Preliminary results from ERAS-007 plus encorafenib and cetuximab (EC) in patients (pts) with metastatic BRAF V600E mutated colorectal cancer (CRC) in HERKULES-3 study: A phase 1b/2 study of agents targeting the mitogen-activated protein kinase (MAPK) pathway in pts with advanced gastrointestinal malignancies (GI cancers)

3557 Background: The RAS/MAPK pathway (including BRAF) is dysregulated in a broad range of cancers including CRC, resulting in downstream activation of ERK1/2. Metastatic CRC with BRAF V600E mutation (BRAF V600E mCRC) has dramatically worse survival than non-BRAF V600E mutated CRCs, and novel therapies are needed. ERAS-007 is a novel, potent, and orally bioavailable inhibitor of ERK. The combination of a BRAF plus EGFR inhibitor (EC) is approved for the treatment of pts with BRAF V600E mCRC; however, only 20% of pts experience an objective response. ERAS-007 alone or in combination with EC showed promising in vitro and in vivo activity in BRAF V600E CRC models to support the combinatorial clinical benefit of ERAS-007+EC in BRAF V600E mCRC. Methods: HERKULES-3 is a Phase 1b/2 study to assess the safety, tolerability, PK, and preliminary clinical activity of ERAS-007 combinations targeting the MAPK pathway in pts with advanced GI cancers. Within this study, we are currently evaluating the safety and tolerability of escalating doses of ERAS-007 + EC in pts with BRAF V600E CRC. Prior BRAF inhibitor and EGFR inhibitor treatment is neither required nor excluded to be enrolled in this study. Results: As of 30 November 2022, 12 patients were dosed with ERAS-007 twice daily-once a week (BID-QW) (75 and 100 mg; n = 10) or once daily once a week (QW) (150 mg; n = 2) in combination with EC (300 mg oral daily + 500 mg/m2 intravenous infusion once every 2 weeks). The treatment-emergent AEs (TEAEs) occurring in ≥20% of pts were fatigue (50%), headache (42%), constipation, diarrhea, nausea, dermatitis acneiform (33% each), and vomiting (25%). No TEAEs led to ERAS-007 discontinuation or death. Grade ≥3 TEAEs were reported in 3 pts (25%). Grade ≥3 treatment-related AEs reported in ≥ 2 patients (17%) include hypertension, headache, confusional state, and skin toxicity. Three pts (25%) died due to disease progression. No DLTs were reported. Out of 4 efficacy evaluable EC naïve pts, one confirmed partial response (PR) and one unconfirmed PR were observed. Evaluation of PK is ongoing and preliminary data will be presented. Conclusions: ERAS-007+EC in pts with BRAF V600E CRC shows acceptable preliminary safety/tolerability and evidence of clinical activity. The highest dose of ERAS-007 evaluated and cleared by the safety review committee to date is 100 mg BID-QW when combined with EC. Observed PK, toxicity, and preliminary activity support continued evaluation of this combination in pts with BRAF V600E CRC. Clinical trial information: NCT05039177 .