The apoptogenic response of human myeloid leukaemia cell lines and of normal and malignant haematopoietic progenitor cells to the proteasome inhibitor PSI

Abstract

Summary. Degradation of several intracellular proteins involved in cell cycle control and tumour growth is regulated by the ubiquitin-dependent multicatalytic protease complex (proteasome). We report that proteasome inhibitor Z-Ile-Glu(OtBu)-Ala-Leucinal (PSI) was cytotoxic on most human myeloid leukaemia cell lines at IC 50 doses ranging from 5 to 25 nmol/l. Additionally, PSI pretreatment enhanced cytotoxicity by taxol and cisplatinum. PSI was more active on leukaemic than on normal CD34 1 bone marrow progenitors because the 50% growth inhibition of colony-forming unit granulocyte macrophage (CFU-GM) from cases of chronic myelogenous leukaemia (CML) and normal subjects was achieved by 15 nmol/l and 50 nmol/l PSI respectively. PSI killed cells by apoptosis as revealed by ultrastructural changes, nuclear DNA fragmentation, cleavage of poly (ADP-ribose) polymerase (PARP) and of b-catenin, and was antagonized by ectopic expression of Bcl-2 but not by inactivating mutations of p53. This event was associated with a slight accumulation of Bcl-2, a decrease of Bax but no changes in Bcl-X L protein expression at any time point. In Ph 1 cell lines BCR-ABL protein was only down-regulated after 48 h of treatment with 10 nmol/l PSI. Altogether, these results indicate that PSI, alone or in association with other cytotoxic agents, has anti-tumour activity against myeloid malignancies and is more effective on leukaemic than on normal haematopoietic progenitor cells.

Sensitivity of human multiple myelomas and myeloid leukemias to the proteasome inhibitor I

“…KMS12, KMS26, KMS27 and KMS34 showed an intermediate sensitivity, whereas RPMI 8226, IM9, SULTAN and ARH77 cells were the least sensitive (IC 50 ranging between 95 and 470 at 72 h). In accordance with our previous findings, 9 PSI was highly cytotoxic on HL60, KG1a, RWLeu4 and AR230, and far less on K562 (Table 1b). When the effect of PSI in these cells was compared with PS-341, the former inhibitor resulted more toxic on the AMLs (KG1a and HL60) while the latter was more toxic, at least after 24 h treatment, on CMLs (K562, RWLeu4 and AR230) (Table 1b).…”

“…9 In the present study, we asked whether MM cells, which are remarkably sensitive to the proteasome inhibitor PS-341, 19,20 are equally sensitive to PSI. Of a panel of 11 MM cell lines tested in time-and dose-dependent assays (Table 1a) CMA01, U266 and H929 cells were, already at 24 h, the most sensitive to PSI.…”

“…8 Several compounds, including synthetic aldehydes (MG-132, PSI, lactacystin, NLVS, epoxomicin, eponemycin, TMC-95A) and boronic acids (PS-341), inhibit the proteasome by binding reversibly or irreversibly to active sites of the 20S core and display varying levels of specificity and metabolic stability. While not all cell types similarly respond to proteasome inhibition, quite invariably transformed cells are far more sensitive to proteasome blockade than normal cells 9,10 and this sensitivity correlates with active cell proliferation. 6 Interest in the clinical development of proteasome inhibitors has arisen from recent findings on the dipeptidyl boronic acid derivative PS-341 or Bortezomib, the first such agent to progress to clinical trials.…”

“…1 Accordingly, a phase III trial is now ongoing in patients with multiple myeloma (MM) at relapse, which becomes refractory to many conventional chemotherapies. 11 The proteasome inhibitors in combination with chemotherapeutic agents or histone deacetylase inhibitors, produce synergistic effects 9,12 that can be exploited to overcome chemoresistance in leukemic cells. Here, we report that proteasome inhibitor I (PSI) induces high level of apoptotic death and enhances the effect of cytotoxic drugs in a number of myeloid cell lines at nanomolar concentration.…”

FoxO tumor suppressors and BCR–ABL-induced leukemia: A matter of evasion of apoptosis

“…lactacystin and tripeptide aldehydes) as bortezomib, induce apoptosis in varying capacities in different leukemic cell lines, including ones that are BCR-ABL-positive, such as AR230 and K562. In fact, proteasome inhibition resulted in decreased BCR-ABL expression, providing one mechanism by which proteasome inhibitors can exert their growth inhibitory effects in this context [230,231].…”