BACKGROUND: Lung cancer is the leading cause of cancer death globally. EGFR mutations are the most common genomic drivers of non-small cell lung cancer (NSCLC), occurring in ~17% and up to 50% of Caucasian and Asian patients, respectively, with exon 19 deletions (ex19del) and L858R substitutions being the most prevalent activating EGFR mutations (EGFRm). Outcomes have improved in patients with EGFR-driven NSCLC since the introduction of EGFR tyrosine kinase inhibitors (TKIs); however, treatment resistance almost inevitably occurs. It has been reported that patients harboring the EGFR L858R mutation, who represent 3.4% of lung adenocarcinoma cases in North America and 23% in Asia, have poorer outcomes than those with EGFR ex19del, suggesting a significant unmet need in this population. BLU-945 and BLU-701 are investigational, reversible, selective, and orally available TKIs optimized for use as single-agent or combination therapy to effectively suppress activating and on-target resistance EGFR mutants while sparing WT EGFR, and have the potential to treat or prevent central nervous system metastases. In vivo studies previously demonstrated the antitumor activity of BLU-945 against EGFR L858R/T790M and EGFRm/T790M/C797S mutants, and BLU-701 against EGFR ex19del and EGFRm/C797S mutants. Because EGFR L858R-driven NSCLC constitutes a large population of patients who may not be receiving the same benefit from third-generation (3G) TKIs as those with EGFR ex19del, studies were conducted to evaluate the antitumor activity of BLU-945 and BLU-701, as single agents and in combination, in preclinical NSCLC tumor models driven by L858R in the absence of the T790M mutation. METHODS: The in vivo antitumor activities of BLU-945 and BLU-701, as single-agents or in combination, were evaluated in 2 EGFR L858R-driven patient-derived xenograft (PDX) subcutaneous tumor models and in an engineered EGFR L858R/C797S-driven Ba/F3 cell line-derived xenograft (CDX) subcutaneous tumor model. RESULTS: Oral daily administration of single-agent BLU-945 and single-agent BLU-701 resulted in sustained tumor regression in 2 PDX models of EGFR L858R NSCLC. Compared with single agents in an EGFR L858R/C797S Ba/F3 CDX tumor model, combination of BLU-945 with BLU-701 resulted in marked antitumor activity and prolonged tumor regression. CONCLUSION: The in vivo antitumor activities of BLU-945 and BLU-701 in preclinical tumor models suggest that both BLU-945 and BLU-701 have the potential to be used in patients with EGFR L858R-driven NSCLC, including those who are treatment naïve or previously treated with 3G TKI. Combining BLU-945 and BLU-701 may enable coverage of frequent on-target resistance mechanisms, including the EGFR C797S mutation, in addition to the common L858R activating mutation. Citation Format: Luz Tavera, Stefanie Schalm, John Campbell, Jian Guo, Clare Medendorp, Maxine Chen, Faris Albayya, Tom Dineen, Zhuo Zhang, Maria Iliou, Ebby Job, Nisha Perez, Yoav Timsit, Scott Wardwell, Katie McGinn, Richard Woessner, Chiara Conti. Antitumor activity of BLU-945 and BLU-701 as single agents and in combination in EGFR L858R-driven models 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 3328.

Gastrointestinal stromal tumor (GIST) is the most common type of sarcoma, with approximately 5,000 patients diagnosed per year in the US. Approximately 80% of patients with GIST present with mutations in the c-KIT oncogene at exon 9 or 11, which leads to constitutive, ligand-independent activation of the KIT receptor tyrosine kinase. For patients with metastatic GIST, frontline therapy with imatinib is effective, with a response rate of approximately 51-54% and median progression-free survival (PFS) of 19-23 months, in a molecularly unselected population. Other agents are approved for advanced GIST, without molecular selection, after progression on imatinib, including sunitinib, regorafenib, and ripretinib; however, response rates are less than 10% with PFS of approximately 5-6 months. Notably, patients who progress on imatinib and other tyrosine kinase inhibitors may develop a variety of on-target resistance mutations in the KIT oncogene, such as those in exon 17 (including at amino acids D816 and D820, activation loop mutation), exon 13 (V654A, ATP-binding region mutation), and less frequently in exon 14 (T670I, gatekeeper mutation). Several KIT inhibitors have been developed to potently target the exon 17 resistance mutations (avapritinib and ripretinib); however, there remains an important medical need in 2nd- and 3rd-line therapy in a molecularly unselected population of imatinib-resistant GIST. This suggests more broad-spectrum KIT inhibition is likely required, a hypothesis supported by the observation of large inter- and intra-patient heterogeneity of KIT secondary mutations across hundreds of samples obtained from patients with GIST treated with avapritinib. Sequencing data from the NAVIGATOR phase 1 trial (NCT02508532) revealed that patients with KIT mutant GIST and with the KIT V654A secondary resistance mutation had a poor response to treatment with avapritinib. To address this, we developed a highly potent and selective inhibitor of KIT V654A. This inhibitor showed dose-dependent modulation of downstream pharmacodynamic markers and induced tumor regression in a mastocytoma xenograft model driven by an exon 11 plus 13 V654A resistance mutation. Importantly, this inhibitor was generally well-tolerated and showed high selectivity over wild-type KIT. These findings suggest this novel KIT inhibitor has the potential to be used as a single agent or combination therapy for patients with imatinib-resistant GIST harboring the KIT V654A mutation. Citation Format: Alexandra R. Grassian, Joseph Kim, Omar Ahmad, Kevin Barvian, Alison Davis, Tom Dineen, Wei Hu, Ebby Job, Ludivine Moine, Kate Newberry, Maria Roche, Doug Shorten, Yeon Sook Choi, Francis Wolenski, Sebastian Bauer, Cesar Serrano, Jonathan Trent, Suzanne George. Efficacy of a highly potent and selective KIT V654A inhibitor for treatment of imatinib resistant GIST [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 LB565.

Abstract Background: EGFR-activating mutations (L858R and ex19del) are major drivers (15-47%) of lung adenocarcinoma. EGFR TKI development has changed the treatment paradigm for EGFR-mutant (EGFR+) NSCLC. However, tumors often develop acquired resistance mutations to current TKIs leading to clinical progression. EGFR+/T790M is the most prevalent acquired resistance mutation after first- and second-generation TKI treatment. Osimertinib, a third-generation TKI which targets EGFR+/T790M, can overcome this resistance, but faces further resistance within 10-18 months. EGFR+/C797S is the most significant on-target resistance mechanism to osimertinib, leading to EGFR+/T790M/C797S double resistant mutants. There are currently no approved targeted therapies for patients with EGFR+/T790M/C797S NSCLC. BLU-945 is a potent and highly selective inhibitor of the EGFR+/T790M/C797S and EGFR+/T790M mutations, with in vivo activity in subcutaneous and intracranial EGFR-mutant tumor models. Method: In vivo antitumor activity of BLU-945 was evaluated in engineered triple mutant cell line-derived xenograft (CDX) models and osimertinib-resistant patient-derived xenograft (PDX) models of NSCLC. Plasma and tumor samples were collected for future pharmacokinetic and pharmacodynamic analyses. In vivo activity was also evaluated in an intracranial implantation model using luciferase-expressing YU-1097 patient-derived-cells harboring EGFRex19del/T790M/C797S resistance mutations, with the tumor burden of intracranial lesions measured by bioluminescence imaging. Results: Oral administration of BLU-945 to tumor-bearing mice showed potent EGFR pathway inhibition and significant single-agent antitumor activity at well-tolerated doses in the engineered osimertinib-resistant EGFRL858R/T790M/C797S CDX model, and an EGFRex19del/T790M/C797S PDX model. In addition, combination of BLU-945 with osimertinib showed enhanced antitumor activity compared with single-agent treatment in the EGFRex19del/T790M/C797S PDX model. Pharmacodynamic assays revealed treatment with BLU-945 resulted in marked inhibition of EGFR, AKT and ERK phosphorylation in the EGFRL858R/T790M/C797S CDX and EGFRex19del/T790M/C797S PDX models. BLU-945 also demonstrated potent activity in a patient-derived model of EGFRex19del/T790M/C797S implanted intracranially. Conclusion: BLU-945 is a potent, selective, and orally available fourth-generation EGFR inhibitor with robust antitumor activity in osimertinib-resistant NSCLC models grown subcutaneously and intracranially. BLU-945 shows activity as a single agent and in combination with other EGFR inhibitors. Clinical development of BLU-945 is expected in 2021. Citation Format: Sun Min Lim, Chae Won Park, Zhuo Zhang, Rich Woessner, Tom Dineen, Faith Stevison, John Hsieh, Meredith Eno, Doug Wilson, John Campbell, Caitlin Utt, Faris Albayya, Nicolas Lamontagne, Marion Dorsch, Klaus Hoeflich, Byoung Chul Cho, Stefanie Schalm. BLU-945, a fourth-generation, potent and highly selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) with intracranial activity, demonstrates robust in vivo antitumor activity in models of osimertinib-resistant non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1467.

Abstract BACKGROUND: Non-small cell lung cancer (NSCLC) represents 80% of lung cancers, the second leading cause of cancer deaths globally. Mutations in the kinase domain of the epidermal growth factor receptor (EGFR) are genomic drivers in a molecular sub-type of NSCLC that is sensitive to tyrosine kinase inhibitors (TKIs). Third-generation, irreversible TKIs, such as osimertinib and lazertinib, have become standard of care and are now widely used as first-line therapy in EGFR-driven metastatic NSCLC. However, resistance invariably arises during treatment. The C797S mutation is the most frequent on-target resistance mechanism in response to third-generation TKIs when used in the first-line setting. There are currently no approved therapies for patients who progress with a C797S mutation. Although first-generation TKIs inhibit EGFR with a C797S mutation, they carry liabilities of 1) insufficient selectivity over wild-type (WT) EGFR, which precludes maximal target coverage and results in dose-limiting adverse events; and 2) limited brain penetration. METHODS: BLU-701 activity was tested in biochemical assays for EGFR mutants and EGFR WT. Cellular activity was evaluated by a phosphorylation specific EGFR AlphaLisa assay in WT cell lines or those expressing EGFR mutations. The in vivo antitumor activity of BLU-701 was assessed in a PC9 ex19del cell line-derived tumor xenograft (CDX) model. RESULTS: We have developed an orally available, single-digit nanomolar, brain-penetrant, WT-sparing, reversible EGFR inhibitor that is active against the C797S resistance mutation. BLU-701 is equally potent against both the sensitizing mutations ex19del and L858R, and the resistance double mutants ex19del/C797S and L858R/C797S. BLU-701 is brain penetrant (Kpu,u >0.9) and demonstrates a selectivity over WT EGFR that compares favorably with osimertinib. Oral administration of BLU-701 to PC9 ex19del tumor-bearing mice resulted in strong and prolonged pathway suppression and tumor regression at tolerated doses. CONCLUSION: Due to its potent pharmacological activity and selectivity for mutant EGFR, BLU-701 has the potential to demonstrate activity in first-line and resistance settings as a single agent and in combination therapy, addressing potential tumor heterogeneity. The pre-clinical data described here supports the clinical development of BLU-701 in EGFR-driven NSCLC. Citation Format: Chiara Conti, John Campbell, Rich Woessner, Jian Guo, Yoav Timsit, Maria Iliou, Scott Wardwell, Alison Davis, Sharon Chicklas, John Hsieh, Meredith Eno, Omar Ahmad, Dilinie Fernando, Kevin Barvian, Joseph Kim, Steven Kazmirski, Emanuele Perola, Tom Dineen, Victoria Brown, Timothy Guzi, Ayşegül Özen, Faith Stevison, Caitlin Utt, Clare Medendorp, Robert Meissner, Marion Dorsch, Klaus Hoeflich. BLU-701 is a highly potent, brain-penetrant and WT-sparing next-generation EGFR TKI for the treatment of sensitizing (ex19del, L858R) and C797S resistance mutations in metastatic NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1262.