Biodistribution and tumour localisation of a daunomycin-monoclonal antibody conjugate in nude mice with human tumour xenografts

Summary The blood kinetics and tissue distribution of a conjugate of daunomycin and a monoclonal antibody (791T/36) have been examined in mice, including nude mice with human tumour xenografts reactive with the antibody. For this the antibody moiety of the conjugate was labelled with ¹²⁵I and the drug moiety assayed by radioimmunoassay. After radioiodination, the preparation had an immunoreactive fraction in isotopic binding tests with 791T cells of 74%. Both drug and antibody moieties were precipitable with anti-mouse Ig anti-serum. Following i.v. injection, blood clearance of the two components of the conjugate was essentially identical, and with the serumborne conjugate both radiolabel and drug were co-precipitable. In mice with 791T xenografts, the tumour showed localisation of both drug and antibody moieties and at the time of analysis (3 days) tumour levels of drug were over 100 times those seen with free drug. In parallel studies with mice with antigen negative xenografts, there was no preferential localisation of antibody or drug moieties of the conjugate. These studies have shown in vivo stability of this conjugate, and site-specific targetting of an anti-tumour anthracycline.     

Evaluation of radio- and chemotoxic effects of125I-UdR on tumour growth and host survival

Summary The toxicity of 5-iodo-2-deoxyuridine (I-UdR) was assayed in male C57 BL/6J mice bearing the syngeneic mammary adenocarcinoma EO 771 by injecting different doses of cold I-UdR or 125-iodine labelled I-UdR. Host survival, tumour growth, DNA-precursor incorporation, whole-body retention and tumour activity loss rates were chosen as biological end points.There was no measurable effect on host survival up to doses of 5 µg I-UdR or 50 µCi¹²⁵I-UdR per mouse during a mean life-span of 25 days. Adjusted to a constant amount of 0.55 µg I-UdR/mouse, radiotoxicity of¹²⁵I-UdR on tumour growth (up to 17 days after implantation), tracer incorporation, whole-body and tumour retention (up to 12 days after¹²⁵I-UdR injection) could be excluded up to a dosage of 50 µCi¹²⁵I-UdR/mouse.It is concluded that in situ evaluation of tumour activity loss rates in carcinoma EO 771 is not disturbed by toxic effects of I-UdR or¹²⁵I-UdR within the dose limits mentioned.     

Localization of anti-osteogenic sarcoma monoclonal antibody 791T/36 in a primary human osteogenic sarcoma and its subsequent xenograft in immunodeprived mice

Summary A primary human osteogenic sarcoma was visualized in situ by external gamma-camera imaging following administration of ¹³¹I-labelled anti-osteogenic sarcoma monoclonal antibody 791T/36. A xenograft of the tumour established in immunodeprived mice also showed localization of ¹³¹I-791T/36 determined by both gamma-camera imaging and organ distribution studies. Radiolabelled normal immunoglobulin showed no tumour localization. Expression of the 791T/36-defined antigen on xenografted tissue was further confirmed by reaction of its in vitro-cultured cells with fluorescein-labelled 791T/36 antibody.     

Eradication of metastatic tumour cells from lymph nodes by local administration of anti-CD3 antibody

The possibility of in vivo removal of metastatic tumour cells from lymph nodes by local intradermal administration of an anti-CD3 monoclonal antibody (mAb) was examined. Murine tumour cells in the lymph nodes were completely eradicated by intradermal injections of the mAb. This treatment was effective for removal of Lewis lung cancer cells from lymph nodes, but not for removal of subcutaneous tumours of this cell line. This treatment induced in vivo cytotoxicity in the regional lymph nodes against the syngeneic tumour cells. The following in vitro studies suggested that the cytotoxicity was probably mediated mainly by CD4⁺ T cells, with slight participation of CD8⁺ T cells. Normal lymph node and spleen cells showed cytotoxicity after in vitro incubation with the mAb for 2 days. Cell sorting with a fluoresceinactivated cell sorter showed that CD4⁺ T cells developed during the incubation to lyse syngeneic tumor cells directly by themselves, macrophages not being involved in this tumour cell lysis. The lytic activity was detected in the cellular fractions, but not in the culture supernatants of these T cells. Furthermore, it was completely blocked by specific antiserum for tumour necrosis factor- (TNF). An immunoprecipitation study revealed that these T cells expressed TNF molecules of 26 kDa, but not of 17 kDa, suggesting that tumour cell lysis was caused by membraneintegrated TNF molecules. These results strongly suggest that local administration of anti-CD3 antibody is a very effective and appropriate procedure for eradication of metastatic tumour cells from regional lymph nodes.     

Differences in biodistribution of the anti-(carcinoembryonic antigen) murine monoclonal antibody CE-25, its F(ab′)2 fragment and its intact mainly human chimeric form CE 4-8-13

The effect of the size of the tumour and the amount of antibody injected on the biodistribution of a family of radioiodinated antibodies was studied. The intact mouse anti-(carcinoembryonic antigen) (anti-CEA) monoclonal antibody CE-25, its F(ab)₂ fragment and the intact human-mouse chimeric from CE 4-8-13 were evaluated in a model system using the human CEA-producing colon xenograft T 380 grown in nude mice. The relative retention (the percentage of the injected dose per gram of tissue), of mouse mAb and F(ab)₂ in tumour and most normal tissues 1 day after injection was independent of the antibody dose; after 4 days the mAb values increased with increasing antibody dose. The relative retention of chimeric mAb increased with increasing antibody dose 1 day after injection and also slightly after 4 days. The relative retention in tumour tissue was lower in bigger xenografts for all antibodies. The relative retention of mouse mAb in small tumours increased from day 1 to day 4; for chimeric mAb this value decreased. In normal tissues the relative retention of mouse mAb decreased from day 1 to day 4, but the relative retention of chimeric mAb in normal tissue dropped rapidly and changed little afterwards. Thus the biokinetics of antibodies is species-dependent: foreign, mainly human, chimeric antibody clears faster from normal mouse tissue than mouse antibody and reaches lower concentrations.     

Immunoscintigraphic localization of renal tumours in an extracorporeal perfusion model with a monoclonal antibody against γ-glutamyltransferase

Summary Monoclonal antibody 138H11 against human -glutamyltransferase has been shown to react immunohistochemically with 98% of all tested clear-cell type and chromophilic renal cell carcinomas, but not with renal chromophobic carcinomas, Duct-Bellini carcinomas or oncocytomas. In normal kidney the target epitopes of mAb 138H11 are located in the luminal brush-border membrane of proximal tubule cells, whereas in renal carcinomas the epitopes are found surrounding the whole tumour cells. These results form the basis of the present immunoscintigraphic study designed to evaluate mAb 138H11 in an extracorporeal perfusion model. Immediately after nephrectomy, human tumour-bearing kidneys were perfused with^99mTc-labelled mAb 138H11 in Euro-Collins solution. High specific uptake in 4/4 renal clear cell carcinomas could be demonstrated by planar immunoscintigraphy and single-photon-emission computed tomography, regions of interest investigation and immunohistochemistry. In contrast, a perfused oncocytoma showed up as an unlabelled lesion. The results indicate a possible use for mAb 138H11 in immunoscintigraphy or even therapy, provided high tumour uptake can be confirmed in patients.     

Identification of a New Functional Domain in Angiopoietin-like 3 (ANGPTL3) and Angiopoietin-like 4 (ANGPTL4) Involved in Binding and Inhibition of Lipoprotein Lipase (LPL)

Angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4 (ANGPTL4) are secreted proteins that regulate triglyceride (TG) metabolism in part by inhibiting lipoprotein lipase (LPL). Recently, we showed that treatment of wild-type mice with monoclonal antibody (mAb) 14D12, specific for ANGPTL4, recapitulated the Angptl4 knock-out (-/-) mouse phenotype of reduced serum TG levels. In the present study, we mapped the region of mouse ANGPTL4 recognized by mAb 14D12 to amino acids Gln²⁹–His⁵³, which we designate as specific epitope 1 (SE1). The 14D12 mAb prevented binding of ANGPTL4 with LPL, consistent with its ability to neutralize the LPL-inhibitory activity of ANGPTL4. Alignment of all angiopoietin family members revealed that a sequence similar to ANGPTL4 SE1 was present only in ANGPTL3, corresponding to amino acids Glu³²–His⁵⁵. We produced a mouse mAb against this SE1-like region in ANGPTL3. This mAb, designated 5.50.3, inhibited the binding of ANGPTL3 to LPL and neutralized ANGPTL3-mediated inhibition of LPL activity in vitro. Treatment of wild-type as well as hyperlipidemic mice with mAb 5.50.3 resulted in reduced serum TG levels, recapitulating the lipid phenotype found in Angptl3^-/- mice. These results show that the SE1 region of ANGPTL3 and ANGPTL4 functions as a domain important for binding LPL and inhibiting its activity in vitro and in vivo. Moreover, these results demonstrate that therapeutic antibodies that neutralize ANGPTL4 and ANGPTL3 may be useful for treatment of some forms of hyperlipidemia.Lipoprotein lipase (LPL)⁵ plays a pivotal role in lipid metabolism by catalyzing the hydrolysis of plasma triglycerides (TGs). LPL is likely to be regulated by mechanisms that depend on nutritional status and on the tissue in which it is expressed (1–3). Two secreted proteins, angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4 (ANGPTL4), play important roles in the regulation of LPL activity (4, 5). ANGPTL3 and ANGPTL4 consist of a signal peptide, an N-terminal segment containing coiled-coil domains, and a C-terminal fibrinogen-like domain. The N-terminal segment as well as full-length ANGPTL3 and ANGPTL4 have been shown to inhibit LPL activity, and deletion of the N-terminal segment of ANGPTL3 and ANGPTL4 resulted in total loss of LPL-inhibiting activity (6, 7). These observations clearly indicate that the N-terminal region of ANGPTL4 contains the functional domain that inhibits LPL and affects plasma lipid levels. The coiled-coil domains have been proposed to be responsible for oligomerization (8); however, it is not known whether the coiled-coil domains directly mediate the inhibition of LPL activity.To define the physiological role of ANGPTL4 more clearly, we characterized the pharmacological consequences of ANGPTL4 inhibition in mice treated with the ANGPTL4-neutralizing monoclonal antibody (mAb) 14D12 (9). Injection of mAb 14D12 significantly lowered fasting TG levels in C57BL/6J mice relative to levels in C57BL/6J mice treated with an isotype-matched anti-KLH control (KLH) mAb (9). These reduced TG values were similar to decreases in fasting plasma TG levels measured in Angptl4 knock-out (-/-) mice. This study demonstrated that mAb 14D12 is a potent ANGPTL4-neutralizing antibody that is able to inhibit systemic ANGPTL4 activity and thereby recapitulate the reduced lipid phenotype found in Angptl4^-/- mice. The readily apparent pharmacological effect of mAb 14D12 prompted new questions about the epitope recognized by mAb 14D12 and how this antibody-antigen binding event affected ANGPTL4 function as an LPL inhibitor.Although ANGPTL4 is able to interact directly with LPL (10), it is not clear which amino acids within ANGPTL4 mediate this interaction. Here we show that amino acids Gln²⁹–His⁵³ of mANGPTL4 contain the epitope for mAb 14D12. This region, hereby designated specific epitope 1 (SE1), also defines a domain that mediates the interaction between ANGPTL4 and LPL and the subsequent inactivation of LPL. With this information we present evidence that ANGPTL3 also contains an SE1 region, and with antibodies specifically reactive with ANGPTL3 SE1 we examine whether the ANGPTL3 SE1 region is involved in LPL binding and inhibition. We also determined whether treatment of C57BL/6 mice with an anti-ANGPTL3 SE1 mAb can recapitulate the phenotype of lower serum TG and cholesterol levels found in Angptl3^-/- mice. Finally we tested the therapeutic potential of an anti-ANGPTL3 SE1 mAb for treatment of hyperlipidemia in apolipoprotein E^-/- (ApoE^-/-) or low density lipoprotein receptor^-/- (LDLr^-/-) mice.     

Imaging of human ovarian tumour xenografts in nude mice using a novel 111In-labelled monoclonal antibody (10B)

Monoclonal antibody (mAb) 10B, directed against the human ovarian adenocarcinoma cell line, HEY, was conjugated with cyclic DTPA anhydride and labelled with ¹¹¹In. The biodistribution of ¹¹¹In-DTPA-10B was determined in non-tumour bearing mice and mice bearing subcutaneous (s.c.) and intraperitoneal (i.p.) HEY tumours. The radiolabel was preferentially targeted to s.c. and i.p. tumours in comparison with a control mAb, ¹¹¹In-DTPA-2G3, which does not bind to HEY cells. Among normal organs, the predominant uptake of radiolabel was into liver and kidney. Subcutaneous tumours were successfully imaged using external gamma scintigraphy following i.v. injection of ¹¹¹In-DTPA-10B. The results suggest that ¹¹¹In-DTPA-10B may be a useful agent for the diagnostic imaging of tumour masses in patients with ovarian cancer.     

Effect of monoclonal antibodies to early pregnancy factor (EPF) on the in vivo growth of transplantable murine tumours

Summary Neutralisation studies with monoclonal antibodies (mAbs) specific for early pregnancy factor (EPF) have shown it to be essential for the continuation of pregnancy in mice and the growth of some tumour cells in vitro. These studies report that the mAbs are also able to limit the growth of two murine tumour lines transplanted s. c. The development of MCA-2 tumours in CBA mice was unaffected by the injection of 1 mg anti-EPF IgM at the time of tumour cell inoculation. However, four doses of 500 µg anti-EPF, injected one dose per day for 4 days after tumour cell inoculation, significantly retarded tumour development such that no tumours were palpable on day 13. A similar dose regimen of control IgM had no effect on tumour size. Dose/response studies revealed that lower doses of anti-EPF administered after tumour cell inoculation were effective in retarding the growth of the MCA-2 tumours. The effect of anti-EPF mAb administration on the growth rate of palpable B16 tumours established s. c. in C57BL/6 mice was also determined. Tumours injected with 6 mg anti-EPF 5/341 or anti-EPF 5/333 mAbs showed significant decrease in the uptake of [³H]thymidine into tumour tissue, measured 16 h after injection. Furthermore, titration of sera for active EPF showed that a significant reduction in the EPF titre was associated with a significant inhibition of tumour DNA synthesis. Thus it appears that neutralisation of EPF retards tumour growth both in vitro and in vivo. In vitro the effects must be due to anti-EPF mAb interfering with a direct mechanism that contributes to the maintenance of cells in the active growing phase. However, in vivo host immunological mechanism that are modified to allow tumour survival may also be affected. The presence of EPF-induced suppressor factors curculating in the serum of tumour-bearing mice has been confirmed and the contribution of such factors to tumour progression must now be investigated.     

Introduction of antibody (PL/IM 430) to a 100 kDa protein into permeabilised platelets inhibits intracellular sequestration of Ca2+

A monoclonal antibody (PL/IM 430), previously found to inhibit the uptake of Ca²⁺ into highly purified platelet intracellular membrane vesicles (Hack, N., Wilkinson, J. M. and Crawford, N. 1988,Biochem. J. 250, 355–361) has been introduced into saponin-permeabilised platelets. At a saponin concentration (20–25 g/ml) commensurate with total LDH release, sequestration of Ca²⁺ into intracellular non-mitochondrial stores is inhibited by the antibody (50% inhibition at 20 g/ml IgG). At higher saponin concentrations when intracellular binding of¹²⁵I-labelled mAb is maximum, inhibition of Ca²⁺ sequestration approaches 70%. The inhibition is specific, control studies with non-platelet directed mouse IgG and mAbs which immunoblot platelet antigens other than the 100 kDa protein did not affect the Ca²⁺ sequestration.No effect of the antibody were observed against IP₃-induced release of prestored Ca²⁺, either in permeabilised platelets or with isolated intracellular membrane vesicles. The mAb PL/IM 430 appears to bind only to the Ca²⁺ translocating channel protein associated with the intracellular membrane (Ca²⁺+Mg²⁺) ATPase and not to Ca²⁺ channels responsive to IP₃.Abbreviations mAb monoclonal antibody - PBS phosphate buffered saline - LDH lactate dehydrogenase     

In vivo cytotoxic efficacy of immunotoxins prepared from anti-CD5 antibody linked to ricin A-chain

Summary The antitumoral efficacy of various anti-CD5 immunotoxins, prepared with whole monoclonal antibody (mAb), F(ab)₂ or Fab fragment linked to native ricin A-chain (RTA) or partially deglycosylated ricin A-chain (dRTA), was examined in vivo in ascitic nude mice bearing a large burden of Ichikawa human tumour cells. We first demonstrated that after systemic administration of IgG-RTA or F(ab)₂-dRTA, the cytotoxic activity of immunotoxin molecules specifically bound to tumour cells was preserved. Secondly we showed, by using different immunotoxins with various targeting capacities, that their cytotoxic effect in vivo was related to the number of immunotoxin molecules bound per cell. However, even when antigen saturation was achieved after i.p. injection, the cytotoxic effect did not exceed 53% of the tumour burden. By contrast, when the immunotoxin was administered i.p. or i.v. with the enhancer monensin conjugated to human serum albumin and injected i.p., 90% of the tumour cells were killed. This potentiating effect was demonstrated even when the tumour localisation was as low as 5% of the saturation level. Such an effect could be completely prevented by addition of unconjugated monoclonal antibody, demonstrating the specificity of the immunotoxin-induced cytotoxicity in the presence of the enhancer. However this enhancement was demonstrated whatever the route of immunotoxin administration, i.p. or i.v., but was only observed when the enhancer was injected i.p. and not i.v.. These results emphasize the importance of optimizing the therapeutic course to improve the antitumoral efficacy of immunotoxins.     

Effect of dose escalation of a monoclonal anti-CEA IgG on tumour localisation and tissue distribution in nude mice xenografted with human colon carcinoma

Summary A monoclonal anti-CEA antibody (1H12) has been examined for the effect of dosage on tumour localisation in immunodeprived mice xenografted with human colon carcinoma. Increased doses produced a linear rise in the absolute concentration found in the tumour but this was found to depend on tumour size, with the smaller tumours (mean weight 44 mg) accumulating significantly more antibody compared to larger tumours (mean weight 146 mg). With the smallest tumour (18 mg), in which saturation was achieved, a 500 g dose produced a concentration in tumour of 60 g/g. In the larger tumours a dose of 256 g produced a mean concentration of 5.2 g/g. Prolonged retention of 1H12 by tumour up to 8 days, observed at doses of 4, 128 and 256 g, indicated that the dynamics of localisation is unaffected by dosage.Increased doses of ¹²⁵I-1H12 caused an increase in the levels of radioactivity associated with all normal tissues studied. Thus at 8 days after injection an increase from 4 to 128 g produced 50% and 42% declines in the tumour to blood and liver ratios, respectively. Cumulative localisation of 1H12 in tumour, from 4 h to 8 days, relative to normal tissue clearance was diminished on increasing dosage. This study shows that attempted therapy with escalated amounts of intact antibody is likely to be limited by a protracted excretory process and measures aimed at accelerating circulatory clearance are necessary.     

Mechanisms of "cytostasis" of tumours in vitro by syngeneic lymphoid cells of tumour bearers.

The cytostasis assay is an in vivo-in vitro radioactive technique which detects antitumour responses of the syngeneic tumour-bearing hosts. Examination and characterization of effector mechanisms at the cellular and humoral levels revealed that the cytostasis assay using Meth A (a 3-methylcholanthrene-induced) tumour was T cell independent. Furthermore, both B cells and macrophages were required. It was concluded that the mechanism involved complement-dependent antibody-mediated lysis of the tumour cells, with B cells producing antibody and macrophages producing the complement components during incubation. However, antibody-dependent cell-mediated cytotoxicity with or without complement could not be completely excluded. Although antibody was detected in vivo, specific antibody against Meth A tumour was produced in vitro by cultured lymphoid cells from the tumour-bearers. Antibody-coated Meth A cells caused regression of some tumours when inoculated into BALB/c mice. When these regressor mice were rechallenged with tumour, they were found to be permanently immune to the tumour. In the light of these findings, the role of antibody in the protection of tumours and its implications are discussed.     

Unusual Water-mediated Antigenic Recognition of the Proinflammatory Cytokine Interleukin-18

The unique cytokine interleukin-18 (IL-18) acts synergistically with IL-12 to regulate T-helper 1 and 2 lymphocytes and, as such, seems to underlie the pathogenesis of various autoimmune and allergic diseases. Several anti-IL-18 agents are in clinical development, including the recombinant human antibody ABT-325, which is entering trials for autoimmune diseases. Given competing cytokine/receptor and cytokine/receptor decoy interactions, understanding the structural basis for recognition is critical for effective development of anti-cytokine therapies. Here we report three crystal structures: the murine antibody 125-2H Fab fragment bound to human IL-18, at 1.5 Å resolution; the 125-2H Fab (2.3 Å); and the ABT-325 Fab (1.5 Å). These structures, along with human/mouse IL-18 chimera binding data, allow us to make three key observations relevant to the biology and antigenic recognition of IL-18 and related cytokines. First, several IL-18 residues shift dramatically (>10 Å) upon binding 125-2H, compared with unbound IL-18 (Kato, Z., Jee, J., Shikano, H., Mishima, M., Ohki, I., Ohnishi, H., Li, A., Hashimoto, K., Matsukuma, E., Omoya, K., Yamamoto, Y., Yoneda, T., Hara, T., Kondo, N., and Shirakawa, M. (2003) Nat. Struct. Biol. 10, 966–971). IL-18 thus exhibits plasticity that may be common to its interactions with other receptors. Related cytokines may exhibit similar plasticity. Second, ABT-325 and 125-2H differ significantly in combining site character and architecture, thus explaining their ability to bind IL-18 simultaneously at distinct epitopes. These data allow us to define the likely ABT-325 epitope and thereby explain the distinct neutralizing mechanisms of both antibodies. Third, given the high 125-2H potency, 10 well ordered water molecules are trapped upon complex formation in a cavity between two IL-18 loops and all six 125-2H complementarity-determining regions. Thus, counterintuitively, tight and specific antibody binding may in some cases be water-mediated.Interleukin (IL)³ -18 is a proinflammatory cytokine that participates in the regulation of innate and acquired immunity (2, 3). IL-18 acts alone or in concert with IL-12 to amplify the induction of proinflammatory and cytotoxic mediators, such as interferon-γ. For example, in IL-18 knock-out mice, levels of interferon-γ and cytotoxic T cells decrease despite the presence of IL-12. Inhibition of IL-18 activity has been found to be beneficial in several autoimmune disease animal models (e.g. collagen-induced arthritis (4) and colitis (5)). Furthermore, IL-18 expression is dramatically increased by the chronic inflammatory state extant in human autoimmune diseases, such as rheumatoid arthritis (6), multiple sclerosis (7, 8), and Crohn''s disease (9). These observations suggest that blockade of IL-18 may be a useful human therapeutic modality (10).Despite functional divergence from the IL-1 cytokine family, IL-18 shares many similarities with IL-1. First, human IL-18 is synthesized as a biologically inactive 24-kDa precursor. Like IL-1β, IL-18 is activated and secreted following cleavage by caspase-1 (and possibly other proteases) that generates the mature 18-kDa polypeptide. Despite low sequence homology to IL-1β (17%), the three-dimensional structure of IL-18 closely resembles the IL-1β β-trefoil fold, as shown by a recent IL-18 NMR structure determination (1). The IL-1 and IL-18 receptors are also homologous; IL-18 binds either to the IL-18Rα chain alone or to the heterodimeric IL-18Rα/IL-18Rβ receptor complex. IL-18 binds to IL-18Rα with ∼20 nm affinity, but signaling occurs only upon formation of the high affinity (0.2 nm) IL-18Rα·IL-18·IL-18Rβ ternary complex (11, 12). Surface mutational analysis has identified two sites for IL-18 binding to IL-18Rα that are similar to those observed in the IL-1β·IL-1Rα binary complex (13) as well as one site important for binding to IL-18Rβ (1).In a recent study, a potent (0.2 nm) IL-18-neutralizing murine monoclonal antibody (mAb), 125-2H, inhibited binding of IL-18 to IL-18Rα alone but not the heterodimeric IL-18Rα/IL-18Rβ receptor complex, despite rendering the ternary complex with IL-18 non-functional (14). The structural basis for the unusual properties of 125-2H are unclear; the authors suggested that conformational changes in IL-18Rα occur upon formation of the IL-18Rα/IL-18Rβ receptor, thereby altering the interactions with 125-2H (14).To understand the intricate interactions between IL-18 and this antibody, we have determined the co-crystal structure of human IL-18 and the 125-2H antigen-binding fragment (Fab) at 1.5 Å resolution. This structure rationalizes epitope mapping data, based on human/murine IL-18 chimeras (14), in which the primary antigenic recognition loop is located near the COOH terminus. A secondary loop bolsters the interactions between IL-18 and several 125-2H complementarity-determining regions (CDRs). Comparison of this complex structure with that of the unbound 125-2H Fab (2.3 Å resolution) shows that 125-2H is preorganized for antigen binding. Last, we also have determined the 1.5 Å resolution crystal structure of the Fab fragment of a fully human mAb, ABT-325, that binds a distinct IL-18 epitope, as confirmed by biochemical studies. ABT-325 is entering clinical trials for a variety of autoimmune disease indications.     

Energy transfer distance measurements in immunoglobulins. II. Localization of the hapten binding sites and the interheavy chain disulfide bond in rabbit antibody

The distance between the hapten combining site and the single interheavy chain disulfide bond in rabbit immunoglobulin G has been determined by measuring the efficiency of energy transfer between chromophores specifically attached at these sites on the molecule. The donor chromophore, DnsLys³, was non-covalently bound in the combining sites of high-affinity antiDns antibody molecules, in one case, and in the combining site of the pepsin Fab′ fragment of antiDns in another. The acceptor chromophore, fluorescein, was covalently attached by disulfide interchange of di-FlCys with sulfhydryls generated by selective reduction of the interheavy chain disulfide bond of whole antiDns antibody and of the (Fab′)₂ pepsin fragment. The presence of acceptor decreased the donor fluorescence lifetime by about 1.0 nanosecond in both cases, i.e. for the whole antibody, from 23.6 to 22.7 nanoseconds, and for the Fab′ fragment from 23.6 to 22.5 nanoseconds. An average separation distance of 81 Å was calculated from an average observed transfer efficiency of 3.7%. This value agrees closely with the over-all length of a Fab′ fragment of a human IgG myeloma protein (Poljak et al., 1972). These results strongly suggest that the antibody combining site is at, or very close to, the tip of the Fab fragment and that the inter-heavy chain disulfide bond is at or near the edge of the C_L?C_H1 domain.     

Localization of an anti-CEA monoclonal antibody in colo-rectal carcinoma xenografts

Summary A mouse monoclonal anti-CEA antibody (11.285.14) has been examined for tumour localization potential by assessing its distribution in immunodeprived mice with xenografts of human colon carcinoma cell lines HCT-8, HRT-18, HT-29, and LS174T and a xenograft (HRVB) established from a primary rectal carcinoma. With four carcinomas (HCT-8, HT-29, LS174T, and HRVB) preferential tumour localization of ¹²⁵I anti-CEA was seen. Compared with ¹³¹I normal IgG₁ localization indices of up to 4.4:1 were achieved. Up to 10% of the injected dose of ¹²⁵I anti-CEA was present/g of tumour tissue and with the largest xenografts examined (3–4 g) up to 40% of the total body reactivity was localized in tumour tissue. The tumour localization of ¹³¹I labelled antibody was visualized by external gamma camera imaging. Overall antibody localization correlated with the CEA content of the xenografts and the fourth colon carcinoma xenograft (HRT-18) and an osteogenic sarcoma xenograft (791T), both with very low CEA levels, showed no localization of the monoclonal antibody.     

A human/mouse chimeric monoclonal antibody against CA125 for radioimmunoimaging of ovarian cancer

Murine monoclonal antibody 196-14 recognizes the ovarian-cancer-associated antigen CA 125, but the epitope it recognizes is different from that of monoclonal antibody OC125. We developed a human/mouse chimeric 196-14 using the variable regions of the murine 196-14 and human heavy-chain (l) and light-chain () constant regions. Cell binding and competitive inhibition assays using chimeric 196-14 labeled with¹²⁵I,¹¹¹In or^99mTc demonstrated that the in vitro immunoreactivity of the chimeric antibody was identical to that of the parental murine monoclonal antibody. However, in mice bearing human ovarian cancer xenografts, the clearance from blood was faster and absolute levels of accumulation in the tumor were lower for the¹²⁵I-labeled or^99mTc-labeled chimeric antibody than for the murine antibody labeled with the corresponding radionuclides. The tumor-to-blood radioactivity ratio was not significantly different between the chimeric antibody and the murine antibody, regardless of the radionuclide used for labeling. Chimeric antibody 196-14 labeled with¹³¹I,¹¹¹In or^99mTc is promising for the radioimmunoimaging of ovarian cancer.     

Pharmacokinetics and lung distribution of a humanized anti-RAGE antibody in wild-type and RAGE-/- mice

A neutralizing antibody to the receptor for the advanced glycation end products (anti-RAGE Ab) was developed as a potential treatment of acute and chronic inflammatory conditions. Previous pharmacology studies demonstrated efficacy of the anti-RAGE antibody in a mouse model of sepsis. We examined pharmacokinetics and lung distribution of [¹²⁵I]anti-RAGE Ab in RAGE^-/- and wild-type (129S5) mice following single IV administration. Serum pharmacokinetics of [¹²⁵I]anti-RAGE Ab was similar in RAGE^-/- and 129S5 mice, with the total body clearance of 0.3 mL/hr/kg and the elimination half-life of 11–12 days, suggesting the target expression had limited impact on overall elimination of [¹²⁵I]anti-RAGE Ab from mice. [¹²⁵I]Anti-RAGE Ab accumulated in the lung of 129S5 mice, with ∼4% of total dose retained in the lung at days 6–27 and the lung AUC_0-∞ of ∼300% of that in serum. The SDS-PAGE analysis suggested that most of retained lung radioactivity was attributed to intact antibody. No accumulation of radioactivity was observed in the lung of RAGE^-/- mice, indicating that lung uptake of [¹²⁵I]anti-RAGE Ab was target-dependent in wild-type mice. These data suggest that the anti-RAGE Ab was able to localize to the site of RAGE expression, the lung, and support the findings in the previous pharmacology studies.Key words: monoclonal antibody, ADME, tissue distribution, sepsis, pharmacokinetics, advanced glycation end products, RAGE, autoimmunity     

The Principal Neutralizing Determinant of HIV-1IIIB: Conformation of the Peptide Bound to a Neutralizing Antibody Studied by 2D-NMR

RP135 is a 24-residue peptide corresponding to the principal neutralizing determinant of the envelope glycoprotein gp120 of the human immunodeficiency virus type 1. We have studied the conformation of RP135 in complex with a neutralizing antibody 0.5 raised against gp120 by 2D NMR spectroscopy. The antigenic determinant recognized by this antibody was mapped using a combination of HOHAHA and ROESY measurements, in which resonances of the Fab and the tightly bound peptide residues are eliminated and the mobile residues of the bound peptide are sequentially assigned. We found that residues Ser⁶ - Thr¹⁹ are part of the epitope, while Lys⁵ and Ile²⁰ are at its boundaries. Difference spectroscopy was applied to study the conformation of the bound peptide representing the epitope within the 52 kDa of the Fab complex. Specific residues of the peptide were deuterated or replaced and the difference between the NOESY spectrum of the complex with the unlabeled residue and the NOESY spectrum of the complex with the modified residue revealed the interactions of the labeled residue both within the peptide and with the Fab fragment. A total of 122 distance restraints derived from the difference spectra enabled the calculation of the structure of the bound peptide. The peptide forms a 10-residue loop, while the two segments flanking this loop interact extensively with each other and possibly form anti-parallel -strands. The loop conformation could be observed due to the unusual large size (17 residues) of the antigenic determinant recognized by 0.5.     

G-CSF/anti-G-CSF antibody complexes drive the potent recovery and expansion of CD11b<Superscript>+</Superscript>Gr-1<Superscript>+</Superscript> myeloid cells without compromising CD8<Superscript>+</Superscript> T cell immune responses

Background

Administration of recombinant G-CSF following cytoreductive therapy enhances the recovery of myeloid cells, minimizing the risk of opportunistic infection. Free G-CSF, however, is expensive, exhibits a short half-life, and has poor biological activity in vivo.

Methods

We evaluated whether the biological activity of G-CSF could be improved by pre-association with anti-G-CSF mAb prior to injection into mice.

Results

We find that the efficacy of G-CSF therapy can be enhanced more than 100-fold by pre-association of G-CSF with an anti-G-CSF monoclonal antibody (mAb). Compared with G-CSF alone, administration of G-CSF/anti-G-CSF mAb complexes induced the potent expansion of CD11b⁺Gr-1⁺ myeloid cells in mice with or without concomitant cytoreductive treatment including radiation or chemotherapy. Despite driving the dramatic expansion of myeloid cells, in vivo antigen-specific CD8⁺ T cell immune responses were not compromised. Furthermore, injection of G-CSF/anti-G-CSF mAb complexes heightened protective immunity to bacterial infection. As a measure of clinical value, we also found that antibody complexes improved G-CSF biological activity much more significantly than pegylation.

Conclusions

Our findings provide the first evidence that antibody cytokine complexes can effectively expand myeloid cells, and furthermore, that G-CSF/anti-G-CSF mAb complexes may provide an improved method for the administration of recombinant G-CSF.