Synthesis and in vitro antitumor activity of oligonucleotide-tethered and related platinum complexes

Probing the DNA Reactivity and the Anticancer Properties of a Novel Tubercidin-Pt(II) Complex

Herein, we reported on the synthesis of a novel Pt(II) neutral complex having as ligand the nucleoside tubercidin, a potent anti-tumor agent extracted from the bacterium Streptomyces Tubercidicus. In detail, the chelation of the metal by a diamine linker installed at C6 purine position of tubercidin assured the introduction of a cisplatin-like unit in the molecular scaffold. The behavior of the synthesized complex with a double-strand DNA model was monitored by CD spectroscopy and compared with that of cisplatin and tubercidin. In addition, the cell viability was evaluated against HeLa, A375 and WM266 human cancer cell lines using the MTT test. Lastly, the results of the apoptotic assay (FITC Annexin V) performed on the HeLa cancer cell line are also reported.

Synthesis of Gemini analogs of 19-norcalcitriol and their platinum(II) complexes

Hormonally active vitamin D₃ metabolite, calcitriol, plays an important role in calcium-phosphate homeostasis, immune system actions and cell differentiation. Although anticancer activity of calcitriol is well documented and thousands of its analogs have been synthesized, none has been approved as a potential drug against cancer. Therefore, we attempted to introduce the cytotoxic effect to the calcitriol molecule by its linking to cisplatin. Herein, we present the synthesis of vitamin D compounds, designed on the basis of molecular modeling and docking experiments to the vitamin D receptor, and characterized by the presence of significantly different two side chains attached to C-20. In this study, a new synthetic approach to Gemini analogs was developed. Preparation of the target 19-norcalcitriol compounds involved separate syntheses of several building blocks (the A-ring, C/D-rings and side-chain fragments). The convergent synthetic strategy was used to combine these components by the different coupling processes, the crucial one being Wittig-Horner reaction of the Grundmann ketone analog with the known 2-methylene A-ring phosphine oxide. Due to the nature of the constructed steroidal side chains (bidentate ligands), which allowed coordination of metal ions, the first conjugate-type platinum(II) complexes of the vitamin D analogs were also successfully prepared and characterized. The target vitamin D compounds, displaying significant affinity for a vitamin D receptor, were assessed in vitro for their anti-proliferative activities towards several cell lines.

Synthesis and pharmacological evaluation of modified adenosines joined to mono-functional platinum moieties

The synthesis of four novel platinum complexes, bearing N6-(6-amino-hexyl)adenosine or a 1,6-di(adenosin-N6-yl)-hexane respectively, as ligands of mono-functional cisplatin or monochloro(ethylendiamine)platinum(II), is reported. The chemistry exploits the high affinity of the charged platinum centres towards the N7 position of the adenosine base system and a primary amine of an alkyl chain installed on the C6 position of the purine. The cytotoxic behaviour of the synthesized complexes has been studied in A549 adenocarcinomic human alveolar basal epithelial and MCF7 human breast adenocarcinomic cancer cell lines, in order to investigate their effects on cell viability and proliferation.

Platinum(IV) coordination compounds containing 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one as nonleaving ligand. Molecular and cytotoxicity in vitro characterization

Novel platinum(IV) coordination compounds with 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO): cis-trans-[PtCl(2)(OH)(2)(NH(3))(HmtpO)] (1), cis-trans-[PtCl(5)(HmtpO)][(CH(3))(2)NH(2)] (2) have been prepared and structurally characterized by spectroscopic methods ((1)H, IR and X-ray crystallography (2)). The X-ray results indicate that the local geometry around the platinum(IV) centre approximates a typical octahedral arrangement with nitrogen atom N3 of the HmtpO and three chloride atoms in equatorial positions. The remaining two axial positions are occupied by two chlorides. The preliminary assessment of antitumor properties of (1) was performed as an in vitro antiproliferative activity against HL-60 human acute promyelocytic leukemia and HCV29T bladder cancer. The cis-trans-[PtCl(2)(OH)(2)(NH(3))(HmtpO)] (1) exhibits higher cytotoxic activity against HL-60 (IC(50)=6.4 μM) than cisplatin.

Synthesis of amphiphilic polythiophene for cell imaging and monitoring the cellular distribution of a cisplatin anticancer drug

A new amphiphilic conjugated polythiophene derivative (PT-Boc) is synthesized via Suzuki coupling reaction. The amphiphilic characteristic makes it form nanoaggregates in water, in which hydrophobic moieties come together to form the inner core. The polymer shows good photostability and no toxicity to human lung epithelial (A549) cells even at a high concentration (100 μg mL(-1) ). It therefore meets the crucial requirement for cellular imaging and other biological applications. The anticancer drug cisplatin is used as a model, and is linked to polythiophene to obtain a conjugate 'PT-Pt' by coordinated interactions between cisplatin and the amine groups of the polythiophene side chain. The PT-Pt can be used for monitoring the cellular distribution of cisplatin by fluorescence microscopy. The amphiphilic polythiophene provides a platform for fluorescent imaging of drugs and biological molecules in living cells.

Characterization of interactions between human serum albumin and tumor-inhibiting amino alcohol platinum(II) complexes using capillary electrophoresis

Platinum(II) complexes with amino alcohol ligands are of growing interest as anticancer agents capable of changing their reactivity toward biomolecules at different pH values. The binding of such compounds to the transport protein, human serum albumin (HSA), under simulated physiological conditions (pH 7.4, 100mM chloride, 37 degrees C) has been studied by capillary electrophoresis (CE), with the objective to acquire and compare their binding parameters. The association constants and stoichiometric ratios of the platinum-HSA adducts were determined by measuring the concentration changes of the peak area response of the Pt complex (after a 48 h incubation of the reaction mixture to attain equilibrium), constructing the binding isotherms, and their mathematical analysis. The investigated Pt(II) compounds were found to show moderate affinity toward HSA, with association constants ranging from 1.0 x 10(3) to 2.4 x 10(4)M(-1). Such binding behavior was attributed to a distinctive structural feature of bis(amino alcohol)platinum(II) complexes, that is, existence of an equilibrium between ring-opened and ring-closed forms in solution.

Cytotoxic efficacy of an anthraquinone linked platinum anticancer drug

Platinum complexes are widely used in cancer chemotherapy; however, they are associated with toxicity, high "non-specific" reactivity and relatively poor pharmacokinetic profiles. In particular, their low cellular uptake and rapid metabolic inactivation means that the amount of "active" drug reaching the nuclear compartment is low. Our strategy to facilitate nuclear accumulation was to introduce a hydrophobic anthraquinone (1C3) moiety to the Pt-complex. Anthraquinones are known to readily intercalate into DNA strands and hence, the Pt-1C3 complex may represent an effective system for the delivery of the platinum moiety to nuclear DNA. Efficacy of the complex was determined by measuring the extent and potency of cytotoxicity in comparison to cisplatin and an anthraquinone based anticancer drug, doxorubicin. The Pt-1C3 complex generated higher levels of cytotoxicity than cisplatin, with a potency of 19 +/- 4 microM in the DLD-1 cancer cell line. However, this potency was not significantly different to that of the 1C3 moiety alone. To examine the reason for the apparent lack of platinum related cytotoxicity, the cellular distribution was characterised. Confocal fluorescence microscopy indicated that the Pt-1C3 complex was rapidly sequestered into lysosomes, in contrast to the nuclear localisation of doxorubicin. In addition, there was negligible DNA associated Pt following administration of the novel complex. Thus, the addition of a 1C3 moiety generated sequestration of the complex to lysosomes, thereby preventing localisation to the nucleus.

Fluorescent Sugar and Uridine Conjugates of 1,8-Naphthalimides with Methyl and Ferrocenyl Headgroups

The first amphiphilic sugar and deoxyuridine conjugates with a 4-ethynyl-1,8-N-methylnaphthalimide linker, a 4-ethynyldeoxyuridine conjugate with a N-undecylferrocenyl headgroup, and a 1,8-naphthalimide with a 2,3,4,6-tetra-O-acetate-β-d-glucopyranoside headgroup have been synthesized. A novel acrylate monomeric precursor for sugar–ethynylnaphthalimide polymers is also reported. The ethynyl tether forms complexes with Co2(CO)8 and Co2(CO)6dppm. The single-crystal X-ray structures of 2′-propynyl-2,3,4,6-tetra-O-acetate-β-d-glucopyranoside 4 and 4-(2′-propynyl-2,3,4,6-tetra-O-acetate-β-d-glucopyranoside)-N-methyl-1,8-naphthalimide 6 are also reported. With the exception of the Co2 complexes, the sugar and deoxyuridine conjugates are strongly fluorescent. ‘On–off’ fluorescent switching is achieved in the deoxyuridine conjugate with an undecylferrocenyl headgroup.

Tumor-inhibiting platinum(II) complexes with aminoalcohol ligands: comparison of the mode of action by capillary electrophoresis and electrospray ionization-mass spectrometry

Capillary electrophoresis (CE) was used as an assay for studying the interaction of (SP-4-2)-bis[(R)-(-)-2-aminobutanol)dichloroplatinum(II) (1) and (SP-4-2)bis(4-aminobutanol)dichloroplatinum(II) (2) with guanosine 5'-monophosphate (GMP). CE kinetic measurements carried out at two physiological pH levels indicated that upon increasing the pH, 1 showed an appreciable change in binding behavior, with the rate of binding increased for more than 10 times as expressed by apparent half-life values of GMP (6.1 and 62.2 h at pH 6.0 and 7.4, respectively). The rate of GMP binding for 2 remained comparatively less affected by pH (half-lives of 8.5 and 10.6 h, respectively). Regardless of the nature of platinum complex and pH, the reaction with GMP tends to be decelerated at increased chloride concentrations in solution, this effect being particularly pronounced when changing from 4 mM (intracellular level) to 100 mM (extracellular level). The kinetic differences of platinum complexes were characterized in terms of the respective GMP-adducts structure, independently identified by means of off-line electrospray ionization-mass spectrometry. Also addressed was the interpretation of binding behavior as based on the structural features of the intact complexes, namely differing inclination to intramolecular chelation.