Pancreatic ductal adenocarcinomas (PDACs) are the second leading cause of cancer death in the
United States, with a survival rate of 3% once it spreads to distant organs. PDAC cells within a tumor are
frequently starved for oxygen due to their high proliferation rate and insufficient vasculature. This degree of
hypoxia in the tumor triggers strong metabolic adaptations on cancer cells that allow their survival and
proliferation. Among these adaptations are altered uptake and utilization of major nutrients, such as glutamine.
However, the precise mechanisms through which pancreas cancer metabolism adapts to hypoxia, and whether
this could be exploited for therapy, remain unknown.
In preliminary studies, we found that, when pancreatic and lung cancers are exposed to low levels of
oxygen, the amino acid aspartate, required for protein and nucleotide synthesis, becomes limiting. Simply
increasing the uptake of exogenous aspartate by expression of a plasma membrane aspartate transporter
strongly promoted the growth rate of cancer cells under hypoxia and in tumors, as well as enhanced their
metastatic potential. These findings provide evidence that aspartate can be a cancer growth-limiting metabolite
in vivo. Furthermore, a CRISPR/Cas9 screen using a library of sgRNAs targeting rate-limiting metabolic
enzymes revealed that GOT2, one of the two enzymes that de novo synthesizes cellular aspartate from
glutamine, is essential for in vitro proliferation under hypoxia of a KRAS/TP53 mutant PDAC cell line. Building
upon these results, I propose to test the hypothesis that targeting de novo aspartate synthesis may have
therapeutic potential in pancreatic tumors at the level of primary tumor growth and metastasis.
Throughout the initial phase of this award, we will define the essentiality of GOT2-mediated aspartate
synthesis in a panel of PDAC cell lines upon being exposed to low tensions of oxygen and, importantly, when
grown as tumors and during colonization of distant organs. Additionally, we will determine the contribution and
impact on cancer proliferation of the two divergent metabolic routes of glutamine conversion into aspartate:
oxidative and reductive metabolism. Building upon the obtained results, we will target aspartate synthesis in
pre-clinical patient-derived models and KRAS/TP53 mutant mouse models and, by using isotope-labeling
metabolomic analysis, we will show which aspartate synthesis route is used by pancreatic tumors in vivo.
Finally, by using in vivo metabolomics and mitochondrial pull-downs in primary and metastatic tumors, I
propose to define whether hypoxia-triggered metabolic rewiring is a determinant of the metastatic potential of
PDAC cells. These analysis will identify which metabolic changes PDAC cells undergo during metastasis,
unveiling potential liabilities that could be targeted in order to decrease spread of PDAC to distant organs.
Altogether, the proposed experiments will define the role of aspartate synthesis in PDAC tumor growth
and metastasis, and will test whether any other metabolic changes are required for PDAC cells to metastasize.