Dolutegravir developmental toxicity is mitigated by magnesium and folate in zebrafish embryos.

Integrase strand transfer inhibitors have transformed human immunodeficiency virus (HIV) therapy, yet the widely prescribed drug dolutegravir (DTG) has been linked to developmental toxicity, and its teratogenic mechanism remains unclear. Here, we used zebrafish to dissect DTG toxicity during early vertebrate development. DTG exposure from 2-4 h post-fertilization (hpf) to 24 hpf produced high mortality and abnormal morphology. Co-treatment with folates partially restored normal morphology, whereas calcium had no effect. Strikingly, supplementation with magnesium (Mg) partially rescued DTG-exposed embryos, implicating Mg availability in protection. In competitive binding assays, Mg increased binding of folate to purified folate receptor (FOLR1) by 30% in the presence of DTG. folr1 mutant embryos contained significantly less endogenous folate than wild-type embryos and displayed marked hypersensitivity to DTG that could not be mitigated by folate supplementation. Critically, Mg supplementation partially rescued DTG toxicity in folr1 mutants, indicating a Folr1-independent component and placing the balance between free DTG and Mg-bound DTG upstream of folate transport. These results support a model in which free DTG antagonizes FOLR1 and Mg modifies DTG developmental toxicity through FOLR1-dependent and -independent processes.