Broad spectrum targeting of tumor vasculature by medicinal plants: An updated review

Deregulated angiogenesis plays a central role in the development and metastasis of solid cancers. Tumor vasculature expressing a variety of biomarkers offers some novel therapeutic options which can be selectively targeted with anti-angiogenic agents without significantly affecting the normal vasculature. However, anti-angiogenic agents currently available commercially (synthetic compounds and humanized monoclonal antibodies) have been designed to target specific molecular markers within the cell signalling networks in addition to being expensive as well as toxic. Therefore, it is highly desirable to search for new therapeutic moieties which can simultaneously treat multiple aberrant pathways yet being less toxic and inexpensive. Several studies have highlighted that medicinal plants either as crude extracts or as pure isolated compounds can meet these criteria. The unique combination of different classes of phytochemicals present in plant extracts have been shown simultaneously to target multiple abnormal pathways in the tumor angiogenic cascade thus arresting growth of tumor cells at various stages. In addition, these phytochemicals have health promoting benefits making them ideal candidates to be pursued for drug development. The current review provides an update on the broad spectrum anti-angiogenic activities of different classes of phytochemicals present in the medicinal plants. Although pre-clinical studies have shown promising results, further studies are required to explore the in-depth molecular mechanisms responsible for the observed pharmacological activities and to test the efficacy of isolated compounds or standardised extracts in properly designed experiments. In addition, long term toxicity studies and data on interaction with other drugs are also required to establish the safety profile of extracts before the commencement of clinical trials.