Effects of Phenyl-1-Pyridin-2yl-Ethanone (PPY)-Based Iron Chelators on the Formation of Methemoglobin

Background

Iron chelators are used in the treatment of iron overload related diseases and are currently receiving a major attention as potential antitumor drugs. In recent studies, the antitumor activity of thiosemicarbazones-class of iron chelator, including Di-2-pyridilketone-4,4- dimethyl-3-thiosemicarbazone (Dp44mT) has been investigated in over 20 phase I and II clinical trials [1, 2,3]. Iron chelators were also considered as anti-HIV-1 agents. However, the main obstacle to using iron chelators in vivois the deleterious side effect of methemoglobinemia induced by some iron chelators that are able to scavenge electrons from the heme-bound iron in hemoglobin. In our previous studies, we developed novel phenyl-1-pyridin-2yl-ethanone (PPY)-based iron chelators that we showed to increase IKBα expression, modulate CDK2 and CDK9 activities and inhibit HIV-1 [4].

Objective

Our objective was to test the effect of PPYeT iron chelator for methemoglobin induction. The methemoglobin induction effect was compared with several additional iron chelators including Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and PPY analogues.

Methods

Fluorometric analysis was carried out in promonocytic THP-1 cells to evaluate the ability of our novel PPYeT iron chelator to reduce labile iron pool (LIP). The effect of PPYet on LIP was compared to the effect to SIH. Subsequently, spectrophotometric analysis was used to measure and quantify the production of methemoglobin in human red blood cells lysates and in isolated intact human red blood cells treated with PPYeT and various other iron chelators including DP44mT and DP4mT.

Results

PPYeT significantly reduced LIP in THP-1 cells overloaded with iron comparing to the cells treated with SIH. In RBC lysates and in intact RBC, PPYeT treatment showed notably lesser production of methemoglobin in comparison to DP44mT and DP4mT chelators. In RBC lysates, PPYeT produced about four-fold less methemoglobin than Dp44mT and ten-fold less than Dp4mT.

Conclusion

The novel compound, PPYeT, shows a remarkably low ability to catalyze the formation of methemoglobin in human RBC lysates and also in intact RBCs as compared to Dp44mT. These findings indicate that PPYeT may be useful for future in vivo studies as it produces less methemoglobinemia. Further studies will evaluate the effect PPYeT as anti-cancer or anti HIV-1 inhibitor in vivo.

Acknowledgments

This work was supported by NIH Research Grants 1P50HL118006, 1R01HL125005, and 5G12MD007597. The content is solely the responsibility of the authors and does not necessarily represent the official view of NHLBI, NIMHD or NIH.

References

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2-Yuan, J.; Lovejoy, D. B.; Richardson, D. R. Novel Di-2-pyridylDerived Iron Chelators with Marked and Selective Antitumor Activity: In Vitro and in Vivo Assessment. Blood2004, 104, 1450−1458.

3-Whitnall, M.; Howard, J.; Ponka, P.; Richardson, D. R. A Class of Iron Chelators with a Wide Spectrum of Potent Antitumor Activity that Overcomes Resistance to Chemotherapeutics. Proceedings of National Academy of Science. U. S. A.2006, 103, 14901−14906.

4. Kumari N, Iordanskiy S, Kovalskyy D, Breuer D, Niu X, Lin X, Xu M, Gavrilenko K, Kashanchi F, Dhawan S et al: Phenyl-1-Pyridin-2yl-ethanone-based iron chelators increase IkappaB-alpha expression, modulate CDK2 and CDK9 activities, and inhibit HIV-1 transcription. Antimicrob Agents Chemother 2014, 58(11):6558-6571.