Anti-mitochondrial therapy in human breast cancer multi-cellular spheroids

Abstract

During multi-cellular tumor spheroid growth, oxygen and nutrient gradients develop inducing specific genetic and metabolic changes in the proliferative and quiescent cellular layers. An integral analysis of proteomics, metabolomics, kinetomics and fluxomics revealed that both proliferative- (PRL) and quiescent-enriched (QS) cellular layers of mature breast tumor MCF-7 multi-cellular spheroids maintained similar glycolytic rates (3–5nmol/min/106 cells), correlating with similar GLUT1, GLUT3, PFK-1, and HKII contents, and HK and LDH activities. Enhanced glycolytic fluxes in both cell layer fractions also correlated with higher HIF-1α content, compared to MCF-7 monolayer cultures. On the contrary, the contents of the mitochondrial proteins GA-K, ND1, COXIV, PDH-E1α, 2-OGDH, SDH and F1-ATP synthase (20 times) and the oxidative phosphorylation (OxPhos) flux (2-times) were higher in PRL vs. QS. Enhanced mitochondrial metabolism in the PRL layers correlated with an increase in the oncogenes h-Ras and c-Myc, and transcription factors p32 and PGC-1α, which are involved in the OxPhos activation. On the other hand, the lower mitochondrial function in QS was associated with an increase in Beclin, LC3B, Bnip3 and LAMP protein levels, indicating active mitophagy and lysosome biosynthesis processes. Although a substantial increase in glycolysis was developed, OxPhos was the predominant ATP supplier in both QS and PRL layers. Therefore, targeted anti-mitochondrial therapy by using oligomycin (IC50=11nM), Casiopeina II-gly (IC50=40nM) or Mitoves (IC50=7nM) was effective to arrest MCF-7 spheroid growth without apparent effect on normal epithelial breast tissue at similar doses; canonical anti-neoplastic drugs such as cisplatin and tamoxifen were significantly less potent.