Preparation, characterization and the anticancer activity of a novel series of triaminemonochloroplatinum(II) cations linked to anthraquinone intercalators

Binding of [Pt(1C3)(dien)](2+) to the duplex DNA oligonucleotide 5'-d(TGGCCA)-3': the effect of an appended positive charge on the orientation and location of anthraquinone intercalation

The binding of a platinum intercalator complex [Pt(1C3)(dien)](2+) (1C3 = 1-[(3-aminopropyl)amino]-anthracene-9,10-dione, dien = 3-azapentane-1,5-diamine) to DNA and to the self-complementary oligonucleotide 5'-d(TGGCCA)-3' has been investigated by UV-visible spectrophotometry and 2D NMR spectroscopy, respectively. The uncomplexed anthraquinone, 1C3, has an apparent DNA binding constant of 1.4 x 10(4), similar to that of ethidium bromide. Addition of the coordinatively saturated {Pt(dien)} moiety increases the binding constant to 3.7 x 10(5) M(-1), showing the effect of the increased positive charge introduced by this moiety. Multiple binding modes are evident from the lack of isosbestic points in the titration spectra and the non-linear nature of the half-reciprocal plot used to calculate the binding constant. [Pt(1C3)(dien)](2+) forms a 2 : 1 adduct with 5'-d(TGGCCA)-3' and is shown by 2D NMR to intercalate primarily in the TG:CA base pairs at the ends of the oligonucleotide with the side chain and {Pt(dien)} situated in the minor groove.

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.

Platinum-acridinylthiourea conjugates show cell line-specific cytotoxic enhancement in H460 lung carcinoma cells compared to cisplatin

Recently, we reported a new class of DNA-targeted hybrid platinum-acridine agents. The parent intercalator, ACRAMTU, a 9-aminoacridine derivative, intercalates into the minor groove of DNA, causing the corresponding prototypical conjugate, PT-ACRAMTU (type I/n=2), to form DNA adducts dissimilar to traditional platinum drugs. Both these agents show cytotoxic activity in leukemic and ovarian cancer cells. Following the use of clonogenic survival assays, we report on the cytotoxic effects of ACRAMTU, PT-ACRAMTU, and three PT-ACRAMTU derivatives, on additional cell lines including colon (RKO), lung (H460), and cisplatin-sensitive (A2780) and cisplatin-resistant (A2780/CP) ovarian cells. While a dose-dependent effect was observed with both ACRAMTU and PT-ACRAMTU, an enhanced cytotoxic effect was seen with PT-ACRAMTU in all cell lines. PT-ACRAMTU appeared to have a similar IC50 value to cisplatin except in H460 lung cancer cells in which PT-ACRAMTU had a twofold lower IC50 value. PT-ACRAMTU appeared to act in a time-dependent manner. In H460 cells the IC50 value of PT-ACRAMTU was 235-fold higher following a 1-h incubation than following a 24-h incubation (0.27 microM), while following an 8-h incubation the IC50 value was 0.41 microM. Three derivatives of PT-ACRAMTU were also tested. A tetraalkylated derivative, type II/n=2, generated the highest IC50 values in all cell lines, while the trialkylated derivative, type III/n=2, generated IC50 values similar to its isomer, PT-ACRAMTU. PT-ACRAMTU with an added CH2 group in the thiourea linker (type I/n=3) showed IC50 values similar to the type I/n=2 prototype in H460 lung cells. An apoptotic response to PT-ACRAMTU appeared to be generated in H460 cells as evidenced by DNA laddering. These results suggest that type I/n=2 and type I/n=3 may be promising agents for the treatment of lung cancer and should be pursued in animal models.

Dinuclear platinum complexes with N,N′-bis(aminoalkyl)-1,4-diaminoanthraquinones as linking ligands. Part I. Synthesis, cytotoxicity, and cellular studies in A2780 human ovarian carcinoma cells

A series of N, N'-bis(aminoalkyl)-1,4-diaminoanthraquinones (aminoalkyl=2-aminoethyl, 3-aminoprop-1-yl and 4-aminobut-1-yl) was functionalized with trans-platinum DNA-binding moieties. Cytotoxicity testing in A2780 human ovarian carcinoma cells revealed high anticancer activity of the formed cationic dinuclear platinum complexes. The cationic dinuclear platinum complexes with the shortest aminoalkyl chain were shown to be the most active, which agrees with the structure-activity relationship found for the corresponding free ligands without platinum. The N, N'-bis(aminoalkyl)-1,4-diaminoanthraquinones partly circumvent cisplatin resistance, whereas their dinuclear platinum complexes were found susceptible to the resistance mechanisms in A2780cisR. The platinum complexes have resistance factors comparable to the control dinuclear complex BBR3005 [(trans-PtCl(NH3)2)2)(micro-(NH2(CH2)6NH2))](NO3)2. The 1,4-diaminoanthraquinone moiety is fluorescent, and thus the cellular processing of the compounds could be monitored by time-lapse digital fluorescence microscopy. The intercalators without platinum were shown to enter the cells within minutes. The platinum complexes enter the cells more slowly. Most likely, the positive charges of the platinum complexes hamper the diffusion through the membrane. Interestingly, the platinum complexes are processed differently than the platinum-free compounds by the cells. After 24 hours the fluorescent platinum complexes are encapsulated in large vesicles in the cytosol. Co-localization of the anthraquinone fluorescence with Lysotracker Green DND-26 shows that these vesicles are acidic compartments, probably lysosomes.

Biophysical characterization and molecular modeling of the coordinative-intercalative DNA monoadduct of a platinum-acridinylthiourea agent in a site-specifically modified dodecamer

The guanine- N7 monoadduct of [Pt(en)Cl(ACRAMTU)](NO(3))(2) (PT-ACRAMTU; en=ethane-1,2-diamine, ACRAMTU=1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea), a dual metalating/intercalating cytotoxic agent, was generated in a double-stranded dodecamer, d(CCTCTCG*TCTCC/GGAGACGAGAGG) (III*), and isolated by preparative reverse-phase high-performance liquid chromatography (HPLC). The adduct was characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), circular-dichroism spectropolarimetry (CD), UV-melting curves, and NMR spectroscopy. In addition, a molecular mechanics/restrained molecular dynamics (MM/rMD) study was performed for this adduct using the AMBER force field. Monoadduction of the sequence leads to a pronounced increase in melting temperature, Delta T(m)= T(m)(III*)- T(m)(III)=9.7 degrees C. Because there is complete enthalpy-entropy compensation, binding occurs without noticeable thermodynamic destabilization. This feature and the CD (induced-ligand circular dichroism) and NMR (upfield shifts of aromatic acridine proton signals) data are indicative of a unique, nondenaturing dual-binding mode that involves partial intercalation of the acridine chromophore. An energy-minimized AMBER model ofIII* demonstrates that platination of G7- N7 of guanine in the major groove and partial insertion of the acridine moiety into the C6G19/G7C18 base step on the 5' face of the modified purine base is feasible and supportive of the experimental results. Differences in the biophysical properties betweenIII* and duplexes containing adducts of the clinical-drug cisplatin are outlined, and possible biological consequences are discussed.

DNA targeted platinum complexes: synthesis, cytotoxicity and DNA interactions of cis-dichloroplatinum(II) complexes tethered to phenazine-1-carboxamides

A series of intercalator-tethered platinum(II) complexes PtLCl2 have been prepared, where L are the diamine ligands N-[2-[(aminoethyl)amino]ethyl]-phenazine-1-carboxamide, N-[3-[(2-aminoethyl)amino]propyl]-phenazine-1-carboxamide, N-[4-[(2-aminoethyl)amino]butyl]-phenazine-1-carboxamide and N-[5-[(aminoethyl)amino]pentyl]-phenazine-1-carboxamide. Measurements of the time-course of unwinding of supercoiled pUC19 plasmid DNA by the phenazine complexes PtLCl2 reveal that the presence of the intercalator leads to enhanced rates of DNA platination when compared with the complex Pt(en)Cl2. The platinum(II) complexes where the polymethylene linker chain contains three, four or five carbon atoms are considerably more cytotoxic against murine P388/W than either cisplatin, Pt(en)Cl2, or the metal-free ligands themselves.

Preparation, characterization, and antitumor properties of cis-PtCl2 complexes linked to anthraquinones through position number 2

A new series of platinum-anthraquinone complexes of the type cis-PtLL'Cl2 [where L is the monodentate AQ-NH-(CH2)n-NH2 and L' = NH3 or LL' is the bidentate ligand AQ-NH-(CH2)n. NH-(CH2)2-NH2] in which the anthraquinone is linked to the diaminedichloroplatinum (II) moiety through position 2 was prepared and screened in vitro for antileukemic activity against P388 cells. All ligands were characterized by 1H and 13C NMR spectroscopy and all complexes by 195Pt NMR. The platinum complexes of anthraquinones which are modified in position 2 are significantly less potent than their analogs which are substituted in position 1. The activity of the complexes is either equal to or lower than the activity of the free ligands themselves. In the attempt to prepare AQ-NH-(CH2)4-NH-(CH2)2-NH2, a new compound, 2-(N-pyrrolidine)anthraquinone, was obtained and its structure was determined by x-ray crystallography. It crystallized in the monoclinic system in the space group P2(1)/c. The unit cell parameters are a = 9.595(1), b = 12.537(2), c = 11.461(1) A, beta = 94.14(2) degrees, V = 1375(1) A3, and z = 4.