We all know we have to eat our greens to be healthy, but have you ever considered that plants could one day do more than just fuel your body? They could save your life from one of the biggest killers worldwide—cancer [1]. For context, cancer occurs when cells divide uncontrollably resulting in masses, known as tumours (Figure 1). Although great advancements have been made in cancer treatment, this disease remains the second leading cause of death globally and cases are estimated to reach 21 million by 2030 [2].

There are many different cancer treatments available to patients, including surgery, radiotherapy, immunotherapy, chemotherapy, cancer vaccinations, hormone therapy, and stem cell transplants (Figure 2) [2]. Often, these conventional treatments are accompanied by severe side effects that may include decreased blood production, gastrointestinal inflammation, hair loss, immunosuppression, heart disease, and nervous system disorders [2].

Despite the negative side effects, cancer drugs, such as chemotherapy, are highly effective at targeting a variety of cancers as they specifically attack rapidly dividing cells, which is a hallmark characteristic of cancer. However, there are cells in our bodies that divide rapidly under normal physiological conditions, such as hair follicle cells and digestive tract cells, and some anticancer treatments also target these normal cells, which gives rise to the harmful side effects listed above [2]. Research is looking to minimize side effects that come along with cancer treatments, such as developing novel drug delivery and targeting systems; however, severe side effects continue to persist with certain treatments along with resistance to cancer drugs.

Research has shown that specific plant compounds have the potential of providing less toxic cancer treatments, seeing as they selectively act on cancerous cells without affecting normal cells [3]. Nearly 80% of the world’s cancer population relies on conventional cancer treatments, and over 60% of cancer drugs on the market are plant-derived [2, 4]. 

Plants have long been utilized in medicine for their healing properties, including their anticancer compounds. Plants will continue to revolutionize the field of cancer therapeutics as they have the potential to be safer, simpler, and less toxic than some conventional treatment methods. They are versatile in that they can be used alone or part of a treatment regimen that may include surgery or radiotherapy. The key is to preserve the biodiversity of anticancer plants to make this a reality. There may be a solution, but first, what are anticancer plants?

There are approximately 400,000 species of plants in existence and only 10% have been studied for the treatment of different diseases [2]. A variety of primary and secondary metabolites (organic substances created by the plant) have been shown to either inhibit cancer cell activity, or activate mechanisms to repair the DNA damage that cancer creates [2]. A lot of these metabolites have already been studied for their potential use as anticancer agents [5]. 

Take taxanes, for example. Taxanes are plant-derived compounds that block cell growth by inhibiting cell division. They are well-established in anticancer treatments in the form of paclitaxel (more commonly known as Taxol®) and docetaxel [6]. These compounds are extracted from the bark and leaves of Pacific Yew trees, and more specifically the English Yew, Eastern hemlock, and European hazelnut shrubs [2]. Taxanes are used to cure a wide range of cancers, including breast, lung, and ovarian cancers [2]. Since its FDA approval in 1992, Taxol has been one of the best-selling drugs ever manufactured due to its effectiveness [7].

There have been thousands of plants identified that contain anticancer properties for a variety of cancers. Of the 35,000 plants species screened by the National Cancer Institute, 3000 were identified as having reproducible anticancer activity [8]. There are currently only four classes of plant-derived anticancer agents on the market today, one of which are the taxanes as previously mentioned [8].

Drug discovery is always evolving and there continues to be an increasing global demand for plant-derived drugs, especially in cancer therapeutics. This has threatened many species of plants and has put medicinal plants at risk for biodiversity loss. Of the nearly 400,000 plant species in existence, 7% are classified as medicinal plants and 13% of which are classified as ‘threatened’ by the International Union for Conservation of Nature [9]. Furthermore, increasing cancer cases, mass cultivation, urbanization, and deforestation are all contributing to the risk of biodiversity loss of medicinal plant species. The demand is only increasing for anticancer plant compounds, with the herbal market expected to reach $5 trillion by 2050 [10]. Therefore, more sustainable practices are necessary to not only keep up with demand/need, but also preserve the biodiversity of these plant species. This begs the question of how is it possible to mass produce anticancer plant compounds without harming the environment and endangering plant species?

A possible solution to preserving medicinal plant species, while simultaneously meeting the global demands for plant-derived anticancer drugs lies in biotechnology. More specifically, the biosynthesis of these unique plant compounds. The process of biosynthesis involves the production of a chemical compound by a living organism. Photosynthesis is a common example of biosynthesis. In this process, plants use sunlight to synthesize their food using carbon dioxide and water. Similarly, biosynthesizing anticancer plant compounds will alleviate the need to cut down and kill various plant species for the purpose of extracting and harvesting their medicinal properties. 

The development of biosynthetic pathways for these compounds are under investigation and advancements have been made to eliminate the heavy reliance on the plant extracts. Biosynthesis will allow for the preservation of medicinal plant species and will also meet the growing demand for these plant compounds in the pharmaceutical industry. As medicine and technology continue to evolve, more effective solutions are on the horizon for cancer treatments.

References

[1] World Health Organization. (2022, February 3). Cancer. World Health Organization. Retrieved from https://www.who.int/news-room/fact-sheets/detail/cancer 

[2] Iqbal, J., Abbasi, B. A., Mahmood, T., Kanwal, S., Ali, B., Shah, S. A., & Khalil, A. T. (2017). Plant-derived anticancer agents: A green anticancer approach. Asian Pacific Journal of Tropical Biomedicine, 7(12), 1129-1150. https://www.sciencedirect.com/science/article/pii/S2221169117308730  

[3] Singh, S., Sharma, B., Kanwar, S. S., & Kumar, A. (2016). Lead phytochemicals for anticancer drug development. Frontiers in Plant Science, 7, 1667. https://www.mdpi.com/1420-3049/21/2/137 

[4] Khan, T., & Gurav, P.(2018). Phytonanotechnology: Enhancing delivery of plant-based anti-cancer drugs. Frontiers in Pharmacology, 8. https://www.frontiersin.org/articles/10.3389/fphar.2017.01002/full 

[5] Greenwell, M., & Rahman, P.K. S. M. (2015). Medicinal plants: Their use in anticancer treatment. Int J Pharm Sci Res, 6(10), 4103-4112. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4650206/ 

[6] Gradishar W. J. (2012). Taxanes for the treatment of metastatic breast cancer. Breast cancer: Basic and Clinical Research, 6, 159–171. 10.4137/BCBCR.S8205

[7] U.S. National Cancer Institute. Taxol® (NSC 125973). Retrieved from https://dtp.cancer.gov/timeline/flash/success_stories/s2_taxol.htm 

[8] Desai, A. G., et al. (2008). Medicinal plants and cancer chemoprevention. Curr. Drug. Metab., 9(7), 581-591. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4160808/ 

[9] Howes, M-J, R., et al. (2020). Molecules from nature: Reconciling biodiversity conservation and global healthcare imperatives for sustainable use of medicinal plants and fungi. New Phytologist Foundation, 2(5), 463-481. https://nph.onlinelibrary.wiley.com/doi/pdf/10.1002/ppp3.10138 

[10] Khazir, J., Mir, B. A., Pilcher, L., & Riley, D. L. (2014). Role of plants in anticancer drug discovery. Phytochemistry Letters, 7, 173-181. https://repository.up.ac.za/bitstream/handle/2263/59253/Khazir_Role_2014.pdf?sequence=1