Invivo anti-cancer activity of 10-methyl-aplog-1, a simplified analog of aplysiatoxin, and its possible signaling pathway associated with G1 arrest.

Naturally occurring protein kinase C (PKC) activators such as phorbol esters, teleocidins, and aplysiatoxins, have the potential to become anti-cancer agents, since they are anti-proliferative against specific cancer cell lines in vitro. However, their potent tumor-promoting and proinflammatory activities have hampered their clinical uses. Recently, we developed 10-methyl-aplog-1 (1), a simplified analog of tumor-promoting debromoaplysiatoxin (DAT), which retained anti-proliferative activity comparable to DAT, but induced neither tumorigenesis nor inflammation on mouse skin. Our previous study suggested that PKCα and δ were involved in the cell line-selective anti-proliferative activity of 1, but the downstream signaling of PKC isozymes remained unknown. In this study, we confirmed that 1 inhibited the growth of three aplog-sensitive cancer cell lines (NCI-H460, HCC-2998, and HBC-4) without severe side effects in mice xenograft models. In addition, in vitro analysis using A549, one of the aplog-sensitive cell lines in vitro, revealed that PKCα induced PP2A-mediated attenuation of the Akt/S6 signaling axis. Since S6 inhibition in A549 was reported to result in G1 arrest, this pathway could be involved in the PKCα-dependent anti-proliferative activity of 1.
Competing Interests: Declaration of competing interest The authors declare no conflict of interests.
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