prostate cancer program overview

Background on Localized Prostate Cancer

Prostate cancer is the second most common form of cancer in men in the US with an estimated 181,000 new cases in 2016. As a result of an increase in life expectancy along with the current practice of formal and informal screening using prostate-specific antigen (PSA) blood tests, disease treatment has shifted towards early detection of low risk disease.

Approximately 80 percent of patients in the US are diagnosed with localized disease. Research has shown that in many cases patients with early localized disease have a low likelihood of the cancer spreading beyond the confines of the prostate; however, men with clinically significant localized disease choose to undergo radical treatment. Radical therapies include surgery to remove the entire prostate and/or radiation. Potential toxicities from radical treatments can be significant and permanent and include erectile dysfunction, incontinence and rectal toxicity.

Men who do not elect radical therapy may enroll in active surveillance, which does not offer any therapeutic benefit but does continue to monitor the patient (typically PSA levels, digital rectal exams and periodic or as indicated biopsies) for any progression of disease. The additional information is used to determine if a patient can remain in active surveillance or should undergo treatment. Once given the diagnosis of prostate cancer, the psychological impact on a man can be profound as is demonstrated by a significant proportion of men (about 10% in most studies) electing to undergo a radical treatment, even though they have had no evidence of biochemical or histopathological progression during their time in active surveillance.

Topsalysin for the Targeted Treatment of Localized Low to Intermediate Risk Prostate Cancer

Topsalysin represents a highly targeted investigational approach for potentially treating localized prostate cancer that is still confined within the encapsulated prostate gland: 1) PRX302 is therapeutically active only within the prostate tissue, and 2) PRX302 can be focally delivered by an intraprostatic injection directly into and around the tumors within the prostate where there are high levels of enzymatically active PSA.

Therefore, PRX302 has the potential to provide a focal targeted therapy for the ablation of localized prostate cancer while potentially avoiding many of the complications and side effects associated with whole gland radical treatments.

The increasing use of multi-parametric magnetic resonance imaging (mpMRI) and advances in mapping previously obtained mpMRI images with live 3D ultrasound images, enables the physician to more accurately locate tumors within the prostate when taking biopsies. This increases the precision with which men with clinically significant lesions are identified. Such a shift is allowing physicians and patients to make more informed decisions about whether to undergo radical treatment or active surveillance. It also enables the injection of PRX302 directly into the tumors located within the prostate The targeted focal treatment of early prostate cancer is in line with current treatments for solid tumors, such as breast or liver, where the goal is to remove the tumor and preserve as much of the organ as possible

Clinical Development in Prostate Cancer

In May 2015, we initiated a single-center, open-label Phase 2a proof of concept clinical trial of topsalysin for the treatment of localized low to intermediate risk prostate cancer. We believe that the highly targeted mechanism by which topsalysin selectively destroys prostate tissue in BPH makes topsalysin a potential targeted focal treatment for localized prostate cancer. The clinical trial utilizes previously obtained magnetic resonance imaging, or MRI, images of each patient’s prostate mapped to real time 3D ultrasound to target the delivery of topsalysin directly into and around a pre-identified clinically significant tumor. A clinically significant tumor was defined in our study as, either a Gleason score 6 (pattern 3+3) and >3mm Maximum Cancer Core Length, or MCCL, or Gleason score 7 (pattern 3+4 or 4+3) < 10 mm MCCL, which is thought to have the potential to progress and would therefore warrant treatment. (A Gleason pattern is a grading system utilized to describe how aggressive a prostate tumor is and how likely it is to spread. Generally, there are five recognized Gleason histological patterns and a higher Gleason pattern indicates a more aggressive tumor.) Patients received a transperineal administration of topsalysin under general anesthesia at a dose higher than used in our completed Phase 3 BPH PLUS-1 trial but less than the highest dose used in our previous prostate cancer trial. The primary objective of the trial was to assess the safety and tolerability of topsalysin when used to selectively target and focally ablate a clinically significant tumor. The potential efficacy was evidenced by histological changes, indicating tumor ablation at six months following treatment. The clinical trial was conducted at a single center, the University College London, which is well known for the focal treatment of prostate cancer in the United Kingdom.

A total of 18 patients with clinically significant, localized low to intermediate risk prostate cancer were enrolled in the Phase 2a proof of concept clinical trial. Biopsy results from all 18 patients enrolled in the Phase 2a proof-of-concept study of topsalysin for the treatment of localized prostate cancer were presented at The European Association of Urology 2017 Annual Meeting. The one-time administration of topsalysin was well tolerated with no serious adverse events and no new safety signals being reported. Topsalysin demonstrated an ability to ablate tumor cells in more than 50 percent of patients (9/18 patients) six months after treatment in a patient population with pre-identified, clinically significant prostate cancer. We believe that the results support advancing topsalysin into an additional Phase 2 study to confirm dosing and optimize delivery.

All 18 patients enrolled completed the study. Biopsy data at six months following treatment showed that:

  • Two men experienced complete ablation of their targeted tumor with no evidence of any tumor remaining at six months;
  • Nine men experienced a partial response, defined as either a reduction in the maximum cancer core length or a reduction in Gleason pattern; and
  • Seven patients had no response to treatment.

We have initiated a second Phase 2 clinical trial to confirm the dose and optimize the delivery of topsalysin for the treatment of localized prostate cancer. This study will utilize previously obtained MRI images of each patient’s prostate mapped to real time 3D ultrasound to target the delivery of topsalysin directly into and around a pre-identified clinically significant tumor. The primary objective of the trial will be safety and tolerability of topsalysin when used to selectively target and focally ablate a clinically significant tumor with potential efficacy assessed by histological and MRI changes. We expect that this clinical trial will enroll approximately 40 patients at two or more trial sites.

Learn more about the clinical development of topsalysin in localized prostate cancer here.