Effect of hematoporphyrin derivative 2 on estrogen receptors in experimental mammary tumors

This study reports the effect of hematoporphyrin derivative 2 (HPD2) on estrogen receptors (ER) in the animal model used to develop the clinical ER assay. Fifty 200‐g female Sprague‐Dawley rats were given 20 mg of dimethylbenzanthracene by gastric intubation. Spontaneous mammary tumors occurred in 35 animals. Animals were anesthetized and 50% of each tumor was removed when the tumors were 2 cm in diameter. Animals were then randomized to receive 5 mg/kg (group A), 10 mg/kg (group B), or 0 mg/kg (group C) HPD2 intravenously 48 hours after biopsy. The remaining tumor was excised 48 hours post HPD2 injection. All samples were weighed, placed on ice, and frozen to −70°C. ER assay was performed by batch run. Results (fmol/mg cytosol) were as follows: All animals (n=35) pre HPD2 34.2 ± 5.4, post HPD2 34.2 ± 5.8; group A: (n=11) pre HPD2 33.9 ± 7.9, post HPD2 37.1 ± 7.8; group B: (n=13) pre HPD2 29.2 ± 3.8, post HPD2 25.5 ± 3.6; group C: (n=11) pre HPD2 40.3 ± 5.2, post HPD2 41.5 ± 7.9. HPD2 does not affect ER in this animal model. Confirmatory studies with human tumor material must be completed.