In vivo effect of the parasite derived peptide GK-1, anti-PD-L1 and GK-1/anti-PD-L1 combination in experimental melanoma. Potential novel treatment pathways.
e21038 Background: Several studies of advanced melanoma patients suggest that combining therapies that target tumor mechanisms of immune evasion with activation of normal immune cell functionality may provide optimal benefits for patients. The synthetic parasite derived GK1 peptide in combination with anti-PD-L1 showed significant longer survival (34 days) compared to GK1 or Anti-PD-L1 alone (23-27 days) in a murine melanoma model (p < 0.05). This means an increase survival increased in 47.82% in the mice treated with GK-1 + anti-PD-L1, 21.7% treated with GK-1, and 6.08% treated with anti-PD-L1. Methods: To elucidate the potential mechanism by which this combination treatment exerts its anti-melanoma effects, C57BL/6 mice were injected with B16-F10-luc2 cells and separated according to treatments in four groups: control, GK-1, anti-PD-L1 and GK-1/anti-PDL-1.Blood samples were collected at day 0, 14, and at euthanization or end of the experiment and monitored for serum cytokines using mice-specific V-PLEX Pro-inflammatory Panel. Results: On day 14, TNF-α levels in the Anti-PD-L1 and GK-1 therapy group was significantly lower compared to control mice. At sacrifice, the combined treatment group demonstrated significant decrease cytokine production in IL-6 and IL-10. Conclusions: The decreased cytokine levels observed in the GK-1/anti-PD-L1 group may explain the significant improved survival. GK-1 is a Th1 response inductor both in vitro and in vivo as it increases IFN-γ, IL-2 but not IL-4 and IL-10. It is noteworthy that when PD-L1 signaling is reduced in T cells these cells proliferate extensively in vitro and produce increased levels of IFN-γ and IL-17, suggesting an enhanced pro-inflammatory phenotype. It has been established that cytokines of Th2 response such as IL-4 and IL-5 and IL-6, have tumor-promoting activity. The anti-melanoma effect of the GK-1/anti-PD-L1 combination observed in the present study could be mediated by decreasing the pro-tumor Th2 response. These results provide novel alternative pathways and potential targets to enhance the clinical effect of the PD-1/PD-L1 blockade pathway.