Induction of apoptosis by a novel copper-based anticancer compound, Casiopeina II, in L1210 murine leukaemia and CH1 human ovarian carcinoma cells
Introduction
Recent developments in chemotherapy are increasingly relying on apoptosis as another powerful weapon in combating cancer. These strategies depend on agents that in addition to interfering with the cell cycle of proliferating cells also trigger the apoptotic pathway thus inhibiting the development of cancer (Benitez-Bribiesca, 1998; Kerr et al., 1994). Observations that apoptosis occurs spontaneously in malignant tumours have led to studies which confirm that many chemotherapeutic agents kill cells by apoptosis (Barge et al., 1997; Horwich, 1989; Huschtscha et al., 1995). This has led to a search for new drugs, which can specifically induce apoptosis.
Morphologically, the process of apoptosis is characterized by cellular condensation, nuclear fragmentation, and finally engulfment or phagocytosis by neighbouring cells (Green and Reed, 1998). The induction of apoptosis involves an extracellular trigger (Collins and Lopez-Rivas, 1993) (e.g. tumour necrosis factor) or an endogenous signal such as cytochrome c (Bossy-Wetzel et al., 1998). This is followed by activation of caspases (Allen et al., 1998; Green and Kroemer, 1998; Nicholson et al., 1995) and of endonucleases (Kroemer et al., 1997; Sakahira et al., 1998), which cause an organized disassembly of nuclear chromatin.
The focus on metal-based anticancer drugs originates from the development of cisplatin as one of the most successful drugs for the treatment of testicular and ovarian tumours (Fricker, 1994). This and the second generation platinum drug, carboplatin, have paved the way for screening a number of metal-based drugs for their antineoplastic activities. Drugs based on metallic compounds (gallium, germanium, tin and bismuth), early-transition metals complexes (titanium, vanadium, niobium, molybdenum and rhenium) and late-transition metal complexes (ruthenium, rhodium, iridium, platinum, copper and gold) have all shown some potential for chemotherapy (Köpf-Maier, 1994). In addition to its well characterized effects on the DNA of proliferating cells, cisplatin is now known to also kill cells by apoptosis (O'Neill et al., 1996).
In the search for new anticancer drugs the proposal that drugs based on endogenous (essential) metals may be less toxic has led to the development of copper-based drugs. This work culminated in the synthesis of a series of copper ligands, which were given the generic name casiopeinas (Ruiz-Ramirez et al., 1993, Ruiz-Ramirez et al., 1995). In this study, we report on the apoptotic effects of [Cu (4,7-dimethyl-1,10-phenanthroline)(glycine)NO3] or casiopeina II (Solans et al., 1993) on the L1210 murine leukaemia and CH1 human ovarian carcinoma cells.
Section snippets
Cytotoxic drugs
Casiopeina II was synthesized and supplied by Dr Lena Ruiz-Ramirez (UNAM, Mexico), and dissolved in 5% sterile glucose. Cisplatin was supplied by The Johnson Matthey Technology Centre and was dissolved in 0.9% sterile saline.
Cell culture
L1210 murine leukaemia and CH1 human ovarian carcinoma cell lines, cisplatin-resistant and sensitive were obtained from the CRC Centre for Cancer Therapeutics, The Institute of Cancer Research (Sutton, Surrey, UK). L1210 cells were maintained in RPMI-1640 medium with 10%
Cell morphology
Human ovarian carcinoma CH1 and murine leukaemia L1210 cells were treated with a range of doses of casiopeina II for 24 hr (Table 1). Cell death by necrosis evaluated by trypan blue exclusion (viability) and cell death by apoptosis at three concentrations of casiopeina II were assessed as nuclear condensation and fragmentation by fluorescence microscopy and are presented together in Fig. 1 for ease of comparison. Necrosis was between 10 to 20% greater than apoptosis. The apoptotic cells showed
Discussion
The induction of apoptosis by chemotherapeutic agents is now a well established mode of cell death in various cancer cell lines. Casiopeina II, a novel copper-based chemotherapeutic agent, was able to induce cell death by apoptosis in (CH1) human ovarian carcinoma cells and (L1210) murine leukaemia cells in both cisplatin sensitive and resistant cell lines.
Nuclear morphology indicates that casiopeina II triggers apoptosis, chromatin condensation and nuclear fragmentation. It should be noted
Acknowledgements
We would like to thank CONACyT-MEXICO, Grant No. 93044, for financing this study.
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