Yeast-derived L-asparaginase seen to be less toxic than an enzyme derived from bacteria.
Findings from a new study suggest that an enzyme from baker’s yeast may treat acute lymphoblastic leukemia (ALL), a common pediatric cancer.
ALL begins in the lymphoblasts, which are immature white blood cells located in bone marrow. Patients with ALL produce too many lymphoblasts, which does not leave adequate space for healthy white blood cells, red blood cells, and platelets. These patients are prone to anemia and infections due to the lack of healthy cells in the blood.
Treatments for ALL include chemotherapy, stem cell transplants, radiation, surgery, and targeted drugs. However, these treatments can cause significant side effects, especially for young patients.
An enzyme from Escherichia coli and Erwinia chrysanthemi, L-asparaginase, has also been used to treat patients. Although this type of treatment can lead to high remission rates, it triggers an immune response in 25% of patients, according to the study, which was published by Scientific Reports.
Due to this treatment’s toxicity, a different substance for ALL treatment is necessary, the authors noted.
In the study, the investigators derived an L-asparaginase-like enzyme from baker’s yeast, Saccharomyces cerevisiae.
"Our goal in this project wasn't to produce the enzyme, but rather to find a new source of the biodrug in microorganisms for use in patients who develop resistance to the bacterial enzyme," said study co-author Marcos Antonio de Oliveira, PhD.
The investigators started by using bioinformatics tools to analyze genomes of fungi that are known to produce asparaginase. They discovered that a gene in S. cerevisiae, ASP1, encodes an enzyme that is similar to L-asparaginase, according to the study.
Since the yeast is eukaryotic, unlike bacteria, it contains a nucleus with genetic information, which is similar to human cells. The researchers hypothesized that enzymes derived from yeast are less likely to cause an immune response, as is the case with bacterial enzymes, according to the study.
The researchers then cloned ASP1, and were able to cause a genetically modified E. coli to create a purified form of L-asparaginase derived from the yeast.
"We were able to obtain the recombinant protein," said first study author Iris Munhoz Costa, MSc. "We then performed studies to characterize its secondary structure and identify important regions called catalytic sites. Finally, we evaluated its efficacy in vitro."
The investigators tested the purified L-asparaginase from yeast, and L-asparaginase from E. coli on 3 groups of leukemia cells; one group of cells were unable to create normal amounts of asparagine (MOLT4), one produced normal levels of asparagine (REH), and the control group were non-malignant cells, according to the study.
The researchers discovered that the purified L-asparaginase derived from yeast killed up to 80% of MOLT4 cells, compared with 90% for the E. coli-derived enzymes. However, the purified enzyme was less toxic to the healthy cells compared with the enzyme derived from E. coli, according to the study.
Both versions of L-asparaginase were ineffective in killing REH cells.
These findings suggest that L-asparaginase may be a safer and more effective treatment for ALL, according to the study authors.
"In this study we characterize the enzyme L-asparaginase from S. cerevisiae,” said study co-author Gisele Monteiro, PhD. “The results show this protein can efficiently annihilate leukemia cells with low cytotoxicity to healthy cells."
The researchers now plan to conduct in vitro trials of the enzyme to understand its toxicity in different types of cells, and whether it elicits an immune response. If the studies show promise, the investigators plan to continue analyzing the yeast-derived L-asparaginase enzyme in animal models, the authors concluded.