Study of STRO-002, an Anti-Folate Receptor Alpha (FolRα) Antibody Drug Conjugate in Ovarian & Endometrial Cancers

This study is a first-in-human Phase 1, open-label, multicenter, dose escalation study with
dose expansion to identify the maximum tolerated dose (MTD), the recommended phase 2 dose
(RP2D) and to evaluate the safety, tolerability, and preliminary anti-tumor activity of
STRO-002 in adult subjects with advanced epithelial ovarian cancer (including fallopian or
primary peritoneal cancer) and endometrial cancer. Fallopian tube and primary peritoneal
cancers are treated in the same manner as epithelial ovarian cancers and are thus included in
this phase 1 study. Subjects eligible for this study exhibit advanced relapsed and/or
progressive disease. The study will consist of two parts: Part 1, dose escalation, and Part
2, dose expansion.

Part 1 (dose escalation) will enroll subjects with relapsed and/or progressive ovarian,
fallopian tube or primary peritoneal cancer. Part 2 (dose expansion) will enroll subjects
with relapsed and/or progressive ovarian, fallopian tube or primary peritoneal cancer (Cohort
A) and subjects with relapsed and/or progressive epithelial endometrial cancer with
sufficient FolRα expression per IHC as assessed by Sponsor (Cohort B).

During dose escalation (Part 1), the initial three dose levels will be evaluated with an
N-of-1 approach followed by a standard 3+3 enrollment for all subsequent dose levels.
Subjects with endometrial cancer will not be enrolled in the dose escalation part of the
study. Subjects will be dosed based on adjusted ideal body weight (AIBW). The starting dose
was determined to be the human equivalent dose (HED) of 1/6 the highest non-severely toxic
dose (HNSTD) identified in the good laboratory practice (GLP) toxicology study in cynomolgus
monkeys. Subsequent doses follow a modified Fibonacci sequence for dose escalation, the
second dose increases by 100% of the initial dose, and thereafter by 80%, then 60%, 50%, 40%,
30% and then 20% of the preceding doses. The first three dose levels will enroll only 1
patient unless there is an instance of a treatment-related, clinically relevant Grade 2
non-hematologic toxicity or a Grade 3 hematologic toxicity of any type is observed during
Cycle 1 (first 21 days). Any event meeting these criteria will be reviewed and confirmed by
the Safety Evaluation Team (SET). When these criteria are met then the dose is expanded with
2 additional subjects and the standard 3+3 trial design is used for all further dose levels.
If these criteria are not met during the first 3 dose levels, the standard 3 +3 trial design
will begin with dose level 4.

The dose escalation phase of the study will be complete when the MTD is determined and the
RP2D for dose expansion is identified. After determination of the RP2D, endometrial cancer
subjects (Cohort B) will be enrolled in the dose expansion part of the study and will be
analyzed for preliminary efficacy independently from the ovarian (including fallopian tube
and primary peritoneal) cancer cohort (Cohort A).

In both Part 1 and Part 2 of the study, STRO-002 will be dosed as an intravenous (IV)
infusion on Day 1 of 21-day cycles. Clinical evaluations and/or laboratory tests will be
performed weekly for Cycles 1-4, and at the beginning of every cycle starting with Cycle 5 as
described in the schedule of assessments. Samples for pharmacokinetics (PK) analysis will
occur at specific times on Days 1, 2, 8, and 15 of Cycles 1 and 2, Days 1, 8 and 15 of Cycles
3 and 4 and at the end of treatment (EOT) visit. Additional clinical evaluations and lab
testing may occur at the discretion of the investigator.

Subjects who receive any dose of STRO-002 will be included in safety analyses. Disease
evaluations will include peripheral blood analysis and scans as appropriate. Disease status
will be evaluated per RECIST 1.1 criteria. Samples will be collected to assess the PK and
immunogenicity of STRO-002. Biomarkers may be assessed from peripheral blood and/or tissue
samples. Subjects will continue to receive study drug until disease progression, unacceptable
toxicity, withdrawal of consent, or end of study (study completion).

Inclusion Criteria:

1. Confirmation of diagnosis

2. Relapsed or relapsed/refractory disease

3. Age ≥ 18 years

4. ECOG performance status (0-1)

5. Life expectancy > 3 months

6. Adequate bone marrow, liver and renal functions

7. QTcF <500 msec

8. Ability to comply with treatment, PK and test schedules

Exclusion Criteria:

1. Low grade ovarian carcinoma (Grade 1).

2. Clear cell, mucinous and sarcomatous ovarian carcinomas.

3. Prior treatment with a FolRα-targeting ADCs or FolRα-targeting vaccines

4. History of severe allergic or anaphylactic reactions to monoclonal antibody therapy or
to antibody-related fusion protein treatment

5. Sensory or motor neuropathy ≥ grade 2

6. Chronic or ongoing active infectious disease requiring systemic treatment such as, but
not limited to, chronic renal infection, chronic chest infection with bronchiectasis,
tuberculosis and active hepatitis C

7. Ongoing immunosuppressive therapy, including systemic corticosteroids. Note:
Physiologic replacement and use of topical or inhaled corticosteroids are allowed.

8. Clinically significant cardiac disease

9. Clinically significant pre-exisiting ocular disorders

10. Significant concurrent, uncontrolled medical condition

11. History or clinical signs of meningeal or active CNS involvement

12. Known severe chronic obstructive pulmonary disease or asthma

13. History of significant cerebrovascular disease

14. Known Human Immunodeficiency Virus seropositivity

15. Positive serology for hepatitis B defined by a positive test for HBsAg

16. Concurrent participation in another therapeutic treatment trial