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Title: Synthesis and evaluation of new metal-porphyrin conjugates for biomedical application
Authors: Spagnul, Cinzia
Keywords: porphyrin, photodynamic therapy, 99mTc-porphyrins conjugates, Re-porphyrin conjugates, Ru-porphyrin conjugates
Issue Date: 26-Mar-2012
Publisher: Università degli studi di Trieste
Abstract: This thesis reports the synthesis, the characterization and the biological evaluation of new classes of metal-porphyrin conjugates for potential bio-medical applications. [Ru([9]aneS3)(N-N)(L)][X]n where N-N = nitrogen chelating ligand such as ethane-1,2- diamine (en) orbpy, L = S-dmso, Cl and X = CF3SO3 or PF6, n = 2 or 1 respectively), [Ru([9]aneN3)(dmso-S)2Cl]Cl, fac-[99mTc (CO)3(H2O)3]+ and [NEt4]2 fac-[ReBr3(CO)3] were chosen as metal fragments. In the first section we describe different synthetic approaches to the preparation of porphyrin conjugates with Ru(II) coordination compounds. Ru (II) fragments were chosen they have shown a promising anticancer activity both in vitro and in vivo, in murine models. Water solubility in an important feature for biomedical application but usually porphyrins are fairly or not water soluble. The conjugation of a metal fragment to a porphyrin, beside increasing the solubility of the porphyrin macrocycle, is an intriguing alternative for making water soluble compounds that are expected to combine the cytotoxicity to the metal fragment to the phototoxicity of the porphyrins for an additive antitumor effect. We varied the number and charge of the peripheral Ru fragments, and described conjugates whose total charge ranges from +4 to +8. We showed that the connection can occur through a single coordination bond (N(pyridyl)–Ru) or through multiple coordination bond (through a chelating bpy unit). We demonstrated that meso-pyridylporphyrins (PyPs), besides being synthetically more affordable, allow to tune the geometry of the conjugates. We showed that in the series of porphyrins with peripheral bpy units at meso positions, it is possible to vary the metal fragment and the length and the flexibility of the connectors between the bpyAc peripheral moieties and the meso C atoms to obtain compounds with different solubility Finally some or those conjugates were evaluated as potential PDT agents. Singlet oxygen quantum yield was evaluated for all of them as useful parameter. The in vitro cell growth inhibition of some of such conjugates toward MDA-MB-231 human breast cancer cells and HBL-100 human non tumorigenic epithelial cells are reported, together with their phototoxic effects onMDAMB-231 cells. All conjugates have IC50 values in the low micromolar range that decrease by 1 order of magnitude upon irradiation of cell cultures with visible light. This make them promising for PDT of cancer. In the second section we describe the first example of 99mTc – porphyrins conjugates where the connection between the metal fragment and the porphyrins macrocycle occurred at the periphery of the cromophore, at meso position. In radiopharmaceutical chemistry it is common to compare the retention time in the HPLC in the radiochromatogram of the 99mTc conjugate with the UV-vis trace of the corresponding non-radioactive Re congener to confirm the success of the labeling and to characterize unambiguously the 99mTc-conjugate. By an accurate characterization of the water soluble porphyrinic precursors and of the Re(I) congeners, we were able to establish, for the first time, that only one [99mTc (CO)3]+ fragment is bounded at the periphery of the porphyrins. Furthermore, all the 99mTc/Re-porphyrin conjugates were obtained with high purity level and reasonable to good yields. The total charge ranges from +1 to +3. Stability studies performed by HPLC on the 99mTc-conjugates revealed an high stability under air at room temperature, in absence or presence of cells up to 30 minutes to 24 hours. Since natural and synthetic porphyrins and metalloporphyrins are the most useful photosensitizers for PDT, we decided to evaluate the water soluble porphyrinic precursors and the Re(I)-porphyrins conjugates as potential photosensitizers for PDT. The in vitro cell uptake, the cell growth inhibition toward HeLa cells are reported, together with their phototoxic effects on the same cell line. All conjugates revealed a negligible cytotoxicity (IC50 values higher than 100 mM) after 24 h of exposure. Those value decrease by 1 order or magnitude upon irradiation with visible light (590-700 nm) at mild light doses ( 5 J/cm2). We found that compounds uptake after 24h exposure is significantly different, and it does not affect appreciably their cytotoxicity. On the contrary, the phototoxicity is directly related to the ability of the compounds to penetrate cells. They proved to have from moderate to good singlet oxygen quantum yields and high photostability. Taken together, those results make them promising for PDT of cancer.
Description: 2010/2011
NBN: urn:nbn:it:units-4455
Appears in Collections:Scienze chimiche

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