SRF231, a fully human CD47 antibody, potentiates the effects of opsonizing antibodies and cytotoxic chemotherapies in preclinical cancer models Kshama A. Doshi, Matthew Rausch, Caroline M. Armet, Li Zhang, Alison M. Paterson, Benjamin H. Lee, Vito J. Palombella, Pamela M. Holland, Marisa O. Peluso Surface Oncology, Inc., Cambridge, MA, USA Poster #2196

SRF231 + Opsonizing Antibodies (Elotuzumab, Daratumumab) Leads to Enhanced Antitumor Activity in Background Xenograft Models

Modified from: Chao M, Weissman I, and Majeti R. A 4000 Isotype 100 μg B CD47-SIRPα blockade ) A • CD47, often referred to as a “Don’t Eat Curr Opin Immunol. 2012;24:225-32. 3 100 Isotype unmasks “don’t eat me” elo 20 μg SRF231 CRR (D25) Me” signal, is widely expressed on 3000 80 Isotype dara 10 µg signal SRF231 30 μg Dose –elo +elo tumor cells and an important checkpoint SRF231 100 µg SRF231 – SRF231 30 μg + elo 60 *** SRF231 30 µg of the innate ADCP 2000 0 µg NA 0% SRF231 30 µg 2000 single dose SRF231 100 μg P<0.0001 SRF231 + dara Antibody Fc-FcR 40 SRF231 10 µg 30 µg 0% 0% • Several unique anti-CD47 molecules are Macrophage interactions activate 1000 SRF231 100 μg + elo SRF231 3 µg SRF231 administration

Percent Surviva l 20 currently being evaluated in the clinic to Prophagocytic Tumor Volume (mm Dara administration Receptor SRF231 administration 100 µg 0% 44% SRF231 administration antagonize the CD47 axis in cancer 0 0 ) 1500 0 10 20 30 elo administration 0 10 20 30 40 50 60 70 80 3 SIRPα • SRF231 is a high-affinity, CD47-targeting antibody FcR Days on Study Days on Study Opsonizing Ab B C that blocks the SIRPα/CD47 interaction and induces CD47 Tumor 11 eg, CD20 10 Isotype FcR (CD32a)-dependent phagocytosis and cell death 3000 SRF231 10 µg 1000 C D 1010

) SRF231 CRR (D28) • SRF231 also potentiates combinatorial activity of agents 3 Isotype 30 µg SRF231 CRR (D34) SRF231 3 µg Dose 109 –elo +elo known to provide additional “Eat Me” signals to tumor cells elo 20 µg Dose –elo +elo SRF231 10 µg + elo 0 µg NA 25% * * 2000 8 10 SRF231 3 µg + elo SRF231 10 µg 3 µg 0% 50% Tumor Volume (mm such as: SRF231 – 0 µg NA 0% 500 7 10 µg 25% 87.5% – Opsonizing hIgG1-containing antibodies that enhance Cell stress/death repeat dosing SRF231 30 µg 10 elo 20 µg 10 µg 10% 30% 30 µg 25% 87.5% upregulates 1000 SRF231 10 µg + elo 106 Fc-FcR interactions BLI (Photons/Second ) LLOQ “eat me signals” SRF231 30 µg + elo 30 µg 30% 50% 5 Tumor Volume (mm 10 SRF231 administration – Chemotherapies that trigger cell death induction pathways 0 0 10 20 30 Elo administration 0 SRF231 administration Days on Study 0 20 40 60 0 10 20 30 40 elo administration Days on Study Days on Study

SRF231 Potentiates the Effects of Opsonizing Antibodies and Figure 4: Enhanced Antitumor Activity Observed with SRF231 +/- Elotuzumab Chemotherapy In Vitro Figure 3: Enhanced Antitumor Activity Observed in OPM2 Multiple Myeloma Xenograft Model in Disseminated MM.1S Multiple Myeloma Xenograft Model Figure 5: Enhanced Antitumor Activity Observed with with Elotuzumab + SRF231 C.B-17 SCID mice were injected IV with MM.1S-Luc tumor cells. Established SRF231 +/- Daratumumab in H929 Xenograft Model OPM2 cells were inoculated subcutaneously (SC) into C.B-17 SCID mice. When tumors reached 100 mm3, disseminated disease was determined by whole-body bioluminescence imaging H929 tumor cells were implanted SC into CB.17 SCID mice. A B Total Phagocytosis 3

) 75 mice were randomized and treated. (A) Animals were dosed intraperitoneally (IP) with 20 μg elo (BLI), and animals were treated with SRF231 +/- elo, IP, qw x 3. (A) Kaplan-Meier When tumors reached an average size of 150 mm , mice + SRF231 + elo CD47 SLAMF7 CD38 60 SRF231 + dara biw x 3 in addition to a single dose of SRF231 on Day 1. (C) C.B-17 SCID mice were implanted with survival curve indicating SRF231 dose-dependent survival benefit (P values were randomized and dosed IP with 30 µg SRF231 tiw x 3 80000 10000 250000 SRF231 + hIgG1 tumors as described above and dosed IP with elo and SRF231 at the indicated doses and schedule. (B,D) calculated by Log- [Mantel-Cox] test). (B) Efficacy plots indicating disease and 10 μg dara on Days 1 and 15. Significant antitumor 200000 (of CD14 45 60000 8000 + 150000 Tables of complete response rate ([CCR], percentage of mice with no palpable tumors) observed with burden as measured by BLI (photons/second) in mice treated with SRF231 +/- elo. activity was observed in the combo arm relative to SRF231 6000 30 40000 1 µg/mL elo or 4000 100000 SRF231 +/- elo on Day 25 (single-dose study) or Day 34 (repeat-dose study), respectively. (C) Table of CRRs observed on Day 28. alone on Day 44 and Day 47; *P<0.05 (unpaired t-test). Relative MFI Relative MFI dara alone 20000 Relative MFI 15 2000 50000 Percent CFSE 0 0 0 0 Jurkat Raji MM1S H929 OPM2 HL-60 Jurkat Raji MM1S H929 OPM2 HL-60 Jurkat Raji MM1S H929 OPM2 HL-60 0.001 0.01 0.1 1 10 100 Cell Lines Antibody (µg/mL) SRF231 Potentiates the Effects of Chemotherapies in Lung Cancer Conclusions Figure 1: SRF231 Potentiates Phagocytosis Induced by Opsonizing Agents, Elotuzumab (anti-SLAMF7), or Xenograft Models Daratumumab (anti-CD38) in Multiple Myeloma

(A) Hematologic cancer cell lines were profiled for CD47, SLAMF7, or CD38 expression via flow cytometry. Relative mean A SRF231 + Cisplatin B SRF231 + Docetaxel • The anti-hCD47 mAb, SRF231, demonstrates both fluorescence intensity (MFI) values reported ( MFI- isotype control MFI). (B) CFSE-labeled MM.1S multiple myeloma Isotype 800 µg Isotype 800 µg single-agent and combinatorial activity with tumor cell targets were cultured with human -derived macrophages at a 2:1 target:effector ratio and incubated 2500 2500 ) ) SRF231 800 µg SRF231 800 µg 3 3 * opsonizing antibodies and cytotoxic with a dose-response of SRF231 in the presence of a single dose of elotuzumab (elo) or daratumumab (dara, 1 μg/mL) or Isotype 800 µg + * Isotype 800 µg + * * 2000 ns * 2000 chemotherapies in in vitro and in vivo hIgG1 control (10 μg/mL) for 2 h at 37°C. Cells were stained with anti-CD14 and analyzed by flow cytometry. Phagocytosis cisplatin 6 mg/kg * docetaxel 10 mg/kg * * A549 Orthotopic * preclinical hematologic and solid tumor denoted by percent CFSE+ tumor cells within CD14+ macrophages. Dotted lines indicate phagocytosis induced by 1 μg/mL 1500 SRF231 800 µg + 1500 SRF231 800 µg + * docetaxel 10 mg/kg cancer models elo or dara alone. 100 cisplatin 6 mg/kg 1000 1000 SRF231 administration • As a single agent, SRF231: SRF231 administration 80 Cisplatin administration 500 500 Docetaxel administration – Was highly potent in the disseminated

A B hIgG4 SRF231 Tumor Volume (mm Tumor Volume (mm 0.061% 3.57% 0.067% 8.69% MM.1S multiple myeloma xenograft model, 105 105 60 0 0 0 10 20 30 40 0 20 40 60 80 and a dose-dependent survival benefit was Days on Study 4 4 Days on Study 10 10 seen with dosing regimens as low as 40 100 3 µg/mouse, qw x 3 SRF231 + Cisplatin 103 103 Isotype

+ hIgG4 + Cisplatin C Isotype – Extended survival in the orthotopic A549 Percent Surviva l 20 100 100 80 SRF231 800 µg Isotype 800 µg ns D Cisplatin alone 0 0 * lung xenograft model Antibody administration SRF231 800 µg ns SRF231 800 µg 90.0% 6.36% 66.0% 25.2% 80 * 80 * 60 Cisplatin 6 mg/kg Docetaxel 10 mg/kg * 0 103 104 105 0 103 104 105 0 * * * • In combination with opsonizing antibodies or cell 60 * 0 10 20 30 40 50 60 SRF231 800 µg + cisplatin 60 SRF231 + docetaxel death-inducing chemotherapies, SRF231: 40 hIgG4 + Cisplatin SRF231 + Cisplatin * 0.013% 5.59% 0.048% 9.71% Days on Study 40 40 SRF231 alone 105 105 – Potentiated the activity of dara (anti-CD38)

Percent Annexin V 20 Percent Survival 20 Percent Survival 20 and elo (anti-SLAMF7) in multiple myeloma 4 4 hIgG4 alone Propidium Iodide (PI) 10 10 0 0 0 xenograft models, with either single- or 0.1 1 10 100 1000 103 103 0 20 40 60 80 0 20 40 60 80 multi-dose administration of SRF231, leading Days on Study Days on Study Cisplatin (µM) to enhanced CRRs and overall survival

0 0 Figure 6: SRF231 Administration Enhances Survival Figure 7: Chemotherapy Combined with SRF231 Leads to Enhanced Antitumor Activity in H-1975 (EGFR Mutant) Lung Q4 – Enhanced antitumor activity trending 72.472.5% 21.9% 49.5% 40.8% in the A549 Lung Orthotopic Xenograft Model Xenograft Model 0 103 104 105 0 103 104 105 towards extended survival in combination AnnexinV+ A549-Luc tumor cells were implanted orthotopically Nude mice were implanted SC with NCI-H-1975 cells. Established tumors were then treated IP with 800 μg SRF231 biw x 3. with cisplatin and led to delayed tumor into the lungs of SCID beige mice. Ten days (A) + 6 mg/kg cisplatin or (B) + 10 mg/kg docetaxel. (A,B) Chemotherapies were administered IV qw x 3. (A) The antitumor Figure 2: SRF231 Potentiates Cell Death Induced by Cisplatin In Vitro regrowth and marked survival benefit in the postimplant, animals were sorted based on BLI benefit observed in the SRF231 + cisplatin combo arm was significantly different than SRF231 alone (Day 22 & Day 25) while (A) -G plates were precoated with 10 μg/mL SRF231 or hIgG4 antibody and incubated at 4°C overnight. Jurkat H-1975 lung xenograft model in imaging and treated IP with 800 μg SRF231 or human the (B) docetaxel combo benefit was significantly different from both single-agent arms (Day 64), along with a 44% CRR in the cells were then seeded on antibody-coated protein-G plates +/- a dose-response of cisplatin. Plates were incubated at combination with docetaxel IgG4 isotype control antibodies biw x 3. combo group. (C,D) Kaplan-Meier survival plots indicate (C) a trend toward extended survival in the SRF231 + cisplatin combo 37°C for 24 h and Annexin V+ tumor cells assessed via flow cytometry. (B) Representative flow cytometry images – Please refer to poster #4515 for more on arm (D) and a significant benefit in the SRF231 + docetaxel combo arm relative to both single-agent arms: corresponding to 10 μg/mL antibody alone (upper panels) or antibody + 0.4 μM cisplatin (lower panels). SRF231 combinations ns = not significant, *P<0.05, ** P<0.001, ***P<0.0001 (A,B unpaired t-test; C,D Log-rank Mantel-Cox).

Presented at AACR 2020