CRPC patients. Abrogating sGC heterodimer formation in castration-sensitive prostate cancer (CSPC) cells inhibited androgen deprivation (AD)-induced senescence, and promoted castration-resistant tumor growth. We found sGC is oxidatively inactivated in CRPC. Paradoxically, AD restored sGC activity in CRPC cells through redox-protective responses evoked to protect against AD-induced oxidative stress. sGC stimulation via its FDA-approved agonist, riociguat, inhibited castration-resistant growth, and the anti-tumor response correlated with elevated cGMP, indicating on-target sGC activity. Consistent with known sGC function, riociguat improved tumor oxygenation, decreasing the PC stem cell marker, CD44, and enhancing radiation-induced tumor suppression. Our studies thus provide the first evidence for therapeutically targeting sGC via riociguat to treat CRPC.

Statement of significance

Prostate cancer is the second highest cancer-related cause of death for American men. Once patients progress to castration-resistant prostate cancer, the incurable and fatal stage, there are few viable treatment options available. Here we identify and characterize a new and clinically actionable target, the soluble guanylyl cyclase complex, in castration-resistant prostate cancer. Notably we find that repurposing the FDA-approved and safely tolerated sGC agonist, riociguat, decreases castration-resistant tumor growth and re-sensitizes these tumors to radiation therapy. Thus our study provides both new biology regarding the origins of castration resistance as well as a new and viable treatment option.

Abstract 4335: Repurposing metformin in early-stage high risk prostate cancer to avoid ADT-induced cardiovascular toxicity

Prostate cancer is the second most common cause of cancer-related deaths in American men. About 20-40% of patients with localized castration-sensitive prostate cancer (CSPC) eventually progress, requiring androgen deprivation therapy (ADT). However ADT inevitably fails, giving rise to castration-resistant prostate cancer (CRPC), which is incurable and fatal. A significant fraction of patients undergoing ADT die of treatment-accelerated cardiovascular disease. Pre-existing metabolic dysfunction has been implicated in PC disease incidence, higher rates of prostatectomy failure, and accelerated progression to CRPC. Thus, there is an unmet need to counter the adverse sequelae of ADT through alternative CSPC treatments that do not exacerbate metabolic syndrome but prevent PC progression. Few studies have evaluated whether targeting the metabolic dysfunction associated with early-stage PC can prevent progression and thus the need for ADT. In a recent clinical trial spearheaded by Dr. Bilusic, metformin, an affordable and well-tolerated insulin-sensitizing diabetes drug, has recently shown promise as monotherapy in biologically-recurrent CSPC, preventing PSA rise in about 40% of high-risk patients. To identify the molecular mechanisms and biomarkers of positive response to metformin in PC patients, we performed preliminary cytokine profiling of responder vs non-responder patient sera. We found that mitigation of inflammatory factors implicated in cardiovascular disease as well as markers of pro-apoptotic response are associated with positive metformin response. We also found that metformin responders exhibited pre-treatment cytokine signatures associated with inflammatory metabolic diseases, including diabetes and hyperinsulinemia, which are conditions known to benefit from metformin treatment. We have been able to model the variability of metformin treatment response in two well-characterized CSPC cell lines, LNCaP (highly responsive) and LAPC4 (minimally responsive). Metformin induced cell death in LNCaP but not in LAPC4, which possesses mutant p53 and high Bcl-2 levels. LAPC4 instead showed markers of senescence, which is associated with an inflammatory phenotype. Metformin also elevated levels of damaging high-potency (short-lived) ROS in LNCaP to a greater extent than in LAPC4. LAPC4 instead exhibited elevated levels of hydrogen peroxide upon metformin treatment, a ROS associated with inflammation. Thus the cell models show congruence with factors of positive response seen in patients. Our findings shed light on the potential mechanism of positive response to metformin in CSPC patients, and lay the groundwork for further investigation, while insight into biomarkers predicting positive response could be immediately useful in the clinic.

Citation Format: Philip Gregory, Beatriz Mateo-Victoriano, Ling Zhang, Cassie Due, Marijo Bilusic, Priyamvada Rai. Repurposing metformin in early-stage high risk prostate cancer to avoid ADT-induced cardiovascular toxicity. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4335.

Metformin for biochemical recurrence of prostate cancer: Immune data from a phase 2 study

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Background: Metformin impacts immune response in several ways. It protects CD8 TILs from apoptotic death, downregulates CD39 and CD73, reduces MDSC activity and suppresses the transcription of PD1 thus enhancing CD8+ T cell antitumor activity (Ma et al, 2000, Nature). There is limited data on the immunologic impact of metformin treatment in hormone sensitive prostate cancer. Methods: We conducted an open label, randomized, phase II trial of bicalutamide with or without metformin of patients with high risk, biochemically recurrent prostate cancer (NCT02614859). Patients were randomized 1:2 to observation for an initial 8 weeks or metformin 1000 mg twice daily. Bicalutamide 50 mg/day was added after 8 weeks to both arms. The study discontinued accrual after interim analysis indicated no difference in PSA at 32 weeks between the two arms; however, metformin monotherapy for 8 weeks induced modest PSA declines observed in 40% of patients. Here we report immune responses in a subgroup of patients (N=12), including systemic cytokine levels and 158 circulating immune cell subsets after 8 weeks of metformin monotherapy. Results: Twelve patients treated at the NCI were analyzed. After 8 weeks, the metformin arm showed increased pDCs and lower Tregs compared to baseline. Significant differences in the percent change of immune parameters after 8 weeks of metformin monotherapy compared to 8 weeks of observation are summarized. Conclusions: Metformin has been shown to reduce markers of immune exhaustion in hormone sensitive prostate cancer which is supported by a greater reduction of PD-1+ and Tim3+ NK cells. Additional immune changes included increases in activated subpopulations of natural killer (NK) cells, which have been reported as a potential predictive biomarker of prolonged treatment response to hormone therapy in prostate cancer (Pasero et al, Oncotarget, 2015). Clinical trial information: NCT02614859 . [Table: see text]

Obesity enriches for tumor protective microbial metabolites and treatment refractory cells to confer therapy resistance in PDAC

Obesity causes chronic inflammation and changes in gut microbiome. However, how this contributes to poor survival and therapy resistance in patients with pancreatic cancer remain undetermined. Our current study shows that high fat diet-fed obese pancreatic tumor bearing mice do not respond to standard of care therapy with gemcitabine and paclitaxel when compared to corresponding control diet-fed mice. C57BL6 mice were put on control and high fat diet for 1 month following with pancreatic tumors were implanted in both groups. Microbiome of lean (control) and obese (high fat diet fed) mice was analyzed. Fecal matter transplant from control mice to obese mice sensitized tumors to chemotherapy and demonstrated extensive cell death. Analysis of gut microbiome showed an enrichment of queuosine (Q) producing bacteria in obese mice and an enrichment of S-adenosyl methionine (SAM) producing bacteria in control diet-fed mice. Further, supplementation of obese animals with SAM sensitized pancreatic tumors to chemotherapy. Treatment of pancreatic cancer cells with Q increased PRDX1 involved in oxidative stress protection. In parallel, tumors in obese mice showed increase in CD133+ treatment refractory tumor populations compared to control animals. These observations indicated that microbial metabolite Q accumulation in high fat diet-fed mice protected tumors from chemotherapy induced oxidative stress by upregulating PRDX1. This protection could be reversed by treatment with SAM. We conclude that relative concentration of SAM and queuosine in fecal samples of pancreatic cancer patients can be developed as a potential biomarker and therapeutic target in chemotherapy refractory pancreatic cancer.

Hypoxia-Driven Oncometabolite L-2HG Maintains Stemness-Differentiation Balance and Facilitates Immune Evasion in Pancreatic Cancer

In pancreatic cancer, the robust fibroinflammatory stroma contributes to immune suppression and renders tumors hypoxic, altering intratumoral metabolic pathways and leading to poor survival. One metabolic enzyme activated during hypoxia is lactate dehydrogenase A (LDHA). As a result of its promiscuous activity under hypoxia, LDHA produces L-2 hydroxyglutarate (L-2HG), an epigenetic modifier, that regulates the tumor transcriptome. However, the role of L-2HG in remodeling the pancreatic tumor microenvironment is not known. Here we used mass spectrometry to detect L-2HG in serum samples from patients with pancreatic cancer, comprising tumor cells as well as stromal cells. Both hypoxic pancreatic tumors as well as serum from patients with pancreatic cancer accumulated L-2HG as a result of promiscuous activity of LDHA. This abnormally accumulated L-2HG led to H3 hypermethylation and altered gene expression, which regulated a critical balance between stemness and differentiation in pancreatic tumors. Secreted L-2HG inhibited T-cell proliferation and migration, suppressing antitumor immunity. In a syngeneic orthotopic model of pancreatic cancer, inhibition of LDH with GSK2837808A decreased L-2HG, induced tumor regression, and sensitized tumors to anti-PD1 therapy. In conclusion, hypoxia-mediated promiscuous activity of LDH produces L-2HG in pancreatic tumor cells, regulating the stemness-differentiation balance and contributing to immune evasion. Targeting LDH can be developed as a potential therapy to sensitize pancreatic tumors to checkpoint inhibitor therapy. SIGNIFICANCE: This study shows that promiscuous LDH activity produces L-2HG in pancreatic tumor and stromal cells, modulating tumor stemness and immune cell function and infiltration in the tumor microenvironment.