In vitro phototoxicity of nifedipine: sequential induction of toxic and non-toxic photoproducts with UVA radiation

Drug and chemical induced photosensitivity from a clinical perspective

Drug photosensitivity is a relatively common occurrence and a range of mechanisms may be involved. Some of these mechanisms will be discussed, including the most common, that of drug phototoxicity. Different types of photosensitivity are addressed with respect to clinical presentation, mechanisms and additionally the contribution to our understanding through clinically directed investigations and regulatory requirements. Repeated controlled therapeutic use of drug phototoxicity, with psoralen-UVA (PUVA) photochemotherapy and photodynamic therapy (PDT) will also be discussed. Finally, the potential for drug-induced photocarcinogenesis will also be covered.

An improved targeted cAMP sensor to study the regulation of adenylyl cyclase 8 by Ca2+ entry through voltage-gated channels

Here we describe an improved sensor with reduced pH sensitivity tethered to adenylyl cyclase (AC) 8. The sensor was used to study cAMP dynamics in the AC8 microdomain of MIN6 cells, a pancreatic β-cell line. In these cells, AC8 was activated by Ca(2+) entry through L-type voltage-gated channels following depolarisation. This activation could be reconstituted in HEK293 cells co-expressing AC8 and either the α1C or α1D subunit of L-type voltage-gated Ca(2+) channels. The development of this improved sensor opens the door to the study of cAMP microdomains in excitable cells that have previously been challenging due to the sensitivity of fluorescent proteins to pH changes.

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.

Instability of calcium channel antagonists during sample preparation for LC–MS–MS analysis of serum samples

1,4-Dihydropyridines calcium channel antagonists (1,4-DHP CCAs) are photolabile and the products of their photodecomposition have no pharmaceutical activity. In our previous work we have presented a screening procedure for eleven 1,4-DHPs in plasma by LC-MS-MS using multiple reaction motoring. The laboratory process includes preparation and storage of stock solutions, plasma storage, solid-phase extraction, reconstitution of extracts and storage time in an autosampler for LC-MS-MS analysis. Prior to validation of the analytical procedure, we have tested the stability of these compounds by exposure to light. Methanolic solutions have been exposed to laboratory and UV light and the stability of the compounds in plasma was tested by exposure of spiked plasma samples to laboratory light at room temperature. Stability during freeze-thaw cycles and stability during 2 month storage at -20 degrees C have been tested as well. Products of photodecomposition have been identified after forced degradation and the degree of degradation has been quantified using LC-UV-DAD and LC-MS-MS, respectively. A 96% degradation after only 2h has been observed when solutions of nifedipine or nisoldipine were exposed to laboratory light in clear glass vials. In plasma samples degradation was 25% in only 2h for both compounds. The main degradation product was produced by oxidation of the dihydropyridinic ring resulting in the pyridine analogue that has been described as the first metabolite in the metabolic pathway. Only minor degradation was found for the other tested compounds after 2h light exposure in methanolic solutions. Furthermore, lercanidipine and nicardipine were also degradated by esterhydrolysis. Several additional minor degradation products were found for the other tested 1,4-DHPs, however, some of them could not be identified. Preconditions for storage and handling of plasma samples prior to and during analysis for 1,4-DHP CCAs are suggested in order to avoid photodecomposition of the analytes.

Solid state photochemistry of 1,4-dihydropyridines

Photochemical behavior of some 1,4-dihydropyridines has been investigated in the solid state. Whereas upon irradiation of 1,4-dihydropyridines in solution phase, their photo-oxidation and formation of pyridine derivatives have been observed, irradiation of these compounds in the solid state decreases their light sensitivity. In many cases photo-oxidation has been observed only in very low yields.

Light induced changes in quinolone levels in rat serum and tissues

Circadian rhythm may induce alterations of the pharmacokinetic properties of several drugs in clinical use. The aim of the study was to investigate whether lighting conditions alter the quinolone (pefloxacin) levels in serum and tissues and to determine any accumulation of the drug in the skin. Thirty male Wistar rats were divided into groups A, B, C, (n=10). The animals of group A were housed under 12h light/12h dark conditions, group B under 24h UV and group C was kept in complete darkness. All animals received 5 doses of 11mg/Kg pefloxacin every 8h for 48h.Pefloxacin levels were determined in serum, skin and femur by the inhibition zone in E.coli. in vitro. Pefloxacin concentrations in serum were increased in 24h darkness living status and decreased in 24h UV conditions as compared to group A animals. Additionally, both skin and femur pefloxacin levels were decreased under dark and UV conditions. In conclusion total light as well as total dark exposure may lead to pefloxacin pharmacokinetic changes which may have implications in the effectiveness of the drug in tissues.

Comparison of an in vitro cellular phototoxicity model against controlled clinical trials of fluoroquinolone skin phototoxicity

Many therapeutic drugs induce phototoxic skin responses following exposure to solar or artificial ultraviolet radiation sources. Several in vitro model systems have been developed to predict drug phototoxicity but none have been conducted in parallel with controlled clinical phototoxicity studies on systemically administered pharmaceuticals. The in vitro phototoxicity of eight fluoroquinolone (FQ) antibiotics (ciprofloxacin, grepafloxacin, lomefloxacin, norfloxacin, ofloxacin, trovafloxacin, BAYy3118, moxifloxacin) was determined by exposing Chinese hamster fibroblasts to UVA radiation. Cell damage was quantified with standard MTT or neutral red assays and an in vitro phototoxic index calculated (PI(vit)=% cell viability with UVA alone /% cell viability with UVA+FQ) for each endpoint. Clinical photosensitizing ability of the eight systemically administered FQ was investigated using double-blind, placebo and positive controlled, clinical skin phototesting of normal subjects. Minimal erythema doses at 365+/-30nm were determined before and after 6-7 days of FQ ingestion and PI(clin) (minimal erythema dose without FQ/minimal erythema dose with FQ) calculated. Linear regression analysis of PI(vit) vs PI(clin) gave correlations of up to 0.893. Principal components analysis of PI(vit), daily dose, plasma levels and photophysical (absorption) properties of the eight FQ showed that phototoxic (arbitrarily defined as PI(clin)> or =2) and non-phototoxic (PI(clin)<2) FQ could be completely discriminated using these parameters, and that the in vitro models were able to rank the relative phototoxic potential of the eight FQ.

Photodynamic effects of 5-aminolevulinic acid-induced porphyrin on human bladder carcinoma cells in vitro

The efficiency of 5-aminolevulinic acid (ALA) in photodynamic therapy (PDT) was investigated in vitro using urothelial carcinoma cells of various differentiation. HCV29, RT4 and J82 cells were cultured in 96-well plates, incubated with 25-100 micrograms/ml ALA in serum-containing medium for 4 h, and irradiated at 630, 635 and 640 nm wavelength with light doses of 15-100 J/cm2. The degree of reduced tetrazolium bromide corresponding to cell viability was determined with a colorimetric MTT assay 0, 24 and 48 h after PDT. A remarkable reduction of mitochondrial activity occurred in poorly (J82) and well differentiated (RT4) malignant urothelial cells. Twenty-four hours after photodynamic treatment with 100 micrograms/ml ALA and 50 J/cm2, the metabolic activity of malignant cells was nearly extinguished, while HCV29 cells, derived from normal urothelium, behaved similarly to non-irradiated control cells. The photosensitivity of cells depended on presence or absence of fetal bovine serum (FBS) in the ALA-incubation medium. A wavelength of 635 nm was up to 60% more effective compared with 630 nm, which is more frequently applied in PDT. From the results of our in vitro studies, we can define a "therapeutic window" for malignant cells without damaging benign cells. The time delayed effects and the strong wavelength dependence are important factors for a clinical application.

Photodistributed nifedipine-induced facial telangiectasia

Five months after starting nifedipine (Adalat), two patients developed photodistributed facial telangiectasia, which became more noticeable with time. Neither patient complained of photosensitivity or flushing. Both patients reported a significant cosmetic improvement after discontinuing the drug. One commenced the closely related drug amlodipine 3 years later, with recurrence of telangiectasia. The photodistribution of the telangiectasia suggests a significant drug/light interaction.

New 4-alkyl-1,4-dihydropyridines: evaluation of photostability and phototoxic potential

The photostability and phototoxic potential of two new 4-alkyl-1,4-dihydropyridines (PCA-4230 and PCA-4248) were investigated. When these 4-alkyl-1,4-dihydropyridines were irradiated with a multilamp photoreactor (band centred at 350 nm), both exhibited a slow photodegradation showing first-order kinetics. The photodegradation rate constants were 0.37 h-1 for PCA-4248 and 0.39 h-1 for PCA-4230 in oxygenated conditions. The photodecomposition was slower for both drugs in the absence of oxygen. In order to evaluate the phototoxicity induced by these drugs, red blood cells and Hep-2 (human laringo carcinoma cell line) were irradiated using a minisolarium, which emits UVA radiation (350-390 nm). The results showed that PCA-4248 and PCA-4230 did not exhibit a phototoxic effect in the two models tested.