Enolen Displays 84% Reduction in Tumor Volume of Localized Prostate Cancer

All patients in a small cohort of those with low- to intermediate-risk localized prostate cancer underwent successful implantation with the enzalutamide (Xtandi)-containing antiandrogen-eluting implant Enolen, according to a news release from the developer, Alessa Therapeutics.¹

In a National Cancer Institute (NCI)–led phase 1 study (NCT06257693), 20 patients undergoing prostatectomy underwent treatment with the implants. All implantations achieved high intraprostatic enzalutamide levels with minimal systemic drug exposure, resulting in no delays to surgery. Additionally, pre–radical prostatectomy MRI showed an 84% reduction in tumor volume among 18 patients over an average duration of 35 days, with 2 pending.

There were no effects on testosterone levels or negative impacts on sexual function. Additionally, reported adverse effects (AEs) were consistent with biopsy-like procedures without impact on future surgery and imaging.

“The preliminary safety and efficacy data from this study are compelling and demonstrate the potential of Enolen to serve as a new treatment option for [patients] with localized prostate cancer that avoids the negative [adverse] effects of current treatments,” said Peter Pinto, MD, chief of the Prostate Cancer Division at the National Cancer Institute and principal investigator on the study.¹ “These initial findings, particularly MRI-documented tumor shrinkage and therapeutic enzalutamide levels in the prostate with minimal systemic exposure, strongly support further development of Enolen.”

Patients in the phase 1 study underwent multiparametric MRI of the prostate at baseline prior to treatment.² Following implantation, patients received standard-of-care prostatectomy 6 to 12 weeks to 4 to 12 months later. Cohort A consisted of 20 patients who received up to 16 implants and had a prostatectomy planned between weeks 6 and 12 after the implant procedure.

The coprimary end points of the study were AEs per Common Terminology Criteria for Adverse Events v5.0 and pharmacokinetics. MRI changes in prostate and tumor volume, prostate-specific antigen changes, and testosterone changes were all secondary end points of the study.

“Being the first study to demonstrate that enzalutamide can be safely and locally administered to the prostate via sustained drug-eluting implants is a significant clinical milestone both for Alessa and for the broader treatment landscape for prostate cancer,” Pamela Munster, MD, chief scientific adviser and founder of Alessa, explained in the news release.¹ “We look forward to continuing our clinical advancement of Enolen, which includes further investigation of dose optimization and duration of drug exposure through 2 additional cohorts underway in this phase 1 trial.”

Those eligible for inclusion in the trial included patients 21 years or older with histologically confirmed adenocarcinoma of the prostate who qualified and were planned to undergo radical prostatectomy. Moreover, at least 1 prostate lesion measurable by MRI greater than or equal to 0.5 cm, a Gleason score of 3+4 or higher, and an ECOG performance status of 0 or 1 were among the eligibility criteria for enrollment in cohort A of the study.

Patients who underwent prior radiotherapy or surgery for prostate cancer, those receiving hormonal therapy for prostate cancer less than 3 months before study treatment, and those unwilling or unable to undergo MRI were excluded from enrollment in the trial. Additional exclusion criteria included those with metastatic disease, a lack of evidence for extracapsular extension of disease, a history of prostate infection within 2 years of treatment, and an increased risk of refractory urinary retention due to implantation per the treating clinician.

References

1. Alessa Therapeutics announces positive preliminary safety and efficacy data from Enolen phase 1 trial. News release. Alessa Therapeutics. March 16, 2026. Accessed March 16, 2026. https://tinyurl.com/jzxmp3s9
2. Enzalutamide implants (Enolen) in patients with prostate cancer. ClinicalTrials.gov. Updated February 27, 2026. Accessed March 16, 2026. https://tinyurl.com/2v44nau5