Synthetic cannabinoid WIN 55,212–2 inhibits growth and induces cell death of oral and pancreatic stem-like/poorly differentiated tumor cells

We report here that synthetic cannabinoid WIN 55,212–2 inhibits tumor cell proliferation and induces cell death of oral and pancreatic tumor cells, and the effect is much more pronounced on stem-like/poorly differentiated OSCSCs and MP2 cells when compared to well-differentiated OSCCs, and PL-12 tumor cells. In addition, WIN 55,212-2 decreases cell surface expression of CD44, CD54, MHC class I and PD-L1 on oral and pancreatic tumor cells with the exception of PD-L1 expression on well-differentiated PL-12 pancreatic tumor cells which exhibits an increase in the expression rather than a decrease. Overall, we demonstrate that WIN 55,212-2 has an increased targeting activity against cancer stem cells/poorly differentiated oral and pancreatic tumor cells when compared to well-differentiated tumor cells, and furthermore, such differences in function do not correlate with the levels of CB1 and CB2 receptor expression on tumor cells, suggesting it's function either through post-receptor mediated activation and/or yet-to-be identified novel receptors. Intraperitoneal (IP) delivery of WIN 55-212-2 in humanized BLT mice is found to impart an activating potential for NK cells demonstrating increased NK cell mediated cytotoxicity and secretion of IFN-γ in our preliminary experiments. These results not only suggest a direct targeting of CSCs/poorly differentiated tumors by WIN 55-212-2 but also by indirect targeting of such tumors through the activation and increased functions of NK cells.