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Objective: To investigate the clinical application of an 111In-labelled anti-MUC1 mucin monoclonal antibody (mAb) imaging for staging invasive bladder cancer., Patients and Methods: Indirect immunohistochemistry was used to confirm the expression of the MUC1 target antigen by metastatic tumours. Twelve patients with bladder cancer (two with superficial and 10 with locally invasive/metastatic disease) underwent planar gamma-scintigraphy 48 h after an intravenous injection with 111In-labelled anti-MUC1 mucin mAb C595., Results: No bladder uptake was detected in the two patients with superficial disease, but scintigraphy showed primary and recurrent bladder tumours and metastases in nine of the remaining 10 patients with invasive disease. In three patients additional staging information was obtained from the mAb imaging which would have altered patient management. There were no reported side-effects., Conclusion: This study confirmed the ability of the mAb technique to detect both primary and recurrent invasive bladder tumours and distant metastases. Some lesions shown by mAb imaging were not detected by other methods. The use of mAb imaging has the potential to improve clinical staging and assist in selecting those patients most likely to benefit from radical therapy.

Objective: To evaluate serum MUC1 levels (a high molecular weight glycoprotein which is upregulated and abnormally glycosylated in bladder cancer and other carcinomas) in patients with a variety of stages and grades of transitional cell carcinoma (TCC) of the bladder, to assess its potential as a tumour marker., Patients and Methods: Blood samples were taken before treatment in 87 patients with TCC of the bladder and in 31 controls undergoing cystoscopy for benign conditions. Serum MUC1 levels were estimated with an enzyme-linked immunosorbent assay using the C595 monoclonal antibody., Results: Of patients with T4 tumours, 47% had MUC1 levels above the normal range (P<0.001); patients with T3 tumours also had significantly higher MUC1 levels than controls. The overall sensitivity was only 24% for all tumours when the upper limit of normal was defined as 4.8 U/mL; the specificity was 97%., Conclusion: Serum MUC1 is not as useful tumour marker for screening, as it has a low sensitivity. However, MUC1 levels are high in advanced disease and serum MUC1 levels may be useful for disease monitoring.

A recombinant diabody fragment based on the anti-MUC1 monoclonal antibody, C595 has been produced in a bacterial expression system. Substitution of a 7-amino-acid linker sequence (Gly6Ser) for the original single-chain (sc)Fv 15-amino-acid linker (Gly4-Ser)3, using polymerase-chain-reaction-based strategies, forces variable heavy (V(H)) and light (V(L)) domains to pair with complementary domains on neighbouring scFv molecules, forming a scFv dimer (diabody). This recombinant protein shows similar binding characteristics to the parental C595 monoclonal antibody. The ability to bind to MUC1 mucin on carcinoma cell surfaces will allow its potential as a diagnostic and therapeutic reagent of clinical utility to be investigated.

Transitional cell carcinoma of the bladder is the fifth commonest cause of death from cancer in men in the United Kingdom. Most patients present early with superficial disease, though with current treatment up to 20% progress to invasive disease, which has a poor prognosis. Better local treatments are required to limit this tumour progression. The ease of access to the bladder via a catheter provides the ideal opportunity for antibody (Ab) targeted therapy. We have previously shown that indium-111 labelled anti-MUC1 mucin Ab C595 selectively localises to bladder tumours after intravesical administration. We have selected copper-67 as an alternative radiolabel with suitable physical characteristics for radioimmunotherapy. This communication demonstrates that C595 can be reproducibly labelled with 67Cu and that the radioimmunoconjugate is both stable and maintains high immunoreactivity. Pilot studies on cystectomy specimens in a novel ex vivo system and in one patient confirmed the ability of this conjugate to localise to tumour after intravesical administration. On the basis of these studies we are now in a position to study the intravesical administration of 67Cu-labelled C595 in patients with bladder cancer with a view to a therapeutic trial.

Recombinant single-chain fragments (scFv) of the murine anti-MUC1 monoclonal antibody C595 have been produced using the original hybridoma cells as a source of variable heavy (V(H))- and variable light (V(L))-chain-encoding antibody genes. The use of the polymerase chain reaction (PCR), bacteriophage (phage) display technology and gene expression systems in E. coli has led to the production of soluble C595 scFv. The scFv has been purified from the bacterial supernatant by peptide epitope affinity chromatography, leading to the recovery of immunoreactive C595 scFv, which was similar in activity to the C595 parent antibody. Analysis by DNA sequencing, SDS-PAGE and Western blotting has demonstrated the integrity of the scFv, while ELISA, FACScan analysis, fluorescence quenching, quantitative immunoreactivity experiments and immunohistochemistry confirm that the activity of the scFv compares favourably with that of the parent antibody. The retention of binding activity to MUC1 antigen on human bladder and breast carcinoma tissue specimens illustrates the potential application of this novel product as an immunodiagnostic and immunotherapeutic reagent.