Biomarker-Guided Drug Combinations May Overcome Treatment Resistance in Advanced Melanoma
Key Insights
MD Anderson researchers demonstrated that adding BCL2 (search) or MCL1 inhibitors to standard BRAF (search)-MEK (search) therapy can overcome acquired resistance in preclinical melanoma (search) models.
Tumors with high BCL2 (search) expression responded to the addition of navitoclax or venetoclax, while high-MCL1 tumors required an MCL1 inhibitor (AZD5991) for complete regression.
BRAF (search)-MEK (search) inhibitors unexpectedly protected heart cells from MCL1 inhibitor toxicity, potentially reviving a drug class stalled by cardiac side effects.
A new preclinical study from The University of Texas MD Anderson Cancer Center has demonstrated that treatment-resistant advanced melanoma (search) can be overcome by tailoring drug combinations to the specific survival proteins that individual tumors rely on. Published in Nature Communications, the research shows that adding inhibitors targeting BCL2 (search) family proteins to standard BRAF (search)-MEK (search) therapy can induce tumor regression in molecularly defined subsets of resistant tumors.
Approximately half of all melanomas carry a BRAF (search) mutation, and the standard of care for nearly a decade has been combined BRAF and MEK (search) inhibition. While most patients initially respond, roughly 80% develop acquired resistance and disease progression within two years. The study, led by Vashisht Gopal Yennu Nanda, Ph.D., associate professor of Melanoma (search) Medical Oncology and Translational Molecular Pathology, and senior author Michael A. Davies, M.D., Ph.D., chair of Melanoma Medical Oncology, sought to understand and address this resistance.
"Targeted therapy works by shutting down the main signal driving melanoma (search) growth, but tumors often have backup systems that keep them alive," Yennu Nanda said. "By identifying which protein a tumor relies on for survival, we may be able to match patients to drug combinations tailored to their specific tumor biology."
The role of BCL2 (search) family survival proteins
Cancer cells frequently evade therapy by increasing production of survival proteins in the BCL2 (search) family — primarily BCL2, BCL-xL, and MCL1. The MD Anderson team confirmed that melanoma (search) tumors express unusually high levels of these proteins compared with most other cancer types, and that BCL2 levels increase in patients following BRAF (search)-MEK (search) inhibitor therapy, likely contributing to treatment resistance.
Using a large collection of patient-derived xenograft (PDX) models established from melanomas with acquired resistance to standard therapy, the researchers tested adding a BCL2 (search) inhibitor — either navitoclax or venetoclax — to the standard two-drug regimen. A subset of previously resistant tumors regressed with the new triple combination.
Biomarker-driven response patterns
The response to BCL2 (search) inhibition was not uniform. Tumors with high baseline levels of BCL2 tended to respond, while tumors with high baseline MCL1 expression tended to resist. To confirm MCL1's role, the researchers artificially raised its levels in tumor cells, which induced resistance to the triple combination.
For tumors overproducing MCL1, the team tested an alternative approach: pairing BRAF (search)-MEK (search) inhibitors with the experimental MCL1 inhibitor AZD5991. In a high-MCL1 PDX model, this combination produced complete tumor regression, with no detectable tumors at the end of the experiment.
Unexpected cardioprotective effect
MCL1 inhibitors have previously demonstrated antitumor activity but have been associated with heart-related side effects in early clinical trials, leading several studies to be paused or halted. In this study, adding BRAF (search)-MEK (search) inhibitors appeared to protect heart cells from the damaging effects of the MCL1 inhibitor.
In laboratory models, the MCL1 inhibitor alone disrupted cardiac cell energy production and caused signs of damage. Adding BRAF (search) and MEK (search) inhibitors largely reversed these effects, potentially because the MEK inhibitor helped restore energy production in heart cells that MCL1 inhibitors otherwise disrupt.
"We did not anticipate that pairing these drugs would reduce MCL1 inhibitor toxicity," Davies said. "If this finding is confirmed in clinical trials, it could give a second life to a class of drugs that has struggled to advance through development. It also reinforces that the most effective combinations are those that eliminate cancer while sparing healthy tissue."
Next steps toward clinical translation
These findings support the design of biomarker-guided clinical trials that match patients to drug combinations based on tumor BCL2 (search) and MCL1 expression. The research team is currently analyzing samples from a recent randomized Phase 2 clinical trial of dabrafenib, trametinib, and navitoclax in BRAF (search)-mutant melanoma (search) patients to determine whether MCL1 expression predicted clinical response. Additional preclinical and translational studies will be needed to evaluate the safety of BRAF-MEK (search) inhibitor and MCL1 inhibitor combinations before they can be evaluated in patients.
"Patients whose melanoma (search) has stopped responding to standard therapies currently have very few effective treatment options," Yennu Nanda said. "Our findings could help address this critical need for these patients by guiding clinicians toward combinations tailored to each individual's tumors."