ALK2 inhibitors display beneficial effects in preclinical models of ACVR1 mutant diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine glioma (DIPG) is a lethal childhood brainstem tumour, with a quarter of patients harbouring somatic mutations in ACVR1, encoding the serine/threonine kinase ALK2. Despite being an amenable drug target, little has been done to-date to systematically evaluate the role of ACVR1 in DIPG, nor to screen currently available inhibitors in patient-derived tumour models. Here we show the dependence of DIPG cells on the mutant receptor, and the preclinical efficacy of two distinct chemotypes of ALK2 inhibitor in vitro and in vivo. We demonstrate the pyrazolo[1,5-a]pyrimidine LDN-193189 and the pyridine LDN-214117 to be orally bioavailable and well-tolerated, with good brain penetration. Treatment of immunodeprived mice bearing orthotopic xenografts of H3.3K27M, ACVR1R206H mutant HSJD-DIPG-007 cells with 25 mg/kg LDN-193189 or LDN-214117 for 28 days extended survival compared with vehicle controls. Development of ALK2 inhibitors with improved potency, selectivity and advantageous pharmacokinetic properties may play an important role in therapy for DIPG patients.

Discovery of potent, orally bioavailable, small-molecule inhibitors of WNT signaling from a cell-based pathway screen.

WNT signaling is frequently deregulated in malignancy, particularly in colon cancer, and plays a key role in the generation and maintenance of cancer stem cells. We report the discovery and optimization of a 3,4,5-trisubstituted pyridine 9 using a high-throughput cell-based reporter assay of WNT pathway activity. We demonstrate a twisted conformation about the pyridine-piperidine bond of 9 by small-molecule X-ray crystallography. Medicinal chemistry optimization to maintain this twisted conformation, cognisant of physicochemical properties likely to maintain good cell permeability, led to 74 (CCT251545), a potent small-molecule inhibitor of WNT signaling with good oral pharmacokinetics. We demonstrate inhibition of WNT pathway activity in a solid human tumor xenograft model with evidence for tumor growth inhibition following oral dosing. This work provides a successful example of hypothesis-driven medicinal chemistry optimization from a singleton hit against a cell-based pathway assay without knowledge of the biochemical target.

Preclinical pharmacokinetics and metabolism of a novel diaryl pyrazole resorcinol series of heat shock protein 90 inhibitors.

CCT018159 was recently identified as a novel inhibitor of heat shock protein (Hsp) 90, a promising target for cancer therapy. Pharmacokinetic and metabolic properties are likely to be important for efficacy and need to be optimized during drug development. Here, we define the preclinical metabolism and pharmacokinetics of CCT018159 and some early derivatives. In addition, we assess in vitro metabolic stability screening and in vivo cassette dosing (simultaneous administration of several compounds to a single animal) as approaches to investigate these compounds. The plasma clearance following individual i.v. administration to mice was rapid (0.128-0.816 L/h), exceeding hepatic blood flow. For CCT066950 and CCT066952, this could be attributed in part to extensive (>80%) blood cell binding. Oral bioavailability ranged from 1.8% to 29.6%. Tissue distribution of CCT066952 was rapid and moderate, and renal excretion of the compounds was minimal (<1% of dose excreted). Compounds underwent rapid glucuronidation both in vivo and following incubation with mouse liver microsomes. However, whereas CCT066965 was metabolized to the greatest extent in vitro, this compound displayed the slowest plasma clearance. The rank order of the compounds from the highest to lowest area under the curve was the same following discrete and cassette dosing. Furthermore, pharmacokinetic variables were similar whether the compounds were dosed alone or in combination. We conclude that the pharmacokinetics of CCT018159 are complex. Cassette dosing is currently the best option available to assess the pharmacokinetics of this promising series of compounds in relatively high throughput and is now being applied to identify compounds with optimal pharmacokinetic properties during structural analogue synthesis.