Pharmacokinetics and derivation of an anticancer dosing regimen for PAC-1, a preferential small molecule activator of procaspase-3, in healthy dogs

Abstract

PAC-1 is a preferential small molecule activator of procaspase-3 and has potential to become a novel and effective anticancer agent. The rational development of PAC-1 for translational oncologic applications would be advanced by coupling relevant in vitro cytotoxicity studies with pharmacokinetic investigations conducted in large mammalian models possessing similar metabolism and physiology as people. In the present study, we investigated whether concentrations and exposure durations of PAC-1 that induce cytotoxicity in lymphoma cell lines in vitro can be achievable in healthy dogs through a constant rate infusion (CRI) intravenous delivery strategy. Time- and dose-dependent procaspase-3 activation by PAC-1 with subsequent cytotoxicity was determined in a panel of B-cell lymphoma cells in vitro. The pharmacokinetics of PAC-1 administered orally or intravenously was studied in 6 healthy dogs using a crossover design. The feasibility of maintaining steady state plasma concentration of PAC-1 for 24 or 48 hours that paralleled in vitro cytotoxic concentrations was investigated in 4 healthy dogs. In vitro, PAC-1 induced apoptosis in lymphoma cell lines in a time- and dose-dependent manner. The oral bioavailability of PAC-1 was relatively low and highly variable (17.8 ± 9.5%). The achievement and maintenance of predicted PAC-1 cytotoxic concentrations in normal dogs was safely attained via intravenous CRI lasting for 24 or 48 hours in duration. Using the dog as a large mammalian model, PAC-1 can be safely administered as an intravenous CRI while achieving predicted in vitro cytotoxic concentrations.

ortho-Formylation of oxygenated phenols

“…This treatment regimen was well tolerated in a large mammalian model (dog) which closely mimics the body size, physiology, and metabolism of humans. 51 Despite being apparently well tolerated in dogs, compound 12 was established as neurotoxic when injected via the tail vain of C57/BL6 mice. PAC-1 has a calculated partitioning ratio of 1.0:0.85 between the blood and the brain, suggesting that a significant amount of PAC-1 (12) may be entering the central nerve system (CNS) causing neurotoxicity.…”

Expression of executioner procaspases and their activation by a procaspase-activating compound in chronic lymphocytic leukemia cells

“…12 These compounds bypass upstream survival factors 11 and directly activate executioner caspases. PAC-1 (chemically, ortho-hydroxy N-acyl hydrazone) is the founding member of this class of compounds, and has shown promise in vitro, 11,13,14 in vivo, 11,15 and as a tool for studying procaspase-3 activation in various systems. 16,17 PAC-1 inhibited growth in primary colon tumors and mouse xenograft models, 11 through zinc ion chelation of executioner procaspase-3 and -7.…”

Zinc-mediated Allosteric Inhibition of Caspase-6

“…Treatment of HL-60 cells with zinc chelators increases apoptosis via activation of caspase-3 (32). The small molecule procaspase-3 activator PAC-1 releases procaspase-3 from zinc-mediated inhibition (33)(34)(35). The details of caspase-3 zinc-mediated inhibition have not been reported.…”