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Myovant to submit lead drug for prostate cancer approval after Phase 3 results

Credit: Elizabeth Regan / Industry Dive

Dive Brief:

  • Myovant Sciences said Tuesday a late-stage trial studying its lead drug in advanced prostate cancer met its primary and secondary goals, clearing the path for the company to next year submit the experimental therapy for Food and Drug Administration approval.

  • The Phase 3 study tested relugolix, a so-called GnRH receptor antagonist, against leuprolide acetate injection, which is a standard androgen deprivation therapy. Two-thirds of 934 enrolled patients received Myovant's treatment while one-third received leuoprolide acetate.

  • Ninety-seven percent of men given Myovant's drug responded to treatment, meaning testosterone was suppressed to castrate levels through 48 weeks. That compared to 89% of study participants in the standard-of-care arm, yielding a between-group difference of about eight percentage points. Following the readout, Myovant's stock sprung up by more than 150% Tuesday morning. 

Dive Insight:

Next year is shaping up to be consequential for Myovant's new drug ambitions, with the company now planning to seek approvals in 2020 for relugolix in both advanced prostate cancer and uterine fibroids.

If approved, relugolix would be the first oral GnRH antagonist for advanced prostate cancer, as older treatments like degarelix are delivered subcutaneously. Leuprolide acetate, designed as a GnRH agonist, works in a different way than relugolix, but is also given via injection.

More convenient delivery could be an advantage should relugolix win through to market. Research done by Myovant found a large majority of men with prostate cancer would prefer a pill to injections, company CEO Lynn Seely said Monday in an interview with BioPharma Dive ahead of the announcement.

Wall Street analysts haven't penciled in much for relugolix's prospects. In August, SVB Leerink's Ami Fadia projected $50 million in peak sales for the drug in prostate cancer, estimating that it would gain only 5% of the market for hormone suppression therapies. Existing physician preferences and pricing were two reasons she cited for the low figure.

Yet Myovant executives are hoping results from the Phase 3 study, dubbed HERO, showcase the potential of oral drugs like relugolix over current options.

Data showed relugolix quickly lowered testosterone to castration levels, defined as less than or equal to 50 nanograms per deciliter. After four days of treatment, approximately 56% of those on Myovant's drug achieved such levels compared to 0% on leuoprolide acetate, according to the company. And at the 15-day mark, 98% of the relugolix arm achieved suppression compared to 12% of the comparator.

Seely said the study also showed testosterone levels recovered faster after patients stopped taking relugolix, which could bring benefit for drug holidays or intermittent therapy.

"Quite frankly, men don't like having their testosterone levels suppressed," Seely said, citing the side effects of hot flashes, fatigue and loss of sexual desire and function.

Nearly all treated patients on either drug experienced an adverse event, with a slightly higher proportion of those on relugolix discontinuing treatment than those on leuprolide acetate.

Results on one secondary measure are still outstanding, with data expected in the third quarter of 2020. That will test if relugolix can further delay the time to onset of castration resistance, a stage of prostate cancer in which tumors are still growing despite low testosterone levels.

Prostate cancer is the second most common tumor type in men, ranking behind only skin cancer. The growth of those tumors is driven by testosterone, which GnRH-focused drugs seek to suppress.

Myovant's anticipated transition to becoming a commercial-stage company comes as it and four other subsidiaries of Roivant Sciences are swapping owners. Earlier this fall, Roivant said it will sell its stakes in Myovant and those other companies to the Japanese pharma Sumitomo Dainippon Pharma for $3 billion.

Seely said that transaction is still going through the regulatory process and said Myovant hopes to benefit from Sumitimo's commercial experience.

In uterine fibroids, Myovant might need that experience, as the company's offering could face off with AbbVie's Orilissa (elagolix), approved in endometriosis and in development for uterine fibroids.

Written by: Andrew Dunn

Published on: Nov. 19, 2019

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