Review Article
Using Oncolytic Viruses to Silence the Multidrug Resistance Genes via RNA Interference
Prittam Goswami and Pranab Roy*
Corresponding Author: Pranab Roy, Department of Molecular Biology, Institute of Child Health, Biresh Guha Street, Kolkata, 700017, West Bengal, India
Received: April 23, 2019; Accepted: April 29, 2019; Published: December 05, 2019;
Citation: Goswami P & Roy P. (2019) Using Oncolytic Viruses to Silence the Multidrug Resistance Genes via RNA Interference. J Genet Cell Biol, 2(3): 88-95.
Copyrights: ©2019 Goswami P & Roy P. 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.

Efflux pumps are omnipresent in almost all types of cells. They participate in the transportation of a wide range of important molecules across the cell membrane. They play primordial roles in detoxification of the cell by disposing off unwanted materials. Since tumor cells emerge from normal cells as a result of mutation, they carry with them the genes coding for the efflux pumps. These efflux pumps are overexpressed by cancer cells. They defend the cancer cells against chemotherapy by actively pumping out the drug molecules that have incurred into the cytoplasm. This leads to drug resistance, which is the major cause for low efficiency of most of the chemotherapeutic drugs. Although many efflux pump inhibitors have been developed, none of them has been clinically approved because of their lack in specificity, which causes them to incur into the normal cells leading to many adverse effects. Moreover, with time, the cancer cells develop resistance against these inhibitors. RNAi mediated gene silencing proved to be effective in silencing the MDR genes under in vitro conditions. However, they prove to be inefficient under in vivo trials due to the lack of a proper transport vector that will be able to transport the pre-interfering RNAs specifically to the tumor site while keeping the normal cells intact. Many oncolytic viruses have been identified and genetically engineered to specifically infect a wide range of tumor cells. This article proposes the use of genetically modified oncolytic viruses as transport vectors for the pre-interfering RNAs to solve the above problems. The strategies proposed in this article can be employed to specifically target the MDR genes present in cancer cells, while keeping the normal cells untouched and can be used adjunct to chemotherapy to make it efficacious.


Keywords: RNAi, Efflux pumps, Chemotherapy


Abnormal cell division as a result of mutation leads to cancer. Today, it is one of the leading causes of mortality globally, leading to 8.8 million deaths every year [1]. In a global survey carried out in 2015, 90.5 million people were said to suffer from cancer, which increases by 14.1 million every year and this rate is expected to surpass 20 million by the end of 2025 [2,3]. The different treatments involved in cancer include chemotherapy, immune therapy, radiation therapy and surgery [4,5]. However, the most widely used therapies against cancer are chemotherapy and radiation therapy [6]. It is evident that with the passage of time the cancer cells become more virulent and their resistance to chemotherapy increase [7]. The increase in resistance of the cancer cells against chemotherapeutic drugs can be attributed to the overexpression of Multidrug Resistance efflux pumps.

The efflux pumps are highly conserved P-glycoproteins that are imminent on the surfaces of both prokaryotic and eukaryotic cells. Dr. Juliano and Dr. Ling were the first to detect the presence of efflux pumps in eukaryotic cells (in Chinese hamster ovary) in 1976 [8]. Since then, many eukaryotic P-glycoproteins have been discovered in the cells of CNS, intestinal epithelium cells, liver cells, renal cells, stem cells, etc. [9-17]. They play important roles in extrusion of toxic materials and are involved in the transportation of many important molecules such as lipids, cholesterol, chloride ions, cytokines and polypeptides across the membrane [18-23]. P-glycoproteins are also evident on the surfaces of CD8+ T cells and Natural killer cells; they help in killing the target cells through the release of perforins and granzyme B [24].

Since the tumor cells emerge from normal cells as a result of mutation, they carry with them the genes coding for the Efflux pumps. An over-expression of efflux pump proteins is evident in a wide range of cancer cells [25-31]. The cancer cells overexpress efflux pumps, which defend them against chemotherapeutic drugs by actively pumping them out of the cell, thus reducing their intracellular concentration. The efflux pumps belong to the ABC (ATP binding cassette) transporter family which utilizes the energy obtained from ATP hydrolysis for the transport of different molecules. The most extensively expressed members of the ABC family involved in Multidrug Resistance are transport proteins ABCB1, ABCC1 and ABG2 [32].

In addition, some of the efflux transporter proteins also act as MHCs (major histocompatibility complex) and play regulatory roles in cell signaling [33]. Several members of the ABC transporter family have been depicted to be involved in evading apoptosis and inducing proliferation of the tumor cells. For example, transport proteins ABCB1 and ABCC1 play anti-apoptotic roles in tumor cells by delaying response to apoptotic signals [34-36]. Similarly, transport proteins ABCC1, ABCC4 and ABCG2 bolster proliferation in cancer cells [37-39].


Over the years many researches have been carried out in developing drugs targeting the efflux pumps, to be used adjunct to chemotherapy. Many inhibitors have been developed against the multidrug resistance efflux pumps such as quinine, quinidine, verapamil, cyclosporin, PSC-833, MS-209 and others [32]. However, they proved to be disappointments with very limited rates of clinical success [32,40-46]. Most of them cause drug related adverse effects due to the lack of specificity, by also damaging the efflux pumps that are present on normal cells [47].

Efforts to silence the MDR genes have already been carried out using different molecular biology tools such as antisense therapy, ribozyme therapy and RNA interference [48-50]. RNA interference via Small interfering RNA and short hairpin RNA designed to inactivate the MDR genes proved to be quite efficient in abating drug resistance in cancer cells [51,52]. Although RNA interference is an efficient technique for gene silencing under in vitro conditions, it fails to meet the expectations when subjected to in vivo due to many factors such as the low bioavailability of the RNA molecules at the target site, as most of them get excreted from the body through urine, many are destroyed due to nuclease activity and the others fail to enter the cell due to their negative charge and large size [53-55]. In addition, many molecules that manage to successfully pass through the membrane through endocytosis get degraded inside the endosome before reaching the cytoplasm [56]. Moreover, using a vector that cannot unload the pre-interfering RNA molecules specifically at the tumor site may abate the expression of efflux pumps in normal cells leading to many adverse effects in the body. The above factors mark the need for a vector that can safely transport the RNA molecules to their target site [51,57-60]. Using oncolytic viruses as transport systems for the pre-interfering RNA molecules can solve these problems.


Tumor cells are formed as a result of mutation in normal cells which gives them the ability to evade immune responses, to proliferate limitlessly and to evade apoptosis. This makes them an interesting target for viruses to grow in. Some oncolytic viruses exist naturally. However, most of them are genetically engineered to make them specific to cancer cell. Some extensively employed oncolytic viruses are Adenovirus, Chicken anemia virus, Parvovirus, Herpes Simplex virus and Newcastle disease virus [61].

The upcoming topics propose the use of Oncolytic viruses in silencing the MDR genes:

Using viral shells as transport vehicles for pre-interfering RNAs

Certain protein receptors are overexpressed on the surfaces of tumor cells. They serve as the entry ligands for many viruses. For example, the intra-cellular adhesion molecule-1 (ICAM-1) and decay accelerating factor (DAF) which serve as entry receptors for coxsackievirus A21 are over expressed by certain cancer cells [62,63]. Similarly, human ovarian cancer cells overexpress α2β1 integrin which serves as the entry receptor for echovirus type 1 [64]. The viruses whose entry receptors are over expressed by cancer cells can be exploited for selectively targeting the tumor cells [61]. This targeting strategy is called transductional targeting.

In case of enveloped viruses, the viral shell comprises of the envelope and the capsid, whereas, in case of non-enveloped viruses it comprises only of the viral capsid. Since, the surface proteins present on viral shells are involved in the transductional targeting of tumor cells; they can be used as transport vehicles for safely transferring the pre-interfering RNAs to the cancer cell, without causing them to intervene into normal cells.

Only the viruses whose entry receptors are overexpressed by the cancer cells can be chosen for this strategy. The part of their genome coding for the capsid, envelope and other associated proteins should be isolated, amplified and expressed in a protein expression system. The proteins formed will then self-assemble to form functional viral shells lacking any genetic material [65-71]. Baculo virus expression system is the most widely used protein expression system for this purpose [72]. At present, many virus-like particles lacking genetic material, that mimic the original virus have being developed using this method, to be used as vaccines to stimulate humoral and cellular immunity [65-80].

Once the viral shells have been synthesized, the next step involves in vitro synthesis of the pre-interfering RNA molecules complementary to the target genes [81]. The pre-interfering RNA molecules to be used can be both short hairpin RNAs as well as short double stranded RNAs. The synthesized RNA molecules should then be loaded into the empty viral vessels. The viral capsids and the interfering RNA molecules can be made to self-assemble under in vitro condition using the protocol developed by Cadena-Nava et al. [82]. This will give rise to genetically modified virus like particles (VLPs) that can be used for the specific targeting of the target genes present in cancer cells (Figure 1)

Step 1 depicts the attachment of the VLP to the cancer cell as a result of ligand-receptor binding. This interaction causes the uptake of the VLP through endocytosis as depicted in step 2. On entering the cancer cell, the VLP will lyse, freeing the RNA molecules into the cytoplasm as in step 3. In step 4 the RNA molecules are cleaved by dicer to form short interfering RNAs. These small interfering RNAs separate into guide RNA and passenger RNA. The guide RNA combines with argonaute and other associated proteins to form the RISC complex which then binds with the target mRNA, leading to its inactivation as depicted in step 5.

The virus like particles on being injected will get dispersed throughout the body though blood. On reaching the tumor cells, the viral receptors will interact with the receptors overexpressed on the surface of tumor cells leading to its attachment [83]. The clustering of receptors will give rise to a signaling cascade which will initiate the uptake of the virus like particle through endocytosis or macro pinocytosis [83]. On entering the cell, the viral capsids will dissolve, releasing the pre-interfering RNA molecules into the cytoplasm. These exogenous dsRNAs or shRNAs will activate the ribonuclease protein Dicer present in the cytoplasm, which will cleave the double stranded or hairpin RNAs to form short stretches of double stranded RNA about 25 bp long [84]. These short double stranded RNAs, also called short interfering RNA will then unwind, giving rise to two short single stranded RNAs called passenger and guide RNA, respectively. The passenger RNA will degenerate, whereas the guide RNA will get loaded up on an Argonaute protein which will then bind with the target mRNA to form the RNA-induced silencing complex (RISC) [85]. The complex formed will block the mRNA from getting translated [86]. The RISC complex can also induce the Argonaute protein “slicer” to cleave the target mRNA and in this way the expression of the target gene can be attenuated to a great extent [87].

Using oncolytic viruses to carry out DNA vector based RNAi

Although the previously described strategy sounds promising, it can be surmised to carry some drawbacks. Firstly, the targeting strategy is limited to transductional targeting and only a few types of cancer cells have been known till date, to overexpress viral entry receptors. Secondly, the proposed virus like particles are not capable of self-replication, they need to be synthesized manually which may lead to an increase in their production cost.

Creating a self-replicable genetically modified DNA virus or a retrovirus, that will be able to replicate inside a wide range of cancer cells and will be to produce pre-interfering RNAs naturally through transcription can help to counter the problems associated with the previous strategy. 

Firstly, the virus should be made nonpathogenic by attenuating its harmful genes. Then, based on the requirement, the virus should be made cancer cell specific by genetically modifying it in accordance with any of the following strategies:

Proapoptotic signaling: Viral intrusion into a normal cell can trigger apoptotic signaling cascade which can bring about many morphological and biochemical changes leading to cell death, thus preventing viral replication [88,89]. Some viruses can synthesize certain proteins which can inhibit apoptotic signaling thus providing them enough time to replicate [90]. However, cancer cells generally have a defective apoptotic pathway [91]. If the viral genes coding for the anti-apoptotic proteins are mutated then the resulting virus will fail to replicate inside normal cells due to its inability to inhibit the virus triggered apoptotic pathway [92]. However, it will be able to grow inside cancer cells.  For example, Onyx-15, a genetically modified adenovirus with attenuated Eb1 gene can grow selectively in p53 deficient cancer cells [93].

Transcriptional targeting: There are certain essential viral genes that are necessary for viral replication. Placing these genes under the regulation of tumor specific promoter can make the virus tumor specific by seizing its ability to replicate under non-tumor environment [94]. Hence the viruses will only be able express its vital genes and replicate it inside tumor cells.

Translation targeting: A virus infected cell produces Type I IFN (interferon) which ceases protein synthesis in its neighboring cells thus making them unfit for viral infection [95]. Engineering viruses to initiate a more potent IFN response in normal cells will prevent the viruses from spreading into its surrounding cells [90]. However, as the cancer cells have a defective IFN pathway the genetically modified viruses will fail to initiate an IFN response in cancer cells thus permitting viral replication inside them. Some viruses can block IFN signaling by encoding certain proteins that can inhibit the IFN signaling pathway [96]. Mutating the IFN inhibiting genes can prevent the viruses from replicating in normal cells [90]. On the other hand, the virus will be able to replicate in cancer cells as they have a defective IFN signaling pathway which cannot suppress viral replication [90].

The gene suppression strategy used here would be based on DNA vector based RNAi technology [88]. After the virus has been made cancer cell specific, the next step involves constructing a gene which on transcription will give rise to shRNAs, complementary to the target gene. The gene should consist of a promoter followed by two complementary sequences separated by a short non-homologous spacer DNA [88]. The two complementary sequences should be made in accordance with the sequence of the mRNA to be silenced. This gene should then be integrated into the genome of the oncolytic virus.

On being subjected to in vivo trials, the genetically modified virus will fail to proliferate inside normal cells. However, on infecting a cancer cell it will be able to replicate itself as well as transcribe the shRNAs which will then form RISC complex with the target mRNA and degrade it using the same procedure that was stated earlier. This will diminish the expression of Multidrug Resistance efflux pumps in the viral infected tumor cells.

The use of genetically engineered DNA viruses and retroviruses offers a wide range of targeting strategies to be employed to target a broad range of cancer cells. Since the viruses are self-replicable, it will be easy to clone them in cancer cell cultures which will also reduce their production cost.


The strategies proposed in this article can be used to abate the expression of Multidrug Resistance efflux pumps in cancer cells. Using the proposed strategy, adjunct to chemotherapy will make it more effective. In the absence of efflux pumps, the cancer cells will fail to defend themselves against the anti-cancer drugs. Hence the chemotherapeutic drugs will be able to eliminate the cancer cells without much difficulty. This strategy can also be used to target other important genes expressed in cancer cells that are also common to normal cells.


There is no conflict of interest among the authors regarding this manuscript.

1.       GBD (2016) Mortality and causes of death collaborators, global, regional and national life expectancy, all-cause mortality and cause-specific mortality for 249 causes of death, 1980-2015: A systematic analysis for the Global Burden of Disease Study 2015. Lancet 388: 1459-1544.

2.       GBD (2016) Disease and injury incidence and prevalence collaborators, global, regional and national incidence, prevalence and years lived with disability for 310 diseases and injuries, 1990-2015: A systematic analysis for the Global Burden of Disease Study 2015. Lancet 388: 1545-1602.

3.       World Health Organization (2014) World cancer report 2014. International Agency for Research on Cancer, p: 64.

4.       World Health Organization (2018) Cancer.

5.       National Cancer Institute (2019) Targeted cancer therapies.

6.       National Cancer Institute (2015) Cancer treatment. Available at:

7.       Cancer Research UK (2017) Why some cancers come back?

8.       Juliano RL, Ling VA (1976) Surface glycoprotein modulating drug permeability in Chinese hamster ovary cell mutants. Biochimica et Biophysica Acta (BBA) – Bio membranes 455: 152-162.

9.       Johnstone RW, Ruefli AA, Smyth MJ (2000) Multiple physiological functions for multidrug transporter P-glycoprotein? Trends Biochem Sci 25: 1-6.

10.    Demeule M, Régina A, Jodoin J, Laplante A, Dagenais C, et al. (2002) Drug transport to the brain: Key roles for the efflux pump P-glycoprotein in the blood-brain barrier. Vascul Pharmacol 38: 339-348.

11.    Bambeke V, Michot JM, Tulkens P (2003) Antibiotic efflux pumps in eukaryotic cells: Occurrence and impact on antibiotic cellular pharmacokinetics, pharmacodynamics and toxicodynamics. J Antimicrob Chemother 51: 1067-1077.

12.    Albrecht C, Viturro E (2006) The ABCA subfamily—gene and protein structures, functions and associated hereditary diseases. Pflugers Arch 453: 581-589.

13.    Takahashi K, Kimura Y, Nagata Y (2005) ABC proteins: Key molecules for lipid homeostasis. Med Mol Morphol 38: 2-12.

14.    Dean M, Fojo T, Bates S (2005) Tumor stem cells and drug resistance. Nature Rev Cancer 5: 275-284.

15.    Cormet-Boyaka E, Huneau JF, Mordrelle A, Boyaka PN, Carbon C, et al. (1998) Secretion of sparfloxacin from the human intestinal Caco-2 cell line is altered by P-glycoprotein inhibitors. Antimicrob Agents Chemother 42: 2607-2611.

16.    Zhao YL, Cai SH, Wang L, Kitaichi K, Tatsumi Y, et al. (2002) Possible involvement of P-glycoprotein in the biliary excretion of grepafloxacin. Clin Exp Pharmacol Physiol 29: 167-172.

17.    Ito T, Yano I, Tanaka K, Ichi Inui K (1997) Transport of quinolone antibacterial drugs by human P-glycoprotein expressed in a kidney epithelial cell line, LLC-PK1. J Pharmacol Exp Ther 282: 955-960.

18.    van Helvoort A, Smith AJ, Sprong H, Schinkel AH, Borst P, et al. (1996) MDR1 P-glycoprotein is a lipid translocase of broad specificity, while MDR 3 P-glycoprotein specifically translocates phosphatidylcholine. Cell 87: 507-517.

19.    Luker GD, Nilsson KR, Covey DF, Piwnica-Worms D (1999) Multidrug resistance (MDR1) P-glycoprotein enhances esterification of plasma membrane cholesterol. J Biol Chem 274: 6979-6991.

20.    Hardy SP, Good fellow HR, Valverde MA, Gill DR, Sepulveda V, et al. (1995) Protein kinase C-mediated phosphorylation of the human multidrug resistance P-glycoprotein regulates cell volume-activated chloride channels. EMBO J 14: 68-75.

21.    Drach J, Gsur A, Hamilton G, Zhao S, Angerler J, et al. (1996) Involvement of P-glycoprotein in the trans membrane transport of interleukin-2 (IL-2), IL-4 and interferon-gamma in normal human T-lymphocytes. Blood 88: 1747-1754.

22.    Sharma RC, Inoue S, Roitelman J, Schimke RT, Simoni RD (1992) Peptide transport by the multidrug resistance pump. J Biol Chem 267: 5731-5734.

23.    Amin ML (2013) P-glycoprotein inhibition for optimal drug delivery. Drug Target Insights 7: 27-34.

24.    Smyth MJ, Trapani JA (1995) Granzymes: Exogenous proteinases that induce target cell apoptosis. Immunol Today 16: 202-206.

25.    Zochbauer-Muller S, Filipits M, Rudas M (2001) P-glycoprotein and MRP1 expression in axillary lymph node metastases of breast cancer patients. Anticancer Res 21: 119-124.

26.    Filipits M, Suchomel R, Dekan G, Haider K, Valdimarsson G, et al. (1996) MRP and MDR1 gene expression in primary breast carcinomas. Clin Cancer Res 2: 1231-1237.

27.    König J, Hartel M, Nies AT, Martignoni ME, Guo J, et al. (2005) Expression and localization of human multidrug resistance protein (ABCC) family members in pancreatic carcinoma. Int J Cancer 115: 359-367.

28.    Steinbach D, Gillet J, Sauerbrey A, Gruhn B, Dawczynski K, et al. (2006) ABCA3 as a possible cause of drug resistance in childhood acute myeloid leukemia. Clin Cancer Res 12: 4357-4363.

29.    Weinstein RS, Jakate S, Dominguez JM, Lebovitz MD, Koukoulis GK, et al. (1991) Relationship of the expression of the multidrug resistance gene product (P-glycoprotein) in human colon carcinoma to local tumor aggressiveness and lymph node metastasis. Cancer Res 51: 2720-2726.

30.    Oda Y, Saito T, Tateishi N, Ohishi Y, Tamiya S, et al. (2005) ATP-binding cassette superfamily transporter gene expression in human soft tissue sarcomas. Int J Cancer 114: 854-862.

31.    Ohtsuki S, Kamoi M, Watanabe Y, Suzuki H, Hori S, et al. (2007) Correlation of induction of ATP binding cassette transporter A5 (ABCA5) and ABCB1 mRNAs with differentiation state of human colon tumor. Biol Pharm Bull 30: 1144-1146.

32.    Szakács G, Paterson JK, Ludwig JA, Booth-Genthe C, Gottesman MM (2006) Targeting multidrug resistance in cancer. Nat Rev Drug Discov 5: 219-234.

33.    Fletcher JI, Haber M, Henderson MJ, Norris MD (2010) ABC transporters in cancer: More than just drug efflux pumps. Nat Rev Cancer 10: 147-156.

34.    Robinson LJ, Roberts WK, Ling TT, Lamming T, Sternberg SS, et al. (1997) Human MDR 1 protein overexpression delays the apoptotic cascade in Chinese hamster ovary fibroblasts. Biochemistry 36: 11169-11178.

35.    Smyth MJ, Krasovskis E, Sutton VR, Johnstone RV (1998) The drug efflux protein, P-glycoprotein, additionally protects drug-resistant tumor cells from multiple forms of caspase-dependent apoptosis. Proc Natl Acad Sci U S A 95: 7024-7029.

36.    Peaston AE, Gardaneh M, Franco AV, Hocker JE, Murphy KM, et al. (2001) MRP1 gene expression level regulates the death and differentiation response of neuroblastoma cells. Br J Cancer 85: 1564-1571.

37.    Kuss B, Corbo M, Lau WM, Fennell DA, Dean NM, et al. (2002) In vitro and in vivo down regulation of MRP1 by antisense oligonucleotides: A potential role in neuroblastoma therapy. Int J Cancer 98: 128-133.

38.    Sassi Y, Lipskaia L, Vandecasteele G, Nikolaev VO, Hatem SN, et al. (2008) Multidrug resistance-associated protein 4 regulates cAMP-dependent signaling pathways and controls human and rat SMC proliferation. J Clin Invest 118: 2747-2757.

39.    Bhattacharya S, Das A, Mallya K, Ahmad I (2007) Maintenance of retinal stem cells by Abcg2 is regulated by notch signaling. J Cell Sci 120: 2652-2662.

40.    Wishart GC, Bissett D, Paul J, Jodrell D, Harnett A, et al. (1994) Quinidine as a resistance modulator of epirubicin in advanced breast cancer: Mature results of a placebo-controlled randomized trial. J Clin Oncol 12: 1771-1777.

41.    Solary E, Witz B, Caillot D, Moreau P, Desablens B, et al. (1996) Combination of quinine as a potential reversing agent with mitoxantrone and cytarabine for the treatment of acute leukemias: A randomized multicenter study. Blood 88: 1198-1205.

42.    Milroy R (1993) A randomised clinical study of verapamil in addition to combination chemotherapy in small cell lung cancer. West of Scotland Lung Cancer Research Group and the Aberdeen Oncology Group. Br J Cancer 68: 813-818.

43.    Dalton WS, Crowley JJ, Salmon SS, Grogan TM, Laufman LR, et al. (1995) A phase III randomized study of oral verapamil as a chemosensitizer to reverse drug resistance in patients with refractory myeloma. A Southwest Oncology Group study. Cancer 75: 815-820.

44.    Yin JL, Wheatley K, Rees JK, Burnett AK (2001) Comparison of ‘sequential’ versus ’standard’ chemotherapy as re-induction treatment, with or without cyclosporine, in refractory/relapsed acute myeloid leukemia (AML): Results of the UK Medical Research Council AML-R trial. Br J Hematol 113: 713-726.

45.    van der Holt B, Löwenberg B, Burnett AK, Knauf WU, Shepherd J, et al. (2005) The value of the MDR1 reversal agent PSC-833 in addition to daunorubicin and cytarabine in the treatment of elderly patients with previously untreated acute myeloid leukemia (AML), in relation to MDR1 status at diagnosis. Blood 106: 2646-2654.

46.    Sonneveld P, Suciu S, Weijermans P, Beksac M, Neuwirtova R, et al. (2001) Cyclosporin A combined with vincristine; doxorubicin and dexamethasone (VAD) compared with VAD alone in patients with advanced refractory multiple myeloma: An EORTC-HOVON randomized phase III study (06914). Br J Hematol 115: 895-902.

47.    Relling MV (1996) Are the major effects of P-glycoprotein modulators due to altered pharmacokinetics of anticancer drugs? Ther Drug Monit 18: 350-356.

48.    Ramachandran C, Wellham LL (2003) Effect of MDR1 phosphorothioate antisense oligodeoxynucleotides in multidrug-resistant human tumor cell lines and xenografts. Anticancer Res 23: 2681-2690.

49.    Stuart DD, Kao GY, Allen TM (2000) A novel, long-circulating and functional liposomal formulation of antisense oligodeoxynucleotides targeted against MDR1. Cancer Gene Ther 7: 466-475.

50.    Masuda Y, Kobayashi H, Holland JF, Ohnuma T (1998) Reversal of multidrug resistance by a liposome-MDR1 ribozyme complex. Cancer Chemother Pharmacol 42: 9-16.

51.    Xu H, Hong FZ, Li S, Zhang P, Zhu L (2012) Short hairpin RNA-mediated MDR1 gene silencing increases apoptosis of human ovarian cancer cell line A2780/Taxol. Chin J Cancer Res 24: 138-142.

52.    Yague E, Higgins CF, Raguz S (2004) Complete reversal of multidrug resistance by stable expression of small interfering RNAs targeting MDR1. Gene Ther 11: 1170-1174.

53.    Guo P, Coban O, Snead NM, Trebley J, Hoeprich S, et al. (2010) Engineering RNA for Targeted siRNA delivery and medical application. Adv Drug Deliv Rev 62: 650-666.

54.    Alexis F, Pridgen E, Molnar LK, Farokhzad OC (2008) Factors affecting the clearance and bio distribution of polymeric nanoparticles. Mol Pharm 5: 505-515.

55.    Aagaard L, Rossi JJ (2007) RNAi therapeutics: Principles, prospects and challenges. Adv Drug Deliv Rev 59: 75-86.

56.    Zhang B, Mallapragada S (2011) The mechanism of selective transfection mediated by penta block copolymers; Part II: Nuclear entry and endosomal escape. Acta Biomater 7: 1580-1587.

57.    Deng Y, Wang CC, Choy KW, Du Q, Chen J, et al. (2014) Therapeutic potentials of gene silencing by RNA interference: Principles, challenges and new strategies. Gene 538: 217-227.

58.    Xu D, Kang H, Fisher M, Juliano RL (2004) Strategies for inhibition of MDR1 gene expression. Mol Pharmacol 66: 268-275.

59.    Pichler A, Zelcer N, Prior JL, Kuil AJ, Piwnica-Worms D (2005) In vivo RNA interference-mediated ablation of MDR1 P-glycoprotein. Clin Cancer Res 11: 4487-4494.

60.    Stevenson M (2004) Therapeutic potential of RNA interference. N Engl J Med 351: 1772-1777.

61.    Singh PK, Doley J, Kumar GR, Sahoo AP, Tiwari AK (2012) Oncolytic viruses and their specific targeting to tumor cells. Indian J Med Res 136: 571-584.

62.    Palmer DH, Young L, Mautner V (2006) Cancer gene-therapy: Clinical trials. Trends Biotechnol 24: 76-82.

63.    Au GG, Lindberg AM, Barry RD, Shafren DR (2005) Oncolysis of vascular malignant human melanoma tumors by Coxsackievirus A21. Int J Oncol 26: 1471-1476.

64.    Shafren DR, Sylvester D, Johansson ES, Campbell IG, Barry RD (2005) Oncolysis of human ovarian cancers by echovirus type 1. Int J Cancer 115: 320-328.

65.    Jiang X, Wang M, Graham DY, Estes MK (1992) Expression, self-assembly and antigenicity of the Norwalk virus capsid protein. J Virol 66: 6527-6532.

66.    Laurent S, Vautherot JF, Madelaine MF, Le Gall G, Rasschaert D (1994) Recombinant rabbit hemorrhagic disease virus capsid protein expressed in baculovirus self-assembles into virus like particles and induces protection. J Virol 68: 6794-6798.

67.    Hale AD, Crawford SE, Ciarlet M, Green J, Gallimore C (1999) Expression and self-assembly of Grimsby virus: Antigenic distinction from Norwalk and Mexico viruses. Clin Vaccin Immunol 6: 142-145.

68.    Li TC, Yamakawa Y, Suzuki K, Tatsumi M, Razak MA, et al. (1997) Expression and self-assembly of empty virus-like particles of hepatitis. J Virol 71: 7207-7213.

69.    Martinez C, Dalsgaard K, de Turiso JL, Cortés E, Vela C, Casal JI (1992) Production of porcine parvovirus empty capsids with high immunogenic activity. Vaccine 10: 684-690.

70.    Brown CS, Lent JV, Vlak JM, Spaan WJ (1991) Assembly of empty capsids by using baculovirus recombinants expressing human parvovirus B19 structural proteins. J Virol 65: 2702-2706.

71.    Christensen J, Alexandersen S, Bloch B, Aasted B, Uttenthal A (1994) Production of mink enteritis parvovirus empty capsids by expression in a baculovirus vector system: A recombinant vaccine for mink enteritis parvovirus in mink. J Gen Virol 75: 149-155.


72.    Noad R, Roy P (2003) Virus-like particles as immunogens. Trends Microbiol 11: 438-444.

73.    Yao Q, Kuhlmann FM, Eller R, Compans RW, Chen C (2000) Production and characterization of simian/human immunodeficiency virus-like particles. AIDS Res Hum Retroviruses 16: 227-236.

74.    Betenbaugh M, Yu M, Kuehl K, White J, Pennock D, et al. (1995) Nucleocapsid and virus-like particles assemble in cells infected with recombinant baculoviruses or vaccinia viruses expressing the M and the S segments of Hantaan virus, the M and the S segments of Hantaan virus. Virus Res 38: 111-124.

75.    Yamshchikov GV, Ritter GD, Vey M, Compans RW (1995) Assembly of SIV virus-like particles containing envelope proteins using a baculovirus expression system. Virology 214: 50-58.

76.    Baumert TF, Ito S, Wong DT, Liang TJ (1998) Hepatitis C virus structural proteins assemble into virus-like particles in insect cells. J Virol 72: 3827-3836.

77.    Latham T, Galarza JM (2001) Formation of wild-type and chimeric influenza virus-like particles following simultaneous expression of only four structural proteins. J Virol 75: 6154-6165.

78.    Sabara M, Parker M, Aha P, Cosco C, Gibbons E, et al. (1991) Assembly of double-shelled rotavirus like particles by simultaneous expression of recombinant VP6 and VP7 proteins. J Virol 65: 6994-6997.

79.    Jiang B, Estes MK, Barone C, Barniak V, O'Neal CM, et al. (1999) Heterotypic protection from rotavirus infection in mice vaccinated with virus-like particles. Vaccine 17: 1005-1013.

80.    French TJ, Roy P (1990) Synthesis of bluetongue virus (BTV) core like particles by a recombinant baculovirus expressing the two major structural core proteins of BTV. J Virol 64: 1530-1536.

81.    Sohail M, Doran G, Riedemann J, Macaulay V, Southern EM (2003) A simple and cost-effective method for producing small interfering RNAs with high efficacy. Nucleic Acids Res 31: e38.

82.    Cadena-Nava RD, Comas-Garcia M, Garmann RF, Rao ALN, Knobler CM, et al. (2011) Self-assembly of viral capsid protein and RNA molecules of different sizes: requirement for a specific high protein/RNA mass ratio. J Virol 86: 3318-3326.

83.    Cossart P, Helenius A (2014) Endocytosis of viruses and bacteria. Cold Spring Harb Perspect Biol 6: a016972.

84.    Bernstein E, Caudy AA, Hammond SM, Hannon GJ (2001) Role for a bidentate ribonuclease in the initiation Step of RNA interference. Nature 409: 363-366.

85.    Nakanishi K (2016) Anatomy of RISC: How do small RNAs and chaperones activate argonaute proteins? Wiley Interdiscip Rev RNA 7: 637-660.

86.     Ahlquist P (2002) RNA-dependent RNA polymerases, viruses and RNA silencing. Science 296: 1270-1273.

87.    Prat AJ, MacRae IJ (2009) The RNA-induced silencing complex: A versatile gene-silencing machine. J Biol Chem 284: 17897-17901.

88.    Sui G, Soohoo C, Affar el B, Gay F, Shi Y, et al. (2002) A DNA vector-based RNAi technology to suppress gene expression in mammalian cells. Proc Natl Acad Sci U S A 99: 5515-5520.

89.    Knipe DM Ed, Howley PM (2001) Field’s Viriology. 4th Edn. Lippincott Williams & Wilkins, pp: 196-206.

90.    Russell SJ, Peng KW (2007) Viruses as anticancer drugs. Trends Pharmacol Sci 28: 326-333.

91.    Wong RSY (2011) Apoptosis in cancer: From pathogenesis to treatment. J Exp Clin Cancer Res 30: 87.

92.    Dobbelstein M (2004) Replicating adenoviruses in cancer therapy. Curr Top Microbiol Immunol 273: 291-334.

93.    Ries S, Korn WM (2002) ONYX-015: Mechanisms of action and clinical potential of a replication-selective adenovirus. Br J Cancer 86: 5-11.

94.    Robson T, Hirst DG (2003) Transcriptional targeting in cancer gene therapy. J Biomed Biotechnol 2003: 110-137.

95.    Stetson DB, Medzhitov R (2006) Type I interferons in host defense. Immunity 25: 373-381.

96.    Devasthanam AS (2014) Mechanisms under lying the inhibition of interferon signaling by viruses. Virulence 5: 270-277.