Background: The role of P-glycoprotein (Pgp) in multidrug resistance (MDR) is uncontested. Expression of Pgp on hematopoietic cells has been correlated with CD34 expression. For acute myeloid leukemia, the prognostic value of Pgp for clinical response is at best equivalent to that of CD34. The current study investigated whether expression of CD34 can be associated with selection for drug resistance.
Methods: Several established MDR cell lines were screened by flow cytometry for expression of CD34. Human ovarian carcinoma cells (A2780), which simultaneously expressed CD34 and Pgp, were identified. Subsequent cloning resulted in a new cell line (A2780-Dx5c) that expressed CD34 in the absence of Pgp. Involvement of non-Pgp-mediated MDR mechanisms was assessed by immunohistochemistry (MRP and LRP), enzyme activity studies (glutathione pathway), cross-resistance patterns, and Northern blot (type II alpha topoisomerase).
Results: A2780-Dx5c was cross-resistant to doxorubicin, daunorubicin, idarubicin, and VP-16. However, unlike the Pgp-expressing cells, it was not cross-resistant to vincristine or amsacrine. The drug resistance was correlated with a decreased level of type II alpha topoisomerase in the A2780-Dx5c cell line compared with the parental cell line. No evidence was found of involvement of MRP, LRP, or the glutathione pathway with drug resistance in this cell line.
Conclusions: A new cell line of nonhematopoietic and nonvascular endothelial origin that expresses CD34 in association with selection for MDR was cloned. A study of MDR mechanisms in this cell line revealed that reduced type II alpha topoisomerase levels were likely responsible for the MDR observed. A study of the causal relation between the selection of drug resistance and the expression of CD34 may provide insight into why CD34 correlates with poor clinical response in patients with acute myeloid leukemia.