Original articleDesign, synthesis and 3D-QSAR studies of novel 1,4-dihydropyridines as TGFβ/Smad inhibitors
Graphical abstract
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.
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