Context Therapeutics (NASDAQ:CNTX) Inc. said Onapristone extended-release (ONA-XR) has shown significantly increased suppression of tumor cell proliferation in postmenopausal patients with progesterone receptor-positive (PR+) early breast cancer.
The positive data came from the window-of-opportunity clinical trial of ONA-XR and was presented during the 2021 San Antonio Breast Cancer Symposium (SABCS), the company said in a statement.
“ONA-XR is being evaluated in four investigator-sponsored clinical trials in hormone-driven breast, ovarian and endometrial cancers,” said Martin Lehr, CEO of Context.
“This readout is the first for the novel PR antagonist, and the results are encouraging early evidence of the potential of ONA-XR to offer a new therapeutic option for hormone-dependent cancers,” added Lehr.
The Phase 0 open-label, single-arm, multicenter ONAWA (SOLTI-1802) trial conducted by Spanish cancer research group SOLTI, enrolled 10 patients with ER+/PR+/HER2- negative tumors and levels of the cell proliferation marker "Ki67" above 10% to evaluate ONA-XR by the rate of Complete Cell Cycle Arrest (CCCR) determined by Ki-67 (≤2.7%) when administered for three weeks prior to surgery (Abstract #511), said Context.
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Secondary endpoints of the trial included safety and correlating biological activity with immunohistochemistry (IHC) of tumor expression (ER, PR, Ser294-PgR, CD24, CD44, ALDH1, Ki-67), estradiol, and progesterone blood levels, and gene expression profile (NanoString nCounter® Breast 360TM panel), it added.
“While no patients achieved a CCCR, tumor Ki-67 expression decreased in six patients, remained stable in one patient, and increased in three patients,” said the company.
It added that a shift towards more endocrine-sensitive disease was detected, implying an increased chance of the tumor responding to anti-estrogen therapy when used in combination with ONA-XR.
Six patients reported adverse events (AEs), of which most were grade 1 or 2, including post-procedural pain, dry mouth, and an increase of gamma-glutamyl transferase (GGT) while one patient experienced Grade 3 reversible GGT and aspartate aminotransferase (AST), it said.
“The data from the ONAWA trial signal the potential of ONA-XR to help inhibit tumor proliferation and shift tumors to a more endocrine treatment-sensitive phenotype during treatment prior to surgery in postmenopausal women with operable breast cancer and improve overall prognosis for these patients,” said co-principal investigator Meritxell Bellet, medical oncologist at Vall d'Hebron University Hospital in Barcelona and an executive board member of SOLTI.
“These results support further evaluation of ONA-XR in the treatment of early breast cancer,” added Bellet.
ONA-XR is a novel, first-in-class small molecule under development as a complete antagonist of the progesterone receptor, a key unchecked mechanism in hormone-driven women’s cancers.