Abstract 4208: The castrate resistant PC-3 cell line with neuroendocrine features is enriched in tumor initiating cells and is resistant to enzalutamide and abiraterone but sensitive to antimetabolites

BACKGROUND. Prostatic small cell carcinoma is increasing in frequency in patients resistant to all forms of androgen ablation. It is a high-grade malignant neoplasm with neuroendocrine features. There are no suitable cellular models to study this particular type of carcinoma. A recent study showed that the PC-3 cell line has neuroendocrine characteristics (1). This report prompted us to determine if this cell line is enriched in tumor initiating cells, and to use this cell line as a model to determine sensitivity to second generation anti androgen treatments and chemotherapeutic agents. METHODS. To determine the percentage of tumor initiating cells (TICs) marker expression comparing LNCaP with PC-3 cells, flow cytometry analysis was used. Functional assays such as migration, invasion, colony formation and sphere formation were used to determine metastatic potential. Secondary and tertiary spheroid assays were used to determine the self-renewal ability. The CellTiter 96® AQueous non-radioactive cell proliferation assay was used to identify response to hormone deprivation and chemotherapeutic drugs. RESULTS. The growth rate of PC-3 was similar to LNCaP cells while the TIC marker CD44 was only expressed on PC-3 cells. Both LNCaP and PC-3 cells expressed α2β1 with the highest expression detected in PC-3 cells. No expression of CD133 was detected in either of the cell lines. PC-3, as compared to LNCaP cells, displayed an increase in 5-minute collagen-I attachment, cell migration, invasion, colony formation and sphere formation in an anchorage-independent environment. PC-3 cells were capable of self-renewal in the secondary and tertiary spheroid assays and expressed neuroendocrine markers such as chromogranin A and EMT marker, Twist. PC-3 cells were able to also grow in androgen-deprived media, and as compared to LNCaP cells, demonstrated resistance to anti-androgen drugs that included enzalutamide and abiraterone and chemotherapy drugs such as doxorubicin and taxotere. Surprisingly, PC-3 cells were more sensitive to methotrexate than LNCaP or DU145 cells. PC3 cells had lower levels of MTAP (methylthioadenosine phosphorylase) and hence may be the reason for their sensitivity to denovo purine synthesis inhibitors such as methotrexate. CONCLUSIONS. The novel findings presented here provide evidence that castrate resistant PC-3 cells are CD44+/ α2β1+/CD24low/CD133_ and possess stem cell properties and may serve as a useful model to study the role of new treatments for prostate cancer with neuroendocrine features. Reference: 1) Prostate. 2011 Nov; 71(15): 1668-79; PC3 is a cell line characteristic of prostatic small cell carcinoma; Tai S, Sun Y, Squires JM, Zhang H, Oh WK, Liang CZ, Huang J Citation Format: Nitu Bansal, Lisa Wu, Nadine Johnson Farley, Philip Tedeschi, Joseph R. Bertino. The castrate resistant PC-3 cell line with neuroendocrine features is enriched in tumor initiating cells and is resistant to enzalutamide and abiraterone but sensitive to antimetabolites. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4208. doi:10.1158/1538-7445.AM2015-4208