A Phase 1b Study of PTC596 in Children With Newly Diagnosed Diffuse Intrinsic Pontine Glioma and High Grade Glioma

This study consists of 3 parts:

• The Phase I (Parts A and C), dose-finding component of the trial, to estimate the maximum tolerated dose (MTD) or recommended phase II dose (RP2D) of PTC596 in combination with RT followed by maintenance therapy with PTC596, in children with newly-diagnosed DIPG and HGG.

Once the RP2D has been determined,

• An early efficacy expansion cohort of up to 17 patients at the RP2D (Part C expansion, and Part D)
• A surgical cohort (part B) of 12 patients with newly diagnosed DIPG who are amenable to undergo biopsy or HGG for whom a second surgical resection is warranted

For patients on cohorts A, C and D, PTC596 will be given orally twice weekly for 6-7 weeks along with daily RT for the first cycle. In subsequent cycles (4 weeks each), all patients will continue with maintenance therapy which will begin immediately after completion of RT for up to 26 cycles (2 years).

For the surgical cohort, patients will be treated with 2 doses of PTC596, on days 1 and 4 prior to biopsy or re-resection; the second dose of PTC596 should ideally be administered 3-6 hrs before surgery. The surgical cycle will end when patients begin RT which should take place at least two weeks after the date of surgery and may restart PTC596 (twice weekly) after starting RT. Following completion of RT, patients will immediately start maintenance therapy with twice weekly PTC596 for up to 26 cycles.

Primary Objectives Parts A, C

• To determine the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of PTC596 given concurrently with radiation in newly-diagnosed patients with DIPG or HGG (Parts A and C)
• To determine the toxicities of PTC596 given concurrently with RT and during maintenance therapy (Parts A, C).
• To characterize the pharmacokinetics of PTC596 given as a capsule and as a tablet in children with newly diagnosed DIPG or HGG when given concurrently with RT and during maintenance (Parts A, C).

Primary Objectives Surgical Cohort -Part B

• To test the ability of PTC596 to inhibit BMI-1 activity in tumor and PBMCs
• To characterize the pharmacokinetics of PTC596 in plasma, cerebrospinal fluid (CSF), and tumor tissue

Secondary Objectives

• To evaluate the overall survival (OS) for newly-diagnosed patients with DIPG treated with PTC596 and compare to historical controls.
• To estimate the progression-free survival (PFS) distribution for newly-diagnosed patients with HGG ttreated with PTC596 and compare to historical controls
• To determine the effects of BMI-1 modulation in DIPG and HGG on BMI-1 levels, H2A monoubiquitination, cell proliferation, cell death, gene regulation, through gene expression profiling and epigenetic studies such as RNA sequencing and ChIP-Seq within the confines of a Phase I study.
• Correlate pre-treatment and post-treatment concentrations of potential biomarkers in biological specimens (e.g., blood and tissue) with response/toxicity, PFS, OS within the confines of a phase I study.
• To examine H3F3A, HIST1H3B (H3.3 and H3.1 genes), ATRX, and DAXX mutations and examine the effects of these alterations using targeted gene, exome, RNA sequencing and methylation arrays of targeted genomic regions in DIPG and HGG.
• To assess the health-related quality-of-life of patients by parent report, and when possible, patient report at key points in therapy using the patient reported outcomes measurement information system (PROMIS) survey.
• To explore tumor volumetric measurements on MRI and correlate with 2-dimensional measurements and compare response criteria.
• To correlate early measures of tumor response (volumetric and 2-dimensional measurements with overall survival.

Inclusion criteria

Age: Patients must be ≥12 months and ≤ 21 years of age at the time of study enrollment.

Diagnosis: Patients with newly-diagnosed diffuse intrinsic pontine gliomas (DIPGs), defined as tumors with a pontine epicenter and diffuse involvement of at least 2/3 of the pons, are eligible without histologic confirmation.

Patients with brainstem tumors that do not meet radiographic criteria or are not considered to be typical diffuse intrinsic pontine gliomas will be eligible if the tumors are biopsied and proven to be high-grade gliomas (such as anaplastic astrocytoma, glioblastoma, H3K27-mutant diffuse midline glioma) or diffuse astrocytoma.

Patients with newly-diagnosed non-brainstem high-grade glioma (HGG) are eligible.

Patients must have had histologically verified high-grade glioma such as anaplastic astrocytoma, glioblastoma, H3 K27 mutant diffuse midline glioma etc.

Patients eligible for the surgical stratum include patients with:

• Newly-diagnosed DIPG who are amenable to undergo biopsy at the recommendation of their treating physician
• Newly-diagnosed HGG for whom a second surgical resection is warranted for further debulking or to achieve a near-total or gross total resection after initial diagnosis has been made but prior to start of therapy.

Disease Status: Patients with disseminated DIPG or HGG are not eligible, and MRI of spine must be performed if disseminated disease is suspected clinically by the treating physician.

Performance Level: Karnofsky ≥ 50 for patients > 16 years of age and Lansky ≥ 50 for patients ≤ 16 years of age. Patients who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score.

Neurologic Status: Patients must be able to swallow oral medications to be eligible for study enrollment.

Patients enrolling on Part A (phase I, capsule formulation) must be able to swallow whole capsules.

Prior Therapy: Patients must not have received any prior anticancer therapy. Prior dexamethasone and/or surgery are permissible.

Organ Function Requirements:

Adequate Bone Marrow Function Defined as:

• Peripheral absolute neutrophil count (ANC) ≥ 1000/mm3

• Platelet count ≥ 100,000/mm3 (transfusion independent, defined as not receiving platelet transfusions for at least 7 days prior to enrollment)

• Hemoglobin >8 g/dL (may be transfused).

Adequate Renal Function Defined as:

• Creatinine clearance or radioisotope GFR ≥ 70ml/min/1.73 m2 or

• A serum creatinine based on age/gender as follows:
• 1 to < 2 years: 0.6 (Male) 0.6 (Female)
• 2 to < 6 years: 0.8 (Male) 0.8 (Female)
• 6 to < 10 years: 1 (Male) 1 (Female)
• 10 to < 13 years: 1.2 (Male) 1.2 (Female)
• 13 to < 16 years: 1.5 (Male) 1.4 (Female)

• 16 years: 1.7 (Male) 1.4 (Female)

Adequate Liver Function Defined as:

• Total bilirubin must be ≤ 1.5 times institutional upper limit of normal for age

• AST(SGOT)/ALT(SGPT) < 3 times institutional upper limit of normal

• Serum albumin ≥ 2g/dL

Adequate Cardiac Function Defined As:

• Ejection fraction of ≥ 55% by echocardiogram.

• QTc ≤ 480 msec.

Adequate Pulmonary Function Defined as

• No evidence of dyspnea at rest, and a pulse oximetry > 94% in room air if there is clinical indication for determination

Adequate Neurologic Function Defined as:

• Patients with seizure disorder may be enrolled if on anticonvulsants and well controlled.

Informed Consent: All patients and/or their parents or legally authorized representatives must sign a written informed consent. Assent, when appropriate, will be obtained according to institutional guidelines.

Exclusion criteria

Diagnosis: patients with a diagnosis of oligodendroglioma or oligoastrocytoma are not eligible. Patients with juvenile pilocytic astrocytoma, are not eligible.

Patients with non-brainstem diffuse astrocytoma (grade 2) are not eligible for the HGG stratum of the study.

Pregnancy or breast-feeding: Pregnant or breast-feeding women will not be entered on this study due to known or unknown risks of fetal and teratogenic adverse events as seen in animal/human studies. Pregnancy tests must be obtained in girls who are post-menarchal. Males or females of reproductive potential may not participate unless they have agreed to use an effective contraceptive method.

Patients of childbearing or child fathering potential must agree to use adequate contraceptive methods (hormonal or barrier method of birth control; abstinence) while being treated on this study and for 3 months after completing therapy. Note: The definition of effective contraception will be based on the judgment of the principal investigator or a designated associate.

Concomitant Medications

• Corticosteroids: Patients receiving corticosteroids are eligible. The use of corticosteroids must be reported.
• Investigational Drugs: Patients who are currently receiving another investigational drug are not eligible.
• Anti-cancer Agents: Patients who are currently receiving other anti-cancer agents are not eligible.
• Anticonvulsants: Patients who are receiving enzyme inducing anticonvulsants as listed in appendix II, are not eligible
• Patients who are receiving rifampin are not eligible.
• Patients who are receiving medications known to prolong QTc interval as listed in appendix III are not eligible.
• Patients who are receiving duloxetine, alosetron or theophylline (CYP1A2 inhibitors) are not eligible
• Patients on beta-blockers are not eligible
• Selective serotonin reuptake inhibitors (SSRIs) such as citalopram (Celexa), escitalopram (Lexapro), Fluoxetine (Prozac), fluvoxamine (Luvox), paroxetine (Paxil), sertraline (Zoloft) should be used with caution but are not contraindicated.
• Anticoagulants: patients who are receiving therapeutic anticoagulants including warfarin, low-molecular weight heparin are not eligible

Nasogastric or G tube administration of PTC596 is not permissible.

Infection: Patients who have an uncontrolled infection are not eligible.

Patients who, in the opinion of the investigator, may not be able to comply with the safety monitoring requirements of the study are not eligible.

Patients with evidence of bowel obstruction, malabsorption, or other contraindication to oral medication are not eligible.

Patients with GI disease or other condition that could affect absorption or predispose subject to gastrointestinal ulceration are not eligible.

Patients with an active peptic ulcer disease or inflammatory bowel disease (including ulcerative colitis and Crohn's disease), diverticulitis, cholecystitis, symptomatic cholangitis or appendicitis are not eligible.

Patients with serious non-healing wounds, ulcers, or bone fractures are not eligible.

Patients with moderate to severe pulmonary problems generally defined by need for medical intervention (e.g., oxygen, medications) and/or limiting activities of daily living (generally CTCAE Grade 2 or higher) or shortness of breath with limited exertion are not eligible. Pulmonary conditions include (but are not limited to) COPD, asthma, and hemi-pneumectomy.

Patients with malignancy related to HIV or solid organ transplant: known history of HIV, HBV surface antigen positivity or positive HCV antibody are not eligible. Viral testing is not required unless clinically indicated in patients without a known history.

Patient with prior or ongoing clinically significant illness, medical or psychiatric condition, medical history, physical findings, ECG findings, or laboratory abnormality that, in the investigator's opinion, could affect the safety of the subject, or alter the absorption, distribution, metabolism, or excretion of the study drugs, or could impair the assessment of study results are not eligible.

Patients with any prior solid organ transplant are not eligible