Modulation of the photobehavior of gefitinib and its phenolic metabolites by human transport proteins.

The photobiological damage that certain drugs or their metabolites can photosensitize in proteins is generally associated with the nature of the excited species that are generated upon interaction with UVA light. In this regard, the photoinduced damage of the anticancer drug gefitinib (GFT) and its two main photoactive metabolites GFT-M1 and GFT-M2 in cellular milieu was recently investigated. With this background, the photophysical properties of both the drug and its metabolites have now been studied in the presence of the two main transport proteins of human plasma, i.e., serum albumin (HSA) and α1-acid glycoprotein (HAG) upon UVA light excitation. In general, the observed photobehavior was strongly affected by the confined environment provided by the protein. Thus, GFT-M1 (which exhibits the highest phototoxicity) showed the highest fluorescence yield arising from long-lived HSA-bound phenolate-like excited species. Conversely, locally excited (LE) states were formed within HAG, resulting in lower fluorescence yields. The reserve was true for GFT-M2, which despite being also a phenol, led mainly to formation of LE states within HSA, and phenolate-like species (with a minor contribution of LE) inside HAG. Finally, the parent drug GFT, which is known to form LE states within HSA, exhibited a parallel behavior in the two proteins. In addition, determination of the association constants by both absorption and emission spectroscopy revealed that the two metabolites bind stronger to HSA than the parent drug, whereas smaller differences were observed for HAG. This was further confirmed by studying the competing interactions between GFT or its metabolites with the two proteins using fluorescence measurements. These above experimental findings were satisfactorily correlated with the results obtained by means of molecular dynamics (MD) simulations, which revealed the high affinity binding sites, the strength of interactions and the involved amino acid residues. In general, the differences observed in the photobehavior of the drug and its two photoactive metabolites in protein media are consistent with their relative photosensitizing potentials.

Cellular photo(geno)toxicity of gefitinib after biotransformation.

Gefitinib (GFT) is a selective epidermal growth factor receptor (EGFR) inhibitor clinically used for the treatment of patients with non-small cell lung cancer. Bioactivation by mainly Phase I hepatic metabolism leads to chemically reactive metabolites such as O-Demethyl gefitinib (DMT-GFT), 4-Defluoro-4-hydroxy gefitinib (DF-GFT), and O-Demorpholinopropyl gefitinib (DMOR-GFT), which display an enhanced UV-light absorption. In this context, the aim of the present study is to investigate the capability of gefitinib metabolites to induce photosensitivity disorders and to elucidate the involved mechanisms. According to the neutral red uptake (NRU) phototoxicity test, only DF-GFT metabolite can be considered non-phototoxic to cells with a photoirritation factor (PIF) close to 1. Moreover, DMOR-GFT is markedly more phototoxic than the parent drug (PIF = 48), whereas DMT-GFT is much less phototoxic (PIF = 7). Using the thiobarbituric acid reactive substances (TBARS) method as an indicator of lipid photoperoxidation, only DMOR-GFT has demonstrated the ability to photosensitize this process, resulting in a significant amount of TBARS (similar to ketoprofen, which was used as the positive control). Protein photooxidation monitored by 2,4-dinitrophenylhydrazine (DNPH) derivatization method is mainly mediated by GFT and, to a lesser extent, by DMOR-GFT; in contrast, protein oxidation associated with DMT-GFT is nearly negligible. Interestingly, the damage to cellular DNA as revealed by the comet assay, indicates that DMT-GFT has the highest photogenotoxic potential; moreover, the DNA damage induced by this metabolite is hardly repaired by the cells after a time recovery of 18 h. This could ultimately result in mutagenic and carcinogenic effects. These results could aid oncologists when prescribing TKIs to cancer patients and, thus, establish the conditions of use and recommend photoprotection guidelines.

Singlet oxygen and radical-mediated mechanisms in the oxidative cellular damage photosensitized by the protease inhibitor simeprevir.

Hepatitis C, a liver inflammation caused by the hepatitis C virus (HCV), is treated with antiviral drugs. In this context, simeprevir (SIM) is an NS3/4A protease inhibitor used in HCV genotypes 1 and 4. It is orally administered and achieves high virological cure rates. Among adverse reactions associated with SIM treatment, photosensitivity reactions have been reported. In the present work, it is clearly shown that SIM is markedly phototoxic, according to the in vitro NRU assay using BALB/c 3T3 mouse fibroblast. This result sheds light on the nature of the photosensitivity reactions induced by SIM in HCV patients, suggesting that porphyrin elevation in patients treated with SIM may not be the only mechanism responsible for SIM-associated photosensitivity. Moreover, lipid photoperoxidation and protein photooxidation assays, using human skin fibroblasts (FSK) and human serum albumin (HSA), respectively, reveal the capability of this drug to promote photodamage to cellular membranes. Also, DNA photo lesions induced by SIM are noticed through comet assay in FSK cells. Photochemical and photobiological studies on the mechanism of SIM-mediated photodamage to biomolecules indicate that the key transient species generated upon SIM irradiation is the triplet excited state. This species is efficiently quenched by oxygen giving rise to singlet oxygen, which is responsible for the oxidation of lipids and DNA (Type II mechanism). In the presence of HSA, the photobehavior is dominated by binding to site 3 of the protein, to give a stable SIM@HSA complex. Inside the complex, quenching of the triplet excited state is less efficient, which results in a longer triplet lifetime and in a decreased singlet oxygen formation. Hence, SIM-mediated photooxidation of the protein is better explained through a radical (Type I) mechanism.

Switching from ultrafast electron transfer to proton transfer in excited drug-protein complexes upon biotransformation.

Photosensitization by drugs is directly related with the excited species and the photoinduced processes arising from interaction with UVA light. In this context, the ability of gefitinib (GFT), a tyrosine kinase inhibitor (TKI) used for the treatment of a variety of cancers, to induce phototoxicity and photooxidation of proteins has recently been demonstrated. In principle, photodamage can be generated not only by a given drug but also by its photoactive metabolites that maintain the relevant chromophore. In the present work, a complete study of O-desmorpholinopropyl gefitinib (GFT-MB) has been performed by means of fluorescence and ultrafast transient absorption spectroscopies, in addition to molecular dynamics (MD) simulations. The photobehavior of the GFT-MB metabolite in solution is similar to that of GFT. However, when the drug or its metabolite are in a constrained environment, i.e. within a protein, their behavior and the photoinduced processes that arise from their interaction with UVA light are completely different. For GFT in complex with human serum albumin (HSA), locally excited (LE) singlet states are mainly formed; these species undergo photoinduced electron transfer with Tyr and Trp. By contrast, since GFT-MB is a phenol, excited state proton transfer (ESPT) to form phenolate-like excited species might become an alternative deactivation pathway. As a matter of fact, the protein-bound metabolite exhibits higher fluorescence yields and longer emission wavelengths and lifetimes than GFT@HSA. Ultrafast transient absorption measurements support direct ESPT deprotonation of LE states (rather than ICT), to form phenolate-like species. This is explained by MD simulations, which reveal a close interaction between the phenolic OH group of GFT-MB and Val116 within site 3 (subdomain IB) of HSA. The reported findings are relevant to understand the photosensitizing properties of TKIs and the role of biotransformation in this type of adverse side effects.

Photoprocesses of the tyrosine kinase inhibitor gefitinib: from femtoseconds to microseconds and from solution to cells.

Gefitinib (GFT) is a tyrosine kinase inhibitor currently used for the treatment of metastatic non-small cell lung cancer. Although it has been suggested that GFT can be phototoxic, there are no systematic studies on this issue. Here, the photosensitizing potential of GFT has been assessed by means of NRU assays and protein photooxidation. In addition, a thorough photophysical study is presented based on ultrafast transient absorption spectroscopy, fluorescence and laser flash photolysis. Transient species generated after excitation of GFT have been characterized in solution and in biological environments (i.e. HSA and HaCaT cells) to gain insight into the mechanisms involved in photodamage. The photobehavior of GFT was strongly medium-dependent. Excitation of the drug resulted in the formation of locally excited (LE) singlet states (1GFT*), which were found to be the main emissive species in non-polar solvents and also within HSA and HaCaT cells. By contrast, in polar solvents, LE states rapidly evolved (∼1 ps) towards the formation of longer-lived intramolecular charge transfer (ICT) states. The triplet excited state of GFT (3GFT*) can be formed through intersystem crossing from 1GFT* in non-polar solvents and from ICT states in the polar ones, or in the particular case of ethanol, by photosensitization using 2-methoxyacetophenone as an energy donor. In the HSA environment, 3GFT* was hardly detected due to quenching of its LE 1GFT* precursor by Trp through an electron transfer process. Accordingly, HSA photooxidation by GFT was demonstrated using the protein carbonylation method. In summary, a good correlation is established between the photophysical behavior and the photobiological properties of GFT, which provides a mechanistic basis for the observed phototoxicity.