Monoclonal antibody-targeted radiotherapy of renal cell carcinoma using a nude mouse model

A rapid and efficient in vivo method for determining the biologic efficacy of monoclonal antibodies in animal models of cancer

The selection of efficacious anti-tumor monoclonal antibodies (MAbs) for biological applications is a lengthy and labor-intensive process. In vitro characterization of one hybridoma fusion may reveal large numbers of tumor antigen-specific hybridomas. Very often, many of these tumor-specific antibodies need to be assessed in vivo using several different murine xenograft tumor prevention models to determine biological efficacy. The production and purification of sufficient quantities of many antigen-specific hybridomas is time-consuming, and several months can pass between initial determination of MAb specificity and bioactivity. Moreover, many tumor-specific MAbs selected using in vitro binding studies have no in vivo anti-tumor efficacy. These studies describe an in vivo screening method either to eliminate non-efficacious MAbs or to rank-order several tumor-specific MAbs in an expeditious manner. Proof-of-concept studies were conducted using two hybridomas secreting fully characterized neutralizing human anti-tumor MAbs (CNTO MAbs). Nu-/nu- mice were injected with CNTO MAb-secreting hybridoma cells in Matrigel cell matrix, followed by injection of target human tumor cells 4 days later (when circulating CNTO MAbs were detected in serum). Both the tumor take-rate and the mean tumor volumes were reduced significantly in mice treated with CNTO MAbsecreting hybridomas compared with mice treated with non-antibody-secreting cells. A panel of human antitumor antigen-specific MAbs with unknown biological efficacy was then evaluated by this method. The hybridomas exhibited a varied pattern of anti-tumor protection, indicating that some hybrids were secreting neutralizing anti-tumor MAbs, while others appeared to be less efficacious. These studies demonstrate a rapid, biologically relevant "yes/no" in vivo screening method for the evaluation of anti-tumor antigen MAbs.

Preparation and biodistribution of copper-67-labeled porphyrins and porphyrin-A6H immunoconjugates

The synthetic porphyrins, N-benzyl-5,10,15,20-tetrakis (4-carboxyphenyl) porphine (N-bzHTCPP) and N-4-nitrobenzyl-5-(4-carboxyphenyl)-10,15,20-tris(4-sulfophenyl) porphine (N-bzHCS3P), represent excellent radiocopper chelating agents that may find utility in antibody-mediated diagnosis and/or therapy. N-bzHCS3P was conjugated to an anti-renal cell carcinoma (RCC) antibody, A6H, and labeled with copper-67. 67CuCS3P-A6H was studied for its biodistribution in human RCC xenograft-bearing nude mice, along with the radiolabeled free porphyrins. The porphyrins resulted in tumor:blood ratios in the range of 3 to 4 after 48 h. The radiolabeled antibody achieved a tumor:blood ratio of over 16 after 45 h, indicating accumulation at the desired site. However, unwanted localization also occurred in the liver and spleen, which will have to be rectified before realizing the full potential of this approach.

Radioimmunotherapy of human head and neck squamous cell carcinoma xenografts with 131I-labelled monoclonal antibody E48 IgG

Monoclonal antibody (MAb) E48 reacts with a 22 kD antigen exclusively expressed in squamous and transitional epithelia and their neoplastic counterparts. Radiolabelled with 99mTc, MAb E48 is capable of targeting metastatic and recurrent disease in patients with head and neck cancer. In this study, the capacity of 131I-labelled MAb E48 to eradicate xenografts of human squamous cell carcinoma of the head and neck (HNSCC) in nude mice was examined. Experimental groups received a single i.v. bolus injection of 400 microCi MAb E48 IgG (number of mice (n = 6, number of tumours (t) = 9) or 800 microCi MAb E48 IgG (n) = 5,t = 7), whereas control groups received either diluent (n = 3,t = 5), unlabelled MAb E48 IgG (n = 4,t = 5) or 800 microCi 131I-labelled isotype-matched control MAb (n = 6,t = 9). A 4.1-fold increase in the median tumour volume doubling time and regression of two out of ten tumours (20%) was observed in mice treated with 400 microCi. In mice treated with 800 microCi. In mice treated with 800 microCi, two out of seven tumours (29%) showed complete remission without regrowth during follow-up (greater than 3 months). Median tumour volume doubling time in the remaining five tumours was increased 7.8-fold. No antitumour effects were observed in mice injected with diluent, unlabelled MAb E48 or 131I-labelled control MAb. In the same xenograft model, chemotherapy with doxorubicin, 5-fluorouracil, cisplatin, bleomycin, methotrexate or 2',2'-difluorodeoxycytidine yielded a less profound effect on tumour volume doubling time. Increases in tumour volume doubling time with these chemotherapeutic agents were 4, 2.2, 2.1, 1.7, 0, and 2.6 respectively. Moreover, no cures were observed with any of these chemotherapeutic agents. From the tissue distribution of 800 microCi MAb E48, the absorbed cumulative radiation doses of tumour and various organs were calculated using the trapezoid integration method for the area under the curve. To tumour xenografts, 12,170 cGy was delivered, blood received 2,984 cGy, whereas in every other tissue the accumulated dose was less than 6% of the dose delivered to tumour. These data, describing the first radiolabelled MAb with therapeutic efficacy against HNSCC, suggest radioimmunotherapy with MAb E48 to be a potential therapeutic modality for the treatment of head and neck cancer.

The impact of tumor size on the efficacy of monoclonal antibody-targeted radiotherapy: studies using a nude mouse model with human renal cell carcinoma xenografts

Monoclonal antibody (Mab)-targeted radiotherapy is a unique approach in cancer therapy. Multiple factors affect the success of treatment. Internal radiation dosimetry and mini-dose Mab-targeted radiotherapy studies reveal that tumor size affects the efficacy of treatment. For tumors with calculated weight greater than 400 mg., intravenous administration of 131I-labeled A6H or A6H-C5H combination delivers significantly less tumor radiation dose (2070 +/- 580 cGy/100 microCi) than those for tumors of weight less than 200 mg. (5260 +/- 2460 cGy/100 microCi). In the mini-dose (an average of 73 to 86 microCi) Mab-targeted radiotherapy study of 109 mice with small tumors (six, 12, or 19 days after implantation), tumors 12 days after implantation (approximately 60 mg. in weight) showed regression in all mice and in 62% of mice gross tumor elimination was observed. In contrast, mini-dose therapy at day 19 (tumor weights approximately 170 mg.) resulted in tumor regression and tumor elimination rates of 33% and 17% respectively. These studies suggest that Mab-targeted radiotherapy is more suitable for treating small tumors.

Dosimetry and pharmacokinetics of monoclonal antibody A6H with human renal cell carcinoma xenografts: single dose study

Implantable miniature thermoluminescent dosimeters and conventional biodistribution analysis were used to determine the locally absorbed radiation dose delivered to three morphologically distinct human renal cell carcinoma xenografts (TK-39, TK-82 and TK-177C; N = 87) following a 50 microCi infusion of 131iodine-labeled monoclonal antibody A6H. Xenografts were clearly detected by radioimmuno-scintigraphy. Pronounced differences were noted among the three xenografts in MAb pharmacokinetics and in the locally absorbed irradiation doses which ranged from 2 to 5 cGy per injected microCi of 131iodine-labelled A6H.

The effect of antigen concentration, antibody valency and size, and tumor architecture on antibody binding in multicell spheroids

Intact IgG1 and F(ab')2 anti-carcinoembryonic antigen antibodies penetrate human colon adenocarcinoma multicell spheroids much more slowly than Fab fragments and the molecular weight and the binding site valency appear to be the most important factor in determining the rate of penetration. The rate is also influenced considerably by the number of antigen binding sites per cell, with a high antigen concentration slowing penetration appreciably. The tumor cell architecture appears to have a minor effect on antibody penetration when compared to antibody size or antigen concentration.

Study of the clinical thermoluminescent dosimeter in the direct measurement of radiation adsorbed dose for radioimmunotherapy

One of the major obstacles facing radioimmunotherapy (RIT) is the lack of a device to measure directly tumor and normal tissue radiation absorbed dose. Calculations based on the clearance and imaging scans have several limitations; hence we design and fabricate a sheathed clinical thermoluminescent dosimeter (TLD) for the measurement of absorbed dose by implantation in humans. Preclinical studies are performed in nine normal rabbits. Complete blood count, body temperature monitoring, clinical observation and necropsy show no untoward effects from the TLD. Consistent bone marrow radiation doses are noted in the four rabbits receiving 131I-labeled monoclonal antibody A6H. By using up to 20 clinical TLDs in one sheath, it will be possible to determine macroscopic heterogeneities in organs undergoing RIT.

Rationale for immunotherapy of renal cell carcinoma

Metastasis to distant organs is the principal cause of death from renal cell carcinoma (RCC). No commonly accepted therapy is available for disseminated RCC at present. Immunotherapy is a mode of therapy that either interferes with the immune system or makes use of drugs that have been derived from soluble mediators of the immune system. Several lines of evidence suggest that combinations of genetically engineered cytokines (e.g. interleukin-2 and interferon alpha) may be particularly active in the treatment of advanced RCC. There are two major rationales for considering immunotherapy for RCC: (1) there is currently no other therapy available, and (2) there is hardly any innovative approach besides immunotherapy. Still, immunotherapy is far from being a standard therapy for disseminated RCC.

Antibody targeted therapy in cancer: comparison of murine and clinical studies

Antibody targeted therapy can be effective in animal models of cancer. Treatment has been less successful in man, though some responses are reported. Understanding the distribution of antibody in man and animals shows how toxicity may be minimized and patients selected for therapy on the basis of efficient antibody localization in the tumour.

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.

Antitumor activity in mice of an immunotoxin made with anti-transferrin receptor and a recombinant form of Pseudomonas exotoxin

LysPE40 is a modified form of Pseudomonas exotoxin that lacks the cell-binding domain and has a chemically reactive lysine residue near the amino terminus. LysPE40 is made in Escherichia coli and secreted into the medium from which it is readily purified. Two immunotoxins were constructed by coupling LysPE40 to an antibody to the human transferrin receptor (TFR) or to an antibody to the human interleukin-2 receptor. These immunotoxins were selectively cytotoxic to receptor-bearing cells in tissue culture. Anti-TFR-LysPE40 given intraperitoneally to mice appeared rapidly in the blood and caused regression of A431 tumors growing as subcutaneous xenografts. These results show that it is possible to cause regression of a solid carcinoma by an immunotoxin if proper targeting can be achieved.

Antibody distribution and dosimetry in patients receiving radiolabelled antibody therapy for colorectal cancer

The distribution of iodine-131 (131I) labelled antibody to carcinoembryonic antigen (CEA) has been studied in 16 patients with colorectal cancer. Levels of tumour and normal tissue radioactivity were measured by serial gamma-camera imaging and counting of blood and urine. Maximum concentrations were found in tumour 8 h after administration and varied up to 9-fold in different patients. Higher levels were found on average in tumour than in any other tissue. Liver, lung and blood were the other tissues in which antibody was concentrated relative to the rest of the body. Antibody cleared from all these tissues over 1 week. Second antibody directed against the antitumour (first) antibody was given 24 h after first antibody in order to accelerate clearance from the blood. This increased the tumour to blood ratio but had little effect on other tissues. Cumulative radiation dose to tumour and normal tissue was estimated. In patients with the most efficient localisation the tumour to body ratio was 20:1 and tumour to blood ratio 5:1. This may be sufficient for effective therapy of cancer in patients selected for efficient antibody localisation. The data may be used to estimate the effect of different therapeutic strategies. For instance, in the time after second antibody administration the average tumour to blood ratio of radiation dose was 11:1, suggesting that two phase systems in which the therapeutic modality is given after a good tumour to normal tissue ratio is obtained may be effective for the majority of patients.