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Although the use of treosulfan (TREO) in conventional donor hematopoietic cell transplantation (HCT) has been extensively evaluated, its use in cord blood transplantation (CBT) for hematologic malignancies has not been reported. Between March 2009 and October 2019, 130 CBT recipients were enrolled in this prospective multicenter phase 2 study. The conditioning regimen consisted of TREO, fludarabine, and a single fraction of 2 Gy total-body irradiation. Cyclosporine and mycophenolate mofetil were used for graft-versus-host disease prophylaxis. The primary end point was incidence of graft failure (GF), and based on risk of GF, patients were classified as low risk (arm 1, n = 66) and high risk (arm 2, n = 64). The median age was 45 years (range, 0.6-65 years). Disease status included acute leukemias in first complete remission (CR; n = 56), in ≥2 CRs (n = 46), and myelodysplastic (n = 25) and myeloproliferative syndromes (n = 3). Thirty-five patients (27%) had received a prior HCT. One hundred twenty-three patients (95%) engrafted, with neutrophil recovery occurring at a median of 19 days for patients on arm 1 and 20 days for patients on arm 2. The 3-year overall survival, relapse-free survival (RFS), transplant-related mortality, and relapse for the combined groups were 66%, 57%, 18%, and 24%, respectively. Among patients who had a prior HCT, RFS at 3 years was 48%. No significant differences in clinical outcomes were seen between the 2 arms. Our results demonstrate that TREO-based conditioning for CBT recipients is safe and effective in promoting CB engraftment with favorable clinical outcomes. This trial was registered at www.clinicaltrials.gov as #NCT00796068.

Aims: The aim of this work is the development of a mechanistic physiologically-based pharmacokinetic (PBPK) model using in vitro to in vivo extrapolation to conduct a drug-drug interaction (DDI) assessment of treosulfan against two cytochrome p450 (CYP) isoenzymes and P-glycoprotein (P-gp) substrates. Methods: A PBPK model for treosulfan was developed de novo based on literature and unpublished clinical data. The PBPK DDI analysis was conducted using the U.S. Food and Drug Administration (FDA) DDI index drugs (probe substrates) midazolam, omeprazole and digoxin for CYP3A4, CYP2C19 and P-gp, respectively. Qualified and documented PBPK models of the probe substrates have been adopted from an open-source online model database. Results: The PBPK model for treosulfan, based on both in vitro and in vivo data, was able to predict the plasma concentration-time profiles and exposure levels of treosulfan applied for a standard conditioning treatment. Medium and low potentials for DDI on CYP3A4 (maximum area under the concentration-time curve ratio (AUCRmₐₓ = 2.23) and CYP2C19 (AUCRmₐₓ = 1.6) were predicted, respectively, using probe substrates midazolam and omeprazole. Treosulfan was not predicted to cause a DDI on P-gp. Conclusion: Medicinal products with a narrow therapeutic index (eg, digoxin) that are substrates for CYP3A4, CYP2C19 or P-gp should not be given during treatment with treosulfan. However, considering the comprehensive treosulfan-based conditioning treatment schedule and the respective pharmacokinetic properties of the concomitantly used drugs (eg, half-life), the potential for interaction on all evaluated mechanisms would be low (AUCR < 1.25), if concomitantly administered drugs are dosed either 2 hours before or 8 hours after the 2-hour intravenous infusion of treosulfan.

Graphical abstract, Highlights • Good safety profile of mesenchymal stromal cells (MSCs) without toxicity findings. • MSC biodistribution showed primary distribution to the lung and short persistence. • No tumor formation observed after 6 months of repeated MSC dosing. • qPCR and in situ hybridization were combined for the detection of MSCs. • Data allow progression into clinical trials for acute Graft-versus-Host disease., Guidelines regulating the development of advanced therapy medicinal products (ATMPs) request nonclinical data for toxicity, biodistribution and tumorigenicity before mesenchymal stromal cell (MSC) products can be administered in large clinical trials. We assessed the biodistribution/persistence, safety and tumorigenicity of MC0518, a human allogeneic MSC product from pooled bone marrow mononuclear cells of eight healthy, adult, unrelated donors, which is currently investigated for the treatment of steroid-refractory acute Graft-versus-Host Disease (aGvHD) after hematopoietic stem cell transplantation. In our GLP studies, immuno-deficient mice were administered repeat doses of MC0518 (once weekly for 6 weeks, i.v.) at doses exceeding the proposed human clinical dose 20-60-fold. No signs of toxicity were observed in the combined biodistribution/toxicity study. Human MSCs in mouse tissues were detected by quantitative PCR (qPCR) and in situ hybridization (ISH). MC0518 showed initial trapping in the lung, occasional distribution into other organs and low tissue persistence beyond 24 h after application. No MSC-induced tumors of human origin were identified after a follow-up of six months. Additionally, we found that the combination of different detection methods (qPCR and ISH) is crucial for a reliable interpretation of biodistribution results. Our data suggest that MC0518 is safe for use in human.

Treosulfan-based conditioning prior to allogeneic transplantation has been shown to have myeloablative, immunosuppressive, and antineoplastic effects associated with reduced non-relapse mortality (NRM) in adults. Therefore, we prospectively evaluated the safety and efficacy of treosulfan-based conditioning in children with hematological malignancies in this phase II trial. Overall, 65 children with acute lymphoblastic leukemia (35.4%), acute myeloid leukemia (44.6%), myelodysplastic syndrome (15.4%), or juvenile myelomonocytic leukemia (4.6%) received treosulfan intravenously at a dose of 10 mg/m2/day (7.7%), 12 g/m2/day (35.4%), or 14 g/m2/day (56.9%) according to their individual body surface area in combination with fludarabine and thiotepa. The incidence of complete donor chimerism at day +28 was 98.4% with no primary and only one secondary graft failure. At 36 months, NRM was only 3.1%, while relapse incidence was 21.7%, and overall survival was 83.0%. The cumulative incidence of acute graft-vs.-host disease was 45.3% for grades I–IV and 26.6% for grades II–IV. At 36 months, 25.8% overall and 19.4% moderate/severe chronic graft-vs.-host disease were reported. These data confirm the safe and effective use of treosulfan-based conditioning in pediatric patients with hematological malignancies. Therefore, treosulfan/fludarabine/thiotepa can be recommended for myeloablative conditioning in children with hematological malignancies.

Background: Further improvement of preparative regimens before allogeneic haemopoietic stem cell transplantation (HSCT) is an unmet medical need for the growing number of older or comorbid patients with acute myeloid leukaemia or myelodysplastic syndrome. We aimed to evaluate the efficacy and safety of conditioning with treosulfan plus fludarabine compared with reduced-intensity busulfan plus fludarabine in this population. Methods: We did an open-label, randomised, non-inferiority, phase 3 trial in 31 transplantation centres in France, Germany, Hungary, Italy, and Poland. Eligible patients were 18–70 years, had acute myeloid leukaemia in first or consecutive complete haematological remission (blast counts

Background An alternative reduced-toxicity conditioning regimen for allogeneic transplantation, based on treosulfan and fludarabine, has recently been identified. The rationale for this study was to investigate the efficacy and safety of this regimen prospectively in patients with a primary myelodysplastic syndrome. Design and Methods A total of 45 patients with primary myelodysplastic syndromes were conditioned with 3×14 g/m2 treosulfan and 5×30 mg/m2 fludarabine followed by allogeneic hematopoietic stem cell transplantation. Subtypes of myelodysplastic syndromes were refractory anemia with excess blasts-2 (44%), refractory cytopenia with multilineage dysplasia (27%), refractory anemia (9%), refractory anemia with ringed sideroblasts (4%), refractory cytopenia with multilineage dysplasia and ringed sideroblasts (4%), refractory anemia with excess blasts-1 (2%), and myelodysplastic syndrome with isolated del (5q) (2%). The myelodysplastic syndrome was unclassified in 7% of the patients. Forty-seven percent of the patients had a favorable karyotype, 29% an unfavorable one, and 18% an intermediate karyotype. Patients were evaluated for engraftment, adverse events, graft- versus -host disease, non-relapse mortality, relapse incidence, overall survival and disease-free survival. Results All but one patient showed primary engraftment of neutrophils after a median of 17 days. Non-hematologic adverse events of grade III–IV in severity included mainly infections and gastrointestinal symptoms (80% and 22% of the patients, respectively). Acute graft- versus -host disease grade II–IV developed in 24%, and extensive chronic graft- versus -host disease in 28% of the patients. After a median follow-up of 780 days, the 2-year overall and disease-free survival estimates were 71% and 67%, respectively. The 2-year cumulative incidences of non-relapse mortality and relapse were 17% and 16%, respectively. Conclusions Our safety and efficacy data suggest that treosulfan-based conditioning therapy is a promising treatment option for patients with myelodysplastic syndromes. [clinicaltrials.gov][1] identifier: [NCT01062490][2] [1]: http://clinicaltrials.gov [2]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01062490&atom=%2Fhaematol%2F96%2F9%2F1344.atom

BACKGROUND AND OBJECTIVE Allogeneic transplantation can not be offered to many patients due to potential side-effects of conventional conditioning. Dose-reduced conditioning approaches improve tolerability, however, treatment efficacy may be reduced as well. We have, therefore, developed a dose intense but toxicity reduced conditioning regimen based on treosulfan and fludarabine and report first results. PATIENTS AND METHODS 65 patients with a median age of 50 years were transplanted from related (n = 21) or unrelated donors (n = 44) after conditioning with treosulfan (3 x 10, 3 x 12 or 3 x 14 g/m(2) i. v.) and fludarabine (5 x 30 mg/m(2) i. v.). 21 patients were in complete remission (CR) and 44 patients had not reached a CR at the time of transplantation. 59 of 65 patients were considered unfit for a conventional conditioning regimen. RESULTS The actuarial overall survival after 3 years is 59.2 %, the event-free survival 40.1 %. Patients with a related donor or transplantation in CR had a better overall (85.4 resp. 74.2 %) and event-free survival (52.2 % resp. 61.9 %). The cumulative incidence of relapse at 3 years was 26.2 %. Non-relapse mortality at day 100 is 17.4 % (cumulative incidence). In stepwise Cox regression analyses for overall survival, event-free survival and non-relapse mortality the covariables transplantation in CR vs. not in CR and the donor status were shown to be influential. CONCLUSIONS These results with a conditioning therapy of treosulfan and fludarabine indicate that patients despite higher age, concomitant disease or after intensive pretreatment can be successfully transplanted without increased treatment-related mortality.

Treosulphan has recently demonstrated antileukaemic activity and potent haematopoietic stem cell toxicity. Dose-escalated treosulphan (3 x 12 or 3 x 14 g/m2) combined with cyclophosphamide (Cy) was chosen for a new preparative regimen before allogeneic haematopoietic stem cell transplantation in 18 patients (median age 44, range 19-64 years) with haematological malignancies, considered ineligible for other myeloablative preparative regimens. Pharmacokinetic studies demonstrated rapid treosulphan plasma clearance and a dose-dependent increase of its maximum plasma concentrations and area under the concentration-time curves. Rapid and sustained white blood cell and platelet recovery and full donor chimerism was attained in all evaluable patients. Nonhaematological regimen-related CTC grades 3-4 adverse events were transient and predominantly consisted of cardiac (28%), gastrointestinal (39%), and hepatic (39%) toxicities. The 1-year nonrelapse mortality was 22%. Principal causes of transplant-related lethal events were infections in three of four affected patients. Only one patient died from regimen-related cardiac toxicity. The 1-year relapse estimate is 22%, overall and progression-free survival estimates are 67 and 56%, respectively. In conclusion, this new treosulphan and Cy combination is an effective, comparatively well-tolerated myeloablative preparative regimen even in patients with an increased risk for regimen-related toxic complications.

Treosulfan (l-threitol-1,4-bismethanesulfonate) is an alkylating agent with routine clinical application in the treatment of ovarian cancer. In this murine study we show that this drug also has the ability to deplete primitive hematopoietic stem cells in a dose-dependent manner as determined by the cobblestone area-forming cell assay and is similar to its parent compound busulfan. Because busulfan is frequently used as part of the conditioning regimen before stem cell transplantation, we investigated an alternative nonmyeloablative protocol in an allogeneic bone marrow transplantation model in which low-dose treosulfan was added to an immune-suppressive regimen consisting of T cell-depleting antibodies, fludarabine, and thymic irradiation. Although this treatment protocol produced minimal myelosuppression, the addition of treosulfan proved to be important for allowing stable multilineage and mixed chimerism in C57BL/6 recipients of major histocompatibility complex-mismatched B10.A bone marrow without evidence of graft-versus-host disease. Donor lymphocyte infusion performed at 10 weeks after bone marrow transplantation had the effect of transforming the state of mixed chimerism to full donor-type cells, again without evidence of graft-versus-host disease. Donor-specific immunologic tolerance in the mixed chimeric animals was indicated by the acceptance of donor-type and rejection of third-party skin grafts. Thus, low-dose treosulfan may be considered as a useful component of a truly nonmyeloablative conditioning protocol in providing for mixed hematopoietic chimerism and, consequently, in establishing a platform for adoptive immunotherapy.

Summary. Multiple myeloma is a non-curable haematological disease involving transformed plasma cells. High rates of complete remission can be achieved with autologous peripheral blood stem cell transplantation. Treosulfan is an alkylating substance that has been used in the treatment of ovarian carcinomas for many years. It has a favourable side-effect profile even at high-dose protocols. Thus, the objective of this study was to evaluate the effect of treosulfan on myeloma cells. The treatment of the myeloma cell lines, NCI-H929 and U266, with treosulfan led to apoptosis in both cell lines in a dose- and time-dependent manner. The induction of apoptosis was accompanied by cleavage of caspases -3 and -9 as well as downregulation of the antiapoptotic protein Mcl-1 and upregulation of the inhibitor of cyclin-dependent kinases, p21WAF1/CIP1. Furthermore, 100 µmol/l treosulfan was capable of inducing cell death in 63·6 ± 23·9% of primary myeloma cells, whereas treatment with the same concentration of melphalan showed 59·7 ± 26% cell death. These in vitro concentrations were at least 10-fold lower than achievable plasma levels, even at conventional doses of treosulfan. Our results suggest that treosulfan might be an appropriate candidate for novel treatment protocols for patients with multiple myeloma.

Gemcitabine plus treosulfan (GeT) is under investigation in metastatic uveal melanoma. In this phase II trial, cisplatin was added to a GeT regimen to investigate the efficacy and toxicity of two alkylating agents in combination with gemcitabine. Patients received 30 or 40 mg/m2 of cisplatin, 1000 mg/m2 of gemcitabine and 3000 mg/m2 of treosulfan on days 1 and 8. Therapy was repeated on day 29. A maximum of six cycles was administered. Nineteen patients were included in the trial, of whom 17 were evaluable for response. No objective response was observed; seven patients (41%) had stable disease and 10 (59%) progressed. The median progression-free survival of all 19 patients was 3.0 months [95% confidence interval (CI), 1.8–3.1]; the median overall survival was 7.7 months (95% CI, 1.9–13.8). Grade 3 and 4 thrombopenia and leucopenia occurred in eight and nine of the 19 patients, respectively. The addition of cisplatin to the GeT regimen results in excessive haematological toxicity without improvement in efficacy.

Background: Treosulfan (Ovastat®), a bifunctional alkylating cytostatic, indicated for the treatment of advanced ovarian carcinoma, was recently found to be active in human lung and breast carcinoma xenografts. Moreover, toxicological evaluation as well as clinical experience revealed the lack of significant nonhematological toxicity which makes treosulfan a promising candidate for high-dose chemotherapy combined with autol-ogous blood stem-cell reinfusion. As a prerequisite for clinical high-dose studies, a formal phase I dose escalation without stem-cell reinfusion was conducted to reassess the maximum tolerated dose and dose-limiting toxicity of treosulfan after intravenous short-term infusion. Patients: A total of 12 patients with chemotherapy-refractory advanced cancer were entered at 3 dose levels (8 g; 10 and 12.5 g/m2 treosulfan i.v). Most patients suffered from advanced small-cell lung cancer (5 patients) or ovarian carcinoma (3 patients). Results: The maximum tolerated dose of treosulfan in this group of heavily pretreated patients was 10 g/m2. The dose-limiting toxicity was reversible thrombocytopenia. There were no nonhematological side effects exceeding WHO grade 2. Conclusions: This phase I dose escalation trial confirmed the lack of significant nonhematologic side effects of treosulfan although a dose of 12.5 g/m2 was infused. A subsequent phase I study of high-dose treosulfan followed by peripheral blood progenitor cells has therefore been initiated.

An alternative reduced-toxicity conditioning regimen for allogeneic transplantation, based on treosulfan and fludarabine, has recently been identified. The safety and efficacy of this new conditioning regimen has been investigated prospectively in patients with AML. A total number of 75 patients with AML in CR were treated with 3 × 14 g/m(2) treosulfan and 5 × 30 mg/m(2) fludarabine, followed by matched sibling or unrelated SCT. Patients were evaluated for engraftment, adverse events, GVHD, and for non-relapse mortality, relapse incidence, overall and disease-free survival (DFS). All patients showed primary engraftment of neutrophils after a median of 20 days. Non-hematological adverse events grade III-IV in severity included mainly infections (59%) and gastrointestinal symptoms (7%). Acute GVHD grade II-IV occurred in 21% and extensive chronic GVHD occurred in 16% of the patients. After a median follow-up of 715 days, the 2-year overall and DFS estimates were 61% and 55%, respectively. The 2-year incidences of relapse and non-relapse mortality reached 34% and 11%, respectively. In summary, our data confirm promising safety and efficacy of the treosulfan-based conditioning therapy in AML patients, ClinicalTrials.gov Identifier: NCT01063660.

Purpose Treosulfan was introduced recently as a conditioning agent for allogeneic blood stem-cell transplantation. The favorable nonhematologic toxicity profile at 3 × 10 g/m2 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/m2, 12 g/m2, or 14 g/m2 of intravenous treosulfan, which was administered on days −6 to −4 combined with fludarabine 30 mg/m2 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 × 14 g/m2 dose was selected for additional studies, because it combines desired characteristics of low toxicity and a low relapse rate.

Treosulfan (Treo) and total body irradiation (TBI) demonstrate a high therapeutic activity in treatment of acute leukemia and lymphoma. We investigated the combination of Treo and TBI prior to bone marrow transplantation (BMT) in rats. Female Lewis rats were treated with Treo on 3 consecutive days followed by TBI with either 5 Gy (n = 28) or 7.5 Gy (n = 48). After conditioning animals received 4 x 10E7 bone marrow cells (BC) from female Lewis rats. Additional 16 rats were transplanted with 4 x 10E7 BC and 1.5 x 10E7 spleen T-cells from female Brown-Norway (BN) rats. Animals were examined daily for clinical signs and toxicity was investigated by necropsy and histology in all animals. Gastrointestinal toxicity was the dose-limiting factor of Treo in combination with TBI. The highest tolerable dose of Treo in combination with 7.5 Gy TBI was 3 x 0.5 g/kg and the highest tolerable dose of Treo in combination with 5 Gy TBI was 3 x 0.6 g/kg. Allogeneic BMT from BN donors resulted in engraftment and survival of 12 out of 16 animals. Gastrointestinal toxicity is the dose-limiting factor in the treatment with Treo and TBI. Furthermore, Treo possesses certain characteristics of a radiosensitizer.

Purpose: Treosulfan (l-threitol-1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. In a pharmacologic study of the bioavailability of treosulfan in a capsule formulation, patients with relapsed ovarian carcinoma were treated with alternating doses of oral and intravenous (i.v.) treosulfan of 1.5 or 2.0 g daily for 5 to 8 days. Methods: A sensitive method for the determination of treosulfan in plasma and urine by reversed-phase high-performance liquid chromatography had previously been developed. Pharmacokinetic analyses of treosulfan were carried on plasma and urine samples from 20 i.v. courses and 20 courses of oral administration. Results: The bioavailability ratio (f) of oral to i.v. administration was calculated as 0.97 ± 0.18 (mean ± SD) using the values AUCoral=82.1 ± 39.4 μg/ml h and AUCi.v.=85.4 ± 30.3 μg/ml h. The peak plasma concentration cmax (29 ± 14 μg/ml vs 65 ± 23 μg/ml) was significantly (P < 0.01) higher after i.v. administration and the tmax after oral administration was 1.5 ± 0.34 h. The terminal half-life of treosulfan was about 1.8 h. The mean urinary excretion of the parent compound was about 15% of the administered total dose over 24 h (range 6–26%). Conclusions: The high and relatively constant bioavailability of treosulfan indicates that capsules provide a satisfactory noninvasive treatment alternative. A feasible and reliable oral treosulfan formulation could provide the basis for the development of long-term low-dose outpatient treatment of patients with malignant diseases.

Treosulfan (L-threitol- 1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. For a clinical and pharmacology study, patients with advanced, refractory, or resistant solid tumors were treated with a single-dose intravenous 30-min infusion of 8 or 10 g/m2 treosulfan. A sensitive method for the determination of treosulfan in plasma and urine by reverse-phase high-performance liquid chromatography was developed. A total of 14 plasma and urine treosulfan pharmacokinetics determinations were analyzed in the 8-g/m2 group and 7 were analyzed in the 10-g/m2 group, the maximum tolerated dose for this group of pretreated patients. The terminal half-life of treosulfan was in the range of 1.8 h. AUC and Cmax values were significantly (P < 0.01) higher in the 10-g/m2 group (AUC 708+/-168 versus 977+/-182 microg ml(-1) h, Cmax 465+/-98 versus 597+/-94 microg/ml). The mean urinary excretion of the parent compound was about 25% of the total dose delivered over 48 h (range 5-49%), and about 20% was excreted during the first 6 h after administration. Currently, a clinical phase I pharmacokinetics and dose-escalation trial with autologous blood stem-cell support has been started at 20 g/m2 treosulfan using a 2-h infusion protocol.

Abstract 963 Background: We showed previously that a transplant conditioning regimen of treosulfan combined with fludarabine was associated with low non-relapse mortality (NRM) and a high probability of survival in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) with low or intermediate risk cytogenetics (Nemecek et al, BBMT 2011). Relapse rates were high, however, in patients with high-risk cytogenetics, which resulted in a 2-year relapse-free survival of 39% in this group. Objective: The objective of the present study was to reduce the relapse incidence and improve overall survival (OS) in patients with high-risk AML or MDS by adding low-dose TBI (2 Gy) to the treosulfan plus fludarabine regimen. Patients and methods: Ninety-six patients with AML (n=60) or MDS (n=36) were enrolled. Patients were 60 years of age or younger (median age: 50 years) and had high-risk MDS, unfavorable or intermediate-risk AML in first complete remission (CR) or any AML beyond first CR. Cytogenetic risk in AML was stratified using the Southwest Oncology Group criteria, while the World Health Organization-based Prognostic Scoring System was used in patients with MDS. Patients received intravenous (IV) treosulfan, 14 g/m2/day on days -6 to -4, IV fludarabine 30 mg/m2/day on days -6 to -2, and 2 Gy TBI on day 0, followed by infusion of marrow (n=11) or peripheral blood stem cells (n=85) from related (n=27) or unrelated (n=69) donors. Donors were single HLA allele-level mismatched in 9 patients and HLA-matched at the allele level in 87 patients. Graft-versus-host disease (GVHD) prophylaxis consisted of methotrexate (10 mg/m2 on days +1, +3, +6 and +11 post-HCT) and tacrolimus (days –1 to +180). Results: All evaluable patients engrafted. With a median follow-up of 12.8 (range, 0.2 – 34.7) months in surviving patients, the estimated 2-year progression-free survival and OS were 59% and 68%, respectively. The cumulative incidences of relapse or progression and NRM at 2 years were 30% and 11%, respectively (Figure 1). The incidences of grade II (grades III-IV) acute and extensive chronic GVHD at 2 years were 48% (11%) and 40%, respectively. Relapse occurred in 39% of patients with AML and 18% of patients with MDS (Figure 2A). OS was 61% among patients with AML and 79% in patients with MDS (Figure 2B). In univariate analyses, cytogenetic risk status did not impact relapse for the entire cohort nor for patients with AML or MDS analyzed separately (Figures 3A and 3B). As a result, 2-year OS rates were similar in patients with favorable/intermediate and unfavorable cytogenetic risk AML (64% and 57%, respectively) or in good/intermediate and poor risk MDS (88% and 71%, respectively). Patients with AML with minimal residual disease (MRD; n=10) or in refractory relapse (n=4) at the time of HCT, had higher relapse rates (87% vs. 25%) and lower OS (25% vs. 81%) at 2 years than patients in remission without MRD at the time of HCT. Conclusions: In summary, treosulfan, in combination with fludarabine and low-dose TBI was an effective conditioning regimen for allogeneic HCT in patients with AML (in CR at the time of HCT) or MDS. Relapse and OS rates in patients with high-risk cytogenetics did not differ significantly from those in patients with low or intermediate risk karyotypes. The relapse rate was particularly low in patients with MDS, including those with high risk cytogenetics, and further trials with treosulfan-based regimens are warranted. For patients with AML who have residual disease at HCT novel regimens need to be developed. The data suggest that in patients with AML high risk as defined by cytogenetics had a different impact on outcome than high risk as defined by other parameters, such as tumor burden. Disclosures: Gyurkocza: medac GmbH, Hamburg, Germany: Research Funding. Off Label Use: Off-label usage of treosulfan, fludarabine, methotrexate and tacrolimus will be discussed. Sickle:medac GmbH, Hamburg, Germany: Research Funding. Baumgart:medac GmbH, Hamburg, Germany: Employment. Deeg:medac GmbH, Hamburg, Germany: Research Funding.

Abstract 2353 Background: The key point in allogeneic hematopoietic stem cell transplantation (allo-HSCT) is to find the optimal balance between the graft-versus-host disease (GVHD) and the graft-versus-leukemia (GVL) effect particularly in the unrelated HSCT settings, without forgetting the important role of conditioning. Objective: To evaluate the toxicity and efficacy of a new reduced intensity conditioning regimen including Treosulfan, followed by allo-HSCT from a 10/10 HLA identical unrelated donor. Materials and Methods: This prospective study included adult patients presenting a hematological malignancy in need of allo-HSCT using a 10/10 HLA identical unrelated donor. Accepted diagnoses were: CML in 1st chronic phase (CP) resistant to imatinib, in 2nd CP or in complete remission (CR) after blast crisis. Multiple myeloma (MM) or chronic lymphocytic leukemia (CLL) in stage B or C in response after relapse post-auto-HSCT. Acute lymphocytic or myeloid leukemia (ALL, AML) patients in CR1 at high risk or The conditioning included: Treosulfan 12g/m2/day intra-venous (day-6 to day-4), fludarabine 30mg/m2/day intra-venous (day-6 to day -2) and ATG 2.5 mg/kg/day (day-2 to day-1). GVHD prophylaxis used cyclosporine A oral (5mg/kg/day) or iv. (3mg/kg/day) from day-1. Peripheral stem cells after mobilization by G-CSF were used as HSC source. Results: Between February 2005 and July 2009, 56 patients were included in 5 different French centers, 30 (54%) males and 26 females with a median age of 57 years (18-65.5). There were 38 (68%) myeloproliferative disorders [29 AML (14 in CR1, 14 CR2 & 1 2 lines. For sex-matching, 49% of patients were sex-mismatched (half of them were F>M). For CMV, 43% were -/-, 25% +/+, 28% +/− and 1% -/+. For ABO matching, 52% were compatible, 24% major incomp. & 24% minor incopm. The median time between diagnosis and allograft was 15 months (4-168). The median number of infused CD34+ cells was 6.5 × 106/Kg(1-17.2) Fifty-four (96%) patients engrafted with a median time to neutrophils (>0.5G/l), and platelets (>50G/l) recovery of 16 days (4-86), 11 (4-82) respectively. Seventeen patients developed aGVHD grade ≥II (8 grade II, 2 grade III & 7 grade IV) with a cumulative incidence at 3 months of 31% (25-38). The cumulative incidence of cGVHD was, at 12 months: 32% (25-39) limited and 6% (2-10) extensive; at 18 months: 34% (27-47) limited and 8% (5-12) extensive. After a median follow-up of 13 months (1-57), the median overall survival (OS) was not reached with a 3 years probability of 52% (38-71). The median time of event free survival (EFS) was 15 months (8 - 57) with a 3-years probability of 47% (35-64). The cumulative incidence of relapse at 3 years was 25% (19-31) and the cumulative incidence of transplant-related mortality (TRM) at 12, 18 and 36 months was 20% (16-27), 23% (16-29) (same at 18 & 36 months) respectively. At the last follow-up, 22 patients died, 7 due to relapse and 15 due to TRM (5 pneumonia, 4 GVHD, 1 secondary malignancy and 6 other causes). We showed in a univariate analysis a higher 3-years OS of patients in CR1 (65%) compared to those Conclusion: We showed very promising results in terms of OS, relapse and TRM with an impressive GVL effect, in heavily pre-treated patients and transplanted using unrelated donors. Treosulfan appears to be a good choice for conditioning especially with a better outcome in AML patients in CR1. Disclosures: No relevant conflicts of interest to declare.

Allogeneic hematopoietic cell transplantation (HCT) offers curative therapy for many patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). However, post-HCT relapse remains a major problem, particularly in patients with high-risk cytogenetics. In this prospective phase II trial, we assessed the efficacy and toxicity of treosulfan, fludarabine, and 2 Gy total body irradiation (TBI) as conditioning for allogeneic HCT in patients with MDS or AML. Ninety-six patients with MDS (n = 36: 15 refractory cytopenia with multilineage dysplasia, 10 refractory anemia with excess blasts type 1, 10 refractory anemia with excess blasts type 2, 1 chronic myelomonocytic leukemia type 1) or AML (n = 60: 35 first complete remission [CR], 18 second CR, 3 advanced CR, 4 refractory relapse) were enrolled; median age was 51 (range, 1 to 60) years. Twelve patients had undergone a prior HCT with high-intensity conditioning. Patients received 14 g/m2/day treosulfan i.v. on days −6 to −4, 30 mg/m2/day fludarabine i.v. on days −6 to −2, and 2 Gy TBI on day 0, followed by infusion of hematopoietic cells from related (n = 27) or unrelated (n = 69) donors. Graft-versus-host disease prophylaxis consisted of tacrolimus and methotrexate. With a median follow-up of 30 months, the 2-year overall survival (OS), relapse incidence, and nonrelapse mortality were 73%, 27%, and 8%, respectively. The incidences of grades II to IV (III to IV) acute and chronic graft-versus-host disease were 59% (10%) and 47%, respectively. Two-year OS was not significantly different between MDS patients with poor-risk and good/intermediate-risk cytogenetics (69% and 85%, respectively) or between AML patients with unfavorable and favorable/intermediate-risk cytogenetics (64% and 76%, respectively). In AML patients, minimal residual disease (MRD; n = 10) at the time of HCT predicted higher relapse incidence (70% versus 18%) and lower OS (41% versus 79%) at 2 years, when compared with patients without MRD. In conclusion, treosulfan, fludarabine, and low-dose TBI provided effective conditioning for allogeneic HCT in patients with MDS or AML and resulted in low relapse incidence, regardless of cytogenetic risk. In patients with AML, MRD at the time of HCT remained a risk factor for post-HCT relapse.