The preclinical pharmacology of WP1066, a potent small molecule inhibitor of the JAK2/STAT3 pathway

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The Stat3 pathway, constitutively activated in many cancers, is associated with the regulation of many survival proteins including survivin, Mcl-1, and the Bcl family. Inhibition of Stat3 signaling leads to an inhibition of cancer cell growth and to the induction of apoptosis. A number of attempts have been made to abrogate Stat3 activity, including the use of ligands to inhibit upstream signaling events or silencing Stat3 with oligonucleotides, none of which have been successful in vivo. We report here on the first potent small molecule inhibitor of Stat3 with demonstrated in vivo activity. Studies of WP1066 in our laboratories demonstrated proapoptotic and antiproliferative activity at concentrations of 3-5 μM, in vitro, in a variety of tumor cell types. In order to determine the utility of this compound in vivo we examined the tissue stability, pharmacokinetics, drug distribution, and bioavailability in CD₁ mice. Briefly, animals (10 per timepoint) were administered WP1066 (10 and 40 mg/kg) as an IV bolus and sacrificed at various out to 24 hours post-dose. Tissues were harvested and following extraction analyzed for WP1066 content using tandem LC/MS. In vitro studies were also conducted to determine the overall stability of this molecule in rodent plasma. For oral bioavailability studies animals were dosed by gavage with 40 mg/kg and samples obtained over the same 24 hour period. The mean achieved peak plasma concentrations following 10 and 40 mg/kg IV doses were 1.05 and 4.31 μM respectively. Mean drug half life was 4.5 hours and terminal concentrations measured at 12 and 18 hours were 0.03 and 0.13 μM, at the low and high doses, respectively. Tissue stability studies demonstrated an in vitro plasma half-life of 2.6 hrs. Preliminary oral bioavailability studies yielded mean peak plasma concentrations of > 1 μM and an estimated bioavailability of 0.2. Studies of U87 tumor bearing mice given drug by IV bolus demonstrated an accumulation of WP1066 in tumor tissue many fold greater than the simultaneously measured plasma concentration. These studies coupled with our in vivo efficacy studies indicate that WP1066 is the first small molecule inhibitor of Stat3 capable of achieving and maintaining tissue concentrations associated with drug activity in vivo.