Cancer has always been a significant health burden and is increasing in prevalence. In fact, almost everyone can recall a friend or family member who has been diagnosed with cancer. Therapy against this group of diseases is constantly improving, but it is costly and may pose significant side effects on the body's healthy cells. Such drawbacks have pushed scientists to explore all possible sources of chemicals which may be used as drugs for treating cancer.
Recent research has demonstrated that plants belonging to the genus Solanum may be a potential source of anti-cancer agents. This large genus of plants includes tomatoes, eggplants and most notably potatoes. Under conditions of stress, particularly insect infestations, such plants produce chemicals known as steroidal glycoalkaloids to hoard off their predators. These chemicals have been known to humanity for centuries, often having been mentioned in literature for toxicity in humans. In Romeo and Juliet, Friar Laurence gives Juliette a mystery concoction to emulate death, in order to trick Romeo into thinking she had died, which inevitably caused him to take his own life. William Shakespeare is most likely referring to the plant called nightshade (Atropa belladonna), which is part of the genus Solanum, since in 1597, in the book The Herbal or General Historie of Plantes John Gerarde documented that minimal quantities of nightshade may induce madness, while moderate amounts will cause a "dead sleepe" and kills in abundance.
Attentive readers may be beginning to wonder how Solanum vegetables are consumed daily across the globe if they contain such toxic chemicals. It all has to do with the concentration of steroidal glycoalkaloids within the vegetables. For example, potatoes have minute quantities of these chemicals, making them safe for consumption. However, the concentration of steroidal glycoalkaloids is not equal across all parts of the potato, with sprouts having the highest concentration. Potato sprouting is commonly known as a sign of imminent spoilage; however, the potatoes are still safe to eat as long as the sprouts are removed. Similarly, greening of the potato peel (which when unintentionally cooked gives potatoes a bitter taste) is often thought to be the growth of mould. In actual fact such greening is indicative of increased steroidal glycoalkaloid production and removing the green peel makes the potato safe to consume. However, it is worth noting that consumption of spoiled potatoes has been attributed to adverse health effects, mainly affecting the gastrointestinal and nervous systems. Consumption of spoiled potatoes during pregnancy has been associated with an increased risk of the foetus developing neural tube defects, such as spina bifida and anencephaly. Although, this link has been made using epidemiological data and experimental evidence is still inconclusive.
So how can such toxic chemicals be used as anti-cancer agents? Of the steroidal glycoalkaloids present within potatoes, 
solanine and chaconine have been investigated against numerous different types of cancer, namely cancer of the liver, breast, stomach, oesophagus, uterus, cervix, prostate and skin. Particularly, solanine has shown promising pre-clinical results on both cell cultures and mouse models. solanine has demonstrated inhibition in tumour growth. The precise mode of action is yet to be determined, however the most prominent published literature suggests an interplay of different cell death mechanisms, referred to as apoptosis and autophagy. Other published literature also suggests that this molecule may diminish cancer's capacity to create new blood vessels, which supply tumours with oxygen and nutrients needed to grow. Additionally, data is also suggesting that solanine inhibits the cancer's ability to spread, a process known as metastasis. Hence, such molecules have the potential to inhibit the growth and spread of cancer. This warrants further studies to elucidate the effect of such molecules on other types of cancer, as well as the clinical efficacy and patients' response to these drugs.
If proven as successful drugs against cancer, steroidal glycoalkaloids have several benefits over traditional cancer therapy. Since these molecules can be derived from natural sources, the costs related to manufacturing drugs would be significantly reduced and more individuals would be able to undergo such treatment regimens. However, it should be noted that eating vegetables containing these chemicals would not cure cancer, since such specific chemicals found within the vegetable need to be purified so that they may be used to kill cancer cells. An additional benefit is the fact that these chemicals can be derived from by-products of the food industry. A handful of studies have demonstrated the possibility of using potato scraps such as the peel as sources of steroidal glycoalkaloids, thus these molecules may be produced sustainably.
Having potatoes, tomatoes and eggplants as the sources of these molecules also begs the question as to whether local agricultural produce which is not sold, as well as domestic and industrial food waste, may one day be utilised to create cancer therapy. Doing so would help fulfil the United Nation's Sustainable Development Goals while promoting more efficient resource management and a circular economy.
However, for now we can only hope that naturally derived chemicals can be used against cancer and keep on funding research which strives to find cures for humanity's ailments.
Prof. Renald Blundell is a biochemist and biotechnologist with a special interest in Natural and Alternative medicine. He is a professor at the Faculty of Medicine and Surgery, University of Malta
Andrea Cuschieri is a Medical and a Master of Science in Biochemistry student at the University of Malta who has in interest in neuroscience and neurosurgery. He is currently investigating the use of solanine against glioblastoma multiforme
Dr Byron Baron is a senior lecturer and resident academic at the centre for molecular medicine and biobanking at the University of Malta. He is involved in a wide array of research projects both locally and abroad, with his main interest being lysine methylation in non-histone proteins. These studies are driven forward through collaborations with teams in the UK, Germany and Japan