SN-38, an active metabolite of irinotecan, inhibits transcription of nuclear factor erythroid 2-related factor 2 and enhances drug sensitivity of colorectal cancer cells.

Nuclear factor erythroid 2-related factor 2 (Nrf2) significantly contributes to drug resistance of cancer cells, and Nrf2 inhibitors have been vigorously pursued. Repurposing of existing drugs, especially anticancer drugs, is a straightforward and promising strategy to find clinically available Nrf2 inhibitors and effective drug combinations. Topoisomerase inhibitors SN-38 (an active metabolite of irinotecan), topotecan, mitoxantrone, and epirubicin were found to significantly suppress Nrf2 transcriptional activity in cancer cells. SN-38, the most potent one among them, significantly inhibited the transcription of Nrf2, as indicated by decreased mRNA level and binding of RNA polymerase II to NFE2L2 gene, while no impact on Nrf2 protein or mRNA degradation was observed. SN-38 synergized with Nrf2-sensitive anticancer drugs such as mitomycin C in killing colorectal cancer cells, and irinotecan and mitomycin C synergistically inhibited the growth of SW480 xenografts in nude mice. Our study identified SN-38 and three other topoisomerase inhibitors as Nrf2 inhibitors, revealed the Nrf2-inhibitory mechanism of SN-38, and indicate that clinically feasible drug combinations could be designed based on their interactions with Nrf2 signaling.

[Characterization of telomerase regulation association gene TRAP and cancer biology].

OBJECTIVE: To investigate expression of TRAP in human tumors and correlativity between TRAP and hTERT and to explore the role of TRAP in tumorigenesis. METHODS: TRAP was expressed in E. coli. and polyclonal antibody was prepared by immunization of New Zealand rabbits. Expressions of TRAP gene and hTERT in human tumors were analyzed by immunohistochemistry. The eukaryotic expression vectors of TRAP were constructed and transferred stably into HeLa cells to be analysed with Northern blot, TRAP-PCR ELISA, growth curve, nude mouse transplantation. RESULTS: Polyclonal antibody was obtained from New Zealand rabbits immunized with TRAP fuse protein, which was inducibly expressed in E. coli., and its specificity was verified in Western blot. TRAP staining was detected in 213 (86.2%) of 247 malignant tumors. On the contrary, TRAP in all tissues adjacent to tumors was negative. There is a obvious difference between borderline, pre-cancerous and benign lesion in the expression of TRAP. Furthermore, hTERT staining was conducted and its result was consistent with that of TRAP. Up-regulation and down-regulation of hTERT expression and telomerase activity were observed respectively in HeLa cells transfected stably with sense and antisence TRAP recombination. Increased proliferation presented in the former and growth inhibition in the latter. Besides, in nude mice, tumorigenecity of sense TRAP-transfected HeLa cells was enhanced while tumor growth of antisense TRAP-transfected HeLa cells was retarded. CONCLUSION: The expression of TRAP, which could be detected in most of human cancers and part of pre-cancerous lesions, was correlated with expression of hTERT. The status of TRAP expression could regulate telomerase activity and present effects on growth and tumorigeneity of cancer cells. This suggests that TRAP is involved in human tumorigenesis through regulation of telermarase activity.