Cancer , a potentially deadly disease that everyone fears and that has defeated humankind in its race to vanquish everything. The studies related to finding a cure for cancer has been on for decades and every time we thing that we are at the brink of finding it a new form of cancer or a new version of cancer arises. This is where I see a new hope in oncolytic viruses.
Oncolytic viruses are viruses that attack only cancer cells. Normally, the viruses have been found to do the same , a specific type of virus infects only a specific type of cell .For example Hepatitis viruses only infect liver cells, meningitis viruses only infect brain cells. So this property of viruses was taken as an advantage and viruses were genetically designed or found in nature and then genetically engineered to infect only cancer cells. These oncolytic viruses not only kill cancer cells but also alert the immune system of our body that causes it to respond to the cancer cells. Although the research on oncolytic viruses has been going on for 30 years, to date only one genetically engineered oncolytic virus has been approved by the Food and Drug Administration(FDA) and that is the modified form of herpes virus to treat melanoma.
Herpes Simplex virus a relatively simple and not so harmful(merely causing cold sores) in its natural state.The Herpes Simplex virus type 1(HSV-1) mutant 1716 lacks both the copies of ICP34.5 gene, therefore it will not be able to replicate in non dividing or terminally differentiated cell and will attack only cancer cell. This is an very effective mechanism of killing only cancer cells and not harming the normal cells.
Oncolytic viruses overcomes the drawback of chemotherapy or radiation therapy with is normally used to kill the cancer cells but the patient ends up having huge side effect as well a compromised immune system which makes the patient susceptible to other infections.
The draw back for this mechanism in treating the cancer cells is that you had to engineer different viruses for different cancer cells .To overcome this, a new type of virus has been engineered , chimeric Vaccinia pox virus also known as CF33.
CF33 strain was engineered by Professor Yumang Fong, CIty of Hope Comprehensive Cancer Centre , Los Angeles, California.Vaccinia is a double stranded DNA virus of the Poxviridae family.We have heard of vaccinia virus in the treatment of small pox, it is an active vaccine component that prevented small pox. It has a characteristic short life cycle and moves from cell to cell rapidly without integrating into the host genome . It has the potential to act as a very good oncolytic agent.
CF33 was created by infecting a cell line with six different strains of vaccinia virus along with rocconpox, rabbitpox and cowpox viruses. So, the presence of nine different strains in the cell allowed a homologous recombination to occur between them and resulted in novel chimeric daughter strains to be developed.These daughter strains have different combination of genes than the parent viruses. Out of the the 100 chimeric viruses that were tested for potency against different cancer cell lines, CF33 was found to be the most potent. CF33 has its cancer selectivity increased by the inactivation of Thymidine kinase gene(TK gene) which makes sure that it targets only cancer cell as oncolytic CF33 will only be able to divide in continuously dividing cells which have a large pool of nucleotide available.In addition CF33 has also been genetically engineered to express human sodium iodide symporter (hNIS) which is a cell surface protein that transfers iodide into the thyroid gland for thyroid hormone synthesis.When this hNIS is expressed in tumor cells hNIS transports radioactive iodine (¹³¹I) or rhenium into the cell for tumor imaging and therapy.
CF33 is the new savior, according to the scientists CF33 has not only eradicated the tumor injected with this virus but also helped shrinking the non injected tumor and activating the immune system at a very low dosage. It basically enters the tumor cells, multiplies and then the cell explodes releasing thousands of virus particles that target the next tumor cell.These virus have seen to kill cancer cells in a petridish and also the tests on mice for cancer treatment have been successful. According to the reports, the clinical trials for these viruses will be starting by 2020.