Data di Pubblicazione:
2011
Citazione:
APPROACHES OF MODULATION OF THERAPEUTIC TARGETS RELEVANT TO DRUG RESISTANCE / C. Giommarelli ; tutor: Nadia Zaffaroni ; direttore: Franco Zunino ; coordinatore: Alberto Panerai. Universita' degli Studi di Milano, 2011 Jan 17. 23. ciclo, Anno Accademico 2010. [10.13130/giommarelli-chiara_phd2011-01-17].
Abstract:
An emerging anticancer strategy is to identify molecular targets that when inhibited pharmacologically, result in pleiotropic downstream effects on pathways relevant to the malignant phenotype, with particular reference to the development of resistance. In recent years, the molecular chaperone Hsp90 has emerged as leading example of such a target-specific therapy. Heat-shock proteins are found at increased levels in many solid tumors and haematological malignancies. Their expression may account for the ability of malignant cells to maintain protein homeostasis even in the hostile hypoxic microenvironment of the tumor. Particularly, Hsp90 has emerged as a target for cancer therapy due to its critical roles in retaining the conformation and the function of its client proteins, many of which are associated with cancer pathology. There are 12 HSP90 inhibitors in clinical trials; all have potencies on the order of 7-35 nM in a cell-based assay and half-lives of 1-3 h in the plasma of rodents. These inhibitors may distribute preferentially to the tumors and may have longer half-lives in the tumors than in the plasma, as in the case of 17-AAG and its active metabolite. However, side effects and poor formulability of 17-AAG restricted its potential of clinical application and motivated many groups to synthesize new compounds. The aim of this project is to identify new Hsp90 inhibitors which could overcome the limitations of available inhibitors and exhibit therapeutic advantages in terms of specificity, therapeutic index and antitumor efficacy. Several compounds have been tested during these years, especially a series of mold metabolites of Ascomycetes, structurally belonging to the class of azaphilones, were found to inhibit the heat shock protein Hsp90. In particular, bulgarialactone B was tested for its binding to Hsp90 using surface plasmon resonance and limited proteolysis assays and for its effects on Hsp90 client proteins expression in a series of human tumor cell lines. This compound showed high affinity for Hsp90, interacting with the 90–280 region of the N-terminal domain and down-regulated the Hsp90 clientproteins Raf-1, survivin, Cdk4, Akt, and EGFR. Bulgarialactone B and other natural azaphilones showed antiproliferative activity in a panel of human tumor cell lines; their conversion into semisyntheticderivatives by reaction with primary amines increased the antiproliferative activity. Preliminary results indicated in vivo activity of bulgarialactone B against an ascitic ovarian carcinoma xenograft, thus supporting the therapeutic potential of this novel series of Hsp90 inhibitors. Moreover, to identify favourable interactions between Hsp90 inhibitors and target-specific agents, combinations between curcumin and two well-known HDAC inhibitors (vorinostat and panobinostat), have been tested. Curcumin, a natural polyphenol, has been described to exhibit effects on signaling pathways, leading to induction of apoptosis. In this study, we observed that curcumin inhibited Hsp90 activity causing depletion of client proteins implicated in survival pathways. Based on this observation, the study was designed to investigate the cellular effects of curcumin combination with the pan- HDAC inhibitors, vorinostat and panobinostat, which induce hyperacetylation of Hsp90, resulting in inhibition of its chaperone function. The results showed that, at subtoxic concentrations, curcumin markedly sensitized tumor cells to vorinostat- and panobinostat-induced growth inhibition and apoptosis. The sensitization was associated with persistent depletion of Hsp90 client proteins (EGFR, Raf-1, Akt, and survivin). In conclusion, our findings document a novel mechanism of action of curcumin and support the therapeutic potential of curcumin/HDAC inhibito
Tipologia IRIS:
Tesi di dottorato
Keywords:
targeted anticancer therapy ; GGT ; Hsp90
Elenco autori:
C. Giommarelli
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