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used for radiolabelling polymer conjugates . Labelling with radioiodine involves either the direct oxidative incorporation of the iodine atom into tyrosine amino acids using chloramine-T or iodogen, or the indirect attachment of chemical groups such as Boulton and Hunter reagent. The radionuclides l23I or 13II can be used for imaging with the gamma camera whereas 124I may be used for PET imaging. Radiolabelling with metals such as "'in and WmTc is usually achieved by the pre-conjugation of a chelating agent such as the bicyclic anhydride of DTPA.

Using the gamma camera, scintigraphic imaging in normal and tumour-bearing experimental models has provided information on the tumour targeting properties of polymer conjugates. Such studies have been extremely valuable in the development and understanding of the tumour targeting and biodistribution of polymeric materials prior to clinical therapeutic trails. A pioneering example of the use of imaging in the clinical development of polymeric drug carriers can be seen in the studies undertaken with the HPMA-doxorubicin copolymer conjugates. These conjugates were initially radiolabeled with l31I and subsequently with 123I by Pimm et al11'14'15. The choice of radionuclide will affect the quality of the images obtained, with being preferable to since its lower gamma energy provides superior image resolution when using the gamma camera. These studies not only demonstrated that it was feasible to radiolabel and image copolymer conjugates, but that it was possible to demonstrate tumour uptake by imaging mice with transplanted tumours. Furthermore specific targeting to the liver was achieved by the addition of galactosamine.

Using the same methodology these radiolabelled conjugates were then used clinically in Phase I studies. Julian et. al.16 used whole body imaging

X-Ray i23I-PK4 SPECT

X-Ray i23I-PK4 SPECT

Figure 1. Images of a patient with hepatoma taken from the Birmingham clinical studies, courtesy of P J Julyan16. Top left: X-ray CT image through the upper abdomen. Top right: SPECT image of mI-HPMA-doxorubicin-galactosamine conjugate taken at the same level as the CT image. Bottom: Fused anatomical and functional images.

Figure 1. Images of a patient with hepatoma taken from the Birmingham clinical studies, courtesy of P J Julyan16. Top left: X-ray CT image through the upper abdomen. Top right: SPECT image of mI-HPMA-doxorubicin-galactosamine conjugate taken at the same level as the CT image. Bottom: Fused anatomical and functional images.

and single photon emission tomography (SPECT imaging) to show invivo biodistribution in patients with malignant disease. An example of targeting

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