Plexxikon has announced positive Phase I trial results of PLX4032 (RG7204), confirming the drug significantly shrank tumours in the majority of metastatic melanoma patients with BRAF V600E mutation.

The primary objectives of the melanoma cohort study included establishing the safety and pharmacokinetics of the drug beyond the dose escalation phase, and demonstration of proof-of-concept in the target population at the maximum tolerated dose of 960mg, twice daily.

The melanoma cohort of the study showed that among 32 patients with metastatic melanoma, there was 81% response rate by RECIST criteria.

There were two complete responses, and 24 partial responses with at least 30% tumour shrinkage.

All but two patients demonstrated tumour regression, and the progression-free survival among these patients was at least seven months.

Plexxikon CEO K Peter Hirth said that the PLX4032 trial represents the first evidence that a treatment that targets activating BRAF mutations can induce significant tumour regressions in patients.

“These data are particularly encouraging, with responses observed at all sites of disease, including challenging visceral lesions in the bone, liver and small bowel,” Hirth added.

The study results were published in the New England Journal of Medicine.