The Long-Acting Echinocandin, Rezafungin, Prevents Pneumocystis Pneumonia and Eliminates Pneumocystis from the Lungs in Prophylaxis and Murine Treatment Models

Rezafungin is a novel echinocandin in Phase 3 development for prevention of invasive fungal disease caused by Candida spp., Aspergillus spp. and Pneumocystis jirovecii in blood and marrow transplantation patients. For such patients, standard antifungal prophylaxis currently comprises an azole for Candida and Aspergillus plus trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis pneumonia (PCP) despite drug-drug-interactions and intolerability that may limit their use, thus, alternatives are desirable. Rezafungin demonstrates a favorable safety profile and pharmacokinetic properties that allow for once-weekly dosing in addition, to antifungal activity against these predominant pathogens. Herein, the in vivo effects of rezafungin against Pneumocystis murina pneumonia were evaluated in immunosuppressed mouse models of prophylaxis and treatment using microscopy and qPCR assessments. In the prophylaxis model, immunosuppressed mice inoculated with P. murina were administered TMP-SMX (50/250 mg/kg 1x/week or 3x/week), caspofungin (5 mg/kg 3x/week), rezafungin (20 mg/kg, 1x/week or 3x/week; 5 mg/kg, 3x/week) intraperitoneally for 2, 4, 6 and 8 weeks, then immunosuppressed for an additional 6 weeks. Rezafungin administered for 4 weeks prevented P. murina from developing infection after rezafungin was discontinued. In the treatment model, immunosuppressed mice with P. murina pneumonia were treated with rezafungin 20 mg/kg 3x/week intraperitoneally for 2, 4, 6 and 8 weeks. Treatment with rezafungin for 8 weeks resulted in elimination of P. murina. Collectively, these studies showed that rezafungin could both prevent infection and eliminate P. murina from the lungs of mice. These findings support the obligate role of sexual reproduction for survival and growth of Pneumocystis spp. and warrant further investigation for treatment of P. jirovecii pneumonia in humans.