Clinical application of monoclonal antibody-drug conjugates for immunotargeting chemotherapy of colorectal carcinoma

Radioimmunodetection of human colon cancer in nude mice by a new monoclonal antibody A7 against human colorectal cancer

The in vivo localization of a monoclonal antibody A7 against a human colorectal cancer was studied in nude mice bearing human solid carcinomas, to evaluate potential applications of this antibody for radioimmunodetection of cancer. The tissue distribution of 125I-labeled A7 MoAb at 3 days after i.v. injection into mice bearing five different kinds of human solid tumors revealed a high uptake ratio by colon cancer, mammary cancer, and glioblastoma. In contrast, the uptake ratio by murine colorectal cancer (Colon-38) was extremely low. In immunoscintigraphic studies, HCT-15, one of the human colon cancer, was clearly visualized with 111In-DTPA-A7 MoAb. Glioblastoma was also imaged with the same extent. These results suggest that A7 MoAb would be applicable to the in vivo radioimmunodetection of colon- and mammary-cancer, and of glioblastoma.

Clinical experience of targeted therapy

Drug targeting (i.e. administration of a drug-carrier conjugate which delivers active drug selectively to a particular tissue) has recently evolved into a new subdiscipline of experimental pharmacy/pharmacology. However, clinical experience with targeted therapy is very limited to date. This review summarizes human studies of targeted therapy. Indications for which drug targeting has been attempted include neoplastic disorders, fungal infections, enzyme replacement, hematologic and immune disorders, and iron storage disease. To date, no single drug targeting system is recommendable for routine clinical use, but present results justify further clinical evaluation in a number of situations.

Development of human anti-murine antibody (HAMA) response in patients

Human anti-mouse antibody (HAMA) response was determined in the serum of 67 patients who received subcutaneously administered radiolabelled murine monoclonal antibodies (MoAb) (50 micrograms-3 mg) for immunolymphoscintigraphy and of 10 patients with advanced colorectal cancer who received murine MoAb-N-acetyl melphalan (MoAb-N-AcMEL) conjugates (amount of MoAb ranged from 120 mg/m2 body surface area to 1000 mg/m2 body surface area) as therapy. A pre-existing low level of apparent human anti-mouse antibody reactivity could be detected in the serum of normal subjects and patients prior to administration of murine MoAb. Subcutaneous administration of low doses of murine MoAb, as used in immunolymphoscintigraphy, was associated with a low incidence (4/67 or 6%) of elevated HAMA response; the use of F(ab')2 fragments was associated with the development of elevated HAMA response in one of three patients. By contrast, therapy with hepatic artery infusion of murine MoAb-N-AcMEL conjugates in three repetitive daily doses (each infusion lasting 2 h) elicited elevated HAMA responses in 10/10 (100%) patients, usually 1-3 weeks after the start of therapy. The HAMA response of patients in the therapy group was higher than those in the immunolymphoscintigraphy study and the use of steroids did not prevent the development of the HAMA response. Further administration of MoAb-N-AcMEL conjugates to a patient, who had already developed HAMA, led to 'serum sickness'-type symptoms and a transient reduction in the HAMA titres. The elevated HAMA response was polyclonal, containing increased levels of both immunoglobulin M and G (IgM and IgG) and was directed against mouse-specific determinant, the isotype (presumed to be the Fc portion), the F(ab')2 and the 'idiotype' of mouse immunoglobulins.

Polyethylene glycol modification of the monoclonal antibody A7 enhances its tumor localization

The F(ab')2 fragment of murine monoclonal antibody A7 was covalently bonded to polyethylene glycol (PEG, molecular weight: 5000) and the conjugate was compared to the parent F(ab')2 fragment by in vitro and in vivo studies. PEG-conjugated antibody fragment retained its antigen-binding activity in a competitive radioimmunoassay. The conjugate had a longer half-life and showed increased accumulation in tumors. Although the tumor: blood ratio for parent F(ab')2 fragment was higher than that for the conjugate, it showed higher value than whole MAb A7. The tissue: blood ratios were kept low with the conjugate, indicating that the conjugate was uptaken to normal organ with lesser extent, as compared with parent F(ab')2 fragment. Our findings indicate that this PEG-conjugated F(ab')2 fragment could be a promising carrier for use in targeting cancer chemotherapy.

Specific cytotoxic effect of neocarzinostatin conjugated to monoclonal antibody A7 on human pancreatic carcinoma

The anti-cancer drug neocarzinostatin (NCS) was bound covalently to the monoclonal antibody A7 to form the conjugate A7-NCS. This antibody was produced by fusing the spleen cells of a mouse immunized against human colonic carcinoma with murine myeloma cells and reacts with a high percentage of human pancreatic carcinoma cell lines and with no normal human pancreas tissue by immunoperoxidase staining. The cytotoxic effect of A7-NCS was tested by measuring the inhibition of 3H-thymidine incorporation into human pancreatic carcinoma cells. The A7-NCS was approximately 2.7 times as effective as free NCS against human pancreatic carcinoma cells which reacted with the monoclonal antibody A7. A7-NCS had almost the same cytotoxicity a free NCS on human pancreatic carcinoma cells which did not react with the monoclonal antibody A7. A7-NCS appeared to be potentially useful as a conjugate for immunotargeting chemotherapy against pancreatic carcinoma.

Antibody mediated targeting of radioisotopes, drugs and toxins in diagnosis and treatment

The recent resurgence of interest in site specific delivery of radioisotopes, chemotherapeutic drugs and toxins for the diagnosis and treatment of cancer, and for the selective manipulation of the immune system, can be directly related to the need for improved diagnosis and the fact that for many cancers, for example lung, colon and gastric, the conventional treatments of surgery, radiotherapy and chemotherapy have reached a plateau in terms of the number of patients cured. To date, because of their specificity, the major emphasis has been on the use of antibodies as carriers and extensive in vitro, in vivo preclinical and clinical evaluation is underway. The aim of this article is to review recent progress, highlight avenues being explored to overcome limitations and to indicate new approaches that are evolving in antibody mediated targeting.

Antibody-penicillin-V-amidase conjugates kill antigen-positive tumor cells when combined with doxorubicin phenoxyacetamide

The two monoclonal antibodies (mAb), L6 (anti-carcinoma), and 1F5 [anti-(B-cell-lymphoma)], were chemically linked to the enzyme penicillin-V amidase (PVA), which hydrolyzes phenoxyacetamides, to explore the potential of using mAb-enzyme conjugates for the localization of chemotherapeutic drugs at tumor cells. The phenoxyacetamide derivatives of doxorubicin and melphalan were prepared, yielding the less toxic amides, doxorubicin-N-p-hydroxyphenoxyacetamide (DPO) and melphalan-N-p-hydroxyphenoxyacetamide (MelPO). These were hydrolyzed by PVA to doxorubicin and melphalan respectively. In vitro studies with the L6-positive lung carcinoma cell line, H2981, and the 1F5-positive B-cell lymphoma line, Daudi, showed that DPO was 80-fold less toxic to H2981 cells and 20-fold less toxic to Daudi cells than doxorubicin, and its toxicity was substantially increased when the H2981 cells were pretreated with L6-PVA or the Daudi cells were pretreated with 1F5-PVA. The cytotoxic effect was antigen-specific, since only the binding mAb-enzyme conjugate increased the cytotoxicity of the prodrug. MelPO was more than 1000-fold less toxic than melphalan to H2981 cells and more than 100-fold less toxic than melphalan to Daudi cells. Pretreatment with the mAb-PVA conjugates did not enhance the toxicity of MelPO in either cell line, because PVA hydrolyzes the phenoxyacetamide bond of MelPO too slowly to generate a toxic level of melphalan.

Antigenic modulation and internalization of monoclonal antibody to human colonic carcinoma cells detected by enzyme-linked immunosorbent assay

We studied antigenic modulation and internalization of monoclonal antibody (MAb) A7 using the enzyme-linked immunosorbent assay (ELISA) and biotin-labelled antibody-staining techniques. Incubation of the colonic SW1116 cell line with an excess of MAb A7 induced modulation of the cell-surface antigen. When the line was assayed by ELISA, a change in cellular reactivity with MAb A7 was seen after 1 hr. After 24 hr, the cellular reactivity showed a 52% decrease in absorbance. Modulation was inhibited by 0.1% sodium azide and acetone fixation, suggesting that this is an energy-dependent phenomenon. The internalization of biotinylated MAb A7 was examined. Internalized biotinylated MAb A7 was detected in cells fixed before labelling with avidin-biotin peroxidase complex. It was observed that the amount of MAb A7 which remained associated with the cell surface had decreased since A7 was internalized.

Immunohistochemical detection of biotin-labeled murine monoclonal antibody in nude mice transplanted with human colon cancer

The tissue localization of biotin-labeled murine monoclonal antibody (MAb) A7 directed against human colonic cancer was examined in tumor-bearing nude mice following intravenous administration. MAb A7 did not react with any murine visceral organs. At 24 hr after biotin-labeled A7 injection, the tumor was stained by the avidin-biotin peroxidase complex method, but no staining was observed after injection of biotin-labeled normal mouse Ig G in the control group. Biotin-labeled MAb was found to be suitable for the detection of the xenografted tumor of nude mice. Our purpose was to provide a new method concerning the distribution of biotin-labeled MAb in vivo.

In vivo efficacy of monoclonal antibody-drug conjugates of three different subisotypes which bind the human tumor-associated antigen defined by the KS1/4 monoclonal antibody

A panel of three hybridomas has been isolated each of which secretes a single species of monoclonal antibody (MoAb) directed against the KS1/4 tumor-associated antigen originally described by Varki et al. (Cancer Res 44: 681, 1984). These MoAbs were designated L1-(IgG2b), L2-(IgG1), and L4-(IgG2a)KS. Binding specificity, immuno-precipitation, and competitive binding analyses indicated that these MoAbs each recognize the same epitope of the KS1/4 antigen. The immunoprecipitation studies indicated that the MoAbs recognized a major antigenic component of 42 kDa and a minor component of 35 kDa. The L-KS antibodies were evaluated as MoAb-drug conjugates against a variety of human tumor targets grown in vivo as nude mouse xenografts. The MoAb-drug conjugates were constructed using protein-A-purified MoAbs conjugated to 4-desacetyl-vinblastine-3-carbohydrazide. Efficacy was determined using various dosing protocols on 2-14 day established tumors of lung, pharynx, colon, and skin origin. Control experiments included the use of dual-flank antigen-positive and negative tumors, free MoAbs, free drug, and mixtures of MoAbs and drug. These studies indicated that significant tumor growth suppression and actual tumor regression could be achieved by the MoAb-vinca conjugates and that this activity was antigen-mediated. The drug conjugates were more efficacious than free drug or free MoAbs administered either singly or in combination with each other.