An Exploratory Study of Pembrolizumab Plus Entinostat in Non-Inflamed Stage III/IV Melanoma

This is an exploratory (n=10-12 evaluable patients), open-label, single-arm, phase II study
in patients with 'non-inflamed' unresectable regional or distant metastatic melanomas
irrespective of prior treatment with PD-1/PD-L1 pathway inhibitors. The primary endpoint is
to assess the incidence of histopathologic conversion of non-inflamed melanomas from patients
with metastatic melanoma to 'inflamed' melanoma following single-agent entinostat "priming"
(entinostat monotherapy). More specifically, patients with metastatic melanomas that have no
evidence of tumor-infiltrating or tumor-associated lymphocytes (TIL/TAL), based on standard
hematoxylin and eosin (H&E) staining of representative tumor sections (non-inflamed
melanomas) will receive weekly entinostat for 3 weeks in cycle 1 (entinostat monotherapy; 5mg
PO, qwk on D1, D8, D15 of cycle 1; cycle length = 21 days). Mandatory tumor tissue biopsies
will be performed in the end of cycle 1, beginning of cycle 2 (day 21±2 days), immediately
before treatment with concurrent entinostat (once weekly × 3) and pembrolizumab (200 mg
q3wks) in cycles 2-9 (see section 5.2.1 drug dosing schema). Correlative studies will be
performed at baseline and in the end of cycle 1, beginning of cycle 2 (day 21±2 days) to
assess whether: (a) 3 weeks of entinostat monotherapy converts TIL/TAL-absent melanomas to
TIL/TAL-present by histopathologic (H&E stain) analysis, (b) 3 weeks of single-agent
entinostat induces changes in gene expression profiling by assessing distinct signatures as
defined by RNA-sequencing signatures (RNA-seq; 'immune-high', innate anti-PD-1 resistance
[IPRES], and epigenetic 1-3), (c) 3 weeks of single-agent entinostat induces changes in
histone-accessible DNA by performing formaldehyde-assisted isolation of regulatory elements
(FAIRE)4, (d) conversion of non-inflamed to inflamed melanomas by single-agent entinostat
and/or antitumor response to the entinostat-pembrolizumab combination is associated with a
baseline signature that consists of distinct somatic mutation gene profile, global histone
modification profile in melanoma tissue or peripheral blood mononuclear cells (PBMC), and/or
abundance of entinostat targets in melanoma cells (HDAC 1, 2, 3, and 11). Up to 12 evaluable
patients will be treated with entinostat plus pembrolizumab for up to 27 weeks (approximately
6 months) based on clinical benefit. Patients who continue to have clinical benefit at 27
weeks may continue therapy with pembrolizumab or any other PD-1/PD-L1 inhibitor, as per
standard of care.Secondary exploratory endpoints involve: (a) assessment of antitumor
response of entinostat administered concurrently with pembrolizumab at week 9 (or earlier if
patient progresses), based on response rate per Response Evaluation Criteria in Solid Tumors
version 1.1 (RECIST v1.1). (b) assessment of the progression-free survival (PFS) rate at 27
weeks (approximately 6 months) of the entinostat-pembrolizumab combination. (c) determine the
safety of the entinostat-pembrolizumab combination in patients with metastatic melanoma per
NCI Common Terminology Criteria for Adverse Events (NCI-CTCAE). (d) assessment of other
exploratory biomarkers in tumor tissue and peripheral blood.

Inclusion Criteria:

- Age ≥ 18 years at the time of consent.

- Subject has provided informed consent and Health Insurance Portability and
Accountability Act (HIPAA) prior to initiation of any study-specific
activities/procedures.

- Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤2.

- Histologically confirmed metastatic (regional or distant) melanoma of any subtype
(cutaneous, mucosal, ocular).

- American Joint Committee on Cancer (AJCC) stage unresectable III or stage IV disease
that is measurable by RECIST v1.1 criteria.

- Must agree to undergo one on-treatment tumor biopsy on day 22 (±2 days) of the study.
Subjects for whom fresh samples cannot be safely provided (e.g., inaccessible tumor
for biopsy or has metastatic lung lesion(s) as the only site of metastatic disease)
will not be eligible for study participation.

- Must have available archival tissue and subjects have consented to allow collection of
archived tumor blocks from previous surgeries confirming or treating unresectable
stage III or distant metastatic disease. If more than one archived tumor blocks are
available, two blocks have to be analyzed for the presence of Tumor-infiltrating
lymphocyte/Tumor-associated lymphocyte (TIL/TALS). Archived tumor tissues must fulfill
the following criteria based on two representative Hematoxylin & Eosin (H&E)-stained
tissue sections: (1) the tumor surface area must be at least 1cm2, (2) no more than
20% of necrosis, (3) the ratio of viable tumor cells to tumor-associated stroma should
be at least 60/40, (4) absolutely no TIL/TAL. Dr. Paula Googe, study pathologist, must
sign off on the eligibility of archived tumor blocks before study enrollment. If
archival tissue is unavailable or insufficient, fresh biopsy should be performed to
confirm unresectable stage III or distant metastatic disease.

- Previous treatment with immune checkpoint inhibitors and chemotherapies is allowed on
condition that the last treatment is at least 28 days prior to first dose of
entinostat. Previous treatment with targeted therapies (e.g. Mitogen-activated protein
kinase, MAPK inhibitors) is allowed on condition that the last treatment was
administered at least 15 days prior to first dose of entinostat).

- Demonstrate adequate organ function as defined in the table below; all screening labs
to be obtained within 21 days prior to entinostat treatment.

*Note: Hematology and other lab parameters that are ≤ grade 2 BUT still meet criteria
for study entry are allowed. Furthermore, changes in laboratory parameters during the
study should not be considered Adverse events (AEs) unless they meet criteria for dose
modification(s) of study medication outlined by the protocol in Section 5.3.1 and/or
worsen from baseline during therapy.

- A female of childbearing potential must have a negative serum pregnancy test during
screening and a negative urine pregnancy test within 3 days prior to receiving the
first dose of study drug. If the screening serum test is done within 3 days prior to
receiving the first dose of study drug, a urine test is not required. A female of
childbearing potential must agree to use effective contraception during the study and
for 120 days after the last dose of study drug. A female of non-childbearing potential
defined as (by other than medical reasons):

-≥45 years of age and has not had menses for >2 years,

- Amenorrheic for <2 years without a hysterectomy and oophorectomy and a
follicle-stimulating hormone value in the postmenopausal range upon pre-study
(screening) evaluation,

- Post hysterectomy, oophorectomy or tubal ligation. Documented hysterectomy or
oophorectomy must be confirmed with medical records of the actual procedure or
confirmed by an ultrasound. Tubal ligation must be confirmed with medical records of
the actual procedure; otherwise the patient must be willing to use 2 adequate barrier
methods throughout the study, starting with the screening visit through 120 days after
the last dose of entinostat,

- If male, agrees to use an adequate method of contraception starting with the first
dose of study drug through 120 days after the last dose of entinostat,

- See section 5.6.2 for information on acceptable methods of contraception.

- Experienced resolution of toxic effect(s) of the most recent prior anti-cancer therapy
to Grade ≤1 (except alopecia or neuropathy) by CTCAE v5.0. Exceptions are patients who
may have developed autoimmune-type side effects that require permanent hormonal
replacement from previous therapies.

- If the patient underwent major surgery or radiation therapy, these procedures must
have occurred at least 15 days prior to the first dose of entinostat. In addition,
patients must have recovered from the toxicity and/or complications from the
intervention.

- Subjects must be willing and able to comply with study procedures based on the
judgement of the investigator or protocol designee.

Exclusion Criteria:

All subjects meeting any of the exclusion criteria at baseline will be excluded from study.

-Is receiving systemic steroid therapy or any other form of immunosuppressive therapy for
autoimmune side effects related to previous use of immunotherapies for melanoma. Exceptions
include episodic (up to 7 days) use of systemic steroids for common conditions while on
study treatment (e.g. Chronic obstructive pulmonary disease (COPD) exacerbation, poison
ivy), use of corticosteroids as replacement doses for adrenal or pituitary insufficiency.

Has a known history of tuberculosis (Bacillus Tuberculosis) or human immunodeficiency virus
(HIV 1/2 antibodies).

Hypersensitivity to pembrolizumab or any of its excipients. Allergy to benzamide or
inactive components of entinostat.

Has known history of biopsy-proven (non-infectious) pneumonitis that required systemic
steroids, or any evidence of current pneumonitis.

Conditions that would preclude adequate absorption of oral medications (malabsorption,
significant nausea and vomiting, resection of >100-cm of proximal small bowel, resection of
>200-cm of distant small bowel).

Has a history or current evidence of any condition, therapy, or laboratory abnormality that
might confound the results of the trial, interfere with the subject's participation for the
full duration of the trial, or is not in the best interest of the subject to participate,
in the opinion of the treating investigator, including but not limited to:

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

ii. Uncontrolled hypertension (>150/90 in more than 60% of recorded BP measurements taken
on 5 or more separate occasions, within 3 weeks of the first dose of entinostat; at least 3
recorded measurements required on each occasion) or diabetes mellitus (HbA1c >9.0 within 15
days from first dose of entinostat),

iii. Active infection requiring systemic antibiotic therapy by the first day of entinostat
treatment,

iv. Known psychiatric or substance abuse disorders that would interfere with cooperation
with the requirements of the trial.

If female, is pregnant or breastfeeding, or, if male, expecting to conceive or father
children within the projected duration of the trial, starting with the pre-screening or
screening visit through 120 days after the last dose of trial treatment.

Known active hepatitis B (e.g., hepatitis B surface antigen-reactive) or hepatitis C (e.g.,
hepatitis C virus ribonucleic acid [qualitative]). Patients with past hepatitis B virus
(HBV) infection or resolved HBV infection (defined as the presence of hepatitis B core
antibody [HBc Ab] and absence of HBs Ag) are eligible. HBV DNA test must be performed in
these patients prior to study treatment if known history of viral hepatitis. Patients
positive for hepatitis C virus (HCV) antibody are eligible, only if polymerase chain
reaction is negative for HCV RNA.

Has received a live vaccine within 30 days of planned start of study therapy. Note:
Seasonal influenza vaccines for injection are generally inactivated flu vaccines and are
allowed; however intranasal influenza vaccines (e.g., Flu-Mist®) are live-attenuated
vaccines and are not allowed.

History of prior malignancy, with the exception of the following:

- Non-melanoma skin cancers, non-invasive bladder cancer, and carcinoma in situ of the
cervix,

- Prior history of prostate cancer provided the patient is not undergoing active
systemic treatment other than hormonal therapy and has documented PSA that is
undetectable (<0.2ng/mL),

- Papillary thyroid cancer, even if patients may have just completed thyroidectomy
within the last 2 years, have not received adjuvant radioactive iodine therapy, and
were only recently diagnosed with asymptomatic papillary thyroid cancer and their
surgery is pending,

- Chronic lymphocytic leukemia (CLL) provided patient has isolated lymphocytosis (Rai
stage 0) and does not require systemic treatment [for "B" symptoms, Richter's
transformation, lymphocyte doubling time (<6 months), lymphadenopathy or
hepatosplenomegaly],

- Lymphoma, hairy-cell leukemia, or myelodysplasia, provided that patient is not on
active systemic treatment and is in complete remission, as evidenced by PET/CT scans
and bone marrow biopsies for at least 3 months,

- History of any other malignancy provided patient has completed therapy and is free of
disease for ≥ 2 years. If patient had other malignancy within the last 2 years from
which he, or she, may have been completely cured by surgery alone, he may be
considered to be enrolled on condition that the risk of development of distant
metastatic disease based on the most recent AJCC staging system is less than 30%.

Has known active (i.e. previously untreated) parenchymal central nervous system (CNS)
metastases that are symptomatic, and/or more than one lesion with the largest diameter
being > 5-mm and/or require antiepileptic drugs or systemic corticosteroids for management
of intracranial symptoms. Patients with carcinomatous meningitis are also excluded.
Exceptions are:

- Subjects with previously treated brain metastases provided they are stable (i.e.
without evidence of progression by brain Magnetic Resonance Imaging (MRI) or head CT
with IV contrast) for at least 2 weeks prior to the first dose of entinostat. Any
neurologic symptoms must have returned to baseline, and have no evidence of new or
enlarging brain metastases, and are not using ongoing systemic corticosteroids for
management of intracranial symptoms for at least 7 days prior to first dose of
entinostat,

- Patients with active (i.e. not treated with stereotactic radiosurgery), single,
asymptomatic, up to 5-mm in largest diameter brain metastases (measured either by
brain MRI with IV contrast or head CT with IV contrast measuring within 2 weeks prior
to the first dose of entinostat).

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 entinostat.

Subject is receiving prohibited medications or treatments as listed in section 5.5 of the
protocol that cannot be discontinued/replaced by an alternative therapy.

Prior treatment with Histone/deacetylase inhibitor (HDACi) for their melanoma.