Discovery of Potent and Selective PI3Kγ Inhibitors

Abstract

The selective inhibition of the lipid signaling enzyme PI3Kγ constitutes an opportunity to mediate immunosuppression and inflammation within the tumor microenvironment but is difficult to achieve due to the high sequence homology across the class I PI3K isoforms. Here, we describe the design of a novel series of potent PI3Kγ inhibitors that attain high isoform selectivity through the divergent projection of substituents into both the "selectivity" and "alkyl-induced" pockets within the adenosine triphosphate (ATP) binding site of PI3Kγ. These efforts have culminated in the discovery of 5-[2-amino-3-(1-methyl-1Hpyrazol-4-yl)pyrazolo[1,5-a]pyrimidin-5-yl]-2-[(1S)-1-cyclopropylethyl]-7-(trifluoromethyl)-2,3-dihydro-1H-isoindol-1-one (4, IC 50 = 0.064 μM, THP-1 cells), which displays >600-fold selectivity for PI3Kγ over the other class I isoforms and is a promising step toward the identification of a clinical development candidate. The structure−activity relationships identified throughout this campaign demonstrate that greater γ-selectivity can be achieved by inhibitors that occupy an "alkyl-induced" pocket and possess bicyclic hinge-binding motifs capable of forming more than one hydrogen bond to the hinge region of PI3Kγ.

Functional Pyrazolo[1,5-a]pyrimidines: Current Approaches in Synthetic Transformations and Uses As an Antitumor Scaffold

“…This reaction is one of the most employed to add functionalized aryls on position 3 or 5; several organometallic species have been evaluated with favorable results, such as boronic esters, boronic acids, and fluoroboranes. The reactions have been carried out mainly using solvents like water mixed with some organic solvent (to maximize solubility) or in dioxane, and carbonates appear to be the preferred base, perhaps due to carbon dioxide formation facilitating the workup [ 67 , 68 , 69 ].…”

“…Similarly, Lindsley and co-workers designed a fast reaction to functionalized the CF 3 –substituted PP 90 with aryls moieties bearing methoxy group (compound 91 ) or fluor atoms (not shown) ( Scheme 26 b) [ 32 ]. Related to these advances, Drew et al employed the same Pd-catalyst bearing dppf as a ligand to perform the coupling of 93 with the isoindolinone 92 , the reaction proceeds by the lability exchange with the halogen added according to the electronic properties of the position 5 against position 3 in the pyrazolo[1,5- a ]pyrimidine 93 ( Scheme 26 c) [ 68 ].…”

“…A related example to the metal-catalyzed C–N bond formation discusses in Section 4 . The authors added the iodine atom at position 2, enabling the later addition of heterocyclic species at this position, delivering the 2,5-diheteroarylpyrazolo[1,5- a ]pyrimidine 97 ( Scheme 27 a) [ 68 ].…”

Targeting phosphatidylinositol 3‐kinase gamma (PI3Kγ): Discovery and development of its selective inhibitors

“…The identification of IPI‐549 was aided by the success of Duvelisib (IPI‐145; Figure 3l). Even though the crystal structure of PI3Kγ bound with IPI‐145 has not been reported so far, the X‐ray crystal structures of IPI‐549 in complex with the human PI3Kγ (PDB ID: 6XRL) was recently reported by Drew et al 70 in August 2020. Starting from the N ‐phenyl‐8‐chloroisoquinolinone moiety in IPI‐145 as a core scaffold to mimic the adenine ring of ATP (Figure 5A), hinge‐binding motifs were explored by introducing at least one hydrogen bond acceptor and 0‐2 hydrogen bond donors at the R 1 position (Figure 5B) to maintain hydrogen bond interactions with PI3Kγ 71 .…”

“… 20 Compared with the co‐crystal structures of the propeller‐shaped ligand, PIK‐39 (Figure 3A), in complex with PI3Kδ (PDB ID: 2WXF) 36 and PI3Kγ (PDB ID: 2CHW), 40 IPI‐549 contains a different propeller‐shaped conformation in the active site of PI3Kγ. There is a twisted orientation between the quinazolinone core and the aminopyrazolopyrimidine amide moiety, which lead to two hydrogen bonds between the aminopyrazolopyrimidine and Val882 of PI3Kγ; in addition, the quinazolinone moiety forms π‐stacking interaction with Trp812 of PI3Kγ 70 . It was postulated that the substituent at the R 2 position (Figure 5C) may access a nonconserved region within PI3Kγ, and the alkyne substituent may form unfavorable interactions with Thr750 of PI3Kδ (corresponding to Lys802 of PI3Kγ), 20,72 which may improve PI3Kγ potency and selectivity, which led to the identification of a methyl alkyne substituent at R 2 20 .…”