Oxamniquine

Genetic Basis of Resistance Development

The development of resistance to oxamniquine in S. mansoni is primarily driven by genetic changes within the parasite.

Epidemiological Studies of Resistance Emergence and Distribution in Endemic Regions

Epidemiological studies have provided insights into the emergence and distribution of this compound resistance in areas where schistosomiasis is endemic. Resistant parasites were detected in Brazil in the 1970s, even before widespread mass drug administration programs. nih.govplos.org Similar observations of poor treatment response in patients were made in East Africa. nih.govplos.org Experimental infections in mice using parasites isolated from patients with poor treatment outcomes confirmed the existence of this compound-resistant parasites in regions like Brazil and Kenya. nih.govresearchgate.netplos.orgscielo.br

Importantly, studies have revealed that this compound resistance alleles were already widespread in Old World S. mansoni populations, predating the extensive deployment of the drug in the 1970s. nih.govplos.orgplos.orgnih.govifremer.frbiorxiv.orgajtmh.org Analysis of parasite populations from areas with minimal this compound usage, such as parts of Africa and the Middle East, showed notable frequencies of resistance alleles. nih.govplos.orgbiorxiv.org For example, studies found this compound resistance allele frequencies ranging from 4.29% in the Middle East to 14.91% in East African parasite populations. nih.govplos.orgbiorxiv.org The presence of the p.E142del allele in both West Africa and Puerto Rico with identical flanking SNPs suggests that resistance alleles were transported to the New World with S. mansoni during the transatlantic slave trade, further indicating that these alleles existed long before this compound was used therapeutically. nih.govplos.orgifremer.frbiorxiv.org This widespread standing variation for resistance has significant implications for how rapidly resistance can spread under drug pressure. nih.govplos.orgplos.org

Data on the frequency of this compound resistance alleles in different Old World populations:

Two specific resistance mutations, p.W120R and p.N171IfsX28, were found to be particularly common (>5%) in East African and Middle-Eastern populations. nih.govbiorxiv.org

Molecular Surveillance and Characterization of Resistance Alleles

Molecular surveillance plays a vital role in monitoring the prevalence and distribution of this compound resistance alleles in parasite populations. nih.govifremer.fr By sequencing the SmSULT-OR gene from parasite samples collected in endemic areas, researchers can identify and characterize existing and emerging resistance mutations. nih.govnih.govnih.gov Studies have involved sequencing SmSULT-OR from individual miracidia obtained from infected patients. nih.gov This approach has led to the identification of various mutations, including previously known ones like p.E142del and p.C35R, as well as novel variants predicted to cause loss-of-function in the sulfotransferase. nih.govnih.govnih.gov

Functional validation of identified mutations is crucial, often involving the expression of recombinant sulfotransferase proteins with the identified mutations and testing their ability to activate this compound in vitro. nih.govnih.govplos.org This helps confirm which genetic variants truly confer resistance. Molecular surveillance efforts, such as those involving large parasite collections, are valuable for regularly updating the understanding of the resistance landscape in different endemic regions. nih.govplos.org However, it is important to pair molecular screening with functional evaluation or computational prediction to determine the phenotypic impact of identified mutations. nih.govplos.org

Research Strategies to Overcome this compound Resistance

Addressing this compound resistance involves several research strategies. One approach focuses on developing new this compound derivatives that can overcome the limitations of the parent compound, including resistance. plos.orgplos.orgnih.govresearchgate.net Guided by structural data of the SmSULT-OR enzyme and its interaction with this compound, researchers are designing and synthesizing novel derivatives. plos.orgnih.govresearchgate.net These efforts aim to create compounds that can be activated by both wild-type and mutated sulfotransferase enzymes or that have alternative mechanisms of action. plos.orgnih.gov Studies have identified promising this compound derivatives with potent activity against S. mansoni, including resistant strains, and even against other Schistosoma species that are not susceptible to the original this compound. plos.orgplos.orgnih.govresearchgate.net For example, derivatives like CIDD-0150610 and CIDD-0150303 have shown high killing rates against S. mansoni, S. haematobium, and S. japonicum in vitro. nih.govresearchgate.net In vivo studies with these derivatives have also demonstrated significant worm burden reductions. nih.govresearchgate.net

Another strategy involves exploring combination therapies, where this compound or its derivatives could be used alongside other antischistosomal drugs like praziquantel, particularly against resistant strains. nih.gov Research into the molecular mechanisms of resistance and the structure of the activating enzyme also provides a framework for rational drug design. scispace.complos.org Furthermore, understanding the population genetics of resistance alleles and their distribution through molecular surveillance can inform treatment strategies and help manage the spread of resistance. nih.govifremer.frbiorxiv.orgfrontiersin.org Advanced genetic tools, such as CRISPR-Cas systems, are also being explored to understand the function of genes related to drug resistance, which could potentially aid in developing new interventions. wellcomeopenresearch.org

Elucidation of Bioactivation Pathways and Host Enzyme Interactions

Oxamniquine functions as a prodrug, requiring enzymatic activation within the Schistosoma worm to exert its schistosomicidal effects. Evidence strongly suggests that a schistosome-specific sulfotransferase enzyme is responsible for this activation. This enzyme is notably absent in drug-resistant parasites. The activation process is hypothesized to involve the conversion of this compound to a reactive ester, likely a sulfate. nih.govresearchgate.netscielo.brnih.govnih.gov

Studies have provided data supporting the role of a sulfotransferase. For instance, parasite extracts lose their activating capability upon dialysis, indicating the requirement of a dialyzable cofactor. nih.govresearchgate.netscielo.br The addition of 3'-phosphoadenosine 5'-phosphosulfate (PAPS), a known sulfate donor, restored the activity of the dialyzate, strongly suggesting the involvement of a sulfotransferase. nih.govresearchgate.netscielo.br Furthermore, classical sulfotransferase substrates such as beta-estradiol and quercetin competitively inhibited the activation of this compound in vitro. nih.govresearchgate.netscielo.br These substrates could also be sulfonated in vitro using extracts from sensitive, but not resistant, schistosomes. nih.govresearchgate.netscielo.br

Gel filtration analysis of the activating factor from sensitive schistosomes revealed an elution profile corresponding to a molecular mass of approximately 32 kDa, consistent with the typical size of sulfotransferase subunits. nih.govresearchgate.netscielo.br Ion exchange and affinity chromatography further confirmed the sulfotransferase nature of the enzyme. nih.govresearchgate.netscielo.br

This selective activation by a parasite enzyme, specifically S. mansoni sulfotransferase (SmSULT-OR), allows for selective toxicity to the worm while minimizing effects on human enzymes. nih.govresearchgate.netfrancis-press.com Structural data, including X-ray crystallography, of the S. mansoni sulfotransferase have guided the development of this compound derivatives aimed at expanding efficacy to other Schistosoma species like S. haematobium and S. japonicum. plos.orgnih.gov

Pharmacokinetic/Pharmacodynamic (PK/PD) Relationship Modeling relevant to Schistosome Biology

Examination of the PK/PD relationship for this compound has revealed an in vitro-in vivo paradox. Maximal clinical plasma concentrations were found to be significantly lower (five to ten times) than the concentrations required for efficacious in vitro schistosomal killing. nih.govresearchgate.netresearchgate.netnih.govresearchgate.net This paradox is particularly relevant due to the parasite's residence in the vasculature between the intestine and the liver. nih.govresearchgate.netnih.govresearchgate.net

Metabolic Fate and Excretion Mechanisms in Mammalian Hosts

In mammalian hosts, this compound undergoes extensive metabolism, primarily in the liver, to inactive metabolites. wikipedia.orgdrugbank.com The major metabolite is the 6-carboxy derivative, which is subsequently excreted, primarily in the urine. wikipedia.org About 70% of an administered dose of this compound is excreted as the 6-carboxy metabolite within 12 hours. wikipedia.org Traces of the 2-carboxy metabolite have also been detected in urine. wikipedia.org this compound is rapidly cleared, with a plasma half-life typically ranging from 1 to 2.5 hours. wikipedia.orgdrugbank.com Studies in dogs have suggested the occurrence of first-pass metabolism in the gut wall. who.int Excretion also occurs via bile. researchgate.netnih.govresearchgate.net

Research on Potential Drug-Drug Interactions involving this compound and other Xenobiotics (e.g., Enzyme Inhibition/Induction)

Research on potential drug-drug interactions involving this compound has indicated that it may decrease the metabolism of several other compounds. drugbank.com This suggests a potential for enzyme inhibition. For example, the metabolism of amoxapine, amphetamine, amprenavir, antipyrine, arformoterol, aripiprazole, aripiprazole lauroxil, diltiazem, diphenhydramine, dolasetron, domperidone, donepezil, doxazosin, doxepin, istradefylline, labetalol, levobetaxolol, lidocaine, lisuride, and lofexidine may be decreased when combined with this compound. drugbank.com Additionally, the serum concentration of doxorubicin and dextroamphetamine (an active metabolite of lisdexamfetamine) can be increased when used in combination with this compound. drugbank.com These findings highlight the potential for pharmacokinetic interactions where this compound may inhibit the metabolism of co-administered drugs.

Synthetic Methodologies and Chemical Derivatization Strategies

The synthesis of oxamniquine derivatives has been a key aspect of developing new antischistosomal agents. An iterative process involving design, synthesis, and testing has been employed to identify promising candidates. nih.govplos.orgplos.orgresearchgate.net Chemical derivatization strategies have focused on modifying the this compound structure to enhance its activity and overcome limitations. nih.govnih.gov For instance, the Mannich reaction has been utilized to synthesize new this compound derivatives, resulting in unexpected cyclized and etherified products. nih.gov Studies on structure-activity relationships (SAR) have indicated that modifications to the side alkylamine group of this compound can maintain activity, although this may be associated with increased toxicity. nih.gov Over 350 this compound derivatives have been designed, synthesized, and tested. plos.orgresearchgate.netdatadryad.orgnih.govbiorxiv.org

In Vitro Efficacy Assessment in Defined Schistosome Models

In vitro efficacy assessment is a critical step in the preclinical evaluation of this compound-inspired compounds. These studies typically involve exposing schistosome parasites to different concentrations of the drug candidates under controlled laboratory conditions. plos.orgplos.orgresearchgate.netdatadryad.orgplos.org

In Vivo Efficacy Studies in Laboratory Animal Models (e.g., Murine and Hamster Models of Schistosomiasis)

In vivo studies using laboratory animal models, such as mice and hamsters, are essential to assess the efficacy of this compound derivatives in a living system. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netplos.orggassergroup.comresearchgate.netnih.govbioworld.comscielo.brscite.aibioline.org.brscielo.brmdpi.com These models allow for the evaluation of worm burden reduction and the assessment of efficacy against different schistosome species and life stages in a more complex environment. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netgassergroup.comresearchgate.netnih.govbioworld.comscielo.brscite.aibioline.org.brscielo.br

Studies in mice infected with S. mansoni, S. haematobium, and S. japonicum have been conducted to evaluate the efficacy of lead this compound derivatives. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netbioworld.com Worm burden reduction is a key metric in these in vivo studies. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netbioworld.comscielo.brscite.ai For example, specific derivatives have shown significant worm burden reductions against S. mansoni, S. haematobium, and S. japonicum in mouse models. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netbioworld.com

Studies have also evaluated the efficacy of these compounds against immature schistosome stages in vivo, as praziquantel is less effective against these forms. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netbioworld.com For example, CIDD-0150303 demonstrated effective reduction in juvenile worm burden against S. mansoni in vivo. plos.orgdatadryad.orgnih.govbiorxiv.orgresearchgate.netbioworld.com

Research into Novel Formulation and Drug Delivery Systems for Optimized Pharmacokinetic Profiles and Stability

Optimizing the pharmacokinetic profile and stability of this compound and its derivatives is a key area of preclinical research to improve efficacy, reduce dosing frequency, and potentially mitigate limitations such as poor solubility or rapid metabolism. Novel formulation and drug delivery systems are being investigated to achieve these goals.

One approach involves the development of prodrugs, where the parent compound is chemically modified to improve its absorption, distribution, metabolism, and excretion (ADME) properties. Studies have explored this compound prodrugs, including polymeric forms, with the aim of achieving prolonged biological action and improved bioavailability researchgate.netakjournals.com. While some early polymeric prodrugs did not show improved worm burden reduction compared to this compound, the concept of using prodrug strategies to enhance pharmacokinetic profiles remains an active area of research nih.gov.

Liposomal encapsulation is another delivery system being investigated. Liposome-entrapped this compound (LOXA) has been tested in murine models of S. mansoni infection. LOXA administered subcutaneously demonstrated a significant reduction in worm burden compared to free this compound, particularly when given around the time of infection. Maximum efficacy, with a 97% reduction in parasite number, was observed with subcutaneous LOXA administered one day before infection scielo.br. This suggests that liposomal formulations can influence the delivery and efficacy of this compound.

Research also focuses on understanding the pharmacokinetic/pharmacodynamic (PK/PD) relationship of this compound and its analogs to inform formulation development. Studies have identified an in vitro-in vivo paradox with this compound, where maximal clinical plasma concentrations are significantly lower than the in vitro concentrations required for worm killing nih.govresearchgate.net. Modeling suggests that the parasite's location in the portal vasculature means that portal concentrations are more relevant to efficacy than systemic plasma concentrations nih.govresearchgate.net. This understanding guides the design of formulations aimed at achieving higher and sustained concentrations in the portal circulation.

Improving physicochemical properties like solubility and permeability is also crucial for optimizing oral absorption and achieving favorable portal concentrations nih.govresearchgate.net. Novel this compound analogs are being designed with optimized properties to enhance oral bioavailability and improve in vivo activity nih.gov.

Additionally, research into novel oral formulations, such as floating tablets, has been explored to potentially prolong gastric residence time and improve drug absorption .

Compound Names and PubChem CIDs

This compound (OXA) is a well-established antischistosomal drug, historically used against Schistosoma mansoni. Its mechanism involves activation by a schistosome sulfotransferase (SULT), leading to parasite death. While effective against S. mansoni, OXA has limitations, including inactivity against S. haematobium and S. japonicum, and the emergence of resistance. This has driven research into developing novel this compound-inspired compounds with broader activity and improved properties.

Research into Novel Formulation and Drug Delivery Systems for Optimized Pharmacokinetic Profiles and Stability

Optimizing the pharmacokinetic profile and stability of this compound and its derivatives is a key area of preclinical research to improve efficacy, reduce dosing frequency, and potentially mitigate limitations such as poor solubility or rapid metabolism. Novel formulation and drug delivery systems are being investigated to achieve these goals.

One approach involves the development of prodrugs, where the parent compound is chemically modified to improve its absorption, distribution, metabolism, and excretion (ADME) properties. Studies have explored this compound prodrugs, including polymeric forms, with the aim of achieving prolonged biological action and improved bioavailability. researchgate.netakjournals.com While some early polymeric prodrugs did not show improved worm burden reduction compared to this compound, the concept of using prodrug strategies to enhance pharmacokinetic profiles remains an active area of research. nih.gov

Liposomal encapsulation is another delivery system being investigated. Liposome-entrapped this compound (LOXA) has been tested in murine models of S. mansoni infection. LOXA administered subcutaneously demonstrated a significant reduction in worm burden compared to free this compound, particularly when given around the time of infection. Maximum efficacy, with a 97% reduction in parasite number, was observed with subcutaneous LOXA administered one day before infection. scielo.br This suggests that liposomal formulations can influence the delivery and efficacy of this compound.

Research also focuses on understanding the pharmacokinetic/pharmacodynamic (PK/PD) relationship of this compound and its analogs to inform formulation development. Studies have identified an in vitro-in vivo paradox with this compound, where maximal clinical plasma concentrations are significantly lower than the in vitro concentrations required for worm killing. nih.govresearchgate.net Modeling suggests that the parasite's location in the portal vasculature means that portal concentrations are more relevant to efficacy than systemic plasma concentrations. nih.govresearchgate.net This understanding guides the design of formulations aimed at achieving higher and sustained concentrations in the portal circulation.

Improving physicochemical properties like solubility and permeability is also crucial for optimizing oral absorption and achieving favorable portal concentrations. nih.govresearchgate.net Novel this compound analogs are being designed with optimized properties to enhance oral bioavailability and improve in vivo activity. nih.gov

Additionally, research into novel oral formulations, such as floating tablets, has been explored to potentially prolong gastric residence time and improve drug absorption.

Q. What analytical methodologies are recommended for quantifying oxamniquine in pharmaceutical formulations and biological matrices?

A validated spectrofluorimetric method using derivatization with 1-dimethylaminonaphthalene-5-sulphonyl chloride (dansyl chloride) is widely employed. This method achieves linearity at 0.02–0.2 µg ml⁻¹, with a detection limit of 0.007 µg ml⁻¹ and quantitation limit of 0.02 µg ml⁻¹ . Key parameters include reaction at pH 10 (sodium carbonate buffer), excitation/emission wavelengths of 335/445 nm, and robustness against minor variations in reagent volume (±0.1 ml) or reaction time (±5 min) . Cross-validation with HPLC or spectrophotometric methods ensures accuracy in dosage forms and spiked plasma (mean recovery: 97.77% ±1.19) .

Q. How does this compound exert its schistosomicidal activity at the molecular level?

this compound is enzymatically activated by sulfotransferases in Schistosoma mansoni to form a reactive ester intermediate, which alkylates parasitic DNA, disrupting replication . Resistance arises from loss-of-function mutations in the sulfotransferase gene (SmSULT), as shown via linkage mapping (LOD = 31 on chromosome 6) and RNAi knockdowns . Crystallographic studies confirm drug-enzyme binding interactions, guiding rational derivative design for broader species efficacy .

Q. What are the primary considerations for designing in vitro assays to evaluate this compound efficacy?

Use juvenile (1–5-day-old) and adult (25-day-old) schistosomula to assess stage-specific susceptibility. Statistical analysis via non-parametric tests (e.g., Kruskal-Wallis) is critical, as strain- and sex-dependent responses exist. For example, R1 strain females show absolute resistance post-day 25, while males exhibit partial susceptibility (17.7% reduction vs. 69.2% in LE strain) . Include controls for baseline parasite viability and validate results across multiple biological replicates.

Advanced Research Questions

Q. How can contradictory data on this compound’s efficacy across Schistosoma strains be resolved methodologically?

Contradictions arise from genetic heterogeneity (e.g., SmSULT mutations) and hybridization events (e.g., S. bovis x S. haematobium hybrids). Combine whole-genome sequencing with functional assays (e.g., CRISPR-Cas9 knockouts) to map resistance loci . For hybrids, perform SNP analysis and in vitro drug exposure trials to quantify hybrid-specific susceptibility . Standardize protocols for parasite age, culture conditions, and drug exposure times to minimize variability .

Q. What experimental strategies are recommended to mitigate false positives/negatives in this compound resistance studies?

• False positives: Use isogenic parasite lines to control for genetic background effects. Confirm resistance via enzymatic assays (e.g., sulfotransferase activity with PAPS cofactor) .
• False negatives: Optimize drug concentration ranges using dose-response curves (e.g., IC₅₀ values) and include sensitive strains as internal controls. Apply orthogonal methods like LC-MS to verify metabolite activation .

Q. How can spectrofluorimetric methods be adapted for high-throughput screening of this compound derivatives?

Automate derivatization steps using microplate readers and robotic liquid handlers. Validate derivative-specific fluorescence profiles (e.g., excitation/emission shifts) and cross-reference with LC-MS for structural confirmation. Use spiked plasma pools to assess matrix effects and recovery rates .

Q. What are the implications of this compound’s species-specific activation for cross-species schistosomiasis control?

S. haematobium lacks functional sulfotransferase orthologs, rendering this compound ineffective. Structure-activity relationship (SAR) studies guided by SmSULT crystallography can identify derivatives with broader specificity. For example, modifying the quinoline scaffold or esterification site may enhance binding to divergent sulfotransferases .

Methodological Resources

• Analytical Validation: Follow ICH Q2B guidelines for specificity, linearity, accuracy, and precision .
• Genetic Mapping: Utilize CRISPR-Cas9 and RNAi for functional genomics in schistosomes .
• Data Reporting: Adhere to standards for qualitative research (e.g., SRQR) and include raw data in supplemental files .