AT rich interacting domain containing protein 1A (ARID1A) is a tumor suppressor gene
frequently mutated in solid tumor malignancies, often loss of function mutations (frameshift
or non-sense). ARID1A encodes a large nuclear protein BAF250a, a vital component of the
Switch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex, which participates in
several nuclear activities including transcription, DNA synthesis and DNA damage repair.
ARID1A alterations are particularly prevalent in ovarian clear cell carcinoma (46-50%),
ovarian and uterine endometrioid carcinomas (24-44%), and cholangiocarcinoma (27%); reported
in up to 27% of gastric carcinoma, esophageal adenocarcinoma, Waldenstrom macroglobulinemia,
pediatric Burkitt lymphoma, hepatocellular carcinoma, urothelial carcinoma, 12% of colorectal
carcinoma (CRC) , 15% of invasive ductal carcinoma of breast, and 7.5% of NSCLC, as a sample
representation reported in the COSMIC database.
ARID1A plays a key role in regulating cell cycle and DNA damage repair, through its critical
role in chromatin regulation. Loss of function of ARID1A leads to dysregulation of many gene
pathways, supporting its role as a tumor suppressor gene. Loss of ARID1A mediates fulvestrant
resistance, demonstrated in multiple elegant studies involving ER+ breast cancer lines,
related to therapeutic pressure and selection [1]. Sporadic deletion of ARID1A in mice leads
to de novo invasive colon adenocarcinoma. Loss of ARID1A leads to deregulation of the MEK/ERK
pathway, critical in kras mutated CRC. ARID1A loss is associated with microsatellite
instability in ovarian and endometrial endometrioid adenocarcinomas and gastric cancer.
Preclinical data demonstrates enhanced clinical activity of check point inhibitors in ARID1A
mutated tumors.
EZH2, enhancer of zeste homologue 2, the enzymatically active core of PRC2 (polycomb
repression complex 2/3) plays a key role in tumorigenesis. Over-expression in tumor cells
leads to histone hypermethylation, tumor proliferation, cell cycle dysregulation, metastases
and angiogenesis.
Tazemetostat is an FDA approved selective small molecule inhibitor of the histone lysine
methyltransferase enhancer of zeste homolog 2 (EZH2). Posttranslational modifications of core
histone proteins of chromatin play an important role in controlling the fidelity of gene
transcription patterns in cells. Paramount among these transcription-controlling
modifications is methylation events at lysine and arginine residues, catalyzed by histone
methyltransferases (HMTs). Genetic alterations in a number of HMTs have been identified in
human cancers where they are purported to play a causal role in malignancies. Tazemetostat
has been shown to produce durable tumor responses in patients with B-cell non-Hodgkin's
lymphoma and epithelioid sarcomas. Responses have also been demonstrated in INI1 and SMARCA4
negative solid tumors patients.
Hypothesis: EZH2 plays a critical role in driving the biology of ARID1A mutated malignancies.
Inhibition of EZH2 with tazemetostat will lead to significant clinical benefit in ARID1A
mutated malignancies.
Cell homeostasis requires a balance in ARID1A and EZH2 through chromatin mediated gene
expression. Loss of ARID1A expression leads to imbalance, with enhanced EZH2 activity in
malignancies. Targeted EZH2 inhibition in ARID1A mutated tumors leads to synthetic lethality
in several malignancies, with upregulation of PI3K interacting protein 1 gene (PI3K1P1) and
associated growth suppression. EZH2 plays a key role in ovarian carcinoma. Benjamin Bitler et
al [2] demonstrated PIK3IP1 as a direct target of ARID1A and EZH2, upregulated by EZH2
inhibition and contributing to synthetic lethality by inhibiting PI3K-AKT signaling. EZH2
inhibition caused in vivo regression of ARID1A-mutated ovarian tumors. A recent published
study suggests the synthetic lethality of targeting EZH2 in ARID1A mutated gastric cancer.
Leo Yamada et al [3] demonstrated selective sensitivity of EZH2 inhibitors against
ARID1A-deficient GC supporting the potential efficacy of targeted therapy using EZH2
inhibitors in this patient population. Targeting EZH2 has also demonstrated potential
synthetical lethality in kras mutated CRC in ARID1A mutated tumors [4].
The Prisma Health Cancer Institute reviewed molecular profiling of current patients and
identified 124 cancer patients with an ARID1A mutation in a spectrum of malignancies
including breast, non-small cell lung cancer, pancreas, uterine, ovarian, cholangiocarcinoma,
hepatocellular, and multiple rare solid tumors. A high frequency of concurrent PTEN and PI3K
pathways mutations along with ARID1A mutations was also seen, suggesting a potentially
significant role of EZH2.
There are no clinical trials addressing therapy in ARID1A mutated malignancies. A current
clinical trial, NCT03348631, is evaluating tazemetostat in patients with recurrent ovarian,
peritoneal, and endometrial cancer, not selected by ARID1A mutation status [5].
These data support the need for further clinical investigation of tazemetostat as monotherapy
and in combination with other agents in solid tumors harboring an ARID1A mutation.
Inclusion Criteria:
- Have voluntarily agreed to provide written informed consent and demonstrated
willingness and ability to comply with all aspects of the protocol.
- Histologically and/or cytologically confirmed advanced or metastatic solid tumor
harboring ARID1A mutation (except epithelioid sarcoma)
- Progression of disease following approved therapies or for which no standard therapy
exists
- For subjects who have experienced any clinically significant toxicity related to a
prior anticancer treatment (i.e., chemotherapy, immunotherapy, and/or radiotherapy):
at the time the subject provides voluntary written informed consent, all toxicities
have either resolved to grade 1 per NCI CTCAE Version 5.0 [11] OR are clinically
stable and no longer clinically significant.
- Have measurable disease as defined by RECIST 1.1.
- Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2.
- Males or females are >18 years of age at the time of providing voluntary written
informed consent.
- Life expectancy >3 months before enrollment.
- Time between prior anticancer therapy and first dose of tazemetostat as follows:
Cytotoxic chemotherapy - At least 21 days Noncytotoxic chemotherapy (e.g., small molecule
inhibitor) - At least 14 days. Nitrosoureas - At least 6 weeks. Monoclonal antibody - At
least 28 days. Radiotherapy - At least 14 days. In addition, at least 6 weeks from prior
radioisotope therapy; and at least 12 weeks from 50% pelvic or total body irradiation.
- Adequate renal function: Creatinine < 2.0 or calculated creatinine clearance ≥ 35
mL/minute per the Cockcroft and Gault formula
- Adequate bone marrow function:
ANC ≥ 750mm3 without growth factor support (filgrastim or pegfilgrastim) for at least 14
days.
Platelets ≥ 75,000mm3 (≥75 × 109/L) evaluated at least 7 days after platelet transfusion.
Hemoglobin ≥9.0 g/dL and may receive transfusion Adequate liver function: Total bilirubin
<1.5 × the upper limit of normal (ULN) (except for unconjugated hyperbilirubinemia of
Gilbert's syndrome); Alkaline phosphatase (ALP) (in the absence of bone disease), ALT, and
AST <3 × ULN (or <5 × ULN if subject has liver metastases).
Exclusion Criteria:
- Subjects with epithelioid sarcoma are excluded.
- Has a prior history of T-Cell Lymphoblastic Lymphoma, T-Cell Acute Lymphoblastic
Leukemia, Myelodysplastic Syndrome, Acute Myeloid Leukemia, or Myeloproliferative
Neoplasm.
- Female subjects who are pregnant or breastfeeding.
- Prior exposure to tazemetostat or other inhibitor(s) of EZH2.
- Subjects with uncontrolled CNS metastases requiring steroids.
- Subjects taking medications that are known potent CYP3A4 inducers/inhibitors
(including St. John's wort)
- Are unwilling to exclude Seville oranges, grapefruit juice, AND grapefruit from their
diet.
- Major surgery within 4 weeks before the first dose of study drug. NOTE: Minor surgery
(e.g., minor biopsy of extracranial site, central venous catheter placement, shunt
revision) is permitted within 1 week prior to enrollment.
- Are unable to take oral medication OR have malabsorption syndrome or any other
uncontrolled gastrointestinal condition (e.g., nausea, diarrhea, vomiting) that might
impair the bioavailability of tazemetostat.
- Significant cardiovascular impairment: history of congestive heart failure greater
than New York Heart Association (NYHA) Class II (Appendix 3), uncontrolled arterial
hypertension, unstable angina, myocardial infarction, or stroke within 6 months of the
first dose of study drug; or cardiac ventricular arrhythmia.
- Have an active infection requiring systemic therapy.
- Known hypersensitivity to any component of tazemetostat.
- Any other major illness that, in the Investigator's judgment, will substantially
increase the risk associated with the subject's participation in this study OR
interfere with their ability to receive study treatment or complete the study.
- Subjects who have undergone a solid organ transplant.
- Prior malignancy in the past 5 years.
