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[Measurement of busulfan concentration in plasma and spinal fluid from transplant patients pretreated with busulfan and cyclophosphamide].

Busulfan (BU) concentrations in the blood and spinal fluid of 7 patients pretreated with BU for bone marrow transplantation (BMT) were measured using gas chromatography. The data from these periodically obtained samples were used to study the relationship between the BU concentration and complications (e.g. vomiting), indicating that vomiting leads to a lower maximum BU level. The trough level of BU concentration at 6 hours after administration was stable at around 500 ng/ml, not showing little effect of vomiting. The BU concentrations in the spinal fluid were virtually the same as those in plasma collected at the same time and the spinal fluid/plasma ratio of the BU concentration averaged 1.06. No veno-occlusive disease (VOD) was noted. Failure of engraftment occurred in one case of myelofibrosis, however, as the plasma BU concentration in this case was not lower than the others, the graft failure was not considered to be due to the preconditioning regimen including BU.

Adolescent

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.

Adolescent

Growth retardation and depigmentation of hair after high-dose busulfan and congenic hematopoietic cell transplantation in mice.

Busulfan, a myeloablative but non-immunosuppressive alkylating agent, is used extensively in clinical bone marrow transplantation (BMT), but the effects of high-dose administration have not been previously evaluated in preclinical BMT settings with young murine recipients. We compared the survival and growth of C57BL/6 mice given graded single doses of busulfan (10-100 mg/kg) or total body irradiation (TBI; 900 cGy) at age 9 days and hematopoietic cell transplantation (HCT; transplantation of congenic bone marrow and spleen cells) 24 h later. The 30-day survival was 87-100% in mice transplanted after 10-40 mg/kg busulfan and 79% after TBI, but fell to 54% and 33%, respectively, after 80 mg/kg and 100 mg/kg busulfan, suggesting that this latter dosage range represents the LD50 for single-dose busulfan in young C57BL/6 mice given stem cell rescue. The weights of 10-week-old mice given HCT after lower doses of busulfan ranged from 87% of control at 10 mg/kg to 64-69% of control in mice conditioned with 35-65 mg/kg busulfan or TBI. Impairment of weight gain was most striking (approximately 50% of control) in mice transplanted after 80-100 mg/kg busulfan. Despite retardation of somatic growth, the brain weights of busulfan-conditioned mice remained at least 90% of control, and there were no obvious neuropathological alterations in the brains of these animals. All mice treated with at least 20 mg/kg busulfan or TBI lost hair by 3-4 weeks after transplant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals

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.

Alkanesulfonates

Dibromomannitol in the treatment of chronic granulocytic leukemia: a prospective randomized comparison with busulfan.

Dibromomannitol (DBM) is a new agent for the treatment of chronic granulocytic leukemia. A propsective evaluation of the drug was undertaken in a randomized comparison with busulfan. Forty previously untreated, Philadelphia chromosome-positive cases were treated, with 20 patients in each treatment group. The protocol provided for continuous maintenance therapy after remission induction, with a crossover to the opposite drug in patients who became refractory to the primary agent but are without evidence of blastic tranformation. There were 14 remissions in the DBM group and 15 in those treated with busulfan. The rate of decrease of the elevated leukocyte count was more rapid with DBM, but prolonged disease control off treatment occurred in only three of 14 cases as opposed to nine of fifteen busulfan-treated patients who required a median delay of 12 mo before maintenance could be initiated. Hypoplasia occurred in one DBM patient and two busulfan cases. Following recovery, crossover to the opposite drug in two cases again resulted in hypopllasia. Increased skin pigmentation, amenorrhea, pulmonary fibrosis, and cytologic dysplasia, commonly associated with busulfan adminstration, were also noted with DBM. The median duration of disease control with busulfan was 34 mo and 26 mo with DBM. There was no signigicant difference in the incidence of blastic transformation, and median survival for both groups was 44 mo. DBM appears to be as effective as busulfan in the treatment of the chronic phase of CGL but with a more predictable myelosuppressive action. The principal advantage of busulfan over DBM is the fact that more than half the busulfan-treated patients experienced prolonged disease control off treatment.

Amenorrhea

Busulfan-induced sideroblastic anemia.

Patients in the stable phase of chronic myelogenous leukemia (CML) are usually treated with busulfan. The bone marrow of patients with CML may be exquisitely sensitive to busulfan, and occasionally such patients develop pancytopenia, secondary to hypoplasia or aplasia of the bone marrow, which is presumed to be due to busulfan-induced marrow toxicity. We report a case of Philadelphia chromosome-positive CML who developed pancytopenia while being treated with busulfan; however, the patient's bone marrow was not hypoplastic or aplastic but rather hyperplastic with sideroblastic changes. Busulfan is not known to cause sideroblastic changes, so this was considered to herald a transformation into acute leukemia. Busulfan was stopped, and only supportive treatment was given. To our surprise approximately 22 weeks after busulfan was stopped, the sideroblastic changes had disappeared and the bone marrow again showed features of CML. This case suggests that busulfan may cause sideroblastic anemia.

Anemia, Sideroblastic

Lymphoid reconstitution after transplantation of congenic hematopoietic cells in busulfan-treated mice.

The effects of pretransplant conditioning with high-dose busulfan, a myeloablative but nonimmunosuppressive alkylating agent, on reconstitution of lymphoid tissues by donor cells after bone marrow transplantation (BMT) has not been extensively examined. We used flow cytometric analyses to study the kinetics and extent of lymphocyte repopulation in C57BL/6 mice (immunophenotype Ly-5.2) given graded doses of busulfan (10 to 100 mg/kg) or total body irradiation (TBI; 900 rad) and hematopoietic cell transplantation (HCT; transplantation of bone marrow and spleen cells) from congenic Ly-5.1 donors. Mice transplanted after 10 mg/kg of busulfan had slow and incomplete lymphoid engraftment; only 6% to 11% of lymphocytes in the peripheral blood, lymph nodes, and spleen were positive for Ly-5.1 at 30 days after transplant, slightly increased to 13% to 20% at 60 days, and stabilized at 40% to 46% by 180 days after HCT. Higher doses of busulfan (20 to 100 mg/kg) provided dose-dependent congenic lymphoid reconstitution. Thirty days after HCT, the range of Ly-5.1 cells in blood, lymph nodes, and spleen of Ly-5.2 recipient mice was 43% to 54% after 20 mg/kg of busulfan, 66% to 71% after 50 to 80 mg/kg, and 77% to 85% after 100 mg/kg. Sixty days after transplant, lymphoid chimerism increased to 57% to 68% in 20 mg/kg recipients, 72% to 79% after 35 mg/kg, and 75% to 90% in animals given 50 mg/kg or greater, as seen in radiation chimeras. Despite slower early reconstitution after lower doses of busulfan, donor lymphocytes exceeded 90% to 95% by 90 to 120 days after HCT in all mice given at least 20 mg/kg. Even though busulfan lacks directly immunosuppressive properties, virtually complete sustained lymphoid reconstitution by transplanted congenic donor stem cells occurs after its administration. These observations suggest that pretreatment with busulfan may be effective in gene therapy strategies that involve infusion of autologous marrow cells into which functional genes have been inserted.

Animals

Pharmacokinetic and metabolic studies of busulfan in rat plasma and brain.

Busulfan kinetics were studied in the rat plasma and brain after an I.P. dose of 14C-busulfan or busulfan (15 mg/kg). The distribution of busulfan to the brain was rapid and the ratio brain/plasma concentration was 0.74 during the time-course of busulfan. The elimination half-lives in plasma and brain were 3h for intact busulfan and 8h for the 14C-radioactivity. The radioactivity remaining in plasma and brain after 24h was mostly busulfan metabolites e.g. sulfolane, 3-hydroxysulfolane and tetrahydrothiophene-1-oxide as identified by gas chromatography-mass spectrometry. The protein binding to rat plasma was low (9.2 +/- 4.4%).

Animals

Toxicological review of busulfan (Myleran).

Busulfan is a bifunctional alkylating agent that appears to be cytotoxic to slowly proliferating or non-proliferating stem cell compartments, although its specific molecular and cellular mechanisms are unknown. It is the drug of preference in treatment of chronic myelogenous or granulocytic leukemia because its cytotoxic activity results in primary damage or destruction of hematopoietic cells. Additional effects resulting from the cytotoxicity of busulfan in hematological and other tissues, as documented by both human and animal model studies, include lethality, sterility, teratogenicity, and alteration of immune function. Busulfan has been shown to be mutagenic to microorganisms, mammalian cells in culture, Drosophila, and rodents. This agent is also considered potentially carcinogenic to humans. Various tissue hyperplasia and preneoplastic cells have been observed in animal model studies with busulfan, and case reports on human patients implicate busulfan as the causative agent in induction of secondary malignancies. Reports from human and animal studies of busulfan's cytotoxicity, teratogenicity, carcinogenicity, and mutagenicity have been reviewed. This information may be useful in a quantitative assessment of the effects of this agent and the identification of significant deficiencies in the data base. Demonstration that busulfan induces mutations in both somatic and germ cells suggests the need to assess its risk to humans.

Animals

Spontaneous regression of syngeneic transplanted tumors in rats pretreated with the antileukemia drug busulfan.

Lethal growth of a syngeneic transplanted tumor (KMT-17) was inhibited in WKA rats pretreated with the antileukemia drug busulfan. The effect of busulfan was short-lasting, and administration of the drug after tumor challenge had little effect on the lethal growth of the tumor. After spontaneous regression of the tumor in rats pretreated with busulfan, specific transplantation resistance to identical tumor was acquired. Busulfan did not exhibit its effect in rats irradiated before tumor challenge. As shown by the Winn test, spleen cells from rats immunized with inactivated tumor cells after busulfan treatment inhibited growth of admixed tumor cells more strongly than did spleen cells from rats immunized without busulfan treatment. Enhancement of immune response to tumor cells rather than tumoricidal activity by busulfan was suggested.

Animals

Recipient preparation for bone marrow transplantation. I. Efficacy of total-body irradiation and busulfan.

The efficacy of total body irradiation and busulfan were studied in recipient preparation for bone marrow transplantation. Male C57BL/6 (B6) mice were prepared for BMT with fractionated TBI or busulfan given in 4 equal doses over 3 days. Both TBI and busulfan are potent stem-cell killers. Both agents resulted in an exponential decrease in CFUs survival with increasing dose down to a 1 x 10(-4) CFUs survival. There appeared to be no break in the curve for either agent. Extrapolated fractional CFUs survival, as related to equivalent donor marrow engraftment or to equivalent 30-day survival without marrow transplantation, appeared lower for TBI as compared to busulfan. This may be due to the effect of busulfan and TBI on different stem-cell populations. Erythroid engraftment was tested after transplanting H-2 compatible LP marrow cells into treated B6 recipients. Greater than 80% of animals demonstrated complete engraftment with 3.4 mg busulfan or 1640 cGy TBI. At these 2 doses, the rate of recovery of donor marrow cellularity and CFUs content in treated recipients were identical for both preparative agents such that a selective effect on the host hematopoietic microenvironment harmful to engraftment was not seen. Complete engraftment in 100% of busulfan-prepared animals could not be achieved as such doses resulted in severe and fatal pulmonary vascular injury at 7-12 weeks posttransplant.

Animals

Escalating doses of etoposide with cyclophosphamide and fractionated total body irradiation or busulfan as conditioning for bone marrow transplantation.

In a phase I study 28 patients with lymphohematopoietic malignancies were treated with escalating doses of etoposide combined with cyclophosphamide 120 mg/kg and either fractionated total body irradiation (TBI) 1320 cGy in 11 fractions (n = 17) or busulfan 16 mg/kg (n = 11). Twenty transplants were allogeneic, seven autologous and one syngeneic. The maximally tolerated dose of etoposide in combination with TBI and cyclophosphamide was 60 mg/kg; at etoposide doses of 65 mg/kg three patients developed life-threatening or fatal mucosal toxicity. In combination with busulfan, the maximally tolerated dose of etoposide was 30 mg/kg. At an etoposide dose of 40 mg/kg two patients developed life-threatening or fatal toxicity (one mucosal, one hepatic). Mucositis requiring narcotic analgesics, hepatotoxicity, hematologic toxicity and interstitial pneumonitis were otherwise similar in TBI and busulfan-treated patients. Skin toxicity was observed significantly more often in the busulfan group. Five deaths occurred before day +30, two in the TBI group and three in the busulfan group. Eleven patients are surviving, ten in continuous complete remission, at a median of 9 (range 3-23) months following transplantation. Etoposide in combination with TBI and cyclophosphamide or busulfan and cyclophosphamide is associated with significant but acceptable toxicities. The maximally tolerated dose of etoposide is higher when combined with TBI than with busulfan. Promising response rates in this high risk group of hematologic malignancies warrant further evaluation of these etoposide containing conditioning regimens.

Adolescent

Busulfan-induced suppression of natural killer cell activity.

The effect of repeated injections of busulfan, an alkylating agent, on immune response of CAF1 mice was studied. A single injection of busulfan or acetone (vehicle to solubilize busulfan) acutely suppressed mitogenic and allogenic responses that normalized at two weeks. Repeated injections of busulfan (four injections), on the other hand, showed a transient suppression of the mitogenic responses. Natural killer (NK) activity during the first ten days after busulfan or acetone injections remained normal. NK activity diminished significantly after two injections of busulfan, remained low after four injections, and did not recover within four months of rest. Prolonged suppression of NK activity may be implicated as playing a role in the emergence of T-cell lymphomas in mice injected with busulfan.

Animals

Lack of relationship between in vitro cell measurements and response to busulfan in chronic myelocytic leukemia.

Twenty-three patients with chronic-phase CML have been treated with intermittent courses of busulfan to determine if the duration of unmaintained remission becomes progressively shorter with successive courses of therapy and to determine whether there was a relationship between cluster and colony formation, suicide index of CFUc, labeling index, percentage of cells in S-phase (as determined by cytofluorographic DNA histogram analysis), in vitro sensitivity of the CFUc to busulfan, and response to busulfan therapy. Serial studies in individual patients and the group as a whole revealed no relationship between changes in the cellular parameters described above and response to busulfan. The white blood cell (WBC) doubling time with serial courses of busulfan in individual patients did not always progressively decrease as has been previously reported. In vitro studies of CFUc in chronic-phase CML appear to be of no value in predicting response to busulfan.

Adolescent

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

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 hematopoiesis 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 beta-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 beta-dihydrotestosterone provide some protective effect on erythroid precursor cells when administered with reference to the cell-cycle-dependent action of busulfan.

Animals

The effect of hepatic enzyme inducers on busulfan neurotoxicity and myelotoxicity.

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 myelosuppressive effects as well. These results suggest that 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.

Animals