Department of Experimental Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy.
Anticancer Drugs. 2013 Sep;24(8):862-70. doi: 10.1097/CAD.0b013e328363ae50.
Activation of the myc oncogene in cancer cells upregulates lactate dehydrogenase A (LDH-A) expression, leading to a sustained glycolytic flux that is needed to produce ATP under hypoxic conditions. We studied the effects of galloflavin (GF), a recently identified LDH inhibitor, on myc overexpressing Burkitt lymphoma (BL) cells. Epstein-Barr virus-infected lymphoblasts were used as a non-neoplastic control. Our results showed that myc overactivation induced a two- to seven-fold increase in LDH-A expression in BL cells compared with non-neoplastic lymphoblasts; this result is consistent with previously reported data. Moreover, GF treatment suppressed LDH activity and inhibited BL cell replication but did not affect lymphoblast viability. Surprisingly, we found that increased levels of the MYC and LDH-A proteins did not lead to a metabolic shift in BL cells toward glycolytic ATP generation. BL cells were treated with GF at doses that achieved 50% inhibition of cell growth and lactate production, and ATP levels were scarcely affected after GF treatment. The same results were also obtained by suppressing LDH activity with oxamate, an LDH specific inhibitor. Our data suggest that LDH activity is important for maintaining a correct NAD/NADH balance in BL cells. LDH inhibition led to decreased NAD cellular levels, which resulted in sirtuin-1 inhibition. Confirming previous studies, sirtuin-1 inhibition caused a reduction in MYC protein levels, depriving BL cells of their most important survival signal. This study further describes the biological functions of the LDH enzyme and suggests that LDH inhibition could be useful for the treatment of cancer.
癌基因 myc 在癌细胞中的激活会上调乳酸脱氢酶 A（LDH-A）的表达，导致在缺氧条件下产生 ATP 所需的持续糖酵解通量。我们研究了最近被鉴定为 LDH 抑制剂的金丝桃素（GF）对过表达 myc 的伯基特淋巴瘤（BL）细胞的影响。埃泼斯坦-巴尔病毒感染的淋巴母细胞被用作非肿瘤对照。我们的结果表明，与非肿瘤性淋巴母细胞相比，myc 的过度激活导致 BL 细胞中 LDH-A 的表达增加了两到七倍；这一结果与之前报道的数据一致。此外，GF 处理抑制了 LDH 活性并抑制了 BL 细胞的复制，但不影响淋巴母细胞的活力。令人惊讶的是，我们发现 MYC 和 LDH-A 蛋白水平的增加并没有导致 BL 细胞向糖酵解 ATP 生成的代谢转变。BL 细胞用 GF 处理，达到 50%抑制细胞生长和乳酸产生的剂量，GF 处理后 ATP 水平几乎没有受到影响。用 oxamate（一种特定的 LDH 抑制剂）抑制 LDH 活性也得到了相同的结果。我们的数据表明，LDH 活性对于维持 BL 细胞中正确的 NAD/NADH 平衡很重要。LDH 抑制导致 NAD 细胞水平降低，从而导致 Sirtuin-1 抑制。证实了之前的研究，Sirtuin-1 抑制导致 MYC 蛋白水平降低，剥夺了 BL 细胞最重要的生存信号。本研究进一步描述了 LDH 酶的生物学功能，并表明 LDH 抑制可能对癌症的治疗有用。
