Design, Synthesis, and In Vitro Activity of Novel Drug Delivery Systems Containing Tuftsin Derivatives and Methotrexate

Toxicity And Surface Modification Of Dendrimers: A Critical Review

As compared to other nano polymers, dendrimers have novel three dimensional, synthetic hyperbranched, nano-polymeric structures. The characteristic of these supramolecular dendritic structures has a high degree of significant surface as well as core functionality in the transportation of drugs for targeted therapy, specifically in host-guest response, gene transfer therapy and imaging of biological systems. However, there are conflicting shreds of evidence regarding biological safety and dendrimers toxicity due to their positive charge at the surface. It includes cytotoxicity, hemolytic toxicity, haematological toxicity, immunogenicity and in vivo toxicity. Therefore to resolve these problems surface modification of the dendrimer group is one of the methods. From that point, this review involves different strategies which reduce the toxicity and improve the biocompatibility of different types of dendrimers. From that viewpoint, we broaden the structural and safe characteristics of the dendrimers in the biomedical and pharmaceutical fields.

Cellular Internalization and Inhibition Capacity of New Anti-Glioma Peptide Conjugates: Physicochemical Characterization and Evaluation on Various Monolayer- and 3D-Spheroid-Based in Vitro Platforms

Most therapeutic agents used for treating brain malignancies face hindered transport through the blood-brain barrier (BBB) and poor tissue penetration. To overcome these problems, we developed peptide conjugates of conventional and experimental anticancer agents. SynB3 cell-penetrating peptide derivatives were applied that can cross the BBB. Tuftsin derivatives were used to target the neuropilin-1 transport system for selectivity and better tumor penetration. Moreover, SynB3-tuftsin tandem compounds were synthesized to combine the beneficial properties of these peptides. Most of the conjugates showed high and selective efficacy against glioblastoma cells. SynB3 and tandem derivatives demonstrated superior cellular internalization. The penetration profile of the conjugates was determined on a lipid monolayer and Transwell co-culture system with noncontact HUVEC-U87 monolayers as simple ex vivo and in vitro BBB models. Importantly, in 3D spheroids, daunomycin-peptide conjugates possessed a better tumor penetration ability than daunomycin. These conjugates are promising tools for the delivery systems with tunable features.

Gemcitabine Peptide-Based Conjugates and Their Application in Targeted Tumor Therapy

A major obstacle in tumor treatment is associated with the poor penetration of a therapeutic agent into the tumor tissue and with their adverse influence on healthy cells, which limits the dose of drug that can be safely administered to cancer patients. Gemcitabine is an anticancer drug used to treat a wide range of solid tumors and is a first-line treatment for pancreatic cancer. The effect of gemcitabine is significantly weakened by its rapid plasma degradation. In addition, the systemic toxicity and drug resistance significantly reduce its chemotherapeutic efficacy. Up to now, many approaches have been made to improve the therapeutic index of gemcitabine. One of the recently developed approaches to improve conventional chemotherapy is based on the direct targeting of chemotherapeutics to cancer cells using the drug-peptide conjugates. In this work, we summarize recently published gemcitabine peptide-based conjugates and their efficacy in anticancer therapy.

Tailoring Uptake Efficacy of HSV-1 gD Derived Carrier Peptides

Regions of the Herpes simplex virus-1 (HSV-1) glycoprotein D (gD) were chosen to design carrier peptides based on the known tertiary structure of the virus entry receptor complexes. These complexes consist of the following: HSV-1 gD–nectin-1 and HSV-1 gD–herpesvirus entry mediator (HVEM). Three sets of peptides were synthesised with sequences covering the (i) N-terminal HVEM- and nectin-1 binding region -5–42, (ii) the 181–216 medium region containing nectin-1 binding sequences and (iii) the C-terminal nectin-1 binding region 214–255. The carrier candidates were prepared with acetylated and 5(6)-carboxyfluorescein labelled N-termini. The peptides were chemically characterised and their conformational features in solution were also determined. In vitro internalisation profile and intracellular localisation were evaluated on SH-SY5Y neuroblastoma cells. Peptide originated from the C-terminal region 224–247 of the HSV-1 gD showed remarkable internalisation compared to the other peptides with low to moderate entry. Electronic circular dichroism secondary structure studies of the peptides revealed that the most effectively internalised peptides exhibit high helical propensity at increasing TFE concentrations. We proved that oligopeptides derived from the nectin-1 binding region are promising candidates—with possibility of Lys²³⁷Arg and/or Trp²⁴¹Phe substitutions—for side-reaction free conjugation of bioactive compounds—drugs or gene therapy agents—as cargos.

Self-assembled peptide nanoparticles for efficient delivery of methotrexate into cancer cells

The low cellular uptake of Methotrexate (MTX), a commonly used anticancer drug, is a big challenge for efficient cancer therapy. Self-assembled peptide nanoparticles (SAPNs) are one of the major classes of peptide vectors that have gained much attention toward novel drug delivery systems. In the present study, different sequences of cell-penetrating peptides including R2W4R2 and W3R4W3 and their SAPNs (R2W4R2-E12 and W3R4W3-E12) were designed for efficient delivery of MTX into MCF7 breast cancer cells. Based on electron microscopy results, the obtained SAPNs were in nano scale with spherical shape. There was a positive relationship between the free energy of water to octanol transferring and cellular penetration of designed nanostructures. The R2W4R2 possessed proper free energy and ability to form a spherical structure and hydrophobic-hydrophobic interactions, therefore, exhibited more cellular penetration than W3R4W3. The cellular uptake of obtained nanoparticles was examined by flow cytometry and fluorescence microscopy, in which, R2W4R2 and R2W4R2-E12 showed more appropriate penetration into MCF7 cells than W3R4W3 and W3R4W3-E12. The cytotoxicity of MTX-loaded peptides and SAPNs was examined by MTT assay. As a result, at higher concentrations, the R2W4R2 and R2W4R2-E12 showed higher cytotoxic behavior than their counterparts. Despite their enhanced cellular internalization, the cytotoxic behavior of MTX-loaded SAPNs at lower concentrations was relatively less than free MTX, which could be ascribed to the gradual nature of drug detachment from these conjugates. Therefore, R2W4R2 could be considered as an efficient choice to enhance the therapeutic efficiency of MTX in cancer treatments.

Cathepsin-sensitive nanoscale drug delivery systems for cancer therapy and other diseases

Cathepsins are an important category of enzymes that have attracted great attention for the delivery of drugs to improve the therapeutic outcome of a broad range of nanoscale drug delivery systems. These proteases can be utilized for instance through actuation of polymer-drug conjugates (e.g., triggering the drug release) to bypass limitations of many drug candidates. A substantial amount of work has been witnessed in the design and the evaluation of Cathepsin-sensitive drug delivery systems, especially based on the tetra-peptide sequence (Gly-Phe-Leu-Gly, GFLG) which has been extensively used as a spacer that can be cleaved in the presence of Cathepsin B. This Review Article will give an in-depth overview of the design and the biological evaluation of Cathepsin-sensitive drug delivery systems and their application in different pathologies including cancer before discussing Cathepsin B-cleavable prodrugs under clinical trials.

Overcharging Effect in Electrospray Ionization Mass Spectra of Daunomycin-Tuftsin Bioconjugates

Peptide-based small molecule drug conjugates for targeted tumor therapy are currently in the focus of intensive research. Anthracyclines, like daunomycin, are commonly used anticancer drug molecules and are also often applied in peptide-drug conjugates. However, lability of the O-glycosidic bond during electrospray ionization mass spectrometric analysis hinders the analytical characterization of the constructs. “Overprotonation” can occur if daunomycin is linked to positively charged peptide carriers, like tuftsin derivatives. In these molecules, the high number of positive charges enhances the in-source fragmentation significantly, leading to complex mass spectra composed of mainly fragment ions. Therefore, we investigated different novel tuftsin-daunomycin conjugates to find an appropriate condition for mass spectrometric detection. Our results showed that shifting the charge states to lower charges helped to keep ions intact. In this way, a clear spectrum could be obtained containing intact protonated molecules only. Shifting of the protonation states to lower charges could be achieved with the use of appropriate neutral volatile buffers and with tuning the ion source parameters.

Nanomedicine-based formulations containing ω-3 polyunsaturated fatty acids: potential application in cardiovascular and neoplastic diseases

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are dietary factors involved in the prevention of cardiovascular, inflammatory, and neoplastic diseases. A multidisciplinary approach – based on recent findings in nutritional science, lipid biochemistry, biotechnology, and biology of inflammation and cancer – has been recently employed to develop ω-3 PUFA-containing nanoformulations with an aim to protect these fatty acids from degradation, increase their bioavailability and delivery to target tissues, and, thus, enhance their bioactivity. In some cases, these nanoformulations were designed to administer ω-3 PUFAs in combination with other nutraceuticals or conventional/innovative drugs. The aim of this strategy was to increase the activities of the compounds contained in the nanoformulation and to reduce the adverse effects often induced by drugs. We herein analyze the results of papers evaluating the potential use of ω-3 PUFA-containing nanomaterials in fighting cardiovascular diseases and cancer. Future directions in this field of research are also provided.

Delivering aminopyridine ligands into cancer cells through conjugation to the cell-penetrating peptide BP16

Peptide conjugates incorporating the N-based ligands (Me2)PyTACN or (S,S')-BPBP at the N- or the C-terminus of the cell-penetrating peptide were synthesized (PyTACN-BP16 (), BP16-PyTACN (), BPBP-BP16 (), and BP16-BPBP ()). Metal binding peptides bearing at the N-terminus the ligand, an additional Lys and a β-Ala were also prepared (PyTACN-βAK-BP16 () and BPBP-βAK-BP16 ()). Moreover, taking into account the clathrin-dependent endocytic mechanism of , the enzymatic cleavable tetrapeptide Gly-Phe-Leu-Gly was incorporated between the ligand and the N- or C-terminus of (BPBP-GFLG-BP16 () and BP16-GLFG-BPBP ()). Analysis of the cytotoxicity of all the peptide conjugates showed that: (i) the position of the ligand influenced the IC50 values, (ii) the incorporation of the βAla-Lys dipeptide rendered non active sequences, (iii) peptide conjugates derived from the (S,S')-BPBP ligand were more active than those bearing (Me2)PyTACN, and (iv) the introduction of the cleavable tetrapeptide significantly enhanced the activity of the BPBP conjugates (IC50 of 4.3 to 11.7 μM ( and ) compared to 26.0 to >50 μM (, and )). The most active peptide was BPBP-GFLG-BP16 () (IC50 of 4.3 to 5.0 μM). This high activity was attributed to its high internalization in MCF-7 cells, as shown by flow cytometry, and to the subsequent release of the ligand by the intracellular cleavage of the enzyme-labile spacer, as observed in cathepsin B enzymatic assays. Therefore, these results pave the way for the design of novel peptide conjugates to be used in pro-oxidant anticancer therapies.

Elegant pH-Responsive Nanovehicle for Drug Delivery Based on Triazine Dendrimer Modified Magnetic Nanoparticles

Owing to properties of magnetic nanoparticles and elegant three-dimensional macromolecule architectural features, dendrimeric structures have been investigated as nanoscale drug delivery systems. In this work, a novel magnetic nanocarrier, generation two (G2) triazine dendrimer modified Fe₃O₄@SiO₂ magnetic nanoparticles (MNP-G2), was designed, fabricated, and characterized by Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The prepared MNP-G2 nanosystem offers a new formulation that combines the unique properties of MNPs and triazine dendrimer as a biocompatible material for biomedical applications. To demonstrate the potential of MNP-G2, the nanoparticles were loaded with methotrexate (MTX), a proven chemotherapy drug. The MTX-loaded MNP-G2 (MNP-G2/MTX) exhibited a high drug-loading capacity of MTX and the excellent ability for controlled drug release. The cytotoxicity of MNP-G2/MTX using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide based assay and MCF-7, HeLa, and Caov-4 cell lines revealed that MNP-G2/MTX was more active against the tumor cells than the free drug in a mildly acidic environment. The results of hemolysis, hemagglutination, and coagulation assays confirmed the good blood safety of MNP-G2/MTX. Moreover, the cell uptake and intracellular distribution of MNP-G2/MTX were studied by flow cytometry analysis and confocal laser scanning microscopy (CLSM). This research suggests that MNP-G2/MTX with good biocompatibility and degradability can be selected as an ideal and effective drug carrier in targeted biomedicine studies especially anticancer applications.

In vitro biological evaluation of new antimycobacterial salicylanilide-tuftsin conjugates

Tuberculosis is caused by Mycobacterium tuberculosis, an intracellular pathogen that can survive in host cells, mainly in macrophages. An increase of multidrug-resistant tuberculosis qualifies this infectious disease as a major public health problem worldwide. The cellular uptake of the antimycobacterial agents by infected host cells is limited. Our approach is to enhance the cellular uptake of the antituberculars by target cell-directed delivery using drug-peptide conjugates to achieve an increased intracellular efficacy. In this study, salicylanilide derivatives (2-hydroxy-N-phenylbenzamides) with remarkable antimycobacterial activity were conjugated to macrophage receptor specific tuftsin based peptide carriers through oxime bond directly or by insertion of a GFLG tetrapeptide spacer. We have found that the in vitro antimycobacterial activity of the salicylanilides against M. tuberculosis H₃₇Rv is preserved in the conjugates. While the free drug was ineffective on infected macrophage model, the conjugates were active against the intracellular bacteria. The fluorescently labelled peptide carriers that were modified with different fatty acid side chains showed outstanding cellular uptake rate to the macrophage model cells. The conjugation of the salicylanilides to tuftsin based carriers reduced or abolished the in vitro cytostatic activity of the free drugs with the exception of the palmitoylated conjugates. The conjugates degraded in the presence of rat liver lysosomal homogenate leading to the formation of an oxime bond-linked salicylanilide-amino acid fragment as the smallest active metabolite.

Comparative analysis of internalisation, haemolytic, cytotoxic and antibacterial effect of membrane-active cationic peptides: aspects of experimental setup

Cationic peptides proved fundamental importance as pharmaceutical agents and/or drug carrier moieties functioning in cellular processes. The comparison of the in vitro activity of these peptides is an experimental challenge and a combination of different methods, such as cytotoxicity, internalisation rate, haemolytic and antibacterial effect, is necessary. At the same time, several issues need to be addressed as the assay conditions have a great influence on the measured biological effects and the experimental setup needs to be optimised. Therefore, critical comparison of results from different assays using representative examples of cell penetrating and antimicrobial peptides was performed and optimal test conditions were suggested. Our main goal was to identify carrier peptides for drug delivery systems of antimicrobial drug candidates. Based on the results of internalisation, haemolytic, cytotoxic and antibacterial activity assays, a classification of cationic peptides is advocated. We found eight promising carrier peptides with good penetration ability of which Penetratin, Tat, Buforin and Dhvar4 peptides showed low adverse haemolytic effect. Penetratin, Transportan, Dhvar4 and the hybrid CM15 peptide had the most potent antibacterial activity on Streptococcus pneumoniae (MIC lower than 1.2 μM) and Transportan was effective against Mycobacterium tuberculosis as well. The most selective peptide was the Penetratin, where the effective antimicrobial concentration on pneumococcus was more than 250 times lower than the HC₅₀ value. Therefore, these peptides and their analogues will be further investigated as drug delivery systems for antimicrobial agents.

Enzyme-triggered delivery of chlorambucil from conjugates based on the cell-penetrating peptide BP16

The undecapeptide KKLFKKILKKL-NH2 (BP16) is a non-toxic cell-penetrating peptide (CPP) that is mainly internalized into cancer cells through a clathrin dependent endocytic mechanism and localizes in late endosomes. Moreover, this CPP is able to enhance the cellular uptake of chlorambucil (CLB) improving its cytotoxicity. In this work, we further explored the cell-penetrating properties of BP16 and those of its arginine analogue BP308. We investigated the influence on the cytotoxicity and on the cellular uptake of conjugating CLB at the N- or the C-terminal end of these undecapeptides. The effect of incorporating the cathepsin B-cleavable sequence Gly-Phe-Leu-Gly in CLB-BP16 and CLB-BP308 conjugates was also evaluated. The activity of CLB was significantly improved when conjugated at the N- or the C-terminus of BP16, or at the N-terminus of BP308. While CLB alone was not active (IC50 of 73.7 to >100 μM), the resulting conjugates displayed cytotoxic activity against CAPAN-1, MCF-7, PC-3, 1BR3G and SKMEL-28 cell lines with IC50 values ranging from 8.7 to 25.5 μM. These results were consistent with the internalization properties observed for the corresponding 5(6)-carboxyfluorescein-labeled conjugates. The presence of the tetrapeptide Gly-Phe-Leu-Gly at either the N- or the C-terminus of CLB-BP16 conjugates further increased the efficacy of CLB (IC50 of 3.6 to 16.2 μM), which could be attributed to its selective release in the lysosomal compartment. Enzymatic assays with cathepsin B showed the release of CLB-Gly-OH from these sequences within a short time. Therefore, the combination of BP16 with an enzymatic cleavable sequence can be used as a drug delivery system for the effective uptake and release of drugs in cancer cells.

Antimycobacterial activity of peptide conjugate of pyridopyrimidine derivative against Mycobacterium tuberculosis in a series of in vitro and in vivo models

New pyridopyrimidine derivatives were defined using a novel HTS in silico docking method (FRIGATE). The target protein was a dUTPase enzyme (EC 3.6.1.23; Rv2697) which plays a key role in nucleotide biosynthesis of Mycobacterium tuberculosis (Mtb). Top hit molecules were assayed in vitro for their antimycobacterial effect on Mtb H37Rv culture. In order to enhance the cellular uptake rate, the TB820 compound was conjugated to a peptid-based carrier and a nanoparticle type delivery system (polylactide-co-glycolide, PLGA) was applied. The conjugate had relevance to in vitro antitubercular activity with low in vitro and in vivo toxicity. In a Mtb H37Rv infected guinea pig model the in vivo efficacy of orally administrated PLGA encapsulated compound was proven: animals maintained a constant weight gain and no external clinical signs of tuberculosis were observed. All tissue homogenates from lung, liver and kidney were found negative for Mtb, and diagnostic autopsy showed that no significant malformations on the tissues occurred.

The rational design of a gemcitabine prodrug with AIE-based intracellular light-up characteristics for selective suppression of pancreatic cancer cells

An enzyme and reduction-activatable gemcitabine prodrug with AIE properties was designed for targeted and image-guided pancreatic cancer therapy.

Leishmania braziliensis: cytotoxic, cytostatic and chemotactic effects of poly-lysine-methotrexate-conjugates

Chemotactic responses play a significant role during Leishmania differentiation, as well as in the course of parasite-host-cell interaction, a process that precedes a successful infection. The present study uses the modified "two-chamber capillary assay" to quantitatively evaluate the chemotactic properties and the toxic activities of methotrexate containing branched chain polymeric polypeptide conjugates in Leishmania. Our results demonstrate that this methodology quantitatively determines the taxis of Leishmania towards/against gradients of compounds. They also demonstrate that chemotaxis produced by the polypeptide-methotrexate conjugates depends on specific chemical characteristics. For example, the N-terminal amino acid (Ser or Glu) location at the branch significantly influences the elicited chemotaxis. Furthermore, the use of different attachment sites in the methotrexate conjugates (α- or γ-carboxylic groups) affect their chemotactic activity. Specific cytotoxic activities and cytostatic effects of the conjugates on parasites and on murine and human cells of the macrophage/monocyte system respectively, suggest that these ligands may be used as a group of anti-Leishmania substances acting selectively on Leishmania and different hosts.

Investigation on chemotactic drug targeting (chemotaxis and adhesion) inducer effect of GnRH-III derivatives in Tetrahymena and human leukemia cell line

GnRH-III has been shown to exert a cytotoxic effect on the GnRH-R positive tumor cells. The chemotactic drug targeting (CDT) represents a new way for drug delivery approach based on selective chemoattractant guided targeting. The major goal of the present work was to develop and investigate various GnRH-III derivatives as potential targeting moieties for CDT. The cell physiological effects (chemotaxis, adhesion, and signaling) induced by three native GnRHs (hGnRH-I, cGnRH-II, and lGnRH-III) and nine GnRH-III derivatives were evaluated in two model cells (Tetrahymena pyriformis and Mono Mac 6 human monocytes). According to our results, the native GnRH-III elicited the highest chemoattractant and adhesion inducer activities of all synthesized peptides in micromolar concentrations in monocytes. With respect to chemoattraction, dimeric derivatives linked by a disulfide bridge ([GnRH-III(C)](2) ) proved to be efficient in both model cells; furthermore, acetylation of the linker region ([GnRH-III(Ac-C)](2) ) could slightly improve the chemotactic and adhesion effects in monocytes. The length of the peptide and the type of N-terminal amino acid could also determine the chemotactic and adhesion modulation potency of each fragment. The application of the chemoattractant GnRH-III derivatives was accompanied by a significant activation of phosphatidylinositol 3-kinase in both model cells. In summary, our work on low-level differentiated model cells of tumors has proved that GnRH-III and some of its synthetic derivatives are promising candidates to be applied in CDT: these compounds might act both as carrier, delivery unit, and antitumor agents.

Enhanced cellular uptake of a new, in silico identified antitubercular candidate by peptide conjugation

Mycobacterium tuberculosis is a successful pathogen, and it can survive in infected macrophages in dormant phase for years and decades. The therapy of tuberculosis takes at least six months, and the slow-growing bacterium is resistant to many antibiotics. The development of novel antimicrobials to counter the emergence of bacteria resistant to current therapies is urgently needed. In silico docking methods and structure-based drug design are useful bioinformatics tools for identifying new agents. A docking experiment to M. tuberculosis dUTPase enzyme, which plays a key role in the bacterial metabolism, has resulted in 10 new antitubercular drug candidates. The uptake of antituberculars by infected macrophages is limited by extracellular diffusion. The optimization of the cellular uptake by drug delivery systems can decrease the used dosages and the length of the therapy, and it can also enhance the bioavailability of the drug molecule. In this study, improved in vitro efficacy was achieved by attaching the TB5 antitubercular drug candidate to peptide carriers. As drug delivery components, (i) an antimicrobial granulysin peptide and (ii) a receptor specific tuftsin peptide were used. An efficient synthetic approach was developed to conjugate the in silico identified TB5 coumarone derivative to the carrier peptides. The compounds were effective on M. tuberculosis H37Rv culture in vitro; the chemical linkage did not affect the antimycobacterial activity. Here, we show that the OT20 tuftsin and GranF2 granulysin peptide conjugates have dramatically enhanced uptake into human MonoMac6 cells. The TB5-OT20 tuftsin conjugate exhibited significant antimycobacterial activity on M. tuberculosis H37Rv infected MonoMac6 cells and inhibited intracellular bacteria.

New pemetrexed-peptide conjugates: synthesis, characterization and in vitro cytostatic effect on non-small cell lung carcinoma (NCI-H358) and human leukemia (HL-60) cells

Pemetrexed (Pem) is a novel antimetabolite type of anticancer drug that demonstrated promising clinical activity in a wide variety of solid tumors, including non-small cell lung carcinoma and malignant pleural mesothelioma. It inhibits enzymes involved in the folate pathway, for which the presence of its free carboxylic groups is necessary. The heteroaromatic ring system of Pem has a modifiable amino group, which opens a possibility to apply a new strategy to conjugate Pem to carrier molecules. Considering this as well as the necessity of untouched carboxylic groups of Pem in the new conjugates, we developed a new synthesis strategy. Here, we describe the synthesis and the characterization of new Pem-peptide conjugates in which cell-penetrating octaarginine or/and lung-targeting H-Ile-Glu-Leu-Leu-Gln-Ala-Arg-NH(2) peptide is attached to the drug by thioether bond. The conjugates characterized by RP-HPLC and MS exhibited cytostatic effect in vitro on non-small cell lung carcinoma as well as on human leukemia cell lines. The IC(50) values of the conjugates were similar, but the conjugates with H-Ile-Glu-Leu-Leu-Gln-Ala-Arg-NH(2) sequence were slightly more effective. Our data show that the in vitro cytostatic effect of the free Pem was essentially maintained after conjugation with cell-penetrating or cell-targeting peptides. Thus, the conjugation strategy reported could lead to the development of a new generation of active Pem conjugates.

Photochemical release of methotrexate from folate receptor-targeting PAMAM dendrimer nanoconjugate

Nanoparticle (NP)-based targeted drug delivery involves cell-specific targeting followed by a subsequent therapeutic action from the therapeutic carried by the NP system. NPs conjugated with methotrexate (MTX), a potent inhibitor of dihydrofolate reductase (DHFR) localized in cytosol, have been under investigation as a delivery system to target cancer cells to enhance the therapeutic index of methotrexate, which is otherwise non-selectively cytotoxic. Despite improved therapeutic activity from MTX-conjugated NPs in vitro and in vivo, the therapeutic action of these conjugates following cellular entry is poorly understood; in particular it is unclear whether the therapeutic activity requires release of the MTX. This study investigates whether MTX must be released from a nanoparticle in order to achieve the therapeutic activity. We report herein light-controlled release of methotrexate from a dendrimer-based conjugate and provide evidence suggesting that MTX still attached to the nanoconjugate system is fully able to inhibit the activity of its enzyme target and the growth of cancer cells.

Novel formulation of a methotrexate derivative with a lipid nanoemulsion

Background

Lipid nanoemulsions that bind to low-density lipoprotein receptors can concentrate chemotherapeutic agents in tissues with low-density lipoprotein receptor overexpression and decrease the toxicity of the treatment. The aim of this study was to develop a new formulation using a lipophilic derivative of methotrexate, ie, didodecyl methotrexate (ddMTX), associated with a lipid nanoemulsion (ddMTX-LDE).

Methods

ddMTX was synthesized by an esterification reaction between methotrexate and dodecyl bromide. The lipid nanoemulsion was prepared by four hours of ultrasonication of a mixture of phosphatidylcholine, triolein, and cholesteryloleate. Association of ddMTX with the lipid nanoemulsion was performed by additional cosonication of ddMTX with the previously prepared lipid nanoemulsion. Formulation stability was evaluated, and cell uptake, cytotoxicity, and acute animal toxicity studies were performed.

Results

The yield of ddMTX incorporation was 98% and the particle size of LDE-ddMTX was 60 nm. After 48 hours of incubation with plasma, approximately 28% ddMTX was released from the lipid nanoemulsion. The formulation remained stable for at least 45 days at 4°C. Cytotoxicity of LDE-ddMTX against K562 and HL60 neoplastic cells was higher than for methotrexate (50% inhibitory concentration [IC₅₀] 1.6 versus 18.2 mM and 0.2 versus 26 mM, respectively), and cellular uptake of LDE-ddMTX was 90-fold higher than that of methotrexate in K562 cells and 75-fold in HL60 cells. Toxicity of LDE-ddMTX, administered at escalating doses, was higher than for methotrexate (LD₅₀ 115 mg/kg versus 470 mg/kg; maximum tolerated dose 47 mg/kg versus 94 mg/kg) in mice. However, the hematological toxicity of LDE-ddMTX was lower than for methotrexate.

Conclusion

LDE-ddMTX was stable, and uptake of the formulation by neoplastic cells was remarkably greater than of methotrexate, which resulted in markedly greater cytotoxicity. LDE-ddMTX is thus a promising formulation to be tested in future animal models of cancer or rheumatic disease, wherein methotrexate is widely used.

In vitro degradation and antitumor activity of oxime bond-linked daunorubicin-GnRH-III bioconjugates and DNA-binding properties of daunorubicin-amino acid metabolites

Bioconjugates with receptor-mediated tumor-targeting functions and carrying cytotoxic agents should enable the specific delivery of chemotherapeutics to malignant tissues, thus increasing their local efficacy while limiting the peripheral toxicity. In the present study, gonadotropin-releasing hormone III (GnRH-III; Glp-His-Trp-Ser-His-Asp-Trp-Lys-Pro-Gly-NH(2)) was employed as a targeting moiety to which daunorubicin was attached via oxime bond, either directly or by insertion of a GFLG or YRRL tetrapeptide spacer. The in vitro antitumor activity of the bioconjugates was determined on MCF-7 human breast and HT-29 human colon cancer cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Their degradation/stability (1) in human serum, (2) in the presence of cathepsin B and (3) in rat liver lysosomal homogenate was analyzed by liquid chromatography in combination with mass spectrometry. The results show that (1) all synthesized bioconjugates have in vitro antitumor effect, (2) they are stable in human serum at least for 24 h, except for the compound containing an YRRL spacer and (3) they are hydrolyzed by cathepsin B and in the lysosomal homogenate. To investigate the relationship between the in vitro antitumor activity and the structure of the bioconjugates, the smallest metabolites produced in the lysosomal homogenate were synthesized and their binding to DNA was assessed by fluorescence spectroscopy. Our data indicate that the incorporation of a peptide spacer in the structure of oxime bond-linked daunorubicin-GnRH-III bioconjugates is not required for their antitumor activity. Moreover, the antitumor activity is influenced by the structure of the metabolites (daunorubicin-amino acid derivatives) and their DNA-binding properties.

Dendrimer toxicity: Let's meet the challenge

Dendrimers are well-defined, versatile polymeric architecture with properties resembling biomolecules. Dendritic polymers emerged as outstanding carrier in modern medicine system because of its derivatisable branched architecture and flexibility in modifying it in numerous ways. Dendritic scaffold has been found to be suitable carrier for a variety of drugs including anticancer, anti-viral, anti-bacterial, antitubercular etc., with capacity to improve solubility and bioavailability of poorly soluble drugs. In spite of extensive applicability in pharmaceutical field, the use of dendrimers in biological system is constrained because of inherent toxicity associated with them. This toxicity is attributed to the interaction of surface cationic charge of dendrimers with negatively charged biological membranes in vivo. Interaction of dendrimers with biological membranes results in membrane disruption via nanohole formation, membrane thinning and erosion. Dendrimer toxicity in biological system is generally characterized by hemolytic toxicity, cytotoxicity and hematological toxicity. To minimize this toxicity two strategies have been utilized; first, designing and synthesis of biocompatible dendrimers; and second, masking of peripheral charge of dendrimers by surface engineering. Biocompatible dendrimers can be synthesized by employing biodegradable core and branching units or utilizing intermediates of various metabolic pathways. Dendrimer biocompatibility has been evaluated in vitro and in vivo for efficient presentation of biological performance. Surface engineering masks the cationic charge of dendrimer surface either by neutralization of charge, for example PEGylation, acetylation, carbohydrate and peptide conjugation; or by introducing negative charge such as half generation dendrimers. Neutral and negatively charged dendrimers do not interact with biological environment and hence are compatible for clinical applications as elucidated by various studies examined in this review. Chemical modification of the surface is an important strategy to overcome the toxicity problems associated with the dendrimers. The present review emphasizes on the approaches available to overcome the cationic toxicity inherently associated with the dendrimers.

Receptor-mediated tumor targeting based on peptide hormones

IMPORTANCE OF THE FIELD

Tumor targeting with peptides is based on the discovery that receptors for many regulatory peptides are overexpressed in tumor cells, compared with their expression in normal tissues. Consequently, these peptides and their analogues can be used as carriers/targeting moieties for the preparation of diagnostic and therapeutic agents that have increased selectivity and decreased peripheral toxicity.

AREAS COVERED IN THIS REVIEW

Here an overview is given of the most relevant gonadotropin-releasing hormone (GnRH) and somatostatin derivatives, as well as of their applications in cancer diagnosis and therapy. For this purpose, recently published data in these areas (mostly articles published from 2000 to 2009) were reviewed.

WHAT THE READER WILL GAIN

In contrast to other regulatory peptides that stimulate the tumor growth, GnRH and somatostatin derivatives have inhibitory effect; therefore, they were used primarily for the preparation of various conjugates to be used in targeted chemotherapy, targeted radiotherapy, photodynamic therapy, boron neutron capture therapy and cancer diagnosis. Some of these conjugates have already found clinical applications, whereas others are now in preclinical and clinical trials.

TAKE HOME MESSAGE

Tumor targeting with hormone peptides provides a basis for the development of new diagnostic and therapeutic approaches for cancer.

Development of an oxime bond containing daunorubicin-gonadotropin-releasing hormone-III conjugate as a potential anticancer drug

Here, we report on the synthesis and biological properties of a conjugate in which daunorubicin (Dau) as chemotherapeutic agent was attached through an oxime bond to gonadotropin-releasing hormone-III (GnRH-III) as targeting moiety. In vitro toxicity and the cytostatic effect of the conjugate on MCF-7 human breast and C26 murine colon cancer cell lines were determined, and the results were compared with those obtained for the free daunorubicin, as well as with the doxorubicin containing derivative. In vivo antitumor effect of daunorubicin-GnRH-III was studied on Balb/c female mice transplanted with C26 tumor. Our data indicate that the daunorubicin-GnRH-III conjugate had a lower toxic effect than the free daunorubicin and it was essentially nontoxic up to 15 mg (Dau content)/kg body weight. The treatment of the C26 tumor bearing mice with the conjugate led to tumor growth inhibition and longer survival time in comparison with the controls and with the administration of the free drug. When mice were treated twice with the conjugate (on days 4 and 7 after tumor transplantation), 46% tumor growth inhibition was obtained. In this case, the increase of the median survival time was 38% compared to the controls.