Abstract 4519: Targeting of cyclin D/Rb/E2F and PI3K/AKT/MTOR pathways with ON 123300 as a therapeutic strategy for mantle cell lymphoma
Authors: Reddy E. Premkumar , Divakar Saikrishna A. , Reddy M.V. Ramana , Cosenza Stephen C. , Baker Stacey J. , Akula Balaiah , Parekh Samir 
Published: May 2015

Abstract
Introduction: This study describes the development of a novel dual specificity kinase inhibitor, ON 123300, which exhibits potent activity against Mantle Cell Lymphomas (MCLs) both in vitro and in vivo. Mantle cell lymphoma is genetically characterized by the t(11;14)(q13;q32) chromosomal translocation which results in constitutive overexpression of cyclin D1. In addition, MCLs also activate other pathways, including aberrant B-Cell Receptor and PI3K/AKT/mTOR signaling. As a result, MCL has a poor clinical outcome with a median survival of 4-5 years. In this study, we show that ON123300, which inhibits both CDK4/6 and PI3K-α (the predominant PI3K catalytic subunit expressed in MCL cells), is a superior inducer of apoptosis of MCL cells when compared to PD0332991, a selective inhibitor of CDK4/6 kinases.
Experimental Procedures: We examined the effects of PD 0332991 and ON123300 on cell cycle progression, modulation of the Rb and PI3K/AKT pathways, and the induction of apoptosis in the Granta 519 and Z138C mantle cell lymphoma cell lines. When Granta 519 and Z138C cells were incubated with increasing concentrations of PD 0332991 and ON 123300, both compounds efficienty inhibited the phosphorylation of the Rb family of proteins. However, ON123300 showed concentration-dependent inhibition of MTOR, AKT, 4EBP1 and S6RB phosphorylation while PD 0332991 had no effect on the phosphorylation status of these proteins. While cells treated with PD 0332991 rapidly accumulated in the G0/G1 stage of cell cycle, cells treated with ON123300 showed an accumulation of cells with a sub-G1 DNA content. These ON123300 treated cells showed cleavage of PARP as well as Caspases 3, 7 and 9 and inhibition of FOXO1 phosphorylation, which was not observed in cells treated with PD 0332991. We tested the effects of ON 123300 in nude mouse xenograft assays using Z138 MCL cells. These studies revealed a strong inhibition of tumor growth when tumor-bearing mice were treated daily with 100 mg/kg of ON123300. In addition, there was little evidence of toxicity as measured by change in the body weight in ON123300-treated mice.
Conclusions: ON123300 targets the CyclinD/CDK/Rb pathway as well as the PI3K/AKT/MTOR pathway to induce apoptosis of MCL cells via intrinsic apoptotic pathways. Mouse xenograft assays show that ON 123300 is a strong inhibitor of MCL tumor growth in vivo. This dual activity against Rb and AKT pathways appears to be an effective therapeutic strategy for the treatment of MCL.
Citation Format: E. Premkumar Reddy, Saikrishna A. Divakar, M.V. Ramana Reddy, Stephen C. Cosenza, Stacey J. Baker, Balaiah Akula, Samir Parekh. Targeting of cyclin D/Rb/E2F and PI3K/AKT/MTOR pathways with ON 123300 as a therapeutic strategy for mantle cell lymphoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4519. doi:10.1158/1538-7445.AM2014-4519