On April 22, 2026 SEED Therapeutics, Inc. ("SEED"), a clinical-stage biotechnology company pioneering rationally designed molecular glue degraders, reported new data demonstrating potent anticancer activity of its RBM39 degrader program in neuroblastoma, a pediatric cancer with high unmet medical need. SEED’s scientific work also identified potential biomarkers predictive of anticancer response that will be further examined in the clinic, with Phase 1 dose escalation projected to be completed by Q1 2027. The findings are being presented at the 2026 Annual Meeting of the American Association for Cancer Research (AACR) (Free AACR Whitepaper), which convenes more than 22,000 scientists, clinicians, and investors this week in San Diego.
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ST-01156, SEED’s clinical-stage RBM39 molecular glue degrader, is currently being evaluated in a Phase 1 dose escalation study (NCT07197554) at six leading U.S. oncology centers.
Highlights At A Glance
Tumor eradication in a rigorous in vivo model: ST-01156 achieved complete tumor regression in neuroblastoma model using a differentiated dosing regimen — a demanding efficacy benchmark in solid tumor oncology.
Active Phase 1 clinical trial: Dose escalation is underway (NCT07197554) at six leading U.S. oncology centers, with clinical sites in additional geographies in preparation.
Biomarker strategy: MYC overexpression (sensitivity) and CDKN2A/B deletion (resistance) were identified as part of SEED’s biomarker program, potentially enabling precision patient enrollment as the trial advances.
Rare Pediatric and Orphan disease opportunity: Neuroblastoma is a high-unmet-need rare pediatric cancer representing a Rare Pediatric Disease and Orphan Disease designation-eligible indication, with potential for expedited regulatory pathways including Priority Review Voucher eligibility.
Scientific Rationale: Why RBM39 Matters
RBM39 is an RNA-binding protein that governs pre-mRNA splicing — a process cancer cells exploit to fuel uncontrolled growth, evade cell death, and repair DNA damage. By degrading RBM39 entirely, rather than merely inhibiting it, SEED’s approach disrupts multiple oncogenic pathways simultaneously: cell cycle progression, metabolic reprogramming, DNA damage response, and programmed cell death (apoptosis — the process by which damaged or cancerous cells are eliminated by the body). This breadth of effect is a key differentiator from conventional targeted therapies.
Molecular glue degraders achieve this by redirecting the cell’s own quality-control machinery — the ubiquitin-proteasome system — to tag and destroy the target protein. SEED’s proprietary RITE3 platform was designed from inception to identify, validate, and optimize molecular glues with a defined therapeutic window, bringing rational drug design to protein targets previously considered undruggable.
Key Data Highlights — AACR (Free AACR Whitepaper) 2026 Poster #5785
Tumor eradication in an in vivo model: ST-01156 achieved complete tumor regression in a neuroblastoma xenograft model — meaning tumors disappeared entirely — using the same dosing schedule now deployed in the Phase 1 trial. This direct correspondence between preclinical and clinical dosing strengthens confidence in the translational path forward.
Consistent potency across a biologically diverse disease: ST-01156 demonstrated potent anticancer activity across ten neuroblastoma models — six established cell lines and four patient-derived models — with IC50 values (the concentration required to kill half of cancer cells) in the low-to-sub-micromolar range. Neuroblastoma is genetically heterogeneous; this breadth of coverage matters.
A clear mechanism of action: Treatment with ST-01156 induced DNA damage, switched on the tumor-suppressing p53/p21 pathway, and reduced the levels of known cancer-driving proteins cMYC and EZH2 — confirming a coherent, multi-pronged path to programmed cancer cell death (apoptosis).
Biomarker roadmap for precision enrollment: SEED’s translational research identified MYC overexpression as a marker of sensitivity to ST-01156, and CDKN2A/B deletion as a marker of resistance. These biomarkers — identifiable through standard tumor profiling — may provide a practical framework for selecting patients most likely to benefit as the Phase 1 trial progresses toward expansion cohorts.
"ST-01156’s advancement into clinical testing in 2026 marks a pivotal milestone for SEED and for patients with RBM39 dependent cancers, including neuroblastoma — a pediatric cancer with very limited effective treatment options. The identification of MYC and CDKN2A/B status as potential biomarkers is the product of SEED’s focus on identifying the patients who will significantly benefit from ST-01156."
— James Tonra, PhD, President & Chief Scientific Officer, SEED Therapeutics
"The RBM39 data we are presenting at AACR (Free AACR Whitepaper) 2026 reflect what SEED’s RITE3 platform was designed to do — not just degrade a difficult target, but understand which patients are most likely to benefit. Seeing ST-01156 achieve complete tumor regression in a neuroblastoma model, at the same dosing schedule now in the clinic, is deeply gratifying and scientifically meaningful. Our focus at SEED is on ensuring that the molecular insight behind this program translates into real outcomes for patients with very few options."
— Lan Huang, PhD, Co-Founder, SEED Therapeutics
Clinical Development Status
ST-01156 is being evaluated in an ongoing Phase 1 dose escalation study (NCT07197554) designed to establish safety, pharmacokinetics, and target engagement. The study enrolls patients enriched for cancer types with demonstrated RBM39 dependency in preclinical research. The trial is currently active at six leading U.S. oncology centers, with additional clinical sites in preparation. Phase 1 dose escalation is projected to be completed by Q1 2027. The dosing schedule employed is consistent with that used in IND-enabling studies and in the in vivo efficacy program reported at AACR (Free AACR Whitepaper) 2026 — providing a robust translational foundation.
AACR 2026 Poster Presentation Details
Title: RBM39 Degrader Anticancer Activity Against Neuroblastoma; MYC and CDKN2A/B as Potential Response Biomarkers
Poster Number: 5785
Session: Proximity-Induced Drug Discovery 2 (Experimental and Molecular Therapeutics)
Authors: James Finn, Imad Salhab, Haihong Jin, Fei Liu, Dong Liu, Yunkai Zhang, Xing Liu, James Tonra, Lan Huang, Dan Lu
(Press release, Seed Therapeutics, APR 22, 2026, View Source [SID1234664710])