Phase I Study of APX005M in Pediatric Central Nervous System Tumors

This is a multicenter phase I trial of APX005M in patients with recurrent or refractory primary malignant central nervous system tumor, or newly diagnosed diffuse intrinsic pontine glioma.

APX005M is a humanized IgG1κ mAb that binds to CD40. APX005M binds to both human and cynomolgus monkey CD40 with high affinity, triggering activation of B cells, monocytes, and dendritic cells and stimulating cytokine release from both human and monkey lymphocytes and monocytes. APX005M does not bind to mouse or rat CD40. CD40 is also expressed on many human tumor cells, and APX005M can mediate a direct cytotoxic effect on CD40+ tumor cells.

Activation of CD40 on tumor cells results in tumor cell apoptosis and inhibition of tumor growth. CD40 agonistic antibodies have demonstrated potent antitumor immune response stimulation in both animal models and cancer patients. Due to its action on both immune and tumor cells, CD40 has been studied as a target for novel cancer immunotherapy.

Apexigen has declared the adult recommended phase 2 dose to be 0.3 mg/kg because no dose limiting toxicities were encountered at that dose and the pharmacodynamic profile was similar to the 1 mg/kg maximally tolerated dose. This phase 1 clinical trial is to study APX005M in children with central nervous system tumors.

• APX005M treatment for recurrent or refractory primary malignant CNS tumor patients (Biological): APX005M dosing will begin at 0.1 mg/kg, the APX005M dose may be increased (0.3, 0.45, 0.6 mg/kg) or decreased (0.03 mg/kg) in subsequent cohorts until the maximum tolerated dose (MTD) is reached or until dose level 3 (0.6 mg/kg) is complete without the MTD being defined. APX005M will be administered at the assigned dose level every 21 days (3 weeks). Patients may continue to receive APX005M for 36 courses (approximately 2 years) or until disease progression, unacceptable toxicity or death, whichever occurs first.
• APX005M treatment for newly diagnosed DIPG patients (Biological): The starting dose of APX005M for the DIPG patients will be one dose level below the recommended phase II dose (RP2D) determined in Stratum 1 patients. The dose may be decreased or increased to the RP2D established in Stratum 1. APX005M will be administered at the assigned dose level every 21 days (3 weeks). Patients may continue to receive APX005M for 36 courses (approximately 2 years) or until disease progression, unacceptable toxicity or death, whichever occurs first.

Primary outcomes

• Number of Patients Who Experienced Dose-limiting Toxicities (DLTs) [6 weeks]: DLTs were defined as adverse events (AE) at least possibly attributed to APX005M that occurred during the first 2 courses (6 weeks) following APX005M administration. DLTs included any APX005M-related AE that led to dose reduction or permanent cessation of therapy or resulted in a treatment delay >2 weeks. Hematologic DLTs included grade 3 neutropenia with fever, any grade 4 hematologic toxicity except lymphopenia, and grade 3 thrombocytopenia on 2 separate days or requiring platelet transfusion on 2 days within a 7-day period. Non-hematologic DLTs included any grade 4 non-hematologic toxicity, grade 3 or higher cytokine release syndrome, or any grade 3 non-hematologic toxicity with some exceptions such as grade 3 nausea/vomiting <5 days or grade 3 diarrhea that responded to treatment within 5 days.
• Maximum Tolerated Dose (MTD) and/or Recommended Phase II Dose (RP2D) of APX005M in Stratum 1 [6 weeks (first 2 courses of treatment)]: Based on the 3+3 design, the MTD of APX005M was empirically defined as the highest dose level at which six patients were treated with at most one patient experiencing a DLT, and the next higher dose level was determined to be too toxic. A total of 12 subjects were to be treated at the MTD/RP2D to further define the toxicity profile. Stratum 1 consisted of patients with recurrent or refractory primary malignant central nervous system tumors.
• Maximum Tolerated Dose (MTD) and/or Recommended Phase II Dose (RP2D) of APX005M in Stratum 2 [6 weeks (first 2 courses of treatment)]: The starting dose level for Stratum 2 was one dose level below the RP2D determined in Stratum 1. If there were no dose-limiting toxicities in the first 3 patients enrolled on Stratum 2, then we escalated to the Stratum 1 RP2D and could treat 6 diffuse intrinsic pontine glioma (DIPG) patients simultaneously. The RP2D was defined as the dose level at which 6 patients were treated with no more than one dose-limiting toxicity. Stratum 2 patients were those with newly diagnosed diffuse intrinsic pontine glioma (DIPG).
• Serum Concentration of APX005M [Up to 12 weeks from start of study drug]: Serial blood samples for APX005M pharmacokinetic studies were collected during courses 1 and 2 at pre-dose, at the end of infusion, and at 4, 24 ± 1 (day 2), and 168 ± 4 hours (day 8) from the start of infusion in that course. During courses 3 and 4, samples were obtained pre-dose and end of induction. Serum concentrations of sotigalimab were measured using a validated electrochemiluminescent (ECL) immunoassay (Method ICD 853 v1.00). Mean serum concentrations with standard deviations were calculated using Phoenix® WinNonlin® v.8.4. Concentrations below the limit of quantitation (0.010 μg/mL) were replaced with 0 to calculate means and SDs.

Secondary outcomes

• Overall Survival for Stratum 2 (DIPG) Patients [1 year]: Overall survival was defined as the time interval from treatment initiation to death from any cause or to date of last follow-up for survivors. Survival was estimated using the method of Kaplan and Meier. The 1-year estimate of survival is reported with a 95% confidence interval; estimates are reported by dose level. Stratum 2 patients were those with newly diagnosed diffuse intrinsic pontine glioma (DIPG).
• Progression-free Survival for Stratum 2 (DIPG) Patients [1 year]: Progression-free survival (PFS) was defined as the time interval from treatment initiation to date of first event (relapsed or progressive disease based on imaging or clinical progression or death from any cause) or to the date of last follow-up for patients without events. PFS was estimated using the method of Kaplan and Meier. The 1-year estimate of PFS is reported with a 95% confidence interval. PFS estimates were reported separately by dose level. Stratum 2 patients were those with newly diagnosed diffuse intrinsic pontine glioma (DIPG).
• Overall Response Rate for Stratum 2 (DIPG) Patients [Up to 2 years]: Complete or partial responses were considered responses. Response was evaluated by imaging or clinical progression. The response rate (percentage of participants with responses) is reported with a 95% Blyth-Still-Casella confidence interval. Response rates are reported separately by dose level.
• Duration of Response for Stratum 2 (DIPG) Patients [Up to 2 years]: Complete or partial responses were considered responses. Response was evaluated by imaging or clinical progression. Duration of response was measured from the time measurement criteria are met for complete or partial response until the first date that recurrent or progressive disease was objectively documented.
• Progression-free Survival for Stratum 1 (Recurrent/Refractory) Patients [1 year]: Progression-free survival (PFS) was defined as the time interval from treatment initiation to date of first event (relapsed or progressive disease based on imaging or clinical progression or death from any cause) or to the date of last follow-up for patients without events. PFS was estimated using the method of Kaplan and Meier. The 1-year estimate of PFS is reported with a 95% confidence interval. PFS estimates were reported separately by dose level. Stratum 1 patients were those with recurrent or refractory primary malignant CNS tumors.

Other outcomes

• Incidence of Anti-APX005M Antibodies [Prior to dosing on courses 1, 2, 3, 4, 7, 10, 14, 18, 22, 26, 30, and 34 and at the end of therapy (up to end of course 36)]: Serial blood samples for anti-drug-antibodies (ADA) were to be collected prior to dosing on courses 1, 2, 3, and 4, then every third course (courses 7 and 10), and then every 4 courses (courses 14, 18, 22, 26, 30, 34) until the end of therapy visit and collected into serum tubes. Percentages of patients with positive anti-drug antibodies with a 95% Blyth-Still-Casella confidence interval are reported by time point.
• Concentration of the Cytokine Tumor Necrosis Factor-alpha (TNF-alpha) [Pre-treatment (week 0), 1 week, 2 week, 3 weeks, 6 weeks and 9 weeks post-treatment]: The cytokine was quantitated using V-PLEX Human Proinflammatory Panel, a multiplex immunoassay kit developed by Meso Scale Diagnostics (MSD). A four-parameter logistic fit calibration curve was generated and used to calculate concentrations in tested samples. Analyses were performed at pre-treatment and 1 week following the first dose of drug and additionally at 2, 3, 6, and 9 weeks following the course 1 drug dose if feasible. The mean concentration of TNF-alpha in pg/ml was reported with a standard deviation. When only one patient was analyzed, the standard deviation was reported as 0 (rather than undefined).
• Concentration of the Cytokine Interleukin-8 (IL-8) [Pre-treatment (week 0), 1 week, 2 week, 3 weeks, 6 weeks and 9 weeks post-treatment]: The cytokine was quantitated using V-PLEX Human Proinflammatory Panel, a multiplex immunoassay kit developed by Meso Scale Diagnostics (MSD). A four-parameter logistic fit calibration curve was generated and used to calculate concentrations in tested samples. Analyses were performed at pre-treatment and 1 week following the first dose of drug and additionally at 2, 3, 6, and 9 weeks following the course 1 drug dose if feasible. The mean concentration of IL-8 in pg/ml was reported with a standard deviation. When only 1 participant analyzed, the standard deviation was reported as 0 (rather than undefined).
• Tumor Mutation Burden Based on Whole Exome Sequencing of Tumor Tissue [Day 0 of treatment]: Tumor mutation burden was defined as the number of somatic mutations per megabase. Average tumor mutation burden was reported with a standard deviation. When only one patient was analyzed, the standard deviation was reported as 0 rather than undefined.
• Tumor Mutation Burden Based on RNA Sequencing of Tumor Tissue [Day 0 of treatment]: Tumor mutation burden was defined as the number of somatic mutations per megabase. Average tumor mutation burden was reported with a standard deviation. When only one patient was analyzed, the standard deviation was reported as 0 rather than undefined.
• Mutation Burden Based on TCR Sequencing [Day 0 and Days 7, 14, and 21 after the start of treatment]: Mutation burden as detected by comparing the TCR sequencing of tumor tissue and/or PBMC. Mean numbers of clonotypes were reported by time point with standard deviations.

Sex: All, ages: 1 Year to 21 Years

Inclusion Criteria:

* Diagnosis -- Stratum 1: Recurrent or refractory primary malignant CNS tumor patients Patients with a histologically confirmed diagnosis of a primary malignant non-brainstem CNS tumor (excluding DIPG patients) that is recurrent, progressive, or refractory. All tumors must have histologic verification at either the time of diagnosis or recurrence except patients with marker (+) CNS germ cell tumors.

Stratum 2: Newly diagnosed DIPG patients (on-hold until pediatric RP2D has been established in Stratum 1) Patients with diffuse intrinsic pontine gliomas (DIPGs) will be eligible 6 to 14 weeks post-completion of radiation therapy if they do not have any evidence of progression. Patients with newly diagnosed DIPGs, defined as tumors with a pontine epicenter and diffuse involvement of 2/3 or more of the pons, are eligible without histologic confirmation. Patients with pontine tumors that do not meet these criteria or not considered to be typical intrinsic pontine gliomas will only be eligible if the tumors have been biopsied and (1) are proven to be an anaplastic astrocytoma, glioblastoma multiforme, gliosarcoma, anaplastic mixed glioma or fibrillary astrocytoma or (2) have a histone mutation typically seen in DIPG. Patients with disseminated disease are not eligible, and MRI of spine must be performed if disseminated disease is suspected by the treating physician.

* Available Pre-trial Tumor Tissue -- Stratum 1: Recurrent or refractory primary malignant CNS tumor patients must have adequate pre-trial frozen or FFPE tumor material (minimum of 10 unstained slides) available for use in the tumor mutation burden studies (section 9.1.5).

Stratum 2: Patients with DIPG who have pre-trial tumor tissue available are requested to submit tissue; however, this is not required for eligibility.

* Age -- Patient must be ≥ 1 and ≤ 21 years of age at the time of enrollment.
* Prior Therapy -- Newly Diagnosed DIPG patients Patients must have not received any prior therapy for treatment of their current CNS malignancy other than radiation therapy.

Refractory/Recurrent patients Patients must have recovered from the acute treatment related toxicities (defined as < grade 1) of all prior chemotherapy, immunotherapy, radiotherapy or any other treatment modality prior to entering this study.

Myelosuppressive chemotherapy -- Patients must have received their last dose of known myelosuppressive anticancer therapy at least 21 days prior to enrollment or at least 42 days if nitrosourea.

Biological agent: Patient must have recovered from any acute toxicity potentially related to the agent and received their last dose of the biologic agent ≥ 7 days prior to study enrollment.

For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur.

Monoclonal antibody treatment and agents with known prolonged half-lives: At least three half-lives must have elapsed prior to enrollment.

Radiation --

Patients must have had their last fraction of:

Craniospinal irradiation (>24Gy) or total body irradiation or radiation to greater than 50% of pelvis > 3 months prior to enrollment.

Focal irradiation >6 weeks prior to enrollment Local palliative irradiation (small port) ≥4 weeks

Autologous Stem Cell Transplant -- Patient must be ≥ 6 months since autologous bone marrow/stem cell transplant prior to enrollment and have CD4 counts above 200/mm3.

Surgery -- Patients must be at least 4 weeks (28 days) from major surgery and fully recovered from all acute effects of prior surgical intervention.

* Inclusion of Women and Minorities -- Both males and females of all races and ethnic groups are eligible for this study
* Neurologic Status -- Patients with neurological deficits should have deficits that are stable for a minimum of 1 week prior to enrollment.

Patients with seizure disorders may be enrolled if seizures are well controlled.

• Performance Status -- Karnofsky Performance Scale (KPS for > 16 years of age) or Lansky Performance Score (LPS for ≤ 16 years of age) assessed within two weeks of enrollment must be ≥ 60. Patients who are unable to walk because of neurologic deficits, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance score.

• Organ Function --

Patients must have adequate organ and bone marrow function as defined below:

Absolute Neutrophil Count (ANC) ≥ 1.0 x 109 cells/ L Platelets ≥ 100 x 109 cells/L (unsupported, defined as no platelet transfusion within 7 days) Hemoglobin ≥ 8 g/dL (may receive transfusions) Total bilirubin ≤1.5 times institutional upper limit of normal (ULN) AST(SGOT)/ALT(SGPT) ≤ 3 x institutional upper limit of normal (ULN) Albumin ≥ 3 g/dl Serum creatinine based on age/gender as noted below. Patients that do not meet the criteria below but have a 24 hour Creatinine Clearance or GFR (radioisotope or iothalamate) ≥ 70 mL/min/1.73 m2 are eligible.

Age Maximum Serum Creatinine (mg/dL) 1 to < 2 years 0.6, 0.6 (M, F); 2 to < 6 years 0.8, 0.8 (M, F); 6 to < 10 years 1, 1 (M, F); 10 to < 13 years 1.2, 1.2 (M, F); 13 to < 16 years 1.5, 1.4 (M, F); ≥ 16 years 1.7, 1.4 (M, F).

• Cardiac Function: Left Ventricular Ejection Fraction (LVEF) > 50% ECG QTc ≤ 450 msec

• Pulmonary Function: Oxygen saturation as measured by pulse oximetry is > 93% on room air and no evidence of dyspnea at rest

• Growth Factors -- Patients must be off all colony- forming growth factor(s) for at least 1 week prior to enrollment (i.e., filgrastim, sargramostim or erythropoietin). 2 weeks must have elapsed if patients received PEG formulations.

* Pregnancy Status -- Female patients of childbearing potential must have a negative serum or urine pregnancy test.
* Pregnancy Prevention -- Female subjects with childbearing potential and male subjects should use effective contraception methods (or abstain from sexual activity) while being treated with APX005M and for 30 days following treatment.
* Informed Consent -- The patient or parent/guardian is able to understand the consent and is willing to sign a written informed consent document according to institutional guidelines.

Exclusion Criteria:

• Concurrent Illness -- Patients with any clinically significant unrelated systemic illness (serious infections Grade ≥ 2 or significant cardiac, pulmonary, hepatic or other organ dysfunction), that in the opinion of the investigator would compromise the patient's ability to tolerate protocol therapy, put them at additional risk for toxicity or would interfere with the study procedures or results.

Patients with a history of any other malignancy, except patients with a secondary brain tumor if the patient's first malignancy has been in remission for at least 5 years from the end of treatment.

• Concurrent Therapy -- Patients who are receiving any other anticancer or investigational drug therapy.

Patients requiring systemic treatment with either corticosteroids (greater than physiologic replacement, defined as dexamethasone 0.75 mg/m2/day) or other immunosuppressive medications within 14 days of study drug administration will be excluded. However, patients who require intermittent use of bronchodilators or local steroid injections will not be excluded from the study. Please see section 5.3 for a list of acceptable and unacceptable concomitant medications as well as reporting requirements.

• Presence of Bulky Tumor --

Patients with bulky tumor on imaging are ineligible. Bulky tumor is defined as:

Tumor with any evidence of uncal herniation or midline shift Tumor that in the opinion of the site investigator, shows significant mass effect

* Allergy -- Patients with a history of severe (Grade ≥ 3) hypersensitivity reaction to a monoclonal antibody are ineligible.
* Allogeneic Hematopoietic Stem Cell Transplantation -- Patients who have received allogeneic hematopoietic stem cell transplantation are ineligible.
* Autoimmune Diseases -- Patients with active autoimmune disease or documented history of autoimmune disease/syndrome that requires ongoing systemic steroids or systemic immunosuppressive agents, except Patients with vitiligo or well controlled asthma/atopy Patients with hypothyroidism stable on hormone replacement or Sjogren's syndrome
* Inability to Participate -- Patients who in the opinion of the investigator are unwilling or unable to return for required follow-up visits or obtain follow-up studies required to assess toxicity to therapy or to adhere to drug administration plan, other study procedures, and study restrictions.
* Bleeding Disorder -- Patients with a known coagulopathy or bleeding diathesis or require the use of systemic anticoagulant medication are not eligible.
* Pregnancy Status -- Female patients must not be pregnant or breast-feeding.

Participant flow

Outcome results

• Number of Patients Who Experienced Dose-limiting Toxicities (DLTs) (Primary), Count of participants, Participants: Stratum 1, Dose Level 1 0; Stratum 1, Dose Level 2 0; Stratum 1, Dose Level 3 2; Stratum 2, Dose Level 2 0; Stratum 2, Dose Level 3 3
• Maximum Tolerated Dose (MTD) and/or Recommended Phase II Dose (RP2D) of APX005M in Stratum 1 (Primary), Number, mg/kg: Stratum 1 0.6
• Maximum Tolerated Dose (MTD) and/or Recommended Phase II Dose (RP2D) of APX005M in Stratum 2 (Primary), Number, mg/kg: Stratum 2 0.3
• Serum Concentration of APX005M (Primary), Mean, μg/mL: Stratum 1, Dose Level 1 0 +/- 0; Stratum 1, Dose Level 2 0 +/- 0; Stratum 1, Dose Level 3 0 +/- 0; Stratum 2, Dose Level 2 0 +/- 0; Stratum 2, Dose Level 3 0 +/- 0
• Overall Survival for Stratum 2 (DIPG) Patients (Secondary), Number, Percent probability: Stratum 2, Dose Level 2 40.0 (4.9 to 75.1); Stratum 2, Dose Level 3 25.0 (0.0 to 55.0)
• Progression-free Survival for Stratum 2 (DIPG) Patients (Secondary), Number, Percent probability: Stratum 2, Dose Level 2 16.7 (0.0 to 37.9); Stratum 2, Dose Level 3 26.7 (0.0 to 58.3)
• Overall Response Rate for Stratum 2 (DIPG) Patients (Secondary), Number, percentage: Stratum 2, Dose Level 2 0 (0.0 to 40.2); Stratum 2, Dose Level 3 0 (0.0 to 63.2)
• Duration of Response for Stratum 2 (DIPG) Patients (Secondary)
• Progression-free Survival for Stratum 1 (Recurrent/Refractory) Patients (Secondary), Number, Percent probability: Stratum 1, Dose Level 1 0.00 (0 to 0); Stratum 1, Dose Level 2 0 (0 to 0); Stratum 1, Dose Level 3 10.7 (0.0 to 59.9)
• Incidence of Anti-APX005M Antibodies (Other pre specified), Number, percentage of patients with positive ADA: Stratum 1, Dose Level 1 0 (0 to 77.64); Stratum 1, Dose Level 2 0 (0 to 63.16); Stratum 1, Dose Level 3 8.33 (0.43 to 34.89); Stratum 2, Dose Level 2 0 (0 to 40.19); Stratum 2, Dose Level 3 0 (0 to 52.71)
• Concentration of the Cytokine Tumor Necrosis Factor-alpha (TNF-alpha) (Other pre specified), Mean, pg/ml: Stratum 1, Dose Level 1 0.95 +/- 0; Stratum 1, Dose Level 2 1.24 +/- 0; Stratum 1, Dose Level 3 0.71 +/- 0.28; Stratum 2, Dose Level 2 0.87 +/- 0.48; Stratum 2, Dose Level 3 0.41 +/- 0.18
• Concentration of the Cytokine Interleukin-8 (IL-8) (Other pre specified), Mean, pg/ml: Stratum 1, Dose Level 1 1.76 +/- 0; Stratum 1, Dose Level 2 5.88 +/- 0; Stratum 1, Dose Level 3 3.03 +/- 0.80; Stratum 2, Dose Level 2 4.91 +/- 5.30; Stratum 2, Dose Level 3 2.52 +/- 1.18
• Tumor Mutation Burden Based on Whole Exome Sequencing of Tumor Tissue (Other pre specified), Mean, mutations per megabase: Stratum 1, Dose Level 1 2.62 +/- 1.03; Stratum 1, Dose Level 2 3.82 +/- 2.79; Stratum 1, Dose Level 3 3.95 +/- 2.34; Stratum 2, Dose Level 2 0.97 +/- 0.0; Stratum 2, Dose Level 3 4.83 +/- 5.94
• Tumor Mutation Burden Based on RNA Sequencing of Tumor Tissue (Other pre specified), Mean, mutations per megabase: Stratum 1, Dose Level 1 3.15 +/- 0.92; Stratum 1, Dose Level 2 3.33 +/- 0.32; Stratum 1, Dose Level 3 3.26 +/- 1.35; Stratum 2, Dose Level 2 ; Stratum 2, Dose Level 3
• Mutation Burden Based on TCR Sequencing (Other pre specified), Mean, Clonotyes: Stratum 1, Dose Level 1 ; Stratum 1, Dose Level 2 ; Stratum 1, Dose Level 3 ; Stratum 2, Dose Level 2 54688.25 +/- 48633.55; Stratum 2, Dose Level 3

Adverse events

Time frame: Approximately 3 years after start of treatment

Serious adverse events by term

Other adverse events by term

24 more terms not shown.

• Study Protocol and Statistical Analysis Plan (PDF, 2022-09-23)

• Ira Dunkel, Study chair, Memorial Sloan Kettering Cancer Center

NIH grants: UM1CA081457