The Generative Brain

Zinc tetracationic porphyrin anti-prion compound (Mario Negri)

This is a preclinical anti-prion compound from the Laboratory of Prion Neurobiology at the Istituto di Ricerche Farmacologiche Mario Negri IRCCS in Milan, published in 2023 as Zn(II)-BnPyP and called VA01 in the group's earlier grant reporting. It is a zinc tetracationic porphyrin, from a family of molecules first studied as light-activated agents in cancer and antibacterial chemistry, that acts on the normal cellular prion protein in two ways at once: binding a pocket in the folded C-terminal part destabilises it and blocks conversion to the disease form, and binding the flexible N-terminal tail sends the protein into the cell for lysosomal degradation, which cuts the substrate available for prion propagation. In cells and in organotypic brain slices it is potent and it blocked several prion strains, including variant and sporadic CJD seeds in cell-free amplification. The problem is delivery. Mice dosed into the abdomen had a brain to plasma ratio of 0.035, brain prion protein fell only about 20 percent after twelve weeks of dosing, and prion-infected mice showed no change in onset or survival. A CJD Foundation funded attempt to carry it into the brain inside brain-targeting nanoparticles kept the activity in the dish but failed in the animal, with the particles ending up in kidney, spleen and liver. Since the 2024 minireview no new experimental result on this compound has appeared in the literature index.

Key facts

  • The compound is a tetracationic porphyrin carrying zinc, named Zn(II)-BnPyP in the 2023 iScience paper by Masone and colleagues with Roberto Chiesa as last author, and named VA01 in the group's 2020 report to the CJD Foundation.
  • It came out of a series of porphyrins first studied as photosensitisers for cancer and bacterial infections; the comparators tested alongside it were Fe(III)-TMPyP, an earlier anti-prion porphyrin, plus Fe(III)-BnPyP, Cu(II)-BnPyP and Zn(II)-TMPyP.
  • The two-part mechanism is the point of the work: binding the C-terminal globular pocket destabilises the native fold and hinders conversion, while binding the N-terminal tail triggers clathrin-dependent endocytosis and lysosomal degradation of surface prion protein.
  • Reported potency: prion protein lowering with an EC50 of about 0.75 micromolar in primary hippocampal neurons, and inhibition of prion replication with an IC50 of 0.7 micromolar in infected ScN2a-22L cells against 1.5 micromolar for the earlier iron porphyrin.
  • In 22L-infected organotypic cerebellar slices, 5 micromolar cut protease-resistant prion protein by more than 85 percent, against about 50 percent for Fe(III)-TMPyP.
  • Strain breadth was tested in protein misfolding cyclic amplification with variant CJD, sporadic CJD of the VV2 subtype, classical scrapie and a bank vole prion generated de novo, and in cells and slices with the RML and 22L mouse strains; the authors argue a substrate-directed mechanism should be less prone to drug resistance.
  • The in vivo result is negative. At 10 mg/kg given intraperitoneally the brain to plasma ratio was 0.035, brain levels reached about 1.5 micromolar only after twelve weeks of dosing every second day, brain prion protein fell only about 20 percent, and in RML-infected mice median onset was 141.5 against 135 days post inoculation and terminal disease 153 against 152 days.
  • Direct delivery into the ventricles, by bolus or osmotic minipump, was unrewarding because the compound diffused poorly through brain tissue; the authors say the pharmacokinetics need improving and that a more drug-like molecule would be desirable.
  • The CJD Foundation funded the programme twice: in 2016 under the Patrick Yobs Memorial Research Grant for a new anti-prion compound that lowers prion protein and inhibits replication, and in 2019 under the Cheryl Molloy Memorial Research Grant for nanoparticle-mediated brain delivery with efficacy tests in prion-infected mice. No amounts are published.
  • The 2019 project loaded the compound into PLGA nanoparticles carrying the g7 glycopeptide. The loaded particles kept the activity in neuronal cultures and infected slices but crossed the blood brain barrier poorly and collected in kidney, spleen and liver; washing off surface-bound compound and attaching the targeting peptide after loading did not help, and the report concludes that the particles failed to deliver it to the brain.
  • The published study was supported by Telethon Italy award GGP15225, the Italian Ministry of Health award RF-2016-02362950, the CJD Foundation in the United States, the Italian prion patient association AIEnP, AIRC and the Spanish Ministry of Science; the funders are stated to have had no role in the work.
  • The work is a multi-centre Italian and Spanish collaboration: Mario Negri for the biology, the Biomolecular NMR Unit at IRCCS Ospedale San Raffaele and the University of Padua for structure, the University of Insubria in Varese for the chemistry, the Istituto Superiore di Sanita in Rome and CIC bioGUNE with CIBERINFEC in Spain for the prion amplification work, plus the ESRF in Grenoble and the University of Santiago de Compostela.
  • The chemistry side began by chance: an organic chemist at Insubria said in 2015 that he joined after a Mario Negri meeting where Chiesa showed porphyrins, and described a three-year Telethon project of about 400,000 euro to study the molecule's pharmacokinetics and pharmacodynamics, naming the blood brain barrier as the obstacle and the move from dish to animal as the costly step.
  • No new experimental result on the compound has been published since. The only later items are the October 2023 erratum on a duplicated figure panel, a 2024 minireview arguing for a new class of dual-mechanism compounds, and a 2026 cell-based tagging method paper that does not report porphyrin data.

Timeline

  1. 2015Interview describing the start of the Insubria chemistry collaboration and a three-year Telethon project of about 400,000 euro on the molecule.
  2. 2016CJD Foundation Patrick Yobs Memorial Research Grant for a new compound that lowers prion protein and inhibits replication.
  3. 2019CJD Foundation Cheryl Molloy Memorial Research Grant for nanoparticle brain delivery and mouse efficacy tests.
  4. 2020Final report to the CJD Foundation written, reporting that the nanoparticles kept activity in vitro but failed to reach the brain.
  5. 2023iScience paper published online describing the dual mechanism, the strain breadth and the negative mouse result.
  6. 2023Erratum published correcting a duplicated figure panel.
  7. 2023Final grant report posted on the CJD Foundation grantee page.
  8. 2024Minireview published online arguing for dual-mechanism compounds aimed at the cellular prion protein.
  9. 2026Cell-based prion protein tagging method published from the same laboratory, with no new porphyrin data.
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