06/25/2024
Cysteine: An Ideal Dietary Target in Cancer Therapy
By Mark Simon, Director, Nutritional Oncology Research Institute
Whether one is incorporating conventional, integrative or alternative cancer treatments, the most optimal diet is essential for a successful outcome. Sugar seems to have become the primary focus these days in constructing the most therapeutic diet. What if there is a far more effective dietary target? Actually, there is and is well supported by extensive scientific evidence.
A low-fat whole foods plant-based diet is growing in acceptance as the best diet for overall health, longevity and for augmenting cancer treatment. Going a step further and refining a plant-based into a powerful targeted dietary therapy involves restricting two amino acids, cysteine and methionine. A plant-based diet tends to be lower in cysteine and methionine but is dependent on the balance of specific food groups.
Cysteine is a non-essential sulfur containing amino acid that is necessary for cancer cells to maintain redox balance. Cancer cells, compared to normal cells, are under extreme oxidative stress (elevated ROS). The glutathione (GSH) antioxidant defense system is up-regulated in cancer cells to achieve a safe oxidative stress level.
Glutathione is synthesized from three amino acids, glutamate, glycine and cysteine. Depriving cancer cells of cysteine halts glutathione synthesis. Deprivation of cysteine must be accompanied by methionine deprivation because a small percentage of cysteine comes from the trans-sulfuration of methionine.
Dietary restriction of cysteine (cystine) and methionine is known to have powerful effects against cancer mainly due to disabling the glutathione antioxidant system. Cysteine itself is an antioxidant. Methionine is essential for protein synthesis. Dietary cysteine and methionine restriction are known to increase the effectiveness of chemotherapy and radiation due to a lowering of glutathione.
Where is cysteine and methionine found in the diet? Mostly in animal proteins but also in significant amounts in nuts, seeds, grains and beans. The least amount of cysteine and methionine is in fruits and vegetables. It is not necessary to limit methionine and cysteine to zero intake as cysteine can be depleted by high dose vitamin B6 (P5P) along with iron as a catalyst. A cysteine and methionine restricted diet should be cycled on and off.
The cancer patient has every reason to incorporate a cysteine and methionine restricted low-fat plant-based diet within their treatment plan. Of course, it is a good idea to limit refined sugar.
References
Min JY, Chun KS, Kim DH. The versatile utility of cysteine as a target for cancer treatment. Front Oncol. 2023 Jan 19;12:997919. doi: 10.3389/fonc.2022.997919. PMID: 36741694; PMCID: PMC9893486.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9893486/
Combs JA, DeNicola GM. The Non-Essential Amino Acid Cysteine Becomes Essential for Tumor Proliferation and Survival. Cancers (Basel). 2019 May 16;11(5):678. doi: 10.3390/cancers11050678. PMID: 31100816; PMCID: PMC6562400.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562400/
Bonifácio, V.D.B., Pereira, S.A., Serpa, J. et al. Cysteine metabolic circuitries: druggable targets in cancer. Br J Cancer 124, 862–879 (2021). https://doi.org/10.1038/s41416-020-01156-1
https://www.nature.com/articles/s41416-020-01156-1
To enable survival in adverse conditions, cancer cells undergo global metabolic adaptations. The amino acid cysteine actively contributes to cancer metabolic remodelling on three different levels: first, in its free form, in redox control, as a component of the antioxidant glutathione or its involve...
