Cancer Therapy Vol 5, page 1 1 Cancer Therapy Vol 5, 1-10, 2007 Reversal of doxorubicin resistance by adenovirus- mediated transfer of cyclooxygenase-2 antisense in multidrug-resistant MCF-7 cells Research Article Marwa W. Kamel 1,2 , Salama A. Salama 1 , Samira Saleh 3 , Abdel-Moneim M. Osman 2 , Mohamed M. Sayed-Ahmed 2 , Ayman Al-Hendy 1, * 1 Department of Obstetrics & Gynecology, University of Texas Medical Branch, Galveston, Texas, USA 2 Department of Pharmacology and Experimental Oncology, Cancer Biology, National Cancer Institute, Cairo University, Egypt 3 Department of Pharmacology, Faculty of Pharmacy, Cairo University, Cairo, Egypt __________________________________________________________________________________ *Correspondence: Ayman Al-Hendy, MD, PhD, FRCSC, FACOG, Department of Obstetrics & Gynecology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555, USA; Telephone: (409) 747-1668; Fax: (409) 747-1669; email: ayalhend@utmb.edu Key words: Gene therapy, drug resistance, breast cancer Abbreviations: Adenomatous Polyp Prevention on Vioxx, (APPROVe); adenovirus vector expressing COX-2 antisense, (Ad-COX-2 AS); cyclooxygenase-2, (COX-2); deoxynucleotide triphosphate mixture, (dNTP); doxorubicin-resistant breast cancer cell line, (MCF- 7/DOX); enzyme-linked chemiluminescence, (ECL); ethylenediaminetetraacetic adid, (EDTA); multidrug-resistance, (MDR); phosphate buffered saline, (PBS); phosphate buffered saline-Tween, (PBS-T); plaque forming units, (PFU); radioimmunoprecipitation, (RIPA); sodium dodecylsulfate, (SDS) Received: 22 November 2006; Accepted: 12 December 2006; electronically published: January 2007 Summary Increased expression of cyclooxygenase-2 (COX-2) has been implicated in many human malignancies, and it is associated with tumor progression, angiogenesis, inhibition of apoptosis, and development of multidrug-resistant (MDR) phenotype. Both selective and nonselective COX-2 inhibitors have been used in clinical trials as adjuvant therapy-too often at the expense of increased systemic toxicity. In the current study, we evaluated whether adenovirus vector expressing COX-2 antisense (Ad-COX-2 AS) has therapeutic potential to modulate the drug resistance and the expression of MDR gene MDR1, antiapoptotic gene Bcl-2, and cell cycle regulating gene cyclin D1 in doxorubicin-resistant breast cancer cell line (MCF-7/DOX). Our data show that MCF-7/DOX cells are more efficiently transduced by adenovirus compared with the parental MCF-7 cell line. Transduction of MCF-7/DOX cells with Ad-COX-2 AS (multiplicity of infection [MOI] of 10, 20, 50, plaque forming units [PFU]/cell) reduced the IC 50 value of doxorubicin by 13-, 19-, and 20-fold, respectively, compared with Ad-LacZ–transduced cells (P < 0.05). Furthermore, Ad-COX-2 AS downregulates the expression of the MDR1, the antiapoptic protein Bcl-2, and the cell cycle regulating protein cyclin D1 in MCF-7/DOX cells. In conclusion, MCF-7/DOX cells are more efficiently transduced with Ad-COX-2 AS compared with parental MCF-7 cells. Transduction of MCF-7/DOX cells with Ad- COX-2 AS reverses their resistance to doxorubicin. The promising efficacy of Ad-COX-2 AS in reversing drug resistance deserves further investigation. I. Introduction There is considerable evidence to suggest that the expression of cyclooxygenase-2 (COX-2) plays an important role in the development of many human malignancies, and that it confers a survival advantage that eventually facilitates tumor development, progression, angiogenesis, and resistance to chemotherapeutic agents (Chow et al, 2005; Tari et al, 2005; Zatelli et al, 2005; Mazhar et al, 2006; Raspollini et al, 2006). The effects of COX-2 overexpression in cancer cells are mediated by interactions with downstream effectors of COX-2. Recent reports suggest that expression of the COX-2 enzyme upregulates expression of MDR1/P-glycoprotein (P-gp), an exponent of resistance to anticancer drugs (Ratnasinghe