Cancer is a disease where the cancer cell divides autonomously and becomes a tumor, causing problems to local tissues, as well as spreading to other parts of the body in a process known as metastasis. It is a personal disease that depends on one’s environmental and genetic factors. Cancer is promoted by genes called oncogenes and prevented by genes called tumor suppressor genes. Cancer is a difficult disease to treat. Conventional treatment with chemotherapy kills not only the cancer cells but also kill all the fast growing cells, resulting in hair loss, nausea, vomiting and loss of appetite.
Ribonucleic acid or RNA is a small molecule in cells that can perform many different functions to keep the cell alive and healthy. RNA is made from DNA, and RNA in turn directs the synthesis of protein. Small RNAs are RNAs of less than 30 nucleotides in length. Small RNAs are being explored by scientists for potential use in targeted cancer cell therapy. Small RNAs are also known as microRNAs or miRNAs.
One type of miRNAs are the small interfering RNAs or siRNA. An siRNA is an RNA of around 22 nucleotides in length that interferes with the expression of a specific gene. It binds to the RNA that has sequence that is matching to its own sequence and results in a degradation of the RNA that is specific for the gene. Introduction of an siRNA specific to an oncogene into a cancer cell can result in reduced expression of the oncogene, therefore inhibiting the growth and division of the cancer cell.
MiRNAs watch over which genes are expressed and play a regulatory role in gene expression, thus keeping the cell alive and healthy. Some miRNAs act as oncoRNAs and are increased in cancer cells. Other miRNAs act as tumor suppressor RNAs and are decreased in cancer cells. One cancer therapy is the introduction of tumor suppressor miRNAs into the cancer cells to prevent their growth and division. Another strategy is the introduction of siRNAs against oncoRNAs to prevent cancer cell growth and division.
One of the limitations of using small RNAs as cancer therapy is the delivery of the small RNAs specifically into the cancer cells. An RNA aptamer is an RNA of around 25 to 60 nucleotides in length that is synthesized and selected to bind specifically to targets of interest. RNA aptamers can be used for the delivery of small RNAs and other drugs to the cancer cells. They can be made to specifically target a protein on the surface of the cancer cell. Thus miRNA-RNA aptamer conjugates can be potentially used as targeted cancer therapy, not only to target the cancer cell, but also to target a specific gene within the cancer cell.