Thibaut Legigan

The First Generation of β-Galactosidase-Responsive Prodrugs Designed for the Selective Treatment of Solid Tumors in Prodrug Monotherapy†

Massive attack: Galactoside prodrugs have been designed that can be selectively activated by lysosomal β-galactosidase located inside cancer cells expressing a specific tumor-associated receptor. This efficient enzymatic process triggers a potent cytotoxic effect, releasing the potent antimitotic agent MMAE and allowing the destruction of both receptor-positive and surrounding receptor-negative tumor cells.

β-Glucuronidase-responsive prodrugs for selective cancer chemotherapy: an update.

The design of novel antitumor agents allowing the destruction of malignant cells while sparing healthy tissues is one of the major challenges in medicinal chemistry. In this context, the use of non-toxic prodrugs programmed to be selectively activated by beta-glucuronidase present at high concentration in the microenvironment of most solid tumors has attracted considerable attention. This review summarizes the major progresses that have been realized in this field over the past ten years. This includes the new prodrugs that have been designed to target a wide variety of anticancer drugs, the prodrugs employed in the course of a combined therapy, the dendritic glucuronide prodrugs and the concept of β-glucuronidase-responsive albumin binding prodrugs.

Synthesis and Antitumor Efficacy of a β-Glucuronidase-Responsive Albumin-Binding Prodrug of Doxorubicin

In this paper we describe the synthesis and biological evaluation of the first β-glucuronidase-responsive albumin-binding prodrug designed for the selective delivery of doxorubicin at the tumor site. This prodrug leads to superior antitumor efficacy in mice compared to HMR 1826, a well-known glucuronide prodrug of doxorubicin that cannot bind covalently to circulating albumin. Furthermore, this compound inhibits tumor growth in a manner similar to that of doxorubicin while avoiding side effects induced by the free drug.

An enzyme-responsive system programmed for the double release of bioactive molecules through an intracellular chemical amplification process

The rise of chemical biology has led to the development of sophisticated molecular devices designed to explore and manipulate biological processes. Within this framework, we developed the first chemical system programmed for the selective internalization and subsequent enzyme-catalyzed double release of bioactive compounds inside a targeted population of cells. This system is composed of five distinct units including a targeting ligand, an enzymatic trigger, a self-immolative linker and two active compounds articulated around a chemical amplifier. Designed as such, this molecular assembly is capable in an autonomous manner to recognize a selected population of cells, penetrate into the intracellular medium through endocytosis and transform a single enzymatic activation step into the release of two active units. Demonstrating that an enzyme-catalyzed amplification process can occur spontaneously under the conditions prevailing within the cells could be an important step toward the development of innovative molecular systems for a diverse range of applications spanning drug delivery, biological sensors and diagnostics.

Selective Release of a Cyclopamine Glucuronide Prodrug toward Stem-like Cancer Cell Inhibition in Glioblastoma

Recent data suggest that inhibition of the Hedgehog pathway could be a therapeutic target for glioblastoma. Alkaloid cyclopamine inhibits Hedgehog signaling, depleting stem-like cancer cells derived from glioblastoma. However, this compound is toxic for somatic stem cells, preventing its use for clinical applications. In this study, we tested a derivatization product of cyclopamine in the form of cyclopamine glucuronide prodrug (CGP-2). This compound was used in vitro and in vivo toward glioblastoma-initiating cells (GIC). Results obtained in vitro indicate that CGP-2 is active only in the presence of β-glucuronidase, an enzyme detected in high levels in necrotic areas of glioblastomas. CGP-2 decreased proliferation and inhibited the self-renewal of all GIC lines tested. Hedgehog pathway blockade by 10 μmol/L of CGP-2 induced a 99% inhibition of clonogenicity on GICs, similar to cyclopamine treatment. Combination of CGP-2 with radiation decreased clonogenic survival in all GIC lines compared with CGP-2 alone. In a subcutaneous glioblastoma xenograft model, a two-week CGP-2 treatment prevented tumor growth with 75% inhibition at 8 weeks, and this inhibition was still significant after 14 weeks. Unlike cyclopamine, CGP-2 had no detectable toxic effects in intestinal crypts. Our study suggests that inhibition of the Hedgehog pathway with CGP-2 is more effective than conventional temozolomide adjuvant, with much lower concentrations, and seems to be an effective therapeutic strategy for targeting GICs. Mol Cancer Ther; 13(9); 2159–69. ©2014 AACR.

Evaluation of Cytotoxic Properties of a Cyclopamine Glucuronide Prodrug in Rat Glioblastoma Cells and Tumors

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. Activation of the developmental hedgehog (Hh) pathway is observed in GBM, particularly in the so-called glioma stem cells (GSCs). An inhibitor of this pathway is the steroidal alkaloid cyclopamine, an antagonist of the Hh coreceptor Smoothened (SMO). To limit the toxicity of cyclopamine toward Hh-dependent non-tumor cells, our group previously reported the synthesis of a prodrug (called 1b), designed to deliver cyclopamine in the presence of β-glucuronidase, an enzyme found in the necrotic area of GBM. Here, we aimed to analyze the in vitro, ex vivo, and in vivo cytotoxic properties of this prodrug in the C6 rat GBM cells. In the presence of β-glucuronidase, the activated prodrug 1b was toxic and downregulated expression of Gli1, a Hh target gene, in C6 cells and C6-GSCs, but not in normal rat astrocytes in which the Hh pathway is weakly activated. In the absence of β-glucuronidase, prodrug 1b displayed no obvious toxicity toward rat brain tissue explants while cyclopamine clearly affected brain tissue viability. When administered to rats bearing fluorescent C6-derived GBM, the prodrug 1b reduced the tumor density more efficiently than cyclopamine. Prodrug 1b thus appears as a promising concept to optimize confinement of cyclopamine cytotoxicity within the tumors, with more limited effects in the surrounding normal brain tissue.

Multivalency to inhibit and discriminate hexosaminidases

A set of multivalent polyhydroxylated acetamidoazepanes based on ethylene glycol, glucoside, or cyclodextrin scaffolds was prepared. The compounds were assessed against plant, mammalian, and therapeutically relevant hexosaminidases. Multimerization was shown to improve the inhibitory potency with synergy, and to fine tune the selectivity profile between related hexosaminidases.

Synthetic deoxynojirimycin derivatives bearing a thiolated, fluorinated or unsaturated N-alkyl chain: identification of potent α-glucosidase and trehalase inhibitors as well as F508del-CFTR correctors

The synthesis of eleven 1-deoxynojirimycin (DNJ) derivatives presenting either a monofluoro, difluoro, thiolated or unsaturated N-alkyl chain of various length is described. Exploiting the unsaturated moiety on the nitrogen, fluorine has been introduced through a HF/SbF5 superacid catalysed hydrofluorination and thiol-ene click chemistry allowed introduction of sulfur. The synthetic derivatives have been tested for their ability to inhibit glycosidases and correct F508del-CFTR. Two of the unsaturated iminosugars exhibited potency similar to Miglustat as F508del-CFTR correctors. The thioalkyl iminosugars as well as the corresponding alkyl iminosugars demonstrated low micromolar α-glucosidases and trehalases inhibition. Introduction of fluorine abolished F508del-CFTR correction and trehalase inhibition.

Surface functionalization by covalent immobilization of an innovative carvacrol derivative to avoid fungal biofilm formation

Carvacrol, an aromatic terpenic compound, known to be antimicrobial was grafted onto gold surfaces via two strategies based on newly-synthesized cross-linkers involving either an ester bond which can be cleaved by microbial esterases, or a covalent ether link. Surface functionalizations were characterized at each step by reflection absorption infrared spectroscopy (RAIRS). The two functionalized gold samples both led to a loss of culturability of the yeast Candida albicans, higher than 65%, indicating that the activity of the freshly-designed surfaces was probably due to still covalently immobilized carvacrol. On the contrary, when a phenyl group replaced the terpenic moiety, the yeast culturability increased by about 30%, highlighting the specific activity of carvacrol grafted on the surfaces. Confocal microscopy analyses showed that the mode of action of the functionalized surfaces with the ester or the ether of carvacrol was, in both cases, fungicidal and not anti-adhesive. Finally, this study shows that covalently immobilization of terpenic compounds can be used to design promising antimicrobial surfaces.