Epigenetic targeting of CD1d increases cytolytic activity of invariant natural killer T cells against non-small cell lung cancer cells

Abstract

Lung cancer is the most common form of cancer-related death in the world, accounting for approximately 19.4% of all cancer mortalities. Currently platinum-based therapies are the gold-standard of care for non-small cell lung cancer (NSCLC), however the prognosis of advanced NSCLC remains bleak. As such there is a drive to identify novel therapeutics that can combat the disease more effectively. Widespread epigenetic alterations are observed in NSCLC, such as aberrant DNA methylation and histone acetylation patterns. The reversible nature of these modifications makes them an attractive prospect as novel therapeutic targets. Lymphocyte subpopulations were enumerated in blood and bronchial lavage (BAL) samples from NSCLC patients and control subjects. Invariant natural killer T (iNKT) cells were found to be significantly depleted from both tissues. iNKT cells can recognize and kill cancer cells in a CD1d-dependent manner, however, we found that NSCLC cell lines do not express CD1d. We hypothesized that CD1d expression in NSCLC is epigenetically regulated and that increasing CD1d expression in NSCLC would increase their susceptibility to iNKT cell lysis. NSCLC cell lines were treated with a panel of DNA methyltransferase inhibitors (DNMTi) and histone deacetylase inhibitors (HDACi) and quantitative polymerase chain reaction amplification of reverse transcribed mRNA and flow cytometry were performed to detect changes in CD1d expression. Both DNMTi and HDACi significantly induced CD1d expression in NSCLC cell lines, and this increase in CD1d expression was associated with increased susceptibility to iNKT cell-mediated cytolytic degranulation. These results indicate that epigenetic targeting therapies can up-regulate CD1d expression in NSCLC, and that over-expression of CD1d leads to increased susceptibility to iNKT cell cytotoxicity. These results indicate that epigenetic manipulation of CD1d is a viable therapeutic option in combatting NSCLC.