Purpose: Although remarkably effective in some patients, precision medicine typically induces only transient responses despite initial absence of resistance-conferring mutations. Using BRAF-mutated myeloma as a model for resistance to precision medicine we investigated if BRAF-mutated cancer cells have the ability to ensure their survival by rapidly adapting to BRAF inhibitor treatment.
Experimental design: Full-length single cell (sc)RNA-seq was conducted on three patients with BRAF-mutated myeloma and one healthy donor. We sequenced 1495 cells before, after one week and at clinical relapse to BRAF/ MEK inhibitor treatment. We developed an in vitro model of dabrafenib-resistance using genetically homogeneous single-cell clones from two cell lines with established BRAF mutations (U266, DP6). Transcriptional and epigenetic adaptation in resistant cells were defined by RNA-seq and H3K23ac ChIP-seq. Mitochondrial metabolism was characterized by metabolic flux analysis.
Results: Profiling by scRNA-seq revealed rapid cellular state changes in response to BRAF/MEK inhibition in myeloma patients and cell lines. Transcriptional adaptation preceded detectable outgrowth of genetically discernible drug-resistant clones and was associated with widespread enhancer remodeling. As a dominant vulnerability, dependency on oxidative phosphorylation (OxPhos) was induced. In treated individuals, OxPhos was activated at the time of relapse and showed inverse correlation to MAPK activation. Metabolic flux analysis confirmed OxPhos as a preferential energetic resource of drug-persistent myeloma cells.
Conclusions: This study demonstrates that cancer cells have the ability to rapidly adapt to precision treatments through transcriptional state changes, epigenetic adaptation and metabolic rewiring, thus facilitating the development of refractory disease while simultaneously exposing novel vulnerabilities.
Copyright ©2021, American Association for Cancer Research.