Carbonyl Reduction of Flubendazole in the Human Liver: Strict Stereospecificity, Sex Difference, Low Risk of Drug Interactions

Flubendazole carbonyl reduction in drug-susceptible and drug-resistant strains of the parasitic nematode Haemonchus contortus: changes during the life cycle and possible inhibition

Carbonyl-reducing enzymes (CREs) catalyse the reduction of carbonyl groups in many eobiotic and xenobiotic compounds in all organisms, including helminths. Previous studies have shown the important roles of CREs in the deactivation of several anthelmintic drugs (e.g., flubendazole and mebendazole) in adults infected with the parasitic nematode Haemonchus contortus, in which the activity of a CRE is increased in drug-resistant strains. The aim of the present study was to compare the abilities of nematodes of both a drug-susceptible strain (ISE) and a drug-resistant strain (IRE) to reduce the carbonyl group of flubendazole (FLU) in different developmental stages (eggs, L1/2 larvae, L3 larvae, and adults). In addition, the effects of selected CRE inhibitors (e.g., glycyrrhetinic acid, naringenin, silybin, luteolin, glyceraldehyde, and menadione) on the reduction of FLU were evaluated in vitro and ex vivo in H. contortus adults. The results showed that FLU was reduced by H. contortus in all developmental stages, with adult IRE females being the most metabolically active. Larvae (L1/2 and L3) and adult females of the IRE strain reduced FLU more effectively than those of the ISE strain. Data from the in vitro inhibition study (performed with cytosolic-like fractions of H. contortus adult homogenate) revealed that glycyrrhetinic acid, naringenin, mebendazole and menadione are effective inhibitors of FLU reduction. Ex vivo study data showed that menadione inhibited FLU reduction and also decreased the viability of H. contortus adults to a similar extent. Naringenin and mebendazole were not toxic at the concentrations tested, but they did not inhibit the reduction of FLU in adult worms ex vivo.

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

BACKGROUND

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.

METHODS

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

RESULTS

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.

CONCLUSION

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

Flubendazole Plays an Important Anti-Tumor Role in Different Types of Cancers

Flubendazole, belonging to benzimidazole, is a broad-spectrum insect repellent and has been repurposed as a promising anticancer drug. In recent years, many studies have shown that flubendazole plays an anti-tumor role in different types of cancers, including breast cancer, melanoma, prostate cancer, colorectal cancer, and lung cancer. Although the anti-tumor mechanism of flubendazole has been studied, it has not been fully understood. In this review, we summarized the recent studies regarding the anti-tumor effects of flubendazole in different types of cancers and analyzed the related mechanisms, in order to provide the theoretical reference for further studies in the future.

Emerging insights on functions of the anthelmintic flubendazole as a repurposed anticancer agent

While flubendazole has been used as a macrofilaricide in humans and animals for some 40 years, work in vitro and in preclinical models over the last decade has suggested its potential use as an anticancer agent. This article reviews recent studies in a range of tumor types indicating novel functions for flubendazole in its control of processes associated with tumor growth, spread and renewal including ferroptosis, autophagy, cancer stem-like cell killing and suppression of intratumoral myeloid-derived suppressor cell accumulation and programmed cell death protein 1. Flubendazole's potential use in clinical oncology will require further understanding of its mechanistic roles, range of inhibition of cancer types, capacity for adjunctive therapy and possible reformulation for enhanced solubility, bioavailability and potency.