Further evaluation of novel structural modifications to scaffolds that engender PLD isoform selective inhibition

Abstract

This letter describes the on-going SAR efforts based on two scaffolds, a PLD1-biased piperidinyl benzimidazolone and a PLD2-biased piperidinyl triazaspirone, with the goal of enhancing PLD inhibitory potency and isoform selectivity. Here, we found that addition of an α-methyl moiety within the PLD2-biased piperidinyl triazaspirone scaffold abolished PLD2 preference, while the incorporation of substituents onto the piperdine moiety of the PLD1-biased piperidinyl benzimidazolone, or replacement with a bioisosteric [3.3.0] core, generally retained PLD1 preference, but at diminished significance. The SAR uncovered within these two allosteric PLD inhibitor series further highlights the inherent challenges of developing isoform selective PLD inhibitors.

Phospholipase D1 Couples CD4+ T Cell Activation to c-Myc-Dependent Deoxyribonucleotide Pool Expansion and HIV-1 Replication

“…If PLD1 inhibition is found to be safe in the future, it could be used to test if these pathogenic processes can be ameliorated. Importantly, certain PLD inhibitors also have demonstrated ability to traverse the blood brain barrier to target HIV-1 replication in myeloid-derived cells in the CNS, unlike some current anti-HIV drugs [ 43 , 44 ]. Furthermore, perturbation of nucleotide pools may be an additional factor beyond recently described effects on innate and adaptive immune responses contributing to PLD inhibitor-mediated blockade of influenza virus replication [ 45 ].…”

Targeting phospholipase D in cancer, infection and neurodegenerative disorders

“…However, halopemide was not a panacea. Many laboratories began to use both halopemide and FIPI as key proof-of-concept tools for PLD1 and PLD2 target validation, which led to potentially flawed conclusions, as both compounds display a considerable amount of ancillary pharmacology at a multitude of biogenic amine receptors, as expected for atypical antipsychotics that have GPCR-privileged structures as a core motif 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 .…”

“…Within the piperidine benzimidazolone core analogues, preference for PLD2 was elusive; thus, a number of bioisosteres of the piperidine benzimidazolone, as well as alternative GPCR-privileged structures, were surveyed 26 , 27 , 28 , 29 , 30 . The structure–activity relationship (SARs) of these compounds were shallow, and more than 99% of the variants studied were devoid of PLD-inhibitory activity; however, an N -phenyl triazaspirone congener ( Fig.…”

“…Initial studies with halopemide and FIPI in assays using a PLD1.d311 truncation construct (which lacked a portion of the pleckstrin homology domain) showed a slight reduction of PLD activity 16 ; however, both VU0359595 and VU0364739 significantly reduced PLD activity (by more than tenfold), which suggests that the pleckstrin homology domain (a domain that is far away from the HKD catalytic active site) is key for the binding of these molecules. Additional enzyme kinetic studies further increased our confidence that these compounds were allosteric 16 , 25 , 26 , 27 , 28 , 29 , 30 . Using a backscattering interferometry technique 33 , it was found that VU0359595 binds to two sites on the PLD1 protein (one with high affinity and the other with low affinity) 34 , which further supports an allosteric mode of inhibition akin to that of allosteric AKT inhibitors 31 , 32 .…”

“…In combination with F244-L245-L246, the PI(4,5)P 2 -binding site forms a hydrophobic pocket in the pleckstrin homology domain that is identical to that of allosteric AKT inhibitors 31 , and thus promotes a high degree of PLD2 selectivity 35 . Not only have these second-generation, halopemide-based and triazaspirone-based PLD inhibitors achieved high selectivity for the individual PLD1 and PLD2 isoenzymes, they have also provided a novel allosteric mechanism for PLD inhibition 16 , 25 , 26 , 27 , 28 , 29 , 30 .…”