One of the side effects of cisplatin therapy in malignant neoplasms is ototoxicity. This effect shows a wide inter-individual range which is more variable than the pharmacokinetic parameters. Oxidative stress has been implicated in cisplatin ototoxicity. The glutathione S-transferase (GST) supergene family encodes isoenzymes that appear to be critical in protection against oxidative stress. Certain GST loci are polymorphic, demonstrating alleles that are null (GSTM1 and GSTT1), encode low-activity variants (GSTP1) or are associated with variable inducibility (GSTM3). The aim of our study was to investigate genetic risk factors involved in the ototoxicity of cisplatin and to determine whether the polymorphisms in five GST genes affect the individual risk of ototoxicity by cisplatin. Two groups of patients were analyzed in this study: group H, 20 patients early and highly sensitive to the ototoxicity of cisplatin; and group N, 19 patients with no hearing impairment under comparable doses of the drug. We found a protective effect for the GSTM3*B allele with a frequency of 0.18 in the group with normal hearing after therapy versus 0.025 in the group with hearing impairment. (chi2=5.37; p=0.02).

Ototoxicity and nephrotoxicity are dose-limiting side effects of cisplatin. Megalin, a member of the low-density lipoprotein receptor family, is highly expressed in renal proximal tubular cells and marginal cells of the stria vascularis of the inner ear -tissues, which accumulate high levels of platinum-DNA adducts. On the assumption that the mechanisms of cisplatin-induced nephro-and ototoxicity involve megalin we analyzed the incidence of the non-synonymous single nucleotide polymorphisms (SNP) rs2075252 and rs4668123 in 25 patients who developed a distinct hearing loss during cisplatin therapy and in 25 patients without hearing impairment after cisplatin therapy. We found no association between cisplatin-induced ototoxicity and any allele of rs4668123 but observed a higher frequency of the A-allele of rs2075252 in the group with hearing impairment than in the group with normal hearing after cisplatin therapy (0.32 versus 0.14) (w 2 ¼ 5.83, Po0.02; odds ratio: 3.45; 95% confidence interval: 1.11-11.2) indicating that SNPs at the megalin gene might impact the individual susceptibility against cisplatin-induced ototoxicity.

Quantitation of target mRNAs using the reverse-transcription polymerase chain reaction found a widespread field of application in diverse biomedical diagnostic assays. However, the problem of varying sample quality has to be solved by correcting target molecule amounts through detection of an endogenous control template. The choice of an appropriate reference gene is still object of debate as pseudogene co-amplification and expression level variations may limit the usefulness of some currently used reference reactions. We compared quantitative expression levels of the commonly used endogenous reference genes beta-actin ( -actin), beta-2-microglobulin ( 2 -MG) and porphobilinogen deaminase (PBDG) using the TaqMan chemistry. With these assays we investigated the respective expression patterns in K562 cells and leucocytes of normal individuals as well as of malignoma patients. In K562 cells 1544+246 -actin, 65±30 2 -MG and 22±8 PBDG copies/cell were detected. In normal leucocytes 491±97 -actin, 40±17 2 -MG and <1 PBDG copies/cell were quantified. Leucocytes of various malignancies exhibited 84±51 -actin, 106±8 2 -MG and <1 PBDG copies/cell. We conclude that 2 -MG is the most suitable reference gene tested as its variation between different sample origins and within distinct cell types was acceptable low. 

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