ABSTRACT. The BCR/ABL fusion protein transforms myeloid stem cells. Both chronic myelogenous leukemias (CML) and a subset of acute lymphoblastic leukemias (ALL) are associated with the expression of BCR/ABL proteins. This knowledge has not yet been translated into any specific tool to control ABL driven neoplastic cells growth. CGP57148B is an ATP-competitive inhibitor of the ABL protein kinase; it has been shown to inhibit the kinase activity of ABL both in vitro and in vivo and to inhibit the growth of v-abl and bcr/abl transfectants, as well as the in vitro formation of bone marrow (BM)-derived colonies in the presence of growth factors in some CML patients. These studies were performed to investigate the activity of CGP57148B on the spontaneous proliferation of both fresh and cultured, leukemic and normal, BCR/ABL positive and negative cells, and to study its mechanism of action. Six cell lines derived from BCR/ABL+ leukemias (K562, BV173, KCL22, KU812, MC3, LAMA84), thirteen BCR/ABL negative lines, both neoplastic (KG1, SU-DHL- 1, U937, Daudi, NB4, NB4.306) and derived from normal cells (PHA blasts, LAK, fibroblasts, LCL, renal epithelial cells, endothelial cells, CD34+ cells), and 14 fresh leukemic samples were tested using a tritiated thymidine uptake assay. The in vivo phosphorylation of the BCR/ABL protein was evaluated by western blot, while apoptosis was detected by the annexin V/propidium binding test. The induction of differentiation was assayed by immunofluorescence using multiple antibodies.

All six BCR/ABL+ lines showed a dose dependent inhibition of their spontaneous proliferative rate, which was not accompanied by differentiation. The treatment caused, within minutes, dephosphorylation of the BCR/ABL protein, followed in 16-24 hours by a decrease in cycling cells and induction of apoptosis. No significant inhibition of DNA synthesis was observed in any BCR/ABL negative normal or neoplastic line at concentrations less than or equal to 3 micromolar, with the exception of fibroblasts and CD34 cells. Proliferation inhibition was observed also when using fresh samples obtained from two Ph+ ALL and 12 consecutive CML patients. Induction of apoptosis was observed in these samples too.

The activity of CGP57148B can be monitored in ex vivo isolated or cultured cells using a simple and reproducible assay, without the need for exogenously added growth factors. This molecule possibly exerts its effects through the inhibition of the kinase activity of BCR/ABL and the subsequent initiation of apoptosis, without inducing cell differentiation. Some normal cells are also affected.

These data support the use of CGP57148B in initial clinical studies; possible toxic effects on BM and fibroblast-derived cells will have to be closely monitored. The in vivo monitoring of patients will have to be focused on the induction of apoptosis in leukemic cells.

Keywords: BCR/ABL, CML, ALL, tyrosine kinase inhibitors, apoptosis.

Reprint requests to: Carlo Gambacorti, M.D., Division of Experimental Oncology D, Istituto Nazionale Tumori, Via Venezian 1, 20133 Milano, Italy, phone: 392239-0818, fax: 392239-0764, e-mail: gambacorti@istitutotumori.mi.it.

ABSTRACT: Gaucher disease, the most common glycolipid storage disease, is caused by glucocerebrosidase deficiency, resulting in accumulation of glucocerebrosides within the macrophages of the reticuloendothelial system. The disease is characterized by great phenotypic heterogeneity, which can be explained only in part by the various mutations in the glucocerebrosidase gene, and by the amount of storage material in affected organs and tissues. Therefore, it has been postulated that some of the biochemical and clinical features may be related to the fact that "Gaucher" cells, as activated macrophages, express and release cytokines such as IL-1beta, IL-8, IL-6 and TNF-alpha which play a role in different physiological processes. In the present study, cytokine mRNA expression was measured in monocytes isolated from Gaucher patients and from healthy controls, using RT-PCR methodology with semiquantitative analysis. We found significantly increased expression of IL-1beta mRNA, as well as a trend to elevated TNF- alpha mRNA in Gaucher patients relative to healthy individuals. There were no statistically significant differences between Gaucher disease patients and controls with respect to two other tested cytokines (IL-6 and IL-8).

Keywords: Gaucher disease, glucocerebroside, glucocerebrosidase, cytokine, TNFalpha, IL-1beta, monocytes/macrophages, polymerase chain reaction, mRNA expression.

Reprint requests to: Ari Zimran, M.D., Gaucher Clinic, Shaare Zedek Medical Center, P.O. Box 3235, Jerusalem 91031, Israel, phone: 972-2-6555330 or 972-2-6555673, fax: 972-2-6795553, e-mail: zimran@md2.huji.ac.il.