Transcript: Starving Cancer with Methionine Restriction
In designing an antibiotic, you couldn't create a drug that destroyed DNA, for example, because that's something that both humans and bacteria share in common. It would kill bacteria, all right, but it might kill us, too. Instead, many antibiotics work by attacking bacterial cell walls, which is something bacteria have that we don't.
Antifungals can attack the unique cell walls of fungus. Pesticides can work by attacking the special exoskeleton of insects. But fighting cancer is harder, because cancer cells are our own cells. So fighting cancer comes down to trying to find and exploit differences between cancer cells and normal cells.
Forty years ago, a landmark paper was published showing for the first time that many human cancers have what's called absolute methionine dependency, meaning that if you grow normal cells in a Petri dish without given them the amino acid methionine, then normal cells thrive; but without methionine, cancer cells die. Normal breast cells, for example, grow no matter what, with or without, but leukemia cells—they need that extra added methionine to grow.
What does cancer do with the methionine? Well, tumors generate gaseous sulfur-containing compounds with it – that, interestingly, specially trained dogs can actually detect. There are mole sniffing dogs that can pick out skin cancer. There are breath-sniffing dogs that can pick out people with lung cancer. Pee-sniffing dogs that can diagnose bladder cancer and, yes, you guessed it, fart-sniffing dogs for colorectal cancer. Doctors can now bring their lab to the lab…
Gives a whole new meaning to the term "pet scan."
Anyway, methionine dependency is not just present in cancer cell lines in a Petri dish. Fresh tumors taken from patients show that many cancers appear to have a biochemical defect that makes them dependent on methionine, including some tumors of the colon, breast, ovary, prostate, and skin. Pharmaceutical companies are fighting to be the first to come out with a drug that decreases methionine levels, but since methionine is sourced mainly from food, a better strategy may be to lower methionine levels by lowering methionine intake, eliminating high methionine foods, or both, to help control cancer growth.
Here's the thinking: look, smoking cessation, consumption of diets rich in plants, and other lifestyle measures can prevent the majority of cancers. Unfortunately, people don't do them, and as a result, each year hundreds of thousands of Americans develop metastatic cancer. Chemotherapy cures only a few types of metastatic cancer…Unfortunately, the vast majority of common metastatic cancers, like breast, prostate, colon, and lung, are lethal. We therefore desperately need novel treatment strategies for metastatic cancer, and dietary methionine restriction may be one such strategy.
So, where is methionine found? Particularly in chicken, and fish. Milk, red meat and eggs have less, but if you really want to stick with lower methionine foods, fruits/nuts/veggies/grains and beans are the best. In other words, "In humans, methionine restriction may be achieved using a predominately vegan diet.”
So why isn't every oncologist doing this? "Despite many promising preclinical and clinical studies in recent years, dietary methionine restriction and other dietary approaches to cancer treatment have not yet gained wide clinical application. Most clinicians and investigators are probably unfamiliar with nutritional approaches to cancer. [That's an understatement.] Many others may consider amino acid restriction as an “old idea,” since it has been examined for several decades. However, many good ideas remain latent for decades if not centuries before they prove valuable in the clinic. With the proper development, dietary methionine restriction, either alone or in combination with other treatments, may prove to have a major impact on patients with cancer.”
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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