C-myc G-quadruplex DNA Research Articles

The binding of a c-MYC promoter G-quadruplex to neurotransmitters: An analysis of G-quadruplex stabilization using DNA melting, fluorescence spectroscopy, surface-enhanced Raman scattering and molecular docking

The interactions of several neurotransmitter and neural hormone molecules with the c-MYC G-quadruplex DNA sequence were analyzed using a combination of spectroscopic and computational techniques. The interactions between indole, catecholamine, and amino acid neurotransmitters and DNA sequences could potentially add to the understanding of the role of G-quadruplex structures play in various diseases. Also, the interaction of the DNA sequence derived from the nuclear hypersensitivity element (NHE) III1 region of c-MYC oncogene (Pu22), 5′-TGAGGGTGGGTAGGGTGGGTAA-3′, has added significance in that these molecules may promote or inhibit the formation of G-quadruplex DNA which could lead to the development of promising drugs for anticancer therapy. The results showed that these molecules did not disrupt G-quadruplex formation even in the absence of quadruplex-stabilizing cations. There was also evidence of concentration-dependent binding and high binding affinities based on the Stern-Volmer model, and thermodynamically favorable interactions in the form of hydrogen-bonding and interactions involving the π system of the aromatic neurotransmitters.

Ruthenium(II) Complexes Coupled by Erianin Via a Flexible Carbon Chain as a Potential Stabilizer of c-myc G-Quadruplex DNA

Herein, two novel ruthenium(II) complexes coupled by erianin via a flexible carbon chain, [Ru(phen)2(L1-(CH2)4-erianin)](ClO4)2 (L1 = 2-(2-(tri-fluoromethyphenyl))-imidazo [4,5f][1-10]phenanthroline (1) and [Ru(phen)2(L2-(CH2)4-eria)](ClO4)2 (L2 = 2-(4-(tri-fluoromethyphenyl))-imidazo [4,5f][1,10]phenanthroline (2), have been synthesized and investigated as a potential G-quadruplex(G4) DNA stabilizer. Both complexes, especially 2, can bind to c-myc G4 DNA with high affinity by electronic spectra, and the binding constant calculated for 1 and 2 is about 15.1 and 2.05 × 107 M-1, respectively. This was further confirmed by the increase in fluorescence intensity for both complexes. Moreover, the positive band at 265 nm in the CD spectra of c-myc G4 DNA decreased treated with 2, indicating that 2 may bind to c-myc G4 DNA through extern groove binding mode. Furthermore, fluorescence resonance energy transfer (FRET) assay indicated that the melting point of c-myc G4 DNA treated with 1 and 2 increased 15.5 and 16.5 °C, respectively. Finally, molecular docking showed that 1 can bind to c-myc G4 DNA in the extern groove formed by base pairs G7-G9 and G22-A24, and 2 inserts into the small groove of c-myc G4 DNA formed by base pairs T19-A24. In summary, these ruthenium(II) complexes, especially 2, can be developed as potential c-myc G4 DNA stabilizers and will be exploited as potential anticancer agents in the future.

Novel Chiral Ru(II) Complexes as Potential c-myc G-quadruplex DNA Stabilizers Inducing DNA Damage to Suppress Triple-Negative Breast Cancer Progression.

Currently, effective drugs for triple-negative breast cancer (TNBC) are lacking in clinics. c-myc is one of the core members during TNBC tumorigenesis, and G-rich sequences in the promoter region can form a G-quadruplex conformation, indicating that the c-myc inhibitor is a possible strategy to fight cancer. Herein, a series of chiral ruthenium(II) complexes ([Ru(bpy)2(DPPZ-R)](ClO4)2, Λ/Δ-1: R = -H, Λ/Δ-2: R = -Br, Λ/Δ-3: R = -C≡C(C6H4)NH2) were researched based on their interaction with c-myc G-quadruplex DNA. Λ-3 and Δ-3 show high affinity and stability to decrease their replication. Additional studies showed that Λ-3 and Δ-3 exhibit higher inhibition against different tumor cells than other molecules. Δ-3 decreases the viability of MDA-MB-231 cells with an IC50 of 25.51 μM, which is comparable with that of cisplatin, with an IC50 of 25.9 μM. Moreover, Δ-3 exhibits acceptable cytotoxic activity against MDA-MB-231 cells in a zebrafish xenograft breast cancer model. Further studies suggested that Δ-3 decreases the viability of MDA-MB-231 cells predominantly through DNA-damage-mediated apoptosis, which may be because Δ-3 can induce DNA damage. In summary, the results indicate that Ru(II) complexes containing alkinyl groups can be developed as c-myc G-quadruplex DNA binders to block TNBC progression.

Investigation of the Interaction between Aloe vera Anthraquinone Metabolites and c-Myc and C-Kit G-Quadruplex DNA Structures

G-quadruplexes are nucleotide sequences present in the promoter region of numerous oncogenes, having a key role in the suppression of gene transcription. Recently, the binding of anthraquinones from Aloe vera to G-quadruplex structures has been studied through various physico-chemical techniques. Intrigued by the reported results, we investigated the affinity of aloe emodin, aloe emodin-8-glucoside, and aloin to selected G-quadruplex nucleotide sequences by NMR spectroscopy. The structural determinants for the formation of the ligand/nucleotide complexes were elucidated and a model of the interactions between the tested compounds and C-Kit and c-Myc G-quadruplex DNA structures was built by integrated NMR and molecular modeling studies. Overall, the obtained results confirmed and implemented the previously reported findings, pointing out the complementarity of the different approaches and their contribution to a more detailed overview of the ligand/nucleotide complex formation. Furthermore, the proposed models of interaction could pave the way to the design of new nature-derived compounds endowed with increased G-quadruplex stabilizing activity.

Deciphering the Binding Insights of Novel Disubstituted Anthraquinone Derivatives with G-Quadruplex DNA to Exhibit Selective Cancer Cell Cytotoxicity.

Anthraquinone-based compounds are well-known as duplex DNA as well as G-quadruplex DNA binders. Implications of various anthraquinone derivatives for specific recognition of G-quadruplex DNA over duplex DNA is a 'challenging' research work that requires adequate experience with molecular design. To address this important issue, we designed and synthesized ten new 2,6-disubstituted anthraquinone-based derivatives with different functionalized piperazinyl side-chains. Among these, particular compounds with certain distant groups have shown selective and significant binding affinities toward the c-MYC and c-KIT G-quadruplex DNA over the duplex DNA, as noticed from various biophysical experiments. The structural difference of quadruplex and duplex DNA was utilized to probe these derivatives for the end-stacking mode of binding with G-quadruplex DNA. The ability of the ligands to halt DNA synthesis by stabilizing G-quadruplex structures is one of the crucial points to further apply them for quadruplex-mediated anti-cancer therapeutics. Interestingly, these ligands trigger apoptosis to exhibit selective cytotoxicity toward cancer cells over normal cells. This was further evidenced by ligand-induced cell cycle arrest as well as cellular apoptotic morphological changes. These blood-compatible ligands provided detailed structure-activity relationship approaches for the molecular design of anthraquinone-based G-quadruplex binders.

Thiazole Containing PNA Mimic Regulates c-MYC Gene Expression through DNA G-Quadruplex.

Peptide nucleic acids (PNAs), besides hybridizing to complementary DNA and RNAs, bind and stabilize DNA secondary structures. Herein, we illustrate the design and synthesis of PNA-like scaffolds by incorporating five-membered thiazole rings as modified bases instead of nucleobases and their subsequent effects on gene regulation by biophysical and in vitro assays. A thiazole-modified PNA trimer selectively recognizes c-MYC G-quadruplex (G4) DNA over other G4s and duplex DNA. It displays a high stabilization potential for the c-MYC G4 DNA and shows remarkable fluorescence enhancement with the c-MYC G4. It is flexible enough to bind at 5' and 3' ends as well as in the groove region of c-MYC G4. Furthermore, the PNA trimer easily permeates the cellular membrane and suppresses c-MYC mRNA expression in HeLa cells by targeting the promoter G4. This study illuminates modified PNAs as flexible molecular tools for selective targeting of noncanonical nucleic acids and modulating gene function.

Arene Ru(II) Complexes with Difluorinated Ligands Act as Potential Inducers of S-Phase Arrest via the Stabilization of c-myc G-Quadruplex DNA.

Here, a series of half-sandwich arene Ru(II) complexes with difluorinated ligands [Ru(η6-arene)(L)Cl] (L1 = 2-(2,3-difluorophenyl)imidazole[4,5f][1,10]-phenanthroline; L2 = 2-(2,4-difluorophenyl)imidazole[4,5f][1,10]-phenanthroline; arene = benzene, toluene, and p-cymene) were synthesized and characterized. Molecular docking analysis showed that these complexes bind to c-myc G-quadruplex DNA through either groove binding or π–π stacking, and the relative difluorinated site in the main ligand plays a role in regulating the binding mode. The binding behavior of these complexes with c-myc G-quadruplex DNA was evaluated using ultraviolet–visible spectroscopy, fluorescence intercalator displacement assay, fluorescence resonance energy transfer melting assay, and polymerase chain reaction. The comprehensive analysis indicated that complex 1 exhibited a better affinity and stability in relation to c-myc G-quadruplex DNA with a DC50 of 6.6 μM and ΔTm values of 13.09 °C, than other molecules. Further activity evaluation results displayed that this class of complexes can also inhibit the growth of various tumor cells, especially complexes 3 and 6, which exhibited a better inhibitory effect against human U87 glioblastoma cells (51.61 and 23.75 μM) than other complexes, even superior to cisplatin (32.59 μM). Owing to a befitting lipophilicity associated with the high intake of drugs by tumor cells, complexes 3 and 6 had favorable lipid-water partition coefficients of −0.6615 and −0.8077, respectively. Moreover, it was found that complex 6 suppressed the proliferation of U87 cells mainly through an induced obvious S phase arrest and slight apoptosis, which may have resulted from the stabilization of c-myc G-quadruplex DNA to block the transcription and expression of c-myc. In brief, these types of arene Ru(II) complexes with difluorinated ligands can be developed as potential inducers of S-phase arrest and apoptosis through the binding and stabilization of c-myc G-quadruplex DNA, and could be used in clinical applications in the future.

Synthesis of copper (II) porphyrin complexes and their interaction with c-myc G-quadruplex DNA

ObjectiveTo synthesize copper (II) porphyrin complexes and study their interactions with c-myc G-quadruplex DNA. MethodsThe 5-p-hydroxyphenyl-10, 15, 20-tris (p-methoxyphenyl) copper (II) porphyrin complex [p-HTMOPPCu (II)] was synthesized by the conventional heating method. Ultraviolet (UV) titration, fluorescence titration, fluorescence resonance energy transfer (FRET) melting point and competitive assays were used to study the interactions between p-HTMOPPCu (II) and c-myc G-quadruplex DNA. ResultsThe UV absorption spectrum and fluorescence spectroscopy results indicated that the complex of p-HTMOPPCu (II) bound better with c-myc G-quadruplex DNA; the FRET melting point assay, and competitive melting point assay demonstrated that p-HTMOPPCu (II) could selectively bind and stabilize c-myc G-quadruplex DNA. Conclusionp-HTMOPPCu (II) can bind and stabilize c-myc G-quadruplex DNA and will potentially be developed into a class of small molecule inhibitors targeting c-myc G-quadruplex DNA for clinical applications in the treatment of tumors.

Tanshinone IIA derivatives induced S-phase arrest through stabilizing c-myc G-quadruplex DNA to regulate ROS-mediated PI3K/Akt/mTOR pathway

Herein, a derivate from tanshinone IIA, 1,6,6-trimethyl-11-phenyl-7,8,9,10-tetrahydro-6H-furo[2′,3′:1,2]phenanthro[3,4-d]imidazole (TA25), has been synthesized and investigated as potential inhibitor against the proliferation, migration and invasion of lung cancer cells. MTT assay and cell colony formation assay results showed that TA25 exhibits acceptable inhibitory effect against the proliferation of lung cancer A549 cells, and the value of IC50 was about 17.9 μM. This result was further confirmed by the inhibition of TA25 against the growth of xenograft lung cancer cells on zebrafish bearing tumor (A549 lung cancer cells). The results of wound-healing assay and FITC-gelatin invasion assay displayed that TA25 could inhibit the migration and invasion of lung cancer A549 cells. Moreover, the studies on the binding properties of TA25 interact with c-myc G-quadruplex DNA suggested that TA25 can bind in the G-quarter plane formed from G7, G11, G16 and G20 with c-myc G-quadruplex DNA through π-π stacking. Further study of the potential anti-cancer mechanism indicated that TA25 can induce S-phase arrest in lung cancer A549 cells, and this phenomenon resulted from the promotion of the production of reactive oxygen species and DNA damage in A549 cells under the action of TA25. Further research revealed that TA25 could inhibit the PI3K/Akt/mTOR signal pathway and increase the expression of p53 protein. Overall, TA25 can be developed into a promising inhibitor against the proliferation, migration and invasion of lung cancer cells and has potential clinical application in the near future.

Interaction of 9-Methoxyluminarine with Different G-Quadruplex Topologies: Fluorescence and Circular Dichroism Studies.

The interactions of G–quadruplexes of different topologies with highly fluorescent 9-methoxyluminarine ligand 9-MeLM were investigated by fluorescence and circular dichroism spectroscopy. The results showed that 9-methoxyluminarine was able to interact and did not destabilize any investigated molecular targets. The studied compound was selectively quenched by parallel c-MYC G-quadruplex DNA, whereas hybrid and antiparallel G4 topology caused only a negligible decrease in the fluorescence of the ligand. A high decrease of fluorescence of the ligand after binding with c-MYC G-quadruplex suggests that this molecule can be used as a selective probe for parallel G-quadruplexes.

Imidazole as a Promising Medicinal Scaffold: Current Status and Future Direction.

Various imidazole-containing compounds have been tested for their medical usefulness in clinical trials for several disease conditions. The rapid expansion of imidazole-based medicinal chemistry suggests the promising and potential therapeutic values of imidazole-derived compounds for treating incurable diseases. Imidazole core scaffold contains three carbon atoms, and two nitrogen with electronic-rich characteristics that are responsible for readily binding with a variety of enzymes, proteins, and receptors compared to the other heterocyclic rings. Herein, we provide a thorough overview of the current research status of imidazole-based compounds with a wide variety of biological activities including anti-cancer, anti-microbial, anti-inflammatory and their potential mechanisms including topoisomerase IIR catalytic inhibition, focal adhesion kinase (FAK) inhibition, c-MYC G-quadruplex DNA stabilization, and aurora kinase inhibition. Additionally, a great interest was reported in the discovery of novel imidazole compounds with anti-microbial properties that break DNA double-strand helix and inhibit protein kinase. Moreover, anti-inflammatory mechanisms of imidazole derivatives include inhibition of COX-2 enzyme, inhibit neutrophils degranulation, and generation of reactive oxygen species. This systemic review helps to design and discover more potent and efficacious imidazole compounds based on the reported derivatives, their ADME profiles, and bioavailability scores that together aid to advance this class of compounds.

Synthesis, docking studies and antitumor activity of phenanthroimidazole derivatives as promising c-myc G-quadruplex DNA stabilizers

Phenanthroimidazole derivatives containing phenanthroline and imidazole heterocyclic aromatic rings are effective agents to inhibit tumor cell growth. Herein, halogen element-modified imidazo[4,5f][1,10]phenanthroline derivatives 1–6 (1, 4-fluorophenyl; 2, 4-chlorophenyl; 3, 4-bromobenyl; 4, 2,3-dichlorophenyl; 5, 3,4-dichlorophenyl; and 6, 2,4-dichlorophenyl) were synthesized, and their antitumor activities were investigated. All of the compounds, especially 4, exhibited an excellent inhibitory effect against nasopharyngeal carcinoma CNE-1 cells. This effect was better than that of doxorubicin. Compound 4 also markedly blocked the proliferation of the CNE-1 cells in a zebrafish xenograft model. The antitumor mechanisms might be attributed to apoptosis induction, which triggered ROS-mediated DNA damage and generated mitochondrial dysfunction by stabilizing c-myc G-quadruplex DNA structure. Results indicated that phenanthroimidazole derivatives could act as promising anticancer agents.

Specific stabilization of promoter G-Quadruplex DNA by 2,6-disubstituted amidoanthracene-9,10-dione based dimeric distamycin analogues and their selective cancer cell cytotoxicity

We have designed and synthesized anthraquinone containing compounds which have oligopyrrole side chains of varying lengths. These compounds stabilized the G-quadruplex DNA formed in the promoter regions of c-MYC oncogenes selectively over the duplex DNA. These observations were recorded using UV–vis spectroscopic titrations, fluorescence measurements and circular dichroism (CD) spectral titrations. The potency of the compounds to stabilize the G4 DNA has been shown from the thermal denaturation experiments. The compound interacts with c-MYC G-quadruplex DNA through stacking mode as obtained from ethidium bromide displacement assay, cyclic voltammetric titration, and docking experiments. Molecular modeling studies suggested that the stacking of the anthraquinone moiety over the G-tetrad of the G4 structures are responsible for the stability of such quadruplex secondary structure. Furthermore, polymerase stop assay also supported the formation of stable G4 structures in the presence of the above-mentioned compounds. The compounds have shown selective cancer cell (HeLa and HEK293T) cytotoxicity over normal cells (NIH3T3 and HDFa) under in vitro conditions as determined from MTT based cell viability assay. Apoptosis was found to be the mechanistic pathway underlying the cancer cell cytotoxicity as obtained from Annexin V-FITC and PI dual staining assay which was further substantiated by nuclear morphological changes as observed by AO/EB dual staining assay. Cellular morphological changes, as well as nuclear condensation and fragmentation upon treatment with these compounds, were observed under bright field and confocal microscopy.

Chiral Ru(ii) complexes act as a potential non-viral gene carrier for directional transportation to the nucleus and cytoplasm.

Guanine-rich DNA sequences can spontaneously fold into four-stranded structures called G-quadruplexes (G4s). G4s have been identified extensively in the promoter regions of several proto-oncogenes, including c-myc, as well as telomeres. G4s have attracted an increasing amount of attention in the field of nanotechnology because of their use as versatile building blocks of DNA-based nanostructures. In this study, we report the self-assembly of c-myc G-quadruplex DNA controlled by a pair of chiral ruthenium(ii) complexes coordinated by 2-(4-phenyacetylenephenyl)-1H-imidazo[4,5f][1,10]phenanthroline (PBEPIP), Λ-[Ru(bpy)2(PBEPIP)](ClO4)2 (Λ-RM0627, bpy = bipyridine) and Δ-[Ru(bpy)2(PBEPIP)](ClO4)2 (Δ-RM0627). Λ-RM0627 could promote the high-order self-assembly of c-myc G-quadruplex DNA into a nanowire structure, whereas Δ-RM0627 could induce DNA condensation into G-quadruplex aggregates. Moreover, in vitro studies on human liver carcinoma HepG2 cells showed that the nanowire of c-myc G-quadruplex DNA promoted by Λ-RM0627 could be localized in the nuclei of cells, whereas the nanoparticle of c-myc G-quadruplex DNA generated by Δ-RM0627 was taken up and localized in the cytoplasm. This study provides examples of the enantioselective self-assembly of G4 DNA molecules controlled by chiral ruthenium(ii) complexes and suggests the potential applications of assembled nanostructures as non-viral DNA vectors for gene therapy.

A short peptide that preferentially binds c-MYC G-quadruplex DNA.

G-quadruplexes (G4s) are non-canonical DNA secondary structures. The identification of selective tools to probe individual G4s over the ∼700 000 found in the human genome is key to unravel the biological significance of specific G4s. We took inspiration from a crystal structure of the bovine DHX36 helicase bound to the G4 formed in the promoter region of the oncogene c-MYC to identify a short peptide that preferentially binds MYC G4 with nM affinity over a small panel of parallel and non-parallel G4s tested.

INDUCTION OF C-MYC G-QUADRUPLEX DNA AND CYTOTOXICITY OF A CALIX[]ARENE-CONTAINING BINUCLEAR RUTHENIUM(II) COMPLEX

Herein, a binuclear ruthenium(II) complex modified by calix[4]arene group has been prepared. The complex as potential inducer and stabilizer of c-myc G-quadruplex DNA and antitumor reagent were studied. Observations revealed that the complex could bind to c-myc Pu27 and Pu22 DNA strongly with constants of 1.18 × 107 (Pu27) and 4.13 × 106 M-1 (Pu22) via groove mode as determined from absorption and luminescence titrations, as well as CD spectra. Results of continuous variation analysis confirmed that the complex interacted with c-myc G-quadruplex DNA through a 1:1 binding stoichiometry. As verified by PCR-stop assay, the replication of c-myc DNA was effectively blocked by the complex with the complete inhibition at the complex concentration of 4.0 μM both for Pu27 and Pu22, suggesting that the complex could efficiently induce the formation of c-myc G-quadruplex DNA. The appearance of blue TMB solution in the visual experiment also proved that the sequences of Pu27 and Pu22 could fold into G-quadruplex under the induction of the complex. Nevertheless, the complex was found to exhibit weak stabilization ability on c-myc G-quadruplex DNA according to FRET assay, which increased the melting point of c-myc DNA only 3-3.5 °C. The experiments on Topoisomerase inhibition and cytotoxicity of the complex showed that it acted as an inhibitor of TopoI and exhibited moderate anticancer activity against MCF-7 and Huh-7 tumor cells.

A benzo(f)quinolinium fused chromophore-based fluorescent probe for selective detection of c-myc G-Quadruplex DNA with a red emission and a large Stocks shift

Accumulating evidence in recent years has suggested that G-Quadruplex DNAs may play important roles in gene expression and genomic stability in vivo. Specially, c-myc G-Quadruplex that exists in the promoter of oncogene is an attractive target in the pathway of cell proliferation and senescence. The development of small-molecule fluorescent probes for c-myc G-Quadruplex DNA has attracted significant attention. This work presented a benzo(f)quinolinium fused chromophore-based fluorescent probe L-1 for the detection of c-myc G-Quadruplex DNA using N-(2-hydroxyethyl)piperazine moiety as a binding unit. This probe exhibiting a red emission and a large Stocks shift was found to be selective and sensitive for “light-up” detection of c-myc quadruplex DNA over duplex DNA and other G-quadruplexes. It stabilized c-myc G-Quadruplex DNA and effective inhibited in vitro DNA synthesis. Binding studies indicated that the fluorescent response of L-1 mainly arised from end-stacking binding mode. Furthermore, L-1 was applicable to visualize the cellular nucleus in living cells.

Novel triazole and morpholine substituted bisnaphthalimide: Synthesis, photophysical and G-quadruplex binding properties

Four bisnaphthalimides derivatives 3a, 3b, 5a and 5b with polyamine linkage have been synthesized and characterized. Different spectroscopic techniques, including UV–Vis spectroscopy, fluorescence spectroscopy, circular dichroism and fluorescence resonance energy transfer (FRET), have been used to explore the interaction of these compounds with G-quadruplex structures (Htelo, c-myc, c-kit). The compounds 3a, 3b and 5b show high affinity toward Htelo, c-myc and c-kit G-quadruplexes (Ka > 4.42 × 106 M−1), and exhibit more than 40-fold selectivity for the quadruplex versus CT DNA. Binding of 3a, 3b to telomeric and oncogenic G-quadruplexes induce strong enhancement of the fluorescence intensity (18–27-fold), whereas the duplex CT DNA induces much weaker fluorescence enhancement (around 2-fold). Being fluorescent, the cellular localization of 3a, 3b can be conveniently tracked by fluorescence imaging. The results indicate that 3a, 3b can readily be taken up by A549 lung cancer cells. Molecular docking studies indicate that 3a, 3b, 5a and 5b mainly bind in the groove and/or loop region of the G-quadruplexes, and hydrogen bonding plays an important role in the interaction of bisnaphthalimide derivatives with G-quadruplexes. CD spectroscopy and FRET melting assay indicate that 3a, 3b and 5b can promote the formation and the stabilization of human telomeric and c-myc G-quadruplex DNA. The compound 3b can inhibit the growth of A549 cells (IC50 = 0.15 μM), with a much higher antitumor activity than amonafide.

Using Molecular Dynamics Free Energy Simulation to Compute Binding Affinities of DNA G-Quadruplex Ligands.

We provide a practical guide for using molecular dynamics simulation to compute the binding affinity of small molecules in complex with G-quadruplex DNA. Such calculations have a number of applications, such as rescoring docking results and validating docked poses, to inform the discovery of G-quadruplex binders with high affinity and selectivity. This chapter describes two binding free energy protocols: the double decoupling method (DDM) and the potential of mean force method (PMF). We illustrate the application of the two methods using a recent case study of the binding of quindoline with the c-MYC G-quadruplex DNA. For this system, the two methods yield absolute binding free energies within ~2kcal/mol of the experimental value. We discuss the advantages and disadvantages of these binding free energy methods.

5-Bromo-oxoisoaporphine platinum(II) complexes exhibit tumor cell cytotoxcicity via inhibition of telomerase activity and disruption of c-myc G-quadruplex DNA and mitochondrial functions

Two platinum(II) complexes [Pt(L)(DMSO)Cl] (1) and [Pt(L)(pn)]Cl (2) with 5-bromo-oxoisoaporphine (H-L) were synthesized. We found that the two new platinum(II) complexes were more selective for Hep-G2 tumor cells than for normal cells (HL-7702, WI-38 and L-o2 cell lines). 5-Bromine-oxoisoaporphine platinum(II) complex 2 was a telomerase inhibitor targeting c-myc G4, and it triggered Hep-G2 cell apoptosis more potently than complex 1. Moreover, they induced cell apoptosis via disruption of mitochondrial functions. Significantly increased ROS level, loss of Δψ, decrease of bcl-2 level, and increase of some of the mitochondria-initiated apoptosis protein levels (including bax, Cyt C, caspase-3, caspase-9, and apaf-1) were observed in Hep-G2 cells. In brief, complexes 1 and 2 triggered Hep-G2 cell apoptosis mainly through inhibiting telomerase activity by interacting with c-myc promoter elements and disruption of mitochondrial pathway. Our results also showed the effects of second ligands on the in vitro antitumor activity in the order of pn > Cl and DMSO.