The structural basis for the selectivity of sulfonamide-based inhibitors of carbonic anhydrase isoforms IX and XII: A comprehensive review of the crystallographic data
Bibliographic record
Abstract
Hypoxia in solid tumours induces carbonic anhydrases (CAs) upregulation, notably CA IX and CA XII, to sustain pH homeostasis. While sulfonamide-based zinc binders show high affinity for these targets, achieving the required selectivity versus the ubiquitous CA II remains challenging. Fortunately, the efforts of the community in obtaining experimental structures of ligand-protein complexes have now generated sufficient samples to rationalize isoform preferences. Herein, we provide our detailed structure-annotated meta-analysis of sulfonamide binding across CA II, CA IX, and CA XII that standardizes residue numbering and interaction taxonomy. We examine 130 X-ray cocrystal structures, CA II (47), CA IX (55), and CA XII (28), to quantify Zn–sulfonamide geometry, entrance-zone contacts (Arg60, Thr199/Thr200, His64 π-cation), conserved water mediation, and occupancy/orientation within the 130s subpocket (residues 131/132/135) that provide the best opportunities for delivering selectivity. From these data, we extract concrete, structure-derived design rules: (i) lowering sulfonamide pKa boosts affinity across isoforms but does not confer selectivity; (ii) directing steric/hydrophobic bulk into the 130s subpocket exploits Phe131/Gly132/Val135 (CA II) versus Val131/Asp132/Leu135 (CA IX) versus Ala131/Ser132/Ser135 (CA XII) differences; (iii) favourable entrance-zone interactions, e.g., salt bridging to Arg60 (IX), halogen bonding to Thr199, and occasional His64 π-cation, enhances IX/XII bias; and (iv) compact, highly polar heads without tailored tails tend to default to preferring CA II. This critical synthesis consolidates the dispersed structural evidence into an isoform-resolved map of selectivity-enabling interactions. This provides public access to a very useful tool for CA IX/XII-selective inhibitor design.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".