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N Farrell

Publications and source records attributed to N Farrell.

At least 19 recordsLinked to original sources
PubMed2001

Novel approaches to polynuclear platinum pro-drugs. Selective release of cytotoxic platinum-spermidine species through hydrolytic cleavage of carbamates.

BBR3464 is a novel trinuclear platinum drug currently in Phase II clinical trials. Polyamine-bridged dinuclear platinum compounds as represented by [[trans-Pt(NH(3))(2)Cl](2)-mu-spermidine-N(1),N(8)]Cl(3) (1) are highly interesting second-generation analogues of BBR3464 because the hydrogen-bonding and electrostatic contributions of the central platinum-amine group in BBR3464 are replicated by the free, noncoordinated "central" quaternary nitrogens of the linear polyamine linker while the presence of two separate Pt-Cl bonds maintains the bifunctional binding mode on the DNA adducts. Preclinical investigations confirm the potency of these species with cytotoxicity in the nanomolar range. This remarkable potency results in a relatively narrow therapeutic index. To enhance the therapeutic index of these drugs, we investigated the potential for "pro-drug" delivery of less toxic and better tolerated derivatives such as the compounds [[trans-Pt(NH(3))(2)Cl](2)-mu-N(4)-R-spermidine-N(1),N(8)]Cl(2) where N(4)-R represents BOC (tert-butyl), CBz (benzyl), and Fmoc (fluorenylmethyl) carbamate blocking groups, 2-4, respectively. The bulky Fmoc derivative showed evidence for conformational isomers by (1)H NMR spectroscopy due to the inequivalence of the two n-propyl and n-butyl side chains of the spermidine moiety. The rate constants for hydrolysis and release of 1 were calculated. Release of cytotoxic 1 at physiologically relevant pH followed the order 4 > 2 > 3. The calculated values for 4 (pH 5, 6.0(+/-3.9) x 10(-10) s(-1); pH 6, 6.5(+/-0.2) x 10(-9) s(-1); pH 7, 6.0(+/-0.2) x 10(-8) s(-1); pH 8, 1.6(+/-0.1) x 10(-7) s(-1)) show a more pronounced pH dependence compared to 2 (pH 5, 4.6(+/-0.1) x 10(-8) s(-1); pH 6, 4.2(+/-0.1) x 10(-8) s(-1); pH 7, 3.2(+/-0.1) x 10(-8) s(-1)). Preliminary biological assays of cellular uptake and cytotoxicity confirm the utility of the pro-drug concept. While blocked-polyamine compounds such as 2-4 are, in general, 2-3 orders of magnitude less cytotoxic than 1, there is significant cell type variability. Specifically, the Fmoc derivative 4 showed significantly enhanced cytotoxicity warranting further study of the pro-drug concept for greater selectivity and/or oral delivery.

Animals↗
PubMed2001

Thermodynamic properties of duplex DNA containing a site-specific d(GpG) intrastrand crosslink formed by an antitumor dinuclear platinum complex.

Bifunctional polynuclear platinum compounds represent a novel class of metal-based antitumor drugs which are currently undergoing preclinical development. A typical agent is [(trans-PtCl(NH(3))(2))(2)H(2)N(CH(2))(4)NH(2)]Cl(2) (1,1/t,t), which coordinates to bases in DNA and forms various types of covalent crosslinks. It also forms a 1,2-d(GpG) intrastrand adduct, the equivalent of the major DNA lesion of 'classical' cisplatin. In the present study differential scanning calorimetry and spectroscopic techniques were employed to characterize the influence of this crosslink on the thermal stability and energetics of 20 bp DNA duplexes site-specifically modified by 1,1/t,t. Thermal denaturation data revealed that the crosslink of 1,1/t,t reduced thermal and thermodynamical stability of the duplex noticeably more than that of 'classical' cisplatin. The energetic consequences of the intrastrand crosslink at the d(GG) site are discussed in relation to the structural distortions induced by this adduct in DNA and to its recognition and binding by HMG domain proteins. It has been suggested that the results of the present work are consistent with different DNA binding modes of cisplatin and polynuclear bifunctional DNA-binding drugs, which might be relevant to their distinct biological effectiveness.

Antineoplastic Agents↗
PubMed2001

Conformation, recognition by high mobility group domain proteins, and nucleotide excision repair of DNA intrastrand cross-links of novel antitumor trinuclear platinum complex BBR3464.

The new antitumor trinuclear platinum compound [(trans-PtCl(NH(3))(2))(2)mu-trans-Pt(NH(3))(2)(H(2)N(CH(2))(6)NH(2))(2)](4+) (designated as BBR3464) is currently in phase II clinical trials. DNA is generally considered the major pharmacological target of platinum drugs. As such it is of considerable interest to understand the patterns of DNA damage. The bifunctional DNA binding of BBR3464 is characterized by the rapid formation of long range intra- and interstrand cross-links. We examined how the structures of the various types of the intrastrand cross-links of BBR3464 affect conformational properties of DNA, and how these adducts are recognized by high mobility group 1 protein and removed from DNA during in vitro nucleotide excision repair reactions. The results have revealed that intrastrand cross-links of BBR3464 create a local conformational distortion, but none of these cross-links results in a stable curvature. In addition, we have observed no recognition of these cross-links by high mobility group 1 proteins, but we have observed effective removal of these adducts from DNA by nucleotide excision repair. These results suggest that the processing of the intrastrand cross-links of BBR3464 in tumor cells sensitive to this drug may not be relevant to its antitumor effects. Hence, polynuclear platinum compounds apparently represent a novel class of platinum anticancer drugs acting by a different mechanism than cisplatin and its analogues.

Base Sequence↗
PubMed2001

Synthesis, characterization, and reactivity of trans-[PtCl(R'R''SO)(A)2]NO3 (R'R''SO = Me2SO, MeBzSO, MePhSO; A= NH3, py, pic). Crystal structure of trans-[PtCl(Me2SO)(py)2]+.

Trans complexes such as trans-[PtCl(2)(NH(3))(2)] have historically been considered therapeutically inactive. The use of planar ligands such as pyridine greatly enhances the cytotoxicity of the trans geometry. The complexes trans-[PtCl(R'R''SO)(A)(2)]NO(3) (R'R''SO = substituted sulfoxides such as dimethyl (Me(2)SO), methyl benzyl (MeBzSO), and methyl phenyl sulfoxide (MePhSO) and A = NH(3), pyridine (py) and 4-methylpyridine or picoline (pic)) were prepared for comparison of the chemical reactivity between ammine and pyridine ligands. The X-ray crystal structure determination for trans-[PtCl(Me(2)SO)(py)(2)]NO(3) confirmed the geometry with S-bound Me(2)SO. The crystals are orthorhombic, space group P2(1)2(1)2(1), with cell dimensions a = 7.888(2) A, b = 14.740(3) A, c =15.626(5) A, and Z = 4. The geometry around the platinum atom is square planar with l(Pt-Cl) = 2.304(4) A, l(Pt-S) = 2.218(5) A, and l(Pt-N) = 2.03(1) and 2.02(1) A. Bond angles are normal with Cl-Pt-S = 177.9(2) degrees, Cl-Pt-N(1) = 88.0(4) degrees, Cl-Pt-N(2) = 89.3(5) degrees, S-Pt-N(1) = 93.8(4) degrees, S-Pt-N(2) = 88.9(4) degrees, and N(1)-Pt-N(2) = 177.2(6) degrees. The intensity data were collected with Mo Kalpha radiation with lambda = 0.710 69 A. Refinement was by full-matrix least-squares methods to a final R value of 3.80%. Unlike trans-[PtCl(2)(NH(3))(2)], trans-[PtCl(2)(A)(2)] (A = py or pic) complexes do not react with Me(2)SO. The solvolytic products of cis-[PtCl(2)(A)(2)] (A = py or pic) were characterized. Studies of displacement of the sulfoxide by chloride were performed using HPLC. The sulfoxide was displaced faster for the pyridine complex relative to the ammine complex. Chemical studies comparing the reactivity of trans-[PtCl(R'R''SO)(amine)(2)]NO(3) with a model nucleotide, guanosine 5'-monophosphate (GMP), showed that the reaction gave two principal products: the species [Pt(R'R''SO)(amine)(2)(N7-GMP)], which reacts with a second equivalent of GMP, forming [Pt(amine)(2)(N7-GMP)(2)]. The reaction pathways were different, however, for the pyridine complexes in comparison to the NH(3) species, with sulfoxide displacement again being significantly faster for the pyridine case.

Antineoplastic Agents↗
PubMed2001

Kinetic analysis of the stepwise formation of a long-range DNA interstrand cross-link by a dinuclear platinum antitumor complex: evidence for aquated intermediates and formation of both kinetically and thermodynamically controlled conformers.

Reported here is a detailed study of the kinetics and mechanism of formation of a 1,4 GG interstrand cross-link by [(trans-PtCl(NH(3))(2))(2)(mu-NH(2)(CH(2))(n)NH(2))](2+) (1,1/t,t (n = 6), 1), the prototype of a novel class of platinum antitumor complexes. The reaction of the self-complementary 12-mer duplex 5'-[d(ATATGTACATAT)(2)] with (15)N-1 has been studied at 298 K, pH 5.4, by [(1)H,(15)N] HSQC 2D NMR spectroscopy. Initial electrostatic interactions with the duplex are observed for 1 and the monoaqua monochloro species (2). Aquation of 1 to yield 2 occurs with a pseudo-first-order rate constant of (4.15 +/- 0.04) x 10(-5) s(-1). 2 then undergoes monofunctional binding to the guanine N7 of the duplex to form 3 (G/Cl) with a rate constant of 0.47 +/- 0.06 M(-(1) s(-1). There is an electrostatic interaction between the unbound [PtN(3)Cl] group of 3 and the duplex, which is consistent with H-bonding interactions observed in the molecular model of the monofunctional (G/Cl) adduct. Closure of 3 to form the 1,4 GG interstrand cross-link (5) most likely proceeds via the aquated (G/H(2)O) intermediate (4) (pseudo-first-order rate constant = (3.62 +/- 0.04) x 10(-5) s(-1)) followed by closure of 4 to form 5 (rate constant = (2.7 +/- 1.5) x 10(-3) s(-1)). When closure is treated as direct from 3 (G/Cl) the rate constant is (3.39 +/- 0.04) x 10(-5) s(-1). Closure is ca. 10-55-fold faster than that found for 1,2 GG intrastrand cross-link formation by the diaqua form of cisplatin. Changes in the (1)H and (15)N shifts of the interstrand cross-link 5 indicate that the initially formed conformer (5(i)) converts irreversibly into other product conformer(s) 5(f). The NMR data for 5(i) are consistent with a molecular model of the 1,4 GG interstrand cross-link on B-form DNA, which shows that the NH(2) protons have no contacts except with solvent. The NMR data for 5(f) show several distinct NH(2) environments indicative of interactions between the NH(2) protons and the DNA. HPLC characterization of the final product showed only one major product peak that was confirmed by ESI-FTICR mass spectroscopy to be a cross-linked adduct of (15)N-1 and the duplex. The potential significance of these findings to the antitumor activity of dinuclear platinum complexes is discussed.

Antineoplastic Agents↗
PubMed2000

Synthesis, characterization, and cytotoxicity of trifunctional dinuclear platinum complexes: comparison of effects of geometry and polyfunctionality on biological activity.

The synthesis of two new isomeric trifunctional dinuclear platinum complexes of formula [¿PtCl(NH(3))(2)¿micro-NH(2)(CH(2))(6)NH(2)-¿PtCl(2)(N H(3))¿](+) (1, 2/c,c and 1,2/t,c) is reported. Their biological activity in selected human tumor cell lines sensitive and resistant to CDDP (cisplatin, cis-[Pt(NH(3))(2)Cl(2)]) is described and compared with the profile for their bifunctional analogues, [¿cis/trans-PtCl(NH(3))(2)¿(2)micro-NH(2)(CH(2))(6)NH(2)](2+ ). The trifunctional dinuclear platinum complexes showed a unique profile of cytotoxicity against human cancer cell lines, with low resistance factors in A2780, CH1, and 41M cell lines. The resistance factor is dependent on the geometry of the Pt coordination spheres - suggesting that these may be associated with DNA-binding modes. Retention of activity against CDDP-resistant cell lines and a different spectrum of activity compared to CDDP and also within different classes of polynuclear platinum complexes suggest that not only are they mechanistically different from mononuclear platinum complexes but also each individual class of polynuclear platinum structure may have its own unique character.

Amines↗
PubMed2000

Sequence specificity, conformation, and recognition by HMG1 protein of major DNA interstrand cross-links of antitumor dinuclear platinum complexes.

Interactions of high mobility group (HMG) domain proteins with DNA modified by cisplatin plays a role in mechanisms underlying its antitumor activity. A structural motif recognized by HMG domain proteins on cisplatin-modified DNA is a stable, directional bend of the helix axis. In the present work, bending induced in DNA by major adducts of a novel class of antitumor compounds, represented by the formula [¿trans-PtCl(NH(3))(2)¿H(2)N(CH(2))(2-6)NH(2)]Cl(2), was investigated. The oligodeoxyribonucleotide duplexes containing various site-specific interstrand cross-links of these bifunctional dinuclear platinum drugs were purified and characterized by Maxam-Gilbert footprinting, chemical probing, and phasing assay. It was demonstrated that the cross-links of the dinuclear compounds bent the helix much less than those of cisplatin. Gel retardation assay revealed very weak recognition of DNA adducts of dinuclear complexes by HMG1 protein. Hence, the mediation of antitumor properties of dinuclear platinum complexes by HMG domain proteins is unlikely so that polynuclear platinum compounds may represent a novel class of platinum anticancer drugs acting by a different mechanism than cisplatin and its analogues. A further understanding of how polynuclear platinum compounds modify DNA and how these modifications are processed in cells should provide a rational basis for the design of new platinum drugs rather than searching for cisplatin analogues.

Antineoplastic Agents↗
PubMed2000

Inversion of the cis geometry requirement for cytotoxicity in structurally novel platinum(II) complexes containing the bidentate N,O-donor pyridin-2-yl-acetate.

Water soluble platinum(II) complexes have been synthesized that contain the N,O-chelate pyridin-2-yl acetate (PyAc) as a novel structural motif in platinum antitumor complexes. The trans-platinum complex trans-[PtCl(PyAc-N,O)(NH3)] (2) (N-donors are trans) and its isomer cis-[PtCl(PyAc-N,O)(NH3)] (4) (N trans to Cl) were prepared from trans-[PtCl2((NH3)(PyAcH)].H2O (1.H2O) and cis-[PtCl2(NH3)(PyAcMe) (3), respectively, employing the bidentate ligand as its methylester (PyAcMe). 2 and 4 are readily formed from the respective dichloro species, even at low pH and in the presence of extra chloride, indicating a high thermodynamic stability of the PyAc chelate ring. 1.H2O and 2-4 were characterized by 1H NMR and IR spectroscopy and elemental analyses. The solid-state structure of 2 was determined: triclinic, P1 (no. 2), with a = 8.170(2) A, b = 9.274(3) A, c = 7.374(2) A, alpha = 108.68(2) degrees, beta = 113.27(2) degrees, gamma = 74.40(2) degrees, V = 479.7(6) A3, Z = 2. The six-membered metallacyclus in 2 adopts a "boat" form, allowing a strainless coordination of platinum. The most promising cytotoxic properties in the above series of compounds have been established for 2 (and 1, which rapidly transforms into 2 at 37 degrees C and neutral pH). Preliminary ID50 values were 0.88 and 1.26 microM, respectively, in cisplatin-sensitive L1210 leukemia. Both compounds proved to be cross-resistant to the clinical drug. Reactions of 2 and 4 with 5'-guanosine monophosphate (5'-GMP) under physiological conditions gave the monofunctional adducts trans- and cis-[Pt(5'-GMP-N7)(PyAc-N,O)(NH3)] (I and II). Chelate-bound carboxylate was not replaced by guanine-N7 when an excess of nucleotide was applied (NMR). In an analogous reaction, 2 reacts with the oligonucleotide d(TCGT) [5'-T(1)-C(2)-G(3)-T(4)-3'] to give the adduct d(TCGT)-N7(3)-Pt(PyAc-O,N)(NH3) (III), which was characterized by a combination of total correlation spectroscopy, double-quantum-filtered correlation spectroscopy, nuclear Overhauser effect spectrometry, and rotating-frame Overhauser enhancement spectroscopy experiments. Binding of the [Pt(PyAc-N,O)(NH3)]+ fragment to N7 of G(3) causes an increase of N-type character of the T(4) and G(3) deoxyribose residues relative to the unplatinated sequence, while those of T(1) and C(2) remain S-type. An internucleotide nuclear Overhauser effect between H6(4) and H2'(3) indicates stacking between guanine and the 3'-thymine base. The most striking feature proved to be the pronounced upfield shift and broadening of the 1H NMR signals assigned to the base protons H5 and H6 in III. Magnetization transfer between H5(2) and H3 of pyridine suggests that this effect is caused by base-base interactions involving the planar ligand on platinum, which must be situated on the 5' face of guanine. Possible implications for the DNA binding and cytotoxic effect of the compounds are discussed.

Acetates↗
PubMed2000

Equilibrium and kinetic studies of the aquation of the dinuclear platinum complex [[trans-PtCl(NH3)2]2(mu-NH2(CH2)6NH2)]2+: pKa determinations of aqua ligands via [1H,15N] NMR spectroscopy.

By the use of [1H,15N] heteronuclear single quantum coherence (HSQC) 2D NMR spectroscopy and electrochemical methods we have determined the hydrolysis profile of the bifunctional dinuclear platinum complex [[trans-PtCl(15NH3)2]2(mu-15NH2(CH2)(6)15NH2)]2+ (1,1/t,t (n = 6), 15N-1), the prototype of a novel class of potential antitumor complexes. Reported are estimates for the rate and equilibrium constants for the first and second aquation steps, together with the acid dissociation constant (pKa1 approximately pKa2 approximately pKa3). The equilibrium constants determined by NMR at 25 and 37 degrees C (I = 0.1 M) were similar, pK1 approximately pK2 = 3.9 +/- 0.2, and from a chloride release experiment at 37 degrees C the values were found to be pK1 = 4.11 +/- 0.05 and pK2 = 4.2 +/- 0.5. The forward and reverse rate constants for aquation determined from this chloride release experiment were k1 = (8.5 +/- 0.3) x 10(-5) s-1 and k-1 = 0.91 +/- 0.06 M-1 s-1, where the model assumed that all the liberated chloride came from 1. When the second aquation step was also taken into account, the rate constants were k1 = (7.9 +/- 0.2) x 10(-5) s-1, k-1 = 1.18 +/- 0.06 M-1 s-1, k2 = (10.6 +/- 3.0) x 10(-4) s-1, k-2 = 1.5 +/- 0.6 M-1 s-1. The rate constants compare favorably with other complexes with the [PtCl(am(m)ine)3]+ moiety and indicate that the equilibrium of all these species favors the chloro form. A pKa value of 5.62 was determined for the diaquated species [[trans-Pt(15NH3)2(H2O)]2(mu-15NH2(CH2)(6)15NH2)]4+ (3) using [1H,15N] HSQC NMR spectroscopy. The speciation profile of 1 and its hydrolysis products under physiological conditions is explored.

Cisplatin↗
PubMed2000

Kinetics and mechanism for reduction of anticancer-active tetrachloroam(m)ine platinum(IV) compounds by glutathione.

Glutathione (GSH) reduction of the anticancer-active platinum(IV) compounds trans-[PtCl4(NH3)(thiazole)] (1), trans-[PtCl4(cha)(NH3)] (2), cis-[PtCl4(cha)(NH3)] (3) (cha=cyclohexylamine), and cis-[PtCl4(NH3)2] (4) has been investigated at 25 degrees C in a 1.0 M aqueous medium at pH 2.0-5.0 (1) and 4.5-6.8 (2-4) using stopped-flow spectrophotometry. The redox reactions follow the second-order rate law d[Pt(IV)]/dt=k[GSH]tot[Pt(IV)], where k is a pH-dependent rate constant and [GSH]tot the total concentration of glutathione. The reduction takes place via parallel reactions between the platinum(IV) complexes and the various protolytic species of glutathione. The pH dependence of the redox kinetics is ascribed to displacement of these protolytic equilibria. The thiolate species GS is the major reductant under the reaction conditions used. The second-order rate constants for reduction of compounds 1-4 by GS- are (1.43 +/- 0.01) x 10(7), (3.86 +/- 0.03) x 10(6), (1.83 +/- 0.01) x 10(6), and (1.18 +/- 0.01) x 10(6) M(-1)s(-1), respectively. Rate constants for reduction of 1 by the protonated species GSH are more than five orders of magnitude smaller. The mechanism for the reductive elimination reactions of the Pt(IV) compounds is proposed to involve an attack by glutathione on one of the mutually trans coordinated chloride ligands, leading to two-electron transfer via a chloride-bridged activated complex. The kinetics results together with literature data indicate that platinum(IV) complexes with a trans Cl-Pt-Cl axis are reduced rapidly by glutathione as well as by ascorbate. In agreement with this observation, cytotoxicity profiles for such complexes are very similar to those for the corresponding platinum(II) product complexes. The rapid reduction within 1 s of the platinum(IV) compounds with a trans Cl-Pt-C1 axis to their platinum(II) analogs does not seem to support the strategy of using kinetic inertness as a parameter to increase anticancer activity, at least for this class of compounds.

Antineoplastic Agents↗
PubMed2000

Steric control of DNA interstrand cross-link sites of trans platinum complexes: specificity can be dictated by planar nonleaving groups.

Recent findings that novel trans-dichloroplatinum(II) complexes exhibit antitumor activity violate the classical structure-activity relationships of platinum(II) complexes. These novel "nonclassical" trans platinum complexes also comprise those containing planar aromatic amines. Initial studies have shown that these compounds form a considerable amount of DNA interstrand cross-links (up to approximately 30%) with a rate markedly higher than clinically ineffective transplatin. The present work has shown, using Maxam-Gilbert footprinting, that trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)], representatives of the group of new antitumor trans-dichloroplatinum complexes containing planar amines, preferentially form DNA interstrand cross-links between guanine residues at the 5'-GC-3' sites. Thus, DNA interstrand cross-linking by trans-[PtCl2(NH3)(quinoline)] and trans-[PtCl2(NH3)(thiazole)] is formally equivalent to that by antitumor cisplatin, but different from clinically ineffective transplatin which preferentially forms these adducts between complementary guanine and cytosine residues. This result shows for the first time that simple chemical modification of the structure of an inactive compound alters its DNA binding site into a DNA adduct of an active drug.

Antineoplastic Agents↗
PubMed2000

Modulation of the chemical and biological properties of trans platinum complexes: monofunctional platinum complexes containing one nucleobase as potential antiviral chemotypes.

Replacement of one of the chloride leaving groups in trans-[PtCl2(NH3)(L)] by the nucleobase 9-ethylguanine gives the nucleobase cations [SP-4-2]-[PtCl(9-ethylguanine)(NH3)(L)]+ (L = NH3, 1; L = quinoline, 3), which are models for the monofunctional adduct on DNA. Displacement of Cl- in 1 and 3 by either 5'-guanosine monophosphate (5'-GMP) or N-acetyl-L-methionine (N-AcMet) showed clear kinetic preference for the sulfur (estimated half-lives of 1.5 and 4 h with N-AcMet against 7 and 17 h for 5'-GMP for 1 and 3, respectively). To further examine the kinetic preference, 1-methylcytosine (1-MeCyt) analogs were prepared, [SP-4-2]-[PtCl(1-Me-Cyt)(NH3)(L)]+ (L=NH3, 2; L=quinoline, 4). The -MeCyt compounds, 2 and 4, resulted in slower rates of substitution by both 5'-GMP and N-AcMet in comparison to 1 and 3 (estimated half-lives for N-AcMet of 5 and 13.5 h and for 5'-GMP of 6 and 14 h for 2 and 4, respectively). Interestingly in this case, however, no selectivity for the sulfur site was observed, a possible explanation being that molecular recognition across the square plane enhances the rate of reaction with 5'-GMP. The affinity of 3 towards S-donor ligands was exploited to remove zinc from the zinc-finger site of the C-terminal finger of the HIV-nucleocapsid protein, NCp7. The ability to eject zinc further suggested the biological antiviral application of [SP-4-2]-[PtCl(nucleobase)(NH3)(L)]+. A preliminary survey against HIV and herpes viruses indeed showed encouraging results with some antiviral specificity, dependent on the exact nature of the compound. The initial results suggest consideration of [SP-4-2]-[PtCl(nucleobase)(NH3)(L)]+ as a novel antiviral chemotype.

Anti-HIV Agents↗
PubMed2000

BBR 3464: a novel triplatinum complex, exhibiting a preclinical profile of antitumor efficacy different from cisplatin.

Multinuclear platinum complexes represent a new class of anticancer agents, distinct in terms of DNA binding features and the profile of antitumor activity from their mononuclear counterparts, in particular cisplatin. Among complexes of this class, BBR 3464, a trinuclear platinum compound has been selected for preclinical development. In the present study, we describe the preclinical evaluation of BBR 3464 in a series of human tumor cell lines and tumor xenografts, with special emphasis on tumor types known to be resistant to cisplatin. In a panel of seven human tumor cell lines naturally resistant to cisplatin (three ovarian and four melanomas), BBR 3464 was extremely potent with IC50 values at least 20-fold lower than cisplatin. Against eight human tumor xenografts including four tumors refractory to cisplatin, BBR 3464 was confirmed to be very active with a tumor weight inhibition >80% in seven of them. The efficacy of BBR 3464 against cisplatin-resistant tumors was consistent with the ability of the drug to completely overcome resistance in three cell systems characterized by acquired resistance to cisplatin. Moreover, BBR 3464 caused a more prolonged effect than cisplatin, which was reflected by higher specific growth delay values. This prolonged effect is likely to be related to a more persistent perturbation of the cell cycle induced by BBR 3464 than by cisplatin, as shown in one ovarian tumor cell line. Finally, the profile of sensitivity to BBR 3464 within the 60-cell-lines screening panel of the National Cancer Institute, NIH (Bethesda, MD) differed from those of established drugs, thus supporting the hypothesis of a distinct mechanism of cytotoxic activity of BBR 3464. The novel trinuclear platinum complex, in light of its innovative antitumor activity profile, has the potential to become a useful clinical agent for the treatment of unresponsive tumors.

Animals↗
PubMed1999

Consequences of nucleic acid conformation on the binding of a trinuclear platinum drug.

BBR3464, a charged trinuclear platinum compound, is the first representative of a new class of anticancer drugs to enter phase I clinical trials. The structure of BBR3464 is characterized by two [trans-PtCl(NH(3))(2)] units linked by a tetraamine [trans-Pt(NH(3))(2)¿H(2)N(CH(2))(6)NH(2)¿(2)] unit. The +4 charge of BBR3464 and the separation of the platinating units indicate that the mode of DNA binding will be distinctly different from those of classical mononuclear drugs such as cisplatin, cis-[PtCl(2)(NH(3))(2)]. The reaction of BBR3464 with three different nucleic acid conformations was assessed by gel electrophoresis. Comparison of single-stranded DNA, RNA, and double-stranded DNA indicated that the reaction of BBR3464 with single-stranded DNA and RNA was faster than that with duplex DNA, and produced more drug-DNA and drug-RNA adducts. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to further characterize the binding modes of BBR3464 with the DNA substrates. BBR3464 binding to different nucleic acid conformations raises the possibility that the adducts of single-stranded DNA and RNA may play a role in the different antitumor efficacies of this novel drug as compared with cisplatin.

Antineoplastic Agents↗
PubMed1999

Effect of geometric isomerism in dinuclear platinum antitumor complexes on DNA interstrand cross-linking.

The requirement for novel platinum antitumor drugs led to the synthesis of dinuclear bisplatinum complexes. To understand the molecular mechanisms underlying the biological activity of this new class of platinum cytostatics, modifications of natural DNA and synthetic oligodeoxyribonucleotide duplexes by dinuclear bisplatinum complexes with equivalent monofunctional coordination spheres, represented by the general formula [{cis-PtCl(NH(3))(2)}(2)(H(2)N-R-NH(2)](2+) (1,1/c,c), in which R is a linear alkane chain, butane or hexane, were studied by various biochemical and molecular biology methods. The results indicated that the major adducts of 1,1/c,c complexes in DNA ( approximately 90%) were interstrand cross-links preferentially formed between guanine residues. Besides 1,2 interstrand cross-links (between guanine residues in neighboring base pairs), 1,3 or 1,4 interstrand cross-links were also possible. In the latter two long-range adducts, the sites involved in the cross-links were separated by one or two base pairs. 1,2, 1,3, and 1,4 interstrand cross-links were formed with a similar rate and were preferentially oriented in the 5' --> 5' direction. In addition, the DNA adducts of these complexes inhibited DNA transcription in vitro. Thus, the binding of the 1,1/c, c complexes modifies DNA in a way that is distinctly different from the modification by the antitumor drug cisplatin. In addition, there are significant differences between the dinuclear 1,1/c,c and 1,1/t, t isomers. The results of this work are consistent with the hypothesis and support the view that platinum drugs that bind to DNA in a fundamentally different manner can exhibit different biological properties including the spectrum and intensity of antitumor activity. The intracellular DNA binding of the dinuclear compounds is compared to the results presented here. It has been suggested that differences in cross-link structure may be an important factor underlying their different biological efficiencies.

Antineoplastic Agents↗
PubMed1999

DNA modifications by a novel bifunctional trinuclear platinum phase I anticancer agent.

The DNA-binding profile of a novel, trinuclear platinum Phase I clinical agent (BBR3464) is summarized. The structure of BBR3464 is best described as two trans-[PtCl(NH3)2] units linked by a tetra-amine [trans-Pt(NH3)2{H2N(CH2)6NH2}2]2+ unit. The +4 charge of BBR3464, the presence of at least two Pt coordination units capable of binding to DNA, and the consequences of such DNA binding are remarkable departures from the cisplatin structural paradigm. The chemical and biological features argue that the drug should be considered the first clinical representative of an entirely new structural class of DNA-modifying anticancer agents. The high charge on BBR3464 facilitates rapid binding to DNA with a t1/2 of approximately 40 min, significantly faster than the neutral cisplatin. The melting temperature of DNA adducted by BBR3464 increased at low ionic strength but decreased in high salt for the same rb. This unusual behavior is in contrast to that of cisplatin. BBR3464 produces an unwinding angle of 14 degrees in negatively supercoiled pSP73 plasmid DNA, indicative of bifunctional DNA binding. Quantitation of interstrand DNA-DNA cross-linking in plasmid pSP73 DNA linearized by EcoRI indicated approximately 20% of the DNA to be interstrand cross-linked. While this is significantly higher than the value for cisplatin, it is, interestingly, lower than that for dinuclear platinum compounds such as [{trans-PtCl(NH3)2}2H2N(CH2)6NH2]2+ (BBR3005) where interstrand cross-linking efficiency may be as high as 70-90%. Either the presence of charge in the linker backbone or the increased distance between platinating moieties may contribute to this relatively decreased ability of BBR3464 to induce DNA interstrand cross-linking. Fluorescence experiments with ethidium bromide were consistent with the formation of long-range delocalized lesions on DNA produced by BBR3464. The sequence preference for BBR3464 on plasmid DNA was determined to the exact base pair by assaying extension of the polynucleotide by VentR(exo+) DNA polymerase. Strong sequence preference for single dG or d(GG) sites was suggested. The presence of relatively few blocks on DNA in comparison to either cisplatin or BBR3005 was indicative of high sequence selectivity. The following appropriate sequence where stop sites occur was chosen: [sequence: see text] molecular modeling on 1,4 interstrand (G'30 to G33) and 1,5 intrastrand (G33 to G29) cross-links further confirmed the similarity in energy between the two forms of cross-link. Finally, immunochemical analysis confirmed the unique nature of the DNA adducts formed by BBR3464. This analysis showed that antibodies raised to cisplatin-adducted DNA did not recognize DNA modified by BBR3464. In contrast, DNA modified by BBR3464 inhibited the binding of antibodies raised to transplatin-adducted DNA. Thus, the bifunctional binding of BBR3464 contains few similarities to that of cisplatin but may have a subset of adducts recognized as being similar to the transplatinum species. In summary, the results point to a unique profile of DNA binding for BBR3464, strengthening the original hypothesis that modification of DNA binding in manners distinct from that of cisplatin will also lead to a distinct and unique profile of antitumor activity.

Antineoplastic Agents↗