Abstract 4195: MIR002: a new POLA1 inhibitor endowed with a large spectrum of antitumor activity

A recent work from Han et al. disclosed DNA polymerase 1 alpha (POLA1) as the key target for the anti-cancer effects of CD437, a molecule belonging to the class of Retinoid Related Molecules (RRMs). Before this evidence, this family of compounds, of which CD437 and ST1926 represent the prototypes, has been characterized for its antiproliferative, antitumor and pro-apoptotic activity. With aim to identify a new RRM with an improved pharmacological profile, we recently selected MIR002 as a novel compound endowed with a potent antitumor activity and a peculiar pharmacological profile. In vitro treatment with MIR002 leads to a G1/S arrest and exerts a potent anti-tumor/proapoptotic activity in a wide range of cancer cell lines, including H460-R9A cells, which are cross resistant to ST1926 and CD437 (IC50>70 fold of H460-R9A vs H460). Moreover, in H460-R9A cells, we identified the L764F mutation in POLA1, already described as a mutation conferring resistance to CD437. We also demonstrated that POLA1 is the molecular target of both MIR002 and ST1926 and that, interestingly, the expression of the L764F mutant, although associated with the resistance to RRM’s, only marginally reduces the cytotoxic effects of MIR002. In order to investigate the activity of MIR002 against tumor growth, we examined a panel of in vivo xenograft tumor models, including those originating from human Non-Small Cell Lung Cancer (NSCLC) and Malignant Pleural Mesothelioma (MPM). In these models, using a q2dx5x3w schedule in doses ranging from 50 to 70 mg/Kg administered orally, we observed a strong tumor growth inhibition (TGI>70%). Interestingly, the combination of MIR002 with Cisplatin (4mg/Kg; qd7x3w; i.v.) in MPM models showed a synergistic antitumor efficacy, reaching a TGI>90%, and cured animals. Interestingly, we previously identified POLA1 as a key pro-proliferative player in 9 primary MPM samples. The ex-vivo analyses indicated that POLA1 expression was strongly modulated upon MIR002 treatment. Furthermore, in the same models, we also observed that the expression/secretion of multiple circulating factors is affected by MIR002 and we identified some of them as potential biomarkers of tumor responsiveness to MIR002. Taken together, our results identify MIR002 as a novel anti-cancer compound and suggest POLA1 as a target for new antitumor strategies to be investigated in Clinical Trials. Citation Format: Claudio Pisano, Lucio Merlini, Sergio Penco, Raffaella Cincinelli, Nadine Darwiche, Mario B. Guglielmi, Antonietta Esposito, Ilaria La Porta, Giacomo Signorino, Gabriele De Rubis, Fabiana Colelli, Francesco Cardile, Alessandra Fucci, Egildo L. D9Andrea, Sabrina Dallavalle. MIR002: a new POLA1 inhibitor endowed with a large spectrum of antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4195. doi:10.1158/1538-7445.AM2017-4195