Some patients with localized prostate cancer were seen to benefit from treatment with topsalysin (PRX302) in a small Phase 2a proof-of-concept trial (NCT02499848), according to Sophiris Bio.
Findings from the trial were presented at this year’s 112th American Urology Association meeting by Edward J. Bass, University College London. The poster was titled “Intra-Prostatic PRX302 Focal Therapy in Treating Clinically Significant Low-Intermediate Risk Prostate Cancer: An Open Label, Proof-of-Concept Study.”
Topsalysin is a recombinant protein designed to be selectively activated by PSA, a protein produced in high levels by prostate cancer cells. It triggers local cell death and tissue disruption without damaging healthy, neighboring tissue.
The prostate-specific activation of topsalysin by active PSA is designed to limit the exposure of non-prostate tissues to the drug’s activity, ensuring a safer treatment.
The study’s objective was to assess the safety and efficacy of topsalysin injections. It enrolled 18 prostate cancer patients, who received a single injection in the prostate region affected by cancer. Patients were then followed at day two, and then at two, six, 12, 24, and 26 weeks. At week 24, researchers collected a prostate biopsy from the treated area.
Follow-up data indicated that a single dose of topsalysin directly targeting pre-identified tumor cells was both safe and well-tolerated. Biopsies collected at 24 weeks after treatment showed that two patients achieve complete tumor response and had no signs of cancer at six months. Seven patients achieved a partial response, presenting a decrease in tumor size or disease severity. The remaining nine patients did not respond to treatment and, in some cases, experienced an increase in tumor size and disease severity.
“Our proof-of-concept study shows that a single intraprostatic administration of [topsalysin] has a biological effect on prostate tumor cells when focally injected with low side-effect profile,” the researchers wrote. “Optimizing the dosing and delivery of [topsalysin] based on tumour size may increase response rates and will be tested in a multicenter phase 2 study.
This larger Phase 2 study (NCT03081481) is now recruiting 40 people with localized prostate cancer at two U.S. sites, in Fort Lauderdale, Florida, and Temple, Texas, to test the safety, efficacy and dosing of topsalysin. More information is available by clicking on the trial’s identification number.
Based on the findings, the researchers believe that topsalysin has the potential to safely eliminate clinically significant lesions, prolonging the time to more radical therapies in this patient population.