Targeting the alterations of Lipid Metabolism in ASS1 Deficient Sarcomas to Induce Synthetic Lethality

Brian Van Tine, MD, PhD,  Washington University in St. Louis
Recipient of the: Sarcoma Foundation of America Research Award

The most common defect in sarcoma is loss of expression of argininosuccinate synthetase 1 (ASS1), which occurs in approximately 90% of sarcomas. This defect primes sarcomas for treatment by the arginine starvation inducing therapy arginine-deiminase (ADI-PEG20). In sarcomas, treatment with ADI-PEG20 induces a cytostatic response. Recently published work by our group has demonstrated that a metabolic rewiring takes place in response to ADI-PEG20. This has led to the first trial of ADI-PEG20 with gemcitabine for the treatment of metastatic sarcoma that should open at Washington University in the next 6 months. As the overall goal of sarcoma metabolic therapy is to develop a biomarker (ASS1) driven synthetic lethal strategy by identifying multiple metabolic targets. The purpose of this proposal is to study the effects that starvation has upon lipids and lipid metabolism. Preliminary data demonstrate that lipid-oxidation increases in response to ADI-PEG20, as it is an energy source needed for cancer survival. By inhibiting lipid-oxidation with the clinically available drug perhexiline, we will derive the necessary preclinical information needed to add perhexiline to future trials. Formally, we hypothesize that arginine deprivation induces ER stress in ASS1 negative tumors, transforming the tumors towards unique lipid biology. This metabolic dependence can be exploited as a therapeutic target with perhexiline. To test this we propose two aims:

Aim 1. To investigate the combination treatment of perhexiline and ADI-PEG20 on metastasis in a conditional ASS1 deficient mouse model that has been generated in our lab, as well as in xenograph mouse models.
Preliminary evidence has demonstrated that the combination of ADI-PEG20 and the beta-oxidation inhibitor perhexiline is synthetic lethal. We hypothesize an ER stress dependent increase in lipid synthesis primes the tumors for fatty acid oxidation, which can be targeted in ASS1 negative tumors. We will use spontaneous and xenograft models to generate the needed in vivo preclinical data to justify its use in future clinical trials.

Aim 2. To elucidate the molecular mechanism that allows for metabolic rewiring in ASS1 negative tumors, leading to lipid beta-oxidation in response to ADI-PEG20. Preliminary evidence has implicated both AMP Kinase and FoxO1 in the stress response to ADI-PEG20. Therefore, we hypothesize that arginine depletion induced ER stress leads to a decrease in AMPK phosphorylation and an induction of fatty acid synthesis. To test this we will perform in vitro and in vivo studies examining the ER stress response. In addition, we will follow the fate of carbon atoms from glutamine as it is utilized as a precursor in the biosynthesis of fatty acids in order to mechanistically dissect the stress response.

Taken together, support for this project by the SFA will help to derive the preclinical data needed for future clinical trials utilize ADI-PEG20 for the treatment of sarcoma.