Synthesis and Characterization of Piperic Acid Conjugates with Homochiral and Heterochiral Dipeptides Containing Phenylalanine and Their Application in Skin Cancer.

The current work demonstrates the synthesis and characterization of piperic acid conjugates with homochiral/heterochiral dipeptides containing phenylalanine as anti-skin cancer agents. The conjugates PA-D Phe-L Phe-OH, FC-1; PA-L Phe-D Phe-OH, FC-2; PA-D Phe-D Phe-OH, FC-3; and PA-D Phe-D Phe-OH, FC-4 were synthesized, characterized and assessed for cytotoxicity against melanoma cell lines of human and murine origin. Among all, PA-D Phe-D Phe (FC-3) conjugate was identified as a potential cytotoxic lead against melanoma cells by delineating the anti-proliferative and anti-migratory potential together with its anti-inflammatory potential against pro-inflammatory interleukins (IL-1β, IL-6, and IL-8). Evidences from western blotting, fractionation and immunocytochemistry experiments suggest that Stat-3 is a critical signaling molecule involved in the FC-3 mechanism of action. The results denote that FC-3 profoundly ablates Stat-3 expression, phosphorylation and nuclear translocation. Stat-3 mRNA analysis revealed that FC-3 did not alter the transcription of Stat-3. However, in cells where proteasome mediated degradation was inhibited, FC-3 failed to check the Stat-3 expression implying that FC-3 auguments the proteosomal degaradation of Stat-3. Of note, FC-3 failed to reverse the IL-6 mediated hyperactivation of Stat-3 in A375 cells. Critically, in Stat-3 deficient cancer cells, the anti-cologenic and anti-migratory potential of FC-3 was significantly subdued. Further, the in vivo efficacy of FC-3 was validated in the two-step (DMBA/TPA) chemically induced mouse skin cancer model. The FC-3-treated cohorts of mice unveiled a significant decrease in the cumulative number of tumors besides attenuation of tumor growth with respect to the vehicle-treated mice. Lastly, in corroboration with our in vitro findings, serum collected from mice groups at various intervals during the treatment regimen demonstrated decrement in IL-1β and IL-6 levels in FC-3 treated groups compared to the vehicle-treated group.