Cytotoxicity of treosulfan and busulfan on pediatric tumor cell lines

Transcriptomic profile of human iPSC-derived podocyte-like cells exposed to a panel of xenobiotics

Podocytes play a critical role in the formation and maintenance of the glomerular filtration barrier and injury to these cells can lead to a breakdown of the glomerular barrier causing permanent damage leading to progressive chronic kidney disease. Matured podocytes have little proliferative potential, which makes them critical cells from a health perspective, but also challenging cells to maintain in vitro. Differentiating podocyte-like cells from induced pluripotent stem cells (iPSC) provides a novel and continuous source of cells. Here, we investigated the effect of a 24-h exposure to eight compounds, including the known glomerular toxins doxorubicin and pamidronate, on transcriptomic alterations in iPSC derived podocytes. Doxorubicin (50 nM), pamidronate (50 μM), sodium arsenite (10 μM), and cyclosporine A (15 μM) had a strong impact on the transcriptome, gentamicin (450 μg/ml), lead chloride (15 μM) and valproic acid (500 μM) had a mild impact and busulfan (50 μM) exhibited no impact. Gene alterations and pathways analysis provided mechanistic insight for example, doxorubicin exposure affected the p53 pathway and dedifferentiation, pamidronate activated several pathways including HIF1alpha and sodium arsenite up-regulated oxidative stress and metal responses. The results demonstrate the applicability of iPSC derived podocytes for toxicological and mechanistic investigations.

High-Dose Treosulfan and Melphalan as Consolidation Therapy Versus Standard Therapy for High-Risk (Metastatic) Ewing Sarcoma

PURPOSE

Ewing 2008R3 was conducted in 12 countries and evaluated the effect of treosulfan and melphalan high-dose chemotherapy (TreoMel-HDT) followed by reinfusion of autologous hematopoietic stem cells on event-free survival (EFS) and overall survival in high-risk Ewing sarcoma (EWS).

METHODS

Phase III, open-label, prospective, multicenter, randomized controlled clinical trial. Eligible patients had disseminated EWS with metastases to bone and/or other sites, excluding patients with only pulmonary metastases. Patients received six cycles of vincristine, ifosfamide, doxorubicin, and etoposide induction and eight cycles of vincristine, actinomycin D, and cyclophosphamide consolidation therapy. Patients were randomly assigned to receive additional TreoMel-HDT or no further treatment (control). The random assignment was stratified by number of bone metastases (1, 2-5, and > 5). The one-sided adaptive-inverse-normal-4-stage-design was changed after the first interim analysis via Müller-Schäfer method.

RESULTS

Between 2009 and 2018, 109 patients were randomly assigned, and 55 received TreoMel-HDT. With a median follow-up of 3.3 years, there was no significant difference in EFS between TreoMel-HDT and control in the adaptive design (hazard ratio [HR] 0.85; 95% CI, 0.55 to 1.32, intention-to-treat). Three-year EFS was 20.9% (95% CI, 11.5 to 37.9) in TreoMel-HDT and 19.2% (95% CI, 10.8 to 34.4) in control patients. The results were similar in the per-protocol collective. Males treated with TreoMel-HDT had better EFS compared with controls: median 1.0 years (95% CI, 0.8 to 2.2) versus 0.6 years (95% CI, 0.5 to 0.9); P = .035; HR 0.52 (0.28 to 0.97). Patients age < 14 years benefited from TreoMel-HDT with a 3-years EFS of 39.3% (95% CI, 20.4 to 75.8%) versus 9% (95% CI, 2.4 to 34); P = .016; HR 0.40 (0.19 to 0.87). These effects were similar in the per-protocol collective. This observation is supported by comparable results from the nonrandomized trial EE99R3.

CONCLUSION

In patients with very high-risk EWS, additional TreoMel-HDT was of no benefit for the entire cohort of patients. TreoMel-HDT may be of benefit for children age < 14 years.

Factors Modifying Outcome After MIBG Therapy in Children With Neuroblastoma-A National Retrospective Study

Background

Neuroblastoma is the most common pediatric extracranial tumor with varied prognoses, but the survival of treated refractory or relapsing patients remains poor.

Objective

This analysis presents the outcomes of children with neuroblastoma undergoing MIBG therapy in Poland in 2006-2019.

Study Design

A retrospective cohort of 55 patients with refractory or relapsed neuroblastoma treated with I-131 MIBG in Poland in 2006-2019 was analyzed. The endpoints were overall survival (OS), event-free survival (EFS), cumulative incidence (CI) of second cancers and CI of hypothyroidism. Survival curves were estimated using the Kaplan-Meier method and compared between the cohorts by the log-rank test. Cox modeling was adopted to estimate hazard ratios for OS and EFS, considering factors with P < 0.2.

Results

Fifty-five patients with a median age of 78.4 months (range 18-193) with neuroblastoma underwent one or more (4 patients) courses of MIBG I-131 therapy. Fifteen patients were not administered chemotherapy, 3 children received standard-dose chemotherapy, and 37 patients were administered high-dose chemotherapy (HDCT) (busulfan-melphalan in 24 and treosulfan-based in 12 patients). Forty-six patients underwent stem cell transplantation, with autologous (35 patients), haploidentical (6), allogeneic (4), and syngeneic grafts (1). The median time from first MIBG therapy to SCT was 22 days. Children with relapsing tumors had inferior OS compared to those with primary resistant disease (21.2% vs 58.7%, p=0.0045). Survival was better in patients without MYCN gene amplification. MIBG therapy was never curative, except in patients further treated with HDCT with stem cell rescue irrespective of the donor type. 31 patients were referred for immune therapy after MIBG therapy, and the 5-year OS in this group was superior to the untreated children (55.2% vs 32.7%, p=0.003), but the difference in the 5-year EFS was not significant (25.6% vs 32.9%, p=ns). In 3 patients, a second malignancy was diagnosed. In 19.6% of treated children, hypothyroidism was diagnosed within 5 years after MIBG therapy.

Conclusion

MIBG therapy can be incorporated into the therapeutic strategy of relapsed or resistant neuroblastoma patients as preconditioning with HDCT rather than stand-alone therapy. Follow-up is required due to the incidence of thyroid failure and risk of second cancers.

Feasibility and Safety of Treosulfan, Melphalan, and Thiotepa-Based Megachemotherapy with Autologous or Allogeneic Stem Cell Transplantation in Heavily Pretreated Children with Relapsed or Refractory Neuroblastoma

The prognosis of resistant or relapsing children with neuroblastoma remains very poor, and the search for new therapies is ongoing. In this analysis, we assessed the toxicity of a treosulfan, melphalan, and thiotepa (TMT) regimen in 17 children with recurrent or refractory neuroblastoma who underwent stem cell transplantation (SCT). For allogeneic SCT, fludarabine and antithymocyte globulin were added. The stem cell source was autologous in 8 patients, haploidentical in 8 patients, and a matched unrelated donor in 1 patient. The reported nonhematologic toxicities included grade 3 mucositis, grade 1 to 3 hypertransaminasemia, and in 3 patients, veno-occlusive disease. No neurologic, cardiac, or dermatologic toxicities were observed. The probability of overall survival (OS) in patients with primary resistance was superior to that in patients with relapsed disease (100% versus 22.6%; P = .046). Post-transplantation dinutuximab beta immunotherapy was associated with superior 5-year OS (66.7% versus 11.4%; P = .0007). The use of an allogeneic donor, previous autologous SCT with busulfan and melphalan, and pretreatment with high-dose metaiodobenzylguanidine therapy demonstrated no effect on outcomes. In 4 patients, TMT megatherapy alone was enough to achieve complete remission. The TMT conditioning regimen was well tolerated in heavily pretreated patients with neuroblastoma. The manageable toxicity and addition of new anticancer drugs with optional post-SCT immunotherapy or chemotherapy support further trials with the TMT regimen in patients with neuroblastoma.

Ocular disposition of treosulfan and its active epoxy-transformers following intravenous administration in rabbits

Treosulfan (TREO) has an established position in chemotherapy of advanced ovarian cancer but has been also applied in uveal melanoma patients. Moreover, it is used as an orphan drug for a myeloablative conditioning prior to stem cell transplantation. In this paper, biodistribution of prodrug TREO and its active monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB) into aqueous humor of the eye was studied for the first time. For that purpose, alone TREO and the mixture of TREO, S,S-EBDM and S,S-DEB were administered intravenously to New Zealand White rabbits. The three analytes were determined in plasma and aqueous humor by validated HPLC methods and pharmacokinetic calculations were performed in WinNonlin. After the infusion of TREO, the aqueous humor/plasma C_max ratio and area under the curve ratio amounted 0.04 and 0.10 for TREO, and 1.1 and 2.2 for S,S-EBDM, respectively. Following the bolus injection of the mixture of the prodrug and its epoxides, the aqueous humor/plasma C_max ratios for TREO, S,S-EBDM and S,S-DEB were 0.05, 0.66, and 4.0, respectively. The presented results indicate a poor penetration of TREO into the eye, which may impair systemic treatment of ocular tumors but is beneficial in terms of a lack of clinically relevant ophthalmic adverse effects.

A phase II study to determine the efficacy and safety of oral treosulfan in patients with advanced pre-treated Ewing sarcoma ISRCTN11631773

We report a prospective Phase II study of efficacy and toxicity for oral treosulfan in advanced Ewing sarcoma. Twenty patients, median age 19 years (range 7-39) from five UK sites, were treated with oral treosulfan 1 g/m(2) daily for 7 days in 28. Primary endpoint was objective response rate. Best response was stable disease in one patient. All patients died of progressive disease, after median 6.41 months. Median progression free survival was 1.8 months. Toxicity was minimal. No activity was demonstrated for treosulfan at this dose. Progression free survival data should be able to be used for comparison when planning future clinical trials.

Busulfan inhibits growth of human osteosarcoma through miR-200 family microRNAs in vitro and in vivo

Osteosarcoma typically arises in tissues of mesenchymal origin, and is the most malignant bone tumor characterized by high local aggressiveness, with poor therapeutic outcome. Busulfan has been widely used to treat CML. So far, there are no reports on the therapeutic effect of busulfan on osteosarcoma. Here, we showed that busulfan dose-dependently reduced the cell viability and proliferation, and induced cell apoptosis, senescence, and reactive oxygen species levels in two osteosarcoma cell lines. Moreover, a series of loss-of-function and gain-of-function experiments further indicated that busulfan may have its anti-osteosarcoma effect by upregulating the microRNA-200 (miR-200) family which subsequently downregulated its target genes ZEB1 and ZEB2. Furthermore, treatment with busulfan potentially inhibited the growth of implanted osteosarcoma in nude mice. Taken together, our data suggest that busulfan may have an anti-osteosarcoma effect through downregulating ZEB1 and ZEB2 through activating the miR-200 family, highlighting a possibility of using busulfan as a novel therapy for osteosarcoma.

Assessing the intracellular concentration of platinum in medulloblastoma cell lines after Cisplatin incubation

Two different analytical approaches, external calibration and isotope dilution analysis both using flow-injection inductively coupled plasma mass spectrometry, have been developed and applied to determine the intracellular platinum concentration after Cisplatin incubation of two different medulloblastoma cell lines (UW228 and DAOY). As the internal or isotopically enriched standard was already used for cell lysis, maximum accuracy of the results was obtained, whereas a new home-built and inert injection system dramatically lowered carry-over effects and analyte loss. With limits of the detection well below 0.4μgL(-1) and typical relative standard deviations of 2%, a strong correlation between the cell viability in MTT assays and the incorporated amount of Pt could be shown, which was subsequently normalized to the protein content of the samples. DAOY cells did significantly ingest more Pt and showed a higher mortality, which supports the fact that transporter expression needs to be taken into account in order to obtain meaningful results.

Escalating topotecan in combination with treosulfan has acceptable toxicity in advanced pediatric sarcomas

Patients with advanced pediatric sarcomas have a poor prognosis and novel combination therapies are needed to improve the response rates. Hematological and organ related toxicities have been observed when administering topotecan in combination with, e.g., high dose thiotepa. This study evaluates the toxicity of escalating doses of topotecan alone or in combination with thiotepa or treosulfan. We compared the toxicity including death of complication (DOC) of topotecan alone or in combination with thiotepa or treosulfan in advanced pediatric sarcomas (n = 12). Ten of 12 patients (0.83) suffered from advanced tumors of the Ewing family (i.e., bone or marrow metastases or relapse <24 month after diagnosis, including one neuroepithelial tumor of the kidney) and two from alveolar rhabdomyosarcoma stage IV (0.17). Median age was 15 years (range 5-28). Ratio of female to male was 1:1. Two patients received topotecan alone (1.25 mg/m(2) q 5d and 1.5 mg/m(2) q 5d), three patients received four courses of topotecan (2 mg/m(2) q d 1-5) in combination with thiotepa (100 mg/m(2) q d 1-5), and seven patients received topotecan (2 mg/m(2) q d 1-5) in combination with treosulfan (10g/m(2) q d 3-5). Overall toxicity was not different between all three groups; mean scores were 1.6, 1.8, and 1.7 according to WHO grading (Scale 0-4). Organ related toxicity ranged between 0 and 4 and was not different as well. DOC was 0/2, 1/3, and 0/7 patients respectively. Escalating therapy with topotecan in combination with treosulfan has acceptable toxicity and warrants further investigation in advanced pediatric sarcomas.

Pharmacology of dimethanesulfonate alkylating agents: busulfan and treosulfan

INTRODUCTION

Among the dimethanesulfonates, busulfan, in combination with other alkylating agents or nucleoside analogues, is the cornerstone of high-dose chemotherapy. It is used, and followed hematopoietic stem cell transplantation, for the treatment of various hematologic malignancies and immunodeficiencies. Treosulfan, which is a hydrophilic analogue of busulfan, was the first dimethanesufonate registered for the treatment of ovarian cancer. Recently, treosulfan has been investigated for the treatment of hematologic malignancies in combination with the same second agents before hematopoietic stem cell transplantation.

AREAS COVERED

This work reviews the pharmacological data of these two dimethanesulfonates alkylating agents. Specifically, the article looks at their chemistry, metabolism, anticancer activity, and their pharmacokinetics and pharmacodynamics.

EXPERT OPINION

Busulfan has been investigated widely for more than three decades leading to a large and precise handling of this agent with numerous studies on activity and pharmacokinetics and pharmacodynamics. In contrast, the behavior of treosulfan is still under investigation and not fully described. The complexity of treosulfan's metabolism and mechanism of action gives rise to the need of a deeper understanding of its pharmacological activity in a context of high-dose chemotherapy. Specifically, there is a great need to better understand its pharmacokinetics/pharmacodynamics relationship.

High-dose chemotherapy and stem cell rescue for high-risk Ewing's family of tumors

The prognosis for high-risk Ewing's tumors has been improved by multimodal radiation and chemotherapy. Ewing's family of tumors requires risk-adapted treatment. Risk stratification is dependent on stage, tumor localization and volume, and the pattern of disease spread at the time of diagnosis and the time of relapse. The concepts for high-dose therapy followed by hematopoietic cell transplantation in Ewing's family of tumors are based on dose-response and dose-intensity relationships. This article will discuss the use of high-dose therapy followed by hematopoietic cell transplantation, focusing on recent progress with respect to agent combinations, dose and outcomes of therapy.

An in-vitro evaluation of the polo-like kinase inhibitor GW843682X against paediatric malignancies

Polo-like kinase 1 (PLK1) is a regulator of mitosis and its upregulation in tumours is often associated with poor prognosis. Although PLK1 inhibitors have already entered phase 1 clinical trials, little is known about their impact on the treatment of paediatric malignancies. Thus, we evaluated the concept of PKL1 inhibition by testing the effects of the PLK1 inhibitor GW843682X alone and in combination with the topoisomerase 1 inhibitor, camptothecin, against a panel of 18 paediatric tumour cell lines. Cytotoxicity was evaluated by MTT test and by caspase 3/7 activation. Expression of target was confirmed by western blot analysis. Expression of ATP binding cassette transporters was analysed by quantitative real-time reverse transcription PCR. GW843682X significantly inhibited cell growth in all 18 cell lines. Concentrations, which inhibited cell growth by 50% compared with untreated controls after 72 h, ranged from 0.02 to 11.7 μmol/l. Apart from the N-Myc-amplified neuroblastoma cell lines, the osteosarcoma cell lines MNNG-HOS and OST, which are highly resistant to standard anticancer drugs, were sensitive to GW843682X. The toxicity of GW843682X was dependent neither on the ATP binding cassette drug transporter expression nor on the p53 mutation status. Neither synergistic nor antagonistic effects were observed for the combination of GW843682X and camptothecin in 14 cell lines. GW843682X showed considerable toxicity against a panel of paediatric tumour cell lines suggesting that PLK1 inhibitors under clinical development should be evaluated against paediatric malignancies too.

Association of telomerase activity with radio- and chemosensitivity of neuroblastomas

BACKGROUND

Telomerase activity compensates shortening of telomeres during cell division and enables cancer cells to escape senescent processes. It is also supposed, that telomerase is associated with radio- and chemoresistance. In the here described study we systematically investigated the influence of telomerase activity (TA) and telomere length on the outcome of radio- and chemotherapy in neuroblastoma.

METHODS

We studied the effects on dominant negative (DN) mutant, wild type (WT) of the telomerase catalytic unit (hTERT) using neuroblastoma cell lines. The cells were irradiated with 60Co and treated with doxorubicin, etoposide, cisplatin and ifosfamide, respectively. Viability was determined by MTS/MTT-test and the GI50 was calculated. Telomere length was measured by southernblot analysis and TA by Trap-Assay.

RESULTS

Compared to the hTERT expressing cells the dominant negative cells showed increased radiosensitivity with decreased telomere length. Independent of telomere length, telomerase negative cells are significantly more sensitive to irradiation. The effect of TA knock-down or overexpression on chemosensitivity were dependent on TA, the anticancer drug, and the chemosensitivity of the maternal cell line.

CONCLUSIONS

Our results supported the concept of telomerase inhibition as an antiproliferative treatment approach in neuroblastomas. Telomerase inhibition increases the outcome of radiotherapy while in combination with chemotherapy the outcome depends on drug- and cell line and can be additive/synergistic or antagonistic. High telomerase activity is one distinct cancer stem cell feature and the here described cellular constructs in combination with stem cell markers like CD133, Aldehyddehydrogenase-1 (ALDH-1) or Side population (SP) may help to investigate the impact of telomerase activity on cancer stem cell survival under therapy.

Allogeneic hematopoietic stem-cell transplantation in patients with hematologic malignancies after dose-escalated treosulfan/fludarabine conditioning

PURPOSE

Treosulfan was introduced recently as a conditioning agent for allogeneic blood stem-cell transplantation. The favorable nonhematologic toxicity profile at 3 x 10 g/m(2) was the basis for dose escalation in this prospective, multicenter trial.

PATIENTS AND METHODS

Fifty-six patients with various hematologic malignancies who were not eligible for standard conditioning were treated with one of three doses: 10 g/m(2), 12 g/m(2), or 14 g/m(2) of intravenous treosulfan, which was administered on days -6 to -4 combined with fludarabine 30 mg/m(2) on days -6 to -2. Patients in complete remission (CR; 42%) or non-CR (58%) received grafts from matched related (47%) or matched unrelated (51%) donors; one patient had a mismatched related donor (2%).

RESULTS

No engraftment failure occurred. Overall, extramedullary toxicity and the nonrelapse mortality rate at 2 years (20%) were low and did not increase with dose. Cumulative incidence of relapse/progression reached 31%. The overall survival and progression-free survival rates were 64% and 49%, respectively, in the total study population. An inverse dose dependency of relapse incidence was indicated in the subgroup receiving transplantations from matched related donors (P = .0568).

CONCLUSION

Treosulfan-based conditioning was feasible at all three doses. The 3 x 14 g/m(2) dose was selected for additional studies, because it combines desired characteristics of low toxicity and a low relapse rate.

Systematic analysis of the antiproliferative effects of novel and standard anticancer agents in rhabdoid tumor cell lines

Rhabdoid tumors are highly aggressive pediatric malignancies. Although the prognosis of children with rhabdoid tumors has improved, it still remains dismal and long-term survivors suffer from severe side effects of current therapeutic approaches. The objective of our study was to explore the toxicity of standard and novel anticancer drugs against rhabdoid tumors in vitro and to prioritize them for future preclinical and clinical studies. Antitumor activity of 10 standard anticancer drugs (doxorubicin, idarubicin, mitoxantrone, actinomycin D, temozolomide, carmustine, oxaliplatin, vinorelbine, methotrexate, thiotepa), five target-specific drugs (sorafenib, imatinib, roscovitine, rapamycin, ciglitazone) and two herbal compounds (curcumin and apigenin) was assessed by a modified 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell proliferation assay on three rhabdoid tumor cell lines, A204, G401, and BT16, derived from different anatomical sites. Comparable with their high clinical activity, anthracyclines inhibited tumor cell proliferation by 50% (GI50) in the nanomolar range. Actinomycin D exhibited the lowest GI50 values overall ranging from 2.8x10(-6) nmol/l for G401 to 3.8 nmol/l for A204 cells while thiotepa was the only alkylating drug that inhibited tumor cell growth in clinically relevant concentrations. Target-specific drugs, such as sorafenib, roscovitine, and rapamycin, showed promising results as well. In this report, we show for the first time that apigenin and curcumin effectively inhibit rhabdoid tumor cell growth. Supporting earlier reports we conclude that cyclin D1 seems to be an excellent target in the treatment of rhabdoid tumors. Idarubicin or mitoxantrone represent potent alternatives to doxorubicin, and vinorelbine may substitute vincristine in future clinical trials.

Dehydroalanine analog of glutathione: an electrophilic busulfan metabolite that binds to human glutathione S-transferase A1-1

Elimination of hydrogen sulfide from glutathione (GSH) converts a well known cellular nucleophile to an electrophilic species, gamma-glutamyldehydroalanylglycine (EdAG). We have found that a sulfonium metabolite formed from GSH and busulfan undergoes a facile beta-elimination reaction to give EdAG, which is an alpha,beta-unsaturated dehydroalanyl analog of GSH. EdAG was identified as a metabolite of busulfan in a human liver cytosol fraction. EdAG condenses with GSH in a Michael addition reaction to produce a lanthionine thioether [(2-amino-5-[[3-[2-[[4-amino-5-hydroxy-5-oxopentanoyl]amino]-3-(carboxymethylamino)-3-oxopropyl]sulfanyl-1-(carboxymethylamino)-1-oxopropan-2-yl]amino]-5-oxopentanoic acid); GSG], which is a nonreducible analog of glutathione disulfide. EdAG was less cytotoxic than busulfan to C6 rat glioma cells. GSH and EdAG were equally effective in displacing a glutathione S-transferase (GST) isozyme (human GSTA1-1) from a GSH-agarose column. The finding of an electrophilic metabolite of GSH suggests that alteration of cellular GSH concentrations, irreversible nonreducible glutathionylation of proteins, and interference with GST function may contribute to the toxicity of busulfan.

Preclinical studies of treosulfan demonstrate potent activity in Ewing's sarcoma

OBJECTIVES

High-dose chemotherapy with the alkylating agent busulfan has been widely used in the treatment of patients with high-risk Ewing's sarcoma. Because of risks for toxicity, busulfan and radiotherapy can not be applied together, leading to the omission of one effective therapy component. Treosulfan is a derivative of busulfan which has a lower side effect profile than busulfan and which can be used together with radiotherapy. We investigated the effect of treosulfan in a panel of Ewing's sarcoma cell lines on cell survival, cell cycle and apoptosis in vitro and compared it to busulfan. Furthermore, the anti-tumor effect of treosulfan was studied in an orthotopic Ewing's sarcoma mouse xenograft model.

METHODS

Cell survival was measured by MTT assay and cell cycle analysis by flow cytometry. Apoptosis was analyzed via detection of DNA fragmentation, Hoechst 33258 staining, Annexin V, and cleavage of caspases-3 and 9. The effect of treosulfan and busulfan on primary tumor growth was assessed in Ewing's sarcoma xenografts in NOD/SCID mice (10 mice per group), pharmacokinetics of treosulfan were analyzed in nude mice.

RESULTS

Treosulfan inhibited cell growth to at least 70% in all cell lines at concentrations achievable in vivo. Treosulfan had a greater effect on the inhibition of cell growth at equivalent concentrations compared to busulfan. The growth inhibitory effect of treosulfan at low concentrations was mainly due to a G2 cell cycle arrest, whereas at higher concentrations it was due to apoptosis. Apoptosis was induced at lower concentrations compared to busulfan. In contrast to busulfan, treosulfan induced cell death in an apoptosis-deficient cell line at concentrations achievable in vivo. In mice, treosulfan suppressed tumor growth at dosages of 2,500 and 3,000 mg/kg. Pharmacokinetic exposures of treosulfan in mice were similar to previous reports in human patients. At maximal tolerated dosages treosulfan had a higher anti-tumor activity than busulfan.

CONCLUSIONS

Our results suggest that treosulfan has efficacy against Ewing's sarcoma cells in vitro and in mice. Therefore, controlled trials examining the role of treosulfan in patients with Ewing's sarcoma are warranted.