A monoclonal antibody (D612) with selective reactivity for malignant and normal gastro-intestinal epithelium

Efficient clearance of poly(ethylene glycol)-modified immunoenzyme with anti-PEG monoclonal antibody for prodrug cancer therapy

The F(ab')(2) fragment of the anti-TAG-72 antibody, B72.3, was covalently linked to Escherichia coli-derived beta-glucuronidase that was modified with methoxypoly(ethylene glycol). The conjugate (B72.3-betaG-PEG) localized to a peak concentration in LS174T xenografts within 48 h after injection, but enzyme activity persisted in plasma such that prodrug administration had to be delayed for at least 4 days to avoid systemic prodrug activation and associated toxicity. Conjugate levels in tumors decreased to 36% of peak levels at this time. Intravenous administration of AGP3, an IgM mAb against methoxypoly(ethylene glycol), accelerated clearance of conjugate from serum and increased the tumor/blood ratio of B72. 3-betaG-PEG from 3.9 to 29.6 without significantly decreasing the accumulation of conjugate in tumors. Treatment of nude mice bearing established human colon adenocarcinoma xenografts with B72. 3-betaG-PEG followed 48 h later with AGP3 and a glucuronide prodrug of p-hydroxyaniline mustard significantly (p< or =0.0005) delayed tumor growth with minimal toxicity compared to therapy with a control conjugate or conventional chemotherapy.

Identification of second malignancies on effusions and fine-needle aspirates using a panel of monoclonal antibodies

The longer survival of neoplastic patients achieved through improvements of therapeutic regimens has increased the relative risk of developing a second primary tumour (SPT). In this context, conventional cytopathology can define tumour histotype only in a small fraction of cases. In this study, we have evaluated whether selected combinations of monoclonal antibodies (MAbs) to tumour-associated antigens (TAAs) can increase the accuracy of conventional morphology in detecting second primary tumours (SPTs) in two particularly difficult areas of cytodiagnosis, namely that of effusions and pulmonary fine-needle aspirates (FNAs). The immunocytochemical (ICC) analysis of 334 cytological specimens demonstrated that the use of our selected panel of MAbs could allow a more efficient identification of SPTs in comparison with conventional morphology. This diagnostic improvement was statistically significant (P < 0.0001). The present findings show that the immunophenotyping of effusions and FNAs, providing a more accurate and objective identification of SPTs, may have significant therapeutic and epidemiological relevance.

Novel acid labile COL1 trityl-linked difluoronucleoside immunoconjugates: synthesis, characterization, and biological activity

LY207702 (1) is a difluorinated purine nucleoside that exhibits impressive antitumor activity in preclinical models. This agent, however, also possesses cardiotoxicity which limits the potential clinical utility of this novel drug candidate. We therefore developed linker chemistry whereby regioselective N6-tritylation of LY207702 (1) allowed this drug to be coupled to epsilon-lysine amino groups of mAb's reactive with human tumor-associated antigens. The resulting immunoconjugates 3 possessed conjugation ratios ranging from 5 to 7 mol of LY207702/mol of mAb, minimal aggregate content (5-10%), and good immunoreactivity. The electronic nature of substituents on the aromatic rings of the trityl group dictated the degree of acid lability of the trityl linker. Increased electronic stabilization of the transient trityl carbocation led to increase in the release rate of free drug, i.e., m-DMT 10a = p-DMT 10b > p-MMT 10d > p-T 10f. Consequently, the more acid labile DMT conjugates 3a and 3b proved to be the most potent cytotoxic agents, and the most stable p-T conjugate 3f exhibited the least antitumor activity when evaluated in vitro and in vivo. p-MeT-linked conjugate 3e, the most stable construct that retained excellent in vivo antitumor activity, was selected for more extensive evaluation. No detectable free drug or metabolite was observed in mouse plasma at a single intravenous dose of p-MeT conjugate 3e, which was consistent with its predicted stability under physiological conditions. This construct did, however, exhibit significant antigen-mediated antitumor activity in vivo. No cardiotoxicity was detected in mice dosed with conjugate 3e (6 mg/kg free drug content per day for 21 days) equivalent to approximately 8 times the total dose required for complete regression of well-established (approximately 1 g) HC1 human colon tumor xenografts in nude mice. Cardiotoxicity was induced in 20% of free drug 1 treated group at the equivalent dose. Cardiomyopathy was, however, observed when the dose of conjugate 3e was increased to 8 mg/kg per day for 21 days. These data suggest that antitumor activity of LY207702 (1) was maintained and its cardiotoxic potential reduced when this agent was administered to human tumor xenograft bearing nude mice as COL1-N6-p-MeT-207702 conjugate 3e.

Macrophage colony-stimulating factor enhancement of antibody-dependent cellular cytotoxicity against human colon carcinoma cells

Antibody-dependent cellular cytotoxicity (ADCC) has been suggested to be an important defense mechanism against tumors. The effects of recombinant human macrophage colony-stimulating factor (rhM-CSF) on ADCC activity of human monocytes were investigated. Human peripheral monocytes were pre-incubated for 72 h with rhM-CSF at various concentrations (50, 100, 200, 400 U/ml) and then used as effector cells in a 24-h 111-Indium release assay. Human carcinoma cell lines LS-174T, CBS, and KLE were used as targets to react with anti-carcinoma monoclonal antibodies (mAbs: murine D612, murine CC49, and chimeric CC49). A significant increase in ADCC activity was observed after monocytes were incubated in 100-400 U/ml of human rhM-CSF. Variation in ADCC activity of monocytes among donors was observed. The enhancement of ADCC activity was blocked by the addition of a neutralizing antibody to rhM-CSF. Less D612 mAb was required for the rhM-CSF-treated monocytes to mediate an equivalent level of ADCC activity as compared to the untreated monocytes. Because of the low levels of rhM-CSF required in these studies to enhance ADCC, treatment of monocytes alone with comparable levels of rhM-CSF did not enhance antibody-independent cytotoxicity. Moreover, it is demonstrated here that recombinant human interleukin-4 (rhIL-4) and rhM-CSF can have a synergistic effect of monocyte-mediated ADCC on human tumor cells. These results thus indicate that rhM-CSF augments ADCC of human peripheral blood monocytes using mAbs to human carcinomas, suggesting a potential role for rhM-CSF in cancer immunotherapy.

Recombinant proteins L and LG: efficient tools for purification of murine immunoglobulin G fragments

In order to improve antibody purification methods, recombinant proteins L and LG were tested in the purification of murine monoclonal immunoglobulin G (IgG) and its fragments. After affinity constant evaluation in different buffer systems, high-performance affinity chromatographic columns were prepared by coupling the proteins to Affi-prep 10 resin and tested with eight different murine monoclonal antibodies and their fragments of different isotypes. Affinity chromatographic experiments confirmed radioimmunoassay results showing that protein L bound 75% of the tested antibody fragments whereas protein LG had affinity for all the tested fragments. These results demonstrate that protein LG is the most powerful Ig-binding tool so far described.

Recombinant proteins L and LG. Two new tools for purification of murine antibody fragments

Several bacterial cell wall proteins, like proteins A and G, with valuable affinity for immunoglobulins have been discovered and are currently employed in immunological techniques. In 1988, protein L, a bacterial cell wall protein with Ig-binding capacity, was isolated from the anaerobic bacterial species Peptostreptococcus magnus. Binding data with immunoglobulin fragments suggested that protein L could selectively bind the variable region of human kappa light chains. More recently a recombinant LG fusion protein was expressed in E. coli containing four repeated Ig-binding domains of protein L (fragment B1-4) and two IgG Fc-binding protein G domains (fragment CDC). Recombinant L and LG proteins were tested in the purification of murine monoclonal IgG and their fragments. After affinity-constant evaluation in different buffer systems, high-pressure affinity-chromatography columns were prepared by coupling the proteins to Affi-prep 10 resin and tested with eight different murine monoclonal antibodies and their fragments of various isotypes. Affinity-chromatography experiments confirming radioimmunoassay results showed 75% fragment-binding capacity of protein L and 100% of protein LG. These results evidenced protein LG as the most powerful Ig-binding tool so far described. Therefore, application of these proteins may be suggested in the purification of murine immunoglobulins and their fragments, including the engineered ones.

Induction of delayed-type hypersensitivity responses by monoclonal anti-idiotypic antibodies to tumor cells expressing carcinoembryonic antigen and tumor-associated glycoprotein-72

The use of anti-idiotypic antibodies as immunogens represents one potential approach to active specific immunotherapy of cancer. Two panels of syngeneic monoclonal anti-idiotypic antibodies were generated. One panel was directed against mAb CC49 and the other to mAb COL-1. mAb CC49 recognizes the pancarcinoma antigen (Ag), tumor-associated glycoprotein-72 (TAG-72), and mAb COL-1 recognizes carcinoembryonic antigen (CEA). Seven anti-idiotypic (AI) antibodies (Ab2) designated AI49-1-7 were generated that recognize the variable region of mAb CC49. These mAb were shown to inhibit the interaction of mAb CC49 (Ab1) with TAG-72 (Ag). Five anti-idiotypic antibodies designated CAI-1-5 were also generated to the anti-CEA mAb, COL-1 (Ab1). These Ab2 were shown to inhibit the interaction between COL-1 (Ab1) and CEA (Ag). Immunization of mice, rats, and rabbits with Ab2 directed against CC49 or COL-1 could not elicit specific Ab3 humoral immune responses, i.e., antibody selectively reactive with their respective target antigens. However, immunization of mice with the CC49 anti-idiotypic antibody (Ab2), designated AI49-3, could induce a delayed-type hypersensitivity response (DTH) specific for tumor cells that express TAG-72. Similarly, immunization of mice with an anti-idiotypic antibody directed against COL-1, designated CAI-1, could induce specific DTH cell-mediated immune responses to murine tumor cells that express human CEA on their surface. These results thus demonstrate that while some anti-idiotype mAb may not be potent immunogens in eliciting Ab3 humoral responses, they are capable of eliciting specific cellular immune responses against human carcinoma-associated antigens. This type of mAb may ultimately be useful in active immunotherapy protocols for human carcinoma.

N-methylformamide effects on cell proliferation and antigenic pattern in HT-29 colon carcinoma cell line

The effects of the differentiating agent N-methylformamide (NMF) on cell proliferation and antigenic pattern of HT-29 colon carcinoma cells have been investigated. The cell line was cultured in the presence, or absence, of 1% NMF and tested for the above mentioned characteristics, both in vitro and after injection into nude mice. The percentage of cells in the various cell cycle compartments was estimated by flow cytometry. The presentation on the cell surface of molecules such as tumour associated antigens (TAAs), HLA class I molecules and epidermal growth factor receptor (EGF-R) was analysed by ELISA, flow cytometry and immunohistochemistry. Results demonstrate that NMF impairs HT-29 cell proliferation with a remarkable accumulation in the G0/G1 phases, as well as inducing a modification of the membrane antigenic pattern. The presence of NMF in the culture medium decreases the TAAs and EGF-R whereas HLA antigen maintains the same level of positivity in the two cell lines. These alterations are consistent with a different behaviour in vivo of the tumours originated from NMF treated and untreated cells. Tumours derived from NMF treated cells show a delay in the appearance and low levels of immunodetectable carcinoembryonic antigen (CEA) molecules.

Selected monoclonal antibodies can increase the accuracy of cytodiagnosis of neoplastic effusions of cryptic origin expanded in a short term culture

The use of a selected panel of monoclonal antibodies (MoAb) to tumor associated antigens (TAA) in immunocytochemical (IIC) tests has been shown, in a preliminary study, to be a powerful diagnostic tool for the identification of the primary solid tumor causing metastatic effusion. Despite this improvement in a minority of neoplastic fluids a number of different causes may still determine false negative (FN) immunocytochemical diagnoses. The aim of the present study was to confirm the diagnostic accuracy of this panel of MoAb. This was done by analyzing in IIC tests a larger number of effusions and by evaluating whether the expansion in short term culture of those fluids with an uncertain malignant morphology could provide an adequate cellular substrate for immunocytodiagnosis. The analysis of 314 effusions confirmed the results of the pilot study and demonstrated that the combination of short term culture and immunocytochemical assays can further increase the sensitivity of this novel diagnostic procedure from 84.3% to 95.3%.

Carcinoembryonic antigen regulation in human colorectal tumor cells by a site-selective cyclic AMP analogue: a comparison with interferon-gamma

Treatment of human colorectal tumor cells (LS174T, HT-29, and WiDr) with analogues of cyclic AMP (cAMP) (dibutyryl-cAMP and 8-Cl-cAMP) selectively enhances the expression of carcinoembryonic antigen (CEA). Dose and temporal kinetics results revealed that 8-Cl-cAMP was approximately 100-fold more potent than dibutyryl-cAMP for increasing CEA expression. Results demonstrated that 8-Cl-cAMP treatment of LS174T quantitatively increased CEA levels in cell extracts 2-fold, increased anti-CEA monoclonal antibody (MAb) binding to the tumor cell surface, and induced the appearance of CEA-related mRNA transcripts. The findings suggest that 8-Cl-cAMP is capable of regulating CEA expression at transcriptional and/or post-transcriptional levels. Other human tumor cells, as well as normal cell types which do not constitutively express CEA, remained CEA-negative following 8-Cl-cAMP treatment. Moreover, the level of expression of other human tumor antigens as well as antigens of the major histocompatibility complex were not changed by 8-Cl-cAMP treatment, suggesting some selectivity for CEA regulation by this cAMP analogue. In vivo administration of 8-Cl-cAMP to athymic mice bearing LS174T tumor xenografts increased the amount of anti-CEA MAb bound to tumor extracts as well as the tumor localization of a radionuclide-conjugated anti-CEA MAb. The results indicate that 8-Cl-cAMP can selectively upregulate CEA expression on human colorectal tumor cells in vitro and in vivo. Interestingly, IFN-gamma treatment of the LS174T cells fails to enhance or induce expression of CEA or any of the histocompatibility leukocyte antigens. Thus, 8-Cl-cAMP treatment regulates CEA expression through another cellular pathway which may involve cAMP-dependent protein kinase.

Characterization, isolation and amino terminal sequencing of a rat colon carcinoma-associated antigen

Monoclonal antibodies have been raised against a cell line derived from a dimethylhydrazine-induced rat colon carcinoma. One of these antibodies (MAb E4) has previously been shown to react slightly with normal small intestine and colon, and not with other normal tissues as determined by immunohistochemistry. Using Western immunoblotting we confirmed this tumor specificity. Therefore, the Mr of approx. 66,000 glycosylated antigen (pE4) recognized by MAb E4 appeared to be a potential marker of colon carcinoma. Fifteen human tumor cell lines were tested by flow cytometry for the expression of pE4. This antigen was not detected on these cells. In the rat colon carcinoma cell, pE4 was exclusively found on the cell membrane. pE4 was purified to near homogeneity by immunoaffinity chromatography. The first 20 N-terminal amino acids were identified. Comparison with the NBRF data bank did not reveal a complete homology with known sequenced proteins but similarities were found with the mouse L3T4 precursor, the env polyprotein of human immunodeficiency virus type I, flagellin from Halobacterium halobium and the gp30 from hepatitis B surface antigen. Homology was always found in transmembranous or hydrophobic domains of these proteins. By indirect immunofluorescence analysis of adherent cells and size exclusion chromatography under native conditions, pE4 was found to interact with other molecules and perhaps to be involved in intercellular contact.

Human recombinant interleukin-6 enhances antibody-dependent cellular cytotoxicity of human tumor cells mediated by human peripheral blood mononuclear cells

The effects of human recombinant interleukin-6 (hrIL-6) on antibody-dependent cellular cytotoxicity (ADCC) activity mediated by human peripheral blood mononuclear cells (PMNC) were investigated. Human PMNC were preincubated for 24 h with various concentrations of hrIL-6 and were used as effector cells in a 4-h 51Cr-release assay. The ability of hrIL-6 to augment ADCC was measured using anti-colorectal carcinoma mAbs D612, 17.1A and 31.1 (each directed against a distinct tumor antigen) and using three human colorectal carcinoma cell lines, LS-174T, WiDr and HT-29, as targets. A significant increase in ADCC activity was observed after PMNC were preincubated in 100-400 U/ml but not in lower concentrations of hrIL-6. Variations in activities of PMNC among donors were observed. Non-specific mAb showed no effect in augmenting ADCC activity. hrIL-6 treatment did not augment non-specific (non-mAb-mediated) cytotoxicity. The enhancement of ADCC activity was blocked by the addition of an antibody against hrIL-6 but not by an antibody to the IL-2 receptor (capable of blocking the induction of lymphokine-activated killer cell cytotoxicity by IL-2), suggesting that hrIL-6 augmentation of ADCC activity may not be mediated through IL-2. These results demonstrate that hrIL-6 augments ADCC activity of human PMNC using mAbs to human tumor antigens and human tumor cells as targets, suggesting a potential role for IL-6 in combination with anti-cancer antibodies for cancer immunotherapy.

Lymphokine-activated killer cell cytotoxicity against human colon carcinomas enhanced by monoclonal antibody D612

The antibody-dependent cellular cytotoxicity (ADCC) properties of a murine monoclonal antibody (MAb), designated D612 (IgG2a), which reacts with human colon carcinomas, was studied using normal human peripheral blood lymphocytes (PBMNC). Although the level of ADCC of PBMNC with D612 varied among different donors, it was 20 to 30 times higher than the lytic activity of control cultures containing isotype-matched control MAb. Incubation of PBMNC with recombinant interleukin-2 (IL-2) resulted in a 2- to 5-fold augmentation in the cytotoxicity of effector cells exposed to MAb. This augmentation was apparent after subtracting nonspecific cellular cytotoxicity from the total cytotoxicity mediated by activated effector cells in the presence of D612. Optimal stimulation of specific ADCC with IL-2 appeared after 24 hr of culture in 500 U/ml of IL-2, resulting in a 3.8 +/- 1.7 fold increase in lytic units. However, stimulation of ADCC was also evident at 10 U/ml of IL-2. Furthermore, antibody dose titrations with untreated and IL-2 activated effectors showed that the threshold dose of MAb needed for efficient ADCC was reduced by 200-fold with IL-2. Depletion of FcR gamma III-positive lymphoid cells markedly reduced D612 ADCC, demonstrating the participation of NK/LAK cells in D612-mediated ADCC. Low levels of ADCC activity were found associated with adherent cells, either untreated or following their activation with gamma-interferon, while D612 was most active with non-adherent effectors. The specificity and ADCC properties of the D612 MAb suggest that it should be considered as a candidate for immunotherapy of colon cancer, particularly when used in combination with IL-2 plus LAK cell treatment.

Use of MoAb D612 in combination with a panel of MoAb for the immunocytochemical identification of metastases from colon-rectum carcinoma

During the course of colon-rectum tumours a number of clinical events may occur in which conventional cytopathology can provide only a partial contribution to the definition of a differential diagnosis, i.e. effusions, distant recurrences and second neoplasias. In the present study we have evaluated whether monoclonal antibody (MoAb) D612, recognising a colon-rectum associated antigen, can be used in this context. To this end, MoAb D612 was employed in combination with a panel of MoAb of well defined tumour specificity in immunocytochemical tests. The immunocytochemical findings obtained were compared with the histological and clinical diagnosis. Of 62 effusions and 40 fine needle aspirates studied, MoAb D612 reactivity correlated with the correct diagnosis in 92.8% of the instances. These results indicate that this reagent may help to improve the current cytopathological diagnosis of colon-rectum tumours by identifying the colonic origin of metastases in patients with unknown primary tumour, differentiating ovarian carcinoma from colon metastases to the ovaries and establishing the presence of a second neoplasia in patients with a previous history other than colon carcinoma.

Chimeric B72.3 mouse/human (IgG1) antibody directs the lysis of tumor cells by lymphokine-activated killer cells

Chimeric mouse/human B72.3 (cB72.3) antibodies having a human IgG1 (gamma 1) or IgG4 (gamma 4) constant region were compared to the native murine IgG1 B72.3 (nB72.3) monoclonal antibody (mAb) for their ability to participate with human effector cells in antibody-dependent cellular cytotoxicity (ADCC). Because the TAG-72 antigen recognized by B72.3 is poorly expressed on tissue-cultured tumor cell lines, the xenografted OVCAR-3 human ovarian carcinoma ascites was used as a cytotoxicity target. The lytic activity of the cB72.3(gamma 1) mAb with peripheral blood lymphocytes was 1.5- to 50-fold greater than that of the nB72.3 mAb and usually the cB72.3(gamma 4) mAb. However, lymphocytes from some donors had similar ADCC activity with either the cB72.3(gamma 1) or cB72.3(gamma 4) mAb. The cB72.3(gamma 1) and the murine anti-colon carcinoma CO17-1A mAb had comparable activity in mediating ADCC against the OVCAR-3 tumor. Exposure of lymphoid cells to interleukin-2 (IL-2) (100-500 U/ml) for 24 h to generate lymphokine-activated killer (LAK) cells augmented ADCC mediated by the cB72.3(gamma 1) mAb 2- to 22-fold. By contrast, LAK cells from most donors expressed weak non-specific cytotoxicity against OVCAR-3 ascites tumor cells. The cB72.3(gamma 1), and to a lesser extent, the cB72.3(gamma 4) chimera also participated with monocytes in mediating ADCC, but the antibody-dependent lytic potency of monocytic effectors was much weaker than that of IL-2-activated lymphoid cells. These studies show that the cB72.3(gamma 1) mAb has appreciable ADCC-mediating properties, suggesting a potential role for its incorporation into treatment strategies utilizing adoptive killer cell and/or lymphokine therapy.

Combinations of monoclonal antibodies can distinguish primary lung tumors from metastatic lung tumors sampled by fine needle aspiration biopsy

Transthoracic fine needle aspiration (FNA) biopsies performed under computed tomography (CT) scan (CT-FNA) have greatly improved the cytodiagnosis of lung tumors. However, the distinction between a primary lesion and a metastatic lesion still may be difficult on the basis of morphologic criteria. To evaluate whether a selected panel of monoclonal antibodies (MoAb) to tumor-associated antigens (TAA) can improve the diagnostic potential of FNA, we have immunocytochemically analyzed 122 pulmonary CT-FNA. Whereas conventional cytology was capable of recognizing only the neoplastic nature of the lesions, the immunocytochemical diagnosis could identify the primary or metastatic nature of the pulmonary masses in 92.5% of the cases. The immunocytochemical findings were confirmed by clinical-histopathologic data. The current results demonstrate that the use of immunocytochemical methods can significantly improve the diagnostic accuracy of conventional cytology of lung masses.