An Open-Label, Phase II Efficacy Trial of Doxorubicin in Combination With Dual Checkpoint Blockade Using Zalifrelimab (AGEN1884) or Botensilimab (AGEN1181) With Balstilimab (AGEN2034) for Advanced or Metastatic Soft Tissue Sarcomas

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Investigational drug late phase More information Active drug More information Started >3 years ago More information High burden on patient More information

Trial Details

Sponsor: University of Colorado, Denver (other)

Phase: 2

Start date: Jan. 28, 2020

Planned enrollment: 65

Trial ID: NCT04028063
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More trial details at ClinicalTrials.gov More info

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Investigational Drug AI Analysis

chevron Show for: Balstilimab (AGEN2034, BAL)

chevron Show for: Botensilimab (AGEN1181, BOT)

chevron Show for: Zalifrelimab (AGEN1884, UGN-301, RebmAb-600)

TrialFetch AI Analysis

Goal: Evaluate whether adding dual immune checkpoint blockade to doxorubicin improves 6‑month progression‑free survival (PFS6mo) versus historical doxorubicin monotherapy in advanced or metastatic soft tissue sarcoma, and to characterize safety and immunologic correlates of response.

Patients: Adults (ECOG 0–1) with advanced or metastatic soft tissue sarcomas not amenable to curative surgery. Eligible histologies include common high‑grade STS subtypes (e.g., UPS, leiomyosarcoma, liposarcoma, synovial sarcoma, MPNST, angiosarcoma, myxofibrosarcoma, SFT, others upon PI review). Part 1 allows 0–1 prior systemic therapies for metastatic disease; Part 2 allows any number of prior lines. Prior anthracyclines or checkpoint inhibitors are not permitted. Measurable or evaluable disease by RECIST 1.1 is required, along with adequate organ function and tumor accessibility for mandated biopsies. Key exclusions include active autoimmune disease requiring systemic therapy, uncontrolled comorbidities, significant cardiac dysfunction, active CNS disease, and chronic infections such as HIV, hepatitis, or TB.

Design: Single‑institution, open‑label, non‑randomized, single‑arm phase II using a Simon two‑stage design with an initial safety lead‑in. Up to 35 patients will be enrolled to obtain 28 evaluable for the primary endpoint in Part 1; early stopping rules for dose‑limiting toxicity (first 6 patients; 9‑week DLT window) and for futility after Stage 1 (first 15 patients). Additional Part 2 cohorts explore botensilimab‑based combinations and dosing with or without balstilimab alongside doxorubicin.

Treatments: Part 1: Doxorubicin with dual checkpoint blockade using balstilimab (anti‑PD‑1) and zalifrelimab (anti‑CTLA‑4). Safety lead‑in: balstilimab 300 mg every 3 weeks up to 2 years; zalifrelimab 1 mg/kg every 6 weeks (up to 4 doses); doxorubicin 75 mg/m2 every 3 weeks starting cycle 2 for 2 cycles. Expansion: balstilimab 300 mg every 3 weeks and zalifrelimab 1 mg/kg every 6 weeks up to 2 years; doxorubicin 75 mg/m2 every 3 weeks for 6 cycles. Part 2: Botensilimab (Fc‑enhanced anti‑CTLA‑4) with doxorubicin at 60 or 75 mg/m2 every 3 weeks for 6 cycles; a third cohort adds balstilimab 450 mg every 3 weeks to botensilimab 75 mg every 6 weeks. Balstilimab (AGEN2034) is a human IgG4 anti‑PD‑1 antibody that restores T‑cell effector function; in cervical cancer, monotherapy produced an ORR around 15% and in combination with zalifrelimab achieved ORRs near 25–36% with manageable immune‑related toxicity. Zalifrelimab (AGEN1884) is an IgG1 anti‑CTLA‑4 antibody that blocks CTLA‑4 and may deplete intratumoral Tregs via Fc engagement; combined with balstilimab it has shown clinically meaningful activity across solid tumors including cervical cancer and signals of activity with doxorubicin in STS. Botensilimab (AGEN1181) is an Fc‑engineered anti‑CTLA‑4 designed for enhanced FcγR engagement and reduced complement activation, aiming to improve T‑cell priming and myeloid activation; early trials have demonstrated responses across immunotherapy‑refractory solid tumors, particularly when combined with balstilimab, with a manageable but class‑consistent immune‑related safety profile.

Outcomes: Primary: PFS at 6 months by RECIST 1.1, targeting improvement from a 43.4% historical benchmark to 63.4%. Secondary: overall response rate, clinical benefit rate, duration of response, and incidence and severity of adverse events. Exploratory: changes in tumor‑infiltrating and circulating immune cell populations and correlation with outcomes.

Burden on patient: Moderate to high. Patients receive IV doxorubicin every 3 weeks for up to 6 cycles plus IV checkpoint inhibitors administered every 3 or 6 weeks for up to 2 years, requiring frequent clinic visits. There is a prolonged 9‑week DLT observation window with close safety monitoring. Mandatory image‑guided core tumor biopsies at baseline and on Cycle 2 Day 5 add procedural risk and scheduling complexity; an optional progression biopsy may be requested. Routine labs, cardiac monitoring for anthracycline exposure (including baseline echocardiogram and potential follow‑up), and serial imaging per RECIST increase visit frequency beyond standard single‑agent doxorubicin. Travel and time commitments are greater due to combination therapy administration and on‑study research procedures, although there are no intensive pharmacokinetic schedules reported.

Last updated: Oct 2025

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University of Colorado Hospital

Aurora, Colorado, 80045, United States

[email protected] / (720)848-0741

Status: Recruiting

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