In the future, splitting PCLs to reflect subclasses with distinct patterns of selectivity may be possible. For example, the histone deacetylase (HDAC) inhibitor PCL class currently has 20 members, each with varying selectivity against the 13 HDAC proteins. Clustering the L1000 gene expression data revealed clear substructure within the PCL, with pan-HDAC-inhibitory compounds forming a distinct cluster, and compounds selective for either HDAC6 or HDAC1,3 and 8 forming distinct clusters (Figure 5A).
