Targeting de novo purine synthesis pathway via ADSL depletion impairs liver cancer growth by perturbing mitochondrial function

Hepatocellular carcinoma (HCC) is among the most common cancer types worldwide; yet, patients with HCC have limited treatment options. There is an urgent need to identify new drug targets that specifically inhibit the growth of HCC cells. Here, we used a newly-engineered CRISPR library targeting ~2,000 druggable genes to perform a high throughput screen, and identified adenylosuccinate lyase (ADSL) - a key enzyme involved in the de novo purine synthesis pathway - as a potential drug target for HCC. ADSL has been implicated as a potential oncogenic driver in some cancers, but its role in liver cancer progression remains unknown. CRISPR-mediated knockout of ADSL impaired colony formation of liver cancer cells by affecting adenosine monophosphate (AMP) production. In the absence of ADSL, the growth of liver tumors is retarded in vivo. Mechanistically, we found that ADSL knockout caused S-phase cell cycle arrest, not by inducing DNA damage, but by impairing mitochondrial function. Using HCC patient data, we also revealed that high ADSL expression occurs during tumorigenesis and is linked to poor survival rate. In conclusion, our findings uncover the role of ADSL-mediated de novo purine synthesis in fueling mitochondrial ATP production to promote liver cancer cell growth. Targeting ADSL may be a therapeutic approach for HCC patients.