CHICAGO – The combination of two oral drugs that target selected molecules in the mitogen-activated protein kinase signaling pathway appears to be safe and active in patients with melanoma, a phase I trial found. The finding was reported at the annual meeting of the American Society of Clinical Oncology.
Among patients with BRAF-mutated melanoma who had not previously received an agent targeting that molecule, the combination of an investigational BRAF inhibitor (GSK436) and an investigational MEK inhibitor (GSK212) achieved a response rate of 50%-77%.
Dr. Jeffrey R. Infante
Both drugs could be used in their full monotherapy doses when combined. And the combination was well tolerated; indeed, certain adverse effects that were seen with each drug when used alone (such as a rash with MEK inhibitor monotherapy) were less common when they were used together.
"The clinical activity in BRAF V600–mutant melanoma is definitely compelling," commented lead investigator Dr. Jeffrey R. Infante, a medical oncologist and director of drug development at the Sarah Cannon Research Institute in Nashville, Tenn. "But like everyone in the audience, I think, we are anxiously awaiting the long-term durability" data. "This combination could have potential implications in multiple tumor types outside of melanoma and have broader impacts in oncology," he added.
"I am really impressed by these data," said discussant Dr. Reinhard Dummer of the University Hospital Zurich. In particular, although the trial was not designed to assess responses and the follow-up is still short, some of the patients had complete remissions, he noted.
"I have to admit, I never thought that we could have complete remissions with kinase inhibitors, so I hope that they will continue," he said. "With this in mind, I think we can reset our goals for melanoma research: We don't want to go for progression-free survival in the future, but we should go for cure."
The reduced rate of the inflammatory rash with the combination was "very surprising," given that the rash is likely a stress response resulting from the MEK inhibitor's effect on the MAP [mitogen-activated protein] kinase pathway in the skin, Dr. Dummer said. "How can it happen that this rash is reduced in the combination with the BRAF inhibitor? This is completely not understandable for me. Cutaneous biologists will have a lot of fun to study this model."
Both drugs, which are manufactured by GlaxoSmithKline, have previously shown activity as single agents in patients who have melanoma with BRAF V600 gene mutations, which are found in about half of cases. "The goal was to ... give [the drugs] together and really hope to get a profound synergy in combination in pathway inhibition," explained Dr. Infante.
Patients were eligible for the trial if they had melanoma or another cancer with a V600 mutation in the BRAF gene. Those who had stable brain metastases after surgery or radiosurgery could enroll.
Patients having certain eye conditions were excluded because of previously identified, related issues associated with MEK inhibitor therapy. But there was no limit on the number of prior therapies.
In part A of the study, the investigators tested for drug-drug interactions. In part B, they performed dose escalation, assessed safety and activity, and enrolled expansion cohorts of patients, such as those who had previously received a BRAF inhibitor.
Among the eight patients in part A, there was no effect of the MEK inhibitor when given daily on the pharmacokinetics of single doses of the BRAF inhibitor, Dr. Infante reported.
Of the 109 patients in part B, fully 93% had melanoma and 91% specifically had the V600E BRAF mutation. The majority (54%) had received at least two prior lines of systemic anticancer therapy.
Dose-escalation results showed that both drugs could be given in combination at their full monotherapy doses (150 mg twice daily of the BRAF inhibitor and 2 mg once daily of the MEK inhibitor), largely without dose-limiting toxicities.
Only one dose-limiting toxicity was seen with the full dose of each drug. The patient developed a neutrophilic panniculitis, manifesting as painful red nodules on the thorax and extremities, in association with fever and chills. It resolved with discontinuation of the drugs and steroid therapy.
Across the dose combinations, 79% of patients experienced an adverse event and 19% experienced a grade 3 or higher adverse event, most often neutropenia, leukopenia, diarrhea, and fever. There was no clear association with doses, according to Dr. Infante.
In a finding as yet without explanation, certain adverse events that had been seen previously with each drug when they were given alone were actually less common when they were combined. Specifically, rash occurred in 25% of patients, whereas historically it has been seen in 75%-80% of those given the MEK inhibitor alone. And squamous cell carcinoma and other hyperproliferative skin lesions were seen in roughly 1%, whereas they have been seen in 7%-15% of those given the BRAF inhibitor alone.