Executive Summary : | In the last two decades, RNA interference-based therapies have made steady progress toward their full clinical potential. From 2018, four siRNA-based drugs including Patisiran, Givosiran, Lumasiran, and Inclisiran were approved by the FDA against various diseases. Moreover, many siRNA drug candidates are being evaluated at advanced stages of clinical trials. With this potential practicality, few challenges are associated with RNAi therapeutics such as high nuclease susceptibility, binding to off-targets due to partial complementarity, unwanted activation of an innate immune response, and intracellular delivery. Furthermore, naked siRNAs are unable to cross the lipophilic cell membrane due to their immunogenic nature, large molecular weight, and negatively charged phosphate groups. The coherent use of chemical modifications in sugar moiety, nucleobase, and the phosphate backbone of siRNAs have improved the overall efficacy of siRNAs and helped to overcome most of these challenges. Our objective is to synthesize folic acid conjugated siRNAs bearing diverse 4’-C-alkylamino-2’-fluoro uridine and cytidine modifications to study their influence on duplex stability, serum stability, gene silencing, and receptor-mediated delivery in cancer cells. Normally, folate receptors are overexpressed in most cancer cells which bind to folic acid with very high binding affinity (10-10 mol/l). A combination of dual ribose modifications and 3’-folate conjugation at the passenger strand will be a novel and efficient approach to achieve significant receptor-mediated delivery and Bcl-2 gene silencing which leads to apoptosis and cancer cell death. So far, all four FDA-approved siRNA drugs are largely modified using 2’-modifications. We hypothesize that the synergistic effect of these 4’-C-alkylamino and 2’-fluoro modifications would augment the serum stability, gene silencing activity, and carrier-free cellular uptake via folate-mediated endocytosis. Here, we propose that the minimal number of these dual ribose modifications could be adequate to attain the desired therapeutic effect compared to extensive 2’-modifications (2’-O-Me, 2’F, and 2’-O-MOE) in siRNAs. Overall, these studies will help to understand more about the RNAi interference mechanism, position-dependent tolerance on guide and passenger strands, in vitro gene silencing potency, and off-target activity of the modified siRNAs. Depending on thermal stability, the modification can be incorporated into siRNA strands to improve strand selection. So, it will be worth trying to study the comparative effects of these novel modifications on siRNAs which will help to design and develop a potential delivery system for tumour cells using the folate conjugation approach. |