Scintigraphic imaging of the hypoxia marker (99m)technetium-labeled 2,2'-(1,4-diaminobutane)bis(2-methyl-3-butanone) dioxime (99mTc-labeled HL-91; prognox): noninvasive detection of tumor response to the antivascular agent 5,6-dimethylxanthenone-4-acetic acid.

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) and combretastatin A4 phosphate (CA-4-P) markedly inhibit tumor blood flow in mice and are both currently in clinical trial. One of the challenges in clinical evaluation of antivascular agents is the monitoring of tumor blood flow inhibition in individual patients. This study investigates, using mouse models, whether a new marker for tissue hypoxia, (99m)technetium-labeled 2,2'-(1,4-diaminobutane)bis(2-methyl-3-butanone) dioxime (99mTc-labeled HL-91; Prognox)] has potential for the scintigraphic monitoring of tumor response to antivascular agents. Determination of radioactivity in dissected tissues 3 h after DMXAA (80 micromol/kg) or CA-4-P (227 micromol/kg) was injected indicated that both drugs inhibited blood flow (86RbCl uptake; 84 and 87%, respectively) and increased 99mTc-labeled HL-91 levels (350 and 300%, respectively) selectively in murine RIF-1 tumors. Planar imaging of 99mTc-labeled HL-91 3 h after DMXAA injection showed a dose-dependent increase in tumor levels above a threshold of 50 micromol/kg; this same threshold was observed for the inhibition of tumor blood flow (determined using Hoechst 33342). DMXAA also inhibited blood flow--and increased 99mTc-labeled HL-91 uptake--in MDAH-MCa-4 mouse mammary carcinomas and in NZMN10 human melanoma xenografts. Whether 99mTc-labeled HL-91 might also be useful as a biomarker for tumor cell killing was investigated by clonogenic assay of surviving cells 15 h after imaging 99mTc-labeled HL-91 in RIF-1 tumors. Log cell kill in individual tumors showed a statistically significant linear correlation (P < 0.001) with 99mTc-labeled HL-91 uptake after 60 micromol/kg (r2 = 0.79) and 70 micromol/kg (r2 = 0.44) but not at 80 micromol/kg DMXAA. The lack of correlation at high doses presumably reflects the insensitivity of the tumor-averaged 99mTc-labeled HL-91 signal to small regions in which tumor blood flow is preserved (which will limit log cell kill). The results indicate the potential of 99mTc-labeled HL-91 for the noninvasive imaging of tumor blood flow inhibition by antivascular drugs in humans.

A novel variant of transthyretin (prealbumin), Thr119 to Met, associated with increased thyroxine binding.

A group of patients with prealbumin associated hyperthyroxinemia possess a common single base substitution in the fourth exon of their transthyretin gene. This cytosine to thymine substitution occurs in the codon for residue 119 and results in the predicted replacement of a threonine residue with a methionine at this position. A new NcoI restriction endonuclease cleavage site is created by the point mutation and can be detected by a rapid and simple assay based on the polymerase chain reaction. This variant transthyretin is inherited in an autosomal dominant manner and is apparently not amyloidogenic but is associated with increased thyroxine binding. As healthy heterozygous individuals have normal serum thyroxine concentrations, the hyperthyroxinemia sometimes found may not be primarily due to the variant.

Detection of protein binding abnormalities in euthyroid hyperthyroxinemia.

This is a procedure for rapidly identifying the three common abnormalities in binding of thyroxin by protein. After incubation with [125I]thyroxin, serum proteins are separated by electrophoresis on agarose gel and binding of thyroxin to the various protein fractions is determined after autoradiography. Quantitatively abnormal binding to albumin or prealbumin and thyroxin autoantibodies is easily demonstrated by this technique. Normally, less than 6% is bound to albumin, and no binding by prealbumin is detected. In dysalbuminemic hyperthyroxinemia, about 30% of the serum thyroxin is bound to albumin; in prealbumin-associated hyperthyroxinemia, 7% is bound to prealbumin. With this procedure these protein-binding abnormalities can be simply identified, and it may be useful when results of a thyroxin assay are not consistent with results of a sensitive thyrotropin assay or the patient's clinical examination.

Detection of familial dysalbuminaemic hyperthyroxinaemia.

A simple test of in vitro thyroxine binding to serum proteins was used to screen serum samples from euthyroid patients with unexplained increases in the free thyroxine index. A diagnosis of familial dysalbuminaemic hyperthyroxinaemia was presumed in 14 unrelated subjects and six first degree relatives. Increased binding of thyroxine to thyroxine binding prealbumin was diagnosed in one woman with four unaffected relatives. Seven patients with familial dysalbuminaemic hyperthyroxinaemia had been treated for presumed thyrotoxicosis: two had typical Graves' disease and one subacute thyroiditis. Four other patients had been mistakenly treated with radioactive iodine or antithyroid drugs. In previously treated patients familial dysalbuminaemic hyperthyroxinaemia was suspected from the combination of a high serum thyroid stimulating hormone concentration and a normal but invalid free thyroxine index. Physicians should be cautious in accepting a diagnosis of thyrotoxicosis based mainly on a raised serum thyroxine concentration.