TAS0612, a novel RSK, AKT, and S6K inhibitor, exhibits antitumor effects in preclinical tumor models.

The mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways are involved in cancer growth and survival; however, the clinical efficacy of single inhibitors of each pathway is limited or transient owing to resistance mechanisms, such as feedback signaling and/or re-expression of receptor-type tyrosine kinases (RTKs). This study identified a potent and novel kinase inhibitor, TAS0612, and characterized its properties. We found that TAS0612 is a potent, orally available compound that can inhibit p90RSK (RSK), AKT, and p70S6K (S6K) as a single agent and showed a strong correlation with the growth inhibition of cancer cells with PTEN loss or mutations, regardless of the presence of KRAS and BRAF mutations. Additional RSK inhibitory activity may differentiate the sensitivity profile of TAS0612 from that of signaling inhibitors that target only the PI3K pathway. Moreover, TAS0612 demonstrated broad-spectrum activity against tumor models wherein inhibition of MAPK or PI3K pathways was insufficient to exert antitumor effects. TAS0612 exhibited a stronger growth-inhibitory activity against the cancer cell lines and tumor models with dysregulated signaling with the genetic abnormalities described above than treatment with inhibitors against AKT, PI3K, MEK, BRAF, and EGFR/HER2. Additionally, TAS0612 demonstrated the persistence of blockade of downstream growth and anti-apoptotic signals, despite activation of upstream effectors in the signaling pathway and FoxO-dependent re-expression of HER3. In conclusion, TAS0612 with RSK/AKT/S6K inhibitory activity may provide a novel therapeutic strategy for cancer patients to improve clinical responses and overcome resistance mechanisms.