Synthesis and biological evaluation of theranostic Trastuzumab–SN38 conjugate for Near-IR fluorescence imaging and targeted therapy of HER2+ breast cancer

Here, we report on the design, synthesis, and biological evaluation of a new theranostic antibody drug conjugate (ADC), Cy5-Ab-SS-SN38, that consists of the HER2-specific antibody trastuzumab (Ab) connected to the near infrared (NIR) pentamethine cyanine dye Cy5 and SN38, which is a bioactive metabolite of the anticancer drug irinotecan. SN38 is bound to an antibody through a glutathione-responsive self-immolative disulfide carbamate linker. For the first time, we explored this linker in ADC and found that it to reduce the drug release rate, which is important for safe drug delivery. The developed ADC exhibited specific accumulation and nanomolar anti-breast cancer activity on HER2-positive (HER2+) cell lines but no effect on HER2-. Animals treated with this ADC exhibited good tolerance. In vivo studies have shown that the ADC had good targeting ability for HER2+ tumors with much higher anticancer potency than trastuzumab itself or a mixture of trastuzumab with SN38. Side-by-side HER2+/HER2-xenograft at the 10 mg/kg dose exhibited specific accumulation and reduction of HER2+ tumor but not accumulation or growth inhibition of HER2-counterpart. The self-immolative disulfide linker implemented in this study was proven to be successful, broadening its utilization with other antibodies for targeted anticancer therapy in general. We believe that the theranostic ADCs comprising the glutathione-responsive self-immolative disulfide carbamate linker are applicable for the treatment and fluorescent monitoring of malignancies and anticancer drug delivery.

Novel Cyclic Peptides for Targeting EGFR and EGRvIII Mutation for Drug Delivery

The epidermal growth factor–epidermal growth factor receptor (EGF-EGFR) pathway has become the main focus of selective chemotherapeutic intervention. As a result, two classes of EGFR inhibitors have been clinically approved, namely monoclonal antibodies and small molecule kinase inhibitors. Despite an initial good response rate to these drugs, most patients develop drug resistance. Therefore, new treatment approaches are needed. In this work, we aimed to find a new EGFR-specific, short cyclic peptide, which could be used for targeted drug delivery. Phage display peptide technology and biopanning were applied to three EGFR expressing cells, including cells expressing the EGFRvIII mutation. DNA from the internalized phage was extracted and the peptide inserts were sequenced using next-generation sequencing (NGS). Eleven peptides were selected for further investigation using binding, internalization, and competition assays, and the results were confirmed by confocal microscopy and peptide docking. Among these eleven peptides, seven showed specific and selective binding and internalization into EGFR positive (EGFR+ve) cells, with two of them—P6 and P9—also demonstrating high specificity for non-small cell lung cancer (NSCLC) and glioblastoma cells, respectively. These peptides were chemically conjugated to camptothecin (CPT). The conjugates were more cytotoxic to EGFR+ve cells than free CPT. Our results describe a novel cyclic peptide, which can be used for targeted drug delivery to cells overexpressing the EGFR and EGFRvIII mutation.

Antibody guided activatable NIR photosensitizing system for fluorescently monitored photodynamic therapy with reduced side effects

Photodynamic therapy (PDT) utilizing an organic dye (photosensitizer) capable of killing cancer cells in the body upon light irradiation is one of the promising non-invasive treatment modalities for many cancers. A known drawback of PDT is a side-effect caused by existing photosensitizers to organs due to insufficient specificity and accidental light exposure of a patient during the delivery of the photosensitizer in the bloodstream. To overcome this issue, we developed a novel antibody guided, activatable photosensitizing system, Ab-mI₂XCy-Ac, where the trastuzumab (Ab) is linked to the non-active (not phototoxic and not fluorescent) dye, mI₂XCy-Ac, that contains the hydroxyl group protected by acetyl (Ac). This targeting, non-photo-active conjugate was shown to be safely (without detectable side-effects) delivered to the targeted tumor, where it is activated by the esterase-mediated acetyl group cleavage and effectively treats the tumor upon NIR light irradiation. It was demonstrated in the Her2 positive BT-474 tumor mouse model that the treatment efficacy of the activatable photosensitizing system is about the same as for the permanently active photosensitizer, Ab-mI₂XCy, while the side-effects are noticeably reduced. In addition, this activatable system enables fluorescence monitoring of the photosensitizer activation events.

A novel, dual action chimera comprising DNA methylating agent and near-IR xanthene-cyanine photosensitizer for combined anticancer therapy

A facile synthesis, biological evaluation and photodynamic properties of novel activatable anticancer molecular hybrids (chimeras) Ch and I-Ch are described. The chimeras consist of DNA methylating methyl triazene moiety and fluorogenic xanthene-cyanine (XCy) or iodinated xanthene-cyanine (I-XCy) photosensitizer. These two anticancer core structures are bound by means of a self-immolative 4-aminobenzyl alcohol linker. The hydrolytic cleavage of the carbamate protecting group promotes activation of both DNA methylating monomethyl triazene and phototoxic xanthene-cyanine dye providing, in addition, a near-IR emission signal for detection of the drug activation events. Preliminary antiproliferative assay demonstrates that the developed chimeras exhibit higher antitumor activity in the breast cancer cell line upon near-IR light irradiation compared to their structural constituents, xanthene-cyanine photosensitizer and monomethyl triazene substance.

[THERANOSTIC TARGETED DRUG DELIVERY - NEW INSIGHTS INTO DIAGNOSIS AND TREATMENT OF CANCER]

Monoclonal antibodies (mAbs) have become a novel therapeutic modality against cancer due to their specificity, affinity and serum stability. These incredible tools capable of linking variable payload, generate antibody drug conjugates (ADCs) that preserve targeting properties and therefore, specifically deliver drugs to the cancer cells. The drugs should exhibit sub-nano to picomolar cytotoxicity usually affecting fundamental oncogenic mechanisms via mitotic inhibition, DNA alkylation and topoisomerase poisoning. The linkers play a pivotal role in ADC design as they link the cytotoxic payload to the antibody. Linkers maintain the stability of the ADCs in the blood circulation securing their delivery to the cancer cell intact but cleaved when internalized to release the payload. Recently, a more advanced version of ADC, namely theranostic (therapeutic and diagnostic) ADC has emerged. These conjugates allow visualization of targeted drug delivery (TDD) vastly impacting the therapeutic index in cancer treatment. Among diagnostic probes, NIR fluorescent dyes provide important real-time information on the efficacy of drug delivery. A two-dye system comprising one switchable and one constantly light emitting cyanine (Cy) linkers provides the ratiometric quantification of the drug released in the tumor. Due to the enormous repertoire of mAbs, the theranostic ADCs can change the future of cancer diagnosis and treatment.

Targeted methylation facilitates DNA double strand breaks and enhances cancer suppression: A DNA intercalating/methylating dual-action chimera Amonafidazene

A DNA intercalating agent Amonafide interferes with topoisomerase 2 (Topo II) activity and prevents re-ligation of DNA strands, leading to double strand breaks (DSB). If DSB repair fails, cells stop dividing and eventually die. In a search of approaches to enhance anti-cancer activities of Topo II inhibitors, we hypothesized that introduction of additional damage in proximity to the DSB may suppress DNA repair and enhance cancer cell killing. Accordingly, chimeric molecules were created that target a DNA alkylating component to the proximity of Topo II-induced DSBs. These chimeras consist of Amonafide or its 4-amino isomer, and DNA methylating methyl triazene moiety Azene protected with a carbamate group, connected via linker. Treatment of cancer cells with the chimeric molecules leads to significantly higher number of DSBs, which were repaired slower compared to Amonafide or monomethyl triazene-treated cells. On the other hand, methyl triazene linked to non-intercalating Amonafide analogs was ineffective. Together, these data strongly support our hypothesis. In line with increased DSBs, the chimeric molecules exhibited significantly higher antiproliferative activity in cancer cell lines compared to Amonafide or monomethyl triazene constituent Azene. We utilized the fluorescent properties of chimera Amonafidazene to develop ''photo-switchable'' reporting system to monitor the prodrug activation. Using this approach, we found that the chimera accumulated and was activated at the tumor sites specifically and demonstrated significantly stronger tumor suppressing activities compared to Amonafide in a xenograft model. Therefore, targeting alkylating groups to the proximity of DSB sites may become an effective approach towards enhancing anti-cancer activities of inhibitors of topoisomerases.

Discovery of Dolastatinol: A Synthetic Analog of Dolastatin 10 and Low Nanomolar Inhibitor of Tubulin Polymerization

We developed a highly potent anticancer agent, dolastatinol, which is a methylene hydroxyl derivative of dolastatin 10. Dolastatinol is a synthetic analog of dolastatin 10, synthesized by a solid-phase peptide Fmoc chemistry protocol on 2-chlorotrityl chloride resin utilizing a pH-triggering self-immolative monosuccinate linker. The introduction of the C-terminus hydroxyl methylene functionality preserves the anticancer properties of the parent dolastatin 10, including strong suppression of the cell proliferation, migration, high cytotoxicity. Our research establishes a new facile route toward the further development of C-terminus-modified dolastatin-10-based microtubule inhibitors for anticancer treatment.

Ratiometric Fluorescence Monitoring of Antibody-Guided Drug Delivery to Cancer Cells

Ratiometric measurements utilizing two independent fluorescence signals from a dual-dye molecular system help to improve the detection sensitivity and quantification of many analytical, bioanalytical, and pharmaceutical assays, including drug delivery monitoring. Nevertheless, these dual-dye conjugates have never been utilized for ratiometric monitoring of antibody (Ab)-guided targeted drug delivery (TDD). Here, we report for the first time on the new, dual-dye TDD system, Cy5s-Ab-Flu-Aza, comprising the switchable fluorescein-based dye (Flu) linked to the anticancer drug azatoxin (Aza), reference pentamethine cyanine dye (Cy5s), and Her2-specific humanized monoclonal Trastuzumab (Herceptin) antibody. The ability of ratiometric fluorescence monitoring of drug release was demonstrated with this model system in vitro in the example of the human breast cancer SKBR3 cell line overexpressing Her2 receptors. The proposed approach for designing ratiometric, antibody-guided TDD systems, where a "drug-switchable dye" conjugate and a reference dye are independently linked to an antibody, can be expanded to other drugs, dyes, and antibodies. Replacement of the green-emitting dye Flu, which was found not detectable in vivo, with a longer-wavelength (red or near-IR) switchable fluorophore should enable quantification of drug release in the body.

Quantification of Drug Release Degree In Vivo Using Antibody-Guided, Dual-NIR-Dye Ratiometric System

Fluorescent dyes linked to drug delivery systems provide important real-time information on the efficacy of drug delivery. However, the quantitative monitoring of drug distribution is challenging because of interferences from the biological sample and instrumental setup. To improve quantification of anticancer drug delivery followed by drug release in tumor, we equipped an antibody-drug conjugate (ADC) with a turn-on near-infrared (NIR) dye, sensitive to drug release, and a reference NIR dye. In this study, chlorambucil (CLB) was chosen as a model anticancer drug and Trastuzumab monoclonal antibody specific to Her2 receptors overexpressed in many tumors was taken as the carrier. The advantage of the obtained dual-dye ratiometric system for drug release monitoring was demonstrated in mice model.

Drug Combination in Cancer Treatment-From Cocktails to Conjugated Combinations

It is well recognized today that anticancer drugs often are most effective when used in combination. However, the establishment of chemotherapy as key modality in clinical oncology began with sporadic discoveries of chemicals that showed antiproliferative properties and which as a first attempt were used as single agents. In this review we describe the development of chemotherapy from its origins as a single drug treatment with cytotoxic agents to polydrug therapy that includes targeted drugs. We discuss the limitations of the first chemotherapeutic drugs as a motivation for the establishment of combined drug treatment as standard practice in spite of concerns about frequent severe, dose limiting toxicities. Next, we introduce the development of targeted treatment as a concept for advancement within the broader field of small-molecule drug combination therapy in cancer and its accelerating progress that was boosted by recent scientific and technological progresses. Finally, we describe an alternative strategy of drug combinations using drug-conjugates for selective delivery of cytotoxic drugs to tumor cells that potentiates future improvement of drug combinations in cancer treatment. Overall, in this review we outline the development of chemotherapy from a pharmacological perspective, from its early stages to modern concepts of using targeted therapies for combinational treatment.

Expedient synthesis and anticancer evaluation of dual-action 9-anilinoacridine methyl triazene chimeras

The efficient synthesis of molecular hybrids including a DNA-intercalating 9-anilinoacridine (9-AnA) core and a methyl triazene DNA-methylating moiety is described. Nucleophilic aromatic substitution (S_N Ar) and electrophilic aromatic substitution (EAS) reactions using readily accessible starting materials provide a quick entry to novel bifunctional anticancer molecules. The chimeras were evaluated for their anticancer activity. Chimera 7b presented the highest antitumor activity at low micromolar IC₅₀ values in antiproliferative assays performed with various cancer cell lines. In comparison, compound 7b outperformed DNA-intercalating drugs like amsacrine and AHMA. Mechanistic studies of chimera 7b suggest a dual mechanism of action: methylation of the DNA-repairing protein MGMT associated with the triazene structural portion and Topo II inhibition by intercalation of the acridine core.

Data on peptidyl platform-based anticancer drug synthesis and triton-x-based micellar clusters (MCs) self-assembly peculiarities for enhanced solubilization, encapsulation of hydrophobic compounds and their interaction with HeLa cells

The data presented here refer to a research article entitled “Self-Assembled Micellar Clusters Based on Triton-X-family Surfactants for Enhanced Solubilization, Encapsulation, Proteins Permeability Control, and Anticancer Drug Delivery” Solomonov et al., 2019. The present article provides the General Procedure for clusterization of Triton-X-based micelles and the effect of (i) metal ion, surfactant, and chelator concentration on the developed clusters formation, (ii) surfactant-chelator relation change, (iii) metal ion-micelles concertation ratio variation, (iv) metal ion replacement, (v) solvent replacement, (vi) kinetics of clusters formation, (vii) hydrophobic fluorescent dye (Coumarin 6) solubilization in aqueous MCs media, (viii) novel anticancer peptidyl drug synthesis and characterization and (ix) the viability of HeLa cells with and without the presence of drug-free Triton-X-based family MCs. These data provide additional insights useful for understanding all aspects of the micellar clusters formation, optimization, and control.

Theranostic system for ratiometric fluorescence monitoring of peptide-guided targeted drug delivery

Novel theranostic system that first combines a cancer-targeting peptide with a long-wavelength dual fluorescent dye IRD in order to provide ratiometric monitoring of anticancer drug delivery is developed and evaluated in pancreatic cancer cell line.

Synthesis and Biological Studies of New Multifunctional Curcumin Platforms for Anticancer Drug Delivery

BACKGROUND

Scientists have extensively investigated curcumin, yielding many publications on treatments of cancer. Numerous derivatives of curcumin were synthesized, evaluated for their anti-oxidant and free-radical scavenging, SAR, ADME properties and tested in anticancer applications.

OBJECTIVE

We decided to exploit curcumin as a bioactive core platform for carrying anticancer drugs, which likely possesses a carboxyl moiety for potential linkage to the carrier for drug delivery.

METHODS

The goal of this work is to develop biolabile multifunctional curcumin platforms towards anticancer drug delivery, including determination of drug release profiling in hydrolytic media, in vitro cytotoxicity, antioxidant properties and blockage of relevant cell survival pathways.

RESULTS

We report on a facile synthesis of the bioactive multifunctional curcumin-based platforms linked to a variety of anticancer drugs like amonafide and chlorambucil, and release of the drugs in a hydrolytic environment. The leading curcumin-based platform has presented antioxidant activity similar to curcumin, but with much more potent cytotoxicity in vitro in agreement with the augmented blockage of the NF-kB cell survival pathway.

CONCLUSION

The approach presented here may prove beneficial for bioactive curcumin-based delivery applications where multiple drug delivery is required in a consecutive and controlled mode.

Gold nanoparticles stabilize peptide-drug-conjugates for sustained targeted drug delivery to cancer cells

Background

Peptide-drug-conjugates (PDCs) are being developed as an effective strategy to specifically deliver cytotoxic drugs to cancer cells. However one of the challenges to their successful application is the relatively low stability of peptides in the blood, liver and kidneys. Since AuNPs seem to have a longer plasma half-life than PDCs, one approach to overcoming this problem would be to conjugate the PDCs to gold nanoparticles (AuNPs), as these have demonstrated favorable physico-chemical and safety properties for drug delivery systems. We set out to test whether PEG coated-AuNPs could provide a suitable platform for the non-covalent loading of pre-formed PDCs and whether this modification would affect the bioavailability of the PDCs and their cytotoxicity toward target cancer cells.

Methods

Peptides specifically internalized by A20 murine lymphoma cells were isolated from a phage library displaying 7mer linear peptides. Peptide specificity was validated by flow cytometry and confocal microscopy. PDCs were synthesized containing a selected peptide (P4) and either chlorambucil (Chlor), melphalan (Melph) or bendamustine (Bend). Gold nanoparticles were sequentially coated with citrate, PEG-6000 and then PDC (PDC-PEG-AuNP). The physico-chemical properties of the coated particles were analyzed by electrophoresis, TEM, UV–VIS and FTIR. Stability of free and PDC-coated AuNP was determined.

Results

Biopanning of the phage library resulted in discovery of several novel peptides that internalized into A20 cells. One of these (P4) was used to synthesize PDCs containing either Chlor, Melph or Bend. All three PDCs specifically killed A20 target cells, however they had short half-lives ranging from 10.6 to 15.4 min. When coated to PEG-AuNPs, the half-lives were extended to 21.0–22.3 h. The PDC-PEG-AuNPs retained cytotoxicity towards the target cells. Moreover, whereas pre-incubation for 24 h of free PDCs almost completely abolished their cytotoxic activity, the PDC-PEG-AuNPs were still active even after 72 h pre-incubation.

Conclusions

Peptide-drug-conjugates hold potential for improving the target efficacy of chemotherapeutic drugs, however their short half-lives may limit their application. This hurdle can be overcome by easily conjugating them to gold nanoparticles. This conjugation also opens up the possibility of developing slow release formulations of targeted drug delivery systems containing PDCs.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0362-1) contains supplementary material, which is available to authorized users.

Novel synthetic cyclic integrin αvβ3 binding peptide ALOS4: Antitumor activity in mouse melanoma models

ALOS4, a unique synthetic cyclic peptide without resemblance to known integrin ligand sequences, was discovered through repeated biopanning with pIII phage expressing a disulfide-constrained nonapeptide library. Binding assays using a FITC-labeled analogue demonstrated selective binding to immobilized αvβ3 and a lack of significant binding to other common proteins, such as bovine serum albumin and collagen. In B16F10 cell cultures, ALOS4 treatment at 72 h inhibited cell migration (30%) and adhesion (up to 67%). Immunofluorescent imaging an ALOS4-FITC analogue with B16F10 cells demonstrated rapid cell surface binding, and uptake and localization in the cytoplasm. Daily injections of ALOS4 (0.1, 0.3 or 0.5 mg/kg i.p.) to mice inoculated with B16F10 mouse melanoma cells in two different cancer models, metastatic and subcutaneous tumor, resulted in reduction of lung tumor count (metastatic) and tumor mass (subcutaneous) and increased survival of animals monitored to 45 and 60 days, respectively. Examination of cellular activity indicated that ALOS4 produces inhibition of cell migration and adhesion in a concentration-dependent manner. Collectively, these results suggest that ALOS4 is a structurally-unique selective αvβ3 integrin ligand with potential anti-metastatic activity.

Toward the development of a novel non-RGD cyclic peptide drug conjugate for treatment of human metastatic melanoma

The newly discovered short (9 amino acid) non-RGD S-S bridged cyclic peptide ALOS-4 (H-cycl(Cys-Ser-Ser-Ala-Gly-Ser-Leu-Phe-Cys)-OH), which binds to integrin α_vβ₃ is investigated as peptide carrier for targeted drug delivery against human metastatic melanoma. ALOS4 binds specifically the α_vβ₃ overexpressing human metastatic melanoma WM-266-4 cell line both in vitro and in ex vivo assays. Coupling ALOS4 to the topoisomerase I inhibitor Camptothecin (ALOS4-CPT) increases the cytotoxicity of CPT against human metastatic melanoma cells while reduces dramatically the cytotoxicity against non-cancerous cells as measured by the levels of γH2A.X, active caspase 3 and cell viability. Moreover, conjugating ALOS4 to CPT even increases the chemo-stability of CPT under physiological pH. Bioinformatic analysis using Rosetta platform revealed potential docking sites of ALOS4 on the α_vβ₃ integrin which are distinct from the RGD binding sites. We propose to use this specific non-RGD cyclic peptide as the therapeutic carrier for conjugation of drugs in order to improve efficacy and reduce toxicity of currently available treatments of human malignant melanoma.

Discovery of peptide drug carrier candidates for targeted multi-drug delivery into prostate cancer cells

Metastatic castration-resistant prostate cancer (mCRPC) remains essentially incurable. Targeted Drug Delivery (TDD) systems may overcome the limitations of current mCRPC therapies. We describe the use of strict criteria to isolate novel prostate cancer cell targeting peptides that specifically deliver drugs into target cells. Phage from a libraries displaying 7mer peptides were exposed to PC-3 cells and only internalized phage were recovered. The ability of these phage to internalize into other prostate cancer cells (LNCaP, DU-145) was validated. The displayed peptides of selected phage clones were synthesized and their specificity for target cells was validated in vitro and in vivo. One peptide (P12) which specifically targeted PC-3 tumors in vivo was incorporated into mono-drug (Chlorambucil, Combretastatin or Camptothecin) and dual-drug (Chlorambucil/Combretastatin or Chlorambucil/Camptothecin) PDCs and the cytotoxic efficacy of these conjugates for target cells was tested. Conjugation of P12 into dual-drug PDCs allowed discovery of new drug combinations with synergistic effects. The use of strict selection criteria can lead to discovery of novel peptides for use as drug carriers for TDD. PDCs represent an effective alternative to current modes of free drug chemotherapy for prostate cancer.

Discovery of potent molecular chimera (CM358) to treat human metastatic melanoma

The resistance of cancer cells to chemotherapeutic agents, whether through intrinsic mechanisms or developed resistance, motivates the search for new chemotherapeutic strategies. In the present report, we demonstrate a facile synthetic strategy towards the discovery of new anti-cancer substances. This strategy is based on simple covalent coupling between known anti-cancer drugs, which results in novel 'chimeric' small molecules. One of these novel compounds, CM358, is the product of an amide bond formation between the known Topoisomerase II (Topo II) inhibitor amonafide (AM) and the known DNA mustard alkylator chlorambucil (CLB). It demonstrates significant enhanced cytotoxicity over an equimolar mixture of AM and CLB in various cancer cell lines and in a xenograft model of human metastatic melanoma. Topo II inhibition as well as in silico docking studies suggest that CM358 is a stronger Topo II binder than AM. This may be attributed, at least partially, to the placement of the CLB moiety in a favorable orientation with respect to DNA cross-linking with nearby guanines. In a human metastatic melanoma (WM 266-4) xenograft model, this compound was profoundly superior to a mixture of AM and CLB in reduction of tumor growth, maintenance of body weight and extension of overall survival.

Recent Innovations in Peptide Based Targeted Drug Delivery to Cancer Cells

Targeted delivery of chemotherapeutics and diagnostic agents conjugated to carrier ligands has made significant progress in recent years, both in regards to the structural design of the conjugates and their biological effectiveness. The goal of targeting specific cell surface receptors through structural compatibility has encouraged the use of peptides as highly specific carriers as short peptides are usually non-antigenic, are structurally simple and synthetically diverse. Recent years have seen many developments in the field of peptide based drug conjugates (PDCs), particularly for cancer therapy, as their use aims to bypass off-target side-effects, reducing the morbidity common to conventional chemotherapy. However, no PDCs have as yet obtained regulatory approval. In this review, we describe the evolution of the peptide-based strategy for targeted delivery of chemotherapeutics and discuss recent innovations in the arena that should lead in the near future to their clinical application.

Dual-drug RGD conjugates provide enhanced cytotoxicity to melanoma and non-small lung cancer cells

To enhance the efficacy of targeted drug delivery, four new peptide-ligand conjugates were synthesized, each consisting of a cyclic RGDfK penta-peptide loaded with two anticancer drugs. The drug release profiles in different media of these new compounds and their cytotoxic activity against melanoma and non-small lung cancer cell lines were evaluated and compared with those of their singly loaded analogs. The cyclic RGDfK penta-peptide was selected as a targeting moiety because of its high affinity and selectivity to the α_v β₃ integrin receptor, which is frequently over-expressed in various types of cancer cells. The peptide's core was modified at the side chain of its Lys residue by coupling it with a sixth amino acid (AA) - either Lys (5a) or Ser (5b) (Lys/Ser splitter), resulting in two functional sites which enabled the loading of two therapeutic equivalents onto a single targeting carrier. Using Lys as a splitter resulted in two primary amines. Consequently, conjugates 1a and 1b were synthesized by coupling of 2 Chlorambucils (CLBs) or 2 Camptothecins (CPTs), respectively, to the primary amines of 5a. Conjugate 1c was synthesized from 5b by loading two equivalents of CLB on the amine and the hydroxyl of the Ser splitter, resulting in a homodimeric system with two distinct conjugation sites - amide and ester. The heterodimeric conjugate 1d of CLB and CPT was synthesized by loading each one of the primary amines of 5a with two different drugs - CLB and CPT. The doubling of drug equivalents loaded onto the targeting peptide correlated with enhanced cytotoxic efficacy of the conjugates towards cancer cells. The versatility of chemical linkages of the drugs to the peptides resulted in conjugates with different drug release profiles. Molecular dynamics simulations performed on conjugate 1d demonstrated that this compound occupies a conformational space similar to the bio-active conformation of an integrin-bound cyclic RGD peptide reference peptide (c(RGDf(NMe)V). The modified position in 1d (relative to the reference peptide) points away from the integrin, leading us to hypothesize that this peptide binds the integrin in a manner similar to that of the reference peptide thereby fulfilling a crucial requirement for targeted delivery. The strategy of dual drug loading on a single peptide carrier, gives rise to drugs with different mechanisms of action and release profiles, thus substantially increasing the efficacy of selective killing of tumor cells and while reducing the risk of the development of drug resistance. © 2015 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 160-171, 2016.

Antiproliferative Effect of Novel Aminoacridine-based Compounds

We tested the antiproliferative activity and mechanism of the action of several novel aminoacridine derivatives. Six different cancer cell lines were used to evaluate the potential cytotoxic effect of eleven aminoacridine-based molecules. A standard MTT assay was used for cell bioavailability analysis. Additionally, the potential cytotoxic effect of the tested compounds on non-cancer cells was investigated in rat skeletal muscle myotubes (L6) and in bovine aortic smooth muscle cells. In order to investigate whether the DNA binding activity of tested compounds correlated with their cytotoxic effect, circular dichroism (CD) measurement and DNA T4 ligase assay were performed. Finally, the potential mutagenic activity of the lead compound 5 was investigated. The cytotoxic effect of compound 5 in cancer cells was obtained in lower concentrations than the well-known: 9- aminoacridine based drug, amsacrine. The lead compound binds to DNA, but in a different mode than the parent molecules. Additionally, compound 5 was not cytotoxic in the effective range of concentrations in non-cancer cells. In identical concentrations, the parent compound (9-aminoacridine) and amsacrine were extremely toxic for both types of these normal cells. Finally, based on CD measurement and T4 ligase assay, it was confirmed that 5 binds to DNA but in different from the parent compounds manner. Important to mention, that compound 5 might have increased mutagenic activity which must be verified in vivo. Based on these in vitro results, we conclude that 5 is a more potent and more selective antiprolifirative compound than amsacrine. Compound 5 was also more effective in HepG2 and P-12 cells. Thus, 5 is suitable for future in vivo biological evaluation and its structure might be used as a basis for developing novel anticancer drugs.

Synthesis, biological studies and molecular dynamics of new anticancer RGD-based peptide conjugates for targeted drug delivery

New cyclic RGD peptide-anticancer agent conjugates, with different chemical functionalities attached to the parent peptide were synthesized in order to evaluate their biological activities and to provide a comparative study of their drug release profiles. The Integrin binding c(RGDfK) penta-peptide was used for the synthesis of Camptothecin (CPT) carbamate and Chlorambucil (CLB) amide conjugates. Substitution of the amino acid Lys with Ser resulted in a modified c(RGDfS) with a new attachment site, which enabled the synthesis of an ester CLB conjugate. Functional versatility of the conjugates was reflected in the variability of their drug release profiles, while the conserved RGD sequence of a selective binding to the αv integrin family, likely preserved their recognition by the Integrin and consequently their favorable toxicity towards targeted cancer cells. This hypothesis was supported by a computational analysis suggesting that all conjugates occupy conformational spaces similar to that of the Integrin bound bio-active parent peptide.

Anti-proliferative activity of the combination of salan Ti(iv) complexes with other organic and inorganic anticancer drugs against HT-29 and NCI-H1229 cells: synergism with cisplatin

Cytotoxic salan Ti(iv) complex demonstrated synergism with cisplatin in vitro toward human colon and lung cancer cells at various ratios.

"Switch off/switch on" regulation of drug cytotoxicity by conjugation to a cell targeting peptide

Bi-nuclear amino acid platforms loaded with various drugs for conjugation to a peptide carrier were synthesized using simple and convenient orthogonally protective solid-phase organic synthesis (SPOS). Each arm of the platform carries a different anticancer agent linked through the same or different functional group, providing discrete chemo- and bio-release profiles for each drug, and also enabling "switch off/switch on" regulation of drug cytotoxicity by conjugation to the platform and to a cell targeting peptide. The versatility of this approach enables efficient production of drug-loaded platforms and determination of favorable drug combinations/modes of linkage for subsequent conjugation to a carrier moiety for targeted cancer cell therapy. The results presented here potentiate the application of amino acid platforms for targeted drug delivery (TDD).

Targeted drug delivery for cancer therapy: the other side of antibodies

Therapeutic monoclonal antibody (TMA) based therapies for cancer have advanced significantly over the past two decades both in their molecular sophistication and clinical efficacy. Initial development efforts focused mainly on humanizing the antibody protein to overcome problems of immunogenicity and on expanding of the target antigen repertoire. In parallel to naked TMAs, antibody-drug conjugates (ADCs) have been developed for targeted delivery of potent anti-cancer drugs with the aim of bypassing the morbidity common to conventional chemotherapy. This paper first presents a review of TMAs and ADCs approved for clinical use by the FDA and those in development, focusing on hematological malignancies. Despite advances in these areas, both TMAs and ADCs still carry limitations and we highlight the more important ones including cancer cell specificity, conjugation chemistry, tumor penetration, product heterogeneity and manufacturing issues. In view of the recognized importance of targeted drug delivery strategies for cancer therapy, we discuss the advantages of alternative drug carriers and where these should be applied, focusing on peptide-drug conjugates (PDCs), particularly those discovered through combinatorial peptide libraries. By defining the advantages and disadvantages of naked TMAs, ADCs and PDCs it should be possible to develop a more rational approach to the application of targeted drug delivery strategies in different situations and ultimately, to a broader basket of more effective therapies for cancer patients.

Photosensitizer-antibiotic conjugates: a novel class of antibacterial molecules

Bacterial resistance to a variety of antibiotics has led to intensive research into the effect of photosensitizers as a cytotoxic agent against bacterial cells. In this study, we synthesized the following conjugates with or without a linker: rose bengal-penicillanic acid (RBPA), rose bengal-linker-penicillanic acid (RBLPA) and rose bengal-linker-kanamycin (RBLKAN). The antibacterial activity of these conjugates was examined on Staphylococcus aureus and Escherichia coli. Exposure of the cultures to 100 J cm(-2) showed that the minimum inhibitory concentration (MIC) of RBPA, RBLPA and RBLKAN on S. aureus was 0.195, 0.156 and 0.004 microm, respectively. The MIC of RBPA, RBLPA and RBLKAN on E. coli was 1.56, 2.5 and 0.156 microm, respectively. In dark control experiments, the MIC of these conjugates was not detected until a concentration that was 16-fold that of the MIC found in the light experiments. RBPA and RBLPA as well as RBLKAN are bactericidal for both bacterial cells. Total eradication of S. aureus and E. coli was observed with RBLKAN (0.078 and 20 microm 16 J cm(-2), respectively). Under these conditions, scanning electron microscopic analysis showed significant damage to these bacteria. However, the photosensitizer and antibiotics individually were not effective.

Synthesis and antifungal activity of beta-trifluoroalkyl aminovinyl ketone derivatives

Ten beta-trifluoroalkyl aminovinyl ketone derivatives were synthesized, and their inhibitory effects on several phytopathogenic fungi, an oomycete and plants were assessed. The various compounds were fungitoxic at the 10-100 microM range, with (Z)-3-amino-4,4,4-trifluoro-1-(4-chlorophenyl)but-2-en-1-one exhibiting the highest inhibitory effect on most of the test pathogens. Alternaria alternata and Neurospora crassa were the most tolerant and sensitive fungi to the compounds, respectively. We propose that (Z)-3-amino-4,4,4-trifluoro-1-phenylbut-2-en-1-one is the minimal structural requirement for a beta-trifluoroalkyl aminovinyl ketone fungitoxic derivative.

Novel Gly building units for backbone cyclization: synthesis and incorporation into model peptides

We report the preparation of novel building units for backbone cyclization that have the general formula Fmoc-Nalpha[CH(R)CO2Al]Gly-OH. These building units were prepared by the reductive alkylation method using allyl esters of several amino acids as starting material and hence, respectively, contain the side chain of these amino acids. These N-alkylated Gly building units were incorporated in model backbone cyclic peptides. The resulting crude backbone cyclic peptides were obtained in high degree of purity according to HPLC and mass spectrometric analyses.