Flubendazole inhibits PD-1 and suppresses melanoma growth in immunocompetent mice

Immune checkpoint inhibitor therapy has revolutionized the clinical management of a diverse range of cancer types, including advanced cutaneous melanoma. While immunotherapy targeting the PD-1/PD-L1 system has become standard of care, overall response rates remain unsatisfactory for most patients and there are no approved small molecule inhibitors of the PD-1/PD-L1 system. Flubendazole (FLU) is an anthelmintic that has been used to treat worm infections in humans and animals for decades.

This study is the first to show that FLU can inhibit melanoma growth with PD-1 suppression in immunocompetent mice.

Here we tested the anti-cancer activity of systemically delivered FLU with suppression of PD-1 in immunocompetent mice.

In C57BL/6J mice bearing subcutaneous B16F10 melanoma, FLU reduced both tumor growth and PD-1 protein levels without affecting levels of PD-L1. FLU's suppression of PD-1 was accompanied by increased CD3+ T cell infiltration. Western blotting with extracts from human Jurkat T cells showed that FLU inhibited PD-1 protein expression, findings confirmed by flow cytometry. To gain mechanistic insights on FLU's ability to suppress PD-1 protein levels, we performed bulk RNA sequencing on extracts of Jurkat T cells exposed to the benzimidazole for 4 h. From a pool of 14,475 genes there were 1218 differentially-expressed genes; 687 with increased expression and 531 with decreased expression. Among the genes induced by FLU was the AP-1 family member, JUN and surprisingly, pdcd1. KEGG pathway analysis showed FLU up-regulated genes over-represented in multiple pathways (p < 0.01), the top hit being amoebiasis. FLU also affected the expression of genes in cancer-associated pathways, both through down-regulation and up-regulation. Gene set enrichment analysis revealed a large number of immunological signature gene sets correlated with FLU treatment, including gene sets associated with T cell differentiation, proliferation and function. The AP-1 inhibitor T5224 rescued PD-1 protein expression from inhibition by FLU.