Pretreatment effects on the uptake/retention kinetics of L-dopa in Harding-Passey melanoma.

Malignant melanoma cells possess a unique biochemical pathway that converts L-3,4-dihydroxyphenylalanine (L-dopa) to the biopigment melanin. Selective cytotoxic incorporation of exogenous L-dopa into melanoma cells in vivo may provide a means of designing specific chemotherapeutic agents useful in the treatment of this disease. Using the Harding-Passey murine melanotic tumor model, a preferential uptake of [3H]L-dopa by the tumor was characterized. Following pretreatment of the tumor-bearing mice with nonradioactive L-dopa, a significant enhancement (p less than 0.01) of [3H]L-dopa incorporation and retention into melanoma for a period of 24 h was observed, when compared with the concomitant tissue distribution and clearance of radioactivity in the control animals. This finding suggests that by initial pretreatment of melanoma with nonradioactive L-dopa, the subsequent selective accumulation of [3H]L-dopa in tumor may provide a useful tool in testing new modalities of therapy in malignant melanoma.

Immunomodulation of murine B16 melanoma metastasis: thymosin, thymectomy and irradiation.

Thymosin, a product of the endocrine system, was used to further define the effects of immunomodulation of metastasis. Adult thymectomized C57BL/6 mice, 4 wk post-irradiation (400 R) had a decrease in the number of pulmonary metastasis (compared to controls) following tail vein injection of 5 X 10(4) B16 melanoma cells. Thymosin fraction 5 (fr. 5) administration (200 micrograms/mouse, 3 times weekly beginning 2 days post-thymectomy) returned the number of metastasis to the nonthymectomized values. Thymosin treatment of sham-operated, sham-operated irradiated, or thymectomized nonirradiated mice did not significantly elevate the number of metastases compared to the respective controls. Variant tumors which have an increase in metastasis following thymectomy and irradiation were also used. Thymosin administration reversed the effects of thymectomy in such variants, resulting in a decrease in metastasis. Metastases in thymosin-treated control mice were not significantly altered. A role for the thymus in metastasis via an endocrine product (thymosin) is suggested by these studies. Since thymosin did not increase metastasis in intact mice with tumors, further clinical trials with thymosin in cancer patients are not counterindicated by our results. These experiments confirm that thymosin fr. 5 is an important probe of the immunoendocrine events involved in tumor growth and metastasis.

Glucocorticoid receptors and the effect of glucocorticoids on the growth of B16 melanoma.

The glucocorticoid receptors were measured and characterized in the transplantable B16 murine melanoma using [3H]-dexamethasone by a charcoal adsorption technique. In the tumor cytosols assayed, the levels of receptors ranged from 44 to 200 fmol/mg protein, and the corresponding Kd's ranged from 2 to 43 nM. Sucrose density gradient analysis showed a peak sedimenting at 7.1S under low-ionic-strength buffer which was completely eliminated with a 100-fold molar excess of unlabeled triamcinolone acetonide in the incubation mixture. This peak of bound radioactivity shifted to the 4.4S region under high-ionic-strength buffer (0.4 M KCl) conditions. Competition experiments, using [3H]dexamethasone and various unlabeled steroids at a 100-fold molar excess, showed characteristics typical of glucocorticoid receptors seen in other tissues. Administration of various glucocorticoids, e.g., dexamethasone, hydrocortisone acetate, and prednisolone, in different doses and regimens showed a marked and significant inhibition of tumor growth as measured by mean tumor diameter and weight. Although glucocorticoid treatment does not seem to affect the incidence of pulmonary metastases, the number of pulmonary nodules appears to be significantly greater in some groups treated with higher doses of these drugs. In survival experiments, administration of hydrocortisone acetate in various doses and regimens also resulted in a significant increase in the median survival of mice compared to 0.9% NaCl solution-treated controls. These results indicate that the growth inhibition of B16 melanoma by glucocorticoids may be a direct effect mediated by interaction with the glucocorticoid receptor.

High incidence and characterization of glucocorticoid receptors in human malignant melanoma.

The glucocorticoid receptor was characterized in biopsy samples from patients with recurrent malignant melanoma. Glucocorticoid receptors were measured by the charcoal-adsorption technique. Tumor cytosol from approximately 86% (25/29) of the patients contained large quantities of receptors (20-324 fmol/mg protein). The dissociation constant of this cytoplasmic receptor was determined to be 2-22 nM. This binding component sedimented at 7.1S on sucrose gradients of low ionic strength and dissociated into lower molecular weight components that sedimented at 4.4S on sucrose gradients of high ionic strength. Receptor binding was specific for glucocorticoids. Although progestins competed well for the binding that is typical for glycocorticoid receptor as reported in the literature, other steroids, e.g., 17 beta-estradiol and 5 alpha-dihydrotestosterone, were only weak competitors. These results demonstrated that this neoplasm contains large quantities of glucocorticoid receptors that are similar in their physicochemical characteristics to those found in normal tissues. This finding in human melanoma biopsy specimens may be of therapeutic value in the management of patients with malignant melanoma.

Estrogen and progesterone receptors and tamoxifen in malignant melanoma.

Tumor biopsies from 68 patients with malignant melanoma were assessed for estrogen receptor (ERc) binding, and 32 of these for progesterone receptor (PRc) binding. Twenty-five patients (37%) had ERc greater than or equal to 5 fmols/mg protein; 14 patients (44%) had PRc greater than or equal to 10 fmols/mg of protein. There was no significant difference between the sexes in relation to the presence or absence of ERc or PRc. The tumor ERc and PRc levels did not predict the survival of these patients. Seventeen patients were treated with tamoxifen; three female patients had objective responses. Two of the patients with complete response had ERc levels of 4.3 and 19 fmols/mg tumor cytosol protein, while the third patient had no detectable ERc.