Abstract LB-002: SQ3370 enhances the safety of chemotherapeutics via local activation therapy

Abstract With systemic chemotherapy, only 1-2% of the administered dose actually reaches a localized tumor, while the remaining leads to adverse off-target toxicities, including immunosuppression. Hence, there is a critical need to locally deliver cytotoxics directly to the tumor. Our patented approach (SQ3370) consists of: (1) SQL70 - a drug-activating biomaterial carrying no payload (2) SQP33 - a chemically-modified prodrug of doxorubicin (Dox) with attenuated activity. SQL70 is injected at the tumor site followed by SQP33 administered systemically. The prodrug first concentrates to the biomaterial at the tumor site due to their complementary chemical reactivities. The active drug is then spontaneously released over multiple days, providing sustained local delivery directly to the tumor region while reducing systemic side effects. Previously, we have shown that the greater safety of SQP33 allows it to be given at over 38 times the dose of standard Dox in SQL70-injected mice. Pharmacokinetic and biodistribution studies in SQ3370-treated rodents and dogs show that SQP33 disappears from plasma within the first hour of administration, likely due to the rapid concentration to SQL70. Without SQL70, SQP33 shows minimal spontaneous conversion to activated Dox. These studies also indicate that a single injection of SQL70 can activate multiple doses of SQP33, maximizing the local therapeutic index. Recent studies demonstrate that SQ3370 treatment enhances therapeutic response and survival in tumor-bearing mice: In a syngeneic MC38 colorectal cancer model, SQ3370 slowed tumor progression in 8/10 mice, showing improved efficacy compared to standard Dox or anti-PD-1 therapy. In mice bearing dual tumors, with one tumor site injected locally with SQL70, we observed that SQP33 can induce a response in both primary and secondary tumors, suggestive of an anti-tumor immune activation effect. Furthermore, we found that SQ3370 synergizes with anti-PD-1, expanding potential treatment options in the clinic and highlighting the advantages of immune-sparing cytotoxic therapy. Collectively, our results demonstrate that SQ3370 enables delivery of cytotoxic drugs to a target site while limiting exposure in off-target tissues in small and large animals, leading to improvements in both safety and efficacy. Citation Format: Nathan A. Yee, Sangeetha Srinivasan, Maksim Royzen, Jose M. Mejia Oneto. SQ3370 enhances the safety of chemotherapeutics via local activation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-002.