Rhodacyanine Derivative Selectively Targets Cancer Cells and Overcomes Tamoxifen Resistance John Koren III1, Yoshinari Miyata2, Janine Kiray1, John C. O’Leary III1, Lana Nguyen1, Jianping Guo 3 , Laura J. Blair1, Xiokai Li2, Umesh K. Jinwal4, Jin Q. Cheng3, Jason E. Gestwicki2, Chad A. Dickey1* 1 Department of Molecular Medicine, USF Health Byrd Alzheimer’s Institute, College of Medicine, University of South Florida, Tampa, Florida, United States of America, 2 Departments of Pathology and Biological Chemistry, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America, 3 Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, United States of America, 4 College of Pharmacy, University of South Florida, Tampa, Florida, United States of America Abstract MKT-077, a rhodacyanine dye, was shown to produce cancer specific cell death. However, complications prevented the use of this compound beyond clinical trials. Here we describe YM-1, a derivative of MKT-077. We found that YM-1 was more cytotoxic and localized differently than MKT-077. YM-1 demonstrated this cytotoxicity across multiple cancer cell lines. This toxicity was limited to cancer cell lines; immortalized cell models were unaffected. Brief applications of YM-1 were found to be non-toxic. Brief treatment with YM-1 restored tamoxifen sensitivity to a refractory tamoxifen-resistant MCF7 cell model. This effect is potentially due to altered estrogen receptor alpha phosphorylation, an outcome precipitated by selective reductions in Akt levels (Akt/PKB). Thus, modifications to the rhodocyanine scaffold could potentially be made to improve efficacy and pharmacokinetic properties. Moreover, the impact on tamoxifen sensitivity could be a new utility for this compound family. Citation: Koren J III, Miyata Y, Kiray J, O’Leary JC III, Nguyen L, et al. (2012) Rhodacyanine Derivative Selectively Targets Cancer Cells and Overcomes Tamoxifen Resistance. PLoS ONE 7(4): e35566. doi:10.1371/journal.pone.0035566 Editor: Leonard Petrucelli, Mayo Clinic, United States of America Received February 9, 2012; Accepted March 17, 2012; Published April 26, 2012 Copyright: 2012 Koren et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Dr. Dickey was supported by the Alzheimer’s Association, CurePSP (Progressive supranuclear palsy), National Institutes of Health/National Institute on Aging (NIH/NIA) R00AG031291 and NINDS (National Institute of Neurological Disorders and Stroke) R01NS073899. Dr. Gestwicki was supported by the NIH R01NS059690. Dr. Cheng was supported by James & Esther King Grant 1KG02-33967. No additional external funding was received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: cdickey@health.usf.edu Introduction MKT-077, a cationic rhodacyanine, has demonstrated cancer specific toxicity and growth inhibition in vitro and in vivo across multiple cancer varieties [1]. It was determined that MKT-077 localized to the mitochondria [1]. MKT-077 entered into clinical trials for the treatment of advanced and refractory solid tumors of various cellular origin, including: kidney, lung, prostate, colon, adenocarcinomas, and melanomas [2,3]. The primary negative side effect observed in both studies was renal toxicity [2,3]. The observed toxicity halted recruitment to one trial as similar animal studies showed irreversible renal toxicity following administration of MKT-077 [2,3]. Later it was discovered that MKT-077 interacted with mortalin (mot-2), a 70-kda heat shock protein (Hsp70) family member, and that the interaction of MKT-077 with mot-2 induced the release of the tumor suppressor p53 from a complex with mot-2 [4]. This mot-2/p53 complex inactivated the tumor suppression abilities of p53 by sequestering it in the cytosol in vivo [5]. Breast cancers are among the most common cancers diagnosed in women [6]. Published data states that treating MCF7 cells, a breast cancer cell model, with MKT-077 produces cytotoxicity and alters growth [1,2]. However, in the results of two published Phase I clinical trials, no patients with a solid breast tumor or refractory breast tumor were included in the study [2,3]. Though there are numerous breast cancer chemotherapies, resistance to breast cancer therapies can arise in roughly 30% of women treated for breast cancer [7]. Known resistances in breast cancers have been observed for not only standard anti-cancer strategies, such as doxorubicin, but also trastuzumab and tamoxifen (4-OHT) [8,9,10]. Breast cancers also have a high prevalence of mutations; mutations which can promote tumorigenesis and survival [11]. While these mutations produce targets for treatments, other mutations can overcome signaling cascade network circuitry to eliminate upstream targets [12,13]. This reduces the number of potential targets, reducing the cadre of treatment options, and increasing the potential for resistance genesis. In addition, resistance can emerge when regulatory proteins are altered to allow pro-survival proteins to act unabated. Several kinases related to cell survival have been implicated in facilitating chemotherapy resistance [14,15,16,17,18]. For example, phosphorylation of the estrogen receptor alpha (ERa) causes ERa to become active regardless of estrogen binding, resulting in resistance to 4-OHT. Thus, strategies to re-sensitize refractory cancer cells to existing therapies are sorely needed. In these data, we identify a functional derivative of MKT-077 that showed increased cytotoxicity across multiple cancer varieties while still retaining the cancer specificity associated with MKT- 077. This enhanced activity was due to the intracellular localization of the compound. In addition, short treatments with PLoS ONE | www.plosone.org 1 April 2012 | Volume 7 | Issue 4 | e35566