Photoactivatable platinum (IV) anticancer complexes

In this work, trans-diazido Pt(IV) complexes with general formula [Pt(N3)2(OH)(OCOR)(pyr)2] (where OCOR is a carboxylate axial ligand) and [Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are aromatic N-heterocyclic ligands) have been synthesised and characterised. The chemical and photochemical properties of these complexes, as well as their photobiological behaviour, have been studied in order to check their potential as photoactivatable anticancer drugs. Four trans-diazido Pt(IV) complexes with general formula trans, trans, trans-[Pt(N3)2(OH)(OCOR)(pyr)2] (OCOR= succinate, 4-oxo-4-propoxybutanoate, Nmethylisatoate and succinate-(RGD)f peptide ligands) have been obtained by axial derivatisation of one hydroxido ligand from trans, trans, trans-[Pt(N3)2(OH)2(pyr)2]. The crystal structures of three axially-derivatised complexes have been determined by X-ray diffraction. Photoirradiation studies have shown an improved photoactivity of the carboxylate versus the dihydroxido complexes at the longer wavelengths. Release of the axial ligands was observed in the studied complexes. This fact is especially relevant in the case of the Pt(IV)-(cRGD)f complex, where the RGD was incorporated as a tumour cell targeting moiety. DFT-TDDFT calculations performed on the complex trans, trans, trans-[Pt(N3)2(OH)(Succ)(pyr)2] showed dissociative transitions at longer wavelength, which could explain the photolability observed in these carboxylate derivatives. Studies of photoactivation of the diazido Pt(IV) complexes in the presence of 5’-GMP indicate the formation of a mono-GMP Pt(II) adduct as main photoproduct, therefore DNA could be considered a potential target site for these anticancer compounds. Additionally, EPR studies showed that azidyl radical release was observed when complexes bearing the succinate and 4-oxo-4-propoxybutanoate ligands were irradiated with green light. No such result was obtained for the dihydroxo precursor showing that these complexes could be phototoxic with longer wavelength light activation. Seven trans-diazido Pt(IV) complexes, trans, trans, trans-[Pt(N3)2(OH)2(L1)(L2)] (where L1 and L2 are pyridine, 2-picoline, 3-picoline, 4-picoline, thiazole or 1-methylimidazole ligands), have been obtained by oxidation of the corresponding trans-[Pt(N3)2(L1)(L2)] precursor. The X-ray crystal structures have been determined for four Pt(IV) diazido complexes from this family of compounds. Photoirradiation studies indicate that the incorporation of a sterically demanding ligand, e.g. trans, trans, trans-[Pt(N3)2(OH)2(2-pic)(pyr)], greatly enhances the photoactivity in these complexes. DFT-TDDFT calculations are in agreement with these results, since higher intensity transitions were observed for such complex at longer wavelength. Phototoxicity studies carried out on A2780, A2780cis and OE19 cell lines with the trans, trans, trans-[Pt(N3)2(OH)2(pyridine)(n-picoline)] family concluded that steric hindrance close to the platinum centre does not favour phototoxicity. Most of the complexes were equally potent in cisplatin resistance against the ovarian cancer cell line (A2780cis), except [Pt(N3)2(OH)2(3-pic)2] and [Pt(N3)2(OH)2(4-pic)2] which exhibited some cross resistance. All of the complexes tested in both OE19 and A2780 cell lines have shown less sensitivity to OE19 than to A2780. Studies in S. pombe yeast strains (WT and ΔRad3) with trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] suggest that DNA is potentially an important target for this type of compounds, although other targets are not excluded. Furthermore, live-cell confocal microscopy was performed on A2780 cells treated with the complex trans, trans, trans-[Pt(N3)2(OH)2(pyr)2] and irradiated with a low dose of blue light. The cell death, monitored by propidium iodide uptake, was captured occurring 2 h 30 min post activation

Platinum(iv) azido complexes undergo copper-free click reactions with alkynes

We report our investigations into the first examples of copper-free 1,3-dipolar cycloaddition (click) reactions of electrophiles with a PtIV azido complex. The Pt-IV azido complex trans, trans, trans-[PtIV(py)2(N3)2(OH)2] (1) was reactive towards dimethyl acetylenedicarboxylate (DMAD) (2), diethyl acetylenedicarboxylate DEACD (3), N-[(1R,8S,9s)-bicyclo[6.1.0]non-4-yn-9-ylmethyloxycarbonyl]-1,8-diamino-3,6-dioxaoctane (BCN) (11) and dibenzocyclooctyne-amine (DBCO) (12) resulting in formation of the corresponding mono (a) and bis-substituted (b) complexes. Complexes of 2 undergo further reactions between the Pt centre and the carbonyl group to form 2a′ and 2b′. This is not seen for the products of the corresponding PtII azido complex trans-[Pt(py)2(N3)2] with acetylene 2. Novel complexes 2a′, 2b′, 11a and 11b have been characterised by multinuclear NMR, IR and UV-vis spectroscopy and ESI-MS. These reactions represent new synthetic routes to novel Pt(IV) complexes

An integrin-targeted photoactivatable Pt(IV) complex as a selective anticancer pro-drug: synthesis and photoactivation studies

A new anticancer agent based on the conjugation of a photoactivatable Pt(IV) pro-drug to a cyclic RGD-containing peptide is described. Upon visible light irradiation, phototoxicity was induced preferentially in SK-MEL-28 melanoma cancer cells overexpressing alphaVbeta3 integrin compared to control DU-145 human prostate carcinoma cells

Platinum(IV)-azido monocarboxylato complexes are photocytotoxic under irradiation with visible light

Complexes trans,trans,trans-[Pt(N-3)(2)(OH)(OCOR)(py)(2)] where py = pyridine and where OCOR = succinate (1); 4-oxo-4-propoxybutanoate (2) and N-methylisatoate (3) have been synthesized by derivation of trans, trans,trans-[Pt(OH)(2)(N-3)(2)(py)(2)] (4) and characterised by NMR and EPR spectroscopy, ESI-MS and X-ray crystallography. Irradiation of 1-3 with green (517 nm) light initiated photoreduction to Pt(II) and release of the axial ligands at a 3-fold faster rate than for 4. TD-DFT calculations showed dissociative transitions at longer wavelengths for 1 compared to 4. Complexes 1 and 2 showed greater photocytotoxicity than 4 when irradiated with 420 nm light (A2780 cell line IC50 values: 2.7 and 3.7 mu M) and complex 2 was particularly active towards the cisplatin-resistant cell line A2780cis (IC50 3.7 mu M). Unlike 4, complexes 1-3 were phototoxic under green light irradiation (517 nm), with minimal toxicity in the dark. A pK(a)(H2O) of 5.13 for the free carboxylate group was determined for 1, corresponding to an overall negative charge during biological experiments, which crucially, did not appear to impede cellular accumulation and photocytotoxicity.NF thanks the Wellcome Trust (201406/Z/16/Z); Cancer Research UK (CR-UK) grant number C5255/A18085 through the Cancer Research UK Oxford Centre and the John Fell Fund for funding. NF thanks Profs. Stephen Faulkner for support. PJS and NF thank the EPSRC (for grant EP/P030572/1 and studentship for ES), PJS also thanks the ERC (grant 247450). L. S. performed this work under the Severo Ochoa Centres of Excellence Programme run by the Spanish State Research Agency, grant no. CEX2018-000867-S (DIPC). L. S. also thanks the Spanish Multi-MetDrugs network (RED2018-102471-T) for fruitful discussio

Comprehensive vibrational spectroscopic investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) diazido anticancer prodrug candidate

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules

An integrin-targeted photoactivatable Pt(iv) complex as a selective anticancer pro-drug: Synthesis and photoactivation studies

A new anticancer agent based on the conjugation of a photoactivatable Pt(iv) pro-drug to a cyclic RGD-containing peptide is described. Upon visible light irradiation, phototoxicity was induced preferentially in SK-MEL-28 melanoma cancer cells overexpressing αVβ3 integrin compared to control DU-145 human prostate carcinoma cell

Sequence-dependent attack on peptides by photoactivated platinum anticancer complexes.

Octahedral platinum(iv) complexes such as trans,trans,trans-[Pt(N3)2(OH)2(pyridine)2] (1) are stable in the dark, but potently cytotoxic to a range of cancer cells when activated by UVA or visible light, and active in vivo. Photoactivation causes the reduction of the complex and leads to the formation of unusual Pt(ii) lesions on DNA. However, radicals are also generated in the excited state resulting from photoactivation (J. S. Butler, J. A. Woods, N. J. Farrer, M. E. Newton and P. J. Sadler, J. Am. Chem. Soc., 2012, 134, 16508-16511). Here we show that once photoactivated, 1 also can interact with peptides, and therefore proteins are potential targets of this candidate drug. High resolution FT-ICR MS studies show that reactions of 1 activated by visible light with two neuropeptides Substance P, RPKPQQFFGLM-NH2 (SubP) and [Lys]3-Bombesin, pEQKLGNQWAVGHLM-NH2 (K3-Bom) give rise to unexpected products, in the form of both oxidised and platinated peptides. Further MS/MS analysis using electron-capture dissociation (ECD) dissociation pathways (enabling retention of the Pt complex during fragmentation), and EPR experiments using the spin-trap DEPMPO, show that the products generated during the photoactivation of 1 depend on the amino acid composition of the peptide. This work reveals the multi-targeting nature of excited state platinum anticancer complexes. Not only can they target DNA, but also peptides (and proteins) by sequence dependent platination and radical mechanisms

Data for Comprehensive vibrational spectroscopic investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) diazido anticancer prodrug candidate

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules