6. Conclusion and Future perspectives
Since cancer is a fatal disease affecting millions of people over worldwide, there is a great necessity of different treatment options to overcome the drug resistance or recurrence conditions in cancer patients. Medicinal plants and their bioactive compounds have been a very good and easily accessible source for the development of novel therapeutics for different diseases. Even though hundreds of plants have been tested for cancer, a very few of them have been studied in vitro and in vivo , and only few of them are under clinical trials. In view of that, information on recent preclinical and clinical studies of medicinal plants, their bioactive compounds and herbal edibles used against CSCs, is compiled in the present study. Phytomedicines targeting Hedgehog, Wnt and Notch signaling pathways as well as those targeting CSC resistance mechanisms have been listed. Treatment of cancer cells with phytocompounds has proven to reduce the resistance to chemotherapy. Further investigations are necessary to find the combinatorial effects of chemotherapeutic agents and plant extracts/compounds. Also, whether combination of two different isolated phytocompounds shows synergism, antagonism or additive effect needs to be explored.
In most of the studies, the main phytoconstituent is purified and then tested. However, in case the whole plant or the extract of a particular plant part is used, the bioactive compound present in it needs to be characterized and its mode of action against CSC should be determined. This is because, there might be presence of more than one bioactive compound, each showing different mechanism; which needs to be investigated. High throughput screening can prove to be useful in selecting phytocompounds for targeting CSCs of a particular type of cancer.
Throughout research is required to ascertain preclinical and clinical safety as well as efficacy of the plant-derived bioactive compounds. Studies based on pharmacodynamic and pharmacokinetic properties of the phytochemicals will provide a better understanding. Poor solubility, decreased stability and shorter circulation time in the blood are the common problems faced in drug treatment and hence nanoparticles-based delivery, liposomes and hydrogel formulations for these phytocompounds can be designed. pH, temperature or tumor microenvironment responsive intelligent nanodrug carriers, specifically targeting CSCs, might be used and needs further exploration.