Tuesday, June 9, 2015

Drugs in Clinical Pipeline: AZ20

AZ20 [(R)-4-(2-(1H-indol-4-yl)-6-(1-(methylsulfonyl)cyclopropyl)pyrimidin-4-yl)-3-methylmorpholine] is an Ataxia telangiectasia mutated and RAD3-related (ATR) inhibitor with the excellent potency and selectivity (IC50 ATR enzyme, cell = 0.005, 0.050 uM, respectively). AZ20 was discovered using a lead discovery and early optimization campaign from an mTOR inhibitor screening hit. The sulfonylmorpholinopyrimidine series has good potency and selectivity for ATR, attractive LE and LLE, but low aqueous solubility. For the above reasons, AZ20 retains some residual recombinant mTOR enzyme inhibitory potency (IC50 mTOR enzyme, cell = 0.038, 2.4 uM, respectively), but shows otherwise excellent kinase selectivity (IC50 ATM, DNA-PK greater than 30 uM). Moreover, AZ20 has poor solubility as expected. Out of a panel of 442 kinases only two, mTOR and PI3Kα, had less than 50% residual activity when incubated with AZ20 at 1 µM [1].

Tumor cells that are deficient in G1 checkpoint controls, in particular p-53, or with other mutations that promote replicative stress, are hypothesized to be more reliant on ATR for survival. In such circumstances, specific inhibition of ATR may lead to enhanced antitumor activity while minimizing normal tissue toxicity. ATR is an important new drug target whose inhibitors have the potential for broad utility in cancer patients as monotherapy or in combination with chemo- or radiotherapy. AstraZeneca is developing various kinase inhibitors, AZ20 is one of them.

The activity of AZ20 is as follows:

IC50 (ATR enzyme assay) = 0.005 uM
IC50 (mTOR enzyme assay) = 0.038 uM
IC50 (ATR cell assay) = 0.050 uM

Common Name: AZ20
Synonyms:  AZ20; AZ-20; AZ 20
IUPAC Name: (R)-4-(2-(1H-indol-4-yl)-6-(1-(methylsulfonyl)cyclopropyl)pyrimidin-4-yl)-3-methylmorpholine
CAS Number: 1233339-22-4
Mechanism of Action: Kinase Inhibitor; ATR Inhibitor
Indication: Various Cancers
Development Stage: Pre-Clinical
Company: AstraZeneca

Ataxia telangiectasia mutated and RAD3-related (ATR) is a serine/threonine protein kinase that, together with ATM and DNA-PK, forms part of the DNA-damage response (DDR) coordinating the cellular response to DNA damage, stress, and cell-cycle perturbation. ATR is essential to the viability of replicating cells responding to accumulation of single strand breaks (SSB) in DNA such as stalled replication forks and to bulky DNA damage lesions such as those formed by chemotherapeutics and ultraviolet (UV) radiation. Sensitization of tumor cells to chemotherapeutic agents has been demonstrated following genetic modulation of ATR activity, with weak ATR inhibitors such as caffeine, and more recently with potent and selective ATR inhibitors such as VE-821. These studies suggest that combination of ATR inhibitors with some cytotoxic agents may be therapeutically beneficial [1]. ATR, ATM, and DNA-PK together with three other proteins mTOR, hSMG-1, and TRRAP are members of an atypical class of protein kinases known collectively as the phosphatidylinositol 3-kinase related kinase (PIKK) family. These proteins are structurally different from classical protein kinases and are more closely related to the PI3-kinase family of phospholipid kinases.

AZ20 shows no significant reversible inhibition of any of the five major cytochrome P450 isoforms, but when tested for time-dependent inhibitory (TDI) activity following incubation with human liver microsomes, was found to inhibit the cytochrome 3A4-mediated metabolism of midazolam by 50% at 10 µM. Inhibition of the CYP3A family of enzymes is of particular concern for drug-drug interaction (DDI) given that they are the major metabolizing enzymes involved in the human metabolism of many drug molecules. In addition to DDI, covalent modification associated with TDI can result in toxicological consequences especially in the liver [1]. However, AZ20 has high mouse free drug exposure at moderate doses despite its low solubility and shows tumor growth inhibition in LoVo xenografts in vivo at well tolerated doses.

1. Foote, K. M.; et. al. Discovery of 4-{4-[(3R)-3-Methylmorpholin-4-yl]-6-[1-(methylsulfonyl)cyclopropyl]pyrimidin-2-yl}-1H-indole (AZ20): a potent and selective inhibitor of ATR protein kinase with monotherapy in vivo antitumor activity. J Med Chem 2013, 56(5), 2125-2138.