## 3 Results and Discussion
### Cell Lysis Induced by Ru(III) Complexes Is Dose-Dependent  
After analyzing the effects of various concentrations of Ru(III) complexes on LoVo human colon cancer cell proliferation, and compared to cisplatin, in the real-time cell analysis assay using the xCELLigence DP-System, cells were subjected to an end-point, colorimetric drug-mediated cytotoxicity method. MTS assay was used in order to better assess the levels of cell lysis induced by drug treatments and discriminate between the Ru(III) complexes under study regarding their ability to kill the LoVo colon tumor cells. Increasing concentrations of Ru(III) complexes with quinolones or CisPt ranging from 3.125 to 200 \(\upmu\)M were used to treat LoVo cultured cells for 24 h. Percentages of cell lysis induced by drug treatments in the LoVo cell line are shown in Figure 3. Untreated cells  
Figure 2: Real-time cell analysis of cytotoxic effects of Ru(III) complexes vs. CisPt. LoVo human colon cancer cells were treated with the reported drug concentrations in 16-well E-plates. Monitoring of Ru(III) complexes-mediated cytolysis was performed by measuring the cell index for several days using the xCELLigence DP-System and compared to CisPt-induced inhibition of proliferation vs. cell lysis. were used as control and considered to have 100% viability. Results were expressed as mean values of three different experiments \(\pm\) standard deviation (SD). Analyzing the cell response to drug treatments, a cytotoxic dose-dependent effect was observed for all Ru(III) complexes and CisPt. Treatments for 24 h with Ru(III) complexes in cosolvents resulted in increased cell lysis rates and implicitly decreased cell viability. Thus, more than 75% of the cells were killed when the LoVo cell line was incubated either with 200 uM or 100 uM of Ru-nf, Ru-levo, Ru-oflo, Ru-cipro, or CisPt. Treatments with 25 or 50 uM drugs induced more than 50% of cell lysis for all the Ru(III) complexes under study as well as CisPt. Even for 6.25 uM or 12.5 uM treatments, the percentages of cell lysis were higher than 25% for all drugs tested, while 3.125 uM induced more than 14% cell lysis (Figure 3). In addition, the inhibitory concentration values (IC) of Ru(III) complexes or CisPt were calculated using the linear regression analysis from the cytotoxicity data of each compound and for different percentages of cell lysis corresponding to drug concentrations. Therefore, the corresponding drug concentrations required to induce the lysis of 50% (IC50), 75% (IC75), or 90% (IC90) of the cells were calculated when the cytotoxicity of Ru(III) complexes was assessed by MTS assay after 24 h of their incubation with LoVo cells compared to cisplatin as positive control (Table 2). In terms of IC50 values, several Ru(III) complexes with quinolones displayed similar activities to the positive control, cisplatin, on LoVo cells. The best cytotoxic activity seemed to have Ru-cipro, Ru-nf, Ru-levo, and Ru-oflo since IC50, IC75, and IC90 values were the lowest (Table 2), and therefore, the toxicity profile is lower compared to cisplatin, which might allow a wide modulation of concentrations to be further used in therapeutic approaches with an improved control of the non-target cell toxicity. Figure 3: Antitumor effect of Ru(III) complexes against LoVo colon cancer cells. Cells lysis was induced by 24 h treatment with scalar concentrations of Ru(III) complexes or CisPt, and compared to untreated control LoVo cells. Data shown are expressed as mean values \(\pm\) standard deviations (SD) of three different experiments (\(n=3\)). The results are similar to those obtained by in vitro treatments with several other ruthenium compounds such as dinuclear Ru(III) complexes, whose effect was studied on different types of cancer cell lines, and when a reduction of cell proliferation was observed after 24 h of exposure to 100 uM of the compounds under study [16]. In addition, some ruthenium organometallic compounds might present collateral sensitivity for cisplatin-resistant cancer cells [59].