CHK1 siRNA Containing Gemcitabine and Chemically Modified Nucleotides Shows Antitumoral Activity in Vitro and in Vivo

Abstract Gemcitabine was shown to augment anti-cancer activity when combined with small molecule CHK1 inhibitors. We had previously demonstrated that we could incorporate gemcitabine molecules into the backbone of an siRNA targeting CHK1 and studied this drugs effects in pancreatic cancer cells [1]. We had optimized the number of gemcitabines to improve efficacy in the combination where the CHK1 siRNA was unmodified [1]. In this manuscript, we extend these studies by using chemically modified siRNAs using the same siRNA sequence targeting CHK1. We varied the 2'-Fluoro and 2'-O-Methyl modification patterns within the sequence, with gemcitabines in the same locations within the same siRNA sequence. We show that adding gemcitabines into the siRNA can demonstrate improved potency, not only against pancreatic cancer cell models but also against lung cancer, ovarian cancer, triple negative breast cancer and colon cancer. We formulated the different versions of CHK1 siRNA + gemcitabine into polypeptide nanoparticles with good control over size (~82-88nm) and zeta potential (34-36mV). When delivered intravenously to mice bearing a pancreatic xenograft tumor, the cocktail showed a reduction in tumor burden. The product demonstrated inhibitory effects in vivo, with no effect on the body weights of the animals. We further examined the ability to improve on the potency of this reagent by inclusion of a second siRNA (targeting WEE1) and demonstrate that, in vitro, the pancreatic cancer cell line, MiaPaca2, is particularly sensitive to a combo of CHK1 siRNA plus gemcitabine together with a second siRNA against WEE1.