Synthesis and anticancer activity evaluation of η(5)-C5(CH3)4R ruthenium complexes bearing chelating diphosphine ligands.

Dalton Transactions View Article Online View Journal Accepted Manuscript This article can be cited before page numbers have been issued, to do this please use: A. RodríguezBárzano, R. M. Lord, A. M. Basri, R. M. Phillips, J. Blacker and P. C. McGowan, Dalton Trans., 2015, DOI: This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/dalton Page 1 of 4 Dalton Transactions View Article Online DOI: 10.1039/C4DT02748E RSCPublishing Journal Name Cite this: DOI: 10.1039/x0xx00000x Received 00th January 2012, Accepted 00th January 2012 Synthesis and anticancer activity evaluation of η5C5(CH3)4R ruthenium complexes bearing chelating diphosphine ligands† A. Rodríguez-Bárzano,a R. M. Lord,a A. M. Basri,a R. M. Phillips,b A. J. Blackera and P. C. McGowan*a DOI: 10.1039/x0xx00000x www.rsc.org/ The complexes [RuCp*(PP)Cl] (Cp* = C5Me5; [1], PP = dppm; [4], PP = Xantphos), [RuCp#(PP)Cl] (Cp# = C5Me4(CH2)5OH; [2], PP = dppm; [5], PP = Xantphos) and [RuCp*(dppm)(CH3CN)][SbF6] [3] were synthesized and evaluated in vitro as anticancer agents. Compounds 1-3 gave nanomolar IC50 values against normoxic A2780 and HT-29 cell lines, and were also tested against hypoxic HT-29 cells, maintaining their high activity. Complex 3 yielded an IC 50 value of 0.55 ± 0.03 µM under a 0.1% O 2 concentration. Numerous organometallic (η6-arene)-ruthenium complexes have been screened as anticancer agents with promising results, for instance, compounds of the types [(η6-arene)Ru(NN)Cl]+ (NN = chelating nitrogen ligands, especially ethylenediamine (en)),1-3 [(η6arene)Ru(NO)Cl] (NO = 3′-fluorophenyl-3-(phenylamino)-2-buten1-one),4 [(η6-arene)Ru(OO)X] (OO = 3-hydroxyflavone derivatives, X = Cl, Br or I)5, 6 or [(η6-arene)Ru(pta)Cl2] (RAPTA) (pta = 1,3,5triaza-7-phosphatricyclo [3.3.1.1] decane).7, 8 Samuelson and coworkers have published the use of η6-p-cymene ruthenium complexes with different diphosphines acting as either monodentate or chelating ligands, which showed good growth inhibitions against several cancer cell lines.9 In contrast, fewer examples of η5cyclopentadienyl (Cp) or pentamethylcyclopentadienyl (Cp*) compounds have been biologically evaluated. Sava reported the synthesis and activity against TS/A adenocarcinoma of the compounds [(η5-C5H5)Ru(pta)2Cl] and [(η5-C5Me5)Ru(pta)2Cl], as equivalents to the RAPTA complexes.10 Compounds of the type [(η5C5H5)Ru(PP)L][X] (PP = 2 × PPh3 or 1,2bis(diphenylphosphino)ethane, L = planar nitrogen σ-bonded ligand and X = CF3SO3 or PF6) have been synthesised by Moreno et al. and some of them show better cytotoxicities than cisplatin. 11-13 However, none of these Cp/Cp* ruthenium complexes has been tested under hypoxic conditions. Some diphosphines have demonstrated cytotoxicity against various cell lines,14 but it has been observed that, upon coordination to metals, diphosphines produce complexes with improved anticancer activity compared to the free ligands; a general hypothesis considers that the metal protects the ligands from oxidation before they interact with the corresponding biological target.15 This journal is © The Royal Society of Chemistry 2012 Here we present the results obtained from cell line assays carried out under normoxic and hypoxic conditions with ruthenium complexes containing chelating diphosphine ligands such as 1,1bis(diphenylphosphino)methane (dppm) and 4,5bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos). The complexes have general structures [RuCp*(PP)Cl] (1, PP = dppm; 4, PP = Xantphos), [RuCp#(PP)Cl] (Cp# = C5Me4(CH2)5OH; 2, PP = dppm; 5, PP = Xantphos) and [RuCp*(PP)(CH3CN)][SbF6] (3, PP = dppm). We investigated the biological activity of both ligands and the effect of complexation. We were interested in assessing the impact of hydrophilic functionalisation of Cp* with an ‒OH group and the different cytotoxicities shown by analogous neutral and charged complexes. The anticancer activities were assessed against A2780 and HT-29 cell lines, for HT-29 both at 21% and 0.1% O2 (hypoxic conditions) concentrations. Complexes 1 and 4 were synthesised from [RuCp*Cl2]2, which was obtained following literature methods.16, 17 A similar method was employed for compounds 2 and 5, starting from the novel [RuCp#Cl2]2 complex (Scheme 1). This in turn was prepared by reaction of (5-hydroxypentyl)-tetramethylcyclopentadiene18 with RuCl3 in ethanol at reflux. Compounds 119, 20 and 421 had been previously reported, but not biologically tested. Complex 3 was obtained from complex 1, acetonitrile and NaSbF6 in methanol at room temperature (Scheme 2). This method was adapted from the published synthesis of [RuCp*(PP)(CH3CN)][PF6] complexes, where PP = chiral diphosphines.22 The structure of complex 3 was determined by single crystal X-ray diffraction. Compound 3 crystallised in a triclinic cell from pentane/chloroform, and the structural solution was performed in the space group P̅. The asymmetric unit comprises one molecule of compound 3, including the counterion SbF6. The molecular structure of 3 is shown in Figure 1 and selected bond lengths and angles are given in Table 1. Compound 3 presents the characteristic piano-stool geometry typical of η5- and η6-organometallic ruthenium species. The N(1)-C(11) triple bond length is 1.153(2) Å. The cytotoxic activities of compounds 1-5, along with cisplatin, dppm and Xantphos were tested on the A2780 and HT-29 cell lines after five-day exposures at 37 ºC and 21% O2. The IC50 results are shown in Table 2. The most active complexes were those formed from dppm, 1, 2 and 3, all with better cytotoxicities, in the nanomolar range, than cisplatin for both HT-29 and A2780 cell lines. J. Name., 2012, 00, 1-3 | 1 Dalton Transactions Accepted Manuscript Published on 05 January 2015. Downloaded by UNIVERSITY OF OTAGO on 06/01/2015 14:01:09. COMMUNICATION View Article Online Dalton Transactions Page 2 of 4 DOI: 10.1039/C4DT02748E Dppm was active by itself, with IC50 values below 1.5 µM. However, 1H and 31P NMR spectroscopy experiments in deuterated DMSO showed no de-coordination of dppm from complexes 1 and 3 after five days. The observation that diphosphines do not dissociate is further reinforced by the fact that complexes 4 and 5 gave moderate to good activities, which are not due to a possible release of the ligand, because Xantphos did not show anticancer behaviour on its own. This contradicts the previous hypothesis that the activities of these types of diphosphine complexes depend on possible de-coordinations of the ligands.15 The extremely different behavior of dppm and Xantphos provides interesting material for further future studies. Complexes 4 and 5 were more active against A2780 cells, with IC50 values close to cisplatin. The presence of the (CH2)5OH chain in the Cp# compounds 2 and 5 produced no great effect on their anticancer activities, compared to those of the Cp* complexes 1 and 4. The best cytotoxicity was observed for the positively charged complex 3. Scheme 1. General synthesis of complexes 1, 2, 4 and 5. Scheme 2. Synthesis of complex 3. Journal Name Fig. S1 in the ESI). The new species formed, after five days, in 48% yield from complex 1 and in 67% yield from complex 3. Mass spectrometry of this new species showed the same peaks observed for the chloride complex 1, where the chloride ligand was lost. By inference, the new species is believed to be the aqua species, which entails that monocationic complex 3 hydrolyses to a higher extent under the same conditions, and this coincides with its higher anticancer activity. Table 1. Selected bond lengths [Å] and angles [°] in the structure of compound 3 with s.u.s. in parenthesis. Ru(1)-N(1) Ru(1)-P(1) Ru(1)-P(2) N(1)-C(11) C(11)-C(12) Ru(1)-Ring Centroid Ru(1)-C(Cp*) P(1)-Ru(1)-P(2) N(1)-C(11)-C(12) C(11)-N(1)-Ru(1) P(2)-C(13)-P(1) 2.0775(16) 2.3201(6) 2.3503(6) 1.153(2) 1.481(3) 1.884 2.25226 71.626(19) 178.5(2) 178.90(16) 93.53(8) Table 2 gives the IC50 results obtained for the most active compounds 1-3 against hypoxic HT-29 cells at an oxygen concentration of 0.1%. Cancerous cells are known to proliferate within hypoxic environments, with oxygen content below 2%, 24 therefore hypoxic experiments tend to reproduce the conditions found in human solid tumours. Apart from cisplatin, whose activity remains practically unmodified, tirapazamine, a drug known to be hypoxia sensitive, 25 was also employed as reference. Interestingly, the IC 50 of dppm under hypoxic conditions increased considerably from 1.47 µM to 17.19 µM. A possible explanation for this is that the active species might be an oxidized form of dppm. However, Samuelson et al. have reported that, while dppm is moderately active against H460 lung cells (IC50 = 18.2 μM), mono-oxidised dppm shows no cytotoxic activity (IC50 > 250 μM),9 and similar conclusions had been drawn by Sadler et al.14 The activities of complexes 13 improved slightly at a low O2 concentration. Complex 3 showed again the best performance, with an IC 50 of 0.55 ± 0.03 µM, and is of particular significance and interest. Table 2. IC50 values for complexes 1-5 along with cisplatin, tirapazamin, dppm and Xantphos. The drugs were incubated for 5 days at 37 ºC. IC50 (µM) at 0.1% O2 IC50 (µM) at 21% O2 Figure 1. ORTEP structure of complex 3 (cation) with thermal ellipsoids set at 50% probability. Hydrogen atoms omitted for clarity. To assess the extent of hydrolysis 23 in complexes 1 and 3, 10 mM samples of both complexes in 0.6 ml of deuterated solvent (90% deuterated DMSO + 10% deuterium oxide) were prepared in NMR tubes and analysed by 1H NMR spectroscopy every 24 hours during five days at room temperature. A new set of peaks at 5.14 and 1.61 ppm appeared gradually in both samples (see 2 | J. Name., 2012, 00, 1-3 Compound A2780 ± HT-29 ± HT-29 ± Cisplatin 1.4 0.3 2.52 0.09 2.4 0.4 Tirapazamine - - 31 3 2.8 0.4 dppm 1 1 1.47 0.02 17.19 0.08 1 1.1 0.2 0.73 0.05 0.66 0.03 2 0.9 0.1 0.791 0.007 0.76 0.03 3 0.70 0.02 0.61 0.01 0.55 0.03 Xantphos >250 - >250 - - - 4 3.6 0.4 10.1 0.5 - - 5 4.0 0.3 11.9 0.7 - - This journal is © The Royal Society of Chemistry 2012 Dalton Transactions Accepted Manuscript Published on 05 January 2015. Downloaded by UNIVERSITY OF OTAGO on 06/01/2015 14:01:09. COMMUNICATION Dalton Transactions View Article Online DOI: 10.1039/C4DT02748E Journal Name COMMUNICATION Conclusions 11. M. H. Garcia, T. S. Morais, P. Florindo, M. F. M. Piedade, V. Moreno, C. Ciudad and V. Noe, J. Inorg. Biochem., 2009, 103, 354-361. 12. V. Moreno, J. Lorenzo, F. X. Avilés, M. H. Garcia, J. P. Ribeiro, T. S. Morais, P. Florindo and M. P. Robalo, Bioinorg.Chem. Appl., 2010, 1-11. 13. V. Moreno, M. Font-Bardia, T. Calvet, J. Lorenzo, F. X. Avilés, M. H. Garcia, T. S. Morais, A. Valente and M. P. Robalo, J. Inorg. Biochem., 2011, 105, 241-249. 14. S. J. Berners-Price, R. E. Norman and P. J. Sadler, J. Inorg. Biochem., 1987, 31, 197-209. 15. S. J. Berners-Price, C. K. Mirabelli, R. K. Johnson, M. R. Mattern, F. L. McCabe, L. F. Faucette, C.-M. Sung, S.-M. Mong, P. J. Sadler and S. T. Crooke, Cancer Res., 1986, 46, 5486-5493. 16. N. Oshima, H. Suzuki and Y. Moro-Oka, Chem. Lett., 1984, 13, 1161-1164. 17. T. D. Tilley, R. H. Grubbs and J. E. 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In summary, a series of Cp*-based diphosphine ruthenium complexes (1-5) was prepared and biologically tested against A2780 and HT-29 cancerous cell lines. Both normoxic and hypoxic studies showed activities in the nanomolar range. The best anticancer activity was obtained with complex 3, which maintained a low IC50 value even under hypoxic conditions with 0.1% O2 concentration, and showed a higher degree of hydrolysis than its neutral analogue 1 under the same conditions. Future studies could include cationic versions of 2, 4, 5 and similar complexes to check whether they are generally more effective. Testing other free and coordinated phosphines and phosphine oxides could shed some light on the effect that the oxidation state and structure of the ligand have on cytotoxic activity. Notes and references a School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK. Fax: +44 (0)113 343 6565; Tel: +44 (0)113 343 6404; Email: P.C.McGowan@leeds.ac.uk b The Institute of Cancer Therapeutics, University of Bradford, Bradford, BD7 1DP, UK. Fax: +44 (0)127 423 3234; Tel: +44 (0)127 423 5367; Email: R.M.Phillips@bradford.ac.uk † We wish to acknowledge Technology Strategy Board for funding. Electronic Supplementary Information (ESI) available: experimental procedures for compounds, cell line experimental and crystal structure determination details (CCDC 957987). See DOI: 10.1039/c000000x/ 1. R. E. Morris, R. E. Aird, P. del Socorro Murdoch, H. Chen, J. Cummings, N. D. Hughes, S. Parsons, A. Parkin, G. Boyd, D. I. Jodrell and P. J. Sadler, J. Med. Chem., 2001, 44, 3616-3621. 2. A. Habtemariam, M. Melchart, R. Fernández, S. Parsons, I. D. H. Oswald, A. Parkin, F. P. A. Fabbiani, J. E. Davidson, A. Dawson, R. E. Aird, D. I. Jodrell and P. J. Sadler, J. Med. Chem., 2006, 49, 6858-6868. 3. S. J. Dougan and P. J. Sadler, Chimia Int. J. 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Name., 2012, 00, 1-3 | 3 Dalton Transactions Accepted Manuscript Published on 05 January 2015. Downloaded by UNIVERSITY OF OTAGO on 06/01/2015 14:01:09. Page 3 of 4 Published on 05 January 2015. Downloaded by UNIVERSITY OF OTAGO on 06/01/2015 14:01:09. 81x41mm (300 x 300 DPI) Dalton Transactions Accepted Manuscript Dalton Transactions View Article Online Page 4 of 4 DOI: 10.1039/C4DT02748E