Ph1b/2 Dose-Escalation Study of Entinostat With Pembrolizumab in NSCLC With Expansion Cohorts in NSCLC, Melanoma, and Colorectal Cancer

SNDX-275-0601 is an open-label, Phase 1b/2 study evaluating the combination of entinostat
plus pembrolizumab in patients with advanced metastatic or recurrent NSCLC or melanoma or
mismatch repair-proficient colorectal cancer. The study has 2 phases, a Dose
Escalation/Confirmation Phase (Phase 1b) and an Expansion Phase (Phase 2). An additional
cohort (Entinostat Monotherapy Immune Correlate [EMIC] Cohort) evaluating single agent
entinostat for 2 weeks followed by the combination will also be evaluated in patients with
NSCLC in the Phase 2 expansion phase.

Toxicities will be assessed by the Investigator using the United States (US) National Cancer
Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE), version 4.03.

Dose Confirmation: The prospective MTD/RP2D identified in the Dose Escalation Phase will be
confirmed in 9 patients in Dose Confirmation Cohort(s) to obtain additional AE, immune
correlate, and anti-tumor activity data on entinostat in combination.

Phase 2 (Expansion): In the Expansion Phase, entinostat in combination will be evaluated
using the RP2D identified in the Dose Escalation/Confirmation Phase. Up to 3 Expansion
Cohorts consisting of distinct subsets of patients with solid tumor cancers may be explored.
Expansion cohorts may include:

1. Cohort 1: NSCLC

2. Cohort 2: Patients with NSCLC (any histology) who have previously been treated and
responded and then progressed on either a PD-1 or PD-L1-blocking antibody

3. Cohort 3: Patients with melanoma who have previously been treated with and unequivocally
progressed on either a PD-1 or PD-L1-blocking antibody

4. Cohort 4: Patients with CRC (mismatch repair-proficient) who have not been previously
treated with a PD-1 or PD-L1 blocking antibody

EMIC Cohort: 15 NSCLC patients Stage 2 of Cohort 1 will be randomly assigned to participate.

Inclusion Criteria:

Patients with NSCLC:

1. Has histologically- or pathologically-confirmed recurrent/metastatic NSCLC.

2. If has adenocarcinoma, required to have previously been tested for anaplastic lymphoma
kinase (ALK) rearrangements and epidermal growth factor receptor (EGFR) mutations,
with results available for collection in this study, and, if positive, has been
treated with prior EGFR or ALK therapy.

3. Received at least 1 chemotherapeutic regimen in the advanced/metastatic setting and
experienced documented, unequivocal progressive disease by either RECIST 1.1 or
clinical assessment.

4. Patients with NSCLC enrolled in Cohort 1 of the Expansion Phase should not have been
previously treated with a PD-1/PD-L1-blocking antibody

Patients in Expansion Phase, Cohorts 2 and 3

5. Previously treated with a PD-1/PD-L1-blocking antibody and experienced experienced
documented, unequivocal radiographic progression of disease by irRECIST, or similar
criteria during or within 12 weeks after last dose of such treatment. Patients must
have received at least 6 weeks of PD-1/PD-L1 therapy for Cohort 3.

Patients with Melanoma:

6. In addition to having been previously treated with a PD-1/PD-L1-blocking antibody
(inclusion #5), has a histologically- or cytologically-confirmed diagnosis of
unresectable or metastatic melanoma and experienced unequivocal progressive disease
during treatment with a BRAF inhibitor if BRAF V600 mutation-positive. Treatment with
BRAF inhibitor may occur AFTER treatment with the checkpoint inhibitor.

Patients in Expansion Phase, Cohort 4 (Colorectal Cancer)

7. Received at least 1 chemotherapeutic regimen in the advanced/metastatic setting and
experienced documented, unequivocal progressive disease by either RECIST 1.1 or
clinical assessment. Must have documented mismatch repair-proficient colon cancer as
determined by either immunohistochemistry for mismatch repair proteins or PCR-based
functional microsatellite instability. Patients with colorectal cancer enrolled in
Cohort 4 should not have been previously treated with a PD-1/PD-L1-blocking antibody
(i.e., pembrolizumab, nivolumab, MEDI36MEDI4376, or GNE PDL1 [MPDL3280A])

All Patients

8. Aged 18 years or older on the day written informed consent is given.

9. If has brain metastases, must have stable neurologic status following local therapy
for at least 4 weeks without the use of steroids or on stable or decreasing dose of
≤10 mg daily prednisone (or equivalent), and must be without neurologic dysfunction
that would confound the evaluation of neurologic and other AEs.

10. Evidence of locally recurrent or metastatic disease based on imaging studies within 28
days before the first study drug dose:

- At least 1 measurable lesion ≥20 mm by conventional techniques or ≥10 mm by
spiral CT scan or MRI, with the last imaging performed within 28 days before the
first study drug dose. If there is only 1 measurable lesion and it is located in
previously irradiated field, it must have demonstrated unequivocal progression
according to RECIST, version 1.1.

11. If receiving radiation therapy, has a 2-week washout period following completion of
the treatment prior to receiving the first study drug dose and continues to have at
least 1 measureable lesion, per above criterion.

12. ECOG performance status of 0 or 1.

13. Has acceptable, applicable laboratory parameters.

14. Female subjects must not be pregnant.

15. If male, agrees to use an adequate method of contraception

15. Experienced resolution of toxic effect(s) of the most recent prior chemotherapy to
Grade 1 or less (except alopecia). If patient underwent major surgery or radiation therapy
of >30 Gy, they must have recovered from the toxicity and/or complications from the
intervention.

17. Willing to have fresh tumor samples collected during screening and at other time points
designated as mandatory, per the Schedule of Study Assessments.

18. Able to understand and give written informed consent and comply with study procedures.

Exclusion Criteria:

Patients meeting any of the following criteria are not eligible for study participation:

1. Diagnosis of immunodeficiency or receiving systemic steroid therapy or any other form
of immunosuppressive therapy within 7 days prior to the first dose of study drug. The
use of physiologic doses of corticosteroids may be approved after consultation with
the Sponsor.

2. Active autoimmune disease that has required systemic treatment in past 2 years (i.e.,
with disease modifying agents, corticosteroids, or immunosuppressive drugs).
Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid
replacement therapy for adrenal or pituitary insufficiency) is not considered a form
of systemic treatment.

3. History of interstitial lung disease (ILD).

4. Allergy to benzamide or inactive components of entinostat.

5. History of allergies to any active or inactive ingredients of pembrolizumab or severe
hypersensitivity (>= Grade 3) to pembroluzumab.

6. History or current evidence of any condition, therapy, or laboratory abnormality that
might confound the results of the study, interfere with the patient's participation
for the full duration of the study, or is not in the best interest of the patient to
participate, in the opinion of the treating Investigator, including, but not limited
to:

- Myocardial infarction or arterial thromboembolic events within 6 months prior to
baseline or severe or unstable angina, New York Heart Association (NYHA) Class
III or IV disease, or a QTc interval > 470 msec.

- Uncontrolled heart failure or hypertension, uncontrolled diabetes mellitus, or
uncontrolled systemic infection.

- Another known additional malignancy that is progressing or requires active
treatment (excluding adequately treated basal cell carcinoma, squamous cell of
the skin, cervical intraepithelial neoplasia [CIN]/cervical carcinoma in situ or
melanoma in situ, or ductal carinoma in situ of the breast). Prior history of
other cancer is allowed, as long as there is no active disease within the prior 5
years.

- Has a history of (non-infectious) pneumonitis that required steroids or current
pneumonitis.

- Active infection requiring systemic therapy.

- Known active central nervous system (CNS) metastases and/or carcinomatous
meningitis.

Note: Patients with previously treated brain metastases may participate provided they
are stable (without evidence of progression by imaging [using the identical imaging
modality for each assessment, either MRI or CT scan] for at least 4 weeks prior to the
first dose of study drug and any neurologic symptoms have returned to baseline), have
no evidence of new or enlarging brain metastases, and are not using steroids for at
least 2 weeks prior to the first dose of study drug or are on stable or decreasing
dose of ≤10 mg daily prednisone (or equivalent). This exception does not include
carcinomatous meningitis which is excluded regardless of clinical stability.

7. Known psychiatric or substance abuse disorders that would interfere with cooperation
with the requirements of the study.

8. Currently participating and receiving study therapy or has participated in a study of
an investigational agent and received study therapy or used an investigational device
within 4 weeks of the first dose of treatment.

9. Received a live virus vaccination within 30 days of the first dose of treatment.

10. Prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to baseline or who
has not recovered (i.e., ≤Grade 1 or at baseline) from AEs due to agents administered
more than 4 weeks earlier.

11. Prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2
weeks prior to study baseline or who has not recovered (i.e., ≤Grade 1 or at baseline)
from AEs due to a previously administered agent.

Note: Patients with ≤Grade 2 neuropathy or ≤Grade 2 alopecia are an exception to this
criterion and may qualify for the study.

Note: If patient underwent major surgery, they must have recovered adequately from the
toxicity and/or complications from the intervention prior to starting therapy.

12. Received transfusion of blood products (including platelets or red blood cells) or
administration of colony stimulating factors (including granulocyte-colony stimulating
factor [G-CSF], granulocyte macrophage-colony stimulating factor [GM-CSF], or
recombinant erythropoietin) within 4 weeks prior to the first dose of study drug.

13. Currently receiving treatment with any other agent listed on the prohibited medication
list such as valproic acid, or other systemic cancer agents within 14 days of the
first dose of treatment.

14. If female, is pregnant, breastfeeding, or expecting to conceive, or if male, expect to
father children within the projected duration of the study, starting with the
screening visit through 120 days after the last dose of study drug.

15. Known history of human immunodeficiency virus (HIV) (HIV 1/2 antibodies).

16. Known active hepatitis B (e.g., hepatitis B surface antigen-reactive) or hepatitis C
(e.g., hepatitis C virus ribonucleic acid [qualitative]).

17. For CRC expansion cohort, no prior history of malignant bowel obstruction requiring
hospitalization in the 6 months prior to enrollment

18. For the CRC expansion cohort, no history of uncontrolled ascites, defined as
symptomatic ascites and/or repeated paracenteses for symptom control in the past 3
months