Design, synthesis and biological evaluation of Ruthenium (II) polypyridyl complexes with redox active ligands.

LB-191

Purpose:
 Tumor cells under hypoxic stress are among the most resistant to radiotherapy and chemotherapy and are also most susceptible toward metastasis, making this subpopulation a particularly attractive chemotherapeutic target.
 We are interested in the development, toxicology and pharmacology of a new class of redox-active drugs that show potentiated DNA- cleavage activity under hypoxic conditions. These drugs are all based on a tetraazapentacene heterocycle which is the pharmacophore. Metal complexation of the drug provides solubility and imparts a cationic charge that helps the drug to tightly bind to DNA (K_b ~ 10⁹ M^-1) and this DNA damage is enhanced in presence of common cellular reductants like glutathione. The present paper presents structural design, studies in cultured malignant and normal cells, as well as animal toxicity and antitumor studies of this new pharmacophore.
 Experimental Design:
 A structure-activity relationship for a series of Ru(II) complexes has been established by synthesizing and screening them for its biological activity.
 Cytotoxicity studies were performed to determine the IC₅₀ using a standard MTT drug sensitivity assay on non-small cell lung cancer (NSCLC) H358 and H226. The control experiments for this were also carried out in normal healthy cells HUVEC and HAVSMC.
 An initial animal toxicity screen was determined in a dose ranging study by intraperitoneal injection in C57BL/6NTac mice to calculate the maximum tolerable dose (MTD). The animals were also autopsied after interval of 0, 24 and 48 hr and the organs liver, spleen, intestine, kidney, heart, lung and brain collected and analyzed for studying the pharmacokinetics of the complex using Atomic Absorption Spectroscopy.
 The in vivo antitumor activities of the most promising complexes were performed using an orthotopic syngeneic mouse melanoma model. For each complex 4 male C57BL/6NTac mice were injected with 1 million B16 mouse melanoma cells subcutaneously. The tumor volume and regression was monitored for the group.
 Results:
 The results of the drug sensitivity assay were determined for a total of 17 complexes (racemic/chiral). The most antipromising activity was shown by complex with a longer bridging redox active ligand tatpp with an IC₅₀ value of about 10 μM, very rare for this class. The complex also showed low animal toxicity in the screen with MTD as high as 100 mg/Kg. Also we found that the complex had a measurable inhibitory effect on tumor growth as measured by the tumor volume.
 Conclusions:
 We report synthesis and biological activity of a novel molecule with anticancer properties that support a potential clinical utility for advanced human cancer.
 Supported by National Cancer Institute grant CA 113747