Momcilovic, M. | Search bioRxiv

bioRxiv2020

Asparagine signals mitochondrial respiration and can be targeted to impair tumour growth

Mitochondrial respiration is critical for cell proliferation. In addition to producing ATP via the electron transport chain (ETC), respiration is required for the generation of TCA cycle-derived biosynthetic precursors, such as aspartate, an essential substrate for nucleotide synthesis. Because mTORC1 coordinates availability of biosynthetic precursors with anabolic metabolism, including nucleotide synthesis, a link between respiration and mTORC1 is fitting. Here we show that in addition to depleting intracellular aspartate, ETC inhibition depletes aspartate-derived asparagine and impairs mTORC1 activity. Providing exogenous asparagine restores mTORC1 activity, nucleotide synthesis, and proliferation in the context of ETC inhibition without restoring intracellular aspartate in a panel of cancer cell lines. As a therapeutic strategy, the combination of ETC inhibitor metformin, which limits tumour asparagine synthesis, and either asparaginase or dietary asparagine restriction, which limit tumour asparagine consumption, effectively impairs tumour growth in several mouse models of cancer. Because environmental asparagine is sufficient to restore proliferation with respiration impairment, both in vitro and in vivo, our findings suggest that asparagine synthesis is a fundamental purpose of mitochondrial respiration. Moreover, the results suggest that asparagine signals active respiration to mTORC1 to communicate biosynthetic precursor sufficiency and promote anabolism.

cancer biology↗

bioRxiv2020

Novel Kras-mutant murine models of non-small cell lung cancer possessing co-occurring oncogenic mutations and increased tumor mutational burden

Despite recent advances in lung cancer immunotherapy, a major obstacle to the progress in the field is the lack of preclinical models that recapitulate the genetic and immunologic complexity of human disease. Conditional genetically engineered mouse models (GEMMs) of non-small cell lung cancer (NSCLC) harbor the common oncogenic mutations of the disease, but these models possess low tumor mutational burden (TMB), which limits their utility in immunotherapy studies. Here, we establish novel Kras-mutant murine models of NSCLC bearing common genetic alterations associated with the disease and increased TMB, by in vitro exposure of cell lines derived from GEMMs of NSCLC [KrasG12D (K), KrasG12DTp53-/- (KP), KrasG12DTp53+/-Lkb1-/- (KPL)] to the alkylating agent N-methyl-N-nitrosourea (MNU). Increased TMB was associated with enhanced anti-tumor T cell responses and improved anti-PD-1 efficacy in syngeneic models, across all genetic backgrounds. However, anti-PD-1 efficacy was comparatively modest in the KPL cell lines with increased TMB, which possessed a distinct immunosuppressed tumor microenvironment (TME) primarily composed of granulocytic myeloid-derived suppressor cells (G-MDSCs). This phenotype is consistent with findings in human NSCLC where LKB1 loss is a driver of primary resistance to PD-1 blockade. In summary, these novel Kras-mutant murine NSCLC models bearing common co-occurring mutations with increased TMB possess clinically relevant TMEs and recapitulate the genetic complexity and therapeutic vulnerabilities of human NSCLC. We anticipate that these immunogenic models will facilitate the development of novel immunotherapies in NSCLC.

cell biology↗