Extracellular signal-regulated kinase-1/2 (ERK1/2) pathway inhibitors are important therapies for treating many cancers. However, acquired resistance to most protein kinase inhibitors limits their ability to provide durable responses. Approximately 50% of malignant melanomas contain activating mutations in BRAF, which promotes cancer cell survival through the direct phosphorylation of the mitogen-activated protein kinase MAPK/ERK 1/2 (MEK1/2) and the activation of ERK1/2. Although the combination treatment with BRAF and MEK1/2 inhibitors is a recommended approach to treat melanoma, the development of drug resistance remains a barrier to achieving long-term patient benefits. Few studies have compared the global proteomic changes in BRAF/MEK1/2 inhibitor-resistant melanoma cells under different growth conditions. The current study uses high-resolution label-free mass spectrometry to compare relative protein changes in BRAF/MEK1/2 inhibitor-resistant A375 melanoma cells grown as monolayers or spheroids. While approximately 66% of proteins identified were common in the monolayer and spheroid cultures, only 6.2 or 3.6% of proteins that significantly increased or decreased, respectively, were common between the drug-resistant monolayer and spheroid cells. Drug-resistant monolayers showed upregulation of ERK-independent signaling pathways, whereas drug-resistant spheroids showed primarily elevated catabolic metabolism to support oxidative phosphorylation. These studies highlight the similarities and differences between monolayer and spheroid cell models in identifying actionable targets to overcome drug resistance.

The decline in the mass and function of bone and muscle is an inevitable consequence of healthy aging with early onset and accelerated decline in those with chronic disease. Termed osteo-sarcopenia, this condition predisposes the decreased activity, falls, low-energy fractures, and increased risk of co-morbid disease that leads to musculoskeletal frailty. The biology of osteo-sarcopenia is most understood in the context of systemic neuro-endocrine and immune/inflammatory alterations that drive inflammation, oxidative stress, reduced autophagy, and cellular senescence in the bone and muscle. Here we integrate these concepts to our growing understanding of how bone and muscle senses, responds and adapts to mechanical load. We propose that age-related alterations in cytoskeletal mechanics alter load-sensing and mechano-transduction in bone osteocytes and muscle fibers which underscores osteo-sarcopenia. Lastly, we examine the evidence for exercise as an effective countermeasure to osteo-sarcopenia.