What's new in antifungals: an update on the in-vitro activity and in-vivo efficacy of new and investigational antifungal agents

High-Throughput Screening of the Repurposing Hub Library to Identify Drugs with Novel Inhibitory Activity against Candida albicans and Candida auris Biofilms

Candidiasis is one of the most frequent nosocomial infections affecting an increasing number of at-risk patients. Candida albicans remains the most frequent causative agent of candidiasis, but, in the last decade, C. auris has emerged as a formidable multi-drug-resistant pathogen. Both species are fully capable of forming biofilms, which contribute to resistance, increasing the urgency for new effective antifungal therapies. Repurposing existing drugs could significantly accelerate the development of novel therapies against candidiasis. Here, we have screened the Repurposing Hub library from the Broad Institute, containing over 6000 compounds, in search for inhibitors of C. albicans and C. auris biofilm formation. The primary screen identified 57 initial hits against C. albicans and 33 against C. auris. Confirmatory concentration-dependent assays were used to validate the activity of the initial hits and, at the same time, establish their anti-biofilm potency. Based on these results, ebselen, temsirolimus, and compound BAY 11-7082 emerged as the leading repositionable compounds. Subsequent experiments established their spectrum of antifungal activity against yeasts and filamentous fungi. In addition, their in vivo activity was examined in the murine models of hematogenously disseminated C. albicans and C. auris infections. Although promising, further in vitro and in vivo studies are needed to confirm their potential use for the therapy of candidiasis and possibly other fungal infections.

Aspergillosis: Epidemiology, Diagnosis, and Treatment

The spectrum of disease produced by Aspergillus species ranges from allergic syndromes to chronic pulmonary conditions and invasive infections. Invasive aspergillosis is a major cause of morbidity and mortality in immunocompromised patients. Risk factors continue to evolve and include newer biological agents that target the immune system and postinfluenza infection; and it has been observed following COVID-19 infection. Diagnosis remains a challenge but non-culture-based methods are available. Antifungal resistance has emerged. Voriconazole remains the treatment of choice but isavuconazole and posaconazole have similar efficacy with less toxicity. Combination therapy is used with extensive infection and in severe immunosuppression.

Diagnosis and treatment of invasive fungal infections: looking ahead

Improved standards of care depend on the development of new laboratory diagnostic and imaging procedures and the development of new antifungal compounds. Immunochromatography technologies have led to the development of lateral flow devices for the diagnosis of cryptococcal meningitis and invasive aspergillosis (IA). Similar devices are being developed for the detection of histoplasmosis that meet the requirements for speed (∼15 min assay time) and ease of use for point-of-care diagnostics. The evolution of molecular tools for the detection of fungal pathogens has been slow but the introduction of new nucleic acid amplification techniques appears to be helpful, for example T2Candida. An Aspergillus proximity ligation assay has been developed for a rapid near-patient bedside diagnosis of IA. CT remains the cornerstone for radiological diagnosis of invasive pulmonary fungal infections. MRI of the lungs may be performed to avoid radiation exposure. MRI with T2-weighted turbo-spin-echo sequences exhibits sensitivity and specificity approaching that of CT for the diagnosis of invasive pulmonary aspergillosis. The final part of this review looks at new approaches to drug discovery that have yielded new classes with novel mechanisms of action. There are currently two new classes of antifungal drugs in Phase 2 study for systemic invasive fungal disease and one in Phase 1. These new antifungal drugs show promise in meeting unmet needs with oral and intravenous formulations available and some with decreased potential for drug-drug interactions. Novel mechanisms of action mean these agents are not susceptible to the common resistance mechanisms seen in Candida or Aspergillus. Modification of existing antifungal susceptibility testing techniques may be required to incorporate these new compounds.

Bioinspired benzoxanthene lignans as a new class of antimycotic agents: synthesis and Candida spp. growth inhibition

In this work we synthetized the bioinspired benzoxanthene lignans (BXLs) 3, 14-22, and the phenazine derivative 23 as potential antimycotic agents. MICs and MFCs against Candida strains were determined. In a preliminary screening, compounds 3, 15, 20, 21, 22 were substantially inactive. Compounds 14 and 17 showed antifungal activity, being able to inhibit the growth of the majority of Candida strains with MIC values in the range 4.6-19.2 µM (14) and 26.0-104.3 µM (17); for three strains, the MICs were lower than those obtained using the antimycotic drug fluconazole. The three BXLs 18, 19 and 23 showed some MIC values lower than that of fluconazole; 18 was also active against two non-albicans Candida strains resistant to fluconazole. Phenazine 23, although active only against one strain (MIC = 1.3 µM), was one order of magnitude more potent than fluconazole. All the BXLs were fungicidal.

Antimicrobial activity of some novel 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives

Background

Infectious diseases, especially those caused by multidrug-resistant bacteria, are becoming a serious problem worldwide because of the lack of effective therapeutic agents. Moreover, most antifungal drugs exhibit low efficacy and high toxicity because of the similarity between fungal and human cells. These issues warrant the search for potential new agents.

Objectives

To synthesize potent 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives, improve the synthetic process, elucidate their structures, and determine their antimicrobial activity.

Methods

2-Iodoaniline was used as an initial reactant in a 3-step process for the synthesis of 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives, including an acylation reaction, a cyclization reaction, and aldol condensation reactions. The structures of the obtained derivatives were investigated and elucidated using spectral methods. Antimicrobial activity toward 5 bacterial strains and 2 fungal strains was determined using Kirby–Bauer and agar dilution methods.

Results

We successfully synthesized 12 novel compounds and elucidated their structures. The derivatives had no antifungal activities. By contrast, they showed remarkable antibacterial activities. Some of them with minimum inhibitory concentrations (MICs) ≤8 μg/mL in both Staphylococcus aureus and methicillin-resistant S. aureus.

Conclusions

A simple and flexible way to synthesize new compounds with a thiazolidin-4-one ring was determined. Some of these new compounds have outstanding effects with low MICs for bacteria. Their further investigation as therapeutic agents is warranted.

Oxygen-responsive transcriptional regulation of lipid homeostasis in fungi: Implications for anti-fungal drug development

Low oxygen adaptation is essential for aerobic fungi that must survive in varied oxygen environments. Pathogenic fungi in particular must adapt to the low oxygen host tissue environment in order to cause infection. Maintenance of lipid homeostasis is especially important for cell growth and proliferation, and is a highly oxygen-dependent process. In this review, we focus on recent advances in our understanding of the transcriptional regulation and coordination of the low oxygen response across fungal species, paying particular attention to pathogenic fungi. Comparison of lipid homeostasis pathways in these organisms suggests common mechanisms of transcriptional regulation and points toward untapped potential to target low oxygen adaptation in antifungal development.

Synthesis and Antifungal Screening of 2-{[1-(5-Alkyl/arylalkylpyrazin-2-yl)ethylidene]hydrazono}-1,3-thiazolidin-4-ones

Two novel thiosemicarbazones and eight novel 2-{[1-(5-alkyl/arylalkylpyrazin-2-yl)ethylidene]hydrazono}-1,3-thiazolidin-4-ones were prepared and tested against a panel of eight fungal strains–Candida albicans ATCC 44859, Candida tropicalis 156, Candida krusei E 28, Candida glabrata 20/I, Trichosporon asahii 1188, Aspergillus fumigatus 231, Lichtheimia corymbifera 272, and Trichophyton interdigitale 445. 1,3-Thiazolidin-4-ones exhibited activity against all strains, the most potent derivative was 2-{[1-(5-butylpyrazin-2-yl)ethylidene]hydrazono}e-1,3-thiazolidin-4-one. Susceptibility of C. glabrata to the studied 1,3-thiazolidin-4-ones (minimum inhibitory concentrations (MICs) were in the range 0.57 to 2.78 mg/L) is of great interest as this opportunistic pathogen is poorly susceptible to azoles and becomes resistant to echinocandins. Antifungal potency of thiosemicarbazones was slightly lower than that of 1,3-thiazolidin-4-ones.

Invasive Aspergillosis: Current Strategies for Diagnosis and Management

Aspergillosis remains a significant cause of morbidity and mortality in the immunocompromised population. The spectrum of disease is broad, ranging from severe and rapidly fatal infection to noninvasive disease. The diversity of patients and risk factors complicates diagnostic and therapeutic decision-making. Invasive procedures are often precluded by host status; noninvasive diagnostic tests vary in their sensitivity and specificity. Advancements in understanding the pathophysiology of invasive aspergillosis and host genetics in differential risk have also occurred. Future work may assist in therapeutic decision-making and patient prognosis. Voriconazole remains the preferred agent for treatment. Additional alternatives have emerged.

Design and synthesis of purine analogues as highly specific ligands for FcyB, a ubiquitous fungal nucleobase transporter

In the course of our study on fungal purine transporters, a number of new 3-deazapurine analogues have been rationally designed, based on the interaction of purine substrates with the Aspergillus nidulans FcyB carrier, and synthesized following an effective synthetic procedure. Certain derivatives have been found to specifically inhibit FcyB-mediated [³H]-adenine uptake. Molecular simulations have been performed, suggesting that all active compounds interact with FcyB through the formation of hydrogen bonds with Asn163, while the insertion of hydrophobic fragments at position 9 and N6 of 3-deazaadenine enhanced the inhibition.

A complex game of hide and seek: the search for new antifungals

Fungal infections directly affect millions of people each year. In addition to the invasive fungal infections of humans, the plants and animals that comprise our primary food source are also susceptible to diseases caused by these eukaryotic microbes. The need for antifungals, not only for our medical needs, but also for use in agriculture and livestock causes a high demand for novel antimycotics. Herein, we provide an overview of the most commonly used antifungals in medicine and agriculture. We also present a summary of the recent progress (from 2010-2016) in the discovery/development of new agents against fungal strains of medical/agricultural relevance, as well as information related to their biological activity, their mode(s) of action, and their mechanism(s) of resistance.