Plasma protein binding rate from structure
Predict the percentage of a drug bound to human plasma proteins, scored by mean absolute error in percentage points.
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| 1 | +# Plasma protein binding rate from structure | |
| 2 | + | |
| 3 | +Only the unbound fraction of a drug in blood can reach its target, so the percentage bound to plasma proteins decides how much of a dose does any work. This benchmark asks for that percentage from the structure. | |
| 4 | + | |
| 5 | +## Task | |
| 6 | + | |
| 7 | +Given a drug as a SMILES string, predict its human plasma protein binding rate as a percentage. The labels in the benchmark files run from $10.1$ to $100$, with a median of $94.7$. Submissions are scored by mean absolute error in percentage points, so lower is better. | |
| 8 | + | |
| 9 | +## Background | |
| 10 | + | |
| 11 | +The data come from a ChEMBL assay deposited by AstraZeneca as part of its 2016 release of in vitro DMPK measurements. Two features make it awkward in a useful way. The labels crowd against the ceiling — most drugs are highly bound — so the interesting range is a few percentage points wide where it matters most; and the assay was run across five species, of which TDC’s benchmark keeps the human subset. | |
| 12 | + | |
| 13 | +## Data and evaluation | |
| 14 | + | |
| 15 | +TDC ships the group as one archive (`admet_group`, Harvard Dataverse file 4426004), loaded with | |
| 16 | +`admet_group(path='data/')` from the `tdc.benchmark_group` module. The group’s `ppbr_az` folder holds 2,231 `train_val` and 559 `test` rows. These are measurements, not compounds: 1,797 distinct SMILES (the count TDC’s leaderboard shows), of which 691 appear more than once with different values, so repeated measurements of the same compound sit in the same split. | |
| 17 | + | |
| 18 | +The split is a scaffold split: TDC holds out a fixed 20% test set (here 559 of 2,790 rows in | |
| 19 | +the group’s files), and the remaining `train_val` part is split again per seed by | |
| 20 | +`group.get_train_valid_split(benchmark=name, split_type='default', seed=seed)` into 87.5% training | |
| 21 | +and 12.5% validation. The leaderboard asks for five independent runs with seeds 1, 2, 3, 4 and 5; | |
| 22 | +`group.evaluate_many` then reports the mean and the standard deviation of the per-seed test scores, | |
| 23 | +rounded to three decimals. The test set never changes, so only the training split moves with the seed. | |
| 24 | + | |
| 25 | +The metric is mean absolute error, $\mathrm{MAE} = \frac{1}{n}\sum_{i=1}^{n} |y_i - \hat{y}_i|$, computed by TDC’s `Evaluator(name='mae')` on the test set; lower is better. | |
| 26 | + | |
| 27 | +Official evaluation code: [`tdc/benchmark_group/base_group.py`](https://github.com/mims-harvard/TDC/blob/main/tdc/benchmark_group/base_group.py) | |
| 28 | +in the TDC repository (MIT licence), whose `evaluate` and `evaluate_many` methods are what the | |
| 29 | +leaderboard numbers come from. The dataset page gives the licence as "Not Specified. CC BY 4.0". | |
| 30 | + | |
| 31 | +## What is known | |
| 32 | + | |
| 33 | +- Best on the leaderboard: Gradient Boost, MAE $7.440 \pm 0.024$ percentage points (submitted by Rob Learsch); its write-up describes a scikit-learn gradient-boosting regressor over Morgan-fingerprint similarities and RDKit descriptors. | |
| 34 | +- Next: MapLight + GNN, $7.526 \pm 0.106$, then MapLight, $7.660 \pm 0.058$ (Notwell and Wood, 2023). | |
| 35 | +- Twenty entries are listed, from MAE $7.440$ to $12.848$. No method has got below $7$: with most labels above 90% bound, an error of seven percentage points is large relative to the range that matters, and the repeated measurements put a floor under what any model can reach. | |
| 36 | + | |
| 37 | +## What would count as progress | |
| 38 | + | |
| 39 | +- A mean MAE on TDC’s fixed test set that beats Gradient Boost (MAE 7.44), averaged over the official | |
| 40 | + seeds 1-5 and produced by `group.evaluate_many`, with the five per-seed numbers reported as well. | |
| 41 | +- The training and inference code, the environment and the fitted model, so that the five runs can be | |
| 42 | + repeated end to end from the `train_val` part alone. | |
| 43 | +- Evidence that the gain is larger than run-to-run noise: the gap between the top two entries here is | |
| 44 | + 0.09 percentage points, so a difference smaller than the reported standard deviation is not a result. | |
| 45 | +- Error on the highly bound compounds (above 95%) reported separately, since that is where a percentage point changes the free fraction most. | |
| 46 | + | |
| 47 | +## References | |
| 48 | + | |
| 49 | +1. AstraZeneca, "Experimental in vitro DMPK and physicochemical data on a set of publicly disclosed compounds" (2016), deposited in ChEMBL as AZ_dataset. [doi:10.6019/CHEMBL3301361](https://doi.org/10.6019/CHEMBL3301361) | |
| 50 | +2. Notwell, J. H. and Wood, M. W., "ADMET property prediction through combinations of molecular fingerprints", arXiv:2310.00174 (2023). [arxiv.org/abs/2310.00174](https://arxiv.org/abs/2310.00174) | |
| 51 | +3. Huang, K. et al., "Therapeutics Data Commons: Machine Learning Datasets and Tasks for Drug Discovery and Development", *NeurIPS Datasets and Benchmarks* (2021), arXiv:2102.09548. [arxiv.org/abs/2102.09548](https://arxiv.org/abs/2102.09548) | |
| 52 | + | |
| 53 | +## Source | |
| 54 | + | |
| 55 | +Imported from [TDC ADMET benchmark group, PPBR_AZ](https://tdcommons.ai/benchmark/admet_group/08ppbr/), curated by Therapeutics Data Commons (Harvard). Open according to the source as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion. | |