3-deazaneplanocin A, a histone methyltransferase inhibitor, improved the chemoresistance induced under hypoxia in melanoma cells

One of common characteristics of solid tumors is low O2 level, so-called hypoxia, which plays a critical role in chemoresistance. Epigenetic mechanism such as DNA methylation and histone modification is involved in cancer development and progression. There is ample evidence that epigenetic drugs reversed acquired chemoresistance in cancer cells under normal O2 level, normoxia. However, it remains unknown whether epigenetic drugs improve acquired chemoresistance under hypoxia. The aim of our study was to investigate whether epigenetic drugs can improve the chemoresistance induced under hypoxia in cancer cells. In murine melanoma B16-BL6 (B16) cells, the culture under hypoxia, 1%O2 caused the elevated expression of hypoxia-inducible factor-1α (HIF-1α) and its target genes. The chemoresistance to 7-ethyl-10-hydroxycamptothecin (SN-38, the active metabolite of irinotecan) was also acquired under hypoxia in B16 cells. In addition, as epigenetic mechanisms, the protein expression of the enhancer of zeste homolog 2 (EZH2), histone methyltransferase and its target histone H3 trimethylation at lysine 27 (H3K27Me3) level increased under hypoxia. The induction of H3K27Me3 under hypoxia was suppressed by EZH2 siRNA and 3-deazaneplanocin A (DZNep), an EZH2 inhibitor. Furthermore, both EZH2 siRNA and DZNep significantly reduced the cell viability after SN-38 treatment and improved the chemoresistance to SN-38 under hypoxia. These results indicated that the chemoresistance to SN-38 under hypoxia would arise from epigenetic mechanism, H3K27Me3 elevation due to EZH2 induction. In conclusion, a histone methyltransferase EZH2 inhibitor, DZNep was capable of tackling acquired chemoresistance via the suppression of histone methylation induced under hypoxic tumor microenvironment.

Relationship between the isoniazid-resistant mutation katGS315T and the prevalence of MDR-/XDR-TB in Osaka, Japan

OBJECTIVE

To determine the prevalence of katGS315T mutations in isoniazid (INH) resistant Mycobacterium tuberculosis and to elucidate the association of katGS315T mutations with the prevalence of multidrug-resistant tuberculosis (MDR-TB).

DESIGN

From 2001 to 2004, 1655 isolates from all newly registered patients who visited the Osaka Prefectural Medical Centre for Respiratory and Allergic Diseases were tested for drug susceptibility. Genotyping was performed using insertion sequence (IS) 6110-restriction fragment length polymorphism (RFLP) in 1629 of 1655 (98.4%) cases. All 145 isolates of INH-resistant M. tuberculosis, including MDR strains, were tested to detect the katGS315T mutation.

RESULTS

Five hundred and sixty isolates (34.4%) shared an RFLP pattern. Of the 145 INH-resistant isolates, 18/48 (37.5%) isolates belonging to the RFLP cluster had katGS315T and 23/97 (23.7%) did not have the mutation. Of the 66 MDR-TB cases, 18/29 (62.1%) isolates belonging to the RFLP cluster had katGS315T and 11/37 (29.7%) did not have the mutation. Of the 29 extensively drug-resistant (XDR) TB cases, 17/21 (80.9%) isolates belonging to the RFLP cluster had katGS315T and 3/8 (37.5%) did not have the mutation.

CONCLUSION

The clustering rate by IS6110-RFLP was very high among MDR-/XDR-TB isolates with katGS315T. Our study indicates a strong correlation between the katGS315T mutation and the transmission dynamics of MDR-TB, and especially XDR-TB.