All- trans-retinoic acid increases cytotoxicity of 1-beta-D-arabinofuranosylcytosine in NB4 cells.
OBJECTIVE
Clinically, the benefits of combining all- trans-retinoic acid (ATRA) with chemotherapy have been well documented in the treatment of acute promyelocytic leukemia (APL). Changes in nucleoside transporter expression and activity have been shown to occur in NB4 cells in vitro following treatment with ATRA. In this study we investigated whether ATRA treatment increases sensitivity to ara-C in NB4 cells. Specifically, we examined the role of ATRA-associated changes in nucleoside transporter expression and activity in eliciting ara-C cytotoxicity.


METHODS
Cellular uptake of [(3)H]-ara-C and nucleoside transporter abundance were determined in untreated cells and cells treated with 1 microM ATRA for 12-72 h using an inhibitor and oil stop procedure, and an equilibrium [(3)H]-NBMPR binding assay, respectively. Cytotoxicity of ara-C and the apoptotic response prior to and following ATRA treatment were determined using the MTT viability assay and the TUNEL assay, respectively.


RESULTS
ATRA treatment increased ara-C cytotoxicity and potency, ara-C transport, and augmented ara-C-induced apoptosis. The combination effect was supraadditive under some conditions and sequence-dependent whereby the maximum effect was seen when the addition of ATRA preceded the addition of ara-C, and when ara-C administration closely followed ATRA administration.


CONCLUSIONS
The ATRA-induced increase in cytotoxicity of ara-C was, in part, the result of an increase in the functional expression of nucleoside transporters, and a role for bcl-2 was also indicated. Our results would suggest that timing of ara-C therapy should be tied to maximal es transporter expression, which is likely to be 24 h after ATRA treatment begins. It remains to be seen whether the response in the clinic can be further enhanced in APL by taking advantage of ara-C transporter regulation by ATRA.
Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
S A
SA
Flanagan
K A
KA
Meckling
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D016923:Cell Death; D003561:Cytarabine / Q000494:pharmacology*; D004347:Drug Interactions; D019254:Genes, bcl-2; D015473:Leukemia, Promyelocytic, Acute / Q000473:pathology*; D033703:Nucleoside Transport Proteins / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D033703:Nucleoside Transport Proteins; D003561:Cytarabine; D014212:Tretinoin