Abstract 3749: Metabolic reprogramming by GCN1 mediates metastatic reactivation and outgrowth at liver metastatic site in response to glutamine deprivation in pancreatic cancer

Introduction: Disseminated tumor cells in the circulation upon extravasation into a secondary organ like the liver encounter hostile conditions like nutrient deprivation and oxidative stress and may undergo dormancy or growth arrest. The molecular drivers and mechanisms that enable disseminated tumor cells to overcome such adverse growth conditions and revert to proliferative stage are unknown.

Method: To identify these molecular drivers, a retroviral cDNA library was generated from a highly metastatic pancreatic cell line (M-4964Liv) derived from a KPC mouse which forms macroscopic liver lesions upon splenic injection in mice. The cDNA library was then transduced into a dormant pancreatic KPC cells (D-4964Liv) cells which does not give liver lesions upon splenic injection in mice. This methodology will allow all the cDNA’s from the metastatic cells to express in the dormant cells but only those cDNA’s which can trigger the dormant cells to outgrow will give rise to a metastatic liver lesion.

Results: The screening strategy led to the identification of general control of amino-acid synthesis 1-like 1 (GCN1L1). The human homologue GCN1 has been shown to regulate the activation of mammalian amino acid sensor general control non-derepressible 2 (GCN2) under amino acid starvation in budding yeast but how GCN1 regulates metastatic reactivation is not known. We show that GCN1 is activated under physiologic glutamine levels in the liver which is around 0.5 mM compared to standard tissue culture levels of 2-4 mM. Mechanistic interrogation revealed that GCN1 activates both the mammalian amino acid sensors: the general control nonderepressible 2 (GCN2) and the mechanistic target of rapamycin complex 1 (mTORC1) leading to metastatic outgrowth in vivo. Contrary, knockdown of GCN1 dramatically impairs the activation of GCN2 and mTORC1 and abrogates liver metastatic outgrowth upon splenic injection in immunocompetent mice.

Conclusions: These results suggest that under physiologic glutamine levels, induction of GCN1 activates two different pathways: One pathway impinges on ATF4 and the other on mTORC1. While ATF4 activation promotes metabolic homeostasis by inducing de novo amino acid synthesis, the activation of mTOR pathway ensures re-entry in to the cell cycle leading to metastatic reactivation and outgrowth.

Citation Format: Surajit Sinha, Jonathan Hernandez, Reed Ayabe, Michael Wach, Samantha Ruff, Alok Ranjan, Kirsten Remmert, Imani Alexander. Metabolic reprogramming by GCN1 mediates metastatic reactivation and outgrowth at liver metastatic site in response to glutamine deprivation in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3749.