European Journal of Medicinal Chemistry 129 (2017) 266e274

Synergistic effects between a copper-based metal Casiopeina III-ia and cisplatin

Silvia Graciela Davila-Manzanilla1*, Yeshenia Figueroa-de-Paz, Carmen Mejia2, Lena Ruiz-Azuara2*

1. Department of Inorganic and Nuclear Chemistry, Facultad de Química, Universidad Nacional Autónoma de México, Av Universidad 3000, Ciudad de México, 04510, Mexico.

2. Facultad de Ciencias Naturales, Universidad Autónoma de Querétaro, Avenida de las ciencias S/N, Juriquilla, Delegación Santa Rosa Jáuregui, 76230, Querétaro.

To whom correspondence should be addressed:  Lena Ruiz-Azuara E-mail:



Additive, subadditive or superadditive interactions observed in combination therapy play an important role in several treatments, particularly for cancer. The isobolographic analysis allows to establish the pharmacological interactions that exist between two drugs that are administered together in equieffective doses. In order to identify if the combination of two compounds presents synergistic interaction, the antiproliferative activity of CasIII-ia with analogue compounds or cisplatin in different molar ratios was evaluated. Results showed that this compound exhibited additive, subadditive or antagonic and superadditive or synergistic interactions, depending on the compound that accompanies it and the proportion of the compounds in the combination. One of the combinations increased the antiproliferative activity from 50 to 77% when the cells were exposed to 4.59 and 9.70 mM to CasIII-ia and cisplatin, respectively. Further studies of the toxicity and biochemical level of the interactions still remain to be studied on a in-vivo xenographed model.

Keywords: Copper compounds, Combination therapy, Fractional analysis, Cytotoxicity 



Pharmacological interaction studies allow us to predict if a combination of two or more drugs will have an effect in the activity of each other when they are administered together. This same principle is applied to the ingestion of food or drink when a person is also consuming a particular drug. The effects may be favorable or detrimental, and are classified as additive, synergistic or superadditive and antagonic or subadditive1.

An additive effect means that if a person consumes a combination of drugs, he might as well consume just one of the drugs, because the effect of the combination will be the same as any just one of them. The superadditive effect is present if the person experiences an increase in the overall effect, compared with what would be the effect of the drugs alone, while the subadditive effects have the opposite overall outcome. The latter is schematized in Figure 1.



Figure 1. Difference between the additive, superadditive and subadditive effects in a combination of drugs.


Although there are several ways to evaluate the combined effect of drugs, in the present work we chose to use Isobolographic analysis, initially proposed by Loewe [1,2], but improved by Chou and Talalay (Median effect equation, 1984)3 and Tallarida (2001, 2006, 2010)4-6. The isobolographic analysis consists on assessing two drugs in equieffective concentrations2, meaning that the concentrations employed must achieve the same level of effect. Usually isoboles may be constructed; isoboles are curves builded up through diverse combinations of concentrations effective at different levels.

We evaluated the antiproliferative activity on cultures of cervix adenocarcinoma (HeLa) cultures to establish the pharmacological interactions when six different copper compounds, Casiopeínas® (general formulas: [Cu(N-N)(acethylacetonate)]NO3 and [Cu(N-N)(glynate)]NO3; N-N dimethylated and tetramethylated phenanthrolines) or cisplatin are combined with a less active copper compound, namely known as Casiopeína III-ia (CasIII-ia: [Cu(4,4′-dimethyl-2,2′-bipyridine)(acethylacetonate)]NO3).The results showed that as the concentration of the more active compound increases, the superadditivity of the combination increases as well. Although, it also depended on the compound employed, being the compounds with tetramethylated phenanthrolines (CasIII-Ma and CasVIII-gly), the ones that yielded the best combinations.

The combination of CasIII-ia and cisplatin was evaluated as well, exhibiting all three interactions: subadditive, additive and superadditive, defined by the increment in the concentration of cisplatin. Figure 2 shows the combination index (CI) of each compound and each combination with CasIII-ia: the lower the CI value, the best activity was obtained with the combination as compared to the effect achieved by the compounds alone.



Figure 2. Combination index (CI) of combinations of CasIII-ia and six Casiopeínas® or cisplatin. The number below represent the combination: CI50 CasIII-ia : CI50 Second compound. 1.- 0.89:0.11; 2.- 0.80:0.20; 3.- 0.67:0.33; 4.- 0.50:0.50; 5.- 0.33:0.67; 6.- 0.20:0.80; 7.- 0.11:0.89. For reference: CI<1, superadditivity; CI=1, additivity; CI>1, subadditivity.



1. Loewe, S. The problem of synergism and antagonism of combined drugs. Arzneimittelforschung 3, 285–290 (1953).
2. Loewe, S. Antagonism and antagonists. Pharmacol. Rev.9, 237–242 (1957).
3. Chou, T. C. & Talalay, P. Quantitative analysis of dose-effect relationships: the combined effects of multiple drugs or enzyme inhibitors. Adv. Enzyme Regul.22, 27–55 (1984).
4. Tallarida, R. J. Drug synergism: its detection and applications. J. Pharmacol. Exp. Ther.298, 865–872 (2001).
5. Tallarida, R. J. An overview of drug combination analysis with isobolograms. J. Pharmacol. Exp. Ther.319, 1–7 (2006).
6. Tallarida, R. J. & Raffa, R. B. The application of drug dose equivalence in the quantitative analysis of receptor occupation and drug combinations. Pharmacol. Ther.127, 165–174 (2010).


[1]It depends on the author, but all terms may be employed.

[2]Because the Isobolographic analysis was initially proposed for in vivo studies, doses (mg/kg, mmol/L) are most commonly mentioned, but for in vitro studies, concentrations (mg/mL, mmol/L) are employed.