Baker’s Yeast Good for Leukemia?

I read an interesting article by Honor Whiteman about the effect baker’s yeast enzyme has in helping to treat leukemia.  The most common form of childhood leukemia is acute lymphoblastic leukemia (ALL), accounting for around 3 in 4 cases in the United States.  The researchers have found in a new study that a compound isolated from baker’s yeast can help to treat this disease.

This is a cancer that begins in lymphoblasts, which are immature white blood cells in the bone marrow.  Those that have ALL make too many lymphoblasts and leave little room for mature, healthy white blood cells, red blood cells and platelets.  These individuals are prone to developing anemia and infections.

Children at the greatest risk of ALL are those under the age of five years old, and the largest majority of deaths from the disease occur in adults.  There are expected to be about 5,970 new cases in 2017 of ALL diagnosed in children and adults in the U.S., and around 1,440 deaths from this disease.

The study co-author Gisele Monteiro of the School of Pharmaceutical Sciences at the University of Sao Paulo in Brazil believes an enzyme isolated from the bacteria Escherichia coli and Erwinia chrysanthemi has been used in the treatment of ALL for decades.  This treatment of bacterial enzyme can lead to high remission rates, but it can trigger mild to severe immune responses in about 25% of patients, indicating need for a less toxic biopharmaceutical for the treatment of ALL.

Scientific Reports has published the study where Monteiro and team have isolated an L-asparaginase-like enzyme from the non-bacterial source Saccharomyces cerevisiae or, as we know it, baker’s yeast or brewer’s yeast.  Their original goal was to find a new source of the biodrug in microorganisms for use in patients who develop resistance to the bacterial enzyme and not to produce the enzyme.

The researchers used bioinformatics tools to analyze the genomes of several fungi known to secrete asparaginase.  They then identified a gene in S. cerevisiae called ASP1 that encodes an enzyme similar to L-asparaginase.  Iris Muhoz Costa, the first study author of the School of Pharmaceutical Sciences at the University of Sao Paul, explains that unlike bacteria, yeast is eukaryotic and contains a membrane-covered nucleus consisting of genetic material, as is the case with human cells.  Their hypothesis is that yeast-derived enzymes are less likely than bacterial enzymes to trigger severe immune responses.  They then cloned the ASP1 gene, and with help of genetic engineering, were able to prompt E. coli to produce a purified form of yeast-derived L-asparaginase.  They were able to obtain the recombinant protein and performed studies to characterize its secondary structure to identify important regions called catalytic sites.  Its efficacy in vitro was then evaluated.

They then tested the purified L-asparaginase from yeast and L-asparaginase from E. coli on 3 groups of human leukemia cells.  One group of cells was unable to produced normal amounts of asparagine (MOLT4), one produced asparagine at normal levels (REH), and the last group was non-malignant (HUVECs).

They found the purified, yeast-derived L-asparaginase killed approximately 70-80% of MOLT4 cells, compared with 90% for E. coli-derived L-asparaginase.  But, the purified L-asparaginase from yeast was found to be less toxic to HUVECs than L-asparaginase from E. coli.  Neither form of L-asparaginase was found to be effective against REH cells and they believe the findings indicate yeast-derived L-asparaginase may be a safer and more effective treatment for ALL.  They are planning in vitro studies of L-asparaginase from yeast to gain a better understanding of its toxicity in various types of cells and the immune response to the enzyme.

Dr Fredda Branyon