Abstract 1625: Ureidomustine, a novel DNA-crosslinking agent shows activity in sarcoma preclinical models and lacks toxicity in normal tissues
Authors: Ambati Srikanth R. , JaeHung Shieh , Pera Benet , Wong Elissa W.P. , Caldas Lopes Eloisi , Peguero Elizabeth , Su Tsann-Long , Moore Malcolm A.S. 
Published: August 2015

Abstract
Ureidomustine (BO-1055) is a water-soluble N- mustard derivative that has antitumor activity against a number of human tumors including prostate, colon cancers and gliomas. In this study, we investigated its pre-clinical activity in sarcoma models.
We tested the activity of BO-1055 on early passages from Ewing sarcoma patient samples and patient-derived xenografts, preclinical models of rhabdomyosarcoma, desmoplastic small round cell tumor (DSRCT) and osteosarcoma. We used cell proliferation, viability, clonogenicity and cell death assays, and immunoblotting for differential expression of proteins in cells that are sensitive and resistant to BO-1055. We studied the toxicity of BO-1055 on cardiac myocytes, hematopoietic stem and progenitor cells (HSPCs), epithelial, mesenchymal and endothelial cells, and performed animal toxicity experiments in mice. Efficacy of BO-1055 was tested in NSG mice bearing A673 xenografts (Ewing sarcoma) treated at doses of 10mg/kg, 20mg/kg and 30mg/kg, Q2D×5, via i.v. injection after the tumors grew to 250-500 mm3. We also investigated the efficacy of this agent in NSG mice bearing A204 xenografts and Ewing sarcoma patient-derived xenografts that were resistant to cyclophosphamide. The antitumor effects of BO-1055 in combination with standard chemotherapeutic agents were also evaluated.
Ureidomustine exhibited significant cytotoxicity against the in vitro growth of Ewing sarcoma and rhabdomyosarcoma with sub μM IC50 values and was more cytotoxic than conventional DNA damaging agents. BO-1055 had less cytotoxicity against a panel of normal HSPCs. BO-1055 had moderate activity (IC50 = 2-4 μM) on DSRCT cells and had only weak activity (IC50&gt;10μM) against osteosarcoma cell lines. Notably, this agent has no cross-resistance to Taxol and Vinblastine. Growth arrest in G2/M phase was noted at 24h and maximal apoptosis and cell death at 48h and 72h after exposure of A673 cells. Apoptosis was due to the induction of caspase 3 and 7 activity in a dose- and time- dependent manner. Cardiotoxicity was evaluated by binding of BO-1055 to hERG, which was significantly less than that of Astemizole indicating that BO-1055 has less propensity for QTc prolongation. BO-1055 significantly suppressed Ewing sarcoma patient-derived xenografts that were resistant to cyclophosphamide. Remarkably, this agent induced complete suppression of tumors in nude mice bearing A204 xenografts, without significant weight loss. In two-drug combination studies, BO-1055 exhibited synergism with etoposide, SN-38 (active metabolite of irinotecan), doxorubicin and PU-H71 (HSP-90 inhibitor).
Because of its broad therapeutic window, lack of cross-resistance, better safety profile and synergistic cytotoxicity with standard drugs, BO-1055 has high potential for clinical application for treatment of Ewing sarcoma and rhabdomyosarcoma patients.
Citation Format: Srikanth R. Ambati, Shieh JaeHung, Benet Pera, Elissa W.P. Wong, Eloisi Caldas Lopes, Elizabeth Peguero, Tsann-Long Su, Malcolm A.S. Moore. Ureidomustine, a novel DNA-crosslinking agent shows activity in sarcoma preclinical models and lacks toxicity in normal tissues. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1625. doi:10.1158/1538-7445.AM2015-1625