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Antibody-drug conjugates (ADCs) have recently gained traction in the biomedical community due to their promise for human therapeutics and an alternative to chemotherapy for cancer. Crucial metrics for ADC efficacy, safety, and selectivity are their drug-antibody ratios (DARs). However, DAR characterization (i.e., determining the average number of conjugated drugs on the antibody) through analytical methods remains challenging due to the heterogeneity of drug conjugation as well as the numerous post-translational modifications possible in the monoclonal antibody. Herein, we report on the use of high-resolution ion mobility spectrometry separations in structures for lossless ion manipulations coupled to mass spectrometry (SLIM IMS-MS) for the rapid and simultaneous characterization of the drug load profile (i.e., stoichiometric distribution of the number of conjugated drugs present on the mAb), determination of the weighted average DAR in both the heavy and light chains of a model antibody-drug conjugate, and calculation of the overall DAR of the ADC. After chemical reduction of the ADC and a subsequent 31.5 m SLIM IMS separation, the various drug-bound antibody species could be well resolved for both chains. We also show significantly higher resolution separations were possible for these large ions with SLIM IMS as compared to ones performed on a commercially available (1 m) drift tube IMS-MS platform. We expect high-resolution SLIM IMS separations will augment the existing toolbox for ADC characterization, particularly to enable the rapid optimization of DAR for a given ADC and thus better understand its potential toxicity and potency.

International audience

Polymeric prodrugs, synthesized by conjugating chemotherapeutic agents to functional polymers, have been extensively investigated and employed for safer and more efficacious cancer therapy. By rational design, a pH and reduction dual-sensitive dextran-di-drugs conjugate (oDex-g-Pt+DOX) was synthesized by the covalent conjugation of Pt (IV) prodrug and doxorubicin (DOX) to an oxidized dextran (oDex). Pt (IV) prodrug and DOX were linked by the versatile efficient esterification reactions and Schiff base reaction, respectively. oDex-g-Pt+DOX could self-assemble into nanoparticles with an average diameter at around 180 nm. The acidic and reductive (GSH) environment induced degradation and drug release behavior of the resulting nanoparticles (oDex-g-Pt+DOX NPs) were systematically investigated by optical experiment, DLS analysis, TEM measurement, and in vitro drugs release experiment. Effective cellular uptake of the oDex-g-Pt+DOX NPs was identified by the human cervical carcinoma HeLa cells via confocal laser scanning microscopy. Furthermore, oDex-g-Pt+DOX NPs displayed a comparable antiproliferative activity than the simple combination of free cisplatin and DOX (Cis+DOX) as the extension of time. More importantly, oDex-g-Pt+DOX NPs exhibited remarkable reversal ability of tumor resistance compared to the cisplatin in cisplatin-resistant lung carcinoma A549 cells. Take advantage of the acidic and reductive microenvironment of tumors, this smart polymer-dual-drugs conjugate could serve as a promising and effective nanomedicine for combination chemotherapy.

This review summarizes recent developments in conjugation techniques for the synthesis of cell-penetrating peptide (CPP)–drug conjugates targeting cancer cells. We will focus on small organic molecules as well as metal complexes that were used as cytostatic payloads. Moreover, two principle ways of coupling chemistry will be discussed direct conjugation as well as the use of bifunctional linkers. While direct conjugation of the drug to the CPP is still popular, the use of bifunctional linkers seems to gain increasing attention as it offers more advantages related to the linker chemistry. Thus, three main categories of linkers will be highlighted, forming either disulfide acid-sensitive or stimuli-sensitive bonds. All techniques will be thoroughly discussed by their pros and cons with the aim to help the reader in the choice of the optimal conjugation technique that might be used for the synthesis of a given CPP–drug conjugate

International audience; We propose to develop a novel drug conjugate from Hyaluronic acid (HA), a biomaterial ubiquitously present in our body, and Ethambutol and Isoniazid, two promising Mycobacterium (M) Tuberculosis (TB) drugs. Nevertheless, in general, the TB drugs are not only associated with some toxicity but also the patients can develop resistance to the drug. The conjugates of HA and MTB drugs are expected to act synergistically to eliminate those shortcomings.

Advancement in chemistry holds a great promise in improving drug encapsulation that leads to superior drug delivery efficiency and the therapeutic efficacy of nano/micro-delivery systems. Drugs are being designed to specifically access the infection sites via covalent conjugation to nano/micro-delivery systems. This chapter focuses on techniques for achieving covalent encapsulation of drugs in nano/micro-delivery systems, how conjugation is applied to selectively influence pharmacokinetic profile, intracellular, and extracellular uptake, specific targeting to disease sites, binding to specific receptors, and controlled/sustained release. In addition, the effect of conjugation on drug efficacy and biosafety of the micro/nanoparticulate drug delivery systems are discussed.

The conjugation reaction of monoclonal antibodies (mAbs) with small-molecule drugs is a central step during production of antibody-drug conjugates (ADCs). The ability to monitor this step in real time can be advantageous for process understanding and control. Here, we propose a method based on UV/Vis spectroscopy in conjunction with partial least squares (PLS) regression for non-invasive monitoring of conjugation reactions. In experiments, the method was applied to conjugation reactions with two surrogate drugs in microplate format as well as at 20 ml scale. All calibrated PLS models performed well in cross-validation ( Q 2 > 0.975 for all models). In microplate format, the PLS models were furthermore successfully validated with an independent prediction set ( R p r e d 2 = 0.9770 resp. 0.8940). In summary, the proposed method provides a quick and easily implementable tool for reaction monitoring of ADC conjugation reactions and may in the future support the implementation of Process Analytical Technologies (PAT).

Nanoparticles are normally classified as “hard”, mainly consisting of metal or metal oxide cores, or “soft”, including polymer-based, liposomes and biomimetic nanoparticles. Soft nanoparticles have been studied in depth for drug formulation and therapeutic delivery applications, albeit hard nanoparticles may offer easier synthesis, smaller size and more effective tumor penetration. Among them, silica nanoparticles maintain excellent biocompatibility and biodegradability and can be finely adjusted in size and shape, easily produced in a large scale and functionalized or loaded with active molecules. To help filling the gap of a poor clinical translation of hard nanoparticles, we have designed and developed three different nonporous silica nanocarriers loading the chemotherapeutic doxorubicin within the core matrix, on the surface or both inside and outside, respectively. A comparative study was performed on drug loading and drug release, silica matrix degradation and nanodrug cytotoxic activity, highlighting unexpected correlation between the strategy adopted for drug incorporation and nanoparticle behavior in a physiological environment. This study offers a new insight on the impact of the choice of the prodrug nanoparticles on the kinetics and efficacy of drug delivery, which may encourage the scientific community in developing a new generation of drug delivery systems based on hard nanocarriers.

Peptide nanomaterials have received a great deal of interest in drug-delivery applications due to their biodegradability, biocompatibility, suitability for large-scale synthesis, high drug-loading capacities, targeting ability, and ordered structural organization. The covalent conjugation of drugs to peptide backbones results in prolonged circulation time and improved stability of drugs. Therapeutic efficacy of gemcitabine, which is used for breast cancer treatment, is severely compromised due to its rapid plasma degradation. Its hydrophilic nature poses a challenge for both its efficient encapsulation into nanocarrier systems and its sustained release property. Here, we designed a new peptide prodrug molecule for the anticancer drug gemcitabine, which was covalently conjugated to the C-terminal of 9-fluorenylmethoxy carbonyl (Fmoc)-protected glycine. The prodrug was further integrated into peptide nanocarrier system through noncovalent interactions. A pair of oppositely charged amyloid-inspired peptides (Fmoc-AIPs) were exploited as components of the drug-carrier system and self-assembled into one-dimensional nanofibers at physiological conditions. The gemcitabine integrated nanoprodrug carrier system exhibited slow release and reduced the cellular viability of 4T1 breast cancer cell line in a time- and concentration-dependent manner.

The thiol-maleimide linkage is widely used for antibody-drug conjugate (ADC) production; however, conjugation of maleimide-drugs could be improved by simplified procedures and reliable conjugate stability. Here, we report the evaluation of electron-rich and cyclic dienes that can be appended to antibodies and reacted with maleimide-containing drugs through the Diels-Alder (DA) reaction. Drug conjugation is fast and quantitative due to reaction acceleration in water, and the linkage is more stable in serum than in the corresponding thiol-maleimide adduct with the same drug. ADCs produced using the DA reaction (DAADCs) are effective in vitro and in vivo, demonstrating the utility of this reaction in producing effective biotherapeutics. Given the large number of commercially available maleimide compounds, this conjugation approach could be readily applied to the production of a wide range of antibody (or protein) conjugates.

Chemotherapy is one of the major therapeutic options for cancer treatment. Chemotherapy is often associated with a low therapeutic window due to its poor specificity towards tumor cells/tissues. Antibody-drug conjugate (ADC) technology may provide a potentially new therapeutic solution for cancer treatment. ADC technology uses an antibody-mediated delivery of cytotoxic drugs to the tumors in a targeted manner, while sparing normal cells. Such a targeted approach can improve the tumor-to-normal tissue selectivity and specificity in chemotherapy. Considering its importance in cancer treatment, we aim to review recent efforts for the design and development of ADCs. ADCs are mainly composed of an antibody, a cytotoxic payload, and a linker, which can offer selectivity against tumors, anti-cancer activity, and stability in systemic circulation. Therefore, we have reviewed recent updates and principal considerations behind ADC designs, which are not only based on the identification of target antigen, cytotoxic drug, and linker, but also on the drug-linker chemistry and conjugation site at the antibody. Our review focuses on site-specific conjugation methods for producing homogenous ADCs with constant drug-antibody ratio (DAR) in order to tackle several drawbacks that exists in conventional conjugation methods.

The tumor suppressor protein p53, the "guardian of the genome", is inactivated in nearly all cancer types by mutations in the TP53 gene or by overexpression of its negative regulators, oncoproteins MDM2/MDMX. Recovery of p53 function by disrupting the p53-MDM2/MDMX interaction using small-molecule antagonists could provide an efficient nongenotoxic anticancer therapy. Here we present the syntheses, activities, and crystal structures of the p53-MDM2/MDMX inhibitors based on the 1,4,5-trisubstituted imidazole scaffold which are appended with aliphatic linkers that enable coupling to bioactive carriers. The compounds have favorable properties at both biochemical and cellular levels. The most effective compound 19 is a tight binder of MDM2 and activates p53 in cancer cells that express the wild-type p53, leading to cell cycle arrest and growth inhibition. Crystal structures reveal that compound 19 induces MDM2 dimerization via the aliphatic linker. This unique dimerization-binding mode opens new prospects for the optimization of the p53-MDM2/MDMX inhibitors and conjugation with bioactive carriers.

SummaryAntibody drug conjugates (ADCs) are a therapeutic class offering promise for cancer therapy. The attachment of cytotoxic drugs to antibodies can result in an effective therapy with better safety potential than nontargeted cytotoxics. To understand the role of conjugation site, we developed an enzymatic method for site-specific antibody drug conjugation using microbial transglutaminase. This allowed us to attach diverse compounds at multiple positions and investigate how the site influences stability, toxicity, and efficacy. We show that the conjugation site has significant impact on ADC stability and pharmacokinetics in a species-dependent manner. These differences can be directly attributed to the position of the linkage rather than the chemical instability, as was observed with a maleimide linkage. With this method, it is possible to produce homogeneous ADCs and tune their properties to maximize the therapeutic window.

WOS: 000331596100013, PubMed ID: 24176888, We describe here the synthesis, characterization, bioconjugation, and application of water-soluble thioglycolic acid TGA-capped CdTe/CdS quantum dots (TGA-QDs) for targeted cellular imaging. Antihuman epidermal growth factor receptor 2 (HER2) antibodies were conjugated to TGA-QDs to target HER2-overexpressing cancer cells. TGA-QDs and TGA-QDs/anti-HER2 bioconjugates were characterized by fluorescence and UV-Vis spectroscopy, X-ray diffraction (XRD), hydrodynamic sizing, electron microscopy, and gel electrophoresis. TGA-QDs and TGA-QDs/anti-HER2 were incubated with cells to examine cytotoxicity, targeting efficiency, and cellular localization. The cytotoxicity of particles was measured using an MIT assay and the no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50), and total lethal concentration (TLC) were calculated. To evaluate localization and targeting efficiency of TGA-QDs with or without antibodies, fluorescence microscopy and flow cytometry were performed. Our results indicate that antibody-conjugated TGA-QDs are well-suited for targeted cellular imaging studies. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [109T573]; Federal Ministry of Education and Research (BMBF)Federal Ministry of Education & Research (BMBF) [01DL12013]; Ege UniversityEge University [2012/FEN/0071], This work is supported by Scientific and Technological Research Council of Turkey (TUBITAK, project number 109T573) and Federal Ministry of Education and Research (BMBF, project number 01DL12013). Also it was partially funded by Ege University Scientific Research Project (2012/FEN/0071). We are grateful to Michael Meyer (Gottfried Wilhelm Leibniz University of Hannover, Institute for Technical Chemistry) for his knowledge and time spent carrying out flow cytometry experiments. In addition our thanks go to F. B. Barlas (Ege University, Faculty of Science, Biochemistry department) for taking fluorescence microscope images.

Antibody drug conjugates (ADCs) are an emerging class of targeted therapeutics with the potential to improve therapeutic index over traditional chemotherapy. Drugs and linkers have been the current focus of ADC development, in addition to antibody and target selection. Recently, however, the importance of conjugate homogeneity has been realized. The current methods for drug attachment lead to a heterogeneous mixture, and some populations of that mixture have poor in vivo performance. New methods for site-specific drug attachment lead to more homogeneous conjugates and allow control of the site of drug attachment. These subtle improvements can have profound effects on in vivo efficacy and therapeutic index. This review examines current methods for site-specific drug conjugation to antibodies, and compares in vivo results with their non-specifically conjugated counterparts. The apparent improvement in pharmacokinetics and the reduced off target toxicity warrant further development of this site-specific modification approach for future ADC development.

Commonly employed pyridinium-oxime (charged) reactivators of nerve agent inhibited acetylcholinesterase (AChE) do not readily pass the blood brain barrier (BBB) because of the presence of charge(s). Conversely, non-ionic oxime reactivators often suffer from a lack of reactivating potency due to a low affinity for the active site of AChE. It was therefore hypothesized that an extra contribution in affinity may be achieved by covalently connecting a peripheral site ligand (PSL) to a non-ionic reactivator, which may result in a higher reactivation potency of the total construct. This validity of this approach, which proved successful for charged pyridinium oximes in earlier work, is now further exemplified with the covalent linkage of a neutral PSL via a spacer to a non-ionic and otherwise almost non-reactivating a-ketoaldoxime. It is demonstrated that the linkage of the PSL resulted in a remarkable increase in reactivation potency of the hybrid compounds. Although the molecules reported here are still inefficient reactivators compared to the current pyridinium oximes, the presented approach holds promise for the future design and synthesis of non-ionic oxime reactivators with improved BBB penetration and may be suited as well for non-oxime reactivators thus further widening the scope in the ongoing search for broad-spectrum reactivators. © 2011 Elsevier Ireland Ltd.

Antibody-Drug Conjugation (ADC) is a rapidly growing area and has been widely explored for cancer therapy. In the past decade, numerous progresses have been reported on the identification of proper antibodies, targets validation, discovery of novel payloads, improvement of linkers, as well as the development of new coupling techniques. We have developed novel conjugation methods, C-lock, K-lock and the combination of the two. C-LockTM conjugation method utilizes a novel linker chemistry to re-connect the reduced disulfide bonds between antibody heavy and light chains, and in the meantime, to introduce a drug to each disulfide bond. While K-LockTM conjugation method is a linker-controlled conjugation technology highly selective on 1 or 2 particular sites among 80-90 Lys side chains of an antibody. The generated ADCs have fewer regioisomers and lower DAR (Drug-Antibody Ratio) while maintaining comparable potency to ADCs from regular conjugation methods. Further purification will give rise to site-specific homogeneous products without needs for cell engineering or enzymatic modification steps. The lead ADCs generated by these technologies showed improved activity both in vitro and in vivo in relevant tumor models, and also exhibited less toxicity compared to commercial standard. To pursue to the next level, we are currently developing dual drug ADCs which have two different payloads conjugated to single antibody; as well as bi-specific ADCs with either single or dual drug conjugations (2nd generation or ADC-2X). Initial results indicated that these ADCs showed improved activity and specificity in relevant tumor cell lines compared to 1st generation ADCs. Detailed results will be reported. All these data proved that our ADC technologies are unique and superior in antibody drug conjugation and are promising for anti-cancer drug development. Citation Format: Gang Chen, Tong Zhu, Dylan Deng, Hong Zhang, David Miao. Development of anti-cancer ADCs with Concortis’ C-and K-lock technology. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 635. doi:10.1158/1538-7445.AM2015-635

Vitamin E succinate selenium-conjugated molecules were synthesized and their apoptogenic properties were evaluated. 4-Methyl-2-phenylselenyl succinate (4) was prepared by the reaction of sodium benzeneselenolate with 2-bromosuccinic anhydrite in methanol solution. The methyl ester was converted to the acid (5) by hydrolysis with aqueous hydrochloric acid. Reaction of the 2-phenylselenyl succinic anhydrite (6) with α-tocopherol (1a), γ-tocopherol (1c), and γ-tocotrienol (2c) in acidic conditions gave the respective esters. The free radical scavenging properties of α-tocopheryl-2-phenylselenyl succinate (7), γ-tocopheryl-2- phenylselenyl succinate (8), and γ-tocotrienyl-2-phenylselenyl succinate (9) were evaluated in comparison with those of α-tocopheryl succinate (10), γ-tocopheryl succinate (11), and γ-tocotrienyl succinate (12), respectively, and the free tocopherols and γ-tocotrienol. Compounds 7-9 induced a statistically significant decrease in prostate cancer cell viability compared to 10-12, respectively, or 5, exhibiting features of apoptotic cell death and associated with caspase-3 activation. These data show that structural modifications of vitamin E components by 5 enhance their apoptogenic properties in cancer cells. © 2005 Elsevier Ltd. All rights reserved. 14 8 2684 2696 Cited By :23

Spectroscopic and rapid kinetic experiments were performed to detail the interaction of human glutathione S-transferases GSTA1-1, GSTM2-2, and GSTP1-1 with 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX). This compound is a representative molecule of a new class of 7-nitro-2,1,3-benzoxadiazole (NBD) derivatives (non-GSH peptidomimetic compounds) that have been designed both to give strong GST inhibition and to accumulate in tumor cells avoiding the extrusion mechanisms mediated by the multidrug resistance protein pumps. We have recently shown that submicromolar amounts of NBDHEX trigger apoptosis in several human tumor cell lines through the dissociation of the JNK.GSTP1-1 complex (Turella, P., Cerella, C., Filomeni, G., Bullo, A., De Maria, F., Ghibelli, L., Ciriolo, M. R., Cianfriglia, M., Mattei, M., Federici, G., Ricci, G., and Caccuri, A. M. (2005) Cancer Res. 65, 3751-3761). Results reported in the present study indicated that NBDHEX behaves like a suicide inhibitor for GSTs. It bound to the H-site and was conjugated with GSH forming a sigma complex at the C-4 of the benzoxadiazole ring. This complex was tightly stabilized in the active site of GSTP1-1 and GSTM2-2, whereas in GSTA1-1 the release of the 6-mercapto-1-hexanol from the sigma complex was the favored event. Docking studies demonstrated the likely localization of the sigma complex in the GST active sites and provide a structural explanation for its strong stabilization.

The application of biodegradable polymers to antibody-drug conjugate (ADC) design can provide numerous advantages, including significantly higher drug-antibody ratios, the use of alternative payloads with potencies considered insufficient for direct conjugation, the improvement of ADC physico-chemical properties, especially for highly hydrophobic payloads, and the potential expansion of protein recognition scaffolds beyond the commonly used IgGs. The basis of the novel polymer-based conjugation system described herein is a hydrophilic, fully biodegradable polyacetal carrier, (poly(1-hydroxymethylethylene hydroxymethylformal) or PHF) modified with chemically orthogonal linkers. A bioconjugation linker is used for efficient covalent attachment of a targeting moiety to the PHF scaffold, while a second, chemically distinct linker is used to attach multiple copies of a drug payload to the polymer to control the mechanism and rate of drug release. Utilizing multiple copies of a proprietary dolastatin derivative chemically conjugated to PHF, we have developed a potent and effective drug conjugation platform for ADC application, which has been named Dolaflexin™. Here, we report the preparation and characterization of a novel trastuzumab DolaflexinTM ADC, employing a maleimide-based bioconjugation approach. The resulting ADC, with a drug-antibody ratio of 20, exhibits enhanced stability and improved pharmacokinetics, with a prolonged plasma half-life and tumor-specific accumulation. Active drug release and accumulation in tumor tissue was also confirmed by LC/MS/MS methods. The activity of this novel trastuzumab-dolaflexin ADC was evaluated in multiple tumor xenograft models with significant variations in target antigen expression levels. Models including BT474 breast cancer, NCI-N87 gastric cancer, and JIMT1 breast cancer models were utilized, and comparisons to a variety of controls and ADC reference standards were made. Significant advantages of the polyacetal polymer-based ADCs in comparison to conventional ADCs, particularly in models with low target antigen expression, were observed. Details of these studies and potential applications for the development of new ADC therapeutics based on this approach will be presented. Citation Format: Alex Yurkovetskiy, Natalya Bodyak, Mao Yin, Joshua D. Thomas, Patrick Conlon, Cheri A. Stevenson, Alex Uttard, LiuLiang Qin, Dmitry R. Gumerov, Elena Ter-Ovaneysan, Venu R. Gurijala, Dennis McGillicuddy, Roberta E. Glynn, Michael DeVit, Laura L. Poling, Peter U. Park, Timothy B. Lowinger. Advantages of polyacetal polymer-based ADCs: Application to low expression targets. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2645. doi:10.1158/1538-7445.AM2014-2645

Using 1H NMR two diastereoisomers of the ethacrynic acid glutathione conjugate (EASG) as well as ethacrynic acid (EA) could be distinguished and quantified individually. Chemically prepared EASG consists of equal amounts of both diastereoisomers. GSTP1-1 stereospecifically catalyzes formation of one of the diastereoisomers (A). The GSTP1-1 mutant C47S and GSTA1-1 preferentially form the same diastereoisomer of EASG as GSTP1-1. Glutathione conjugation of EA by GSTA1-2 and GSTA2-2 is not stereoselective. When human melanoma cells, expressing GSTP1-1, were exposed to ethacrynic acid, diastereoisomer A was the principal conjugate formed, indicating that even at physiological pH the enzyme catalyzed reaction dominates over the chemical conjugation. Copyright (C) 1998 Federation of European Biochemical Societies.

The drug salbutamol (SBL) is a beta-agonist that may be used illegally as an animal growth promoter. SBL is also a good example of a drug which is excreted in the form of glucuronides and sulfates. Such metabolites cause complexities in analysing for the presence of drug residues. In the majority of cases a process of deconjugation and sample clean-up is required prior to analysis. This is both time consuming and causes some loss of accuracy. In this study, the urine of calves treated with SBL orally for 3 d was collected during and after medication. Samples were assayed before and after hydrolysis by two different methods, radioimmunoassay (RIA) and a newly developed biosensor immunoassay (BIA). Some samples were also analysed by GC-MS. The results clearly showed that both screening assays (RIA and BIA) found high concentrations of SBL residues throughout the study. This was especially true in the BIA method. It was also demonstrated that urine sample analysis without the need for deconjugation or clean-up could be achieved. Results obtained by GC-MS tended to be an order of magnitude lower than the corresponding screening test results. This work showed that biosensor based veterinary drug residue testing procedures can be developed which can generate results in real time without the need for time consuming sample preparation.

In this article the importance of blood proteins for drug dosing regimes is discussed. A simple mathematical model is presented for estimating recommended drug doses when the concentration of blood proteins is decreased. Practical guidance for drug dosing regimes is discussed and given in the form of a figure. It is demonstrated that correction of drug dosing regimes is needed only for when there is a high level of drug conjugation with blood proteins and a high degree of hypoalbuminaemia. An example of the use of this model is given.

In this communication we describe a novel acid-cleavable linker strategy for antibody–drug conjugation. Functional disulfide bridging of the single interchain disulfide bond of a trastuzumab Fab fragment yields a homogeneous antibody–drug conjugate bearing a thiomaleamic acid linker. This linker is stable at physiological pH and temperature, but quantitatively cleaves at lysosomal pH to release the drug payload.

Nonenzymatic and glutathione S-transferase (GST) catalyzed glutathione (GSH) conjugation has been postulated as a mechanism by which alkylating cytostatic drugs can be inactivated intracellularly. In this study, we describe studies on the glutathione-dependent biotransformation of thiotepa (tris(1-aziridinyl)phosphine sulfide), a trifunctional alkylating agent. 31P NMR studies showed that thiotepa is stable in 0.07 M phosphate buffer, pH 7.4 (t( 1/2 ) = 3300 min). In the presence of glutathione, the rate of disappearance of thiotepa increased greatly (t( 1/2 ) = 282 min). Both monoglutathionyl thiotepa and diglutathionyl thiotepa conjugates were identified by 31P NMR and mass spectrometry. Addition of GST A1-1 (α) to an incubation of thiotepa and GSH further increased the rate of disappearance of thiotepa (t( 1/2 ) = 100 min) and increased the rate of formation of monoglutathionyl thiotepa. The rate of formation of diglutathionyl thiotepa was not altered, suggesting that the formation of diglutathionyl thiotepa is not catalyzed by GST A1-1. The role of purified human GST on the formation of monoglutathionyl thiotepa was further studied by HPLC. In incubations with 0.2 mM thiotepa, 1 mM GSH, and 40 μM GST, both GST A1-1 and P1-1 enhanced the formation of the monoglutathionyl conjugate 30-35-fold above the nonenzymatic formation, while GST A2-2 and M1a-1a did not catalyze the rate of formation of this conjugate. K(m)s for the GST A1-1 (α) and P1-1 (π) catalyzed formation of monoglutathionyl thiotepa were in the 5-7 mM range. Since the pH in tumors might be lower than in normal cells, the pH dependency of the GST P1-1 catalyzed formation of monoglutathionyl thiotepa was also studied. At all pHs tested (range, 5.5-8.5), a marked catalytic effect of both GST P1-1 and A1-1 on the formation of monoglutathionyl conjugates was noted. The role of GST on the formation of monoglutathionyl conjugates of tepa (tris(1-aziridinyl)phosphine oxide), the major metabolite formed from thiotepa, was also studied. Both GST A1-1 and P1-1 could enhance the formation of the glutathione conjugate 37-46-fold above the spontaneous levels, while GST M1a-1a and A2-2 again did not increase the rate of formation of this conjugate. The results of these studies show that the aziridine moieties in thiotepa/tepa are substrates for both GST A1-1 and P1- 1. Thus, GST catalyzed glutathione conjugation of thiotepa might be an important factor in the development of drug resistance towards thiotepa.

Chitin, a homopolymer of N-acetylglucosamine, is obtained from a variety of sources. They form the structural component of fungal cell wall and plants. They are commercially obtained from shrimp and crab shell waste from the fishing industry. Recent advances in understanding the structure and properties of chitin and its derivatives has opened a lot of new avenues for its applications. Improvements in the properties of chitin for a particular application can be easily brought about by chemical modifications. The applicability of chitin in many areas and its easy manipulation has resulted in a considerable amount of research being done on the possible applications of chitinase.