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During glutamine sufficiency, both Notch‐positive and Notch‐negative T‐ALL cells promote glutamine catabolism, leading to mammalian target of rapamycin complex 1 (mTORC1) activation and cell growth and proliferation. However, during glutamine scarcity, only Notch‐negative T‐ALL cells can perform a metabolic adaptation by promoting glutamine synthesis. By contrast, Notch‐positive T‐ALL cells maintain glutamine catabolism during glutamine restriction, leading to glutamine addiction and mTORC1 dependency., The cellular receptor Notch1 is a central regulator of T‐cell development, and as a consequence, Notch1 pathway appears upregulated in > 65% of the cases of T‐cell acute lymphoblastic leukemia (T‐ALL). However, strategies targeting Notch1 signaling render only modest results in the clinic due to treatment resistance and severe side effects. While many investigations reported the different aspects of tumor cell growth and leukemia progression controlled by Notch1, less is known regarding the modifications of cellular metabolism induced by Notch1 upregulation in T‐ALL. Previously, glutaminolysis inhibition has been proposed to synergize with anti‐Notch therapies in T‐ALL models. In this work, we report that Notch1 upregulation in T‐ALL induced a change in the metabolism of the important amino acid glutamine, preventing glutamine synthesis through the downregulation of glutamine synthetase (GS). Downregulation of GS was responsible for glutamine addiction in Notch1‐driven T‐ALL both in vitro and in vivo. Our results also confirmed an increase in glutaminolysis mediated by Notch1. Increased glutaminolysis resulted in the activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway, a central controller of cell growth. However, glutaminolysis did not play any role in Notch1‐induced glutamine addiction. Finally, the combined treatment targeting mTORC1 and limiting glutamine availability had a synergistic effect to induce apoptosis and to prevent Notch1‐driven leukemia progression. Our results placed glutamine limitation and mTORC1 inhibition as a potential therapy against Notch1‐driven leukemia.

The leading cause of cutaneous squamous cell carcinomas (cSCCs) is exposure to ultraviolet radiation (UV). Unlike most other cancers, the incidence rates of cSCCs are still on the rise and the treatment options currently available are limited. We have recently found that dihydroorotate dehydrogenase (DHODH), which is the rate-limiting enzyme in the de novo pyrimidine synthesis pathway, plays a critical role in UVB-induced energy metabolism reprogramming. Using a multistage model of UVB radiation-induced skin cancer, we show that UVB-induced DHODH upregulation is mainly regulated transcriptionally by STAT3. Our results indicate that chronic inhibition of DHODH by leflunomide (LFN) blocks UVB-induced tumor initiation. Human tumor xenograft studies showed that LFN treatment reduces growth of established tumors when used in combination with a genotoxic agent, 5-fluorouracil (5-FU). Our data suggest that DHODH is a promising target for chemoprevention and combination therapy of UVB-induced cSCCs.

We investigated whether raising HDL-cholesterol levels with cholesteryl ester transfer protein (CETP) inhibition improves glucose homeostasis in dyslipidemic and insulin resistant hamsters. Compared with vehicle, torcetrapib 30 mg/kg/day (TOR) administered for 10 days significantly increased by ∼40% both HDL-cholesterol levels and 3 H-tracer appearance in HDL after 3 H-cholesterol labeled macrophages i.p. injection. TOR significantly reduced fasting plasma triglycerides, glycerol and free fatty acids levels by 65%, 31% and 23%, respectively. TOR also reduced blood glucose levels and plasma insulin by 20% and 49% respectively, which led to a 60% reduction in HOMA-IR index (all p 3 H-2-deoxyglucose and insulin injection, TOR significantly increased glucose uptake in oxidative soleus muscle, liver and heart by 26, 33 and 70%, respectively. Raising HDL levels with the CETP inhibitor torcetrapib improves glucose homeostasis in dyslipidemic and insulin resistant hamsters. Whether similar effect would be observed with other CETP inhibitors should be investigated.

Reverse cholesterol transport (RCT) promotes the egress of cholesterol from peripheral tissues to the liver for biliary and fecal excretion. Although not demonstrated in vivo, RCT is thought to be impaired in patients with metabolic syndrome, in which liver steatosis prevalence is relatively high. Golden Syrian hamsters were fed a nonpurified (CON) diet and normal drinking water or a high-fat (HF) diet containing 27% fat, 0.5% cholesterol, and 0.25% deoxycholate as well as 10% fructose in drinking water for 4 wk. Compared to CON, the HF diet induced insulin resistance and dyslipidemia, with significantly higher plasma non-HDL-cholesterol concentrations and cholesteryl ester transfer protein activity. The HF diet induced severe liver steatosis, with significantly higher cholesterol and TG levels compared to CON. In vivo RCT was assessed by i.p. injecting ³H-cholesterol labeled macrophages. Compared to CON, HF hamsters had significantly greater ³H-tracer recoveries in plasma, but not HDL. After 72 h, ³H-tracer recovery in HF hamsters was 318% higher in liver and 75% lower in bile (P < 0.01), indicating that the HF diet impaired hepatic cholesterol fluxes. However, macrophage-derived cholesterol fecal excretion was 45% higher in HF hamsters than in CON hamsters. This effect was not related to intestinal cholesterol absorption, which was 89% higher in HF hamsters (P < 0.05), suggesting a possible upregulation of transintestinal cholesterol excretion. Our data indicate a significant increase in macrophage-derived cholesterol fecal excretion in a hamster model of metabolic syndrome, which may not compensate for the diet-induced dyslipidemia and liver steatosis.

Cholesteryl ester transfer protein (CETP) inhibitors dalcetrapib and anacetrapib differentially alter LDL- and HDL-cholesterol levels, which might be related to the potency of each drug to inhibit CETP activity. We evaluated the effects of both drugs at similar levels of CETP inhibition on macrophage-to-feces reverse cholesterol transport (RCT) in hamsters. In normolipidemic hamsters, both anacetrapib 30 mg/kg QD and dalcetrapib 200 mg/kg BID inhibited CETP activity by ~60%. After injection of 3H-cholesteryl oleate labeled HDL, anacetrapib and dalcetrapib reduced HDL-cholesteryl esters fractional catabolic rate (FCR) by 30% and 26% (both P

Objective— This study aimed to investigate whether cholesteryl ester transfer protein inhibition promotes in vivo reverse cholesterol transport in dyslipidemic hamsters. Methods and Results— In vivo reverse cholesterol transport was measured after an intravenous injection of 3 H-cholesteryl-oleate–labeled/oxidized low density lipoprotein particles ( 3 H-oxLDL), which are rapidly cleared from plasma by liver-resident macrophages for further 3 H-tracer egress in plasma, high density lipoprotein (HDL), liver, and feces. A first set of hamsters made dyslipidemic with a high-fat and high-fructose diet was treated with vehicle or torcetrapib 30 mg/kg (TOR) over 2 weeks. Compared with vehicle, TOR increased apolipoprotein E–rich HDL levels and significantly increased 3 H-tracer appearance in HDL by 30% over 72 hours after 3 H-oxLDL injection. However, TOR did not change 3 H-tracer recovery in liver and feces, suggesting that uptake and excretion of cholesterol deriving from apolipoprotein E-rich HDL is not stimulated. As apoE is a potent ligand for the LDL receptor, we next evaluated the effects of TOR in combination with the LDL-lowering drug berberine, which upregulates LDL receptor expression in dyslipidemic hamsters. Compared with TOR alone, treatment with TOR+berberine 150 mg/kg resulted in lower apolipoprotein E–rich HDL levels. After 3 H-oxLDL injection, TOR+berberine significantly increased 3 H-tracer appearance in fecal cholesterol by 109%. Conclusion— Our data suggest that cholesteryl ester transfer protein inhibition alone does not stimulate reverse cholesterol transport in dyslipidemic hamsters and that additional effects mediated by the LDL-lowering drug berberine are required to upregulate this process.