Role of insulin-like growth factor binding protein 2 in lung adenocarcinoma: IGF-independent antiapoptotic effect via caspase-3.

Insulin-like growth factor (IGF) signaling plays a pivotal role in cell proliferation and mitogenesis. Secreted IGF-binding proteins (IGFBPs) are important modulators of IGF bioavailability; however, their intracellular functions remain elusive. We sought to assess the antiapoptotic properties of intracellular IGFBP-2 in lung adenocarcinomas. IGFBP-2 overexpression resulted in a decrease in procaspase-3 expression; however, it did not influence the phosphorylation status of either IGF receptor or its downstream targets, including Akt and extracellular signal-regulated kinase. Apoptosis induced by camptothecin was significantly inhibited by IGFBP-2 overexpression in NCI-H522 cells. Conversely, selective knockdown of IGFBP-2 using small-interfering RNA resulted in an increase in procaspase-3 expression and sensitization to camptothecin-induced apoptosis in NCI-H522 cells. LY294002, an inhibitor of phosphatidyl-inositol 3-kinase, caused a decrease in IGFBP-2 levels and enhanced apoptosis in combination with camptothecin. Immunohistochemistry demonstrated that intracellular IGFBP-2 was highly expressed in lung adenocarcinomas compared with normal epithelium. Intracellular IGFBP-2 and procaspase-3 were expressed in a mutually exclusive manner. These findings suggest that intracellular IGFBP-2 regulates caspase-3 expression and contributes to the inhibitory effect on apoptosis independent of IGF. IGFBP-2, therefore, may offer a novel therapeutic target and serve as an antiapoptotic biomarker for lung adenocarcinoma.

ATP citrate lyase: activation and therapeutic implications in non-small cell lung cancer.

Enhanced glucose and lipid metabolism is one of the most common properties of malignant cells. ATP citrate lyase (ACLY) is a key enzyme of de novo fatty acid synthesis responsible for generating cytosolic acetyl-CoA and oxaloacetate. To evaluate its role in lung cancer progression, we here analyzed ACLY expression in a subset of human lung adenocarcinoma cell lines and showed a relationship with the phosphatidyl-inositol-3 kinase-Akt pathway. The introduction of constitutively active Akt into cells enhanced the phosphorylation of ACLY, whereas dominant-negative Akt caused attenuation. In human lung adenocarcinoma samples, ACLY activity was found to be significantly higher than in normal lung tissue. Immunohistochemical analysis further showed phosphorylated ACLY overexpression in 162 tumors, well-correlating with stage, differentiation grade, and a poorer prognosis. Finally, to show the therapeutic potential and mechanism of ACLY inhibition for lung cancer treatment, we assessed the effect of RNA interference targeting ACLY on lipogenesis and cell proliferation in A549 cells. ACLY inhibition resulted in growth arrest in vitro and in vivo. Interestingly, increased intracellular lipids were found in ACLY knockdown cells, whereas de novo lipogenesis was inhibited. Supplementation of insulin could rescue the proliferative arrest elicited by ACLY inhibition; however, in contrast, fatty acid palmitate induced cell death. Taken together, these findings suggest that ACLY is involved in lung cancer pathogenesis associated with metabolic abnormality and might offer a novel therapeutic target.

Cardiotonic agent SCH00013 prolongs survival of cardiomyopathic hamsters.

The authors examined the effects of long-term treatment with SCH00013, a novel cardiotonic agent with calcium-sensitizing action, on survival of hereditary cardiomyopathic BIO 14.6 hamsters. Sixty-nine male hamsters at 223 days of age were divided into untreated, SCH00013-low (approximately 1 mg/kg/d), and SCH00013-high (approximately 10 mg/kg/d) groups. Survival curves were constructed in the three groups. The first deaths in the untreated, SCH00013-low, and SCH00013-high groups were found at 263, 290, and 314 days of age, respectively. A 50% mortality rate was observed at 392 days in the untreated group, 396 days in the SCH00013-low group, and 445 days in SCH00013-high group. The survival time distribution of the SCH00013-high group was significantly different from that of the untreated group (P < 0.005). However, histomorphometric examinations revealed that the degree of progression of calcification and fibrosis in the ventricular wall of the BIO 14.6 hamsters was not different between the untreated and SCH00013-treated groups. Plasma concentration of this agent was 2 microM at the end of the second week of continuous administration via drinking water in SCH00013-high group. Thus, SCH00013 was beneficial for the survival of cardiomyopathic hamsters, suggesting that this agent is a possible candidate for the treatment of chronic heart failure.