BLU-945, a highly potent and selective 4th-generation EGFR TKI for the treatment of EGFR+/T790M/C797S resistant NSCLC 1296P Stefanie Schalm1, Tom Dineen1, Sun Min Lim2, Chae-Won Park2, John Hsieh1, Rich Woessner1, Zhuo Zhang1, Kevin Wilson1, Meredith Eno1, Doug Wilson1, Brett Williams1, John Campbell1, Chris De Savi1, Faith Stevison1, Caitlin Utt1, Timothy Guzi1, Marion Dorsch1, Klaus Hoeflich1, Byoung Chul Cho2 1Blueprint Medicines Corporation, Cambridge, Massachusetts, USA; 2Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, South Korea

BLU-945 inhibits EGFR+/T790M/C797S driven pathway activation BLU-945 demonstrates intracranial activity when administered orally Background Figure 4: In an (A) -resistant EFGR ex19del/T790M/C797S patient-derived cell line Table 2: BLU-945 potently inhibits EGFR+/T790M/C797S and EGFR+/T790M autophosphorylation xenograft (PDCX) model, (B) oral administration of BLU-945 led to significant tumor regression Figure 6: Oral administration of BLU-945 100 mg/kg resulted in intracranial activity in a • Osimertinib, a 3rd-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor A. B. NCI-H1975 L858R/T790M-luc intracranial model Cellular pEGFR inhibition IC50 (nM) PDC YU-1097 (ex19del/T790M/C797S) (TKI), has favorably impacted the treatment of patients with EGFR-driven non-small cell lung Osimertinib Cell lines Engineered Ba/F3 cell lines Vehicle, BLU-945, Osimertinib, del19 del19/T790M ex19del/T790M/C797S 500 Vehicle BID (n=6) cancer (NSCLC) and extended overall survival compared with older EGFR TKIs, including the BID 100 mg/kg BID 25 mg/kg QD st 1 NCI-H1975 PC-9 A431 L858R L858R/ ex19del/ Osimertinib, 25mg/kg QD (n=7) 1 -generation agent gefitinib 450 Compound (L8585R/T790M) (ex19del) (EGFR WT) T790M/C797S T790M/C797S BLU-945, 100mg/kg BID (n=6) 1750 1750 1750 • The C797S mutation is the most frequent on-target resistance mechanism to osimertinib and 400 2 BLU-945 1.2 129.5 544.4 21.5 2.9 4.4 0 1 2 3 4 5 SEM 6 6 6 there are no targeted therapies approved for patients with disease progression ± 1500 1500 1500 ) Years 3 350 • We are developing targeted agents to treat C797S-driven resistance with the goal of improving >10,000 3.9 140.6 5.9 6655.5 4524.8 1250 1250 1250 patient outcomes and prolonging clinical benefit Gefitinib 4679.8 1.8 16.5 4.6 6707.7 4864.7 T790M (p14) C797S (p14) 300 th 250 – BLU-945 (Figure 1) is a 4 -generation EGFR TKI designed to target the Osimertinib 4.7 2.1 115.9 11.0 7754.6 >10,000 1000 1000 1000 EGFR+(L858R or ex19del)/T790M/C797S triple mutant following treatment with a * * 200 st st nd 3,4 1 -line 1 -generation EGFR TKI and 2 -line osimertinib Figure 2: BLU-945, but not osimertinib, inhibits the EGFR pathway in 150 750 750 750 th – A second 4 -generation EGFR TKI aims to target the EGFR+/C797S double mutant following (A) ex19del/T790M/C797S and (B) L858R/T790M/C797S driven Ba/F3 cell lines ACG → ATG TGC → TCC

Mean tumorvolume (mm 100 treatment with 1st-line osimertinib3 500 500 500 A. B. • PDCX model developed from patient who 50 Osimertinib BLU-945 Osimertinib BLU-945 Bioluminescencephotons/sec / 10 • Here we describe preclinical data for BLU-945 supporting initiation of clinical development in Bioluminescencephotons/sec / 10 Bioluminescencephotons/sec / 10 progressed on gefitinib and osimertinib 250 250 250

0 0 EGFR-driven NSCLC Drug concentration (nM) Drug concentration (nM) 1000 300 1000 0 10 100 300 1 10 100 0 10 10 300 1 10 100 300 6 hrs • RNA sequencing (RNA-seq) analysis of PDX 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 pEGFR (Y1068) pEGFR (Y1068) 0 0 0 Figure 1: Rationale for the development of BLU-945 targeting EGFR+/T790M/C797S model suggests EGFR amplification and Days post treatment initiation 0 5 10 15 0 5 10 15 0 5 10 15 EGFR EGFR allelic heterogeneity Days post treatment initiation Days post treatment initiation Days post treatment initiation pAKT (S473) pAKT (S473) • Oral administration of BLU-945 (100 mg/kg BID) was sufficient for tumor regression in this T790M C797S AKT AKT PDCX model T790M pERK pERK Conclusions 1st-generation Osimertinib C797S • BLU-945 was well tolerated in the PDCX animal model EGFR TKI ERK ERK C797S BLU-945 pS6 pS6 st rd • BLU-945 is a potentially best-in-class oral, selective, potent, T790M BLU-945 combination with 1 -and 3 -generation EGFR TKIs resulted in th S6 S6 4 -generation EGFR TKI with activity against the Osimertinib Blueprint further improved tumor regression compared with BLU-945 alone EGFR+ C797S GAPDH GAPDH EGFR+(L858R or ex19del)/T790M/C797S triple mutants Ba/F3 ex19del/T790M/C797S Ba/F3 L858R/T790M/C797S Figure 5: BLU-945 showed significant tumor regression in combination with osimertinib (A) Methods or (B) gefitinib, in a NSCLC PDX (ex19del/T790M/C797S) model with EGFR amplification and • In preclinical models, BLU-945 demonstrated potent, robust EGFR BLU-945 has antitumor activity on EGFR+/T790M and allelic heterogeneity pathway inhibition and antitumor activity at well-tolerated doses in the • BLU-945 activity on EGFR mutants and EGFR wild-type (WT) was tested in biochemical assays EGFR+/T790M/C797S driven cancers • PDX (ex19del/T790M/C797S) model developed from patient with NSCLC (poorly-moderately NCI-H1975 CDX model and osimertinib-resistant CDX and PDX models and cellular phosphorylation-specific EGFR AlphaLisa assays Figure 3: Oral administration of BLU-945 showed significant tumor regression in differentiated adenocarcinoma) who progressed through >5 lines of therapy, including of NSCLC chemotherapy, icotinib, erlotinib, and osimertinib • The in vivo antitumor activity of BLU-945 was evaluated in an NCI-H1975 cell line-derived tumor (A) NCI-H1975 NSCLC CDX (L858R/T790M) tumor model similar to covalent drug osimertinib • Combination of BLU-945 with either 1st-generation (gefitinib) or xenograft (CDX) model, as well as in osimertinib-resistant CDX-derived and patient-derived and (B) an osimertinib resistant Ba/F3 CDX (ex19del/T790M/C797S) model; – RNA-seq analysis of PDX model suggested EGFR amplification and allelic heterogeneity rd xenograft (PDX) models of NSCLC (C) PD analysis for 3A 3 -generation (osimertinib) EGFR TKI showed enhanced antitumor A. B. activity compared with single agent treatment in an A. B. LUPF104 (ex19del/T790M/C797S) LUPF104 (ex19del/T790M/C797S) 1000 NCI-H1975 (L858R/T790M) 1000 Ba/F3 ex19del/T790M/C797S Results BLU-945 + osimertinib BLU-945 + gefitinib EGFR+/T790M/C797S-driven PDX model, suggesting potential for monotherapy and/or combination therapy in the clinical setting BLU-945 is a highly potent and selective EGFR+ T790M/C797S inhibitor 1500 1500 750 750 • BLU-945 demonstrated robust antitumor activity in an NCI-H1975 SEM • Highly potent inhibitor of EGFR+/T790M/C797S and EGFR+/T790M resistant mutants SEM 1250 1250 SEM SEM ± ± Vehicle ) ) ± ± 3 3 ) ) L858R/T790M-luc intracranial model 3 • Excellent EGFR WT and overall kinome selectivity Vehicle, BID 3 BLU-945, 100 mg/kg BID BLU-945, 30 mg/kg BID 1000 1000 Osimertinib, 25 mg/kg QD • BLU-945 only inhibits 1% of the kinome >90% at a concentration of 3 µM BLU-945, 150 mg/kg QD Gefitinib, 18.75 mg/kg QD • Clinical development of BLU-945 monotherapy is expected to begin with 500 500 BLU-945, 100 mg/kg BID BLU-945 100 mg/kg + • Selectivity profile enables combinations to cover wide spectrum of resistant mechanisms 750 750 an international phase 1 dose-escalation trial in patients with Osimertinib, 25 mg/kg QD osimertinib 5 mg/kg Table 1: BLU-945 is a subnanomolar EGFR+/T790M/C797S and EGFR+/T790M BLU-945 100 mg/kg + EGFR-driven NSCLC in the first half of 2021, and future clinical

umorvolume (mm gefitinib 18.75 mg/kg inhibitor with >900-fold selectivity over EGFR WT 500 500 250 250 development of BLU-945 in combination with other TKIs across multiple Mean tumorvolume (mm Meant Mean tumorvolume (mm 250 Mean tumorvolume (mm 250 treatment settings is planned Enzyme activities IC50 (nM) at 1 mM ATP with enzyme-inhibitor pre-incubation

L8585R L858R/ L858R/ ex19del ex19del/ ex19del/ EGFR WT 0 0 References 0 0 0 10 20 3040 50 0 10 20 30 40 50 1. Ramalingam SS et al. N Engl J Med. 2020;382:41–50; 2. Lazzari C et al. J Thorac Dis. 2020;12:2851–2858; 3. Leonetti A et al. Br J Cancer. 2019;121:725–737; Compound T790M T790M/C797S (746–750) T790M T790M/C797S 0 5 10 15 0 5 10 15 4. Mok, TS et al. N Engl J Med. 2017;376:629–640. Days post treatment initiation Days post treatment initiation Days post treatment initiation Days post treatment initiation BLU-945 7.1 0.4 0.5 71.4 0.8 0.8 736.3 Acknowledgments Some of the cell assays and in vivo experiments were conducted at Pharmaron Beijing Co., Ltd (China), Shangai LIDE Biotech Co., Ltd (China), WuXi AppTec Co., Ltd a BLU-945,100 mg/kg BIDa C. Vehicle BLU-945, 30 mg/kg BID Vehicle Vehicle Vehicle • Single agent BLU-945 was sufficient for tumor stasis in this model (China). Medical writing support was provided by Cristina Tomas, PhD, and editorial support was provided by Michelle Seddon, Dip Biotech Co., Psych, all of Paragon, Erlotinib 0.3 3132.7 5654.7 0.2 1394.7 1906.6 9.8 2 h 2 h 6 h 12 h 6 h 2 h 2 h 6 h 12 h 6 h Knutsford, UK, supported by Blueprint Medicines Corporation, Cambridge, MA, according to Good Publication Practice guidelines. • Co-dosing BLU-945 with either osimertinib or gefitinib led to significant tumor regression Gefitinib 0.1 1667.2 3921.8 0.1 632.7 1219.7 3.5 p-EGFR p-EGFR Disclosures p-ERK p-ERK • Single agent and combination doses were well tolerated in the animal model Study sponsored by Blueprint Medicines Corporation. BW, CS, CU, DW, FS, JC, JH, KH, KW, MD, ME, RW, SS, TD, TG, and ZZ are employees of Blueprint Medicines Corporation, or were at the time the work presented was developed, and own stock. BCC received research funding from Abbvie, AstraZeneca, Bayer, Blueprint Medicines Osimertinib 0.9 0.6 5461.6 0.8 0.6 649.9 1.6 GAPDH GAPDH • Data suggest that BLU-945 can be combined with other EGFR TKIs to address Corporation, Champions Oncology, Dizal Pharma, Dong-A ST, Eli Lilly, GIInnovation, Janssen, Medpacto, MOGAM Institute, MSD, Novartis, Ono, Yuhan; consulted for AstraZeneca, Blueprint Medicines Corporation, BMS, Boehringer-Ingelheim, Eli Lilly, Janssen, Medpacto, MSD, Novartis, Ono, Pfizer, Roche, Takeda, Yuhan; owns stock in a ATP, ; IC50, half maximal inhibitory concentration. BID, twice daily; PD, pharmacodynamic; QD, once daily; SEM, standard error of the mean. Dosed for 3 days. allelic EGFR heterogeneity Bridgebio therapeutics, Gencurix Inc, KANAPH Therapeutic Inc., TheraCanVac Inc.; participated in scientific advisory board for KANAPH Therapeutic Inc; reports royalties from Champions Oncology; and is the founder of Daan biotherapeutics. C-WPand SML and have no disclosures.

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