Torin 2 Derivative, NCATS-SM3710, Has Potent Multistage Antimalarial Activity through Inhibition of P. falciparum Phosphatidylinositol 4-Kinase (Pf PI4KIIIβ)

Abstract

Drug resistance is a constant threat to malaria control efforts making it important to maintain a good pipeline of new drug candidates. Of particular need are compounds that also block transmission by targeting sexual stage parasites. Mature sexual stages are relatively resistant to all currently used antimalarials except the 8-aminoquinolines that are not commonly used due to potential side effects. Here, we synthesized a new Torin 2 derivative, NCATS-SM3710 with increased aqueous solubility and specificity for Plasmodium and demonstrate potent in vivo activity against all P. berghei life cycle stages. NCATS-SM3710 also has low nanomolar EC50s against in vitro cultured asexual P. falciparum parasites (0.38 ± 0.04 nM) and late stage gametocytes (5.77 ± 1 nM). Two independent NCATS-SM3710/Torin 2 resistant P. falciparum parasite lines produced by growth in sublethal Torin 2 concentrations both had genetic changes in PF3D7_0509800, annotated as a phosphatidylinositol 4 kinase (Pf PI4KIIIβ). One line had a point mutation in the putative active site (V1357G), and the other line had a duplication of a locus containing Pf PI4KIIIβ. Both lines were also resistant to other Pf PI4K inhibitors. In addition NCATS-SM3710 inhibited purified Pf PI4KIIIβ with an IC50 of 2.0 ± 0.30 nM. Together the results demonstrate that Pf PI4KIIIβ is the target of Torin 2 and NCATS-SM3710 and provide new options for potent multistage drug development.

Retrospective assessment of rat liver microsomal stability at NCATS: data and QSAR models

“…Improving the t 1/2 beyond 30 min has generally been shown to decrease clearance and increase bioavailability 14 , 15 . We employ this cutoff internally at NCATS and several projects have benefitted from this approach 16 , 17 . The raw data set was preprocessed to generate training and test data for the purpose of building and validating prediction models.…”

The Medicines for Malaria Venture Malaria Box contains inhibitors of protein secretion in Plasmodium falciparum blood stage parasites

“…Specifically, we used Brefeldin A which blocks vesicular trafficking between the ER and Golgi 61 , and Torin 2. The latter is a known trafficking inhibitor which likely targets Plasmodium phosphatidylinositol 4-kinase (PI4KIII β ), blocks vesicular trafficking at the Golgi and has also been found to deplete proteins at the PVM 27,28 . These control compounds caused accumulation of Hyp1-Nluc in the parasite (Brefeldin A) and in the parasite and PV (Torin 2) (Figure 2A).…”

“…One source of druggable targets is the parasite's protein trafficking system and inhibitors of PfPI4KIIIβ which block Golgi apparatus to plasma vesicular membrane trafficking have been identified [26][27][28][29] . As typical eukaryotes, Plasmodium parasites traffic proteins via the endoplasmic reticulum (ER) en route to specialised parasite compartments including the algalderived apicoplast, the apical secretory organelles (the rhoptries, micronemes and dense granules), and the specialised membranous sac (parasitophorous vacuole membrane (PVM)) encasing the parasite within the RBC 30 .…”

Plasmodium Kinases as Potential Drug Targets for Malaria: Challenges and Opportunities

“…There is still considerable interest in developing new PI4KIIIβ inhibitors with distinct chemotypes as backups for MMV390048. Further, several other chemotypes that inhibit Plasmodium PI4K have been reported. − While a structure of Plasmodium PI4KIIIβ is yet to be elucidated, high-resolution structures of human PI4KIIIβ (e.g., PDB 4D0L) are now available, , providing valuable information for understanding selectivity and a template from which to build a Pf PI4KIIIβ homology model . This coupled with enzyme inhibition data and multiple inhibitor-bound structures of related human PI3K proteins provides a wealth of valuable information to optimize inhibitors for Pf PI4KIIIβ potency and selectivity.…”