An Early Phase 1 interventional study of Granzyme-B targeted [64Cu]-labeled PET radiotracer in Healthy Volunteer, sponsored by Ratio Therapeutics, Inc.. Recruiting at 1 site in United States. Open to participants aged 18 Years to 60 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-01.
Sponsored by Ratio Therapeutics, Inc. · Early Phase 1, Interventional, and Diagnostic
This is an exploratory clinical study of copper-64 [Cu-64]-labeled granzyme B (GzmB)-targeted compounds for PET/CT imaging. The goal is to determine how GzmB-Targeted [Cu-64]-labeled compounds are distributed in the body by assessing PET/CT images and blood samples, and to assess the safety profile after a single intravenous dose.
Up to 6 healthy volunteers (3 female, 3 male) will receive one injection of a GzmB-targeted [Cu-64]-labeled compound, then undergo multiple whole-body PET/CT scans, blood and urine tests over about 24 hours, and a follow-up phone call around Day 7. Up to 2 GzmB-Targeted [Cu-64]-labeled compounds may be assessed (i.e. maximum of 12 healthy volunteers in total in the study).
Researchers will look at the blood activity of GzmB-Targeted [Cu-64]-labeled compound and the organ distribution and movement of the product in the body. They will also evaluate any changes in physical examination assessments, vital signs, ECG, and clinical laboratory measurements from pre-administration to post-administration.
Granzyme B (GzmB) is a cytotoxic serine protease released by activated T cells and natural killer cells, and its release acts as a functional marker of immune engagement. GzmB-Targeted [Cu-64]-labeled compounds are being developed as PET/CT tracers to image immune activation and inflammation. This first-in-human Phase 0 study in adult healthy volunteers is designed to characterize the pharmacokinetics, biodistribution, radiation dosimetry, and safety of GzmB-targeted [Cu-64]-labeled compounds.
Up to 6 participants (3 female, 3 male) will receive a single dose of a GzmB-targeted [Cu-64]-labeled compound, followed by serial whole-body PET/CT imaging, blood and urine sampling for pharmacokinetics and excretion, and safety assessments over approximately 24 hours post-dose, with a telephone follow-up at about 7 days. Up to 2 GzmB-Targeted [Cu-64]-labeled compounds may be assessed in the clinical trial (i.e. a maximum of 12 healthy volunteers in total in the study).
Data from this study will support lead candidate selection and inform further clinical development of a [Cu-64]-labeled GzmB-targeted imaging agent.
Ratio Therapeutics, Inc. is the lead sponsor of 3 studies on the registry; 1 is open to participants now.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Autoimmune disease
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Arm Description: Single IV administration of \[Cu-64\]RTX-4001, a Granzyme-B-targeted PET radiotracer, in healthy adult volunteers.
Drug: Granzyme-B targeted [64Cu]-labeled PET radiotracer
Arm Description: Single IV administration of \[Cu-64\]RTX-4002, a Granzyme-B-targeted PET radiotracer, in healthy adult volunteers.
Drug: Granzyme-B targeted [64Cu]-labeled PET radiotracer
Single intravenous administration of a Granzyme-B targeted \[64Cu\]-labeled positron emission tomography (PET) radiotracer to assess pharmacokinetics, biodistribution, and radiation dosimetry in adult healthy volunteers.
Determine the maximum concentration (Cmax) of radiation (Pharmacokinetics) in the blood after a single dose of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. Radiation (PK) to be measured by gamma counter (KBq/mL).
Time frame: 24 hour period post injection.
Determine the time to maximum concentration (Tmax) in the blood after a single dose of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. Time to maximum concentration to be measured in hours (h).
Time frame: 24 hour period post injection
Determine the area under the curve (AUC) in blood after a single injection of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. AUC to be calculated by kilobecquerel x hours/milliliter (KBq x h/mL)
Time frame: 24 hour period post injection.
Determine the elimination half-life in the blood post a single injection of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. Elimination to be measured by time to half of the product being excreted from the blood (as measured by gamma counter) in hours (h)
Time frame: 24 hour period post injection
Determine the clearance in the blood after single injection of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. Clearance to be measured by milliliter/minute.
Time frame: 24 hour period post injection
Determine the volume of distribution in the blood after a single injection of the GzmB-Targeted [Cu-64]-labeled compound
Blood samples will be collected Pre-dose, immediately post-dose, 45 minutes, 1 \& 4 hours, \& 24 hours post dose. Volume to be measured by Liter
Time frame: 24 hour period post injection
Evaluate the organ distribution of radioactivity for a single dose of GzmB-targeted [Cu64]-labeled compound
Measuring the uptake in organs from a PET/CT. Imaging timepoints will be collected at 20 minutes post dose, 1 \& 4 hours and 24 hours post dose
Time frame: 24 hour period post injection
Evaluate the safety profile for a single dose of the GzmB-Targeted [Cu-64]-labeled compound in adult healthy volunteers
Determine the incidence, and severity of Treatment Emergent Adverse Events (TEAEs including SAEs).
Time frame: From injection to 8 days post injection
Evaluate the radiation absorbed dose estimates for organs for a single dose of the GzmB-Targeted [Cu-64]-labeled compound
Imaging timepoints will be collected at 20 minutes post dose, 1 \& 4 hours, and 24 hours post dose. PET/CT will be used to assess the whole body effective dose as measured by mGy/MBq.
Time frame: 24 hour period post injection
Evaluate the whole body effective dose estimated for a single dose of the GzmB-Targeted [Cu-64]-labeled compound
Imaging timepoints will be collected at 20 minutes post dose, 1 \& 4 hours, and 24 hours post dose. PET/CT will be used to assess the whole body effective dose as measured by mSv/MBq.
Time frame: 24 hour period post injection
Examine whole-body excretion of a single dose of the GzmB-Targeted [Cu-64] labeled compound
Urine samples will be evaluated for radioactivity levels of GzmB-Targeted \[Cu-64\]-labeled compound. Samples will be measured by gamma counter to evaluate the amount of radiation excreted in each interval Ae(t) (kBq)
Time frame: Samples will be taken continuously starting immediately post-dose through 24 hours post injection
Determine the total cumulative excretion over time in the urine (mL/min) for the GzmB-Targeted [Cu-64]-labeled compound
Samples will be taken continuously starting immediately post-dose through 24 hours post injection. Includes all quantified radioactivity as measured by gamma counter in urine up to the least measured timepoint.
Time frame: A 24 hour period post injection
Determine the renal clearance for the GzmB-Targeted [Cu-64]-labeled compound
Urine samples will be taken continuously starting immediately post-dose through 24 hours post injection. Renal clearance is the volume of urine entirely cleared of a substance by the kidneys over time L/h
Time frame: 24 hour period post injection
Plan to share: No
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Started Jul 2026 (actual). Primary completion is estimated for Dec 2026, 5 months after the start.
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