Int. J. Devl Neuroscience 19 (2001) 541–547 Medroxyprogesterone acetate alone or synergistic with chemotherapy suppresses colony formation and DNA synthesis in C6 glioma in vitro Meric A. Altinoz a, *, Ayhan Bilir a , Engin Ozar b , Funda Durmaz Onar a , Aydin Sav c a Histology and Embryology Department, Istanbul Medical School, 34390 Istanbul, Turkey b Immunology program in DETAM, Istanbul Uniersity, 34390 Istanbul, Turkey c Department of Pathology, Institute of Neurology, Marmara Uniersity, 34390 Istanbul, Turkey Received 8 May 2001; accepted 19 July 2001 Abstract We have studied the effects of medroxyprogesterone acetate (MPA) on C6 glioma growth in vitro in order to prove the hypothesis that it could arrest growth and induce drug sensitisation in a glial tumour as it does in breast cancer cells. Plating, thymidine-labelling index, ultra-structure, and soft agar colony growth were determined after incubation with MPA, and/or cisplatin, procarbazine and methotrexate (MTX). MPA (1 g/ml) reduced the thymidine-labelling index by 41 and 73% at 48 and 96 h, respectively, and decreased colony growth by 61%. Soft agar colony inhibition by MPA was almost as potent as MTX (0.3 g/ml), but the latter drug showed very high cytotoxicity. Electron microscopy revealed that in medroxyprogesterone treated cells myeloid bodies developed, but MTX treatment caused mainly necrosis. Medroxyprogesterone increased procarbazine and cisplatin-induced colony growth and S-phase inhibition, but reduced MTX-induced thymidine-labelling inhibition. In conclusion, progesterone may inhibit growth and sensitize to drugs. © 2001 ISDN. Elsevier Science Ltd. All rights reserved. Keywords: Medroxyprogesterone; Chemotherapy; Procarbazine www.elsevier.nl/locate/ijdevneu 1. Introduction Human malignant glial tumours express progesterone receptors (PR) in correlation with their grade (Assimak- oupoulou et al., 1998; Carrol et al., 1995; Khalid et al., 1997). Malignant brain tumours contain significantly lower progesterone levels than does normal brain tissue (Von Schoultz et al., 1990), and additionally decreased intracellular free retinoic acid decreases due to aberrant high expression of its receptor in acute promyelocytic leukaemia, in which exogenous retinoic acid induces differentiation and regression of disease (Chen et al., 1997; Wolff and Jurgens, 1994). We questioned, if progesterone may regress the growth of a malignant glial cell line. Thus, we deter- mined the effects of medroxyprogesterone acetate (MPA) on proliferation, colony formation, and ultra- structure of C6 glioma. We further examined interac- tions of MPA with cisplatin, methotrexate (MTX) and procarbazine, because of the reported sensitising effects of MPA on chemotherapy in breast cancer (Zibera et al., 1995). 2. Materials and methods 2.1. Cell culture and drugs C6 cells established from American Type Culture Collection (ATCC) were maintained using RPMI-1640 (Biological Industries, Haemek, Israel) with 15% heat inactivated fetal calf serum (FCS), 0.2 mM glutamine, 50 g/ml neomycin and 100 g/ml streptomycin. The Abbreiations: MPA, medroxyprogesterone acetate; PR, proges- terone receptor; MTX/MT, methotrexate; CIS, cisplatin; PC, procar- bazine; Dex, dexamethasone; TLI, thymidine labelling index. * Corresponding author. Present address: General S ¸u ¨ kru ¨ Kanath Sok, Tanja Apartment, No. 36/8 Bakirkoy, Istanbul, Turkey. Tel.: +90-212-570-7743; fax: +90-212-511-7871. E-mail address: maltinoz@hotmail.com (M.A. Altinoz). 0736-5748/01/$20 © 2001 ISDN. Elsevier Science Ltd. All rights reserved. PII:S0736-5748(01)00045-4