Modulating cysteine metabolism to induce cell death in small cell lung cancer

SUMMARY Small cell lung cancer (SCLC) is a fatal form of lung cancer whose development is closely associated with tobacco smoking. Patients with SCLC have a median overall survival of only 8-10 months after initial diagnosis. SCLC development is frequently associated with mutations in TP53 (p53), RB, and related tumor suppressor

genes that govern transit through the cell cycle. Disruption of these genes leads to small, rapidly dividing cells. Despite identical mutations, SCLC cells can adopt one of several distinct transcriptional/epigenetic states, including neuroendocrine and non-neuroendocrine states. How these cell states differ is poorly understood. It is

also unclear how best to induce cell death in different SCLC cell states. In this research, we focus on the unique metabolism of SCLC cells to identify new and exploitable vulnerabilities that can be used to kill SCLC cells. In preliminary RNA sequencing and mass spectrometry-based metabolomics studies we find that SCLC

metabolism is cell state-dependent. Our results pinpoint a cell-state-specific role for cystine/cysteine (Cys) metabolism in SCLC biology. We find that both neuroendocrine and non-neuroendocrine SCLC cells require Cys to proliferate. In the absence of Cys, non-neuroendocrine cells stop dividing whereas neuroendocrine cells die.

Intriguingly, cell death responses are also cell state-dependent: ASCL1high neuroendocrine cells primarily die from apoptosis while NEUROD1high neuroendocrine cells die from ferroptosis. These findings suggest cell state- specific differences in SCLC metabolism may regulate distinct sensitivities to apoptotic versus non-apoptotic cell

death. In this research, we will determine how Cys deprivation triggers cell state-specific lethal mechanisms in SCLC cells. We propose three Specific Aims. We will first determine how distinct neuroendocrine cell states dictate the choice to die by apoptosis versus ferroptosis, focusing on the role of the GCN2/ATF4 amino acid sensing

pathway and polyunsaturated phospholipid metabolism. Next, we will determine how the Notch and the NRF2 signaling pathways govern the responses of neuroendocrine versus non-neuroendocrine cell states to Cys deprivation. Finally, we will develop a novel Cys-degrading enzyme therapy that selectively targets SCLC cells

to induce cell death by recognizing specific cell surface antigens. These studies will test our central hypothesis, which is that Cys metabolism represent a novel targetable vulnerability for SCLC. Altogether, this research will unveil novel links between cell state, metabolism, and cell death in SCLC. Ultimately, we aim to show how

targeting this metabolic network could lead to new treatments for this devastating disease.