Vulvovaginal candidiasis (VVC) is an inflammatory mucosal infection in the lower reproductive tracts of women. Among women of different ages, more reported cases of VVC are in the reproductive age. Also, 75% of women experience at least one episode of VVC in their lifetime, and 8% experience a recurrence of infection, at least four episodes per year. Global statistics show that 138 million women worldwide experience recurrent VVC each year, with an annual prevalence of 3,871/100,000. According to base case estimates considering the increase in female population worldwide, the expected number of individuals affected with recurrent VVC is predicted to rise to over 158 million by 2030. As a result, 20,240,664 more VVC-affected cases are added to the predicted increase in female population from 3.34 to 4.181 billion people (Żyrek et al., 2021).

The global statistics of VVC are hiked by Candida, a predominant fungal colonizer of the vaginal lumen (Ahangari et al., 2019). Candida albicans and several other related species, Candida glabrata, Candida tropicalis, Candida parapsilosis, and Candida krusei cause VVC (Guinea, 2014). Interestingly, C. albicans, the primary causative agent of VVC, is categorized as a critical fungal priority pathogen (CFPP) by the WHO (World Health Organization) (Fisher and Denning, 2023). C. albicans is also a benevolent partner of the microbiome of healthy individuals and is capable of switching from a commensal to a pathogenic state under adverse conditions driven by various predisposition factors (Mukaremera et al., 2017). Several predisposition factors are associated with VVC, which include diabetes mellitus (DM), elevated endogenous estrogens (from pregnancy or obesity), immunosuppression (i.e., transplant patients, antimetabolite medications or chemotherapy, or HIV infection), broad-spectrum antibiotic use, and other environmental factors (Gonçalves et al., 2016). Recent studies have shown that patients with DM are more prone to candidiasis, as glucose plays a significant role in the colonization and proliferation of these pathogens in the host (Gürsoy et al., 2018). Host-influenced (predisposition) factors are critical in driving C. albicans morphogenetic lifestyle changes from yeast to hyphal and enable it to cross its boundary from commensal to pathogenic form and vice versa (Mukaremera et al., 2017). C. albicans, in its lifestyle transition, express various virulence traits that increase its survival fitness in the host and lead to the rapid evolution of resistance to antifungals (Slutsky et al., 1985; Sudbery et al., 2004). The survival fitness of C. albicans enhances them to effectively colonize the host and leads to the spread of infection in an asymptomatic/symptomatic mode causing severe mucosal inflammation in affected individuals (Farhan et al., 2019). Mucosal inflammation is a symptomatic response in patients who may exhibit vaginal itching, vaginal burning, dyspareunia, and edema, and may form a thick or sticky discharge (Sheppard, 2020). It is quite alarming that no new class of antifungals has reached the recipients since the 2000s to treat VVC. The loss of productivity is mainly due to the eukaryotic nature of fungal cells, difficulties with compound permeability across the fungal cell wall and membrane, and a lack of interest from the pharmaceutical industry; the development of novel antifungal agents has generally been slow (Roemer and Krysan, 2014).

Infection and therapy must go hand in hand for a better cure. Once it fails, the global economic burden also increases with the emergence of antifungal resistance. Recent estimates show that the global VVC treatment market value will reach USD 986.5 million. In the next 10 years, the compound annual growth rate (CAGR) will be 4.1% according to a VVC treatment market report (Denning et al., 2018). In parallel, it would be a tremendous challenge for both high-/low-income countries, and there is a pressing need to address this global health-associated risk. Finding solutions through innovations relies on molecular information on the various drivers (predisposition factors), molecular pathways, and associated virulence that affect the pathogen colonization and cause infection in the host. Hence, in this review, we focus on the predisposition factors leading to the virulence of candidiasis, existing treatment strategies with their disadvantages, and how this can be tackled by deciphering possible drug targets and probable mode of drug delivery to cross the preclinical phase by appropriate in vivo models.

VVC recurrence relies on various intrinsic and extrinsic factors. The key host-specific factors, such as the pH of the vaginal environment, age and hormonal status, local defense mechanisms, pregnancy, allergies, psychosocial stress, metabolic issues, immunosuppression, and individual genetic susceptibility, are essential. Additionally, behavioral risk factors including oral contraceptives, overuse of antimicrobials, glucocorticoids, inhibitors of the sodium-glucose co-transporter-2 (SGLT2), intrauterine devices (IUDs), spermicides, and condoms, as well as sexual, hygienic, and dressing habits, demand intervention ( Table 1 ) (Patel et al., 2004).

The dysbiosis of the healthy microbiome in the vagina by various predisposition factors leads to the initiation of the virulence mechanism in C. albicans. The evolution of yeast-like fungi to an invasive pathogen depends on many fungal factors along with the host. Such host–pathogen interaction relies on many stages, including adhesion, invasion, biofilm formation, and spread of infection (Willems et al., 2020) ( Figure 1 ).

Based on the severity of the infection, uncomplicated or complicated VVC, treatment strategies are classified into four different classes of antifungal agents. The various classes of antifungals clinically available include azoles, polyenes, echinocandins, and pyrimidine analogs (de Oliveira Santos et al., 2018) ( Table 2 ). Azoles are heterocyclic compounds with ring structures containing at least one nitrogen and target the cytochrome P450 enzyme-lanosterol 14α-demethylase encoded by ERG11, producing ergosterol from lanosterol (de Oliveira Santos et al., 2018). Similarly, polyenes are polyunsaturated organic compounds containing at least three single and double carbon–carbon bonds, known to destroy the ergosterol content in the fungal cell membrane, leading to the loss of cell membrane permeability and causing antimycotic activity (Letscher-Bru, 2003).

On the other hand, echinocandins are amphiphilic lipopeptides that inhibit beta-1,3-glucan synthase encoded by FKS1 and FKS2 (Letscher-Bru, 2003). Pyrimidine analogues mimic the structure of natural pyrimidines, with a potential antimycotic ability by converting 5-fluorouracil to 5-fluoro deoxyuridine catalyzed by cytosine deaminase and thus interfere with the synthesis of DNA, RNA, and protein (Lee et al., 2021).

Like two sides of a coin, although antifungals are a solution, there also exists the problem of acquired resistance to such antifungals, which is mainly overseen ( Table 2 ). The acquired resistance to antifungals refers to the capacity of C. albicans to evolve defense mechanisms that lessen their susceptibility to them or make them inactive. The molecular changes often involve mutations ranging from point mutations to chromosomal rearrangements. These mutations can have varied effects on drug resistance, from directly preventing the drug from binding to its target to causing gene expression alterations that encourage physiological conditions that increase drug resistance (Berman and Krysan, 2020). In recent years, there has been an increase in reports of the formation of drug-resistant strains, particularly those that become resistant to several different medications. Additionally, it has been shown that these resistant phenotypes can emerge during an illness and in response to therapy, posing even another risk to patients (Lee et al., 2021; Kalimuthu et al., 2022).

C. albicans adapt to various changes in the environment due to their high genetic flexibility. When exposed to antifungals, the yeast cell population undergoes a selection process that favors a group of cells with superior stress tolerance (Lee et al., 2021). The majority of acquired resistance mechanisms fall into two categories: (1) mutations that increase the target’s expression or change its affinity for the drug, and (2) mutations that decrease the amount of drug that accumulates intracellularly by either increasing the biological activity or overexpression of drug efflux pumps (Ksiezopolska and Gabaldón, 2018).

There are several ways C. albicans resist azoles, including (1) altering the biosynthesis of sterols to replace ergosterol, (2) overexpressing the target enzyme to increase activity in the presence of the antifungal medication, (3) overexpressing drug efflux pumps to lower the intracellular concentration of the drug, and (4) altering the target gene sequence to decrease the binding affinity. Point mutations in the ERG11 gene have been linked to the development of resistance in C. albicans. Interestingly, 21 of the 140 distinct point mutations for the ERG11 (lanosterol 14-alpha-demethylase) gene have been directly linked to fluconazole resistance. Also, suppression of the ERG3 gene expression confers azole resistance (Ksiezopolska and Gabaldón, 2018). Resistance to echinocandins is not as widespread as resistance to azoles, but it is far from uncommon and firmly correlated with prior medication exposure. By mutating specific spots in the FKS1 gene, C. albicans may circumvent the effects of echinocandins. Ergosterol levels in the cell membrane are typically associated with resistance to polyenes. It has been determined that mutations in the genes encoding the ergosterol synthesis-related enzymes ERG2, ERG3, ERG5, ERG6, and ERG11 are the cause of the lower abundance of the enzyme seen in polyene-resistant (Walker et al., 2013). Point mutations in the FCY1, FCY2, and FUR1 genes and C. albicans deficient to the genes FPS1 and FPS2 have all been linked to decreased susceptibility to flucytosine. Variations in FCY1 and FUR1 inactivate enzymes involved in the pyrimidine pathway and changes in FCY2 interfere with drug uptake. The absence of FPS1 and FPS2 lowered the drug accumulation in the cell (Chapeland-Leclerc et al., 2005). The emergence of resistance to these existing antifungals shows the need for next-generation antifungals with a novel mechanism of action.

In accordance with the clinically available treatment regimens, the exploration of medications in clinical trials for vaginal candidiasis encompasses various approaches. The investigation of potential treatments involves the study of Salvia officinalis, clotrimazole, and their combination (Ahangari et al., 2019). Similarly, the effectiveness of TOL-463 and ibrexafungerp in treating candidiasis is currently in the preliminary stages of research (Marrazzo et al., 2019; Azie et al., 2020). Additionally, researchers are specifically examining oteseconazole’s potential for managing recurrent VVC (Sobel et al., 2022). Furthermore, the exploration extends to boric acid as a potential therapeutic option for non-albicans yeast infections (Ray et al., 2007). However, with a restricted range of clinically accessible antifungals and ongoing challenges in developing novel antifungal classes, the emergence of antifungal resistance poses a persistent threat to the advancement of antifungal treatments. Multidrug-resistant fungus species have recently emerged, and their incidence has increased, spurring research into new treatments. The clinical limits of off-target effects and drug interactions make it an exciting option to optimize these pharmacological classes to increase fungal-specific, on-target effectiveness (Revie et al., 2018). Given the potential of spreading resistance, the scientific community and the pharmaceutical industry focus on developing antifungals with a novel mechanism of action against a fungal-specific pathway and potentiating the activity of the existing antifungals. Given that up to 80% of hits turn out to be false positives, discovering novel targets specific to fungus has proven difficult (Murphy and Bicanic, 2021).

Exploring possible therapeutic targets ( Table 3 ) for candidiasis based on key pathways while considering biological functions and mechanisms is crucial (Spampinato and Leonardi, 2013). It is essential to identify therapeutic targets for candidiasis to treat candidiasis effectively. C. albicans central pathways that involve ergosterol biosynthesis, cell wall formation, mitochondrial function, signal transduction pathways, DNA replication and repair, and protein synthesis present promising drug targets for treatment. However, substantial experimental validation of their biological efficacy is required to ensure the effectiveness and safety of these pharmacological targets ( Table 4 ) (Mazu et al., 2016).

In the era of “antimicrobial resistance”, addressing candidiasis might entail a tactic of utilizing a combined treatment strategy involving specific anti-virulence/anti-infective agents alongside less effective antifungal drugs (Mota Fernandes et al., 2021). More specifically, the anti-infective/anti-virulence agents inhibit virulence traits without affecting the pathogen growth and, thus, do not exert selective pressure on the pathogen to develop resistance. Such anti-infective/anti-virulence drugs may potentiate the existing failed antifungals exhibiting a synergistic effect in fighting infections, an exciting backbone to develop next-generation antifungals. There are several strategies involved in the design and development of next-generation antifungal/anti-infective agents. Antifungal therapeutics from natural sources have drawn attention because they exhibit structural diversity and uniqueness in functional modes of action, making them desirable candidates to thwart the development of drug resistance (Seleem et al., 2017). Several such natural compounds, for example, piperine, cinnamaldehyde, berberine, and curcumin, are known to downregulate the virulence traits of C. albicans (Priya and Pandian, 2020; Yong et al., 2020; Rajasekar et al., 2021; Deng et al., 2022). Similarly, quorum-sensing molecules established to target biofilm formation and restore the pathogen’s susceptibility are also gaining attention. The sesquiterpene alcohol farnesol (C₁₅H₂₆O) was initially identified as a quorum-sensing molecule generated by C. albicans. Farnesol is produced by enzymatically phosphorylating farnesyl pyrophosphate, which inhibits the generation of hyphae in a concentration-dependent manner. The inhibition is achieved by negatively regulating the RAS1-cAMP-PKA pathway by targeting CYR1. Farnesol has recently become a prospective drug due to its antifungal efficacy (Nikoomanesh et al., 2023). Probiotic vaginal colonization, particularly with Lactobacillus sp., has also been widely studied and shown to have a significantly lower risk of VVC and to even treat VVC. Probiotics function by aiding in the vaginal microbiome’s restoration of balance and safeguarding against the overgrowth of C. albicans. They accomplish this by creating metabolic by-products that stop the growth of infections, such as organic acids, hydrogen peroxide, bacteriocins, and biosurfactants (Fuochi et al., 2019). In addition to probiotics, targeted antifungal therapy may be used as part of personalized medicine depending on the specific Candida strain infecting the patient and how they react to various antifungal medications. It deals with the problem of antimicrobial resistance and offers patients therapy options because of resistance to previous antifungal medications (Wu et al., 2022).

Another evolved strategy is the drug repurposing approach that is gaining importance in diseases like cancer and requires expansion in infectious diseases as well. It involves identifying new therapeutic applications for already approved, withdrawn, abandoned, and experimental drugs. It also has the added benefit of reducing the typical drug development period by up to 5–7 years (Ashburn and Thor, 2004). Notably, C. albicans are resistant to various classes of antifungal drugs available on the market, including the most recent ones (Pappas et al., 2016). Hence, combining the existing antifungals with newly developed anti-infectives can potentially overcome the problem of drug resistance, by acting through a different mechanism.

In summary, the next-generation antifungals are a novel class of antifungals with new targets with novel therapeutic indications, and old targets with a new therapeutic indication may be the probable first-line approaches (Bouz and Doležal, 2021). Furthermore, the development of a suitable drug delivery system is equally important in the process of drug development, which would increase the biological efficacy of the drugs, or else the nonspecific delivery leads to the accumulation of drugs in the body, causing increased toxicity.

Systems for delivering organ (vagina)-specific medications offer a promising alternative for treating vaginal candidiasis (Pandey et al., 2020). Antifungal drugs, such as topical creams or oral tablets, are used in traditional treatment methods for vaginal candidiasis. These techniques might have limitations, like low patient compliance, systemic adverse effects, and the potential for antifungal resistance (Lírio et al., 2019). Advancements in drug delivery have an array of advantages over traditional approaches and the advancement is the direct delivery of antifungal drugs to the infection site, which enhances local drug concentrations while minimizing systemic exposure ( Figure 2 ). Their focused and localized strategy and formulations with sustained release enhance therapy effectiveness, patient comfort, and acceptance (Garg et al., 2020). Drugs administered via vaginal routes are absorbed in three main ways: (1) transcellular, via concentration-dependent gradient; (2) paracellularly, through tight junctions present in between the cells; and (3) vesicular or receptor-mediated transport. The breakdown of drugs in the vaginal lumen and membrane penetration are the two primary phases in drug absorption from the vagina. Therefore, any factor affecting the physiology of the vagina and formulation elements like drug dissolution and membrane transport may change how a drug will be absorbed from vaginal drug delivery devices (Richardson and Illum, 1992). Different physiological factors influencing drug absorption in the vaginal cavity include physiological factors like epithelial thickness of the vagina, vaginal fluid, mucus, pH, and physiochemical factors like lipophilicity, molecular weight, solubility, and degree of ionization (Hussain and Ahsan, 2005).

Using bio-adhesive, nanoparticle-based, and other new delivery systems for vaginal drug delivery is a novel concept (Table 5 ). Bio-adhesive formulations can speed up the healing of fungal infections by administering medications for a longer duration at a steady rate. Using time-release additives can achieve controlled-release medication delivery systems (Osmałek et al., 2021). Other new delivery techniques include phase change polymers, thermoplastic polymers, and mucoadhesive thermo-sensitive gels. Researchers have recently made advancements with hydrogels made with mucoadhesive polymers because of their capacity to interact with the mucus layer and epithelial cells, extending the duration of the drug’s residence time in the vaginal cavity and enhancing drug absorption, thereby achieving good patient compliance (Aka-Any-Grah et al., 2010; Fan et al., 2022).

Development of novel drugs with a suitable drug delivery system can only be successful from in vitro and, importantly, in vivo studies. Most of the drugs and treatment strategies fail in the preclinical validation. Thus, testing and proving these medications in appropriate animal models closely related to the human host can be a better way to reach the beneficiaries.

The evaluation of the efficacy and safety of a new drug candidate includes in vitro and in vivo studies that can be carried out throughout all stages of drug development. Studies in vitro concentrate on key factors that could affect medication release in vivo (Rayner et al., 2021). Basic knowledge of drug pharmacodynamics must be provided, and the selection and application of the right models, as well as accurate data interpretation, are crucial for decision-making and the successful advancement of drug candidates for clinical trials. Understanding a drug’s properties and effects on a living organism requires the use of in vivo investigations before the medicine is made available for purchase (Gallo, 2010).

The infectious mammalian models are used to understand the pathogenicity, pharmacokinetics, vaccination attempts involving immunization, and immune responses. Thus, mammalian species would seem most logical to simulate a human host; mice, rats, and rabbits are the earliest recognized animal models ( Table 6 ) (Conti et al., 2014). Since the 19th century, these animal models have been explored for C. albicans-mediated vaginal candidiasis (Naglik et al., 2008; Conti et al., 2014; Cassone and Sobel, 2016). The mouse model exhibits various benefits, including its inexpensive cost, rapid reproduction, short generation time, and general acceptance in biological and genetic research. Although the mouse’s macroscopic anatomy differs from the humans, both have similar histological characteristics, cyclic estrus/menstrual cycles, and fundamental functions. Also, the murine vaginal microbiota is notably like humans, and although there may be differences between strains, Staphylococcus, Enterococcus, and Lactobacillus appear to be present consistently (Grasso et al., 1998; Vrbanac et al., 2018). Similarly, like the mouse model, rats have the potential to be an effective vaginal model since they are simple to procure, are inexpensive, and have a reproductive cycle that is similar to that of humans. Wistar and Sprague Dawley female rats are used in many current studies to study the vaginal environment. While the estrus cycle affects the vaginal flora in rats like that in humans, certain bacteria, such as Gram-negative rods, Streptococci, and members of the Bacteroidaceae family, may not be present. Generally, a less diversified vaginal microbiome is thought to be more stable and, therefore, healthier in people (Moalli et al., 2005; Levy et al., 2020).

For FDA-mandated preclinical assessments of vaginal irritation, the rabbit serves as the gold standard model; as a result, these investigations frequently use rabbit vaginal tissue models. European (O. cuniculus) and New Zealand White rabbits are frequent breeds used in these experiments. Compared to some other animal models, the rabbit’s reproductive system and vaginal environment are similar to those of humans, making it a valuable model for researching vaginal candidiasis. Also, the microbial composition of the rabbit’s vagina is like that of humans (Acartürk and Robinson, 1996; Shi et al., 2022). Other large animals like rhesus macaques (Macaca mulatta) are also being used for vaginal infection studies. However, these models’ cost, maintenance, and ethical clearance make it difficult (Steele et al., 1999).

Establishing efficient therapies for VVC requires a thorough understanding of the risk factors, pathophysiology, and treatment that can limit the resistance generated. To overcome drug resistance and improve the results for people with VVC, it may be necessary to identify new therapeutic targets and investigate suitable drug delivery modalities. Furthermore, personalized medicine approaches hold promise in the management of VVC. Considering individual genetic susceptibility and host-specific factors, tailored treatment strategies can be developed to improve therapeutic outcomes. The therapeutic measures may involve probiotics, immunomodulatory agents, or combination therapies targeting multiple virulence factors and associated pathways without developing resistance.

HD: Drafted the article or revised it critically for important intellectual content, which is part of her doctoral studies. AS: Approved the version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors contributed to the article and approved the submitted version.