CBP-501 is a chemically modified duodecapeptide and an analog of M-phase inducer phosphatase 3 (CDC25C) that increase cisplatin influx into tumor cells through an interaction with calmodulin enhancing cisplatin cytotoxicity, and affects cell cycle progression by abrogating DNA repair at the G2 checkpoint. CBP501 selectively inhibits the kinases MAPKAP-K2, C-TAK1, and CHK1 in vitro. Cell lines exposed to CBP501 plus bleomycin show a dose-dependent reduction of phosphorylated Ser216 on CDC25C. In addition to these effects on the G2 checkpoint, CBP501 also increases platinum concentration and DNA-platinum adduct formation in tumor cells through binding with calmodulin. In an in vitro panel testing the sensitivity of several tumor-derived cell lines to CBP501 in combination with a variety of anti-cancer agents, the combination of CBP501 with cisplatin was particularly effective against all four mesothelioma cell lines tested. Unfortunately, CBP-501 does not improve the efficacy of standard chemotherapy for malignant pleural mesothelioma.