Fouad Brahimi

Ligand-dependent TrkA activity in brain differentially affects spatial learning and long-term memory.

In the central nervous system, the nerve growth factor (NGF) receptor TrkA is expressed primarily in cholinergic neurons that are implicated in spatial learning and memory, whereas the NGF receptor p75NTR is expressed in many neuronal populations and glia. We asked whether selective TrkA activation may have a different impact on learning, short-term memory, and long-term memory. We also asked whether TrkA activation might affect cognition differently in wild-type mice versus mice with cognitive deficits due to transgenic overexpression of mutant amyloid-precursor protein (APP mice). Mice were treated with wild-type NGF (a ligand of TrkA and p75NTR) or with selective pharmacological agonists of TrkA that do not bind to p75NTR. In APP mice, the selective TrkA agonists significantly improved learning and short-term memory. These improvements are associated with a reduction of soluble Aβ levels in the cortex and AKT activation in the cortex and hippocampus. However, this improved phenotype did not translate into improved long-term memory. In normal wild-type mice, none of the treatments affected learning or short-term memory, but a TrkA-selective agonist caused persistent deficits in long-term memory. The deficit in wild-type mice was associated temporally, in the hippocampus, with increased AKT activity, increased brain-derived neurotrophic factor precursor, increased neurotrophin receptor homolog-2 (p75-related protein), and long-term depression. Together, these data indicate that selective TrkA activation affects cognition but does so differently in impaired APP mice versus normal wild-type mice. Understanding mechanisms that govern learning and memory is important for better treatment of cognitive disorders.

Multiple mechanisms of action of ZR2002 in human breast cancer cells: A novel combi‐molecule designed to block signaling mediated by the ERB family of oncogenes and to damage genomic DNA

The mechanism of action of ZR2002, a chimeric amino quinazoline designed to possess mixed EGFR tyrosine kinase (TK) inhibitory and DNA targeting properties, was compared to those of ZR01, a reversible inhibitor of the same class and PD168393, a known irreversible inhibitor of EGFR. ZR2002 exhibited 4‐fold stronger EGFR TK inhibitory activity than its structural homologue ZR01 but was approximately 3‐fold less active than the 6‐acrylamidoquinazoline PD168393. It preferentially blocked EGF and TGFα‐induced cell growth over PDGF and serum. It also inhibited signal transduction in heregulin‐stimulated breast tumour cells, indicating that it does not only block EGFR but also its closely related erbB2 gene product. In contrast to its structural homologues, ZR2002 was capable of inducing significant levels of DNA strand breaks in MDA‐MB‐468 cells after a short 2 hr drug exposure at a concentration as low as 10 μM. Reversibility studies using whole cell autophosphorylation and growth assays in human breast cell lines showed that in contrast to its reversible inhibitor counterpart ZR01, ZR2002 induced irreversible inhibition of EGF‐stimulated autophosphorylation in MDA‐MB‐468 cells and irreversible inhibition of cell growth. Moreover despite possessing a weaker binding affinity than PD168393, it induced a significantly more sustained antiproliferative effect than the latter after a pulse 2 hr exposure. More importantly, in contrast to ZR01 and PD168393, ZR2002 was capable of inducing significant levels of cell death by apoptosis in MDA‐MB‐468 cells. The results in toto suggest that the superior antiproliferative potency of ZR2002 may be due to its ability to induce a protracted blockade of receptor tyrosine kinase‐mediated signaling while damaging cellular DNA, a combination of events that may trigger cell‐killing by apoptosis.

The Combi-Targeting Concept: In vitro and In vivo Fragmentation of a Stable Combi-Nitrosourea Engineered to Interact with the Epidermal Growth Factor Receptor while Remaining DNA Reactive

Purpose: JDA58 (NSC 741282), a “combi-molecule” optimized in the context of the “combi-targeting concept,” is a nitrosourea moiety tethered to an anilinoquinazoline. Here, we sought to show its binary epidermal growth factor receptor (EGFR)/DNA targeting property and to study its fragmentation in vitro and in vivo. Experimental Design: The fragmentation of JDA58 was detected in cells in vitro and in vivo by fluorescence microscopy and tandem mass spectrometry. EGFR phosphorylation and DNA damage were determined by Western blotting and comet assay, respectively. Tumor data were examined for statistical significance using the Students t test. Results: JDA58 inhibited EGFR tyrosine kinase (IC50, 0.2 μmol/L) and blocked EGFR phosphorylation in human DU145 prostate cancer cells. It induced significant levels of DNA damage in DU145 cells in vitro or in vivo and showed potent antiproliferative activity both in vitro and in a DU145 xenograft model. In cell-free medium, JDA58 was hydrolyzed to JDA35, a fluorescent amine that could be observed in tumor cells both in vitro and in vivo. In tumor cells in vitro or in vivo, or in plasma collected from mice, the denitrosated species JDA41 was the predominant metabolite. However, mass spectrometric analysis revealed detectable levels of the hydrolytic product JDA35 in tumor cells both in vitro and in vivo. Conclusions: The results in toto suggest that growth inhibition in vitro and in vivo may be sustained by the intact combi-molecule plus JDA35 plus JDA41, three inhibitors of EGFR, and the concomitantly released DNA-damaging species. This leads to a model wherein a single molecule carries a complex multitargeted-multidrug combination.

Synthesis of pyrimidinopyridine-triazene conjugates targeted to abl tyrosine kinase.

The synthesis and abl tyrosine kinase inhibitory activities of alkyltriazenes conjugated to phenylaminopyrimidines are described. Significant abl inhibitory activities were observed only when a benzamido spacer was inserted between the 1,2,3-triazene chain and the 2-phenyaminopyridopyrimidine moiety.

Bivalent Diketopiperazine-Based Tropomysin Receptor Kinase C (TrkC) Antagonists

Bivalent molecules containing two beta-turn mimics with side chains that correspond to hot-spots on the neurotrophin NT-3 were prepared. Binding assays showed the mimetics to be selective TrkC ligands, and biological assays showed one mimetic to be an antagonist of the TrkC receptor.

A peptidomimetic of NT-3 acts as a TrkC antagonist

Neurotrophins are a family of growth factors that regulate the peripheral and central nervous system. We designed and tested a mini-library of small molecules peptidomimetics based on beta-turns of the neurotrophin growth factor polypeptides NT-3, which is the natural ligand for TrkC receptors. Biological studies identified a peptidomimetic 2Cl that exhibited selective antagonism of TrkC. 2Cl reduces TrkC activation and signaling promoted by NT-3, and selectively blocks ligand-dependent cell survival. 2Cl also blocks ligand-independent TrkC activation and signals that take place when the receptor is over-expressed. This work adds to our understanding of how the neurotrophins function through Trk receptors, and demonstrates that peptidomimetics can be designed to selectively disturb neurotrophin-receptor interactions, and receptor activation.

The combi-targeting concept : Evidence for the formation of a novel inhibitor in vivo

With the purpose of developing drugs that can block multiple targets in tumor cells, molecules termed combi-molecules or TZ–I have been designed to be hydrolyzed in vitro to TZ+I, where TZ is a DNA-damaging species and I is an inhibitor of the epidermal growth factor receptor (EGFR). Using HPLC and liquid chromatography–mass spectrometry (LC–MS), we investigated the mechanism of in vivo degradation of a prototype of one such combi-molecule, ZRBA1, which when administered i.p. rapidly degraded into FD105 (Cmax=50 μmol/l, after 30 min), a 6-aminoquinazoline that was N-acetylated to give FD105Ac (IAc) (Cmax=18 μmol/l, after 4 h). A similar rate of acetylation was observed when independently synthesized FD105 was administered i.p. More importantly, the EGFR binding affinity of IAc was 3-fold greater than that of I, indicating that the latter is converted in vivo into an even more potent EGFR inhibitor. The results in toto suggest that while in vitro TZ–I is only hydrolyzed to I+TZ, further acetylation of I in vivo leads to a third component – a highly potent EGFR inhibitor with a delayed Cmax.

Enhancement of the cytotoxic potential of the mixed EGFR and DNA-targeting 'combi-molecule' ZRBA1 against human solid tumour cells by a bis-quinazoline-based drug design approach.

ZRBA1 is a quinazoline-based molecule termed ‘combi-molecule’ designed to block the epidermal growth factor receptor (EGFR) and further degrade to FD105, an EGFR inhibitor plus a DNA-alkylating agent. To augment the potency of ZRBA1, we designed JDE52, a bistriazene that, following degradation, was ‘programmed’ to yield higher concentrations of the free inhibitor FD105 and a more cytotoxic bifunctional DNA-damaging species. The results indicated that JDE52 was capable of inducing significant blockade of EGFR phosphorylation, DNA strand breaks and interstrand cross-links in human cells. The fluorescent property of FD105, the secondary inhibitor that both JDE52 and ZRBA1 are capable of releasing, has permitted the analysis of its levels in tumour cells by ultraviolet flow cytometry. It was found that JDE52 was indeed capable of significantly releasing higher levels of fluorescence (P<0.05) in human tumour cells when compared with ZRBA1. Apoptosis was triggered by JDE52 at a faster rate than ZRBA1 and led to higher levels of cell killing. The results in toto suggest that the superior potency of JDE52, when compared with ZRBA1, may be imputed to mechanisms associated with the generation of higher intracellular concentrations of FD105 and to the induction of DNA cross-links. These combined mechanisms (blockade of EGFR-tyrosine kinase and induction of cross-links) contributed to an accelerated rate of apoptosis by JDE52. This study conclusively demonstrated that designing molecules as prodrugs of high levels of quinazoline inhibitors of EGFR and bifunctional DNA cross-linking species is a valid strategy to enhance the potency of mixed EGFR-DNA-targeting combi-molecules.

The Paradoxical Signals of Two TrkC Receptor Isoforms Supports a Rationale for Novel Therapeutic Strategies in ALS

Full length TrkC (TrkC-FL) is a receptor tyrosine kinase whose mRNA can be spliced to a truncated TrkC.T1 isoform lacking the kinase domain. Neurotrophin-3 (NT-3) activates TrkC-FL to maintain motor neuron health and function and TrkC.T1 to produce neurotoxic TNF-α; hence resulting in opposing pathways. In mouse and human ALS spinal cord, the reduction of miR-128 that destabilizes TrkC.T1 mRNA results in up-regulated TrkC.T1 and TNF-α in astrocytes. We exploited conformational differences to develop an agonistic mAb 2B7 that selectively activates TrkC-FL, to circumvent TrkC.T1 activation. In mouse ALS, 2B7 activates spinal cord TrkC-FL signals, improves spinal cord motor neuron phenotype and function, and significantly prolongs life-span. Our results elucidate biological paradoxes of receptor isoforms and their role in disease progression, validate the concept of selectively targeting conformational epitopes in naturally occurring isoforms, and may guide the development of pro-neuroprotective (TrkC-FL) and anti-neurotoxic (TrkC.T1) therapeutic strategies.

A bioanalytical investigation on the exquisitely strong in vitro potency of the EGFR-DNA targeting type II combi-molecule ZR2003 and its mitigated in vivo antitumour activity.

ZR2003 is a type II of combi-molecule designed to target DNA and the epidermal growth factor receptor (EGFR) without requirement for hydrolysis. In human tumour cell lines cultured as monolayers, it showed 6.5-35 fold greater activity than Iressa. Further evaluation in 3D organ-like multilayer aggregates showed that it could block proliferation at submicromolar level. However, despite the superior potency of ZR2003 over Iressa in vitro, its activity xenograft models was not significantly different from that of Iressa. To rationalize these results, we determined the tumour concentration of both ZR2003 and Iressa in vivo and more importantly in vitro in multicellular aggregates. The results showed that in A431 and 4T1 xenografts, the level of ZR2003 absorbed in the tumours were consistently 2-fold less than those generated by Iressa. Likewise, in the multicellular aggregates model, the penetration of ZR2003 was consistently lower than Iressa. In serum containing media, the level of extractable or free ZR2003 was also inferior to those of Iressa. The results from this bioanalytical study, suggest that the discrepancy between the in vitro and in vivo potency of ZR2003 when compared with Iressa, may be imputed to its significantly lower tumour concentration.