How Dietary Methionine Influences Lung Cancer Initiation and Chemosensitivity

Methionine is a metabolite obtained primarily through diet, and is a precursor for post-translational histone methylations such as those catalyzed by the Polycomb Repressive Complex 2 (PRC2). Our laboratory’s data suggest that PRC2-dependent histone methylation is compromised in both the bronchiolar epithelium of COPD patients and in aggressive chemotherapy resistant lung cancers. Our research has indicated that levels and activity of the enzyme cystathionine beta synthase (CBS) are responsible for changes in histone methylation, and it has been well documented that CBS is a methionine-sensing enzyme. Therefore, this research offers an avenue to connect dietary methionine to histone modification through CBS activity. Primary Hypothesis: Dietary methionine levels directly influence the enzyme cystathionine beta synthase (CBS), which in turn leads to either stabilization or de-stabilization of histone methyltransferase complexes such as PRC2. We hypothesize that low methionine leads to low CBS, stabilization of histone methyltransferases and more well differentiated lung cells that will be less likely to become malignant, or if already malignant, more targetable with common chemotherapeutics. Objectives: The objectives of this proposal are to explore how methionine levels and CBS activity change histone methylation, and how these changes in epigenetic programming alter potential for lung cell transformation and lung cancer chemotherapy responses. The biological endpoints that will be assessed will be the transformation of lung cells and organoids, and number, grade and chemosensitivity of lung cancers in vivo. Description of Proposed Project: In Aim 1, we will use normal human lung epithelial cells from both murine and human sources. We will culture these cells in differing methionine conditions and activate the common oncogene KRAS to induce malignant transformation. Transformation potential will be assessed through growth in anchorage independent conditions and growth sub-cutaneously in Nude mice. CBS protein expression and activity as well as PRC2 activity will be assessed during the transformation process. In Aim 2, we will use an inducible mouse model of lung cancer. Cohorts will be given methionine restriction chow at either an early (tumor initiation) or late (tumor treatment) timepoint. Those given methionine restriction late will be assessed for tumor response to the chemotherapy carboplatin. In parallel, we will use primary lung cancer organoids from these mice to test chemosensitivity in vitro in low, regular or high methionine media. Both CBS and PRC2 activity will be assessed and correlated to functional readouts.