Decitabine effect on human tumor expression of various transporters

Abstract

2540 Background: We reported that immunohistochemistry (IHC) expression of the platinum/copper transporter CTR1 in human tumors correlated inversely with DNA methylation and was increased by the DNA demethylating agent decitabine (D. Stewart et al, Proc ASCO 2008). Decitabine also increased expression of folate transporters in platinum-resistant cell lines that have decreased expression of folate transporters and of small GTPases such as RHOA that regulate endocytosis (D Shen et al. Br J Cancer 2004). Methods: Tumors were biopsied pre decitabine and on cycle 1 day 12 in 31 patients with refractory malignancies in a phase I study of decitabine given days 1–5 ± 8–12 each cycle. We used IHC to assess the folate carriers FOLR1 and RFC1, the glucose transporter GLUT4 and the endocytosis regulating small GTPase RHOA. Scores of 0–300 were calculated by multiplying staining intensity (0–3) by % cells staining. LINE assays were used to assess % global DNA methylation. Results: DNA methylation did not correlate with FOLR1, RFC1 and GLUT4 scores but did correlate inversely with RHOA (r= -0.58, p=0.006). Median tumor IHC scores post vs pre decitabine were 80 vs 80 (range, 0–270 vs 0–210, p=0.89) for FOLR1, 90 vs 90 (range, 15–300 vs 0–300, p=0.17) for RFC1, 0 vs 0 (range 0- 140 vs 0–70, p=0.61) for GLUT4, and 77.5 vs 50 (range, 0–210 vs 0–210, p=0.03) for RHOA. If only tumors with pre decitabine scores <150 were included, post vs pre RFC1 differences were significant (95 vs 80, p=0.004). Outcomes were similar whether or not 4 melanoma patients (in whom melanin pigment decreased the reliability of IHC scoring) were included. Conclusions: As previously noted with the copper/platinum transporter CTR1, treatment with the DNA demethylating agent decitabine was associated with a significant increase in tumor expression of the endocytosis regulator RHOA in resistant human tumors. Expression of the folate transporter RFC1 was also increased if only patients with levels that were initially low were included. This suggests that decitabine should be tested for its ability to increase uptake of chemotherapy in resistant tumors. Promoter methylation for these transporters has not yet been assessed. Supported in part by NIH grant UO1 CA062461–10 & R21 CA112895–01A1. No significant financial relationships to disclose.