Calicheamicin derivatives conjugated to monoclonal antibodies: determination of loading values and distributions by infrared and UV matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization mass spectrometry

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Antibody-drug conjugates in cancer therapy: innovations, challenges, and future directions

The emergence of antibody-drug conjugates (ADCs) as a potential therapeutic avenue in cancer treatment has garnered significant attention. By combining the selective specificity of monoclonal antibodies with the cytotoxicity of drug molecules, ADCs aim to increase the therapeutic index, selectively targeting cancer cells while minimizing systemic toxicity. Various ADCs have been licensed for clinical usage, with ongoing research paving the way for additional options. However, the manufacture of ADCs faces several challenges. These include identifying suitable target antigens, enhancing antibodies, linkers, and payloads, and managing resistance mechanisms and side effects. This review focuses on the strategies to overcome these hurdles, such as site-specific conjugation techniques, novel antibody formats, and combination therapy. Our focus lies on current advancements in antibody engineering, linker technology, and cytotoxic payloads while addressing the challenges associated with ADC development. Furthermore, we explore the future potential of personalized medicine, leveraging individual patients' molecular profiles, to propel ADC treatments forward. As our understanding of the molecular mechanisms driving cancer progression continues to expand, we anticipate the development of new ADCs that offer more effective and personalized therapeutic options for cancer patients.

Antibody drug conjugate: the "biological missile" for targeted cancer therapy

Antibody-drug conjugate (ADC) is typically composed of a monoclonal antibody (mAbs) covalently attached to a cytotoxic drug via a chemical linker. It combines both the advantages of highly specific targeting ability and highly potent killing effect to achieve accurate and efficient elimination of cancer cells, which has become one of the hotspots for the research and development of anticancer drugs. Since the first ADC, Mylotarg® (gemtuzumab ozogamicin), was approved in 2000 by the US Food and Drug Administration (FDA), there have been 14 ADCs received market approval so far worldwide. Moreover, over 100 ADC candidates have been investigated in clinical stages at present. This kind of new anti-cancer drugs, known as "biological missiles", is leading a new era of targeted cancer therapy. Herein, we conducted a review of the history and general mechanism of action of ADCs, and then briefly discussed the molecular aspects of key components of ADCs and the mechanisms by which these key factors influence the activities of ADCs. Moreover, we also reviewed the approved ADCs and other promising candidates in phase-3 clinical trials and discuss the current challenges and future perspectives for the development of next generations, which provide insights for the research and development of novel cancer therapeutics using ADCs.

Comparison of analytical methods for antibody conjugates with application in nuclear imaging - Report from the trenches

INTRODUCTION

Monoclonal antibodies (mAbs) are widely used in nuclear imaging. Radiolabelling with positron emitting radionuclides, typically radiometals, requires the incorporation of a bifunctional chelator for the formation of the radiometal-mAb complex. Additionally, mAbs can be conjugated with small molecules capable to undergo bioorthogonal click reactions in vivo, enabling pre-targeting strategies. The determination of the number of functionalities attached to the mAb is critically important to ensure a good labelling yield or to guarantee pre-targeting efficacy. In this work, we compare three different analytical methods for the assessment of average functionalisation and heterogeneity of the conjugated mAbs.

METHODS

Two selected mAbs (Trastuzumab and Bevacizumab) were randomly conjugated through lysine residues with 3-10 equivalents p-isothiocyanatobenzyl-desferrioxamine (p-NCS-Bz-DFO) or 20-200 equivalents trans-cyclooctene-N-hydroxysuccinimide ester (TCO-NHS). The DFO- or TCO-to-mAb ratio were determined using three different methods: direct titration (radiometric for DFO-conjugated mAbs, photometric for TCO-conjugated mAbs), MALDI/TOF MS mass analysis (Matrix-Assisted Laser Desorption-Ionization/Time of Flight Mass Spectrometry), and UPLC/ESI-TOF MS mass analysis (Ultra High Performance Liquid Chromatography/Electrospray Ionization-Time of Flight Mass Spectrometry).

RESULTS

Radiometric and photometric titrations provided information on the average number of DFO and TCO functionalities per mAb respectively. MALDI/TOF MS provided equivalent results to those obtained by titration, although investigation of the heterogeneity of the resulting mixture was challenging and inaccurate. UPLC/ESI-TOF MS resulted in good peak resolution in the case of DFO-conjugated mAbs, where an accurate discrimination of the contribution of mono-, di- and tri-substituted mAbs could be achieved by mathematical fitting of the spectra. However, UPLC/ESI-TOF MS was unable to discriminate between different conjugates when the smaller TCO moiety was attached to the mAbs.

CONCLUSIONS

The three techniques offered comparable results in terms of determining the average number of conjugates per mAb. Additionally, UPLC/ESI-TOF MS was able to shed a light on the heterogeneity of the resulting functionalised mAbs, especially in the case of DFO-conjugated mAbs. Finally, while using a single analytical method might not be a reliable way to determine the average functionalisation and assess the heterogeneity of the sample, a combination of these methods could substantially improve the characterization of mAb conjugates.

Denaturing and Native Mass Spectrometric Analytics for Biotherapeutic Drug Discovery Research: Historical, Current, and Future Personal Perspectives

Mass spectrometry (MS) plays a key role throughout all stages of drug development and is now as ubiquitous as other analytical techniques such as surface plasmon resonance, nuclear magnetic resonance, and supercritical fluid chromatography, among others. Herein, we aim to discuss the history of MS, both electrospray and matrix-assisted laser desorption ionization, specifically for the analysis of antibodies, evolving through to denaturing and native-MS analysis of newer biologic moieties such as antibody-drug conjugates, multispecific antibodies, and interfering nucleic acid-based therapies. We discuss challenging therapeutic target characterization such as membrane protein receptors. Importantly, we compare and contrast the MS and hyphenated analytical chromatographic methods used to characterize these therapeutic modalities and targets within biopharmaceutical research and highlight the importance of appropriate MS deconvolution software and its essential contribution to project progression. Finally, we describe emerging applications and MS technologies that are still predominantly within either a development or academic stage of use but are poised to have significant impact on future drug development within the biopharmaceutic industry once matured. The views reflected herein are personal and are not meant to be an exhaustive list of all relevant MS performed within biopharmaceutical research but are what we feel have been historically, are currently, and will be in the future the most impactful for the drug development process.

Antibody conjugation and formulation

In an era where ultra-high antibody concentrations, high viscosities, low volumes, auto-injectors and long storage requirements are already complex problems with the current unconjugated monoclonal antibodies on the market, the formulation demands for antibody-drug conjugates (ADCs) are significant. Antibodies have historically been administered at relatively low concentrations through intravenous (IV) infusion due to their large size and the inability to formulate for oral delivery. Due to the high demands associated with IV infusion and the development of novel antibody targets and unique antibody conjugates, more accessible routes of administration such as intramuscular and subcutaneous are being explored. This review will summarize various site-specific and non-site-specific antibody conjugation techniques in the context of ADCs and the demands of formulation for high concentration clinical implementation.

Analytical techniques for the characterization of Antibody Drug Conjugates: Challenges and prospects

Antibody drug conjugates are increasingly being researched for the treatment of cancer. Accurate and reliable characterization of ADCs is inevitable for their development as potential therapeutic agent. Different analytical techniques have been used in order to decipher heterogeneous nature of antibody drug conjugates, enabling successful characterization. This review will summarize specially three major analytical tools i.e. UV-Vis spectroscopy, liquid chromatography, and mass spectrometry used in characterization of antibody drug conjugates. In this review, major challenges during analysis due to the inherent features of analytical techniques and antibody drug conjugates are summarized along with the modifications intended to address each challenge.

Methods to Design and Synthesize Antibody-Drug Conjugates (ADCs)

Antibody-drug conjugates (ADCs) have become a promising targeted therapy strategy that combines the specificity, favorable pharmacokinetics and biodistributions of antibodies with the destructive potential of highly potent drugs. One of the biggest challenges in the development of ADCs is the application of suitable linkers for conjugating drugs to antibodies. Recently, the design and synthesis of linkers are making great progress. In this review, we present the methods that are currently used to synthesize antibody-drug conjugates by using thiols, amines, alcohols, aldehydes and azides.

Antibody-Drug Conjugates: Design, Formulation and Physicochemical Stability

The convergence of advanced understanding of biology with chemistry has led to a resurgence in the development of antibody-drug conjugates (ADCs), especially with two recent product approvals. Design and development of ADCs requires the synergistic combination of the monoclonal antibody, the linker and the payload. Advances in antibody science has enabled identification and generation of high affinity, highly selective, humanized or human antibodies for a given target. Novel linker technologies have been synthesized and highly potent cytotoxic drug payloads have been created. As the first generation of ADCs utilizing lysine and cysteine chemistries moves through the clinic and into commercialization, second generation ADCs involving site specific conjugation technologies are being evaluated and tested. The latter aim to be better characterized and controlled, with wider therapeutic indices as well as improved pharmacokinetic-pharmacodynamic (PK-PD) profiles. ADCs offer some interesting physicochemical properties, due to conjugation itself, and to the (often) hydrophobic payloads that must be considered during their CMC development. New analytical methodologies are required for the ADCs, supplementing those used for the antibody itself. Regulatory filings will be a combination of small molecule and biologics. The regulators have put forth some broad principles but this landscape is still evolving.

Native mass spectrometry and ion mobility characterization of trastuzumab emtansine, a lysine-linked antibody drug conjugate

Antibody-drug conjugates (ADCs) are biochemotherapeutics consisting of a cytotoxic chemical drug linked covalently to a monoclonal antibody. Two main classes of ADCs, namely cysteine and lysine conjugates, are currently available on the market or involved in clinical trials. The complex structure and heterogeneity of ADCs makes their biophysical characterization challenging. For cysteine conjugates, hydrophobic interaction chromatography is the gold standard technique for studying drug distribution, the naked antibody content, and the average drug to antibody ratio (DAR). For lysine ADC conjugates on the other hand, which are not amenable to hydrophobic interaction chromatography because of their higher heterogeneity, denaturing mass spectrometry (MS) and UV/Vis spectroscopy are the most powerful approaches. We report here the use of native MS and ion mobility (IM-MS) for the characterization of trastuzumab emtansine (T-DM1, Kadcyla(®)). This lysine conjugate is currently being considered for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer, and combines the anti-HER2 antibody trastuzumab (Herceptin(®)), with the cytotoxic microtubule-inhibiting maytansine derivative, DM1. We show that native MS combined with high-resolution measurements and/or charge reduction is beneficial in terms of the accurate values it provides of the average DAR and the drug load profiles. The use of spectral deconvolution is discussed in detail. We report furthermore the use of native IM-MS to directly determine DAR distribution profiles and average DAR values, as well as a molecular modeling investigation of positional isomers in T-DM1.

Antibody drug conjugates: design and selection of linker, payload and conjugation chemistry

Antibody drug conjugates (ADCs) have emerged as an important pharmaceutical class of drugs designed to harness the specificity of antibodies with the potency of small molecule therapeutics. The three main components of ADCs are the antibody, the linker, and the payload; the majority of early work focused intensely on improving the functionality of these pieces. Recently, considerable attention has been focused on developing methods to control the site and number of linker/drug conjugated to the antibody, with the aim of producing more homogenous ADCs. In this article, we review popular conjugation methods and highlight recent approaches including "click" conjugation and enzymatic ligation. We discuss current linker technology, contrasting the characteristics of cleavable and non-cleavable linkers, and summarize the essential properties of ADC payload, centering on chemotherapeutics. In addition, we report on the progress in characterizing to determine physicochemical properties and on advances in purifying to obtain homogenous products. Establishing a set of selection and analytical criteria will facilitate the translation of novel ADCs and ensure the production of effective biosimilars.

Approaches to Interchain Cysteine-Linked ADC Characterization by Mass Spectrometry

Therapeutic antibody-drug conjugates (ADCs) harness the cell-killing potential of cytotoxic agents and the tumor targeting specificity of monoclonal antibodies to selectively kill tumor cells. Recent years have witnessed the development of several promising modalities that follow the same basic principles of ADC based therapies but which employ unique cytotoxic agents and conjugation strategies in order to realize therapeutic benefit. The complexity and heterogeneity of ADCs present a challenge to some of the conventional analytical methods that industry has relied upon for biologics characterization. This current review will highlight some of the more recent methodological approaches in mass spectrometry that have bridged the gap that is created when conventional analytical techniques provide an incomplete picture of ADC product quality. Specifically, we will discuss mass spectrometric approaches that preserve and/or capture information about the native structure of ADCs and provide unique insights into the higher order structure (HOS) of these therapeutic molecules.

Analytical methods for physicochemical characterization of antibody drug conjugates

Antibody-drug conjugates (ADCs), formed through the chemical linkage of a potent small molecule cytotoxin (drug) to a monoclonal antibody, have more complex and heterogeneous structures than the corresponding antibodies. This review describes the analytical methods that have been used in their physicochemical characterization. The selection of the most appropriate methods for a specific ADC is heavily dependent on the properties of the linker, the drug, and the choice of attachment sites (lysines, inter-chain cysteines, Fc glycans). Improvements in analytical techniques such as protein mass spectrometry and capillary electrophoresis have significantly increased the quality of information that can be obtained for use in product and process characterization, and for routine lot release and stability testing.

Self-assembled monolayers for MALDI-TOF mass spectrometry for immunoassays of human protein antigens

This paper reports a method that combines self-assembled monolayers with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to perform immunoassays on clinical samples. The immunosensors are prepared by immobilizing His-tagged protein G (or A) to a monolayer presenting the Ni2+ chelates, followed by immobilization of IgG antibodies with specificity for the intended analyte. The SAMDI mass spectrometry technique confirms the presence of the two proteins on the immunosensor and additionally provides a label-free analysis of antigens that bind to the sensor. This paper reports examples of detecting several proteins from human serum, including multianalyte assays that resolve each analyte according to their mass-to-charge ratio in the SAMDI spectra. An example is described wherein SAMDI is used to identify a proteolytic fragment of cystatin C in cerebral spinal fluids from patients diagnosed with multiple sclerosis. The SAMDI-TOF immunoassay, which combines well-defined surface chemistries for the selective and reproducible localization of analytes with mass spectrometry for label-free detection of analytes, may offer an alternative methodology to address many of the issues associated with standardized clinical diagnostics.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

Label-Free Detection of Proteins in Crude Cell Lysate with Antibody Arrays by a Surface Plasmon Resonance Imaging Technique

We established a label-free method of measuring proteins in crude cell lysate using antibody arrays and surface plasmon resonance (SPR) imaging. The refractivity of the running buffer was adjusted with that of the lysate to overcome the bulk effect. The chemistries of the fabricated arrays were investigated to reduce nonspecific adsorption on the array surface. We found that the hydrophilicity of the poly(ethylene glycol) moiety and lower electrostatic charge on the surface provided a specific measurement of antigen-antibody interaction. We validated the system by measuring the expression of eight proteins in the mouse brain and comparing the results to those by conventional Western blotting. The detection limit of the antibody array was approximately 30 ng/mL in crude cell lysate, on the same order as that of previous SPR research. The system enabled quick, label-free, and high-throughput analysis of abundant proteins with minimal sample volume ( approximately 200 muL). It is expected that our SPR antibody array will be applicable for direct protein expression profiling of cell lysate, as well as for cell phenotyping, food analysis, discovery of new biomarkers, and immunological disease diagnostics.

Structural characterization of the maytansinoid-monoclonal antibody immunoconjugate, huN901-DM1, by mass spectrometry

Immunoconjugates are being explored as novel cancer therapies with the promise of target-specific drug delivery. The immunoconjugate, huN901-DM1, composed of the humanized monoclonal IgG1 antibody, huN901, and the maytansinoid drug, DM1, is being tested in clinical trials to treat small cell lung carcinoma (SCLC). huN901-DM1 contains an average of three to four DM1 drug molecules per huN901 antibody molecule. The drug molecules are linked to huN901 through random modification of huN901 at epsilon-amino groups of lysine residues, thus yielding a heterogeneous population of conjugate species. We studied the drug distribution profile of huN901-DM1 by electrospray time-of-flight mass spectrometry(ESI-TOFMS), which showed that one to six DM1 drug molecules were attached to an antibody molecule. Both light and heavy chains contained linked drugs. The conjugation sites in both chains were determined by peptide mapping using trypsin and Asp-N protease digestion. Trypsin digestion identified modified lysine residues, since these residues were no longer susceptible to enzymatic cleavage after conjugation with the drug. With respect to Asp-N digestion, modified peptides were identified by observing a mass increase corresponding to the modification. The two digestion methods provided consistent results, leading to the identification of 20 modified lysine residues in both light and heavy chains. Each lysine residue was only partially modified. No conjugation sites were found in complementarity determining regions (CDRs). Using structural models of human IgG1, it was found that modified lysine residues were on the surface in areas of structural flexibility and had large solvent accessibility.

Mass Spectral Analyses of Labile DOTA-NHS and Heterogeneity Determination of DOTA or DM1 Conjugated Anti-PSMA Antibody for Prostate Cancer Therapy

Prostate specific membrane antigen (PSMA) is a well-characterized glycoprotein overexpressed on the surface of prostate cancer cells. The novel radiopharmaceutical 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) radiolabeled with Yttrium (90Y) or Indium (111In) conjugated with anti-PSMA genetically engineered humanized monoclonal antibody (huJ591) has been investigated to target prostate cancer cells. The immunoconjugate of huJ591 with the analog of the cytotoxic drug maytansine, DM1 (N2'-deacetyl-N2'-(3-mercapto-1-oxopropyl)-maytansine) has also been developed at Millennium Pharmaceuticals. Activation of the DOTA molecule, resulting in 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid mono-(N-hydroxysuccinimidyl) ester (DOTA-NHS), allows conjugation with the anti-PSMA antibody through lysine residues in the antibody. The objectives of the study were to characterize the unstable chemical properties of DOTA-NHS before bioconjugation with huJ591, evaluate the binding profiles of DOTA to huJ591, and calculate trace metal elements (which may disturb 90Y or 111In labeling efficacy to the DOTA-huJ591 conjugate). A novel LC/MS/MS (Liquid Chromatography/Mass Spectrometry/Mass Spectrometry) quantitation method was developed to monitor the stability of DOTA-NHS in solid form and its bioconjugation chemistry reactions. Meanwhile, metal analysis was quantified by Inductively Coupled Plasma Mass Spectrometry (ICP/MS) to estimate the amounts of trace metals in DOTA-NHS and ensure radiolabeling efficiency of the conjugate at the radiopharmacy. MALDI-TOF MS (Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry) was used to identify levels of DOTA or DM1conjugation in DOTA-huJ591 and DM1-huJ591 conjugates, respectively.

Analysis of the composition of immunoconjugates using size-exclusion chromatography coupled to mass spectrometry

Recombinant monoclonal antibody drug products play an increasingly important role in the treatment of various diseases. Antibodies are large, multi-chain proteins and antibody preparations often contain several molecular variants, which renders them heterogeneous. The heterogeneity is further increased in immunoconjugates prepared by covalently linking several drug molecules per antibody molecule. As part of the product characterization, the molecular weights of the antibodies or their drug conjugates need to be measured. Electrospray ionization mass spectrometry (ESI-MS) is well suited for the analysis of recombinant antibodies and immunoconjugates. Sample preparation is an important element of ESI-MS analysis, in particular samples need to be freed of interfering charged species, such as salts and buffer components. In this paper, Amicon centrifugal filters, reversed-phase high-performance liquid chromatography (HPLC), and size-exclusion HPLC were evaluated for sample desalting. Size-exclusion HPLC, using aqueous acetonitrile as the mobile phase, directly coupled to ESI-MS provided the best performance and was optimized for the study of immunoconjugates. The results showed that antibodies carrying covalently linked maytansinoid molecules generated charge envelope profiles that differ from those of the non-conjugated antibody. For the determination of the distribution of the various conjugate species in an immunoconjugate sample prepared by randomly linking in the average 3.6 drug molecules per antibody molecule, the experimental conditions needed to be carefully selected to allow acquisition of the whole spectrum containing the charge envelopes of all species.

Tumor-activated prodrugs--a new approach to cancer therapy

Systemic cytotoxic (antiproliferative) anticancer drugs rely primarily for their therapeutic effect on cytokinetic differences between cancer and normal cells. One approach aimed at improving the selectivity of tumor cell killing by such compounds is the use of less toxic prodrug forms that can be selectively activated in tumor tissue (tumor-activated prodrugs; TAP). There are several mechanisms potentially exploitable for the selective activation of TAP. Some utilize unique aspects of tumor physiology such as selective enzyme expression or hypoxia. Others are based on tumor-specific delivery techniques, including activation of prodrugs by exogenous enzymes delivered to tumor cells via monoclonal antibodies (ADEPT) or generated in tumor cells from DNA constructs containing the corresponding gene (GDEPT). Whichever activating mechanism is used, only a small proportion of the tumor cells are likely to be competent to activate the prodrug. Therefore, TAP need to fully exploit these "activator" cells by being capable of killing activation-incompetent cells as well via a "bystander effect." A wide variety of chemistries have been explored for the selective activation of TAP. Examples are given of the most important-the reduction of quinones, N-oxides, and nitroaromatics by endogenous enzymes or radiation; the cleavage of amides by endogenous peptidases; and hydrolytic metabolism by a variety of exogenous enzymes, including phosphatases, kinases, amidases, and glycosidases.

Synthesis and Characterization of a Cobalamin−Colchicine Conjugate as a Novel Tumor-Targeted Cytotoxin

Colchicine was derivatized at C7 with p-alkoxyacetophenone and conjugated to cobalamin (vitamin B(12)) through an acid-labile hydrazone linker. The cobalamin moiety leads to preferential uptake of the cobalamin-colchicine prodrug by cancer cells, whereupon the hydrazone linker undergoes hydrolysis in the lysosome to unmask colchicine, which acts as a potent cytotoxin by stabilizing microtubules and causing cell death. The bioconjugate is stable in cell culture media and at neutral pH but undergoes hydrolysis with a half-life of 138 min at pH 4.5. The colchicine-cobalamin bioconjugate exhibits nanomolar LC(50) values against breast, brain, and melanoma cancer cell lines in culture. Attachment of colchicine to cobalamin is expected to increase the therapeutic index of the drug by limiting the side effects caused by the current nonselective administration of tubulin-targeted chemotherapeutic drugs.

The use of MassARRAY technology for high throughput genotyping

This chapter will explore the role of mass spectrometry (MS) as a detection method for genotyping applications and will illustrate how MS evolved from an expert-user-technology to a routine laboratory method in biological sciences. The main focus will be time-of-flight (TOF) based devices and their use for analyzing single-nucleotide-polymorphisms (SNPs, pronounced snips). The first section will describe the evolution of the use of MS in the field of bioanalytical sciences and the protocols used during the early days of bioanalytical MALDI TOF mass spectrometry. The second section will provide an overview on intraspecies sequence diversity and the nature and importance of SNPs for the genomic sciences. This is followed by an exploration of the special and advantageous features of mass spectrometry as the key technology in modern bioanalytical sciences in the third chapter. Finally, the fourth section will describe the MassARRAY technology as an advanced system for automated high-throughput analysis of SNPs.

The role of the laser pulse duration in infrared matrix-assisted laser desorption/ionization mass spectrometry

The role of the laser pulse duration in matrix-assisted laser desorption/ionization mass spectrometry with infrared lasers (IR-MALDI-MS) emitting in the 3 microm wavelength range has been evaluated. Mass spectrometric performance and characteristics of the IR-MALDI process were examined by comparing a wavelength-tuneable mid-infrared optical parametric oscillator (OPO) laser of 6 ns pulse duration, tuned to wavelengths of 2.79 and 2.94 microm, with an Er:YAG laser (lambda = 2.94 microm) with two pulse durations of 100 and 185 ns, and an Er:YSGG laser (lambda = 2.79 microm) with a pulse duration of 75 ns. Threshold fluences for the desorption of cytochrome C ions were determined as a function of the laser pulse duration for various common IR-MALDI matrices. For the majority of these matrices a reduction in threshold fluence by a factor of 1.2-1.9 was found by going from the 75-100 ns long pulses of the Erbium lasers to the short 6 ns OPO pulse. Within the experimental accuracy threshold fluences were equal for the 100 and the 185 ns pulse duration of the Er:YAG laser. Some pronounced pulse duration effects related to the ion formation from a glycerol matrix were also observed. The effect of the laser pulse length on the duration of ion emission was furthermore investigated.

Quantitative determination of noncovalently bound acridinium in protein conjugates by liquid chromatography/electrospray ion trap mass spectrometry

A sensitive and robust liquid chromatography/electrospray ion trap mass spectrometry (LC/MS/MS) method has been developed for the quantitative determination of noncovalently bound acridinium free acid in protein-acridinium conjugates. The lower level of quantitation (LOQ) for acridinium free acid was determined to be 0.6 ng. The assay was validated with a linear concentration range of 0.6-60 ng. The method requires minimum sample handling and is specific, reproducible, and provides a new aspect for protein-acridinium conjugate characterization.

Region-selective labeling of antibodies as determined by electrospray ionization-mass spectrometry (ESI-MS)

The electrospray ionization-mass spectrometry (ESI-MS) analysis of three sets of monoclonal antibody-acridinium-9-carboxamide conjugates is described. The conjugates (nine total) were enzymatically digested using papain and the resulting fragments [Fc heavy chain, Fab, or F(ab')(2)] were analyzed using liquid chromatography/ESI-MS. The average number of labels per fragment were calculated using Sigma nx%, where n is the number of acridinium molecules covalently bound to the fragment and x% is the percent relative area of the corresponding peaks in the mass spectrum. When these values were normalized against the molecular weight of their respective region, antibody-dependent labeling patterns were observed. For antibodies T (anti-L-T(4)) and F (anti-FITC), there was a preference for conjugation of the Fab region over the Fc region. For antibody B (anti-biotin), the trend was reversed.

Pairing of oligosaccharides in the Fc region of immunoglobulin G

The Fc portion of immunoglobulin G (IgG) expresses paired oligosaccharides with microheterogeneities, which are associated with efficiencies of effector functions and with pathological states. A comparison of electrospray ionization mass spectrometry data obtained using a variety of Fc fragments derived from human and mouse IgG that do and do not retain the inter-chain disulfide bridge(s) revealed that (1) the Fc portion can be asymmetric as well as symmetric with respect to glycosylation and (2) the ratios of the individual glycoforms are different from what is expected from the random pairing.

Contributions of mass spectrometry to structural immunology

Mass spectrometry has made important contributions to the field of immunology in the past decade. A variety of mass spectrometric-based techniques have been applied to study the structures of macromolecules that play a vital role in the immune response. These include traditional molecular mass measurements to identify post-translational modifications and structural heterogeneity, mass mapping of proteolysis products, sequencing by tandem mass spectrometry and conformational analysis. Antigen-antibody and other immune complexes have been detected by mass spectrometry, providing an avenue to study macromolecular assemblies that are important to immune function. By virtue of the ability of mass spectrometry based techniques to analyze complex biological mixtures, mass spectrometry has also been employed to identify and sequence protein epitopes important in both the humoral and cellular immune responses. This has been achieved through a combination of immunoaffinity and mass spectrometric techniques, and the coupling of high-performance chromatographs to mass spectrometers. These approaches are important for the identification of pathogens and show promise for the early diagnosis of disease associated with viral and bacterial infection and malignancy. These investigations will enable the mechanisms associated with normal and impaired immune function to be elucidated. Mass spectrometry has been utilized to characterize the structure of peptide mimics, multiple antigenic peptides and other constructs in the design of synthetic immunogens. Information derived from these studies will aid in the development of novel therapeutics and vaccines.

Monoclonal antibody drug conjugates in the treatment of cancer

Monoclonal antibodies directed to tumor-associated antigens have been chemically conjugated to drugs with different mechanisms of action and different levels of potency. Monoclonal-antibody-directed drug delivery has the potential to both improve efficacy and reduce systemic toxicity. Several immunoconjugates have demonstrated impressive antigen-specific antitumor activity in preclinical models. Phase I trials of a calicheamicin immunoconjugate for treatment of acute myeloid leukemia and a doxorubicin immunoconjugate for treatment of carcinoma have recently been completed.

Receptor-mediated and enzyme-dependent targeting of cytotoxic anticancer drugs

This review is a survey of various approaches to targeting cytotoxic anticancer drugs to tumors primarily through biomolecules expressed by cancer cells or associated vasculature and stroma. These include monoclonal antibody immunoconjugates; enzyme prodrug therapies, such as antibody-directed enzyme prodrug therapy, gene-directed enzyme prodrug therapy, and bacterial-directed enzyme prodrug therapy; and metabolism-based therapies that seek to exploit increased tumor expression of, e.g., proteases, low-density lipoprotein receptors, hormones, and adhesion molecules. Following a discussion of factors that positively and negatively affect drug delivery to solid tumors, we concentrate on a mechanistic understanding of selective drug release or generation at the tumor site.

Analysis of phospho- and glycopolypeptides with infrared matrix-assisted laser desorption and ionization

The analytical characteristics of infrared (IR) matrix-assisted laser desorption and ionization (MALDI) were investigated for the analysis of phosphopeptides, a phosphopolypeptide, and glycopeptides. Two commercially available instruments, a high-resolution delayed extraction (DE) reflectron time-of-flight (RETOF) mass spectrometer and a high-power pulsed Er:YAG laser, were interfaced to produce a high-resolution MALDI-DE-RETOF instrument that is easy to use and can be switched between UV- and IR-MALDI mode within seconds. In the interface design, particular attention was paid to maintaining the same professional operating environment for the new IR-MALDI mode as exists for the commercial UV-MALDI mode. This instrument configuration facilitates comparative observation and investigation of the relative analytical merits of IR- and UV-MALDI. The results of studies of the tryptic alpha-casein phosphopeptides, RP1 (a Thr45-monophosphorylated congener of the recombinant protein hirudin variant 1), and fetuin Asn81 tryptic glycopeptides are presented. The elimination of labile substituents such as phosphoric acid and sialic acid is suppressed in IR-MALDI-RETOF mass spectrometry, with concomitant higher analyte ion yields. These results reflect the advantages that accrue from deposition of significantly less internal energy in the case of IR-MALDI.