Gregg Timony

Rationally designed high-affinity 2-amino-6-halopurine heat shock protein 90 inhibitors that exhibit potent antitumor activity

Heat shock protein 90 (Hsp90) is a molecular chaperone protein implicated in stabilizing the conformation and maintaining the function of many cell-signaling proteins. Many oncogenic proteins are more dependent on Hsp90 in maintaining their conformation, stability, and maturation than their normal counterparts. Furthermore, recent data show that Hsp90 exists in an activated form in malignant cells but in a latent inactive form in normal tissues, suggesting that inhibitors selective for the activated form could provide a high therapeutic index. Hence, Hsp90 is emerging as an exciting new target for the treatment of cancer. We now report on a novel series of 2-amino-6-halopurine Hsp90 inhibitors exemplified by 2-amino-6-chloro-9-(4-iodo-3,5-dimethylpyridin-2-ylmethyl)purine (30). These highly potent inhibitors (IC50 of 30 = 0.009 microM in a HER-2 degradation assay) also display excellent antiproliferative activity against various tumor cell lines (IC50 of 30 = 0.03 microM in MCF7 cells). Moreover, this class of inhibitors shows higher affinity for the activated form of Hsp90 compared to our earlier 8-sulfanylpurine Hsp90 inhibitor series. When administered orally to mice, these compounds exhibited potent tumor growth inhibition (>80%) in an N87 xenograft model, similar to that observed with 17-allylamino-17-desmethoxygeldanamycin (17-AAG), which is a compound currently in phase I/II clinical trials.

Dimeric ansamycins—A new class of antitumor Hsp90 modulators with prolonged inhibitory activity

The geldanamycin derivative 17‐allyamino‐17‐demethoxygeldanamycin (17‐AAG) is a clinical stage ATP‐competitive HSP90 inhibitor that induces degradation of HSP90 client proteins. 17‐AAG contains 1 ansamycin moiety and is highly potent in conventional cell killing assays. Since active Hsp90 exists as a dimer, we hypothesized that dimeric compounds containing 2 ansamycin pharmacophores might inhibit Hsp90 function more efficiently than 17‐AAG. Here, we show that monomeric and dimeric ansamycins exert their activity in distinct ways. Under conditions of continuous exposure, 17‐AAG induced client degradation and cell growth inhibition more readily than the dimeric drugs CF237 and CF483. By contrast, 24 hr treatment of various tumor cells with 17‐AAG followed by drug washout caused temporary client degradation and cell cycle arrest but minimal cell death, whereas both dimers induced massive apoptosis. CF237 remained bound to Hsp90 for days after drug withdrawal and, while both monomeric and dimeric compounds caused accumulation of the inactive intermediate Hsp90 complex, this effect disappeared following washout of 17‐AAG but not CF237. The dimer was also retained for longer in tumor xenografts and displayed superior antitumor activity in vivo. These results indicate that monomeric and dimeric Hsp90 inhibitors have distinct biological profiles and work differentially toward target inhibition.

Results From the First-in-Human Study With Ozanimod, a Novel, Selective Sphingosine-1-Phosphate Receptor Modulator

The sphingosine‐1‐phosphate 1 receptor (S1P1R) is expressed by lymphocytes, dendritic cells, and vascular endothelial cells and plays a role in the regulation of chronic inflammation and lymphocyte egress from peripheral lymphoid organs. Ozanimod is an oral selective modulator of S1P1R and S1P5R receptors in clinical development for the treatment of chronic immune‐mediated, inflammatory diseases. This first‐in‐human study characterized the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of ozanimod in 88 healthy volunteers using a range of single and multiple doses (7 and 28 days) and a dose‐escalation regimen. Ozanimod was generally well tolerated up to a maximum single dose of 3 mg and multiple doses of 2 mg/d, with no severe adverse events (AEs) and no dose‐limiting toxicities. The most common ozanimod‐related AEs included headache, somnolence, dizziness, nausea, and fatigue. Ozanimod exhibited linear PK, high steady‐state volume of distribution (73–101 L/kg), moderate oral clearance (204–227 L/h), and an elimination half‐life of approximately 17 to 21 hours. Ozanimod produced a robust dose‐dependent reduction in total peripheral lymphocytes, with a median decrease of 65% to 68% observed after 28 days of dosing at 1 and 1.5 mg/d, respectively. Ozanimod selectivity affected lymphocyte subtypes, causing marked decreases in cells expressing CCR7 and variable decreases in subsets lacking CCR7. A dose‐dependent negative chronotropic effect was observed following the first dose, with the dose‐escalation regimen attenuating the first‐dose negative chronotropic effect. Ozanimod safety, PK, and PD properties support the once‐daily regimens under clinical investigation.

Cardiac Safety of Ozanimod, a Novel Sphingosine‐1‐Phosphate Receptor Modulator: Results of a Thorough QT/QTc Study

Ozanimod is a novel, selective, oral sphingosine‐1‐phosphate (1 and 5) receptor modulator in development for multiple sclerosis and inflammatory bowel disease. This randomized, double‐blind, placebo‐controlled, positive‐controlled, parallel‐group thorough QT study characterized the effects of ozanimod on cardiac repolarization in healthy subjects. Eligible subjects were randomized to 1 of 2 groups: ozanimod (escalated from 0.25 to 2 mg over 14 days) or placebo (for 14 days). A single dose of moxifloxacin 400 mg or placebo was administered on days 2 and 17. The primary end point was the time‐matched, placebo‐corrected, baseline‐adjusted mean QTcF (ΔΔQTcF). A total of 113/124 (91.1%) subjects completed the study. The upper limits of the 2‐sided 90% confidence intervals for ΔΔQTcF for both ozanimod 1 and 2 mg were below the 10‐millisecond regulatory threshold. No QTcF >480 milliseconds or postdose change in QTcF of >60 milliseconds was observed. There was no evidence of a positive relationship between concentrations of ozanimod and its active metabolites and ΔΔQTcF. Although ozanimod blunted the observed diurnal increase in heart rate, excursions below predose heart rates were no greater than with placebo. Results demonstrate that ozanimod does not prolong the QTc interval or cause clinically significant bradycardia, supporting ozanimods evolving favorable cardiac safety profile.