The Phase 2a trial assessing the safety and efficacy of Rexahn Pharmaceuticals’ Supinoxin — an oral inhibitor of the β-catenin pathway in metastatic triple negative breast cancer (TNBC) patients who failed prior treatments — has dosed its first patient.

Rexahn CEO Peter D. Suzdak, PhD, called the event “a major milestone” for Supinoxin.

“Our decision to focus initially on triple negative breast cancer underscores our commitment to developing our targeted treatments for cancers that are difficult to treat and for which there are limited treatment options,” Suzdak said in a news release  “There is currently no approved drug treatment for TNBC and no established standard of care, so there is a tremendous unmet medical need.”

Supinoxin is an orally administered, small molecule that inhibits the β-catenin pathway by preventing its interaction with the protein p68. The β-catenin pathway is often activated in cancer cells, leading to the production of various tumor-promoting genes and inducing tumor proliferation and metastasis.

Rexahn’s therapy has shown promising anti-tumor activity, inhibiting tumor growth in preclinical models of TNBC. In addition, experiments in lab-cultured cells revealed that it works in synergy against the disease with commonly used drugs like Taxol (paclitaxel), Platinol (cisplatin) and Adriamycin (doxorubicin).

“Supinoxin has a unique mechanism of action,” said Ely Benaim, MD, the company’s chief medical officer. “It targets a key biological pathway implicated in cancer cell proliferation. We have seen very promising activity in our preclinical models of triple negative breast cancer so we look forward to the preliminary readout from this first clinical study, which we anticipate later this year.”

In a prior dose-escalating Phase 1 trial in patients with metastatic, refractory cancers, Supinoxin was shown to be safe and well tolerated, with no dose limiting toxicities or treatment-related adverse events. The study recruited 14 patients with breast, ovarian, colorectal or neuroendocrine tumors, seven of which achieved stable disease. Three patients remained on Supinoxin treatment for more than one year.

Now, Rexahn is starting a Phase 2a proof-of concept trial (NCT02003092) assessing the safety and efficacy of Supinoxin in patients with metastatic TNBC who failed prior chemotherapy regimens.

The open-label study will recruit 10 patients, but can be extended to up to 50 patients, based on data from the initial cohort of patients. Participants will be enrolled at seven centers across the United States and will receive Supinoxin orally once a week for three weeks, followed by one week rest of each four-week cycle, for up to six cycles.

The study’s primary endpoint is progression-free survival, and based on the initial data, Rexahn may conduct additional trials assessing Supinoxin in combination with other drugs used to treat TNBC patients.