Discovery of a small-molecule protein kinase Cd-selective activator with promising application in colon cancer therapy

Abstract

Protein kinase C (PKC) isozymes play major roles in human diseases, including cancer. Yet, the poor understanding of isozymes-specific functions and the limited availability of selective pharmacological modulators of PKC isozymes have limited the clinical translation of PKC-targeting agents. Here, we report the first small-molecule PKCd-selective activator, the 7a-acetoxy-6ß-benzoyloxy-12-O-benzoylroyleanone (Roy-Bz), which binds to the PKCd-C1-domain. Roy-Bz potently inhibited the proliferation of colon cancer cells by inducing a PKCd-dependent mitochondrial apoptotic pathway involving caspase-3 activation. In HCT116 colon cancer cells, Roy-Bz specifically triggered the translocation of PKCd but not other phorbol ester responsive PKCs. Roy-Bz caused a marked inhibition in migration of HCT116 cells in a PKCd-dependent manner. Additionally, the impairment of colonosphere growth and formation, associated with depletion of stemness markers, indicate that Roy-Bz also targets drug-resistant cancer stem cells, preventing tumor dissemination and recurrence. Notably, in xenograft mouse models, Roy-Bz showed a PKCd-dependent antitumor effect, through anti-proliferative, pro-apoptotic, and anti-angiogenic activities. Besides, Roy-Bz was non-genotoxic, and in vivo it had no apparent toxic side effects. Collectively, our findings reveal a novel promising anticancer drug candidate. Most importantly, Roy-Bz opens the way to a new era on PKC biology and pharmacology, contributing to the potential redefinition of the structural requirements of isozyme-selective agents, and to the re-establishment of PKC isozymes as feasible therapeutic targets in human diseases. ; We thank European Union (FEDER funds POCI/01/0145/FEDER/007728, FCOMP-01-0124-FEDER-028417 and POCI-01-0145-FEDER-007440, through Programa Operacional Factores de Competitividade—COMPETE) and National Funds (FCT/MEC, Fundação para a Ciência e Tecnologia and Ministério da Educação e Ciência) under the Partnership Agreement PT2020 UID/MULTI/ 04378/2013, UID/NEU/04539/2013, UID/DTP/04567/2016, and the project (3599-PPCDT) PTDC/DTP-FTO/1981/2014—POCI-01-0145-FEDER-016581, as well as Centro 2020 Regional Operational Programmes (CENTRO-01-0145-FEDER-000012: HealthyAging2020). FCT fellowships: SFRH/BD/87109/2012 (C. Bessa), SFRH/BD/117949/2016 (L. Raimundo), and SFRH/BD/128673/2017 (J. B. Loureiro).