Regular expressions were used to extract amino acid substitution patterns from assay descriptions, starting from 376,233 assay-protein target pairs in the ChEMBL 31 database with data suitable for regression modelling. Assay descriptions are extracted and curated in ChEMBL from the primary literature sources in a combined manual and semi-automated pipeline. Of note, genetic alterations other than amino acid substitutions were deemed out of the scope for the initial stage of this project. As exemplified in Figure (step 2) for the assaytarget pair CHEMBL832660 -P47900, these expression patterns could extract true substitutions, such as Y306F, but also incorrect patterns from the assay description, like P2Y. This first step yielded potential substitutions in 52,922 assay-target pairs. Therefore, exceptions were defined from other fields related to the assay and the target protein, in particular cell type, target preferred name, and target synonyms. This helped to refine the pipeline by rejecting extracted patterns such as P2Y that map to a part of the name of the assay target (purinoceptor P2Y1 in this case, UniProt accession P47900) and does not refer to a proline to tyrosine substitution. Indeed, 34,676 assay-target pair substitutions raised at least one exception flag. Of note, these exceptions are less of an issue in the original ChEMBL variant annotation pipeline, since some manual curation is performed. The substitution patterns that had not been flagged as exceptions were validated in the next step by checking the existence of the WT amino acid at the specified position in the target sequence. For example, in the case of the aforementioned Y306F substitution pattern, P2Y1 has indeed a tyrosine residue at position 306 of its sequence, hence this extracted substitution was validated. At this point, several additional exceptions were introduced by extracting patterns that were likely to be falsely validated, such as M1, as substitutions are unlikely to appear at the first position of the sequence, yet they would be given a false valid status as the starting codon AUG codes for methionine. This resulted in 8,455 assay-target pairs with WT sequencevalidated extracted substitutions.