Glucocorticoid-induced apoptosis and treatment sensitivity in acute lymphoblastic leukemia of children

Comparision of the apoptotic effects on lymphoblasts and on increase of myeloid lineage cells of a short-time, high-dose methylprednisolone and the conventional-dose prednisolone treatments in children with acute lymphoblastic leukemia

The authors compare the apoptotic effect on the lymphoblasts and the proliferative effect on the myeloid lineage cells of a short-course high-dose methylprednisolone (HDMP) and the conventional-dose prednisolone treatments in children with acute lymphoblastic leukemia (ALL). The patients were divided into 2 groups. Group I (n = 10) received HDMP (30 mg/kg/day for 7 days) in a single dose before 6 a.m. perorally. Group II (n = 10) received prednisolone (2 mg/kg/day for 7 days) in 3 doses. The apoptotic percentages of lymphpblasts and the percentages of blasts and myeloid lineage cells were determined after performing the bone marrow aspiration (BMA) at diagnosis on the 0th, 3rd, and 7th days of the treatments in all patients. The mean apoptotic percentages of the lymphoblasts on the 3rd day were significantly higher than those on the 0th and 7th days in both groups (p < .05). The highest apoptosis was determined on the 3rd day in group I. The mean percentages of the blast cells on the 7th day were significantly lower than those on the 0th and the 3rd days in both groups (p < .05). The lowest lymphoblast percentage was determined on the 7th day in group I. The mean percentages of the CD13+ and CD33+ cells on the 7th day were significantly higher than those on the 0th and the 3rd days in both groups (p < .05). The highest percentages of the CD13+ and CD33+ cells were found on the 7th day in group I. Prednisolone and HDMP showed no proliferative effect on the CD14+ cells. These findings indicate that a short-course HDMP treatment shows a more effective apoptosis on the lymphoblasts and on the increase of the myeloid lineage cells when compared to the prednisolone treatment. The authors suggest that HDMP may be used in the treatment of patients with ALL instead of prednisolone.

Glucocorticoid-induced apoptosis and glucocorticoid resistance: molecular mechanisms and clinical relevance

The ability of glucocorticoids (GC) to efficiently kill lymphoid cells has led to their inclusion in essentially all chemotherapy protocols for lymphoid malignancies. This review summarizes recent findings related to the molecular basis of GC-induced apoptosis and GC resistance, and discusses their potential clinical implications. Accumulating evidence suggests that GC may induce cell death via different pathways resulting in apoptotic or necrotic morphologies, depending on the availability/responsiveness of the apoptotic machinery. The former might result from regulation of typical apoptosis genes such as members of the Bcl-2 family, the latter from detrimental GC effects on essential cellular functions possibly perpetuated by GC receptor (GR) autoinduction. Although other possibilities exist, GC resistance might frequently result from defective GR expression, perhaps the most efficient means to target multiple antileukemic GC effects. Numerous novel drug combinations are currently being tested to prevent resistance and improve GC efficacy in the therapy of lymphoid malignancies.

Apoptosis in acute leukemia

In leukemias and malignant tumors the balance between apoptosis and cell proliferation is dysregulated. This review deals with the apoptosis in acute leukemia. There are several publications about the molecular basis of decreased apoptosis in acute lymphoid leukemia (ALL) and AML. However, there have been contradictory results. Different results are published about the correlation of the spontaneous and induced apoptosis in leukemia with prognosis. The potential causes of these contradictions are discussed.

Correlation of membrane glucocorticoid receptor levels with glucocorticoid-induced apoptotic competence using mutant leukemic and lymphoma cells lines

We have studied the presence and functional implications of membrane glucocorticoid receptor (mGR) in several wild type (WT) and mutant mouse lymphoid cell lines (nuclear transfer decrease, NT(-); nuclear transfer increase, NT(i); and receptorless, R(-)). Direct fluorescent antibody staining revealed large aggregates of mGR-specific fluorescing antigens in the plasma membrane of the WT and mGR-enriched (mGR(++)) S-49 cells. While R(-) cells totally lacked mGR, this receptor level was low in NT(-) and NT(i) groups. FACS analysis corroborated these results, showing a approximately 4-10-fold difference between the highest mGR levels (mGR(++)) and the R(-) and NT(i) cells. Membrane extracts were analyzed for mGR by immunoblotting. Multiple receptor forms, ranging in M(r) from 94,000 to > 200,000, were observed in the WT cells, while only smaller peptides (85,000-94,000) were found in NT(-) cells. No detectable immunoreactive bands were identified in either membrane or cytosol immunoprecipitates of NT(i) and R(-) cell groups. Within 48 h post dexamethasone exposure > 98% of WT and mGR(++) S-49 cells underwent apoptosis, compared to 0-30% in the mutant cells, albeit the total receptor number is two to three times higher in NT(i) compared to WT. These results suggest a better correlation between the quantity and quality of mGRs (rather than total cellular GRs) and the ability of glucocorticoids (GCs) to lyse lymphoid cells.

Expression of the Death Gene Bik/Nbk Promotes Sensitivity to Drug-Induced Apoptosis in Corticosteroid-Resistant T-Cell Lymphoma and Prevents Tumor Growth in Severe Combined Immunodeficient Mice

Members of the Bcl-2 gene family have been implicated in the regulation of cell death induced by cytostatic drugs. In some malignancies such as B-cell lymphoma, there is evidence that high expression of Bcl-2 is an independent negative prognostic marker and the overexpression of Bcl-2 has been shown to confer resistance to cytotoxic drugs by preventing drug-induced apoptosis. This function of Bcl-2 can be antagonized by apoptosis-promoting members of the Bcl-2 family. We previously showed that overexpression of Bax restores the chemosensitivity of Bax-deficient breast cancer cell lines. Therefore, we investigated whether the death-promoting Bcl-2 homologue Bik/Nbk can enhance cytostatic drug-induced apoptosis. As a model, we used the T-cell leukemia H9 (CD3+ and CD4+CD8−), which is resistant to corticosteroid-induced cell death and does not express endogenous Bik/Nbk. Sensitivity for drug-induced apoptosis was increased 10- to 39-fold in cells transfected with the full-length coding sequence of Bik/Nbk. In addition, apoptosis induced via CD95/Fas or heat shock was increased to a similar extent. These data show that Bik/Nbk, which, unlike Bax, carries only a BH3 but no BH1 or BH2 domain may be a target to enhance chemosensitivity. The complete suppression of tumor growth in a severe combined immunodeficient mouse xenotransplant model suggests that, in analogy to Bax, Bik/Nbk may function as a tumor suppressor gene.

Dysfunctional glucocorticoid receptor with a single point mutation ablates the CCAAT/enhancer binding protein-dependent growth suppression response in a steroid-resistant rat hepatoma cell variant

We used glucocorticoid-resistant and -sensitive hepatoma cell variants to characterize the mechanism of hepatoma cell resistance to the growth inhibitory effects of glucocorticoids. BDS1 hepatoma cells express transcriptionally active glucocorticoid receptors and undergo a stringent G1 cell cycle arrest in response to glucocorticoids that is dependent on the induced expression of the CCAAT/enhancer binding protein alpha (C/EBPalpha) transcription factor. In contrast, EDR1 hepatoma cells, which express normal levels of glucocorticoid receptors, fail to growth arrest or express C/EBPalpha when treated with glucocorticoids. Ectopic expression of wild-type rat glucocorticoid receptors into EDR1 cells restored the growth suppression response, suggesting a defect in the EDR1 receptor. DNA sequence analysis revealed a single point mutation causing a cysteine-to-tyrosine substitution at amino acid position 457 (C457Y-GR) in the zinc finger region of the glucocorticoid receptor that mediates both receptor-DNA and receptor-protein interactions. Glucocorticoid activation of the alpha1-acid glycoprotein (AGP) promoter, a liver acute-phase response gene, requires receptor-DNA binding as well as an interaction with C/EBPalpha. In contrast to the wild-type glucocorticoid receptor, ectopic expression of C/EBPalpha in EDR1 cells, or coexpression of C/EBPalpha along with the C457Y-GR into receptor-deficient EDR3 cells was required to partially restore glucocorticoid responsiveness of the AGP promoter by the EDR1 glucocorticoid receptor. Constitutive expression of the wild-type glucocorticoid receptor, but not the C457Y-GR mutant, was sufficient to restore the glucocorticoid growth suppression response to receptor-deficient EDR3 cells. Thus, we have identified a glucocorticoid-resistant hepatoma cell variant with a single point mutation in the zinc finger region of the glucocorticoid receptor gene that ablates the glucocorticoid growth suppression response and attenuates transcriptional activation of the AGP promoter.