Drugs in Clinical Pipeline: Afuresertib

Afuresertib [N-((S)-1-amino-3-(3-fluorophenyl)propan-2-yl)-5-chloro-4-(4-chloro-1-methyl-1H-pyrazol-5-yl)thiophene-2-carboxamide] is an orally available, ATP-competitive, pan-AKT kinase inhibitor. Cells treated with Afuresertib show decreased phosphorylation of several substrates downstream of AKT. Afuresertib has desirable pharmaceutical properties and daily oral dosing results in a sustained inhibition of AKT activity as well as inhibition of tumor growth in several mouse tumor models of various histologic origins.

Afuresertib is also time dependant and fully reversible inhibitors of the AKT kinase family with K_i of 0.08, 2 and 2.6 nM against AKT1, AKT2 and AKT3, respectively. It is in Phase I human trials.

The activity of Afuresertib is as follows:

K_i (AKT1 enzyme assay) = 0.08 nM

K_i (AKT2 enzyme assay) = 2 nM

K_i  (AKT3 enzyme assay) = 2.6 nM

Common Name: Afuresertib

Synonyms:  GSK GSK-2110183; GSK 2110183; GSK2110183; GSK-2110183B; GSK 2110183B; GSK2110183B

IUPAC Name: N-((S)-1-amino-3-(3-fluorophenyl)propan-2-yl)-5-chloro-4-(4-chloro-1-methyl-1H-pyrazol-5-yl)thiophene-2-carboxamide

CAS Number: 1047644-62-1; 1047645-82-8 (hydrochloride)

Mechanism of Action: Kinase Inhibitor; pan-AKT Inhibitors

Indication: Various Cancers; Solid Tumors

Development Stage: Phase I

Company: GlaxoSmithKline

The AKTs are a family of serine-threonine kinases and an integral component in the signaling cascade downstream of PI3K and PTEN which work to catalyze the formation of PIP3 membrane lipids from PIP2 and back, respectively. PIP3 lipids tether the AKT kinases to the membrane via their plextrin homology domain which enables activation by phosphorylation on Thr308 by PDK1 and Ser473 by the mTORC2 complex. Activated AKT phosphorylates a variety of proteins (e.g. FOXO, TSC1/2, PRAS40, GSK3β) involved in cell survival, growth and proliferation. Given the importance of this pathway in various cancers, a number of small molecules targeting PI3K with and without mTOR inhibition are being evaluated in patients. Several AKT inhibitors have also entered clinical development; however some of them block activation of AKT rather than inhibiting kinase activity.Activation of the PI3K-AKT pathway is common in many human malignancies leading to an increase in cell survival, growth and proliferation; all necessary hallmarks of a cancer cell. This pathway is up-regulated in cancer cells as a result of a variety of genetic alterations including over-expression of or activating mutations in receptor tyrosine kinases (e.g. ERBB2 or MET), activating mutations in PI3K subunits, loss or promoter methylation of PTEN and over-expression of or mutations in the AKTs.

Afuresertib inhibit the kinase activity of the E17K AKT 1 mutant protein in a standard kinase assay with EC₅₀ of 0.2 nM. Afuresertib was tested against a diverse panel of kinase assays at GlaxoSmithKline and Millipore. Initially, the compounds were tested at 0.5 and 10 µM in all available kinase assays and were followed up with full IC₅₀ curves against a subset of enzymes that showed strong inhibition against 0.5 µM, for which in-house assay were not available. Kinase selectivity was evaluated at 0.5 and 10 µM compound concentration against a panel of 261 different kinase assays, including more than 225 unique kinases together with some mutant forms and some orthologs from mouse, rat or yeast origin. The majority of the enzymes tested (~90%) showed more than 50% inhibition at 0.5 µM of both compounds. Most of the enzymes that were inhibited greater than 50% at 0.5 µM belonged to the AGC family including PKA, PKC, and PKG isoforms. IC₅₀ values were generated for some enzymes (PKA, PKCβ1, PKCβ2, PKG1α, PKG1β = 1.3, 430, greater than 1000, 0.9, 4.0 nM, respectively) [1]. 

Oral administration of Afuresertib to mice delays the growth of various human tumor xenografts in a dose-dependent manner. Afuresertib potently inhibits cell proliferation of various cell lines derived from hematologic malignancies, as tested in a 3-day proliferation assay. The frequency of sensitivity was particularly high in T-cell acute lymphoblastic leukemia (T-ALL; 19 of 20), B-cell ALL (B-ALL; 9 of 13), chronic lymphocytic leukemia (CLL; 6 of 7), and non-Hodgkin lymphoma (NHL; 8 of 11) cell lines (with median effective concentration greater than 1 uM) [2].

Phase I Study

An open-label phase 1 study to evaluate the maximum tolerated dose (MTD), safety, pharmacokinetics, and clinical activity of afuresertib-an oral AKT inhibitor-in patients with advanced hematologic malignancies is reported [2]. 

Methodology

Seventy-three patients were treated at doses ranging from 25 to 150 mg per day. The MTD was established at 125 mg per day because of 2 dose-limiting toxicities in the 150-mg cohort (liver function test abnormalities). The most frequent adverse events were nausea (35.6%), diarrhea (32.9%), and dyspepsia (24.7%). Maximum plasma concentrations and area under the plasma concentration-time curves from time 0 to 24 hours were generally dose proportional at greater than 75-mg doses; the median time to peak plasma concentrations was 1.5 to 2.5 hours post dose, with a half-life of approximately 1.7 days. Three multiple myeloma patients attained partial responses; an additional 3 attained minimal responses. Clinical activity was also observed in non-Hodgkin lymphoma, Langerhan's cell histiocytosis, and Hodgkin disease. 

Results

Single-agent afuresertib showed a favorable safety profile and demonstrated clinical activity against hematologic malignancies, including multiple myeloma.

Phase I Study in Combination with Trametinib

To identify the maximum tolerated dose (MTD) and recommended Phase II dose of MEK/AKT inhibitor combination of trametinib and afuresertib [6].

Methodology

Eligibility criteria were advanced solid tumors, 18 years or older, Eastern Cooperative Oncology Group performance status 0 or 1, and adequate organ function. Exclusion criteria included Type 1 diabetes, active GI disease, leptomeningeal disease, or current evidence/risk of retinal venous occlusion/central serous retinopathy. Twenty patients were enrolled. Dose-limiting toxicities (Grade 2 esophagitis; Grade 3 aspartate aminotransferase increased, mucosal inflammation and hypokalemia) were reported at starting dose (1.5 mg trametinib/50 mg afuresertib once daily continuously), exceeding the MTD. Subsequent de-escalation cohorts (1.5 mg/25 mg or 1.0 mg/50 mg trametinib/afuresertib) were defined as MTDs for continuous dosing. Intermittent dosing schedule [1.5 mg trametinib (continuous)/50 mg afuresertib (Days 1-10 every 28 days)] was evaluated and considered tolerable. No patients were enrolled in Phase II.

Results

The most common adverse events reported (=10 % of all patients) included: diarrhea (60 %), dermatitis acneiform (55 %), maculo-papular rash (45 %), fatigue (30 %), dry skin (25 %), nausea (25 %), dyspnea (20 %), and vomiting (20 %). Continuous daily dosing of trametinib/afuresertib combination was poorly tolerated. Evaluation of intermittent dose schedule showed greater tolerability.

References:

1. Dumble, M.; et. al. Discovery of novel AKT inhibitors with enhanced anti-tumor effects in combination with the MEK inhibitor. PLoS One 2014, 9(6), e100880.
2. Spencer, A.; et. al. The novel AKT inhibitor afuresertib shows favorable safety, pharmacokinetics, and clinical activity in multiple myeloma. Blood 2014, 124(14), 2190-2195.

3. ClinicalTrials.gov Repeat Dose Safety Study for Compound to Treat Hematologic Cancer. NCT00881946 (retrieved 05-05-2015)

4. ClinicalTrials.gov A Study of the Safety and Activity of the MEK Inhibitor Given Together With the AKT Inhibitor to Patients With Multiple Myeloma or Solid Tumor Cancers. NCT01476137 (retrieved 05-05-2015)

5. ClinicalTrials.gov Ph 1b Study to Evaluate GSK2110183 in Combination With Bortezomib and Dexamethasone in Subjects With Multiple Myeloma (PKB115125). NCT01428492 (retrieved 05-05-2015)
6. Tolcher, A. W.; et. al. Phase I study of the MEK inhibitor trametinib in combination with the AKT inhibitor afuresertib in patients with solid tumors and multiple myeloma. Cancer Chemother Pharmacol 2015, 75(1), 183-189.