Pasithea Therapeutics Corp. disclosed interim data from its first‑in‑human Phase 1 study of the macrocyclic MEK inhibitor PAS‑004, with a data cutoff of November 10, 2025. The study enrolled patients with MAPK‑driven advanced solid tumors and is the first clinical assessment of the drug’s safety, pharmacokinetics, and early anti‑tumor activity.
Among 21 efficacy‑evaluable patients, the overall disease‑control rate was 42.8%. In the BRAF‑mutated subset, 71.4% (5 of 7) achieved disease control. One patient experienced an unconfirmed partial response, with a 31.9% reduction in target lesions after more than 11 months of therapy, while a second patient maintained durable stable disease with only 1.6% shrinkage after six months.
All treatment‑related adverse events were Grade 1 or 2, and no ocular or cardiovascular toxicity was observed. No dose‑limiting toxicities or treatment discontinuations occurred. Pharmacokinetic analysis showed dose‑proportional exposure, with an area under the curve exceeding 5,400 ng·h/mL at the 30 mg capsule dose (Cohort 6).
Pasithea is a micro‑cap, debt‑free biotechnology company with no revenue and negative earnings per share. The interim data reinforce the drug’s potential for neurofibromatosis type 1‑associated plexiform neurofibromas and other MAPK‑driven malignancies, positioning PAS‑004 as a next‑generation MEK inhibitor designed to avoid the ocular and cardiovascular toxicities seen with earlier agents.
Investors reacted negatively, citing the limited efficacy signals despite the favorable safety and pharmacokinetic profile. The market’s disappointment reflects the high bar for early‑stage oncology data and the expectation of stronger clinical signals in a competitive therapeutic area.
CEO Tiago Reis Marques emphasized that the safety, PK, and anti‑tumor activity support PAS‑004 as a best‑in‑class MEK inhibitor for NF1‑PN. He highlighted sustained pathway inhibition and high drug exposure as key drivers for future efficacy, while noting that the program will continue to advance in subsequent trials.
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