Metabolism and mechanisms of action of bendamustine: rationales for combination therapies

Bendamustine for the treatment of chronic lymphocytic leukemia and rituximab-refractory, indolent B-cell non-Hodgkin lymphoma

BACKGROUND

Bendamustine is a mechlorethamine derivative with a purine-like benzimidazole ring, which may enhance its clinical efficacy. Bendamustine was approved by the US Food and Drug Administration (FDA) for the treatment of chronic lymphocytic leukemia (CLL) in March 2008 and for the treatment of rituximab-refractory, indolent B-cell non-Hodgkin lymphoma (NHL) in October 2008.

OBJECTIVE

This article reviews the pharmacologic and pharmacodynamic properties of bendamustine, together with data on efficacy and toxicity from trials investigating the use of bendamustine for the treatment of various hematologic malignancies, including CLL, NHL, and multiple myeloma (MM).

METHODS

MEDLINE and International Pharmaceutical Abstracts (1970-April 15, 2009) were searched using the terms bendamustine, bendamustin, Treanda, Ribomustin, SDX-105, IMET-3393, and Cytostasan. References from relevant articles were also reviewed for additional sources and material. The databases of the American Society of Hematology (2004-2008) and the American Society of Clinical Oncology (1995-2008) were searched for relevant abstracts.

RESULTS

Bendamustine is a mechlorethamine derivative with structural similarity to chlorambucil and other drugs from the nitrogen mustard class, as well as a benzimidazole ring, which may act as an antagonist to purines and amino acids. It has good oral bioavailability but has been studied almost exclusively in the intravenous formulation. It undergoes extensive first-pass metabolism by cytochrome P450 1A2 to active metabolites gamma-hydroxy bendamustine and N-desmethyl-bendamustine, but clinical activity appears to be associated primarily with the parent compound. The t(1/2) of bendamustine is approximately 40 minutes. While bendamustine has 2 moieties with possible antitumor effect, it is unclear to what extent the benzimidazole ring enhances the efficacy of the drug. Numerous studies including in vitro assays have reported, however, that bendamustine has little cross-resistance with other alkylating agents and remains active even in extensively pretreated patients. FDA approval for use in CLL was based on findings from a randomized, open-label, Phase III study comparing bendamustine with chlorambucil as single-agent therapy in treatmentnaive patients with CLL (Binet stage B or C). Bendamustine was administered intravenously at a dose of 100 mg/m2 on days 1 and 2, while chlorambucil was administered orally at 0.8 mg/kg daily, both over 4-week cycles for up to 6 cycles. At interim analysis (the data used for FDA approval), bendamustine was associated with a greater overall response (68% vs 39%; P < 0.001), median progression-free survival (21.7 vs 9.3 months; P < 0.001) and median duration of remission (18.9 vs 6.1 months; P < 0.001) compared with chlorambucil. FDA approval for rituximabrefractory, indolent B-cell NHL followed a Phase III, open-label, single-arm study evaluating bendamustine monotherapy in patients who did not respond to rituximab or had progressive disease within 6 months of rituximab therapy. Bendamustine 120 mg/m(2) was administered intravenously on days 1 and 2 of a 21-day cycle for up to 8 cycles. At interim analysis, the overall response rate was 84%, including 29% complete response. The median progression-free survival was 9.7 months. The efficacy of bendamustine has also been reported in the treatment of MM in clinical studies, and bendamustine has been approved in Europe for treating MM, NHL, CLL, breast cancer, and Hodgkin lymphoma. Dose-limiting toxicity is primarily hematologic. Treatment-associated infections have been reported in some studies; however, nonhematologic adverse events have rarely been dose limiting. The most common nonhematologic adverse events include fatigue, nausea, xerostomia, and pyrexia.

CONCLUSIONS

Bendamustine is a mechlorethamine derivative with a purine-like benzimidazole ring, which may enhance its clinical efficacy. It has been approved in the United States for the treatment of CLL and rituximab-refractory, indolent B-cell NHL. It has been approved in Europe for use in other malignancies, and clinical studies have reported activity in MM.

The role of bendamustine in the treatment of indolent non-Hodgkin lymphoma

There is no consensus on recommendations for the treatment of relapsed and refractory indolent non-Hodgkin lymphoma (NHL). Bendamustine hydrochloride (bendamustine) has recently been approved for treatment of these patients. Bendamustine is a uniquely structured alkylating agent that lacks cross-resistance with other alkylators. This agent has a high degree of activity against a variety of tumor cell lines. Clinically, bendamustine has demonstrated activity against indolent NHL, chronic lymphocytic lymphoma, multiple myeloma and mantle cell lymphoma. Moreover, studies have validated its activity in patients with indolent NHL who are resistant to purine analogs and rituximab. The cytotoxic activity of bendamustine has been shown to be synergistic with rituximab in hematological malignancies. The incidence of alopecia is significantly less than with other alkylating agents. Myelosuppression is the major toxicity associated with bendamustine.

Beyond monoclonal antibodies: new therapeutic agents in non-Hodgkin's lymphomas

The availability of active monoclonal antibodies, either as single agents or in combination with cytotoxic agents, has improved treatment results in non-Hodgkin's lymphoma (NHL). Despite this and the increasing number of available active monoclonal antibodies, alone or conjugated with radioisotopes, not all types of lymphoma are sensitive to these biological agents and often they become resistant because of different molecular mechanisms. New molecular targets in neoplastic cells are emerging and provide the rationale for novel discovery initiatives. In fact, a greater knowledge of the biology of lymphoma and the identification of compounds selectively active against a potential therapeutic pathway have already improved the time to progression and survival time of patients with some subtypes of NHL. The growing list of new drugs provides the exciting prospect of developing disease-specific and even patient-specific therapies. The aim of this review is to identify and discuss non-monoclonal antibody new therapeutic agents in terms of mechanism of action and clinical results. The preclinical and clinical features of proteasome inhibitors, histone deacetylase inhibitors, thalidomide and lenalidomide, mammalian target of rapamycin inhibitors, antisense oligonucleotides, heat shock protein inhibitors, protein kinase C inhibitors, antiangiogenic agents, and new cytotoxics are reviewed.

Bendamustine in the treatment of non-Hodgkin's lymphomas

PURPOSE

To review available data using bendamustine alone and in combination with other chemotherapeutic agents in treatment of patients with non-Hodgkin's lymphomas.

METHODS

Internet database searches and literature review.

RESULTS

Bendamustine was approved in March 2008 by the United States Food and Drug Administration for the treatment of patients with chronic lymphocytic leukemia. Many trials have been performed over the last decade using bendamustine not only as monotherapy, but also in combination with other agents including rituximab, vincristine, mitoxantrone, fludarabine, and other agents as therapy for patients with relapsed non-Hodgkin's lymphomas, and recently was approved for use in therapy of patients with relapsed indolent lymphomas considered refractory to rituximab therapy. As monotherapy, bendamustine induces good responses with only minor side effects. In combination with other agents, efficacy improves, especially when given in combination with rituximab. The drug has also been studied in combination with rituximab as initial therapy for indolent lymphomas, and has excellent activity with less toxicity than R-CHOP (rituximab - cyclophosphamide, hydroxydaunorubicin [Adriamycin], Oncovin [vincristine], and prednisone/prednisolone).

CONCLUSION

Overall, bendamustine has demonstrated promising results as therapy for non-Hodgkin's lymphomas and should be included in the armamentarium of agents used to treat relapsed indolent non-Hodgkin's lymphomas and may prove valuable as initial therapy for these diseases. Further studies are being conducted to demonstrate the efficacy of this drug in combination with other agents.

Bendamustine, but not fludarabine, exhibits a low stem cell toxicity in vitro

PURPOSE

We investigated the in vitro toxicity of bendamustine and fludarabine to hematopoietic progenitors and stem cells from healthy donors.

METHODS

Clonogenic agar colony assays, non-clonogenic long-term liquid cultures (LTC) and apoptosis assays were used to assess the cytotoxicity of both the agents.

RESULTS

Total colony-forming units (CFU) were more sensitive to fludarabine than to bendamustine in agar colony assays (IC(50) 0.7 microM/L and 8.5 microM/L, respectively). Using the Bliss independence model and combining the two agents yielded additive inhibition of progenitors. Non-clonogenic assays, including LTC and an apoptosis assay detecting activated caspases showed that stem cells are characterized by low sensitivity to bendamustine. In contrast, fludarabine strongly inhibited the viability and growth of stem cells in LTC.

CONCLUSIONS

Our data show that bendamustine is characterized by lower in vitro toxicity to hematopoietic progenitors and stem cells than fludarabine and might thus be preferable in regimens prior to stem cells apheresis.

Bendamustine as a model for the activity of alkylating agents

Attempts to administer personalized standard cytotoxic chemotherapy based on individual patient characteristics have been disappointing. Alkylating agents are one of the oldest classes of anticancer medicine with a wide variety of molecular actions and thus the potential for broad utility. Bendamustine hydrochloride, a new addition to this class, was previously developed in the 1960s and has now been trialled in hematological malignancies and many solid tumor types as monotherapy or in combination with the known standard of care. It appears to occupy a particular role in resistant or refractory hematological disease and it was approved by the US FDA for the treatment of chronic lymphocytic leukemia in March 2008. Further trials will reveal whether it is likely to become incorporated into front-line regimens in non-Hodgkin's lymphoma and other malignancies.

Salvage chemotherapy for metastatic breast cancer: results of a phase II study with bendamustine

BACKGROUND

Bendamustine, a bifunctional alkylating agent with anticipated purin-like properties is active in metastatic breast cancer (MBC) patients. This multicenter phase II trial defines the toxicity and activity of bendamustine in heavily pretreated patients.

PATIENTS AND METHODS

Fifty-one patients were included. Patients had a median number of 2 prior chemotherapeutic regimens for MBC (range 0-7) consisting of anthracyclines and taxanes: 26 patients (51%); anthracyclines: nine patients (17.6%); taxanes: seven patients (13.7%); others: five patients (9.8%). Bendamustine was administered four weekly at a dose of 120 mg/m(2) on days 1 and 2.

RESULTS

Fifty patients were assessable. Of total, 200 courses were administered. We observed no complete response (CR); 10 patients [20%; 95% confidence interval (CI): 10.0% to 33.7%] achieved a partial response (PR), 14 patients (28%) remained stable for at least 6 months resulting in a clinical benefit rate (CR + PR + stable disease) of 48% (95% CI: 33.7%to 52.6%). Median time to progression was 3.4 months (range 1-51.1). The median duration of remission was 6.6 months (range 1.8-48.7). The treatment was well tolerated with mainly hematologic toxic effects.

CONCLUSION

Single-agent bendamustine is an active treatment in patients with MBC independent of the previous treatment. The low toxicity profile favors its use as a single agent.

Metabolic profile of [(14)C]bendamustine in rat urine and bile: preliminary structural identification of metabolites

Bendamustine, a bifunctional alkylating agent, is currently in clinical trials for the treatment of hematological and other malignancies. Although it has been used in the former East Germany for more than 30 years, very limited information is available on its biotransformation. The objective of this investigation was to obtain information on the structures of metabolites excreted into rat urine and bile to understand the metabolic fate of bendamustine in vivo. Metabolites of [(14)C]bendamustine hydrochloride in rat urine and bile were determined using liquid chromatography-mass spectrometry (MS) in parallel with on-line radioactivity detection in samples obtained after i.v. dosing of 3 mg/kg. A total of 17 radioactive peaks were identified in rat urine and 10 in rat bile (2 were unique to bile). Four of these metabolites had been previously reported, whereas 15 are novel. Proposed structures of all metabolites detected are based on MS(n) spectra generated from a linear ion trap mass spectrometer. These results suggest that the major metabolic pathways in rat are oxidative and/or hydrolytic dehalogenation, oxidation, carboxylic acid formation, N-dealkylation, sulfation, and glutathione and cysteine (probably via glutathione) conjugation. The cysteine-conjugated compounds are observed in their N-acetylated cysteine (mercapturic acid) forms.

A phase I study of bendamustine hydrochloride administered once every 3 weeks in patients with solid tumors

The present phase I trial was planned to assess the maximum tolerated dose, the dose-limiting toxicity and the pharmacokinetics of bendamustine hydrochloride in a once every 3 weeks schedule, and to recommend a safe dose for future phase II studies. Included were patients with refractory solid tumors. Bendamustine hydrochloride was administered as a short intravenous infusion over 30 min. The starting dose was defined at 160 mg/m2 and dose escalation used increments of 20 mg/m2. Plasma and urine samples were analyzed using validated high-pressure liquid chromatography/fluorescence assays. Twenty-six patients (14 men, 12 women) were enrolled for the study. At 280 mg/m2, one out of four patients developed a thrombocytopenia grade 4, two experienced grade 3 fatigue and three experienced cardiac toxicity (grade 2). The latter toxicity was considered dose limiting also and further dose escalation was stopped. Plasma pharmacokinetics parameters of bendamustine hydrochloride and its metabolites were assessed in 15 patients. Mean pharmacokinetic parameters of bendamustine hydrochloride were a tmax of 32.3 min, a t1/2 of 37.8 min, a volume of distribution of 14.2 l/m and a clearance of 287.8 ml/min/m2. No dose dependency of bendamustine hydrochloride was observed within the used dose range. The metabolites comprised only 23% of the overall area under the concentration-time curve. The maximum tolerated dose of bendamustine hydrochloride on day 1 q 3 weeks is 280 mg/m2. Fatigue and cardiac toxicity were dose limiting. The plasma pharmacokinetics data of bendamustine and its metabolites were in accordance with previous reports. The recommended dose for future trials is 260 mg/m2 every 3 weeks.

A phase I study of bendamustine hydrochloride administered day 1+2 every 3 weeks in patients with solid tumours

The aim of the study was to determine the maximum tolerated dose (MTD), the dose limiting toxicity (DLT), and the pharmacokinetic profile (Pk) of bendamustine (BM) on a day 1 and 2 every 3 weeks schedule and to recommend a safe phase II dose for further testing. Patients with solid tumours beyond standard therapy were eligible. A 30-min intravenous infusion of BM was administered d1+d2 q 3 weeks. The starting dose was 120 mg m(-2) per day and dose increments of 20 mg m(-2) were used. Plasma and urine samples were analysed using validated high-performance liquid chromatography/fluorescence assays. Fifteen patients were enrolled. They received a median of two cycles (range 1-8). The MTD was reached at the fourth dose level. Thrombocytopaenia (grade 4) was dose limiting in two of three patients at 180 mg m(-2). One patient also experienced febrile neutropaenia. Lymphocytopaenia (grade 4) was present in every patient. Nonhaematologic toxicity including cardiac toxicity was not dose limiting with this schedule. Mean plasma Pk values of BM were tmax 35 min, t(1/2) 49.1 min, Vd 18.3 l m(-2), and clearance 265 ml min(-1) m(-2). The mean total amount of BM and its metabolites recovered in the first micturition was 8.3% (range 2.7-26%). The MTD of BM in the present dose schedule was 180 mg m(-2) on day 1+2. Thrombocytopaenia was dose limiting. The recommended dose for future phase II trials with this schedule is 160 mg m(-2) per day.

Fludarabine and bendamustine in refractory and relapsed indolent lymphoma--a multicenter phase I/II Trial of the east german society of hematology and oncology (OSHO)

The therapy of patients with relapsed or refractory indolent lymphoma relies on the development of new drug combinations. The drugs bendamustine and fludarabine have cytotoxic activity as monotherapy in indolent lymphoma and show synergism in vitro. In this study, we combined both drugs in a multicenter clinical phase I/II trial to evaluate their toxicity and efficacy. Bendamustine was given at 30 or 40 mg/m2/d (dose levels 1 and 2), fludarabine at 30 mg/m2/d, each drug on days 1 to 3. Six cycles were to be given every 4 weeks. A total of 29 patients with relapsed or refractory indolent lymphoma were included in the study. During phase I, 9 patients were treated at dose level 1 and 7 patients at dose level 2. Thirteen patients were added to the study during phase II. Fourteen patients had follicular lymphoma, 11 patients mantle cell lymphoma, 2 patients lymphoplasmocytic and 2 patients nodal marginal zone lymphoma. Median age was 62 years (range 39-74). All patients were in stages III or IV of their disease and had received prior chemotherapy with or without additional radio- or immunotherapy. The dose limiting toxicity was hematotoxicity in all cases and occurred in 3 of 7 evaluable patients at dose level I and in 3 of 7 patients at dose level 2. One patient at dose level 2 died of sepsis in neutropenia with persistent thrombocytopenia. The study was continued at dose level 1 (phase II). Analysis of 19 evaluable patients treated at dose level 1 reveiled hematotoxicity CTC grade III in 47% and grade IV in 26%. Neutropenic fever occurred in 4 patients (21%). On an intent-to-treat basis, 45% or 32% of all patients at dose level 1 reached CR or PR, respectively. Nine of 9 patients with mantle cell lymphoma responded to therapy. The overall response rate was 77%. Eight of 15 responders relapsed after a median follow-up time of 14 months (range 2-43). The major complication of fludarabine in combination with bendamustine is hematotoxicity. Dose level 1 with 30 mg/m2/d of both drugs on days 1 to 3 was defined as the recommended dose. Despite unfavorable prognostic features (histologic subtype, stage of disease, pretreatment) response rates were good with this regimen.

Carboplatin in Combination with Bendamustine in Previously Untreated Patients with Extensive-Stage Small Cell Lung Cancer (SCLC)

BACKGROUND AND OBJECTIVE

Bendamustine is an alkylating agent with high efficacy in non-Hodgkin's lymphoma and multiple myeloma. Even in solid tumours, monotherapy with bendamustine has resulted in subjective remissions and has been associated with a low rate of side effects. The current dose-finding study was designed to determine the maximum tolerated dose (MTD) of combined carboplatin/bendamustine in previously untreated patients with extensive-stage small cell lung cancer (SCLC).

PATIENTS AND METHODS

Carboplatin was administered as a 1-hour infusion on day 1 at increasing dose levels, and bendamustine was administered as a short infusion on days 1 and 2 at increasing dose levels (80-120 mg/m(2)). The regimen was administered every 3 weeks. Four dose levels were planned, starting with 80 mg/m(2) bendamustine and carboplatin area under the curve (AUC) 5 (dose level I). The other dose levels were 100 mg/m(2) bendamustine and carboplatin AUC 5 (dose level II), 100 mg/m(2) bendamustine and carboplatin AUC 6 (dose level III), and 120 mg/m(2) bendamustine and carboplatin AUC 6 (dose level IV). A minimum of three patients were enrolled at each dose level.

RESULTS

Dose-limiting toxicities, which included fatigue, infection and tachyarrhythmia, were observed at dose level III. The recommended dose for phase II studies was therefore established at dose level II. The majority of haematological and non-haematological toxicities observed were only mild (grade 1 or 2) in patients at dose levels I and II. None of the patients developed severe alopecia. Objective responses were observed in eight of the ten patients involved in this trial.

CONCLUSION

Because of its acceptable toxicity and favourable preliminary antitumour efficacy, the combination of carboplatin and bendamustine appears to be a potentially useful chemotherapeutic option in patients with extensive SCLC.