Cancer is abnormal cell growth with the potential to invade or spread to other parts of the body. Cancer is a leading cause of death in both developed and developing countries and it is increasing medical burden worldwide, due to population growth and aging. To date, cancer is mainly treated using surgical resection, radiotherapy, and chemotherapy.
All of these treatment approaches has different side effects including recurrence of cancer and then there are those cancer that are of metastatic nature means they spread in the whole body. As a result of which, the traditional therapies fail in case of metastatic cancer. Therefore, researchers are working to develop a new, effective therapy with low or no toxicity in normal cells.
The solution to this problem are the stem cels which has provided a hopeful option in the fight against cancer. So what are stem cells?
Stem cells are special human cells that are able to develop into many different cell types. Stem cells can be embryonic or somatic stem cells. These somatic stem cells can be hematopoietic stem cells (blood stem cells), mesenchymal stem cells, neural stem cells, epithelial stem cells. All of them has their own specific function.
Why stem cells? Potential therapeutic carriers
Stem cells have unique properties, such as their ability to self-renew indefinitely. Also can form single cell derived clonal cell populations and can differentiate into various cell types.
For the treatment of cancer, stem cells can be used because they have the ability to migrate towards cancer cells. Similarly they can secrete bioactive factors and can cause immunosuppression which can promote tumor targeting. Preclinical stem cell based strategies show great promise for use in targeted anti-cancer therapy applications.
Stem cell modifications for cancer therapy:
Stem cells can be modified through multiple mechanisms for potential use in cancer therapies. The common modifications include:
- Enzyme/prodrug therapy: This therapy is also called suicide gene therapy in which the stem cells are engineered to express enzymes that convert non-toxic prodrugs into cytotoxic products. When modified stem cells are transplanted into tumor-bearing models, they localize o tumor tissues, where exogenous enzyme-like cytosine deaminase converts the prodrug into a cytotoxic molecule, ultimately damaging the tumor cells. As a result, the amount, timing, and location of drug release can be precisely controlled.
- Viral therapy: Virus delivery by mesenchymal stem cells is a promising approach for targeted cancer therapy. Oncolytic viruses, unlike traditional attenuated viruses, conditionally replicate in tumor cells. These oncolytic viruses have increased spread in the body and hide from the immune system. Those oncolytic viruses’ transduced stem cells are still able to home to tumor cells and thus showed better antitumor effects than the viruses alone. Similarly, after radiotherapy, stem cells delivered oncolytic viruses increased the survival rate in cancer-like glioma.
- Nanoparticle carriers: Delivery systems based on nanoparticle carriers often contain high concentration reagents which have different sort of negative effects. It includes failure to target micrometastatic lesions, insufficient dissemination in solid tumors but these limitations can be overcome by using stem cells as nanoparticle delivery agents. Stem cells are also capable of reducing unrestricted uptake of nanoparticles by normal cells and thus protecting host therapeutic agents from host immunosurveillance. It showed very promising results in the case of brain tumors. This approach increased intratumoral drug distribution and promoted tumor cell apoptosis more than other drug delivery systems.
- Regenerative medicine: stem cells can be used to repair human tissues after chemotherapy because of their self-renew and differentiation capabilities. This treatment aims to reconstitute bone marrow under marrow failure conditions and also to treat blood cell genetic diseases. It works by supplying stem cells that differentiate into the desired type of blood cell.
- Immunotherapy: For curing hematological malignances, an immune mediated antitumor effect following allogeneic hematopoietic stem cells transplantation is sufficient. Introduction of genes encoding T cell receptors directed against tumor-associated antigens makes stem cells attractive for us in cancer immunotherapy.
POTENTIAL APPLICATIONS OF STEM CELLS:
Various strategies have been developed for cancer treatment using stem cell therapy. Some of the potential applications of stem cell therapy in cancer are:
- Hematopoietic stem cells transplantation has been primarily used as a standard procedure for treatment of multiple myeloma, leukemia and lymphomas after rounds of high dose radiotherapy or chemotherapy.
- Mesenchymal stem cells transplantation after cancer treatment helps maintain the undifferentiated state of hematopoietic stem cells, also these cells have immunomodulatory effects that effectively reduces strong immune responses in patients.
- The rationales for using stem cells carriers in cancer treatment are to protect therapeutic agents for rapidly biological degradation and reduce systemic side effects.
- Stem cell based anti-cancer vaccines offer more applications to treat cancers.
Challenges to stem cell therapy:
- Tumors commonly relapse regardless of strong initial therapeutic effects. Stem cell therapy using a single agent generally cannot eliminate tumors. Therefore, an optimum drug combination should be rationally selected.
- Normal stem cells share some characteristics with cancer stem cells. Stem cell therapy may increase cancer risk. Thus prevention of tumor formation by transplanted stem cells required additional study and research.
Stem cell therapeutics can be a potential treatment for cancer because of their unique characteristics.
|Author Syeda Maham|