Zhiyong Tian

Synthesis, cytotoxicity and apoptosis of naphthalimide polyamine conjugates as antitumor agents.

Several naphthalimide polyamine conjugates were synthesized and evaluated for in vitro cytotoxicity against human leukemia K562, murine melanoma B16, Chinese hamster ovary CHO cell lines. Both triamine moieties and the length of spacers were crucial in elevating the potency of 1,8-naphthalimide. The typical compounds 5a and 5d exhibited excellent cell selectivity to cancer cells through the human hepatoma BEL-7402 and human normal hepatocyte QSG-7701 screens. In addition, 5d could disturb the cell cycle in B16 cells. The research on caspase activity and cytochrome c indicated that 5d could induce B16 cell apoptosis via both the mitochondrial and membrane death receptor pathways, and the Bcl-2 family numbers were involved in the control of apoptosis.

Spectroscopic study on the interaction between mononaphthalimide spermidine (MINS) and bovine serum albumin (BSA).

The interaction mononaphthalimide spermidine (MINS, 1) and bovine serum albumin (BSA) was studied by UV/vis absorption, fluorescence and circular dichroism spectra (CD) under physiological conditions (pH=7.4). The observed spectral quenching of BSA by compound 1 indicated compound 1 could bind to BSA. Further fluorescent tests revealed that the quenching mechanism of BSA by compound 1 was overall static. Meanwhile, the obtained binding constant and thermodynamic parameters on compound-BSA interaction showed that the type of interaction force of compound 1 and BSA was mainly hydrophobic. The analysis of synchronous, three-dimensional fluorescence and CD showed that compound 1 had weak influence on the conformational changes in BSA. Molecular docking simulation was performed and docking model in silico suggested that the configuration of compound 1 was localized in enzymatic drug site II in BSA. Furthermore, naphthalimide moiety of compound 1 greatly contributed to the hydrophobic interaction between compound 1 and BSA protein, as confirmed by experimental data.

Conjugation of substituted naphthalimides to polyamines as cytotoxic agents targeting the Akt/mTOR signal pathway.

Though several naphthalimide derivatives have exhibited antitumor activity in clinical trials, some issues such as toxicity prompted further structural modifications on the naphthalimide backbone. A series of naphthalimides conjugated with polyamines were synthesized to harness the polyamine transporter (PAT) for drug delivery, which was beneficial for the tumor cell selectivity. Bioevaluation in human hepatoma HepG2 cells treated with alpha-difluoromethylornithine (DFMO) or spermidine (Spd), human hepatoma Bel-7402 and normal QSG-7701 hepatocyte confirmed the PAT recognition and cell selectivity. In addition, the novel naphthalimide polyamine conjugate kills cells via apoptosis, and the Akt/mTOR signal pathway was first identified as the upstream cellular target through the apoptotic mechanism research. The presence of DFMO or Spd only either elevated or attenuated the cell apoptosis, but did not change the signal pathway. Collectively, the proper polyamine recognition element (i.e., homospermidine) mediated effective drug delivery via the PAT, and helped the proper cytotoxic goods (i.e., diverse naphthalimides) exert antitumor properties.

Spectroscopic study on the interaction between naphthalimide-polyamine conjugates and DNA.

The interaction of naphthalimide-polyamine conjugates with herring sperm DNA was studied by UV/vis absorption and fluorescent spectra under physiological conditions (pH=7.4). The observed spectral quenching of compounds by DNA and the displacement of EB from DNA-EB complex by compounds indicated that these naphthalimide-polyamine conjugates could intercalate into the DNA base pairs. The UV test also showed that these compounds caused the conformational alteration of DNA. Further caloric fluorescent tests revealed that the quenching mechanism was a static type, which Ksv of 1-DNA, 2-DNA and 1-DNA-EB, 2-DNA-EB 3-DNA-EB was 1.208×10(4), 7.792×10(3) and 1.712×10(4), 1.287×10(4), 2.874×10(4), respectively, at room temperature. The obtained quenching constant, binding constant and thermodynamic parameters suggested that binding strength was associated with substituted groups on naphthalene backbone, and the type of interaction force included mainly hydrogen bonding and weak van der Waals. The binding process was mainly driven by hydrogen bond and van der Waals. Additionally, the effect of NaCl on compounds-DNA interaction provided further evidence that their interaction modes were dependent on substituted groups.

Synthesis and Bioevaluation of 5-Fluorouracil Derivatives

A series of six novel 5-fluorouracil derivatives 1-6 were synthesized and their structures confirmed by (1)H- and (13)C-NMR, MS and elemental analysis. The preliminary in vitro antitumor activities against B16, K562 and CHO cells and the in vivo inhibitions of liver cancer H(22) demonstrated that some of these compounds effectively inhibit the growth of tumor cells, but the in vivo trials in mice revealed that the compounds also exhibited serious liver and lung tissue toxicity. The hydrolysis experiments indicated that this type of compound did not readily liberate 5-fluorouracil, as expected.

Study on the Synthesis, Biological Activity and Spectroscopy of Naphthalimide-Diamine Conjugates

Eleven novel naphthalimide-diamine conjugates were synthesized and their structures were confirmed by elemental analysis, 1H-NMR, 13C-NMR and MS. Their in vitro antitumor activities were assessed using MTT assays on two cancerous cell lines K562, HCT116, and one normal hepatoma cell line QSG 7701. Compound 7f exhibited potent antitumor activity on HCT116 cells and favorable cell selectivity toward QSG 7701 compared with the positive control, amonafide. Moreover, 7f could block HeG2 cells in the G2/M phase and induce HeG2 cells apoptosis. The interaction of compound 7f with herring sperm DNA was studied by UV/vis absorption and fluorescence spectroscopy under physiological conditions (pH = 7.4). The observed spectral quenching of compound 7f by DNA and the displacement of EB from DNA-EB complex by compound 7f indicated that compound 7f could intercalate into DNA base pairs, which was also corroborated by the effect of KI on compound-DNA interaction. Further caloric fluorescent tests revealed that the quenching mechanism was a static type. Meanwhile, the binding constants, thermodynamic parameters and the effect of NaCl on compound-DNA interaction showed that the type of interaction force was mainly hydrogen bonds and the binding process was driven by hydrogen and van der Waals bonding.

Antitumor effects and preliminary systemic toxicity of ANISpm in vivo and in vitro.

Polyamines as a vector to ferry toxic agents have attracted attention, and naphthalimide–polyamine conjugates show potent activity and tumor cell selectivity. The present study was carried out to evaluate the antitumor effects and preliminary systemic toxicity of ANISpm, a novel 3-amino-naphthalimide–spermine conjugate. The polyamine transport system recognition of ANISpm, supported by &agr;-difluoromethylornithine (DFMO)/spermidine (Spd) experiments, is in accordance with its potent cell selectivity between human hepatoma HepG2 cells and normal QSG7701 hepatocyte. The antiproliferative effect is because of ANISpm-induced cell apoptosis, a common characteristic of both naphthalimide and polyamine analogs. Various apoptotic assessment assays have shown that ANISpm can induce apoptosis through the PI3K/Akt signal pathway. The apoptotic signaling cascade involves Akt inactivation, which results in a series of cellular events. The downstream pathway includes Bad dephosphorylation, dissociation of 14-3-3 and Bad, and binding to Bcl-xL, which triggers the disruption of the mitochondrial membrane, release of cytochrome c, and caspases’ cascade activation. Furthermore, the Akt/mTOR signal pathway is also involved in ANISpm-mediated cell-cycle arrest. Additive DFMO or Spd, which only enhances or attenuates ANISpm-mediated cell apoptosis, respectively, does not alter the signal pathway. In addition, preliminary toxicology evaluation showed that ANISpm had no obvious system toxicity at a dose of 2.5 mg/kg, which exerted potent antitumor activity in vivo, especially hematotoxicity. Thus, ANISpm merits further investigation as a potential chemotherapeutic agent against hepatocellular carcinoma.

Reactive oxygen species (ROS) accumulation induced by mononaphthalimide-spermidine leads to intrinsic and AIF-mediated apoptosis in HeLa cells

Developing polyamine conjugates having the potential of transporting naphthalimide selectively into tumor cells is attractive. However, the evaluation of their cytotoxic mechanism has not been comprehensive. This study focused on the effects of mononaphthalimide spermidine (MNISpd) conjugate on apoptosis induction and the relationship between MNISpd-induced apoptosis and reactive oxygen species (ROS) in HeLa cells. Our findings indicated that 9 µM MNISpd induced apoptosis in HeLa cells during a 48-h period. MNISpd induced apoptosis in HeLa cells following cytochrome c release, elevation of caspase 3/9 activity, apoptosis-inducing factor (AIF) translocation and up-/down-regulation of Bax/Bcl-2 protein expression, respectively, and these effects were completely antagonized by pre-incubation with 10 mM NAC for 2 h. MNISpd induced significant ROS accumulation following up-regulation of polyamine oxidase (PAO) activity and complex variations in glutathione levels. It is concluded that MNISpd-induced apoptosis is related to intrinsic caspase-dependent and AIF-mediated caspase-independent apoptosis pathways in HeLa cells. MNISpd-induced apoptosis correlates to MNISpd-induced ROS production resulting from GSH (reduced form of glutathione) pool depletion, and PAO is likely to be the source of ROS.

Spectroscopic and molecular modeling methods to study the interaction between naphthalimide-polyamine conjugates and DNA.

The effect of polyamine side chains on the interaction between naphthalimide-polyamine conjugates (1-7) and herring sperm DNA was studied by UV/vis absorption and fluorescent spectra under physiological conditions (pH=7.4). The diverse spectral data and further molecular docking simulation in silico indicated that the aromatic moiety of these compounds could intercalate into the DNA base pairs while the polyamine motif might simultaneously locate in the minor groove. The triamine compound 7 can interact more potently with DNA than the corresponding diamine compounds (1-6). The presence of the bulky terminal group in the diamine side chain reduced the binding strength of compound 1 with DNA, compared to other diamine compounds (2-6). In addition, the increasing methylene number in the diamine backbone generally results in the elevated binding constant of compounds-DNA complex. The fluorescent tests at different temperature revealed that the quenching mechanism was a static type. The binding constant and thermodynamic parameter showed that the binding strength and the type of interaction force, associated with the side chains, were mainly hydrogen bonding and hydrophobic force. And the calculated free binding energies of molecular docking are generally consistent with the stability of polyamine-DNA complexes. The circular dichroism assay about the impact of compounds 1-7 on DNA conformation testified the B to A-like conformational change.

Spectroscopic Study on the Interaction between Naphthalimide-Polyamine Conjugates and Bovine Serum Albumin (BSA)

The effect of a naphthalimide pharmacophore coupled with diverse substituents on the interaction between naphthalimide-polyamine conjugates 1–4 and bovine serum albumin (BSA) was studied by UV absorption, fluorescence and circular dichroism (CD) spectroscopy under physiological conditions (pH = 7.4). The observed spectral quenching of BSA by the compounds indicated that they could bind to BSA. Furthermore, caloric fluorescent tests revealed that the quenching mechanisms of compounds 1–3 were basically static type, but that of compound 4 was closer to a classical type. The Ksv values at room temperature for compound-BSA complexes-1-BSA, 2-BSA, 3-BSA and 4-BSA were 1.438 × 104, 3.190 × 104, 5.700 × 104 and 4.745 × 105, respectively, compared with the value of MINS, 2.863 × 104 at Ex = 280 nm. The obtained quenching constant, binding constant and thermodynamic parameter suggested that the binding between compounds 1–4 with BSA protein, significantly affected by the substituted groups on the naphthalene backbone, was formed by hydrogen bonds, and other principle forces mainly consisting of charged and hydrophobic interactions. Based on results from the analysis of synchronous three-dimensional fluorescence and CD spectra, we can conclude that the interaction between compounds 1–4 and BSA protein has little impact on the BSA conformation. Calculated results obtained from in silico molecular simulation showed that compound 1 did not prefer either enzymatic drug sites I or II over the other. However, DSII in BSA was more beneficial than DSI for the binding between compounds 2–4 and BSA protein. The binding between compounds 1–3 and BSA was hydrophobic in nature, compared with the electrostatic interaction between compound 4 and BSA.