Krzysztof Józwiak


Head of Laboratory of Medicinal Chemistry and Neuroengineering, Department of Chemistry, Faculty of Pharmacy, Medical University of Lublin, ul. Chod??ki 4a 4, 20-093 Lublin, Poland

Abstract:

Fenoterol (FEN), a β2-AR selective agonist is used in therapy of asthma as a racemic mixture of (R,R)- and (S,S)- isomers. Rational drug design approach were used to develop a number of FEN derivatives modified at the aminoalkyl tail in various stereoisomeric forms [1,2]. The compounds were tested in β2-AR binding studies using two different radioligands, [3H]-CGP- 12177 and [3H]- (R,R)-4-methoxyFEN what evidenced significantly different binding affinities towards inactive and active forms of the receptor, respectively [3]. Parallel Van’t Hoff analyses of binding data showed that the thermodynamics of complex formation highly depends on the stereochemistry of FEN and a marker ligand used [3,4].

The compounds were also widely characterized for functional activities using induced cAMP accumulation measurement, cardiomyocyte contractility assay and proliferation inhibition tests for a number of cancer cell lines. The results suggested that stereochemistry of a molecule affected the coupling properties of the receptor to different G proteins upon agonist binding. In cardiomyocyte contractility studies, the addition of pertussis toxin has no effect on the activity of (R,R)-FEN, (R,R)-4-methoxyFEN and (R,R)-4-aminoFEN, indicating that the receptor selectively couples Gs protein signaling upon binding of these compounds [4]. Conversely, pertussis toxin significantly affected cellular effects elicited by (R,R)-1-naphtylFEN and (R,R)-4-methoxy-1-naphtylFEN, showing that binding of these derivatives activate the receptor to forms able to couple Gs and Gi proteins. Molecular modeling simulations of binding to the β2-AR models linked this difference with dichotomous interactions of derivatives with Y308 residue of β2-AR model. Subsequent studies on Y308A mutant of β2-AR confirmed that binding affinities of Gs selective FEN derivatives are significantly reduced comparing to the β2-AR WT data, while Y308A mutation did not affect affinities for the group of derivatives eliciting both Gs and Gi signaling patterns.

The overall data demonstrate that stereochemistry and chemical constitution of a FEN derivative influence the magnitude of binding affinity, thermodynamics of local ligand - receptor interactions and the global mechanism of β2- AR activation. Even a small change of ligand stereoconfiguration allows observation of biased agonism in respect to Gs or Gi intracellular signaling. This medicinal chemistry project opens new perspectives for development novel potent and highly selective β2-AR agonists. For example, (R,R)-FEN and (R,R)-4-methoxyFEN is currently clinically tested for treatment of congestive heart failure, (R,R)-ethylFEN derivatives emerges as potent inhibitors of mitogenesis of brain tumor cells in in vitro studies.