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Not yet recruitingNCT07850921Updated Sep 30, 2026

REGN21353 Alone or in Combination With Nezastomig for Metastatic Castration-Resistant Prostate Cancer in Adult Participants

A Phase 1/2 interventional study of REGN21353 and Nezastomig in Metastatic Castration-Resistant Prostate Cancer and mCRPC, sponsored by Regeneron Pharmaceuticals. Not yet recruiting. Open to male participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-30.

Sponsored by Regeneron Pharmaceuticals · Phase 1/2, Interventional, and Treatment

Phase
Phase 1/2
Study type
Interventional
Enrollment
192
Allocation
Non-randomized
Ages
18 Years and older
Sex
Male
01

Study summary

This study will test an experimental Regeneron drug called REGN21353 ("study drug") to see if it can help treat previously treated prostate cancer that has spread (also called metastatic castration-resistant prostate cancer or mCRPC). Some participants may get additional experimental drugs in combination with REGN21353. These additional drugs are nezastomig and sarilumab. "Experimental" means that the drugs are being tested and have not been approved for use in prostate cancer by a country's national health agency that gives approval for new medicines to be prescribed.

The study is looking at:

  • What is the best dose of REGN21353 alone and together with nezastomig for treating prostate cancer
  • What side effects REGN21353 alone and together with nezastomig might cause
  • How well REGN21353 alone and together with nezastomig works
  • How much REGN21353 alone and together with nezastomig is in the blood at different times
  • If the body reacts to REGN21353 alone or together with nezastomig, in a way that may cause them to not work as well
  • How REGN21353 alone and together with nezastomig could affect prostate cancer, which can help researchers understand why REGN21353 alone or together with nezastomig work better in some than others
02

Conditions studied

  • Metastatic Castration-Resistant Prostate Cancer
  • mCRPC

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Keywords

  • Prostate cancer
  • Metastatic prostate cancer
  • Castration resistant prostate cancer
  • Advanced prostate cancer
  • Stage 4 prostate cancer
  • Prostate cancer that has spread
  • Hormone refractory prostate cancer
  • Androgen-resistant prostate cancer
  • Androgen-independent prostate cancer
  • PSA progression
  • Androgen receptor pathway inhibitor (ARPI)
  • Luteinizing hormone-releasing hormone (LHRH)
  • Androgen deprivation therapy (ADT)
03

Who can participate

Ages eligible
18 Years and older
Sexes eligible
Male
Accepts healthy volunteers
No

Eligibility criteria

Key Inclusion Criteria:

  1. Is male with histologically or cytologically confirmed adenocarcinoma of the prostate without pure small cell carcinoma
  2. Has metastatic castration-resistant prostate cancer with prostate-specific antigen value as described in the protocol and that has progressed within 6 months prior to screening
  3. Has received ≥2 lines of prior systemic therapy approved in the metastatic and/or castration-resistant setting (in addition to androgen deprivation therapy) including at least one androgen receptor pathway inhibitor (eg, abiraterone, enzalutamide, apalutamide, or darolutamide)
  4. Has had either orchiectomy or be on luteinizing hormone-releasing hormone (LHRH) agonist or antagonist therapy with serum testosterone levels as described in the protocol and agree to stay on LHRH agonist or antagonist therapy during the trial
  5. Is able and willing to provide tumor tissue, either archival or newly obtained
  6. Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
  7. Has adequate organ, bone marrow, renal and hepatic function

Key Exclusion Criteria:

  1. Has not recovered (ie, grade ≤1 or baseline) from immune-mediated adverse event within 3 months prior to initiation of trial intervention therapy except for endocrinopathies adequately managed with hormone replacement
  2. Has permanently discontinued anti-cancer immune modulating therapies due to immune-mediated adverse events
  3. Has another malignancy that is progressing or requires active treatment, except non-melanoma skin cancer that has undergone potentially curative therapy or any tumor that has been deemed to be effectively treated with definitive local control
  4. Has ongoing or recent (within 5 years) evidence of significant autoimmune disease (including any history of systemic vasculitis) that required treatment with systemic immunosuppressive treatments
  5. Has active liver metastases
  6. Has current evidence of or history of central nervous system metastases as described in the protocol
  7. Has encephalitis, meningitis, neurodegenerative disease (with the exception of mild dementia that does not interfere with activities of daily living), or uncontrolled seizures in the year prior to first dose of trial intervention
  8. Has a known history of, or any evidence of, interstitial lung disease or active, noninfectious pneumonitis (past 5 years). A history of radiation pneumonitis in the radiation field is permitted
  9. Has active or recent infection requiring hospitalization or treatment with intravenous anti-infectives within 2 weeks of first dose of trial intervention
  10. Has significant cardiovascular disease

Note: Other protocol defined Inclusion/ Exclusion criteria apply

04

Study design

Phase
Phase 1 / Phase 2
Primary purpose
Treatment
Allocation
Non-randomized
Intervention model
Sequential assignment
Masking
None (open label)
Enrollment
192 participants (estimated)

Study arms

  • Experimental
    Module 1: monotherapy

    Drug: REGN21353 · Drug: Sarilumab Prophylaxis (Contingency)

  • Experimental
    Module 2: combination

    Drug: REGN21353 · Drug: Nezastomig · Drug: Sarilumab Prophylaxis (Contingency)

Interventions

  • DrugREGN21353

    Administered per the protocol

  • DrugNezastomig

    Administered per the protocol

    Also known as: REGN5678

  • DrugSarilumab Prophylaxis (Contingency)

    May be administered as pretreatment, per the protocol

    Also known as: REGN88, SAR153191, KEVZARA®

05

What researchers measure

Primary outcomes

  1. Occurrence of Treatment Emergent Adverse Events (TEAEs)

    Dose escalation

    Time frame: Up to 5 years

  2. Occurrence of Dose-Limiting Toxicities (DLTs)

    Dose escalation

    Time frame: Up to 42 days

  3. Occurrence of Serious Adverse Events (SAEs)

    Dose escalation

    Time frame: Up to 5 years

  4. Occurrence of Adverse Events of Special Interests (AESIs)

    Dose escalation

    Time frame: Up to 5 years

  5. Composite Response Rate (CRR) of ≥50% decline of prostate specific antigen (PSA) and/or confirmed radiographic response of complete response (CR) or partial response (PR)

    Dose expansion

    Time frame: Up to 5 years

Secondary outcomes

  1. (CRR) of ≥50% decline of prostate specific antigen (PSA) and/or confirmed radiographic response of complete response (CR) or partial response (PR)

    Dose escalation

    Time frame: Up to 5 years

  2. Occurrence of TEAEs

    Dose expansion

    Time frame: Up to 5 years

  3. Occurrence of SAEs

    Dose expansion

    Time frame: Up to 5 years

  4. Occurrence of AESIs

    Dose expansion

    Time frame: Up to 5 years

  5. Percentage of participants with ≥50% reduction in PSA confirmed by a second PSA test ≥3 weeks later

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  6. Percentage of participants with ≥90% reduction in PSA confirmed by a second PSA test ≥3 weeks later

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  7. REGN21353 serum concentrations

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  8. Nezastomig serum concentrations

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  9. Occurrence of Anti-Drug Antibodies (ADA) to REGN21353

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  10. Occurrence of ADA to nezastomig

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  11. Magnitude of ADA to REGN21353

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

  12. Magnitude of ADA to nezastomig

    Dose Escalation and Dose Expansion

    Time frame: Up to 5 years

06

Study locations

No study locations are listed for this record.

07

References and documents

Individual participant data

Plan to share: Yes — All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing

Supporting information: Study protocol, Sap, Icf, Csr, Analytic code

No publications or documents are linked to this record.

08

Registry details

Key details

Study ID
NCT07850921
Lead sponsor
Regeneron Pharmaceuticals
Responsible party
Sponsor
First posted
Sep 30, 2026
Start date
Jun 28, 2027 (estimated)
Primary completion
Jul 28, 2031 (estimated)
Completion
Jul 28, 2031 (estimated)
Last update
Sep 30, 2026

Study contacts

Clinical Trials Administrator
Contact
clinicaltrials@regeneron.com
844-734-6643
Clinical Trial Management
study director · Regeneron Pharmaceuticals

Oversight

Data monitoring committee
No
FDA-regulated drug
Yes
FDA-regulated device
No
View the source record on ClinicalTrials.gov ↗

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