INVERSE CORRELATION OF CELL-PROLIFERATION AND EXPRESSION OF PROGESTERONE RECEPTORS IN TUMOR SPHEROIDS AND MONOLAYER-CULTURES OF HUMAN MENINGIOMAS

OBJECTIVE: The progesterone receptor (PgR) can be detected in 60 to 70 % of meningiomas using immunohistochemistry in situ. Whereas in monola yer tissue cultures the PgR is only rarely expressed, we were able rec ently to demonstrate the preservation of the PgR in fragment spheroid cultures of meningiomas. The aim of the present study was to evaluate the stability of PgR expression in meningioma spheroids in vitro and t he correlation of PgR expression and cell proliferation in spheroids a nd whether meningioma cells reaggregated to spheroids from monolayer c ultures to reexpress the PgR again. METHODS: Tumor fragment spheroids (Weeks 1-6) and cell monolayers (Passages 1 and 3) of 55 PgR-positive meningiomas were investigated by immunohistochemistry for the expressi on of PgRs and their proliferative activity, as demonstrated by positi vity for the proliferation-related antigen Ki-67. To study PgR reexpre ssion in reaggregated spheroids, Northern blots were performed. In add ition, a reverse transcriptase-polymerase chain reaction technique was established and evaluated in combination with immunohistochemistry. G rowth of meningioma spheroids was quantified in the presence of proges terone and the specific antagonist onapristone. RESULTS: The PgR remai ned stable in sphere ids for 6 weeks in 9 of 13 cases that were able t o be evaluated. All tumor fragment spheroids exhibited a proliferation index of 5 to 40% Ki-67-positive cells. Monolayer cell cultures, on t he other hand, failed to express PgRs but revealed higher proliferatio n indices (40-90%) to a significant extent. The detection of PgR messe nger ribonucleic acid in reaggregated spheroids by means of reverse tr anscriptase-polymerase chain reaction correlated to the nuclear expres sion of PgR in immunohistochemistry. Neither progesterone nor its anta gonist onapristone altered spheroid growth in vitro. CONCLUSION: The e xpression of the PgR in meningiomas is preserved in spheroid cultures with low proliferation indices for at least 6 weeks, whereas monolayer cell cultures with a high proliferative activity lack PgR expression. The inverse pattern of Ki-67-positive cells in the outer regions of t he spheroids and PgR-expressing tumor cells in the spheroid centers le ads us to the conclusion that proliferating meningioma tumor cells do not express PgRs. This might also explain why tumor cell growth in vit ro was neither affected by progesterone nor by onapristone. Monolayer cell cultures can be reaggregated to spheroids, the consequence being a reexpression of PgRs and, therefore, a down-regulation of proliferat ion.