Abstract 5468: Tirapazamine as a strategy to prevent cell dissemination and overcome drug resistance
Authors: Muz Barbara , de la Puente Pilar , Azab Feda , Luderer Micah , Azab Abdel Kareem 
Published: August 2015

Introduction: Multiple myeloma (MM) and Waldenström's macroglobulinemia (WM) are lymphoplasmacytic malignancies which are characterized by continuous spread through cell trafficking in and out of the BM. We have recently shown that the spread process in these diseases is mediated by hypoxia. Moreover, despite the introduction of novel therapies, cancer patients relapse due to the development of a drug-resistant stem cell-like subpopulation, which we recently found to be, at least in part, promoted by hypoxia. Therefore, in this study we aimed to overcome spread and drug resistance in MM and WM by inhibition of the hypoxic responses in these cells. Tirapazamine (TPZ) is a hypoxia-activated pro-drug causing cell apoptosis, which has been shown to improve cancer patient outcome when combined with radiotherapy. We use TPZ for the first time in hematologic malignancies to target the drug-resistant cancer cells and sensitize them to therapy.

Procedures: Cell survival was tested on MM (MM1.s, H929, OPM1, RPMI8226) and WM (BCWM.1, MWCL.1) cell lines exposed to normoxia (21% O2) or hypoxia (1% O2) for 24hrs in the presence of bortezomib and carfilzomib, different concentrations of TPZ (in order to obtain an IC50), or combination of those drugs using MTT assay. For adhesion assay, cancer cells were pre-labeled with calcein-AM, treated with TPZ, applied to unlabeled endothelial cells, non-adherent cells were washed after 1hr, and adherent cells were analyzed by a fluorescent reader. Chemotactic properties of cells were tested using a transwell chamber and the migrated cells were counted by flow cytometry. For in vivo study, 5 × 106 MM1s-Luc-GFP cells were injected i.v. into 6 SCID mice and tumor progression was monitored for 3 weeks by bioluminescent imaging. All mice were treated with (1) high-dose bortezomib (1.5mg/kg) only (n = 3), or (2) bortezomib and TPZ (40mg/kg; n = 3), all administered i.p. sequentially twice a week. Bone marrow and peripheral blood were collected and analyzed for the presence of GFP+ cells by flow cytometry.

Summary of data: We found that hypoxia induced drug resistance to bortezomib and carfilzomib of MM and WM cells, and that TPZ was active in a dose-dependent manner only in hypoxic conditions. Combination of TPZ with bortezomib and carfilzomib, resensitized cancer cells to death in hypoxia. Addition of TPZ increased adhesion of cancer cells to endothelial cells, and decreased chemotactic properties of cancer cells in hypoxia in vitro. Moreover, post-treatment residual cancer cells were further decreased using TPZ, preventing recurrence of MM in vivo.

Conclusion: We report that TPZ prevents hypoxia-induced metastasis and overcomes hypoxia-induced drug resistance in MM and WM. This is the first study to show the efficacy of TPZ in hematologic malignancies in general and in MM and WM in particular. This data provide a preclinical basis for future clinical trials testing efficacy of TPZ in MM and WM.

Citation Format: Barbara Muz, Pilar de la Puente, Feda Azab, Micah Luderer, Abdel Kareem Azab. Tirapazamine as a strategy to prevent cell dissemination and overcome drug resistance. [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 5468. doi:10.1158/1538-7445.AM2015-5468