In vitro activity: DNA single- and double-strand breaks caused by Bendamustine are more extensive and significantly more durable than those caused by cyclophosphamide, cisplatinum, or carmustine. Bendamustine specifically regulates, transcriptionally and posttranslationally, genes involved in apoptosis, DNA repair, and mitotic checkpoints. Bendamustine uniquely regulates DNA repair pathways in non–Hodgkin's lymphoma cells compared with other alkylators. Bendamustine inhibits mitotic checkpoints and induces mitotic catastrophe. Treatment with Bendamustine results in a 60% to 80% down-regulation of the mRNA expression of all three of these genes [polo-like kinase 1 (PLK-1), Aurora Kinase A, and cyclin B1] in SU-DHL-9 cells. Twenty-six percent of the Bendamustine-treated MCF-7/ADR cells showed micronucleation compared with only 6% in DMSO control cells. Using Bendamustine alone in concentrations from 1 μg/mL to 50 μg/mL, a dose- and time-dependent manner of cytotoxicity from 30.4% to 94.8% after 48 hours could be observed. The LD50 for untreated and pretreated CLL cells is 7.3 or 4.4 μg /mL, respectively. Myeloid and breast carcinoma cell lines are resistant towards Bendamustine with the exception of HL-60 cells which exhibit an intermediate sensitivity. Bendamustine is found to have a very low clastogenic effect as compared with equimolar doses of lomustine.

Cell Assay: SU-DHL-1 and SU-DHL-9 cells are preincubated for 30 minutes with either 6 mM methoxyamine or 50 μM O6-benzylguanine, inhibitors of Ape-1 base excision repair enzyme, or alkylguanyl transferase enzyme, respectively. The cells are then exposed to various concentrations of Bendamustine for 72 hours. Cytotoxicity is evaluated by the MTT viability assay and an IC50 is determined as the drug concentration that inhibited by 50% the viability value of the untreated control. Analyses are done.