Purine Analog-Like Properties of Bendamustine Underlie Rapid Activation of DNA Damage Response and Synergistic Effects with Pyrimidine Analogues in Lymphoid Malignancies

Abstract

Bendamustine has shown considerable clinical activity against indolent lymphoid malignancies as a single agent or in combination with rituximab, but combination with additional anti-cancer drugs may be required for refractory and/or relapsed cases as well as other intractable tumors. In this study, we attempted to determine suitable anti-cancer drugs to be combined with bendamustine for the treatment of mantle cell lymphoma, diffuse large B-cell lymphoma, aggressive lymphomas and multiple myeloma, all of which are relatively resistant to this drug, and investigated the mechanisms underlying synergism. Isobologram analysis revealed that bendamustine had synergistic effects with alkylating agents (4-hydroperoxy-cyclophosphamide, chlorambucil and melphalan) and pyrimidine analogues (cytosine arabinoside, gemcitabine and decitabine) in HBL-2, B104, Namalwa and U266 cell lines, which represent the above entities respectively. In cell cycle analysis, bendamustine induced late S-phase arrest, which was enhanced by 4-hydroperoxy-cyclophosphamide, and potentiated early S-phase arrest by cytosine arabinoside (Ara-C), followed by a robust increase in the size of sub-G1 fractions. Bendamustine was able to elicit DNA damage response and subsequent apoptosis faster and with shorter exposure than other alkylating agents due to rapid intracellular incorporation via equilibrative nucleoside transporters (ENTs). Furthermore, bendamustine increased the expression of ENT1 at both mRNA and protein levels and enhanced the uptake of Ara-C and subsequent increase in Ara-C triphosphate (Ara-CTP) in HBL-2 cells to an extent comparable with the purine analog fludarabine. These purine analog-like properties of bendamustine may underlie favorable combinations with other alkylators and pyrimidine analogues. Our findings may provide a theoretical basis for the development of more effective bendamustine-based combination therapies.

Esters of Bendamustine Are by Far More Potent Cytotoxic Agents than the Parent Compound against Human Sarcoma and Carcinoma Cells

“…A very recent study on several hematologic malignancies revealed IC 50 values between approximately 10 μM and 250 μM. Especially mantle cell lymphoma, Burkitt’s lymphoma and T-cell acute lymphoblastic leukemia derived cell lines were relatively sensitive to bendamustine treatment [ 50 ]. The IC 50 value (approximately 50 μM) reported by Hiraoka et al [ 50 ] for Jurkat cells is in good agreement with our data.…”

“…Especially mantle cell lymphoma, Burkitt’s lymphoma and T-cell acute lymphoblastic leukemia derived cell lines were relatively sensitive to bendamustine treatment [ 50 ]. The IC 50 value (approximately 50 μM) reported by Hiraoka et al [ 50 ] for Jurkat cells is in good agreement with our data. Published plasma levels of 1 after intravenous administration (C max = 6 μg/mL (≈ 17 μM) [ 51 ]; C max = 11 μg/mL (≈ 31 μM) [ 52 ]) suggest that the chemotherapy with bendamustine must be considered ineffective in case of tumor entities showing IC 50 values in the two- to three-digit micromolar range in vitro.…”

Autophagy Inhibition Potentiates the Anticancer Effects of a Bendamustine Derivative NL-101 in Acute T Lymphocytic Leukemia

“…We speculate that NL-101-induced cell cycle arrest at different stages is possibly due to its "alkylation activity," exhibiting similar concentration-dependent properties as bendamustine. Indeed, a considerable part of research has found that bendamustine alone can induce S phase arrest in different cell lines due to inducing DNA strand breaks [15,42]. Moreover, Beeharry et al found that in a wide panel of cancer cell lines, bendamustine presented concentrationdependent effects on cell cycle checkpoint [33].…”

Kinetics of T‐cell subset reconstitution following treatment with bendamustine and rituximab for low‐grade lymphoproliferative disease: a population‐based analysis

“…Bendamustine belongs to the alkylating agent class of cytotoxic drugs. It contains a nitrogen mustard group responsible for alkylating activity (Gandhi & Burger, ) and, potentially, purine analogue‐like properties which may be responsible for the rapid onset of action and unique synergistic capabilities (Hiraoka et al , ), although this is somewhat controversial (Gandhi & Burger, ). The lymphodepleting capabilities of alkylator agents including bendamustine are well recognised (Kufe et al , ).…”