Priyamvada Rai

Castration-resistant prostate cancer (CRPC) remains incurable and fatal, creating a dire need for new safe and effective treatment strategies. We recently reported that the soluble guanylyl cyclase (sGC) stimulator, riociguat, cooperates with standard-of-care androgen deprivation (AD) to inhibit castration-resistant tumor burden by oxygenating hypoxic tumor niches and inducing tumor apoptosis. We further found that AD restores the sensitivity of CRPC cells to riociguat, which requires a redox-active functional sGC complex to stimulate cyclic GMP (cGMP) production. As redox reprogramming is a feature of the low-androgen PC milieu, to better establish the parameters of riociguat efficacy, we wished to determine whether redox-inactive forms of sGC persist in the castrate setting. To do so, we treated CRPC LNAI tumor-bearing animals with cinaciguat, an sGC activator which preferentially acts on the oxidized sGC complex. We found that, compared to riociguat, cinaciguat did not significantly increase intratumoral or systemic cGMP levels in the castrate setting. Nor did cinaciguat treatment significantly decrease tumor burden or oxygenate the hypoxic CRPC tumors. Given the preferential activity of cinaciguat on the redox-inactive sGC complex, our results indicate that the low-androgen castrate setting maintains the sGC complex in its functionally reduced state, affirming the critical benefit of AD for riociguat efficacy in the lethal castration-resistant disease stage.

Sex differences in immune responses impact cancer outcomes and treatment response, including in glioblastoma (GBM). However, host factors underlying distinct immune-cancer interactions are poorly understood. Here we identify γ-aminobutyric acid (GABA) as a female-specific driver of GBM-promoting immune response. We demonstrated that GABA receptor B (GABBR) signaling enhances the T cell suppressive function of granulocytic myeloid-derived suppressor cells (gMDSCs) from female mice by upregulating the cationic amino acid transporter 2–L-arginine–nitric oxide synthase 2 (NOS2) pathway. GABBR agonism promotes GBM growth in female preclinical models through gMDSCs, while GABBR antagonism extends survival and reduces NOS2 in tumor-infiltrating gMDSCs only in female mice. Immune cells from female participants with GBM have enriched GABA transcriptional signatures and a higher GABA concentration compared to male counterparts. Collectively, these results highlight the sex-specific immunomodulatory role of GABA in tumorigenesis, supporting future assessment of GABA pathway inhibitors for cancer immunotherapy.

Figures, legends and references associated with Supplementary figures

Randomized clinical trials have highlighted the importance of weight control and exercise in improving cancer outcomes, yet the molecular mediators of these benefits remain poorly understood. Recent studies in Type 2 diabetic patients reported that the insulin-sensitizing drug, metformin, exerts its anorexigenic and anti-obesogenic effects through elevation of N-lactoyl-phenylalanine (Lac-Phe), a metabolite also reported to underlie the metabolic benefits of exercise in healthy individuals. Because metformin can be repurposed for oncology, we investigated whether the metformin/Lac-Phe link extends to cancer by profiling serum Lac-Phe levels in non-diabetic prostate cancer patients from BIMET-1, a prospective metformin trial, as well as those receiving metformin for metabolic dysfunction. Irrespective of disease stage, anticancer outcomes, or hormone therapy status, metformin treatment significantly and consistently increased serum Lac-Phe in these cancer patients to concentrations that approximated levels reported after strenuous exercise. Moreover, patients on the metformin arm of BIMET-1 exhibited improved weight management following anti-androgen therapy relative to those in the control group. By generalizing the metformin/Lac-Phe axis, our study provides a new molecular context for the metabolic benefits of repurposing metformin in cancer patients.

Metabolic dysfunction is a hallmark of CD8 ⁺ T cell exhaustion in the tumor microenvironment. Thus, there is growing interest in developing strategies that enhance anti-tumor functions of CD8 ⁺ T cells via metabolic reprogramming. Here, we identify dipeptidyl peptidase 4 (DPP-4) as a previously unknown regulator of CD8 ⁺ T cell function and metabolism. We discovered that DPP-4 is upregulated in exhausted CD8 ⁺ T cells. Pharmacological inhibition of DPP-4 with the FDA-approved anti-diabetic drug sitagliptin transcriptionally and metabolically reprogrammed CD8 ⁺ T cells, increasing spare mitochondrial respiratory capacity, proliferation, cytotoxic mediator production, and antigen-specific cancer cell killing capability. The functional effects of sitagliptin were dependent on upregulation of glutamate decarboxylase 1 (GAD1), an enzyme that feeds glutamate into the tricarboxylic acid (TCA) cycle, highlighting a new role for GAD1 in CD8 ⁺ T cell respiration and proliferation. We found that systemic inhibition of DPP-4 in preclinical mouse glioblastoma (GBM) models prolongs survival in a CD8 ⁺ T cell-dependent manner, and retrospective clinical cohort analysis revealed better outcomes in GBM patients using DPP-4 inhibitors. Importantly, preconditioning of Chimeric Antigen Receptor (CAR) T-cells with DPP-4 inhibition enhanced their cytotoxicity, persistence, and therapeutic efficacy in pediatric GBM. Together, our findings provide mechanistic and biological rationale for repurposing readily accessible DPP-4 inhibitors to enhance anti-tumor CD8 ⁺ T cell responses.

Castration-resistant prostate cancer (CRPC) is incurable and fatal, making prostate cancer the second leading cancer-related cause of death for American men. CRPC results from therapeutic resistance to standard-of-care androgen deprivation (AD) treatments, through incompletely understood molecular mechanisms, and lacks durable therapeutic options. In this study, we identified enhanced soluble guanylyl cyclase (sGC) signaling as a mechanism that restrains CRPC initiation and growth. Patients with aggressive, fatal CRPC exhibited significantly lower serum levels of the sGC catalytic product cyclic GMP (cGMP) compared with the castration-sensitive stage. In emergent castration-resistant cells isolated from castration-sensitive prostate cancer populations, the obligate sGC heterodimer was repressed via methylation of its β subunit. Genetically abrogating sGC complex formation in castration-sensitive prostate cancer cells promoted evasion of AD-induced senescence and concomitant castration-resistant tumor growth. In established castration-resistant cells, the sGC complex was present but in a reversibly oxidized and inactive state. Subjecting CRPC cells to AD regenerated the functional complex, and cotreatment with riociguat, an FDA-approved sGC agonist, evoked redox stress-induced apoptosis. Riociguat decreased castration-resistant tumor growth and increased apoptotic markers, with elevated cGMP levels correlating significantly with lower tumor burden. Riociguat treatment reorganized the tumor vasculature and eliminated hypoxic tumor niches, decreasing CD44+ tumor progenitor cells and increasing the radiosensitivity of castration-resistant tumors. Thus, this study showed that enhancing sGC activity can inhibit CRPC emergence and progression through tumor cell–intrinsic and extrinsic effects. Riociguat can be repurposed to overcome CRPC, with noninvasive monitoring of cGMP levels as a marker for on-target efficacy.Significance: Soluble guanylyl cyclase signaling inhibits castration-resistant prostate cancer emergence and can be stimulated with FDA-approved riociguat to resensitize resistant tumors to androgen deprivation, providing a strategy to prevent and treat castration resistance.

Figures, legends and references associated with Supplementary figures

Castration-resistant prostate cancer (CRPC) is incurable and fatal, making prostate cancer the second leading cancer-related cause of death for American men. CRPC results from therapeutic resistance to standard-of-care androgen deprivation (AD) treatments, through incompletely understood molecular mechanisms, and lacks durable therapeutic options. In this study, we identified enhanced soluble guanylyl cyclase (sGC) signaling as a mechanism that restrains CRPC initiation and growth. Patients with aggressive, fatal CRPC exhibited significantly lower serum levels of the sGC catalytic product cyclic GMP (cGMP) compared with the castration-sensitive stage. In emergent castration-resistant cells isolated from castration-sensitive prostate cancer populations, the obligate sGC heterodimer was repressed via methylation of its β subunit. Genetically abrogating sGC complex formation in castration-sensitive prostate cancer cells promoted evasion of AD-induced senescence and concomitant castration-resistant tumor growth. In established castration-resistant cells, the sGC complex was present but in a reversibly oxidized and inactive state. Subjecting CRPC cells to AD regenerated the functional complex, and cotreatment with riociguat, an FDA-approved sGC agonist, evoked redox stress-induced apoptosis. Riociguat decreased castration-resistant tumor growth and increased apoptotic markers, with elevated cGMP levels correlating significantly with lower tumor burden. Riociguat treatment reorganized the tumor vasculature and eliminated hypoxic tumor niches, decreasing CD44+ tumor progenitor cells and increasing the radiosensitivity of castration-resistant tumors. Thus, this study showed that enhancing sGC activity can inhibit CRPC emergence and progression through tumor cell–intrinsic and extrinsic effects. Riociguat can be repurposed to overcome CRPC, with noninvasive monitoring of cGMP levels as a marker for on-target efficacy. Significance: Soluble guanylyl cyclase signaling inhibits castration-resistant prostate cancer emergence and can be stimulated with FDA-approved riociguat to resensitize resistant tumors to androgen deprivation, providing a strategy to prevent and treat castration resistance.

Triple-negative (ER^-PR^-HER2^-) breast cancers (TNBC) are highly aggressive and difficult to treat. TNBC exhibit high genomic instability, which enables them to adapt and become resistant to chemo/radiation therapy, leading to rapid disease relapse and mortality. The pro-survival factors that safeguard genome integrity in TNBC cells are poorly understood. LBH is an essential mammary stem cell-specific transcription regulator in the WNT pathway that is aberrantly overexpressed in TNBC, correlating with poor prognosis. Herein, we demonstrate a novel role for LBH in promoting TNBC cell survival. Depletion of LBH in multiple TNBC cell models triggered apoptotic cell death both in vitro and in vivo and led to S-G2M cell cycle delays. Mechanistically, LBH loss causes replication stress due to DNA replication fork stalling, leading to ssDNA breaks, ɣH2AX and 53BP1 nuclear foci formation, and activation of the ATR/CHK1 DNA damage response. Notably, ATR inhibition in combination with LBH downmodulation had a synergistic effect, boosting TNBC cell killing and blocking in vivo tumor growth. Our findings demonstrate, for the first time, that LBH protects the genome integrity of cancer cells by preventing replicative stress. Importantly, they uncover new synthetic lethal vulnerabilities in TNBC that could be exploited for future multi-modal precision medicine.