Abstract 6419: Novel ferrous iron-dependent prodrug strategy for KRAS-driven pancreatic cancer: The preclinic efficacy and safety test
Authors: Jiang Honglin , Muir Ryan , Renslo Adam , Collisson Eric 
Published: September 2020

Genomic KRAS alterations are identified in &gt;90% of pancreatic adenocarcinomas (PDA), but there are no efficient targeted therapies for these patients. RAF-MEK-MAPK is frequently cited as a frequent potentiator in RAS-driven malignancies. Directly inhibiting the biochemical output of oncogenic Ras and Raf via MEK inhibition has been an interest for almost two decades and is now approved. However, it has not lived up to its full potential. Because MEK function is essential in many healthy tissues, on-target side effects accumulate in the eye, skin and other organs, substantially limiting the clinical tolerance of MEK inhibition (MEKi). Inspired by the remarkable pharmacology of antimalarial endoperoxides, we have extended the concept of Fe2+-dependent pharmacology to other disease states, which are characterized by elevated levels or aberrant production of free redox-active Fe2+by reimagining the 1,2,4-trioxolane ring as a selective detector of free Fe2+. We re-engineered the trioxolane pharmacophore to produce a new scaffold (denoted “TRX” herein); enabling Fe2+dependent release of a drug payload. We next found that mutant Kras alone is sufficient to initiate an elevated labile iron pool and is necessary to maintain elevated Fe2+levels in PDA. These findings encouraged us to link an FDA-approved, orally bioavailable cobimetinib (COBI) to a trioxolane pharmacophore (yielding TRX-COBI). We first assessed the stability TRX-COBI by profiling of the prodrug and parent in the plasma of normal mice after intraperitoneal (IP) administration and found the TRX-Conjugated form to be very stable, with only 3% (by AUC) of TRX-COBI being deconjugated in serum. Next, we applied orthotopically (in the pancreas) KrasG12D, Tp53 flox/floxcells grafted into syngeneic, immunocompetent FVB mice and treated the mice with MEKi or TRX-MEKi and harvested the tumors and skin after 2 weeks. We find that TRX-MEK (dosed equimolar to MEKi), inhibits pERK in PDA tumors in vivo. Additionally, these same animals demonstrate decreased skin toxicity in tail skin. To validate these findings further, we used a patient derived xenograft (PDX 232) from a KRAS mutated PDA and compared the therapeutic efficacy of COBI payloads. It shows that TRX-COBI potently inhibited pERK in human PDX cells in nude mice, and was as efficacious as the parent drug. In addition, when combined with SHP2 inhibitor, higher dose of TRX-COBI was tolerable and showing better tumor growth inhibition in another lung PDX model carrying KRASG12C. Together, these results show the in vivo activity, stability and mitigated toxicity of the TRX-prodrug approach in KRAS-driven pancreatic cancer.

Citation Format: Honglin Jiang, Ryan Muir, Adam Renslo, Eric Collisson. Novel ferrous iron-dependent prodrug strategy for KRAS-driven pancreatic cancer: The preclinic efficacy and safety test [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6419.