Motivation

Recently I published a paper on OOMMPPAA, my 3D matched-molecular pair tool to aid drug discovery. The tool is available to try here, download here and read about here. OOMMPPAA aims to tackle the big-data problem in drug discovery – where X-ray structures and activity data have become increasingly abundant. Below I will explain what a 3D MMP is.

What are MMPs?

MMPs are two compounds that are identical apart from one structural change, as shown in the example below. Across a set of a thousand compounds, tens of thousands of MMPs can be found. Each pair can be represented as a transformation. Below would be Br >> OH. Within the dataset possibly hundreds of Br >> OH will exist.

An example of an MMP

Each of these transformations will also be associated with a change in a measurable compound property, (solubility, acidity, binding energy, number of bromine atoms…). Each general transformation (e.g. Br>>OH) therefore would have a distribution of values for a given property. From this distribution we can infer the likely effect of making this change on an unmeasured compound. From all the distributions (for all the transformations) we can then predict the most likely transformation to improve the property we are interested in.

The issue with MMPs

Until recently the MMP approach had been of limited use for predicting compound binding energies. This is for two core reasons.

1) Most distributions would be pretty well normally distributed around zero. Binding is complex and the same change can have both positive and negative effects.

2) Those distributions that are overwhelmingly positive, by definition, produce increased binding against many proteins. A key aim of drug discovery is to produce selective compounds that increase binding energy only for the protein you are interested in. So increasing binding energy like that is not overall very useful.

3D MMPs to the rescue

3D MMPs aim to resolve these issues and allow MMP analysis to be applied to binding energy predictions. 3D MMPs use structural data to place the transformations in the context of the protein. One method, VAMMPIRE, asks what is the overall effect of Br>>OH when it is near to a Leucine, Tyrosine and Tryptophan (for example). In this way selective changes can be found.

Another method by BMS aggregates these changes across a target class, in their cases kinases. From this they can ask questions like, “Is it overall beneficial to add a cyclo-proply amide in this region of the kinase binding site”.

What does my tool do differently?

OOMMPPAA differs from the above in two core ways. First, OOMMPPAA uses a pharmacophore abstraction to analyse changes between molecules. This is an effective way of increasing the number of observations for each transition. Secondly OOMMPPAA does not aggregate activity changes into general trends but considers positive and negative activity changes separately. We show in the paper that this allows for more nuanced analysis of confounding factors in the available data.