Irreversible Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors Research Articles

Plasma ctDNA biomarker study in patients with non-small cell lung cancer with EGFR exon 20 insertion mutation treated with sunvozertinib.

8563 Background: There are limited reports on biomarker studies of non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) exon 20 insertion mutation (exon20ins). Sunvozertinib (DZD9008), an oral, potent, irreversible and selective EGFR tyrosine kinase inhibitor (TKI), has been granted conditional approval in China for the treatment of NSCLC with EGFR exon20ins in the ≥ second-line setting. Here we report biomarker analysis of EGFR exon20ins in large sample size, by pooling data from WU-KONG series of studies. Methods: Serial plasma ctDNA samples were collected from baseline until progressive disease (PD). Next generation sequencing was used to assess EGFR exon20ins in baseline plasma ctDNA, and to analyze genetic alterations in baseline and PD plasma ctDNA to identify potential resistance mechanisms to sunvozertinib. Droplet digital PCR was used to dynamically monitor the quantity of EGFR exon20ins during treatment. In addition, association between baseline EGFR exon20ins and disease characteristics as well as antitumor activity of sunvozertinib was analyzed. Furthermore, in vitro and in vivo experiments were performed to explore potential approach which may overcome the resistance to sunvozertinib. Results: A total of 121 patients were included in this biomarker analysis, among them 81 out of 121 (66.9%) had detectable EGFR exon20ins in baseline plasma ctDNA. There was a positive correlation between detectable EGFR exon20ins and higher number of metastasis sites. In addition, higher EGFR exon20ins abundance was positively correlated with more metastasis sites and brain metastasis. Patients with EGFR exon20ins negative in plasma ctDNA achieved a higher objective response rate (ORR) (68.0% vs. 45.8%) and longer median progression free survival (PFS) (7.4 months vs. 5.5 months) with sunvozertinib treatment. In patients with baseline detectable EGFR exon20ins, the mutant allele decreased over time with treatment in majority of patients (12/14, 85.7%), and the earliest clearance of EGFR exon20ins occurred after one week of treatment. In patients who developed disease progression, 12 of 18 (66.7%) maintained EGFR exon20ins at PD, and among them, 3 concurrently acquired EGFR C797S, all in cis with exon20ins. In addition, EGFR G724S and other genetic aberrations in EGFR downstream signaling pathway, were also detected. Exploratory work on overcoming resistance to sunvozertinib suggests that combination of golidocitinib, a selective JAK1 inhibitor, with chemotherapy could be a potential approach. Conclusions: This study showed that positive EGFR exon20ins in plasma ctDNA is associated with advanced disease characteristics. Sunvozertinib can effectively clear EGFR exon20ins in plasma ctDNA, confirming its direct effect on EGFR pathway. The resistance to sunvozertinib can be through EGFR-dependent and EGFR-independent mechanisms.

The effect of food on the pharmacokinetics of Sutetinib maleate capsule, an irreversible EGFR tyrosine kinase inhibitor, in healthy Chinese subjects.

Sutetinib is an irreversible inhibitor of epidermal growth factor receptor (EGFR) and showed favorable efficacy and safety in patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) harbouring nondrug-resistant rare EGFR mutations. To evaluate the potential food effect, eighteen healthy Chinese subjects were enrolled in a single-centre, randomized, open-label, two-sequence, two-period crossover study. Sutetinib was administered as a single oral 100mg under fasting or fed conditions, and pharmacokinetic sampling was performed following each dose and analysed by a validated liquid chromatography/mass spectrometry method. Safety and tolerability were also evaluated. Food intake slightly decreased maximum plasma concentration (Cmax) and area under the plasma concentration-time curve from time 0 to infinity (AUC0 - inf) of sutetinib (geometric least-squares mean [GLSM] ratio, 80.94% and 86.11%; 90% confidence interval [CI], 68.43-95.72 and 75.88-97.73) and its active metabolite sutetinib N-Oxide (GLSM ratio, 75.58% and 84.00%; 90% CI, 65.69-86.95 and 75.42-93.56), respectively. In addition, the time to maximum plasma concentration (Tmax) of both sutetinib and its metabolite has been prolonged by 2h under fed conditions. A total of 31 adverse events (AEs) occurred during the study, with no serious adverse events (SAE) reported, and no obvious difference was observed between the fasting and fed groups. Our results demonstrated that a high-fat and high-calorie diet caused a significant delay in drug absorption and a marginal reduction in drug exposure. Sutetinib was generally well tolerated in healthy Chinese subjects. (This trial was registered at http://www.chinadrugtrials.org.cn . The registration No. is CTR20201933, and the date of registration is 2020-10-16).

Next-generation EGFR tyrosine kinase inhibitors to overcome C797S mutation in non-small cell lung cancer (2019-2024).

Lung cancer is a leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) accounts for the major portion (80-85%) of all lung cancer cases. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are commonly used as the targeted therapy for EGFR-mutated NSCLC. The FDA has approved first-, second- and third-generation EGFR-TKIs as therapeutics options. Osimertinib, the third-generation irreversible EGFR-TKI, has been approved for the treatment of NSCLC patients with the EGFRT790M mutation. However, due to the EGFRC797S mutation in the kinase domain of EGFR, resistance to osimertinib is observed and that limits the long-term effectiveness of the drug. The C797S mutation is one of the major causes of drug resistance against the third-generation EGFR TKIs. The C797S mutations including EGFR double mutations (19Del/C797S or L858R/C797S) and or EGFR triple mutations (19Del/T790M/C797S or L858R/T790M/C797S) cause major resistance to the third-generation EGFR-TKIs. Therefore, the discovery and development of fourth-generation EGFR-TKIs to target triple mutant EGFR with C797S mutation is a challenging topic in medicinal chemistry research. In this review, we discuss the discovery of novel fourth-generation EGFR TKIs, medicinal chemistry approaches and the strategies to overcome the C797S mutations. In vitro activities of EGFR-TKIs (2019-2024) against mutant EGFR TK, anti-proliferative activities, structural modifications, binding modes of the inhibitors and in vivo efficacies in animal models are discussed here.

Abstract B089: MUC1-C is a common driver of acquired osimertinb resistance in NSCLC

Abstract Background: Osimertinib is an irreversible EGFR tyrosine kinase inhibitor approved for the first-line treatment of patients with metastatic NSCLC harboring EGFR exon 19 deletions or L858R mutations. Patients treated with osimertinib invariably develop acquired resistance by mechanisms involving additional EGFR mutations, MET amplification and other pathways. There is no known involvement of the oncogenic MUC1-C protein in acquired osimertinib resistance. Methods: H1975/EGFR(L858R/T790M) and patient-derived NSCLC cells with acquired osimertinib resistance (EMT, MET amplified, C797S mutation, or PCBP2-BRAF fusion) were investigated for MUC1-C dependence in studies of EGFR pathway activation, clonogenicity and self-renewal capacity. Results: We demonstrate that MUC1-C is upregulated in H1975 osimertinib drug tolerant persister (DTP) cells and is necessary for activation of the EGFR pathway. H1975 cells selected for stable osimertinib resistance (H1975-OR) and MGH700-2D cells isolated from a patient with acquired osimertinib resistance are shown to be dependent on MUC1-C for induction of (i) p-EGFR, p-ERK and p-AKT, (ii) EMT, and (iii) the resistant phenotype. We report that MUC1-C is also required for p-EGFR, p-ERK and p-AKT activation and self-renewal capacity in acquired osimertinib-resistant (i) MET amplified MGH170-1D #2 cells, (ii) MGH121 Res#2/EGFR(T790M/C797S) cells, and (iii) MGH845-1R5/EGFR(19del)/PCBP2-BRAF fusion cells. Importantly, targeting MUC1-C in these diverse models reverses osimertinib resistance. To extend these results, we established MET amplified MGH170-1D #2 tumors in mice and found that treatment with GO-203 inhibitor, which is a cell-penetrating peptide that blocks MUC1-C homodimerization, nuclear localization, and function, results in more pronounced inhibition and that the GO-203+osimertinib combination is more effective than either agent alone. In support of these results, high MUC1 expression is associated with poor prognosis for patients with EGFR mutant NSCLCs and those treated with osimertinib. Conclusions: Our findings demonstrate that MUC1-C is a common effector of osimertinib resistance and is a potential target for the treatment of osimertinib resistant NSCLCs. Citation Format: Naoki Haratake, Hiroki Ozawa, Yoshihiro Morimoto, Nami Yamashita, Tatsuaki Daimon, Atrayee Bhattacharya, Keyi Wang, Ayako Nakashoji, Hideko Isozaki, Aaron Hata, Donald Kufe. MUC1-C is a common driver of acquired osimertinb resistance in NSCLC [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B089.

MUC1-C Is a Common Driver of Acquired Osimertinib Resistance in NSCLC

IntroductionOsimertinib is an irreversible EGFR tyrosine kinase inhibitor approved for the first-line treatment of patients with metastatic NSCLC harboring EGFR exon 19 deletions or L858R mutations. Patients treated with osimertinib invariably develop acquired resistance by mechanisms involving additional EGFR mutations, MET amplification, and other pathways. There is no known involvement of the oncogenic MUC1-C protein in acquired osimertinib resistance. MethodsH1975/EGFR (L858R/T790M) and patient-derived NSCLC cells with acquired osimertinib resistance were investigated for MUC1-C dependence in studies of EGFR pathway activation, clonogenicity, and self-renewal capacity. ResultsWe reveal that MUC1-C is up-regulated in H1975 osimertinib drug-tolerant persister cells and is necessary for activation of the EGFR pathway. H1975 cells selected for stable osimertinib resistance (H1975-OR) and MGH700-2D cells isolated from a patient with acquired osimertinib resistance are found to be dependent on MUC1-C for induction of (1) phospho (p)-EGFR, p-ERK, and p-AKT, (2) EMT, and (3) the resistant phenotype. We report that MUC1-C is also required for p-EGFR, p-ERK, and p-AKT activation and self-renewal capacity in acquired osimertinib-resistant (1) MET-amplified MGH170-1D #2 cells and (2) MGH121 Res#2/EGFR (T790M/C797S) cells. Importantly, targeting MUC1-C in these diverse models reverses osimertinib resistance. In support of these results, high MUC1 mRNA and MUC1-C protein expression is associated with a poor prognosis for patients with EGFR-mutant NSCLCs. ConclusionsOur findings reveal that MUC1-C is a common effector of osimertinib resistance and is a potential target for the treatment of osimertinib-resistant NSCLCs.

Evaluation of the risk of diarrhea induced by epidermal growth factor receptor tyrosine kinase inhibitors with cultured intestinal stem cells originated from crypts in humans and monkeys

Severe diarrhea is a common side effect of epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). We aimed to evaluate the risk of EGFR-TKI-induced diarrhea using spheroids of human and monkey crypt-derived intestinal stem cells. Intestinal spheroids exhibited higher toxic susceptibility to EGFR-TKIs than Caco-2 cells. As concentration of EGFR-TKIs increased, cellular ATP first decreased relative to the control condition, followed by an increase in LDH release, in contrast with their simultaneous changes with traditional cytotoxic anticancer drugs. The toxic sensitivity of spheroids to various EGFR-TKIs corresponded to clinical diarrhea incidence. Afatinib, a second-generation EGFR-TKI, exhibited higher toxic sensitivity compared with the first-generation ones, corresponding to the clinical evidence that afatinib-induced diarrhea is almost inevitable and severe. By contrast, the third-generation osimertinib, which reduces the risk of diarrhea, showed mitigated cytotoxicity compared with afatinib. For irreversible EGFR-TKIs, the decreased ATP level persisted or its recovery was delayed even after drug removal compared with reversible ones. Furthermore, the highest drug accumulation in spheroids (TKIspheroids) and inhibition potency against EGFR (TKIspheroids/Ki) were observed for afatinib. This system would be useful for predicting the risk of EGFR-TKI-induced diarrhea; moreover, on-target cytotoxicity against intestinal stem cells might contribute to clinically observed diarrhea.

Phase 3 study of durvalumab with SBRT for unresected stage I/II, lymph-node negative NSCLC (PACIFIC-4/RTOG3515).

TPS8607 Background: Stereotactic body radiation therapy (SBRT) is a standard treatment for patients with unresectable (UR) stage I/II, lymph-node negative NSCLC, with excellent safety and high rates of primary tumor control. Despite predominant regional and distant failure that increases with tumor size, no adjuvant therapy is approved for these patients. Durvalumab is a selective, high-affinity, human IgG1 monoclonal antibody that blocks PD-L1 binding to PD-1/CD80. In the placebo-controlled, phase 3 PACIFIC trial of patients with stage III UR-NSCLC without disease progression on/after concurrent chemoradiotherapy, durvalumab improved progression-free survival (PFS) and overall survival (OS) with manageable safety (Antonia, et al. 2017; 2018), leading to its approval in stage III UR-NSCLC. Osimertinib is a 3rd-generation, irreversible CNS-active EGFR tyrosine kinase inhibitor that selectively inhibits NSCLC tumors with EGFR-sensitizing mutations (EGFRm). In the recent placebo-controlled, phase 3 ADAURA trial, osimertinib demonstrated statistically significant and clinically meaningful improvement in disease-free survival (DFS) (HR, 0.20 [99.12% CI, 0.14–0.30], P < 0.001) in patients with resected stage IB-IIIA EGFRm NSCLC (Wu, et al. 2020), leading to its approval in an adjuvant setting. Based on data for durvalumab and osimertinib in the early-stage setting, PACIFIC-4 is designed to assess the efficacy and safety of durvalumab combined with SBRT in patients with stage I/II UR-NSCLC and osimertinib after SBRT in patients with stage I/II EGFRm UR-NSCLC. Methods: PACIFIC-4 (NCT03833154) is an international, phase 3 study with two independent cohorts. Eligible patients are ≥18 years of age with stage T1-T3, N0, M0 unresected NSCLC and ECOG PS 0–2. The main cohort of approximately 630 patients will be randomized (1:1) in a double-blind manner, stratified by tumor size and location, to receive durvalumab (1500 mg IV) or placebo every 4 weeks for up to 26 cycles with concurrent standard of care (SoC) SBRT. The primary endpoint in this cohort is PFS (RECIST v1.1) by blinded independent central review; other endpoints include OS, health-related quality of life, and safety. The protocol was amended (v4) to exclude patients with an identified EGFRm from the main cohort and add a separate cohort of approximately 60 patients with EGFRm (L858R or Ex19del) who will receive osimertinib 80 mg PO QD, following SoC SBRT, for up to 36 months. The primary endpoint in this cohort is 4-year PFS (RECIST v1.1) by independent central review; secondary endpoints include PFS, OS, and safety. Trial recruitment is ongoing. Previously presented at the European Lung Cancer Congress (ELCC) 2022, FPN (Final Publication Number): 122TiP, Clifford Robinson et al. – Reused with permission. Clinical trial information: NCT03833154 .

Drug-drug interaction potential of SH-1028, a third-generation EGFR-TKI: in vitro and clinical trials.

SH-1028 is an irreversible third-generation EGFR tyrosine kinase inhibitor (EGFR-TKI) for the treatment of locally advanced or metastatic non-small cell lung cancer (NSCLC). Considering the possibility of combination therapy in patients with NSCLC, we investigated the drug-drug interaction (DDI) potential of SH-1028 both in vitro and in clinical trials. The in vitro studies were conducted to determine the potential of SH-1028 as a substrate, inducer, or inhibitor of cytochrome P450 (CYP) subtypes. A phase I drug-drug interaction study in healthy volunteers was performed to evaluate the impact of co-administering rifampicin (a strong CYP3A4 inducer) and itraconazole (a strong CYP3A4 inhibitor) on the pharmacokinetics of SH-1028. The in vitro experiments showed that SH-1028 was mainly metabolized by CYP3A4. The activities of CYP1A2, 2B6, 2C19, 2D6 and 3A4 enzymes were slightly inhibited in vitro with SH-1028. SH-1028 has no obvious induction effect on CYP1A2 and CYP2B6 activities, but has potential induction effect on CYP3A4 mRNA expression. However, SH-1028 may not induce or inhibit human CYPs significantly at the clinically expected dose (200mg). The geometric mean ratios of pharmacokinetic parameters and their corresponding 90% confidence intervals for SH-1028 in combination and alone did not fall within the range of 80-125%. It is speculated that itraconazole and rifampicin affect the metabolism of SH-1028. In the clinical application of SH-1028, special attention should be paid to the interaction between SH-1028 and drugs or foods that affect the activity of CYP3A4. (Clinical trial registration number: CTR20210558).

Small Molecule EGFR Inhibitors as Anti-Cancer Agents: Discovery, Mechanisms of Action, and Opportunities.

Epidermal growth factor receptors (EGFRs) are a class of receptor tyrosine kinase that are also called ErbB1 and HER1. EGFR tyrosine kinase activity inhibition is considered a promising therapeutic strategy for the treatment of cancer. Many small-molecule inhibitors of EGFR tyrosine kinase (EGFR-TK), from medicinally privileged molecules to commercial drugs, have been overviewed. Particular attention has been paid to the structure of the molecule and its mechanism of action if reported. Subsequent classification of the molecules under discussion has been carried out. Both natural and synthetic and reversible and irreversible EGFR-tyrosine kinase inhibitors have been discussed. Various types of cancers that are caused by overexpression of the EGFR gene, their possible molecular origins, and their natures have also been counted in this article. Because the EGFR signaling pathway controls the proliferation, growth, survival, and differentiation of cells, and the mutated EGFR gene overproduces EGFR protein, which ultimately causes several types of cancer, proper understanding of the molecular dynamics between the protein structure and its inhibitors will lead to more effective and selective EGFR-TKIs, which in turn will be able to save more lives in the battle against cancer.

The landscape of therapeutic vulnerabilities in EGFR inhibitor osimertinib drug tolerant persister cells

Third-generation EGFR tyrosine kinase inhibitors (EGFR-TKIs), including osimertinib, an irreversible EGFR-TKI, are important treatments for non-small cell lung cancer with EGFR-TKI sensitizing or EGFR T790M resistance mutations. While patients treated with osimertinib show clinical benefit, disease progression and drug resistance are common. Emergence of de novo acquired resistance from a drug tolerant persister (DTP) cell population is one mechanism proposed to explain progression on osimertinib and other targeted cancer therapies. Here we profiled osimertinib DTPs using RNA-seq and ATAC-seq to characterize the features of these cells and performed drug screens to identify therapeutic vulnerabilities. We identified several vulnerabilities in osimertinib DTPs that were common across models, including sensitivity to MEK, AURKB, BRD4, and TEAD inhibition. We linked several of these vulnerabilities to gene regulatory changes, for example, TEAD vulnerability was consistent with evidence of Hippo pathway turning off in osimertinib DTPs. Last, we used genetic approaches using siRNA knockdown or CRISPR knockout to validate AURKB, BRD4, and TEAD as the direct targets responsible for the vulnerabilities observed in the drug screen.

372P Global real-world (rw) study of patients (pts) with epidermal growth factor receptor (EGFR) mutated advanced non-small cell lung cancer (NSCLC) treated with first-line (1L) osimertinib: Interim analysis of an rw pt registry in Germany

EGFR tyrosine kinase inhibitors (TKIs) are the standard 1L treatment for pts with advanced NSCLC with EGFR mutations (EGFRm). Osimertinib is a third-generation, irreversible EGFR TKI that selectively inhibits sensitizing and T790M mutations, and is effective in NSCLC central nervous system metastases. In this global rw study, an interim analysis was conducted to evaluate the characteristics and outcomes in pts with advanced EGFRm NSCLC receiving 1L osimertinib in Germany.

363P A multicentre, real-world observational study of efficacy and safety of first-line osimertinib treatment in patients with epidermal growth factor receptor (EGFR) activating mutation-positive advanced non-small cell lung cancer (Reiwa study)

Osimertinib is a third-generation, irreversible EGFR-tyrosine kinase inhibitor (TKI) that selectively inhibits both EGFR-TKI-sensitizing and EGFR-T790M-resistant mutations. In a phase III trial (FLAURA), osimertinib showed efficacy superior to that of first-generation gefitinib and erlotinib, with a similar safety profile and lower rates of serious adverse events. Osimertinib is currently being used as the first-line treatment for patients with advanced EGFR mutation-positive NSCLC. However, the efficacy and safety of osimertinib treatment in clinical practice have not been fully verified.

66 (PB056) - Anti-tumor activity of BDTX-1535, an irreversible CNS penetrant inhibitor of multiple EGFR extracellular domain alterations, in preclinical glioblastoma models

Background: EGFR genetic alterations, including mutation and amplification, are very common in glioblastoma multiforme (GBM), however, no targeted therapy has been approved for this disease. EGFR oncogenic mutations in GBM promote EGFR oncogenic covalent homodimer formation which leads to paradoxical activation and renders reversible inhibitors ineffective. An effective EGFR inhibitor in GBM must meet four conditions:1Highly potent and selective against a broad range of extracellular domain mutations and amplified EGFR,2Wild-type EGFR sparing,3Irreversible binding to circumvent paradoxical activation,4High CNS penetration. Our MAP discovery platform led to the identification of MasterKey inhibitor BDTX-1535, an irreversible 4th-generation CNS penetrant EGFR tyrosine kinase inhibitor (TKI) that potently and selectively targets a broad range of EGFR alterations in GBM. Materials and Methods: BDTX-1535 preclinical exposure was evaluated in multiple species in plasma and brain. Antitumor activity was assessed across a broad range of mouse PDX and allograft models, including an intracranial PDX. 2540 tumors were sequenced with the Tempus xT NGS assay. Mutational frequencies and co-expression status of oncogenic EGFR variants were assessed. The relationship between treatment history and oncogenic EGFR mutational frequency was analyzed. Results: BDTX-1535 is a small molecule that irreversibly inhibits a spectrum of EGFR alterations expressed in GBM together with EGFR amplification, while sparing inhibition of normally expressed wild type EGFR. BDTX-1535 avoids efficacy limiting paradoxical activation that can occur with reversible EGFR inhibitors. BDTX-1535 exhibits good oral bioavailability and a CNS Kpuu of 0.55 and 0.48 in rat and dog, respectively, comparing favorably with other CNS penetrant TKIs. Tumor regression and survival advantage were observed across all tumor models with EGFR amplification or mutation, including in an intracranial PDX model. EGFR mutations and amplification are commonly expressed in GBM. Consistent with published data, EGFR mutations, variants, and copy number gain were frequently co-expressed. For example, among tumors expressing EGFRvIII, ∼95% co-expressed at least one other variant, and among tumors expressing EGFRvVI, ∼45% co-expressed at least one other variant. Within a subset of GBM patients with longitudinal sequencing data, oncogenic EGFR mutations were expressed and persisted following front-line treatment. Conclusions: BDTX-1535 is a potent, CNS penetrant, irreversible small molecule EGFR inhibitor that shows efficacy against a broad range of extracellular domain mutations and EGFR amplification found in GBM patients. RWE findings demonstrate a heterogeneous EGFR mutational profile in GBM patients, with persistent prevalence over time. BDTX-1535 is currently in a phase I clinical study (NCT05256290). Conflict of interest: Ownership: Black Diamond Therapeutics Tempus Labs

64 (PB054) - BDTX-1535, a fourth generation EGFR inhibitor, targeting intrinsic and acquired resistance mutations in NSCLC

Background: The classical mutations of the epidermal growth factor receptor (EGFR) in NSCLC are the exon 19 del and exon 21 (L858R) mutations. The 3rd generation EGFR tyrosine kinase inhibitor (TKI), osimertinib, has become the first-line treatment of choice for NSCLC patients with these mutations. Resistance to 3rd generation TKIs can be driven by gain of secondary EGFR alterations, e.g., substitution at cysteine-797 to serine (C797S). Real world evidence shows that in addition to C797S, other EGFR alterations are also acquired upon osimertinib treatment, including kinase domain mutations (e.g., S768I), extracellular domain alterations (e.g., EGFRvIII, A289X), and EGFR amplification. In addition to the classical mutations, NSCLC tumors express a wide spectrum of primary kinase domain mutations including G719X in exon 18, S768I in exon 20, and L861Q in exon 21, which confer intrinsic resistance to approved TKIs. NCCN guidelines recommend the use of afatinib or osimertinib, however, there remains a need for an EGFR TKI that targets these mutations with high potency, good tolerability, and CNS penetration. Our MAP platform allowed us to select MasterKey inhibitor BDTX-1535, a 4th-generation CNS penetrant EGFR TKI, that potently and selectively targets multiple intrinsic and acquired resistance EGFR alterations. Materials and Methods: BDTX-1535 preclinical exposure was evaluated across species, and PK and Kpuu values were calculated in brain and plasma. Antitumor activity was assessed across a broad range of mouse PDX and allograft models. Results: BDTX-1535 is a potent and selective, CNS penetrant, wild type sparing, irreversible EGFR TKI targeting Exon 18–21 alterations which are associated with intrinsic or acquired resistance to 3rd generation EGFR inhibitors. These include a broad range of kinase domain EGFR mutations (e.g., C797S, L718Q, G724S, S768I), extracellular domain alterations (e.g., EGFRvIII, A289X), and EGFR amplification. Mouse xenograft and allograft studies showed that BDTX-1535 consistently achieves regression of tumors carrying these mutations at well tolerated doses without significant EGFR wild type associated toxicities. BDTX-1535 is orally bioavailable with a CNS Kpuu of 0.55 and 0.48 in rat and dog, respectively, and active in an intracranial PDX model. Conclusions: BDTX-1535 is a 4th generation CNS penetrant EGFR TKI discovered using the MAP platform which allows MasterKey targeting of EGFR alterations associated with intrinsic or acquired resistance to 3rd generation EGFR TKIs, while sparing wild type EGFR. This broad spectrum coverage of resistance mutations in conjunction with CNS penetration properties allows BDTX-1535 to address a key unmet medical need in EGFR mutant lung cancer. BDTX-1535 is currently under phase I clinical investigation (NCT05256290). Conflict of interest: Ownership: Black Diamond Therapeutics

The reversible fourth-generation EGFR tyrosine kinase inhibitor OBX02-011 overcomes C797S-mediated resistance in lung cancer.

Osimertinib is an irreversible third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) that was initially developed to overcome the EGFR T790M mutation and is used as a standard therapy in patients with advanced non-small cell lung cancer (NSCLC) with EGFR-activating mutations. Despite the remarkable initial efficacy, osimertinib, like other EGFR-TKIs, is limited by the emergence of acquired resistance. As the EGFR mutation C797S has been identified as a key driver of acquired resistance to osimertinib, development of a drug that targets this clinically relevant mutation could help improve patient outcomes. Here, we report the discovery and preclinical efficacy of OBX02-011, a reversible fourth-generation EGFR TKI that overcomes the EGFR C797S mutation. Compared to approved EGFR TKIs, OBX02-011 showed potent anticancer effects and inhibited EGFR-related signaling in various models, including those harboring the EGFR C797S mutation. Additionally, in transgenic mouse models (EGFRL858R/T790M/C797S), OBX02-011 treatment effectively inhibited tumor growth and EGFR activity, leading to enhanced survival. Collectively, these results suggest that OBX02-011 may be a promising new EGFR TKI to overcome C797S-mediated resistance in NSCLC.

Tumor growth inhibition modeling to support the starting dose for dacomitinib.

Dacomitinib is a second-generation, irreversible EGFR tyrosine kinase inhibitor for first-line treatment of patients with metastatic non-small cell lung cancer and EGFR-activating mutations. A high rate of dose reductions in the pivotal trial led to an observed inverse exposure-response (ER) relationship with the primary end points. Three ER models were developed to determine if the starting dose from the pivotal trial, 45 mg once daily (q.d.) dose, is appropriate: a longitudinal logistic regression model for adverse event-related dose changes, a Claret tumor growth inhibition (TGI) model, and a Cox model for progression-free survival (PFS) based on the TGI model predictions. This analysis included 266 patients taking dacomitinib with a starting dose of 45 mg (N=250) or 30 mg (N=16) q.d. The ER relationships with the time-varying exposure metrics, most recent maximum plasma concentration (Cmax ) and average concentration (Cavg ) from the first dose, were established for the dose reduction and TGI models, respectively. The TGI model characterized the tumor inhibition over time with constant growth rate (kL =0.0012 years-1 ) and highly variable kill rate (kD =1.002 years-1 /[μg/L]θcavg , coefficient of variation [CV]=89%) and drug resistance (λ=14.47 years-1 , CV=96%) leading to prolonged tumor shrinkage. The ER relationship was characterized using an exposure parameter with a power parameterization (θcavg=0.454, p < 0.0001). The Cox model found that baseline tumor size (p=0.0166) and week 8 tumor shrinkage rate (p=0.0726) were the best predictors of PFS. Simulations of dose reductions and drug interruptions on tumor shrinkage over time showed greater and more prolonged tumor shrinkage with a starting dose of 45 mg q.d.

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In This Issue

Abstract 1125: Elucidating the transcriptomic response to EGFR-targeted therapy in EGFR-driven glioblastoma

Abstract Glioblastoma (GBM) is the most common malignant brain tumor in adults with a dismal 15-month median survival. Standard therapy consisting of surgical resection, radiation, and temozolomide has been unsuccessful in meaningfully extending survival and preventing recurrence; thus, novel therapeutics are urgently needed. One proposed targeted treatment strategy for GBM involves using small molecule inhibitors against common genetic mutations. Epidermal growth factor receptor (EGFR) is the most commonly overexpressed oncogene in GBM (~56%). While EGFR tyrosine kinase inhibitors (TKI) have shown promise in other cancers, GBM clinical trials with EGFR TKI have failed. One reason for this failure is the development of adaptive therapeutic resistance. Understanding the mechanisms behind drug resistance is essential for the development of novel, effective therapeutics for GBM. To better understand adaptive resistance in GBM, we utilized two genetically engineered mouse astrocyte lines harboring common GBM mutations: Cdkn2a-/-, EGFRvIII (CEv3) and Cdkn2a-/-, Pten-/-, EGFRvIII (CEV3P). CDKN2A and PTEN are commonly deleted or otherwise inactivated tumor suppressor genes in GBM while the vIII variant of EGFR is the single most common oncogene mutation, making it an attractive therapeutic target. Cell lines CEv3 and CEv3P are both sensitive to neratinib, an irreversible second-generation EGFR TKI, at IC50 of 0.24μM and 0.13µM, respectively. To better understand adaptive response to neratinib treatment, we profiled the transcriptome with RNA sequencing at 0, 4, 24, and 48 hours. Our data shows that kinome rewiring is detectable after just 4 hours of treatment and sustained through 48 hours, with differential expression of 70% or more of the expressed kinome. We propose that differentially expressed kinases in response to neratinib can potentially activate alternative signaling pathways that bypass EGFR inhibition, which ultimately confers resistance to EGFR targeted therapy. Furthermore, we hypothesize that the epigenome is directly responsible for this adaptive kinome response through BRD4 dependent enhancer remodeling. Because dual therapy against EGFR and BRD4 has shown promising results in other cancers, targeting the epigenome through BRD4 represents a potential combination therapy with EGFR TKI in GBM. To profile BRD4-associated epigenomic changes, we used Cleavage Under Targets and Release Using Nuclease (CUT&amp;RUN) to interrogate several regulatory marks (H3K4me1, K3K4me3, H3K27ac) in addition to BRD4. We seek to integrate RNA sequencing and CUT&amp;RUN data to determine if kinases differentially expressed following neratinib treatment correlate with epigenetic marks for their respective enhancer(s). This work will provide insight into the adaptive resistance mechanism of EGFR driven GBM. Citation Format: Benjamin Lin, Julia Ziebro, Kasey R. Skinner, Abigail Shelton, Erin Smithberger, Ryan Bash, Frank B. Furnari, Ryan Miller. Elucidating the transcriptomic response to EGFR-targeted therapy in EGFR-driven glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1125.

Abstract 3346: BBT-207, a novel, 4th generation, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) with broad-spectrum activity to both treatment-emergent and drug-naïve mutants for the treatment of NSCLC

Abstract Background: Activating mutations in EGFR, e.g., L858R (L) and Del19 (D), are observed in 14.1-32.3% of NSCLC worldwide and defines a druggable entity. Single agent EGFR TKI treatment was established in clinical trials. However, a treatment-emergent mutation of T790M (T) was identified as a major source of drug resistance. Irreversible 2nd and 3rd generation EGFR TKIs were shown effective. Mutant-specific inhibition by 3rd generation EGFR TKIs reduced adverse events such as skin toxicities. The emergence of a missense mutation at C797 (C), to which irreversible TKIs covalently bind, limited their efficacy. Patients harboring treatment-emergent C mutations are left with few therapeutic options. Despite anecdotal reports of efficacy from 1st generation TKIs, these complex molecular variants involving C797 are an increasing clinical concern. To prevent the emergence of drug-resistant subclones, a broad-spectrum EGFR TKI against both treatment-emergent and drug-naïve mutants is required. Such a 4th generation EGFR TKI must also enable monotherapy, allowing precise dose adjustment in case of toxicity. Method: Derived from BBT-176 which is under clinical evaluation (NCT04820023), we synthesized BBT-207 and other related molecules. Using Promega ADP-Glo™ kinase assay, we tested compounds against wild-type (WT) and mutated EGFR proteins. Ba/F3 cells harboring WT and mutated EGFR genes were created and cell viability was measured by CellTiter-Glo® and SpectraMax iD3®. In vivo anti-tumor activity was evaluated in Ba/F3 cell-derived xenograft models and an Osimertinib-resistant patient-derived xenograft model. Single dose pharmacokinetic (PK) study was performed in animals. Results: BBT-207 showed IC50 values &amp;lt; 10 nM against EGFR triple mutants (DTC and LTC) and comparable IC50 values against double mutants (DC and LC), while Osimertinib was ineffective in both groups. BBT-207 was also as active as Gefitinib to single mutants (D and L). Double mutants containing T790M (DT and LT) were inhibited effectively by BBT-207 and Osimertinib at similar concentrations, while not by Gefitinib. In in vivo models to which Osimertinib was inactive (LC and DTC), significant tumor growth inhibition was observed from BBT-207 alone, which was enhanced by the addition of Osimertinib. PK studies in mouse, rat, dog and monkey were consistent with high exposure and sustained drug concentrations above the IC50 values, with evidence of penetration into the central nervous system. Conclusion: BBT-207 is a reversible, mutant-specific, broad-spectrum TKI, active to clinically observed mutations of EGFR and is expected to be compatible with monotherapy of QD schedule in humans. BBT-207 is well-positioned to augment the treatment of EGFR mutated NSCLC, either for acquired drug resistance or in earlier line. Citation Format: Taiguang Jimmy Jin, Sang-Uk Kang, Chulwon Kim, Jehrod Brenneman, Mihee Song, Pavel Printsev, Bo-Bae Seo, Yong-Hee Lee, Sang-Yoon Lee. BBT-207, a novel, 4th generation, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) with broad-spectrum activity to both treatment-emergent and drug-naïve mutants for the treatment of NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3346.

LUNG CANCER METASTASES IN THE BRAIN: MAJOR RESPONSE WITH AFATINIB

TYPE: Late Breaking Abstract TOPIC: Lung Cancer INTRODUCTION: Lung cancer (LC) is the leading cause of cancer-related death worldwide and it is responsible for nearly 50% of brain metastasis (BM) cases. Afatinib is a second-generation irreversible EGFR tyrosine kinase inhibitor, indicated in the treatment of metastatic LC with activating EGFR mutations. CASE PRESENTATION: A 71-year-old woman, ECOG PS 1, was diagnosed with stage IVb LC (T3N0M1b), EGFR mutated (exon 18: Glu790Lys, Lys744Asn, Gly719Ser). Staging brain MRI showed 2 left brain lesions, suggestive of BM, not surgically approachable: one in the parietal region (20x16mm) and another (3mm) in the temporo-occipital transition. In the Multidisciplinary Tumor Board was decided treatment with afatinib and stereotactic brain surgery (SBS). To plan SBS another brain MRI was performed showing a significant reduction of the left parietal lesion (10x8mm; figure 1) and complete disappearance of the other lesion, after 8 days of treatment, and SBS was canceled. Reevaluation after 3 months revealed partial imaging response on the lung and brain (BM with 9mm, major axis). Due to grade 2-3 skin rash and paronychia, the treatment dose was reduced until 20mg/day, with good tolerance. DISCUSSION: Despite having incomplete blood-brain barrier penetration, afatinib has the potential to treat LC BM, with a reported intracranial response rate ranging from 35%-72.9%. This efficacy was demonstrated in this case report, allowing brain radiation sparing strategy. CONCLUSIONS: This case report shows the effectiveness of afatinib in BM from EGFR mutated lung adenocarcinoma. DISCLOSURE: No significant relationships. KEYWORD: Brain metastases