A systematic review of selected plants and their metabolites with anticolorectal cancer effects

Colorectal cancer is among the most common malignancy and the third prime cause of cancer-associated mortalities. Long-term inflammation of the colon can promote carcinogenesis by facilitating oxidative stress which enhances deoxyribonucleic acid damage resulting in the tumor initiation step. The existing chemotherapeutic options are often associated with adverse reactions and emergence of drug resistance. The carefully selected plants are cited to demonstrate anticancer properties as has been revealed in this review. Of significance, these plant species are widely available, especially in Africa The major goal was to present an updated comprehensive review of herbal plants used to treat colon cancer around the world. More specifically, the goal of this study was to analyse a group of selected plant species with proven efficacy, safety, and pharmacological effects on colon cancer models for further research. A systematic search of relevant literature was performed considering all the articles published until November 2021 through searching six library databases and a web search engine, Google scholar. It was created using MeSH terms and free text describing plant species and colorectal cancer. For subsequent investigation, all articles describing the use of medicinal plants to treat colorectal cancer and/or their pharmacological evaluation were maintained. The plant species investigated in this research for their pharmacotherapeutic effects were: Withania somnifera, Zingiber officinale, Moringa oleifera, Azadirachta indica and Aloe barbadensis. The search yielded a total of 4803 papers published between the year 2000–2021 for further analysis. A total of 4726 articles (reports, reviews, and less relevant research papers) were excluded as they did not meet the inclusion criteria. A cumulative sum of 77 articles including research papers and reviews detailing in vivo and in vitro experiments of the specific plants of interest, with demonstrated activity met the inclusion criteria, and have been discussed in the present review. The pharmacological activities of the selected plant species have been demonstrated to inhibit cyclooxygenase 2, inhibit immunomodulation, suppress angiogenesis, inhibit proliferation, induce apoptosis, and reduction of oxidative stress with sufficient anti-colorectal cancer effects. These essential mechanisms make them befitting alternative options to synthetic chemotherapeutic options. In vivo studies are however encouraged in Moringa oleifera that has a significant gap identified through our search. In addition, more research is encouraged to document sufficient dose levels enough to elicit anti-colorectal cancer effects among the reviewed plants.