Application of Advanced Bioanalytical Techniques to Studies of Oxaliplatin Chemotherapy

Oxaliplatin is a platinum anticancer drug approved for medical use in treating gastrointestinal cancers. Organic cation transporters (OCTs) may contribute to the tissue accumulation and unwanted toxicities of oxaliplatin. The overall aim of this thesis was to develop new bioanalytical methodologies for studies of oxaliplatin chemotherapy when given with OCT inhibitors (cimetidine or ergothioneine) for modulating oxaliplatin toxicities. To quantify intact oxaliplatin in human plasma, an ultraperformance liquid chromatographyinductively coupled plasma mass spectrometry bioanalytical method was developed and validated. This improved method detected intact oxaliplatin at a retention time of 1.1 minutes at concentrations 10 nM in 1 µL of methanol-deproteinised human plasma. To quantify ergothioneine in cell lysates, a high-performance liquid chromatography-ultraviolet bioanalytical method was established. These bioanalytical methods were applied to studies of mechanisms whereby ergothioneine reduces platinum accumulation in HEK293-rOCTN1 and HEK293-MOCK cells during oxaliplatin exposure, which identified two mechanisms: 1) ergothioneine inhibition of OCTN1-dependent uptake of oxaliplatin, and 2) ligand displacement reactions between ergothioneine and oxaliplatin in extracellular fluids forming positively-charged Pt(diaminocyclohexane)-ergothioneine conjugates with reduced capacity for cellular uptake. In an analysis of a clinical pharmacokinetic dataset, linear equations were established for estimating area-under-the-plasma-concentration-versus-time-curve (AUC) from end-of-infusion plasma concentrations of intact oxaliplatin (AUC = 2.231*end-ofinfusion plasma concentration) and free platinum (AUC = 2.335*end-of-infusion plasma concentration). Together with other techniques, these AUC estimation methods were applied to a preliminary blinded analysis of samples from patients (n=15) treated on the CITRON clinical trial, which aimed to demonstrate whether cimetidine alters oxaliplatin pharmacokinetics. Within-subject ratios of end-of-infusion plasma concentration and AUC of intact oxaliplatin and free platinum, when oxaliplatin was given with cimetidine or placebo, were close to one (mean ratios, 1.06-1.07) with 95% confidence intervals overlapping with one, suggesting that cimetidine does not alter the pharmacokinetics of oxaliplatin in cancer patients. In conclusion, an improved bioanalytical method for the quantification of intact oxaliplatin in human plasma was developed and validated. Together with other techniques, this method was applied to studies of the clinical pharmacology of oxaliplatin focusing on its use with the OCT inhibitors, cimetidine and ergothioneine, for modulating oxaliplatin toxicities.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Pharmacology

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2024

Author dc:creator

• Ho, John

Advisors dc:contributor.advisor

• McKeage, Mark
• Hartinger, Christian

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/70359

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/70359