Pasithea Therapeutics disclosed that its next‑generation macrocyclic MEK inhibitor, PAS‑004, achieved dose‑proportional tablet exposure in a Phase 1/1b study of adults with neurofibromatosis type 1. The 4 mg and 8 mg tablets produced roughly three‑fold higher area‑under‑the‑curve and peak concentrations than the 22 mg capsule, while keeping the peak‑to‑trough ratio below two at steady state. The data also show reduced inter‑patient variability and a similar time to maximum concentration, indicating a more predictable and potentially more convenient dosing schedule.
The improved tablet pharmacokinetics suggest that lower tablet doses could reach therapeutic exposure, which may enhance patient adherence and reduce manufacturing complexity. The linear, dose‑proportional response and flat concentration–time curve support once‑daily dosing, a key differentiator in the MEK inhibitor market where many agents require twice‑daily or more frequent administration.
In a separate Phase 1 study of PAS‑004 in patients with MAPK‑driven advanced solid tumors, the company reported a 71.4 % disease‑control rate in the seven BRAF‑mutated patients evaluated, including one melanoma patient who achieved a partial response that has persisted for more than 11 months. All treatment‑related adverse events were Grade 1 or 2, with no ocular or cardiovascular toxicity and only mild rash, nausea, diarrhea, or vomiting. Pharmacokinetic analysis confirmed dose‑proportional exposure and a flat curve, reinforcing sustained pathway inhibition.
CEO Dr. Tiago Reis Marques said the data “demonstrate the safety, PK and anti‑tumor activity of PAS‑004 and support its potential to be a best‑in‑class MEK inhibitor for NF1‑PN.” He added that the profile aligns with the needs of NF1 patients. Dr. Rebecca Brown, a UAB expert, noted that the drug’s tolerability “has allowed no dose interruptions or modifications.” Despite these positives, investors expressed disappointment because the efficacy signals were modest, with only one confirmed partial response among a small cohort.
The market reaction reflected the gap between the company’s optimistic framing and investor expectations for stronger early efficacy. Investors were looking for more robust clinical activity to justify the drug’s potential, and the limited disease‑control rate and single partial response fell short of those expectations. In the competitive MEK inhibitor landscape, where combination therapies such as Tafinlar + Mekinist dominate, PAS‑004’s promise hinges on demonstrating clear clinical advantage in larger, later‑stage trials. The NF1 market remains underserved, and a differentiated, well‑tolerated MEK inhibitor could capture significant unmet need if efficacy is proven.
Overall, the tablet PK data strengthen PAS‑004’s development profile by enabling lower, more convenient dosing, while the interim Phase 1 results provide early evidence of safety and modest activity. The company will need to confirm these findings in larger studies to satisfy investors and secure its position in the competitive MEK inhibitor field.
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