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A study testing ASP5541 compared to abiraterone acetate in patients with advanced prostate cancer

Verified siteRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study involves people with prostate cancer that has spread to other parts of the body. The study looks at two specific types of this condition: one where the cancer no longer responds to treatments that lower male hormones and another where the cancer still responds to such treatments. The study uses a medicine called ASP5541, which is given as an injection into the muscle. Some people in the study will also take steroid tablets called prednisone or prednisolone along with the injection. For comparison, some people will receive a different medicine called abiraterone acetate, which is taken as a tablet together with prednisone or prednisolone. The purpose of this study is to find out how well ASP5541 works in treating prostate cancer and to check how safe it is for patients to use.

The study is divided into three groups of people. The first group includes people whose cancer has spread and no longer responds to hormone treatments. These people will receive either ASP5541 with a steroid or abiraterone acetate with a steroid. The second group includes people whose cancer has spread but still responds to hormone treatments. Some people in this group will receive ASP5541 without steroids, while others will receive abiraterone acetate with steroids. The third group includes people from Japan with either type of prostate cancer who will receive ASP5541 with steroids. All people in the study will continue to receive treatments that keep male hormone levels low.

During the study, doctors will measure a substance in the blood called PSA, which is a marker for prostate cancer activity. They will check how much the PSA levels drop and whether they become very low or undetectable. Doctors will also use imaging tests such as CT scans, MRI scans, and bone scans to see if the cancer grows or shrinks. The study will monitor how long it takes before the cancer gets worse and will track any side effects that people experience. Safety checks will include blood tests, heart tests called electrocardiograms, blood pressure measurements, and general physical examinations. The study will also ask people to complete questionnaires about their pain levels and overall well-being.

The research process

The trial runs in 9 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial Treatment Assignment

    Upon joining the study, you will be assigned to one of three groups based on your specific type of prostate cancer and other medical factors.

    Group 1 is for participants with metastatic castration-resistant prostate cancer, which means prostate cancer that has spread to other parts of the body and no longer responds to hormone therapy that lowers testosterone.

    Group 2 is for participants with metastatic hormone-sensitive prostate cancer, which means prostate cancer that has spread to other parts of the body but still responds to hormone therapy.

    Group 3 is specifically for Japanese participants with either metastatic castration-resistant prostate cancer or metastatic hormone-sensitive prostate cancer.

  2. Step 2

    Medication Administration

    If you are assigned to Group 1, you will receive either ASP5541 (also called abiraterone decanoate) combined with prednisone or prednisolone, or you will receive abiraterone acetate combined with prednisone or prednisolone.

    If you are assigned to Group 2, you will receive either ASP5541 without additional steroids, or abiraterone acetate combined with prednisone or prednisolone.

    If you are assigned to Group 3, you will receive ASP5541 combined with prednisone or prednisolone.

    ASP5541 (abiraterone decanoate) is given as an injection into the muscle.

    Abiraterone acetate, prednisone, and prednisolone are taken by mouth.

  3. Step 3

    Regular Monitoring and Assessments

    Throughout the study, you will undergo regular monitoring to evaluate how the treatment is working and to check for any side effects.

    Blood tests will be performed regularly to measure prostate-specific antigen (PSA), which is a protein produced by the prostate that can indicate how the cancer is responding to treatment.

    Blood tests will also check your general health, including blood cell counts, kidney and liver function, and levels of certain chemicals in your blood.

    Urine tests will be conducted to assess kidney function and other health indicators.

    If you are in Group 2, additional urine tests will measure potassium and creatinine levels to monitor for specific side effects.

    Blood tests will measure testosterone levels to ensure hormone therapy is working effectively.

    Electrocardiograms (ECGs), which are tests that measure the electrical activity of your heart, will be performed at scheduled intervals.

    Your vital signs, including blood pressure, heart rate, and temperature, will be measured regularly.

    Physical examinations will be conducted to assess your overall health.

    Your activity level and ability to perform daily tasks will be evaluated using the ECOG performance status score.

  4. Step 4

    Imaging Studies

    Imaging scans will be performed at scheduled times to check if the cancer has grown or spread.

    These may include bone scans, which look for cancer in the bones, CT scans (computed tomography), MRI scans (magnetic resonance imaging), or PSMA-PET scans (prostate-specific membrane antigen positron emission tomography).

    The scans help determine if the treatment is controlling the cancer or if the disease is progressing.

  5. Step 5

    Questionnaires

    You will be asked to complete questionnaires about your symptoms and quality of life.

    These questionnaires will include questions about pain levels using the Brief Pain Inventory-Short Form (BPI-SF).

    The information you provide helps assess how the treatment affects your daily life and well-being.

  6. Step 6

    Safety Monitoring

    The study team will monitor you for any side effects or adverse reactions to the treatment.

    Special attention will be given to certain side effects, such as low potassium levels in the blood (hypokalemia) and high blood pressure (hypertension), particularly in Group 2.

    Any serious or unexpected side effects will be recorded and managed appropriately.

    If you are in Group 3, safety monitoring will be particularly focused on how Japanese participants respond to the treatment.

  7. Step 7

    Contraception Requirements

    Throughout the treatment period and for a specified time afterward, you must follow specific contraception requirements.

    If you have a female partner who can become pregnant, you must use approved methods of birth control during treatment and for 7 months after your final dose of ASP5541 or for 3 months after your final dose of abiraterone acetate.

    If your partner is pregnant, you must use a condom during sexual activity throughout the treatment period and for the same time periods after your final dose.

    You must not donate sperm during treatment and for 7 months after your final dose of ASP5541 or for 3 months after your final dose of abiraterone acetate.

  8. Step 8

    Study Restrictions

    You must not participate in any other interventional study while receiving treatment in this study.

    You are expected to attend all scheduled visits and follow all study procedures.

    You must inform the study team of any changes in your health or any new medications you are taking.

  9. Step 9

    Duration of Participation

    The study is expected to continue until May 2032, though your individual participation time may vary depending on how you respond to treatment and your overall health.

    The study team will inform you of the specific schedule for your visits and assessments.

    Your participation will continue as long as the treatment is beneficial and you do not experience unacceptable side effects.

Who can join the trial?

12 criteria

  • You must be male and at least 18 years old at the time you agree to join the study
  • You must have prostate cancer that has been confirmed by tissue examination showing a specific type called adenocarcinoma, which means cancer that started in gland cells of the prostate, without certain aggressive features
  • You must have cancer that has spread to other parts of your body, shown on imaging tests such as bone scans, CT scans (detailed x-ray pictures), MRI (magnetic imaging), or PSMA-PET (a special scan that finds prostate cancer cells)
  • Your physical condition must be rated as 0 or 1 on a scale called ECOG performance status, which measures how well you can perform daily activities, or rated as 2 if your limitations are due to bone pain
  • If your cancer is hormone-sensitive, meaning it still responds to hormone treatment, you must be expected to live at least 12 months
  • If your cancer is castration-resistant, meaning it no longer responds to hormone treatment that lowers testosterone, you must be expected to live at least 6 months
  • You must be able to understand and follow all study requirements and procedures, including filling out questionnaires about how you feel
  • You must agree to use effective birth control methods with any female partner who can become pregnant during the treatment and for 7 months after your last dose of the study drug ASP5541, or for 3 months after your last dose if you receive the drug called abiraterone acetate
  • You must agree to use a condom with any pregnant partner during treatment and for 7 months after your last dose of ASP5541, or for 3 months after your last dose of abiraterone acetate
  • You must agree not to donate sperm during treatment and for 7 months after your last dose of ASP5541, or for 3 months after your last dose of abiraterone acetate
  • You must provide your written agreement to participate in the study after understanding all requirements and restrictions
  • You must agree not to join another research study while you are receiving the study drug in this trial

Who cannot join the trial?

6 criteria

  • The study is only for male patients, so women cannot participate
  • Patients who are children or adolescents cannot participate, as the study is only for adults and elderly people
  • Patients who do not have prostate cancer cannot participate in this study
  • Patients who have already received treatment with androgen receptor pathway inhibitors, which are medicines that block certain hormones that help prostate cancer grow, may not be eligible
  • Patients whose cancer has not spread to other parts of the body may not be eligible, as the study focuses on metastatic cancer, which means cancer that has spread beyond the prostate to other organs or bones
  • Patients who do not meet the specific disease stage requirements for each group in the study cannot participate
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Investigated drugs

  • ASP5541

    is an investigational medication being studied for the treatment of advanced prostate cancer. In this trial, it is being tested alone or in combination with steroids called prednisone or prednisolone to see how well it works and how safe it is for patients with different types of prostate cancer that has spread to other parts of the body.

  • Prednisone

    is a steroid medication that is commonly used to reduce inflammation and suppress the immune system. In this trial, it is being given together with some of the investigational treatments to help manage side effects and improve outcomes for patients with prostate cancer.

  • Prednisolone

    is a steroid medication similar to prednisone that helps reduce inflammation in the body. In this trial, it may be used as an alternative to prednisone and is given in combination with some of the treatments being studied for prostate cancer.

  • Abiraterone acetate

    is an approved medication used to treat prostate cancer by blocking the production of male hormones that can help cancer cells grow. In this trial, it is being used as a comparison treatment to see how the investigational medication ASP5541 performs against this standard therapy.

What is already known about the treatment

  • ASP5541

    ASP5541 is an investigational medication currently being studied in clinical trials for the treatment of advanced prostate cancer, specifically in patients with metastatic castration-resistant prostate cancer and metastatic hormone-sensitive prostate cancer. This drug is being tested both with and without steroid medications like prednisone or prednisolone, and its effectiveness is being compared to abiraterone acetate, an existing treatment for prostate cancer. ASP5541 is designed to block the androgen receptor pathway, which is a system in the body that helps prostate cancer cells grow and survive by responding to male hormones. The medication belongs to a class of drugs called androgen receptor pathway inhibitors, which work by interfering with the cancer cells' ability to use hormones for growth.

  • Abiraterone Acetate

    Abiraterone acetate is an approved oral medication used in combination with prednisone or prednisolone for treating advanced prostate cancer in patients whose disease has progressed despite hormone therapy. This drug works by blocking an enzyme called CYP17A1, which is necessary for the production of male hormones (androgens) in the testicles, adrenal glands, and prostate tumor tissue itself, thereby starving the cancer cells of the hormones they need to grow. It is classified as an androgen biosynthesis inhibitor and represents a standard treatment option for both metastatic castration-resistant prostate cancer and metastatic hormone-sensitive prostate cancer. In this clinical trial, abiraterone acetate serves as the comparison treatment to evaluate how well the investigational drug ASP5541 performs.

Investigated diseases

Prostate Cancer – Prostate cancer is a disease that occurs when abnormal cells grow uncontrollably in the prostate gland, which is a small walnut-shaped organ in men located below the bladder. The cancer typically develops slowly and may initially remain confined to the prostate gland. As the disease progresses, it can spread beyond the prostate to nearby tissues and organs. In more advanced stages, the cancer cells may travel through the bloodstream or lymphatic system to distant parts of the body, particularly bones. Metastatic castration-resistant prostate cancer refers to a stage where the cancer has spread to other parts of the body and continues to grow despite treatments that lower testosterone levels. Metastatic hormone-sensitive prostate cancer describes cancer that has spread beyond the prostate but still responds to treatments that reduce hormone levels in the body.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2024-517653-27-00Protocol code5541-CL-0201Estimated enrolment218 patientsSponsorAstellas Pharma Global Development Inc.

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