Antitumor activity and pharmacologic characterization of the depsipeptide analog as a novel histone deacetylase/ phosphatidylinositol 3‐kinase dual inhibitor

Histone deacetylase (HDAC)/phosphatidylinositol 3-kinase (PI3K) dual inhibition is a promising strategy for the treatment of intractable cancers because of the advantages of overcoming potential resistance and showing synergistic effects. Therefore, development of an HDAC/PI3K dual inhibitor is reasonably attractive. Romidepsin (FK228, depsipeptide) is a potent HDAC inhibitor. We previously reported that depsipeptide and its analogs have an additional activity as PI3K inhibitors and are defined as HDAC/PI3K dual inhibitors. Subsequently, we identified FK-A11 as the most potent analog and reported its biochemical, biological, and structural properties as an HDAC/PI3K dual inhibitor. In this study, we reveal the in vitro and in vivo efficacy of FK-A11 in HT1080 fibrosarcoma and PC3 prostate cancer cell xenograft mouse models. FK-A11 showed in vivo antitumor activity by both i.v. and i.p. administration in a dose-dependent manner. In both xenograft models, FK-A11 showed superior antitumor effects compared to other depsipeptide analogs in accordance with in vitro anti-cell proliferation effects and the potency of HDAC/PI3K dual inhibition. In addition, we showed evidence of HDAC/PI3K dual inhibition accompanying antitumor efficacy in xenograft tumor tissues by immunohistochemistry. We also detailed pharmacokinetic characterization of FK-A11 in mice. These findings will be essential for guiding further preclinical and clinical studies.