In Vitro and In Vivo Evaluation of Cysteine and Site Specific Conjugated Herceptin Antibody-Drug Conjugates

Antibody drug conjugates (ADCs) are monoclonal antibodies designed to deliver a cytotoxic drug selectively to antigen expressing cells. Several components of an ADC including the selection of the antibody, the linker, the cytotoxic drug payload and the site of attachment used to attach the drug to the antibody are critical to the activity and development of the ADC.The cytotoxic drugs or payloads used to make ADCs are typically conjugated to the antibody through cysteine or lysine residues. This results in ADCs that have a heterogeneous number of drugs per antibody. The number of drugs per antibody commonly referred to as the drug to antibody ratio (DAR), can vary between 0 and 8 drugs for a IgG₁ antibody. Antibodies with 0 drugs are ineffective and compete with the ADC for binding to the antigen expressing cells. Antibodies with 8 drugs per antibody have reduced in vivo stability, which may contribute to non target related toxicities.In these studies we incorporated a non-natural amino acid, para acetyl phenylalanine, at two unique sites within an antibody against Her2/neu. We covalently attached a cytotoxic drug to these sites to form an ADC which contains two drugs per antibody.We report the results from the first direct preclinical comparison of a site specific non-natural amino acid anti-Her2 ADC and a cysteine conjugated anti-Her2 ADC. We report that the site specific non-natural amino acid anti-Her2 ADCs have superior in vitro serum stability and preclinical toxicology profile in rats as compared to the cysteine conjugated anti-Her2 ADCs. We also demonstrate that the site specific non-natural amino acid anti-Her2 ADCs maintain their in vitro potency and in vivo efficacy against Her2 expressing human tumor cell lines. Our data suggests that site specific non-natural amino acid ADCs may have a superior therapeutic window than cysteine conjugated ADCs.     

Novel immunoconjugates comprised of streptonigrin and 17-amino-geldanamycin attached via a dipeptide-p-aminobenzyl-amine linker system

Cytotoxic agents streptonigrin and 17-amino-geldanamycin were linked to monoclonal antibodies (mAbs), forming antibody–drug conjugates (ADCs) for antigen-mediated targeting to cancer cells. The drugs were conjugated with a linker construct that is labile to lysosomal proteases and incorporates a valine-alanine-p-aminobenzyl (PAB)-amino linkage for direct attachment to the electron-deficient amine functional groups present in both drugs. The resulting ADCs release drug following internalization into antigen-positive cancer cells. The drug linkers were conjugated to mAbs cAC10 (anti-CD30) and h1F6 (anti-CD70) via alkylation of reduced interchain disulfides to give ADCs loaded with 4 drugs/mAb. The streptonigrin ADCs were potent and immunologically specific on a panel of cancer cell lines in vitro and in a Hodgkin lymphoma xenograft model. We conclude that streptonigrin ADCs are candidates for further research, and that the novel linker system used to make them is well-suited for the conjugation of cytotoxic agents containing electron-deficient amine functional groups.     

Topo II inhibition and DNA intercalation by new phthalazine-based derivatives as potent anticancer agents: design,synthesis, anti-proliferative,docking, and in vivo studies

This research presents the design and synthesis of a novel series of phthalazine derivatives as Topo II inhibitors, DNA intercalators, and cytotoxic agents. In vitro testing of the new compounds against HepG-2, MCF-7, and HCT-116 cell lines confirmed their potent cytotoxic activity with low IC₅₀ values. Topo II inhibition and DNA intercalating activities were evaluated for the most cytotoxic members. IC₅₀ values determination demonstrated Topo II inhibitory activities and DNA intercalating affinities of the tested compounds at a micromolar level. Amongst, compound 9d was the most potent member. It inhibited Topo II enzyme at IC₅₀ value of 7.02 ± 0.54 µM with DNA intercalating IC₅₀ of 26.19 ± 1.14 µM. Compound 9d was then subjected to an in vivo antitumor examination. It inhibited tumour proliferation reducing solid tumour volume and mass. Additionally, it restored liver enzymes, proteins, and CBC parameters near-normal, indicating a remarkable amelioration in their functions along with histopathological examinations.     

Effects of antibody,drug and linker on the preclinical and clinical toxicities of antibody-drug conjugates

Antibody-drug conjugates (ADCs) represent a new class of cancer therapeutics. Their design involves a tumor-specific antibody, a linker and a cytotoxic payload. They were designed to allow specific targeting of highly potent cytotoxic agents to tumor cells whilst sparing normal cells. Frequent toxicities that may be driven by any of the components of an ADC have been reported. There are currently more than 50 ADCs in active clinical development, and a further ～20 that have been discontinued. For this review, the reported toxicities of ADCs were analysed, and the mechanisms for their effects are explored in detail. Methods to reduce toxicities, including dosing strategies and drug design, are discussed. The toxicities reported for active and discontinued drugs are important to drive the rational design and improve the therapeutic index of ADCs of the future.     

Synthesis,cytotoxic activity,and DNA binding properties of antitumor cis-1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine cinnamoyl esters

Monocinnamoyl esters at position 2 of (±)-cis-1,2-dihydroxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one and their acetyl derivatives at position 1 were prepared as stabilized analogues of the anticancer alkylating agent S23906-1. Monocinnamoyl esters at position 2 were slower DNA alkylators than the reference 2-monoacetate. Mixed esters bearing an acetyl ester group at position 1 and a cinnamoyl ester group at position 2 alkylated DNA slower than S23906-1. A strong correlation was observed between cytotoxicity and DNA alkylation kinetics, with slower alkylators displaying more potent antiproliferative activities. The most cytotoxic compounds proved to be significantly active in vivo against murine C-38 adenocarcinoma implanted in mice, but less potent than S23906-1.     

First studies on tumor associated carbonic anhydrases IX and XII monoclonal antibodies conjugated to small molecule inhibitors

We report for the first time Antibody-Drug-Conjugates (ADCs) containing human (h) Carbonic Anhydrase (CA; EC 4.2.1.1) directed Monoclonal Antibodies (MAbs) linked to low molecular weight inhibitors of the same enzymes by means of hydrophilic peptide spacers. In agreement with the incorporated CA directed MAb fragments, in vitro inhibition data of the obtained ADCs showed sub-nanomolar K_I values for the tumour associated CAs IX and XII which were up to 10-fold more potent when compared to the corresponding unconjugated MAbs. In addition, the introduction of the CA inhibitor (CAI) benzenesulfonamide allowed the ADCs to potently inhibit the housekeeping tumoral off-target human CA II isoform. Such results are supporting the definition of an unprecedented reported class of ADCs able to hit simultaneously multiple hCAs physiologically cooperative in maintaining altered cellular metabolic pathways, and therefore ideal for the treatment of chronic diseases such as cancers and inflammation diseases.     

Design and characterization of homogenous antibody-drug conjugates with a drug-to-antibody ratio of one prepared using an engineered antibody and a dual-maleimide pyrrolobenzodiazepine dimer

Most strategies used to prepare homogeneous site-specific antibody-drug conjugates (ADCs) result in ADCs with a drug-to-antibody ratio (DAR) of two. Here, we report a disulfide re-bridging strategy to prepare homogeneous ADCs with DAR of one using a dual-maleimide pyrrolobenzodiazepine (PBD) dimer (SG3710) and an engineered antibody (Flexmab), which has only one intrachain disulfide bridge at the hinge. We demonstrate that SG3710 efficiently re-bridge a Flexmab targeting human epidermal growth factor receptor 2 (HER2), and the resulting ADC was highly resistant to payload loss in serum and exhibited potent anti-tumor activity in a HER2-positive gastric carcinoma xenograft model. Moreover, this ADC was tolerated in rats at twice the dose compared to a site-specific ADC with DAR of two prepared using a single-maleimide PBD dimer (SG3249). Flexmab technologies, in combination with SG3710, provide a platform for generating site-specific homogenous PBD-based ADCs with DAR of one, which have improved biophysical properties and tolerability compared to conventional site-specific PBD-based ADCs with DAR of two.     

Potential drugs used in the antibody–drug conjugate (ADC) architecture for cancer therapy

Cytotoxic small-molecule drugs have a major influence on the fate of antibody–drug conjugates (ADCs). An ideal cytotoxic agent should be highly potent, remain stable while linked to ADCs, kill the targeted tumor cell upon internalization and release from the ADCs, and maintain its activity in multidrug-resistant tumor cells. Lessons learned from successful and failed experiences in ADC development resulted in remarkable progress in the discovery and development of novel highly potent small molecules. A better understanding of such small-molecule drugs is important for development of effective ADCs. The present review discusses requirements making a payload appropriate for antitumor ADCs and focuses on the main characteristics of commonly-used cytotoxic payloads that showed acceptable results in clinical trials. In addition, the present study represents emerging trends and recent advances of payloads used in ADCs currently under clinical trials.     

Antibody drug conjugates

Antibody drug conjugates (ADCs) have emerged as a viable option in targeted delivery of highly potent cytotoxic drugs in treatment of solid tumors. At the time of writing, only two ADCs have received regulatory approval with >40 others in clinical development. The first generation ADCs suffered from a lack of specificity in amino acid site-conjugations, yielding statistically heterogeneous stoichiometric ratios of drug molecules per antibody molecule. For the second generation ADCs, however, site-specific amino acid conjugation using enzymatic ligation, introduction of unnatural amino acids, and site-specific protein engineering hold promise to alleviate some of the current technical limitations. The rapid progress in technology platforms and antibody engineering has introduced novel linkers, site-specific conjugation chemistry, and new payload candidates that could possibly be exploited in the context of ADCs. A search using the Clinical Trial Database registry (www.clinicaltrials.gov), using the keyword ‘antibody drug conjugate’, yielded ~270 hits. The main focus of this article is to present a brief overview of the recent developments and current challenges related to ADC development.     

Antibody-drug conjugates: recent advances in conjugation and linker chemistries

The antibody-drug conjugate (ADC), a humanized or human monoclonal antibody conjugated with highly cytotoxic small molecules (payloads) through chemical linkers, is a novel therapeutic format and has great potential to make a paradigm shift in cancer chemotherapy. Thisnewantibody-based molecular platform enables selective delivery of a potent cytotoxic payload to target cancer cells, resulting in improved efficacy, reduced systemic toxicity, and preferable pharmacokinetics (PK)/ pharmacodynamics (PD) and biodistribution compared to traditional chemotherapy. Boosted by the successes of FDA-approved Adcetris® and Kadcyla®, this drug class has been rapidly growing along with about 60 ADCs currently in clinical trials. In this article, we briefly review molecular aspects of each component (the antibody, payload, and linker) of ADCs, and then mainly discuss traditional and new technologies of the conjugation and linker chemistries for successful construction of clinically effective ADCs. Current efforts in the conjugation and linker chemistries will provide greater insights into molecular design and strategies for clinically effective ADCs from medicinal chemistry and pharmacology standpoints. The development of site-specific conjugation methodologies for constructing homogeneousADCs is an especially promising path to improving ADC design, which will open the way for novel cancer therapeutics.     

Emulsified Phosphatidylserine,Simple and Effective Peptide Carrier for Induction of Potent Epitope-Specific T Cell Responses

Background

To induce potent epitope-specific T cell immunity by a peptide-based vaccine, epitope peptides must be delivered efficiently to antigen-presenting cells (APCs) in vivo. Therefore, selecting an appropriate peptide carrier is crucial for the development of an effective peptide vaccine. In this study, we explored new peptide carriers which show enhancement in cytotoxic T lymphocyte (CTL) induction capability.

Methodology/Principal Findings

Data from an epitope-specific in vivo CTL assay revealed that phosphatidylserine (PS) has a potent adjuvant effect among candidate materials tested. Further analyses showed that PS-conjugated antigens were preferentially and efficiently captured by professional APCs, in particular, by CD11c⁺CD11b⁺MHCII⁺ conventional dendritic cells (cDCs) compared to multilamellar liposome-conjugates or unconjugated antigens. In addition, PS demonstrated the stimulatory capacity of peptide-specific helper T cells in vivo.

Conclusions/Significance

This work indicates that PS is the easily preparable efficient carrier with a simple structure that delivers antigen to professional APCs effectively and induce both helper and cytotoxic T cell responses in vivo. Therefore, PS is a promising novel adjuvant for T cell-inducing peptide vaccines.     

Site-specific antibody drug conjugates for cancer therapy

Antibody therapeutics have revolutionized the treatment of cancer over the past two decades. Antibodies that specifically bind tumor surface antigens can be effective therapeutics; however, many unmodified antibodies lack therapeutic activity. These antibodies can instead be applied successfully as guided missiles to deliver potent cytotoxic drugs in the form of antibody drug conjugates (ADCs). The success of ADCs is dependent on four factors—target antigen, antibody, linker, and payload. The field has made great progress in these areas, marked by the recent approval by the US Food and Drug Administration of two ADCs, brentuximab vedotin (Adcetris^®) and ado-trastuzumab emtansine (Kadcyla^®). However, the therapeutic window for many ADCs that are currently in pre-clinical or clinical development remains narrow and further improvements may be required to enhance the therapeutic potential of these ADCs. Production of ADCs is an area where improvement is needed because current methods yield heterogeneous mixtures that may include 0–8 drug species per antibody molecule. Site-specific conjugation has been recently shown to eliminate heterogeneity, improve conjugate stability, and increase the therapeutic window. Here, we review and describe various site-specific conjugation strategies that are currently used for the production of ADCs, including use of engineered cysteine residues, unnatural amino acids, and enzymatic conjugation through glycotransferases and transglutaminases. In addition, we also summarize differences among these methods and highlight critical considerations when building next-generation ADC therapeutics.     

Design,synthesis and biological evaluation of phenol-linked uncialamycin antibody-drug conjugates

Uncialamycin is one of the structurally simpler and newer members of enediyne family of natural products. It exhibits highly potent activity against several types of bacteria and cancer cells. Described herein is a strategy for the targeted delivery of this cytotoxic agent to tumors using an antibody-drug conjugate (ADC) approach. Central to the design of ADC were the generation of potent and chemically stable uncialamycin analogues and attachment of protease cleavable linkers to newly realized phenolic handles to prepare linker-payloads. Conjugation of the linker-payloads to tumor targeting antibody, in vitro activity and in vivo evaluation are presented.     

Design,synthesis, nuclear localization,and biological activity of a fluorescent duocarmycin analog,HxTfA

HxTfA 4 is a fluorescent analog of a potent cytotoxic and antimalarial agent, TfA 3, which is currently being investigated for the development of an antimalarial vaccine, PlasProtect®. HxTfA contains a p-anisylbenzimidazole or Hx moiety, which is endowed with a blue emission upon excitation at 318?nm; thus enabling it to be used as a surrogate for probing the cellular fate of TfA using confocal microscopy, and addressing the question of nuclear localization. HxTfA exhibits similar selectivity to TfA for A-tract sequences of DNA, alkylating adenine-N3, albeit at 10-fold higher concentrations. It also possesses in vitro cytotoxicity against A549 human lung carcinoma cells and Plasmodium falciparum. Confocal microscopy studies showed for the first time that HxTfA, and by inference TfA, entered A549 cells and localized in the nucleus to exert its biological activity. At biologically relevant concentrations, HxTfA elicits DNA damage response as evidenced by a marked increase in the levels of γH2AX observed by confocal microscopy and immunoblotting studies, and ultimately induces apoptosis.     

Cytotoxic effect of (1-methyl-1H-imidazol-2-yl)-methanamine and its derivatives in PtII complexes on human carcinoma cell lines: A comparative study with cisplatin

The synthesis and pharmacological characterisation of (1-methyl-1H-imidazol-2-yl)-methanamine and its derivatives in Pt^II complexes are described. Six out of eleven new Pt^II complexes showed a significant cytotoxic effect on NCI-H460 lung cancer cell line with EC₅₀ values between 1.1 and 0.115 mM, determined by MTT assay. Compound Pt-4a showed a particularly more potent cytotoxic effect than the previously described Pt^II complex with 2,2′-bipyridine, [Pt(bpy)Cl₂], with an EC₅₀ value equal to 172.7 μM versus 726.5 μM respectively, and similar potency of cisplatin (EC₅₀ = 78.3 μM) in NCI-H460 cell line. The determination of the intracellular and DNA-bound concentrations of ¹⁹⁵Pt, as marker of the presence of the complexes, showed that the cytotoxic compound Pt-4a readily diffused into the cells to a similar extent of cisplatin and directly interacted with the nuclear DNA. Pt-4a induced both p53 and p21^Waf expression in NCI-H460 cells similar to cisplatin. A direct comparison of the cytotoxic effect between compound Pt-4a and cisplatin on 12 different cancer cell lines demonstrated that compound Pt-4a was in general less potent than cisplatin, but it had a comparable cytotoxic effect on non-small-cell lung cancer NCI-H460 cells, and the colorectal cancer cells HCT-15 and HCT-116. Altogether, these results suggested that the Pt^II complex with 1-methyl-1H-imidazol-2-yl)-methanamine (compound Pt-4a), displayed a significant cytotoxic activity in cancer cells. Similarly to cisplatin this compound interacts with nuclear DNA and induces both p53 and p21^waf, and thus it represents an interesting starting point for future optimisation of new Pt^II complexes forming DNA adducts.     

Molecular modelling studies,synthesis and biological activity of a series of novel bisnaphthalimides and their development as new DNA topoisomerase II inhibitors

A series of bisnaphthalimide derivatives were synthesized and evaluated for growth-inhibitory property against HT-29 human colon carcinoma. The N,N′-bis[2-(5-nitro-1,3-dioxo-2,3-dihydro-1H-benz[de]-isoquinolin-2-yl)]propane-2-ethanediamine (9) and the N,N′-Bis[2-(5-nitro-1,3-dioxo-2,3-dihydro-1H-benz[de]-isoquinolin-2-yl)]butylaminoethyl]-2-propanediamine (12) derivatives emerged as the most potent compounds of this series. Molecular modelling studies indicated that the high potency of 12, the most cytotoxic compound of the whole series, could be due to larger number of intermolecular interactions and to the best position of the naphthalimido rings, which favours π–π stacking interactions with purine and pyrimidine bases in the DNA active site. Moreover, 12 was designed as a DNA topoisomerase II poison and biochemical studies showed its effect on human DNA topoisomerase II. We then selected the compounds with a significant cytotoxicity for apoptosis assay. Derivative 9 was able to induce significantly apoptosis (40%) at 0.1 μM concentration, and we demonstrated that the effect on apoptosis in HT-29 cells is mediated by caspases activation.     

Efficient spontaneous site-selective cysteine-mediated toxin attachment within a structural loop of antibodies

BackgroundSite-specific coupling of toxin entities to antibodies has become a popular method of synthesis of antibody-drug conjugates (ADCs), as it leads to a homogenous product and allows a free choice of a convenient site for conjugation.MethodsWe introduced a short motif, containing a single cysteine surrounded by aromatic residues, into the N-terminal FG-loop of the C_H2 domain of two model antibodies, cetuximab and trastuzumab. The extent of conjugation with toxic payload was examined with hydrophobic interaction chromatography and mass spectrometry and the activity of resulting conjugates was tested on antigen-overexpressing cell lines.ResultsAntibody mutants were amenable for rapid coupling with maleimide-based linker endowed toxin payload and the modifications did not impair their reactivity with target cell lines or negatively impact their biophysical properties. Without any previous reduction, up to 50% of the antibody preparation was found to be coupled with two toxins per molecule. After the isolation of this fraction with preparative hydrophobic interaction chromatography, the ADC could elicit a potent cytotoxic effect on the target cell lines.ConclusionBy fine-tuning the microenvironment of the reactive cysteine residue, this strategy offers a simplified protocol for production of site-selectively coupled ADCs.General significanceOur unique approach allows the generation of therapeutic ADCs with controlled chemical composition, which facilitates the optimization of their pharmacological activity. This strategy for directional coupling could in the future simplify the construction of ADCs with double payloads (“dual warheads”) introduced with orthogonal techniques.     

Cytotoxic activity of hirsutanone,a diarylheptanoid isolated from Alnus glutinosa leaves

BackgroundThe low efficacy of cancer therapy for the treatment of patients with advanced disease makes the development of new anticancer agents necessary. Because natural products are a significant source of anticancer drugs, it is important to explore cytotoxic activity of novel compounds from natural origin.PurposeThe aim of this work is to evaluate the cytotoxic capacity of hirsutanone, a diarylheptanoid isolated from Alnus glutinosa leaves. Hirsutanone cytotoxic way of action was also studied.Material and methodsThe cytotoxic ability of Alnus glutinosa leaves ethyl acetate extract was studied over HeLa and PC-3 cell lines, with the MTT colorimetric assay. Hirsutanone was isolated from this extract using chromatographic methods, and its structure elucidated by spectroscopic analysis. HT-29 cell viability after hirsutanone treatment was determined using SRB assay. In order to understand hirsutanone way of action, cytotoxicity was evaluated adding the diarylheptanoid and antioxidants. DNA topoisomerase II (topo II) poison activity, was also evaluated using purified topo II and a supercoiled form of DNA that bears specific topo II recognition and binding region; topo II poisons stabilize normally transient DNA-topo II cleavage complexes, and lead an increased yield of linear form as a consequence of a lack of double-strand breaks rejoining.ResultsThe diarylheptanoid hirsutanone was isolated from Alnus glutinosa (L.) Gaertn. (Betulaceae) leaves extract that showed cytotoxic activity against PC-3 and HeLa cell lines. Hirsutanone showed cytotoxic activity against HT-29 human colon carcinoma cells. Pre-treatment with the antioxidants NAC (N-acetylcysteine) and MnTMPyP (Mn(III)tetrakis-(1-methyl-4-pyridyl)porthyrin) reduced this activity, suggesting that reactive oxygen species (ROS) participate in hirsutanone-induced cancer cell death. Using human topo II and a DNA supercoiled form, hirsutanone was found to stabilize topo II-DNA cleavage complexes, acting as a topo II poison.ConclusionOur data suggest that, like curcumin, an induction of oxidative stress and topo II-mediated DNA damage may play a role in hirsutanone-induced cancer cell death. Since both compounds share similar structure and cytotoxic profile, and curcumin is in clinical trials for the treatment of cancer, our results warrant further studies to evaluate the anticancer potential of hirsutanone.