Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5219_Библиотеки_им_академика_М_И_Перельмана.pdf
220
A. Kumar etal.
8.5 Role ofBiofilm andExtracellular Polymeric Substances
(EPS) Matrix: Mechanisms Regulating Antifungal Drug
Resistance inCandida Species
Candida species are known for their capability to form biolms on diverse surfaces
within the human body and medical devices used in patient care (Silva etal. 2009).
Commonly affected sites include urinary and vascular catheters, heart valves, joint
replacements, and cardioverter debrillators (Horton and Nett 2020; Elving etal.
2002; Kojic and Darouiche 2004). Among Candida species, C. albicans is a pri-
mary offender, followed by C. glabrata, while C. tropicalis is notably associated
with urinary tract infections. Conversely, C. parapsilosis is implicated in catheterrelated infections and affects the skin, particularly in healthy individuals (Cavalheiro
and Teixeira 2018). These biolms play a crucial role in facilitating Candida colonization, persistence, and initiation of infections (Silva etal. 2017). Additionally,
Candida species can also contribute to biolm formation during mucosal infections
(Cavalheiro and Teixeira 2018). The biolm-forming ability of these species is a
pivotal factor in their resistance to antifungal agents (Horton and Nett 2020). Each
Candida species produces a distinctive biolm, exhibiting unique morphological
features, extracellular matrix (ECM), and resistance capabilities (Bhattacharya
etal. 2020). A study by Mukherjee etal. afrms that biolm formation plays a signicant role in early-stage antifungal resistance. The study also emphasizes the
involvement of efux pumps in biolm-related resistance, a phenomenon previously reported in C. albicans, C. glabrata, and C. tropicalis biolms (Mukherjee
etal. 2003). Biolm-forming strains are primarily involved in systemic candidiasis
in immunocompromised patients. These biolms serve as the reservoir of ongoing
infections if not adequately eliminated. Notably, biolm aids the fungus in tolerating clinically prevalent antifungal drugs and gradually developing resistance to
these treatments (Cavalheiro and Teixeira 2018).
8.5.1 Biofilm Architecture Among Candida Species
Biolms represent microbial communities with a substantial extracellular matrix.
The ability to form biolms is very crucial among the virulence properties in
Candida pathogenesis (García-Sánchez etal. 2004). The process of biolm forma-
tion encompasses distinct phases and cell types. Initially, yeast cells attach and colonize biotic or abiotic surfaces. Subsequent to adhesion, rapid cell division, termed
proliferation, forms the foundational layer of the biolm in the shape of a monolayer of microcolonies (Cavalheiro and Teixeira 2018; Silva etal. 2017). The maturation phase follows, characterized by the development of a lamentous network,
including hyphae and pseudohyphae. Mature biolms can disperse from their initial
location, establishing new colonies at new places. Key genes such as BCR1, EFG1,
TEC1, ROB1, NDT80, and BRG1 play pivotal roles in regulating biolm formation,
inuencing characteristics, and contributing to phenotype development across
Candida species (Silva etal. 2017; Roy and Gow 2023).
8 Unravelling Drug Resistance in Candida Species: Genetic, Biolm…
Fig. 8.5 Candida species leverage their intricate cell wall architecture as a pivotal defence mecha-
nism, enabling them to resist and thrive in host infections. This structural complexity serves as a
shield against immune cells and biolm formation, providing protection against antifungal drugs.
The fungus adeptly utilizes this defence strategy to withstand commonly employed clinical antifungals, gradually paving the way for the development of resistance. (a) Illustration dictating the
role of cell wall in Candida spp. (b) Image depicting the complex cell wall architecture, which
collectively contributes to antifungal resistance and immune response evasion, ultimately fostering
virulence and resistance. (c) Depiction of the complex biolm of Candida spp., which consists of
various cell types, including yeast cells, blastospores, persister cells, hyphae, and ECM, combinedly offering enhanced antifungal resistance to Candida species
221
Biolm characteristics vary signicantly among Candida species, highlighting
distinct compositions in their extracellular matrix (Roy and Gow 2023). In the case
of C. albicans biolms, a bilayer structure is evident, incorporating yeast, hyphae,
and pseudohyphae. The basal layers primarily consist of yeast cells and blastospores, enveloped by a dense matrix containing hyphal forms. Major constituents of
C. albicans biolms include carbohydrates, proteins, hexosamines, and phosphorous (García-Sánchez etal. 2004).
In contrast, C. glabrata biolms feature a compact, single, or multilayer structure
dominated by blastospores, devoid of hyphal and lamentous forms. These biolms
display elevated levels of glycans and proteins, contributing to their unique composition (Rodrigues etal. 2016). C. auris biolms are characterized by the rich mannanglucan complex, creating drug-resistant barriers. The extracellular matrix composition
mainly differs among all the strains of Candida but overall carbohydrates and proteins are abundant in the biolm matrix (Chowdhary etal. 2017; Horton and Nett
2020). Notably, C. auris’s biolm displays resilience 14days post-desiccation.
Candida parapsilosis biolms exhibit a carbohydrate-rich composition with
reduced protein levels, showcasing aggregated blastospores alongside yeast cells
and pseudohyphae (Fig.8.5). Candida tropicalis biolms present a dense organiza-
tion of yeast cells with noticeable lamentous structures, featuring lower levels of
both glycans and proteins (Silva etal. 2012). Each Candida species demonstrates
222
A. Kumar etal.
distinct biolm characteristics, inuencing their pathogenicity and resistance proles (García-Sánchez etal. 2004).
8.5.2 Composition andFunctionality ofExtracellular Matrix
inBiofilms
The composition of the biolm includes approximately 25% carbohydrate, 55%
protein, 15% lipid, and 5% nucleic acid (Mitchell etal. 2016). Nearly half of the
extracellular matrix (ECM) protein percentage is derived from the extracellular
vesicles (EVs). The composition of extracellular polymeric substances (EPS) varies among their cellular types, including planktonic EPS and biolm EPS. The
endosomal sorting complexes required for transport (ESCRT) system help Candida
albicans in controlling the expression of hyphal genes and Vps4 protein plays a
key role in determining the hyphae polarity as its deletion leads to the multiple
hyphae formation (Zarnowski etal. 2018). Earlier it was reported that the ESCRT
pathway induced hyphae formations in alkaline conditions by the Rim101 (Yang
etal. 2020). It was reported that the ESCRT mutants, known for disrupted EPS
biogenesis, exhibit susceptibility to various drugs such as Amphotericin-B,
Terbinane, clotrimazole, and micafungin (Yang et al. 2018). ESCRT was rstly
recognised as the machinery that aids in membrane-budding formation which then
leads to the development of multivesicular bodies (Olmos 2022). Nuclear magnetic
resonance (NMR) has shown that the fungal EPS mainly contains beta-glucans and
mannans (Zarnowski et al. 2014). Within the biolm matrix, the abundance of
α-1,2-mannan, α-1,6 mannan, and β-1,6 glucan surpasses that found in the cell wall
(Mitchell etal. 2015). Mannan plays a crucial role in restricting the drug’s permeability in the matrix and thus contributes to drug resistance (Taff etal. 2012). These
biolm components, even when non-covalently attached to drugs, prevent their
entry and reduce their drug efcacy, as observed in amphotericin-B, anidulafungin,
and ucytosine (Al-Fattani and Douglas 2006). In an experiment inhibiting ECM
formation and the number of persister cells in biolm by using scorpion venom,
increased susceptibility to various antifungals was observed. Thus, the ECM establishes its role in drug barriers as cell walls, by sequestering drugs and hindering
permeability (Baillie 2000). Thus, it actively supports cells in developing resistance, with β-1,3-glucans specically implicated in uconazole resistance (Nett
etal. 2007).
In the later stages of biolm growth, mature biolms exhibit reduced dependence
on ergosterol, indicating that drugs targeting ergosterol may be less efcient due to
lower ergosterol levels (O’Meara etal. 2016). A study revealed the potential presence of extracellular DNA in the biolms, evidenced by increased sensitivity to
antifungal drugs amphotericin-B and echinocandins upon treatment with Dnase
(Martins etal. 2012). The resistance mechanisms in Candida biolms are multifactorial, involving the extracellular matrix (ECM), persister cells, and drug efux
transporters (Fig.8.5c).
8 Unravelling Drug Resistance in Candida Species: Genetic, Biolm…
223
In the case of C. albicans biolms, they are primarily composed of hyphae, a
diverse, complex extracellular matrix (ECM), and yeast cells (Gulati and Nobile
2016). Different Candida species of biolms have their unique characterization
with their array of cell types. Biolms are intricate three-dimensional structures,
with yeast cells adhering to both biological and non-biological substrates at their
base (Atiencia-Carrera etal. 2022). The processes of seeding, branching, budding,
and proliferation contribute to the growth of the biolm biomass (Arastehfar
etal. 2020).
The extracellular matrix (ECM) plays a critical role in the structure of biolms,
acting as a protective shield that encompasses the entire biolm organization (Baillie
2000). This protective covering serves to counter the effects of immune cells and
antifungal medications (Ajetunmobi etal. 2023). The ECM effectively hinders drug
accessibility to yeast cells, contributing to antifungal resistance, and provides a possible barrier against the actions of immune cells, further enhancing the biolm’s
protection (Vediyappan et al. 2010). Notably, C. albicans lamentation-defective
mutants (lacking EFG1) haven’t the ability to adhere, and display an increased pattern of susceptibilities (Watamoto etal. 2010). Conversely, Kuhn etal. demonstrated
that C. parapsilosis biolms, despite having lower levels of ECM and a less complex structure than C. albicans, exhibit comparable resistance to antifungals
(Pannanusorn etal. 2014).
It’s important to note that different Candida species exhibit variations in their
biolm-forming abilities, primarily due to differences in their morphology, the
composition of their ECM, and the patterns of resistance they develop against antifungal drugs (Hawser and Douglas 1995).
The resistance exhibited by cells in biolm formation compared to their plank-
tonic counterparts demonstrates a substantial four- to eightfold increase across a
spectrum of antifungal drugs in the later stages of biolm development (Modiri
etal. 2019). This heightened resistance has been notably observed in both C. albi-
cans and C. parapsilosis, indicating the pivotal role of biolm formation in confer-
ring resistance to antifungal agents (Katragkou etal. 2008).
Adherence of the cells in biolm is a crucial factor inuencing resistance
(Watamoto etal. 2010). Matrix components, particularly mannans and glucans, play
a pivotal role by sequestering the drug uconazole, contributing to azole resistance
(Kuhn etal. 2002). The biolm itself acts as a barrier, impeding the efcacy of
amphotericin-B treatment. Notably, the absence of glucans in the matrix renders
C. albicans cells more susceptible to amphotericin-B and uconazole (Gulati and
Nobile 2016).
An intriguing trend emerges as various stages of biolm formation are examined
in C. albicans. Specically, it is observed thatgene expression of MDR1 transiently
increases as biolm development progresses and peaks at the 24-h biolms.(Ramage
2002). This trend holds for antifungal drugs such as amphotericin-B and
uconazole.
In conclusion, unravelling the intricate world of Candida biolms has provided
insights into their complex composition, dynamics, and the formidable challenges
they pose in the context of antifungal resistance. The biolm’s diverse matrix, rich
224
A. Kumar etal.
in carbohydrates, proteins, lipids, and nucleic acids, forms a resilient fortress that
actively thwarts the efcacy of conventional antifungal drugs (Muzny and Schwebke
2015). The extracellular matrix (ECM), acting as a pivotal player in this defence
mechanism, not only shields against immune responses but also becomes a strategic
ally in the development of drug resistance (Ramage etal. 2012). As we navigate
through the complexities of the ECM composition of Candida biolms, it becomes
evident that a comprehensive understanding of their biology is essential for devising
effective therapeutic interventions (Sanglard 2016). Future research endeavours
should aim to decipher the molecular intricacies that drive ECM formation and
resistance mechanisms, paving the way for innovative approaches to combat
Candida infections.
8.5.3 The Role ofPersister Cells inBiofilm
Persister cells, a crucial component within C. albicans biolms, assume a pivotal
role in the intricate landscape of drug resistance (Fig. 8.5c) (Wuyts et al. 2018).
These cells exhibit dormancy, heightened tolerance to antifungal medications, and
altered target binding, thereby providing a shield against the effects of drugs (Li etal.
2015). Notably, these biolm-associated persister cells showcase resistance to
amphotericin-B, a phenomenon not observed in planktonic conditions (Sun etal.
2016). Furthermore, they upregulate expressions of efux pump genes, such as CDR,
amplifying their defence mechanisms within the biolm environments (Lewis 2010).
Distinct persister cells within C. albicans biolm empower the fungus to with-
stand elevated concentrations of antifungal drugs (Brauner etal. 2016). These persister cells capable of triggering biolm reseeding after exposure to high doses of
treatments play a crucial role in the resilience of the biolm (Lewis 2010). The antifungal resistance mechanisms in Candida biolms are predominantly governed by
extracellular matrix (ECM) characteristics, such as adhesion, high cell density,
slower growth rate, quorum sensing, impermeability of drugs within the biolm,
drug sequestering, and immobilization (Roy and Gow 2023; Ajetunmobi etal. 2023;
Dominguez etal. 2018). Persister cells are characterized by metabolic quiescence
and the ability to withstand high drug doses (Fig.8.5c). These cells are very few, but
their number increases after extensive antifungal drug treatment (Al-Dhaheri and
Douglas 2008). The cells orchestrate stress tolerance signalling pathways and behave
similarly to glucose-starved planktonic cells (Wuyts etal. 2018). They withstand the
accumulation of reactive oxygen species (ROS) induced by antifungal drugs in mitochondria (Lin and Austriaco 2014). Furthermore, they regulate the production of
ECM levels within the biolm and support their persistence strategy through specic
enzymatic induction. Genes such as BGL2, XOG1, KRE1, and SKN1 are observed to
be upregulated in persister cells (Wuyts etal. 2018). While Hsp90, a heat-shock factor, is also upregulated in persister cells, aiding in the dispersal of C. albicans biolms (Melo etal. 2007). The upregulation of these proteins mainly contributes to the
heightened production of ECM and extracellular vesicles, further solidifying the role
of persister cells in the intricate web of biolm resilience (Sun etal. 2016).
8 Unravelling Drug Resistance in Candida Species: Genetic, Biolm…
225
The persister cells within C. albicans biolms mark a signicant breakthrough in
understanding drug resistance dynamics (Li etal. 2015).Unravelling the molecular
intricacies that govern persister cell behavior may help in exploring novel therapeutics to combat their resilience mechanisms. This knowledge could reshape the landscape of antifungal interventions, improving outcomes for patients facing
challenging biolm-related conditions.
8.6 Signalling Pathways andGenetic Upregulations
The regulation of drug resistance in biolms is a complex interplay involving
diverse signalling pathways and genetic upregulations. Several stress-inducing
pathways, including the MAPK pathway, HSP90 pathway, and calcineurin signalling, are activated during Candida biolm formation (Robbins etal. 2011). HSP90
pathway is responsible for so many virulence characteristics from drug resistance to
morphogenetic conversion from yeast form to lamentous one in C. albicans (Noble
et al. 2010). These pathways predominantly promote azole resistance, adding
another layer of complexity to the intricate dynamics of drug resistance within biolms (Robbins etal. 2011; O’Meara etal. 2017).
One notable aspect is the increased expression of efux pumps during biolm
formation, contributing signicantly to the biolm’s resistance pattern (Albertson
et al. 1996). In C. glabrata, the biolm offers enhanced protection, particularly
against azole group drugs, when compared to other antifungals (Ramage et al.
2012). This heightened resistance is exemplied by the early upregulation of ABC
transporter genes (CDR1, CDR2, and MDR1) within the initial 6h of biolm formation (Mukherjee etal. 2003). Additionally, the role of PDR1 in biolm conditions
becomes evident, showcasing the multifaceted nature of drug resistance mechanisms (Harris etal. 2021).
Turning our attention to C. albicans, specic genes such as agglutinin-like
sequence (ALS3) and hyphal wall protein (HWP1) play pivotal roles in biolm formation and adhesion regulation (Shapiro et al. 2011). Interestingly, caspofungin
treatment triggers the activation of these genes in C. albicans biolms, a response
not observed in planktonic cells (Melo etal. 2007). The ALS gene family is the most
important and largest family in C. albicans which mostly regulates the adhesion of
cells and biolm formation (Desai and Mitchell 2015). Whereas the ALS1 and ALS3
genes are particularly involved in the host epithelial cell attachments and as well to
endothelial cells in systemic candidiasis (Muzny and Schwebke 2015). The hyphal
wall protein is another protein that also controls biolm adhesion regulation and is
mainly produced by the HWP1 gene (Desai and Mitchell 2015). Biolms, owing to
their clustered cell structure, induce a mechanism of tolerance against uconazole
during the biolm formation process (Ramage etal. 2012).
In conclusion, the differential expression of signalling pathways and the involve-
ment of genetic regulation of factors involved in biolm formation are important in
shaping the resistance pattern, particularly in the context of biolm development.
This intricate interplay underscores the dynamics and adaptive nature of microbial
226
A. Kumar etal.
communities and their responses to antifungal agents. As we unravel these complexities, it becomes increasingly apparent that targeted and nuanced approaches
are essential in effectively combating fungal infections within biolms, where
efux pump genes play a pivotal role in the survival and resilience of these structures (Gulati and Nobile 2016; Pannanusorn etal. 2014; Douglas 2003).
8.7 Role ofTranscription Factors inDrug Resistance
In fungal pathogens, transcription factors play a central role in orchestrating
responses to antifungal stress. They regulate the expression of drug efux pumps,
cell wall integrity, stress response, and other pathways crucial for survival in the
presence of antifungal agents. By modulating gene expression, these transcription
factors inuence the overall resistance prole of fungal pathogens. Additionally,
transcription factors may govern the activation of stress response pathways, leading
to enhanced fungal tolerance to antifungal agents. Understanding the intricate network of transcriptional regulation in fungal drug resistance is essential for developing targeted therapeutic interventions. Understanding transcription factors in drug
resistance provides valuable information for the identication of novel antifungal
therapy, addressing a growing concern in the context of fungal infections with available limited arsenal of effective antifungal drugs.
The intricate regulation of drug resistance is a sophisticated process that adapts
to specic stresses on fungal pathogens, requiring a comprehensive understanding
of the complex regulatory circuits activated in response to distinct stimuli. In C. gla-
brata, the Pdr1, a zinc-nger transcription factor (Zn(2)-Cys(6)), takes centre stage
as an important regulator of resistance genes by binding to their DNA sequences.
Pdr1 orchestrates the regulation of genes, including Cdr1 and Pdh1 (Cdr2), utilizing
pleiotropic drug response elements (PDRE) (Vermitsky et al. 2006; Caudle et al.
2011; Paul etal. 2011). The occurrence of gain-of-function (GOF) mutations in
CgPdr1 amplies its activity, resulting in the high expression of ABC transporters.
Notably, Pdr1’s inuence extends beyond ATP-binding cassette (ABC) efux
pumps, encompassing the activation of efux pumps within the major facilitator
superfamily (MFS) (Ferrari etal. 2009; Paul et al. 2011; Tsai et al. 2006). This
underscores the pivotal role of Pdr1 as a master regulator, shaping the landscape of
drug resistance in C. glabrata (Noble 2013).
The transcription factor Stb5 is involved in the drug resistance of C. glabrata
which is noteworthy, as it acts as a key negative regulator of azole resistance.
Elevated levels of Stb5 expression render the organism more susceptible to azole
drugs, whereas the deletion of Stb5 leads to a modest increase in azole resistance.
Importantly, Stb5 operates in coordination with Pdr1, sharing common transcriptional targets and functioning as a repressor of pleiotropic drug resistance. In
Candida albicans, the central controller of drug resistance is Tac1, an activator with
Zn(2)-Cys(6) DNA binding properties. Tac1 governs the expression of genes such
as Cdr1 and Cdr2, and variations in its gene sequence impact its regulatory function.
Positive autoregulation and gain-of-function (GOF) mutations play roles in shaping
8 Unravelling Drug Resistance in Candida Species: Genetic, Biolm…
227
its regulatory network. Notably, despite functional similarities, Tac1 lacks sequence
homology with the Pdr1 of Candida glabrata (Coste etal. 2006).
C. albicans also possesses another noteworthy regulator of multidrug resistance
transporters, namely, the transcription factor Mrr1. Operating as an activator, Mrr1
inuences the MFS multidrug transporter Mdr1, contributing to the emergence of
multidrug resistance in clinical isolates resistant to azoles. Like the transcriptional
regulators C. glabrata Pdr1 and C. albicans Tac1, Mrr1 is a Zn(2)-Cys(6) transcrip-
tion factor, with its gene sequence prone to gain-of-function (GOF) mutations that
amplify protein activity. Like Tac1, Mrr1 seemingly undergoes auto-regulation and is
activated by Hap43 (Dunkel etal. 2008a; Morschhäuser etal. 2007; Singh etal. 2011).
In C. albicans, the transcription factor Mrr2 is involved in drug resistance as it
regulates the expression of Cdr1 (Schillig and Morschhäuser 2013). Despite the
lack of signicant homology between Mrr1 and Mrr2, a closely related to Mrr1in
C. parapsilosis, also named Mrr1, upregulate in azole-resistant strains, potentially
contributing to the heightened expression of C. parapsilosis Mdr. Additionally,
Cta4, a transcription factor in C. albicans known for its involvement in nitrosative
stress resistance, has been identied to contribute to azole drug resistance in S. cere-
visiae (Coste etal. 2008). Furthermore, other regulators like Znc1 and Hal9 play
roles in drug resistance in C. albicans through diverse mechanisms.
The resistance to azole drugs is related to the expression of ergosterol biosyn-
thetic pathway genes, as azole drugs inhibit the function of Erg11, leading to a
decrease in ergosterol levels in the cell. The transcription factor Upc2 is pivotal in
azole drug resistance in C. albicans, by controlling genes related to ergosterol biosynthesis. Homologs of Upc2in C. parapsilosis and C. glabrata contribute to azole
resistance and regulate the ergosterol pathway. In C. glabrata, Upc2A, not Upc2B,
prominently participates in resistance against azoles. However, Upc2B controls the
expression of Erg2 and Erg3 in the ergosterol biosynthetic pathway, with both
Upc2A and Upc2B being essential for the expression of the sterol transporter Aus1
(Nagi etal. 2011). Azole resistance in C. auris is a multifaceted phenomenon involving various contributing factors. Research indicates that specic mutations in
ERG11 and the overproduction of Cdr1 contribute to resistance against uconazole
(FLZ). The presence of a CDR1 homolog in C. auris, conrmed by targeted gene
deletion, underscores its role in mediating azole resistance. Within the C. auris
genome, three genes encode Mrr1 homologs, and two genes encode Tac1 homologs.
Deletion of TAC1b has been observed to decrease resistance to uconazole and
voriconazole across different strain backgrounds. This emphasizes the involvement
of the encoded transcription factor, Tac1b, in azole resistance among distinct clades
of C. auris strains. Intriguingly, the mutants exhibited minimal or no impact on
CDR1 expression, suggesting that Tac1b may enhance azole resistance through a
mechanism independent of CDR1 (Jangir etal. 2023).
Gaining insights into the intricate regulatory networks and pivotal transcription
factors across diverse Candida species is crucial for formulating successful
approaches in the battle against drug resistance. The pursuit of targeting transcription factors within Candida species emerges as a highly promising therapeutic strategy to counter antifungal drug resistance. Transcription factors assume a central
228
role in coordinating the activation of genes vital for key pathways, such as drug
efux pumps, cell wall integrity, and stress responses. By disrupting the regulatory
networks governed by these transcription factors, there lies the potential to manipulate the overall resistance prole exhibited by Candida pathogens.
A. Kumar etal.
8.8 Contribution ofEpigenetic Modification ontheDrug
Resistance inCandida spp.
As seen in most eukaryotes, fungal nucleosome is also composed of the same four
histone proteins, H2A, H2B, H3, and H4. The dynamic nature of the nucleosome is
maintained by the so-called chromatin modiers which consist of three main players: (1) Enzymes which perform post-translational modication of the histone proteins (lysine deacetylases—KDACs and lysineacetyl transferases—KATs), (2)
Chromatin remodellers, which in an ATP-dependent way, move the nucleosomes
with respect to the DNA associated with it, (3) Different types of histone-like proteins, which are incorporated in non-canonical nucleosomes to regulate gene expression (O’Kane etal. 2020).
Typically, epigenetic modications leading to antifungal resistance are mediated
through post-translational modications (PTMs), or RNA interference (RNAi)
mechanisms. While reports on RNAi-based epigenetic inheritance in Candida species are currently absent, numerous studies have implicated PTMs in the development of epigenetic modications associated with antifungal resistance (Rabaan
etal. 2023). For instance, the fungicidal properties of the histone acetyltransferase
inhibitor CPTH2 (cyclopentylidene-[4-(4-chlorophenyl)thiazol-2-yl]hydrazone)
against C. albicans, along with its selective growth-inhibitory activity against
Candida species within the CTG clade, have been demonstrated (Tscherner and
Kuchler 2019). Similarly, the deletion of the CgADA2 gene, responsible for catalysing H3K9 acetylation in C. glabrata, rendered the strain sensitive to azoles, polyenes, and echinocandins. However, the expression of CgPDR1-dependent
multidrug-resistance genes remained unaffected in the Cgada2Δ mutant (Yu etal.
2018). Furthermore, the critical role of lysine 27 residue acetylation in Hsp90 for
voriconazole and caspofungin resistance in A. fumigatus has been established.
Recent ndings indicate that CgSnf2 and CgRtt106 (a histone chaperone) bind to
the promoter of the CgCDR1 gene, regulating the azole-induced expression of
PDR-network genes in C. glabrata. Mutants lacking Cgrtt106 and Cgsnf2 display
increased susceptibility to azoles (Robbins etal. 2012).
In summary, chromatin architecture, histone post-translational modications,
and epigenetic regulation collectively govern the expression of crucial multidrugresistance genes in prevalent Candida pathogens, such as C. albicans and C. gla-
brata. Exploring the epigenetic regulation of drug resistance opens avenues for
further research. Identifying agents targeting fungal-specic histone-modifying
enzymes or gene-silencing mechanisms holds promise for the development of novel
antifungal drugs.
8 Unravelling Drug Resistance in Candida Species: Genetic, Biolm…
229
8.9 Conclusion andFuture Perspectives
As we navigate the ever-changing landscape of antifungal therapy, the ongoing
struggle against drug resistance in Candida species necessitates a deeper understanding of the underlying mechanisms to enhance treatment effectiveness. Gaining
profound insights into the intricate molecular and cellular mechanisms responsible
for antifungal resistance is crucial for devising targeted strategies to combat this
escalating issue. In this chapter, we explore potential future directions that hold the
key to unlocking our understanding of antifungal drug resistance in Candida species. The increasing prevalence of antifungal resistance poses a signicant hurdle in
the management of Candida infections. Deeper insights into the genetic alteration
of Candida species have the potential to pave the way for groundbreaking insights
into the biology of these essential fungal pathogens and revolutionize our current
understanding. In recent years, the elds of molecular biology and genomics have
yielded signicant discoveries regarding the mechanisms behind antifungal drug
resistance in Candida species. Despite these advancements, there is still much to
uncover about Candida spp., especially about various intricate mechanisms evolved
by Candida to mediate antifungal resistance. Investigations into the impact of nongenetic factors, such as biolm formation and overexpression of efux pumps, hold
great potential in our ght against antifungal drug resistance. Combination therapies present an exciting prospect in targeting drug efux pumps. Simultaneous use
of inhibitors of efux pumps, along with conventional antifungal drugs, may create
a synergistic effect, amplifying the therapeutic impact. This strategy could not only
enhance the efcacy of existing drugs but also potentially reduce the emergence of
resistance, as the combination approach imposes a higher barrier for fungal adaptation. Advancements in nanotechnology offer a futuristic approach to drug delivery
and targeting efux pumps. Developing nanocarriers loaded with antifungal agents
and efux pump inhibitors can improve drug penetration into fungal cells, circumventing efux pump-mediated resistance. This nanotherapeutic approach may
enhance the bioavailability of antifungal drugs, providing a more efcient and targeted treatment strategy. Additionally, the advent of precision medicine and personalized antifungal therapies based on the specic drug resistance proles of individual
Candida isolates holds promise. Tailoring treatment strategies to the unique characteristics of each infection, including the expression levels of efux pumps, could
optimize therapeutic outcomes and minimize the risk of resistance development.
While challenges such as off-target effects and potential toxicity need to be
addressed, the ongoing research into drug efux pumps in Candida species provides
a fertile ground for innovation. Collaborative efforts between researchers, clinicians, and pharmaceutical industries are essential to propel these future prospects
into tangible clinical applications. By focusing on drug efux pumps, we have the
opportunity to revolutionize antifungal therapies, improve patient outcomes, and
address the persistent challenge of drug-resistant Candida infections in the years to
come. One such avenue for intervention is the inhibition of key transcription factors
known to govern multidrug resistance. For instance, the Tac1p transcription factor,
which regulates the expression of efux pumps like Cdr1p and Mdr1p, has been