Cytotoxicity, mutagenicity, cellular uptake, DNA and glutathione interactions of lipophilic trans-platinum complexes tethered to 1-adamantylamine

The mechanism of antiproliferative activity of the oxaliplatin pyrophosphate derivative involves its binding to nuclear DNA in cancer cells

(1R,2R-diaminocyclohexane)(dihydropyrophosphato) platinum(II), also abbreviated as RRD2, belongs to a class of potent antitumor platinum cytostatics called phosphaplatins. Curiously, several published studies have suggested significant mechanistic differences between phosphaplatins and conventional platinum antitumor drugs. Controversial findings have been published regarding the role of RRD2 binding to DNA in the mechanism of its antiproliferative activity in cancer cells. This prompted us to perform detailed studies to confirm or rule out the role of RRD2 binding to DNA in its antiproliferative effect in cancer cells. Here, we show that RRD2 exhibits excellent antiproliferative activity in various cancer cell lines, with IC50 values in the low micromolar or submicromolar range. Moreover, the results of this study demonstrate that DNA lesions caused by RRD2 contribute to killing cancer cells treated with this phosphaplatin derivative. Additionally, our data indicate that RRD2 accumulates in cancer cells but to a lesser extent than cisplatin. On the other hand, the efficiency of cisplatin and RRD2, after they accumulate in cancer cells, in binding to nuclear DNA is similar. Our results also show that RRD2 in the medium, in which the cells were cultured before RRD2 accumulated inside the cells, remained intact. This result is consistent with the view that RRD2 is activated by releasing free pyrophosphate only in the environment of cancer cells, thereby allowing RRD2 to bind to nuclear DNA.

Synthesis of an amantadine-based novel Schiff base and its transition metal complexes as potential ALP, α-amylase, and α-glucosidase inhibitors

A Schiff base ligand HL, (E)-2-((adamantan-1-ylimino)methyl)-6-allylphenol, was synthesized by condensation of amantadine with 3-allyl-2-hydroxybenzaldehyde, followed by the synthesis of its Zn(ii), Co(ii), Cr(iii), and VO(iv) complexes under reflux conditions. The synthesized compounds were comprehensively elucidated by using different spectroscopic and analytical techniques: UV-Vis, ¹H and ¹³C-NMR, FT-IR, ESI-MS, thermal, and single-crystal XRD analysis. The chemical composition of the synthesized compounds was also verified by molar conductance and elemental analysis. An octahedral geometry for Cr(iii) and Co(ii) complexes, tetrahedral for Zn(ii) complex, and square pyramidal geometry have been proposed for VO(iv) complexes. The antidiabetic activities of the synthesized compounds were also evaluated by performing in vitro α-amylase and α-glucosidase inhibition studies. The Co(ii) complex exhibited the highest α-glucosidase inhibitory activity, whereas oxovanadium(iv) and zinc(ii) complexes were also found to be effective against α-amylase. In alkaline phosphatase (ALP) inhibition studies, the HL was found to be inactive, while the complexes showed remarkable enzyme inhibition in the following order: VO > Zn > Co, in a concentration-dependent manner.

Conjugation of triphenylantimony(V) with carvacrol against human breast cancer cells

The organoantimony derivative of formula trans-O,O-[Ph₃Sb^V(Carv)₂] (TPAC) (CarvH = carvacrol) is obtained by the oxidation of triphenylstibine (Ph₃Sb^III) with hydrogen peroxide in the presence of carvacrol (CarvH). Physical methods such as X-ray Fluorescence (XRF) spectroscopy, single crystal and powder X-ray diffraction analysis (XRD and PXRD), Attenuated Total Reflection Fourier Transform Infra-red (ATR-FTIR) spectroscopy, Thermogravimetric Differential Thermal Analysis (TG-DTA) and Differential Scanning Calorimetry (DTG/DSC), confirm the retention of the formula of TPAC throughout the sample mass in solid state, while UV-Vis spectroscopy in the solution. TPAC is the first example of carvacrol (the main ingredient of oregano) covalently bonded to any metal ion. Only the trans-O,O-[Ph₃Sb(Carv)₂] isomer was isolated suggesting stereo-selectivity of the preparation route. TPAC inhibits in vitro both human breast adenocarcinoma cell lines: MCF-7 (positive to hormones receptor (HR +)), MDA-MB-231 (negative to hormones receptor (HR-)) stronger than normal human fetal lung fibroblast cells (MRC-5). The MCF-7 cells morphology, DNA fragmentation, Acridine Orange/Ethidium Bromide (AO/EB) Staining, cell cycle arrest and mitochondrial membrane permeabilization tests suggest an apoptotic pathway for cell death, especially, through the mitochondrion damage. The binding type of TPAC toward the calf thymus CT-DNA was initially deduced ex vivo from the differentiation of the DNA solution viscosity. Fluorescence spectroscopy confirms the interaction mode suggested. Spectroscopic evidence (FTIR, UV-Vis) suggest that glutathione (GSH) (a tripeptide over-expressed in tumor cells) induces conversion of non-active pentavalent antimony, which is contained in TPAC, to active trivalent one, providing a new strategy for the development of targeted chemotherapeutics.

Synthesis, crystal structures, DFT studies, antibacterial assays and interaction assessments with biomolecules of new platinum(ii) complexes with adamantane derivatives

Synthesis, crystal structures and antibacterial activities of new Pt(ii) complexes with adamantane derivatives are presented in this article.

Half-sandwich Os(ii) and Ru(ii) bathophenanthroline complexes: anticancer drug candidates with unusual potency and a cellular activity profile in highly invasive triple-negative breast cancer cells

There is an urgent need to discover new, selective compounds to add to the limited arsenal of chemotherapeutics displaying selective toxicity for aggressive triple-negative breast cancer (TNBC) cells. The effect of two, recently developed metal-based half-sandwich complexes [Os(η6-pcym)(bphen)(dca)]PF6 (Os-dca) and [Ru(η6-pcym)(bphen)(dca)]PF6 (Ru-dca) [pcym = 1-methyl-4-(propan-2-yl)benzene (p-cymene); bphen = 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline); dca = dichloroacetate] on triple-negative breast cancer cells MDA-MB-231 is reported. The complexes display selective toxicity in several tumor cells (at submicromolar concentrations), and a prominent effect is observed against highly progressive triple negative breast cancer MDA-MB-231 cells for Os-dca. The lower potency of Ru-dca in comparison with Os-dca is apparently connected with a relatively quick release of the dca ligand due to the hydrolysis of Ru-dca before this complex enters the cells. Remarkably, both Os-dca and Ru-dca reduce successfully metastasis-related properties of the triple-negative breast cancer cells such as migration, invasion, and re-adhesion. The anti-metastatic effects of Os-dca and Ru-dca are associated with their ability to suppress matrix metalloproteinase activity and/or production and reduce the expression of aquaporins. Further detailed mechanistic studies reveal that Os-dca reverses Warburg's effect and oncosis seems to be a prominent mode of cell death that predominates over apoptosis. As such, Os-dca can efficiently overcome the resistance of cancer cells to clinically-used apoptotic inducers cisplatin and carboplatin. The cytostatic and anti-metastatic properties of Os-dca in MDA-MB-231 provide a strong impetus for the development of new metal-based compounds to target hardly treatable human TNBC cells and displaying different modes of action compared to the antitumor metallodrugs in clinical use.

Stimuli-Responsive Therapeutic Metallodrugs

The success of platinum-based anticancer agents has motivated the exploration of novel metal-based drugs for several decades, whereas problems such as drug-resistance and systemic toxicity hampered their clinical applications and efficacy. Stimuli-responsiveness of some metal complexes offers a good opportunity for designing site-specific prodrugs to maximize the therapeutic efficacy and minimize the side effect of metallodrugs. This review presents a comprehensive and up-to-date overview on the therapeutic stimuli-responsive metallodrugs that have appeared in the past two decades, where stimuli such as redox, pH, enzyme, light, temperature, and so forth were involved. The compounds are classified into three major categories based on the nature of stimuli, that is, endo-stimuli-responsive metallodrugs, exo-stimuli-responsive metallodrugs, and dual-stimuli-responsive metallodrugs. Representative examples of each type are discussed in terms of structure, response mechanism, and potential medical applications. In the end, future opportunities and challenges in this field are tentatively proposed. With diverse metal complexes being introduced, the foci of this review are pointed to platinum and ruthenium complexes.

Anticancer kiteplatin pyrophosphate derivatives show unexpected target selectivity for DNA

One of the promising new antitumor platinum complexes is a large-ring chelate complex [PtCl₂(cis-1,4-DACH)] (DACH = diaminocyclohexane) (kiteplatin). Recently, new platinum(ii) derivatives of kiteplatin with pyrophosphate as a carrier ligand have been synthesized and tested on a panel of human cancer cell lines. These derivatives of kiteplatin were found to be more effective than clinically used anticancer platinum drugs. The design of kiteplatin pyrophosphate derivatives was based on the concept of pyrophosphate coordinated platinum complexes, phosphaplatins. Phosphaplatins have been shown to function without binding to DNA and hence DNA has been excluded as the target of phosphaplatins in contrast to conventional antitumor platinum drugs. Cytotoxicity, major cellular targets and DNA interactions of the new anticancer platinum drug were characterized by standard biochemical methods and methods of molecular and cellular biology. We demonstrate that, in contrast to what has been reported on closely related phosphaplatins, the derivatives of kiteplatin with the pyrophosphate carrier ligand are activated in the cellular environment. This activation, which yields species capable of platination of DNA, very likely comprises the hydrolytic release of the pyrophosphate ligand that could be enzymatically catalyzed. Collectively, these data provide convincing evidence that unexpectedly DNA is an important target for the biological activity of the kiteplatin pyrophosphate derivatives, although the overall mechanism of action might be different from those of conventional platinum drugs.

In Vitro and in vivo Evaluation of Electrochemotherapy with trans-platinum Analogue trans-[PtCl2(3-Hmpy)2]

Background

Cisplatin is used in cancer therapy, but its side effects and acquired resistance to cisplatin have led to the synthesis and evaluation of new platinum compounds. Recently, the synthesized platinum compound trans-[PtCl₂(3-Hmpy)₂] (3-Hmpy = 3-hydroxymethylpyridine) (compound 2) showed a considerable cytotoxic and antitumour effectiveness. To improve compound 2 cytotoxicity in vitro and antitumour effectiveness in vivo, electroporation was used as drug delivery approach to increase membrane permeability (electrochemotherapy).

Materials and methods

In vitro, survival of sarcoma cells with different intrinsic sensitivity to cisplatin (TBLCl2 sensitive, TBLCl2Pt resistant and SA-1 moderately sensitive) was determined using a clonogenic assay after treatment with compound 2 or cisplatin electrochemotherapy. In vivo, the antitumour effectiveness of electrochemotherapy with compound 2 or cisplatin was evaluated using a tumour growth delay assay. In addition, platinum in the serum, tumours and platinum bound to the DNA in the cells were performed using inductively coupled plasma mass spectrometry.

Results

In vitro, cell survival after treatment with compound 2 electrochemotherapy was significantly decreased in all tested sarcoma cells with different intrinsic sensitivity to cisplatin (TBLCl2 sensitive, TBLCl2Pt resistant and SA-1 moderately sensitive). However, this effect was less pronounced compared to cisplatin. Interestingly, the enhancement factor (5-fold) of compound 2 cytotoxicity was equal in cisplatin-sensitive TBLCl2 and cisplatin-resistant TBLCl2Pt cells. In vivo, the growth delay of subcutaneous tumours after treatment with compound 2 electrochemotherapy was lower compared to cisplatin. The highest antitumour effectiveness after cisplatin or compound 2 electrochemotherapy was obtained in TBLCl2 tumours, resulting in 67% and 11% of tumour cures, respectively. Compound 2 induced significantly smaller loss of animal body weight compared to cisplatin. Furthermore, platinum amounts in tumours after compound 2 or cisplatin electrochemotherapy were approximately 2-fold higher compared to the drug treatment only, and the same increase of platinum bound to DNA was observed.

Conclusions

The obtained results in vitro and in vivo suggest compound 2 as a potential antitumour agent in electrochemotherapy.

Recent Advances in Platinum (IV) Complex-Based Delivery Systems to Improve Platinum (II) Anticancer Therapy

Cisplatin and its platinum (Pt) (II) derivatives play a key role in the fight against various human cancers such as testicular, ovarian, head and neck, lung tumors. However, their application in clinic is limited due to dose- dependent toxicities and acquired drug resistances, which have prompted extensive research effort toward the development of more effective Pt (II) delivery strategies. The synthesis of Pt (IV) complex is one such an area of intense research fields, which involves their in vivo conversion into active Pt (II) molecules under the reducing intracellular environment, and has demonstrated encouraging preclinical and clinical outcomes. Compared with Pt (II) complexes, Pt (IV) complexes not only exhibit an increased stability and reduced side effects, but also facilitate the intravenous-to-oral switch in cancer chemotherapy. The overview briefly analyzes statuses of Pt (II) complex that are in clinical use, and then focuses on the development of Pt (IV) complexes. Finally, recent advances in Pt (IV) complexes in combination with nanocarriers are highlighted, addressing the shortcomings of Pt (IV) complexes, such as their instability in blood and irreversibly binding to plasma proteins and nonspecific distribution, and taking advantage of passive and active targeting effect to improve Pt (II) anticancer therapy.

Cyclodextrin capped gold nanoparticles as a delivery vehicle for a prodrug of cisplatin

In this work, we explore the use of a quick coupling mechanism for "arming" a cyclodextrin coated gold nanoparticle (AuNP) delivery vehicle, 2, with an adamantane-oxoplatin conjugate that is a prodrug of cisplatin, 3, to produce a cytotoxic nanodrug, 4. The two-part arming system, which utilizes the well-known guest-host interaction between β-cyclodextrin and adamantane, may be useful for rapidly constituting polyfunctional nanodrugs prior to their application in chemotherapy. The 4.7 ± 1.1 nm delivery vehicle, 2, coated with per-6-thio-β-cyclodextrin (βSCD), was characterized using transmission electron microscopy and absorption spectroscopy, and the density of surface-attached βSCD molecules, ∼210 βSCD/AuNP, was determined using thermogravimetric analysis. Because (13)C NMR spectra of βSCD used in the study exhibited disulfide linkages and the observed surface density on the AuNP exceeded that possible for a close-packed mono layer, a fraction of the surface-attached βSCD molecules on the particle were oligomerized through disulfide linkages. Determination of the binding constant, K, for the 3-βCD interaction using (1)H NMR chemical shifts was complicated by the self-association of 3 to form a dimer through its conjugated adamantane residue. With a dimerization constant of K2 = 26.7 M(-1), the value of K for the 3-βCD interaction (1:1 stoichiometry) is 400-800 M(-1), which is lower than the value, K = 1.4 × 10(3) M(-1), measured for the 2-3 interaction using ICP-MS. Optical microscopy showed that when neuroblastoma SK-N-SH cells are treated with the nanodrug, 4 (2+3), clusters of gold nanoparticles are observed in the nuclear regions of living cells within 24 h after exposure, but, at later times when most cells are dying or dead, clustering is no longer observed. Treating the cells with 4 for 72 h gave percent inhibitions that are lower than that of cisplatin, suggesting that the Pt(IV) ions in 4 may be incompletely reduced to cytotoxic Pt(II) species in the cell.

Activation of trans geometry in bifunctional mononuclear platinum complexes by a non-bulky methylamine ligand

In order to shed light on the mechanism that underlies activity of bifunctional mononuclear Pt(II) analogs of transplatin we examined in the present work a DNA binding mode of the analog of transplatin, namely trans-[Pt(CH3NH2)2Cl2], in which NH3 groups were replaced only by a small, non-bulky methylamine ligand. This choice was made because we were interested to reveal the role of the bulkiness of the amines used to substitute NH3 in transplatin to produce antitumor-active Pt(II) drug. The results indicate that trans-[Pt(CH3NH2)2Cl2] forms a markedly higher amount of more distorting intrastrand cross-links than transplatin which forms in DNA preferentially less distorting and persisting monofunctional adducts. Also importantly, the accumulation of trans-[Pt(CH3NH2)2Cl2] in tumor cells was considerably greater than that of transplatin and cisplatin. In addition, the results of the present work demonstrate that the replacement of ammine groups by the non-bulky methylamine ligand in the molecule of ineffective transplatin results in a radical enhancement of its activity in tumor cell lines including cisplatin-resistant tumor cells. Thus, activation of the trans geometry in bifunctional mononuclear Pt(II) complexes can be also accomplished by replacement of ammine groups in transplatin by non-bulky methylamine ligands so that it is not limited only to the replacement by relatively bulky and stereochemically more demanding amino ligands.

Cellular accumulation and DNA interaction studies of cytotoxic trans-platinum anticancer compounds

Forty years after the discovery of the anticancer effects of cisplatin, scientists are still pursuing the development of platinum complexes with improved properties regarding side effects and resistance, which are two main problems in cisplatin treatment. Among these compounds, trans-configured platinum complexes with oxime ligands emerged as a new class with features distinct from those of established anticancer agents, including different DNA binding behavior, increased cellular accumulation, and a different pattern of protein interaction. We report herein on the reactivity with biomolecules of three novel pairs of cis- and trans-configured acetone oxime platinum(II) complexes and one pair of 3-pentanone oxime platinum(II) complexes. Cellular accumulation experiments and in vitro DNA platination studies were performed and platinum contents were determined by inductively coupled plasma mass spectrometry. The trans-configured complexes were accumulated in SW480 cells in up to 100 times higher amounts than cisplatin and up to 50 times higher amounts than their cis-configured counterparts; r (b) values (number of platinum atoms per nucleotide) were more than tenfold increased in cells treated with trans complexes compared with cells treated with cisplatin. The interaction of the complexes with DNA was studied in cell-free experiments with plasmid DNA (pUC19), in capillary zone electrophoresis with the DNA model 2-deoxyguanosine 5'-monophosphate, and in in vitro experiments showing the degree of DNA damage in the comet assay. Whereas incubation with cis compounds did not induce degradation of DNA, the trans complexes led to pronounced strand cleavage.

Thermodynamics of translesion synthesis across a major DNA adduct of antitumor oxaliplatin: differential scanning calorimetric study

Differential scanning calorimetry (DSC) was used to measure the thermodynamic changes associated with translesion synthesis across major lesion induced in DNA by antitumor oxaliplatin [1,2-d(GG) intrastrand cross-link]. Insertion of matched nucleotides dC at the primer terminus (across unique 3'- or 5'-dG in the unplatinated template) and subsequent extensions resulted in an incremental increase in thermodynamic parameters. In contrast, incorporation of dC opposite either platinated dG in the intrastrand cross-link formed in the template strand and subsequent extensions by one nucleotide resulted only in little changes in thermodynamics. A similar thermodynamic delay was observed for a control template primer containing a dG:dT mismatch across 3'- or 5'-dG in the template and subsequent Watson-Crick primer extensions. The thermodynamic scarcity generated by either the lesion or mismatches was not localized but extended to the 5'-downstream sites, which may be connected with the phenomenon termed "short-term memory" of replication errors retained by some DNA polymerases responding to DNA damages or mismatches. Interestingly, formation of the 1,2-d(GG) intrastrand cross-link of oxaliplatin altered the overall DSC profiles of the dG:dT mismatch template/primers only in a very small extent. While addition of matched nucleotide dC across either dG in the template strand was thermodynamically favored over the presence of a mismatched dT (ΔΔG(0)(310) was 7.6 or 6.8 kJ mol(-1), ΔΔH was 14 or 49 kJ mol(-1)), no such thermodynamic advantage was observed with the 1,2-d(GG) intrastrand cross-link of oxaliplatin at these positions (ΔΔG(0)(310) was 2.8 or -0.3 kJ mol(-1), ΔΔH was 4 or 9 kJ mol(-1)). The equilibrium thermodynamic data also provide insight into the processes associated with misincorporation of incorrect nucleotides during replication bypass across major cross-links of antitumor oxaliplatin. On the other hand, besides thermodynamic effects also kinetic factors play an important role in the processing of the cross-links of antitumor platinum drugs. The impact of the two effects in overall processing DNA adducts by a particular DNA polymerase will depend on its nature.

New synthesis of 6[3-(1-adamantyl)-4-methoxyphenyl]-2-naphthoic acid and evaluation of the influence of adamantyl group on the DNA binding of a naphthoic retinoid

6[3-(1-Adamantyl)-4-methoxyphenyl]-2-naphthoic acid (Adapalene®), a synthetic aromatic retinoid specific for RARβ and RARγ receptors, has been prepared utilizing a Pd/C-mediated Suzuki coupling between 6-bromo-2-naphthoic acid and 4-methoxyphenyl boronic acid, followed by introduction of an adamantyl group in the position 3 of the formed 6-(4-methoxyphenyl)-2-naphthoic acid. The interaction of 6-(4-methoxyphenyl)-2-naphthoic acid/ethyl ester and the 3-adamantyl analogs with DNA was studied in aqueous solution at physiological conditions by UV-vis spectroscopy. The calculated binding constants K(ligand-DNA) ranged between 1.1×10(4) M(-1) and 1.1×10(5) M(-1), the higher values corresponding to those of the adamantylated compounds. Molecular modeling studies have emphasized that the intercalative binding of adapalene and its derivatives to DNA is mainly stabilized by hydrophobic interactions related to the presence of the adamantyl group.

Differences in the cellular response and signaling pathways between cisplatin and monodentate organometallic Ru(II) antitumor complexes containing a terphenyl ligand

The new monofunctional Ru(II)-arene complex [(η⁶-arene)Ru(II)(en)Cl]+, where en = 1,2-diaminoethane and the arene is para-terphenyl (complex 1) exhibits promising cytotoxic effects in human tumor cells including those resistant to conventional cisplatin (J. Med. Chem.2008, 51, 5310). The present study is focused on the cellular pharmacology of 1 to elucidate more deeply the mechanisms underlying its antitumor effects. We have identified several cellular mechanisms induced by 1 in human ovarian carcinoma cells, including inhibition of DNA synthesis, overexpression and activation of p53, expression of proapoptotic proteins p21(WAF1) and Bax, G₀/G₁ arrest, and nuclear fragmentation as a result of apoptotic, and, to a much lower extent, also necrotic processes. Thus, 1 inhibits growth of the cancer cells through induction of apoptotic cell death and G₀/G₁ cell cycle arrest. Further investigations have shown that 1 induces apoptosis by regulating the expression of Bcl-2 family proteins. There were significant differences in cellular responses to the treatment with 1 and with conventional cisplatin, particularly in the kinetics and the extent of these responses. In addition, the distinct p53 activation profile of 1 compared with cisplatin provides an explanation for the activity of this ruthenium drug against cisplatin-resistant cells. Hence complex 1 may provide an alternative therapy in patients with acquired cisplatin resistance, particularly with respect to its very low mutagenicity and different mode of action compared to platinum antitumor drugs in clinical use.

Peroxotitanates for biodelivery of metals

Metal-based drugs are largely undeveloped in pharmacology. One limiting factor is the systemic toxicity of metal-based compounds. A solid-phase, sequestratable delivery agent for local delivery of metals could reduce systemic toxicity, facilitating new drug development in this nascent area. Amorphous peroxotitanates (APT) are ion-exchange materials with high affinity for several heavy metal ions and have been proposed to deliver or sequester metal ions in biological contexts. In the current study, we tested a hypothesis that APTs are able to deliver metals or metal compounds to cells. We exposed fibroblasts (L929) or monocytes (THP1) to metal-APT materials for 72 h in vitro and then measured cellular mitochondrial activity (SDH-MTT method) to assess the biological impact of the metal-APT materials versus metals or APT alone. APT alone did not significantly affect cellular mitochondrial activity, but all metal-APT materials suppressed the mitochondrial activity of fibroblasts (by 30-65% of controls). The concentration of metal-APT materials required to suppress cellular mitochondrial activity was below that required for metals alone, suggesting that simple extracellular release of the metals from the metal-APT materials was not the primary mechanism of mitochondrial suppression. In contrast to fibroblasts, no metal-APT material had a measurable effect on THP1 monocyte mitochondrial activity, despite potent suppression by metals alone. This latter result suggested that "biodelivery" by metal-APT materials may be cell type-specific. Therefore, it appears that APTs are plausible solid-phase delivery agents of metals or metal compounds to some types of cells for potential therapeutic effect.