Julian Topaly

Synergistic activity of the new ABL-specific tyrosine kinase inhibitor STI571 and chemotherapeutic drugs on BCR-ABL-positive chronic myelogenous leukemia cells.

The ABL-specific tyrosine kinase inhibitor STI571 (formerly CGP57148B) induced cytogenetic remissions in 33% of chronic myelogenous leukemia (CML) patients in a phase I trial (Druker et al 1999). Combination therapy may increase this proportion. We tested whether combinations of STI571 and cytarabine or other chemotherapeutic agents such as hydroxyurea, mafosfamide or etoposide would display synergistic activity in BCR-ABL-positive chronic myelogenous leukemia (CML) cell lines derived from patients in blast crisis. In addition, the toxicity of these combinations on BCR-ABL-negative cells was investigated. A tetrazolium-based MTT assay was used to quantify growth inhibition after 48 h of exposure to cytotoxic agents alone and in simultaneous combination with STI571. The drug interactions were analyzed using the median-effect method of Chou and Talalay. The combination index (CI) was calculated according to the classic isobologram equation. At growth inhibition levels of over 50%, STI571 + cytarabine as well as STI571 + etoposide were significantly synergistic (CI < 1, P < 0.05) in the BCR-ABL-positive cell lines evaluated. At 60% inhibition or higher, a similar synergistic pattern became apparent for STI571 + mafosfamide (P < 0.05), while STI571 + hydroxyurea showed ambiguous, cell line-dependent synergism (BV173), additivity (EM-3) or antagonism (K562) in CML cell lines. Furthermore, the BCR-ABL-negative HL-60, KG1A and normal CD34+ progenitor cells were not affected by 0.8 μM STI571, a concentration which produced more than 50% growth inhibition in all BCR-ABL-positive cells tested, and no potentiation of growth inhibition was observed in these BCR-ABL-negative cells when STI571 was combined with chemotherapeutic agents. Our in vitro data with CML blast crisis cell lines strongly suggest that combinations of STI571 with cytarabine or etoposide be rapidly considered for clinical testing.

A combination of granulocyte-colony-stimulating factor (G-CSF) and plerixafor mobilizes more primitive peripheral blood progenitor cells than G-CSF alone: results of a European phase II study

BACKGROUND AIMS Previous studies in xenograft models have shown that human peripheral blood progenitor cells (PBPC) mobilized with the CXCR4 antagonist plerixafor (AMD3100) have a higher bone marrow (BM) reconstitution potential than granulocyte-colony-stimulating factor (G-CSF)-mobilized PBPC. METHODS PBPC obtained during G-CSF-supported mobilization before and after a supplementary administration of AMD3100 from patients with multiple myeloma and non-Hodgkins lymphoma (n=15; phase II study) were investigated for co-expression of primitive and lineage-associated markers, their proliferative activity in vitro and repopulation potential after clinical transplantation. RESULTS A significant increase in primitive CD34+ CD38(-) cells was observed in intraindividual comparisons of all patients after administration of G-CSF+AMD3100 (peripheral blood: median 8-fold, range 2,4-fold - 39-fold) compared with G-CSF alone. Using a long-term culture-initiating cell assay, this increase was confirmed. After transplantation of G-CSF+AMD3100-mobilized PBPC, the time to leukocyte reconstitution > 1 x 10(3)/microL and platelet reconstitution > 2 x 10(4)/microL was 14 (10-19 days) and 13 days (10-15 days), respectively. A complete and stable hematologic reconstitution (platelets > 1.5 x 10(5)/microL) was observed in 91% of all patients within 35 days. CONCLUSIONS An additional application of AMD3100 to a standard G-CSF mobilization regimen leads to a significant increase in primitive PBPC with high repopulation capacity.

Synergistic activity of imatinib and 17-AAG in imatinib-resistant CML cells overexpressing BCR-ABL – Inhibition of P-glycoprotein function by 17-AAG

Overexpression of BCR-ABL and P-glycoprotein (Pgp) are two of the known mechanisms of imatinib resistance. As combination therapy may allow to overcome drug resistance, we investigated the effect of combination treatment with imatinib and 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heat-shock protein 90 (Hsp90) inhibitor, on different imatinib-sensitive and imatinib-resistant CML cell lines. In imatinib-sensitive cells, combination index (CI) values obtained using the method of Chou and Talalay indicated additive (CI=1) or marginally antagonistic (CI>1) effects following simultaneous treatment with imatinib and 17-AAG. In imatinib-resistant cells both drugs acted synergistically (CI<1). In primary chronic-phase CML cells additive or synergistic effects of the combination of imatinib plus 17-AAG were discernible. Annexin V/propidium iodide staining showed that the activity of imatinib plus 17-AAG is mediated by apoptosis. Combination treatment with imatinib plus 17-AAG was more effective in reducing the BCR-ABL protein level than 17-AAG alone. Monotherapy with 17-AAG decreased P-glycoprotein activity, which may increase intracellular imatinib levels and contribute to the sensitization of CML cells to imatinib. The results suggest that combination of imatinib and 17-AAG may be useful to overcome imatinib resistance in a clinical setting.

Mobilization of peripheral blood stem cells for autologous transplant in non-Hodgkin's lymphoma and multiple myeloma patients by plerixafor and G-CSF and detection of tumor cell mobilization by PCR in multiple myeloma patients

This report describes the first investigational use of plerixafor in Europe and the determination of tumor cell mobilization by polymerase chain-reaction after plerixafor treatment in a subset of patients with multiple myeloma (MM). Thirty-five patients (31 MM and 4 NHL) received granulocyte colony-stimulating factor (G-CSF) (10 μg/kg) each morning for 4 days. Starting the evening of Day 4, patients recieved plerixafor 0.24 mg/kg. Apheresis was initiated 10–11 h later, in the morning of Day 5. This regimen of G-CSF treatment each morning before apheresis and plerixafor treatment in the evening was repeated for up to 5 consecutive days. Mobilization with plerixafor and G-CSF resulted in a median 2.6-fold increase in peripheral blood (PB) CD34+ cell count compared with before plerixafor treatment. All patients collected ⩾2 × 106 CD34+ cells/kg and 32 of 35 patients collected ⩾5 × 106 CD34+ cells/kg. After plerixafor treatment, 3 of 7 patients had a small increase and 4 of 7 patients had a small decrease in PB tumor cells. No G-CSF was given post transplant. The median number of days to polymorphonuclear leukocyte and platelet engraftment was 14.0 and 11.0, respectively. There were no reports of graft failure. Plerixafor was generally well tolerated. Mobilization of PB CD34+ cells was consistent with previous clinical trials. The addition of plerixafor did not significantly increase the relative number of PB MM tumor cells.

Level of CD 20-expression and efficacy of rituximab treatment in patients with resistant or relapsing B-cell prolymphocytic leukemia and B-cell chronic lymphocytic leukemia.

Rituximab (IDEC C2B8) is a chimeric human-mouse monoclonal anti-CD20 antibody that has been proven to be effective for the treatment of patients with CD20 positive leukemia and lymphoma. The level of CD20-expression in patients with B-cell chronic lymphocytic leukemia (B-CLL) is low in comparison to other B-cell lymphomas and normal B-cells. Previous experience with rituximab treatment in small series of patients with B-CLL suggest that it is less effective in B-CLL than in follicular lymphomas. We analyzed the correlation between CD20-expression level and efficacy of rituximab treatment in eight patients with refractory or relapsed B-CLL and two patients with B-cell prolymphocytic leukemia (B-PLL). We could not identify any correlation between CD20-expression and efficacy of rituximab treatment.

Imatinib combined with mitoxantrone/etoposide and cytarabine is an effective induction therapy for patients with chronic myeloid leukemia in myeloid blast crisis.

Despite advances in drug therapy and allogeneic stem cell transplantation (allo‐SCT), the prognosis of patients with chronic myeloid leukemia (CML) in blast crisis remains poor. Imatinib has demonstrated synergistic effects in vitro with mitoxantrone, etoposide, and cytarabine.

Functional characterization of podia formation in normal and malignant hematopoietic cells

Hematopoietic cells extend multiple podia of yet unknown function. Our morphological studies using scanning electron microscopy and functional studies using time‐lapse video microscopy suggest that podia formed by CD34+ hematopoietic stem cells (HSC) on the bone marrow stroma component fibronectin are characteristic of lamellipodia at the leading edge and uropodia at the trailing edge, cytoskeletal structures that have previously been shown to be responsible for cell locomotion of lymphocytes. In the leukemic cells studied here, stroma‐derived factor‐1α (SDF‐1α) led to a significant eightfold increase in transmigration (BCR‐ABL‐positive BV173 leukemia cell line;P<0.05) and podia formation in all BCR‐ABL‐positive leukemic cell lines studied (BV173, K562, 32Dp210) and in two of three BCR‐ABL‐negative lines (HL60, 32D, not KG1a). We could show that SDF‐1α exposure led to a down‐regulation of the gene expression of the chemokine receptors CCR4, CXCR4, and CXCR5, which are associated with cell motility and podia formation, indicating a negative feedback control. In BCR‐ABL‐positive leukemic cells, the effects of SDF‐1α on podia formation and cell migration were independent of BCR‐ABL‐tyrosine kinase activity. Our data are compatible with the hypothesis that formation of specific podia by hematopoietic cells is associated with egression of these cells from the bone marrow.

Efficient mobilization of peripheral blood stem cells following CAD chemotherapy and a single dose of pegylated G-CSF in patients with multiple myeloma

High-dose chemotherapy followed by autologous blood stem cell transplantation is the standard treatment for myeloma patients. In this study, CAD (cyclophosphamide, adriamycin, dexamethasone) chemotherapy and a single dose of pegfilgrastim (12 mg) was highly effective in mobilizing peripheral blood stem cells (PBSCs) for subsequent transplantation, with 88% of patients (n=26) achieving the CD34+ cell harvest target of ⩾7.50 × 106 CD34+ cells/kg body weight, following a median of two apheresis procedures (range 1–4) and with first apheresis performed at a median day 13 after CAD application (range 10–20). Patients treated with pegfilgrastim showed a reduced time to first apheresis procedure from mobilization compared with filgrastim-mobilized historical matched controls (n=52, P=0.015). The pegfilgrastim mobilization regimen allowed for transplantation of a median of 3.58 × 106 CD34+ cells/kg body weight while leaving sufficient stored cells for a second high-dose regimen and back-ups in most patients. Engraftment following transplantation was comparable to filgrastim, with a median time of 14 days to leucocyte ⩾1.0 × 109/l (range 10–21) and 11 days to platelets ⩾20 × 109/l (range 0–15). The results of this study thus provide further support for the clinical utility of pegfilgrastim for the mobilization of PBSC following chemotherapy in cancer patients scheduled for transplantation.

Peripheral blood progenitor cell (PBPC) counts during steady-state haemopoiesis enable the estimation of the yield of mobilized PBPC after granulocyte colony-stimulating factor supported cytotoxic chemotherapy: an update on 100 patients

Peripheral blood progenitor cells (PBPC) can be mobilized using chemotherapy and granulocyte colony‐stimulating factor (G‐CSF). We and others previously reported a correlation of steady‐state PBPC counts and the PBPC yield during mobilization in a small group of patients. Here we present data on 100 patients (patients: 25 non‐Hodgkins lymphoma (NHL), five Hodgkins disease, 35 multiple myeloma (MM), 35 solid tumour) which enabled a detailed analysis of determinants of steady‐state PBPC levels and of mobilization efficiency in patient subgroups. Previous irradiation (P = 0.0034) or previous chemotherapy in patients with haematological malignancies (P = 0.0062) led to a depletion of steady‐state PB CD34+ cells. A correlation analysis showed steady‐state PB CD34+ cells (all patients: r = 0.52, P < 0.0001; NHL patients, r = 0.69, P = 0.0003; MM patients: r = 0.66, P = 0.0001) and PB colony‐forming cells can reliably assess the CD34+ cell yield in mobilized PB. In patients with solid tumour a similar trend was observed in mobilization after the first chemotherapy cycle (r = 0.51, P = 0.05) but not if mobilization occurred after the second or further cycle of a sequential dose‐intensified G‐CSF‐supported chemotherapy regimen, when premobilization CD34+ counts were 18‐fold elevated (P = 0.004). When the patients with MM (r = 0.63, P = 0.0008) or with NHL (r = 0.65, P = 0.006) were analysed separately, a highly significant correlation of the steady‐state PB CD34+ cell count to the mean leukapheresis CD34+ cell yield was found, whereas no correlation was observed for patients with a solid tumour. For patients with haematological malignancies estimates could be calculated which, at a specific steady‐state PB CD34+ cell count, could predict with a 95% probability a defined minimum progenitor cell yield. These results enable recognition of patients who mobilize PBPC poorly and may assist selection of patients for novel mobilization regimens.

Combination therapy with imatinib mesylate (sti571): synopsis of in vitro studies

Chronic myelogenous leukaemia (CML) is the first malignancy in which knowledge about the pathomechanisms of the disease has led to the development of a specific and highly effective molecular therapy. The first clinical trials with the tyrosine kinase inhibitor imatinib mesylate showed high response rates with minimal toxicity and raised hope for a possible cure of CML by drug therapy alone. However, not all patients show a complete response and even in responders relapses continue to occur, particularly in advanced phases of the disease. Combination therapy with imatinib and established or investigational antileukaemic agents may lead to an increase in the response rates and remission duration. This review summarizes relevant in vitro studies in the hope that translation of promising preclinical data into clinical trials will lead to further increases in the life expectancy of CML patients.