Synthesis and development of novel metallodrugs based on benzimidazole with therapeutic activity towards cancer and Alzheimer's disease

Abstract

The aim of this work has been the design of new precious metal-based drugs containing benzimidazole-based ligands with a handle for functionalization. The work methodology is divided in four different steps. First of all, we design and synthesize the new compounds, which are characterized by mass spectrometry, elemental analysis, NMR spectroscopy and X-ray diffraction. Secondly, their stability in DMSO and pseudo-physiological conditions is studied by NMR, RP-HPLC or absorption spectroscopy. Next, their antitumor activity is evaluated in different human cancer cell lines; sensitive (A2780) and cisplatin resistant (A2780cisR) ovarian carcinoma cells are commonly employed. Finally, their mechanisms of action were studied. In addition, theoretical calculations QC were undertaken in the case of some ruthenium models. In Chapter 2 smart design and efficient synthesis of half-sandwich benzimidazole Ru(II), Ir(III) and Rh(III) cyclometalated complexes with an ester as a handle for functionalization of the types [(?6-p-cymene)RuCl(?2-N,C-L)], [(?5-C5Me5)IrCl(?2-N,C-L)] and [(?5-C5Me5)RhCl(?2-N,C-L)] (HL = methyl 1-alkyl-2-phenylbenzimidazolecarboxylate) are reported with promising cytotoxic activity. In Chapter 3 butyl substituent on benzimidazole metal compounds was used for further structure-activity relationship SAR study. It described divergent synthesis of novel C^N cyclometalated benzimidazole ruthenium(II), osmium(II) and iridium(III). Phenyl ring on benzimidazole was most derivatized by different substituent like electron donating substituents (OCH3), electron withdrawing substituents (NO2), aromatic substituents (Ph), neutral substituents (H, CH3) as well as fluoro substituent (F, CF3) of benzimidazole ruthenium as well as analogues of iridium and osmium complexes. The cytotoxic activity of the new Ru(II), Os(II) and Ir(III) compounds has been evaluated in a panel of human cancer cell lines in order to establish a SAR in these families of compounds. Phenyl substitution shows increased potency in Ru, Os and Ir complexes as compared to their parent compounds in all cell lines. In general, ruthenium complexes are more active than the corresponding iridium complexes. In addition, some of the metal complexes effectively inhibit angiogenesis in the human umbilical vein endothelial cell line EA.hy926, with the ruthenium derivatives with R2 = Ph and CF3 substituents being the best performers. In order to study the effect of aromaticity on the activity of the above complexes we have succeeded in chapter 4 on the synthesis of methyl 1-butyl-2-(naphthalen-2-yl)-1H-benzo[d]imidazole-5-carboxylate ruthenium, iridium and osmium derivatives, together with the 1-butyl-2-(pyren-1-yl)-1H-benzo[d]imidazole-5-carboxylate iridium and osmium derivatives. The heterocyclic aromaticity with extra contribution from hetero-atom was studied by selecting benzo[b]thiophen-2-yl as an aromatic partner with benzimidazole. The C^N cyclometalated benzimidazole linked to the benzothiophene Ru(II), Ir(III), and Os(II) compounds were synthesized. In chapter 5 we synthesized fifteen luminiscent heteroleptic Ir(III) antitumor agents of the type [Ir(C^N)2(N^N)][PF6]. The different N^N ligands were 2,2'-bipyridine, 1,10-phenanthroline, 2-(pyridin-2-yl)-1H-benzo[d]imidazole, methyl 1-butyl-2-(pyridin-2-yl)-1H-benzo[d]imidazole-5-carboxylate, and methyl 1-butyl-2-(isoquinolin-3-yl)-1H-benzo[d]imidazole-5-carboxylate. The new compounds show very high cytotoxicity in A2780 cells (81 and 86 being approximately 7x more cytotoxic than CDDP), and, interestingly, they are also very active towards the breast tumor cell lines MDA-MB-231 (approximately 100x more cytotoxic than CDDP in many cases), and MCF-7, while most of them show low toxicity in the non-tumorigenic BGM cells. According to confocal luminiscence imaging studies they were located in the actin cortex predominantly. These preliminary results have the potential to open up the door to a new large family of theranostic agents. We successfully synthesized in chapter 6 the Ir(III) compounds with short linear polyethylene glycol (PEG) linkers for conjugation to improve the lipophilicity and cytotoxicity. Moreover, benzimidazole Ir(III) complex functionalized with a dansyl fluorescence tag was efficiently synthesised for its cellular internalization studies. On the other hand, the synthesis of bis-cyclometalated C^N iridium(III) compounds functionalized with a dopamine group to make efficent and effective drugs. In chapter 7 we have effectively synthesised half-sandwich benzimidazole N^N precious metal complexes. 2-pyridyl-benzimidazole Ru, Ir and Pt compounds have already shown that they inhibit aggregation of A?1-42 in vitro as shown by both thioflavin T fluorescence assay and transmission electron microscopy. An iridium complex was able to rescue the toxicity of A?1?42 in primary cortical neurons effectively.