Impact of cyclometalated ruthenium(II) complexes on lactate dehydrogenase activity and cytotoxicity in gastric and colon cancer cells

• Lactate dehydrogenase (LDH) inhibition kinetics by polypyridine Ru(II) complexes measured
• Cyclometalated Ru(II) complex is more cytotoxic than its coordination analog.
• LDH is inhibited by cyclometalated Ru(II) complex in cancer cells.
• Cyclometalated and coordination Ru complexes inhibit LDH by different mechanisms.
• Molecular docking revealed the sites of interaction of LDH with Ru compounds.

Lactate dehydrogenase (LDH) is a redox enzyme often overexpressed in cancer cells allowing their survival in stressful metabolic tumor environment. Ruthenium(II) complexes have been shown to impact on the activity of purified horseradish peroxidase and glucose oxidase but the physiological relevance remains unclear. In this study we investigated how ruthenium complexes impact on the activity of LDH in vitro and in cancer cells and performed a comparative study using polypyridine ruthenium(II) complex [Ru(bpy)3]2 + (1) and its structurally related cyclometalated 2-phenylpyridinato counterpart [Ru(phpy)(bpy)2]+ (2) (bpy = 2,2′-bipyridine, phpyH = 2-phenylpyridine). We show that the cytotoxicity in gastric and colon cancer cells induced by 2 is significantly higher compared to 1. The kinetic inhibition mechanisms on purified LDH and the corresponding inhibition constants Ki or i0.5 values were calculated. Though complexes 1 and 2 are structurally very similar (one Ru−C bond in 2 replaces one Ru−N bond in 1), their inhibition modes are different. Cyclometalated complex 2 behaves exclusively as a non-competitive inhibitor of LDH from rabbit muscle (LDHrm), strongly suggesting that 2 does not interact with LDH in the vicinities of either lactate/pyruvate or NAD+/NADH binding sites. Sites of interaction of 1 and 2 with LDHrm were revealed theoretically through computational molecular docking. Inhibition of LDH activity by 2 was confirmed in cancer cells. Altogether, these results revealed an inhibition of LDH activity by ruthenium complex through a direct interaction structurally tuned by a Ru−C bond.

Polypyridine ruthenium(II) derivative [Ru(bpy)3]2 + and highly cytotoxic cyclometalated 2-phenylpyridinato analog [Ru(phpy)(bpy)2]+ (bpy = 2,2′-bipyridine, phpyH = 2-phenylpyridine) inhibit the activity of lactate dehydrogenase in vitro and in cancer cells. The sites of interaction of the complexes with the enzyme were revealed through molecular docking calculations.Figure optionsDownload as PowerPoint slide