ACCUMULATION OF TC-99M-LOW-DENSITY LIPOPROTEIN IN HUMAN-MALIGNANT GLIOMA

Low-density lipoprotein (LDL) uptake in gliomas was studied to find ou t if LDL has potential as a drug carrier of boron, especially for boro n neutron capture therapy. Single photon emission tomography (SPET) wa s performed 2 h and 20 h after intravenous injection of autologous Tc- 99m-labelled LDL in four patients with untreated and five patients wit h recurrent glioma. Tc-99m-LDL uptake was compared with the uptake of Tc-99m-labelled human serum albumin (HSA), an established blood pool m arker. The intra- and peritumoral distributions of radioactivity in th e SPET images were not identical for radiolabelled LDL and HSA. The me an LDL tumour to brain ratio, determined from transversal SPET slices at 20 h post injection, was 1.5 in untreated and 2.2 in recurrent glio mas; the corresponding ratios for HSA were 1.6 and 3.4. The brain to b lood ratio remained constant at 2 h and 20 h in both types of tumours. These data are not consistent with highly selective, homogeneous upta ke of LDL in gliomas. However, the different tumoral distribution and rate of uptake of Tc-99m-LDL, as compared with Tc-99m-HSA, indicate th at the uptake of LDL is different from that of HSA and that further st udies on the mechanism of LDL uptake in glioma are warranted.