Eagle Prepares Clinical Trials of New Form of Fulvestrant to Treat ER-positive Breast Cancer

Eagle Pharmaceuticals is preparing a pilot study that may pave the way for a pivotal clinical trial evaluating its new formulation of fulvestrant as a treatment for estrogen receptor (ER)-positive breast cancer.

The company believes its new formulation will block estrogen receptors more effectively than AstraZeneca‘s original formulation, approved as Faslodex for some hormone receptor (HR)-positive breast cancers.

“The opportunity to develop a new treatment option that has the potential to better address the epidemic of breast cancer affecting millions of women in the U.S. and worldwide is an important priority for Eagle,” Scott Tarriff, CEO of Eagle Pharmaceuticals, said in a press release.

“If successful, the Eagle product could provide a meaningful improvement and a new option to treat this breast cancer patient population,” he added.

Fulvestrant is a form of hormone therapy for breast cancer. It works by selectively blocking estrogen receptors, halting that hormone’s effect on tumor cells. As a consequence, it slows or stops the growth of HR-positive breast cancers, which depend on estrogen to proliferate.

Faslodex is approved for HR-positive advanced breast cancer in women who have been through menopause, including those who have not used hormone therapy and those whose cancer progressed after taking a hormonal treatment.

Is is also indicated as an add-on treatment for women whose HR-positive breast cancer has spread to other parts of the body, both for those naive to hormone therapy and those whose cancer worsened following such therapy.

While its efficacy is extensively demonstrated, recent studies have shown that the therapy Faslodex does not inhibit all estrogen receptors in some patients, and that greater estrogen receptor availability during treatment is associated with early disease progression.

Eagle launched a Phase 1 trial (NCT03324061) to evaluate its initial fulvestrant formulation in healthy post-menopausal women. The 2018 study enrolled 600 people who were randomly assigned to either Eagle’s formulation or Faslodex.

Data suggested that Eagle’s formulation had unique properties that could potentially allow for greater inhibition of estrogen receptors. Supported by these findings, the company undertook additional research and development work to further enhance its proprietary formulation.

Based on meetings with the FDA, the company designed a clinical program for this new form of fulvestrant, designed to demonstrate that it blocks a greater number of estrogen receptors, potentially resulting in better outcomes for patients compared to current treatment options.

Should results from the planned series of clinical trials be positive, Eagle expects to use their data to support a request for regulatory approval of its new formulation.

“Following a thorough review of the data from our previous study, we believe that our fulvestrant product has a unique profile that may allow it to achieve a greater level of estrogen receptor inhibition, and we are encouraged by the guidance provided by FDA to develop a clinical path to further explore the potential of our novel formulation,” Tarriff said.

The program includes a first, pilot study in healthy women designed to assess the treatment’s safety, as well as its stability, metabolism, and bioavailability (its pharmacokinetics, essentially how the body affects a drug).

Eagle then plans to launch a pivotal efficacy trial for patients with ER-positive breast cancer, evaluating the treatment’s ability to inhibit estrogen receptors. Depending on recruitment rates and other factors, this study may conclude within 12 months.