MCL-1 expression of non-small cell lung cancer as a prognostic factor and MCL-1 as a promising target for gene therapy.

e24236 Background: MCL-1 is an important member in the pro-survival Bcl-2 family, plays a critical role in multidrug resistance. We investigated the significance for MCL-1 expression of non- small cell lung cancer (NSCLC) and the effect of inhibition of MCL-1 gene with siRNA (si-MCL-1) in NSCLC cells. Methods: Tumor tissues from 80 patients underwent R0 resection with NSCLC without any neoadjuvant therapy were analyzed. The intratumoral expressions of MCL-1 and Ki-67 were evaluated with immunohistochemistry in the tumor nucleus. Apoptotic index (AI) was defined as number of apoptotic cells, detected by TUNEL. Subsequently, we tested two MCL-1 overexpressing lung cancer cells, adenocarcinoma cell H358 and squamous carcinoma cell RERF, were used. Real-time RT-PCR was performed to evaluate gene expressions. The siRNA targeting MCL-1 (si-MCL-1) was transfected into cells. MTT assay was used to evaluate the cell viability and IC50. Results: The percentage of MCL-1 positive tumor nucleus varied greatly (median = 25.0%; mean±SD = 26.8±20.9%). A sample was classified as MCL-1 high tumor if > 25% of the nucleus in the tumor exhibited positive stainings. Among 80 patients with NSCLCs, 36(45.0%) were MCL-1 high status. The 5-year survival rate for patients with MCL-1 high tumors was significantly worse than that for patients with MCL-1 low tumors (68.3% vs. 93.1%, p = 0.0057). Regarding to the tumor proliferation, the Ki-67 index was significantly higher in the MCL-1 high tumor than that in MCL-1 low tumor (19.7±16.3% vs. 8.4±11.1%, p = 0.005). There was no significant relation between the AI and MCL-1 status. Si-MCL-1 effectively downregulated the MCL-1 expression (up to 80% at day 3) and significantly reduced the percentage of viable cells in these two cell lines as detected by MTT assay (p < 0.001, respectively). Multivariate analysis demonstrated MCl-1 expression to be a significant prognostic factor (hazard ratio, 4.069; p = 0.0405) Conclusions: MCL-1 expression is prognostic factor in NSCLC. The si-MCL-1 has an anti-proliferation effect against MCL-1-overexpressing NSCLC cells. MCL-1 appear to be a promising target for gene therapy.