Ma. Stalteri et Sj. Mather, TC-99M LABELING OF THE ANTITUMOR ANTIBODY PR1A3 BY PHOTOACTIVATION, European journal of nuclear medicine, 23(2), 1996, pp. 178-187
Irradiation of antibody with ultraviolet light leads to reduction of d
isulphide bonds, Thus irradiation can be used to generate free thiols
prior to direct labelling of antibody with technetium-99m, and has a p
otential advantage over methods using chemical reducing agents such as
mercaptoethanol or tin, in that no purification step is needed to rem
ove excess reducing agent. We have used the photoactivation method dev
eloped by Sykes et al. to label the anti-tumour antibody PR1A3 with Tc
-99m. The antibody was irradiated at 300 nm using a Rayonet photochemi
cal reactor with eight RMR3000 lamps. In a typical experiment, the ant
ibody solution was injected into a nitrogen-filled borosilicate glass
vial and purged with nitrogen. A degassed solution containing stannous
fluoride and methylene diphosphonate was then added to the antibody a
nd the vial was irradiated, Following the irradiation, [Tc-99m]pertech
netate was injected into the vial and the reaction mixture was incubat
ed for 30 min at room temperature before being analysed by size-exclus
ion high-pressure liquid chromatography and instant thin-layer chromat
ography, Labelling yields greater than 95% were obtained using antibod
y concentrations ranging from 0.5 mg/ml to 5 mg/ml. Irradiation times
as short as 5 min and tin to antibody ratios in the range between 11 a
nd 32 mu g tin per mg antibody gave high labelling yields, Labelling y
ields greater than 95% were obtained after storage of the photoactivat
ed antibody at -70 degrees C for several weeks. The stability of the T
c-99m-labelled photoactivated PR1A3 was similar to that of Tc-99m-labe
lled mercaptoethanol-reduced PR1A3, The mean immunoreactive fraction w
as 77% for the photoactivation-labelled PR1A3, compared to 93% for PR1
A3 labelled by mercaptoethanol reduction, Biodistribution studies were
carried out using Tc-99m-photoactivation-labelled PR1A3 or PR1A3 labe
lled by mercaptoethanol reduction in Balb/c mice and in nude mice with
MKN45 human tumour xenografts. There was no significant difference in
tumour uptake between the mice that received photoactivated PR1A3 and
those that received mercaptoethanol-reduced PR1A3, There was also no
significant difference in uptake in most organs in Balb/c mice; howeve
r, the photoactivated antibody cleared more rapidly from the blood, an
d whole-body clearance was also faster for the photoactivated PR1A3, I
n conclusion, the photoactivation technique provides a very convenient
''one-pot'' method for labelling antibodies with Tc-99m.