Original article 2-Acetylpyridine thiosemicarbazones: Cytotoxic activity in nanomolar doses against malignant gliomas Josane A. Lessa a , Isolda C. Mendes a , Paulo R.O. da Silva b , Marcella A. Soares b , Raquel G. dos Santos b , Nivaldo L. Speziali c , Nelilma C. Romeiro d, e , Eliezer J. Barreiro d , Heloisa Beraldo a, * a Departamento de Química, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG, Brazil b Centro de Desenvolvimento da Tecnologia Nuclear, CDTN, 31270-901, Belo Horizonte, MG, Brazil c Departamento de Física, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte, MG, Brazil d LASSBiodLaboratório de Avaliação e Síntese de Substâncias Bioativas, Faculdade de Farmácia, Universidade Federal do Rio de Janeiro, PO Box 68023, 21941-902 Rio de Janeiro, RJ, Brazil e LICC-NUPEM-UFRJdLaboratório Integrado de Computação Científica, Núcleo em Ecologia e Desenvolvimento Sócio-ambiental de Macaé, Universidade Federal do Rio de Janeiro, 27901-000 Macaé, Rio de Janeiro, RJ, Brazil article info Article history: Received 27 July 2010 Received in revised form 31 August 2010 Accepted 8 September 2010 Available online 17 September 2010 Keywords: 2-Acetylpyridine thiosemicarbazones Glioma Cytotoxicity abstract 2-Acetylpyridine N(4)-phenyl thiosemicarbazone (H2Ac4Ph), and its N(4)-ortho-tolyl (H2Ac4oT), N(4)- meta-tolyl (H2Ac4mT), N(4)-para-tolyl (H2Ac4pT), N(4)-ortho-chlorophenyl (H2Ac4oClPh), N(4)-meta- chlorophenyl (H2Ac4mClPh) and N(4)-para-chlorophenyl (H2Ac4pClPh) derivatives were assayed for their cytotoxicity against RT2 (expressing p53 protein) and against T98 (expressing mutant p53 protein) glioma cells. The compounds were highly cytotoxic against RT2 (IC 50 ¼ 24e1.4 nM) and T98 cells (IC 50 ¼ 50e1.0 nM). IC 50 for cisplatin ¼ 5 (RT2) and 17 mM (T98). The thiosemicarbazones presented haemolytic activity with IC 50 > 10 3 M, indicating a very good therapeutic index. SAR studies suggested that stereo properties are critical to define the potential activity of the studied compounds against the RT2 cell line, while electronic properties seem to be important for interaction with the biological target in T98 cells. Ó 2010 Elsevier Masson SAS. All rights reserved. 1. Introduction Thiosemicarbazones constitute an interesting class of compounds with wide pharmacological versatility [1]. a(N)-heterocyclic thio- semicarbazones and their metal complexes have been extensively investigated as potential anticancer agents [2]. This search for an effective anticancer agent led to the onset of clinical studies of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP; Tri- apine Ò , Vion Pharmaceuticals Inc, New Haven, CT) [3,4]. It has been demonstrated that the mechanism of action of a(N)- heterocyclic thiosemicarbazones involves inhibition of ribonucle- oside diphosphate reductase (RDR), a rate-limiting enzyme in DNA syntheses, which catalyzes the conversion of ribonucleotides into desoxiribonucleotides [2e5]. It has been suggested that thio- semicarbazones may act by various mechanisms to inhibit RDR activity [6]. The cytotoxic activity of thiosemicarbazones and their metal complexes against a variety of human solid tumor cell lines as well as against leukemia has been demonstrated by other authors [7e11] and by our group [12e16]. We recently demonstrated that 2-pyr- idineformamide thiosemicarbazones and their gallium(III) and tin (IV) complexes present cytotoxicity against malignant glioma [17,18]. In the present work 2-acetylpyridine N(4)-phenyl thio- semicarbazone (H2Ac4Ph) and its N(4)-ortho-tolyl (H2Ac4oT), N (4)-meta-tolyl (H2Ac4mT), N(4)-para-tolyl (H2Ac4pT), N(4)-ortho- chlorophenyl (H2Ac4oClPh), N(4)-meta-chlorophenyl (H2Ac4mClPh) and N(4)-para-chlorophenyl (H2Ac4pClPh) derivatives (Fig. 1) were assayed for their cytotoxic activity against malignant glioma cells. Malignant gliomas frequently have abnormalities in p53 protein expression or function. We used two glioma cell lines exhibiting different p53 status: the rat glioma RT2 cells, which express wild- type p53 and human glioma T98 cells, expressing mutant p53. Structureeactivity relationships (SAR) were investigated. 2. Results and discussion 2.1. Characterization of the thiosemicarbazones The thiosemicarbazones were prepared as described in the literature [19]. Microanalyses and NMR data are compatible with the * Corresponding author. Tel.: þ55 31 3499 5740; fax: þ55 31 3499 5700. E-mail address: hberaldo@ufmg.br (H. Beraldo). Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech 0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmech.2010.09.021 European Journal of Medicinal Chemistry 45 (2010) 5671e5677