Oxamniquine

Starting Materials and Initial Reactions

X-ray Crystallography

X-ray structures of Schistosoma mansoni sulfotransferase (SmSULT-OR) complexed with this compound derivatives revealed critical binding interactions, such as hydrogen bonding between the hydroxymethyl group and Tyr154. Soaking experiments with CIDD-0149830 and CIDD-0072229 demonstrated that derivatives adopt conformations similar to this compound but with enhanced affinity for S. haematobium and S. japonicum sulfotransferases.

Table 2: Crystallographic Data for this compound Derivatives

In Vitro Assays for Efficacy

Adult schistosomes are incubated with derivatives at concentrations ranging from 35.75 μM to 143 μM to assess lethality. Dose-response curves for CIDD-0149830 showed 100% mortality in all three Schistosoma species within seven days, outperforming this compound. Racemic mixtures are evaluated alongside enantiomers to determine stereochemical impacts on bioactivity.

Hycanthone

Hycanthone, another schistosomicide, shares mechanistic similarities with OXM, including DNA intercalation and reliance on enzymatic activation. However:

• Structural Differences: Hycanthone lacks OXM’s nitro group and isopropylaminomethyl side chain, which are critical for SULT-mediated activation .
• Resistance Profile: Both drugs face cross-resistance in S. mansoni strains with impaired SULT activity.

Table 1: Structural and Functional Comparison of OXM and Hycanthone

Dehatridine

Dehatridine, an alkaloid, exhibits schistosomicidal activity via docking to the S. mansoni Sm14 fatty-acid-binding protein. Compared to OXM:

• Docking Efficiency : Dehatridine has a lower docking score (−147.1 kcal/mol) than OXM (−86.6 kcal/mol), suggesting stronger target affinity .
• Mechanistic Overlap : Both interact with Tyr and Arg residues in target proteins, but Dehatridine’s pi-interactions may enhance stability .

Praziquantel (PZQ)

PZQ, the first-line treatment for all schistosome species, contrasts with OXM in key areas:

• Spectrum of Activity: PZQ is effective against S. mansoni, S. hematobium, and S. mansoni .
• Mechanism : PZQ disrupts calcium homeostasis in parasite teguments, unlike OXM’s nucleic acid synthesis inhibition .
• Clinical Efficacy : At 40 mg/kg, PZQ achieves higher cure rates (CR) than OXM 40 mg/kg (RR = 1.09, p = 0.034) but shows comparable efficacy to OXM 50 mg/kg .

Table 2: Clinical and Pharmacokinetic Comparison of OXM and PZQ

This compound Derivatives (CIDD-0066790)

Recent derivatives address OXM’s limitations:

• Structural Modifications : Derivatives like CIDD-0066790 retain OXM’s core structure but introduce side-chain adjustments to enhance binding to ShSULT (e.g., avoiding Val-139 clashes in S. hematobium) .
• Broad-Species Efficacy : CIDD-0066790 kills S. mansoni, S. hematobium, and S. japonicum in vitro, overcoming species-specific resistance .
• Mechanistic Insights: X-ray crystallography confirms derivative binding to sulfotransferase active sites, with improved turnover rates compared to OXM .

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.

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 .