Project 2

PROJECT 2 SUMMARY INVESTIGATING CYSTEINE ESSENTIALITY IN LUNG CANCER Cancer cells accumulate significant intracellular cysteine due to increased cystine uptake and loss of homeostatic control. Cysteine-derived molecules are crucial for cancer cell survival and proliferation as a consequence of their sulfur moiety, which facilitates diverse functions, including enzyme catalysis, energy

transfer, and redox metabolism. Consistently, we have found that many lung cancer cell lines are highly sensitive to cystine starvation and lack the capacity for de novo cysteine synthesis, suggesting they are dependent on exogenous cystine as a source of cysteine. Importantly, the recently developed cyst(e)inase enzyme depletes

extracellular cystine and cysteine efficiently, suggesting it may have therapeutic efficacy against lung cancer. However, intracellular metabolic circuits can modify the cellular response to starvation independent of transsulfuration capacity. Thus, understanding the compensatory mechanisms to cysteine starvation is crucial

for efficient therapeutic targeting of cysteine in lung cancer. Importantly, our results suggest the glutathione synthesis machinery, an important target of the NRF2 transcription factor, has a glutathione-independent role to protect cells against cysteine starvation-induced ferroptosis. In addition, the tumor microenvironment has

significant levels of alternative sources of cysteine, including glutathione, cystathionine and protein, that are lacking in cell culture and may promote survival in the absence of cystine. The central hypothesis of this proposal is that tissue of origin, metabolic responses to cystine starvation, and alteration in sulfur sources within the tumor

microenvironment influence cystine essentiality in lung cancer, thereby leading to targetable metabolic vulnerabilities. We will test this hypothesis in the following specific aims: In Aim 1 we will evaluate the influence of tissue and cell of origin on cysteine metabolism and essentiality. In Aim 2 we will decipher metabolic circuits that dictate responsiveness to cysteine limitation.

In Aim 3 we will evaluate cysteine metabolism in the tumor microenvironment. The ultimate goal, and the overall impact, of this project is to characterize key determinants of cysteine metabolism and dependence in lung cancer in order to define opportunities for therapeutic intervention.