Original article
Design, synthesis and 3D-QSAR studies of novel 1,4-dihydropyridines as TGFβ/Smad inhibitors

https://doi.org/10.1016/j.ejmech.2015.03.027Get rights and content

Highlights

  • Synthesis of novel DHPs and SAR studies reveal possibility of incorporating polar groups.

  • Structural examination of pathway selectivity against TGFβ over Activin A.

  • Absolute configuration of active (+)-enantiomers by X-ray crystallography.

  • 3D-QSAR model reinforces a specific mode of action for DHPs as new TGFβ inhibitors.

Abstract

Targeting TGFβ/Smad signaling is an attractive strategy for several therapeutic applications given its role as a key player in many pathologies, including cancer, autoimmune diseases and fibrosis. The class of b-annelated 1,4-dihydropyridines (DHPs) represents promising novel pharmacological tools as they interfere with this pathway in a novel fashion, i.e. through induction of TGFβ receptor type II degradation. In the present work, >40 rationally designed, novel DHPs were synthesized and evaluated for TGFβ inhibition, substantially expanding the current understanding of the SAR profile. Key findings include that the 2-position tolerates a wide variety of polar functionalities, suggesting that this region could possibly be solvent-exposed within the (thus far) unknown cellular target. A structural explanation for pathway selectivity is provided based on a diverse series of 4″-substituted DHPs, including molecular electrostatic potential (MEP) calculations. Moreover, the absolute configuration for the chiral 4-position was determined by X-ray crystal analysis and revealed that the bioactive (+)-enantiomers are (R)-configured. Another key objective was to establish a 3D-QSAR model which turned out to be robust (r2 = 0.93) with a good predictive power (r2pred = 0.69). This data further reinforces the hypothesis that this type of DHPs exerts its novel TGFβ inhibitory mode of action through binding a distinct target and that unspecific activities that would derive from intrinsic properties of the ligands (e.g., lipophilicity) play a negligible role. Therefore, the present study provides a solid basis for further ligand-based design of additional analogs or DHP scaffold-derived compounds for hit-to-lead optimization, required for more comprehensive pharmacological studies in vivo.

Introduction

The superfamily of transforming growth factor-β (TGFβ) ligands comprises of a series of structurally closely related cytokines that modulate a plethora of cellular processes such as cell division, proliferation, differentiation, migration, adhesion and apoptosis in a tissue context-specific manner [1]. They play a key role during embryogenesis but also for homeostasis in adult tissues. Disruption or pathologic alterations of these pathways are associated with a number of diseases such as cancer, autoimmune diseases and fibrosis [2]. Therefore, the pharmacologic modulation of TGFβ-dependent processes is of great therapeutic relevance, underlined by the many ‘biologicals’ and small molecules currently in clinical trials for distinct applications [3], [4]. In general, three strategies are being investigated for therapeutic intervention with TGFβ signaling: 1) inhibition at the translational level by anti-sense oligonucleotides, 2) blockade of ligand–receptor interaction using antibodies and 3) inhibition of TGFβ receptor kinases (TGFβRI + II) by small molecules [4], [5]. The latter approach provides several advantages over biological agents, because small molecules can be administered orally and may reach and infiltrate target tissues more efficiently than biomacromolecules. In addition, target and pathway selectivity can often be greater by using defined and pharmacologically optimized small molecule agents [6]. In this regard, the herein presented compound class of dihydropyridines might be of particular therapeutic value in a regenerative medicine setting.

We previously reported on a novel class of TGFβ inhibitors, b-annelated 1,4-dihydropyridines (DHPs), which were identified in a phenotypic screen for small molecules that stimulate cardiac differentiation of stem cells, with ITD-1 (1) as the hit compound (Fig. 1) [7]. It was shown that these DHPs inhibit TGFβ signaling via a novel mode of action, which is the downregulation of the TGFβ type II receptor (TGFβRII), giving these 1,4-DHPs the name ITDs (i.e., inducers of TGFβ receptor degradation). This novel mechanism sets these compounds apart from the “classic” TGFβ inhibitors that typically target the receptor kinase domains, with the consequence of redundant activity on closely related signaling pathways or kinases, respectively. An initial focused medicinal chemistry study was done which revealed a rather steep SAR profile for the observed biological activity [8].

Here, we report on the extension of these SARs with additional, more versatile substituted and functionalized derivatives addressing distinct shortcomings of our current SAR picture of these compounds (Fig. 1). Along these lines, it was key to determine the – up to now – unknown absolute configuration of the active (+)-enantiomers. In addition, the entire dataset known until today was used to establish a quantitative correlation between structure and activity via a 3D-QSAR analysis. The primary aim was here to further reinforce the selective nature of observed TGFβ inhibiting activity, possibly addressing one relevant target and ruling out unspecific effects in the cellular assays. This work eventually sets the basis for the design of novel DHPs or DHP scaffold-derived compounds for rational hit-to-lead optimization that will allow conducting more comprehensive pharmacological studies in an in vivo setting.

Section snippets

Chemistry

As indicated in the introduction, our preliminary understanding of the structure activity relationships for this novel class of TGFβ/Smad signaling inhibitors has been limited and generated rather lipophilic derivatives which, accordingly, suffer from the respective pharmaceutical and pharmacokinetic shortcomings (e.g., solubility, ADME aspects, formulation technologies). Therefore, several DHP derivatives were designed to incorporate heteroatom-containing, polar functional groups but also to

Conclusion

Targeting the TGFβ pathway is an attractive pharmacological strategy for several therapeutic applications given its role as a key player in many pathologies, including cancer, autoimmune diseases and fibrosis. The herein presented subclass of b-annelated 1,4-dihydropyridines represent promising novel pharmacological tools since they interfere with TGFβ/Smad signaling in an unprecedented fashion, namely through induction of TGFβ receptor type II degradation. Here, we reported on a substantial

General

Unless otherwise stated, all reagents were obtained from commercially available sources and were used without purification. The reaction process was monitored by TLC with silica gel plates (thickness 250 mm, Indicator F-254) under UV light. Flash column chromatography was performed on a CombiFlash Rf200 (Teledyne ISCO, Lincoln). Reactions under microwave irradiation were performed in a CEM, Discover Intellivent Explorer Automated Reactor. NMR spectra of compounds were recorded with a Varian

Acknowledgment

Financial support by the Bundesministerium für Bildung und Forschung (BMBF) is gratefully acknowledged (grant 1316053). We also thank the excellent technical support by our NMR facility team of Dr. Hiller.

References (21)

  • E. Willems et al.

    Small molecule-mediated TGF-beta type II receptor degradation promotes cardiomyogenesis in embryonic stem cells

    Cell Stem Cell

    (2012)
  • A. Radadiya et al.

    Synthesis and 3D-QSAR study of 1,4-dihydropyridine derivatives as MDR cancer reverters

    Eur. J. Med. Chem.

    (2014)
  • R. Derynck et al.

    TGFβ and the TGFβ family

  • K. Wharton et al.

    TGFbeta family signaling: novel insights in development and disease

    Development

    (2009)
  • J.M. Yingling et al.

    Development of TGF-beta signalling inhibitors for cancer therapy

    Nat. Rev. Drug Discov.

    (2004)
  • N.S. Nagaraj et al.

    Targeting the transforming growth factor-beta signaling pathway in human cancer

    Expert Opin. Investig. Drugs

    (2010)
  • D. Bonafoux et al.

    Strategies for TGF-beta modulation: a review of recent patents

    Expert Opin. Ther. Pat.

    (2009)
  • D. Langle et al.

    Small molecules targeting in vivo tissue regeneration

    ACS Chem. Biol.

    (2014)
  • D. Schade et al.

    Synthesis and SAR of b-annulated 1,4-dihydropyridines define cardiomyogenic compounds as novel inhibitors of TGFbeta signaling

    J. Med. Chem.

    (2012)
  • H. Meyer et al.

    Liebigs Ann. Chem.

    (1977)
There are more references available in the full text version of this article.

Cited by (0)

View full text