Randomized phase II trial of pemetrexed/cisplatin with or without CBP501 in patients with advanced malignant pleural mesothelioma

• CBP501 enhances cisplatin cytotoxicity and blocks DNA repair at the G2 checkpoint.
• Patients with pleural mesothelioma received pemetrexed/cisplatin ± CBP501.
• This trial met its primary endpoint of PFS at 4 months.
• CBP501 did not improve response rate and overall survival over standard chemotherapy.

BackgroundCBP501, a synthetic duodecapeptide, increases cisplatin influx into tumor cells through an interaction with calmodulin enhancing cisplatin cytotoxicity, and effects cell cycle progression by abrogating DNA repair at the G2 checkpoint. In phase I clinical trials of CBP501 alone or in combination with cisplatin, the most common toxicity was infusion-related urticaria. Activity of CBP501 plus cisplatin was observed in patients with ovarian cancer and mesothelioma, including some patients previously treated with cisplatin.MethodsChemotherapy naïve patients with unresectable MPM were stratified by histology and performance status, and randomized 2:1 to pemetrexed/cisplatin plus CBP501 25 mg/m2 IV (Arm A) or pemetrexed/cisplatin alone (Arm B). The primary endpoint was progression free survival (PFS) at 4 months.Results65 patients were randomized, and 63 were treated. Patient characteristics in the two arms were balanced. Based on independent radiology review of the treated population, 25/40 patients (63%) in Arm A and 9/23 (39%) in Arm B had PFS ≥ 4 mo; the median PFS was 5.1 mo (95% CI, 3.9, 6.5) vs 3.4 mo (2.5, 6.7). Median OS was 13.3 mo (9.2, 16.3) in Arm A and 12.8 (6.5, 16.1) in Arm B. Adverse events were not different than expected from standard chemotherapy, and comparable in the two arms, aside from infusion reactions which occurred in 70% of patients treated with CBP501.ConclusionsWhile this randomized phase II trial met its primary endpoint of PFS at 4 months, other parameters such as response rate and overall survival suggest that the addition of CBP501 does not improve the efficacy of standard chemotherapy for MPM.