Abstract 1345: Tumor selective localization of CRLX101, an investigational nanoparticle-drug conjugate of camptothecin

CRLX101, an investigational nanoparticle-drug conjugate (NDC) containing the payload camptothecin, is currently being clinically evaluated in multiple treatment-refractory solid tumors. In preclinical models, CRLX101 is believed to release camptothecin in the tumor in a slow and prolonged manner due to its long circulation half-life. CRLX101 has been shown preclinically to be a dual inhibitor of topoisomerase 1 and hypoxia-inducible factor 1α. It has demonstrated striking anti-tumor activity in several different tumor models. Camptothecin itself was identified as an active anti-tumor agent preclinically but was not developed clinically due to its poor tolerability in patients. The development of CRLX101, which has not shown significant toxicity in over 300 patients to date, offers a unique opportunity to improve cancer treatment in a meaningful way. We hypothesized that CRLX101 utilizes the enhanced permeability and retention (EPR) effect to accumulate selectively in tumors. In this study, we sought to mechanistically dissect the process of CRLX101 entry and accumulation into tumor cells using multiple methods, both in vitro and in xenograft tumors in vivo. Using confocal microscopy, we detected camptothecin fluorescence in CRLX101-treated tumor cells in culture as well as in tumor tissue from mice treated with CRLX101. We can co-localize this camptothecin with intact nanoparticles using an anti-PEG antibody that specifically detects the PEG loops in the NDCs. More recently, we have shown that camptothecin and anti-PEG co-localize specifically in tumors of patients treated with CRLX101 but not in adjoining normal tissue. We can also demonstrate that macropinocytosis and activation of actin polymerization play a role in the process by which tumor cells take up CRLX101. Using an anti-CD31 antibody, we can visualize the distance traversed by CRLX101 from the tumor vasculature over time. We have developed novel analytical methods to precisely quantify both released and CRLX101-conjugated camptothecin over time in CRLX101 treated tumor cells in vitro, as well as in tumor tissue from mice treated with CRLX101 in vivo. Using cell viability assays, we can correlate the kinetics of camptothecin released inside tumor cells to the degree of tumor cell kill. We believe that these data are an important step forward in understanding the precise mechanism(s) underlying selective delivery of CRLX101 into tumor tissue. Citation Format: Christian G. Peters, Douglas Lazarus, Donna Brown, Ningning Zhang, Adam P. Stockmann, Roy Case, Ellen Rohde, Scott Eliasof, Lata Jayaraman. Tumor selective localization of CRLX101, an investigational nanoparticle-drug conjugate of camptothecin. [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 1345.