Prostate cancer medicine may slow progression of SBMA: Real-world study
A medicine called leuprorelin acetate, approved in the U.S. to treat prostate cancer, can slow the progression of physical disability in people with spinal and bulbar muscular atrophy (SBMA), according to an analysis of a real-world study from Japan.
Given certain limitations in the study’s design, the researchers stressed that the results of this new analysis need to be interpreted cautiously. But the team concluded that the findings support the idea that this cancer drug could be repurposed to alter the course of SBMA, a rare adult-onset form of spinal muscular atrophy (SMA).
SBMA, also called Kennedy’s disease, is a genetic disorder marked by muscle weakness that usually starts being noticeable in early adulthood and then gets progressively worse as time goes on. It’s caused by mutations in the AR gene, which encodes instructions to make a receptor protein that responds to the hormone testosterone. In SBMA, the genetic alteration in AR leads to the production of an abnormally large androgen receptor protein that has an altered structure.
Leuprorelin acetate is sold under the brand name Lupron Depot, among others, and works to reduce testosterone levels. In the U.S., it’s approved to treat prostate cancer as well as certain gynecological and hormonal conditions.
The study detailing the findings, titled “Therapeutic impact of leuprorelin acetate on spinal and bulbar muscular atrophy: pre- and post-marketing observational study,” was published in the Journal of Neurology.
In Japan, leuprorelin was approved in 2017 as a treatment for SBMA based on a handful of short-term clinical trials that showed the medicine improved swallowing ability in patients. However, because these studies were short, little is known about how leuprorelin affects long-term motor function in people with SBMA.
Scientists looked at long-term use of prostate cancer medicine in SBMA
To address this gap in knowledge, scientists from institutions in the Asian nation analyzed long-term data from 91 people with SBMA who had multiple motor function assessments performed before and after starting treatment with leuprorelin.
Prior to starting treatment, average scores on the ALSFRS-R — a standardized measure of motor function that was originally developed to track disease progression in amyotrophic lateral sclerosis — worsened at a rate of about 0.5 points per year on average. But in the years after starting leuprorelin, ALSFRS-R scores worsened at a significantly slower rate, of 0.2 points per year on average.
Other measures of motor function, such as the modified Norris scores that assess limb and bulbar function (face and tongue), also showed slower rates of worsening after starting leuprorelin. So too did tests of grip strength and levels of a muscle damage marker called creatinine.
[These findings] provide new insights into the long-term effects of leuprorelin acetate and support its potential as a disease-modifying therapy for SBMA.
“The results suggested that leuprorelin acetate slowed disease progression across multiple outcomes, including the ALSFRS-R, modified Norris scores, grip strength, and serum [blood] creatinine levels,” the researchers wrote.
According to the team, these findings “provide new insights into the long-term effects of leuprorelin acetate and support its potential as a disease-modifying therapy for SBMA.” A disease-modifying therapy is a treatment that can demonstrably alter the trajectory of a disease by targeting the underlying cause, not merely easing symptoms.
Findings suggest SBMA progression may not always be linear
In further analyses, the researchers compared outcomes between patients who started on leuprorelin within a decade of SBMA onset versus later on. These results showed no clear differences between the two groups, indicating that earlier initiation of leuprorelin doesn’t necessarily translate to better outcomes.
“In the present analysis, no distinct long-term treatment advantage was observed in patients with a disease duration of less than 10 years,” the researchers wrote.
These findings shed new light on evidence regarding this SMA type.
“Although previous studies have shown that SBMA follows a relatively linear progression, this assumption may not hold true in all cases,” the investigators noted. “Disease progression can vary across different stages of SBMA, potentially affecting the accuracy of treatment effect estimates.”
The scientists also noted that, due to this study’s design, it’s impossible to tease out the actual effects of treatment versus a potential placebo effect — when patients expect a therapeutic benefit because they are aware of what therapy they are being given. This means the data need to be interpreted with caution, per the team.
Still, the findings overall support the notion that leuprorelin treatment can meaningfully slow the progression of SBMA, according to the researchers, who added that “future studies should aim to mitigate potential biases, apply more rigorous methodologies, and investigate the impact of treatment timing on clinical outcomes.”
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