PSMB7 is associated with anthracycline resistance and is a prognostic biomarker in breast cancer.

BACKGROUND: To date individual markers have failed to correctly predict resistance against anticancer agents in breast cancer. We used gene expression patterns attributable to chemotherapy-resistant cells to detect potential new biomarkers related to anthracycline resistance. One of the genes, PSMB7, was selected for further functional studies and clinical validation. METHODS: We contrasted the expression profiles of four pairs of different human tumour cell lines and of their counterparts resistant to doxorubicin. Observed overexpression of PSMB7 in resistant cell lines was validated by immunohistochemistry. To examine its function in chemoresistance, we silenced the gene by RNA interference (RNAi) in doxorubicin-resistant MCF-7 breast cancer cells, then cell vitality was measured after doxorubicin treatment. Microarray gene expression from GEO raw microarray samples with available progression-free survival data was downloaded, and expression of PSMB7 was used for grouping samples. RESULTS: After doxorubicin treatment, 79.8+/-13.3% of resistant cells survived. Silencing of PSMB7 in resistant cells decreased survival to 31.8+/-6.4% (P>0.001). A similar effect was observed after paclitaxel treatment. In 1592 microarray samples, the patients with high PSMB7 expression had a significantly shorter survival than the patients with low expression (P<0.001). CONCLUSION: Our findings suggest that high PSMB7 expression is an unfavourable prognostic marker in breast cancer.

Acute renal failure following the use of rosiglitazone in a chronic kidney disease patient.

Drug-induced acute interstitial nephritis is a well-recognised and important reversible cause of acute renal failure. Peroxisome-proliferator activated receptor-gamma agonists, such as rosiglitazone, have been proven to be safe in chronic kidney disease patients. We describe a 65-year-old man with long-standing diabetes mellitus and hypertension, presenting with a five-day history of fluid overload and uraemic symptoms. There was no ingestion of analgesics, alternative medicine and other nephrotoxic drugs, the only new prescription being rosiglitazone, which was commenced during his last clinic follow-up two weeks prior to presentation. He required haemodialysis with minimal improvement in renal profile, despite cessation of the offending drug. Renal biopsy revealed findings consistent with acute interstitial nephritis. An episode of upper gastrointestinal bleeding with bleeding duodenal ulcer limited the use of steroids. He was treated with a course of mycophenolate mofetil which showed good gradual response and he remained stable with residual renal impairment.

The PI3K inhibitor LY294002 blocks drug export from resistant colon carcinoma cells overexpressing MRP1.

Multidrug resistance may be achieved by the activation of membrane transporters, detoxification, alterations in DNA repair or failure in apoptotic pathways. Recent data have suggested an involvement of mitogenic signalling pathways mediated by Ras and phosphoinositol-3-kinase (PI3K/Akt) in controlling multidrug resistance. Since these pathways are important targets for therapeutic interference, we sought to investigate whether blocking effectors kinases by specific inhibitors would result in a sensitization toward cytotoxic drugs. We found that cotreatment of drug-resistant HT29RDB colon cancer cells with the topoisomerase inhibitor doxorubicin and the PI3K-inhibitor LY294002 resulted in massive apoptosis, while cotreatment with the Mek inhibitors PD98059 or U0126 had no effect. This suggested that the PI3K-pathways controls cell survival and drug resistance in these cells. Besides blocking Akt phosphorylation, the PI3K-inibitor increased the intracellular doxorubicin concentration threefold. LY294002 inhibits drug export in a competitive manner as revealed by measuring drug efflux in the presence and the absence of inhibitor. The efficacy of drug efflux inhibition by LY294002 was similar to that achieved by the MRP1 inhibitors MK571 and genistein. We conclude that the PI3K inhibitor LY294002 may have therapeutic potential when combined with doxorubicin in the treatment of MRP1-mediated drug resistance.

Use of transcriptional regulatory sequences of telomerase (hTER and hTERT) for selective killing of cancer cells.

Telomerase (hTER and hTERT) plays a crucial role in cellular immortalization and carcinogenesis. Telomerase activity can be detected in about 85% of different malignant tumors, but is absent in most normal cells. In situ hybridization analysis showed that high levels of hTER and hTERT expression are present in bladder cancer, while no signal was detected in normal tissue. Therefore, in this work we propose to use hTER and hTERT transcriptional regulatory sequences to control the expression of a cytotoxic gene in bladder tumor cells, resulting in the selective destruction of this cell population. Expression vectors containing the diphtheria toxin A-chain (DT-A) gene were linked to hTER and hTERT transcriptional regulatory sequences, respectively. Inhibition of protein synthesis occurred in bladder and hepatocellular carcinoma cells transfected with the plasmids containing the DT-A gene under the control of the hTER or hTERT promoters in correlation with their activity. These studies support the feasibility of using hTER and hTERT transcriptional regulatory sequences for targeted patient-oriented gene therapy of human cancer.