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Ovarian cancer data supports registration-enabling trial of luvelta for women with platinum-resistant ovarian cancer Potential benefit to 8 out of 10 platinum-resistant ovarian cancer patients, including addressing unmet need in patients with low-medium FolRα expression Promising clinical activity and tolerability of luvelta as both a monotherapy and in combination across multiple cancers may provide for a significant commercial opportunity Jan. 04, 2024 -- Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), is hosting an investor webcast today highlighting the significant potential of luveltamab tazevibulin (luvelta), a novel folate receptor-α (FolRα) targeting ADC. The presentation will include an overview of the clinical data supporting luvelta’s broad opportunity to address the unmet need in several FolRα-expressing cancers, including platinum-resistant ovarian cancer (PROC), endometrial cancer, CBFA2T3::GLIS2 (CBF/GLIS; RAM phenotype) acute myeloid leukemia (AML), and non-small cell lung cancer (NSCLC). “Luvelta has been studied in over 180 patients to-date, and has demonstrated both promising clinical activity and a tolerable safety profile. We are optimistic about its potential to change the cancer treatment landscape,” said Bill Newell, Sutro’s Chief Executive Officer. “This includes the potential to be the first ADC to treat ovarian cancer patients with low to medium FolRα expression, which could double the current eligible patient population relative to the FolRα-targeting ADC on the market. In 2024, we look forward to advancing two synergistic registrational clinical trials for luvelta in ovarian cancer and CBF/GLIS AML, while continuing to progress the development of additional indications.” The event will feature presentations by key members of Sutro's senior management team and external oncology expert, Bradley Monk, M.D., Professor, the Division of Gynecologic Oncology, University of Arizona College of Medicine and Creighton University School of Medicine and Vice President and Co-Director, GOG Partners. Sutro management and Dr. Monk will participate in a Q&A session at the end of the presentation. Luvelta FolRα-targeting ADC Franchise Upcoming Milestones: The registration-directed trial, REFRαME-O1, in PROC is enrolling, with 26 active sites across 5 countries and an anticipated ~140 sites in ~20 countries by the end of 2024. Part 1 of the trial is expected to be completed in the first half of 2024. Initiation of REFRαME-P1, a registration-enabling trial for pediatric patients with CBF/GLIS AML, is planned for the first half of 2024. An Investigational New Drug (IND) application submission is planned in non-small cell lung cancer (NSCLC) in the first half of 2024. Continued clinical development is planned in endometrial cancer and in combination with bevacizumab for the treatment of ovarian cancer. Compelling Luvelta Data: Sutro presented an aggregated analysis of nearly 100 women with ovarian cancer from Company’s Phase 1 program. Treatment with luvelta demonstrated improved clinical outcomes and tolerability compared to historical results with standard of care chemotherapy in an evaluable patient population matching the eligibility criteria for the REFRαME-O1 trial. The safety profile across the aggregated analysis remained consistent with previously reported data. Safety data from an additional cohort with prophylactic G-CSF treatment showed significant reduction of neutropenia and resulting dose delays. New data in combination with bevacizumab demonstrated clinical activity in treated patients regardless of FolRα expression level. Preclinical data in a model of NSCLC demonstrated that a single dose of luvelta produced potent anti-tumor activity and that the combination of luvelta and PD-1 blockade (avelumab) demonstrated benefit and complete tumor regression. Promising clinical data in late-stage endometrial cancer and CBF/GLIS AML have been presented at ESMO and ASH in 2023. Luveltamab tazevibulin, abbreviated as “luvelta” and formerly known as STRO-002, is a FolRα-targeting antibody-drug conjugate (ADC) designed to treat a broad range of patients with ovarian cancer, including those with lower FolRα-expression who are not eligible for approved treatment options targeting FolRα. Developed and manufactured with Sutro’s cell-free XpressCF® platform, luvelta is a homogeneous ADC with four hemiasterlin cytotoxins per antibody, precisely positioned to efficiently deliver to the tumor while ensuring systemic stability after dosing. Sutro recently initiated REFRαME-O1, a Phase 2/3 registration-directed study for patients with platinum-resistant ovarian cancer. The Company has ongoing trials in patients with endometrial cancer and in combination with bevacizumab in patients with ovarian cancer. In the first half of 2024, the Company expects to initiate REFRαME-P1, a Phase 2/3 registration-directed study for patients with CBF/GLIS2 acute myeloid leukemia, a rare subtype of pediatric cancer, and expects to file an Investigational New Drug (IND) Application for the initiation of a non-small cell lung cancer study. The U.S. Food and Drug Administration (FDA) has granted luvelta a Fast Track designation for Ovarian Cancer, as well as Orphan and Rare Pediatric Disease designations for CBF/GLIS2 Pediatric AML. Sutro Biopharma, Inc., is a clinical-stage company relentlessly focused on the discovery and development of precisely designed cancer therapeutics, transforming what science can do for patients. Sutro’s fit-for-purpose technology, including cell-free XpressCF®, provides the opportunity for broader patient benefit and an improved patient experience. Sutro has multiple clinical stage candidates, including luveltamab tazevibulin, or luvelta, a registrational-stage folate receptor alpha (FolRα)-targeting ADC in clinical studies. A robust pipeline, coupled with high-value collaborations and industry partnerships, validates Sutro’s continuous product innovation. Sutro is headquartered in South San Francisco. For more information, follow Sutro on social media @Sutrobio, or visit www.sutrobio.com. 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– Complete remission seen in 42% of patients with CBF/GLIS AML with ≥5% blasts and 75% of pediatric patients with CBF/GLIS AML with <5% blasts; treatment with luvelta was either alone or in combination – – Luvelta was generally well-tolerated – – Data supports potential further development in CBF/GLIS AML – SOUTH SAN FRANCISCO, Calif., Dec. 11, 2023 (GLOBE NEWSWIRE) -- Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), today announced that its research collaborators presented data on anti-leukemic activity from the compassionate use of luveltamab tazevibulin (luvelta), a novel folate receptor-α (FR-α) targeting ADC, in pediatric patients with relapsed/refractory CBFA2T3-GLIS2 (CBF/GLIS) acute myeloid leukemia (AML), commonly known as RAM phenotype AML. Data demonstrated that treatment with luvelta produced meaningful clinical responses, including complete remission (CR); and prolongs overall survival (OS) enabling some patients to receive potentially curative therapies such as hematopoietic stem cell transplant. These patients were treated under the single patient IND mechanism. These data were featured in a poster presentation at the 65th American Society of Hematology Annual Meeting and Exposition (ASH 2023) in San Diego, CA. “Treatment with luvelta led to notable response in a significant subset of patients who had exhausted all therapeutic options,” said Soheil Meshinchi, M.D., Ph.D., presenter and primary author. “Response varied from deep remissions to disease stabilization with minimal toxicity – mostly in outpatient setting. Luvelta was well tolerated as long-term maintenance therapy with little to no hematopoietic toxicity.” CBF/GLIS subtype AML is a rare and highly lethal form of leukemia found exclusively in infants and young children, with the average age of onset at 18 months 1. There are no therapies specifically approved to target this form of leukemia and it is resistant to conventional chemotherapy, with an induction failure rate of over 80%2. Due to a lack of effective treatment, children diagnosed with the disease have a dismal two-year survival rate of 15%3. Recent studies have shown that FOLR1, which encodes for FolRα, is silent in normal hematopoiesis, but is uniquely induced by the CBF/GLIS fusion4. Under compassionate use, 25 pediatric patients with relapsed/refractory CBF/GLIS subtype AML were treated with luvelta at doses up to 4.3 or 5.2mg/kg every two to four weeks for a median duration of 15.9 weeks (3-73.1), with the majority of patients receiving at least five doses (68%). Of the 25 treated patients, 19 had ≥5% blasts (morphologic disease, or MD) and 8 had <5% blasts (sub-morphologic disease, or SMD)5. Collective results show that treatment with luvelta produced clinically meaningful and durable responses across a broad range of patients in various settings including in patients with or without prior stem cell transplant and in monotherapy or in combination with cytotoxic therapy. These data were generated by the treating physicians and collected and enabled for presentation by Sutro. “It is clear from these data that luvelta is providing an ongoing and promising impact on the lives of infants and young children with this rare leukemia,” said Bill Newell, Sutro’s Chief Executive Officer. “These results add to the growing body of research supporting the development of luvelta, which has now seen positive clinical results across three different tumor types, including those with potentially low or variable folate receptor-α expression.” ASH Presentation Highlights: Overall, anti-leukemic activity was seen with luvelta either as a single agent or in combination. 19 patients had ≥5% blasts and 8 patients had <5% blasts5. A CR/CRh was observed in 8 out of 19 (42%) patients with ≥5% blasts treated with luvelta, with 5 out of 8 CR/CRh patients reaching a minimal residual disease (MRD)-negative CR (63%).6 out of 8 patients with <5% blasts experienced an MRD-negative CR (75%). Patients whose leukemia experienced an MRD-negative CR had an improved outcome over those who did not experience an MRD-negative CR.Treatment with luvelta also enabled some children to bridge to stem cell transplant, which is potentially curative therapy.Luvelta was well-tolerated as a monotherapy agent and in combination with standard of care therapies with minimal hematopoietic toxicity and can be delivered as outpatient therapy.As of September 17, 2023, 8 patients remain on treatment, with 5 of the 8 (63%) in continued remission and on luvelta maintenance. The poster titled, “Anti-leukemic Activity of Luveltamab Tazevibulin (LT, STRO-002), a Novel Folate Receptor-α (FR-α)-targeting Antibody Drug Conjugate (ADC) in Relapsed/Refractory CBFA2T3::GLIS2 AML,” will be accessible through the News & Events page of the Investor Relations section of the company’s website at www.sutrobio.com. *1: National Institutes of Health [NIH], 2022; Quessada et al 2021; Masseti et al 2019*2: Smith JL, et al. Comprehensive Transcriptome Profiling of Cryptic CBFA2T3-GLIS2 Fusion-Positive AML Defines Novel Therapeutic Options: A COG and TARGET Pediatric AML Study. Clin Cancer Res. 2020 Feb 1;26(3):726-737. doi: 10.1158/1078-0432.CCR-19-1800. Epub 2019 Nov 12. PMID: 31719049; PMCID: PMC7002196.*3: Tang T, et al. Targeting FOLR1 in high-risk CBF2AT3-GLIS2 pediatric AML with STRO-002 FOLR1-antibody-drug conjugate, Blood Adv. 2022 Nov 22;6(22):5933-5937. doi: 10.1182/bloodadvances.2022008503. PMID: 36149945; PMCID: PMC9701621. *4: Le Q, et al. Targeting FOLR1 in High-Risk CBFA2T3-GLIS2 AML with Stro-002 FOLR1-Directed Antibody-Drug Conjugate, Blood, Volume 138, Supplement 1, 2021, Page 209, ISSN 0006-4971, https://doi.org/10.1182/blood-2021-153076.*5: Two patients initially presented with <5% blasts, received luvelta and proceeded to BMT. Both relapsed post-transplant with ≥5% blasts and re-started luvelta. About Luveltamab TazevibulinLuveltamab tazevibulin, abbreviated as “luvelta” and formerly known as STRO-002, is a FolRα-targeting antibody-drug conjugate (ADC) designed to treat a broad range of patients with ovarian cancer, including those with lower FolRα-expression who are not eligible for approved treatment options targeting FolRα. Developed and manufactured with Sutro’s cell-free XpressCF® platform, luvelta is a homogeneous ADC with four hemiasterlin cytotoxins per antibody, precisely positioned to efficiently deliver to the tumor while ensuring systemic stability after dosing. Sutro recently initiated REFRaME, a Phase 2/3 registration-directed study for patients with platinum-resistant ovarian cancer. The company has ongoing trials in patients with endometrial cancer and in combination with bevacizumab in patients with ovarian cancer. The company is also assessing the clinical path forward for CBF/GLIS2 acute myeloid leukemia, a rare subtype of pediatric cancer, as well as non-small cell lung cancer. The U.S. Food and Drug Administration (FDA) has granted luvelta a Fast Track designation for Ovarian Cancer, as well as Orphan and Rare Pediatric Disease designations for CBF/GLIS2 Pediatric AML. About Sutro Biopharma Sutro Biopharma, Inc., is a clinical-stage company relentlessly focused on the discovery and development of precisely designed cancer therapeutics, transforming what science can do for patients. Sutro’s fit-for-purpose technology, including cell-free XpressCF®, provides the opportunity for broader patient benefit and an improved patient experience. Sutro has multiple clinical stage candidates, including luveltamab tazevibulin, or luvelta, a registrational-stage folate receptor alpha (FolRα)-targeting ADC in clinical studies. A robust pipeline, coupled with high-value collaborations and industry partnerships, validates Sutro’s continuous product innovation. Sutro is headquartered in South San Francisco. For more information, follow Sutro on social media @Sutrobio, or visit www.sutrobio.com. Forward-Looking StatementsThis press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, anticipated preclinical and clinical development activities, timing of announcements of clinical results, trial initiation, and regulatory filings, potential benefits of luvelta and the Company’s other product candidates and platform, potential future milestone and royalty payments, the Company’s expectations about its cash runway, and potential market opportunities for luvelta and the Company’s other product candidates. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. Although the Company believes that the expectations reflected in such forward-looking statements are reasonable, the Company cannot guarantee future events, results, actions, levels of activity, performance or achievements, and the timing and results of biotechnology development and potential regulatory approval is inherently uncertain. Forward-looking statements are subject to risks and uncertainties that may cause the Company’s actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties related to the Company’s ability to advance its product candidates, the receipt and timing of potential regulatory designations, approvals and commercialization of product candidates and the Company’s ability to successfully leverage Fast Track designation, the market size for the Company’s product candidates to be smaller than anticipated, clinical trial sites, supply chain and manufacturing facilities, the Company’s ability to maintain and recognize the benefits of certain designations received by product candidates, the timing and results of preclinical and clinical trials, the Company’s ability to fund development activities and achieve development goals, the Company’s ability to protect intellectual property, the value of the Company’s holdings of Vaxcyte common stock, and the Company’s commercial collaborations with third parties and other risks and uncertainties described under the heading “Risk Factors” in documents the Company files from time to time with the Securities and Exchange Commission. These forward-looking statements speak only as of the date of this press release, and the Company undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date hereof. ContactEmily WhiteSutro Biopharma (650) 823-7681ewhite@sutrobio.com

- A total of 17 pediatric patients were treated with STRO-002 on a compassionate use basis; eight patients achieved complete remission, of which seven patients were MRD negative - - Safety and efficacy profile in this patient population provides added confidence to advance clinical development of STRO-002, which is currently being studied in patients with advanced ovarian and endometrial cancers - - FDA recently granted Orphan Drug Designation to STRO-002 in this patient population - SOUTH SAN FRANCISCO, Calif., Dec. 10, 2022 (GLOBE NEWSWIRE) -- Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs), today announced that its research collaborators at Fred Hutchinson Cancer Research Center presented data from the Compassionate Use Program on anti-leukemic activity of STRO-002, a novel folate receptor-α (FR-α) targeting ADC, in pediatric patients with relapsed/refractory CBFA2T3-GLIS2 (CBF/GLIS) acute myeloid leukemia (AML), commonly known as RAM phenotype AML, in an oral presentation at the 64th American Society of Hematology Annual Meeting and Exposition (ASH 2022) in New Orleans, LA. STRO-002 was provided to 17 pediatric patients with CBF/GLIS subtype AML on a compassionate use basis. Clinical results from these patients were compiled by Sutro and presented as an oral presentation by Soheil Meshinchi, M.D., Ph.D., Professor, Clinical Research Division, at Fred Hutchinson Cancer Research Center; Professor, Division of Pediatric Hematology-Oncology, at the University of Washington School of Medicine; and Principal Investigator for the program, titled, “Anti-Leukemic Activity of STRO-002 a Novel Folate Receptor-α (FR-α)-Targeting ADC in Relapsed/Refractory CBFA2T3-GLIS2 AML.” “I am heartened to observe such encouraging results in children with this rare disease who have a dismal prognosis with conventional therapies and no treatment options,” commented Dr. Meshinchi. “The clinical responses to STRO-002 in this group of patients who have relapsed or are refractory to standard of care treatments, suggest that this drug is particularly promising and provides hope for patients and families impacted by this devastating disease.” CBF/GLIS subtype AML is a rare, serious and life-threatening disease affecting pediatric patients with a median age of 1.5 years1 and the prevalence of CBF/GLIS in childhood is approximately 1 to 3% of pediatric AML cases1. These high-risk children with AML have an extremely poor prognosis with a 5-year overall survival of approximately 20%2. Patients are highly refractory to standard of care therapies and there are currently no approved therapies specifically targeting CBF/GLIS subtype AML. Recent studies have shown that FOLR1, which encodes for FolRα, is silent in normal hematopoiesis, but is uniquely induced by the CBF/GLIS fusion3. Preclinical data presented last year at ASH 2021 demonstrated that patients with CBF/GLIS AML may benefit from STRO-002. “We are encouraged by the positive results of our compassionate use program in children with a rare form of AML with STRO-002, which was recently granted Orphan Drug Designation by FDA in this patient population,” said Bill Newell, Sutro’s Chief Executive Officer. “These results underscore our confidence in the efficacy and tolerability for STRO-002, in addition to the development path forward for patients with ovarian and endometrial cancers.” ASH 2022 Data Highlights: 17 pediatric patients were treated with STRO-002 on a compassionate use basis.All 17 patients were relapsed/refractory to standard of care AML treatments. The median age of the patients is two years old and the median number of prior therapies is two. Eight of the patients had previously undergone a stem cell transplant (SCT).STRO-002 was well-tolerated as a monotherapy agent and in combination with standard of care therapies.In the 17 patients treated, Best Overall Response (BOR) includes eight patients with complete remission (CR), of which seven patients were minimal residual disease (MRD) negative.47% of the patients achieved complete remission and 53% of the patients achieved partial response or stable disease.Responders were seen in various settings including in patients with or without prior stem cell transplant and in monotherapy or in combination with cytotoxic therapy. The presentation will be made available today in the “Clinical/Scientific Presentation and Publication Highlights” section of Sutro Biopharma’s website at www.sutrobio.com and a whitepaper with details about this rare indication and Sutro’s compassionate use program is available on the Company’s website here. *1: National Institutes of Health [NIH], 2022; Quessada et al 2021; Masseti et al 2019*2: Smith JL, et al. Comprehensive Transcriptome Profiling of Cryptic CBFA2T3-GLIS2 Fusion-Positive AML Defines Novel Therapeutic Options: A COG and TARGET Pediatric AML Study. Clin Cancer Res. 2020 Feb 1;26(3):726-737. doi: 10.1158/1078-0432.CCR-19-1800. Epub 2019 Nov 12. PMID: 31719049; PMCID: PMC7002196. *3: Le Q, et al. Targeting FOLR1 in High-Risk CBFA2T3-GLIS2 AML with Stro-002 FOLR1-Directed Antibody-Drug Conjugate, Blood, Volume 138, Supplement 1, 2021, Page 209, ISSN 0006-4971, https://doi.org/10.1182/blood-2021-153076. About STRO-002 STRO-002 is an optimized FolRα-targeting antibody-drug conjugate (ADC) with a drug-antibody ratio (DAR) of 4, which is precisely conjugated using non-natural amino acids attached to stable protease-cleavable linkers and hemiasterlin-derivative warheads. STRO-002 potentially has a dual mechanism of action against the tumor through cytotoxic killing and through inducing immunogenic cell death. STRO-002 was designed with Sutro's proprietary cell-free protein synthesis and site-specific conjugation platform, which enables precise design, rapid empirical optimization, and manufacture of site-specific homogenous ADCs. About Sutro Biopharma Sutro Biopharma, Inc., headquartered in South San Francisco, is a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs). Sutro has two wholly owned ADCs in the clinic—STRO-002, a folate receptor alpha (FolRα)-targeting ADC, in clinical studies for ovarian and endometrial cancers; and STRO-001, a CD74-targeting ADC, in clinical studies for B-cell malignancies. Additionally, Sutro is collaborating with Bristol Myers Squibb (BMS) on CC-99712, a BCMA-targeting ADC in the clinic for patients with multiple myeloma; with Merck KGaA, Darmstadt, Germany, known as EMD Serono in the U.S. and Canada (EMD Serono), on M1231, a MUC1-EGFR bispecific ADC in clinical studies for patients with solid tumors, particularly non-small cell lung cancer (NSCLC) and esophageal squamous cell carcinoma; with Merck, known as MSD outside of the United States and Canada, on MK-1484, a selective IL-2 agonist in clinical studies as a monotherapy and in combination with pembrolizumab for the treatment of solid tumors; and with Astellas Pharma (Astellas) on novel modality, immunostimulatory antibody-drug conjugates (iADCs). Sutro’s platform technology also enabled the spin out of Vaxcyte and the creation of VAX-24, a 24-valent pneumococcal conjugate vaccine in clinical studies for the prevention of invasive pneumococcal disease. Sutro’s rational design and precise protein engineering has enabled six product candidates in the clinic. Follow Sutro on Twitter, @Sutrobio, and at www.sutrobio.com to learn more about our passion for changing the future of oncology. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, anticipated preclinical and clinical development activities, timing of announcements of clinical results and regulatory filings, potential benefits of STRO-002 and the Company’s other product candidates and platform, potential future milestone and royalty payments, and potential market opportunities for STRO-002 and the Company’s other product candidates. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. Although the Company believes that the expectations reflected in such forward-looking statements are reasonable, the Company cannot guarantee future events, results, actions, levels of activity, performance or achievements, and the timing and results of biotechnology development and potential regulatory approval is inherently uncertain. Forward-looking statements are subject to risks and uncertainties that may cause the Company’s actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties related to the Company’s ability to advance its product candidates, the receipt and timing of potential regulatory designations, approvals and commercialization of product candidates and the Company’s ability to successfully leverage Fast Track designation, the market size for the Company’s product candidates to be smaller than anticipated, the impact of the COVID-19 pandemic on the Company’s business, clinical trial sites, supply chain and manufacturing facilities, the Company’s ability to maintain and recognize the benefits of certain designations received by product candidates, the timing and results of preclinical and clinical trials, the Company’s ability to fund development activities and achieve development goals, the Company’s ability to protect intellectual property, the value of the Company’s holdings of Vaxcyte common stock, and the Company’s commercial collaborations with third parties and other risks and uncertainties described under the heading “Risk Factors” in documents the Company files from time to time with the Securities and Exchange Commission. These forward-looking statements speak only as of the date of this press release, and the Company undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date hereof. Investor ContactAnnie J. Chang Sutro Biopharma(650) 801-5728ajchang@sutrobio.com Media ContactAmy BonannoSolebury Strategic Communications(914) 450-0349abonanno@soleburystrat.com