Efficacy of CD101, a Novel Echinocandin, in Prevention of Pneumocystis Pneumonia (PCP): Thwarting the Biphasic Life Cycle of Pneumocystis
Authors: Cushion Melanie , Ashbaugh Alan , Lynch Keeley , Linke Michael J. , Bartizal Ken 
Published: October 2019

Abstract
Background: Pneumocystis spp. are the obligate pathogenic fungi that cause PCP in immunocompromised mammalian hosts. The life cycle of Pneumocystis is thought to be biphasic with asexual replication by trophic forms and sexual production leading to formation of asci/cysts. There is evidence to suggest that infection is initiated by cyst inhalation and asci formation may be essential for the Pneumocystis life cycle. We have previously reported (Cushion, et al. 2010; 5:e8524) that currently available echinocandins are not suitable for monotherapy as large numbers of trophic forms remained after 3 weeks of treatment and asci re-appeared and replication resumed after treatment discontinuation. We evaluated the effects of CD101, a novel long-acting echinocandin, on trophic and cyst forms of Pneumocystis murina and its efficacy in preventing infection in a mouse model of PCP.
Methods: Mice (C3H/HeN) were immunosuppressed throughout this 6-week study by dexamethasone (4 mg/L) in acidified drinking water. Infection with P. murina was by intranasal inoculation (2 x 106/50 µL). Mice were divided into groups to receive either vehicle (untreated control), trimethoprim/sulfamethoxazole (TMP/SMX 50/250 mg/kg x 3 per week), or CD101 (20, 2, or 0.2 mg/kg once or 3x per week) intraperitoneally at the time mice were inoculated. After 6 weeks, mice were humanely euthanized and lungs were processed for analysis by homogenization. Slides made from the lung homogenates were prepared for quantification of trophic forms by rapid Wright-Giemsa stain and of asci by cresyl echt violet staining. The reduction in P. murina burden (nuclei of trophic forms and asci) in treatment and untreated control groups was evaluated. The nuclei and asci counts for each lung were log transformed and analyzed by ANOVA. Individual groups were compared by Dunn's test for multiple comparisons (GraphPadPrismv.6).
Results: The reduction in nuclei and asci counts for all groups are shown in the Figure. Statistically significant reductions in nuclei levels compared with untreated controls were demonstrated with all CD101-treated groups except for the 0.2 mg/kg once weekly group. CD101 efficacy was comparable to that of TMP/SMX for 3 of the CD101 dose groups; no nuclei were observed by microscopic evaluation following CD101 dosages of 2 or 20 mg/kg 3x per week or 20 mg/kg once weekly. In terms of asci reduction, all CD101 groups demonstrated statistically significant reductions compared with untreated controls. CD101 efficacy was comparable to that of TMP/SMX for 5 of the CD101 dose groups (all but the 0.2 mg/kg once weekly group), with no asci observed by microscopic evaluation.
Conclusion: Asci/cysts appear to be critical for replication as well as transmission of Pneumocystis. CD101 inhibited the formation of both trophic forms and asci of P. murina in thismouse model of PCP in immunocompromised mice. These data demonstrate that CD101 is a viable candidate for prophylactic therapy of PCP.
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Disclosures
Cushion: Univ. of Cincinnati: Employment; Cincinnati VAMC: Research Funding; Cidara Therapeutics, Inc.: Research Funding. Bartizal:Cidara Therapeutics, Inc.: Employment, Other: Stockholder.