Blood, Vol. 95 No. 7 (April 1), 2000:
pp. 2356-2363
Retroviral transfer of the hENT2 nucleoside transporter cDNA
confers broad-spectrum antifolate resistance in murine bone marrow
cells
Divyen H. Patel,
James A. Allay,
Judith A. Belt, and
Brian P. Sorrentino
From the Division of Experimental Hematology and the Departments of
Molecular Pharmacology and Biochemistry, St. Jude Children's Research
Hospital, Memphis, TN.
Antifolate drugs such as methotrexate are commonly used in cancer
chemotherapy. It may be possible to increase the antitumor activity of
antifolates by the coadministration of drugs that inhibit nucleoside
transport, thereby blocking the capacity of tumor cells to salvage
nucleotide precursors. An important limitation of this approach is
severe myelosuppression caused by many of these drug combinations. For
this reason, we have developed a gene therapy strategy to protect bone
marrow cells against combined treatment with antifolates and
nitrobenzylmercaptopurine riboside (NBMPR), a potent inhibitor of the
es nucleoside transporter. A retroviral vector (MeiIRG) was
constructed that expressed the NBMPR-insensitive ei
transporter, hypothesizing that transduced bone marrow cells would
survive drug treatment because of the preservation of nucleoside
salvage pathways. In vitro clonogenic assays confirmed that the MeiIRG
vector did protect myeloid progenitors against the toxic effects of 3 different antifolates when each was combined with NBMPR. On testing
this system in vivo, decreased myelosuppression was observed in mice
transplanted with MeiIRG-transduced bone marrow cells and subsequently
treated with trimetrexate and NBMPR-P. In these mice, significant
increases were noted in absolute neutrophil count nadirs, reticulocyte
indices, and the numbers of myeloid progenitors in the bone marrow.
Furthermore, a survival advantage was associated with transfer of the
MeiIRG vector, indicating that significant dose intensification was
possible with this approach. In summary, the MeiIRG vector can decrease
the toxicity associated with the combined use of antifolates and
NBMPR-P and thereby may provide a strategy for simultaneously
sensitizing tumor cells while protecting hematopoietic cells.
