P6.08 - Cationic porphyrin-phenazine conjugates as quadruplex DNA ligands and potential agents for anticancer therapy

Abstract

ABSTRACT Introduction: Telomeres are guanine-rich DNA sequences at the ends of chromosomes. Telomeric DNA forms G-quadruplexes (G4-DNA), and stabilization of these structures with small molecules can inhibit telomerase, an enzyme responsible for telomere elongation upon cellular division. It is highly active at majority of tumor cells, so G4-DNA and telomerase are considered as targets for the development of novel anticancer drugs. We present porphyrin conjugate with phenazine derivative and its metal complexes as selective G4-DNA ligands and potential antitumor agents. Materials and methods: Conjugates of tricationic porphyrin TMP3 and its Zn(II) and Mn(III) complexes with imidazo[4, 5-b]phenazine (ImPhz) intercalating agent were synthesized as previously reported [ 1 ]. Their binding affinity to G4 and dsDNA was studied using FID (Fluorescent Interacalator Displacement) method. The level of telomerase inhibition was determined by TRAP (Telomeric Repeat Amplification Protocol) in vitro assay. Antiproliferative activity of conjugates was tested on a mouse Lewis lung carcinoma cell culture. Results: All compounds show strong affinity to Tel22 G4-DNA. Dissociation constants for non-metalated conjugate, its Zn and Mn complex are 20.1, 46.3 and 3.8 µM, respectively. All ligands have a good selectivity for quadruplex over duplex DNA. The ratio between G4 and dsDNA constants is 5 for TMP3-ImPhz and 8 and 10 for its Zn and Mn complexes. High affinity of conjugates for G4-DNA is associated with a good ability to inhibit telomerase. The most efficient Zn complex completely inhibits the enzyme at 2.5 µM concentration being several times more active than non-conjugated porphyrins. Non-metalated conjugate shows inhibition effect at 5 µM, whereas Mn derivative is less active. Compounds display antiproliferative activity in vitro in micromolar range, with EC50 values for TMP3-ImPhz, its Mn and Zn complex to be 21.8, 11.2 and 5.9 µM, respectively. Conclusion: All studied compounds have strong binding affinity and selectivity for quadruplex DNA. They are efficient telomerase inhibitors and demonstrate good antiproliferative activity. Thus, these conjugates can be considered as potential agents for anticancer therapy.