Palisade Bio (Nasdaq: PALI) has opened enrollment in a Phase Ib clinical trial evaluating PALI-2108, a first-in-class oral PDE4 inhibitor prodrug, in patients with fibrostenotic Crohn’s disease. The PALI-2108 first-in-human program began with a completed Phase Ia study in healthy volunteers and a parallel ulcerative colitis cohort; the fibrostenotic Crohn’s disease (FSCD) arm now extends the molecule into a patient population for which no drug has ever received regulatory approval.
FSCD — defined by progressive intestinal wall fibrosis, stricture formation, and obstructive symptoms — affects an estimated 30–50% of Crohn’s disease patients within two decades of diagnosis, and its management currently depends on repeated endoscopic balloon dilation or surgical resection, both of which carry recurrence rates exceeding 50%. The Palisade Bio PALI-2108 program is, to date, the only clinical-stage effort built around a gut-restricted PDE4 mechanism specifically designed to engage both the inflammatory and fibrotic axes of stricturing disease.
The FSCD cohort (NCT07428096) is an open-label, single-arm, Phase Ib exploratory study enrolling six adults aged 18–60 with ileal or ileocolonic fibrostenotic Crohn’s disease confirmed by intestinal ultrasound and endoscopy. Participants receive PALI-2108 orally once daily for 14 days in the fed state. Dosing follows a sentinel-based titration scheme: two initial subjects escalate from 5 mg to 20 mg, after which a Safety Review Committee evaluates tolerability before assigning subsequent patients to target doses of 25 mg or 30 mg, with protocol-specified titration and allowance for dose reduction. The primary endpoints are safety and tolerability, measured by incidence of adverse events, clinically significant laboratory abnormalities, ECG findings, and vital sign changes over the 14-day dosing period.
Scientific rationale
The biological logic of PALI-2108 rests on two premises. The first is that PDE4 inhibition is a validated anti-inflammatory mechanism: by blocking the hydrolysis of intracellular cyclic AMP, PDE4 inhibitors suppress production of TNF-α and other pro-inflammatory cytokines in immune cells. Apremilast (Amgen) and roflumilast (AstraZeneca), both systemic PDE4 inhibitors approved for non-GI indications, have demonstrated this pharmacology in clinical use. The second premise is that elevated cAMP also modulates profibrotic signaling in stromal cells — attenuating fibroblast and myofibroblast activation, reducing collagen synthesis, and interfering with TGF-β–driven remodeling. Preclinical data cited by the company show that PALI-0008, the active metabolite, selectively inhibits PDE4B and PDE4D without activity against nine other phosphodiesterase family members tested at 10 μM, and that it suppresses TNF-α in LPS-stimulated whole blood assays and reduces PDE4B mRNA expression in colon tissue in a dose-dependent manner in a DSS colitis mouse model.
The prodrug design addresses the central limitation that has prevented systemic PDE4 inhibitors from advancing as a PDE4 inhibitor for ulcerative colitis or Crohn’s disease: dose-limiting nausea, emesis, and CNS effects (headache, depression) driven by systemic PDE4D inhibition. PALI-2108 carries a D-glucuronic acid moiety that renders it pharmacologically inert until it reaches the terminal ileum and colon, where bacterial β-glucuronidase cleaves the conjugate and releases PALI-0008 locally. Company disclosures indicate that PALI-0008 remains detectable in colon tissue at concentrations near or above its IC₉₀ for at least 36 hours after dosing, while systemic exposure is minimized. Palisade Bio holds granted patents in Canada (CA 3,174,137) and Japan covering this gut-microbiota bioactivated PDE4 inhibitor prodrug platform. The Palisade Bio clinical trial program has also received a strategic equity investment from the Crohn’s & Colitis Foundation’s IBD Ventures program, a signal of disease-community endorsement for the FSCD indication.