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Modulation of intermediary metabolism in cancer therapy
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Figure 5. Modulation of mammalian target of rapamycin signaling enhances sensitivity to BH3 mimetics independently of autophagy. (A) Apoptotic sensitivity of K562 resistant [E] cells exposed to A-1331852 (10 nM) for 4 h was restored following pharmacological inhibition of mTOR signaling using rapamycin (100 nM) or torin-1 (10 nM) for 16 h. (B) Inhibition of mTOR-regulated autophagy using 3-MA (10 mM) or bafilomycin A1 (100 nM) for 1 h, followed by torin-1 (10 nM) for a further 16 h, resulted in varying effects on A-1331852-mediated apoptosis. (C) Genetic knockdown of ATG5 and ATG7 for 72 h failed to revert torin-1 (10 nM)-mediated sen- sitization of apoptosis in K562 resistant [E] cells, following A-1331852 (10 nM) for 4 h. Western blots confirmed the knockdown efficiency of ATG5 and ATG7 short interfering (si) RNA. ***P⩽0.001. Error bars = mean ± standard error of mean (n=3). (D) Scheme representing glutamine uptake by SLC1A5 (inhibited by GPNA), glutaminolysis (inhibited by CB-839) to generate α-ketoglutarate, reductive carboxylation of a-ketoglutarate to generate citrate, which produces acetyl-CoA by a reac- tion catalyzed by ACLY (inhibited by SB204990), which eventually results in lipogenesis (inhibited by GSK2194069) and cholesterogenesis (inhibited by statins). Glutamine uptake, metabolism and its downstream signaling cascade can feed into mTOR signaling (inhibited by torin-1), all of which promote cell growth. In this study, we demonstrate that modulation of these distinct intermediary metabolic pathways could successfully sensitize cancer cells to BH3 mimetic-mediated apop- tosis. PS: phosphatidylserine; DMSO: dimethylsulfoxide; TCA: tricarboxylic acid.
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Figure 6. Inhibition of glutami- nase and HMG-CoA reductase circumvents resistance to navi- toclax-mediated apoptosis in primary chronic lymphocytic leukemia cells. Chronic lympho- cytic leukemia cells isolated from five patients during the ini- tial lead-in-period (L1D1) or day 1 of cycle 5 (C5D1) were cul- tured ex vivo on a feeder layer for 24 h and then exposed for a further 24 h to (A) CB-839 (50 nM) or (B) simvastatin (10 nM), and removed from the feeder layer for further exposure to navitoclax (50 nM) for 4 h. The extent of apoptosis was assessed as before. *P⩽0.05. Error bars = mean ± standard error of mean (n=5). PS: phos- phatidylserine; DMSO: dimethyl- sulfoxide.
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