Novel Para-Aminobenzoic Acid Analogs and Their Potential Therapeutic Applications

A "building block" is a key component that plays a substantial and critical function in the pharmaceutical research and development industry. Given its structural versatility and ability to undergo substitutions at both the amino and carboxyl groups, para-aminobenzoic acid (PABA) is a commonly used building block in pharmaceuticals. Therefore, it is great for the development of a wide range of novel molecules with potential medical applications. Anticancer, anti-Alzheimer's, antibacterial, antiviral, antioxidant, and anti-inflammatory properties have been observed in PABA compounds, suggesting their potential as therapeutic agents in future clinical trials. PABA-based therapeutic chemicals as molecular targets and their usage in biological processes are the primary focus of this review study. PABA's unique features make it a strong candidate for inclusion in a massive chemical database of molecules having drug-like effects. Based on the current literature, further investigation is needed to evaluate the safety and efficacy of PABA derivatives in clinical investigations and better understand the specific mechanism of action revealed by these compounds.

Diagnosis by Microbial Culture, Breath Tests and Urinary Excretion Tests, and Treatments of Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth (SIBO) is characterized as the increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract and accompanies various bowel symptoms such as abdominal pain, bloating, gases, diarrhea, and so on. Clinically, SIBO is diagnosed by microbial culture in duodenum/jejunum fluid aspirates and/or the breath tests (BT) of hydrogen/methane gases after ingestion of carbohydrates such as glucose. The cultural analysis of aspirates is regarded as the golden standard for the diagnosis of SIBO; however, this is invasive and is not without risk to the patients. BT is an inexpensive and safe diagnostic test but lacks diagnostic sensitivity and specificity depending on the disease states of patients. Additionally, the urinary excretion tests are used for the SIBO diagnosis using chemically synthesized bile acid conjugates such as cholic acid (CA) conjugated with para-aminobenzoic acid (PABA-CA), ursodeoxycholic acid (UDCA) conjugated with PABA (PABA-UDCA) or conjugated with 5-aminosalicylic acid (5-ASA-UDCA). These conjugates are split by bacterial bile acid (cholylglycine) hydrolase. In the tests, the time courses of the urinary excretion rates of PABA or 5-ASA, including their metabolites, are determined as the measure of hydrolytic activity of intestinal bacteria. Although the number of clinical trials with this urinary excretion tests is small, results demonstrated the usefulness of bile acid conjugates as SIBO diagnostic substrates. PABA-UDCA disulfate, a single-pass type unabsorbable compound without the hydrolysis of conjugates, was likely to offer a simple and rapid method for the evaluation of SIBO without the use of radioisotopes or expensive special apparatus. Treatments of SIBO with antibiotics, probiotics, therapeutic diets, herbal medicines, and/or fecal microbiota transplantation are also reviewed.

Plasmodium Para-Aminobenzoate Synthesis and Salvage Resolve Avoidance of Folate Competition and Adaptation to Host Diet

Folate metabolism is essential for DNA synthesis and a validated drug target in fast-growing cell populations, including tumors and malaria parasites. Genome data suggest that Plasmodium has retained its capacity to generate folates de novo. However, the metabolic plasticity of folate uptake and biosynthesis by the malaria parasite remains unresolved. Here, we demonstrate that Plasmodium uses an aminodeoxychorismate synthase and an aminodeoxychorismate lyase to promote the biogenesis of the central folate precursor para-aminobenzoate (pABA) in the cytoplasm. We show that the parasite depends on de novo folate synthesis only when dietary intake of pABA by the mammalian host is restricted and that only pABA, rather than fully formed folate, is taken up efficiently. This adaptation, which readily adjusts infection to highly variable pABA levels in the mammalian diet, is specific to blood stages and may have evolved to avoid folate competition between the parasite and its host.

Methionine Antagonizes para-Aminosalicylic Acid Activity via Affecting Folate Precursor Biosynthesis in Mycobacterium tuberculosis

para-Aminosalicylic acid (PAS) is a second-line anti-tubercular drug that is used for the treatment of drug-resistant tuberculosis (TB). PAS efficacy in the treatment of TB is limited by its lower potency against Mycobacterium tuberculosis relative to many other drugs in the TB treatment arsenal. It is known that intrinsic metabolites, such as, para-aminobenzoic acid (PABA) and methionine, antagonize PAS and structurally related anti-folate drugs. While the basis for PABA-mediated antagonism of anti-folates is understood, the mechanism for methionine-based antagonism remains undefined. In the present study, we used both targeted and untargeted approaches to identify factors associated with methionine-mediated antagonism of PAS activity. We found that synthesis of folate precursors as well as a putative amino acid transporter, designated MetM, play crucial roles in this process. Disruption of metM by transposon insertion resulted in a ≥30-fold decrease in uptake of methionine in M. bovis BCG, indicating that metM is the major facilitator of methionine transport. We also discovered that intracellular biotin confers intrinsic PAS resistance in a methionine-independent manner. Collectively, our results demonstrate that methionine-mediated antagonism of anti-folate drugs occurs through sustained production of folate precursors.

Review on Abyssomicins: Inhibitors of the Chorismate Pathway and Folate Biosynthesis

Antifolates targeting folate biosynthesis within the shikimate-chorismate-folate metabolic pathway are ideal and selective antimicrobials, since higher eukaryotes lack this pathway and rely on an exogenous source of folate. Resistance to the available antifolates, inhibiting the folate pathway, underlines the need for novel antibiotic scaffolds and molecular targets. While para-aminobenzoic acid synthesis within the chorismate pathway constitutes a novel molecular target for antifolates, abyssomicins are its first known natural inhibitors. This review describes the abyssomicin family, a novel spirotetronate polyketide Class I antimicrobial. It summarizes synthetic and biological studies, structural, biosynthetic, and biological properties of the abyssomicin family members. This paper aims to explain their molecular target, mechanism of action, structure⁻activity relationship, and to explore their biological and pharmacological potential. Thirty-two natural abyssomicins and numerous synthetic analogues have been reported. The biological activity of abyssomicins includes their antimicrobial activity against Gram-positive bacteria and mycobacteria, antitumor properties, latent human immunodeficiency virus (HIV) reactivator, anti-HIV and HIV replication inducer properties. Their antimalarial properties have not been explored yet. Future analoging programs using the structure⁻activity relationship data and synthetic approaches may provide a novel abyssomicin structure that is active and devoid of cytotoxicity. Abyssomicin J and atrop-o-benzyl-desmethylabyssomicin C constitute promising candidates for such programs.

Deletion of sigB Causes Increased Sensitivity to para-Aminosalicylic Acid and Sulfamethoxazole in Mycobacterium tuberculosis

Although the de novo folate biosynthesis pathway has been well studied in bacteria, little is known about its regulation. In the present study, the sigB gene in Mycobacterium tuberculosis was deleted. Subsequent drug susceptibility tests revealed that the M. tuberculosis ΔsigB strain was more sensitive to para-aminosalicylic acid (PAS) and sulfamethoxazole. Comparative transcriptional analysis was performed, and downregulation of pabB was observed in the ΔsigB strain, which was further verified by a quantitative reverse transcription-PCR and Western blot assay. Then, the production levels of para-aminobenzoic acid (pABA) were compared between the sigB deletion mutant and wild-type strain, and the results showed that sigB deletion resulted in decreased production of pABA. In addition, SigB was able to recognize the promoter of pabB in vitro Furthermore, we found that deleting pabC also caused increased susceptibility to PAS. Taken together, our data revealed that, in M. tuberculosis, sigB affects susceptibility to antifolates through multiple ways, primarily by regulating the expression of pabB To our knowledge, this is the first report showing that SigB modulates pABA biosynthesis and thus affecting susceptibility to antifolates, which broadens our understanding of the regulation of bacterial folate metabolism and mechanisms of susceptibility to antifolates.

Impact of Chemical Analogs of 4-Hydroxybenzoic Acid on Coenzyme Q Biosynthesis: From Inhibition to Bypass of Coenzyme Q Deficiency

Coenzyme Q is a lipid that participates to important physiological functions. Coenzyme Q is synthesized in multiple steps from the precursor 4-hydroxybenzoic acid. Mutations in enzymes that participate to coenzyme Q biosynthesis result in primary coenzyme Q deficiency, a type of mitochondrial disease. Coenzyme Q₁₀ supplementation of patients is the classical treatment but it shows limited efficacy in some cases. The molecular understanding of the coenzyme Q biosynthetic pathway allowed the design of experiments to bypass deficient biosynthetic steps with analogs of 4-hydroxybenzoic acid. These molecules provide the defective chemical group and can reactivate endogenous coenzyme Q biosynthesis as demonstrated recently in yeast, mammalian cell cultures, and mouse models of primary coenzyme Q deficiency. This mini review presents how the chemical properties of various analogs of 4-hydroxybenzoic acid dictate the effect of the molecules on CoQ biosynthesis and how the reactivation of endogenous coenzyme Q biosynthesis may achieve better results than exogenous CoQ₁₀ supplementation.

Total synthesis of albicidin: a lead structure from Xanthomonas albilineans for potent antibacterial gyrase inhibitors

The peptide antibiotic albicidin, which is synthesized by the plant pathogenic bacterium Xanthomonas albilineans, displays remarkable antibacterial activity against various Gram-positive and Gram-negative microorganisms. The low amounts of albicidin obtainable from the producing organism or through heterologous expression are limiting factors in providing sufficient material for bioactivity profiling and structure-activity studies. Therefore, we developed a convergent total synthesis route toward albicidin. The unexpectedly difficult formation of amide bonds between the aromatic amino acids was achieved through a triphosgene-mediated coupling strategy. The herein presented synthesis of albicidin confirms the previously determined chemical structure and underlines the extraordinary antibacterial activity of this compound. The synthetic protocol will provide multigram amounts of albicidin for further profiling of its drug properties.

Production of P-aminobenzoic acid by metabolically engineered escherichia coli

The production of chemical compounds from renewable resources is an important issue in building a sustainable society. In this study, Escherichia coli was metabolically engineered by introducing T7lac promoter-controlled aroF(fbr), pabA, pabB, and pabC genes into the chromosome to overproduce para-aminobenzoic acid (PABA) from glucose. Elevating the copy number of chromosomal PT7lac-pabA-pabB distinctly increased the PABA titer, indicating that elevation of 4-amino-4-deoxychorismic acid synthesis is a significant factor in PABA production. The introduction of a counterpart derived from Corynebacterium efficiens, pabAB (ce), encoding a fused PabA and PabB protein, resulted in a considerable increase in the PABA titer. The introduction of more than two copies of PT7lac-pabAB (ce-mod), a codon-optimized pabAB (ce), into the chromosome of a strain that simultaneously overexpressed aroF(fbr) and pabC resulted in 5.1 mM PABA from 55.6 mM glucose (yield 9.2%). The generated strain produced 35 mM (4.8 g L(-1)) PABA from 167 mM glucose (yield 21.0%) in fed-batch culture.

Nanotechnology as a therapeutic tool to combat microbial resistance

Use of nanoparticles is among the most promising strategies to overcome microbial drug resistance. This review article consists of three parts. The first part discusses the epidemiology of microbial drug resistance. The second part describes mechanisms of drug resistance used by microbes. The third part explains how nanoparticles can overcome this resistance, including the following: Nitric oxide-releasing nanoparticles (NO NPs), chitosan-containing nanoparticles (chitosan NPs), and metal-containing nanoparticles all use multiple mechanisms simultaneously to combat microbes, thereby making development of resistance to these nanoparticles unlikely. Packaging multiple antimicrobial agents within the same nanoparticle also makes development of resistance unlikely. Nanoparticles can overcome existing drug resistance mechanisms, including decreased uptake and increased efflux of drug from the microbial cell, biofilm formation, and intracellular bacteria. Finally, nanoparticles can target antimicrobial agents to the site of infection, so that higher doses of drug are given at the infected site, thereby overcoming resistance.

Nanotechnology as a therapeutic tool to combat microbial resistance

Use of nanoparticles is among the most promising strategies to overcome microbial drug resistance. This review article consists of three parts. The first part discusses the epidemiology of microbial drug resistance. The second part describes mechanisms of drug resistance used by microbes. The third part explains how nanoparticles can overcome this resistance, including the following: Nitric oxide-releasing nanoparticles (NO NPs), chitosan-containing nanoparticles (chitosan NPs), and metal-containing nanoparticles all use multiple mechanisms simultaneously to combat microbes, thereby making development of resistance to these nanoparticles unlikely. Packaging multiple antimicrobial agents within the same nanoparticle also makes development of resistance unlikely. Nanoparticles can overcome existing drug resistance mechanisms, including decreased uptake and increased efflux of drug from the microbial cell, biofilm formation, and intracellular bacteria. Finally, nanoparticles can target antimicrobial agents to the site of infection, so that higher doses of drug are given at the infected site, thereby overcoming resistance.