Leflunomide suppresses the growth of LKB1-inactivated tumors in the immunocompetent host and attenuates distant cancer metastasis.

LKB1-inactivated tumors are vulnerable to the disruption of pyrimidine metabolism, and leflunomide emerges as a therapeutic candidate because its active metabolite, A77-1726, inhibits dihydroorotate dehydrogenase, which is essential for de novo pyrimidine biosynthesis. However, it is unclear whether leflunomide inhibits LKB1-inactivated tumors in vivo, and whether its inhibitory effect on the immune system will promote tumor growth. Here, we carried out a comprehensive analysis of leflunomide treatment in various LKB1-inactivated murine xenograft, PDX, and genetically engineered mouse models. We also generated a mouse-tumor derived cancer cell line, WRJ388, that could metastasize to the lung within a month after subcutaneous implantation in all animals. This model was used to assess the ability of leflunomide to control distant metastasis. Leflunomide treatment shrank a HeLa xenograft and attenuated the growth of an H460 xenograft, a PDX, and lung adenocarcinoma in the immune-competent GEMM. Interestingly, leflunomide suppressed tumor growth through at least three different mechanisms. It caused apoptosis in HeLa cells, induced G1 cell cycle arrest in H460 cells, and promoted S-phase cell cycle arrest in WRJ388 cells. Finally, leflunomide treatment prevented lung metastasis in 78% of the animals in our novel lung cancer metastasis model. In combination, these results demonstrated that leflunomide utilizes different pathways to suppress the growth of LKB1-inactivated tumors, and it also prevents cancer metastasis at distant sites. Therefore, leflunomide should be evaluated as a therapeutic agent for tumors with LKB1-inactivation.