Residual injury to the hemopoietic microenvironment following sequential radiation and busulfan

Our earlier studies in mice showed that sequential radiation and cyclophosphamide suppressed marrow stromal cells (MSC) and prevented local hemopoietic repopulation for several months. Because others have shown that busulfan administration caused marrow aplasia, we studied its ability, combined with radiation, to produce a peristent microenvironmental defect in mice. Intraperitoneal administration of four weekly doses of 20 mg/kg busulfan, starting one week after 1500 rad leg irradiation, produced a severe microenvironmental lesion for 6 months reflected by lack of repopulation in femoral marrow to greater than 50 % of normal by MSC, hemopoietic stem cells (CFU-S), and granulocyte-macrophage precursors. Differential marrow cell counts revealed that precursors of hemopoietic cells were more profoundly affected than their progeny. Hemopoietic stem cells and MSC failed to recover in busulfan-treated mice at 6 months to the same extent as those treated with cyclophosphamide. In addition, the busulfan-treated mice had an excessive number of myeloid blast cells and a severe erythroid depletion suggesting that these animals were preleukemic. We conclude that: 1) sequential radiation and busulfan administration caused long-term microenvironmental damage reflected by incomplete repopulation of the femoral marrow and suppression of MSC, and 2) multiple courses of busulfan prevented hemopoieticrepopulation longer than a similar regimen of cyclophosphamide.     

Antitumor Activity and Neutrophil-selective Hematopoietic Toxicity of Busulfan Analogs in Mice

The antitumor activity and hematopoietic toxicity of two busulfan analogs were evaluated in comparison with those of busulfan. Although a program of five daily ip treatments with busulfan was not effective in treating sarcoma 180-bearing mice, a fluorine-containing busulfan analog, 1,4-butanediol di-2,2,2-trifluoroethanesulfonate (BFS), and a water-soluble analog, 1,4-butanediol diisethionate (BIT), were significantly effective when given on the same schedule. Busulfan did not appreciably prolong the life span of either P388- or Meth A-bearing mice, whereas BFS and BIT produced significant increases in the life span. It is worth noting that both the analogs were definitely less toxic to the host mice than busulfan. All the drugs examined exhibited suppressive effects on the counts of total WBCs, neutrophils, and lymphocytes. Relative toxicity toward neutrophils versus lymphocytes was increased significantly in the BFS and BIT treatments compared with busulfan treatment. It seems that the toxicity of busulfan in host mice might be due to unidentified side effects other than bone marrow suppression. These results suggest that BFS and BIT could be improved substitutes for busulfan.     

Dose-dependent neurotoxicity of high-dose busulfan in children: a clinical and pharmacological study

Busulfan is known to be neurotoxic in animals and humans, but its acute neurotoxicity remains poorly characterized in children. We report here a retrospective study of 123 children (median age, 6.5 years) receiving high-dose busulfan in combined chemotherapy before bone marrow transplantation for malignant solid tumors, brain tumors excluded. Busulfan was given p.o., every 6 hours for 16 doses over 4 days. Two total doses were consecutively used: 16 mg/kg, then 600 mg/m2. The dose calculation on the basis of body surface area results in higher doses in young children than in older patients (16 to 28 mg/kg). Ninety-six patients were not given anticonvulsive prophylaxis; 7 (7.5%) developed seizures during the 4 days of the busulfan course or within 24 h after the last dosing. When the total busulfan dose was taken into account, there was a significant difference in terms of neurotoxicity incidence among patients under 16 mg/kg (1 of 57, 1.7%) and patients under 600 mg/m2 (6 of 39, 15.4%) (P less than 0.02). Twenty-seven patients were given a 600-mg/m2 busulfan total dose with continuous i.v. infusion of clonazepam; none had any neurological symptoms. Busulfan levels were measured by a gas chromatographic-mass spectrometry assay in the plasma and cerebrospinal fluid of 9 children without central nervous system disease under 600 mg/m2 busulfan with clonazepam:busulfan cerebrospinal fluid:plasma ratio was 1.39. This was significantly different (P less than 0.02) from the cerebrospinal fluid:plasma ratio previously defined in children receiving a 16-mg/kg total dose of busulfan. This study shows that busulfan neurotoxicity is dose-dependent in children and efficiently prevented by clonazepam. A busulfan dose calculated on the basis of body surface area, resulting in higher doses in young children, was followed by increased neurotoxicity, close to neurotoxicity incidence observed in adults. Since plasma pharmacokinetic studies showed a faster busulfan clearance in children than in adults, this new dose may approximate more closely the adult systemic exposure obtained after the usual 16-mg/kg total dose, with potential inferences in terms of anticancer or myeloablative effects. The busulfan dose in children and infants undergoing bone marrow transplantation should be reconsidered on the basis of pharmacokinetic studies.     

Late tissue-specific toxicity of total body irradiation and busulfan in a murine bone marrow transplant model

Total body irradiation (TBI) and busulfan were compared for late effects in a murine model of bone marrow transplantation (BMT). Male C57BL/6 mice were given fractionated TBI or busulfan given in 4 equal daily doses followed by infusion of 10(7) syngeneic bone marrow cells. Total doses of 16.4 Gy TBI and 3.4 mg busulfan were chosen for their equivalence in inducing near complete engraftment of allogeneic marrow from donor mice of the LP strain. The two treatment groups had a late wave of mortality starting at about 80 weeks after transplantation. Specific tissue damage was manifested in bone marrow stem cells, splenic T-cell precursors, hair greying and cataract formation for both TBI and busulfan but to varying degrees. Severe nephrotoxicity and anemia were observed only after TBI. Although both busulfan and TBI kill early marrow stem cells and are effective preparative agents in bone marrow transplantation, their effects on other stem cell and organ systems are not similar. In addition, many of the injuries seen are late to occur. The delayed expression of injury deserves careful long-term evaluation of BMT recipients before the therapeutic potential of effective preparative regimens can be fully appreciated.     

Induction of sister chromatid exchanges and chromosomal aberrations by busulfan in Philadelphia chromosome-positive chronic myeloid leukemia and normal bone marrow

Cytogenetic effects of busulfan in vitro were studied in normal bone marrow (nine cases) and Philadelphia chromosome (Ph)-positive cells (10 cases) of patients with chronic myeloid leukemia. The frequency of chromosome aberrations and sister chromatid exchange (SCE) increased dose dependently. While there were no significant differences between normal and leukemic cells with regard to the induction of chromosome aberrations, the frequency of SCE was significantly lower in Ph-positive cells than in normal bone marrow. This difference was not only apparent on the basis of the SCE frequency per cell, but also when the SCE frequency was correlated to the relative chromosome length as shown by the SCE rate per chromosome group. Longitudinal studies of three patients who received long term busulfan treatment did not show a significant change in the frequency of induced SCE. It can be suggested that the lower frequency of induced SCE in Ph-positive cells reveals less sensitivity of the leukemic cells to DNA damage by busulfan. Our data provide evidence for the inability of busulfan treatment to eradicate or even reduce Ph-positive cells in chronic myeloid leukemia. Evaluation of cell proliferation by sister chromatid differentiation shows longer cell cycle times for the Ph-positive cells. Busulfan affected the cell cycle duration of leukemia and normal cells very little.     

The effect of hepatic enzyme inducers on busulfan neurotoxicity and myelotoxicity

Summary Anticonvulsants are commonly used empirically to prevent seizures in patients receiving high-dose busulfan in preparation for bone marrow transplantation. This study evaluates the effects of two anticonvulsants with enzyme-inductive properties, phenytoin and phenobarbital, and an enzyme inducer without anticonvulsant properties, Aroclor 1254, on the myelotoxicity and acute neurotoxicity of busulfan in a murine model. To assess the neuroprotective effects of these agents, we studied the effects of a single dose of 100 mg/kg i.p. busulfan, previously shown in this model to be uniformly lethal due to neurotoxicity. A significantly greater proportion of mice survived when pretreated with phenytoin or phenobarbital as compared with Aroclor 1254 pretreatment or an untreated control group. Busulfan myelotoxicity was studied in another group of mice treated with 135–150 mg/kg given in divided doses over 6 days. The proportion of animals surviving the otherwise myeloablative effects of this regimen were significantly improved by Aroclor 1254, high-dose phenytoin, and phenobarbital pretreatment. We conclude that anticonvulsants offer protection from the acute neurotoxicity of busulfan. However, these enzyme-inducing agents may reduce the myelosuppresive effects as well. These results suggest than an inducible enzyme system such as microsomal or glutathione S-transferases plays an important role in busulfan metabolism, warranting concern over concomitant administration of agents that either induce or inhibit these enzymes.     

Acute cholecystitis after autologous bone marrow transplantation for acute myeloid leukemia

Background: We investigated the incidence of acute cholecystitisin patients with acute myeloid leukemia (AML) undergoing autologousbone marrow transplantation in complete remission. Patients and methods: Thirty-five consecutive acute myeloidleukemia patients were given oral busulfan4 mg/kg/day for 4days and IV cyclophosphamide 50 mg/kg/day for 4 days followedby reinfusion of autologous bone marrow purged with 4-hydroperoxycyclophosphamide. Results: Five of 35 patients developed clinical evidence ofacute cholecystitis, manifested by fever, nausea, vomiting,right-upper-quadrant pain, and abdominal guarding, within 18days after autologous bone marrow infusion.Ultrasonography andCT scans of the abdomen supported the diagnosis of cholecystitis.Three patients underwent cholecystectomy, while two patientswere treated medically; all recovered uneventfully. A reviewof 338 consecutive bone marrow transplant patients who underwentmarrow transplantation for a variety of diseases and were treatedwith other high-dose cytotoxic regimens during the same timeperiod revealed significantly fewer cases of cholecystitis,i.e. two, (p <0.0001). Conclusions: Five of 35 AML patients undergoing autologous bonemarrow transplant using busulfan, cyclophosphamide, and purgedbone marrow developed evidence of acute cholecystitis. Thesefindings suggest that the busulfan/cyclophosphamide preparativeregimen may be associated with acute cholecystitis. The trueincidence of this injury and its pathogenesis remain to be elucidated. acute myeloid leukemia, autologous bone marrow transplant, cholecystitis, busulfan, cyclophosphamide     

Busulfan disposition and hepatic veno-occlusive disease in children undergoing bone marrow transplantation

Hepatic veno-occlusive disease (HVOD) is a frequent life-threatening toxicity in patients undergoing bone marrow transplantation (BMT) after the administration of a high-dose busulfan-containing regimen. Recent studies have shown that the morbidity and mortality of HVOD may be reduced in adults by pharmacologically guided dose adjustment of busulfan. We analyzed the pharmacodynamic relationship between busulfan disposition and HVOD in 61 children (median age, 5.9 years) with malignant disease. Busulfan, given at a dose ranging from 16 mg/kg to 600 mg/m², was combined with one or two other alkylating agents (cyclophosphamide, melphalan, thiotepa). Only 3 patients received the standard busulfan/cyclophosphamide (BUCY) regimen. A total of 24 patients (40%) developed HVOD, which resolved in all cases. A pharmacokinetics study confirmed the previously reported wide interpatient variability in busulfan disposition but did not reveal any significant alteration in children with HVOD. The mean area under the concentration-time curve (AUC) after the first dose of busulfan was higher in patients with HVOD (6,811±2,943 ng h ml^–1) than in patients without HVOD (5,760±1,891 ng h ml^–1;P=0.10). This difference reflects the higher dose of busulfan given to patients with HVOD. No toxic level could be defined and, moreover, none of the toxic levels identified in adults were relevant. The high incidence of HVOD in children given 600 mg/m² busulfan may be linked to the use of more intensive than usual high-dose chemotherapy regimens and/or drug interactions. Before the prospective evaluation of busulfan dose adjustment in children, further studies are required to demonstrate firmly the existence of a pharmacodynamic relationship in terms of toxicity and allogeneic engraftment, especially when busulfan is combined with cyclophosphamide. The maximal tolerated and minimal effective AUCs in children undergoing BMT are likely to depend mainly upon the disease, the nature of the combined high-dose regimen, and the type of bone marrow transplant.     

The role of busulfan in bone marrow transplantation

High-dose busulfan is an important component in many conditioning protocols for hematopoietic stem cell transplantation (HSCT) or bone marrow transplantation (BMT) in both adults and children. During the past 12y several studies have reported the wide inter-individual variability in busulfan disposition. Age, disease status, hepatic function, circadian rhythmicity, drug interactions and bioavailability, were identified as factors contributing to the high inter-individual variability found in busulfan disposition. Traditionally, a standard busulfan dose of 4mg/kg/d for four days is used in most BMT/HSCT protocols. Many investigations have pointed out the pharmacodynamic relationship between a high busulfan systemic exposure and the occurrence of BMT related toxicity including hepatic veno-occlusive disease (VOD), interstitial pneumonia and alopecia in adult patients. However, studies in young patients have shown a high rate of graft failure and subsequently relapse which most probably is due to the low systemic exposure despite the standard dose schedule. In children and infants VOD was not observed with the standard doses. Increasing interest for the drug and new modification strategies for children led to higher rate of VOD and CNS toxicity when busulfan was administered according to the body surface area. More pharmacodynamic studies are required to establish the relation between the systemic exposure to busulfan and the therapeutic efficacy, especially in young children undergoing BMT or HSCT. In the present time an accurate and effective busulfan plasma level monitoring combined with dose adjustment based on the known pharmacological parameters may improve the clinical outcome for patients undergoing BMT.     

Treatment of recurrent and refractory pediatric solid tumors with high-dose busulfan and cyclophosphamide followed by autologous bone marrow rescue.

PURPOSE: The purpose of this study was to determine the toxicities of and responses to high-dose busulfan and cyclophosphamide with autologous bone marrow transplant (ABMT) in patients with recurrent or refractory pediatric solid tumors. PATIENTS AND METHODS: We treated 18 patients (ages, 2 to 38 years; median, 14) who had tumors that were resistant to conventional chemotherapy and radiotherapy with busulfan 16 mg/kg and cyclophosphamide 200 mg/kg. Seventeen patients received bone marrow purged with 4-hydroperoxycyclophosphamide; one received unpurged marrow. RESULTS: Despite extensive prior treatment, including radiotherapy in 16 patients, toxicity generally was acceptable. For seven patients with measurable disease, there were three partial responses of 2, 10, and 20 months' duration, three patients with stable disease (SD), and one early, toxic death. Of the 11 patients with no measurable disease at the time of transplantation, one patient with osteosarcoma continues in remission at 57+ months and one third of the patients survived for at least 16 months. Mucositis was the predominant nonhematopoietic toxicity. CONCLUSION: Although the high-dose busulfan and cyclophosphamide combination showed modest activity, changes in the preparative regimen should be considered to improve the response rate in refractory tumors.     

Protective effect of testosterone of 5β-dihydrotestosterone pretreatment on CFU-E numbers in busulfan-treated rabbits

Summary Busulfan is known to damage hematological stem cells. On the other hand, numerous steroid hormones have a stimulating effect on hematopoiesis. We wished to find out whether steroids have a protective effect on hematopoisis in the case of busulfan treatment. This possibility was tested in vitro in rabbit bone marrow cultures, with and without in vivo pretreatment, with regard to erythropoiesis.The stimulating effect of testosterone or 5-dihydrotestosterone on the CFU-E number in rabbit bone marrow cultures was blocked in the presence of busulfan. When rabbits were pretreated with either steroid before the administration of busulfan, however, the reduction of the CFU-E number seen after busulfan therapy alone was compensated.These results indicate that testosterone and the nonandrogenic 5-dihydrotestosterone provide some protective effect on erythroid precursor cells when administered with reference to the cell-cycle-dependent action of busulfan.Dedicated to Prof. Dr. Werner Kaufmann, Köln, on the ocassion of his 60th birthdaySupported by the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen, FRG     

Clinical and pharmacologic effects of high dose single agent busulfan with autologous bone marrow support in the treatment of solid tumors

A Phase I-II clinical trial of high dose single agent busulfan (16-20 mg/kg) administered over a 4-day period was undertaken. Pharmacokinetic measurements reveal that steady state total plasma busulfan levels between 2 and 10 microM were achieved by the second day and maintained through the remaining treatment period. Urinary excretion of mutagenic activity monitored by the Salmonella mutagenesis assay persisted for up to 48 h following the last dose of busulfan. The treatment showed specificity for myelocytic precursors as evidenced by selective depression of granulocytes with relative sparing of lymphocytic elements, and by differences in DNA damage as measured by a nucleoid sedimentation assay. Dose limiting toxicity was mucositis, anorexia, and hepatic toxicity. Transient autoimmune disorders were observed in three of the six patients. Partial responses were seen in two of five patients with melanoma, but these lasted for only 2 and 3 months. High dose busulfan represents an alkylating agent with marked myelocytic selectivity and may be useful for inclusion in intensive combination regimens.     

Enhanced cutaneous radiation effects following high-dose busulfan therapy

Summary Fifteen patients received irradiation after combined chemotherapy with high-dose busulfan followed by autologous or allogeneic bone marrow transplantation. Of nine patients irradiated between day 30 and day 70 after their engraftment, seven developed an increased radiation response in the skin: four showed enhanced reactions during irradiation, and three had a total or severe definitive alopecia more than 16 months after CNS irradiation. Six patients were irradiated after day 70; they had either normal reactions or none at all within the cutaneous radiation portals. The possibility that busulfan might be a radiosensitizer is raised.     

In vitro studies on the mechanism of action of hepsulfam in chronic myelogenous leukemia patients

In the present study we have characterized the cytotoxicity and DNA damage induced by hepsulfam and busulfan in cells isolated from both chronic myelogenous leukemia (CML) patients and normal donors. hepsulfam inhibited colony-forming units-granulocyte, macrophage to a greater extent than busulfan in peripheral blood cells (PBCs) isolated from CML patients. Normal PBCs were equally sensitive to both agents and were more sensitive than the cells isolated from CML patients. Hepsulfam induced DNA interstrand cross-links in PBCs and bone marrow from both CML and normal volunteers, whereas busulfan produced few or no DNA interstrand cross-links. In addition, hepsulfam induced higher levels of DNA interstrand cross-linking than busulfam in three samples isolated from CML patients in blast crisis. Busulfan did however cause a small number of DNA strand breaks to be formed in human cells. Both agents produced similar levels of DNA-protein cross-links in PBCs from CML patients. These results suggest that the mechanism of DNA reactivity of hepsulfam and busulfan differ and that hepsulfam may prove useful in the treatment of CML.     

Overexpression of glutathione-S-transferase, MGSTII, confers resistance to busulfan and melphalan

A major obstacle to hematopoietic gene therapy is the lack of appropriate in vivo selection protocols that can raise the presently low numbers of gene-altered stem cells to therapeutically useful levels. Overexpression of glutathione-S-transferases (GST), in combination with busulfan treatment, may provide an exploitable selection mechanism for hematopoietic gene therapy strategies. GST provides a major route of detoxification of a variety of xenobiotics, including alkylating agents used for myeloablative chemotherapy. The only known route of clearance of busulfan is by GST-mediated conjugation. Using a fibroblast cell line as a model, we have tested the effects of overexpression of three human GST (GSTA1, GSTP1, and MGSTII) on cell survival under a busulfan or melphalan challenge. In two separate assay formats using chronic exposure to busulfan, MGSTII conferred a reproducible twofold selective advantage. GSTA1 and GSTP1 had no effect on busulfan resistance, and melphalan resistance was not affected by expression of any of the GSTs in these assays. In an acute (24-hour) melphalan exposure assay, MGSTII conferred about a twofold selective advantage. Busulfan was not toxic in this assay. RTPCR analysis of human bone marrow CD34+ cells showed that MGSTII is not highly expressed in this stem/early progenitor population. These data indicate that MGSTII may be a useful selective agent in hematopoietic gene therapy.     

Bone marrow transplantation in a BN rat model of acute myelogenous leukemia (AML)

A rat model of acute myelogenous leukemia is described. The leukemia originally induced by 7,12 dimethylbenzanthracine in the Brown Norway (BN) rat can be transferred by the inoculation of leukemic blasts intravenously into normal female BN rats. The survival of animals given 1–100 × 10⁶ leukemic blasts ranges from 15 to 25 days following tumor transfer, with the lowest number of cells injected giving the longest survival times. If 1 × 10⁶ blasts are injected and, 2 weeks later, groups of rats receive lethal doses of cyclophosphamide (CY), busulfan (BU) or total body irradiation (TBI) followed 24 h later by a syngeneic marrow graft, only animals which receive the CY conditioning survive more than 2 weeks (survival > 100 days) following the transplant. All other animals die with marrow failure (early death) or florid leukemia.Preliminary studies with an allogeneic (ACI marrow graft given to the BN rat) marrow graft suggests that leukemic rats may accept a histoincompatible graft without leukemic relapse following cyclophosphamide conditioning and postgraft immunosuppression. The anti-leukemic effect of cyclophosphamide, therefore, appears to be greater for this disease than is busulfan or total body irradiation.     

Evaluation of dimethylaminosulfonates of alkane diols as a novel group of anticancer agents

A series of title compounds has been synthesized and evaluated by the cytotoxicity assays conducted in vitro in seven human tumor cell lines, initially in MT-4 and H-9, followed by U-937, PM-1, MCF-7, Hep-3B, and K-562. These compounds were simultaneously compared with the existing clinical drug, busulfan and also with an experimental drug, hepsulfam. IC(50) values of these agents in T-cell lymphoma and leukemic cell lines indicate that two of these agents hexsulfamyl and octsulfamyl (compounds 3 and 4) were significantly more potent than busulfan and were comparable in antileukemic activity with hepsulfam. In order to determine the effect of these agents on normal proliferating cells, the toxicity of 3 and 4 was also determined in vitro against human peripheral blood mononuclear cells (PBMC) and against murine bone marrow progenitor cells. PBMC assay data indicate that these agents were generally less toxic than hepsulfam. The results of the colony forming unit-erythroid (CFU-E) and granulocyte-macrophage colony forming unit (CFU-GM) assays, however, indicate that these agents were more toxic than hepsulfam to erythroid progenitor cells than to granulocyte-macrophage progenitors. The toxicity of octsulfamyl was further assessed in vivo in normal Swiss mice by measuring drug-induced changes in hematological parameters, femoral bone marrow cellularity and splenic cellularity as well as hepatotoxicity and nephrotoxicity on day 7 and 14 following drug treatment at the dose of 1.0 mg/kg body weight from days 1 to 5. The results indicate that the compound did not adversely affect hematopoiesis. Marginal bone marrow suppression was observed on day 7, which gradually tends to reach normalcy on day 14. The other parameters were within normal limit.     

High-dose 1,2,4-triglycidylurazol given in regimens preparatory to bone marrow transplantation

Summary To elucidate its potential role in the framework of bone marrow transplantation, we studied the toxicologic and pharmacologic properties of high doses of the triepoxide derivate 1,2,4-triglycidylurazol (TGU) in a preclinical dog model. Dose-dependent and dose-limiting gastrointestinal toxicity occurred in a dose range between 40 and 75 mg/kg, with the lethal dose for 50% of animals (LD₅₀) being estimated at 60 mg/kg. Severe and life-threatening hematologic toxicity developed at all dose levels examined but was generally reversible. The combination of TGU and total-body irradiation produced synergistic gastrointestinal toxicity, necessitating reductions of the TGU dose by 50% as compared with the single-agent dose. In contrast, the combination of TGU and high-dose busulfan resulted in no apparent nonhematologic synergistic toxicities. The immunosuppressive properties of TGU given in this combination enabled sustained histocompatible allogeneic marrow engraftment in three of four animals. The pharmacokinetics of TGU were not influenced by prior total-body irradiation or high-dose busulfan. We conclude that the myelotoxic, pharmacologic and immunosuppressive properties of high-dose TGU observed in this preclinical model seem to render the drug particularly suitable for use in regimens preparatory to bone marrow transplantation.This work was supported by grant SFB 102 C10 from the Deutsche Forschungsgemeinschaft