Transporter-Mediated Protection against Thiopurine-Induced Hematopoietic Toxicity

Abstract

Thiopurines are effective immunosuppressants and anticancer agents, but intracellular accumulation of their active metabolites (6-thioguanine nucleotides, 6-TGNs) causes dose-limiting hematopoietic toxicity. Thiopurine S-methyltransferase (TPMT) deficiency is known to exacerbate thiopurine toxicity. However, many patients are highly sensitive to thiopurines for unknown reasons. We show that Mrp4 is abundant in myeloid progenitors and tested the role of the multidrug-resistance protein 4 (Mrp4), an ATP binding cassette (ATP) transporter of monophosphorylated nucleosides, in this unexplained thiopurine sensitivity. Mrp4-deficient mice experienced Mrp4 gene dosage–dependent toxicity caused by accumulation of 6-TGNs in their myelopoietic cells. Therefore, Mrp4 protects against thiopurine-induced hematopoietic toxicity by actively exporting thiopurine nucleotides. We then identified a single-nucleotide polymorphism (SNP) in human MRP4 (rs3765534) that dramatically reduces MRP4 function by impairing its cell membrane localization. This SNP is common (>18%) in the Japanese population and indicates that the increased sensitivity of some Japanese patients to thiopurines may reflect the greater frequency of this MRP4 SNP.

Highly Potent Activation of Nrf2 by Topical Tricyclic Bis(Cyano Enone): Implications for Protection against UV Radiation during Thiopurine Therapy

“…Of note, in our previous experience (unpublished), such systemic effects on any of these systems were not observed when sulforaphane, another potent Nrf2 activator, was topically administered under similar experimental conditions. MRP4 participates in the export of nucleoside monophosphate analogs (41)(42)(43), and its inducible gene expression is known to be regulated by Nrf2 (40,44,45). Furthermore, silencing of mrp4 increases the 6-TG incorporation in DNA of Hepa1c1c7 cells treated with this thiopurine (36).…”

Accuracy of genotyping using the TaqMan PCR assay for single nucleotide polymorphisms responsible for thiopurine sensitivity in Japanese patients with inflammatory bowel disease

“…Multidrug resistance protein 4 (MRP4/ABCC4) belongs to the MRP family of drug transporters (20)(21)(22)(23) (21). Direct sequence analyses in our laboratory indicated that the allelic frequency of MRP4 G2269A was 14.7% in the Japanese population (24).…”

Recent Advances in Pharmacogenomic Technology for Personalized Medicine

“…Recent studies have revealed that ABCC4 protects against thiopurine-induced hematopoietic toxicity by actively exporting thiopurine nucleotides (Krishnamurthy et al, 2008;Ban et al, 2010). ABCC4 is reportedly involved in the transport of antiviral agents, such as azidothymidine, adefovir, tenofovir, lamivudine, and ganciclovir (Shuetz et al, 1999;Adachi et al, 2002;Anderson et al, 2006;Imaoka et al, 2007), as well as anticancer drugs including 6-MP, 6-TG, methotrexate, and the camptothecins (Lee at al., 2000;Chen et al, 2002;Wielinga et al, 2002;Tian et al, 2005).…”

“…Despite this situation, few data are available regarding the functions of these variants. Krishnamurthy et al have recently shown that patients carrying SNP 2269G>A (Glu757Lys) in the human ABCC4 gene have severely reduced ABCC4 function resulting from an impairment of its cell membrane localization (Krishnamurthy et al, 2008). ABCC4 protects against thiopurine-induced hematologic toxicity by actively exporting 6-TGN, a toxic metabolite in the thiopurine drug metabolic pathway.…”