First-Ever Clinical Trial Testing PSMA-Targeted Antibody and Radioactive Alpha Particles for Treatment of Advanced Prostate Cancer

Radiation is one of the most common treatments for prostate cancer. Using radiation, physicians are able to cure some men with cancer confined to the prostate, as well as improve symptoms for men with metastatic disease. There are many different types of radiation treatments.

One type of treatment includes injecting radioactive isotopes into the blood in order to directly reach the prostate cancer cells regardless of where they are located in the body, including the cells that have spread to the bone and other organs. For example, Radium-223 (Xofigo) is FDA-approved to treat prostate cancer that has metastasized to the bone and has been shown to improve both the quality and duration of the lives of men with advanced prostate cancer.

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Red marker = PSMA, Green = radiation, demonstrating that the drug targets the cancer cell directly.

Radioimmunotherapy or radioligand therapy involves the practice of attaching a radioactive isotope to a cancer-targeting antibody or small molecule that binds only to a specific cancer-related molecule on a tumor cell. This is similar to a “lock and key” scenario, where the antibody or molecule resembles the key that will only recognize a very specific lock (the cancer-related molecule).

Essentially all prostate cancers have a specific “lock” called prostate-specific membrane antigen (PSMA). This “lock” is a protein that sits on the surface of most prostate cancer cells but is absent from most other normal places in the body.

Physicians and scientists have engineered very specific “keys” in the form of monoclonal antibodies and molecules that will bind only to PSMA. When we attach radioactive particles to these keys, we are able to deliver what we call “molecularly targeted” radiotherapy.

For example, J591 is a monoclonal antibody (an engineered protein) that recognizes PSMA. Actinium-225 (225Ac) is a small radioactive particle that emits alpha-particles, a powerful form of radiation requiring fewer particles to cause damage to the cancer cells. When these are attached to one another, we call the compound 225Ac-J591 (a radioactive particle linked with a monoclonal antibody). It is designed so that J591 will recognize the PSMA on the prostate cancer cells and bring the radioactive particle 225Ac with it into prostate cancer cells wherever it goes in the body.

Our physicians and scientists are building on prior laboratory-based research presented at the 2017 Meeting for the Annual Association for Cancer Research (AACR) and are now studying the role this experimental therapy may have for men with advanced prostate cancer that has spread throughout the body. Thanks to generous support from the Prostate Cancer Foundation and the NIH SPORE award, Dr. Scott Tagawa, medical oncologist and Director of the Weill Cornell Medicine Genitourinary (GU) Oncology Program, and his team are conducting the first-ever clinical trial testing the PSMA-targeted antibody and radioactive alpha particles (225Ac-J591) for treatment of advanced prostate cancer. This promising new and unique approach has the potential to lead to another treatment option for those patients who are not experiencing the best clinical outcomes possible from standard of care therapies. Some men in Germany have received 225Ac linked to PSMA-617 with a handful of cases published with impressive responses. However, no formal studies have been performed and there are reports of bothersome dry mouth (xerostomia) and the potential for delayed kidney damage (seen in mice).

“We look forward to advancing science and also making this treatment available to men with advanced prostate cancer in the near future, says Dr. Scott Tagawa. “Our goal is to translate the existing knowledge base into true clinical gains for prostate cancer patients and it’s great that in October, 2017, we are able to treat our first patient.”

 

 

 

Using Alpha and Beta Radioisotopes to Kill Cancer Cells

Radionuclides, also known as radioisotopes, are particles that emit energy. The different particles they emit vary and some types emit damaging radiation (also called ionizing particles). This is a good thing when we’re using radiation as a way to kill cancer cells. The two main categories of radiation particles used to kill cancer cells are alpha and beta particles.

Several radioisotopes – using both alpha and beta particles — have been approved by the Food and Drug Administration (FDA) for clinical use in cancer treatment. Historically, bone-seeking radioisotopes were used for patients with painful tumors in the bone. For example, Strontium-89 (Metastron) and samarium-153 (Quadramet) are beta-emitters that are taken up like calcium into bone and were approved to decrease pain. More recently, the alpha-emitting agent radium-223 (Xofigo) was approved for men with metastatic castration-resistant disease that has spread to the bone. However, unlike the previous beta-emitting agents, radium-223 was FDA-approved because it leads to longer overall survival rather than just symptom relief. Radium-223 is an alpha particle that mimics calcium and is delivered and taken up by the bone cells. This generally occurs near tumor cells, and while we don’t know the exact mechanism of action, we suspect that in addition to being in close proximity to some tumor cells, this creates a less hospitable environment for the tumor cells that have spread to the bone.

Additionally, we can now utilize different targeting agents to take radionuclides directly to the tumor cells. Radioimmunotherapy or radioligand therapy involves the practice of attaching a radioactive isotope to a cancer-targeting antibody or small molecule that binds only to a specific cancer-related molecule on a tumor cell. This is similar to a “lock and key” scenario, where the antibody or molecule resembles the key that will only recognize a very specific lock (the cancer-related molecule).

As it turns out, essentially all prostate cancer cells have a specific “lock” called prostate-specific membrane antigen (PSMA). This lock sits on the surface of each prostate cancer cell. We have engineered very specific monoclonal antibodies and molecules that will bind only to PSMA, leading to the opportunity for “molecularly targeted” (radio-)therapy.

In terms of attaching the radioactive isotopes, we can use both alpha and beta particles depending on the location and size of the tumor.Alpha vs beta radiationAlpha particles have the advantage of a very high amount of energy and a short path length. The amount of energy is high enough so that only a small number (1-10) of alpha particles lead to lethal damage to cells. An advantage of the short path length is that only the cells in close proximity to the alpha particle are destroyed, sparing other healthy and normal tissues. However, because of the short path length travelled, the alpha particle needs to be delivered into or right next to the tumor cell. In fact, even a piece of paper (or skin) is enough to block an alpha particle. Other alpha particles are being developed to be delivered as lethal payloads when attached to carrier molecules. One of these, actinium-225 (225Ac) is an alpha-emitting radionuclide that emits 4 alpha particles. In humans the 225Ac particle has been used as part of a compound linked to an antibody to treat leukemia and it also has been linked to a PSMA-recognizing peptide to treat men with late-stage prostate cancer with initial examples published last year.

Beta particles emit a lower energy, but can travel further distances. Because of their lower energy levels, more particles are required to cause lethal damage to cells.

This video provides a great overview of the process:

Additional research is needed to decipher the best radionuclides to use for which diseases in which clinical situations. We at Weill Cornell Medicine and NewYork-Presbyterian Hospital will have both alpha and beta radionuclides linked to PSMA compounds available in the clinic this year, initially with a clinical trial using 177Lu-PSMA-617, to be followed by 225Ac-J591, then the combination of 177Lu-J591 and 177Lu-PSMA-617.

Lutetium 177 Radioimmunotherapy Clinical Trial Open for Men with Rising PSA Levels

We have an open clinical trial using radioimmunotherapy for men who have been diagnosed with prostate cancer, and whose PSAs are rising despite initial hormonal therapy but have no evidence of metastatic disease on scans (no tumors seen on CT/MRI and bone scan). This clinical trial is investigating whether attaching Lutetium 177 with the monoclonal antibody J591 (177Lu-J591) can delay or prevent the disease progression to overt metastatic disease in men with “biochemical progression”.

J591 can recognize a protein antigen known as PSMA (also known as anti-prostate-specific membrane antigen) that is present on the surface of nearly all prostate cancer tumors and circulating tumor cells.

The targeted treatment in this trial uses J591 as a delivery vehicle for the radioactive treatment (Lutetium 177) to be delivered directly to the prostate cancer cells that may be hiding or circulating in the body (for example in lymph nodes, the blood stream or the bones).

The Lutetium 177-J591 treatment approach may be ideal for men who are experiencing rising PSA levels after primary prostate cancer treatment and early hormonal therapy, but whose bone and CT scans remain negative. Even though we can’t detect the presence of cancer on these traditional imaging scans, we know from prior research that these men have what we call “micro-metastatic” disease, meaning that the prostate cancer cells are increasing throughout the body because otherwise PSA levels would not be so high or increasing at such a rapid rate. Unfortunately, even with traditional hormonal manipulation, metastases become evident in these men after months. Although we have treated many men with overt metastatic prostate cancer and demonstrated anti-tumor responses, we have also shown that we are able to target these micro-metastatic sites (tumors that are too small to be seen on CT or bone scan), and the properties of 177-Lu make it more optimal for tumors that are too small to be seen on conventional imaging.

Many patients fall in this category in a broad sense and usually these men feel completely fine. Approximately 50,000 new men per year in the U.S. suffer a biochemical relapse (rising PSA after surgery or radiation) and some of these men will have further PSA rises despite the most common type or hormonal therapy, which are injections to bring down testosterone levels. The goal is to intervene earlier on in order to bring more men to cure and suppress the disease from further progression and metastases.

Men in this phase II study will be randomized and all patients will receive oral hormonal therapy as part of treatment which also serves to boost their PSMA level (i.e. increase the number of “locks” per tumor cell). Since PSMA is the target for 177Lu-J591, radioimmunotherapy increased expression of PSMA can lead to more targeting of the otherwise invisible tumor cells. Two-thirds of patients will receive 177Lu-J591 at the highest tolerated dose that improved outcomes based on our prior study and the remaining one-third will get J591 with a diagnostic isotope (111Indium). The isotope 111-Indium (abbreviated 111In) is also an energetic radioactive particle, but it does not generally give off enough energy to kill cancer cells while still allowing researchers to take more detailed pictures of where the prostate cancer is located in the body.

Our goal is to ultimately cure the men who fall in this category by eradicating microscopic deposits of cancer, and the Weill Cornell Genitourinary Oncology team is available for patient consultations and to speak with physicians who are interested in referring patients to this trial, which is available at a number of sites across the country.

Learn more about how this treatment works in this article and video: