Nature has long been the source of many of the pharmaceuticals used to treat various illnesses, including different types of cancer. An estimated 60% of all cancer drugs originate from natural products, such as trees, shrubs, fruits and vegetables, and marine animals. Perhaps one of the best-known examples is Taxol (paclitaxel), which is used to treat breast, ovarian, cervical and lung cancer. The drug is derived from the Pacific yew tree (Taxus brevifolia) found in parts of British Columbia. The yew provided the starting point, but the supply of trees wasn’t enough to meet the demand. Fortunately, a semi-synthetic version of the chemical was developed for large-scale manufacturing purposes.
Researchers continue to explore the natural world for novel anti-cancer medications. The goal is to identify substances from nature that can be given in pharmaceutical-level (rather than naturopathic) doses.
In CML research, one question that needs to be urgently addressed is how to kill leukemia stem cells residing in bone marrow. These stem cells are the source of CML, promote its progression, and can cause resistance to treatment. Tyrosine kinase inhibitors (TKIs), such as Gleevec, Sprycel, Tasigna and Bosulif, are highly effective in suppressing CML. But they have a limited ability to kill these leukemia stem cells disease (Bhatia and colleagues. Blood 2003;101:4701- 4707). The reason why TKIs aren’t effective against these cells isn’t known, but it’s believed that leukemia cells have access to novel survival pathways that are untouched by TKIs (Chen and colleagues. Anticancer Agents Med Chem 2010;10:111-115). Unfortunately, as long as these leukemia cells remain viable, there’s a potential for CML to re-emerge if drug resistance develops or the TKI is stopped.
Natural substances may provide the means to specifically target leukemia stem cells. One example is a medication – Synribo – that is already in use against CML. Synribo (homoharringtonine, now called omacetaxine) is derived from another yew variety: the Japanese or Korean plum yew (also called the cowtail pine). Synribo has been shown to be highly effective in people who have not responded to prior TKIs (Cortes and colleagues. Clin Lymphoma Myeloma Leuk 2013;13:584-591).
Other substances now being studied come from the world of food and drink. Sarsparilla, a beverage once used as a tonic, is derived from a flowering plant called Smilax (also known as catbriers, greenbriers and prickly ivy). Smilax root has long been used to treat inflammatory conditions, but is now being investigated for its anti-cancer properties (Seelinger and colleagues. Int J Oncol 2012;41:1164-1172).
Smilax was named after a nymph in Greek mythology, who was transformed into a plant after an unhappy love affair with Crocus, who changed into the flowering plant that bears his name. A happy coincidence is that the crocus has also been found to be toxic to leukemia cells, in part by blocking the CML cancer gene BCR-ABL (in a way that’s similar to how TKIs work) (Geromichalos and colleagues. Food Chem Toxicol 2014;74:45-50).
One of the cancer-fighting ingredients of crocus is the spice saffron. Another bright yellow spice, curcumin, which is derived from turmeric (a member of the ginger family), also has potent effects on CML. A recent laboratory study found that curcumin shut down BCR-ABL production, and inhibited the proliferation of CML cells in animals (Taverna and colleagues. Oncotarget 2015;6:21918-21933). Other studies of curcumin have found that it also has the ability to kill leukemic stem cells (Martinez-Castillo and colleagues. PLoS One 2016;11:e0165971).
Another important source of anti-cancer substances for researchers is traditional Chinese and Japanese medicines. Examples include the Chinese herb bái tóu wēng (Pulsatilla chinensis) (Liu and colleagues. Pharm Biol 2015;53:1-9); the herbal supplement Sho-Saiko-To (Yang and colleagues. Oncotarget 2014;5:8188-8201); and the Japanese bramble (Rubus parvifolius) (Ge and colleagues. Asian Pac J Cancer Prev 2014;15:5455-5461).
Perhaps the most unusual source of anti-cancer drugs is the jellyfish. Researchers have recently reported that jellyfish extract was effective at targeting and killing leukemic stem cells by inducing them to self-destruct in laboratory experiments (Ha and colleagues. Peer J 2017;5:e2895). All are being studied as possible anti-leukemia agents.
Studies of these and many other substances are ongoing. The results are preliminary, and taking any of these as supplements (if available) is not recommended. But the above research shows that scientists are busily ransacking nature’s storehouse in their search for a CML cure.