This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Yan, T. Articles by Kinsella, T. J. Search for Related Content PubMed PubMed Citation Articles by Yan, T. Articles by Kinsella, T. J.

Research Articles: Therapeutics

Methoxyamine potentiates iododeoxyuridine-induced radiosensitization by altering cell cycle kinetics and enhancing senescence

Department of Radiation Oncology, Case Comprehensive Cancer Center, University Hospitals of Cleveland and Case Western Reserve University School of Medicine, Cleveland, Ohio

Requests for reprints: Timothy J. Kinsella, Department of Radiation Oncology, University Hospitals of Cleveland /Ireland Cancer Center, LTR 6068, 11100 Euclid Avenue, Cleveland, OH 44106-6068. Phone: 216-844-2530; Fax: 216-844-4799. E-mail: timothy.kinsella{at}uhhs.com

Abstract

We previously reported that methoxyamine (an inhibitor of base excision repair) potentiates iododeoxyuridine (IUdR)–induced radiosensitization in human tumor cells. In this study, we investigated the potential mechanisms of this enhanced cell death. Human colorectal carcinoma RKO cells were exposed to IUdR (3 µmol/L) and/or methoxyamine (3 mmol/L) for 48 hours before ionizing radiation (5 Gy). We found that IUdR/methoxyamine altered cell cycle kinetics and led to an increased G₁ population but a decreased S population before ionizing radiation. Immediately following ionizing radiation (up to 6 hours), IUdR/methoxyamine–pretreated cells showed a stringent G₁-S checkpoint but an insufficient G₂-M checkpoint, whereas a prolonged G₁ arrest, containing 2CG1 and 4CG1 cells, was found at later times up to 72 hours. Levels of cell cycle–specific markers [p21, p27, cyclin A, cyclin B1, and pcdc2(Y15)] and DNA damage signaling proteins [H2AX, pChk1(S317), and pChk2(T68)] supported these altered cell cycle kinetics. Interestingly, we found that IUdR/methoxyamine pretreatment reduced ionizing radiation–induced apoptosis. Additionally, the extent of cell death through necrosis or autophagy seemed similar in all (IUdR ± methoxyamine + ionizing radiation) treatment groups. However, a larger population of senescence-activated ß-galactosidase-positive cells was seen in IUdR/methoxyamine/ionizing radiation–treated cells, which was correlated with the increased activation of the senescence factors p53 and pRb. These data indicate that IUdR/methoxyamine pretreatment enhanced the effects of ionizing radiation by causing a prolonged G₁ cell cycle arrest and by promoting stress-induced premature senescence. Thus, senescence, a novel ionizing radiation–induced tumor suppression pathway, may be effectively targeted by IUdR/methoxyamine pretreatment, resulting in an improved therapeutic gain for ionizing radiation. [Mol Cancer Ther 2006;5(4):893–902]

Grant support: NIH grants CA50595 and CA112963 (T.J. Kinsella).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 9/ 9/05; revised 12/12/05; accepted 1/25/06.