Diana C. West

Malaria-infected mice are cured by a single oral dose of new dimeric trioxane sulfones which are also selectively and powerfully cytotoxic to cancer cells.

A new series of 6 dimeric trioxane sulfones has been prepared from the natural trioxane artemisinin in five or six chemical steps. One of these thermally and hydrolytically stable new chemical entities (4c) completely cured malaria-infected mice via a single oral dose of 144 mg/kg. At a much lower single oral dose of only 54 mg/kg combined with 13 mg/kg of mefloquine hydrochloride, this trioxane dimer 4c as well as its parent trioxane dimer 4b also completely cured malaria-infected mice. Both dimers 4c and 4b were potently and selectively cytotoxic toward five cancer cell lines.

Discovery and Canine Preclinical Assessment of a Nontoxic Procaspase-3–Activating Compound

A critical event in the apoptotic cascade is the proteolytic activation of procaspases to active caspases. The caspase autoactivating compound PAC-1 induces cancer cell apoptosis and exhibits antitumor activity in murine xenograft models when administered orally as a lipid-based formulation or implanted s.c. as a cholesterol pellet. However, high doses of PAC-1 were found to induce neurotoxicity, prompting us to design and assess a novel PAC-1 derivative called S-PAC-1. Similar to PAC-1, S-PAC-1 activated procaspase-3 and induced cancer cell apoptosis. However, S-PAC-1 did not induce neurotoxicity in mice or dogs. Continuous i.v. infusion of S-PAC-1 in dogs led to a steady-state plasma concentration of ∼10 μmol/L for 24 to 72 hours. In a small efficacy trial of S-PAC-1, evaluation of six pet dogs with lymphoma revealed that S-PAC-1 was well tolerated and that the treatments induced partial tumor regression or stable disease in four of six subjects. Our results support this canine setting for further evaluation of small-molecule procaspase-3 activators, including S-PAC-1, a compound that is an excellent candidate for further clinical evaluation as a novel cancer chemotherapeutic.

Parallel synthesis and biological evaluation of 837 analogues of procaspase-activating compound 1 (PAC-1).

Procaspase-Activating Compound 1 (PAC-1) is an ortho-hydroxy N-acyl hydrazone that enhances the enzymatic activity of procaspase-3 in vitro and induces apoptosis in cancer cells. An analogue of PAC-1, called S-PAC-1, was evaluated in a veterinary clinical trial in pet dogs with lymphoma and found to have considerable potential as an anticancer agent. With the goal of identifying more potent compounds in this promising class of experimental therapeutics, a combinatorial library based on PAC-1 was created, and the compounds were evaluated for their ability to induce death of cancer cells in culture. For library construction, 31 hydrazides were condensed in parallel with 27 aldehydes to create 837 PAC-1 analogues, with an average purity of 91%. The compounds were evaluated for their ability to induce apoptosis in cancer cells, and through this work, six compounds were discovered to be substantially more potent than PAC-1 and S-PAC-1. These six hits were further evaluated for their ability to relieve zinc-mediated inhibition of procaspase-3 in vitro. In general, the newly identified hit compounds are two- to four-fold more potent than PAC-1 and S-PAC-1 in cell culture, and thus have promise as experimental therapeutics for treatment of the many cancers that have elevated expression levels of procaspase-3.

Differential effects of procaspase-3 activating compounds in the induction of cancer cell death.

The evasion of apoptosis is a key characteristic of cancer, and thus strategies to selectively induce apoptosis in cancer cells hold considerable promise in personalized anticancer therapy. Structurally similar procaspase activating compounds PAC-1 and S-PAC-1 restore procaspase-3 activity through the chelation of inhibitory zinc ions in vitro, induce apoptotic death of cancer cells in culture, and reduce tumor burden in vivo. Ip or iv administrations of high doses of PAC-1 are transiently neurotoxic in vivo, while S-PAC-1 is safe even at very high doses and has been evaluated in a phase I clinical trial of pet dogs with spontaneously occurring lymphoma. Here we show that PAC-1 and S-PAC-1 have similar mechanisms of cell death induction at low concentrations (less than 50 μM), but at high concentrations PAC-1 displays unique cell death induction features. Cells treated with a high concentration of PAC-1 have a distinctive gene expression profile, unusual cellular and mitochondrial morphology, and an altered intracellular Ca(2+) concentration, indicative of endoplasmic reticulum (ER) stress-induced apoptosis. These studies suggest strategies for anticancer clinical development, specifically bolus dosing for PAC-1 and continuous rate infusion for S-PAC-1.

Preparation of the caspase-3/7 substrate Ac-DEVD-pNA by solution-phase peptide synthesis

This protocol describes the gram-scale solution-phase synthesis of the colorimetric caspase-3/7 substrate Ac-DEVD-pNA. The caspase enzymes are integral to cellular inflammation and apoptotic cascades, and are commonly studied by cell biologists, medicinal chemists and chemical biologists. In particular, the assessment of caspase enzymatic activity is a standard method to evaluate cell death pathways and new apoptosis-modulating agents. Caspase enzymatic activity can be conveniently monitored with peptidic chromogenic or fluorogenic substrates, with certain peptide sequences imparting selectivity for certain caspases. The synthesis of these peptide substrates is typically carried out by solid-phase synthesis, a method that is not ideal for production of the gram quantities needed for high-throughput screening. Described herein is a facile method for the synthesis of the Ac-DEVD-pNA caspase-3/7 substrate using solution-phase peptide synthesis. This protocol, involving iterative PyBOP-mediated couplings and Fmoc deprotections, is rapid (about 5 d), operationally simple and can be used to generate over 1 g of product at a fraction of the cost of the commercial substrate.