Mucosal Antibodies to the C Terminus of Toxin A Prevent Colonization of Clostridium difficile.

Mucosal immunity is considered important for protection against Clostridium difficile infection (CDI). We show that in hamsters immunized with Bacillus subtilis spores expressing a carboxy-terminal segment (TcdA26-39) of C. difficile toxin A, no colonization occurs in protected animals when challenged with C. difficile strain 630. In contrast, animals immunized with toxoids showed no protection and remained fully colonized. Along with neutralizing toxins, antibodies to TcdA26-39 (but not to toxoids), whether raised to the recombinant protein or to TcdA26-39 expressed on the B. subtilis spore surface, cross-react with a number of seemingly unrelated proteins expressed on the vegetative cell surface or spore coat of C. difficile These include two dehydrogenases, AdhE1 and LdhA, as well as the CdeC protein that is present on the spore. Anti-TcdA26-39 mucosal antibodies obtained following immunization with recombinant B. subtilis spores were able to reduce the adhesion of C. difficile to mucus-producing intestinal cells. This cross-reaction is intriguing yet important since it illustrates the importance of mucosal immunity for complete protection against CDI.

DTS-108, a novel peptidic prodrug of SN38: in vivo efficacy and toxicokinetic studies.

PURPOSE: Irinotecan is a prodrug converted to the active cytotoxic molecule SN38 predominantly by the action of liver carboxylesterases. The efficacy of irinotecan is limited by this hepatic activation that results in a low conversion rate, high interpatient variability, and dose-limiting gastrointestinal toxicity. The purpose of this study was to evaluate a novel peptidic prodrug of SN38 (DTS-108) developed to bypass this hepatic activation and thus reduce the gastrointestinal toxicity and interpatient variability compared with irinotecan. EXPERIMENTAL DESIGN: SN38 was conjugated to a cationic peptide (Vectocell) via an esterase cleavable linker. The preclinical development plan consisted of toxicity and efficacy evaluation in a number of different models and species. RESULTS: The conjugate (DTS-108) is highly soluble, with a human plasma half-life of 400 minutes in vitro. Studies in the dog showed that DTS-108 liberates significantly higher levels of free SN38 than irinotecan without causing gastrointestinal toxicity. In addition, the ratio of the inactive SN38-glucuronide metabolite compared with the active SN38 metabolite is significantly lower following DTS-108 administration, compared with irinotecan, which is consistent with reduced hepatic metabolism. In vivo efficacy studies showed that DTS-108 has improved activity compared with irinotecan. A significant dose-dependent antitumoral efficacy was observed in all models tested and DTS-108 showed synergistic effects in combination with other clinically relevant therapeutic agents. CONCLUSIONS: DTS-108 is able to deliver significantly higher levels of SN38 than irinotecan, without the associated toxicity of irinotecan, resulting in an increased therapeutic window for DTS-108 in preclinical models. These encouraging data merit further preclinical and clinical investigation.

Preclinical toxicity, toxicokinetics, and antitumoral efficacy studies of DTS-201, a tumor-selective peptidic prodrug of doxorubicin.

PURPOSE: There is a clear clinical need for cytotoxic drugs with a lower systemic toxicity. DTS-201 (CPI-0004Na) is a peptidic prodrug of doxorubicin that shows an improved therapeutic index in experimental models. The purpose of the current study was to complete its preclinical characterization before initiation of phase I clinical trials. EXPERIMENTAL DESIGN: The preclinical development program consisted of a detailed assessment of the general and cardiac toxicity profiles of DTS-201 in mice, rats, and dogs, together with mass balance and antitumoral efficacy studies in rodents. Neprilysin and thimet oligopeptidase expression, two enzymatic activators of DTS-201, was also characterized in human breast and prostate tumor biopsies. RESULTS: The target organs of DTS-201 toxicity in rodents and dogs are typically those of doxorubicin, albeit at much higher doses. Importantly, chronic treatment with DTS-201 proved to be significantly less cardiotoxic than with doxorubicin at doses up to 8-fold higher in rats. The mass balance study showed that [14C] DTS-201 does not accumulate in the body after intravenous administration. The improved therapeutic index of DTS-201 compared with free doxorubicin was confirmed in three tumor xenograft models of prostate, breast, and lung cancer. Neprilysin and/or thimet oligopeptidase are expressed in all experimental human tumor types thus far tested as well as in a large majority of human breast and prostate tumor biopsies. CONCLUSION: DTS-201 gave promising results in terms of general toxicity, cardiovascular tolerance, and in vivo efficacy in xenograft mouse models compared with free doxorubicin. Taken together, these results and the confirmation of the presence of activating enzymes in human tumor biopsies provide a strong rationale for a phase I clinical study in cancer patients.

Improved therapeutic efficacy of doxorubicin through conjugation with a novel peptide drug delivery technology (Vectocell).

Improvement in the therapeutic index of doxorubicin, a cytotoxic molecule, has been sought through its chemical conjugation to short (15-23 amino acid) peptide sequences called Vectocell peptides. Vectocell peptides are highly charged drug delivery peptides and display a number of characteristics that make them attractive candidates to minimize many of the limitations observed for a broad range of cytotoxic molecules. The studies reported here characterized the in vitro and in vivo efficacy of a range of Vectocell peptides conjugated to doxorubicin through different linkers. These studies show that the in vivo therapeutic index of doxorubicin can be improved by conjugation with a specific Vectocell peptide (DPV1047) through an ester linker to C14 of doxorubicin, in both colon and breast tumor models. This conjugate was also shown to have significant in vivo antitumoral activity in a model resistant to doxorubicin, suggesting that this conjugate is able to circumvent the multidrug resistance (MDR) phenotype. These experiments therefore provide support for the use of the Vectocell technology with other cytotoxic agents.

Novel human-derived cell-penetrating peptides for specific subcellular delivery of therapeutic biomolecules.

Short peptide sequences that are able to transport molecules across the cell membrane have been developed as tools for intracellular delivery of therapeutic molecules. This work describes a novel family of cell-penetrating peptides named Vectocell peptides [also termed DPVs (Diatos peptide vectors)]. These peptides, originating from human heparin binding proteins and/or anti-DNA antibodies, once conjugated to a therapeutic molecule, can deliver the molecule to either the cytoplasm or the nucleus of mammalian cells. Vectocell peptides can drive intracellular delivery of molecules of varying molecular mass, including full-length active immunoglobulins, with efficiency often greater than that of the well-characterized cell-penetrating peptide Tat. The internalization of Vectocell peptides has been demonstrated to occur in both adherent and suspension cell lines as well as in primary cells through an energy-dependent endocytosis process, involving cell-membrane lipid rafts. This endocytosis occurs after binding of the cell-penetrating peptides to extracellular heparan sulphate proteoglycans, except for one particular peptide (DPV1047) that partially originates from an anti-DNA antibody and is internalized in a caveolar independent manner. These new therapeutic tools are currently being developed for intracellular delivery of a number of active molecules and their potentiality for in vivo transduction investigated.

A novel four transmembrane spanning protein, CLP24. A hypoxically regulated cell junction protein.

A novel hypoxically regulated intercellular junction protein (claudin-like protein of 24 kDa, CLP24) has been identified that shows homology to the myelin protein 22/epithelial membrane protein 1/claudin family of cell junction proteins, which are involved in the modulation of paracellular permeability. The CLP24 protein contains four predicted transmembrane domains and a C-terminal protein-protein interaction domain. These domains are characteristic of the four transmembrane spanning (tetraspan) family of proteins, which includes myelin protein 22, and are involved in cell adhesion at tight, gap and adherens junctions. Expression profiling analyses show that CLP24 is highly expressed in lung, heart, kidney and placental tissues. Cellular studies confirm that the CLP24 protein localizes to cell-cell junctions and co-localizes with the beta-catenin adherens junction-associated protein but not with tight junctions. Over-expression of CLP24 results in decreased adhesion between cells, and functional paracellular flux studies confirm that over-expression of the CLP24 protein modulates the junctional barrier function. These data therefore suggest that CLP24 is a novel, hypoxically regulated tetraspan adherens junction protein that modulates cell adhesion, paracellular permeability and angiogenesis.

The relevance of alternative RNA splicing to pharmacogenomics.

The importance of alternative RNA splicing in the generation of genetic diversity is now widely accepted. This article highlights how alternative RNA splicing can have an impact on drug efficacy and safety, and demonstrates its potential pharmacogenomic value. The analysis of the repertoire of alternative RNA splicing events could potentially identify markers of pharmacogenomic relevance with high sensitivity and specificity and also provides a route through which genes can be selected for single nucleotide polymorphism (SNP) genotyping. Recent methodological advances, including microarray and splice-dedicated expression profiling, have made it possible to perform high-throughput alternative splicing analyses.