Preparation and preclinical evaluation of humanised A33 immunoconjugates for radioimmunotherapy

Abstract

Summary A humanised IgGl/k version of A33 (hA33) has been constructed and expressed with yields up to 700 mg 1' in mouse myeloma NS0 cells in suspension culture. The equilibrium dissociation constant of hA33 (KD= 1.3 al., 1990, 1994). A phase I/II study has been conducted (Welt et al., 1994) with this murine antibody, in which some tumour responses were observed at the maximum tolerated dose (75 mCi m-2). The major limiting toxicity was haematological, as observed in almost all therapy studies with radioimmunoconjugates. All patients treated developed a human anti-mouse antibody (HAMA) response after one administration, and this led to very rapid clearance of the conjugate upon retreatment, consistent with all previous results with rodent antibodies. These data suggest that A33 is a promising antibody for successful radioimmunotherapy of colon cancer, and the purpose of this study has been to design and develop a second generation reagent based upon it. The key to the development of successful radioimmunotherapy will be the identification of reagents capable of delivering a killing dose to tumour cells without unacceptable toxicity to normal tissues. To this end we are evaluating several alternative radioimmunotherapeutic strategies including the use of isotopes which require internalisation into the cell for cytotoxicity, such as 125I (which are less toxic to normal tissues), and engineering the antibody for the optimal delivery of highly cytotoxic agents such as 90Y.The radioisotope 9'Y has been used in several radioimmunotherapy studies and is an attractive isotope for this purpose owing to its appropriate physical properties. As a pure high-energy P-emitter 9Y has advantages over the more

Targeted Chemoradiation in Metastatic Colorectal Cancer: A Phase I Trial of 131I-huA33 with Concurrent Capecitabine

“…It is also expressed on normal colonic epithelial cells but no other normal tissues (6). The humanized IgG1 antibody huA33 has high affinity for its target antigen (9), is internalized on binding, and is safe and tolerable when given to patients alone (10,11), in combination with chemotherapy (12), and when radiolabeled (13). 131 I-huA33 can cause targeted delivery of radiation to colon cancer cells and is retained in the tumor for 6 wk (13).…”

A Phase I Trial of Humanized Monoclonal Antibody A33 in Patients with Colorectal Carcinoma: Biodistribution, Pharmacokinetics, and Quantitative Tumor Uptake

“…In view of the long retention time of mAb A33 in tumors, high tumor uptake, and minimal gut toxicity observed in these trials, a humanized version of mAb A33 was constructed to enable repeated dosing without immunogenicity (21). Two phase I trials with huA33 have been conducted, with huA33 alone and huA33 with chemotherapy in patients with colorectal carcinoma (22,23).…”

Preparation, characterisation and tumour targeting of cross-linked divalent and trivalent anti-tumour Fab' fragments

“…We have been evaluating alternative reagents comprising multivalent Fab's produced by chemical cross-linking. Chemically cross-linked di-Fab (DFM) and tri-Fab (TFM) have been prepared from the mouse-human chimeric Fab' fragment of B72.3 (King et al, 1994) and an engineered human form of the antibody (King et al, 1995). Biodistribution studies with these antibodies have revealed higher tumour accumulation than seen with scFvs, although clearance from the blood is still rapid.…”