No dose-limiting toxicities and no Grade ≥2 treatment-emergent adverse events through four dose levels; Plasma exposures exceed those predicted by nonclinical PK/PD modeling to be pharmacologically active
(MADRID, SPAIN) – Lamassu Biotech today announced initial safety and pharmacokinetic data from the ongoing first-in-human Phase 1/2a clinical trial (LB-SA53-101) of SA53, an oral MDM2 inhibitor, at the European Society for Medical Oncology (ESMO) Congress 2026.
Across four single-patient dose-escalation cohorts (0.054 to 0.44 mg/kg/day on a 3-day dosing schedule), SA53 has produced no dose-limiting toxicities (DLTs) and no Grade ≥2 treatment-emergent adverse events. MDM2 inhibition has shown antitumor activity by restoring the body’s natural p53 tumor-suppression pathway. Earlier MDM2 inhibitors have been limited by severe, dose-dependent hematologic toxicities, most notably thrombocytopenia. In this initial dose escalation, SA53 has reached plasma exposures predicted by nonclinical modeling to be pharmacologically active without dose-limiting toxicity.
The findings were presented in Madrid by Peter Anderson, MD, PhD, an investigator on the trial at Cleveland Clinic.
Study Highlights:
- No Dose-Limiting Toxicities: No DLTs, no Grade ≥2 treatment-emergent adverse events, and no serious adverse events (SAEs) through 0.44 mg/kg/day.
- Hematologic Profile: Platelet nadirs were Grade 1 or lower, and neutrophil counts remained within normal limits in all patients.
- Pharmacokinetics: Cmax increased approximately dose-proportionally across cohorts, and plasma exposures at the current dose level exceed those predicted by nonclinical PK/PD modeling to be pharmacologically active.
“Targeting the MDM2-p53 interaction has long held therapeutic promise, but drug development across this class has historically been limited by severe systemic toxicities,” said Greg Palmer, PhD, Co-founder and Chief Scientific Officer of Lamassu Biotech. “Our initial data shows that SA53 has reached exposures predicted to be pharmacologically active without dose-limiting toxicities. These early results support continued dose escalation toward defining the recommended Phase 2 dose.”
SA53 is an investigational oral small molecule designed to selectively inhibit MDM2, thereby reactivating the wild-type p53 tumor suppressor protein, often termed the “Guardian of the Genome.” Functional, wild-type p53 is preserved in roughly half of human cancers. An MDM2 inhibitor that avoids the historical serious class toxicities could therefore offer therapeutic utility across a broad cancer patient population.
The Phase 1 dose-escalation portion of the multicenter Phase 1/2a study remains ongoing. It aims to establish the maximum tolerated dose and recommended Phase 2 dose (RP2D) and to further characterize preliminary single-agent antitumor activity. Patient screening and enrollment are active.
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About Lamassu Biotech
Lamassu Biotech is a clinical-stage biopharmaceutical company focused on developing targeted small-molecule therapeutics for high-unmet-need oncology and metabolic indications. The company’s lead pipeline programs include SA53, a targeted MDM2 inhibitor in Phase 1/2a development for p53 wild-type cancers, and RABI-767, a lipase inhibitor advancing in clinical trials and animal health. Working in close collaboration with premier medical research institutions, Lamassu accelerates bedside delivery of precision medicines. For more information, visit LamassuBiotech.com.