Вирустарды емдік құрал ретінде қолдану биотехнологиясы

Treatment using biotechnology to convert viruses into therapeutic agents

Virotherapy is a treatment using biotechnology to convert viruses into therapeutic agents by reprogramming viruses to treat diseases. There are three main branches of virotherapy: anti cancer oncolytic viruses, viral vectors for gene therapy and viral immunotherapy. These branches use three different types of treatment methods: gene overexpression, gene knockout, and suicide gene delivery. Gene overexpression adds genetic sequences that compensate for low to zero levels of needed gene expression. Gene knockout uses RNA methods to silence or reduce expression of disease causing genes. Suicide gene delivery introduces genetic sequences that induce an apoptotic response in cells, usually to kill cancerous growths. In a slightly different context, virotherapy can also refer more broadly to the use of viruses to treat certain medical conditions by killing pathogens.

Chester M. Southam, a researcher at Memorial Sloan Kettering Cancer Center, pioneered the study of viruses as potential agents to treat cancer.

Oncolytic virotherapy is not a new idea – as early as the mid 1950s doctors were noticing that cancer patients who suffered a non related viral infection, or who had been vaccinated recently, showed signs of improvement; this has been largely attributed to the production of interferon and tumour necrosis factors in response to viral infection, but oncolytic viruses are being designed that selectively target and lyse only cancerous cells. In the 1940s and 1950s, studies were conducted in animal models to evaluate the use of viruses in the treatment of tumours. In the 1940s–1950s some of the earliest human clinical trials with oncolytic viruses were started.

It is believed that oncolytic virus achieve their goals by two mechanisms: selective killing of tumor cells as well as recruitment of host immune system. One of the major challenges in cancer treatment is finding treatments that target tumor cells while ignoring non cancerous host cells. Viruses are chosen because they can target specific receptors expressed by cancer cells that allow for virus entry. One example of this is the targeting of CD46 on multiple myeloma cells by measles virus. The expression of these receptors are often increased in tumor cells. Methods of delivery tested include intratumoral, intravenous, intraperitoneal, and more. Types of tumor that are currently being study with oncolytic viruses include CNS tumors, renal cancer, head and neck cancer, ovarian cancer, and more. Two genes were removed from the virus – one that shuts down an individual cell's defenses, and another that helps the virus evade the immune system – and a gene for human GM CSF was added. The drug works by replicating in cancer cells, causing them to burst; it was also designed to stimulate an immune response but as of 2016, there was no evidence of this. The drug was created and initially developed by BioVex, Inc. and was continued by Amgen, which acquired BioVex in 2011. It was the first oncolytic virus approved in the West.

RIGVIR is a virotherapy drug that was approved by the State Agency of Medicines of the Republic of Latvia in 2004. It is wild type ECHO 7, a member of echovirus family. The potential use of echovirus as an oncolytic virus to treat cancer was discovered by Latvian scientist Aina Muceniece in the 1960s and 1970s. As of 2017 there was no good evidence that RIGVIR is an effective cancer treatment. On March 19, 2019, the manufacturer of ECHO 7, SIA LATIMA, announced the drug's removal from sale in Latvia, quoting financial and strategic reasons and insufficient profitability. However, several days later an investigative TV show revealed that State Agency of Medicines had run laboratory tests on the vials, and found that the amount of ECHO 7 virus is of a much smaller amount than claimed by the manufacturer. In March 2019, the distribution of ECHO 7 in Latvia has been stopped.

Although oncolytic viruses are engineered to specifically target tumor cells, there is always the potential for off target effects leading to symptoms that are usually associated with that virus.

The use of viral material to deliver a gene starts with the engineering of the viral vector. Though the molecular mechanism of the viral vector differ from vector to vector, there are some general principles that are considered. In diseases that are secondary to a genetic mutation that causes the lack of a gene, the gene is added back in. In diseases that are due to the overexpression of a gene, viral genetic engineering may be introduced to turn off the gene. In the former, the viral vector is delivered directly to the organ or the tissue of the patient. In the later, the desired tissue is first retrieved, genetically modified, and then transferred back to the patient. The molecular mechanisms of gene delivery and/or integration into cells vary based on the viral vector that is used. Luxturna is the first gene therapy approved in the US for the treatment of a monogenetic disorder. It has been authorized for use in the EU since 2018. In 2019, the FDA approved Zolgensma, an AAV vector based gene therapy product for the treatment of spinal muscular atrophy in children under the age of two. As of August 2019, it is the world's most expensive treatment, at a cost of over two million USD. Novartis is still seeking marketing approval for the drug in the EU as of 2019. This causes the T lymphocytes to attack the cells that express the undesired protein. Currently two therapies, Tisagenlecleucel and Axicabtagene ciloleucel are FDA approved to treat acute lymphoblastic leukemia and diffuse large B cell lymphoma respectively. It was the first gene therapy approved in the EU. The drug never received FDA approval in the US, and was discontinued by its manufacturer in 2017 due to profitability concerns. it is no longer authorized for use in the EU. However, responses to viral vectors at immune privileged sites such as the eye may be reduced compared to other sites of the body. As with other forms of virotherapy, prevention of off target genome editing is a concern. In addition to viral gene editing, other genome editing technologies such as CRISPR gene editing have been shown to be more precise with more control over the delivery of genes.

Viral immunotherapy in the context of cancer stimulates the body's immune system to better fight against cancer cells. Rather than preventing causes of cancer, as one would traditionally think in the context of vaccines, vaccines against cancer are used to treat cancer. The mechanism is dependent upon the virus and treatment. Oncolytic viruses, as discussed in previous section, is stimulate host immune system through the release of tumor associated antigens upon lysis as well as through the disruption of the cancer's microenvironment which helps them avoid the host immune system. One such protozoa that potential virotherapy treatments have explored is Naegleria fowleri, which causes primary amebic meningoencephalitis (PAM). With a mortality rate of 95%, this disease causing eukaryote has one of the highest pathogenic fatality rates known. Chemotherapeutic agents that target this amoeba for treating PAM have difficulty crossing blood brain barriers. However, the driven evolution of virulent viruses of protozoal pathogens (VVPPs) may be able to develop viral therapies that can more easily access this eukaryotic disease organism by crossing the blood brain barrier in a process analogous to bacteriophages. These VVPPs would also be self replicating and therefore require infrequent administration, with lower doses, thus potentially reducing toxicity. While these treatment methods for protozoal disease may show great promise in a manner similar to bacteriophage viral therapy, a notable hazard is the evolutionary consequence of using viruses capable of eukaryotic pathogenicity. VVPPs will have evolved mechanisms of DNA insertion and replication that manipulate eukaryotic surface proteins and DNA editing proteins. VVPP engineering must therefore control for viruses that may be able to mutate and thereby bind to surface proteins and manipulate the DNA of the infected host.