Discovery of pyrrolo[2,3-d]pyrimidine derivatives as potent Axl inhibitors: Design, synthesis and biological evaluation

Recent discovery and development of AXL inhibitors as antitumor agents

AXL, a receptor tyrosine kinase (RTK), plays a pivotal role in various cellular functions. It is primarily involved in processes such as epithelial-mesenchymal transition (EMT) in tumor cells, angiogenesis, apoptosis, immune regulation, and chemotherapy resistance mechanisms. Therefore, targeting AXL is a promising therapeutic approach for the treatment of cancer. AXL inhibitors that have entered clinical trials, such as BGB324(1), have shown promising efficacy in the treatment of melanoma and non-small cell lung cancer. Additionally, novel AXL-targeted drugs, such as AXL degraders, offer a potential solution to overcome the limitations of traditional small-molecule AXL inhibitors targeting single pathways. We provide an overview of the structure and biological functions of AXL, discusses its correlation with various cancers, and critically analyzes the structure-activity relationship of AXL small-molecule inhibitors in cellular contexts. Additionally, we summarize multiple research and development strategies, offering insights for the future development of innovative AXL inhibitors.

Disrupting EGFR-HER2 Transactivation by Pertuzumab in HER2-Positive Cancer: Quantitative Analysis Reveals EGFR Signal Input as Potential Predictor of Therapeutic Outcome

Pertuzumab (Perjeta®), a humanized antibody binding to the dimerization arm of HER2 (Human epidermal growth factor receptor-2), has failed as a monotherapy agent in HER2 overexpressing malignancies. Since the molecular interaction of HER2 with ligand-bound EGFR (epidermal growth factor receptor) has been implied in mitogenic signaling and malignant proliferation, we hypothesized that this interaction, rather than HER2 expression and oligomerization alone, could be a potential molecular target and predictor of the efficacy of pertuzumab treatment. Therefore, we investigated static and dynamic interactions between HER2 and EGFR molecules upon EGF stimulus in the presence and absence of pertuzumab in HER2+ EGFR+ SK-BR-3 breast tumor cells using Förster resonance energy transfer (FRET) microscopy and fluorescence correlation and cross-correlation spectroscopy (FCS/FCCS). The consequential activation of signaling and changes in cell proliferation were measured by Western blotting and MTT assay. The autocorrelation functions of HER2 diffusion were best fitted by a three-component model corrected for triplet formation, and among these components the slowly diffusing membrane component revealed aggregation induced by EGFR ligand binding, as evidenced by photon-counting histograms and co-diffusing fractions. This aggregation has efficiently been prevented by pertuzumab treatment, which also inhibited the post-stimulus interaction of EGFR and HER2, as monitored by changes in FRET efficiency. Overall, the data demonstrated that pertuzumab, by hindering post-stimulus interaction between EGFR and HER2, inhibits EGFR-evoked HER2 aggregation and phosphorylation and leads to a dose-dependent decrease in cell proliferation, particularly when higher amounts of EGF are present. Consequently, we propose that EGFR expression on HER2-positive tumors could be taken into consideration as a potential biomarker when predicting the outcome of pertuzumab treatment.

Design, Synthesis and In-Silico Studies of Piperidine-Dihydropyridine Hybrids as Anticancer Agents

In this study, we designed, synthesized and characterized a novel series of piperidine-dihydropyridine hybrid compounds and characterized them by 1H-NMR, 13C NMR, mass spectrometry (MS), and elemental analysis. Subsequently, we assessed their in vitro anticancer potentials against the human breast adenocarcinoma cell line MCF-7 and the lung cancer cell line A-549. Several of these compounds demonstrated significant activity, with IC50 values ranging from 15.94 μM to 48.04 μM for A-549 and 24.68 μM to 59.12 μM for MCF-7, when compared to the reference drug Cisplatin.Notably, a compound featuring a 3-fluoro substitution in the carboxamide series exhibited robust inhibitory effects, with an IC50 of 15.94±0.201 μM against A-549 cells and an IC50 of 22.12±0.213 μM against MCF-7 cells, respectively. Additionally, a compound containing a cyclobutyl ring displayed potent activity, with an IC50 of 16.56±0.125 μM against A-549 and an IC50 of 24.68±0.217 μM against MCF-7 cells, respectively. Furthermore, molecular docking studies against the Epidermal Growth Factor Receptor (EGFR) (PDB ID: 2J6M) revealed favourable binding scores and interactions, suggesting their potential as promising candidates for further investigation in the context of anticancer drug development.

Structure-activity relationship study of 1,6-naphthyridinone derivatives as selective type II AXL inhibitors with potent antitumor efficacy

The role of AXL in various oncogenic processes has made it an attractive target for cancer therapy. Currently, kinase selectivity profiles, especially circumventing MET inhibition, remain a scientific issue of great interest in the discovery of selective type II AXL inhibitors. Starting from a dual MET/AXL-targeted lead structure from our previous work, we optimized a 1,6-naphthyridinone series using molecular modeling-assisted compound design to improve AXL potency and selectivity over MET, resulting in the potent and selective type II AXL-targeted compound 25c. This showed excellent AXL inhibitory activity (IC50 = 1.1 nM) and 343-fold selectivity over the highly homologous kinase MET in biochemical assays. Moreover, compound 25c significantly inhibited AXL-driven cell proliferation, dose-dependently suppressed 4T1 cell migration and invasion, and induced apoptosis. Compound 25c also showed noticeable antitumor efficacy in a BaF3/TEL-AXL xenograft model at well-tolerated doses. Overall, this study presented a potent and selective type II AXL-targeted lead compound for further drug discovery.

Discovery of a 1,6-naphthyridin-4-one-based AXL inhibitor with improved pharmacokinetics and enhanced in vivo antitumor efficacy

The receptor tyrosine kinase AXL has emerged as an attractive target in anticancer drug discovery. Herein, we described the discovery of a new series of 1,6-naphthyridin-4-one derivatives as potent AXL inhibitors. Starting from a low in vivo potency compound 9 which was previously reported by our group, we utilized structure-based drug design and scaffold hopping strategies to discover potent AXL inhibitors. The privileged compound 13c was a highly potent and orally bioavailable AXL inhibitor with an IC50 value of 3.2 ± 0.3 nM. Compound 13c exhibited significantly improved in vivo antitumor efficacy in AXL-driven tumor xenograft mice, causing tumor regression at well-tolerated dose, and demonstrated favorable pharmacokinetic properties (MRT = 16.5 h, AUC0-∞ = 59,815 ng h/mL) in Sprague-Dawley rats. These results suggest that 13c is a promising therapeutic candidate for AXL-targeting cancer treatment.

Structure-based drug discovery of novel fused-pyrazolone carboxamide derivatives as potent and selective AXL inhibitors

As a novel and promising antitumor target, AXL plays an important role in tumor growth, metastasis, immunosuppression and drug resistance of various malignancies, which has attracted extensive research interest in recent years. In this study, by employing the structure-based drug design and bioisosterism strategies, we designed and synthesized in total 54 novel AXL inhibitors featuring a fused-pyrazolone carboxamide scaffold, of which up to 20 compounds exhibited excellent AXL kinase and BaF3/TEL-AXL cell viability inhibitions. Notably, compound 59 showed a desirable AXL kinase inhibitory activity (IC50: 3.5 nmol/L) as well as good kinase selectivity, and it effectively blocked the cellular AXL signaling. In turn, compound 59 could potently inhibit BaF3/TEL-AXL cell viability (IC50: 1.5 nmol/L) and significantly suppress GAS6/AXL-mediated cancer cell invasion, migration and wound healing at the nanomolar level. More importantly, compound 59 oral administration showed good pharmacokinetic profile and in vivo antitumor efficiency, in which we observed significant AXL phosphorylation suppression, and its antitumor efficacy at 20 mg/kg (qd) was comparable to that of BGB324 at 50 mg/kg (bid), the most advanced AXL inhibitor. Taken together, this work provided a valuable lead compound as a potential AXL inhibitor for the further antitumor drug development.

Discovery of AXL Degraders with Improved Potencies in Triple-Negative Breast Cancer (TNBC) Cells

AXL kinase is heavily involved in tumorigenesis, metastasis, and drug resistance of many cancers, and several AXL inhibitors are in clinical investigations. Recent studies demonstrated that the N-terminal distal region of AXL plays more important roles in cell invasiveness than its C-terminal kinase domain. Therefore, degradation of AXL may present a novel superior therapeutic approach than the kinase inhibitor therapy. Herein, we report the discovery of a series of new AXL PROTAC degraders. One representative compound 6n potently depletes AXL with a DC₅₀ value of 5 nM in MDA-MB-231 TNBC cells. It also demonstrates significantly improved potencies against the AXL signaling activation, cell proliferation, migration and invasion of TNBC cells comparing with the corresponding kinase inhibitor. Moreover, the compound exhibits promising therapeutic potential both in patient-derived organoids and a xenograft mouse model of MDA-MB-231 cells.

Discovery of 10H-Benzo[b]pyrido[2,3-e][1,4]oxazine AXL Inhibitors via Structure-Based Drug Design Targeting c-Met Kinase

Receptor tyrosine kinase AXL exerts pivotal roles in cancer cell survival, metastasis, and drug resistance. Pharmacologic or genetic targeting of the aberrant AXL signaling has proven preferable antitumor efficacies in both preclinical and clinical studies, which highlights AXL as an attractive antitumor drug target. By conformational restriction of the anilinopyrimidine 10e and systematic structure-activity relationship (SAR) exploration, we discovered 10H-benzo[b]pyrido[2,3-e][1,4]oxazine 16j as a potent and orally bioavailable AXL inhibitor. As a type II AXL inhibitor, compound 16j displayed about 15-fold selectivity for AXL over its highly homologous kinase c-Met. And it significantly blocked cellular AXL signaling, inhibited AXL-mediated cell proliferation, and impaired growth arrest-specific protein 6 (Gas6)/AXL-stimulated cell migration and invasion. Moreover, 16j exhibited significant antitumor efficacy in AXL-driven xenograft model at a well-tolerant dosage, causing tumor stasis or regression.

AXL kinase inhibitors- A prospective model for medicinal chemistry strategies in anticancer drug discovery

Deviant expressions of the tyrosine kinase AXL receptor are strongly correlated with a plethora of malignancies. Henceforth, the topic of targeting AXL is beginning to gain prominence due to mounting evidence of the protein's substantial connection to poor prognosis and treatment resistance. This year marked a milestone in clinical testing for AXL as an anti-carcinogenic target, with the start of the first AXL-branded inhibitor study. It is critical to emphasize that AXL is a primary and secondary target in various kinase inhibitors that have been approved or are on the verge of being approved while interpreting the present benefits and future potential effects of AXL suppression in the clinical setting. Several research arenas across the globe resolutely affirm the crucial significance of AXL receptors in the case study of several pathophysiologies including AML, prostate cancer, and breast cancer. This review endeavors to delve deeply into the biological, chemical, and structural features of AXL kinase; primary AXL inhibitors that target the enzyme (either purposefully or unintentionally); and the prospects and barriers for turning AXL inhibitors into a feasible treatment alternative. Furthermore, we analyse the co-crystal structure of AXL, which remains extensively unexplored, as well as the mutations of AXL that may be valuable in the development of novel inhibitors in the upcoming future and take a comprehensive look at the medicinal chemistry of AXL inhibitors of recent years.

The Expanding Role of Pyridine and Dihydropyridine Scaffolds in Drug Design

Pyridine-based ring systems are one of the most extensively used heterocycles in the field of drug design, primarily due to their profound effect on pharmacological activity, which has led to the discovery of numerous broad-spectrum therapeutic agents. In the US FDA database, there are 95 approved pharmaceuticals that stem from pyridine or dihydropyridine, including isoniazid and ethionamide (tuberculosis), delavirdine (HIV/AIDS), abiraterone acetate (prostate cancer), tacrine (Alzheimer's), ciclopirox (ringworm and athlete's foot), crizotinib (cancer), nifedipine (Raynaud's syndrome and premature birth), piroxicam (NSAID for arthritis), nilvadipine (hypertension), roflumilast (COPD), pyridostigmine (myasthenia gravis), and many more. Their remarkable therapeutic applications have encouraged researchers to prepare a larger number of biologically active compounds decorated with pyridine or dihydropyridine, expandeing the scope of finding a cure for other ailments. It is thus anticipated that myriad new pharmaceuticals containing the two heterocycles will be available in the forthcoming decade. This review examines the prospects of highly potent bioactive molecules to emphasize the advantages of using pyridine and dihydropyridine in drug design. We cover the most recent developments from 2010 to date, highlighting the ever-expanding role of both scaffolds in the field of medicinal chemistry and drug development.

A Gadolinium DO3A Amide m-Phenyl Boronic Acid MRI Probe for Targeted Imaging of Sialated Solid Tumors

We developed a new probe, Gd-DO3A-Am-PBA, for imaging tumors. Our results showed active targeting of Gd-DO3A-Am-PBA to sialic acid (SA) moieties, with increased cellular labeling in vitro and enhanced tumor accumulation and retention in vivo, compared to the commercial Gadovist. The effectiveness of our newly synthesized probe lies in its adequate retention phase, which is expected to provide a suitable time window for tumor diagnosis and a faster renal clearance, which will reduce toxicity risks when translated to clinics. Hence, this study can be extended to other tumor types that express SA on their surface. Targeting and MR imaging of any type of tumors can also be achieved by conjugating the newly synthesized contrast agent with specific antibodies. This study thus opens new avenues for drug delivery and tumor diagnosis via imaging.