Vepafestinib is a pharmacologically advanced RET-selective inhibitor with high CNS penetration and inhibitory activity against RET solvent front mutations.

RET receptor tyrosine kinase is activated in various cancers (lung, thyroid, colon and pancreatic, among others) through oncogenic fusions or gain-of-function single-nucleotide variants. Small-molecule RET kinase inhibitors became standard-of-care therapy for advanced malignancies driven by RET. The therapeutic benefit of RET inhibitors is limited, however, by acquired mutations in the drug target as well as brain metastasis, presumably due to inadequate brain penetration. Here, we perform preclinical characterization of vepafestinib (TAS0953/HM06), a next-generation RET inhibitor with a unique binding mode. We demonstrate that vepafestinib has best-in-class selectivity against RET, while exerting activity against commonly reported on-target resistance mutations (variants in RETL730, RETV804 and RETG810), and shows superior pharmacokinetic properties in the brain when compared to currently approved RET drugs. We further show that these properties translate into improved tumor control in an intracranial model of RET-driven cancer. Our results underscore the clinical potential of vepafestinib in treating RET-driven cancers.

Discovery of Futibatinib: The First Covalent FGFR Kinase Inhibitor in Clinical Use.

Deregulating fibroblast growth factor receptor (FGFR) signaling is a promising strategy for cancer therapy. Herein, we report the discovery of compound 5 (TAS-120, futibatinib), a potent and selective covalent inhibitor of FGFR1-4, starting from a unique dual inhibitor of mutant epidermal growth factor receptor and FGFR (compound 1). Compound 5 inhibited all four families of FGFRs in the single-digit nanomolar range and showed high selectivity for over 387 kinases. Binding site analysis revealed that compound 5 covalently bound to the cysteine 491 highly flexible glycine-rich loop region of the FGFR2 adenosine triphosphate pocket. Futibatinib is currently in Phase I-III trials for patients with oncogenically driven FGFR genomic aberrations. In September 2022, the U.S. Food & Drug Administration granted accelerated approval for futibatinib in the treatment of previously treated, unresectable, locally advanced, or metastatic intrahepatic cholangiocarcinoma harboring an FGFR2 gene fusion or other rearrangement.

TAS2940, a novel brain-penetrable pan-ERBB inhibitor, for tumors with HER2 and EGFR aberrations.

Genetic alterations in human epidermal growth factor receptor type 2 (HER2)/epidermal growth factor receptor (EGFR) are commonly associated with breast and lung cancers and glioblastomas. Cancers with avian erythroblastosis oncogene B (ERBB) deregulation are highly metastatic and can cause primary brain tumors. Currently, no pan-ERBB inhibitor with remarkable brain penetration is available. Here, TAS2940, a novel irreversible pan-ERBB inhibitor with improved brain penetrability, was evaluated for its efficacy against several ERBB aberrant cancer models. The selectivity of TAS2940 was evaluated by enzymatic kinase assays. The inhibitory effects of TAS2940 against ERBB genetic alterations were examined using MCF10A cells expressing various HER2 or EGFR mutations and other generic cell lines harboring deregulated ERBB expression. In vivo efficacy of TAS2940 was examined following oral treatment in subcutaneous or intracranial xenograft cancer models. TAS2940 was highly potent against cells harboring HER2/EGFR alterations. TAS2940 could selectively inhibit phosphorylation of targets and the growth of cancer cells with ERBB aberrations in vitro. TAS2940 also inhibited tumor growth in xenograft mouse models with ERBB aberrations: HER2 amplification, HER2/EGFR exon 20 insertions, and EGFR vIII mutation. TAS2940 was effective in the intracranial xenograft models of HER2/EGFR cancers and improved the survival of these mice. TAS2940 has promising therapeutic effects in preclinical study against cancers harboring HER2/EGFR mutations, especially metastatic and primary brain tumors. Our results highlight potential novel strategies against lung cancers with brain metastases harboring HER2/EGFR exon 20 insertions and glioblastomas with EGFR aberrations.

Futibatinib Is a Novel Irreversible FGFR 1-4 Inhibitor That Shows Selective Antitumor Activity against FGFR-Deregulated Tumors.

FGFR signaling is deregulated in many human cancers, and FGFR is considered a valid target in FGFR-deregulated tumors. Here, we examine the preclinical profile of futibatinib (TAS-120; 1-[(3S)-[4-amino-3-[(3,5-dimethoxyphenyl)ethynyl]-1H-pyrazolo[3, 4-d] pyrimidin-1-yl]-1-pyrrolidinyl]-2-propen-1-one), a structurally novel, irreversible FGFR1-4 inhibitor. Among a panel of 296 human kinases, futibatinib selectively inhibited FGFR1-4 with IC50 values of 1.4 to 3.7 nmol/L. Futibatinib covalently bound the FGFR kinase domain, inhibiting FGFR phosphorylation and, in turn, downstream signaling in FGFR-deregulated tumor cell lines. Futibatinib exhibited potent, selective growth inhibition of several tumor cell lines (gastric, lung, multiple myeloma, bladder, endometrial, and breast) harboring various FGFR genomic aberrations. Oral administration of futibatinib led to significant dose-dependent tumor reduction in various FGFR-driven human tumor xenograft models, and tumor reduction was associated with sustained FGFR inhibition, which was proportional to the administered dose. The frequency of appearance of drug-resistant clones was lower with futibatinib than a reversible ATP-competitive FGFR inhibitor, and futibatinib inhibited several drug-resistant FGFR2 mutants, including the FGFR2 V565I/L gatekeeper mutants, with greater potency than any reversible FGFR inhibitors tested (IC50, 1.3-50.6 nmol/L). These results indicate that futibatinib is a novel orally available, potent, selective, and irreversible inhibitor of FGFR1-4 with a broad spectrum of antitumor activity in cell lines and xenograft models. These findings provide a strong rationale for testing futibatinib in patients with tumors oncogenically driven by FGFR genomic aberrations, with phase I to III trials ongoing. SIGNIFICANCE: Preclinical characterization of futibatinib, an irreversible FGFR1-4 inhibitor, demonstrates selective and potent antitumor activity against FGFR-deregulated cancer cell lines and xenograft models, supporting clinical evaluation in patients with FGFR-driven tumors. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/22/4986/F1.large.jpg.

TAS6417/CLN-081 Is a Pan-Mutation-Selective EGFR Tyrosine Kinase Inhibitor with a Broad Spectrum of Preclinical Activity against Clinically Relevant EGFR Mutations.

Despite the worldwide approval of three generations of EGFR tyrosine kinase inhibitors (TKI) for advanced non-small cell lung cancers with EGFR mutations, no TKI with a broad spectrum of activity against all clinically relevant mutations is currently available. In this study, we sought to evaluate a covalent mutation-specific EGFR TKI, TAS6417 (also named CLN-081), with the broadest level of activity against EGFR mutations with a prevalence of ≥1%. Lung cancer and genetically engineered cell lines, as well as murine xenograft models were used to evaluate the efficacy of TAS6417 and other approved/in-development EGFR TKIs (erlotinib, afatinib, osimertinib, and poziotinib). We demonstrate that TAS6417 is a robust inhibitor against the most common EGFR mutations (exon 19 deletions and L858R) and the most potent against cells harboring EGFR-T790M (first/second-generation TKI resistance mutation). In addition, TAS6417 has activity in cells driven by less common EGFR-G719X, L861Q, and S768I mutations. For recalcitrant EGFR exon 20 insertion mutations, selectivity indexes (wild-type EGFR/mutant EGFR ratio of inhibition) favored TAS6417 in comparison with poziotinib and osimertinib, indicating a wider therapeutic window. Taken together, we demonstrate that TAS6417 is a potent EGFR TKI with a broad spectrum of activity and a wider therapeutic window than most approved/in-development generations of EGFR inhibitors. IMPLICATIONS: TAS6417/CLN-081 is a potent EGFR TKI with a wide therapeutic window and may be effective in lung cancer patients with clinically relevant EGFR mutations.

TAS0728, A Covalent-binding, HER2-selective Kinase Inhibitor Shows Potent Antitumor Activity in Preclinical Models.

Activated HER2 is a promising therapeutic target for various cancers. Although several reports have described HER2 inhibitors in development, no covalent-binding inhibitor selective for HER2 has been reported. Here, we report a novel compound TAS0728 that covalently binds to HER2 at C805 and selectively inhibits its kinase activity. Once TAS0728 bound to HER2 kinase, the inhibitory activity was not affected by a high ATP concentration. A kinome-wide biochemical panel and cellular assays established that TAS0728 possesses high specificity for HER2 over wild-type EGFR. Cellular pharmacodynamics assays using MCF10A cells engineered to express various mutated HER2 genes revealed that TAS0728 potently inhibited the phosphorylation of mutated HER2 and wild-type HER2. Furthermore, TAS0728 exhibited robust and sustained inhibition of the phosphorylation of HER2, HER3, and downstream effectors, thereby inducing apoptosis of HER2-amplified breast cancer cells and in tumor tissues of a xenograft model. TAS0728 induced tumor regression in mouse xenograft models bearing HER2 signal-dependent tumors and exhibited a survival benefit without any evident toxicity in a peritoneal dissemination mouse model bearing HER2-driven cancer cells. Taken together, our results demonstrated that TAS0728 may offer a promising therapeutic option with improved efficacy as compared with current HER2 inhibitors for HER2-activated cancers. Assessment of TAS0728 in ongoing clinical trials is awaited (NCT03410927).

Discovery of 3-Ethyl-4-(3-isopropyl-4-(4-(1-methyl-1 H-pyrazol-4-yl)-1 H-imidazol-1-yl)-1 H-pyrazolo[3,4- b]pyridin-1-yl)benzamide (TAS-116) as a Potent, Selective, and Orally Available HSP90 Inhibitor.

The molecular chaperone heat shock protein 90 (HSP90) is a promising target for cancer therapy, as it assists in the stabilization of cancer-related proteins, promoting cancer cell growth, and survival. A novel series of HSP90 inhibitors were discovered by structure-activity relationship (SAR)-based optimization of an initial hit compound 11a having a 4-(4-(quinolin-3-yl)-1 H-indol-1-yl)benzamide structure. The pyrazolo[3,4- b]pyridine derivative, 16e (TAS-116), is a selective inhibitor of HSP90α and HSP90ß among the HSP90 family proteins and exhibits oral availability in mice. The X-ray cocrystal structure of the 16e analogue 16d demonstrated a unique binding mode at the N-terminal ATP binding site. Oral administration of 16e demonstrated potent antitumor effects in an NCI-H1975 xenograft mouse model without significant body weight loss.

Structural basis of human p70 ribosomal S6 kinase-1 regulation by activation loop phosphorylation.

p70 ribosomal S6 kinase (p70S6K) is a downstream effector of the mTOR signaling pathway involved in cell proliferation, cell growth, cell-cycle progression, and glucose homeostasis. Multiple phosphorylation events within the catalytic, autoinhibitory, and hydrophobic motif domains contribute to the regulation of p70S6K. We report the crystal structures of the kinase domain of p70S6K1 bound to staurosporine in both the unphosphorylated state and in the 3'-phosphoinositide-dependent kinase-1-phosphorylated state in which Thr-252 of the activation loop is phosphorylated. Unphosphorylated p70S6K1 exists in two crystal forms, one in which the p70S6K1 kinase domain exists as a monomer and the other as a domain-swapped dimer. The crystal structure of the partially activated kinase domain that is phosphorylated within the activation loop reveals conformational ordering of the activation loop that is consistent with a role in activation. The structures offer insights into the structural basis of the 3'-phosphoinositide-dependent kinase-1-induced activation of p70S6K and provide a platform for the rational structure-guided design of specific p70S6K inhibitors.