Pre-Clinical Evaluation of a Novel DNA Crosslinking Agent, Bo-1055 in B-Cell Lymphoma

Some B-cell lymphoma including mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL) remain incurable using conventional chemotherapeutic approaches. Therefore it is important that new treatment strategies be developed. We have evaluated the efficacy of a number of novel, third generation, DNA-directed alkylating agents that have DNA specific binding domain by linking DNA-affinic molecules to N-mustard pharmacophore via a urea, carbamate or hydrazinecarboxamide linker (Kapuriya et al. Bioorganic & Medicinal Chem. 19:471–485; 2011). One of these, the water-soluble ureidomustine BO-1055, was screened for toxicity against a panel of human lymphoma cell lines including MCL (JEKO-1, Z-138, HBL-2), DLBCL (OCILy10, OCILy19) and a spontaneous murine B-cell lymphoma. We also screened BO1055 against a panel of normal human cells including mesenchymal stromal cells (IC50 >10uM), bone marrow-derived endothelium (IC50 >10uM) lung basal epithelium, bronchial epithelium and myofibroblasts (IC50s >10uM) and purified cord blood CD34+ cells in suspension culture or colony-forming assay (for hematopoietic progenitor cells) (IC50 >10uM) and in cobblestone area-forming assay (for hematopoietic stem cells) (IC50 9.1uM). The mean IC50±SD (uM) in MCL cell lines was JEKO-1 (0.266±0.27), Z-138 (0.182±0.15), HBL2 (0.161±0.34), In DLBCL lines OCILy10 (0.117±0.21), OCILy19 (0.287±0.17) and murine B-cell lymphoma (0.463±0.39). Our results indicated that BO-1055 has a significant therapeutic window (50-100-fold) between its toxicity against human B-cell lymphomas compared to various normal human cell types. We evaluated BO-1055 cardiotoxicity in the HL-1 cardiomyocyte line and observed a 227-fold less cytotoxicity compared to Doxorubicin. Treatment with BO-1055 resulted in accumulation of cells in S-phase and up-regulation of proteins involved in DNA repair [MRE11, p-P95/NBS1 (ser343), RAD50, p-ATR (ser428)] while Bcl-6, an important B-cell lymphoma biomarker, was down-regulated. Xenograft experiments in NSG mice bearing JEKO-1 GFP/luciferase+ tumors treated with BO-1055 (30mg/kg) 3x/week showed complete tumor remission after 2 weeks of treatment as monitored by luciferase image. Our results suggest that BO-1055 has potent activity against B-cell lymphoma and present a strong rationale for its further therapeutic development as an alkylating agent due to his low toxicity against normal tissue and high toxicity against hematopoietic tumors.