No dose-limiting toxicities were observed in the first three patients treated with PAS-004 at the initial dose in Pasithea’s Phase 1/1b NF1 study, prompting an external safety committee to clear escalation to the 8 mg tablet dose. The sponsor reports the first three patients in Cohort 2 are already enrolled, with initial interim data from the first two cohorts targeted for Q1 2026.
The core development is a textbook 3+3 dose-escalation decision in an adult NF1 population with plexiform neurofibromas, advancing a macrocyclic MEK inhibitor that Pasithea is simultaneously testing in advanced cancers. The NF1 trial (NCT06961565) runs in two parts across Australia, South Korea, and the U.S. Part A will enroll up to 24 participants across four dose levels (4, 8, 12, 18 mg) to establish a recommended Part B dose. Part B will then randomize roughly 24 participants to the selected dose and a lower dose for up to six 28-day cycles, to define the RP2D. Beyond safety, the study is set to characterize PK/PD and generate early signals on PN volume, cutaneous neurofibroma burden, pain, function, and quality of life, with exploratory tissue and molecular analyses in CNs.
Strategically, the move positions Pasithea to compete in an increasingly segmented MEK landscape by targeting adult NF1, a population with fewer labeled options than pediatrics and a need for chronic, tolerable regimens. A macrocyclic scaffold could be a differentiator if it translates to steadier exposure or improved tolerability under prolonged dosing, but those attributes remain to be proven. The inclusion of cutaneous endpoints and symptom measures suggests the company is angling for a broader clinical value proposition than volumetric PN shrinkage alone. The Q1 2026 timing for initial interim data—despite rapid enrollment into Cohort 2—signals a measured escalation pace and the need to accrue sufficient exposure and imaging timepoints before calling a signal.
For sites, the protocol brings a familiar MEK monitoring burden but adds operational complexity with volumetric MRI, dermatologic assessments, and layered PROs. That mix typically requires a coordinated imaging core lab, standardized acquisition protocols, and robust ePRO processes—logistics that will pressure smaller centers unless the sponsor and CRO provide strong enablement. Cross-border site distribution may help recruitment in a dispersed adult NF1 population, but it also raises harmonization needs for imaging and symptom scales across regions. Vendors focused on central imaging, digital symptom capture, and remote safety surveillance stand to benefit if the study scales on schedule.
Sponsors and regulators will be watching whether PAS-004 can maintain a clean safety profile as doses escalate to 12 mg and 18 mg and whether PD readouts tie to early volumetric changes. With pediatric NF1 already established as a MEK-sensitive setting and multiple adult programs moving in parallel, differentiation will likely hinge on chronic tolerability and consistency of symptom relief rather than headline response rates alone. Alignment on adult endpoints—particularly the weight regulators’ place on volumetric reduction versus pain and function—remains a live question that could shape Part B refinement and any subsequent pivotal strategy.
Near term, the key catalysts are the absence of DLTs at higher doses, selection of the Part B dose, and the character of the first PN and CN signals in early 2026. Any signal that sustained dosing is feasible with manageable class-associated toxicities would justify the adult NF1 bet and inform the design of a registrational path. Conversely, tolerability setbacks or inconclusive PD-efficacy linkage would push PAS-004 back into a crowded MEK field competing largely on class sameness rather than differentiation.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
