A Phase 2a Trial of Immune Modulation in Combination With Ultrasound-mediated Blood Brain Barrier Opening in Patients With Newly Diagnosed Glioblastoma

Brain tumor treatment is hampered by the blood-brain barrier (BBB). This barrier prevents drugs carried in the bloodstream from getting into the brain. If the BBB can be opened, making it temporarily more permeable, drugs may able to better reach the brain tumor. In this trial we will implant a novel device with 9 ultrasound emitters, allowing temporary and reversible opening of the BBB to maximize brain penetration of drugs that modulate the immune system. The device will be implanted after radiation is completed. Immune modulating drugs will be given every 3 weeks in conjunction with activation of the device to open the BBB. The objectives of this trial are to establish whether it is safe and feasible to administer immune modulating drugs in this manner, and identify whether the treatment is effective in treating glioblastoma.

More details:

Eligible patients will undergo implant of the Soncloud-9 device within 1-5 weeks of completion of radiotherapy. About 1-3 weeks after surgery, patients will undergo sonication and intravenous administration of balstilimab, botensilimab and liposomal doxorubicin. Brain MRI will be done to quantify extent of blood brain barrier opening. The dose for balstilimab is 450 mg every 3 weeks. The dose for botensilimab is 1mg/kg every 6 weeks. The dose for liposomal doxorubicin is 30 mg every 3 weeks. Sonication and administration of study agents will continue every 3 weeks (21 days= 1 cycle) for a total of 9 cycles (approx. 6 months). Additional cycles may be considered if deemed beneficial and in the patient's best interest. Blood samples for circulating tumor DNA will also be collected before and after each sonication. The first 6 patients will comprise a safety run-in cohort with intensified safety monitoring through the end of the second cycle.

Overview

Balstilimab (AGEN2034; BAL) is an investigational, fully human IgG4 monoclonal antibody targeting PD‑1. It has been evaluated as monotherapy and in combination with the CTLA‑4 antibody zalifrelimab in previously treated recurrent/metastatic cervical cancer, with published phase 2 data. A U.S. BLA for second‑line cervical cancer was submitted in April 2021, accepted for Priority Review in June 2021, and voluntarily withdrawn in October 2021 after full approval of pembrolizumab in the same setting; development has continued in combinations. (pubmed.ncbi.nlm.nih.gov)

Mechanism of action

• Target: PD‑1 (programmed death‑1). Balstilimab binds PD‑1 with high affinity and blocks interactions with PD‑L1 and PD‑L2, restoring antitumor T‑cell activity. (ascopubs.org)
• Antibody class: Fully human IgG4 monoclonal antibody. Preclinical/meeting‑abstract work has described a differentiated activity profile compared with other PD‑1 inhibitors, though the mechanistic basis is still being investigated. (ascopubs.org)

Efficacy

Cervical cancer (previously treated, recurrent/metastatic)

• Balstilimab monotherapy (open‑label, single‑arm, phase 2; n=140 efficacy‑evaluable): Confirmed ORR 15.0% (95% CI, 10.0–21.8), including 3.6% complete responses; median duration of response (DoR) 15.4 months. ORR 20.0% in PD‑L1–positive tumors and 7.9% in PD‑L1–negative tumors. DCR 49.3%. Dosing: 3 mg/kg IV every 2 weeks (up to 24 months). (pubmed.ncbi.nlm.nih.gov)

• Balstilimab + zalifrelimab (open‑label, single‑arm, phase 2; n=125 efficacy‑evaluable): Confirmed ORR 25.6% (95% CI, 18.8–33.9), with 10 complete and 22 partial responses; median DoR not reached at median follow‑up 21 months (response durability 64.2% at 12 months). ORR 32.8% in PD‑L1–positive and 9.1% in PD‑L1–negative tumors. DCR 52%. Dosing: balstilimab 3 mg/kg Q2W + zalifrelimab 1 mg/kg Q6W (up to 24 months). (pubmed.ncbi.nlm.nih.gov)

Other tumor types (early signals)

• Soft tissue sarcoma (single‑arm phase 2 of doxorubicin + zalifrelimab + balstilimab): Best ORR 33.3% (95% CI, 17.3–52.8); the study did not meet its predefined PFS improvement endpoint. (pubmed.ncbi.nlm.nih.gov)

Note: Additional early‑phase combination studies with botensilimab (next‑generation CTLA‑4) have reported responses in ovarian and other solid tumors, but these are primarily from conference presentations and company communications and remain exploratory. (cancernetwork.com)

Safety

• Balstilimab monotherapy (phase 2 cervical cancer): Most common grade ≥3 treatment‑related AEs were immune‑mediated enterocolitis (3.1%) and diarrhea (1.9%). Overall safety was consistent with PD‑1 inhibitors. (pubmed.ncbi.nlm.nih.gov)

• Balstilimab + zalifrelimab (phase 2 cervical cancer): Grade ≥3 treatment‑related AEs occurred in 20.0%; common immune‑mediated AEs included hypothyroidism (14.2%) and hyperthyroidism (7.1%). Serious TRAEs occurred in 10.3%; three treatment‑related deaths (pneumonitis, immune‑mediated nephritis, diabetes mellitus) were reported. (ascopubs.org)

• Doxorubicin + zalifrelimab + balstilimab in soft tissue sarcoma: Grade 3/4 TRAEs in 45%; immune‑mediated AEs requiring immunosuppression in 9%. (pubmed.ncbi.nlm.nih.gov)

Further reading

• Phase 2 balstilimab monotherapy in cervical cancer (Gynecologic Oncology, 2021). (pubmed.ncbi.nlm.nih.gov)
• Phase 2 balstilimab + zalifrelimab in cervical cancer (Journal of Clinical Oncology, 2021/2022). (pubmed.ncbi.nlm.nih.gov)
• ASCO abstract: differentiated activity profile of balstilimab (mechanistic/meeting data). (ascopubs.org)
• Regulatory history: BLA acceptance/withdrawal (company notices). (investor.agenusbio.com)
• Soft tissue sarcoma combination study (PubMed, 2025). (pubmed.ncbi.nlm.nih.gov)

Notes: Balstilimab is not FDA‑approved as of October 7, 2025. Efficacy and safety summaries above reflect non‑randomized trials; comparative effectiveness versus approved PD‑1 inhibitors has not been established. (investor.agenusbio.com)

Last updated: Oct 2025

Overview

Botensilimab (AGEN1181; BOT) is an Fc‑engineered, next‑generation anti–CTLA‑4 monoclonal antibody being developed primarily in combination with the anti–PD‑1 antibody balstilimab (BAL). Early clinical activity has been reported across “cold” or immunotherapy‑refractory tumors, especially microsatellite‑stable (MSS) metastatic colorectal cancer (mCRC) without active liver metastases and in relapsed/refractory metastatic sarcomas. Fast Track designation has been granted by the FDA for BOT/BAL in non‑MSI‑H mCRC without active liver involvement. (pmc.ncbi.nlm.nih.gov)

Mechanism of action

• Target: CTLA‑4.
• Engineering: Human IgG1 with enhanced Fcγ receptor binding to amplify Fc‑dependent effector functions.
• Proposed immunobiology: Improves antigen‑presenting cell/T‑cell co‑engagement, expands effector/memory T cells, depletes intratumoral Tregs via FcγR‑mediated mechanisms, repolarizes myeloid cells, and shows activity independent of tumor neoantigen burden; FcγRIIA/IIIa expression may serve as response biomarkers. (aacrjournals.org)

Efficacy

Microsatellite‑stable metastatic colorectal cancer (MSS mCRC)

• Phase 1 (expanded) Nature Medicine report (NCT03860272): In heavily pretreated MSS mCRC, responses were concentrated in patients without active liver metastases (NLM). Among 77 NLM patients with median 13‑month follow‑up, confirmed ORR was 22% (later noted as 23% with an additional response), disease control 73%, and median duration of response (DOR) not reached. (pmc.ncbi.nlm.nih.gov)
• ASCO 2024 update (abstract 3556): In the same NLM cohort, ORR 22–23%, DCR 73%, and estimated median OS 20.9 months; activity observed across multiple non‑liver sites (peritoneum, soft tissue, pleura, brain). (ascopubs.org)
• Randomized phase 2 (ASCO GI 2025, NCT05608044): BOT±BAL vs standard of care (regorafenib or trifluridine/tipiracil) in refractory NLM MSS mCRC. Confirmed ORR was higher with BOT+BAL than BOT alone; the 75 mg BOT + BAL arm achieved ORR 19% (95% CI 10–31), while SOC had 0% responses. These data informed selection of 75 mg BOT Q6W + BAL for further study. (ascopubs.org)
• ESMO‑GI 2025 (Phase 1 expansion, n=123 NLM): Confirmed ORR 20%, DCR 69%, median OS 20.9 months, with 42% two‑year survival. (biospace.com)

Relapsed/refractory metastatic sarcomas

• Phase Ib (JCO 2025): BOT (1 or 2 mg/kg Q6W) + BAL in 64 patients; among 52 evaluable, ORR 19.2% (all PRs), DOR median 21.7 months, median PFS 4.4 months, and 12‑month OS 69%. Subtype activity included angiosarcoma ORR 27.8%. (pmc.ncbi.nlm.nih.gov)

Neoadjuvant, resectable colorectal cancer

• NEST‑1 (phase 2, ASCO GI 2024): Single pre‑op dose of BOT 75 mg plus two doses of BAL was feasible and did not delay surgery; pathologic tumor regression was observed in both pMMR/MSS and dMMR/MSI‑H disease, with several major/complete pathologic responses reported. (ascopubs.org)

Combination with chemotherapy

• ASCO GI 2025 (FOLFOX‑3B phase 1): In MSS mCRC, BOT + BAL added to FOLFOX/bevacizumab showed high preliminary response rates (partial responses in 4/7 at BOT 25 mg and 6/7 at BOT 75 mg; median PFS ~8 months overall, not reached at higher dose) with acceptable tolerability in a small cohort. (ascopubs.org)

Safety

• Immune‑related toxicities typical of checkpoint blockade predominate. In the randomized phase 2 MSS mCRC study, grade ≥3 treatment‑related AEs occurred in 35% with BOT 75 mg + BAL and 42% with BOT 150 mg + BAL; treatment‑related immune‑mediated diarrhea/colitis was more frequent at the higher BOT dose. No treatment‑related deaths were reported. (ascopubs.org)
• In metastatic sarcomas (JCO 2025), the safety profile was manageable; grade 3 treatment‑related diarrhea/colitis occurred in ~6% and responses were durable. (pmc.ncbi.nlm.nih.gov)
• In early neoadjuvant CRC (NEST‑1), treatment was delivered safely without surgical delays. (ascopubs.org)

Development status and next steps

• Regulatory: FDA Fast Track designation for BOT/BAL in non‑MSI‑H mCRC without active liver metastases. Following End‑of‑Phase 2 discussions, FDA advised proceeding to a randomized phase 3 trial and did not support accelerated approval based on response rates alone; the selected registrational dose is BOT 75 mg Q6W + BAL. (investor.agenusbio.com)
• Planned/ongoing trials: A global phase 3 study in refractory NLM MSS mCRC is planned with BOT 75 mg + BAL vs standard of care. (agenus2023ir.q4web.com)

Further reading

• Nature Medicine phase 1 MSS mCRC (open access): Botensilimab + balstilimab in relapsed/refractory MSS mCRC. (pmc.ncbi.nlm.nih.gov)
• Cancer Discovery mechanistic study of Fc‑enhanced anti–CTLA‑4 (botensilimab). (aacrjournals.org)
• ASCO 2024 abstract: Non‑liver metastatic MSS mCRC efficacy update. (ascopubs.org)
• ASCO GI 2025 abstract: Randomized phase 2 BOT±BAL vs SOC in refractory NLM MSS mCRC. (ascopubs.org)
• JCO 2025 full article: BOT + BAL in relapsed/refractory metastatic sarcomas (open access). (pmc.ncbi.nlm.nih.gov)
• ASCO GI 2025 abstract: BOT/BAL with FOLFOX/bevacizumab in MSS mCRC (FOLFOX‑3B). (ascopubs.org)
• ASCO GI 2024 abstract: NEST‑1 neoadjuvant BOT/BAL in resectable CRC. (ascopubs.org)

Notes: Reported efficacy in MSS mCRC is largely confined to patients without active liver metastases in early‑phase studies; definitive benefit will require results from randomized phase 3 testing. (pmc.ncbi.nlm.nih.gov)

Last updated: Oct 2025

Inclusion Criteria:

* Have newly diagnosed pathologically proven glioblastoma, isocitric dehydrogenase-1/2 wild-type

* Tumor with methyl guanine methyl transferase (MGMT) gene promoter unmethylated

* Available paraffin embedded tumor tissue for the study

* Have completed standard radiotherapy with or without temozolomide

* 18 years of age or older

* Able to undergo contrast-enhanced MRI

* Have an Eastern Cooperative Oncology Group/World Health Organization performance status ≤ 2

* Size and location of the residual tumor and/or resection cavity must allow to be able to be covered by the sonication field

* Have not received any prior treatment with immunotherapeutic agents treatments for glioblastoma or other indications

* Have the ability to understand and willingness to sign a written informed consent prior to registration on study.

* Be willing and able to comply with the protocol.

* Have adequate organ and bone marrow function

* Agree to use adequate contraception if appropriate

Exclusion Criteria: Patients will be ineligible if they have:

* Multifocal tumor (unless all localized in a 50-mm diameter area accessible to ultrasound field) or tumor located in the posterior fossa.

* Uncontrolled epilepsy.

* Received other investigational agents within 2 weeks of registration

* Received prior therapy with or have history of allergic reactions attributed to compounds of similar chemical or biologic composition to agents used in this study.

* Contraindication to checkpoint inhibitor therapy (e.g., history of autoimmune disease)

* Uncontrolled illness

* History of active malignancy other than the brain tumor within 12 months prior to registration.

* Are pregnant or breastfeeding.