Abstract
BackgroundSince proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients.MethodsTo investigate this hypothesis, we conducted a whole genome microarray study to identify difference in the expression of genes between isogenic doxorubicin-sensitive and doxorubicin-resistant MCF-7 breast tumour cells. We then assessed the degree of over-representation of doxorubicin pharmacokinetic and pharmacodynamic genes in the dataset of doxorubicin resistance genes.ResultsOf 27,958 Entrez genes on the array, 7.4 per cent or 2,063 genes were differentially expressed by ≥ 2-fold between wildtype and doxorubicin-resistant cells. The false discovery rate was set at 0.01 and the minimum p value for significance for any gene within the “hit list” was 0.01. Seventeen and 43 per cent of doxorubicin pharmacokinetic genes were over-represented in the hit list, depending upon whether the gene name was identical or within the same gene family, respectively. The most over-represented genes were within the 1C and 1B families of aldo-keto reductases (AKRs), which convert doxorubicin to doxorubicinol. Other genes convert doxorubicin to other metabolites or affect the influx, efflux, or cytotoxicity of the drug. In further support of the role of AKRs in doxorubicin resistance, we observed that, in comparison to doxorubicin, doxorubincol exhibited dramatically reduced cytotoxicity, reduced DNA-binding activity, and strong localization to extra nuclear lysosomes. Pharmacologic inhibition of the above AKRs in doxorubicin-resistant cells increased cellular doxorubicin levels, restored doxorubicin cytotoxicity and re-established doxorubicin localization to the nucleus. The properties of doxorubicinol were unaffected.ConclusionsThese findings demonstrate the utility of using curated pharmacokinetic and pharmacodynamic knowledge bases to identify highly relevant genes associated with doxorubicin resistance. The induction of one or more of these genes was found to be correlated with changes in the drug’s properties, while inhibiting one specific class of these genes (the AKRs) increased cellular doxorubicin content and restored drug DNA binding, cytotoxicity, and subcellular localization.
Highlights
Since proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients
These findings indicate that a significant amount of the transcriptome appears altered as these cells are selected for doxorubicin resistance
In addition to our previously reported finding of increased expression of the Aldo-keto reductase (AKR) 1C isoforms [17], the current study reveals other changes in gene expression that would be expected to affect the cytotoxicity of doxorubicin
Summary
Since proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients. Progress in restoring drug sensitivity for drug-resistant tumours, by inhibiting drug efflux transporters, has been incremental at best [12,13] This limited progress demands that a more nuanced approach be taken, including the identification of all proteins that likely affect the pharmacokinetics and pharmacodynamics of doxorubicin. Genome profiling is a method that can provide data on gene expression and/or allelic variations across biological samples, often using whole genome approaches This promises to be a great aid to oncologists in identifying and treating drug-resistant tumours. Extensive comparisons between the biochemical properties of doxorubicin and one of its metabolites (doxorubicinol) provided us with significant insight into how a simple hydroxylation reaction can strongly affect the biochemical and cellular properties of doxorubicin, including dramatically reduced cytotoxicity, diminished DNA- binding activity, altered cellular accumulation of the drug and altered subcellular localization
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call