Synthesis of 123I-4-(3-dimethylaminopropylamino)-7-iodoquinoline

Binding of [3H]flunitrazepam and [3H]spiperone to melanoma cell membrane preparations

Binding of [3H]flunitrazepam and [3H]spiperone to membrane preparations isolated by high speed centrifugation of hamster, rabbit and human melanoma cell homogenates was analyzed. All melanoma cell types expressed a high density of specific binding sites for [3H]flunitrazepam (3-4 pmol/mg protein) with a high affinity (Kd about 30 nM). This binding was independent of melanin content of cells and could be classified, based on competition experiments, as a Ro 5-4864-like binding type. Specific [3H]spiperone binding to these cell lines clearly revealed at least two types of binding sites: a low affinity, high capacity type of binding site (Kd greater than 100 nM, Bmax about 50 pmol/mg protein) and a high affinity, low capacity binding site (Kd less than 1 nm, Bmax 30 fmol/mg protein). Binding of spiperone to the low affinity, high capacity site appeared displaceable by NM 113 and dependent on melanin content of the cells and probably represents binding to melanin. Analysis of drug binding to melanoma membrane cell preparations and correlation with drug effects should include the possible involvement of binding to melanin.

Melanoma affine radiopharmaceuticals I. A comparative study of 131I-labeled quinoline and tyrosine derivatives

We compared two melanoma-specific radioiodine labeled compounds 4-(3-dimethylaminopropylamino)-7-iodoquinoline (I) and L-3-iodo-alpha-methyltyrosine (IV) using three hamster groups. Two groups consisted of hamsters with subcutaneous or subscleral melanotic melanoma, and the third had healthy animals as controls. For the chosen tumor model and in comparison with the quinoline derivative (I), the tyrosine derivative (IV) proved to have some better properties as a melanoma-specific radio-pharmaceutical. This result holds for the first 24 h after administration, thus recommending (IV) for the 123I label. While in that time period (I) did not sufficiently accumulate in the melanoma to compete with the high background activities, especially in the abdominal organs, (IV) had its highest tumor concentration 1 h after administration. The derivative (IV) cleared more slowly from the tumor tissue than from the other organs thus increasing the tumor-to-organ ratio. There was no obvious difference in the biodistribution of (I) and (IV) in relation to the site of the melanoma growth, i.e. eyes and skin. Generally, all three groups of hamsters exhibited similar accumulation and clearance characteristics for each radiopharmaceutical. In contrast to (I), which took part in the formation of the biopolymer melanin, (IV) acted as a reversible inhibitor of the enzyme tyrosine hydroxylase. The affinity to the tyrosine hydroxylase and not the function as a melanin precursor lead to an accumulation of (IV) in the melanoma tissue.