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.

Success of Abiraterone Trials Prompts ‘Mind Shift’ in Prostate Cancer Treatment

The below has been adapted and excerpted from an article in Healio in which Dr. David Nanus HeadshotNanus comments on The LATITUDE and STAMPEDE trials — results of which were presented at this year’s ASCO Annual Meeting and subsequently published in The New England Journal of Medicine. Read the full story here.

Abiraterone acetate is poised to challenge docetaxel as the standard addition to androgen deprivation therapy for treatment of newly diagnosed, metastatic castration-resistant prostate cancer. The LATITUDE and STAMPEDE trials showed the addition of abiraterone acetate and prednisone to androgen deprivation therapy (ADT) reduced risk for death by nearly 40%.

Docetaxel — an IV chemotherapy — can cause nausea, constipation, diarrhea, neutropenia or fatigue during its 18-week dosing schedule. Abiraterone, an oral adrenal inhibitor traditionally used in later-line therapy, is administered until disease progression and has relatively few side effects.

Docetaxel became the standard of care in patients with metastatic hormone-resistant prostate cancer following results from the CHAARTED study, published in 2015 in The New England Journal of Medicine. The results, based on median follow-up of 28.9 months, showed docetaxel improved median overall survival (OS) from 44 months to 57.6 months.

Abiraterone typically has been reserved as second-line therapy for men resistant to ADT. The LATITUDE and STAMPEDE trials — both supported by Janssen, the manufacturer of abiraterone — evaluated whether abiraterone would be more beneficial if used earlier.

Although abiraterone conferred unprecedented survival benefits and is better tolerated, not all oncologists agree it should replace docetaxel in the absence of a head-to-head comparative trial.

HemOnc Today asked urologic oncologists and researchers about the promise of abiraterone; the potential impact of its long-term use; if its cost in comparison with docetaxel is prohibitive; and whether abiraterone soon will be challenged by other therapies for the treatment of metastatic hormone-resistant prostate cancer.

“Abiraterone is a whole new paradigm because your patient is not coming in for an infusion every few weeks for six cycles,” David M. Nanus, MD, professor of medicine and urology at Weill Cornell Medicine, told HemOnc Today. “With six cycles of docetaxel, patients are often wiped out by the time they’re done, and it might take a few months to recover afterward.”

Based on the findings of the LATITUDE and STAMPEDE trials and the potential of targeted therapy, oncologists with whom HemOnc Today spoke agreed researchers are on the precipice of significantly extending the lives of men with prostate cancer.

In addition to the enthusiasm surrounding abiraterone and its potential to be the new standard of care in the treatment of metastatic, castration-resistant prostate cancer, several ongoing clinical trials are investigating other strategies to reduce androgen exposure. Results of those trials also could be practice changing, and again raise questions about the standard of care.

 

Liquid Biopsies in Prostate Cancer: Ready for Prime Time?

Beltran and Lab
(From L to R) Dr. Himisha Beltran, Dr. Raymond Pastore and Dr. Bishoy Faltas

Recent studies in advanced prostate cancer have identified emerging treatment targets and mechanisms of treatment resistance. At the 2017 European Society of Medical Oncology (ESMO) Annual Meeting, Dr. Himisha Beltran chaired and moderated a session evaluating the use of liquid biopsies – blood tests used to glean information about tumors – as a useful clinical tool for prostate cancer management.

While there are no formal guidelines on who, when, how and what to test for in prostate cancer, Dr. Beltran’s expertise provided important guidance to the global oncology community on this topic, as the prospect that a blood test might reveal many insights about the cancer and the tumor makeup has led oncologists to feel excited. Several steps are still needed for broad clinical implementation.

As tumors grow, some of their cells may enter into the bloodstream. These cells are known as circulating tumor cells (CTCs) and travel throughout the body along with fragments of tumor cell DNA known as circulating tumor DNA (ctDNA). Compared with traditional biopsies which extract tissue directly from the tumor, liquid biopsies offer a less invasive way for doctors to detect molecular biomarkers and learn more about what’s going on with someone’s cancer. Liquid biopsies can also better capture tumor heterogeneity, as CTCs and ctDNA can provide a window into the entire tumor (and metastatic sites), compared with a traditional biopsy in which typically only one part of the tumor is sampled. Thus, with a simple blood test, doctors can potentially access a more comprehensive view of an individual’s cancer, which can then help them determine the best treatment for that person. Blood testing can also be more easily repeated throughout the course of treatment in order to monitor disease changes in response to therapy, so liquid biopsy offers ways to detect treatment resistance and resistance mutations early on and throughout the course of the disease.

Red Blood Cells

There is an emerging role for molecular testing in advanced prostate cancer since this information can better inform treatment decisions involving targeted therapies, such as PARP inhibitors, platinum-based chemotherapy, and immunotherapies. Liquid biopsies such as ctDNA may provide information about the genomic alterations present in the cancer, which can be used to help predict how people might respond to certain therapies.

Through liquid biopsies, physicians and researchers can also better detect signs of therapy resistance that may be emerging. For example, if a patient has a gene amplification or mutation detected in ctDNA that involves the androgen receptor (AR) gene, or AR splice variants expressed in CTCs, this may indicate that potent AR-targeted therapies may be less likely to work. This is because the cancer cells may develop various ways to reactivate androgen receptor signaling by acquiring extra copies of the AR gene (gene amplification), activating AR mutations, and/or AR splice variants (such as the AR-V7 variant), all of which result in downstream over-activity of the AR-pathway. Knowing this information up front may spare people from the side effects from a treatment likely to be ineffective. Current research is focused on developing more effective AR pathway inhibitors in this setting. CTCs may also identify other features of the cancer such as localization of the AR in response to taxanes as observed in the TAXYNERGY trial, tumor heterogeneity, and expression of emerging therapeutic targets.

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.

While liquid biopsies do have promise for these indications and can help guide decisions on the most appropriate treatments for prostate cancer patients, it is important that both patients and clinicians understand the advantages and limitations of available and emerging technologies. Undergoing treatment at a center of excellence that contributes to research on emerging trends allows individuals the opportunity to be among the first to access cutting-edge technologies that may benefit them.