Spero Therapeutics (SPRO) SPR720 Phase 2a Clinical Trial in NTM-PD Has Been Placed on Clinical Hold by FDA

(Updated - February 5, 2021 8:04 AM EST)

Spero Therapeutics, Inc. (Nasdaq: SPRO), a multi-asset clinical-stage biopharmaceutical company focused on identifying, developing and commercializing treatments in high unmet need areas involving multi-drug resistant bacterial infections and rare diseases, today announced that the United States Food and Drug Administration (FDA) informed Spero that a clinical hold has been placed on its Phase 2a clinical trial of SPR720, Spero’s investigational oral antimicrobial agent being evaluated in patients with nontuberculous mycobacterial pulmonary disease (NTM-PD).

Spero received verbal notification of the clinical hold for the SPR720 Phase 2a trial but has not yet received written notice from the FDA. The clinical hold follows the notification by Spero to the FDA of its decision to pause dosing in its ongoing Phase 2a clinical trial of SPR720 as a precautionary measure following events in its ongoing animal toxicology study of SPR720. The decision to implement the pause was made based on a recommendation from Spero’s Safety Review Board (SRB), following review of data from an ongoing toxicology study of SPR720 in adult non-human primates in which mortalities with inconclusive causality to treatment were observed. The animal study is being conducted to assess the potential toxicity of SPR720 over a 4-month duration. A concurrent 4-month study of SPR720 in rats is proceeding uneventfully. These studies are meant to support longer-term treatment with SPR720 beyond the 28 days currently supported by IND-enabling toxicology studies. Spero is in discussion with FDA to evaluate the findings and determine the further development pathway for the SPR720 clinical program. No serious adverse events have been observed in any human study participants.

“At Spero, patient safety is of primary importance and we are committed to working with FDA to evaluate findings from our ongoing primate toxicology study in an effort to determine whether these findings are drug-related and what impact, if any, the study may have on the further evaluation of SPR720 in the Phase 2a clinical trial,” said Ankit Mahadevia, MD. “Prior, extensive clinical and non-clinical evaluation of SPR720 supports our belief that SPR720, if approved, has the potential to offer a new safe and well-tolerated treatment option for patients suffering from NTM-PD.”

Spero initiated the Phase 2a clinical trial (SPR720-201) in December 2020. The trial is designed as a multi-center, partially-blinded, placebo-controlled, proof-of-concept clinical trial of SPR720 with target enrollment of approximately 90 treatment-inexperienced study participants with NTM-PD due to Mycobacterium avium complex (MAC). Patients enrolled in the trial are randomized to receive either 500 mg or 1,000 mg of oral SPR720 once daily, placebo, or standard-of-care (SOC), consisting of a macrolide and ethambutol, plus the option of adding a rifamycin.

The safety, tolerability and PK of orally administered SPR720 was previously evaluated in a Phase 1 clinical trial (SPR720-101) that was completed in December 2019, with clinical data presented at Infectious Disease Society of America (IDSA) IDWeek™ 2020 Conference in October 2020. In the Phase 1 clinical trial, SPR720 was given to study participants as single oral doses ranging from 100 mg to 2,000 mg and as repeat total daily doses ranging from 500 mg to 1,500 mg for up to 7 to 14 days. Across seven SAD and five MAD cohorts, a total of 96 healthy volunteers (including a cohort of healthy elderly (age ≥ 65 years) volunteers) were randomized to receive SPR720 or placebo. Data indicated that SPR720 was generally well-tolerated at doses up to 1,000 mg daily over the maximum studied duration of 14 days. There were no serious adverse events reported in the Phase 1 clinical trial and all participants completed the trial.

SPR720 has also been assessed in a series of completed non-clinical GLP toxicology and safety pharmacology studies, including IND-enabling 28- and 31-day GLP studies in non-human primates and rats, respectively. There were no remarkable findings observed in these completed studies and the results supported the advancement of SPR720 into the now complete Phase 1 trial and the current Phase 2a clinical trial that is being conducted under the in-effect IND pursuant to institutional review board oversight.

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