gms | German Medical Science

Objective: For most types of pituitary adenomas, such as primary prolactinomas or pituitary adenomas that produce growth hormone, a successful drug-based therapeutic approach has been established. In contrast, non-hormone secreting adenomas must be removed surgically, which carries its risks. Thus, there is a need to explore new treatment options. In this study we have investigated the effect of anti-proliferative anti-estrogens and the metalloprotease-disintegrin ADAM12 as a potential target for anti-invasive treatment.

Methods: To assess the effect of treatment with anti-estrogens, viability based assays (WST-1 and Cell Titer Glo®) were performed after treating TtT-GF (mouse) and GH3 (rat) pituitary adenoma cells, with anti-estrogens (bazedoxifene, clomiphene, fulvestrant and raloxifene) for up to 5 days. The mechanism of cell death induced by these drugs was further analyzed by Caspase-Glo® assays and FACS analysis. Invasion, migration and angiogenesis assays were performed after treatment with either anti-estrogens or ADAM12 knockdown. To confirm the results, human pituitary adenoma cells were isolated from primary tumor material of null-cell-adenomas via neurosphere formation assay and viability as well as invasive behaviour was determined.

Results: All anti-estrogens reduced cell viability in a dose dependent manner for TtT-GF, GH3 and primary human adenoma cells. For TtT-GF cells the semi-lethal doses were identified as 5,5 ± 2,4 µM clomiphene, 13 ± 1,9 µM raloxifene and 40 ± 1,6 µM bazedoxifene, whereas fulvestrant showed no effect at all. Compared to this, GH3 cells showed a reduced viability with an IC50 of 10 ± 3,5 µM clomiphene, 25 ± 2,6 µM raloxifene, 40 ± 3,2 µM bazedoxifene and 60 ± 2,1 nM fulvestrant . The underlying mechanism of cell death was identified as apoptosis. With regard to invasion, ADAM12 inhibition in TtT-GF cells reduced invasive behaviour of cells and led to reduced EGF/EGFR signalling.

Conclusion: Treatment of pituitary adenoma cells with anti-estrogens caused a significant reduction of cell viability by inducing apoptosis in all cells from rat, mouse and human. These results indicate the ER-α pathway as a potential therapeutic target in the treatment of pituitary adenomas. Likewise ADAM12 inhibition in pituitary adenoma cells was sufficient to block cell invasion and migration. An optimized therapy, especially for invasive adenomas, could consist of a combination of anti-estrogens and ADAM12 inhibitors.