The vacuolar fusion regulated by HOPS complex promotes hyphal initiation and penetration in Candida albicans.

The transition between yeast and hyphae is crucial for regulating the commensalism and pathogenicity in Candida albicans. The mechanisms that affect the invasion of hyphae in solid media, whose deficiency is more related to the pathogenicity of C. albicans, have not been elucidated. Here, we found that the disruption of VAM6 or VPS41 which are components of the homotypic vacuolar fusion and protein sorting (HOPS) complex, or the Rab GTPase YPT72, all responsible for vacuole fusion, led to defects in hyphal growth in both liquid and solid media, but more pronounced on solid agar. The phenotypes of vac8Δ/Δ and GTR1OE-vam6Δ/Δ mutants indicated that these deficiencies are mainly caused by the reduced mechanical forces that drive agar and organs penetration, and confirmed that large vacuoles are required for hyphal mechanical penetration. In summary, our study revealed that large vacuoles generated by vacuolar fusion support hyphal penetration and provided a perspective to refocus attention on the role of solid agar in evaluating C. albicans invasion.

Discovery of a Novel Potent Tetrazole Antifungal Candidate with High Selectivity and Broad Spectrum.

Thirty-one novel albaconazole derivatives were designed and synthesized based on our previous work. All compounds exhibited potent in vitro antifungal activities against seven pathogenic fungi. Among them, tetrazole compound D2 was the most potent antifungal with MIC values of <0.008, <0.008, and 2 µg/mL against Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus, respectively, the three most common and critical priority pathogenic fungi. In addition, compound D2 also exhibited potent activity against fluconazole-resistant C. auris isolates. Notably, compound D2 showed a lower inhibitory activity in vitro against human CYP450 enzymes as well as a lower inhibitory effect on the hERG K+ channel, indicating a low risk of drug-drug interactions and QT prolongation. Moreover, with improved pharmacokinetic profiles, compound D2 showed better in vivo efficacy than albaconazole at reducing fungal burden and extending the survival of C. albicans-infected mice. Taken together, compound D2 will be further investigated as a promising candidate.

From Synergy to Monotherapy: Discovery of Novel 2,4,6-Trisubstituted Triazine Hydrazone Derivatives with Potent Antifungal Potency In Vitro and In Vivo.

Invasive fungal infections pose a serious threat to public health and are associated with high mortality and incidence rates. The development of novel antifungal agents is urgently needed. Based on hit-to-lead optimization, a series of 2,4,6-trisubstituted triazine hydrazone compounds were designed, synthesized, and biological evaluation was performed, leading to the identification of compound 28 with excellent in vitro synergy (FICI range: 0.094-0.38) and improved monotherapy potency against fluconazole-resistant Candida albicans and Candida auris (MIC range: 1.0-16.0 µg/mL). Moreover, 28 exhibited broad-spectrum antifungal activity against multiple pathogenic strains. Furthermore, 28 could inhibit hyphal and biofilm formation, which may be related to its ability to disrupt the fungal cell wall. Additionally, 28 significantly reduced the CFU in a mouse model of disseminated infection with candidiasis at a dose of 10 mg/kg. Overall, the triazine-based hydrazone compound 28 with low cytotoxicity, hemolysis, and favorable ADME/T characteristics represents a promising lead to further investigation.

Late consolidation of rRNA structure during co-transcriptional assembly in E. coli by time-resolved DMS footprinting.

The production of new ribosomes requires proper folding of the rRNA and the addition of more than 50 ribosomal proteins. The structures of some assembly intermediates have been determined by cryo-electron microscopy, yet these structures do not provide information on the folding dynamics of the rRNA. To visualize the changes in rRNA structure during ribosome assembly in E. coli cells, transcripts were pulse-labeled with 4-thiouridine and the structure of newly made rRNA probed at various times by dimethyl sulfate modification and mutational profiling sequencing (4U-DMS-MaPseq). The in-cell DMS modification patterns revealed that many long-range rRNA tertiary interactions and protein binding sites through the 16S and 23S rRNA remain partially unfolded 1.5 min after transcription. By contrast, the active sites were continually shielded from DMS modification, suggesting that these critical regions are guarded by cellular factors throughout assembly. Later, bases near the peptidyl tRNA site exhibited specific rearrangements consistent with the binding and release of assembly factors. Time-dependent structure-probing in cells suggests that many tertiary interactions throughout the new ribosomal subunits remain mobile or unfolded until the late stages of subunit maturation.

Design, synthesis and evaluation of novel deferasirox derivatives with high antifungal potency in vitro and in vivo.

Here we designed and synthesized 58 deferasirox derivatives with the aim of discovering novel antifungal agents. Most compounds exhibited moderate to excellent in vitro antifungal activities against Cryptococcus neoformans H99 with MIC values ranging from 0.25 µg/mL to 16 µg/mL, including ten compounds with MIC values less than 1 µg/mL that were further screened against an additional six pathogenic fungi. This class of compounds showed high potency against Candida glabrata with MIC values ranging from <0.125 µg/mL to 1 µg/mL. We identified that compound 54 has high potency against 14 strains of Candida glabrata spp. and Cryptococcus spp. with MIC values ranging from <0.125 µg/mL to 1 µg/mL. In addition, compound 54 significantly reduced the CFU in a mouse model of disseminated infection with Cryptococcus neoformans H99 at a dose of 10 mg/kg, which is comparable to FLC. Further investigations on compound 54 are currently in progress.

Design, synthesis and in vitro biological studies of novel triazoles with potent and broad-spectrum antifungal activity.

A series of novel triazole derivatives containing aryl-propanamide side chains was designed and synthesised. In vitro antifungal activity studies demonstrated that most of the compounds inhibited the growth of six human pathogenic fungi. In particular, parts of phenyl-propionamide-containing compounds had excellent, broad-spectrum antifungal activity against Candida albicans SC5314, Cryptococcus neoformans 22-21, Candida glabrata 537 and Candida parapsilosis 22-20 with MIC values in the range of ≤0.125 µg/mL-4.0 µg/mL. In addition, compounds A1, A2, A6, A12 and A15 showed inhibitory activities against fluconazole-resistant Candida albicans and Candida auris. Preliminary structure-activity relationships (SARs) are also summarised. Moreover, GC-MS analysis demonstrated that A1, A3, and A9 interfered with the C. albicans ergosterol biosynthesis pathway by inhibiting Cyp51. Molecular docking studies elucidated the binding modes of A3 and A9 with Cyp51. These compounds with low haemolytic activity and favourable ADME/T properties are promising for the development of novel antifungal agents.

Discovery of novel triazoles containing benzyloxy phenyl isoxazole side chain with potent and broad-spectrum antifungal activity.

As a continuation study, 29 novel triazoles containing benzyloxy phenyl isoxazole side chain were designed and synthesized based on our previous work. The majority of the compounds exhibited high potency in vitro antifungal activities against eight pathogenic fungi. The most active compounds 13, 20 and 27 displayed outstanding antifungal activity with MIC values ranging from <0.008 µg/mL to 1 µg/mL, and showed potent activity against six drug-resistant Candida auris isolates. Growth curve assays further confirmed the high potency of these compounds. Moreover, compounds 13, 20 and 27 showed a potent inhibitory activity on biofilm formation of C. albicans SC5314 and C. neoformans H99. Notably, compound 13 showed no inhibition of human CYP1A2 and low inhibitory activity against CYP2D6 and CYP3A4, suggesting a low risk of drug-drug interactions. With high potency in vitro and in vivo and good safety profiles, compound 13 will be further investigated as a promising candidate.

Novel antifungal triazoles with alkynyl-methoxyl side chains: Design, synthesis, and biological activity evaluation.

Previous work led to the rational design, synthesis and testing of novel antifungal triazole analogues bearing alkynyl-methoxyl side chains. Tests of in vitro antifungal activity showed Candida albicans SC5314 and Candida glabrata 537 gave MIC values of ≤0.125 µg/mL for most of the compounds. Among these, compounds 16, 18, and 29 displayed broad-spectrum antifungal activity against seven human pathogenic fungal species, two fluconazole-resistant C. albicans isolates and two multi-drug resistant Candida auris isolates. Moreover, 0.5 µg/mL of 16, 18, and 29 was more effective than 2 µg/mL of fluconazole at inhibiting fungal growth of the strains tested. The most active compound (16) completely inhibited the growth of C. albicans SC5314 at 16 µg/mL for 24 h, affected biofilm formation and destroyed the mature biofilm at 64 µg/mL. Several Saccharomyces cerevisiae strains, overexpressing recombinant Cyp51s or drug efflux pumps, indicated 16, 18, and 29 targeted Cyp51 without being significantly affected by a common active site mutation, but were susceptible to target overexpression and efflux by both MFS and ABC transporters. GC-MS analysis demonstrated that 16, 18, and 29 interfered with the C. albicans ergosterol biosynthesis pathway by inhibition at Cyp51. Molecular docking studies elucidated the binding modes of 18 with Cyp51. The compounds showed low cytotoxicity, low hemolytic activity and favorable ADMT properties. Importantly, compound 16 showed potent in vivo antifungal efficacy in the G. mellonella infection model. Taken together, this study presents more effective, broad-spectrum, low toxicity triazole analogues that can contribute to the development of novel antifungal agents and help overcome antifungal resistance.

Design, Synthesis and Structure-Activity Relationship Studies of Nicotinamide Derivatives as Potent Antifungal Agents by Disrupting Cell Wall.

Fungal infections pose a serious challenge to human health due to the limited paucity of antifungal treatments. Starting as a hit compound screened from our compound library, a series of nicotinamide derivatives have been successfully synthesized via a facile one-step coupling reaction of aromatic carboxylic acid and amine. The synthesized compounds were evaluated for their antifungal activity against Candida albicans SC5314. Among the 37 nicotinamide derivatives screened, compound 16g was found to be the most active against C. albicans SC5314, with an MIC value of 0.25 µg/mL and without significant cytotoxicity. The rudimentary structure-activity relationships study revealed that the position of the amino and isopropyl groups of 16g was critical for its antifungal activity. In particular, compound 16g showed potent activity against six fluconazole-resistant C. albicans strains with MIC values ranging from 0.125-1 µg/mL and showed moderate activity against the other seven species of Candida, three strains of Cryptococcus neoformans, and three strains of Trichophyton. Furthermore, compound 16g showed fungicidal, anti-hyphal, and anti-biofilm activities in vitro, which were related to its ability to disrupt the cell wall of C. albicans. Taken together, 16g is a promising compound that is fungal-specific by targeting the cell wall and could be used as a lead compound for further investigation.

Design, synthesis, and evaluation of novel tetrazoles featuring isoxazole moiety as highly selective antifungal agents.

In an effort to develop novel azole antifungals with potent activity and high selectivity, a series of (2R,3R)-3-((3-substitutied-phenyl-isoxazol-5-yl)methoxy)-2-(2,4-difluorophenyl)-1-(1H-tetrazol-1-yl)butan-2-ol derivatives were designed and synthesized based on our previously work. All compounds exhibited moderate to excellent in vitro antifungal activities against Candida albicans SC5314 and Cryptococcus neoformans H99, but inactive against Aspergillus fumigatus 7544. Among them, the most active compound 10h displayed outstanding antifungal activity against fluconazole-resistant C. albicans 103, C. glabrata 537 and C. auris 922 with MIC values of ≤0.008 µg/mL. In addition, compound 10h was superior to FLC in inhibiting the filamentation of FLC-resistant C. albicans 103. Notably, compound 10h showed no inhibition of human CYP3A4 with IC50 values of >100 µM, low cytotoxicity at 32 µg/mL and low hERG inhibition with IC50 values of 6.22 µM, suggesting a low risk of drug-drug interactions and good safety profiles. Furthermore, compound 10h exhibited excellent PK profiles and showed remarkable in vivo efficacy in a mouse model of C. albicans and C. neoformans infection. Taken together, compound 10h will be further investigated as a promising lead antifungal agent.

Discovery of Novel Orally Bioavailable Triazoles with Potent and Broad-Spectrum Antifungal Activity In Vitro and In Vivo.

In our continuing efforts to discover novel triazoles with improved antifungal activity in vitro and in vivo, a series of 41 novel compounds containing 1,2,3-triazole side chains were designed and synthesized via a click reaction based on our previous work. Most of the compounds showed moderate to excellent broad-spectrum antifungal activity in vitro. Among them, the most promising compound 9A16 displayed excellent antifungal and anti-drug-resistant fungal ability (MIC80 = 0.0156-8 µg/mL). In addition, compound 9A16 showed powerful in vivo efficacy on mice systematically infected with Candida albicans SC5314, Cryptococcus neoformans H99, fluconazole-resistant C. albicans 100, and Aspergillus fumigatus 7544. Moreover, compared to fluconazole, compound 9A16 showed better in vitro anti-biofilm activity and was more difficult to induce drug resistance in a 1 month induction of resistance assay in C. albicans. With favorable pharmacokinetics, an acceptable safety profile, and high potency in vitro and in vivo, compound 9A16 is currently under preclinical investigation.

Discovery of Novel Thiosemicarbazides Containing 1,3,5-Triazines Derivatives as Potential Synergists against Fluconazole-Resistant Candida albicans.

The clinical prevalence of antifungal drug resistance has been increasing over recent years, resulting in the failure of treatments. In an attempt to overcome this critical problem, we sought novel synergistic enhancers to restore the effectiveness of fluconazole against resistant Candida albicans. Based on the structural optimization of hit compound 8 from our in-house library, a series of novel 1,3,5-triazines derivatives was designed, synthesized, and biologically evaluated for synergistic activity in combination with fluconazole. Among them, compounds 10a-o, which contain thiosemicarbazides side chains, exhibited excellent in vitro synergistic antifungal potency (MIC80 = 0.125-2.0 µg/mL, FICI range from 0.127 to 0.25). Interestingly, compound 10l exhibited moderate C. albicans activity as monotherapy with an MIC80 value of 4.0 µg/mL, and also on several Cryptococcus strains (MIC80 ranging from ≤ 0.125-0.5 µg/mL) and C. glabrata (MIC80 ≤ 0.125 µg/mL). These effects were fungal-selective, with much lower levels of cytotoxicity towards human umbilical vein endothelial cells. Here, we report a series of thiosemicarbazides containing 1,3,5-triazines derivatives as potent synergists with fluconazole, and have preliminarily validated compound 10l as a promising antifungal lead for further investigation.

Design, synthesis, and in vitro evaluation of novel antifungal triazoles containing substituted 1,2,3-triazole-methoxyl side chains.

In order to develop new triazole derivatives, we optimized the lead compound a6 by structural modifications to obtain a series of (2R,3R)-3-((1-substituted-1H-1,2,3-triazol-4-yl) methoxy)-2-(2,4-difluorophenyl)-1-(1H-1,2,4-triazol-1-yl) butan-2-ol, compounds 5-36. Most of the target compounds exhibited excellent in vitro antifungal activity against Candida albicans 10231 and Candida glabrata 537 with MIC ≤ 0.125 µg/mL. Of particular note, compounds 6, 22, 28, 30 and 36 were highly active against Candida neoformans 32609 with MIC ≤ 0.125 µg/mL and showed broad-spectrum antifungal activity including against fluconazole-resistant Candida auris 891. In addition, compounds 6 and 22 demonstrated inhibitory effects on filamentation in the azole-resistant C. albicans isolate. Moreover, compounds 6 and 22 were minimally toxic to HUVECs and possessed weak inhibitory effects on the human CYP3A4 and CYP2D6. SARs and docking study further indicated that ortho-substituted groups in the terminal phenyl ring can promote the compounds to improve their antifungal activity.

Discovery of Novel 7-Hydroxy-5-oxo-4,5-dihydrothieno[3,2-b]pyridine-6-carboxamide Derivatives with Potent and Selective Antifungal Activity against Cryptococcus Species.

Cryptococcus neoformans and Cryptococcus gattii can cause fatal invasive infections, especially in immunocompromised patients. However, few antifungal drugs are available to help treat cryptococcosis. In this study, by compound library screening, we presented the first report of hit compound P163-0892, which had potent in vitro and in vivo antifungal activity against Cryptococcus spp. In vitro tests showed that P163-0892 was not cytotoxic and had highly selective and strong antifungal activities against Cryptococcus spp. with MIC values less than 1 µg/mL. Synergism of P163-0892 and fluconazole was also observed in vitro. The in vivo antifungal efficacy of P163-0892 was assessed in a wax moth larval fungal infection model, and treatment with 10 mg/kg P163-0892 caused a significant reduction in fungal burden and significant extension of the survival time. Taken together, our data indicate that the hit compound P163-0892 warrants further investigation as a novel anti-Cryptococcus agent.

Design, Synthesis, and In Vitro and In Vivo Antifungal Activity of Novel Triazoles Containing Phenylethynyl Pyrazole Side Chains.

A series of triazole derivatives containing phenylethynyl pyrazole moiety as side chain were designed, synthesized, and most of them exhibited good in vitro antifungal activities. Especially, compounds 5k and 6c showed excellent in vitro activities against C. albicans (MIC = 0.125, 0.0625 µg/mL), C. neoformans (MIC = 0.125, 0.0625 µg/mL), and A. fumigatus (MIC = 8.0, 4.0 µg/mL). Compound 6c also exerted superior activity to compound 5k and fluconazole in inhibiting hyphae growth of C. albicans and inhibiting drug-resistant strains of C. albicans, and it could reduce fungal burdens in mice kidney at a dosage of 1.0 mg/kg. An in vivo efficacy evaluation indicated that 6c could effectively protect mice models from C. albicans infection at doses of 0.5, 1.0, and 2.0 mg/kg. These results suggested that compound 6c deserves further investigation.

Design, synthesis, and in vitro evaluation of novel triazole analogues featuring isoxazole moieties as antifungal agents.

In order to develop novel antifungal agents, based on our previous work, a series of (2R,3R)-3-((3-substitutied-isoxazol-5-yl)methoxy)-2-(2,4-difluorophenyl)-1-(1H-1,2,4-triazol-1-yl) butan-2-ol (a1-a26) were designed and synthesized. All of the compounds exhibited good in vitro antifungal activities against eight human pathogenic fungi. Among them, compound a6 showed excellent inhibitory activity against Candida albicans and Candida parasilosis with MIC80 values of 0.0313 µg/mL. In addition, compounds a6, a9, a12, a13 and a14 exhibited moderate inhibitory activities against fluconazole-resistant isolates with MIC80 values ranging from 8 µg/mL to 16 µg/mL. Furthermore, compounds a6, a12 and a23 exhibited low inhibition profiles for CYP3A4. Clear SARs were analyzed, and the molecular docking experiment was carried out to further investigate the relationship between a6 and the target enzyme CYP51.

Design, synthesis, and structure-activity relationship studies of novel triazole agents with strong antifungal activity against Aspergillus fumigatus.

The incidence of invasive fungal infections has dramatically increased for several decades. In order to discover novel antifungal agents with broad spectrum and anti-Aspergillus efficacy, a series of novel triazole derivatives containing 1,2,3-benzotriazin-4-one was designed and synthesized. Most of the compounds exhibited stronger in vitro antifungal activities against tested fungi than fluconazole. Moreover, 6m showed comparable antifungal activity against seven pathogenic strains as voriconazole and albaconazole, especially against Aspergillus fumigatus (MIC = 0.25 µg/ml), and displayed moderate antifungal activity against fluconazole-resistant strains of Candida albicans. A clear SAR study indicated that compounds with groups at the 7-position resulted in novel antifungal triazoles with more effectiveness and a broader-spectrum.

Role of Era in assembly and homeostasis of the ribosomal small subunit.

Assembly factors provide speed and directionality to the maturation process of the 30S subunit in bacteria. To gain a more precise understanding of how these proteins mediate 30S maturation, it is important to expand on studies of 30S assembly intermediates purified from bacterial strains lacking particular maturation factors. To reveal the role of the essential protein Era in the assembly of the 30S ribosomal subunit, we analyzed assembly intermediates that accumulated in Era-depleted Escherichia coli cells using quantitative mass spectrometry, high resolution cryo-electron microscopy and in-cell footprinting. Our combined approach allowed for visualization of the small subunit as it assembled and revealed that with the exception of key helices in the platform domain, all other 16S rRNA domains fold even in the absence of Era. Notably, the maturing particles did not stall while waiting for the platform domain to mature and instead re-routed their folding pathway to enable concerted maturation of other structural motifs spanning multiple rRNA domains. We also found that binding of Era to the mature 30S subunit destabilized helix 44 and the decoding center preventing binding of YjeQ, another assembly factor. This work establishes Era's role in ribosome assembly and suggests new roles in maintaining ribosome homeostasis.