Pyrrolo[2,3-d]pyrimidine derivatives as inhibitors of RET: Design, synthesis and biological evaluation

Pyrazolopyridine-based kinase inhibitors for anti-cancer targeted therapy

The need for effective cancer treatments continues to be a challenge for the biomedical research community. In this case, the advent of targeted therapy has significantly improved therapeutic outcomes. Drug discovery and development efforts targeting kinases have resulted in the approval of several small-molecule anti-cancer drugs based on ATP-mimicking heterocyclic cores. Pyrazolopyridines are a group of privileged heterocyclic cores in kinase drug discovery, which are present in several inhibitors that have been developed against various cancers. Notably, selpercatinib, glumetinib, camonsertib and olverembatinib have either received approval or are in late-phase clinical studies. This review presents the success stories employing pyrazolopyridine scaffolds as hinge-binding cores to address various challenges in kinase-targeted drug discovery research.

Ligand-Enabled C6-Selective C-H Arylation of Pyrrolo[2,3-d] Pyrimidine Derivatives with Pd Catalysts: An Approach to the Synthesis of EGFR Inhibitor AEE-788

Herein, we report the Pd(II)-catalyzed direct C-H arylation of pyrrolo[2,3-d]pyrimidine derivatives with aryl iodides, which is enabled by bidentate pyridine-pyridine ligands. A range of aryl iodides proved to be suitable coupling partners affording the desired products in good yields with high levels of C6 selectivity. This protocol features good tolerance of reactive functional groups, mild reaction conditions, and a simple reaction system, which provides an expeditious route to an essential class of 6-arylpyrrolo[2,3-d]pyrimidines frequently found in bioactive compounds, and provides a step-economical access to the second-generation EGFR inhibitor AEE-788.

Discovery of 9H-pyrimido[4,5-b]indole derivatives as dual RET/TRKA inhibitors

Aberrant RET kinase signaling is activated in numerous cancers including lung, thyroid, breast, pancreatic, and prostate. Recent approvals of selective RET inhibitors, pralsetinib and selpercatinib, has shifted the focus of RET kinase drug discovery programs towards the development of selective inhibitors. However, selective inhibitors invariably lose efficacy as the selective nature of the inhibitor places Darwinian-like pressure on the tumor to bypass treatment through the selection of novel oncogenic drivers. Further, selective inhibitors are restricted for use in tumors with specific genetic backgrounds that do not encompass diverse patient classes. Here we report the identification of a pyrimido indole RET inhibitor found to also have activity against TRK. This selective dual RET/TRK inhibitor can be utilized in tumors with both RET and TRK genetic backgrounds and can also provide blockade of NTRK-fusions that are selected for from RET inhibitor treatments. Efforts towards developing dual RET/TRK inhibitors can be beneficial in terms of encompassing more diverse patient classes while also achieving blockade against emerging resistance mechanisms.

Revisiting Aurora Kinase B: A promising therapeutic target for cancer therapy

Cancer continues to be a major health concern globally, although the advent of targeted therapy has revolutionized treatment options. Aurora Kinase B is a serine-threonine kinase that has been explored as an oncology therapeutic target for more than two decades. Aurora Kinase B inhibitors show promising biological results in in-vitro and in-vivo experiments. However, there are no inhibitors approved yet for clinical use, primarily because of the side effects associated with Aurora B inhibitors. Several studies demonstrate that Aurora B inhibitors show excellent synergy with various chemotherapeutic agents, radiation therapy, and targeted therapies. This makes it an excellent choice as an adjuvant therapy to first-line therapies, which greatly improves the therapeutic window and side effect profile. Recent studies indicate the role of Aurora B in some deadly cancers with limited therapeutic options, like triple-negative breast cancer and glioblastoma. Herein, we review the latest developments in Aurora Kinase B targeted research, with emphasis on its potential as an adjuvant therapy and its role in some of the most difficult-to-treat cancers.

Discovery of N-Trisubstituted Pyrimidine Derivatives as Type I RET and RET Gatekeeper Mutant Inhibitors with a Novel Kinase Binding Pose

Mutations of the rearranged during transfection (RET) kinase are frequently reported in cancer, which make it as an attractive therapeutic target. Herein, we discovered a series of N-trisubstituted pyrimidine derivatives as potent inhibitors for both wild-type (wt) RET and RETV804M, which is a resistant mutant for several FDA-approved inhibitors. The X-ray structure of a representative inhibitor with RET revealed that the compound binds in a unique pose that bifurcates beneath the P-loop and confirmed the compound as a type I inhibitor. Through the structure-activity relationship (SAR) study, compound 20 was identified as a lead compound, showing potent inhibition of both RET and RETV804M. Additionally, compound 20 displayed potent antiproliferative activity of CCDC6-RET-driven LC-2/ad cells. Analysis of RET phosphorylation indicated that biological activity was mediated by RET inhibition. Collectively, N-trisubstituted pyrimidine derivatives could serve as scaffolds for the discovery and development of potent inhibitors of type I RET and its gatekeeper mutant for the treatment of RET-driven cancers.

Discovery of imidazo[1,2-a]pyridine-thiophene derivatives as FLT3 and FLT3 mutants inhibitors for acute myeloid leukemia through structure-based optimization of an NEK2 inhibitor

FMS-like tyrosine kinase 3 (FLT3) with an internal tandem duplication (ITD) mutation has been validated as a driver lesion and a therapeutic target for acute myeloid leukemia (AML). Currently, several potent small-molecule FLT3 kinase inhibitors are being evaluated or have completed evaluation in clinical trials. However, many of these inhibitors are challenged by the secondary mutations on kinase domain, especially the point mutations at the activation loop (D835) and gatekeeper residue (F691). To overcome the resistance challenge, we identified a novel series of imidazo[1,2-a]pyridine-thiophene derivatives from a NIMA-related kinase 2 (NEK2) kinase inhibitor CMP3a, which retained inhibitory activities on FTL3-ITD^D835V and FLT3-ITD^F691L. Through this study, we identified the imidazo[1,2-a]pyridine-thiophene derivatives as type-I inhibitors of FLT3. Moreover, we observed compound 5o as an inhibitor displaying equal anti-proliferative activities against FLT3-ITD, FTL3-ITD^D835Y and FLT3-ITD^F691L driven acute myeloid leukemia (AML) cell lines. Meanwhile, the apoptotic effects of compound supported its mechanism of anti-proliferative action. These results indicate that the imidazo[1,2-a]pyridine-thiophene scaffold is promising for targeting acquired resistance caused by FLT3 secondary mutations and compound 5o is an interesting lead in this direction.

Targeting Rearranged during Transfection in Cancer: A Perspective on Small-Molecule Inhibitors and Their Clinical Development

Rearranged during transfection (RET) is a receptor tyrosine kinase essential for the normal development and maturation of a diverse range of tissues. Aberrant RET signaling in cancers, due to RET mutations, gene fusions, and overexpression, results in the activation of downstream pathways promoting survival, growth, and metastasis. Pharmacological manipulation of RET is effective in treating RET-driven cancers, and efforts toward developing RET-specific therapies have increased over the last 5 years. In 2020, RET-selective inhibitors pralsetinib and selpercatinib achieved clinical approval, which marked the first approvals for kinase inhibitors specifically developed to target the RET oncoprotein. This Perspective discusses current development and clinical applications for RET precision medicine by providing an overview of the incremental improvement of kinase inhibitors for use in RET-driven malignancies.

Chasing the Target: New Phenomena of Resistance to Novel Selective RET Inhibitors in Lung Cancer. Updated Evidence and Future Perspectives

Simple Summary

REarranged during Transfection (RET) is an emerging target for several types of cancer, including non-small cell lung cancer (NSCLC). The recent U.S. FDA approval of pralsetinib and selpercatinib raises issues regarding the emergence of secondary mutations and amplifications involved in parallel signaling pathways and receptors, liable for resistance mechanisms. The aim of this review is to explore recent knowledge on RET resistance in NSCLC in pre-clinic and in clinical settings and accordingly, the state-of-the-art in new drugs or combination of drugs development.

Abstract

The potent, RET-selective tyrosine kinase inhibitors (TKIs) pralsetinib and selpercatinib, are effective against the RET V804L/M gatekeeper mutants, however, adaptive mutations that cause resistance at the solvent front RET G810 residue have been found, pointing to the need for the development of the next-generation of RET-specific TKIs. Also, as seen in EGFR- and ALK-driven NSCLC, the rising of the co-occurring amplifications of KRAS and MET could represent other escaping mechanisms from direct inhibition. In this review, we summarize actual knowledge on RET fusions, focusing on those involved in NSCLC, the results of main clinical trials of approved RET-inhibition drugs, with particular attention on recent published results of selective TKIs, and finally, pre-clinical evidence regarding resistance mechanisms and suggestion on hypothetical and feasible drugs combinations and strategies viable in the near future.

Discovery of pyrazolo-thieno[3,2-d]pyrimidinylamino-phenyl acetamides as type-II pan-tropomyosin receptor kinase (TRK) inhibitors: Design, synthesis, and biological evaluation

Tropomyosin receptor kinase (TRK) represents an attractive oncology target for cancer therapy related to its critical role in cancer formation and progression. NTRK fusions are found to occur in 3.3% of lung cancers, 2.2% of colorectal cancers, 16.7% of thyroid cancers, 2.5% of glioblastomas, and 7.1% of pediatric gliomas. In this paper, we described the discovery of the type-II pan-TRK inhibitor 4c through the structure-based drug design strategy from the original hits 1b and 2b. Compound 4c exhibited excellent in vitro TRKA, TRKB, and TRKC kinase inhibitory activity and anti-proliferative activity against human colorectal carcinoma derived cell line KM12. In the NCI-60 human cancer cell lines screen, compound 4g demonstrated nearly 80% of growth inhibition for KM12, while only minimal inhibitory activity was observed for the remaining 59 cancer cell lines. Western blot analysis demonstrated that 4c and its urea cousin 4k suppressed the TPM3-TRKA autophosphorylation at the concentrations of 100 nM and 10 nM, respectively. The work presented that 2-(4-(thieno[3,2-d]pyrimidin-4-ylamino)phenyl)acetamides could serve as a novel scaffold for the discovery and development of type-II pan-TRK inhibitors for the treatment of TRK driven cancers.