Saracatinib

Saracatinib (AZD0530) is a potent, orally bioavailable, ATP-competitive inhibitor of the Src family of non-receptor tyrosine kinases, originally developed by AstraZeneca as an anticancer agent and subsequently repositioned as a candidate therapeutic for Alzheimer's disease, temporal lobe epilepsy, bone resorption disorders, pulmonary fibrosis, and fibrodysplasia ossificans progressiva. The compound inhibits c-Src with an IC50 of 2.7 nM in cell-free kinase assays and is comparably potent against all tested Src family members (c-Yes, 4 nM; Lyn, 5 nM; Fyn, 10 nM; Fgr, 10 nM; Blk, 11 nM; Lck, less than 4 nM), with substantially lower potency against v-Abl (30 nM), wild-type EGFR (66 nM), and the negative regulatory kinase Csk (greater than 1000 nM). The dual Src/Fyn inhibitory profile is pharmacologically distinctive: Fyn kinase is the principal intracellular mediator of amyloid-beta oligomer synaptotoxicity in the brain, operating through a signaling cascade in which oligomeric amyloid-beta binds cellular prion protein at the neuronal surface and activates Fyn to phosphorylate tau and drive synaptic loss, while Src itself is essential for osteoclast-mediated bone resorption through regulation of the podosome actin ring.

In oncology, saracatinib advanced through a comprehensive Phase I program establishing a maximum tolerated dose of 175 mg in the published literature, a plasma half-life of approximately 40 hours, 4- to 5-fold accumulation on chronic dosing with steady state achieved after 10 to 17 days, and dose-dependent inhibition of Src-pathway phosphorylation biomarkers in tumor biopsies. Thirteen Phase II trials across solid tumor indications (breast, gastric, colorectal, prostate, ovarian, pancreatic, thymic, osteosarcoma, melanoma, renal, and lung cancers) produced uniformly negative efficacy results for tumor response, with the single exception of a non-small-cell lung cancer trial that demonstrated tumor stabilization. The compound was subsequently deprioritized for oncology development by AstraZeneca.

The repositioning toward Alzheimer's disease was driven by the Bhatt, Nygaard, and Bhatt laboratory demonstrations that Fyn kinase is a convergence point for amyloid-beta and tau pathology, and the Kaufman et al. (2015) preclinical study showing that saracatinib at 5 mg/kg in aged APP/PS1 transgenic mice fully rescued established spatial memory deficits, restored synaptic density (presynaptic SV2a and postsynaptic PSD-95 puncta) to wild-type levels, reduced insoluble total tau by 74 percent and phosphorylated tau species by 53 to 61 percent, and suppressed microglial activation, all without altering amyloid-beta plaque burden or APP metabolism. A Phase Ib trial (Nygaard et al. 2015) in 24 patients with mild-to-moderate Alzheimer's disease demonstrated safety, tolerability, and substantial central nervous system penetration at 100 to 125 mg daily, with CSF drug concentrations of 2.5 to 14.0 nM corresponding to the efficacious range in mouse brain. A Phase 2a multicenter randomized placebo-controlled trial (the Connect study; van Dyck et al. 2019; 159 participants, 52 weeks) did not demonstrate statistically significant effects on the primary endpoint of cerebral glucose metabolism decline or on secondary clinical or biomarker endpoints, though trends toward reduced hippocampal and entorhinal cortex atrophy were observed. Gastrointestinal adverse events, predominantly diarrhea, led to discontinuation in approximately one quarter of treated participants.

In temporal lobe epilepsy, saracatinib at 25 mg/kg in the published literature for three days then in the published literature for four additional days, initiated four hours after kainate-induced status epilepticus in rats, prevented epilepsy development in four of eight treated animals, significantly reduced spontaneous recurrent seizures and epileptiform spikes over four months of continuous video-EEG monitoring, suppressed reactive astrogliosis and microgliosis, reduced hippocampal proinflammatory cytokines (TNF-alpha, IL-1-beta), attenuated nitroxidative stress markers, and prevented neurodegeneration in the dentate gyrus, CA1, CA3, and thalamus. The antiepileptogenic mechanism operates through the Fyn-PKC-delta-NOX2-iNOS signaling axis.

Saracatinib produces potent, dose-dependent inhibition of osteoclast-mediated bone resorption in healthy volunteers, with serum C-telopeptide (sCTX) reductions of up to 88 percent and urinary NTX reductions of 67 percent at 250 mg, without affecting bone formation markers. This pharmacology supports potential applications in osteoporosis, cancer-induced bone disease, and osteolytic bone metastases.

The compound is not approved by any regulatory authority. It is supplied as a research-grade preparation by multiple chemical suppliers and remains under active preclinical and early clinical investigation for neurological, musculoskeletal, and fibrotic indications. Investigators should obtain analytical confirmation of identity and purity on every lot.