Derivatised phenanthroline transition metal chelates : targeted chemotherapeutic agents = I-Derivatised phenanthroline transition metal chelates: i-targeted chemotherapeutic agents

Abstract

The derivatisation of 1,10-phenanthroline at the 2-position afforded two classes of compounds with two different bridging groups in this study. The first group comprised two amide-bridged tetradentate N4-donor ligands and were chelated to copper(II), nickel(II) and palladium(II). The ligand chelation occurred with concomitant deprotonation of the amide N-H, resulting in a monoanionic ligand and monocationic complexes when coordinated to the divalent metal ions. The ligands N-(quinolin-8-yl)-1,10-phenanthroline-2-carboxamide, HL1, and N-(pyridin-2-ylmethyl)-1,10-phenanthroline-2-carboxamide, HL2, were characterised by NMR, IR and UV/vis spectroscopy as well as mass spectrometry. The second class of compounds were imine-bridged copper(II) chelates. These chelates were synthesised via a templating condensation reaction between various salicylaldehyde derivates and 1,10-phenanthrolin-2-ylmethanaminium chloride, yielding eight additional copper(II) chelates. The metal chelates were characterised by IR, UV/vis and EPR spectroscopy, and mass spectrometry. HL1, [Cu(L4)(NO3)] and [Cu(L7)](NO3) were further studied by X-ray diffraction. The copper(II) chelates exhibit two different solid-state structures with the nitrate counter ion coordinated to the metal centre in [Cu(L4)(NO3)], but in the outer coordination sphere for [Cu(L7)](NO3). The paramagnetic copper(II) chelates were studied with EPR spectroscopy, which confirmed the square planar coordination geometries of these chelates in solution. The metal chelates were designed to be chemotherapeutic agents, exerting their cytotoxicity through DNA intercalation and, for the copper(II) chelates, DNA cleavage through the catalytic production of ROS. The ability of the copper(II) chelates to catalyse the production of hydroxyl radical in situ in the presence of ascorbic acid and hydrogen peroxide was studied via a hydroxyl radical assay using Rhodamine B as an analogue for the aromatic DNA bases. Competitive binding studies determined the affinity of the metal chelates towards ct-DNA, [Cu(L1)](PF6) has the highest binding constant: 5.91 × 106 M-1. DFT calculations were performed on the ligands and metal chelates to determine the geometry-optimised structures, vibrational frequencies, 1H and 13C NMR chemical shifts and electronic transitions. The B3LYP/6-311G (d,p) level of theory was used for the ligands, copper(II) and nickel(II) chelates and the B3LYP/LanL2DZ level of theory for the palladium(II) chelates. The TD-DFT method was used for the energy calculations. The experimental and calculated results were compared where possible, and a reasonable correlation was found. The cytotoxicity of five amide-based chelates was evaluated against four human cancer cell lines, namely A549, TK-10, HT29 and U251, using an MTT assay. The screened chelates exhibited favourable anticancer activity with the mean IC50 values against the four cancer cell lines ranging from ca. 12 to 35 μM. Importantly, it was found that the combination of the copper(II) ion and the ligand was essential for enhanced cytotoxicity. The complex [Cu(L1)](PF6) was identified as the lead drug candidate based on the high DNA affinity and cytotoxicity. This compound was most cytotoxic towards the glioblastoma cell line U251 with an IC50 value of 7.59 μM. The imine-based chelates were screened against three human cancer cell lines: MDA-MB, HELA, and SHSY5Y, and a healthy human cell line, HEK293. The selectivity index of these chelates for neoplastic versus the healthy cell line was calculated. The imine-based chelates showed a high selectivity towards the triple-negative breast cancer MDA-MB, an order of magnitude more toxic to the tumour cell than the healthy one. This selectivity index is significantly improved over that of cisplatin. A gel mobility shift assay investigated the interactions between the copper(II) chelates and plasmid DNA. The in vivo biodistribution of [Cu(L1)](PF6) was determined using the copper-64 radiolabelled analogue of [Cu(L1)]Cl and microPET-CT scanning. The initial biodistribution studies suggested that the complex has good serum stability and showed that there was no significant accumulation in any organs. The subsequent study involved a xenograft model using the A549 cell line and showed significant uptake and retention of the complex in the tumour. The cytotoxicity of the chelate when synthesised with the non-radioactive isotopes of copper and the uptake of the radiolabelled equivalent in a tumour model suggest that this complex could have application as a “theranostic agent”.

Iqoqa.

Ukukhishwa kwe-1,10-phenanthroline endaweni ye-2 kunikeze amakilasi amabili enhlanganisela namaqembu amabili ahlukene ukuhlanganisa kulolu cwaningo. Iqembu lokuqala lalihlanganisa ama-amide-bridged tetradentate N4-donor ligands futhi ayenziwe ngethusi (II), nickel (II) kanye ne-palladium (II). I-ligand chelation yenzeke ngokuchithwa okuhambisanayo kwe-amide N-H, okuholela ku-monoanionic ligand kanye ne-monocationic complexes lapho ixhunywe kuma-ion ensimbi e-divalent. Ama-ligands N-(quinolin-8-yl)-1,10-phenanthroline-2-carboxamide, HL1, kanye ne-N-(pyridin-2-ylmethyl) -1,10-phenanthroline-2-carboxamide, HL2, abenophawu lwe-NMR, IR kanye ne-UV/vis spectroscopy kanye ne-mass spectrometry. Ikilasi lesibili lama-compounds bekungama-imine-bridged copper (II) chelates. Lawa ma-chelates ahlanganiswa ngokusabela kokujiya kwesifanekiso phakathi kokuphuma kwe-salicylaldehyde okuhlukahlukene kanye ne-1,10-phenanthrolin-2-ylmethanaminium chloride, ekhiqiza ama-chelate ethusi ayisishiyagalombili (II). Ama-chelates ensimbi abonakala nge-IR, UV/vis kanye ne-EPR spectroscopy, kanye ne-mass spectrometry. I-HL1, [Cu(L4) (NO3)] kanye ne-[Cu(L7)] (NO3) zaphinde zacwaningwa nge-X-ray diffraction. Ama-chelates ethusi (II) abonisa izakhiwo ezimbili ezihlukene zesimo esiqinile ezine-ion yekhawunta ye-nitrate exhunywe esikhungweni sensimbi ku-[Cu(L4) (NO3)]], kodwa kwi-outer coordination sphere ye-[Cu(L7)] (NO3). Ama-chelates e-paramagnetic copper (II) ahlolisiswa nge-EPR spectroscopy, eqinisekisa i-square planar coordination geometries yalawa ma-chelates esixazululweni.

Ama-chelates ensimbi ayeklanyelwe ukuba abe ama-chemotherapeutic agents, asebenzisa i-cytotoxicity yawo ngokusebenzisa i-DNA intercalation futhi, kuma-chelates ethusi (II), i-DNA cleavage ngokukhiqizwa okunamandla kwe-ROS. Ikhono le-copper (II) chelates lokugqugquzela ukukhiqizwa kwe-hydroxyl radical in situ lapho kukhona i-ascorbic acid ne-hydrogen peroxide yacwaningwa nge-hydroxyl radical assay kusetshenziswa i-Rhodamine B njenge-analogue yezisekelo ze-DNA enamakha. Izifundo ezibophayo ezincintisanayo zinqume ukuhambisana kwama-chelates ensimbi ku-ct-DNA, [Cu(L1)](PF6) inokuhambisana okuphezulu kakhulu okubophayo: 5.91 × 106 M-1.

Izibalo ze-DFT zenziwa kuma-ligands kanye nama-chelates ensimbi ukuze kunqunywe izakhiwo ezilungiselelwe i-geometry-optimized, amaza okudlidliza, amashifu amakhemikhali e-1H kanye ne-13C NMR kanye nokuguqulwa kwe-electronic. Izinga le-B3LYP/6-311G (d,p) lethiyori lasetshenziselwa ama-ligands, ithusi(II) ne-nickel(II) chelates kanye nezinga le-B3LYP/LanL2DZ lethiyori ye-palladium(II) chelates. Indlela ye-TD-DFT isetshenziselwe izibalo zamandla. Imiphumela yokuhlolwa nebaliwe yaqhathaniswa lapho kwenzeka khona, futhi kwatholakala ukuhlobana okunengqondo.

I-cytotoxicity yama-chelates amahlanu asekelwe ku-amide yahlolwa ngokumelene nemigqa yeseli yomdlavuza wabantu emine, okuyi-A549, TK-10, HT29 kanye ne-U251, kusetshenziswa i-MTT assay. Ama-chelate ahloliwe abonise umsebenzi omuhle wokulwa nomdlavuza ngamavelu amaphakathi we-IC50 ngokumelene nemigqa yeseli yomdlavuza emine kusukela ku-ca. 12 kuya ku-35 μM. Okubalulekile, kwatholakala ukuthi inhlanganisela ye-ion yethusi (II) kanye ne-ligand yayibalulekile ekuthuthukisweni kwe-cytotoxicity. Inkimbinkimbi [Cu(L1)] (PF6) ikhonjwe njengekhandidethi yesidakamizwa esihamba phambili ngokususelwe ekuhlobaneni okuphezulu kwe-DNA kanye ne-cytotoxicity. Le nhlanganisela ibiyi-cytotoxic kakhulu ibheke kumugqa weseli we-glioblastoma u-U251 onenani le-IC50 elingu-7.59 μM. Ama-chelate asekelwe ku-imine ahlolelwa imigqa emithathu yamangqamuzana omdlavuza womuntu: i-MDA-MB, i-HELA, ne-SHSY5Y, kanye nolayini wamaseli womuntu onempilo, i-HEK293. Inkomba yokukhetha yalawa ma-chelates we-neoplastic ngokumelene nomugqa weseli onempilo ibaliwe. Ama-chelates asekelwe ku-imine abonise ukukhetha okuphezulu kumdlavuza webele we-triple-negative MDA-MB, ukuhleleka kobukhulu obunobuthi obuningi engqamuzaneni yesimila kunaleyo enempilo. Le nkomba yokukhetha ithuthukiswe kakhulu kune-cisplatin. Ukuhlolwa kwe-gel mobility shift assay kuphenye ukusebenzisana phakathi kwe-copper(II) chelates ne-plasmid DNA.

I-in vivo biodistribution ye-[Cu(L1)](PF6) inqunywe kusetshenziswa i-analogue ene-radiolabelled ye-copper-64 ye-[Cu(L1)]Cl ne-microPET-CT scanning. Ucwaningo lokuqala lwe-biodistribution luphakamise ukuthi inkimbinkimbi inokusimama okuhle kwe-serum futhi yabonisa ukuthi kwakungekho ukuqoqwa okuphawulekayo kunoma yiziphi izitho. Ucwaningo olwalandela lwaluhilela imodeli ye-xenograft esebenzisa ulayini weseli we-A549 futhi lwabonisa ukuthatheka okubalulekile nokugcinwa kwenkimbinkimbi esimilanjeni. I-cytotoxicity ye-chelate lapho ihlanganiswa nama-isotopes ethusi angewona ama-radioactive kanye nokuthathwa kwe-radiolabelled okulingana nemodeli yesimila kuphakamisa ukuthi le nkimbinkimbi ingaba nesicelo "njenge-ejenti yokwelapha".