FDA Grants Fast Track Designation to OPN-6602 for Multiple Myeloma

The FDA has granted fast track designation to OPN-6602, an investigational oral dual inhibitor of EP300 and CREB-binding protein (CBP), for the treatment of relapsed or refractory multiple myeloma in patients who have received at least 4 prior lines of therapy, according to a news release.¹

The agent is currently being investigated in a phase 1b clinical trial (NCT06433947) as monotherapy and in combination with dexamethasone.²

About OPN-6602 and the Phase 1 Trial

OPN-6602 is an orally bioavailable small molecule designed to inhibit 2 closely related epigenetic coactivators, EP300 and CBP. Through EP300/CBP inhibition, OPN-6602 downregulates expression of IRF4 and MYC, 2 transcription factors that drive growth of multiple myeloma cells.^1,3

The first patient was dosed in the phase 1 trial in August 2024 at The START Center for Cancer Research in Grand Rapids, Michigan, with Andrew Sochacki, MD, serving as principal investigator.⁴ The trial is expected to enroll up to 130 patients with relapsed or refractory multiple myeloma at 11 sites across the US.²

The open-label phase 1 study consists of 3 cohorts: a dose-escalation monotherapy arm, a dose-escalation arm combining OPN-6602 with dexamethasone, and a dose-expansion cohort. In the combination arm, patients will receive OPN-6602 daily along with dexamethasone at 40 mg on days 1, 8, and 15 of each cycle. Primary outcomes include the number and type of dose-limiting toxicities, treatment-emergent adverse events, and clinical laboratory test abnormalities.

Enrollment criteria require patients to have relapsed or refractory disease after at least 3 prior therapies including proteasome inhibitor, immunomodulatory agents, and anti-CD38 antibodies, and meet specific organ function standards, with exclusion criteria encompassing certain myeloma subtypes, recent prior treatments including stem cell transplant, and conditions such as active infections or poorly controlled diabetes.

Opna Bio expects to complete the single-agent, dose-escalation phase of the trial in 2026, with further development of OPN-6602 in combination with other standard-of-care agents in multiple myeloma planned thereafter.

Preclinical Evidence Supporting Clinical Development

Preclinical data presented at the American Society of Hematology (ASH) meeting in December 2024 showed that in human-derived multiple myeloma models, OPN-6602 suppresses tumor growth while downregulating key myeloma-driving genes, with synergistic effects observed in combination with dexamethasone, pomalidomide (Pomalyst), and mezigdomide.³ In xenograft models, it achieved 71% tumor growth inhibition, which reached 100% when combined with dexamethasone, and all animal models had tumor regressions when given triplet combinations.

Unmet Need in Multiple Myeloma

Although newer therapies have substantially extended survival in multiple myeloma, most patients eventually experience disease relapse or become refractory to available treatments, leaving a persistent need for novel therapeutic approaches in the later-line setting.

Fast track designation is designed to facilitate and expedite the development and review of therapies that address serious conditions with unmet medical need. The status confers several benefits, including more frequent communications with the FDA, potential eligibility for accelerated approval and priority review, and the opportunity for rolling submission of a new drug application (NDA). OPN-6602 previously received orphan drug designation from the FDA in January 2025.

“Opna Bio has been a pioneer in the EP300/CBP inhibitor space, and OPN-6602 was selected for its potency, selectivity, and optimized pharmacokinetic properties,” Reinaldo Diaz, chief executive officer of Opna Bio, stated in the news release. “We are encouraged by the progress of the study to date and look forward to reporting emerging clinical data at an upcoming scientific congress.”¹

REFERENCES

1. Opna Bio announces fast track designation granted to OPN-6602 for the treatment of multiple myeloma. News release. Opna Bio. April 15, 2026. Accessed April 15, 2026. https://tinyurl.com/34tnfkkh

2. Study to Assess Safety and Tolerability of OPN-6602 in Subjects With Relapsed and/​or Refractory Multiple Myeloma. ClinicalTrials.gov. Updated April 13, 2026. Accessed April 15, 2026. https://clinicaltrials.gov/study/NCT06433947

3. Matusow B, Saghafinia S, Li PP, et al. OPN-6602, an orally bioavailable EP300/CBP bromodomain inhibitor, targets multiple myeloma through suppression of IRF4 and MYC. Blood. 2024;144(suppl 1):1908. doi: 10.1182/blood-2024-208181

4. Opna Bio doses first patient in phase 1 study in multiple myeloma with OPN-6602, an EP300/CBP bromodomain inhibitor. News release. Opna Bio. August 26, 2024. Accessed April 15, 2026. https://tinyurl.com/57r9p7kw