March 02, 2017
You may have heard the old wives’ tale of feed a cold, starve a fever. Turns out that this isn’t particularly good advice (although some studies do suggest that with a fever, you shouldn’t force-feed yourself). It also turns out to have probably originated in the 19th century and not from Chaucer in the 14th as many websites claim.
But while starving a fever is probably never a good idea, starving a cancer can be. Not by following the medical myth that since cancers use a lot of sugar, you can starve them by cutting down on sugar in your diet. Instead you can starve some cancers by denying them the amino acid asparagine (Asn).
On their way to becoming cancerous, acute lymphoblastic leukemia (ALL) cells lose their ability to make Asn. This means that unlike the cells around it, they need to pull Asn from the blood to make their proteins and to survive.
Doctors exploit this weakness by injecting L-asparaginase amidohydralase (L-ASNase) into patients which starves the cancer cell by depleting Asn levels in the blood. The cells around the cancer cells are fine because they can still make Asn.
Right now doctors use L-ASNase from two different bacterial sources: Escherichia coli and Erwinia chrysanthemi. But if a recent study by Costa and coworkers in Scientific Reports holds up, they might want to think about switching to using the Saccharomyces cerevisiae L-ASNase encoded by the ASP1 gene.
An older study had suggested that the yeast enzyme might be too weak to be useful. This new study finds that this is not the case.
The difference between the older study and this one was the purification protocol. The older study purified the native enzyme through multiple chromatography steps while this study used a single affinity chromatography step. The purified yeast and E. coli versions have comparable activity in this study.
They are also comparable in terms of being able to work with very low concentrations of Asn. This is important as Asn levels are very low in the blood.
What makes the yeast enzyme potentially better is that it is much worse at hydrolyzing a second amino acid, glutamine, than are the bacterial versions. This higher specificity for Asn is important because one of the major side effects of the current treatment is neurotoxicity caused by decreased levels of glutamine in the blood. Since the yeast version hydrolyzes glutamine at a lower rate, they predict patients may not suffer as badly from this side effect with the yeast version.
Of course this is all for naught if the yeast enzyme can’t kill cancer cells! Or if it kills cells indiscriminately.
The S. cerevisiae version was nearly as good as the E.coli version in tissue culture. After 72 hours of incubation, both versions had little effect on normal cells (HUVEC), and both were cytotoxic to the L-ASNase-sensitive cell line MOLT-4 with the E. coli version killing 95% of MOLT-4 cells and the yeast version killing 85% of them.
Taken together these results suggest that the S. cerevisiae version may be an alternative to the bacterial versions. It may be able to kill cancer cells with fewer side effects.
But the yeast version is not the only alternative in town. Another group is engineering the E. coli version to lessen its propensity for hydrolyzing glutamine. Either way it looks like certain leukemia patients may be getting an effective cancer treatment with fewer side effects.
Beer, wine, bread, chocolate, and now maybe a treatment for a nasty form of leukemia. Yeast may be humanity’s best friend. #APOYG!
by Barry Starr, Ph.D., Director of Outreach Activities, Stanford Genetics