Antitumor activity of panRAF inhibition in BRAF V600E metastatic colorectal cancer.

Abstract

616 Background: BRAF V600E mutations, present in <10% of patients with metastatic colorectal cancer (mCRC), are associated with low responses to chemotherapy and poor survival outcomes. Targeted therapies against BRAF and EGFR have shown promising clinical activity. The panRAF inhibitor (PRI) LSN3074753 inhibits dimerization of all RAF isoforms to impede downstream MEK activation, with no reflexive MAPK reactivation common with other BRAF inhibitors. Anti-tumor activity of PRI has not been compared to BRAF + EGFR inhibition in patient-derived xenograft (PDX) models of BRAF V600E mCRC. Methods: Two PDX models of BRAF V600E mCRC (B1003 and C0999) were generated. C0999 featured a concomitant KRAS G12D mutation following resistance to the BRAF V600E kinase inhibitor vemurafenib. Mice were treated daily with oral PRI or with the combination of vemurafenib + intraperitoneal cetuximab. Tumor volumes were measured twice weekly. B1003 and C0999 cell cultures were established to test the interaction between PRI and palbociclib or BYL319 (PI3K inhibitor). Results: PRI was tolerated at a dose of 60 mg/kg and demonstrated a reduced tumor volume in the B1003 model after 28 days when compared to untreated controls (P=.03). No difference in tumor volume was seen between PRI and vemurafenib + cetuximab (P=.08). Assessment of anti-tumor activity by PRI in the vemurafenib-resistant BRAF V600E/KRAS G12D C0999 model will be reported. Cell culture from both the B1003 and C0999 models demonstrated synergism for PRI with palbociclib (ED50 .41 and .62 for the 2 models, respectively) and with BYL319 (ED50 .48 and .86, respectively). Conclusions: panRAF inhibition demonstrates similar anti-tumor activity to BRAF + EGFR inhibition in PDX models of BRAF V600E and represents a promising treatment strategy for further combination studies targeting additional critical signaling pathways in mCRC.