Combined BRAF, MEK, and heat‐shock protein 90 inhibition in advanced BRAF V600‐mutant melanoma

• Published in: Cancer Vol. 130; no. 2; pp. 232 - 243
• Main Authors: Eroglu, Zeynep, Chen, Y. Ann, Smalley, Inna, Li, Jiannong, Markowitz, Joseph K., Brohl, Andrew S., Tetteh, Leticia, Taylor, Hayley, Sondak, Vernon K., Khushalani, Nikhil I., Smalley, Keiran S. M.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-01-2024
• Subjects: Antineoplastic Combined Chemotherapy Protocols - adverse effects; Biopsy; BRAF; CD4 antigen; CD8 antigen; Exanthema - chemically induced; Exanthema - drug therapy; Gene sequencing; Heat shock proteins; Heat-Shock Proteins - genetics; Heat-Shock Proteins - therapeutic use; heat‐shock protein 90 (HSP90); Hsp90 protein; Humans; Immune system; Inhibitors; Injury prevention; Lymphocytes; Lymphocytes T; MEK; MEK inhibitors; Melanoma; Melanoma - drug therapy; Melanoma - genetics; Melanoma - pathology; Mitogen-Activated Protein Kinase Kinases - genetics; Mutants; Mutation; Protein Kinase Inhibitors - adverse effects; Proto-Oncogene Proteins B-raf; Shock resistance; single cell; Skin Neoplasms - drug therapy; Skin Neoplasms - genetics; Skin Neoplasms - pathology; Survival; Toxicity; Vemurafenib; melanoma; MEK; heat-shock protein 90 (HSP90); single cell; BRAF
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/cncr.35029

Background
Resistance to BRAF and MEK inhibitors in BRAF V600‐mutant melanoma is common. Multiple resistance mechanisms involve heat‐shock protein 90 (HSP90) clients, and a phase 1 study of vemurafenib with the HSP90 inhibitor XL888 in patients with advanced melanoma showed activity equivalent to that of BRAF and MEK inhibitors.
Methods
Vemurafenib (960 mg orally twice daily) and cobimetinib (60 mg orally once daily for 21 of 28 days) with escalating dose cohorts of XL888 (30, 45, 60, or 90 mg orally twice weekly) was investigated in a phase 1 trial of advanced melanoma, with a modified Ji dose‐escalation design.
Results
Twenty‐five patients were enrolled. After two dose‐limiting toxicities (DLTs) (rash and acute kidney injury) in the first cohort, lower doses of vemurafenib (720 mg) and cobimetinib (40 mg) were investigated with the same XL888 doses. Three DLTs (rash) were observed in 12 patients in the XL888 60‐mg cohort, and this was determined as the maximum tolerated dose. Objective responses were observed in 19 patients (76%), and the median progression‐free survival was 7.6 months, with a 5‐year progression‐free survival rate of 20%. The median overall survival was 41.7 months, with a 5‐year overall survival rate of 37%. Single‐cell RNA sequencing was performed on baseline and on‐treatment biopsies; treatment was associated with increased immune cell influx (CD4‐positive and CD8‐positive T cells) and decreased melanoma cells.
Conclusions
Combined vemurafenib and cobimetinib plus XL888 had significant toxicity, requiring frequent dose reductions, which may have contributed to the relatively low progression‐free survival despite a high tumor response rate. Given overlapping toxicities, caution must be used when combining HSP90 inhibitors with BRAF and MEK inhibitors.
Resistance to BRAF and MEK inhibitors in BRAF V600‐mutant melanoma is common, and many of the resistance mechanisms involve heat‐shock protein 90 client proteins. The combination of vemurafenib plus cobimetinib plus XL888 was evaluated in a phase 1 trial of patients with advanced melanoma and had significant toxicity, requiring frequent dose reductions, which may have contributed to the relatively low progression‐free survival despite a high tumor response rate.