Developing engineered inhibitors of tRNA modifying enzymes

Project Summary/Abstract Liver cancer is a growing public health concern, with new cases expected to rise by over 55% by 2040. Liver cancer was the third most common cause of cancer fatalities in 2020. Hepatocellular carcinoma (HCC) accounts for over 90% of all liver cancer cases. Current frontline therapies for HCC are inadequate: the 5-year survival rate for patients is below 15%, making it the second most lethal form of cancer. The goal of this Small Business Transition Grant proposal is to substantially speed pre-clinical development of a promising new approach to treat HCC and support the entrepreneurial training of an early career scientist as he assumes a leadership role in a burgeoning small business. Our research has discovered a new and targetable vulnerability of HCC cells. HCC cells are dependent on the high expression of multiple tRNA-modifying enzymes to support their proliferation and metastasis. We have developed a novel therapeutic approach to irreversibly inhibit these enzymes to slow cancer growth and halt disease progression. Using engineered tRNAs containing 5-fluoro-uracil (5-FU), an FDA-approved chemotherapeutic agent, we can target multiple tRNA modifying enzymes using the same molecule. This multi-target activity dramatically increases therapeutic efficacy. Our preliminary data indicates that CLB-001 has an IC50 that is over 7,000 times lower than that of free 5-FU alone in HCC cells. Our lead candidate engineered tRNA containing 5-FU, CLB-001, exhibits a nanomolar IC50 in HCC cells and outperforms the standard of care (sorafenib) in vivo. Notably, CLB-001 has a wide therapeutic index in vitro and exhibits no signs of toxicity in vivo at effective dose levels. To advance the pre-clinical development of our therapeutic tRNAs, we will: (1) Develop additional in vitro-optimized therapeutic tRNAs for HCC treatment, (2) validate the efficacy of these tRNAs in patient-derived tumoroid models of HCC, (3) perform preliminary dose-escalation toxicology studies in mice, (4) demonstrate in vivo efficacy in orthotopically-implanted patient-derived xenograft and syngeneic models of HCC, and (5) obtain pre-clinical pharmacokinetic and toxicology data in rats on the pathway to an IND submission. The development of a therapeutic tRNA as a potent HCC therapy has the potential to improve the clinical outcomes for millions of HCC patients worldwide.