Abstract LB-274: Overcoming colorectal cancer resistance to death receptor agonists: Design and delivery of treatment combinations

Death Receptor 5 (DR5) is a key upregulated marker in colorectal cancer (CRC), overexpressed in over 90% of patients. There is a dire clinical need for drugs that can deliver targeted cell killing via this receptor. Over the past decade, various DR5 agonists have shown poor clinical efficacy, including both engineered antibodies and TRAIL, the natural ligand for this receptor. Comprehensive studies suggest that there are three major obstacles to success of these agents: 1) potency, 2) delivery, and 3) resistance. If these issues are addressed, DR5 will be an excellent therapeutic target for a variety of cancers, and provide a novel means for substantially advancing the clinical treatment of CRC. To improve delivery and overcome drug resistance, we have developed a platform that harnesses the power of genetic screening and protein engineering to design and deliver efficacious protein drug combinations. To pinpoint the genetic drivers of CRC resistance to a multivalent DR5 agonist (DRA), we used a CRISPR/Cas9 knockout screen. The screen identified genes that confer sensitivity to the DRA in resistant CRC cell lines. Over twenty small molecule drugs targeting pathways and proteins identified from the screens were then tested in combination with the DRA to identify highly synergistic combinations using cytotoxicity assays. Clonogenic, time-to-progression, and cell viability assays showed that pharmacological blockade of XIAP, Bcl-X L , and CDK4/6 strongly enhances antitumor activity of DRA in established human CRC cell lines and patient-derived CRC cells. To address the need for sustained delivery of therapeutic proteins, we developed injectable depots of anti-cancer proteins recombinantly fused to thermally responsive elastin-like polypeptide (ELP) biopolymers. The bioactive DRA-ELP fusions undergo temperature-driven phase transition upon subcutaneous injection in vivo , resulting in the formation of a gel-like depot suitable for sustained drug delivery. A single 30 mg/kg injection of the gel-like DRA-ELP depot induced significant tumor regression in Colo205 mouse xenografts. By addressing both delivery and resistance issues with our protein engineering and genomics platform, we have overcome key obstacles to clinical translation of a pro-apoptotic DRA. Citation Format: Mandana T. Manzari, Xinghai Li, Grace Anderson, Kris Wood, Ashutosh Chilkoti. Overcoming colorectal cancer resistance to death receptor agonists: Design and delivery of treatment combinations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-274.