The preclinical testing strategy for the development of novel chemical entities for the treatment of asthma.

Identifying and developing novel chemical entities (NCE) for the treatment of asthma is a time-consuming process and liabilities that endanger the successful progression of a compound from research into the patient are found throughout all phases of drug discovery. In particular the failure of advanced compounds in clinical studies due to lack of efficacy and/or safety concerns is tremendously costly. Therefore, in order to try and reduce the failure rate in clinical trials various in vitro and in vivo tests are performed during preclinical development, to rapidly identify liabilities, eliminate high risk compounds and promote promising potential drug candidates. To achieve this objective, numerous prerequisites have to be met regarding the physico-chemical properties of the compound, and bioactivity or model systems are needed to rate the therapeutic potential of new compounds. Drug liabilities such as target and species specificity, formulation issues, pharmacokinetics as well as pharmacodynamics and the toxic potential of the compound have to be analyzed in great detail before a compound can enter a clinical trial. A particularly challenging aspect of developing novel NCEs for the treatment of asthma is choosing and setting up in vivo models believed to be predictive for human disease. Numerous companies have in the past and are currently developing NCEs targeting many different pathways and cells with the aim to treat asthma. However, currently the only NCE having a significant market share are long-acting beta-agonists (LABA), inhaled and orally active steroids and leukotriene receptor antagonists. In the past many novel NCE for the treatment of asthma were effective in animal models but failed in the clinic. In this review we outline the prerequisites of novel NCE needed for clinical development.

Mice vaccinated with allergen-pulsed myeloid dendritic cells are not protected from developing allergen-induced Th2 responses.

BACKGROUND: Dendritic cells (DC) play a decisive role in the induction of allergen-induced Th1 and Th2 responses. Since the induction of allergen-specific Th1 responses has shown to inhibit allergen-induced Th2-type inflammation, in this study we investigated whether manipulated myeloid-derived DC pulsed with the specific allergen would predominantly induce allergen-specific Th1 responses thereby reducing the development of Th2 responses. METHODS: Murine bone marrow (BM)-DC were generated and pulsed with ovalbumin (OVA) and CpG oligodeoxynucleotides (CpG-ODN). Langerhans cells (LC) were also isolated and pulsed in vitro with OVA. Subsequently, mice were vaccinated intravenously with either CpG/OVA-pulsed BM-DC or OVA-pulsed LC, and the protocol to induce OVA-specific Th2 responses using OVA/alum sensitization was initiated. Airway inflammation and OVA-specific serum antibody levels were evaluated 6 days after the intranasal challenge with OVA. RESULTS: The application ofCpG/OVA-pulsed BM-DC was unable to reduce airway eosinophilia and inflammation in OVA/alum-immunized mice. OVA-specific IgG1 or IgE serum levels were also not reduced. The experiments using LC pulsed with OVA yielded similar results. However, mice vaccinated with CpG/OVA-pulsed BM-DC had greatly enhanced levels of serum OVA-specific IgG2a, suggesting the induction of allergen-specific Th1 responses in vivo. Moreover, allergen-induced mast cell degranulation was decreased using this approach. CONCLUSIONS: Taken together, our results demonstrated that the vaccination with OVA-pulsed BM-DC matured with CpG-ODN or OVA-pulsed LC did not result in a reduction in allergen-specific Th2 responses in a murine model of severe atopic asthma. Other DC-based vaccination strategies should be evaluated in order to prevent the development of allergic disorders.

Application of heat killed Mycobacterium bovis-BCG into the lung inhibits the development of allergen-induced Th2 responses.

We have previously reported that an infection of the lung with BCG-inhibited ovalbumin (OVA)-induced airway eosinophilia. In the current study, we investigated if the intranasal application of heat killed (HK)-BCG or purified protein derivative (PPD) from Mycobacterium tuberculosis had the same effect. For this purpose we treated mice intranasally with either live BCG, HK-BCG or PPD and analyzed if the mice developed airway eosinophilia after immunization and intranasal challenge with OVA. Our results clearly showed that an intranasal vaccination with live and HK-BCG but not PPD, given 4 or 8 weeks prior to allergen airway challenge, resulted in a strong suppression of airway eosinophilia. The inhibition of airway eosinophilia correlated with reduced levels of IL-5 production by T cells from the lymph node of the lungs and a strong reduction in Th2 cell numbers present in the airways of OVA-challenged mice. Furthermore, HK-BCG-induced suppression of airway eosinophilia was strongly reduced in IFN-gamma deficient mice. HK-BCG in contrast to live BCG may also be a promising candidate for a prospective asthma vaccine in humans since negative side effects due to mycobacterial infection can be ruled out.