Global Analysis of the Evolution and Mechanism of Echinocandin Resistance in Candida glabrata

The evolution of drug resistance has a profound impact on human health. Candida glabrata is a leading human fungal pathogen that can rapidly evolve resistance to echinocandins, which target cell wall biosynthesis and are front-line therapeutics for Candida infections. Here, we provide the first global analysis of mutations accompanying the evolution of fungal drug resistance in a human host utilizing a series of C. glabrata isolates that evolved echinocandin resistance in a patient treated with the echinocandin caspofungin for recurring bloodstream candidemia. Whole genome sequencing identified a mutation in the drug target, FKS2, accompanying a major resistance increase, and 8 additional non-synonymous mutations. The FKS2-T1987C mutation was sufficient for echinocandin resistance, and associated with a fitness cost that was mitigated with further evolution, observed in vitro and in a murine model of systemic candidemia. A CDC6-A511G(K171E) mutation acquired before FKS2-T1987C(S663P), conferred a small resistance increase. Elevated dosage of CDC55, which acquired a C463T(P155S) mutation after FKS2-T1987C(S663P), ameliorated fitness. To discover strategies to abrogate echinocandin resistance, we focused on the molecular chaperone Hsp90 and downstream effector calcineurin. Genetic or pharmacological compromise of Hsp90 or calcineurin function reduced basal tolerance and resistance. Hsp90 and calcineurin were required for caspofungin-dependent FKS2 induction, providing a mechanism governing echinocandin resistance. A mitochondrial respiration-defective petite mutant in the series revealed that the petite phenotype does not confer echinocandin resistance, but renders strains refractory to synergy between echinocandins and Hsp90 or calcineurin inhibitors. The kidneys of mice infected with the petite mutant were sterile, while those infected with the HSP90-repressible strain had reduced fungal burden. We provide the first global view of mutations accompanying the evolution of fungal drug resistance in a human host, implicate the premier compensatory mutation mitigating the cost of echinocandin resistance, and suggest a new mechanism of echinocandin resistance with broad therapeutic potential

Post-transcriptional control during chronic inflammation and cancer: a focus on AU-rich elements

A considerable number of genes that code for AU-rich mRNAs including cytokines, growth factors, transcriptional factors, and certain receptors are involved in both chronic inflammation and cancer. Overexpression of these genes is affected by aberrations or by prolonged activation of several signaling pathways. AU-rich elements (ARE) are important cis-acting short sequences in the 3′UTR that mediate recognition of an array of RNA-binding proteins and affect mRNA stability and translation. This review addresses the cellular and molecular mechanisms that are common between inflammation and cancer and that also govern ARE-mediated post-transcriptional control. The first part examines the role of the ARE-genes in inflammation and cancer and sequence characteristics of AU-rich elements. The second part addresses the common signaling pathways in inflammation and cancer that regulate the ARE-mediated pathways and how their deregulations affect ARE-gene regulation and disease outcome

Cryptococcal meningitis: epidemiology, immunology, diagnosis and therapy.

HIV-associated cryptococcal meningitis is by far the most common cause of adult meningitis in many areas of the world that have high HIV seroprevalence. In most areas in Sub-Saharan Africa, the incidence of cryptococcal meningitis is not decreasing despite availability of antiretroviral therapy, because of issues of adherence and retention in HIV care. In addition, cryptococcal meningitis in HIV-seronegative individuals is a substantial problem: the risk of cryptococcal infection is increased in transplant recipients and other individuals with defects in cell-mediated immunity, and cryptococcosis is also reported in the apparently immunocompetent. Despite therapy, mortality rates in these groups are high. Over the past 5 years, advances have been made in rapid point-of-care diagnosis and early detection of cryptococcal antigen in the blood. These advances have enabled development of screening and pre-emptive treatment strategies aimed at preventing the development of clinical infection in patients with late-stage HIV infection. Progress in optimizing antifungal combinations has been aided by evaluation of the clearance rate of infection by using serial quantitative cultures of cerebrospinal fluid (CSF). Measurement and management of raised CSF pressure, a common complication, is a vital component of care. In addition, we now better understand protective immune responses in HIV-associated cases, immunogenetic predisposition to infection, and the role of immune-mediated pathology in patients with non-HIV associated infection and in the context of HIV-associated immune reconstitution reactions

The use of new probes and stains for improved assessment of cell viability and extracellular polymeric substances in Candida albicans biofilms

Phenotypic and genotypic cell differentiation is considered an important feature that confers enhanced antifungal resistance in candidal biofilms. Particular emphasis has been placed in this context on the viability of biofilm subpopulations, and their heterogeneity with regard to the production of extracellular polymeric substances (EPS). We therefore assessed the utility of two different labeled lectins Erythrina cristagalli (ECA) and Canavalia ensiformis (ConA), for EPS visualization. To evaluate the viability of candidal biofilms, we further studied combination stains, SYTO9 and propidium iodide (PI). The latter combination has been successfully used to assess bacterial, but not fungal, viability although PI alone has been previously used to stain nuclei in fungal cells. Candida albicans biofilms were developed in a rotating disc biofilm reactor and observed in situ using confocal scanning laser microscopy (CSLM). Our data indicate that SYTO9 and PI are reliable vital stains that may be used to investigate C. albicans biofilms. When used together with ConA, the lectin ECA optimized EPS visualization and revealed differential production of this material in mature candidal biofilms. The foregoing probes and stains and the methodology described should help better characterize C. albicans biofilms in terms of cell their viability, and EPS production. © Springer 2005.link_to_subscribed_fulltex