FDA Grants Fast Track Designation to STX-0712 for R/R CMML

The FDA has granted fast track designation to STX-0712, an investigational cytotoxicity targeting chimera (CyTAC), for the treatment of relapsed/refractory (R/R) chronic myelomonocytic leukemia (CMML), a disease for which effective second-line options remain largely limited.¹

Fast track status is intended to facilitate the development and expedite the review of drugs that treat serious conditions and fulfill an unmet medical need; it also enables more frequent interactions between the sponsor and the FDA throughout the development and review process.

CMML is a clonal hematopoietic malignancy that shares features of both myelodysplastic syndromes and myeloproliferative neoplasms and is characterized by persistent monocytosis and a variable risk of transformation to acute myeloid leukemia (AML). The disease follows an aggressive clinical course in many patients, and therapeutic options are limited, particularly after hypomethylating agent failure.

"Fast [t]rack designation for STX-0712 reinforces the significant need for new treatment options for people living with CMML," said Philip Vickers, president and CEO of Solu Therapeutics, in a news release.¹ "By directly depleting CCR2-positive malignant monocytes and bone marrow blasts that drive disease in CMML, STX-0712 has the potential to offer a highly specific and targeted approach. We look forward to continuing to work closely with the FDA as we advance through clinical development and work to bring this potential therapy to patients as quickly as possible."

A phase 1, open-label, multicenter study (NCT06950034) evaluating STX-0712 as monotherapy in patients with R/R CMML and AML is currently enrolling. Initial clinical data from this study are planned for submission to a hematology conference later in 2026.

Mechanism of Action

STX-0712 is built on Solu Therapeutics' proprietary CyTAC platform, which combines the target-binding capability of small molecules with the cytotoxic potency of biologic agents. The agent targets CCR2, a G-protein coupled receptor expressed at high levels on malignant monocytes and bone marrow blasts that are considered key cellular drivers of CMML and AML. By selectively engaging CCR2-positive cells, STX-0712 is designed to eliminate these disease-driving populations while minimizing effects on nonmalignant cells.

Phase 1 Trial Design

The ongoing phase 1 study is structured as a dose-escalation and -expansion trial designed to evaluate the safety, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of STX-0712 in patients with advanced hematologic malignancies, including R/R CMML and R/R monocytic or monocytic-predominant AML.² The study initiated treatment of its first patient in March 2025.

The trial's dose-escalation component focuses on patients with CMML that is resistant or refractory, defined as disease that has not responded to at least 4 cycles of hypomethylating agents or has demonstrated progression. Given preliminary safety after at least 2 doses, investigators may open a second cohort to enroll patients with AML. For dose expansion, approximately 20 patients are expected to be enrolled in each cohort, during which patients will receive a single intravenous infusion of STX-0712 every 21 days.

Primary completion is estimated for the end of 2026, with full study completion expected in mid-2027.

REFERENCES

1. Solu Therapeutics Granted FDA Fast Track Designation for STX-0712 for Treatment of Chronic Myelomonocytic Leukemia. News release. Solu Therapeutics. May 27, 2026. Accessed May 28, 2026. https://tinyurl.com/3kr2u4x6

2. A Phase 1 Study of STX-0712 in Patients With Advanced Hematological Malignancies (CMML and AML). ClinicalTrials.gov. Updated February 9, 2026. Accessed May 28, 2026. https://clinicaltrials.gov/study/NCT06950034