The uptake and in vivo quantitation of monoclonal antibodies (MAbs) has been measured non-invasively using positron emission tomography (PET) and 124iodine in 9 patients with breast ductal carcinoma. Blood-flow measurements were also made using 15oxygen-labelled water and PET to evaluate antibody delivery; 7 patients were studied with HMFGI antibody and 2 patients with a non-specific antibody. Tumour uptake ranged from 2-7.7 x 10(-3)% of injected dose per gram of tissue. Values for normal tissues including liver, lung and bone were also obtained. In 2 out of 7 patients studied with the specific antibody, uptake was greater than that seen with the non-specific antibody. There was no correlation between antibody uptake and blood flow. This report exemplifies the potential of PET for the non-invasive and accurate quantitative assessment of targeted antibody which is a prerequisite to therapy.

The pharmacokinetics of intraperitoneal (i.p.) radiolabelled monoclonal antibody (MAb) was studied in 35 patients receiving 40 i.p. injections. Eleven patients received 131I‐labelled MAb, 24 received 90Y‐labelled MAb, and 5 patients received a second 131I MAb treatment after having developed human anti‐mouse antibodies (HAMA). All patients had blood and urine isotope activity monitored for 5 days after MAb injection. The radiation dose to bone marrow from the vascular compartment in the marrow was calculated by applying the MIRD formula to the measured blood activity. In HAMA negative patients, peak blood isotope activity was observed at 40 hr post injection with a mean of 26% and 21% of the injected 131I and 90Y activity respectively. Sixty‐five percent of the injected 131I activity, but only 12% of the administered 90Y, was excreted in the urine. Myelosuppression limited the administered 131I and 90Y activities to below 160 and 20 mCi respectively. In patients receiving 131I labelled MAbs, the marrow is irradiated by MAb within its circulation, producing myelosuppression that can be predicted by applying the MIRD formula to the blood isotope activity. This is not true for 90Y‐labelled MAbs, where bone absorption of yttrium (which cannot be measured in patients) is the dominant radiation source for bone‐marrow irradiation. Patients with HAMA present clear 131 MAb rapidly with a decreased radiation dose to marrow and reduced myelosuppression. Giving patients intravenous antimouse immunoglobulin to clear 131I‐labelled MAb absorbed from the peritoneal cavity could decrease the toxicity observed in these patients. Patients receiving 90Y DTPA‐chelated MAbs are unlikely to benefit, as catabolized yttrium is not excreted, and is concentrated in liver, spleen and bone. On the other hand, the use of i.v. chelating agents such as EDTA may scavenge non‐protein‐bound (90Y with increased excretion in the urine and less myelosuppression.

Indium-III-hydroxyquinoline labelled platelets, though useful in the detection ofthrombus, have not gained widespread use owing to the time and technical skill required for their preparation. A study was therefore conducted evaluating a new method of imaging thrombus with platelets radiolabelled with a "'In labelled monoclonal antibody, P256, directed to the platelet surface glycoprotein complex IIb/IIIa. When the number of receptors occupied by P256 was less than 3% of the total available on the platelet surface platelet function, as assessed by platelet aggregometry, was undisturbed. P256 was radiolabelled with "'In using diethylenetriaminepenta-acetic acid, which achieved a specific activity of 185 MBq (5 mCi)/mg. No impairment of immunoreactivity was detected at this specific activity. Platelets were labelled with radiolabelled monoclonal antibody in vitro in two patients at a receptor occupancy of 6% and in vivo-that is, by direct intravenous injection of P256-in six patients at a receptor occupancy of 1%. In vivo recovery and biodistribution kinetics suggested that after in vitro labelling platelets were minimally activated. The "'In kinetics recorded after intravenous P256 suggested rapid and efficient radiolabelling of platelets and gave no indication of platelet activation. Of the six patients who received intravenous P256, three had documented thrombus, two

Summary In recent years, radiolabelled monoclonal antibodies have been evaluated for their use in the diagnosis and treatment of neoplastic disease. One isotope which has not been assessed for antibody targeting iS 32P, even though it has many favourable radiobiological characteristics and has been used clinically for the treatment of certain neoplastic disorders such as polycythaemia rubra vera. The main drawback so far in using 32P has been the absence of a general method for phosphorylating antibodies. We have now developed a novel process for the phosphorylation of immunoglobulins which is rapid, efficient and allows high specific activities to be achieved (>l10Ciyg-1). The Recently, however, a novel method for the covalent coupling of the strong chelating group diethylenetriaminepentaacetic acid (DTPA) to antibodies has been developed (Hnatowich et al., 1983a; Scheinberg et al., 1982;Paxton et al., 1985) which allows antibodies to be labelled with metallic radionuclides such as "'1In (Hnatowich et al., 1983a, b; Scheinberg et al., 1982;Paxton et al., 1985) and 99mTC (Lanteigne & Hnatowich, 1984).More recently another metallic radionuclide, 90Y, has been used to label DTPA-linked antibodies (Hnatowich et al., 1985) and promising radioimmunotherapeutic results have been reported (Order et al., 1986). This isotope is of considerable interest because of its pure f-ray particle emission, high emission energy, half-life and stable daughter products. However the use of 90Y does have disadvantages requiring the availability of a 90Sr-90Y generator and, in common with other chelated metallic radionuclides, there is a loss of 90Y from the antibody and large uptake by liver, kidneys, bone and bone marrow (Hnatowich et al., 1985).Another isotope with many of the ideal propeties of 90Y is 32p. Though having a longer half-life (14 days) than 90Y, this isotope has been used clinically in cancer therapy for many years (Today's drugs, 1967;Boye et al., 1984 advantageous for attacking tumours with low vascularity. Until now there has been no simple method for conjugating 32p to antibodies. In this communication we describe a simple, rapid procedure for phosphorylating antibodies which allows high specific activities to be achieved without any significant impairment of antibody function. Kemptide (Kemp et al., 1976), a heptapeptide substrate (Leu. Arg. Arg. Ala. Ser. Leu. Gly) for the cAMP-dependent protein kinase, is first covalently linked to the antibody and then phosphorylated with 32P-y-ATP and protein kinase. The antibody 32P-Kemptide conjugates show no impairment of antibody function, are stable in serum, and have a slow rate of clearance in mice (t,,2=2 days). Materials and methods ReagentsMonoclonal antibody secreting hybridomas were kindly provided by the following: OX7, Dr A

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