The Retinoid Derivative Drug, Acitretin, Modulates CD38 Expression on MEC-1 Cells and Primary Chronic Lymphocytic Leukemia (CLL) Cells and Reduces Migration in Response to the Chemokine CXCL12

Abstract

Background: CD38 is a cell surface receptor and ectoenzyme expressed in a variety of haematological malignancies. In CLL, CD38 expression is a marker of poor prognostic disease and is now attracting growing interest as a target molecule for anti CLL therapy.Retinoids modulate CD38 expression due to the presence of the Retinoic Acid Response Element (RARE) DNA sequence in the promotor region of the CD38 gene. In this study we demonstrate that the retinoic acid derivative, acitretin, upregulates the expression of CD38 on the MEC-1 cell line and on primary CLL cells from CD38 positive patients. We propose that, by doing so, Acitretin may render these cells more susceptible to the actions of anti CD38 monoclonal antibody drugs and thus have a potential role as an adjunct to such therapies.Methods: Primary CLL cells were freshly isolated from whole blood of CLL patients using the FICOLL density centrifugation technique. The CLL like cell line MEC-1 was obtained from DSMZ, Germany.MEC-1 cells and cells from three CD38 negative and five CD38 positive patients were treated with 10micM acitretin for 24, 48 and 72hrs. CD38 expression was measured by FACS analysis at baseline and at the different time points. Results are expressed as fold increase in Mean Fluorescence Intensity (MFI).Migration assays were performed using 2x10^6 cells per well incubated with 10microM acitretin overnight in 1%FBS. Cells were subsequently transferred to chamber inserts overlying 10%FBS media containing 200ng/ml CXCL12 in all wells, except negative controls. Cells were then allowed to migrate for 4hrs. Migration was calculated as percentage of cells in lower chamber to upper chamber.Results: Acitretin increased the expression of CD38 on MEC-1 cells by a mean of 7.4 fold and on cells from CD38 positive patients by a mean of 3.4 folds (n=5). Acitretin, however, did not modulate CD38 expression levels on primary CLL cells from CD38 negative patients (n=3).Migration of primary CLL cells from 11/14 patients toward the CXCL12 chemokine was reduced in response to Acitretin treatment as compared to untreated controls. Mean migration of treated cells was 12.3% versus 27.3% mean migration in untreated controls.Conclusion: Our findings re-affirm the potent effect of retinoid drugs as upregulators of CD38 expression and suggest that their use in CLL therapeutics in conjunction with anti CD38 monoclonal antibodies should be explored. We also propose that acitretin appears to exert a favourable blocking effect on CLL cell migration towards micro-environmental chemokines such as CXCL12, warranting further evaluation. DisclosuresMurphy:Celgene: Honoraria.