Pharmacokinetics of liposomal busulphan in man

Drug Targeting and Therapeutic Management of Chronic Myeloid Leukemia: Conventional and Nanotherapeutic Drug Options

Chronic myeloid leukemia (CML) is a blood cancer predominantly affecting older adult patients. According to the American Cancer Society, an estimated 8,860 people will be diagnosed with CML in 2022. Treatments for CML have evolved with a focus on CML phase severity or progression. Overall, there have been some breakthrough treatment options for a high percentage of patients with CML. This is largely due to the discovery of tyrosine kinase inhibitors (TKI); however, drug resistance continues to present a significant challenge for the management of CML disease.  The use of interferon (IFN), antimetabolites, and bone marrow transplants provide alternative treatment options, but also present with limitations including severe side effects, toxicity, and graft versus host disease. Nanomedicine has demonstrated benefits in terms of efficacy, often reducing or eliminating unwanted toxicities associated with the use of conventional drug agents. This review summarizes rational molecular targets of CML drugs and provides highlights of current FDA-approved agents for the treatment of CML. Additionally, this communication includes an overview of the limitations of conventional treatments and how nanomedicine has addressed challenges encountered during CML treatment. .

Comparison of algorithms for oral busulphan area under the concentration-time curve limited sampling estimate

BACKGROUND AND OBJECTIVES

Therapeutic drug monitoring (TDM) of the first dose of busulphan during conditioning prior to allogeneic stem cell transplantation provides the possibility of improving the clinical outcome via dose adjustment of subsequent doses. The plasma area under the concentration-time curve (AUC) for busulphan is generally accepted as the parameter that gives the best exposure estimate; however, the sampling frequency needed for reliable AUC calculation remains controversial. The aim of the present investigation was to develop and evaluate a limited sampling model for oral busulphan.

METHODS

We have compared models using three to four samples with standard WinNonlin(®) adaptive compartment modeling based on eight samples as reference. The evaluated study population included both adult and pediatric patients, but the linear model was devised using analysis of only pediatric patient plasma concentrations. The present model was developed using data from 23 patients with a mean age of 38 years (range 13-59 years) and was evaluated in 20 pediatric patients with a mean age of 6 years (range 0.1-13 years) as well as 23 adult patients (mean age 43 years; range 18-67 years).

RESULTS

In 23 patients, the mean AUC from a curve fitting model (Purves method) and a single compartment model had an intraclass correlation coefficient (ICC) of 0.947. From a log-log plot of AUC values it was evident that using this estimate of the AUC would affect dose adjustment decisions for very few of the patients. Applying the linear model using three samples resulted in an ICC of 0.932, mostly due to worse performance in the adult population.

CONCLUSIONS

The present results support the use of limited sampling in clinical TDM for oral busulphan provided adequate algorithms and sampling times are used. Moreover, they also demonstrate the caution that is needed when transferring a pharmacokinetic model from a pediatric population to an adult population.

Challenges and opportunities in the delivery of cancer therapeutics

The idea that cancer is not one but many diseases has completely changed the oncology landscape and promoted the development of personalized cancer therapy. Based on a better understanding of the mechanisms of cancer cell proliferation and tumor growth, novel therapies have emerged to address unmet medical needs and effectively treat pre-identified, responsive patients. These novel therapies require specific drug-delivery strategies that depend on the type and location of cancer, as well as the type of drugs administered, that is, a small molecule, a peptide, a therapeutic protein or a monoclonal antibody. Systemic cancer drugs are administered through three major routes that show different challenges with regard to delivery: these are oral administration, intravenous infusion and subcutaneous injection. This review presents and discusses the challenges and opportunities of the drug-delivery systems for each of these administration routes. It will be shown that, for the good of the patients, every time a drug-delivery system is used to administer anticancer drugs, the patients get a major benefit from that specific system: either improved efficacy, a better tolerability and toxicity profile, or even a combination of both effects.

Therapeutic drug monitoring is essential for intravenous busulfan therapy in pediatric hematopoietic stem cell recipients

Busulfan is widely used for myeloablative conditioning in HSCT. Intravenous busulfan has been introduced to reduce interindividual variability in plasma levels especially in pediatric patients. TDM of intravenous busulfan was performed in 34 pediatric HSCT patients with malignant (n = 9) and non-malignant (n = 25) diseases (50% of patients <three yr) in a single-center analysis (2006-2009). Intravenous busulfan was administered twice daily in a four-h infusion according to recommended weight-based doses. Busulfan drug levels were measured, and pharmacokinetic analysis was performed. The targeted busulfan exposure was aimed to range between AUC of 9000-12, 000 ng/mL/h. In 23/34 patients (68%), the busulfan dose had to be adjusted at least once. In 16/23 patients (70%), the dose had to be increased in a range of 7 to 33%, while in 7/23 patients (30%), the dose had to be decreased by 7-20%. The need of dose adjustment was not related to weight, age, or underlying disease. Seven out of 34 patients (21%) <20 months experienced VOD despite that their total AUCs were within the target AUC. TDM of intravenous busulfan is essential to increase the efficacy and safety of busulfan-based conditioning protocols in pediatric HSCT recipients.

Busulfan systemic exposure after oral administration of extemporeanously prepared high-dose busulfan capsules

Purpose. The aim of the study was to analyze patients’ busulfan (BU) exposure after oral administration of extemporeanously prepared BU capsules prior to blood stem cell transplantation.

Methods. Patients were treated with 1 mg/kg body weight BU administered orally every 6h on each of 4 consecutive days prior to blood stem cell transplantation. Each BU dose was administered in 1 gelatine capsule to be swallowed and containing the individually calculated dose of pure BU active substance. Blood samples were obtained from 6 adult patients 0, 30, 60, 90, 120, 180, 240, 300, and 360 min after the 1st, 5th, and 13th BU dose, frozen and analyzed subsequently by using a HPLC assay with UV detection. In addition, in two patients concomitant TDM was executed. BU exposure was monitored concurrently and BU doses were targeted to achieve a steady-state plasma concentration (CSS) of 600—900 ng/mL or 900—1100 ng/mL depending on the underlying disease. In these patients blood samples were obtained 0, 60, 120, 180, 240, and 360 min after the 1st, 5th, 9th, and 13th BU dose and analyzed concurrently.

Results. For the six patients monitored retrospectively, the time to reach peak plasma BU concentration (Cmax) ranged from 1 to 5 h (mean 2.4 h). BU Cmax — values varied from 728 to 1807 ng/ mL (mean 1174 ng/mL), and BU clearance (CL/F) from 2.32 to 3.75 mL/min/kg (mean 2.97 mL/min/ kg). The mean BU steady state (CSS) concentration calculated was 973 ng/mL (range 754—1226 ng/mL) with a mean AUC of 5818 ng·h/mL (range 4521— 7171 ng·h/mL). One of the two patients receiving targeted BU doses required an upward dose adjustment. None of the eight patients suffered from vomiting during BU therapy.

Conclusions. BU active substance encapsulated without further excipients in gelatine capsules is highly suitable for oral BU therapy. However, therapeutic drug monitoring and BU dose adjustment is still advisable to achieve optimal systemic BU exposure in each individual patient.

Busulfan in hematopoietic stem cell transplantation

The development of intravenous busulfan (Bu) and its incorporation in the preparative regimens for allogeneic stem cell transplantation has changed transplantation for myelogenous malignancies. Bypassing the oral route to achieve 100% bioavailability translated into improved control over drug administration, with increased safety and reliability of generating therapeutic Bu levels, maximizing antileukemic efficacy. Bu-nucleoside analog-based conditioning chemotherapy, thus far represented by fludarabine (Flu), is becoming the conditioning chemotherapy regimen of choice for patients with acute myelogenous leukemia (AML) at many transplant centers. The use of busulfan Bu-based conditioning is extending rapidly also to hematopoietic stem cell transplantation (HSCT) for lymphoid malignancies, genetic diseases, and umbilical cord blood transplantation.

Randomized comparison of four-times-daily versus once-daily intravenous busulfan in conditioning therapy for hematopoietic cell transplantation

Sixty patients were randomized to receive intravenous busulfan (iBU) either as 0.8 mg/kg, over 2 hours 4 times a day (BU4 arm) or 3.2 mg/kg, over 3 hours once a day (BU1 arm) in conditioning therapy for hematopoietic cell transplantation. The complete pharmacokinetic parameters for the first busulfan dose were obtained from all patients and were comparable between the 2 arms: for the BU4 and BU1 groups, elimination half-life (mean+/-SD) was 2.75+/-0.22 versus 2.83+/-0.21 hours, estimated daily AUC was 6058.0+/-1091.9 versus 6475.5+/-1099.4 microM.min per day, and clearance was 2.05+/-0.36 versus 1.91+/-0.31 mL/min/kg, respectively. Times to engraftment after transplantation were similar between the 2 arms. No significant differences were evident in the occurrence of acute graft-versus-host disease (aGVHD) and hepatic veno-occlusion disease (VOD). Moreover, other toxicities observed within 100 days after transplantation were not significantly different between the 2 arms. The cumulative incidence of nonrelapse mortality was 20.8% in BU4 arm and 13.3% in BU1 arm. In conclusion, our randomized study demonstrates that the pharmacokinetic profiles and posttransplant complications are similar for once-daily iBU and traditional 4-times-daily iBU.

Risk assessment in haematopoietic stem cell transplantation: conditioning

After the introduction of cyclophosphamide and total body irradiation in the 1970s, a variety of conditioning regimens has been developed. However, none has proven to be superior. Fractionation of the irradiation results in less toxic side-effects, but the total dose has to be increased to obtain similar immunosuppressive effects. Data from randomized trials indicate that among patients with myeloid leukaemia, busulfan in combination with cyclophosphamide results in similar outcome, while a regimen containing total body irradiation is probably still the best for patients with acute lymphoblastic leukaemia. Busulfan treatment can be optimized by targeted steady-state concentration or with the use of intravenous preparations. Intensified regimens decrease the relapse incidence, but because of a higher mortality from transplant-related causes survival is unchanged. Reduced-intensity conditioning can reduce transplant-related mortality and offer otherwise ineligible patients a potentially curative treatment. Long-term results are unknown.

Correction of X-linked chronic granulomatous disease by gene therapy, augmented by insertional activation of MDS1-EVI1, PRDM16 or SETBP1

Gene transfer into hematopoietic stem cells has been used successfully for correcting lymphoid but not myeloid immunodeficiencies. Here we report on two adults who received gene therapy after nonmyeloablative bone marrow conditioning for the treatment of X-linked chronic granulomatous disease (X-CGD), a primary immunodeficiency caused by a defect in the oxidative antimicrobial activity of phagocytes resulting from mutations in gp91(phox). We detected substantial gene transfer in both individuals' neutrophils that lead to a large number of functionally corrected phagocytes and notable clinical improvement. Large-scale retroviral integration site-distribution analysis showed activating insertions in MDS1-EVI1, PRDM16 or SETBP1 that had influenced regulation of long-term hematopoiesis by expanding gene-corrected myelopoiesis three- to four-fold in both individuals. Although insertional influences have probably reinforced the therapeutic efficacy in this trial, our results suggest that gene therapy in combination with bone marrow conditioning can be successfully used to treat inherited diseases affecting the myeloid compartment such as CGD.

Myeloablative and immunosuppressive properties of treosulfan in mice

OBJECTIVE

Treosulfan is a prodrug with a specific clinical activity in ovarian carcinoma and other solid tumors. Due to its myeloablative and immunosuppressive effects, its use in conditioning regimens prior to allogeneic stem cell treatment (SCT) has been proposed. In the present preclinical study, myeloablative as well as immunosuppressive properties of treosulfan were compared with those of busulfan and cyclophosphamide.

METHODS

Three groups of BALB/c mice were treated with treosulfan, cyclophosphamide, or busulfan at sublethal doses that maintained survival without bone marrow support. The control group was left untreated. At different intervals, colony-forming unit granulocyte macrophage assay was performed on marrow cells. Additionally, immunological analyses were performed using spleen cells.

RESULTS

We found that treosulfan and busulfan induced a high and persisting degree of myeloablation, as compared with cyclophosphamide. Moreover, treosulfan was more effective in depletion of splenic B and T cells in comparison with busulfan and cyclophosphamide. Furthermore, T cells isolated from the spleens of treosulfan- or busulfan-treated mice were not responsive to allogeneic cells compared with that observed in controls and cyclophosphamide-treated mice. Treatment with treosulfan induced only interleukin-2 production in spleen cells for a short time and had no significant effect on synthesis of tumor necrosis factor-alpha and/or interferon-gamma as compared with that observed in splenic T cells isolated from mice treated with either busulfan or cyclophosphamide.

CONCLUSION

Our findings suggest that treosulfan possesses both myeloablative and immunosuppressive properties and may be used as a single agent for conditioning prior to bone marrow transplantation.

Intravenous busulfan in children prior to stem cell transplantation: study of pharmacokinetics in association with early clinical outcome and toxicity

We studied the pharmacokinetics of intravenous busulfan (Bu) in children in order to further optimize intravenous Bu dosing in relation to toxicity and survival. A total of 31 children undergoing Bu-based conditioning for allogeneic SCT were enrolled in a study. The starting dose was 1.0 mg/kg (age < 4 years) and 0.8 mg/kg (age > or =4 years), four doses per day during 4 days. Dose adjustment was allowed up to a maximum dose of 1.0 mg/kg per dose if the target area under the serum concentration-time curve (AUC) was not reached. Pharmacokinetic studies were performed after the first dose. Donor engraftment was established in 28 out of 31 patients. The average AUC after the first dose was the same in children < 4 years as in children > or =4 years. Mean clearance was higher in children < 4 years than in children > or =4 years. In 35% of all patients, total AUC was within the target AUC. The other children's AUCs were below the target range. No relationships were found between systemic exposure to Bu and toxicity or clinical outcome. We concluded that, in accordance with previous data, within the observed AUCs no clear relationship was observed between Bu AUC and outcome with respect to toxicity, engraftment and relapse.

Conditioning Regimens Including High-Dose Busulfan Cause a High Incidence of Transplant-Related Mortality after Myeloablative Stem Cell Transplantation

BACKGROUND

Transplant-related mortality (TRM) significantly decreases the long-term survival of patients with hematopoietic diseases who undergo hematopoietic stem cell transplantation (HSCT).

METHODS

We retrospectively evaluated the risk factors for TRM of 58 consecutive patients with hematopoietic disease who underwent allogeneic myeloablative HSCT between April 1994 and June 2002.

RESULTS

Thirty-one patients died after HSCT, 16 of whom were diagnosed as TRM. The actuarial incidence of TRM was 57.6 % in patients who received conditioning chemotherapies including high-dose busulfan and 19.4 % in those who did not (p = 0.008). Multivariate Cox model analysis revealed that disease status, graft versus host disease (GVHD) grades III-IV and the use of high-dose busulfan were significant and independent risk factors for TRM.

CONCLUSION

These results suggest that high-dose busulfan as a conditioning therapy for allogeneic HSCT should be used cautiously, especially in patients with advanced disease.

Intravenous busulfan for allogeneic hematopoietic stem cell transplantation in infants: clinical and pharmacokinetic results

SUMMARY

High-dose busulfan is an important component of myeloablative regimens. Variable drug exposure may occur following oral administration. Therefore, the use of intravenous busulfan has been advocated. Previous work has suggested a cumulative dosage of 16 mg/kg for haematopoietic transplantation in children less than 3 years of age, but only limited data are available in infants. Pharmacokinetics of intravenous busulfan administered at the suggested dosage were studied in 14 infants (median age 4.7 months). Busulfan plasma concentrations were measured by either GC-MS or HPLC-UV. In seven patients, the dose was decreased to target an area- under- the- curve of 600-1300 micromol min. The median total dose given was 13.8 mg/kg. All patients engrafted. Severe veno-occlusive disease occurred in one patient. Our study demonstrates that a cumulative dosage of 16 mg/kg is associated with higher exposure than expected in infants. We suggest an initial dose of 0.8 mg/kg followed by pharmacokinetically guided dose adjustment.

N-acetyl-L-cysteine does not affect the pharmacokinetics or myelosuppressive effect of busulfan during conditioning prior to allogeneic stem cell transplantation

Busulfan is currently used as a main component in the conditioning regimen prior to allogeneic stem cell transplantation (SCT). Several studies have shown a correlation between exposure to busulfan and transplantation-related liver toxicity, such as venoocclusive disease (VOD) in patients undergoing SCT. Busulfan is metabolized mainly through glutathione (GSH). During high-dose therapy, busulfan may deplete hepatocellular levels of GSH. As part of the conditioning therapy, busulfan is usually followed by high doses of cyclophosphamide. The activation of cyclophosphamide yields a cytotoxic metabolite, 4-hydroxy cyclophosphamide, which is highly reactive and detoxified through GSH. According to recent studies using cell lines and animal models N-acetyl-L-cysteine (NAC), a GSH precursor, does not hamper the myeloablative effect of busulfan during conditioning. In the present study, we administered NAC during conditioning to 10 patients at risk of VOD due to pretransplant liver disorders or elevated liver enzymes. No side effects related to the NAC infusions were observed and busulfan concentrations were not affected. All patients became pancytopenic and engrafted with 100% donor cells. None of the patients developed VOD or liver failure. Increased liver enzymes during conditioning decreased or normalized in all patients. We suggest that NAC therapy is safe and does not impair the myeloablative effect of busulfan during conditioning prior to SCT.

Risk factors for moderate-to-severe acute graft-vs.-host disease after allogeneic stem cell transplantation in children

Severe acute graft-vs.-host disease (aGVHD) remains a major cause of transplantation-related mortality. However, because of a graft-vs.-leukaemia effect, a mild (grade I) aGVHD is desirable. As risk factors predisposing for aGVHD are not necessarily the same in children and adults, we have performed a retrospective analysis of risk factors (RFs) for grade II-IV aGVHD in 258 paediatric patients undergoing allogeneic stem cell transplantation at our centre. Thirty-two potential RFs were assessed with univariate analysis in logistic regression. Eleven factors were selected for further evaluation in stepwise elimination multivariate analysis. Three independent RFs were found: (1) donor other than human lekocyte antigen (HLA)-identical sibling [odds ratio (OR) 6.1, p < 0.001); (2) single drug [cyclosporine A (CsA) or methotrexate (Mtx)] graft-vs.-host disease (GVHD) prophylaxis (OR 7.0, p < 0.001); and (3) ABO disparity of any kind (OR 2.4, p = 0.02). The RFs were additive: moderate-to-severe aGVHD was seen in none of the patients without any RFs; in 16% with one RF; in 32% with two RFs and in 67% with all three RFs present. Single drug GVHD prophylaxis (CsA or Mtx), any kind of ABO mismatch, and non-sibling donors are RFs for grade II-IV acute GVHD in paediatric SCT. We encourage the use of combination GVHD prophylaxis in children. ABO mismatch should be considered when choosing between otherwise equally suitable donors.

The effect of metronidazole on busulfan pharmacokinetics in patients undergoing hematopoietic stem cell transplantation

Busulfan (Bu) is an important component of some myeloablative regimens prior to stem cell transplantation (SCT). Over the last few years it has been shown that other drugs administered concomitantly can influence Bu pharmacokinetics. In the present study, we compared Bu concentrations (trough levels) in three groups of patients. Group A (n=5) received metronidazole as graft-versus-host disease prophylaxis during Bu treatment. Group B (n=9) received Bu only for 2 days followed by 2 days of Bu and metronidazole. Group C (n=10) was a control group that received Bu without metronidazole. The mean Bu levels for Group A receiving metronidazole during conditioning was significantly (P<0.001) higher (948+/-280 ng/ml), compared to those observed in the control group (507+/-75 ng/ml). In Group B, the administration of metronidazole resulted in a significant (P<0.001) increase in Bu levels (807+/-90 ng/ml) during the last 2 days, compared to 452+/-68 ng/ml during the first 2 days. In Group A, one patient died with multiorgan failure, three experienced veno-occlusive disease (VOD) and one developed hemorrhagic cystitis. Elevated liver transaminases (AST, ALT) and bilirubin were detected in all Group A patients. In Group B, six patients had elevated liver function tests but no VOD was observed. We conclude that metronidazole should not be administered simultaneously with Bu to avoid the high plasma levels of Bu, which may lead to severe toxicity and/or treatment related mortality.

A phase II trial of liposomal busulphan as an intravenous myeloablative agent prior to stem cell transplantation: 500 mg/m(2) as a optimal total dose for conditioning

We conducted a phase I/II trial, to evaluate the efficacy and safety of an intravenous liposomal formulation of busulphan (LBu) as a myeloablative agent for stem cell transplantation (SCT). The liposomal busulphan was administered as a 3 h infusion twice daily over 4 consecutive days. Six adults received 1.6-2 mg/kg/dose and 18 children received 1.8-3 mg/kg/dose. Pharmacokinetic parameters were studied after the first and the last dose of busulphan. No significant difference in clearance, AUC, elimination half-lives or distribution volume between the first and the last dose was found in either groups. A significantly (P < 0.005) higher clearance was observed in children after the first and the last dose (3.61 and 3.79 ml/min/kg, respectively) compared to adults (2.40 and 2.33 ml/min/kg, respectively). The elimination half-lives after the first and the last dose were significantly (P < 0.005) shorter in children (2.59 and 2.72 h, respectively) compared to adults (3.35 and 3.61 h, respectively). Clearance correlated significantly with age. However, no significant correlation with age was observed when clearance was adjusted to the body surface area. Two cases of VOD following a total dose of 24 mg/kg were observed. Six patients experienced mucositis. No other organ toxicity was observed. We conclude that intravenous liposomal busulphan pharmacokinetics is age dependent. A dosage schedule based on body surface area should be used especially in young children to reduce the age-dependent difference in kinetics. An intravenous liposomal dose of busulphan of 500 mg/m(2) is suggested to reach a similar systemic exposure and myeloablative effect in both children and adults. Moreover, the novel liposomal form of busulphan showed a favorable toxicity profile and seems safe as a part of the high-dose therapy prior to SCT.

The effect of modulation of glutathione cellular content on busulphan-induced cytotoxicity on hematopoietic cells in vitro and in vivo

Busulphan is used in conditioning regimens prior to SCT. A relationship between exposure to busulphan, expressed as an area under the plasma concentration time curve (AUC), and effect and/or adverse effects, such as veno-occlusive disease (VOD), was reported. Exhaustion of glutathione (GSH) contributes to VOD and modulation of intracellular levels of GSH influences bulsulphan-induced toxicity in hepatocytes. Thus, increase of GSH might serve as prophylaxis against VOD. However, it should not interfere with the myeloablative effects of busulphan. We investigated the relationship between exposure to busulphan, and its in vitro toxicity to CD34(+) hematopoietic progenitors from volunteers using clonogenic assays. Busulphan inhibited colony formation by CD34(+) cells in an AUC-dependent manner. Myeloid progenitors were more sensitive than erythroid progenitors, expressed as 100% inhibition of colony formation (68.7 +/- 7.5 microg.h/ml and 140.3 +/- 35.7, respectively). The observed exposure corresponds to the total AUC obtained in patients treated with busulphan (1 mg/kg/day) for 4 days. Secondly, we studied the effect of modulation of GSH cellular levels on busulphan-induced toxicity in vitro in CD34(+) cells from volunteers, and in vivo in bone marrow cells from Balb/c mice. The intracellular concentration of GSH was increased or decreased by treatment with N-acetylcysteine or buthionine sulfoximine, respectively. Neither in vitro nor in vivo treatment with GSH modulators affected the hematological toxicity of busulphan. Thus, N-acetylcysteine would not interfere with the myeloablative effect of busulphan and therefore it is a potential candidate for VOD prophylaxis during busulphan-based conditioning regimens.

Pharmacokinetics of intravenous busulfan in children prior to stem cell transplantation

AIMS

Intravenous formulations of busulfan have recently become available. Although busulfan is used frequently in children as part of a myeloablative regimen prior to bone marrow transplantation, pharmacokinetic data on intravenous busulfan in children are scarce. The aim was to investigate intravenous busulfan pharmacokinetics in children and to suggest a limited sampling strategy in order to determine busulfan systemic exposure with the minimum of inconvenience and risk for the patient.

METHODS

Plasma pharmacokinetics after the first administration was investigated in six children using nonlinear mixed effect modelling.

RESULTS

Pharmacokinetics showed little variability and were described adequately with a one-compartment model (population estimates CL,av=0.29 l h(-1) kg(-1); V,av=0.84 l kg(-1); t(1/2)=1.7-2.8 h). Combined with limited sampling and a Bayesian fitting procedure, the model can adequately estimate the systemic exposure to intravenous busulfan, which in children appears to be at the lower end of the adult range.

CONCLUSIONS

Busulfan systemic exposure in children during intravenous administration can be estimated adequately with limited sampling and a Bayesian fitting procedure from a one-compartment model. Intravenous busulfan pharmacokinetics in children should be the subject of more research.