Post-Transplant Methotrexate Administration Leads to Improved Curability of Mice Bearing a Mammary Tumor Transplanted with Marrow Transduced with a Mutant Human Dihydrofolate Reductase cDNA

Abstract

To test the concept that protection of bone marrow progenitor cells via introduction of a drug resistance gene would allow larger and curative doses of chemotherapy to be administered, we used mice bearing a transplanted breast cancer as a model system. Mice bearing the E0771 tumor were treated with lethal doses of cyclophosphamide (CPA) and rescued from toxicity by administration of bone marrow transduced with a mutant dihydrofolate reductase (DHFR) cDNA (Ser-31) in a retroviral construct. Animals receiving marrow not transduced with mutant DHFR cDNA died from methotrexate (MTX) toxicity, whereas mice transduced with mutant DHFR cDNA containing marrow were able to tolerate MTX treatment post-transplant; 44% of the mice had no demonstrable tumor when sacrificed on day 52. Another control group of mice treated with CPA and transplanted but not treated with MTX post-transplant succumbed to tumor regrowth. These data provide a strong rationale for the use of drug resistance genes to protect marrow from drug toxicity because the increase in dose tolerated may result in an improved cure rate of chemosensitive tumors.

Selection of drug-resistant transduced cells with cytosine nucleoside analogs using the human cytidine deaminase gene

“…It was reported that mice transplanted with DHFR -transduced BMCs had evidence of improved curability and reduced drug toxicities to methotrexate (MTX ), an antifolate drug. 8 Trimetrexate and a nucleoside transport inhibitor ( to prevent thymidine rescue ) also showed promising results for in vivo selection in DHFR transplanted mice. 15 However, only modest results were obtained more recently in mice using methotrexate alone as the selective agent.…”

Retroviral transfer and long-term expression of human cytidine deaminase cDNA in hematopoietic cells following transplantation in mice

“…The data presented here using the MFG-CD construct clearly demonstrate the feasibility of obtaining in vivo long-term persistence of CD and long-1549 term expression of human CD in hematopoietic cells. We plan to transplant CD transduced marrow cells into tumor-bearing mice to determine if curability with cytosine nucleoside analogues can be obtained using chemoprotection as reported by Zhao et al 24 for the DHFR gene and methotrexate therapy. Future improvements in vectors to increase efficiency of transduction and expression of CD in human hematopoietic cells will facilitate the use of this gene for chemoprotection to increase the therapeutic effectiveness of cytosine nucleoside analogues in cancer therapy.…”

Drug selection of MDR1-transduced hematopoietic cells ex vivo increases transgene expression and chemoresistance in reconstituted bone marrow in mice

“…49 DHFR-transduced hematopoietic cells can be enriched in vivo following administration of antifolates. 50,51 Although taxol selection has been shown to result in enrichment of MDR1-transduced bone marrow cells, 19 …”