Yasutomi Asano

Discovery, synthesis and biological evaluation of isoquinolones as novel and highly selective JNK inhibitors (2)

A novel series of 4-phenylisoquinolones were synthesized and evaluated as c-Jun N-terminal kinase (JNK) inhibitors. Initial modification at the 2- and 3-positions of the isoquinolone ring of hit compound 4, identified from high-throughput screening, led to the lead compound 6b. The optimization was carried out using a JNK1-binding model of 6b and several compounds exhibited potent JNK inhibition. Among them, 11g significantly inhibited cardiac hypertrophy in rat pressure-overload models without affecting blood pressure and the concept of JNK inhibitors as novel therapeutic agents for heart failure was confirmed.

Antitumor activity of a novel and orally available inhibitor of serine palmitoyltransferase.

Metabolic reprogramming is an essential hallmark of neoplasia. Therefore, targeting cancer metabolism, including lipid synthesis, has attracted much interest in recent years. Serine palmitoyltransferase (SPT) plays a key role in the initial and rate-limiting step of de novo sphingolipid biosynthesis, and inhibiting SPT activity prevents the proliferation of certain cancer cells. Here, we identified a novel and orally available SPT inhibitor, compound-2. Compound-2 showed an anti-proliferative effect in several cancer cell models, reducing the levels of the sphingolipids ceramide and sphingomyelin. In the presence of compound-2, exogenously added S1P partially compensated the intracellular sphingolipid levels through the salvage pathway by partially rescuing compound-2-induced cytotoxicity. This suggested that the mechanism underlying the anti-proliferative effect of compound-2 involved the reduction of sphingolipid levels. Indeed, compound-2 promoted multinuclear formation with reduced endogenous sphingomyelin levels specifically in a compound-2-sensitive cell line, indicating that the effect was induced by sphingolipid reduction. Furthermore, compound-2 showed potent antitumor activity without causing significant body weight loss in the PL-21 acute myeloid leukemia mouse xenograft model. Therefore, SPT may be an attractive therapeutic anti-cancer drug target for which compound-2 may be a promising new drug.

Pharmacological characterization of synthetic serine palmitoyltransferase inhibitors by biochemical and cellular analyses.

Human serine palmitoyltransferase (SPT) is a PLP-dependent enzyme residing in the endoplasmic reticulum. It catalyzes the synthesis of 3-ketodihydrosphingosine (3-KDS) from the substrates palmitoyl-CoA and l-serine. It is a rate-limiting enzyme for sphingolipid synthesis in cells. In the present study, we characterized and pharmacologically profiled a series of tetrahydropyrazolopyridine derivatives that potently inhibit human SPT enzymatic activity, including two cell-active derivatives and one fluorescent-labelled derivative. These SPT inhibitors exhibited dual inhibitory activities against SPT2 and SPT3. We used a fluorescent-labelled probe to molecularly assess the inhibitory mechanism and revealed its binding to the SPT2 or SPT3 subunit in the small subunit (ss) SPTa/SPT1/SPT2/or ssSPTa/SPT1/SPT3 functional complexes. One of the SPT inhibitors exhibited a significantly slow dissociation from the SPT complex. We confirmed that our SPT inhibitors suppressed ceramide content in non-small-cell lung cancer cell line, HCC4006, by performing a target engagement analysis. The potency of ceramide reduction correlated to that observed in a recombinant SPT2 enzyme assay. We thus elucidated and provided a fundamental understanding of the molecular mode of action of SPT inhibitors and developed potent, cell-active SPT inhibitors that can be used to clarify the biological function of SPT.

Discovery of novel serine palmitoyltransferase inhibitors as cancer therapeutic agents

We pursued serine palmitoyltransferase (SPT) inhibitors as novel cancer therapeutic agents based on a correlation between SPT inhibition and growth suppression of cancer cells. High-throughput screening and medicinal chemistry efforts led to the identification of structurally diverse SPT inhibitors 4 and 5. Both compounds potently inhibited SPT enzyme and decreased intracellular ceramide content. In addition, they suppressed cell growth of human lung adenocarcinoma HCC4006 and acute promyelocytic leukemia PL-21, and displayed good pharmacokinetic profiles. Reduction of 3-ketodihydrosphingosine, the direct downstream product of SPT, was confirmed under in vivo settings after oral administration of compounds 4 and 5. Their anti-tumor efficacy was observed in a PL-21 xenograft mouse model. These results suggested that SPT inhibitors might have potential to be effective cancer therapeutics.