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

Unraveling the future: Innovative design strategies and emerging challenges in HER2-targeted tyrosine kinase inhibitors for cancer therapy

Human epidermal growth factor receptor 2 (HER2) is a transmembrane receptor-like protein with tyrosine kinase activity that plays a vital role in processes such as cell proliferation, differentiation, and angiogenesis. The degree of malignancy of different cancers, notably breast cancer, is strongly associated with HER2 amplification, overexpression, and mutation. Currently, widely used clinical HER2 tyrosine kinase inhibitors (TKIs), such as lapatinib and neratinib, have several drawbacks, including susceptibility to drug resistance caused by HER2 mutations and adverse effects from insufficient HER2 selectivity. To address these issues, it is essential to create innovative HER2 TKIs with enhanced safety, effectiveness against mutations, and high selectivity. Typically, SPH5030 has advanced to phase I clinical trials for its strong suppression of four HER2 mutations. This review discusses the latest research progress in HER2 TKIs, with a focus on the structural optimization process and structure-activity relationship analysis. In particular, this study highlights promising design strategies to address these challenges, providing insightful information and inspiration for future development in this field.

Management of HER2 alterations in non-small cell lung cancer - The past, present, and future

HER2 mutations, which account for 2-4% of non-small cell lung cancer (NSCLC), are distinct molecular alterations identified via next generation sequencing (NGS). Previously, treatment outcomes in HER2-mutant metastatic NSCLC were dismal, showing limited clinical benefit with platinum-based chemotherapy with or without immunotherapy. In contrast to HER2-altered breast and gastric cancer, HER2-mutant NSCLC does not benefit from HER2 targeting agents such as trastuzumab or TDM1. HER2 mutations are also inherently different from HER2 overexpression and amplification. Currently, trastuzumab deruxtecan, a HER2 targeting antibody drug conjugate (ADC) is the first and only approved treatment option for patients with HER2-mutant metastatic NSCLC after failure with standard treatment. In this review, we summarized the biology of HER2 and detection of HER2 overexpression, amplification and mutations, as well as general landscape of landmark and ongoing clinical trials encompassing from chemotherapy to targeted agents, including tyrosine kinase inhibitors (TKIs), ADCs and investigational agents.

4-Aminopyrazolopyrimidine scaffold and its deformation in the design of tyrosine and serine/threonine kinase inhibitors in medicinal chemistry

Deformation of the 4-aminopyrazolopyrimidine scaffold in designing small-molecule inhibitors.

Prolonged Response to HER2-Directed Therapy in Three Patients with HER2-Amplified Metastatic Carcinoma of the Biliary System: Case Study and Review of the Literature

HER2 amplification, which results in overexpression of the receptor tyrosine kinase HER2, has been described in a wide variety of malignancies. HER2-targeting agents have been incorporated into the treatment paradigms for HER2-overexpressing breast and gastric cancer. More recently, these agents have shown promise in other gastrointestinal malignancies, such as colon cancer and biliary tract tumors. This study discusses two patients with gallbladder carcinoma and a third with ampullary carcinoma who were able to achieve marked responses to HER2-directed therapy. These cases underscore the importance of molecular analysis for HER2 amplification/HER2 overexpression, irrespective of tumor histology, and highlight a need for further investigation of HER2-directed therapy beyond breast and gastroesophageal cancers. KEY POINTS: Current guidelines recommend molecular assessment for HER2 overexpression exclusively in breast and gastric adenocarcinoma. The focus of this report is on three cases (two biliary tract and one ampullary carcinoma) in which amplification of HER2 or overexpression of HER2 was detected and treatment with HER2-directed therapy resulted in robust responses. These cases exemplify responsiveness of non-breast/gastric histologies to HER2-directed therapies, highlighting several promising new settings for these agents. Testing for amplification of HER2 or overexpression of HER2 should be considered especially in rare diseases with limited treatment options.

Preclinical Activity of HER2-Selective Tyrosine Kinase Inhibitor Tucatinib as a Single Agent or in Combination with Trastuzumab or Docetaxel in Solid Tumor Models

HER2 is a transmembrane tyrosine kinase receptor that mediates cell growth, differentiation, and survival. HER2 is overexpressed in approximately 20% of breast cancers and in subsets of gastric, colorectal, and esophageal cancers. Both antibody and small-molecule drugs that target HER2 and block its tyrosine kinase activity are effective in treating HER2-driven cancers. In this article, we describe the preclinical properties of tucatinib, an orally available, reversible HER2-targeted small-molecule tyrosine kinase inhibitor. In both biochemical and cell signaling experiments, tucatinib inhibits HER2 kinase activity with single-digit nanomolar potency and provides exceptional selectivity for HER2 compared with the related receptor tyrosine kinase EGFR, with a >1,000-fold enhancement in potency for HER2 in cell signaling assays. Tucatinib potently inhibits signal transduction downstream of HER2 and HER3 through the MAPK and PI3K/AKT pathways and is selectively cytotoxic in HER2-amplified breast cancer cell lines in vitro. In vivo, tucatinib is active in multiple HER2⁺ tumor models as a single agent and shows enhanced antitumor activity in combination with trastuzumab or docetaxel, resulting in improved rates of partial and complete tumor regression. These preclinical data, taken together with the phase-I tucatinib clinical trial results demonstrating preliminary safety and activity, establish the unique pharmacologic properties of tucatinib and underscore the rationale for investigating its utility in HER2⁺ cancers. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/4/976/F1.large.jpg.

A first-in-human phase I study of TAS0728, an oral covalent binding inhibitor of HER2, in patients with advanced solid tumors with HER2 or HER3 aberrations

TAS0728 is an oral covalent binding inhibitor of human epidermal growth factor receptor 2 (HER2). A first-in-human open-label, dose-escalation, phase I study (NCT03410927) was initiated to investigate the safety and dose-limiting toxicity (DLT) and to determine the maximum tolerated dose (MTD) and/or recommended phase II dose of TAS0728 in adults with advanced solid tumors with HER2 or HER3 overexpression, amplification or mutation. In total, 19 patients received TAS0728 at escalating doses from 50 to 200 mg BID for 21-day cycles. Following escalation of the dose to 200 mg BID, a total of two DLTs were observed, both cases of Grade 3 diarrhea (lasting >48 h and not responsive to aggressive antidiarrheal treatment). Following de-escalation of the dose to 150 mg BID, another DLT of Grade 3 diarrhea was observed in one patient. Additionally, at 150 mg BID, one patient had a fatal cardiac arrest after receiving 1 cycle (21 days) of TAS0728. The etiology of the cardiac arrest event was not clear, however causal relationship to TAS0728 could not be excluded due to the temporal association observed. Partial responses were observed in 2 of 14 patients evaluable for TAS0728 treatment response. The study was stopped due to unacceptable toxicity during the dose-escalation as the overall risk-benefit ratio no longer favored the dose level being tested, therefore the MTD was not determined. ClinicalTrials.gov registration number: https://clinicaltrials.gov/ct2/show/NCT03410927 ; registered on January 25, 2018.

Acquired resistance to trastuzumab/pertuzumab or to T-DM1 in vivo can be overcome by HER2 kinase inhibition with TAS0728

HER2‐targeting antibodies (trastuzumab, pertuzumab) and a HER2‐directed antibody‐drug conjugate (trastuzumab emtansine: T‐DM1) are used for the treatment of HER2‐overexpressing breast cancer. However, these treatments eventually become ineffective due to acquired resistance and there is an urgent need for alternative therapies. TAS0728 is a small‐molecule, irreversible selective HER2 kinase inhibitor. In the present study, we established new in vivo models of cancer resistance by continuous exposure to a combination of trastuzumab and pertuzumab or to T‐DM1 for evaluating the effect of TAS0728 on HER2 antibody‐resistant populations. Treatment with trastuzumab and pertuzumab or with T‐DM1 initially induced tumor regression in NCI‐N87 xenografts. However, tumor regrowth during treatment indicated loss of drug effectiveness. In tumors with acquired resistance to trastuzumab and pertuzumab or to T‐DM1, HER2‐HER3 phosphorylation was retained. Switching to TAS0728 resulted in a significant anti‐tumor effect associated with HER2‐HER3 signal inhibition. No alternative receptor tyrosine kinase activation was observed in these resistant tumors. Furthermore, in a patient‐derived xenograft model derived from breast cancer refractory to both trastuzumab/pertuzumab and T‐DM1, TAS0728 exerted a potent anti‐tumor effect. These results suggest that tumors with acquired resistance to trastuzumab and pertuzumab and to T‐DM1 are still dependent on oncogenic HER2‐HER3 signaling and are vulnerable to HER2 signal inhibition by TAS0728. These results provide a rationale for TAS0728 therapy for breast cancers that are refractory to established anti‐HER2 therapies.

Elucidating target specificity of the taccalonolide covalent microtubule stabilizers employing a combinatorial chemical approach

The taccalonolide microtubule stabilizers covalently bind β-tubulin and overcome clinically relevant taxane resistance mechanisms. Evaluations of the target specificity and detailed drug-target interactions of taccalonolides, however, have been limited in part by their irreversible target engagement. In this study, we report the synthesis of fluorogenic taccalonolide probes that maintain the native biological properties of the potent taccalonolide, AJ. These carefully optimized, cell-permeable probes outperform commercial taxane-based probes and enable direct visualization of taccalonolides in both live and fixed cells with dramatic microtubule colocalization. The specificity of taccalonolide binding to β-tubulin is demonstrated by immunoblotting, which allows for determination of the relative contribution of key tubulin residues and taccalonolide moieties for drug-target interactions by activity-based protein profiling utilizing site-directed mutagenesis and computational modeling. This combinatorial approach provides a generally applicable strategy for investigating the binding specificity and molecular interactions of covalent binding drugs in a cellular environment.