Dysregulated PI3K/Akt/mTOR (PAM) pathway signaling occurs in ~30% of human cancers, making it a rational target for new therapies; however, the effectiveness of some PAM pathway inhibitors, such as mTORC rapalogs, may be compromised by a compensatory feedback loop leading to Akt activation. In this study, the p70S6K/Akt dual inhibitor, M2698 (previously MSC2363318A), was characterized as a potential anti-cancer agent through examination of its pharmacokinetic, pharmacodynamic and metabolic properties, and anti-tumor activity. M2698 was highly potent in vitro (IC50 1 nM for p70S6K, Akt1 and Akt3 inhibition; IC50 17 nM for pGSK3β indirect inhibition) and in vivo (IC50 15 nM for pS6 indirect inhibition), and relatively selective (only 6/264 kinases had an IC50 within 10-fold of p70S6K). Orally administered M2698 crossed the blood-brain barrier in rats and mice, with brain tumor exposure 4-fold higher than non-disease brain. Dose-dependent inhibition of target substrate phosphorylation was observed in vitro and in vivo, indicating that M2698 blocked p70S6K to provide potent PAM pathway inhibition while simultaneously targeting Akt to overcome the compensatory feedback loop. M2698 demonstrated dose-dependent tumor growth inhibition in mouse xenograft models derived from PAM pathway-dysregulated human triple-negative (MDA-MB-468) and Her2-expressing breast cancer cell lines (MDA-MB-453 and JIMT-1), and reduced brain tumor burden and prolonged survival in mice with orthotopically implanted U251 glioblastoma. These findings highlight M2698 as a promising PAM pathway inhibitor whose unique mechanism of action and capacity to pass the blood-brain barrier warrant clinical investigation in cancers with PAM pathway dysregulation, and those with central nervous system involvement.
Keywords: Akt; M2698; MSC2363318A; PAM pathway; blood-brain barrier; p70S6K.