**1. Introduction**

434 Chronic Obstructive Pulmonary Disease – Current Concepts and Practice

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Recent drug development for chronic obstructive pulmonary disease (COPD) has focused on strategies aimed at reducing the underlying inflammation by selective inhibition of phosphodiesterases (PDE), specifically the PDE4 isoforms. The anti-inflammatory and bronchodilator activities of PDE4 inhibitors have been well documented (Giembycz &Field 2010), however their clinical development has been hampered by their low therapeutic ratio and dose-dependent systemic side effects. PXS TPI1100 is an inhaled drug candidate consisting of two modified antisense oligonucleotides (AON) directed at PDE isoforms 4B, 4D and 7A. PXS TPI1100 has been designed to reduce the recruitment and persistence of inflammatory cells in COPD through an unique mechanism of action and has the potential to be a novel, highly effective approach for this respiratory disease.

In this chapter, we will present the rationale for the design of PXS TPI1100 including a summary of the PDE families and the proposed role they play in regulating inflammation in the lung. Next we will present an overview of the discovery and selection process for the drug candidate, including a summary of the key results from pre-clinical pharmacology, both *in vitro* models as well as two *in vivo* models of neutrophilic inflammation: cigarette smoke mouse model and LPS challenge model. These results will be compared to the first-in-class PDE4 inhibitor, roflumilast (Daxas/Daliresp). We shall conclude with the expected development plan for PXS TPI1100 including the design of upcoming clinical study trials.

#### **2. Chronic obstructive pulmonary disease**

COPD is a respiratory disease of airway obstruction and lung damage and is sometimes called chronic bronchitis and/or emphysema. COPD kills millions of people each year and it is currently the fourth leading cause of death worldwide, with forecasts to be the third leading cause by 2020 (ref www.goldcopd.com). COPD, as defined by the Global Initiative for Chronic Lung Disease (GOLD) is *"a preventable and treatable disease with some extrapulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterized by airflow limitation that is not fully reversible. The airflow limitation is* 

A Multi-Targeted Antisense Oligonucleoitde-Based

**2.2 Phosphodiesterases as targets for COPD** 

Therapy Directed at Phosphodiesterases 4 and 7 for COPD 437

PDE4 is a member of the PDE family of enzymes whose function is to selectively catalyze the hydrolysis of cycle adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP) (Bender &Beavo 2006). Second messengers perform intracellular signaling and cAMP is a key member. The level of cAMP can be regulated by its rate of degradation which is controlled by PDEs (Figure 1). As such, the regulation of PDEs is sophisticated and complex. This family currently includes 11 members (PDE1 to PDE11) of which there are multiple isoforms or splice variants. Several different PDEs can be expressed in a single cell type, and the localization of these PDEs within a cell regulates the local concentration of cAMP or cGMP. Besides being regulated through differential genetic expression, PDEs can be biochemically regulated by phosphorylation, binding of Ca2+/calmodulin and various protein-protein interactions (Bender &Beavo 2006). The PDEs with higher affinity for cAMP than cGMP include PDE3, PDE4, PDE7, PDE8 and PDE11 (similar affinities). These multiple isoforms and their differential expression across cell types

Fig. 1. Cartoon of the cAMP pathway, which is presumably activated upon binding of a stimuli to its receptor embedded in the cell membrane. Known components of this pathway include the calcium/calmodulin-activated adenylyl cyclase, the phosphodiesterase (PDE), and cAMP-dependent protein kinase (PKA) with its catalytic and regulatory subunits. Activation of PKA will lead to phosphorylation of cytoplasmic and nuclear targets. In the lung, inhibition of the PDE will lead to an elevation of the intracellular levels of cAMP resulting with a reduction of the bronchoconstriction, mucus secretion, cellular

inflammation and in the long term decrease the emphysema/oedema.

*usually progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases"* (Gold 2009). Symptoms of COPD include chronic cough, excessive sputum production, wheeze, shortness of breath and chest tightness. The 4 stages of COPD, designated as Mild, Moderate, Severe and Very Severe, are defined according to lung function as assessed by spirometry, usually the post-bronchodilator ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC). The cellular and molecular mechanisms that contribute to COPD pathogenesis remain incompletely understood yet it is believed that COPD is caused by underlying inflammation characterized by increased presence of neutrophils, macrophages and CD8+ T cells (Gold 2009). Products of neutrophils induce mucus hypersecretion and are implicated both in the generation of mucus metaplasia in chronic bronchitis and the destruction of lung tissue in emphysema. Macrophages are also sources of proteinases and antiproteinases in the lung, oxidative stress and mucus hypersecretion (Ward 2010). Exacerbations play a large role in the disease progression of COPD, and exacerbations become more frequent and more severe as COPD progresses (Hurst et al. 2010).
