Topoisomerase I Inhibitors in the Treatment of Primary CNS Malignancies: An Update on Recent Trends
ABSTRACT High grade primary CNS gliomas hold some of the worst prognoses of any malignancy, with the vast majority of patients dying within two years of diagnosis, even with aggressive modern treatments. Surgical resection and radiotherapy are cornerstones of treatment when possible. In spite of many years of research, only recently has management with chemotherapy been able to prolong survival in patients with high grade gliomas, albeit only modestly at best. Topoisomerase I (TOP1) inhibitors target an enzyme critical for DNA replication and cell-cycle progression; they cross the blood-brain barrier and have antitumor activity against glioblastoma cells in vitro. The most frequently associated toxicities are neutropenia and diarrhea, but are often manageable. The two most used agents are irinotecan and topotecan. Due to enhanced cytochrome CY3A4/5 enzyme activity, irinotecan dose must be adjusted with concomitant enzyme-inducing antiepileptic drug usage; the data is less clear regarding the effects on topotecan. Clinical trials in patients with recurrent malignant glioma have evaluated TOP1 inhibitors as monotherapy and in combination with other agents. There is evidence for using topotecan with radiotherapy. Irinotecan has limited efficacy as monotherapy, but shows promise in combination with other agents, particularly temozolomide and bevacizumab. Newer generation TOP1 inhibitors are currently being evaluated in phase I trials. TOP1 inhibitors show promising activity in patients with primary CNS malignancies and warrant further study.
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ABSTRACT: Many anticancer drugs reduce the integrity of DNA, forming strand breaks. This can cause mutations and cancer or cell death if the lesions are not repaired. Interestingly, DNA repair-deficient cancer cells (e.g., those with BRCA1/2 mutations) have been shown to exhibit increased sensitivity to chemotherapy. Based on this observation, a new therapeutic approach termed 'synthetic lethality' has been developed, in which radiation therapy or cytotoxic anticancer agents are employed in conjunction with selective inhibitors of poly(ADP-ribose)polymerase-1 (PARP-1). Such combinations can cause severe genomic instability in transformed cells resulting in cell death. The synergistic effects of combining PARP-1 inhibition with anticancer drugs have been demonstrated. However, the outcome of this therapeutic strategy varies significantly between cancer types, suggesting that synthetic lethality may be influenced by additional cellular factors. This review focuses on the outcomes of the combined action of PARP-1 inhibitors and agents that affect the activity of DNA topoisomerases.Future medicinal chemistry 01/2012; 4(1):51-72. DOI:10.4155/fmc.11.175 · 4.00 Impact Factor
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ABSTRACT: Gliomas are the most common tumors in the central nervous system. This study aims to investigate the expressions of transforming growth factor-β1 (TGF-β1) and epithelial cadherin (E-cadherin) in human brain glioma tissues and the correlation between their expressions with clinical pathological features and clinical significance. The expressions of mRNA or protein of TGF-β1 and E-cadherin were detected by using reverse transcription polymerase chain reaction (RT-PCR) and Western blot in these tissues. Positive rates of the expression of TGF-β1 and E-cadherin were 62.9 % and 38.6 % in brain tissues of glioma patients. The expressions of mRNA or protein for TGF-β1 in brain glioma tissues were significantly higher than that in normal brain tissues (p < 0.01). Their expressions in well-differentiated glioma brain tissues were lower than those in poorly differentiated glioma brain tissues (p < 0.01). A negative correlation was found between TGF-β1 and E-cadherin in brain glioma tissues (r = -0.302, p < 0.011). The cell numbers of C6 glioma through Transwell chambers were decreased significantly (p < 0.01), and the expression of TGF-β1 was downregulated significantly (p < 0.01). However, the expression of E-cadherin was upregulated significantly (p < 0.01) after transfecting TGF-β1 siRNA. The expression changes of TGF-β1 and E-cadherin may be related to the emergence and the development of glioma. Downregulation of TGF-β1 expression using siRNA can decrease the invasive capability of C6 glioma cells.Tumor Biology 04/2012; 33(5):1477-84. DOI:10.1007/s13277-012-0398-z · 3.61 Impact Factor
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ABSTRACT: PURPOSE: The current treatment strategies for glioblastoma have limited health and survival benefits for the patients. A common obstacle in the treatment is chemoresistance. A possible strategy to evade this problem may be to combine chemotherapeutic drugs with agents inhibiting resistance mechanisms. The aim with this study was to identify molecular pathways influencing drug resistance in glioblastoma-derived cells and to evaluate the potential of pharmacological interference with these pathways to identify synergistic drug combinations. METHODS: Global gene expressions and drug sensitivities to three chemotherapeutic drugs (imatinib, camptothecin and temozolomide) were measured in six human glioblastoma-derived cell lines. Gene expressions that correlated to drug sensitivity or resistance were identified and mapped to specific pathways. Selective inhibitors of these pathways were identified. The effects of six combinations of inhibitors and chemotherapeutic drugs were evaluated in glioblastoma-derived cell lines. Drug combinations with synergistic effects were also evaluated in non-cancerous epithelial cells. RESULTS: Four drug combinations had synergistic effects in at least one of the tested glioblastoma-derived cell lines; camptothecin combined with gefitinib (epidermal growth factor receptor inhibitor) or NSC 23766 (ras-related C3 botulinum toxin substrate 1 inhibitor) and imatinib combined with DAPT (Notch signaling inhibitor) or NSC 23766. Of these, imatinib combined with DAPT or NSC 23766 did not have synergistic effects in non-cancerous epithelial cells. Two drug combinations had at least additive effects in one of the tested glioblastoma-derived cell lines; temozolomide combined with gefitinib or PF-573228 (focal adhesion kinase inhibitor). CONCLUSION: Four synergistic and two at least additive drug combinations were identified in glioblastoma-derived cells. Pathways targeted by these drug combinations may serve as targets for future drug development with the potential to increase efficacy of currently used/evaluated chemotherapy.Cancer Chemotherapy and Pharmacology 06/2013; 72(2). DOI:10.1007/s00280-013-2197-7 · 2.57 Impact Factor