Press Release: ZEBRAFISH ORGAN TOXICITY SCREENING ASSAYS

Allison Poulos allison at onecell.com
Tue Oct 23 09:45:36 EST 2001


PHYLONIX AWARDED PHASE II SBIR TO DEVELOP

Cambridge, MA (October 17, 2001) Phylonix announced that it had 
recently received a Phase II Small Business Innovation Grant 
(SBIR) from the National Institutes of Health to develop a rapid 
predictive assay for organ toxicity drug screening using zebrafish 
embryos.  

Many compounds that pass preliminary cell based testing, fail 
ADMET evaluation, a prerequisite for eventual FDA approval. 
Furthermore, many potential therapeutics that do not cause 
immediate lethality, induce toxic effects in specific organs and 
tissues. There is a clear need for a rapid, predictive, vertebrate 
model for drug toxicity screening.  

According to Dr. Catherine Willett, Principal Investigator for this 
research, "We have developed a quantititative method to study two 
basic parameters of compound toxicity, LC50 and liver-
gastrointestinal toxicity. We found good correlation between 
compound effects in zebrafish and mammalian systems. Using a 
subtractive cDNA method after drug treatment, we also isolated 
genes involved in the toxic chemical response and found extremely 
high homology with known mammalian genes".  

"ADMET testing is a significant bottleneck for drug 
commercialization. We are developing a family of whole animal 
assays that are amenable to high throughput screening using the 
convenient, quantitative microplate format," Dr. Willett continued.  

Zebrafish Background

Laboratory animals are critical for defining the mechanisms of drug 
activity and for testing therapeutic regimens, however, only a few 
useful models have been developed. Zebrafish has several 
important advantages for drug screening: they are small, 
inexpensive to maintain and easily bred in large numbers. Eggs are 
externally fertilized and a single mating produces 100-200 eggs. 
Single embryos can be maintained in fluid volumes as small as 100 
microliters for the first six days of development and cultured in 
microtiter wells. Chemicals can then be added directly to the fish 
water, permeating the intact embryo. Standard microtiter plate 
readers can be used for measurement, making this format 
particularly attractive for eventual high thoroughput drug screening.  

Whole embryo testing has previously been performed on 
invertebrates, including fruitfly and nematode, however, these 
organisms are not closely related to humans and they lack many 
of the same organs and enzymes. Use as comparative models for 
toxicity effects in humans is limited. All essential components of 
vertebrate form and organ development are mimicked in the 
transparent zebrafish and their molecular basis is either identical or 
similar, underscoring the potential for use in research on human 
diseases.  

Embryo toxicity testing in mammals falls into two categories: 
culture assays using either rat or mouse embryos, and in utero 
assays in which compounds are injected into the peritoneum of a 
pregnant mouse or rat. Although the whole-embryo mouse and rat 
culture technique is a validated method for toxicity testing in 
vertebrates, this method is complicated and expensive. Embryos 
must be carefully explanted with the visceral yolk sac and 
ectoplacental cone intact at 8.5 days of development. Embryo 
culture time is also limited to 48 hrs. In addition, due to the 
complexity of culture conditions, the incidence of both false 
positives and false negatives is high. The in utero approaches avoid 
these issues; however, they are complicated by the possibility of 
compound metabolization in the mother liver. While this approach 
is useful for examining prenatal effects, it does not address the 
issue of toxic effects on postnatal development.  

Company Background

Phylonix Pharmaceuticals, Inc. is a developmental biology 
company focused on developing and marketing novel in vivo 
zebrafish based assays for therapeutic and industrial screening for 
cancers, central nervous system and cardiovascular diseases, 
apoptosis, and organ toxicity. The Company is assembling embryo 
and chemical sample handling instrumentation to automate 
analysis. The Company has established a state of the art 
aquaculture facility. Initially, the Company offers drug screening 
services, primarily to the pharmaceutical industry. Long term, the 
Company expects to contribute to the study and treatment of 
human diseases by genetic screening, gene cloning, and target 
identification using zebrafish as a model system.  







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