Metastases are the leading cause of mortality in patients with cancer. Metastasis formation requires cancer cells to adapt their cellular phenotype. However, how metabolism supports this adaptation of cancer cells is poorly defined. We use 2D versus 3D cultivation to induce a shift in the cellular phenotype of breast cancer cells. We discover that proline catabolism via proline dehydrogenase (Prodh) supports growth of breast cancer cells in 3D culture. Subsequently, we link proline catabolism to in vivo metastasis formation. In particular, we find that PRODH expression and proline catabolism is increased in metastases compared to primary breast cancers of patients and mice. Moreover, inhibiting Prodh is sufficient to impair formation of lung metastases in the orthotopic 4T1 and EMT6.5 mouse models, without adverse effects on healthy tissue and organ function. In conclusion, we discover that Prodh is a potential drug target for inhibiting metastasis formation.

Most tumors have an aberrantly activated lipid metabolism 1 , 2 , which enables them to synthesize, elongate and desaturate fatty acids to support proliferation. However, only particular subsets of cancer cells are sensitive toward approaches targeting fatty acid metabolism, and in particular fatty acid desaturation 3 . This suggests that many cancer cells harbor an unexplored plasticity in their fatty acid metabolism. Here, we discover that some cancer cells can exploit an alternative fatty acid desaturation pathway. We identify various cancer cell lines, murine hepatocellular carcinomas (HCC), and primary human liver and lung carcinomas that desaturate palmitate to the unusual fatty acid sapienate to support membrane biosynthesis during proliferation. Accordingly, we found that sapienate biosynthesis enables cancer cells to bypass the known stearoyl-CoA desaturase (SCD)-dependent fatty acid desaturation. Thus, only by targeting both desaturation pathways the in vitro and in vivo proliferation of sapienate synthesizing cancer cells is impaired. Our discovery explains metabolic plasticity in fatty acid desaturation and constitutes an unexplored metabolic rewiring in cancers.

Extracellular matrix (ECM) is a major component of the local environment, i.e. the niche, that can determine cell behavior 1 . During metastatic growth, cancer cells shape the ECM of the metastatic niche by hydroxylating collagen to promote their own metastatic growth 2 , 3 . However, only particular nutrients might support the ability of cancer cells to hydroxylate collagen because nutrients dictate which enzymatic reactions are active in cancer cells 4 , 5 . Here, we discovered that breast cancer cells rely on the nutrient pyruvate to drive collagen-based ECM remodeling in the lung metastatic niche. Specifically, we discovered that pyruvate uptake induces the production of α-ketoglutarate. This metabolite in turn activated collagen hydroxylation by increasing the activity of the enzyme collagen prolyl-4-hydroxylase (P4HA). Strikingly, inhibition of pyruvate metabolism was sufficient to impair collagen hydroxylation and consequently the growth of breast cancer-derived lung metastases in different mouse models. In summary, we provide a mechanistic understanding of the link between collagen remodeling and the nutrient environment in the metastatic niche.