Improving platinum(II)-based anticancer drug delivery using cucurbit[n]urils

Despite the synthesis of hundreds of new platinum(II) and platinum(IV)-based complexes each year as potential anticancer drugs, only three have received world-wide approval: cisplatin, carboplatin and oxaliplatin. The next big advance in platinum-based chemotherapy is not likely to come from the development of new drugs, but from the controlled and targeted delivery of already approved drugs or those in late stage clinical trials. Encapsulation of platinum drugs inside macromolecules has already demonstrated promise, and encapsulation within cucurbit[n]urils has shown particular potential. Partial or full encapsulation within cucurbit[n]urils provides steric hindrance to drug degradation by peptides and proteins, and the use of different sized cucurbit[n]urils allows for the tuning of drug release rates, cytotoxicity and toxicity

PAMAM dendrimers as drug delivery vehicles for platinum anticancer drugs

Poster describing PAMAM dendrimers as drug delivery vehicles for platinum anticancer drugs

Host-guest complexes of the antituberculosis drugs pyrazinamide and isoniazid with cucurbit[7]uril

The potential use of cucurbit[7]uril (CB[7]) as an excipient in oral formulations for improved drug physical stability or for improved drug delivery was examined with the antituberculosis drugs pyrazinamide (pyrazine-2-carboxamide) and isoniazid (isonicotinohydrazide). Both drugs form 1:1 host-guest complexes with CB[7] as determined by H-1 nuclear magnetic resonance spectrometry, electrospray ionisation mass spectrometry and molecular modelling. Drug binding is stabilised by hydrophobic effects between the pyridine and pyrazine rings of isoniazid and pyrazinamide, respectively, to the inside cavity of the CB[7] macrocycle as well as hydrogen bonds between the hydrazide and amide groups of each drug to the CB[7] carbonyl portals. At pH 1.5, isoniazid binds CB[7] with a binding constant of 5.6 x 10(5) M-1, whilst pyrazinamide binds CB[7] at pH 7 with a much smaller binding constant (4.8 x 10(3) M-1). Finally, CB[7] prevents drug melting through encapsulation. Where previously pyrazinamide displays a typical melting point of 189 A degrees C and isoniazid 171 A degrees C, by differential scanning calorimetry, no melting or degradation at temperatures up to 280 A degrees C is observed for either drug once bound by CB[7]

Examination of cucurbit[7]uril and its host-guest complexes by diffusion nuclear magnetic resonance

The self-diffusion of cucurbit[7]uril (CB[7]) and its host−guest complexes in D2O has been examined using pulsed gradient spin−echo nuclear magnetic resonance spectroscopy. CB[7] diffuses freely at a concentration of 2 mM with a diffusion coefficient (D) of 3.07 × 10-10 m2 s-1. At saturation (3.7 mM), CB[7] diffuses more slowly (D = 2.82 × 10-10 m2 s-1) indicating that it partially self-associates. At concentrations between 2 and 200 mM, CsCl has no effect on the diffusion coefficient of CB[7] (1 mM). Conversely, CB[7] (2 mM) significantly affects the diffusion of 133Cs+ (1 mM), decreasing its diffusion coefficient from 1.86 to 0.83 × 10-9 m2 s-1. Similar changes in the rate of diffusion of other alkali earth metal cations are observed upon the addition of CB[7]. The diffusion coefficient of 23Na+ changes from 1.26 to 0.90 × 10-9 m2 s-1 and 7Li+ changes from 3.40 to 3.07 × 10-9 m2 s-1. In most cases, encapsulation of a variety of inorganic and organic guests within CB[7] decreases their rates of diffusion in D2O. For instance, the diffusion coefficient of the dinuclear platinum complex trans-[{PtCl(NH3)2}2μ-dpzm]2+ (where dpzm is 4,4'-dipyrazolylmethane) decreases from 4.88 to 2.95 × 10-10 m2 s-1 upon encapsulation with an equimolar concentration of CB[7]

Polyamide platinum anticancer complexes designed to target specific DNA sequences

Two new platinum complexes, trans-chlorodiammine[N-(2-aminoethyl)-4-[4-(N-methylimidazole-2-carboxamido)-N-methylpyrrole-2-carboxamido]-N-methylpyrrole-2-carboxamide]platinum(II) chloride (DJ1953-2) and trans-chlorodiammine[N-(6-aminohexyl)-4-[4-(N-methylimidazole-2-carboxamido)-N-methylpyrrole-2-carboxamido]-N-methylpyrrole-2-carboxamide]platinum(II) chloride (DJ1953-6) have been synthesized as proof-of-concept molecules in the design of agents that can specifically target genes in DNA. Coordinate covalent binding to DNA was demonstrated with electrospray ionization mass spectrometry. Using circular dichroism, these complexes were found to show greater DNA binding affinity to the target sequence:  d(CATTGTCAGAC)2, than toward either d(GTCTGTCAATG)2, which contains different flanking sequences, or d(CATTGAGAGAC)2, which contains a double base pair mismatch sequence. DJ1953-2 unwinds the DNA helix by around 13°, but neither metal complex significantly affects the DNA melting temperature. Unlike simple DNA minor groove binders, DJ1953-2 is able to inhibit, in vitro, RNA synthesis. The cytotoxicity of both metal complexes in the L1210 murine leukaemia cell line was also determined, with DJ1953-6 (34 μM) more active than DJ1953-2 (>50 μM). These results demonstrate the potential of polyamide platinum complexes and provide the structural basis for designer agents that are able to recognize biologically relevant sequences and prevent DNA transcription and replicatio

Anionic PAMAM dendrimers as drug delivery vehicles for transition metal-based anticancer drugs

The use of anionic half-generation poly(amidoamine) dendrimers as drug delivery vehicles for [Pt(S,S-dach)(5,6-Me2phen)]2+ (56MESS) (where S,S-dach = 1S,2S-diaminocyclohexane; 5,6-Me2phen = 5,6-dimethyl-1,10-phenanthroline) and [{Δ,Δ-Ru(phen)2}2(μ-bb7)]4+ (Rubb7) (where phen = 1,10-phenanthroline; bb7 = 1,7-bis[4-(4′-methyl-2,2′-bipyridyl)heptane]) has been studied by nuclear magnetic resonance spectroscopy. From one- and two-dimensional 1H NMR spectra both 56MESS and Rubb7 were found to bind to the surface of generation 3.5, 4.5, 5.5 and 6.5 dendrimers through electrostatic interactions. The higher charge and larger size of Rubb7 resulted in stronger binding to all dendrimer generations (Kb 2 × 105 M−1) compared with 56MESS (Kb 1 × 104 M−1). Interestingly, there appeared to be no observable trend between dendrimer size and binding constant strength. The size of the free and 56MESS-bound dendrimers were examined using pulsed-gradient spin-echo NMR. The dendrimers ranged in hydrodynamic diameter from 11 to 20 nm and in all cases were larger than their corresponding full-generation dendrimer. Upon the addition of 56MESS the diameter of the dendrimers increased, consistent with surface binding

Side-on binding of p-sulphonatocalix[4]arene to the dinuclear platinum complex trans-[{PtCl(NH3)2}2μ-dpzm]2+ and its implications for anticancer drug delivery

The utility of p-sulphonatocalix[4]arene (s-CX[4]) as a drug delivery vehicle for multinuclear platinum anticancer agents, using trans-[{PtCl(NH3)2}2μ-dpzm]2+ (di-Pt; where dpzm = 4,4′-dipyrazolylmethane) as a model complex, has been examined using 1H nuclear magnetic resonance, electrospray ionisation mass spectrometry, molecular modelling and in vitro growth inhibition assays. s-CX[4] binds di-Pt in a side-on fashion in a ratio of 1:1, with the dpzm ligand of the metal complex located within the s-CX[4] cavity with binding further stabilised by ion-ion interactions and hydrogen bonding between the metal complex am(m)ine groups and the s-CX[4] sulphate groups. Partial encapsulation of di-Pt within the cavity does not prevent binding of 5′-guanosine monophosphate to the metal complex. When bound to two individual guanosine molecules, di-Pt also remains partially bound by s-CX[4]. The cytotoxicity of free di-Pt and s-CX[4] and their host guest complex was examined using in vitro growth inhibition assays in the A2780 and A2780cis human ovarian cancer cell lines. Free di-Pt has an IC50 of 100 and 60 μM, respectively, in the cell lines, which is significantly less active than cisplatin (1.9 and 8.1 μM, respectively). s-CX[4] displays no cytotoxicity at concentrations up to 1.5 mM and does not affect the cytotoxicity of di-Pt, probably because its low binding constant to the metal complex (6.8 × 104 M−1) means the host-guest complex is mostly disassociated at biologically relevant concentrations