Role of the cyclin-dependent kinases p21CDKN1A inhibitor in the DNA repair processes in human cells
The DNA must be replicated and transmitted properly to avoid genomic instability, pathogenetic basis of several human diseases, such as cancer; to this end, cells have developed a complex system to monitor and signal DNA damage (checkpoints), and DNA repair systems.
For many years the laboratory research has been directed to some proteins that regulate the cell cycle, and appear also to be involved in the DNA repair processes. Among these proteins, the cyclin-dependent kinase inhibitors p21CDKN1A plays a very important role in cell cycle control, mainly in the “checkpoint” of G1 phase and in the inhibition of DNA synthesis by associating with PCNA, a cofactor necessary for the activity of many enzymes involved in the DNA metabolism. Recently, our research has demonstrated that p21, in cooperation with p27, an important member of CDK-inhibitor family, is involved in the induction in controlling the entry / exit from the temporary cell cycle (quiescence). In addition, p21 appear to promote the efficiency of DNA repair processes, like the Nucleotide Excision Repair (NER). In fact, p21 is required to regulate the activity of histone acetyltransferase (HAT) p300 in modulating the interaction with PCNA. This function of p21 could influence the acetylation of other factors involved in NER. Among these, we are studying the protein that binds to damaged DNA (DDB2), which, combined with DDB1 in complex DDB plays a role in the recognition of DNA damage induced by UV in the Global Genome Repair (GGR-NER). Recently we have demonstrated that DDB2, a protein required for repair after DNA damage induced by ultraviolet radiation, co-localizes with both p21 and PCNA to DNA damage sites. In particular, DDB2 directly interact with PCNA and this binding is important for DDB2 degradation.
Biological activity of natural products and their synthetic derivatives
Since many years the main research of the laboratory has focused on biological activity of natural or synthetic derived compounds with a potential role in the prevention of human pathological processes, such as cancer. Our work have clarified the mechanism of action, through the identification of protein targets, of the antiproliferative and/or antioxidant effect of some natural agents, such as beta-carotene, anthocyanins and, more recently, stilbenes. In particular, in experiments with different synthetic derivatives of resveratrol, which is the most studies among the stilbenic compounds, we have demonstrated that the 4′-hydroxystyryl moiety of the molecule is the specific structural determinant required for the inhibition of cell proliferation, but not for antioxidant activity, which is dependent on the three-hydroxyl groups in the molecule. A potential mechanism underlying this antiproliferative activity seems to be related to its ability to block DNA synthesis, through inhibition of DNA polymerase. We are currently evaluating new synthetic analogues, and in particular 4,4′-dihydroxystilbene, containing two 4-hydroxystyryl moieties, which is more effective in inhibiting tumour proliferation, and thus with potential pharmacological interest.
Fluoroquinolones as potential photodynamic agents in cancer therapy
A second research project currently in progress aims at evaluating the biological activity of new compounds that have a fluoroquinolone-based structure for their use as photodynamic therapy, with the main goal to investigate their mechanisms of action (cell localization, DNA adducts formation, apoptosis). The fluoroquinolone drugs widely used in broad-spectrum antibiotic therapy, but that could be applied in photodynamic therapy targeted to destroy only the cells of some epithelial tumors after localized irradiation. The exact mechanism underlying the photoreactivity of fluoroquinolones remains poorly defined, but the interesting thing is that some of them are active even in the absence of oxygen: if this mechanism, shown in studies chemical is reproducible even in tissues and organs, may be advantageous to use these molecules in cancer therapy, since the tumor mass has a very low oxygen partial pressure.