Presentation Authors: HIMANSHU ARORA*, Manish Kuchakulla, Joshua M Hare, RANJITH RAMASAMY, MIAMI, FL
Introduction: 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, a recent study showed that resistance emerges in response to sustained CSF-1R blockade therapy in certain cancer types. These effects remain unexplored in castration resistance prostate cancer (CRPC). In the present study, we evaluated the hypothesis that sustained CSF-1R blockade therapy induces therapeutic resistance in CRPC cells. Moreover, in one of our recent studies, we demonstrated the role of increased nitric oxide (NO) in reducing tumor burden in murine models for CRPC. Molecular events showed that NO impacts the TME and macrophage differentiation through suppression of Interleukin 34 (IL-34), which is also a ligand for CSF1 receptor (CSF1R). Therefore, as a next step we explored the hypothesis that combinatorial GSNO-CSF1R inhibitor therapy suppresses tumor growth and resistance development in CRPC.
Methods: GW2580, a CSF1-receptor inhibitor which is a key regulator in macrophage differentiation was tested in-vitro(22RV1 cells) and in-vivo(CRPC murine models- castrated SCID mice xenografted with 22RV1 cells), singularly and in combination with S-Nitrosoglutathione (GSNO)( an active NO donor). In-vivo dosage of 40mg/kg/day was used for GW2580 and 10mg/kg/day for GSNO were considered to evaluate the efficacy of CSF1R-inhibition, and CSF1R-inhibition in presence of increased NO levels on tumor burden and resistance development in CRPC.
Results: Phosphatidylinositol 3-kinase (PI3K) pathway activity has been associated with resistance towards CSF1R inhibition therapy (GW2580) which is regulated by macrophage-derived growth factors. We found that PI3K signaling markers were significantly increased when CSF1R inhibition therapy is given to 22RV1 cells although GW2580 was able to suppress 22Rv1 cell proliferation in androgen deprived conditions. Additionally, levels of androgen receptor and its variants (markers largely studied for resistance development in CRPC) were induced upon CSF1R inhibition, thus suggesting towards possibility of resistance development. Importantly, in the presence of increased NO levels, CSF1R inhibition was able to show its cell proliferation capabilities without inducing P13K signaling pathway or AR, ARV7 levels. Furthermore, we investigated the impact of the combination GSNO-CSF1R inhibition therapy in in-vivo. Results validated the findings that P13K signaling, AR and ARV7 levels were induced upon CSF1R inhibition therapy and were reduced when CSF1R is inhibited in the presence of increased NO levels. Moreover, we evaluated macrophage infiltration, profiled cytokines and performed functional assays to establish the significance of combinational therapy of CSF1R inhibition and increased NO levels.
Conclusions: Our findings suggest a critical role of increased nitric oxide levels on safe and specific action of CSF1R inhibition therapy for castration resistance prostate cancer. These results demonstrate that NO has the potential to enhance the therapeutic effects of CSF1R inhibition by averting resistance development.
Source of Funding: Supported by the American Urological Association Research Scholar Award and Stanley Glaser Award to RR. J.M.H. is supported by NIH grants 1R01 HL137355, 1R01 HL107110, 1R01 HL134558, 5R01 CA136387, 5UM1 HL113460 and Soffer Family Foundation.