Preclinical and Clinical Studies on Tea Polyphenols for Anti-Cancer Therapy

Cancer is one of the most serious diseases affecting the world's human population, being placed in second position after cardiovascular diseases. The urge for an effective, sustainable oncotherapy has paved the path for phytotherapy. Tea, Camellia sinensis, a well-known beverage with significant medicinal benefits, contains bioactive metabolites with anticancer activities. There are different varieties of tea with varied ratios of phytochemicals resulting from processing and post-harvesting techniques. Numerous literature reviews suggest that the major tea polyphenols, including catechins such as EGCG, Epicatechins, gallic acid, Theaflavins, and Kaempferol, possess anti-inflammatory, antioxidant, and anticancer properties. A number of clinical trials with different doses of tea catechins have been performed in vitro and in vivo to evaluate the effectiveness of tea on different malignancies, cancer metastasis, with registered patents to maintain the research integrity. Though these polyphenols play a promising role in cancer prevention through modulation of molecular events and signalling pathways such as MAPK, PI3K/AKT pathways, they have poor bioavailability when administered in their pure form. This drawback is addressed through the use of the nanoencapsulation method and combination therapy, with multiple research studies aimed at overcoming this limitation. The efficacy of the tea polyphenols can be increased with the use of an integrated multi-omics study, as included in this review, demonstrating the advancement of technology to incorporate metabolomics, transcriptomics, and epigenomics in the field of oncology and phytotherapy to meet the need for an improved therapeutic system to decrease the increasing mortality rate of cancer patients.