INDUCTION OF CYCLOPHOSPHAMIDE-RESISTANCE BY ALDEHYDE-DEHYDROGENASE GENE-TRANSFER

The identification of genes inducing resistance to anticancer chemothe rapeutic agents and their introduction into hematopoietic cells repres ents a promising approach to overcome bone marrow toxicity, the limiti ng factor for most high-dose chemotherapy regimens. Because resistance to cyclophosphamide has been correlated with increased levels of expr ession of the aldehyde-dehydrogenase (ALDH1) gene in tumor cell lines in vitro, we tested whether ALDH1 overexpression could directly induce cyclophosphamide resistance. We have cloned a full-length human ALDH1 cDNA and used retroviral vectors to transduce it into human (U937) an d murine (L1210) hematopoietic cell lines that were then tested for re sistance to maphosphamide, an active analogue of cyclephosphamide. Ove rexpression of the ALDH1 gene resulted in a significant increases in c yclophosphamide resistance in transduced L1210 and U937 cells (50% inh ibition concentration [IC50], approximate to 13 mu mol/L). The resista nt phenotype was specifically caused by ALDH1 overexpression as shown by its reversion by disulfiram, a specific ALDH1 inhibitor, ALDH1 tran sduction into peripheral blood human hematopoietic progenitor cells al so led to significant increases (4- to 10-fold; IC50, approximate to 3 to 4 mu mol/L) in cyclophosphamide resistance in an in vitro colony-f orming assay. These findings indicate that ALDH1 overexpression is suf ficient to induce cyclophosphamide resistance in vitro and provide a b asis for testing the efficacy of ALDH1 gene transduction to protect bo ne marrow cells from high-dose cyclophosphamide in vivo. (C) 1996 by T he American Society of Hematology.