Abstract 4780: RXDX-107 exhibits multiple mechanisms of intracellular delivery and results in extensive drug-induced interstrand crosslinks in solid tumor preclinical models

Abstract

Abstract RXDX-107 is a dodecanol alkyl ester of bendamustine, which is then encapsulated in human serum albumin (HSA) to form nanoparticles. Bendamustine is an alkylating agent that induces interstrand DNA crosslinks (ICLs) and causes cell death via several pathways, including intrinsic apoptosis. The activity of bendamustine in the treatment of solid tumor malignancies has not been impressive, possibly due to the pharmacokinetic and limited biodistribution properties of bendamustine. RXDX-107 was designed to improve tissue biodistribution over bendamustine, which may result in superior efficacy and tolerability in patients with solid tumors. In preclinical studies, RXDX-107 displayed significant anti-tumor activity in multiple solid tumor cell lines, cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models of advanced solid tumors, such as breast, lung, and ovarian cancer. In this study, we further evaluated the mechanism of action of RXDX-107, particularly the means of entry and accumulation of drug into tumor cells. We have developed a novel analytical method to precisely quantify both dodecanol alkyl ester of bendamustine and released bendamustine in tissue culture medium and cells. Our data demonstrate that RXDX-107 is transported into cells in three active forms. Firstly, RXDX-107 slowly releases bendamustine into the extracellular medium, and released bendamustine then enters into cells. Secondly, the dodecanol alkyl ester of bendamustine is transported into cells and causes ICLs. And lastly, by measuring macropinocytosis, we also determined that human serum albumin nanoparticles mediate the intracellular entry of RXDX-107. Each of these mechanisms results in the formation of ICLs. In addition, comet assay data demonstrate that RXDX-107 displayed stronger induction of ICLs than bendamustine, and the induced ICLs persist over 48 hours in multiple solid tumor cell lines. Taken together, our data demonstrate that RXDX-107 enters and accumulates into cells via multiple mechanisms, and causes extensive and superior ICLs compared to bendamustine in several solid tumor cell lines, thereby providing a strong rationale for further investigation of this agent in solid tumor indications. Citation Format: Leenus Martin, Roopal Patel, Michael Johnson, Jerry Cao, Peter Chua, Colin Walsh, Jennifer Oliver, Pratik Multani, Robert Wild, Ralph Lin, Gary G. Li. RXDX-107 exhibits multiple mechanisms of intracellular delivery and results in extensive drug-induced interstrand crosslinks in solid tumor preclinical models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4780.