Summary

Benzimidazoles are members of a group of heterocyclic compounds extensively used in the treatment of diseases in human and veterinary medicine. They are commonly used as anti-helmintic, anti-nematode and anti-protozoal agents. In addition, many of them have found application as fungicides in the post-harvest treatment of fruits and vegetables. In the last years, the anti-cancer activity presented by several members of the benzimidazole family has attracted considerable attention. Benzimidazoles are frequently used in form of cyclodextrins inclusion complexes, due to their low solubility in water, in order to enhance their bioavailability. 
Colchicine is a natural tricyclic alkaloid used in the treatment of gout, rheumatism and Mediterranean fever. Its efficacy as a neurotoxin in the research on epilepsy and Alzheimer´s disease has also been studied. Recently, colchicine has received considerable attention in cancer research due to its potential activity.
The anti-cancer properties of both, benzimidazoles and colchicine, are thought to result from their ability to interfere in tubulin polymerization and, as a consequence, in the process of mitosis. However, the exact mechanism of action is not well understood. Currently, there are several ongoing studies on the possible use of these drugs in cancer research. 
The aim of the present investigation on agents capable to inhibit tubulin polymerization is to gain insight into the mechanism of their interactions with tubulin. The understanding of drug-protein interactions, is crucial to explain the bio-distribution, metabolism, elimination and pharmacological effect of drugs in human organism.
For this reason, laser flash photolysis has been used here to study interactions between excited anti-mitotic agents (benzimidazoles and colchicines) and proteins or cyclodextrins, which are important to enhance solubility of various drugs including benzimidazoles. 
This technique is capable to provide information about the nature of drug/protein interactions (binding domain, distribution etc.). 
Unlike the other commonly employed methods, laser flash photolysis is very sensitive, requires low concentration of substrates as well as short adcquisition times and provides highly reproducible results. 
Generally, little is known about the singlet excited state of benzimidazoles and colchicines, while there is no data on the corresponding triplet excited states. In a first stage, photophysical and photochemical characterization of the selected compounds has been undertaken. Thus, the triplet excited states of 
2-aminobenzimidazole, thiabendazole and lumicolchicineshave been characterized. In the last case, the the strategy has been based on the generation in situ through the isomerization of colchicine. Besides, aminyl radical of 2-aminobenzimidazole has been identified and its formation has been used as a probe for mechanistic studies on reactivity between triplet excited state of different aromatic ketons and 2-aminobenzimidazole. 
The second research phase consisted of the evaluation of the use of transient species derived from these drugs as probes for studies of their interactions with biomolecules and cyclodextrins. Thus, the interactions of thiabendazole triplet excited state with cyclodextrins of a different size have been studied, while colchicine and lumicolchicines have been chosen for the study of their interaction with proteins. Human and bovine serum albumins were selected as model proteins.
Current efforts are directed to extend this methodology to study the interactions of benzimidazoles and colchicine with tubulin, in order to gain insight into the mechanism of action of antimitotic agents.