Topical Cream-Based Dosage Forms of the Macrocyclic Drug Delivery Vehicle Cucurbit[6]uril

The macrocycle family of molecules called cucurbit[n]urils are potential drug delivery vehicles as they are able to form host-guest complexes with many different classes of drugs. This study aimed to examine the utility of Cucurbit[6]uril (CB[6]) in topical cream-based formulations for either localised treatment or for transdermal delivery. Cucurbit[6]uril was formulated into both buffered cream aqueous- and oily cream-based dosage forms. The solid state interaction of CB[6] with other excipients was studied by differential scanning calorimetry and the macrocycle''s transdermal permeability was determined using rat skin. Significant solid state interactions were observed between CB[6] and the other dosage form excipients. At concentrations up to 32% w/w the buffered aqueous cream maintained its normal consistency and could be effectively applied to skin, but the oily cream was too stiff and is not suitable as a dosage form. Cucurbit[6]uril does not permeate through skin; as such, the results imply that cucurbituril-based topical creams may potentially only have applications for localised skin treatment and not for transdermal drug delivery.     

Acid-controlled release complexes of podophyllotoxin and etoposide with acyclic cucurbit[n]urils for low cytotoxicity

The targeted or responsive systems are appealing therapeutic platforms for the development of next-generation precision medications. So, we design and prepare acid-controlled release complexes of podophyllotoxin (POD) and etoposide (VP-16) with pH-labile acyclic cucurbit[n]urils, and their characteristics and inclusion complexation behaviors were investigated via fluorescence spectroscopy, nuclear magnetic resonance and X-ray power diffraction. Cells incubated with complexes have been analyzed by high-content analysis (HCA), and cytotoxicity tests have been completed by MTT assay. The results showed that complexes with different binding constants can release the drug substance in the physiological pH environment of cancer cells, maintain good anticancer activity, and have low cytotoxicity. This provides a strategy about targeted and responsive systems of POD and VP-16 for clinical application.     

Compacting effect of BBR3464, a new-generation trisplatinum anticancer agent,on DNA

BBR3464 is a trinuclear platinum compound of formula [{trans-PtCl(NH₃)₂}₂-μ-trans-Pt(NH₃)₂{NH₂(CH₂)₆NH₂}₂]⁴⁺. It is a new-generation platinum chemotherapeutic agent that exhibits cytotoxicity at ten to thousand times lower dose limit compared to the well-known platinum drug cisplatin, in cisplatin-sensitive as well as in cisplatin-resistant cells. DNA is thought to be the primary cellular target of BBR3464. In this work, we have applied high-resolution atomic force microscopy (AFM) for the first time, to obtain direct information on BBR3464-induced structural changes of DNA. It is found that the DNA molecules get compacted after treatment with BBR3464, for the drug:DNA molar ratio and the drug treatment period of 0.01 and 48 h, respectively. These values of molar ratio and incubation period have been obtained previously, as a result of biochemical optimization studies carried out for achieving maximum drug effects. The DNA structural changes, as observed in AFM topographs, have been correlated to the bulk level spectroscopic information. A remark on the significance of BBR3464-induced DNA compaction with respect to the available AFM reports on DNA modification by cisplatin has been made.     

A mechanism-based, solution-phase method for screening combinatorial mixtures of potential platinum anticancer drugs

 We report a new, mechanism-based approach to the screening of pools of potential platinum antitumor drugs. A platinum complex of L-lysine, [Pt(Lys)Cl₂] or Kplatin, was selected from mixtures of platinum-amino acid compounds based on the ability of its DNA adducts to bind HMG1 in a gel mobility shift assay. Kplatin, unlike most other platinum antitumor drug candidates, is an (N,O)-chelated complex which binds DNA forming two isomeric 1,2-d(GpG) intrastrand DNA cross-links. Kplatin-modified DNA is specifically recognized by HMG1, HMG1 domain B, and testis-specific HMG, all of which bind to the major cisplatin-DNA adducts. Kplatin is toxic towards the human tumor cell lines HeLa and KM12 with LC₅₀ values of 59.2±7.8 μM and 74 μM, respectively. Received: 16 July 1997 / Accepted 31 October 1997     

Cucurbit[7]uril encapsulated cisplatin overcomes cisplatin resistance via a pharmacokinetic effect

The cucurbit[n]uril (CB[n]) family of macrocycles has been shown to have potential in drug delivery where they are able to provide physical and chemical stability to drugs, improve drug solubility, control drug release and mask the taste of drugs. Cisplatin is a small molecule platinum-based anticancer drug that has severe dose-limiting side-effects. Cisplatin forms a host-guest complex with cucurbit[7]uril (cisplatin@CB[7]) with the platinum atom and both chlorido ligands located inside the macrocycle, with binding stabilised by four hydrogen bonds (2.15-2.44 ?). Whilst CB[7] has no effect on the in vitro cytotoxicity of cisplatin in the human ovarian carcinoma cell line A2780 and its cisplatin-resistant sub-lines A2780/cp70 and MCP1, there is a significant effect on in vivo cytotoxicity using human tumour xenografts. Cisplatin@CB[7] is just as effective on A2780 tumours compared with free cisplatin, and in the cisplatin-resistant A2780/cp70 tumours cisplatin@CB[7] markedly slows tumour growth. The ability of cisplatin@CB[7] to overcome resistance in vivo appears to be a pharmacokinetic effect. Whilst the peak plasma level and tissue distribution are the same for cisplatin@CB[7] and free cisplatin, the total concentration of circulating cisplatin@CB[7] over a period of 24 hours is significantly higher than for free cisplatin when administered at the equivalent dose. The results provide the first example of overcoming drug resistance via a purely pharmacokinetic effect rather than drug design or better tumour targeting, and demonstrate that in vitro assays are no longer as important in screening advanced systems of drug delivery.     

X-ray crystal structure and properties of tris(tetrathiafulvalenium) hexachloroplatinate

The title salt has been prepared by the diffusion of tetrathiafulvalene (TTF) and [NBuⁿ₄]₂[PtCl₆] in acetonitrile. Crystals (black plates) are tetragonal, space group P4/mbm, with a=11.757(2), c=11.707(2) Å, and Z=2. The block-diagonal least-squares refinement, based on 804 independent reflections with ∣F_o∣> 3σ(F), yields an R factor of 0.11. The structure is comprised of TTF-trimer units which are arranged perpendicularly to each other, forming a two-dimensional layer with somewhat close sulfur- sulfur contact among the trimers. The salt exhibits the electrical resistivity of 87 Ω cm as a compacted pellet at 25 °C. Binding energies of platinum 4f electrons of the [PtCl₆]²⁻ anion suggest an extreme reduction from the platinum(IV) state.     

Bacterial mutagenicity investigation of epoxides: drugs,drug metabolites,steroids and pesticides

Although it has been observed that many epoxides are ultimate mutagens, surprisingly little is known about epoxides to which man may be extensively exposed, e.g., physiological compounds, drugs, drug metabolites and pesticides. We have now investigated 35 such and related epoxides for mutagenicity, using reversion of his^?Salmonella typhimurium TA98 and TA100 as biological end-point. None of the tested steroids (12 compounds), vitamin K epoxides (3 compounds) and pesticides (dieldrin, endrin, HEOM (1,2,3,4,9,9-hexachloro-6,7-epoxy-1,4,4a5,6,7,8,8a-octahydro-1,4-methanonaphthalene), heptachlor epoxide) showed any mutagenic activity. Negative results were also obtained with the antibiotics oleandomycin, anti-capsin and asperlin, the cardiotonic drug resibufogenin, the widely used parasympatholytic drugs butylscopolamine and scopolamine, the sedatives valtratum, didovaltratum and acevaltratum, the tranquilizer oxanamide as well as with the drug metabolites carbamazepine 10,11-oxide and diethylstilbestrol α,β-oxide. Three barbiturate epoxides, formed by metabolism of allobarbital, alphenal and secobarbital, caused weak but reproducible mutagenic effects at high concentrations. The cytostatic agent ethoglucide was the only drug having substantial mutagenic activity. Its mutagenic potency was similar to those of the control epoxides styrene 7,8-oxide, p-bromostyrene 7,8-oxide and m-bromostyrene 7,8-oxide, but much lower than those of benzo[a]pyrene 4,5-oxide, benzo[e]pyrene 4,5-oxide and 7,12-dimethylbenz[a]-anthracene 5,6-oxide.Some epoxides were also tested in other Salmonella typhimurium strains or in the presence of rat-liver S9 mix. Positive results were only obtained with compounds that had already been detected as mutagens in the direct test with strain TA100.     

The coordination chemistry of bidentate tellurium ligands. I. Complexes of palladium,platinum, and mercury with large chelate rings

Complexes formed from the reaction of palladium(II) and platinum(II) halides with (p-EtO·C₆H₄)Te(CH₂)_nTe(C₆H₄OEt-p) (Lⁿ, n = 6, 7, 8, 9, 10) are reported together with data for some mercury(II) complexes, [HgLⁿCl₂] which are used for comparative purposes. The compounds [MLⁿX₂] (M  Pd, Pt; n = 7, 8 (Pt only), 9, 10; X  Cl, Br) have molecular weights in molten naphthalene which fluctuate about the monomer value. [ML⁶X₂] (M  Pd, Pt; X  Cl, Br) are totally insoluble and are believed to be polymeric. The palladium(II) complexes have trans dichloro groups whereas the platinum compounds show cis dichloro groups in the solid state.¹³C NMR spectra are valuable to confirm the coordination of the ligand; the methylene resonance of the TeCH₂ group undergoes a 19–20 ppm downfield shift on coordination. ¹²⁵Te NMR spectra of the Pd(II) and Pt(II) complexes show two broad resonances the chemical shifts of which imply the presence of cis and trans isomers in CDCl₃ solution. A more detailed variable temperature high field study of [PtL⁸Cl₂] (¹²⁵Te and ¹⁹⁵Pt NMR) reveals a complex solution chemistry involving at least two cis and two trans species. The temperature range over which the solution is stable (−10 to 70 °C) is insufficient to allow a totally unambiguous interpretation but a model based on monomer ⇍ dimer equilibria provides a self consistent interpretation.     

Solution equilibria leading to the formation of metal-metal bonds in partially oxidized bisoxalatoplatinate(II) systems

The reaction between [Pt^II(Ox)₂]²⁻ and an appropriate oxidant resulted in the formation of the dimeric unbridged platinum complex [{Pt^III(Ox)₂ }₂]²⁻ where (Ox) is oxalate. This complex was moderately stable under ambient conditions and was studied via a variety of NMR and spectrophotometric techniques. Reaction of the [{Pt^III(Ox)₂}₂]²⁻ complex with [Pt^II(Ox)₂]²⁻ in the presence of H⁺ lead to the formation of a series of longer platinum oligomers with non-integral oxidation states, culminating in the formation of partially oxidized platinum polymers of general formula [{Pt(Ox)₂}_n]ⁿ⁻. The concentration of H⁺ was an important factor leading to higher oligomers and the approximate number of protons associated with each oligomer was determined. The analogous [{Pt^III(Mal)₂}₂]²⁻ complex, where (Mal) is the malonate anion, was also synthesized and studied but was shown to be significantly less stable.     

A Systematic In Silico Search for Target Similarity Identifies Several Approved Drugs with Potential Activity against the Plasmodium falciparum Apicoplast

Most of the drugs in use against Plasmodium falciparum share similar modes of action and, consequently, there is a need to identify alternative potential drug targets. Here, we focus on the apicoplast, a malarial plastid-like organelle of algal source which evolved through secondary endosymbiosis. We undertake a systematic in silico target-based identification approach for detecting drugs already approved for clinical use in humans that may be able to interfere with the P. falciparum apicoplast. The P. falciparum genome database GeneDB was used to compile a list of ≈600 proteins containing apicoplast signal peptides. Each of these proteins was treated as a potential drug target and its predicted sequence was used to interrogate three different freely available databases (Therapeutic Target Database, DrugBank and STITCH3.1) that provide synoptic data on drugs and their primary or putative drug targets. We were able to identify several drugs that are expected to interact with forty-seven (47) peptides predicted to be involved in the biology of the P. falciparum apicoplast. Fifteen (15) of these putative targets are predicted to have affinity to drugs that are already approved for clinical use but have never been evaluated against malaria parasites. We suggest that some of these drugs should be experimentally tested and/or serve as leads for engineering new antimalarials.     

Cellular accumulation and DNA platination of two new platinum(II) anticancer compounds based on anthracene derivatives as carrier ligands

The anticancer properties of two new fluorescent platinum(II) compounds, cis-[Pt(A9opy)Cl₂] and cis-[Pt(A9pyp)(dmso)Cl₂] are described. These compounds are highly active against several human tumor cell lines, including human ovarian carcinoma sensitive and cisplatin-resistant cell lines (A2780 and A2780R). To study the cellular processing of these new compounds, a series of in vitro studies have been performed, including the investigation of intracellular platinum accumulation and DNA-platination experiments in A2780 and A2780R cells. Compared to cisplatin, both compounds are accumulated highly in both sensitive and resistant cell lines, and more platinum has been found to bind to the nuclear DNA. Interestingly, cis-[Pt(A9opy)Cl₂] shows high accumulation and DNA adduct formation in the resistant cell line A2780R, as compared to the sensitive counterpart A2780 cell line. This suggests that cis-[Pt(A9opy)Cl₂] is able to overcome some of the well-known resistance mechanisms in this cell line, such as decreased cellular uptake and increased DNA repair.     

Toxicity of platinum(II) amino acid (N,O) complexes parallels their binding to DNA as measured in a new solid phase assay involving a fluorescent HMG1 protein construct readout

 The compound [Pt(lysine)Cl₂] (Kplatin) was previously identified in a study of platinum amino acid complexes as a potential antitumor drug candidate. The DNA binding properties, high mobility group (HMG)-domain protein affinity for the platinated DNA, and cytotoxicity against HeLa cells of Kplatin and three related (N,O) chelated platinum(II) amino acid complexes, [Pt(arginine)Cl₂] (Rplatin), K[Pt(N_e-acetyllysine)Cl₂] (NacKplatin), and K[Pt(norleucine)Cl₂] (Norplatin), are reported. The four complexes have identical PtCl₂(N,O) coordination environments. A new solid phase screening methodology was devised in which platinated DNA probes are covalently attached to a nylon support and tested for their ability to bind a fluorescently labeled HMG-domain protein. The fluorescent HMG-domain protein was generated by expressing a fusion of the green fluorescent protein (GFP) with recombinant rat HMG1. Binding revealed by the solid phase method correlated well with the results of gel mobility shift and HeLa cytotoxicity assays. These results suggest that the net charge on the complex, rather than the nature of the side chain, is the most important factor underlying the DNA binding properties and toxicity of amino acid (N,O) chelated platinum complexes. This property explains why Kplatin was previously selected from the pool of platinum amino acid complexes based on the ability of its DNA adducts to bind HMG1. Received: 3 February 1999 / Accepted: 7 April 1999     

Structural characterization and DNA interactions of new cytotoxic transplatin analogues containing one planar and one nonplanar heterocyclic amine ligand

trans-Diaminedicholoroplatinum(II) complexes with one planar and one non-planar heterocyclic amine ligand were designed as new potential antitumor drugs. The X-ray crystallographic structures of trans-[PtCl₂(4-picoline)(piperidine)] and trans-[PtCl₂(4-picoline)(piperazine)]·HCl revealed that the piperidine and piperazine ligands bind to the platinum through the equatorial position and that the ligands adopt the chair conformation. The nonplatinated amine of the piperazine can form hydrogen bonds with atoms that are approximately 7.5 Å away from the Pt binding site. DNA is considered a major pharmacological target of platinum compounds. Hence, to expand the database correlating structural features of platinum compounds and DNA distortions induced by these compounds, which may facilitate identification of more effective anticancer platinum drugs, we describe the DNA binding mode in a cell-free medium of trans-[PtCl₂(4-picoline)(piperidine)] and trans-[PtCl₂(4-picoline)(piperazine)]·HCl. Interestingly, the overall impact of the replacement of the second ammine group in transplatin by the heterocyclic ligands appears to change the character of the global conformational changes induced in DNA towards that induced by cisplatin. The clinical ineffectiveness of the parent transplatin has been proposed to be also associated with its reduced capability to form bifunctional adducts in double-helical DNA. The results of the present work support the view that replacement of both ammine groups of transplatin by heterocyclic ligands enhances cytotoxicity probably due to the marked enhancement of the stability of intrastrand cross-links in double-helical DNA.     

Structure and spectral characteristics of diquat-cucurbituril complexes from density functional theory

Electronic structure, ¹H NMR and infrared spectra of diquat (6,7-dihydrodipyrido[1,2-b:1′,2′-e] pyrazine-5,8-diium or DQ²⁺) encapsulated by cucurbit[n]uril (n?=?7,8) hosts are obtained using the density functional theory. Theoretical calculations have shown that both CB[7] or CB[8] host possesses strong affinity toward DQ²⁺ compared to its reduced cation or neutral species. Calculated ¹H NMR spectra reveal that H_α protons on bi-pyridinium rings of DQ²⁺@CB[8] complex are de-shielded owing to C=O?H interactions. On the other hand aromatic (H_β and H_δ) of DQ²⁺ within the CB[8] cavity exhibit significant shielding. The complexation of CB[8] with DQ²⁺ splits the carbonyl stretching vibration (1788 cm^?1) into two distinct vibrations which correspond to 1765 cm^?1 arising from hydrogen bonded carbonyls and the 1792 cm^?1 band from non-interacting ones. Further, the CN stretching vibration in DQ²⁺ exhibits a frequency blue-shift of 6 cm^?1 on its encapsulation within the CB[8] cavity. The direction of frequency shift has been explained on the basis of natural bond orbital analyses.

Structure and biological evaluation of new cyclic and acyclic laxaphycin-A type peptides

Five new laxaphycins were isolated and fully characterised from the bloom forming cyanobacteria Anabaena torulosa sampled from Moorea, French Polynesia: three acyclic laxaphycin A-type peptides, acyclolaxaphycin A (1), [des-Gly¹¹]acyclolaxaphycin A (2) and [des-(Leu¹⁰-Gly¹¹)]acyclolaxaphycin A (3), as well as two cyclic ones, [l-Val⁸]laxaphycin A (4) and [d-Val⁹]laxaphycin A (5). The absolute configuration of the amino acids, established using advanced Marfey’s analysis for compounds 2–5, highlights a conserved stereochemistry at the Cα carbons of the peptide ring that is characteristic of this family. To the best of our knowledge, this is the first report of acyclic analogues within the laxaphycin A-type peptides. Whether these linear laxaphycins with the aliphatic β-amino acid on the N-terminal are biosynthetic precursors or compounds obtained after enzymatic hydrolysis of the macrocycle is discussed. Biological evaluation of the new compounds together with the already known laxaphycin A shows that [l-Val⁸]laxaphycin A, [d-Val⁹]laxaphycin A and [des-Gly¹¹]acyclolaxaphycin induce cellular toxicity whereas laxaphycin A and des-[(Leu¹⁰-Gly¹¹)]acyclolaxaphycin A do not affect the cellular viability. An analysis of cellular death shows that the active peptides do not induce apoptosis or necrosis but instead, involve the autophagy pathway.     

Synthesis and characterization of hexa-n-propylcyclotriphosphazene

Dynamic vacuum thermolysis of (CH₃)₃SiN = P(n-Pr)₂(OPh) yielded hexa-n-propylcyclotriphosphazene, [N = P(n-Pr)₂]₃. It was found that pure [N = P(n-Pr)₂]₃is insoluble in most solvents, however, [N = P(n-Pr)₂]₃ can be crystallized directly from the crude reaction mixture using hot hexanes. The molecular structure of hexa-n-propylcyclotriphosphazene has been determined by single-crystal X-ray diffraction and multinuclear NMR studies.     

Simulations on the possibility of formation of complexes between fluorouracil drug and cucurbit[n]urils: ab initio van der Waals DFT study

The binding geometry of fluorouracil/cucurbit[n]urils (CB[n]s) complexes with n?=?5–8 is investigated using the first-principles van der Waals density functional (vdW-DF) method, involving full geometry optimization. Such host-guest complexes are typically calculated using conventional DFT method, which significantly underestimates non-local dispersion forces (or vdW contributions) and therefore affects interactions between respected entities. We address here the role of vdW forces for the fluorouracil and CB[n]s molecules which can form directional hydrogen bonds with each other. It was found that the inclusion of dispersion interactions significantly affects the host-guest binding properties and the hydrogen bonding between the molecules provides the main binding mechanism, while results in the same geometries for the considered complexes. The 0.84 eV binding energy, for the thermodynamically favorable state, reveals that the interaction of fluorouracil with CB[n]s is an exothermic interaction and typical for strong hydrogen bonding. Furthermore, we have investigated the binding nature of these host-guest systems in aqueous solution with ab initio MD simulations adopting vdW-DF method. These findings afford evidence for the applicability of the vdW-DF approach and provide a realistic benchmark for the investigation of the host-guest complexes.

Fast cleavage of a diselenide induced by a platinum(II)-methionine complex and its biological implications

Platinum-based anticancer drugs such as cisplatin induce increased oxidative stress and oxidative damage of DNA and other cellular components, while selenium plays an important role in the antioxidant defense system. In this study, the interaction between a platinum(II) methionine (Met) complex [Pt(Met)Cl₂] and a diselenide compound selenocystine [(Sec)₂] was studied by electrospray ionization mass spectrometry, high performance liquid chromatography mass spectrometry, and ¹H NMR spectroscopy. The results demonstrate that the diselenide bond in (Sec)₂ can readily and quickly be cleaved by the platinum complex. Formation of the selenocysteine (Sec) bridged dinuclear complex [Pt₂(Met-S,N)₂(μ-Sec-Se,Cl)]³⁺ and Sec chelated species [Pt(Met-S,N)(Sec-Se,N)]²⁺ was identified at neutral and acidic media, which seems to result from the intermediate [Pt(Met-S,N)(Sec-Se)Cl]⁺. An accelerated formation of S-Se and S-S bonds was also observed when (Sec)₂ reacted with excessive glutathione in the presence of [Pt(Met)Cl₂]. These results imply that the mechanism of activity and toxicity of platinum drugs may be related to their fast reaction with seleno-containing biomolecules, and the chemoprotective property of selenium agents against cisplatin-induced toxicity could also be connected with such reactions.     

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is ¹H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.     

Benzofuro[3,2-d]pyrimidines inspired from cercosporamide CaPkc1 inhibitor: Synthesis and evaluation of fluconazole susceptibility restoration

In a context of growing resistance to classical antifungal therapy, the design of new drugs targeting alternative pathways is highly expected. Benzofuro[3,2-d]pyrimidine derivatives, derived from (?)-cercosporamide, were synthesized and evaluated as potential Candida albicans PKC inhibitors in the aim of restoring susceptibility to azole treatment. Co-administration assay of benzofuropyrimidinedione 23 and fluconazole highlighted a synergistic effect on inhibition of cell growth of a Candida albicans resistant strain.