12 Upon binding halide ions such as chloride, SPQ is quenched, resulting in a decrease in fluorescence without a shift in wavelength. Intracellular chloride concentration was measured using a fluorescent indicator for chloride, SPQ as previously described. Finally, reports of ivermectin overdoses also support the evaluation of high doses of ivermectin in humans, as in the majority of these cases no serious adverse events were reported. 10 Even at a dose of 120 mg (∼2 mg/kg), no serious adverse effects were noted. 9 Likewise, to evaluate the safety of oral ivermectin, healthy volunteers received 30-120 mg on days 1, 4, and 7 and then a further dose in week 3. In this study, no significant adverse effects were reported. For example, in patients with spinal injury and resultant muscle spasticity, up to 1.6 mg/kg ivermectin was administered subcutaneously twice weekly for up to 12 weeks. 8 This brief and low-dose treatment is sufficient to achieve an antiparasitic effect, but higher doses and treatment beyond 1 day have been safely administered for other conditions. 7 In humans, when used to treat onchocerciasis, 100-200 μg/kg ivermectin is administered as a single dose. For example, the LD 50 of oral ivermectin in mice, rats, and rabbits ranges from 10 to 50 mg/kg. As part of the development of this agent as an antiparasitic agent, ivermectin was extensively evaluated for its pharmacology, safety, and toxicity in humans and animals. Ivermectin is a derivative of avermectin B1 and licensed for the treatment of the parasitic infections, strongyloidiasis and onchocerciasis, as well as other worm infestations (eg, ascariasis, trichuriasis, and enterobiasis), but has not been previously tested as an anticancer agent.
From this screen, we identified the antiparasitic agent, ivermectin. Here, we used a chemical screen to identify known drugs with previously unrecognized activity against leukemia. Given this finding, ketoconazole was rapidly advanced into clinical trials for patients with prostate cancer where it displayed clinical efficacy in early studies. 3 Likewise, the antifungal agent ketoconazole inhibits the production of androgens from the testes and adrenals in rats. Thus, ribavirin may be efficacious for the treatment of AML. In this study of 13 patients treated with ribavirin, there was 1 complete remission and 2 partial remissions. 1, 2 As such, ribavirin was recently evaluated in a phase I dose escalation study in patients with relapsed or refractory M4/M5 acute myeloid leukemia (AML). For example, the broad spectrum antiviral ribavirin was found to suppress oncogenic transformation by disrupting the function and subcellular localization of the eukaryotic translation initiation factor eIF4E.
Thus, given its known toxicology and pharmacology, ivermectin could be rapidly advanced into clinical trial for leukemia.Īntimicrobials with previously unrecognized anticancer activity can be rapidly repositioned for this new indication given their extensive prior pharmacology and toxicology testing. Finally, ivermectin synergized with cytarabine and daunorubicin that also increase reactive oxygen species production. Ivermectin also increased reactive oxygen species generation that was functionally important for ivermectin-induced cell death. Chloride influx was accompanied by plasma membrane hyperpolarization, but did not change mitochondrial membrane potential. Ivermectin increased intracellular chloride ion concentrations and cell size in leukemia cells. As an antiparasitic, ivermectin binds and activates chloride ion channels in nematodes, so we tested the effects of ivermectin on chloride flux in leukemia cells. Ivermectin also delayed tumor growth in 3 independent mouse models of leukemia at concentrations that appear pharmacologically achievable. As a potential antileukemic agent, ivermectin induced cell death at low micromolar concentrations in acute myeloid leukemia cell lines and primary patient samples preferentially over normal hematopoietic cells.
From these screens, we identified ivermectin, a derivative of avermectin B1 that is licensed for the treatment of the parasitic infections, strongyloidiasis and onchocerciasis, but is also effective against other worm infestations. To identify known drugs with previously unrecognized anticancer activity, we compiled and screened a library of such compounds to identify agents cytotoxic to leukemia cells.