A. van Langevelde

Aspects of 99mTechnetium binding from an ethane-1-hydroxy-1,1-diphosphonate-99mTc complex to bone

In vivo and in vitro experiments were under-taken to study factors influencing 99mTc binding from an EHDP complex to bone. In vivo 99mTc (IV) complexes of EHDP, ATP, citrate and ascorbate were injected into rats. The effects of pretreatment of rats with EHDP on EHDP- and ATP-Tc (IV) injection were examined. Citrate and ascorbate gave no bone scintigram, ATP gave a bone scintigram inferior to EHDP-Tc (IV). EHDP pretreatment deteriorated EHDP- and ATP-Tc (IV) scintigrams. Micro-autoradiography showed that Tc-activity is only found in the bone matrix of 15-day-old rats and that EHDP-pretreatment diminishes this labelling. In vitro experiments showed that EHDP also diminishes labelling of hydroxyapatite by EHDP-Tc (IV), but that an excess of Ca can augment this labelling. It is suggested that Tc (IV) binds to bone because EHDP binds to bone, permitting released Tc (IV) to bind to bone separately.

Potential radiopharmaceuticals for the detection of ocular melanoma

In order to investigate the possibility of using [1-11C] labelled 3,4-dihydroxyphenylalanine (DOPA) and tyrosine as radiopharmaceuticals for the detection of eye melanoma, the biodistributions of the same 1- and 3-14C-labelled compounds were investigated in Syrian golden hamsters with Greene melanoma. The results of these investigations were compared with positron emission tomography (PET) images of 11C labelled DOPA and tyrosine. The synthesis of these 11C labelled compounds procures of DL mixture, from which D and L forms can be separated. One h after intravenous injection, both 14C labelled DL-, L-and D-DOPA showed a high uptake in tumour tissue, that of DL- and D-DOPA being the highest. These high uptakes, together with relatively low uptake in bone, skin and eye resulted in high tumour/non tumour ratio (for DL-DOPA 5.9, 4.5 and 6.6 respectively). Extraction of the tumour tissue with trichloroacetic acid showed that L-DOPA was mainly incorporated into melanin, whereas D-DOPA was not. Also, the uptake 1 h after intravenous injection of 1-14C-L- and DL-tyrosine into the tumour were high, but L- and DL- were less different; tumour/non tumour ratios were favorable. PET images of the tumour obtained 40–80 min after injection of the [1-11C] labelled DOPA and tyrosine confirmed that melanoma detection was promising and that D-DOPA produced a better melanoma image than L-DOPA.

Potential radiopharmaceuticals for the detection of ocular melanoma. Part I. 5-iodo-2-thiouracil derivatives

The tissue distribution of a number of 5-[131I]-iodo-2-thiouracil derivatives was measured in Syrian golden hamsters with Greene melanoma. These compounds were rapidly (in less than 1 h) distributed in all tissues, while in most tissues fast elimination (T1/2 1–3 h) was observed. Because of retention of the 131I activity in the tumour, high tumour/non-tumour tissue ratios were found (e.g. tumour/eye 2.3–10, tumour/skin 1.5–3) suggesting that some of these compounds might be used as melanoma delineating agents, when labelled with 123I.

Scintimetric Detection of Choroidal Malignant Melanoma with [123I]-5-Iodo-2-Thiouracil

[123I]-5-iodo-2-thiouracil (123I-ITU) was evaluated as a radiopharmaceutical for tumor detection in 10 patients with proven choroidal melanoma. Uptake of 123I-ITU was measured with a specially designed single eye probe collimator, 24 h after administration of 123I-ITU. Increased uptake in the tumor-bearing eye as compared to the fellow nontumor bearing eye was found in 7 out of 10 cases when the probe was located 3.5 cm in front of the eye (p less than 0.01). By using a double pinhole collimator tests were positive in 3 out of 10 123I-ITU studies only. Tests with 123I-ITU were compared with 67Ga tests in the same patients. The 67Ga tests with the single eye probe collimator were positive in 6 out 10 cases when the probe was located 6 cm in front of the eye. With the double pinhole collimator tests were positive in 7 out of 10 67Ga studies. It is concluded that 123I-labeled thiouracil is at least as useful as a radiopharmaceutical for ocular melanoma diagnosis as 67Ga-citrate, provided measurements are performed with a single eye probe.

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.

A patient study with radioiodine labelled 5-iodo-2-thiouracil

In the sequence of our studies on radiopharmaceuticals for melanoma detection, the results were most promising for a possible use of 5-iodo-2-thiouracil (ITU) as a radiopharmaceutical for diagnosis and therapy (Van Langevelde et al. 1983, 1986a, 1988). Experiments with animal models have shown that thiouracils are false precursors of melanin and can be incorporated as such with high affinity into melanin synthesizing melanomas implanted in hamsters or mice (Whittaker 1971). The use of iodothiouracil, labelled with a radioactive iodine isotope, as a tumour seeking radiopharmaceutical was first suggested by Larsson et al. (1982). The distribution of several radioiodine labelled thiouracil derivatives after i.v. injection in hamsters with a Greene melanoma was investigated and optimal results were obtained with ITU (Van Langevelde 1983), when the hamsters were pretreated with NaI (4 mg per animal). NaI not only inhibited the radioactive iodide uptake in the thyroid, but in addition enhanced the tumour uptake of ITU. Tumour/blood and tumour/muscle ratios of 2.7 and 2.4 respectively were found 24 h after i.v. injection. The mean uptake percentage of 0.7% dose per g organ in tumour was only exceeded by uptake in kidneys, liver and intestines. Coderre et al. (1986) also investigated the distribution of ITU in hamsters and mice. They found higher uptake in tumour and lower uptake in blood, liver and kidney and as a consequence higher ratios than we did. They also suggested the use of ITU as a radiopharmaceutical for diagnosis and therapy of melanoma. Van Langevelde et al. (1986b) could show that an analogue of e-MSH, a hormone known to stimulate melanogenesis, sugmented the incorporation of ITU into the melanin of the hamster melanoma by 85%. To accomplish the increase this analogue, 4-norleucine, 7-D-phenylalanine~-MSH, had to be administered by osmotic pump for 30 h at I lig/h. Though the analogue did diminish the growth rate of melanoma cells in culture, there was no influence on the hamster tumour growth. Cytarabine is not very effective in halting melanoma growth in the hamster, but pretreatment of the hamster with cytarabine (5 mg/100 g per day s.c.) for 4 days prior to ITU injection increased the ITU uptake in melanoma by 75%. The cytarabine dose needed only temporarily reduced the tumour growth rate (Van der Plas et al. 1986). ITU is used therapeutically as a thyroid inhibitor and its properties, when used in humans, are known.

Iodine Labelled 5-Iodo-2-Thiouracil as a Melanoma Seeking Agent: A Potential Drug for Diagnosis and Treatment

Adequate treatment of malignant melanoma places medical science before a difficult problem. Disseminated melanomas have poor prognoses. Moreover malignant melanomas are known to be radioresistant to a high degree. Recent investigations, however, cast doubt on this notorious reputation (1). It has been proposed that a high radiation dose per fraction, rather than total dose, may be a critical factor in the treatment of melanomas by means of irradiation (2,3).

Uptake of 123I-5-iodo-2-thiouracil, a possible radiopharmaceutical for noninvasive detection of ocular melanoma, in melanotic and amelanotic melanomas in hamsters

The uptake of 123I-5-iodo-2-thiouracil in melanotic and amelanotic melanoma implanted in Syrian golden hamsters was studied. A selective accumulation was found in the tumours. Uptake of 123ITU in melanotic melanomas was 4 to 5 times the uptake in amelanotic ones. For both tumours high ratios of tumour versus non-tumour were found. The high accumulation of 123ITU in both kinds of tumours and the high tumour versus non-tumour ratios suggest that 123ITU may be a promising radiopharmaceutical for the detection of ocular melanoma.

Reduced Tumor Progression In Vivo by an Inhibitor of Poly(ADP-Ribose) Synthetase (3-Aminobenzamide) in Combination with X-Rays or the Cytostatic Drug DTIC

Poly(ADP-ribose) synthetase activity is strongly stimulated by DNA strand breaks (1–3). Both ionizing radiations and monofunctional alkylating agents increase the activity of poly(ADP-ribose) synthetase with a concomitant (transient) decrease in cellular NAD content (4). The involvement of poly(ADP-ribose) synthetase in DNA damage and/or repair is supported by the observation that inhibitors of this enzyme have been found to retard DNA strand rejoining and potentiate the biological effects (e.g., cell killing, chromosomal alterations) of X-rays and chemical mutagenic carcinogens in vitro (5–11) and in vivo (10, 12). In view of the ability of inhibitors of poly(ADP-ribose) synthetase to increase cell killing without enhancing the mutagenic effect of alkylating agents (9, 13), the utility of these inhibitors for improvement of chemotherapy of tumor cells has been investigated in vitro and in vivo. They were found to increase the antitumor activity of N-methyl-N-nitrosourea (14) and bleomycin (10,15). Differential radiosensitization of human tumor cells by 3-aminobenzamide (3AB) in vitro correlates well with the clinical radiocurability of tumors in vivo (16).