Sutro Biopharma Presentation

37th Annual J.P. Morgan Healthcare Conference

Bill Newell, CEONASDAQ: STRO

Forward Looking Statements

• This presentation and the accompanying oral presentation contain “forward-looking” statements that are based on our management’sbeliefs and assumptions and on information currently available to management. Forward-looking statements include all statements other than statements of historical fact contained in this presentation, including information concerning our future financial performance, business plans and objectives, timing and success of our planned development activities, our ability to obtain regulatory approval, the potential therapeutic benefits and economic value of our product candidates, potential growth opportunities, financing plans, competitive position, industry environment and potential market opportunities.

• Forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. These factors, together with those that may be described in greater detail under the heading “Risk Factors” in documents the company files from time to time with the Securities and Exchange Commission, may cause our actual results, performance or achievements to differ materially and adversely from those anticipated or implied by our forward-looking statements.

• You should not rely upon forward-looking statements as predictions of future events. Although our management believes that the expectations reflected in our forward-looking statements are reasonable, we cannot guarantee that the future results, levels of activity, performance or events and circumstances described in the forward-looking statements will be achieved or occur. Moreover, none of us assumes responsibility for the accuracy and completeness of the forward-looking statements. We undertake no obligation to publicly update any forward-looking statements for any reason after the date of this presentation to conform these statements to actual results or to changes in our expectations, except as required by law.

• This presentation also contains estimates and other statistical data made by independent parties and by us relating to market size and growth and other data about our industry. This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions, and estimates of our future performance and the future performance of the markets in which we operate are necessarily subject to a high degree of uncertainty and risk.

• Solely for convenience, the trademarks and tradenames referred to in this presentation appear without the ® and ™ symbols, but those references are not intended to indicate, in any way, that we will not assert, to the fullest extent under applicable law, our rights, or the right of the applicable licensor to these trademarks and tradenames.

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Sutro’s Vision – Changing the Future of Oncology

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Sutro Biopharma – 4Q 2018 Accomplishments and Financial Overview

ü IPO (Oct 1, 2018 closing) raised $85MM + $10MM private placement from Merck

ü STRO-001: Orphan Drug Designation for Multiple Myeloma

ü STRO-002: IND Open

ü Appointment of Shalini Sharp, Ultragenyx CFO, to Sutro Board

ü Achieved $10MM Manufacturing Milestone from Celgene

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• * Pro forma cash of ~$212MM, including IPO proceeds (net of underwriting discounts) & proceeds from Merck investment at IPO

Actual Cash, Cash Equivalents & Marketable Securities (Sep 30, 2018): $123MM*

• Estimated Cash Runway with IPO & Merck Investment Proceeds into 2021

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Product Candidate Anticipated Clinical Milestone Worldwide Rights

STRO-001CD74 ADCMultiple Myeloma/Lymphoma

Phase 1: • Initial Safety Data expected by Mid 2019• Initial Efficacy Data expected by YE 2019

STRO-002 FolRα ADCOvarian and EndometrialCancers

Phase 1: • IND Open• Trial Initiation expected 1Q 2019 • Initial Safety Data expected 4Q 2019

BCMA ADCMultiple Myeloma

Phase 1: • IND Submission & Trial Initiation anticipated

by Mid 2019

(a)

Important Clinical Milestones Anticipated in 2019Building on 2018 momentum

(a) Celgene will automatically obtain worldwide rights to the first product candidate to achieve IND clearance in the United States and Sutro is eligible for milestones and royalties on this product candidate.

Clinical Stage Company Robust Pipeline of Wholly Owned and Partnered Programs

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(a)

(a) There are a total of four programs to which Celgene currently has ex-U.S. rights and Sutro currently has U.S. rights. Celgene will automatically obtain worldwide rights to the first product candidate to achieve IND clearance in the United States. Celgene can obtain worldwide rights to the second product candidate to have an active IND in the United States by making certain payments to Sutro. For the programs that would potentially be the third and fourth to enter clinical development, Sutro owns U.S. rights and Celgene owns ex-U.S. rights.

(b) EMD Serono is the U.S. healthcare business of Merck KGaA, Darmstadt, Germany.

PRODUCT CANDIDATE / PROGRAM DISCOVERY PRECLINICAL PHASE 1WHOLLY OWNED/ COLLABORATION

PARTNER

STRO-001CD74 ADC

STRO-002FolRα ADC

Multiple Oncology & I/O Programs

Cytokine-based

BCMA ADC

Multiple bispecific antibodies

Multiple mono- and bispecific ADCs

Multiple Myeloma (Orphan Drug Designation); Lymphomas: DLBCL, Mantle Cell, Follicular

Ovarian and Endometrial Cancer – IND Open

Oncology

Oncology & Autoimmune

Multiple Myeloma

ImmunoOncology

Oncology

(b)

Worldwide Rights

Collaborations Demonstrate Sutro’s Robust Discovery Engine ~$350 million in payments received from collaborators

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• Entered into in July 2018

• Immune-modulating cytokine derivatives

for cancer & autoimmune disease

– Up to three research programs

– Second largest preclinical I/O deal done

by Merck

• $90M in total funding received in 2018

including equity investments

• Up to $1.6B in potential future milestones

• MSD to low teen percentage royalties on

WW sales

• BCMA ADC: IND expected mid 2019

• Expect patient enrollment to begin upon

IND Clearance

• Sutro retains U.S. development &

commercial rights to two programs

• Over $220M total funding received to date

including equity investments

• Over $1B in potential future milestones

plus MSD to low teen percentage royalties

• Spinout using XpressCF™ to make potential best-in-

class pneumococcal conjugate vaccine

• Near-term 1000L production on schedule utilizing

XpressCF™

• >$170M in equity funding raised

• Sutro current ~5.6% ownership & SD percentage

royalties

• Developing ADCs for multiple cancer

targets

– Lead program is a bispecific ADC

• Up to $52.5M in potential future

milestones per program, plus low to MSD

percentage royalties

XpressCF™ Platform AdvantageDevelopment of potential best-in-class protein therapeutics

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Potential Best-in-Class Protein Therapeutics Differentiated Attributes of XpressCF™

• Rapid generation of diverse protein structures enables empirical assessment and selection of optimal candidates

• Can accelerate time to IND by 9 - 15 months compared to conventional technologies

• Homogeneous drug products generated precisely according to specifications

• Cell-free protein production process generates homogenous products from DNA sequences in <24 hours

• Consistent production method used across scale-up — from discovery to commercial manufacturing

• Enables site-specific, efficient and complete conjugation to non-natural amino acids

BispecificsCytokine-basedI/O TherapeuticsADCs

9

XpressCF™ Platform Has Broad CapabilitiesPositions Sutro as a leading protein engineering company

Sutro’s Platform Uniquely Leverages the Advantages of Both Protein Discovery and Protein Engineering Technologies

Commercial Scale Facilitated with Spray Drying Advancements

Rapid Protein Discovery Precise Protein Engineering

Novel methodologies for identifying protein therapeutics with desired functions

Proprietary approaches to improving protein function through designed structural alterations

XpressCF™ Platform Technology

STRO-001: CD74 – Phase 1 Potential First & Best-in-Class ADC for B Cell Malignancies

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Building a Franchise in B Cell MalignanciesInitial clinical strategy targets Multiple Myeloma and NHL

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• Increasingly treated as a chronic disease– Majority of patients relapse or become

resistant to treatment– Physician demand for additional

therapeutic options as patients progress

Unmet Need for B Cell Malignancies:

B Cell MalignanciesPrevalence ~ 600 k

Incidence ~ 100 k

Multiple MyelomaPrevalence ~ 95 kIncidence ~ 30 k

DLBCL

Mantle Cell

MultipleMyeloma

Other (Marginal zone, etc)

Follicular Lymphoma

Chronic Lymphocytic

Leukemia

Aggressive NHLPrevalence ~ 216 kIncidence ~ 27 k

Indolent NHLPrevalence ~ 293 kIncidence ~ 42 k

Relative Prevalence of B Cell Malignancies

Source: SEER data; data includes U.S. only and excludes extremely small B-cell malignancy subtypes; incidence rates based per annum.Source: Company filings and Evaluate Pharma.

Phase 1 Dose Escalation Data Will Drive Potential Expansion of Clinical Program• Multiple Myeloma• Diffuse Large B Cell Lymphoma• Follicular Lymphoma• Mantle Cell Lymphoma

STRO-001: Overcoming Therapeutic WindowLimitations of 1st Generation ADC’s

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Property Description

Stability

Safety • Homogenous design results in a single species product creating more precise dosing and potential for improved therapeutic index

• Warhead is covalently conjugated to two specific sites on the antibody (DAR = 2) using a stable non-cleavable linker

Potency • Optimized positioning of linker / maytansinoid derivative warhead for effective targeting of CD74-positive tumor cells

Selectivity• Hydrophilic nature of potent intracellular catabolites translates to low

permeability to surrounding cells once cancer cell is killed – reduces potential for toxicity to surrounding normal tissue

Designed to optimize multiple properties to widen therapeutic index

STRO-001 in Multiple MyelomaPotent preclinical anti-tumor activity

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3

Vehicle

1 mg/kgSTRO-001

Similar response with 3 and 10 mg/kg STRO-001

ay 28

D21 D28D14D7

phot

ons/

seco

nd

phot

ons/

seco

ndph

oton

s/se

cond

Bioluminescent Imaging of Tumor Cells Survival in MM1S-luc Xenograft Model

STRO-001 Results in Significant Reduction of Tumor Burden in Single Doses of 1, 3 and 10 mg/kg STRO-001 Results in Meaningful Survival Benefits

Source: Sutro Biopharma report, Evaluation of STRO-001 Efficacy Against Established Disseminated MM1S-luc Human Multiple Myeloma in Female NSG Mice, Report TR-PHRM-0071-V1.0, dated July 20, 2017.

STRO-001 in DLBCL and Mantle CellPromising preclinical efficacy

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Single dose IV

10 mg/kg of STRO-001 Induced Complete Tumor Regression in All 7 Mice and Resulted in No Tumor

Re-Growth 90 Days Post Treatment

Tumor Growth in Murine Xenograft DLBCL Model

Survival in Murine Xenograft Mantle Cell Model

10 mg/kg of STRO-001 Resulted in 100% Survival on Day 135

Source: Sutro Biopharma report, Efficacy of STRO-001 in Tumors in SCID Mice, TR-PHRM-0072-V1.0, dated July 11, 2017; Sutro Biopharma report, Evaluation of STRO-001 Efficacy in Disseminated Mino Model in SCID Mice, Report TR-PHRM-0011-V1.0, dated July 13, 2017.

STRO-001 Phase 1 Clinical Trial Design – Initial Safety Data Anticipated Mid-2019– Initial Efficacy Anticipated by YE 2019

MTD

Ad

van

ced

an

d/o

r R

efra

cto

ry M

ult

iple

M

yelo

ma

Ad

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an

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ry N

HL

Dose Level 2

Dose Level n

RP2D

RP2D

Clinical Data will drive expansion

Part 1 — Dose Escalation (2 Cohorts) Part 2 — Dose Expansion (4 Cohorts)

n = 40 Multiple Myeloma

n = 40 DLBCL

n = 40 Mantle Cell Lymphoma

n = 40 Follicular Lymphoma

MTD

Dose Level 1

28-day cycle:Dosing on days 1 & 15

15

n = 30

Dose Level 1

28-day cycle:Dosing on days 1 & 15

n = 30

Dose Level 2

Dose Level n

Up to:

Up to:

STRO-002: FolRα – IND OpenFirst Patient Anticipated in Q1 19Potential Best-in-Class ADC for Ovarian and Endometrial Cancers

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Negative10%

Low10%

Medium16%High

64%

Negative7%

Low15%

Medium24%

High54%

Ovarian Endometrial

STRO-002: Targeting FolRα in Ovarian and Endometrial Cancers

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FolRαü Clinically validated target

ü Expressed on a variety of tumor types

ü Limited expression in normal tissue

FolRα Expression Appears to Correlate with Disease Progression in Ovarian Cancer

FolRα expressed in more than 90% of evaluated ovarian and endometrial cancer tissue samples(a)

(a) Source: Sutro Biopharma report, Expression Of Folate Receptor Alpha In Ovarian And Endometrial Cancer Samples, TR-TPPD-0039-V1.0, dated March 12, 2018.

STRO-002: Overcoming Therapeutic Window Limitations of 1st Generation ADCs

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STRO-002 Properties Implications for Best-in-Class Potential

• Homogeneous ADC product generated from Sutro’s XpressCF™ platform

• Optimized and consistent drug-antibody ratio (DAR = 4)

• Potent hemiasterlin-derivative warhead

• Proprietary cleavable linker with optimized pharmacology

• Potential for improved therapeutic index

• Many constructs tested to identify STRO-002, the candidate with potential for best potency and safety

• Efficacious, potent killing of tumor cells

• Potential for improved safety; rapid clearance of catabolite after release & cell killing in tumor

No ocular toxicity observed in NHP study

STRO-002 in Ovarian CancerPotent preclinical anti-tumor activity

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Single Dose of 10 mg/kg STRO-002 Resulted in Tumor Regression

Tumor Growth in OVCAR3 Murine Ovarian Xenograft Model

Source: Sutro Biopharma report, Evaluation of STRO-002 Efficacy in the Treatment of Established and Large OVCAR-3 Human Ovarian Xenograft Tumors, TR-TPPD-0116-V1.0, dated December 20, 2017.

STRO-002 in Ovarian CancerDesign features facilitate improved potency and specificity

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STRO-002 Demonstrates More Potent Cell Killing Compared to the Benchmark and Has Minimal Off-Target Activity

Source: Sutro Biopharma report, STRO-002 Cell Killing Compared to SP8435, TR-TPPD-0021-V1.0, dated May 18, 2018.

STRO-002: A Potentially Superior FolRα ADC Improved stability can widen therapeutic index

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* not detectable

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Mouse Tumor Model – Free Warhead in Tumor vs. Blood After Dosing

STRO-002 Free Warhead

Heterogeneous BenchmarkFree Warhead

no observable warhead*

No Evidence of STRO-002 Free Warhead Circulating in the Blood Post Dosing

Source: Sutro Biopharma report, In Vivo Catabolite Profiling for SP8193 and SP8435 in Tumor and Plasma, TR-PHRM-0036-V1.1, dated January 8, 2018.

* not detectable

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Mouse Tumor Model –Free Warhead in Tumor vs. Blood After Dosing

STRO-002 Free Warhead

Heterogeneous BenchmarkFree Warhead

no observable warhead *

* not detectable

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Mouse Tumor Model –Free Warhead in Tumor vs. Blood After Dosing

STRO-002 Free Warhead

Heterogeneous BenchmarkFree Warhead

no observable warhead *

Part 1 — Dose Escalation (1 Cohort) Part 2 — Dose Expansion (2 Cohorts)

STRO-002 Phase 1 Clinical Trial Design– Initial safety data anticipated in Q4 2019

Sing

le A

gent

Com

bina

tion

Stud

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Antic

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Dose Level 1

Dose Level 2

Dose Level n

IND open in 4Q18 & FPI projected for 1Q19

MTD-2

MTD-1

MTD

n = 1

n = 1

n = 3 - 6

n = 1 - 6 RP2D

RP2D

n = 40 Ovarian

n = 40 Endometrial

TBD Endometrial + Combo Therapy

TBD Ovarian + Combo Therapy

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Up to:

Anticipated combination study

William Newell, JDChief Executive Officer and Member of the Board of Directors

Trevor Hallam, PhD Chief Scientific Officer

Arturo Molina, MD, MS, FACP Chief Medical Officer

Shabbir Anik, PhD Chief Technical Operations Officer

Ed AlbiniChief Financial Officer

Steve WorsleyChief Business Officer

Linda FitzpatrickChief People and Communications Officer

Nicki Vasquez, PhDSr. VP Alliance Management / Portfolio Strategy & Operations

Lynx

Experienced Leadership Team

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Senior Management Team and Previous Experience

Neurex

Sutro Biopharma Presentation

37th Annual J.P. Morgan Healthcare Conference

Bill Newell, CEONASDAQ: STRO