Proline Analogues in Drug Design: Current Trends and Future Prospects

Proline analogues are versatile chemical building blocks that enable modular construction of small-molecule drugs and pharmaceutical peptides. Over the past 15 years, the FDA has approved over 15 drugs containing proline analogues in their structures, five in the last three years alone (daridorexant, trofinetide, nirmatrelvir, rezafungin, danicopan). This perspective offers an analysis of the most common types of proline analogues currently trending in drug design. We focus on examples of fluoroprolines, α-methylproline, bicyclic proline analogues, and aminoprolines, while also highlighting proline analogues that remain underrepresented. We supplement our analysis with physicochemical information regarding the specific molecular properties of these moieties. Additionally, we discuss several intriguing cases where nonproline residues were replaced with proline analogues as a strategy to eliminate unwanted hydrogen bond donor sites. In conclusion, we present some suggestions for the future exploration of this promising class of molecular entities in drug discovery.

Enhancing the Anticancer Potential of Targeting Tumor-Associated Metalloenzymes via VEGFR Inhibition by New Triazolo[4,3-a]pyrimidinone Acyclo C-Nucleosides Multitarget Agents

The role of metalloenzymes in tumor progression had broadened their application in cancer therapy. Of these, MMPs and CAs are validated druggable targets that share some pivotal signaling pathways. The majority of MMPs or CAs inhibitors are designed as single-target agents. Despite their transient efficacy, these agents are often susceptible to resistance. This set the stage to introduce dual inhibitors of correlated MMPs and CAs. The next step is expected to target the common vital signaling nodes as well. In this regard, VEGFR-2 is central to various tumorigenesis events involving both families, especially MMP-2 and CA II. Herein, we report simultaneous inhibition of MMP-2, CA II, and VEGFR-2 via rationally designed hybrid 1,2,4-triazolo[4,3-a]pyrimidinone acyclo C-nucleosides. The promising derivatives were nanomolar inhibitors of VEGFR-2 (8; IC₅₀ = 5.89 nM, 9; IC₅₀ = 10.52 nM) and MMP-2 (8; IC₅₀ = 17.44 nM, 9; IC₅₀ = 30.93 nM) and submicromolar inhibitors of CA II (8; IC₅₀ = 0.21 µM, 9; IC₅₀ = 0.36 µM). Docking studies predicted their binding modes into the enzyme active sites and the structural determinants of activity regarding substitution and regioselectivity. MTT assay demonstrated that both compounds were 12 folds safer than doxorubicin with superior anticancer activities against three human cancers recording single-digit nanomolar IC₅₀, thus echoing their enzymatic activities. Up to our knowledge, this study introduces the first in class triazolopyrimidinone acyclo C-nucleosides VEGFR-2/MMP-2/CA II inhibitors that deserve further investigation.

Identification of a Common Pharmacophore for Binding to MMP2 and RGD Integrin: Towards a Multitarget Approach to Inhibit Cancer Angiogenesis and Metastasis

During tumor angiogenesis different growth factors, cytokines and other molecules interact closely with each other to facilitate tumor cell invasion and metastatic diffusion. The most intensively studied as molecular targets in anti-angiogenic therapies are vascular endothelial growth factor (VEGF) and related receptors, integrin receptors and matrix metalloproteinases (MMPs). Considering the poor efficacy of cancer angiogenesis monotherapies, we reasoned combining the inhibition of αvβ3 and MMP2 as a multitarget approach to deliver a synergistic blockade of tumor cell migration, invasion and metastasis. Accordingly, we identified a common pharmacophore in the binding cavity of MMP2 and αvβ3, demonstrating such approach with the design, synthesis and bioassays of tyrosine-derived peptidomimetics carrying the necessary functional groups to bind to key pharmacophoric elements of MMP2 and αvβ3 RGD integrin.

Multitargeting application of proline-derived peptidomimetics addressing cancer-related human matrix metalloproteinase 9 and carbonic anhydrase II

A series of d-proline peptidomimetics were evaluated as dual inhibitors of both human carbonic anhydrases (hCAs) and human gelatinases (MMP2 and MMP9), as these enzymes are both involved in the carcinogenesis and tumor invasion processes. The synthesis and enzyme inhibition kinetics of d-proline derivatives containing a biphenyl sulfonamido moiety revealed an interesting inhibition profile of compound XIV towards MMP9 and CAII. The SAR analysis and docking studies revealed a stringent requirement of a trans geometry for the two arylsulfonyl moieties, which are both necessary for inhibition of MMP9 and CAII. As MMP9 and CAII enzymes are both overexpressed in gastrointestinal stromal tumor cells, this molecule may represent an interesting chemical probe for a multitargeting approach on gastric and colorectal cancer.

Occurrence of the d-Proline Chemotype in Enzyme Inhibitors

Natural and nonnatural amino acids represent important building blocks for the development of peptidomimetic scaffolds, especially for targeting proteolytic enzymes and for addressing protein–protein interactions. Among all the different amino acids derivatives, proline is particularly relevant in chemical biology and medicinal chemistry due to its secondary structure’s inducing and stabilizing properties. Also, the pyrrolidine ring is a conformationally constrained template that can direct appendages into specific clefts of the enzyme binding site. Thus, many papers have appeared in the literature focusing on the use of proline and its derivatives as scaffolds for medicinal chemistry applications. In this review paper, an insight into the different biological outcomes of d-proline and l-proline in enzyme inhibitors is presented, especially when associated with matrix metalloprotease and metallo-β-lactamase enzymes.