Combined CDK4/6 and ERK1/2 inhibition enhances anti-tumor activity in NF1-associated plexiform neurofibroma [sciatic nerve]

Purpose: Plexiform neurofibromas (PNF) are peripheral nerve sheath tumors that cause significant morbidity in persons with neurofibromatosis type 1 (NF1), yet treatment options remain limited. To identify novel therapeutic targets for PNF, we applied an integrated multi-omics approach to quantitatively profile kinome activation in a mouse model that has predicted therapeutic responses in clinical trials for NF1-associated PNF with high fidelity. Experimental Design: Utilizing RNA sequencing combined with chemical proteomic profiling of the functionally enriched kinome using multiplexed inhibitor beads coupled with mass spectrometry, we identified molecular signatures predictive of response to CDK4/6 and RAS/MAPK pathway inhibition in PNF. Informed by these results, we evaluated the effectivity of the CDK4/6 inhibitor, abemaciclib, and the ERK1/2 inhibitor (LY3214996) alone and in combination to reduce PNF tumor burden in Nf1flox/flox;PostnCre mice. Results: Converging signatures of CDK4/6 and RAS/MAPK pathway activation were identified within the transcriptome and kinome that were conserved in both murine and human PNF. We observed robust synergism of the CDK4/6 inhibitor, abemaciclib, in combination with the ERK1/2 inhibitor (LY3214996) in primary Nf1-/- Schwann cell cultures. Consistent with these findings, the combination of abemaciclib (CDK4/6i) and LY3214996 (ERK1/2i) synergized to suppress molecular signatures of MAPK activation and exhibited enhanced anti-tumor activity in Nf1flox/flox;PostnCre mice in vivo. Conclusion: These findings provide rationale for the clinical translation of CDK4/6 inhibitors alone and in combination with therapies targeting the RAS/MAPK pathway for the treatment of PNF and other peripheral nerve sheath tumors in persons with NF1. Overall design: RNAseq of sciatic nerve from Nf1 flox/flox PostnCre+ (Nf1) mice treated with Vehicle, abemaciclib (CDK4/6i), LY3214996 (ERK1/2i), or abemaciclib (CDK4/6i) and LY3214996 (ERK1/2i) for 1 week 24 experimental samples