Despite recent advances in the development of novel therapies against castration resistant prostate cancer, the advanced form of the disease remains a major treatment challenge. Aberrant sphingolipid signaling through sphingosine kinases and their product sphingosine-1-phosphate can promote proliferation, drug resistance, angiogenesis and inflammation. The sphingosine kinase 2 inhibitor ABC294640 is undergoing clinical testing in cancer patients, and in this study we investigated the effects this first-in-class inhibitor in castration resistant prostate cancer. In vitro, ABC294640 decreased prostate cancer cell viability as well as the expression of c-Myc and the androgen receptor while lysosomal acidification increased. ABC294640 also induced a greater than 3-fold increase in dihydroceramides that inversely correlated with inhibition of dihydroceramide desaturase (DEGS) activity. Expression of sphingosine kinase 2 was dispensable for the ABC294640-mediated increase in dihydroceramides. In vivo, ABC294640 diminished the growth rate of TRAMP-C2 xenografts in syngeneic hosts and elevated dihydroceramides within tumors as visualized by MALDI imaging mass spectroscopy. The plasma of ABC294640 treated mice contained significantly higher levels of C16- and C24:1-ceramides (but not dihydro-C16-ceramide) compared to vehicle treated mice. In summary, our results suggest that ABC294640 may reduce the proliferative capacity of castration resistant prostate cancer cells through both, inhibition of sphingosine kinase 2 and dihydroceramide desaturase, which provides a foundation for future exploration of this small molecule inhibitor for the treatment of advanced disease.

Immunotherapy represents an extremely promising treatment approach for cancer patients. The success in this field has been signified by multiple recent approvals of checkpoint inhibitors across a range of cancer types. Subsequently, there is an increasing need to understand why certain patients and diseases benefit from these treatments while others do not, as well as how to maximize the benefits from these treatments. To address some of these questions, we used an in vivo screening platform, MuScreen, which allows for evaluation of multiple syngeneic models and treatment modalities.We have characterized baseline and treated tumor immune infiltrates for a panel of syngeneic models using flow cytometry. The correlation between responsiveness and effects of checkpoint inhibitors (e.g., anti-PD-1), and macrophage targeted agents (e.g., CSF1R inhibition) on immune infiltrates including tumor-associated macrophages (TAMs) were investigated in 6 syngeneic models. Furthermore, M1/M2 polarization of macrophages was investigated to explore the potential role of these cells in establishing an immunosuppressed tumor microenvironment that may affect response to therapy. Here, we show that the baseline immune cell population varies across models, and that immune checkpoint inhibitors and macrophage-targeted agents had variable efficacy across different tumor models. We also present the correlation of immune cell infiltration, including tumor infiltrating lymphocytes (TILs), TAMs, and responsiveness to immunotherapy intervention. Having an in-depth understanding of the immune make up of a model in which an immunomodulatory compound is screened is paramount for successful translation into the clinic. A well-characterized and fully profiled panel of syngeneic models such as the MuScreen platform allows for finding the right model for screening test compounds to be used alone or in combination with immunotherapy. Citation Format: Yuki Kato Maves, Hooman Izadi, Elvira C. Talaoc, Deborah Yan, Charlene Echegaray, Andrew Calinisan, Krystal Moya, Heather Venant, Mitchell Garland, Radhika Iyer, Shounak Gosh, Stephanie Songco, Jayant Thatte, Tommy Broudy. Comparative study of anti-PD1 and CSF1R inhibition on tumor-infiltrating lymphocytes and macrophage populations across a panel of syngeneic tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2811. doi:10.1158/1538-7445.AM2017-2811