Abstract A32: NISCH promoter hypermethylation, smoking and lung cancer: A case control study

Abstract

Abstract Lung cancer is the most common cancer worldwide, both in terms of incidence and mortality. The high mortality of lung cancer is attributable to the presence of metastatic disease in nearly two thirds of patients at diagnosis. Detection of early stage lung cancer amenable to curative resection could potentially result in a manifold increase in survival rates. Epigenetic alterations seemingly contribute to cancer initiation and progression. Cancer specific methylation patterns of tumor suppressor genes, which precede precursor lesions, could possibly herald earlier diagnosis of lung cancer and may even have important preventive or therapeutic implications. Our aim was to evaluate the promoter hypermethylation of tumor suppressor gene NISCH in cfDNA from plasma of lung cancer patients and its possible correlation with smoking status and various clinicopathological parameters. NISCH codes for a nonadrenergic imidazoline-1 receptor protein nischarin that anchors to the inner layer of the plasma membrane. The orthologous mouse protein has been shown to bind alpha-5 beta-1 integrin and influence cytoskeletal organization. Forty histopathologically confirmed lung cancer cases were enrolled along with thirty smoker and thirty nonsmoker controls. Plasma cfDNA was extracted and subjected to bisulfite treatment followed by conventional methylation specific PCR. DNA methylated using CpG methylase by the whole genome methylation protocol, was used as positive control and Nuclease free PCR grade water was used as negative control. The serum nischarin levels were estimated using commercially available ELISA kits. Statistical analysis was performed using SPSS 22.0 software. We observed that frequency of promoter hypermethylation of tumor suppressor NISCH was significantly higher in lung cancer patients and in non-cancerous smokers as compared to lifelong nonsmoker controls. This difference in methylation status of NISCH between lung cancer cases, smoker and nonsmoker controls was found to be significant (P<0.05). There was no significant association between methylation status of tumor suppressor gene NISCH and clinicopathologic variables- staging, tumor size, lymph node status, metastasis and histopathological grading. We observed a higher frequency of NISCH methylation in adenocarcinoma as compared to Squamous Cell Carcinoma. Methylation status of tumor suppressor gene NISCH was found to be significantly higher among smokers as compared to nonsmokers. But there was no significant difference in the frequency of NISCH methylation between smoker lung cancer patients and nonsmoker lung cancer patients. There was no significant difference in methylation status of NISCH with type or duration of smoking. The pack years and packs per day were significantly higher in those with methylated NISCH as compared to the unmethylated group. There was no significant association of serum nischarin levels with methylation status of NISCH, demographic variables or any clinicopathological parameters. Our findings suggest that NISCH methylation occurs in high frequencies in cfDNA from plasma of lung cancer patients. Though it was not found to correlate with stage, tumor size, lymph node status, metastases or histological grade, it was found to be significantly associated with adenocarcinomas in our study. Hence, NISCH methylation could serve as a part of blood based biomarker panel for early diagnosis of lung cancer. In addition, since NISCH is found to be highly methylated in both high risk heavy smoker controls as well as lung cancer cases irrespective of smoking status, it can be hypothesized that NISCH methylation may be the common primogenitor at which varied etiologies for lung cancer converge. Hence, in the future, it may be investigated as a universal therapeutic target for lung cancers regardless of clinicopathological heterogeneity. Citation Format: Kritika Krishnamurthy, TK Mishra, Alpana Saxena, MK Daga, Nita Khurana, Masroor Mirza. NISCH promoter hypermethylation, smoking and lung cancer: A case control study. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr A32.