Progress update #6 (final): Current conclusion and next phase

Previous post delivered a five-category universal peptide site and a prodrug redesign loop with 9 fully-gated Tier 1 indications.

Objective: Close the series: state verdicts against the pre-registered gates and define the experimental phase that turns computation into evidence.

Work completed: Synthesised both tracks against the original hypothesis.

Evidence (the final scorecard):

• The three original questions, answered as far as computation can.

(1) Synergy or additivity? Mechanistic synergy is supported for the top 26 targets by dual Loewe/Bliss agreement and is a property of the dual-essential context; the other 36 show moderate synergy so it is not general to cytotoxic combinations.

(2) Can one agent deliver both inhibitors while preserving selectivity? Yes by design, conditionally in pharmacokinetics: the prodrug carries both warheads with a 13.46 h activation half-life, and the synergy window holds with 96.3% probability in the tumour microenvironment. The macrophage-compartment ratio is the one identified quantitative failure mode with a defined fix (linker redesign for preferential SC2 release) if the fixed-ratio assay confirms it.

(3) Is there a conserved, universal, targetable site? Yes, twice over: the first-pass atlas found 18 cross-category human reference sites (top: residues 87–101, composite 0.552), and the blank-slate re-investigation (zero annotation, experimental structures, negative control) independently recovered one universal groove (Site Slot 3, 38 pockets, dual-method confirmed in all five categories).

• Final verdicts.

Track A: GO. Nine Tier 1 priority indications (M. tuberculosis, TNBC, ovarian, RCC, HCC, AML/MDS, Plasmodium, ER+ breast, colorectal), all with Tier A-experimental carboxypeptidase evidence, AUC/IC₅₀ ≥ 2.0 and dual-confirmed synergy. 49 Tier 2 proceed with redesign. Four targets are CHALLENGING (GBM, P. aeruginosa, A. baumannii, rabies), the last two are HALT-tier.

Track B: GO. One universal, non-catalytic, sensor-compatible (ODDD-dominant) site across bacteria, fungi, parasites, cancer and the viral-relevant host ISC complex.

The experimental programme (critical path):

Tests (1)–(8) form the first milestone; later tests proceed only if it passes.

(1) Synthesis: make lead prodrug; confirm identity, purity, batch consistency (NMR/HRMS, chromatography).

(2) Assay readiness: measure solubility and stability in storage/assay media; develop LC–MS/MS methods.

(3) Prodrug conversion: measure time-dependent release in assay media, plasma and trigger conditions (incl. glutathione); assess adduct stability.

(4) Direct target assays: measure RNR and SufS activity separately with prodrug and released species.

(5) Cellular dose–response and target engagement: MIC or IC₅₀, intracellular drug species, dNTP pools (RNR), Fe–S-enzyme activity (SufS).

(6) Selectivity counterscreens: microbial RNR/SufS vs human RNR/NFS1; cancer vs non-malignant cells; interference and cytotoxicity controls; transferrin-receptor competition if relevant.

(7) Tier 1 indication screen: dose–response in pathogen and cancer models.

(8) Genetic and combination confirmation: perturbation/rescue in the strongest models; checkerboard/isobologram combinations (TB, AML/HL-60, Plasmodium); repeat with an independent batch.

Full go: activity is reproducible, dose-dependent, supported by pathway engagement, with an indication-appropriate selectivity window.

Follow-on discovery and preclinical programme:

(9) Early DMPK/PK: permeability, plasma stability, protein binding, preliminary IV/PO PK; link exposure to potency.

(10) In-vivo proof-of-concept: efficacy, tolerability, exposure, biomarkers in selected models; HCC distribution and GBM focused-ultrasound/BBB delivery only if those advance and delivery is a proven barrier. P. aeruginosa efflux-pump-inhibitor combination and A. baumannii/Tier 2 models only after Tier 1 supports expansion.

(11) Preclinical candidate decision: select candidate and formulation on reproducible pharmacology, mechanism, selectivity, exposure and safety; then plan repeat-dose toxicology and IND-enabling studies.

What changed: The hypothesis has become a prioritised experimental programme.

Current interpretation: The programme sits at its designed boundary: computation has done all it honestly can (prioritization, gating, falsification by internal control, mapping each risk to an experiment). Any next failure is experimental, and cheap to find.

Next step:

Track A: synthesise prodrug and warheads; run first-milestone experiments.

Track B: one tier of independent higher-fidelity confirmation (finer grid with cavity merging, short MD on top candidates, biological-dimer modelling), then sensor-integrated peptide design against the universal site.

The series ends where the bench begins.