The literature describes the role of DNA methylation in regulation of tumour suppressor genes, DNA repair genes, but not much attention has been paid to drug metabolising enzymes (DMEs). Some evidence has been reported and includes methylation of the promoter regions of CYP450 and ABC transporters. Cotreatment with decitabine (DAC) and paclitaxel (PAC) has been reported in several studies, but few of these have reported in a focused manner on the effect on DMEs. As a consequence, the major DMEs involved in the detoxification of PAC (namely ABCB1, CYP2C8 and CYP3A4) were investigated. The aldehyde dehydrogenase enzymes (ALDH1A1, ALDH2 and ALDH3A1) were also explored, as they have recently been shown to play a chemo-protective role against taxanes. Analysis of the CpG island methylation level indicated that all the above-mentioned DMEs were densely methylated and that treatment of MCF-7 cells with DAC for 24 h resulted in a decrease in methylation within the gene promoter region. Furthermore, correlation of decrease in DNA methylation with increase in mRNA level of ABCB1, CYP3A4, ALDH2 and ALDH3A1 was observed, but not for CYP2C8 and ALDH1A1. However, only the ABCB1 protein level was shown to significantly increase. Chemosensitivity of DAC combined with PAC was tested in MCF-7 cells: treatment with DAC for 24 h was followed by PAC exposure on days 4, 6 or 8. Evaluation of the cotreatment on cell survival demonstrated that the cytotoxic potential of PAC was reduced proportionally to the exposure time to DAC before PAC treatment, suggesting that ABCB1 protein confers chemo-protection on the cells. To investigate whether this resistance was applicable to other taxanes with proven efficacy against MDR-resistant cells, the preclinical agent Lx2-32c (aziditaxel) was evaluated. Lx2-32c also lost potency similar to PAC, indicating that ABCB1 is responsible for loss of activity of these two taxanes. The same experiments were also carried out in HeLa cells as they were shown to contain low level of DNA methylation of the above-mentioned DME genes including the ABCB1 gene. DAC treatment did not lead to significant reactivation at protein level and cotreatment of DAC and PAC produced a synergistic effect on cell killing. In conclusion, our data demonstrate that cotreatment of DAC and PAC can produce a synergistic effect, but that it is affected by the re-expression of DMEs. Our observations provide useful information for clinical evaluation of combination strategies comprising DAC and PAC, and chemotherapeutics in general that are affected by DMEs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4088. doi:1538-7445.AM2012-4088