RNA-seq of AsPC-1 cell line-derived xenograft mouse tumors treated with a MEK-RAF molecular glue, IK-595

MAPK pathway alterations are the most common oncogenic drivers. Among the approved therapies targeting this pathway are MEK and RAF inhibitors. However, therapeutic resistance and toxicities have limited their clinical success. To overcome these liabilities, we developed IK595, a potent MEK-RAF molecular glue. IK-595 traps MEK in an inactive complex with all RAF isoforms. In addition, IK-595 precludes CRAF-mediated MEK reactivation and ARAF heterodimerization allowing for prolonged target engagement and durable MAPK pathway inhibition. This project aimed to explore gene expression modulation by IK-595 in AsPC-1 cell line-derived xenograft mice at different time points following last dose. Tumor RNA-seq was performed in AsPC-1 tumor-bearing mice treated with three doses of vehicle or IK-595 (at 6 mg/kg QOD). Tumors from the drug-treated mice were collected and profiled at the following time points after the last dose: 2 hours, 4 hours, 8 hours, 24 hours, and 48 hours (four animals per time point group) - to understand longitudinal gene expression changes after dosing. A significant reduction in most ERK1/2 target genes was observed as early as 2 hours after the last dose, with maximal inhibition observed at 8 hours. Partial recovery of ERK1/2 target gene expression occurred at 24 hours, with most genes returning to baseline levels by 48 hours. While elevated pathway activation following chronic treatment of MAPK pathway inhibitors is known to be associated with resistance in the literature, the expression of ERK1/2 target genes in our study never rebounded above baseline levels upon IK-595 treatment.