Analysis of Heme Functions in Therapy Resistance and Tumorigenesis in Non-small Cell Lung Cancer

Lung cancer remains the leading cause of cancer-related death in the United States, 84% of them being non-small cell lung cancer (NSCLC). Early-stage treatment includes surgery and radiotherapy followed by periodic radiographic imaging for routine surveillance. These curative treatments have shown promise in some lung cancer patients while being ineffective for majority (30–60%) of the patients who are predicted to have advanced disease, particularly local or distant metastasis. This limit overall survival rates in these patients to less than 60%. Moreover, despite the advent of personalized therapy which includes various targeted therapies and immunotherapies, there has not been a significant improvement in the 5-year survival rate. Therefore, there is a pressing need to further optimize current strategies while continuing to explore novel strategies to improve therapeutic outcomes for patients with lung cancer, based on individual patient needs. Numerous studies are now focusing on the importance of mitochondrial respiration or oxidative phosphorylation (OXPHOS) in cancer progression. However, very little is known about its role and potential as a therapeutic target in non-small cell lung cancer (NSCLC). Several studies in our lab show that NSCLC cells display elevated levels of intracellular heme. This increased level of heme is either through de novo heme synthesis or heme uptake. Our lab has also demonstrated elevated mitochondrial respiration/oxidative phosphorylation (OXPHOS) in NSCLCs. Studies in our lab show that elevated expression of enzymes involved in heme biosynthesis, uptake, and degradation, as well as oxygen-utilizing hemoproteins in resistant cells post treatment with vascular disrupting agents. Limiting oxidative functions using Cyclopamine tartrate (CycT), inhibition of heme uptake with heme sequestering peptides (HSP2) and heme synthesis using succinyl acetone, have all shown promise in delaying growth and progression of NSCLC cells and tumor xenografts. Another feature of NSCLC tumor is its heterogeneity. NSCLCs exhibit widespread inter- and intra-tumoral heterogeneity as well as incidences of subtype transdifferentiation. This kind of plasticity enable them to develop drug resistance and pose great challenges for their treatment. In this study I aimed to understand the comparative dependence of the two major NSCLC subtypes, adenocarcinoma (ADC) and squamous cell carcinoma (SCC), on heme and OXPHOS, for their growth and progression. I observed that both ADC and SCC have similar demands for heme uptake and synthesis in cell culture. My results also suggest that OXPHOS activities are elevated in both ADC and SCC to support tumorigenic functions in culture. I used the Genetically Engineered Mouse Model (GEMM), KLLuc to study NSCLC tumor heterogeneity since tumors developed in these mice consists of both ADC and SCC phenotypes. My findings in vitro were corroborated in this model, using immunohistochemistry (IHC) and histology. Bioluminescence imaging and histology studies demonstrate that heme sequestering peptides successfully reduce tumor development and progression in KLLuc mice.