Tuesday, August 4, 2015

Drugs in Clinical Pipeline: VS-5584

VS-5584 [5-(9-isopropyl-8-methyl-2-morpholin-4-yl-9H-purin-6-yl)-pyrimidin-2-ylamine] is a novel low-molecular weight compound with high and equivalent potency against Mammalian target of Rapamycin (mTOR) and all Phosphoinositide 3-kinase (PI3K) class I isoforms but with no relevant activity for more than 400 lipid and protein kinases. VS-5584 is a potent inhibitor of mTOR (IC50 = 37 nM) as well as class I PI3K isoforms (IC50: PI3Kα = 16 nM; PI3Kβ = 68 nM; PI3Kγ = 25 nM; PI3Kδ = 42 nM). The Ambit full panel screening revealed that besides mTOR and the PI3K family, only NEK2 and BTK showed potential binding (less than 5%) of VS-5584. All other evaluated kinases showed negligible binding when tested up to 10 µM VS-5584. Further analysis of 320 kinases (including NEK2 and BTK) in a radiometric kinase assay platform showed that no kinase showed an IC50 less than 300 nM except for the PIKK family [1].

VS-5584 shows robust modulation of cellular PI3K/mTOR pathways, inhibiting phosphorylation of substrates downstream of PI3K and mTORC1/2. A large human cancer cell line panel screen (436 lines) revealed broad antiproliferative sensitivity and that cells harboring mutations in PI3KCA are generally more sensitive toward VS-5584 treatment. VS-5584 exhibits favorable pharmacokinetic properties after oral dosing in mice and is well tolerated. VS-5584 induces long-lasting and dose-dependent inhibition of PI3K/mTOR signaling in tumor tissue, leading to tumor growth inhibition in various rapalog-sensitive and -resistant human xenograft models. Furthermore, VS-5584 is synergistic with an EGF receptor inhibitor in a gastric tumor model [1].

VS-5584, a novel purine analog, was generated with the aid of computational chemistry as a small-molecule ATP competitive inhibitor of PI3K and mTOR kinases with favorable pharmaceutical properties by S*BIO Pte Ltd (Singapore). It has been licensed to Verastem which now has patent protection of VS-5584 through 2029. VS-5584 has undergone IND-enabling testing and is in Phase 1 trial in patients with advanced cancer since the second half of 2013.

The activity of VS-5584 is as follows:

IC50 (mTOR enzyme assay) = 37 ± 7 nM
IC50 (PI3Kα enzyme assay) = 16 ± 3 nM
IC50 (PI3Kβ enzyme assay) = 68 ± 9 nM
IC50 (PI3Kγ enzyme assay) = 25 ± 5 nM
IC50 (PI3Kδ enzyme assay) = 42 ± 8 nM
IC50 (DNA-PK enzyme assay) = 1270 ± 321 nM
IC50 (Vps34 enzyme assay) = 7470 ± 1300 nM

Common Name: VS-5584
Synonyms:  VS-5584; VS 5584; VS5584; SB2343; SB-2343; SB 2343
IUPAC Name: 5-(9-isopropyl-8-methyl-2-morpholin-4-yl-9H-purin-6-yl)-pyrimidin-2-ylamine
CAS Number: 1246560-33-7
Mechanism of Action: Kinase Inhibitor; Dual-Kinase Inhibitor; mTOR Inhibitor; PI3K Inhibitor
Indication: Various Cancers
Development Stage: Phase I
Company: S*BIO Pte Ltd/Verastem

In mammals, mTOR is the catalytic subunit in 2 distinct complexes, mTORC1 and mTORC2. mTORC1 controls cellular growth by integrating signals from growth factor receptors and intracellular nutrient status. mTORC2 is less well understood but plays a role in the regulation of cellular survival and cell migration. The mTOR signaling pathway has been suggested to be involved in multiple anticancer drug resistance mechanisms toward chemotherapeutics but also signal transduction inhibitors. Rapamycin and its analogs block mTORC1 activity and have shown single-agent activity in a small subsets of cancers. However, resistance has been shown to develop through activation of the PI3K signaling pathway including activation of mTORC2.

The phosphoinositide-3-kinase (PI3K) family of lipid kinases is involved in a diverse set of cellular functions, including cell growth, proliferation, motility, differentiation, glucose transport, survival, etc. PI3K’s can be categorized into class I, II, or III, depending on their subunit structure, regulation, and substrate selectivity. Class IA PI3K’s are activated by receptor tyrosine kinases and consist of a regulatory subunit (p85) and a catalytic subunit (p110). There are three catalytic isoforms: p110α, β, and δ. A single class IB PI3K, activated by GPCRs, consists of only one member: a p110γ catalytic subunit and a p101 regulatory subunit. The primary in vivo substrate of the class I PI3K’s is phosphatidylinositol (4,5) diphosphate (PtdIns(4,5)P2), which upon phosphorylation at the 3-position of the inositol ring to form phosphatidylinositol triphosphate (3,4,5)P3 (PIP3) serves as a second messenger by activating a series of downstream effectors that mediate the cellular functions mentioned above. The PI3K isoforms have different distributions and share similar cellular functions, which are context dependent. In particular, p110α pathway deregulation has been demonstrated in ovarian, breast, colon, and brain cancers. Hence, inhibitors targeting PI3K activities are major interest area for cancer treatment and therapy.

Important finding about VS5584:

Modulation of PI3K/mTOR signaling pathways by VS-5584: The effects of VS-5584 was tested in various cell lines such as PC3 (a prostate cancer cell line with PTEN deletion), MV4-11 cells (harboring FLT3-ITD), Colo205 (BRAF V600E, mTOR P1193L) and MDA-MB-231 (BRAF G464V, KRAS G13D). The researchers report that  data shows VS-5584 effectively permeates cells to modulate signaling pathways downstream of PI3K/mTOR independent of the genetic background of the cells.

VS-5584 potently blocks proliferation in a broad spectrum of tumor cells: As the PI3K/mTOR signaling pathway regulates important functional responses including cell proliferation, the effects of VS-5584 on a panel of 51 cancer cell lines derived from both liquid and solid tumors of human origin were investigated. Overall, VS-5584 showed high antiproliferative activity in a broad spectrum of cancer cells, with H929 (multiple myeloma) showing the highest sensitivity in our panel (IC50 = 48 nM).

VS-5584 is efficacious in a PTENnull human prostate PC3 xenograft model.

Therapeutic effects of VS-5584 in a rapamycin-resistant human colorectal COLO-205 xenograft model: a well-tolerated dose of VS-5584 blocks mTOR and PI3K signaling in tumor tissue and reduces the number of functional blood vessels in the tumor and is efficacious in a rapalog-resistant COLO-205 xenograft model.

VS-5584 is efficacious in a FLT3-ITD AML xenograft model: VS-5584 is also efficacious at low and well-tolerated dose in liquid tumor model, namely the FLT3-ITD harboring MV4-11 xenograft model.

VS-5584 is efficacious as a single agent and has synergistic effects in combination with an EGFRi in a gastric xenograft model.

VS-5584 has very good pharmacokinetic properties and effectively blocks mTORC1 and 2 as well as PI3K signaling in tumor tissue after once daily oral dosing. It is highly efficacious and well tolerated in all xenograft models tested so far, including models resistant to rapalogs and standard of care therapies [1].

VS-5584 potently inhibited survival and proliferation of established (A375, A-2058 and SK-MEL-3 lines) and primary human melanoma cells, but was non-cytotoxic to non-cancerous human skin keratinocytes and B10BR murine melanocytes. VS-5584 induced caspase-dependent apoptotic death in melanoma cells, and its cytotoxicity was alleviated by the caspase inhibitors. At the molecular level, VS-5584 blocked AKT-mTOR activation and downregulated cyclin D1 expression in melanoma cells, while the expressions of Bcl-xL and Bcl-2 were not affected by VS-5584 treatment [2]. VS-5584 failed to affect Bcl-xL and Bcl-2 expressions in tested melanoma cells. Importantly, the Bcl-xL/Bcl-2 inhibitor ABT-737, or siRNA-mediated knockdown of Bcl-xL/Bcl-2, remarkably enhanced the activity of VS-5584 against melanoma cells in vitro and in vivo.

1. Hart, S.; et. al. VS-5584, a Novel and Highly Selective PI3K/mTOR Kinase Inhibitor for the Treatment of Cancer. Mol Cancer Ther 2013, 12(2), 151-161.
2. Shao, Z.; et. al. VS-5584, a Novel PI3K-mTOR Dual Inhibitor, Inhibits Melanoma Cell Growth In Vitro and In Vivo. PLoS One 2015, 10(7), e0132655.