Targeting cell cycle proteins in breast cancer cells by sirna using lipidsubstituted

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1 Targeting cell cycle proteins in breast cancer cells by sirna using lipidsubstituted polyethylenimine Parmar, Manoj B (Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada) Montazeri Aliabadi, Hamidreza (Department of Chemical and Materials Engineering, Faculty of Engineering, Mahdipoor, Parvin (Department of Chemical and Materials Engineering, Faculty of Engineering, Kucharski, Cezary (Department of Chemical and Materials Engineering, Faculty of Engineering, Maranchuk, Robert (Dept of Medical Microbiology and Immunology, Faculty of Medicine and Dentistry, University of Albert) Hugh, Judith C (Dept of Laboratory Medicine and Pathology, Faculty of Medicine and Dentistry, Uludag, Hasan (Department of Chemical and Materials Engineering, Faculty of Engineering, Introduction There are significant limitations (side effects) to all breast cancer chemotherapy regimens, radiation and surgical treatments, which urgently warrant a search for alternative and more effective therapies. Control of breast cancer growth based on RNA interference (RNAi) using small interfering RNA (sirna) has been a promising approach in recent years. The sirna-mediated silencing of a unique or over-expressed cell cycle protein that is essential for unregulated cell growth could lead to malignant cell death and, in turn, control tumor growth without affecting the normal tissues. The cell cycle constitutes a series of events that leads to regulated cell division. Given the unregulated cell cycle progression in cancer cells, proteins involved in cell cycle are promising targets to stop undesired growth of breast cancer cells. The sirna delivery with biomaterials is more preferable to avoid side-effects associated with viruses. The objectives of this study were to find the best sirna delivery system in order to exert a maximum therapeutic effect, and to identify the most effective cell cycle protein

2 target(s) for silencing in breast cancer cells. Materials and Methods To identify the best carrier for sirna delivery, we screened low molecular weight (2.0 kda) linoleic acid, caprylic acid and α-linoleic acid substituted polyethylenimines (PEI) with commercially available carriers by inhibition of cell growth. The uptake of sirna-carrier complexes was determined by flow cytometry and the up-taken complexes per cell were calculated by confocal microscopy. To explore the potential cell cycle proteins as therapeutic targets, we screened an sirna library in MDA-MB-231 and MDA- MB-435 cells using PEI-LA as a delivery agent. The identified targets were evaluated in breast cancer cells by inhibition of cell growth assay and digital-pcr. The efficacy of dicer-substrate sirna (27 base-pairs longer sirna; DsiRNA) against identified targets was determined. The efficacy of DsiRNA against CDC20 was subsequently assessed in a xenograft model. All experimental protocols using animals were approved by the Animal Care and Use Committee: Health Sciences at the University of Alberta in accordance with the directions of the Canadian Council on Animal Care. Results The linoleic acid-substituted PEI (PEI-LA) has delivered the sirna most successfully to MDA-MB-435, and was chosen for the entire study. The schematic representation of the synthesis of PEI-LA is shown in Fig 1. The flow cytometry and confocal microscopy indicated a better delivery by PEI-LA at higher ratio of sirna:pei-la. Out of 169 cell cycle protein targets, the sirna against cell division cycle protein 20 (CDC20), a recombinase RAD51, and serine-threonine protein kinase CHEK1 diminished the cell growth most significantly in MDA-MB-435 cells. These identified targets with another well-studied cell cycle protein, kinesin spindle protein (KSP), were then evaluated in MDA-MB-435, MDA- MB-231 and MCF7 cells using independently prepared sirnas. KSP was the most successful target among all identified cell cycle proteins as around 80% MDA-MB-435 cell growth was inhibited by KSP sirna. However, the significant down-regulation of mrna transcript of all proteins was found by digital-pcr. We also explored the efficacy of DsiRNAs against CDC20, RAD51 and CHEK1. All DsiRNAs decreased the cell growth significantly. However, CDC20 was the most effective DsiRNA since it inhibited MDA-MB- 435 and MCF7 cell growth approximately 80%. We further evaluated the efficacy of CDC20 DsiRNA in vivo by injecting DsiRNA/PEI-LA complexes to breast cancer xenografts weekly and bi-weekly subcutaneously in the vicinity of tumor. In the weekly injection group, a significant decreased in the growth of CDC20 DsiRNA treated tumor compared

3 to scrambled DsiRNA treated tumor was achieved on day 14 and 17 (Fig 2A). In the biweekly injection groups, the slower growth was evident with CDC20 DsiRNA treated group from the beginning of the study, where the differences between the CDC20 and scrambled DsiRNA were significant on day 7, 14 and 17 (Fig 2B). Discussion and Conclusion The identified cell cycle proteins could be promising targets to treat breast cancer by non-viral RNAi therapy. CDC20 DsiRNA was able to decrease the tumor growth in both weekly and bi-weekly injection groups. DsiRNA dose used here was 2 µg (~0.08 mg/kg/day), which was quite low compared to 4-10 µg of sirna used in intratumoral injections in previous studies and some higher doses (up to 40 µg of sirna) used in other modes of administrations (Behlke, 2006). Moreover, we reduced the number of injections in our study to weekly and bi-weekly, leading to a large interval between the injections. The synthetic PEI-based lipophilic polymers were successfully undertaken the required sirna delivery. The presented study has enlightened the importance of cell cycle protein targets in cell survival and breast cancer therapy, and has given the safe and nontoxic delivery system (PEI-LA) for the down-regulation of cell cycle proteins.

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5 Fig 1: Schematic representation of the synthesis of PEI-LA.

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7 Fig 2: Effect of CDC20 DsiRNA treatment in vivo. Xenografts of MDA-MB-435 in nude mice were treated with a scrambled DsiRNA (CsiRNA) and CDC20 DsiRNA. (A) Weekly injection; n=6 and n=5 in CsiRNA and CDC20 groups. (B) Bi-weekly injection; n=3 and n=4 in CsiRNA and CDC20 groups. Significance (p 0.05) Acknowledgements Manoj Parmar is a recipient of Women and Children's Health Research Institute (WCHRI) Graduate Studentship Grant and Alberta Innovates-Health Solutions (AIHS) Graduate Studentship. This study was supported by operating grants from Canadian Breast Cancer Foundation (CBCF) and Natural Sciences and Engineering Council of Canada (NSERC). References 1. Behlke, M. A. Progress towards in vivo use of sirnas, Mol. Ther. 2006, 13, doi: /j.ymthe