Abstract
Two series of piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives were prepared via a Buchwald–Hartwig cross-coupling reaction and then evaluated for their ability to inhibit the drug efflux activity of CaCdr1p and CaMdr1p transporters of Candida albicans overexpressed in a Saccharomyces cerevisiae strain. In the initial screening of twenty-nine piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives, twenty-three compounds behaved as dual inhibitors of CaCdr1p and CaMdr1p. Only four compounds showed exclusive inhibition of CaCdr1p or CaMdr1p. Further biological investigations were developed and for example, their antifungal potential was evaluated by measuring the growth of control yeast cells (AD1-8u−) and efflux pump-overexpressing cells (AD-CDR1 and AD-MDR1) after exposition to variable concentrations of the tested compounds. The MIC80 values of nineteen compounds ranging from 100 to 901 μM for AD-CDR1 demonstrated that relative resistance index (RI) values were between 8 and 274. In comparison, only seven compounds had RI values superior to 4 in cells overexpressing Mdr1p. These results indicated substrate behavior for nineteen compounds for CaCdr1p and seven compounds for CaMdr1p, as these compounds were transported via MDR transporter overexpressing cells and not by the AD1-8u− cells. Finally, in a combination assay with fluconazole, two compounds (1d and 1f) have shown a synergistic effect (fractional inhibitory concentration index (FICI) values ≤ 0.5) at micromolar concentrations in the AD-MDR1 yeast strain overexpressing CaMdr1p-protein, indicating an excellent potency toward chemosensitization.
Highlights
Transplantation surgery, cancer chemotherapy, and HIV infections have led to a worldwide rise of the immunocompromised population, and of bacterial and fungal opportunistic infections.[1]
Twenty-nine compounds have been selected on their potential to inhibit fungal multidrug resistance pumps as pyrrolo[1,2-a]quinoxaline template was already used and efficient for the inhibition of bacterial efflux pumps.[32,33]
We broadened our horizon to look into the role of these compounds to inhibit the CaCdr1p and CaMdr1p transporters in pathogenic yeast C. albicans
Summary
Invasive fungal infections include Candida, Aspergillus, and Cryptococcus,[2] with opportunistic strains of Candida albicans accounting for approximately 50–60% causes of candidiasis, in immunocompromised patients. The pyrrolo[1,2-a]quinoxaline heterocyclic framework constitutes the basis of an important class of compounds possessing interesting biological activities These compounds have been reported as key intermediates for the assembly of several heterocycles including antipsychotic agent,[18] anti-HIV agent,[19] adenosine A3 receptor modulator,[20] antiparasitic agents,[21,22,23,24,25] and antitumor agents.[26,27,28,29,30,31] We previously demonstrated that the pyrrolo[1,2-a]quinoxaline heterocyclic scaffold could lead to the preparation of bacterial multidrug resistance pump inhibitors.[32,33]. In this context and as part of a programme on the development of new efflux pump inhibitors (EPIs), we decided to broaden the structural diversity and used the pyrrolo[1,2-a] quinoxaline moiety as a template for the design of new derivatives 1 and 2 in which a piperazine is incorporated in position 1, 4 or 9 of the heterocyclic core in analogy with the EPI pyrimidine and quinoline derivatives I–III, quinine and MS-209 used in the various multidrug resistance therapies (Fig. 1).[34,35,36,37,38]
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