Phototoxicity testing

Recently, a standardized protocol for using the guinea pig for phototoxicity testing has been proposed (Nilsson et al., 1993), which has been the subject of an international validation exercise. This is detailed below in Figure 11.3. 

Nilsson, R., Maurer, T. and Redmond, N. (1993). A standard protocol for phototoxicity testing Results from an interlaboratory study. Contact Dermatitis 28, 285-290. 

In Vitro 3T3 NRU Phototoxicity Test (Original Guideline, adopted 13 April 2004) (Software Phototox Version 2.0)... 

EU test method B 41, Phototoxicity - in vitro 3T3 NRU phototoxicity test... 

Ultraviolet and visible light Phototoxicity potential assessed by 3T3 phototoxicity test... 

Spielmann, H.. Balls, M., Dupuis, J., Pape, W.J.W., Pechovitch, G., De Sdva, O., Holzhiitter, H.G., Clothier, R. et al. (1998) EU/COLIPA In vitro phototoxicity validation study, results of phase 11 (bHnd trial), part 1 the 3T3 NRU phototoxicity test. Toxicology In Vitro An International Journal Published in Association with BIBRA 12, 305-327. 

In Vitro Phototoxicity Testing a Procedure Involving Multiple Endpoints... 

The red blood cell phototoxicity test (photo-RBC test) is based on the ability of a light-activated substance to produce lysis of freshly isolated erythrocytes and to... 

As shovm in Figure 19.4, the D7 strain of S. cerevisiae is a particularly useful tool because of its ability to assess various genotoxic events such as intergenic and intragenic mitotic recombination as well as point mutagenesis [37, 38[. In a recent paper, we showed that the D7 yeast strain could detect the phototoxicity of most of chemicals used in the validated phototoxicity test 3T3 NRU, except the antibiotics... 

The phototoxicity test 3T3 NRU was proposed in 1994 and is so far the only in vitro method that has been validated by European regulatory authorities for predicting the photoirritant potential of substances [5,40,41]. In this test, the mouse fibroblasts cell line Balb/c 3T3 is exposed to simulated solar UV (or, more frequently, solar UVA) in the presence of the test compound after an incubation of 1 h in the dark. Evaluation of cytotoxicity is performed 24h post-exposure using the neutral red uptake (NRU) method. N RU permits to distinguish live and dead cells, since intact cells retain this dye (detailed method in INVITOX protocol 78). The validation was performed with substances selected on the basis of their in vivo photoirritant or phototoxic properties. Some of these structures are shown in Table 19.1. 

Commission directive 67/548/EEC 3T3 NRU phototoxicity test Regulation included into Annex Vof Council Directive 67/548/EEC part B.41 on phototoxicity in April 2000 and OECD Test Guideline 432, adopted April 2004. 

Pape, W.J., Maurer, X, Pfaimenbecker, U. and Steiling, W. (2001) The red blood cell phototoxicity test (photohaemolysis and haemoglobin oxidation) EU/COLIPA validation programme on phototoxicity (phase II). Alternatives to Laboratory Animals, 29, 145-162. 

Spielmann, H., Lowell, W.W., Holzle, E. et at (1994) In vitro phototoxicity testing. The report and recommendations of ECVAM workshop 2. Alternatives to Laboratory Animals, 22, 314—348. 

C O LI P A international in vitro phototoxicity test validation study and the ECVAM/... 

Loveday KS, Bergman CL. Trends in phototoxicity testing. Drug Cosm Ind 1994 155 30-37. 

Phototoxicity testing is not often included in the safety assessment of new pharmaceuticals however, such studies may be conducted if phototoxicity is expected on the basis of reports on chemicals of similar structure or pharmacological class. Information on UV absorption spectrum of a compound may prompt phototoxicity testing. Sometimes reports of phototoxicity after a drug has reached the marketplace prompt laboratory studies of phototoxicity to determine if the drug is causing phototoxicity and, if so, by what mechanism. 

---