On May 28, 2025 Strand Therapeutics, a leader in next-generation mRNA-based therapeutics, reported exciting preliminary Phase 1 clinical data for its lead investigational candidate, STX-001, in patients with advanced solid tumors (Press release, Strand Therapeutics, MAY 28, 2025, View Source [SID1234653470]). The study marks the first clinical evidence of Strand’s proprietary programmable mRNA technology platform and represents a major milestone in the company’s mission to bring next-generation mRNA therapies to patients with cancer.
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In the ongoing first-in-human Phase 1, open-label, dose-escalation clinical trial, STX-001 demonstrated a favorable safety profile and encouraging signs of anti-tumor activity as a monotherapy in patients with immune checkpoint inhibitor-refractory solid tumors, including melanoma and other solid tumor indications. As of the April 3rd, 2025 data cutoff, the trial had enrolled 22 patients across multiple sites in the United States and Australia. All patients were treated with STX-001 as a monotherapy (without combination with immune checkpoint inhibitors, etc.) with injections to surface accessible lesions.
The data will be presented at The 2025 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting in Chicago on June 1 by Sarina Piha-Paul, M.D., professor of Investigational Cancer Therapeutics at The University of Texas MD Anderson Cancer Center.
"This investigational therapy has the potential to address an important unmet need in patients with checkpoint inhibitor-refractory advanced cancers," said Dr. Piha-Paul. "We’re observing systemic immune activation and antitumor responses, including in non-injected lesions, across multiple tumor types, which is encouraging and supports continued evaluation."
Key highlights from the Phase 1 trial include:
Preliminary Clinical Activity: Multiple RECIST responses were observed, including a confirmed complete response and multiple partial responses. Furthermore, there were multiple cases of prolonged disease stabilization.
Safety and Tolerability: STX-001 was well-tolerated up to 300 µg. Treatment-related adverse events were consistent with STX-001’s intended mechanism of action of immune activation.
Pharmacodynamic Activity: Biomarker analysis confirmed dose-dependent increase in plasma IL-12 and IFN-γ, as well as infiltration of immune cells within the tumor microenvironment.
"This is a transformative moment for Strand and for the field of synthetic mRNA therapeutics," said Jake Becraft, PhD, CEO and Co-founder of Strand Therapeutics. "The Phase 1 data for STX-001 provide early clinical validation of our platform’s ability to deliver programmable, tumor-localized immunotherapy safely and effectively. Our mRNA medicines as a therapeutic modality offer the potential capability to broaden pathways to treatment for patients while seamlessly integrating into the existing healthcare ecosystem."
STX-001 encodes IL-12, an immunomodulatory protein, which the company has designed such that it can reprogram the tumor microenvironment and stimulate a systemic anti-tumor immune response. Unlike traditional mRNA therapies, Strand’s approach uses self-replicating mRNA, ensuring localized and durable therapeutic activity.
The company is currently conducting dose expansion in the Phase 1 trial. Upon completion, the company plans to transition into a Phase 2 trial of STX-001 as a monotherapy. The company also plans to initiate dose escalation of STX-001 in combination with checkpoint inhibitors and expand into additional solid tumor indications. In addition, Strand is advancing a broader pipeline powered by the company’s first-in-class cell-type specific mRNA engineering platform, including advancing STX-003, an intravenously administered version of STX-001, to patients in 2026.
ASCO Poster Presentation Information:
Abstract Title: Phase I dose escalation trial of STX-001, an LNP-encapsulated self-replicating mRNA expressing IL-12, in patients (pts) with advanced solid tumors.
Session Type: Poster
Date and Time: June 1, 9:00 AM-12:00 PM CDT
Abstract Number: 9556
Location: Hall A
Full abstract is available on the ASCO (Free ASCO Whitepaper) Annual Meeting Website.
The study, an open-label, dose escalation trial, evaluated the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary antitumor activity of STX-001 in patients with advanced solid tumors. STX-001 was well-tolerated up to 300 µg, with dose-dependent and manageable treatment-related adverse events. Promising early clinical activity was observed, including multiple RECIST responses and durable disease stabilization. Findings support the further development of STX-001 as a monotherapy and in combination with checkpoint inhibitors for the treatment of solid tumors.
Additional Commentary
Professor Georgina Long AO, BSc, PhD, MBBS, FRACP, FAHMS, AAHMS, FAA, Medical Director of Melanoma Institute Australia (MIA), and Chair of Melanoma Medical Oncology and Translational Research at MIA and Royal North Shore Hospital, The University of Sydney: "I am encouraged by this early data. While intratumoral therapies offer a promising approach by initiating immune activation at the injected tumor site, they have historically struggled to generate robust systemic responses. STX-001 may represent a meaningful step forward, with early clinical evidence showing cases of regression of non-injected lesions, a sign of systemic immune engagement."
Tasuku Kitada, PhD, Co-Founder, President, and Head of R&D at Strand Therapeutics: "Patients who are refractory to immune checkpoint inhibitors urgently need new treatment options. While IL-12 has long been recognized as a powerful immune stimulator, its clinical potential has been limited by toxicity, and to date, no IL-12–based therapies have been approved by the FDA. STX-001 is designed to overcome these challenges, delivering localized IL-12 expression to activate the tumor microenvironment and drive systemic immune responses, all while seeking to minimize toxicities. These early data suggest we may finally be able to realize the promise of IL-12 in cancer therapy."
About STX-001
STX-001 is an investigational multi-mechanistic, synthetic self-replicating mRNA technology that expresses an IL-12 cytokine for an extended period of time, directly injected into the tumor microenvironment in order to promote immune modulation and antitumor activity. The company received IND clearance from the U.S. Food and Drug Administration (FDA) in December 2023 to initiate a Phase 1/2 clinical trial for STX-001, and announced its first patient dosed just before the 2024 ASCO (Free ASCO Whitepaper) Annual Meeting. Additional study details can be found at clinicaltrials.gov, using identifier: NCT06249048.