Synthesis and induction of apoptosis by metallic complexes of lawsone

B de las Heras1, C Torrejón1, I Cuadrado1, S Oramas2, R Hernández3, A Estévez-Braun2, S Hortelano4. 1Departamento de Farmacolog í a, Facultad de Farmacia, Universidad Complutense de Madrid, 28040, Spain, 2Instituto Universitario de Bio-Org á nica Antonio Gonz á lez, Universidad de La Laguna, 38206, Spain, 3Departamento de Inorg á nica, Universidad de La Laguna, 38206, Spain, 4Centro Nacional de Microbiolog í a. Instituto de Salud Carlos III, Unidad de Inflamaci ó n y C á ncer, 28220, Spain

A variety of naturally occurring and synthetic substituted 1,4-nafthoquinones have demonstrated anticancer activity. Lawsone (2-hydroxy-1,4,p-naphthoquinone) has recognized to possess a wide range of biological activities such as antibacterial, anti-inflammatory, antifungal, antiviral… Since the development of cisplatin and related platinum complexes as anticancer drugs, the search of new metallic anticancer complexes has attracted much attention.

In the present work, a series of metallic complexes of the lawsone (2-6) were synthesized. The metallic complexes were prepared by mixing of ethanolic solutions of lawsone (1) and the corresponding transition metal acetates from a 2:1 mol ratio. These lawsone-derivatives were tested for their ability to inhibit cell viability in the mouse leukemic macrophagic RAW 264.7 cell line. Significant inhibition of cell growth activity was observed in vitro for the copper complex of lawsone (4) with an IC50 value of 2.5 µM. This compound was selected for further evaluation in other human cancer cell lines such as HeLa, HT-29 and HepG2. Compound 4 induced a significant apoptosis in HepG2 cells. Mechanisms involved in the apoptotic potential of this compound were investigated in this cell tumor line. The caspase-3, -8- and 9 activities were measured. Caspase 3 activity was increased by 8-fold after treatment with compound 4 for 24 h vs control cells (**p<0.01, Student’s t test). Immunoblot analysis of the expression of Bax, Bcl-2, Bcl-xl and caspase-3 was also carried out (n=3). The results obtained showed that compound 4 induces apoptosis in HepG2 by a mechanism that involves modulation of apoptosis-related proteins (Bax, Bcl-2, Bcl-XL…) and caspase activation.

The present study demonstrated that metallic complexes of lawsone, in particular the copper complex (4) induces apoptosis via both mitochondrial and membrane death receptor pathways, involving the Bcl-2 family proteins. Taken together, these results provide a role for lawsone derivatives as apoptotic inducers in tumor cells.