Impact of In Vivo Triazole and Echinocandin Combination Therapy for Invasive Pulmonary Aspergillosis: Enhanced Efficacy against Cyp51 Mutant Isolates

Abstract

Previous studies examining combination therapy for invasive pulmonary aspergillosis (IPA) have revealed conflicting results, including antagonism, indifference, and enhanced effects. The most commonly employed combination for this infection includes a mold-active triazole and echinocandin. Few studies have evaluated combination therapy from a pharmacodynamic (PD) perspective, and even fewer have examined combination therapy against both wild-type and azole-resistant Cyp51 mutant isolates. The current studies aim to fill this gap in knowledge. Four Aspergillus fumigatus isolates were utilized, including a wildtype strain, an Fks1 mutant (posaconazole susceptible and caspofungin resistant), and two Cyp51 mutants (posaconazole resistant). A neutropenic murine model of IPA was used for the treatment studies. The dosing design included monotherapy with posaconazole, monotherapy with caspofungin, and combination therapy with both. Efficacy was determined using quantitative PCR, and results were normalized to known quantities of conidia (conidial equivalents [CE]). The static dose, 1-log kill dose, and associated PD target area under the curve (AUC)/MIC ratio were determined for monotherapy and combination therapy. Monotherapy experiments revealed potent activity for posaconazole, with reductions of 3 to 4 log 10 Aspergillus CE/ml with the two "low"-MIC isolates. Posaconazole alone was less effective for the two isolates with higher MICs. Caspofungin monotherapy did not produce a significant decrease in fungal burden for any strain. Combination therapy with the two antifungals did not enhance efficacy for the two posaconazole-susceptible isolates. However, the drug combination produced synergistic activity against both posaconazole-resistant isolates. Specifically, the combination resulted in a 1-to 2-log 10 decline in burden that would not have been predicted based on the monotherapy results for each drug. This corresponded to a reduction in the freedrug posaconazole AUC/MIC ratio needed for stasis of up to 17-fold. The data suggest that combination therapy using a triazole and an echinocandin may be a beneficial treatment strategy for triazole-resistant isolates.

The Strength of Synergistic Interaction between Posaconazole and Caspofungin Depends on the Underlying Azole Resistance Mechanism of Aspergillus fumigatus

“…Interestingly, the strongest synergy was found for the group of isolates harboring the tandem repeats at the promoter region of cyp51A and for the group with substitutions at the M220 hot spot region. Our results are supported by a murine model of pulmonary aspergillosis in which POSA monotherapy and CAS monotherapy demonstrated suboptimal outcomes (40% to 50% survival); however, the drug combination led to enhanced efficacy (70% to 80% survival), mostly for the groups infected with POSA-resistant isolates with drug MICs of 2 and 8 mg/liter, respectively (20). These two resistant isolates were also reported to contain G138C and TR 34 /L98H mutations in cyp51A.…”

“…Moreover, in vitro and in vivo studies showed synergy between POSA and CAS against A. fumigatus wild-type strains (18,19). Lepak and colleagues, however, showed that therapy using a combination of POSA and CAS (POSA/CAS) in vivo did not enhance efficacy for POSA-susceptible isolates but produced synergistic activity against two POSA-resistant isolates (20).…”

Antifungal Pharmacokinetics and Pharmacodynamics

“…The echinocandins also exhibit activity against Aspergillus species, and animal model studies show similar PK/PD characteristics including concentration-dependent effects and efficacy linked to AUC/MIC and C max /MIC (Wiederhold et al 2004;Lewis et al 2008Lewis et al , 2011Lepak et al 2013b). However, unlike the cidal activity observed against Candida species, drug exposure against Aspergillus results in growth inhibition without significant organism killing.…”

“…However, synergistic interaction may not occur at all doses, and therefore combination PK/PD analysis requires dose-ranging experiments. An additional in vivo study has incorporated a wide dose-ranging combination therapy design for invasive aspergillosis (Lepak et al 2013b). Both wild-type and drug-resistant (Cyp51 mutant) Aspergillus isolates were included in the study of echinocandin/azole combination therapy in the neutropenic murine invasive pulmonary aspergillosis model.…”

APX001 Pharmacokinetic/Pharmacodynamic Target Determination against Aspergillus fumigatus in an In Vivo Model of Invasive Pulmonary Aspergillosis

“…Additionally, we found marked in vivo killing activity, with a 1-to 2-log 10 kill for all but one strain. This potency was perhaps surprising, given that echinocandins, which also impact the cell wall, lead to stunted growth in vitro (i.e., MEC measurement) and in vivo usually achieve only a net static effect against A. fumigatus with little to no observable decrease in the fungal burden from that at the start of therapy (34). In fact, the concentration-dependent decrease in the A. fumigatus fungal burden in the murine IPA model for APX001 is comparable to that for posaconazole and isavuconazole in this model (35,36).…”