Purging of G-CSF-mobilized peripheral autografts in acute leukemia with mafosfamide and amifostine to protect normal progenitor cells

Rationale for assessing the therapeutic potential of resveratrol in hematological malignancies

Promising results from pre-clinical studies on the naturally-occurring polyphenol resveratrol have generated considerable interest and somewhat excessive expectations regarding the therapeutic potential of this compound for treating or preventing various diseases, including cardiovascular and neurodegenerative disorders and cancer. Resveratrol has potent inhibitory activity in vitro against various tumor types, including cell lines derived from virtually all blood malignancies. Pharmacological studies have shown that resveratrol is safe for humans but has poor bioavailability, due to its extensive hepatic metabolism. Curiously, a substantial proportion of the orally administered resveratrol can reach the bone marrow compartment. Notably, various pathways dysregulated in blood cancers are known to be molecular targets of resveratrol, thus substantiating the potential utility of this agent in blood malignancies. In this review, we primarily focus on the scientific evidence that supports the potential utility of resveratrol for the management of select hematological malignancies. In addition, potential clinical trials with resveratrol are suggested.

In vitro testing of drug combinations employing nilotinib and alkylating agents with regard to pretransplant conditioning treatment of advanced-phase chronic myeloid leukemia

PURPOSE

The prognosis of patients with advanced-phase chronic myeloid leukemia (CML) remains dismal despite the availability of targeted therapies and allogeneic stem cell transplantation (allo-SCT). Increasing the antileukemic efficacy of the pretransplant conditioning regimen may be a strategy to increase remission rates and duration. We therefore investigated the antiproliferative effects of nilotinib in combination with drugs that are usually used for conditioning: the alkylating agents mafosfamide, treosulfan, and busulfan.

METHODS

Drug combinations were tested in vitro in different imatinib-sensitive and imatinib-resistant BCR-ABL-positive cell lines. A tetrazolium-based MTT assay was used for the assessment and quantification of growth inhibition after exposure to alkylating agents alone or to combinations with nilotinib. Drug interaction was analyzed using the median-effect method of Chou and Talalay, and combination index (CI) values were calculated according to the classic isobologram equation.

RESULTS

Treatment of imatinib-sensitive, BCR-ABL-positive K562 and LAMA84 cells with nilotinib in combination with mafosfamide, treosulfan, or busulfan resulted in synergistic (CI < 1), additive (CI ~ 1), and predominantly antagonistic (CI > 1) effects, respectively. In imatinib-resistant K562-R and LAMA84-R cells, all applied drug combinations were synergistic (CI < 1) at higher growth inhibition levels.

CONCLUSIONS

Our in vitro data warrant further investigation and may provide the basis for nilotinib-supplemented conditioning regimens for allo-SCT in advanced-phase CML.

The significance of minimal residual disease in stem cell grafts and the role of purging: is it better to purge in vivo or in vitro?

Contamination of autologous graft by tumor, in addition to incomplete tumor eradication, can partly explain why relapse remains the commonest cause of treatment failure after autologous stem cell transplantation (ASCT) in patients with malignant hematologic disorders. Monitoring of minimal residual disease (MRD) is now recognized as an important diagnostic tool for assessment either of the response to treatments aimed at maximal cytoreduction and the individual risk of relapse. In order to improve cure rates, many strategies to achieve in vivo or in vitro reduction, if not eradication, of residual disease have been proposed. We discuss the significance of MRD and the role of purging in the ASCT setting, focusing on acute myeloid leukemia, chronic myeloid leukemia, multiple myeloma and follicular lymphoma.

Autologous stem cell transplantation for acute myeloid leukemia

Autologous bone marrow transplant (ABMT) and stem cell transplantation (ASCT) are important treatment modalities for acute myeloid leukemia (AML). The role of ASCT in first remission patients remains controversial. Phase II and phase III studies demonstrate that patients with favorable-risk cytogenetics benefit from ASCT, with reduction in relapse and improvement in leukemia-free survival (LFS). Patients with poor-risk cytogenetics do not appear to benefit significantly from ASCT and should preferentially be treated with allogeneic transplant. The role of ASCT for patients with intermediate risk disease is uncertain. It appears that ASCT in first remission will improve disease-free survival compared to standard chemotherapy. Sufficient patients who relapse after chemotherapy treatment can be salvaged with ASCT in second remission such that the beneficial effect on overall survival is blunted. ASCT produces equivalent results to ABMT but with reduced morbidity. The collection of stem cells during recovery from intensive dose consolidation therapy appears to be an attractive strategy that can increase the percentage of patients who are able to receive their intended transplant. Consolidation therapy prior to stem cell collection and transplant has been shown to decrease the relapse rate and improve outcomes, but the optimal nature of this consolidation therapy is unknown. For patients with AML in second remission, ABMT/ASCT offers a substantial salvage rate, and is particularly effective for patients with acute promyelocytic leukemia.

New approaches to hematopoietic cell transplantation in oncology

The use of high-dose chemotherapy followed by autologous HCT and the use of allogeneic HCT in children and adolescents with high-risk ALL, AML, and NBL has successfully improved outcomes. For other diseases, however, the role of HCT in treatment remains a subject of further research. The availability of HCT was significantly expanded by developing alternative graft sources that currently include BM, peripheral blood, and UCB from autologous and allogeneic related or unrelated donors. Progress in autologous HCT has been achieved by the identification of more effective and less toxic preparative regimens and by ex vivo purging of stem cell products. In allogeneic HCT, graft-versus-leukemia or graft-versus-tumor effects are being exploited increasingly to lower relapse rates. In addition, immunomodulation to promote tolerance, as well as allogeneic antitumor reactions have been achieved by antibody therapy, cytokine therapy, or cell-based immunotherapy. Future improvements are likely, as evidenced by promising preliminary results in the development of stem cell collection techniques, in vitro stem cell expansion, and purging techniques of stem cell grafts. The development of less intensive or nonmyeloablative preparative regimens may further reduce regimen-related morbidity and mortality Specific immunotherapy may facilitate tolerance induction in mismatched allogeneic HCT and support allogeneic HCT in the setting of donor-host HLA disparity. Ultimately, advances in cytokine therapy, tumor-specific vaccines, and gene therapy may decrease or even eradicate recurrence of the malignant disease after HCT.

Purging of contaminating breast cancer cells from hematopoietic progenitor cell preparations using activation enhanced cell death

Activation enhanced cell death (AECD) involves stimulating cells with growth or activation signals while concurrently blocking calcium influx. In this study, we have evaluated the effect of AECD on human breast cancer cells. MCF-7 or MDA-MB-231 cells treated with Ca2+ influx blockers econazole or ketotifen for 24 h underwent a dose-dependent, irreversible loss of viability, and clonogenicity. Two-hour treatment of these cells with higher concentrations of the drugs also resulted in loss of clonogenicity, but morphological indicators of cell death were apparent only after longer incubation. Loss of clonogenicity could be enhanced almost 10-fold by co-stimulation of the cells with the agonists EGF or bombesin. Econazole was also effective in inducing cell death in multi-drug resistant MCF-7adr cells. Human hemopoietic progenitor cell sensitivity to econazole or ketotifen was evaluated by colony assay. Under conditions resulting in 2.5-3 logs of breast cancer cell loss, 60-70% of hemopoietic progenitors could be recovered. We further evaluated the effect of econazole on breast cancer cells present in mobilized hemopoietic cells obtained from patients undergoing high dose chemotherapy with autologous stem cell support. In six of eight samples evaluated, cytokeratin-positive breast cancer cells could be detected by immunofluorescence microscopy and colony formation. Breast cancer colonies were reduced 60-500-fold or more after exposure to econazole while hemopoietic colonies were typically reduced only 2-fold. In all cases, addition of EGF as an activator either had no evaluable effect or enhanced breast cancer cell loss. We conclude that Ca2+ influx blockade with concurrent EGF stimulation is a promising approach for purging breast cancer cells from hemopoietic progenitor cell preparations.

Stem cell toxicity of oxazaphosphorine metabolites in comparison to their antileukemic activity

The oxazaphosphorine agent cyclophosphamide (CP) is an alkylating agent with a relative low stem cell toxicity. The aim of this study was to further evaluate the stem cell toxicity of the active metabolites of CP and its structural analogue ifosfamide (IFO) in comparison to their antileukemic efficacy. Cells of different malignant hematologic disorders (HL-60, HS-Sultan and THP-1) and CD34+ stem cells were treated with cytotoxic CP-metabolite mafosfamide (MAFO) and IFO-metabolites 4-hydroxy-IFO (4-OH-IFO) and chloroacetaldehyde. The clonogenity of the cells was investigated by using a colony-forming assay. All metabolites reduced the formation of both tumor-derived colonies and stem cell-derived CFU-GMs in a concentration-dependent manner. Our data showed a relative tumor-specific, stem cell protecting action of the substances tested with a higher toxicity against tumor cells (IC(50) against HS-Sultan: MAFO 1.1 microM; 4-OH-IFO 1.3 microM; CAA 3 microM) than against stem cells (IC(50) MAFO 14.8 microM; 4-OH-IFO 16.9 microM; CAA 14 microM). However, while the cytotoxic action of 4-OH-IFO corresponded to MAFOs activity, CAAs cytotoxic effect against the hematologic tumor cells was lower. In conclusion, the results confirm the observed cytotoxicity of CAA against solid tumors for cells of malignant hematologic disorders. Although the relative cytotoxic specificity of CAA is lower than for 4-OH-IFO and MAFO, also CAA, like 4-OH-IFO and MAFO, was found to be in part a tumoricidal, stem cell protecting substance.

Autologous stem cell transplantation for adult acute leukemia

Autologous stem cell transplantation using marrow or peripheral blood is routinely used to consolidate patients with acute myelocytic leukemia in complete remission. The situation is less clear for adult acute lymphocytic leukemia in which results achieved with all strategies are disappointing. In acute myelocytic leukemia, autografts should be done in patients with good and standard risk factors. Patients with high-risk acute myelocytic leukemia defined by poor cytogenetics or failure to achieve remission with the first induction course, should proceed to allogeneic stem cell transplantation with the best available human leukocyte antigen-identical donor (family or unrelated), and the nature of the conditioning regimen (myelo-ablative or non-myelo-ablative) should be decided in relation to age, and the patient's clinical condition. Results of autografting in acute myelocytic leukemia rely strongly on the quality of the graft. Higher doses of infused stem cells translate into lower relapse rates. Marrow purging with cyclophosphamide derivatives also diminishes the relapse incidence. Autologous stem cell transplantations using peripheral blood are presently preferred to marrow as the source of stem cells, but an aggressive prior in vivo purge (high-dose consolidation course(s) before cytaphereses) is then mandatory. In good-risk acute myelocytic leukemia, autografting is superior to high-dose ARA-C; in standard-risk acute myelocytic leukemia, both are supposedly equivalent. There is no prospective randomized study testing the two approaches in the good-standard-risk population. We presently test the combination of marrow and blood both purged by mafosfamide. In adult acute lymphocytic leukemia, good-risk patients get the best benefit from autografting over conventional chemotherapy. Maintenance chemotherapy after transplant is likely to bring benefit. Research in progress aims at facilitating access of the largest number of patients to autografting and at introducing posttransplant immunomodulation maneuvers such as tumor vaccination.