The effect of a chemotherapy drug cocktail on myotube morphology, myofibrillar protein abundance, and substrate availability

Cachexia, a condition prevalent in many chronically ill patients, is characterized by weight loss, fatigue, and decreases in muscle mass and function. Cachexia is associated with tumor burden and disease‐related malnutrition, but other studies implicate chemotherapy as being causative. We investigated the effects of a chemotherapy drug cocktail on myofibrillar protein abundance and synthesis, anabolic signaling mechanisms, and substrate availability. On day 4 of differentiation, L6 myotubes were treated with vehicle (1.4 μl/ml DMSO) or a chemotherapy drug cocktail (a mixture of cisplatin [20 μg/ml], leucovorin [10 μg/ml], and 5‐fluorouracil [5‐FLU; 50 μg/ml]) for 24–72 h. Compared to myotubes treated with vehicle, those treated with the drug cocktail showed 50%–80% reductions in the abundance of myofibrillar proteins, including myosin heavy chain‐1, troponin, and tropomyosin (p < 0.05). Cells treated with only a mixture of cisplatin and 5‐FLU had identical reductions in myofibrillar protein abundance. Myotubes treated with the drug cocktail also showed >50% reductions in the phosphorylation of AKT(Ser473) and of mTORC1 substrates ribosomal protein S6(Ser235/236), its kinase S6K1(Thr389) and eukaryotic translation initiation factor 4E‐binding protein 1 (all p < 0.05). Drug treatment impaired peptide chain initiation in myofibrillar protein fractions and insulin‐stimulated glucose uptake (p = 0.06) but increased the expression of autophagy markers beclin‐1 and microtubule‐associated proteins 1A/1B light chain 3B (p < 0.05), and of apoptotic marker, cleaved caspase 3 (p < 0.05). Drug treatment reduced the expression of mitochondrial markers cytochrome oxidase and succinate dehydrogenase (p < 0.05). The observed profound negative effects of this chemotherapy drug cocktail on myotubes underlie a need for approaches that can reduce the negative effects of these drugs on muscle metabolism.