Tag: Prostate Cancer Research

Update in PSMA-Targeting for Imaging and Therapy

Prostate-specific membrane antigen (PSMA) is a protein concentrated on the surface of prostate cancer cells with limited expression on other locations in the body.  As covered previously on the blog, PSMA can be exploited for both imaging and treatment utilizing either large monoclonal antibodies or small molecule targeting agents. 

PSMA-targeting entails attaching a radionuclide (a particle that gives off radiation) to an antibody or small molecule designed to recognize and bind to PSMA. Research into PSMA-targeting has led to promising investigational treatments and transformed how we can detect prostate cancer. In December 2020, the U.S. Food and Drug Administration (FDA) gave limited approval for 68Ga-PSMA11 PET scans for patients with high-risk localized prostate cancer and patients with rising prostate specific antigen (PSA) levels following radiation or surgery. This form of FDA approval allowed for specific facilities in California to use this agent outside of the clinical trial environment. 68Ga-PSMA PET, which has been used elsewhere in the world without strict regulation, allows doctors to better detect recurrent and hidden prostate cancer and consequently, to choose the best type of therapy for each patient.

Weill Cornell has a dedicated team of physicians that study and interpret 68Ga-PSMA PET imaging. Numerous studies have demonstrated that 68Ga-PSMA PET is more effective than traditional scans (such as CT or MRI) in finding metastatic prostate cancer (sites where the cancer has spread elsewhere, including microscopically) and in a small head-to-head study was also better than 18F-fluciclovine (Axumin) PET/CT. There are a number of ongoing trials at Weill Cornell and elsewhere evaluating the use of PSMA targeted imaging, which currently remain the only way to obtain PSMA PET outside of California, with additional approvals of PSMA PET agents expected in the first half of 2021.

At the 2021 Genitourinary (GU) Cancers Symposium, researchers presented a head-to-head comparison of 68Ga-PSMA11 PET vs. MRI in detecting and staging localized prostate cancer (disease mainly confined within the prostate) in 74 patients. The two imaging methods had similar performance, with PSMA PET a little better for tumors outside of the prostate and MRI better for identifying tumor invasion of structures adjacent to the prostate. It may be that the combination of both methods will further enhance prostate cancer staging and a study is currently being done at WCM to evaluate this combination.

Additionally, a number of studies on PSMA-therapeutics were presented at the 2021 Genitourinary Cancers Symposium. There is an ongoing trial investigating PSMA-targeted radionuclide therapy (PSMA-TRT) with radioactive iodine in combination with the prostate cancer drug enzalutamide; radioactive iodine (Iodine-131) is conjugated to the small molecule 1095. An initial study of 10 patients receiving PSMA-directed/TGFβ-insensitive CAR-T cells (immune cells that have been engineered to recognize PSMA) demonstrated safety and efficacy. In this study, 60% of patients experienced PSA decline, ranging from 11.6 to 98.3%, and post-treatment biopsies demonstrated CAR-T cells infiltrating the tumor microenvironment. Furthermore, there is an ongoing clinical trial of a bispecific antibody (REGN5678) that connects PSMA with immune cells, which can subsequently destroy the cancer cell; this bispecific antibody is combined with a medication called cemiplimab that further strengthens the body’s immune response. 

There are multiple agents utilizing PSMA small molecules to carry the beta-emitting radionuclide lutetium-177 (177Lu) to PSMA-positive areas in the body (mostly areas of cancer spread). Updated results of a prospective head-to-head comparison of 177Lu-PSMA-617 vs. cabazitaxel (a type of chemotherapy) in 200 patients with advanced prostate cancer were presented at the 2021 Genitourinary Cancers Symposium.  In the data initially shared at ASCO 2020, the main objective was met, with more patients receiving 177Lu-PSMA-617 having PSA response compared to cabazitaxel chemotherapy.  In the updated report, patients receiving 177Lu-PSMA-617 had longer disease control (both by PSA measurements and scans), with fewer side effects and more improvements in quality-of-life. Recently, VISION, the multicenter phase III clinical trial comparing 177Lu-PSMA-617 + standard of care against standard of care alone in patients with advanced metastatic prostate cancer, has shown that patients receiving 177Lu-PSMA-617 lived longer and had longer disease control. Full results will be presented at an upcoming research conference, and we hope that this study leads to FDA approval in the future.

In general, tumors spread to other parts of the body via the bloodstream. The ability to capture these tumor cells, called circulating tumor cells (CTCs), has led to significant prognostic information along with the ability to study the cells as part of a “liquid biopsy”.  When a number of different types of therapy is able to decrease or clear CTCs from the circulation, those therapies generally make patients live longer.

Scans before and after treatment with PSMA-targeted radionuclide therapy (PSMA-TRT).

Weill Cornell researchers examined several sequential prospective clinical trials utilizing various PSMA-TRT agents. In an analysis of 116 patients, 70% treated with PSMA-TRT and with CTC counts before and after therapy had a decline in CTC counts. Some PSMA-targeting agents (i.e. the carrier molecules) may have anti-cancer effects on their own. While it appears that agents labeled with radioactive particles are more effective, some patients treated with anti-PSMA antibody J591 alone had control of CTC counts.

Alpha and beta-emitting radionuclides have different properties.  In 2020, we presented preliminary information at ASCO that a single dose of the potent alpha-emitter actinium-225 (225Ac) linked to antibody J591 (225Ac-J591) was safe, and despite lack of selection of patients with PSMA PET and prior 177Lu-PSMA therapy in the majority, 60% had PSA decline.

At the 2021 GU Cancers Symposium, investigators presented the design of WCM’s ongoing clinical trial investigating either fractionated (2) or multiple-dose (1-4 doses) of 225Ac-J591.  This study (NCT04506567) is one of many PSMA-targeted therapeutic clinical trials open at Weill Cornell Medicine and NewYork-Presbyterian Hospital.

Antibodies and Small Molecules: Two Different Tools to Target PSMA

Prostate-specific membrane antigen (PSMA) is a molecular marker present on the surface of virtually all prostate cancer cells. It can be targeted by different molecular agents that bind to PSMA. This enables a targeted approach to find and image or treat prostate cancer cells wherever they are in the body, including the cells that have escaped (metastasized) to other organs.

The most commonly used agents to target PSMA fall into two categories: small molecules (also known as peptides, ligands, or inhibitors) or antibodies (also termed monoclonal antibodies).

Small molecule- and antibody-based molecules that bind to PSMA have different physical characteristics and these have implications on the way the molecules circulate through the body.

For example, peptides and other small molecules that target PSMA are much smaller than antibodies – approximately 100-fold smaller. As a result of their small size, peptides are able to quickly travel through blood vessels and disperse throughout all body tissues – both normal and tumor – and they are also rapidly excreted by the kidney into the urine and bladder.

Conversely, the larger antibodies tend to stay within the circulating blood and flow more selectively through the larger, abnormal blood vessels within tumors than the vessels in normal tissues. Their large size also prevents them from being excreted by the kidneys. Because of these properties, peptides can penetrate tumors, as well as normal tissues, rapidly and then disappear from the body quickly, in minutes to hours; antibodies take longer to travel and enter the tumor, but this is compensated for by the longer amount of time they spend in the body (days to weeks) and their decreased likelihood to penetrate into normal tissues.

Imaging

From a diagnostic imaging perspective, small molecules are typically better, as the rapid excretion of the radiolabeled peptide quickly minimizes the radioactive background “noise” seen on a scan. Additionally, using small molecules means that patients can be injected with imaging agents and then undergo scans quickly thereafter (on the same day within 1-3 hours). Physicians can see good contrast of the cancerous cells compared to other parts of the body with this method. In comparison, patients must return approximately 3-8 days after infusion with a monoclonal antibody for scans. Some of the benefit of using small molecules is offset by the fact that they are excreted via the urine and accumulate in the urinary bladder. This may lead to an intense signal in the urinary bladder area of the scan, adjacent to the prostate gland and lymph nodes in the pelvis, thereby possibly obscuring these potential sites of tumor. On the other hand, some antibodies are taken up by the liver, obscuring visualization of that organ. Antibody fragments such as so-called “mini-bodies” (derived from the whole antibody), are half the size of a normal antibody, but still large enough so as not to be excreted in the urine, and as such, they may provide improved imaging of the prostate and the pelvic area. This is currently under investigation at Weill Cornell Medicine and NewYork-Presbyterian Hospital.

The nuances of these molecular targeting agents aside, it is clear that both peptide-, antibody or mini-body-based agents provide significantly improved targeted molecular imaging of prostate cancer compared with conventional modalities such as bone, CT, and MR scans and also have some advantages over glucose (FDG), sodium fluoride (bone), choline, or fluciclovine (FACBC) PET scans.

Treatment

From a therapeutic perspective, there are theoretical advantages to the faster tumor penetration of the smaller molecule targeting agents, but this may be offset by their quick disappearance and their ability to impact normal tissue. The longer time antibodies spend circulating in the body theoretically provides for a greater amount of the treatment agent to get internalized into the cancer cells, allowing greater uptake of the payload agent (such as a radionuclide) that is being delivered to kill the cancer cells. Additionally, some antibodies may also be engineered to generate an immune response.

Does uptake in different body areas lead to side effects?

The different characteristics of small molecules and antibodies confer advantages and disadvantages when targeting PSMA on cancer cells within the body. Because of their small size, small molecules/peptides can penetrate through the depths of the tumor very quickly, but they also readily target normal tissues that express low levels of PSMA such as the salivary glands, small intestine, and kidneys. When using as a therapeutic delivery vehicle, this might lead to dry mouth, nausea, or delayed kidney damage. Luckily, no significant kidney damage has been seen in humans to date, but the number of patients treated on prospective clinical trials remains small and follow up is short. An antibody, on the other hand, does not target salivary glands or kidneys because its larger size leads to relatively restricted access to those normal sites. However, it circulates in the body for a longer period of time including high flow through the bone marrow. Antibodies tagged with radioactive particles may therefore contribute to non-specific side effects such as temporary decreased blood counts. This is a common (expected) toxicity related to the dose and schedule of the radiolabeled antibody.

Currently, it is not known whether peptide-based or antibody-based targeted PSMA prostate cancer treatments provide better results, but both approaches offer therapeutic benefit to patients. At Weill Cornell Medicine and NewYork-Presbyterian Hospital – where we have two decades of experience pioneering prostate cancer imaging and treatment with PSMA-targeted agents – we are the only center in the world currently able to offer both types of imaging and treatment modalities and plan to combine both within individual patients. We hypothesize that will be able to use the favorable properties of each targeting agent at slightly lower than maximal doses to deliver a higher amount of therapeutic payload to tumor with less to normal organs, further improving the tumor kill : side effect ratio and have initiated a clinical trial testing this approach.

References

Phase I Trial of 177lutetium-Labeled J591, a Monoclonal Antibody to Prostate-Specific Membrane Antigen, in Patients with Androgen-Independent Prostate Cancer

Phase II Study of Lutetium-177-Labeled Anti-Prostate-Specific Membrane Antigen Monoclonal Antibody J591 for Metastatic Castration-Resistant Prostate Cancer 

 

Treating Prostate Cancer with Taxane Therapies: What the Latest Research Shows

For people with advanced prostate cancer, taxane chemotherapy is the only chemo shown to improve survival. Taxanes target microtubules, which are structures in cells that are involved in cell division, as well as the trafficking of important proteins. The important androgen receptor (AR) protein is trafficked via microtubules from the cell surface into the nucleus, where it binds DNA and leads to cancer cell growth. In prostate cancer, taxane chemotherapies work in part by binding microtubules and leading to stabilization of these tracks, preventing the AR from moving into the nucleus, a novel mechanism we discovered here at Weill Cornell Medicine.

Two taxanes are approved for men with prostate cancer, docetaxel (Taxotere) and cabazitaxel (Jevtana). Docetaxel was approved for men with metastatic castration-resistant prostate cancer (mCRPC) in 2004 based upon longer overall survival and improved quality of life compared to the previous standard chemotherapy mitoxantrone (which was approved because it helped relieve cancer symptoms). Importantly, even if tumors become resistant to the first taxane used, the other can still have anti-tumor activity and lead to improved outcomes. Cabazitaxel was approved following treatment with and cancer progression during or after treatment with docetaxel in 2010 because of improved survival compared to mitoxantrone. In addition to these chemotherapy drugs, patients are usually given low-dose prednisone. While docetaxel and cabazitaxel are similar, men whose tumors have grown despite taking one drug often respond to the other. For oncologists, the challenge has been pinpointing when exactly to switch treatments.

As part of the approval of cabazitaxel, the FDA mandated that the drug maker address two questions. One question was, with two taxanes approved, is cabazitaxel better than docetaxel in controlling cancer growth? Two doses were studied in early phase clinical trials across different cancer types and the optimal dose (20 mg per body size versus the approved dose of 25 mg) was unknown. The second question was whether a lower dose (with presumably less toxicity) was as good as the full dose. In addition, our Weill Cornell Medicine team asked the scientific questions of whether switching the drugs earlier leads to better overall response rather than the traditional approach, and how can we assess the biomarkers response and resistance to the drugs?

In the current issue of the major cancer publication the Journal of Clinical Oncology, three significant studies designed to answer these questions and which highlight the impact of taxanes are published together.

The FIRSTANA trial enrolled 1168 men with chemo-naïve mCRPC, testing whether cabazitaxel administered at the standard 25 mg or lower 20 mg (per body size) dose were more effective than docetaxel (all drugs given every three weeks). The results demonstrated that cabazitaxel at either dose was not superior to docetaxel. In the first large head-to-head study, differences in side effect profiles between the drugs were highlighted. Of significance, docetaxel is available as a generic drug and is cheaper on health care systems, so it is helpful to know that we can achieve similar outcomes by starting with the more economical drug. In the current treatment era, most men receive one of the oral hormonal drugs (such as abiraterone or enzalutamide) prior to chemotherapy in the mCRPC setting, but unfortunately only a very small fraction of them were treated in this manner in the FIRSTANA study.  There is some evidence that prior treatment with potent oral hormonal therapy drugs diminishes response to taxane chemotherapy and it is possible that this effect is different between the two taxanes, so this remains an open question.

PROSELICA was a study which enrolled 1200 men with mCRPC who had cancer that progressed following treatment with docetaxel. It was designed to show that a lower dose of cabazitaxel (20 mg per body size) was non-inferior to the approved dose (25 mg per body size). Half of the men received treatment with each dose. The primary endpoint of the clinical trial examined overall survival. Though there were more prostate specific antigen (PSA) reductions that lasted longer with the higher dose, overall survival was essentially the same in both groups. Additionally, there were more severe side effects with the higher dose. This trial met its endpoint of showing that the lower dose was not inferior, and a new (lower) standard dose of 20 mg per body size is now an acceptable treatment, receiving FDA approval in September 2017. Importantly, the study confirmed that the drug is effective at both doses even in men who developed resistance to the similar drug, docetaxel. Though there was a higher percentage (approximately a quarter), like in the FIRSTANA trial, only a fraction of patients were previously treated with abiraterone/enzalutamide and it is unknown how having a more contemporary group with nearly all patients receiving at least one of those drugs would affect the outcome.

Top Boxes_Taxynergy
In the photos from a sub-optimally responding patient on the right, almost all of the androgen receptor (AR, labeled in green) is in the nucleus (indicated by the arrow which is overlayed in blue on the right), meaning that the taxane chemotherapy treatment was unable to block AR from moving to the nucleus and thus unable to kill the prostate cancer cells.

In a collaborative effort between academic investigators at Weill Cornell Medicine (WCM)/NewYork-Presbyterian (NYP) and Johns Hopkins, and Pharma, the TAXYNERGY study evaluated two main questions. With the background assumption that activity between the two taxanes (docetaxel and cabazitaxel) were similar but different enough that tumors that had resistance to one drug could respond to the other, the primary clinical question was whether we could increase the response rate in the overall patient population by switching drugs if individual patients had suboptimal response initially. The randomized study was determined to be positive, with more patients achieving deeper PSA declines than compared to the prior benchmark.

Our latest research published in the Journal of Clinical Oncology also reports on updates to the TAXYNERGY trial, which showed additional evidence of using cancer cells circulating in the blood, also referred to as circulating tumor cells or CTCs, as a primary biomarker for determining chemotherapy response. This research validated prior work demonstrating the mechanism of action of taxane chemotherapy in prostate cancer. Furthermore, this research proved that with a simple blood draw or “liquid biopsy,” within one week of a patient’s first chemotherapy treatment, we’re able to determine whether men with metastatic prostate cancer are responding to therapy. If they are not optimally responding, we may be able to change treatment to the other taxane chemotherapy very early on, optimizing the likelihood of controlling the cancer’s growth by using the other, similar taxane chemotherapy. This carries great significance in that it prevents men from continuing with treatment that is not working and has associated side effects.

At Weill Cornell Medicine and NewYork-Presbyterian, when it comes to cancer care, we continue to explore new ways to improve treatment responses and provide the best clinical outcomes possible.

Additional research examining liquid biopsies in men with prostate cancer continues. In a collaborative effort funded by a Movember – Prostate Cancer Foundation (PCF) grant, CTCs are being collected before and after therapy to validate previous AR variant biomarkers and to explore additional technologies that might predict response or discover additional mechanisms of drug resistance. We continue to validate the platform of circulating tumor DNA (also called cell-free DNA) with a panel that is more specific and useful for prostate cancer than commercially available platforms.

Through a grant from the Prostate Cancer Foundation (PCF), Dr. Beltran and colleagues at WCM are working as part of an international consortium to develop, validate, and implement a ctDNA platform for prostate cancer. This targeted genomic sequencing test, called PCF SELECT, identifies tumor mutations in ctDNA from metastatic prostate cancer patients to guide treatment selection based on precision medicine. It is currently undergoing centralized development, and the long-term goal is that this ctDNA test will be widely used by the clinical prostate cancer community for precision medicine applications.