The zone of localization of antibodies; the specific localization of antibodies to rat kidney

Using antibodies to target cancer therapeutics

INTRODUCTION

Over a half a century ago, radiolabeled antibodies were shown to localize selectively in tissues based on the expression of unique antigens. Antibodies have since become the de facto targeting agent, even inspiring the development of non-antibody compounds for targeting purposes.

AREAS COVERED

In this article, we review various aspects of how antibodies are transforming the way cancer is being detected and treated, with the growing demand for unconjugated and many new antibody conjugates. While unconjugated antibodies continue to garner most of the attention, interest in new antibody drug conjugates and immunotoxins has expanded over the past few years. However, there continues to be active research with new radioimmunoconjugates for imaging and therapy, particularly with α-emitters, as well as antibody-targeted cytokines and other biological response modifiers.

EXPERT OPINION

The increasing number of new agents being developed and tested clinically suggests that antibody-targeted compounds will have an expanding role in the future.

Improved cancer therapy and molecular imaging with multivalent, multispecific antibodies

Antibodies are highly versatile proteins with the ability to be used to target diverse compounds, such as radionuclides for imaging and therapy, or drugs and toxins for therapy, but also can be used unconjugated to elicit therapeutically beneficial responses, usually with minimal toxicity. This update describes a new procedure for forming multivalent and/or multispecific proteins, known as the dock-and-lock (DNL) technique. Developed as a procedure for preparing bispecific antibodies capable of binding divalently to a tumor antigen and monovalently to a radiolabeled hapten-peptide for pretargeted imaging and therapy, this methodology has the flexibility to create a number of other biologic agents of therapeutic interest. A variety of constructs, based on anti-CD20 and CD22 antibodies, have been made, with results showing that multispecific antibodies have very different properties from the respective parental monospecific antibodies. The technique is not restricted to antibody combination, but other biologics, such as interferon-alpha2b, have been prepared. These types of constructs not only allow small biologics to be sustained in the blood longer, but also to be selectively targeted. Thus, DNL technology is a highly flexible platform that can be used to prepare many different types of agents that could further improve cancer detection and therapy.

Radioimmunoimaging with longer-lived positron-emitting radionuclides: potentials and challenges

Radioimmunoimaging and therapy has been an area of interest for several decades. Steady progress has been made toward clinical translation of radiolabeled monoclonal antibodies for diagnosis and treatment of diseases. Tremendous advances have been made in imaging technologies such as positron emission tomography (PET). However, these advances have so far eluded routine translation into clinical radioimmunoimaging applications due to the mismatch between the short half-lives of routinely used positron-emitting radionuclides such as (18)F versus the pharmacokinetics of most intact monoclonal antibodies of interest. The lack of suitable positron-emitting radionuclides that match the pharmacokinetics of intact antibodies has generated interest in exploring the use of longer-lived positron emitters that are more suitable for radioimmunoimaging and dosimetry applications with intact monoclonal antibodies. In this review, we examine the opportunities and challenges of radioimmunoimaging with select longer-lived positron-emitting radionuclides such as (124)I, (89)Zr, and (86)Y with respect to radionuclide production, ease of radiolabeling intact antibodies, imaging characteristics, radiation dosimetry, and clinical translation potential.

The persistence in mice of certain foreign proteins and azoprotein tracer-antigens derived from them

Methods have been devised whereby the persistence of foreign antigens in mice can be detected. A highly diffusible, blue azo dye, echt-säure-blau was coupled to bovine γ-globulin and human serum albumin and injected into the animals. In this way deep blue tracer antigens were obtained. These were promptly stored in cells widely distributed throughout the body, especially in the reticulo-endothelial elements of the liver, spleen and mesenteric lymph nodes. The dye as such was not stored but rapidly excreted. A blue coloration in the organs just mentioned was still perceptible after 85 to 120 days in the case of the azoglobulin and 36 to 44 days in that of the azoalbumin. To determine whether these substances had actually persisted, as well as to learn how long uncoupled globulin and albumin remained after injection, recourse was had to the phenomenon of reversed passive anaphylaxis, which was found to be characterized by extraordinary changes in the vessels of the ears (EVR) in the mouse, plainly visible under the microscope when called forth by an antiserum specific for the antigen to which the animal had been sensitized. So sensitive is the vascular response that as little as 0.5 to 0.1 µg. of protein as antigen, previously injected into the peritoneal cavity of a 30 gm. mouse, can be detected a few days later by an intravenous injection of antiserum. By means of the EVR the globulin antigen has been detected in the blood and livers of injected mice for as long as 56 and 101 days, respectively; the albumin and azoalbumin for only 21 and 36 days. In the mesenteric lymph nodes of injected mice the albumin and azoalbumin antigens were found after 42 and 44 days, respectively. The hepatic tissue and that of the mesenteric lymph nodes of mice injected with azoalbumin, containing in consequence stored blue material, when transferred to recipient mice yielded positive tests for antigen (EVR) as long as blue color could be perceived in these tissues with the unaided eye, or at low magnification. After the color had disappeared from the tissues the transfer tests were found to be negative. This fact speaks for the antigenicity of the colored material. In summary it is plain that certain antigenic proteins, after introduction into the blood stream of mice, are stored in certain tissues and that they may persist there for weeks or even months, far longer than has generally been supposed. This persistence of antigen within the body, especially after detectable amounts of antigen have apparently disappeared from the blood, provides a reason for prolonged antibody formation, a phenomenon for which no adequate explanation has hereto been offered.

EXPERIMENTAL GLOMERULONEPHRITIS. V. STUDIES ON THE INTERACTION OF NEPHROTOXIC ANTIBODIES WITH TISSUE OF THE RAT

A direct correlation between the amount of kidney-fixing antibody and the degree of associated renal injury was demonstrated for rabbit and duck nephrotoxic antibodies. No evidence for a qualitative difference among nephrotoxic antibodies of a given type was obtained. It appeared that duck nephrotoxic antibody was directed against a wider spectrum of rat renal antigens than was rabbit nephrotoxic antibody. In order to produce immediate proteinuria an amount of rabbit or duck gamma-2 kidney-fixing antibody capable of occupying approximately 45 per cent or more of the capillary filtration surface was needed. For immediate proteinuria an amount of rabbit gamma-2 kidney-fixing antibody capable of reacting with more than one-half of the available antigenic sites was needed. Less than twice that amount of rabbit antibody completely saturated available antigenic sites in the kidney. Virtually all nephrotoxic antibodies in hyperimmune rabbit nephrotoxic sera were of the gamma-2 variety while nephrotoxic antibodies in comparable duck nephrotoxic sera were found in gamma-2 (with 5.8 and 7.4S sedimentation coefficients) and gamma-1M fractions. Gamma-1M duck nephrotoxic antibody was 60 times more potent a nephritogen than gamma-2 duck nephrotoxic antibody on a molecular basis. Mercaptoethanol abolished the nephrotoxicity of gamma-1M duck antibody and reduced that of gamma-2 duck antibodies but had no effect on rabbit gamma-2. In no case did mercaptoethanol treatment have an effect on the kidney-fixing properties of the antibodies involved. After injection of nephrotoxic antibodies there appeared to be a prompt fixation of a majority of the antibody to tissue antigens primarily in the kidney. However, a small amount of potentially kidney-fixing antibody remained in the circulation for a considerable period apparently reflecting a dissociation of less avid antibodies with an equilibrium between fixed and free antibody. The role of this more easily dissociable antibody in the progression of nephrotoxic nephritis is not certain but it is possible that it could play a role in the early progression of the disease.

Targeting potential of antibody conjugates

Although the use of conjugates of enzymes has been considered, their use has not been very actively pursued. Much more interest has focused on the possibilities offered by the use of toxins, their subunits or of ribosome inhibitors. Conjugates of holotoxin which were very active and specific in vitro have been prepared. High in vivo activity and some specificity together with reduced whole body toxicity has been described. When A chain subunits or ribosome inhibiting proteins are used, the results are more mixed. Some very active and specific conjugates are known but others have relatively low activity. The reasons for this may be associated with the particular antigen to which the antibody component is directed, the nature of the A chain or inhibitor and the type and physiological state of the target cell. Application to man seems likely in the first instance to involve the removal of undesirable cells from bone marrow transplants.

Analytical pathology. IV. The role of localized antibodies in the pathogenesis of nephrotoxic nephritis in the rat

The principal objective of this investigation was to define the roles of injected and autogenous, kidney-localizing antibodies in the pathogenesis of rat nephrotoxic nephritis by relating data obtained with fluorescent antibody techniques to clinical and histologic observations. Such an analysis of the nephritis that developed in 28 rats after injection with the crude gamma-globulin fraction of nephrotoxic serum has led us to the following conclusions:- The renal localization of nephrotoxic antibodies is primarily and, perhaps, exclusively in the membranes of the glomerular tufts. These antibodies are demonstrable, as antigens, in the glomeruli for up to 3 months after injection. In the acute stage of the nephritis, non-antibody, autogenous globulins are present in the glomerular tufts, probably as components of edema fluid. From 6 and 9 days to 3 months after injection, autogenous antibodies are localized in the glomerular tufts in a pattern that corresponds closely to that of the nephrotoxins. The essential requirements for the operation of the mechanism postulated by Kay are fulfilled in rat nephrotoxic nephritis.