Investigating the Proline Cycle as a Potential Cancer Therapy Target

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Modified Project Summary/Abstract Proline biosynthesis and catabolism share a common intermediate, Δ1-pyrroline-5-carboxylate (P5C), and the enzymatic interconversion of proline and P5C is known as the “proline cycle”. The first enzyme of catabolism, proline dehydrogenase (PRODH), catalyzes the FAD-dependent oxidation of proline to P5C, while the last enzyme of biosynthesis, P5C reductase (PYCR1), catalyzes the NAD(P)H-dependent reduction of P5C to proline. Together, PRODH and PYCR1 form the proline cycle, a novel pathway that effects the net transfer of electrons from NAD(P)H in the cytoplasm to the synthesis of ATP in mitochondria. Recent studies have shown that metastatic breast cancer cells alter their metabolism to harness the proline cycle for energy production, suggesting the hypothesis that PRODH and PYCR1 are potential cancer therapy targets. This idea is supported by in vivo data showing that the inhibition of PRODH by a proline analog impairs the formation of lung metastases in orthotopic mouse models of breast cancer. These results motivate this short-term project to develop chemical probes against PRODH and PYCR1 using focused and high-throughput screening approaches. The set of probes to be developed will enable future studies to mechanistically dissect the role of proline metabolism in cancer progression and assess the tractability of the proline cycle as a cancer therapy target. We expect that this knowledge will result in the long-term in new therapeutic strategies against cancer.