Abstract 6053: Increased nitric oxide augments the action of CSF-1R inhibition against tumor associated macrophages in castration resistant prostate cancer (2020)

Abstract Introduction and Objectives: Prostate cancer (PCa) is the most common non-skin cancer among American men, and growing evidence suggests that targeting the tumor microenvironment (TME) could be essential in combating the progression of metastasis and resistance development in cancer. In this context, the colony-stimulating factor 1 (CSF1)/colony-stimulating factor 1 receptor (CSF1R) axis has gained the most attention, and various approaches targeting either the ligands or the receptor are currently in clinical development. However, as a class, CSF1R inhibitors have proved mostly disappointing in early clinical trials when used as monotherapy. Researchers believe their true potential can be tapped by combining them with other anticancer drugs. Sensitization to CSF-1R blockage therapy is tumor microenvironment (TME) driven. In one of our studies, we demonstrated that increased nitric oxide (NO) reduces tumor burden in murine models for CRPC by targeting TME . Therefore, in the present study, we evaluated the hypothesis that Increased Nitric oxide augments the action of CSF-1R inhibition against tumor associated macrophages in castration resistant prostate cancer. Methods: The castrated SCID mice were treated with CSF1R inhibitor (GS2580) at the dosage of 40mg/kg/day IP or/and GSNO at the dosage of 10mg/kg/day IP. After 4 weeks mice were humanely sacrificed. Tumor RNA and proteins to analyze the markers that are important for prostate cancer progression using qPCR, western blot and cytokine antibody array. RNA library was generated, and RNA sequencing was performed using RNA isolated from tumors. Molecular analyses were performed using standard procedures. GraphPad Prism (GraphPad Software) was used for statistical analysis. All data were presented as the means ± SEM. Results: Mice which recieved CSF1R inhibition showed significant reduction in tumor burden (p&amp;lt;0.05), however, in over 50% of the mice, the expression of markers like AR, pERK, p-GSK, and VEGF was found to be increased. Next, to study if increased Nitric oxide levels are able to augment the action of CSF1Ri against CRPC, we studied the effects of GSNO monotherapy, CSF1Ri monotherapy and GSNO+CSF1Ri combination on overall tumor burden. Results revealed that the most significant reduction in tumor burden were in mice that recieved the combination of GSNO-CSF1Ri, compared to GSNO or CSF1Ri monotherpies. Furthermore, RNA sequencing analysis demonstrated that the combination therapy is capable of targeting (suppressing) tumor immunology (signature of interferon-alpha, gama, and Myc signaling were significantly reduced). This was further supported by cytokine antibody array and immunostaning which showed that several cytokines like CXCL5, FGF4, IGFBP-3, MCP-4, IL-6, TNFalpha, expression of CRRPC markers- AR, ARV7, PSA, TMRPSS2, p-GSK, p-ERK, p90RSK, and markers of anti-inflamatorry macrophages (F4/80, CD206 etc) were suppressed in tumor proteins from mice which received combination therapy. Conclusions: Our findings suggest that CSF1R inhibition induced changes against CRPC are augmented in the presence of increased NO levels therefore demonstrating the therapeutic potential of increased NO levels against CRPC. Citation Format: Yash Soni, Manish Kuchakulla, Rehana Qureshi, Van Booven Derek J, Joshua M. Hare, Ranjith Ramasamy, Himanshu Arora. Increased nitric oxide augments the action of CSF-1R inhibition against tumor associated macrophages in castration resistant prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6053.