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to recur in an untreatable form.
There are different chemotherapy resistance mechanisms but very often resistance develops when the cancer cells start to over express genes that disable or exclude the chemotherapy drugs. A common method is for cancer cells to over express efflux proteins like the mul-tidrug resistance (MDR) proteins that pump these chemotherapy drugs from the cells. RNA interference (RNAi) provides a method for reducing the expression of such proteins. RNAi may be effected by small inter-fering RNAs (siRNAs). When the synthetic double stranded siRNA en-ters the cells, it binds the RNA induced silencing complex (RISC). The guide antisense strand stays in the complex, while the passenger strand leaves. The antisense strand then guides the RISC complex by gamma-Glu-Cys pairing to complementary mRNA which the RISC complex then cleaves (Dykxhoorn et al., 2003; Petrova et al., 2003). After transfection, gene silencing (knockdown) of mRNA due to RNA interference commonly lasts from 3 to 7 days in dividing cells, and 3–4 weeks in non-dividing cells (Bartlett and Davis, 2006). The stability of RNAi is affected by the
RNA phosphodiester's structure which is more prone to nuclease de-gradation than that of DNA. Cancer cells have previously been re-sen-sitized to chemotherapeutic treatment by silencing MDR1 with siRNAs (Stege et al., 2010; Yu et al., 2015). The expression of proteins from other cancer related genes like oncogenes and migration genes EGFR (Chen et al., 2012), BCR/ABL1 (Mahmodabady et al., 2010), K-ras (Perepelyuk et al., 2017), EphA2 (Ozcan et al., 2015), TMEM98 (Ming et al., 2015) could also be silenced in a similar fashion using siRNAs. Combinational therapy with gene therapy and anticancer drugs has also been proven effective against cancer cells (Babu et al., 2017).
The biggest impediment to siRNA based treatment is serum stability and cellular internalization of siRNA to the cytoplasm – as it is easily degraded, negatively charged and large. siRNA is usually comprised of about 40 nucleotides, weighs 12–13 kDa, and is about 10 nm long. To deliver siRNA into the cytoplasm and protect it from nucleases the development of new carriers is required. Nanoparticles may be used as such siRNA carriers as well as carriers of hydrophobic drugs to improve their pharmacokinetic properties (Manju and Shaoqin, 2014). Many nano-particulate systems have been developed for siRNA delivery in-cluding liposomes, cationic lipid and polymer complexes and solid polymer particles, these systems have different advantages and limita-tions. Cationic lipid complexes are one of the most common non-viral carriers of both DNA and RNA into the cells and their use is attractive as lipid/siRNA complexes are simple and fast to produce and typically yield high transfection rates. They can be applied for co-delivery of anticancer drugs as well (Pandey et al., 2016). Quaternary amine lipids like DOTAP and lipofectamine use a clathrin dependent pathway for cellular entry (Sahay et al., 2010). This is possible if the diameter of the particles is below 500 nm (Kou et al., 2013).
This study aims at improving combinational therapy with siRNA and anticancer chemotherapy drugs. The anticancer drug used in this study is etoposide which is representative of many other hydrophobic anti-cancer drugs with poor bioavailability, low solubility and high resistance (Nitiss, 2009; Wang et al., 2014). Etoposide is a topoisome-rase inhibitor that finds application in the treatment of cancers like refractory testicular tumors, small cell lung carcinoma and glio-blastoma. Etoposide and siRNA is delivered to lung and oral cancer cells using the cationic quaternary amine lipid MDEA. MDEA is a biode-gradable and inexpensive lipid currently used in a wide variety of personal care products such as hair conditioners with apparent safety in external applications (Gizaw et al., 2008; Gizaw et al., 2009). But MDEA has not, to our knowledge, been applied to drug delivery studies before nor has its cytotoxicity profile been established. We demonstrate that it forms nanoparticles with siRNA and that these can deliver functional siRNA and etoposide to cancer cells in the presence of serum.