•ANTMHspd was able to bind to herring sperm DNA by intercalation and groove.•Polyamine conjugate could result in the B to A-like DNA conformational change.•The hydrogen bonding and hydrophobic force played an important role in the binding process of ANTMHspd conjugates and DNA.•The fluorescent quenching mechanism of polyamine conjugate to DNA-EB, as well as DNA to polyamine conjugate is a static type.The interaction between anthracenyl-methyl homospermidine conjugate (ANTMHspd) with herring sperm DNA was investigated by UV/vis absorption, fluorescent spectra, circular dichroism (CD) spectroscopy and 1HNMR under physiological conditions (pH = 7.4). The observed hypochromism effect and fluorescence quenching of ANTMHspd by DNA, and the displacement of EB from DNA-EB system by ANTMHspd suggested that ANTMHspd might interact with DNA by the combined mode of intercalation and groove binding. Further fluorescent tests at different temperatures revealed that the quenching mechanism was a static type. The quenching constant, binding constant and thermodynamic parameter obtained from fluorescence showed that the type of interaction force included mainly hydrogen bonding and van der Waals, which promoted the binding process. The CD test revealed that ANTMHspd could cause the B to A-like conformational change while ANTMHspd is not a typical DNA intercalator. The 1H NMR tests showed that ANTMHspd partially intercalated DNA. The effect of NaCl and KI on ANTMHspd–DNA interaction provided additional evidences of intercalation. Molecular docking simulation was carried out and the docking model in silico suggested that the binding modes of ANTMHspd and DNA were groove binding and intercalation, with the anthracene moiety inserted in DNA base pairs and the polyamine chain embedded in the DNA groove.Download high-res image (150KB)Download full-size image

The interaction of herring sperm DNA with the 1,4,5,8-naphthalene diimide–spermine conjugate (NDIS) was studied by UV/vis absorption, fluorescence and CD spectroscopic methods. Compared with the 1,8-naphthalimide–spermidine conjugate (NIS), the values of KSV (quenching constant) and Kb (binding constant) of NDIS were larger, and the hypochromic effect in the UV/vis spectra and the quenching effect in the fluorescence of NDIS were more significant. The interaction mode between NDIS and DNA was mainly groove binding. The fluorescence experiments at varying temperatures showed that the binding process of NDIS and DNA was static, as both hydrogen bonds and hydrophobic forces played a major role in the binding of NDIS and DNA. The CD spectrum indicated that NDIS caused a conformational change, like the B to A-DNA transition, and the tests using KI and NaCl and 1H NMR spectroscopy indicated that NDIS was not a classical DNA inserter. All the results demonstrated that both the polyamine side chain and the aromatic rings affect the process of NDIS binding to DNA, which is thus obviously different from that of NIS. The conclusion was confirmed by the in silico molecular docking experiments.

The interaction of herring sperm DNA with the 1,4,5,8-naphthalene diimide–spermine conjugate (NDIS) was studied by UV/vis absorption, fluorescence and CD spectroscopic methods. Compared with the 1,8-naphthalimide–spermidine conjugate (NIS), the values of KSV (quenching constant) and Kb (binding constant) of NDIS were larger, and the hypochromic effect in the UV/vis spectra and the quenching effect in the fluorescence of NDIS were more significant. The interaction mode between NDIS and DNA was mainly groove binding. The fluorescence experiments at varying temperatures showed that the binding process of NDIS and DNA was static, as both hydrogen bonds and hydrophobic forces played a major role in the binding of NDIS and DNA. The CD spectrum indicated that NDIS caused a conformational change, like the B to A-DNA transition, and the tests using KI and NaCl and 1H NMR spectroscopy indicated that NDIS was not a classical DNA inserter. All the results demonstrated that both the polyamine side chain and the aromatic rings affect the process of NDIS binding to DNA, which is thus obviously different from that of NIS. The conclusion was confirmed by the in silico molecular docking experiments.

•Five plausible channels for the product (uracil) release step are detected.•The thermodynamic and dynamic properties for the two most favorable channels are obtained.•The key residues that are responsible for the barrier of product release have been found.•The full cycle of the enzymatic catalysis is determined.Yeast cytosine deaminase (yCD) is critical in gene-directed enzyme prodrug therapy as it catalyzes the hydrolytic deamination of cytosine. The product (uracil) release process is considered as rate-limiting in the whole enzymatic catalysis and includes the cleavage of the uracil-metal bond and the delivery of free uracil out of the reactive site. Herein extensive combined random acceleration molecular dynamics (RAMD) and molecular dynamics (MD) simulations coupled with the umbrella sampling technique have been performed to study the product transport mechanism. Five channels have been identified, and the thermodynamic and dynamic characterizations for the two most favorable channels have been determined and analyzed. The free energy barrier for the most beneficial pathway is about 13 kcal/mol and mainly results from the cleavage of hydrogen bonds between the ligand uracil and surrounding residues Asn51, Glu64, and Asp155. The conjugated rings of Phe114 and Trp152 play gating and guiding roles in the product delivery via π ⋯ π van der Waals interactions with the product. Finally, the full cycle of the enzymatic catalysis has been determined, making the whole process computationally more precise.The kinetic model for the yCD catalytic process.Download high-res image (193KB)Download full-size image

The highly homologous hydroxynitrile lyases from Manihot esculent (MeHNL) and Hevea brasiliensis (HbHNL) both belong to the α/β-hydrolase superfamily, and they convert cyanohydrins into the corresponding ketone (aldehyde) and hydrocyanic acid, which is important for biosynthesis for carbon–carbon formation. On the basis of extensive MM and ab initio QM/MM MD simulations, one-dimensional and two-dimensional free energy profiles on the whole enzymatic catalysis by MeHNL have been explored, and the effects of key residues around the channel on the delivery of substrate and product have been discussed. The residue Trp128 plays an important gate-switching role to manipulate the substrate access to the active site and product release. In particular, the release of acetone and HCN has been first detected to follow a stepwise mechanism. The release of HCN is quite facile, while the escape of acetone experiences a barrier of ∼10 kcal/mol. The chemical reaction is an endergonic process with a free energy barrier of ∼17.1 kcal/mol, which dominates the entire enzymatic efficiency. Such energy costs can be compensated by the remarkable energy release during the initial substrate binding. Here the carbon–carbon cleavage is the rate-determining step, which differs from that of HbHNL. The protonation state of Lys237 plays an important role in carbon–carbon bond cleavage by restoring the Ser80Ala mutant system to the wild system, which explains the discrepancy between MeHNL and HbHNL at the molecular or atomic scale. The present results provide a basis for understanding the similarity and difference in the enzymatic catalysis by MeHNL and HbHNL.Keywords: biosynthesis; hydroxynitrile lyases; mechanism; product release; QM/MM MD; α/β-hydrolase superfamily

•Six flavonoid-polyamine conjugates were synthesized.•Combination of 8a with aspirin resulted in additive inhibition of in vitro tumor cell growth and migration.•8a-aspirin combination inhibited H22 liver tumor growth and pulmonary metastasis in vivo.•8a increased the expression of apoptosis-related proteins, an effect that was further amplified by aspirin.A series of polyamine conjugates of flavonoids with a naphthalene motif were synthesized and evaluated for their anti-hepatocellular carcinoma properties using in vitro and in vivo assays. Compound 8a displayed favorable selectivity between hepatocellular carcinoma cells and normal hepatocyte cells, and the combination of 8a with aspirin resulted in additive inhibition of in vitro tumor cell growth and migration. The 8a-aspirin combination also inhibited H22 liver tumor growth and pulmonary metastasis and improved body weight index in animal models. Preliminary mechanistic studies indicated that 8a increased the expression of apoptosis-related proteins such as p-p38, p-JNK, p53 and Bcl-2, an effect that was further amplified by aspirin. Therefore, a cocktail therapy of flavonoid-polyamine conjugates with aspirin has potential use as an antitumor therapy.Six novel flavonoid-polyamine conjugates with naphthalene motif were synthesized. Compound 8a displayed favorable selectivity between HepG2 and QSG7701 cells. The combination of 8a with Aspirin generated better additive anti-metastasis effects in vivo, and no weight loss in the treated mice.

•The binding strength was associated with side chain effects of polyamine.•Polyamine conjugates could bind to herring sperm DNA by intercalation and groove.•Compounds 1–7 could cause the B to A-like DNA conformational change.•The type of interaction force was mainly hydrogen bonding and hydrophobic force.•The fluorescent quenching mechanism is a static type.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.

•Polyamine-conjugate caused the conformational alteration of BSA.•MINS bound to BSA.•By and large, the fluorescent quenching mechanism was a static type.•The type of interaction force was mainly hydrophobic.•Docking model for compound 1 with BSA was also investigated.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.The interaction between mononaphthalimide spermidine (MINS) with bovine serum albumin (BSA) was studied by UV/vis absorption, fluorescent and dichroism spectra (CD) under physiological conditions. Docking model for compound 1 with BSA was also investigated.

Quantum dots (QDs) have shown great potential in monitoring and imaging cancer cells because of their unique photochemical and photophysical properties. However, it is little-known whether QDs affect the cellular internalization, proliferation and apoptosis. Here a new class of multifunctional QDs capped with ligands that possess L-Lys or L-Arg and naphthalimide (NI), linked by carboxyl groups (L-Lys-NI@QDs and L-Arg-NI@QDs, respectively), have been synthesized. We found that these QDs are of controllable sizes, in the range of 4 to 5 nm and have strong optical emission properties. The cellular uptake of NI derivative-capped QDs was monitored by flow cytometry and confocal microscopy. The results of in vitro cytotoxicity revealed that NI derivative-capped QDs, with better cell selectivity, could inhibit the growth of multiple cancer cells more potently than amonafide. They effectively inhibited the proliferation of cells due to apoptosis, which was confirmed by Hoechst 33342, annexin V-FITC and JC-1 staining and mitochondrial membrane potential (MMP) experiments. The most potent NI derivative-capped QDs, L-Arg-NI@CdSe/ZnS, were verified to efficiently induce apoptosis via a reactive oxygen species (ROS) mediating mitochondrial dysfunction, and were more effective in promoting programmed cell death in HepG2 cells in a preliminary mechanistic study.

A series of 4-dimethylamine flavonoid derivatives 5a–5r were designed, synthesized and evaluated as potential multi-functional anti-Alzheimer agents. The results showed that most of the synthesized compounds exhibited high acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity at the micromolar range (IC50, 1.83–33.20 μM for AChE and 0.82–11.45 μM for BChE). A Lineweaver–Burk plot indicated a mixed-type inhibition for compound 5j with AChE, and molecular modeling study showed that 5j targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Besides, the derivatives showed potent self-induced Aβ aggregation inhibitory activity at 20 μM with percentage from 25% to 48%. In addition, some compounds (5j–5q) showed potent oxygen radical absorbance capacity (ORAC) ranging from 1.5- to 2.6-fold of the Trolox value. These compounds should be further investigated as multi-potent agents for the treatment of Alzheimer’s disease.Eighteen 4-dimethylamine flavonoid derivatives were synthesized as anti-Alzheimer agents with high inhibition activity for both acetylcholinesterase, butyrylcholinesterase and β-amyloid self-aggregation, they also showed potent peroxyl radical absorbance activity.

Recently several reports have indicated that elevated expression of DKK1 is tightly associated with the progression of hepatocellular carcinoma (HCC). However, the biological function of DKK1 in HCC has not yet been well documented.In this study, the role of DKK1 in tumor cell proliferation, migration and invasion was investigated using MTT, colony formation, wound scratch, transwell assays, and also human HCC samples.Both gain- and loss-of-function studies showed that DKK1 did not influence the tumor cell proliferation and colony formation, while dramatically promoted HCC cell migration and invasion. Subsequent investigations revealed that β-catenin was an important target of DKK1. The blocking of β-catenin by pharmacological inhibitor antagonized the function of DKK1, whereas introduction of β-catenin by transfection with plasmids or treatment with GSK3β inhibitor phenocopied the pro-migration and pro-invasion effects of DKK1. We further disclosed that DKK1 exerted its pro-invasion function, at least in part, by promoting β-catenin expression, in turn, upregulating the expression of matrix metalloproteinase 7 (MMP7), which was independent of the canonical Wnt signaling pathway. Moreover, introduction of MMP7 significantly enhanced the ability of HCC cells to invade extracellular matrix gel in vitro. Consistently, in human HCC tissues, DKK1 level was positively correlated with β-catenin expression, as well as tumor metastasis.Taken together, these results demonstrated that DKK1 is overexpressed in HCC; moreover, ectopic expression DKK1 promotes HCC cell migration and invasion at least partly through β-catenin/MMP7 signaling axis, suggesting that DKK1 may be a promising target for HCC therapy.

With the aim of up-regulating antitumor efficacy and down-regulating adverse effects, three types of aromatic imide and diimides were designed to couple with different polyamines. The in vitro assays revealed that two naphthalene diimide–polyamine conjugates could inhibit the growth of multiple cancer cell lines more potently than amonafide. 9f, the most potent compound, was verified to efficiently induce apoptosis via a ROS mediated mitochondrial pathway in a preliminary mechanistic study. The comprehensive in vivo trials on three H22 tumor transplant models demonstrated that 9f improved the indexes in terms of inhibitive effect and lifespan extension and reduced the hematotoxicity which is one of main drawbacks of amonafide. More importantly, the obviously elevated ability in preventing lung cancer metastasis was observed, which increased the value of 9f as a promising lead compound. This work supported that the versatile function of polyamines may endow some intriguing biological features to the parent drugs.

Polyamine metabolism is an intriguing tumor therapeutic target. The present study was designed to assess the synergistic antitumor effects of NPC-16, a novel polyamine naphthalimide conjugate, with celecoxib and to elucidate the mechanism of these effects on human colorectal cancer cells.Cell proliferation was assessed by the MTT assay. Cell apoptosis and mitochondria membrane potential were evaluated by high content screening analysis. Intracellular polyamine content was detected by HPLC. Protein expression was detected by western blot analysis.The co-treatment with celecoxib enhanced NPC-16-induced apoptosis in HCT116 (COX-2 no expression), HT29 (COX-2 higher expression) and Caco-2 (COX-2 higher expression) colorectal cancer cells, which was mediated by the elevated NPC-16 uptake via the effect of celecoxib on polyamine metabolism, including the up-regulated spermidine/spermine N1-acetyltransferase (SSAT) activity and reduced intracellular polyamine levels. The presence of celecoxib does not result in obviously different effect on the NPC-16-triggered apoptosis in diverse COX-2 expressed colorectal cell lines, suggesting that COX-2 was not one vital factor in the apoptotic mechanism. Furthermore, this synergistic apoptosis was involved in the PKB/AKT signal pathway, Bcl-2 and caspase family members. Z-VAD-FMK, a cell permeable pan caspase inhibitor, almost completely inhibited celecoxib and NPC-16 co-induced apoptosis, indicating that this apoptosis was caspase dependent.Co-treatment of celecoxib and NPC-16 could induce colorectal cancer cell apoptosis via COX-2-independent and caspase-dependent mechanisms. The combination therapy with these agents might provide a novel therapeutic model for colorectal cancer.

Hepatocellular carcinoma (HCC) is one of the main causes of death in cancer. Some naphthalimide derivatives exert high anti-proliferative effects on HCC. In this study, it is confirmed that 3-nitro-naphthalimide and nitrogen mustard conjugate (NNM-25), a novel compound conjugated by NNM-25, displayed more potent therapeutic action on HCC, both in vivo and in vitro, than amonafide, a naphthalimide drug in clinical trials. More importantly, preliminary toxicological evaluation also supported that NNM-25 exhibited less systemic toxicity than amonafide at the therapeutic dose. The antitumor mechanism of conjugates of naphthalimides with nitrogen mustard remains poorly understood up to now. Here, we first reported that apoptosis might be the terminal fate of cancer cells treated with NNM-25. Inhibition of p53 by siRNA resulted in a significant decrease of NNM-25-induced apoptosis, which corroborated that p53 played a vital role in the cell apoptosis triggered by NNM-25. NNM-25 inhibited the PARP-1 activity, AKT phosphorylation, up-regulated the protein expression of p53, Bad, and mTOR as well as down-regulating the protein expression of Bcl-2 and decreasing mitochondrial membrane potential. It also facilitated cytochrome c release from mitochondria to cytoplasm, activated caspase 8, caspase 9, and caspase 3 in HepG2 cells in vitro, as also authenticated in H22 tumor-bearing mice in vivo. Collectively, the conjugation of naphthalimides with nitrogen mustard provides favorable biological activity and thus is a valuable strategy for future drug design in HCC therapy.

A new series of polyamine–toxic cargo conjugates was synthesized with aryl aldehydes conjugating to hydrazino-containing triamine skeletons. The in vitro cytotoxicity of target compounds was evaluated in several cancer cell lines (e.g., L1210, HeLa and B16) and the cellular entry of these polyamine conjugates via polyamine transporter was investigated on SPD- or DFMO-treated B16 cell line. Of these compounds, 6c show significant cytotoxicity on L1210, HeLa and B16 cell lines (IC50 value, 3.74 μmol/L, 5.66 μmol/L and 4.04 μmol/L, respectively). The polyamine transporter assay demonstrated the suitability of hydrazino-containing polyamine backbones for application as vectors in drug delivery systems.

Aryl-guanidino polyamine conjugates were prepared to evaluate their recognition for polyamine transporter (PAT) via a-difluoromethylornithine (DFMO) and spermidine (SPD)-treated B16 cell lines. The potent synergistic effects of DFMO on guanidino polyamine conjugates indicated that the presence of DFMO strongly facilitates the transport of conjugates into cells via PAT on cell membrane. The apoptotic mechanisms of triamine conjugates 10 and 1 (with and without guanidine groups) revealed that they induced apoptosis of Hela cells through the mitochondrial pathway associated with lysosomes, while DFMO strongly synergizes the function of 10 without changing the apoptotic route. Taken together, guanidino polyamine conjugates can target PAT for transport as normal polyamine ones, and the presence of guanidine in the polyamine vectors does not seem to alter the cellular targets of the conjugates, which may depend mainly on the pharmacophore.

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 α-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 cellsviaapoptosis, 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.

Two novel mononaphthalimide homospermidine derivatives (2a, 2b) with three or four methylene unit as linkages were synthesized and evaluated for cytotoxicity against human leukemia K562, murine melanoma B16 and Chinese hamster ovary CHO cell lines. The presence of homospermidine motif could greatly elevate the potency of 1,8-naphthalimide. Conjugate 2b with longer spacer exhibited higher in vitro cytotoxicity than 2a. The DNA binding experiments indicated that conjugates 2b could bind to herring sperm DNA. The topoisomerase II poison trials revealed that 2b could inhibit the activity of top. II.

A series of four novel hydrazine-modified diamine conjugates (7a-b, 8a-b) were synthesized and evaluated for cytotoxicity against Melanoma B16, α-difluoromethylornithine (DFMO)-treated B16, spermidine (SPD)-treated B16, Mouse leukemia L1210 and Hela cell lines. Both the DFMO-B16 and SPD-B16 experiments indicated that conjugates 7a-b and 8a-b could recognize the polyamine transporter (PAT) and enter the cells in part or in whole via PAT, although they were not as efficient as the reference, 9-anthracenemethyl homospermidine (1).

Four novel dicyclic arene–homospermidine conjugates (6a–d) were synthesized and evaluated for cytotoxicity in L1210, α-difluoromethylornithine (DFMO) treated L1210, melanoma B16, spermidine (SPD) treated B16, and Hela cells. In the DFMO-treated L1210 experiments, 6a–d were more sensitive to DFMO than naphthalene-homospermidine (6e), suggesting that 6a–d can utilize the polyamine transporter (PAT) to enter the cells as well as 6e. The diminished cytotoxicity in the SPD/B16 experiments also supported this conclusion. In summary, the homospermidine is an efficacious vector to ferry dicyclic arenes into cells via PAT.

Arsenic trioxide (ATO) has been identified as an effective treatment for acute promyelocytic leukemia (APL) but is much less effective against solid tumors such as hepatocellular carcinoma (HCC). In the search for ways to enhance its therapeutic efficacy against solid tumors, we have examined its use in combination with a novel derivative of β-elemene, N-(β-elemene-13-yl)tryptophan methyl ester (ETME). Here we report the effects of the combination on cell viability, apoptosis, the cell cycle and mitochondria membrane potential (MMP) in HCC SMMC-7721 cells. We found that the two compounds acted synergistically to enhance antiproliferative activity and apoptosis. The combination also decreased the MMP, down-regulated Bcl-2 and pro-proteins of the caspase family, and up-regulated Bax and BID, all of which were reversed by the p53 inhibitor, pifithrin-α. In addition, the combination induced cell cycle arrest at the G2/M phase and reduced tumor volume and weight in an xenograft model of nude mice. Overall, the results suggest that ETME in combination with ATO may be useful in the treatment of HCC patients particularly those unresponsive to ATO alone.This paper demonstrates that the combination of the β-elemene derivative, ETME, and arsenic trioxide (ATO) synergistically induces apoptosis and cell cycle arrest of hepatocellular carcinoma cells and reduces tumor volume and weight in an xenograft model in nude mice by a mechanism involving p53.Download full-size image

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 α-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 cellsviaapoptosis, 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.

Quantum dots (QDs) have shown great potential in monitoring and imaging cancer cells because of their unique photochemical and photophysical properties. However, it is little-known whether QDs affect the cellular internalization, proliferation and apoptosis. Here a new class of multifunctional QDs capped with ligands that possess L-Lys or L-Arg and naphthalimide (NI), linked by carboxyl groups (L-Lys-NI@QDs and L-Arg-NI@QDs, respectively), have been synthesized. We found that these QDs are of controllable sizes, in the range of 4 to 5 nm and have strong optical emission properties. The cellular uptake of NI derivative-capped QDs was monitored by flow cytometry and confocal microscopy. The results of in vitro cytotoxicity revealed that NI derivative-capped QDs, with better cell selectivity, could inhibit the growth of multiple cancer cells more potently than amonafide. They effectively inhibited the proliferation of cells due to apoptosis, which was confirmed by Hoechst 33342, annexin V-FITC and JC-1 staining and mitochondrial membrane potential (MMP) experiments. The most potent NI derivative-capped QDs, L-Arg-NI@CdSe/ZnS, were verified to efficiently induce apoptosis via a reactive oxygen species (ROS) mediating mitochondrial dysfunction, and were more effective in promoting programmed cell death in HepG2 cells in a preliminary mechanistic study.