Developmental Toxicity Assessment in Zebrafish - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 19

2.2.6 Determination of Teratogenicity and
Calculation of Teratogenic Index

Teratogenicity is evaluated by comparing compound concentrations that cause
lethality and concentrations that cause developmental defects. Following the defi-
nition used for performing FETAX, the teratogenic index (TI) is defined as the
LC 50 /EC 50 ratio for each compound. A compound is considered teratogenic if the TI
is

1, indicating that the concentration at which 50% of the zebrafish exhibit
developmental abnormalities is lower than the concentration at which 50% lethality
is observed. A TI

>

1, the toxicity
assessment must be performed at the exact LC 50 concentration to determine if
zebrafish exhibit malformations at that concentration. Obtaining a TI

< 1 is considered nonteratogenic. If the TI ¼

¼ 1 is unlikely.

2.3 RESULTS

2.3.1 Results Based on TI ¼ LC 50 /EC 50

To demonstrate different outcomes in zebrafish, we present results for four test
compounds: (1) SSR101010 (FAAH inhibitor, Sanofi-Aventis), a nonteratogenic drug
(rat and rabbit), (2) M100907 (5HT antagonist, Sanofi-Aventis), a teratogenic drug
(rat and rabbit), (3) valproic acid (an anticonvulsant, Bristol-Myers Squibb), a weak
teratogenic drug (mammalian models), and (4) 9-cis-retinoic acid (a cytostatic agent,
Bristol-Myers Squibb), a potent teratogenic drug (mammalian models).
Table 2.3 summarizes the LC 50 and EC 50 for these four drugs. SSR101010 was
not very soluble and precipitation was observed at concentrations

5 m M; however,

since no lethality was observed at any test concentration (up to 500 m M), LC 50 was not

determined. M100907 precipitated at concentrations 200 m M, which exhibited

Table 2.3 LC 50 and EC 50 of Test Drugs

Drug LC 50 EC 50 TI (LC 50 /EC 50 ) Teratogenic

SSR101010 a ND b ND b ND b

No

M100907 a >1.04 c ND 95.8 Ye s

Valproic acid d

59.8 28.7 2.08 Yes

9-cis-Retinoic acid d ND e ND e ND e Ye s

ND: not determined, since 50% lethality was not observed at soluble concentrations. At 400 mM,
precipitation was observed; however, 100% lethality was observed.
a Sanofi-Aventis, proprietary compounds.
b Not determined, since no lethality and no abnormality were observed.
c TI based on the highest soluble concentration divided by the EC 50 .
d Bristol-Myers Squibb, validation compounds.
e Not determined, since no lethality was observed at the lowest testing concentration, 0.1 mM; however,
abnormality was observed in 100% treated animals.