Phenylalanine
| Evidence Level: L5 | Predicted Indications: 2 |
Table of Contents
Phenylalanine: From Dietary Amino Acid to Predicted Use in Sclerosing Cholangitis
One-Sentence Summary
Phenylalanine is an essential amino acid with no authorised UK marketing licence and no established therapeutic indication. The TxGNN model predicts a possible link to Sclerosing Cholangitis (score 99.43%), but this is a model-level prediction only — there are no supporting clinical trials, and the limited literature is largely unrelated or, in one case, points to the opposite (pathogenic) direction.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Not established — phenylalanine is an essential dietary amino acid with no recorded therapeutic indication |
| Predicted New Indication | Sclerosing Cholangitis |
| TxGNN Prediction Score | 99.43% |
| Evidence Level | L5 |
| UK Market Status | Not Marketed |
| Number of Marketing Authorisations | 0 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Detailed mechanism of action data for phenylalanine as a therapeutic agent is not available. As an essential dietary amino acid, its known biological role is as a protein building block and metabolic precursor to tyrosine and the catecholamines — it is not currently used as a treatment for any disease, and holds no UK marketing authorisation.
The predicted association with sclerosing cholangitis does not appear to be backed by a coherent mechanistic story. Of the four literature items retrieved, only one meaningfully engages with a related hepatobiliary condition — a cohort study on plasma tyrosine (not phenylalanine itself) and fatigue in primary biliary cirrhosis/primary sclerosing cholangitis. More importantly, one preclinical study (PMID 8000512) found that FMLP, a synthetic peptide containing phenylalanine, actually induces small duct cholangitis in rats — a pathogenic, not therapeutic, direction. This finding should be treated as a caution flag rather than supportive evidence, and it directly undermines rather than supports the repurposing hypothesis.
Given this pattern, the internal evidence review correctly classifies this candidate as Evidence Level L5 (model prediction only, no genuine supporting studies) with a Hold recommendation. A second predicted indication (congenital prothrombin deficiency, score 99.26%) is even weaker: its only associated trial concerns Nitisinone — a different drug with an opposing mechanism — and the trial itself was withdrawn with zero enrolment. Neither candidate currently offers a credible mechanistic or clinical basis for repurposing.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 15790420 | 2005 | Cohort | BMC Gastroenterology | Examined plasma tyrosine (not phenylalanine) and fatigue in primary biliary cirrhosis and primary sclerosing cholangitis patients |
| 32025163 | 2020 | Cohort/Metabolomics | Journal of Clinical and Experimental Hepatology | Serum metabolomic profiling in cholangiocarcinoma vs benign hepatobiliary disease; not specific to phenylalanine or a treatment context |
| 8000512 | 1994 | Animal study | Journal of Gastroenterology | Caution flag: FMLP (a phenylalanine-containing peptide) induced small duct cholangitis in rats — a pathogenic, not therapeutic, effect |
| 2103382 | 1990 | Methodology | Journal of Gastroenterology and Hepatology | Radioimmunoassay methodology paper on enterohepatic circulation of bacterial chemotactic peptides; no treatment relevance |
Safety Considerations
Please refer to the SmPC and BNF for safety information. Report suspected adverse reactions via the Yellow Card Scheme.
(Note: label warnings, contraindications and DDI data for this candidate are currently a Blocking data gap — see Next Steps.)
Conclusion and Next Steps
Decision: Hold
Rationale: There are no clinical trials supporting this indication, and the literature evidence is either unrelated or — in one animal study — indicates the opposite (pathogenic) mechanistic direction. Combined with the absence of a UK marketing authorisation and a Blocking data gap on product label warnings/contraindications, this candidate does not currently meet the threshold to advance past initial screening (S0).
To proceed, the following is needed:
- TFDA/MHRA product label warnings and contraindications (Blocking gap — required before any safety pre-screen)
- DrugBank-sourced mechanism of action data for phenylalanine
- Independent assessment of PMID 8000512 to confirm whether it represents a genuine contraindication signal
- Completion of pending
similarity_to_originaland route-compatibility assessments - Re-evaluation should stronger mechanistic or clinical evidence emerge; the second candidate (congenital prothrombin deficiency) can be deprioritised, as its sole associated trial concerns a mismatched drug (Nitisinone) that was withdrawn with zero enrolment
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.