Intracellular localization of titanium within xenografted sensitive human tumors after treatment with the antitumor agent titanocene dichloride

Abstract

In the present study, the intracellular localization of titanium was analyzed in three xenografted human adenocarcinomas of the colon sigmoideum (S 90), the stomach (M-Stg 4), and the lung (L 261) in dependence on the time after application of a single therapeutic dose (80 mg/kg) of the organometallic antitumor agent titanocene dichloride (C5H5)2TiCl2. The investigations were performed by use of electron energy loss spectroscopy (EELS), a method which allows microanalysis in ultrathin sections, in combination with electron spectroscopic imaging (ESI), which offers the possibility to image the two-dimensional localization and distribution of light- and medium-weight elements in animal tissues. In all three tumors which were studied, titanium was at first detected within the nucleus and, some hours and days later, it was additionally found in cytoplasmic lysosomes. In the colon and lung tumors S 90 and L 261, already 12 hr after treatment, titanium was traceable as tender granules in the nuclear chromatin. During the following days, it was then accumulated in certain areas of the nuclear heterochromatin and, in the case of the L 261 tumor, also in the nucleolus. Maximum concentrations were attained in the nuclei and nucleoli at 48 hr after substance application. Thereafter, titanium was increasingly incorporated into cytoplasmic lysosomes which are known to be involved in intracellular degrading and digesting processes and which occurred in increased numbers in treated tumor cells. Regarding the stomach carcinoma M-Stg 4, titanium was recognized in the nuclear heterochromatin only 1 and 2 days after application of titanocene dichloride. At 48 hr, it was additionally detected in cytoplasmic lysosomes. In all cases where titanium was found accumulated in the nucleus and in lysosomes, phosphorus was simultaneously enriched in a similar local distribution and a concentration which even exceeded that within phosphorus-rich areas, e.g., the nuclear heterochromatin and cytoplasmic ribosomes. These results confirm a primary interaction of titanium-containing metabolites deriving from titanocene complexes with nucleic acid molecules, especially with nuclear DNA. They suggest the formation of aggregates between nucleic acids and titanium-containing metabolites which are obviously extruded out of the nuclei and incorporated into cytoplasmic lysosomes, known to be involved in intracellular digesting processes.