High-throughput reactive oxygen species (ROS) assay: An enabling technology for screening the phototoxic potential of pharmaceutical substances

KoCVAM-led development of phototoxicity alternative test method using reconstructed human epidermis model (KeraSkin™)

Phototoxicity is an acute toxic reaction induced by topical skin exposure to photoreactive chemicals followed by exposure to environmental light and thus chemicals that absorb UV are recommended to be evaluated for phototoxic potential. There are currently three internationally harmonized alternative test methods for phototoxicity. One of them is the in vitro Phototoxicity: RhE Phototoxicity test method (OECD TG498). Korean center for the Validation of Alternative Methods (KoCVAM) developed an in vitro phototoxicity test method using a KeraSkin™ reconstructed human epidermis model (KeraSkin™ Phototoxicity Assay) as a 'me-too' test method of OECD TG498. For the development and optimization of KeraSkin™ Phototoxicity Assay, the following test chemicals were used: 6 proficiency chemicals in OECD TG498 (3 phototoxic and 3 non-phototoxic), 6 reference chemicals in OECD Performance Standard No. 356 (excluding the proficiency test chemicals, 3 phototoxic and 3 non-phototoxic) and 13 additional chemicals (7 phototoxic and 6 non-phototoxic). Based on the test results generated from the test chemicals above, the overall predictive capacity of KeraSkin™ Phototoxicity Assay was calculated. In particular, the assay exhibited 100 % accuracy, 100 % sensitivity, and 100 % specificity. Therefore, it fulfills the requirements to be included as a 'me-too' test method in OECD TG498.

Effects of radical scavengers for reactive oxygen species on vitamin K-induced phototoxicity under UVA irradiation

Vitamin K possesses efficacy as a topical dermatological agent. However, vitamin K is phototoxic and susceptible to photodegradation. Herein, we investigated the mechanisms underlying the phototoxicity of phylloquinone (PK, vitamin K1) and menaquinone-4 (MK-4, vitamin K2) under ultraviolet A (UVA) irradiation using various reactive oxygen species (ROS) scavengers. This resulted in the production of superoxide anion radicals via type I and singlet oxygen via type II photodynamic reactions, which were quenched by the ROS scavengers: superoxide dismutase and sodium azide (NaN3). In HaCaT cells, MK-4 and PK induced the production of intracellular ROS, particularly hydrogen peroxide, in response to UVA irradiation. Furthermore, the addition of catalase successfully decreased maximum ROS levels by approximately 30%. NaN3 and catalase decreased the maximum reduction in cell viability induced by UVA-irradiated PK and MK-4 in cell viability by approximately 2-7-fold. Additionally, ROS scavengers had no effect on the photodegradation of PK or MK-4 at 373 nm. Therefore, the phototoxicities of PK and MK-4 were attributed to the generation of singlet oxygen and hydrogen peroxide, underscoring the importance of photoshielding in circumventing phototoxicity.

Solid lipid nanoparticles of lutein with improved dissolution behavior and oral absorption

The present study aimed to develop solid lipid nanoparticles of lutein (SLN/LT) with improved dissolution behavior and oral absorption. SLN/LT were prepared by a flash nanoprecipitation method using a multi-inlet vortex mixer, and their physicochemical, photochemical, and pharmacokinetic properties were evaluated. The mean particle size of SLN/LT re-dispersed in water was 237 nm, and small spherical particles with no significant aggregation were observed. LT significantly generated singlet oxygen upon exposure to pseudo-sunlight (250 W/m2, 1 h), suggesting its high photoreactivity. The remaining LT in LT solution, crystalline LT, and SLN/LT after irradiation with pseudo-sunlight (250 W/m2, 2 h) were 56.3, 86.7, and 101%, respectively. SLN/LT showed improved dissolution behavior of LT in simulated intestinal fluid, and the dissolved amounts of LT at 2 h were at least 50 times higher than that of crystalline LT. Orally administered SLN/LT (100 mg-LT/kg) exhibited enhanced oral absorption of LT, as evidenced by a relative bioavailability of 3.7 to crystalline LT in rats. SLN/LT may be a promising dosage form for orally available LT supplements, possibly leading to enhanced nutritional functions of LT.

Drug-Induced Photosensitivity-From Light and Chemistry to Biological Reactions and Clinical Symptoms

Photosensitivity is one of the most common cutaneous adverse drug reactions. There are two types of drug-induced photosensitivity: photoallergy and phototoxicity. Currently, the number of photosensitization cases is constantly increasing due to excessive exposure to sunlight, the aesthetic value of a tan, and the increasing number of photosensitizing substances in food, dietary supplements, and pharmaceutical and cosmetic products. The risk of photosensitivity reactions relates to several hundred externally and systemically administered drugs, including nonsteroidal anti-inflammatory, cardiovascular, psychotropic, antimicrobial, antihyperlipidemic, and antineoplastic drugs. Photosensitivity reactions often lead to hospitalization, additional treatment, medical management, decrease in patient's comfort, and the limitations of drug usage. Mechanisms of drug-induced photosensitivity are complex and are observed at a cellular, molecular, and biochemical level. Photoexcitation and photoconversion of drugs trigger multidirectional biological reactions, including oxidative stress, inflammation, and changes in melanin synthesis. These effects contribute to the appearance of the following symptoms: erythema, swelling, blisters, exudation, peeling, burning, itching, and hyperpigmentation of the skin. This article reviews in detail the chemical and biological basis of drug-induced photosensitivity. The following factors are considered: the chemical properties, the influence of individual ranges of sunlight, the presence of melanin biopolymers, and the defense mechanisms of particular types of tested cells.

An approach to evaluate metabolite-related phototoxicity with combined use of photochemical properties and skin deposition

Some chemicals have been reported to cause metabolite-related phototoxicity, and this study aimed to verify the applicability of photosafety assessment based on photochemical and pharmacokinetic properties to evaluate the metabolite-related phototoxicity risk. The phototoxic risk of imipramine (IMI) and its metabolite, desipramine (DMI), was evaluated by photochemical and pharmacokinetic analyses. IMI and DMI were found to have similar photoreactivities based on the generation of reactive oxygen species. The skin concentrations of IMI and DMI reached maximal levels at approximately 1 and 4 h, respectively, after oral administration of IMI (10 mg/kg), and DMI showed high skin deposition compared with IMI. According to the results, DMI was identified as a contributor to phototoxicity induced by orally-taken IMI. In in vivo phototoxicity testing, ultraviolet A irradiation from 3 to 6 h after oral administration of IMI (100 mg/kg) caused more potent phototoxic reactions compared with that from 0 to 3 h, and DMI yielded by metabolism of IMI would be associated with phototoxic reactions caused by orally-administered IMI. In addition to the data on IMI, a parent chemical, photochemical and pharmacokinetic profiling of its metabolite, DMI, led to reliable phototoxicity prediction of orally-administered IMI. Thus, characterization of the photosafety of metabolites would generate reliable information on the phototoxicity risk of parent chemicals, and the proposed strategy may facilitate comprehensive photosafety assessment of drug candidates in pharmaceutical development.

[Establishment and International Harmonization of Photosafety Testing Strategy]

Considerable attention has been drawn to predict a photosafety hazard on new chemicals. A number of phototoxins tend to generate reactive oxygen species (ROS) via energy transfer mechanisms following UV/VIS excitation, including superoxide and singlet oxygen. Then, ROS assay has been designed to assess photoreactivity of pharmaceuticals, of which the principle is to monitor types I and II photochemical reactions of the test chemicals when exposed to simulated sunlight. This simple analytical test could be used to screen potential chemical scaffolds, leads, and candidate drugs to identify and/or select away from those having phototoxic potential. The validation study for the ROS assay has been being carried out by the Japan Pharmaceutical Manufacturers Association (JPMA), supervised by the Japanese Center for the Validation of Alternative Methods (JaCVAM). Although several false positives appeared, the ROS assay on 42 coded chemicals has provided no false negative predictions. The validation study tentatively indicates satisfactory outcomes in terms of transferability, intra- and inter-laboratory variability, and predictive capacity. Thus, a negative result in this ROS assay would indicate a very low probability of phototoxicity, whereas a positive result would be a flag for follow-up assessment. Upon international harmonization activities supported by several agencies and industrial groups, ROS assay was successfully adopted as International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) S10 guideline (2014) and Organisation for Economic Co-operation and Development (OECD) test guideline 495 (2019).

Ester derivatives of phyllohydroquinone effectively deliver the active form of vitamin K1 topically, owing to their non-photosensitivity

Topical application of phylloquinone (PK) is beneficial to the skin; however, its topical use is limited in Europe owing to its photosensitive properties such as photodegradation and phototoxicity. We evaluated the suitability of ester derivatives of phyllohydroquinone (PKH), the active form of PK, for topical application to overcome the abovementioned problems of PK. We used the PKH derivatives PKH-1,4-bis-N,N-dimethylglycinate hydrochloride (PKH-DMG) and PKH-1,4-bis-hemisuccinate (PKH-SUC) for our studies. Photostability was determined by measuring the residual concentration after irradiation with artificial sunlight and multi-wavelength light. Phototoxicity after ultraviolet A (UVA) irradiation was assessed by measuring drug-induced singlet oxygen and intracellular reactive oxygen species (ROS) generation, and cell viability of a human epidermal keratinocyte cell line (HaCaT). Delivery of PKH into HaCaT cells was assessed by measuring PK epoxide (PKO) levels. The PKH derivatives showed higher photostability than PK. After UVA irradiation, PK induced high singlet oxygen levels and intracellular ROS generation, and reduced cell viability, whereas the PKH derivatives showed no effects. The PKH derivatives increased intracellular PKO levels. AUC_{PKO(0-72 h)} values after PKH-DMG and PKH-SUC treatments were 0.741- and 22.9-fold higher than that after PK treatment, respectively. In conclusion, PKH derivatives act as PKH prodrugs and are suitable for topical application without the need for special protection from light.

Comparative analysis of the phototoxicity induced by BRAF inhibitors and alleviation through antioxidants

BACKGROUND

Small molecules tackling mutated BRAF (BRAFi) are an important mainstay of targeted therapy in a variety of cancers including melanoma. Albeit commonly reported as side effect, the phototoxic potential of many BRAFi is poorly characterized. In this study, we evaluated the phototoxicity of 17 distinct agents and investigated whether BRAFi-induced phototoxicity can be alleviated by antioxidants.

METHODS

The ultraviolet (UV) light absorbance of 17 BRAFi was determined. Their phototoxic potential was investigated independently with a reactive oxygen species (ROS) and the 3T3 neutral red uptake (NRU) assay in vitro. To test for a possible phototoxicity alleviation by antioxidants, vitamin C, vitamin E phosphate, trolox, and glutathione (GSH) were added to the 3T3 assay of selected inhibitors.

RESULTS

The highest cumulative absorbance for both UVA and UVB was detected for vemurafenib. The formation of ROS was more pronounced for all compounds after irradiation with UVA than with UVB. In the 3T3 NRU assay, 8 agents were classified as phototoxic, including vemurafenib, dabrafenib, and encorafenib. There was a significant correlation between the formation of singlet oxygen (P = .026) and superoxide anion (P < .001) and the phototoxicity observed in the 3T3 NRU assay. The phototoxicity of vemurafenib was fully rescued in the 3T3 NRU assay after GSH was added at different concentrations.

CONCLUSION

Our study confirms that most of the BRAF inhibitors exhibited a considerable phototoxic potential, predominantly after exposure to UVA. GSH may help treat and prevent the phototoxicity induced by vemurafenib.

Ubiquinone modified printed carbon electrodes for cell culture pH monitoring

The measurement of pH is important throughout many biological systems, but there are limited available technologies to enable its periodical monitoring in the complex, small volume, media often used in cell culture experiments across a range of disciplines. Herein, pad printed electrodes are developed and characterised through modification with: a commercially available fullerene multiwall carbon nanotube composite applied in Nafion, casting of hydrophobic ubiquinone as a pH probe to provide the electrochemical signal, and coated in Polyethylene glycol to reduce fouling and potentially enhance biocompatibility, which together are proven to enable the determination of pH in cell culture media containing serum. The ubiquinone oxidation peak position (E_pa) provided an indirect marker of pH across the applicable range of pH 6-9 (R² = 0.9985, n = 15) in complete DMEM. The electrochemical behaviour of these sensors was also proven to be robust; retaining their ability to measure pH in cell culture media supplemented with serum up to 20% (v/v) [encompassing the range commonly employed in cell culture], cycled > 100 times in 10% serum containing media and maintain > 60% functionality after 5 day incubation in a 10% serum containing medium. Overall, this proof of concept research highlights the potential applicability of this, or similar, electrochemical approaches to enable to detection or monitoring of pH in complex cell culture media.

Photo-induced oxidative damage to dissolved free amino acids by the photosensitizer polycyclic musk tonalide: Transformation kinetics and mechanisms

Residue from the polycyclic musks (PCMs) in household and personal care products may harm human beings through skin exposure. To understand the health effects of PCMs when exposed to sunlight at molecular level, both experimental and computational methods were employed to investigate the photosensitized oxidation performance of 19 natural amino acids, the most basic unit of life. Results showed that a typical PCM, tonalide, acts as a photosensitizer to significantly increase photo-induced oxidative damage to amino acids. Both common and exceptional transformation pathways occurred during the photosensitization damage of amino acids. Experimental tests further identified the different mechanisms involved. The common transformation pathway occurred through the electron transfer from α amino-group of amino acids, accompanying with the formation of O₂^•-. This pathway was controlled by the electronic density of N atom in α amino-group. The exceptional transformation pathway was identified only for five amino acids, mainly due to the reactions with reactive oxygen species, e.g. ¹O₂ and excited triplet state molecules. Additionally, tonalide photo-induced transformation products could further accelerate the photosensitization of all amino acids with the common pathway. This study may support the protection of human health, and suggests the possible need to further restrict polycyclic musks use.

Phototoxicity Evaluation of Pharmaceutical Substances with a Reactive Oxygen Species Assay Using Ultraviolet A

With ultraviolet and visible light exposure, some pharmaceutical substances applied systemically or topically may cause phototoxic skin irritation. The major factor in phototoxicity is the generation of reactive oxygen species (ROS) such as singlet oxygen and superoxide anion that cause oxidative damage to DNA, lipids and proteins. Thus, measuring the generation of ROS can predict the phototoxic potential of a given substance indirectly. For this reason, a standard ROS assay (ROS assay) was developed and validated and provides an alternative method for phototoxicity evaluation. However, negative substances are over-predicted by the assay. Except for ultraviolet A (UVA), other UV ranges are not a major factor in causing phototoxicity and may lead to incorrect labeling of some non-phototoxic substances as being phototoxic in the ROS assay when using a solar simulator. A UVA stimulator is also widely used to evaluate phototoxicity in various test substances. Consequently, we identified the applicability of a UVA simulator to the ROS assay for photoreactivity. In this study, we tested 60 pharmaceutical substances including 50 phototoxins and 10 non-phototoxins to predict their phototoxic potential via the ROS assay with a UVA simulator. Following the ROS protocol, all test substances were dissolved in dimethyl sulfoxide or sodium phosphate buffer. The final concentration of the test solutions in the reaction mixture was 20 to 200 μM. The exposure was with 2.0~2.2 mW/cm² irradiance and optimization for a relevant dose of UVA was performed. The generation of ROS was compared before and after UVA exposure and was measured by a microplate spectrophotometer. Sensitivity and specificity values were 85.7% and 100.0% respectively, and the accuracy was 88.1%. From this analysis, the ROS assay with a UVA simulator is suitable for testing the photoreactivity and estimating the phototoxic potential of various test pharmaceutical substances.

Evaluation of skin phototoxicity study using SD rats by transdermal and oral administration

Guinea pigs are the most frequently used animals in phototoxicity studies. However, general toxicity studies most often use Sprague-Dawley (SD) rats. To reduce the number of animals needed for drug development, we examined whether skin phototoxicity studies could be performed using SD rats. A total of 19 drugs that had previously been shown to have phototoxic potential and 3 known phototoxic compounds were administered transdermally to guinea pigs and SD rats. Eleven of the potentially phototoxic drugs and 2 of the known phototoxic compounds were also administered orally to guinea pigs and SD rats. After administration, the animals were irradiated with UV-A (10 J/cm(2)) and UV-B (0.25 J/cm(2) in guinea pigs and 0.031 J/cm(2) in SD rats) with doses based on standard phototoxicity study guidelines and the results of a minimum erythema dose test, respectively. In the transdermal administration study, all of the known phototoxic compounds and 7 of the drugs induced phototoxic reactions. In the oral administration study, both known phototoxic compounds and 5 drugs induced phototoxic reactions in both species; one compound each was found to be toxic only in SD rats or guinea pigs. The concordance rate of guinea pigs and SD rats was 100% in the transdermal administration study and 85% in the oral administration study. This study demonstrated that phototoxicity studies using SD rats have the same potential to detect phototoxic compounds as studies using guinea pigs.

Development of a novel nanoparticle formulation of thymoquinone with a cold wet-milling system and its pharmacokinetic analysis

The present study aimed to develop a nanoparticle (NP) formulation of thymoquinone (TQ), a potent anti-oxidant chemical, with use of a cold wet-milling (CWM) system to improve its dissolution behavior and pharmacokinetic properties. The NP formulation of TQ (TQ/CWM) was prepared by CWM system, and its physicochemical properties were characterized in terms of particle size distribution, morphology, crystallinity, and dissolution. The photochemical properties of TQ were also examined upon UV/VIS absorption, reactive oxygen species (ROS) generation, and photostability. Pharmacokinetic studies were carried out in rats. Application of the CWM system to TQ led to successful development of nano-sized TQ. The mean diameter of TQ in TQ/CWM was calculated to be 143nm, and TQ particles in TQ/CWM were found to be amorphous. There was a marked improvement in dissolution rate compared with TQ. TQ showed significant generation of singlet oxygen and superoxide upon exposure to simulated sunlight, suggesting its high photoreactivity, and solid samples such as TQ and TQ/CWM exhibited higher photostability than TQ solution. In comparison with TQ, enhanced TQ exposure was observed with a ca. 6-fold increase of oral bioavailability, and the Tmax was shown to be a quarter. From these findings, the NP approach employing the CWM system might be a promising dosage option for improving the nutraceutical values of TQ.

Intra-/inter-laboratory validation study on reactive oxygen species assay for chemical photosafety evaluation using two different solar simulators

A previous multi-center validation study demonstrated high transferability and reliability of reactive oxygen species (ROS) assay for photosafety evaluation. The present validation study was undertaken to verify further the applicability of different solar simulators and assay performance. In 7 participating laboratories, 2 standards and 42 coded chemicals, including 23 phototoxins and 19 non-phototoxic drugs/chemicals, were assessed by the ROS assay using two different solar simulators (Atlas Suntest CPS series, 3 labs; and Seric SXL-2500V2, 4 labs). Irradiation conditions could be optimized using quinine and sulisobenzone as positive and negative standards to offer consistent assay outcomes. In both solar simulators, the intra- and inter-day precisions (coefficient of variation; CV) for quinine were found to be below 10%. The inter-laboratory CV for quinine averaged 15.4% (Atlas Suntest CPS) and 13.2% (Seric SXL-2500V2) for singlet oxygen and 17.0% (Atlas Suntest CPS) and 7.1% (Seric SXL-2500V2) for superoxide, suggesting high inter-laboratory reproducibility even though different solar simulators were employed for the ROS assay. In the ROS assay on 42 coded chemicals, some chemicals (ca. 19-29%) were unevaluable because of limited solubility and spectral interference. Although several false positives appeared with positive predictivity of ca. 76-92% (Atlas Suntest CPS) and ca. 75-84% (Seric SXL-2500V2), there were no false negative predictions in both solar simulators. A multi-center validation study on the ROS assay demonstrated satisfactory transferability, accuracy, precision, and predictivity, as well as the availability of other solar simulators.

Establishment and intra-/inter-laboratory validation of a standard protocol of reactive oxygen species assay for chemical photosafety evaluation

A reactive oxygen species (ROS) assay was previously developed for photosafety evaluation of pharmaceuticals, and the present multi-center study aimed to establish and validate a standard protocol for ROS assay. In three participating laboratories, two standards and 42 coded chemicals, including 23 phototoxins and 19 nonphototoxic drugs/chemicals, were assessed by the ROS assay according to the standardized protocol. Most phototoxins tended to generate singlet oxygen and/or superoxide under UV-vis exposure, but nonphototoxic chemicals were less photoreactive. In the ROS assay on quinine (200 µm), a typical phototoxic drug, the intra- and inter-day precisions (coefficient of variation; CV) were found to be 1.5-7.4% and 1.7-9.3%, respectively. The inter-laboratory CV for quinine averaged 15.4% for singlet oxygen and 17.0% for superoxide. The ROS assay on 42 coded chemicals (200 µm) provided no false negative predictions upon previously defined criteria as compared with the in vitro/in vivo phototoxicity, although several false positives appeared. Outcomes from the validation study were indicative of satisfactory transferability, intra- and inter-laboratory variability, and predictive capacity of the ROS assay.

Novel solid self-emulsifying drug delivery system of coenzyme Q₁₀ with improved photochemical and pharmacokinetic behaviors

The present study was undertaken to develop a solid self-emulsifying drug delivery system of coenzyme Q(10) (CoQ(10)/s-SEDDS) with high photostability and oral bioavailability. The CoQ(10)/s-SEDDS was prepared by spray-drying an emulsion preconcentrate containing CoQ(10), medium-chain triglyceride, sucrose ester of fatty acid, and hydroxypropyl cellulose, and its physicochemical, photochemical, and pharmacokinetic properties were evaluated. The CoQ(10)/s-SEDDS powder with a diameter of ca. 15 μm was obtained by spray-drying, in which the CoQ(10) was mostly amorphized. The CoQ(10)/s-SEDDS exhibited immediate self-emulsification when introduced to aqueous media under gentle agitation, forming uniform fine droplets with a mean diameter of ca. 280 nm. There was marked generation of reactive oxygen species, in particular superoxide, from CoQ(10) exposed to simulated sunlight (250W/m(2)), suggesting potent photoreactivity. Nano-emulsified solution of CoQ(10) under light exposure underwent photodegradation with 22-fold higher degradation kinetics than crystalline CoQ(10), although the CoQ(10)/s-SEDDS was less photoreactive. After the oral administration of CoQ(10)/s-SEDDS (100 mg-CoQ(10)/kg) in rats, enhanced exposure of CoQ(10) was observed with increases in both C(max) and AUC of ca. 5-fold in comparison with those of orally administered crystalline CoQ(10). From the improved physicochemical and pharmacokinetic data, the s-SEDDS approach upon spray-drying might be a suitable dosage option for enhancing nutraceutical and pharmaceutical values of CoQ(10).

In vitro photochemical and phototoxicological characterization of major constituents in St. John's Wort (Hypericum perforatum) extracts

Extracts from St. John's Wort (SJW: Hypericum perforatum) have been used for the treatment of mild-to-moderate depression. In spite of the high therapeutic potential, orally administered SJW sometimes causes phototoxic skin responses. As such, the present study aimed to clarify the phototoxic mechanisms and to identify the major phototoxins of SJW extract. Photobiochemical properties of SJW extract and 19 known constituents were characterized with focus on generation of reactive oxygen species (ROS), lipid peroxidation, and DNA photocleavage, which are indicative of photosensitive, photoirritant, and photogenotoxic potentials, respectively. ROS assay revealed the photoreactivity of SJW extract and some SJW ingredients as evidenced by type I and/or II photochemical reactions under light exposure. Not all the ROS-generating constituents caused photosensitized peroxidation of linoleic acid and photodynamic cleavage of plasmid DNA, and only hypericin, pseudohypericin, and hyperforin exhibited in vitro photoirritant potential. Concomitant UV exposure of quercitrin, an SJW component with potent UV/Vis absorption, with hyperforin resulted in significant attenuation of photodynamic generation of singlet oxygen from hyperforin, but not with hypericin. In conclusion, our results suggested that hypericin, pseudohypericin, and hyperforin might be responsible for the in vitro phototoxic effects of SJW extract.

No time to lose--high throughput screening to assess nanomaterial safety

Nanomaterials hold great promise for medical, technological and economical benefits. Knowledge concerning the toxicological properties of these novel materials is typically lacking. At the same time, it is becoming evident that some nanomaterials could have a toxic potential in humans and the environment. Animal based systems lack the needed capacity to cope with the abundance of novel nanomaterials being produced, and thus we have to employ in vitro methods with high throughput to manage the rush logistically and use high content readouts wherever needed in order to gain more depth of information. Towards this end, high throughput screening (HTS) and high content screening (HCS) approaches can be used to speed up the safety analysis on a scale that commensurate with the rate of expansion of new materials and new properties. The insights gained from HTS/HCS should aid in our understanding of the tenets of nanomaterial hazard at biological level as well as assist the development of safe-by-design approaches. This review aims to provide a comprehensive introduction to the HTS/HCS methodology employed for safety assessment of engineered nanomaterials (ENMs), including data analysis and prediction of potentially hazardous material properties. Given the current pace of nanomaterial development, HTS/HCS is a potentially effective means of keeping up with the rapid progress in this field--we have literally no time to lose.

High-throughput screening strategy for photogenotoxic potential of pharmaceutical substances using fluorescent intercalating dye

The aim of the present study was to provide an intercalator-based photogenotoxicity (IBP) assay as a high-throughput in vitro screening system for predicting the photogenotoxic potential of pharmaceutical substances. The conditions of the high-throughput IBP assay using thiazole orange (TO), a fluorescent intercalating dye, were optimized and validated by a fluorescence titration experiment and reproducibility/robustness test. The IBP assay was applied to 27 phototoxic and 5 weak/non-phototoxic commercially available compounds, and other phototoxicity screenings were also carried out for comparison; these included the reactive oxygen species (ROS) assay for overall phototoxic potential and the DNA-photocleavage assay for photogenotoxic risk. According to the results from the comparative experiments, a decreased level of intercalated TO in the IBP assay could theoretically be related to the DNA-photocleaving behaviors of phototoxic drugs, but not to their ROS-generating abilities. The IBP assay could predict the photodynamic DNA impairment caused by irradiated drugs with a prediction accuracy of 78%. These findings suggest that the IBP assay could be a fast and reliable tool for predicting the photogenotoxic potential of a large number of drug candidates at early stages of drug discovery.

Reactive oxygen species assay-based risk assessment of drug-induced phototoxicity: classification criteria and application to drug candidates

We have previously demonstrated that the phototoxic potential of chemicals could be partly predicted by the determination of reactive oxygen species (ROS) from photo-irradiated compounds. In this study, ROS assay strategy was applied to 39 marketed drugs and 210 drug candidates in order to establish provisional classification criteria for risk assessment of drug-induced phototoxicity. The photosensitizing properties of 39 model compounds consisting of phototoxic and non-phototoxic chemicals, as well as ca. 210 drug candidates including 11 chemical series were evaluated using ROS assay and the 3T3 neutral red uptake phototoxicity test (NRU PT). With respect to marketed drugs, most phototoxic drugs tended to cause type I and/or II photochemical reactions, resulting in generation of singlet oxygen and superoxide. There seemed to be a clear difference between phototoxic drugs and non-phototoxic compounds in their abilities to induce photochemical reactions. A plot analysis of ROS data on the marked drugs provided classification criteria to discriminate the photosensitizers from non-phototoxic substances. Of all drug candidates tested, 35.2% compounds were identified as phototoxic or likely phototoxic on the basis of the 3T3 NRU PT, and all ROS data for these phototoxic compounds were found to be over the threshold value. Furthermore, 46.3% of non-phototoxic drug candidates were found to be in the subthreshold region. These results verify the usefulness of the ROS assay for understanding the phototoxicity risk of pharmaceutical substances, and the ROS assay can be used for screening purposes in the drug discovery stage.