Talabostat

Summary

Talabostat (also known as PT‑100, Val‑boroPro) is an investigational oral small‑molecule inhibitor of dipeptidyl peptidases (DPP4, DPP8/9). It is being explored primarily as an immunomodulatory agent to boost anti‑cancer immunity, often in combination with checkpoint‑inhibitor antibodies such as pembrolizumab.

Mechanism of Action

Talabostat binds the active sites of DPP4 and the intracellular DPP8/9 enzymes, blocking their proteolytic activity. In immune cells this inhibition triggers activation of the CARD8 and NLRP1 inflammasomes, leading to caspase‑1 cleavage, pyroptotic cell death and release of IL‑1β and IL‑18. The resulting cytokine surge can prime innate and adaptive immune responses, providing a rationale for synergy with PD‑1 blockade.

What the Research Shows

Pre‑clinical work showed that talabostat activates CARD8 in AML cells and NLRP1 in keratinocytes, causing caspase‑1‑dependent pyroptosis. Clinical data are limited to early‑phase trials. A 2025 phase‑2 basket study combining talabostat with pembrolizumab in 31 patients with diverse solid tumours reported a disease‑control rate of 47% and one unconfirmed partial response, with median progression‑free survival of 2.7 months. In a 2026 phase‑2 trial in small‑cell neuroendocrine prostate cancer, the composite response rate was 20% and overall response 13%, with median overall survival of 13.7 months. Earlier phase‑II studies of talabostat plus cisplatin in melanoma (12.5% response among evaluable patients) and plus docetaxel in NSCLC (two partial responses, one complete response) did not show clear efficacy beyond historical expectations. Across studies, adverse events were predictable, most commonly hypotension, fatigue, and gastrointestinal symptoms.

Reported Benefits

Talabostat can stimulate inflammasome pathways, potentially enhancing anti‑tumour immunity and improving disease control when paired with checkpoint inhibitors. Early trials have documented stable disease in nearly half of treated patients and occasional partial or complete responses, especially in select tumour types such as small‑cell neuroendocrine prostate cancer. Its oral formulation offers convenient dosing compared with intravenous agents.

Limitations of the Evidence

Evidence of clinical benefit remains modest and derived from small, non‑randomised phase‑II cohorts. Response rates are low, and disease control often reflects stable disease rather than tumour regression. No regulatory approval exists, and the optimal dosing schedule, patient selection criteria, and contribution of talabostat versus the checkpoint inhibitor remain uncertain. Larger, controlled studies are needed to confirm efficacy.

Safety Considerations

Talabostat is generally well‑tolerated, but hypotension is the most frequent serious adverse event, occurring in >20% of patients and leading to a grade‑4 dose‑limiting event in one trial. Other common toxicities include fatigue, diarrhea, rash, nausea, dizziness, pruritus, and thrombocytopenia. Most events are manageable with dose adjustments or supportive care, but clinicians should monitor blood pressure and electrolytes closely.

How It Is Administered

The compound is administered orally, often twice daily, with dosing regimens ranging from 0.2–0.3 mg BID in combination studies to 300–400 µg BID when paired with chemotherapy. In combination trials, pembrolizumab is given intravenously every three weeks. Formulations are typically tablets or capsules designed for systemic absorption.

Routes of Administration

Goals & Uses

• Solid tumor oncologyOncologyModerate
• Colorectal cancer treatmentOncologyModerate
• Combination immunotherapy enhancementOncologyLow
• ImmunomodulationImmunologyModerate
• Metastatic melanoma treatmentOncologyModerate
• NLRP1 inflammasome activation researchImmunology/researchHigh
• Anti-tumor immunostimulationOncologyModerate
• Inflammatory bowel diseaseGastroenterologyLow
• Hematologic malignancy treatmentOncologyLow

Contraindications

• Uncontrolled infectionInfectious DiseaseModerate
• Severe hepatic impairmentOrganHighLiver function concerns
• Known hypersensitivity to boronic‑acid compoundsAllergyModerate
• Severe inflammatory syndromeImmunologicHigh
• Active autoimmune diseaseAutoimmunityHigh

Adverse Effects

• Cytokine release / flu-like symptomsImmunologicCommon
• ThrombocytopeniaHematologicUncommonLow platelet count
• Edema (peripheral/facial)Fluid/electrolyteCommon
• AnemiaHematologicUncommonLow red blood cell count or hemoglobin
• HypotensionCardiovascularCommonLow blood pressure
• NauseaGastrointestinalCommonFeeling of sickness or urge to vomit
• FatigueGeneralCommonLow energy or tiredness
• VomitingGastrointestinalCommonForceful expulsion of stomach contents
• Elevated liver enzymesHepaticUncommonIncrease in AST/ALT or other hepatic markers

Drug Interactions

• Other DPP‑IV inhibitorsHigh
• Immunosuppressants (e.g., corticosteroids)Moderate
• Antihypertensive agentsModerate
• Other DPP4 inhibitors (gliptins)Moderate
• Insulin or sulfonylureasModerate

Population Constraints

• Pediatric patientsAgeRelative
• Elderly patients (≥75 years)AgeRelative
• Pregnant or lactating womenReproductiveAbsolute
• Patients with severe hepatic impairmentHepaticRelative
• Pregnant womenReproductiveAbsolute

Regulatory Status

• European UnionInvestigationalNo marketing authorization.
• United StatesInvestigationalNever submitted for NDA; discontinued development.
• United KingdomInvestigationalNo approval; only used in research.

Investigational agent; clinical development discontinued after phase II due to limited efficacy and safety concerns.

Evidence & Sources

• The NLRP1 Inflammasome in Human Skin and Beyond
  Journal ArticleModerateFenini G, et al.2020-01-01T00:00:00.000000Z
• A phase 2 basket study of talabostat, a small-molecule inhibitor of dipeptidyl peptidases, administered in combination with pembrolizumab in patients with advanced solid cancers
  Journal ArticleModerateAhmed J, et al.2025-01-01T00:00:00.000000Z
• Phase 2 study of talabostat, a small molecule inhibitor of dipeptidyl peptidases (DPP), administered in combination with pembrolizumab in patients with small cell neuroendocrine prostate cancer
  Journal ArticleModerateAggarwal R, et al.2026-01-01T00:00:00.000000Z
• Phase II assessment of talabostat and cisplatin in second-line stage IV melanoma
  Journal ArticleModerateEager RM, et al.2009-01-01T00:00:00.000000Z
• Phase II trial of talabostat and docetaxel in advanced non-small cell lung cancer
  Journal ArticleModerateEager RM, et al.2009-01-01T00:00:00.000000Z

Frequently Asked Questions