**2. Challenge of aerosol drug delivery in lung cancer**

#### **2.1 Aerosol deposition**

Effective drug delivery to the lungs *via* the airways requires a detailed knowledge of aerosols. The main parameters that should be considered are the particle size, the inspiratory flow rate, the volume of the inhalation and the calibre of the patient's airways. The model developed by Weibel divides the lungs into 23 serial branching generations. The first sixteen form the conducting bronchial airways and the last seven, the respiratory zone (or alveolar region) (Weibel et al., 1963). The lungs may also be divided in three parts, upper (apex), middle and lower (base). Thus the major challenge involved in delivering drugs into the lungs is provided by the complex structure of the respiratory tract.

The Airways: A Promising Route for the Pulmonary Delivery of Anticancer Agents 55

added when the volume is lower. Ultrasonic nebulisers use a high-frequency piezoelectric system to produce ultrasound, which then nebulises a drug solution. This system is not compatible with all molecules because the ultrasound can destroy certain drugs. In vibrating-mesh nebulisers, the drug solution is compressed by perforated membranes that are vibrating rapidly. All types of nebuliser are only half as efficient with nasal inhalation as

A pMDI is a handheld device that contains a drug in solution or suspension and a gas like hydrofluoroalkane to propel the solution/suspension. It must be shaken before use to mix gas with the drug solution/suspension. The most important component of the pMDI is the metering valve (Hess et al., 2008). This is because the pMDI canister is used inverted, and the valve prevents the drug from leaking due to gravity. The advantages of this system are its small size, ease of use, and its portability. However, good coordination between hand movements and inhalation is needed for efficient drug deposition. Devices with an automatic release have been developed for patients with coordination disorders. A valve holding chamber can also be placed between the MDI and the patient to ensure that aerosol

The drug used in the DPI system is formulated as a dry powder. The devise has a dosing principle and an inhaler (Pedersen, 1996). The powder is broken down into small particles by the force of the patient's inhalation. DPI is available in multi-dose and single-dose models. The single-dose model has a single drug capsule that must be manually inserted

Education is essential for effective drug delivery *via* the airways. Nurses, physicians and pharmacists must all learn how to use inhalers so as to prevent their misuse or inadequate treatment. Mishandling of aerosol devices like the pMDI is associated with decreased asthma control (Giraud and Roche, 2002). Patients must be also educated to inhale properly in order to maximize drug deposition in the intended lung compartment. Most of the anticancer drugs presently being evaluated in clinical trials have been administered to the airways with nebulisers. Nebulisers and endotracheal sprays have generally been used to

Official sources, such as the European Respiratory Society, have not yet established procedures for using anticancer drugs to treat lung cancer. They have only discussed the lack of evidence for using opiates and bronchodilators in palliative care (Boe et al., 2001). Herein, we propose some advices based on official recommendations established for other respiratory diseases (such as COPD and asthma). Certain steps should be scrupulously respected if a drug is administered *via* the airways. The choice of the device is critical because they are not compatible for all drugs. Physicians may prefer not to use pMDI or DPI systems for patients with coordination disorders or memory deficiency. A mouthpiece is the most suitable means of improving lung deposition and is safer for the patient as it avoids injuring the eyes. The manufacturer's instructions (formulation, solution volume and type of driver gas) should be respected to ensure optimal drug deposition, and effective treatment. Nebulisers should be cleaned carefully to prevent bacterial contamination and subsequent lung infections. Maintenance procedures are available for all nebulisers and they should be communicated to the patient. Single-dose nebulisers may be most suitable for hospitalised

with oral inhalation (Everard et al., 1993).

is retained in the chamber and released when the patient breathes.

deliver anticancer drugs in preclinical studies to animals.

patients, with replacement every 24 hours.

into the device by the patient. These drug capsules must not be ingested.

**2.3 Recommendations for delivering anticancer drugs** *via* **the airways** 

Aerosols generally have a polydisperse particle size distribution, and particle size is one of the most important factors influencing aerosol deposition in the lungs. The mass median aerodynamic diameter (MMAD) is usually used to estimate the particle size distribution. The MMAD describes an aerosol in terms of its mass and size. It is defined as 50 % of the mass of the particles less than MMAD and 50 % greater than the MMAD (Soderlom, 1989). Analysis of lung depositions indicated that almost all particles with a MMAD >5 µm are deposited in the oropharynx. Most of those with a MMAD of 2 to 6 µm are deposited in the bronchi (conducting airways) and fine particles with a MMAD <2 µm are deposited in the alveolar region. Most of the particles smaller than 1 µm are presumably exhaled (Newman et al., 1983).

The depositing of particles in the lungs also depends on several other parameters. One is the inspiratory flow rate (IFR). The particles display high velocity and turbulence when the IFR increases, causing them to be deposited in the conducting airways (Dolovich et al., 2000). Thus drug deposition in the upper airways can be improved by increasing the IFR. In contrast, a low IFR and gas density help aerosols to penetrate into the lung periphery (Anderson et al., 1990). The penetration of particles into the alveolar region also depends on the inhaled volume. Particles are better deposited in the lung peripheries of patients with a high FEV1 (forced expiratory volume in one second) (Pavia et al. 1976). Similarly, rapid exhalation following a short breath hold can influence particle deposition in the large airway. The calibre of the airways also modulates particle deposition. There is excessive mucus secretion and accumulation in some respiratory diseases, such as cystic fibrosis and certain tumours, which leads to obstruction of the airways. This reduction in airway calibre has a negative influence on the deposition and distribution patterns of aerosols. Particle deposition is dramatically decreased in cystic fibrosis patients, even from aerosols with fine particles (<2µm), because of the secretions and reduced airway calibre (Dolovich, 2009).

The diameter of the airways of children is much smaller than those of adults. Hence, particles are deposited mainly in the oropharynx or upper airways because they impact rapidly on the bronchus barrier. The breathing patterns of children also differ from those of adults. Their tidal volume is smaller (volume of air displaced between normal inspiration and expiration) and their respiratory rate higher than those of adults, which prevents drugs from being deposited in the alveolar region. Co-operation and compliance complicate the administration of drug to children *via* the airways. Cries can be assimilated to a rapid exhalation, leading to deposition of drug almost exclusively on the surface of the oropharynx (Schüepp et al., 2004).

Few studies focused on the deposition of inhaled particles in the lungs of the elderly. They have shown that the particle deposition in old and younger patients with lung diseases were similar. However, some pulmonary delivery devices are unsuitable for patients suffering from memory loss and disorders of movement coordination (Allen et al., 2008).

#### **2.2 Technology of delivery devices**

Several devices have been developed to generate aerosol particles. They include nebulisers, pressurized-metered dose inhalers (pMDI) and dry powder inhalers (DPI). Nebulisers are widely used for drug inhalation, and there are three types of nebuliser: pneumatic (or jet), ultrasonic and vibrating-mesh. Pneumatic nebulisers use compressed air to aerosolise drug solutions. These solutions are carried into the gas stream and dispersed into droplets due to surface tension (Hess et al., 2008). A fill volume of 4-5 ml is optimal and normal saline is

Aerosols generally have a polydisperse particle size distribution, and particle size is one of the most important factors influencing aerosol deposition in the lungs. The mass median aerodynamic diameter (MMAD) is usually used to estimate the particle size distribution. The MMAD describes an aerosol in terms of its mass and size. It is defined as 50 % of the mass of the particles less than MMAD and 50 % greater than the MMAD (Soderlom, 1989). Analysis of lung depositions indicated that almost all particles with a MMAD >5 µm are deposited in the oropharynx. Most of those with a MMAD of 2 to 6 µm are deposited in the bronchi (conducting airways) and fine particles with a MMAD <2 µm are deposited in the alveolar region. Most of the particles smaller than 1 µm are presumably exhaled (Newman

The depositing of particles in the lungs also depends on several other parameters. One is the inspiratory flow rate (IFR). The particles display high velocity and turbulence when the IFR increases, causing them to be deposited in the conducting airways (Dolovich et al., 2000). Thus drug deposition in the upper airways can be improved by increasing the IFR. In contrast, a low IFR and gas density help aerosols to penetrate into the lung periphery (Anderson et al., 1990). The penetration of particles into the alveolar region also depends on the inhaled volume. Particles are better deposited in the lung peripheries of patients with a high FEV1 (forced expiratory volume in one second) (Pavia et al. 1976). Similarly, rapid exhalation following a short breath hold can influence particle deposition in the large airway. The calibre of the airways also modulates particle deposition. There is excessive mucus secretion and accumulation in some respiratory diseases, such as cystic fibrosis and certain tumours, which leads to obstruction of the airways. This reduction in airway calibre has a negative influence on the deposition and distribution patterns of aerosols. Particle deposition is dramatically decreased in cystic fibrosis patients, even from aerosols with fine particles (<2µm), because of the secretions and reduced airway calibre (Dolovich, 2009). The diameter of the airways of children is much smaller than those of adults. Hence, particles are deposited mainly in the oropharynx or upper airways because they impact rapidly on the bronchus barrier. The breathing patterns of children also differ from those of adults. Their tidal volume is smaller (volume of air displaced between normal inspiration and expiration) and their respiratory rate higher than those of adults, which prevents drugs from being deposited in the alveolar region. Co-operation and compliance complicate the administration of drug to children *via* the airways. Cries can be assimilated to a rapid exhalation, leading to deposition of drug almost exclusively on the surface of the

Few studies focused on the deposition of inhaled particles in the lungs of the elderly. They have shown that the particle deposition in old and younger patients with lung diseases were similar. However, some pulmonary delivery devices are unsuitable for patients suffering

Several devices have been developed to generate aerosol particles. They include nebulisers, pressurized-metered dose inhalers (pMDI) and dry powder inhalers (DPI). Nebulisers are widely used for drug inhalation, and there are three types of nebuliser: pneumatic (or jet), ultrasonic and vibrating-mesh. Pneumatic nebulisers use compressed air to aerosolise drug solutions. These solutions are carried into the gas stream and dispersed into droplets due to surface tension (Hess et al., 2008). A fill volume of 4-5 ml is optimal and normal saline is

from memory loss and disorders of movement coordination (Allen et al., 2008).

et al., 1983).

oropharynx (Schüepp et al., 2004).

**2.2 Technology of delivery devices** 

added when the volume is lower. Ultrasonic nebulisers use a high-frequency piezoelectric system to produce ultrasound, which then nebulises a drug solution. This system is not compatible with all molecules because the ultrasound can destroy certain drugs. In vibrating-mesh nebulisers, the drug solution is compressed by perforated membranes that are vibrating rapidly. All types of nebuliser are only half as efficient with nasal inhalation as with oral inhalation (Everard et al., 1993).

A pMDI is a handheld device that contains a drug in solution or suspension and a gas like hydrofluoroalkane to propel the solution/suspension. It must be shaken before use to mix gas with the drug solution/suspension. The most important component of the pMDI is the metering valve (Hess et al., 2008). This is because the pMDI canister is used inverted, and the valve prevents the drug from leaking due to gravity. The advantages of this system are its small size, ease of use, and its portability. However, good coordination between hand movements and inhalation is needed for efficient drug deposition. Devices with an automatic release have been developed for patients with coordination disorders. A valve holding chamber can also be placed between the MDI and the patient to ensure that aerosol is retained in the chamber and released when the patient breathes.

The drug used in the DPI system is formulated as a dry powder. The devise has a dosing principle and an inhaler (Pedersen, 1996). The powder is broken down into small particles by the force of the patient's inhalation. DPI is available in multi-dose and single-dose models. The single-dose model has a single drug capsule that must be manually inserted into the device by the patient. These drug capsules must not be ingested.

Education is essential for effective drug delivery *via* the airways. Nurses, physicians and pharmacists must all learn how to use inhalers so as to prevent their misuse or inadequate treatment. Mishandling of aerosol devices like the pMDI is associated with decreased asthma control (Giraud and Roche, 2002). Patients must be also educated to inhale properly in order to maximize drug deposition in the intended lung compartment. Most of the anticancer drugs presently being evaluated in clinical trials have been administered to the airways with nebulisers. Nebulisers and endotracheal sprays have generally been used to deliver anticancer drugs in preclinical studies to animals.

#### **2.3 Recommendations for delivering anticancer drugs** *via* **the airways**

Official sources, such as the European Respiratory Society, have not yet established procedures for using anticancer drugs to treat lung cancer. They have only discussed the lack of evidence for using opiates and bronchodilators in palliative care (Boe et al., 2001). Herein, we propose some advices based on official recommendations established for other respiratory diseases (such as COPD and asthma). Certain steps should be scrupulously respected if a drug is administered *via* the airways. The choice of the device is critical because they are not compatible for all drugs. Physicians may prefer not to use pMDI or DPI systems for patients with coordination disorders or memory deficiency. A mouthpiece is the most suitable means of improving lung deposition and is safer for the patient as it avoids injuring the eyes. The manufacturer's instructions (formulation, solution volume and type of driver gas) should be respected to ensure optimal drug deposition, and effective treatment. Nebulisers should be cleaned carefully to prevent bacterial contamination and subsequent lung infections. Maintenance procedures are available for all nebulisers and they should be communicated to the patient. Single-dose nebulisers may be most suitable for hospitalised patients, with replacement every 24 hours.

The Airways: A Promising Route for the Pulmonary Delivery of Anticancer Agents 57

compatible with lung deposition. A study by Gagnadoux et al. showed that the cytotoxicity of a nebulised formulation of the nucleoside analog gemcitabine (GCB) was similar to that of the native drug when tested against NCI-H460 and A549 Non-Small Cell Lung Cancer (NSCLC) cells (Gagnadoux et al., 2006). Another study of the cytotoxicity of a nebulised farnesol formulation containing polysorbate 80 (Tween 80) in vitro for NSCLC lines (H460 and A549) showed that the anticancer properties of nebulised farnesol were essentially the same as those of the native drug (Wang et al., 2003). The cytotoxic effects of doxorubicin before and after encapsulation were compared *in vitro* using growth inhibition assays. Azarmi et al. (2006) studied doxorubicin (DOX)-loaded nanoparticles formulated as a dry powder by spray-freezedrying. The cytotoxic effects of free DOX, carrier particles containing blank nanoparticles and DOX-loaded nanoparticles were assessed using H460 and A549 lung cancer cells. The DOXnanoparticles were more cytotoxic for both cell lines a higher than were the blank nanoparticles and the free DOX. The aerosolisation of therapeutic proteins such as anticancer antibodies has also been tested. The results showed that some inhalers are suitable for limiting the formation of aggregates and preserving the pharmacological activity of the antibody *in vitro* (Maillet et al., 2008). Cetuximab, a chimeric IgG1 that targets the epidermal growth factor receptor (EGFR), was tested with three types of nebulisers: jet, mesh and ultrasonic. The immunological and pharmacological properties of nebulised cetuximab were evaluated using A431 cells. Flow cytometric analyses and assays of EGFR-phosphorylation and the inhibitions of A431 cell growth demonstrated that the mesh and jet nebulisers did not destroy the ability

The structure of the human nasal system is very different from that of all other animals except the non-human primates. The nasal anatomy of primates (human and non-human) is much simpler than that of the majority of animals (Gross et al., 1991.). Rodents cannot breathe through their mouths. Particles must be smaller than 3 µm if they are to reach the airways of rodents (Miller et al., 2000). One way to avoid nasal deposition is to introduce a catheter connected to a high pressure syringe into the trachea to deliver aerosols directly into the lungs. There are two types of tracheo-bronchial anatomy, dichotomous division and monopodial division (McBride et al. 1991). The human respiratory tract is considered to undergo dichotomous branching, while those of rats, mice and dogs are monopodial. This anatomical difference does not seem to influence aerosol deposition in the lungs, but further studies are needed to confirm this. The transition between bronchial airways and the alveolar region is gradual in humans; humans have respiratory bronchioles, while rodents do not (Tyler et al., 1993). Inhaled particles are cleared faster from the alveoli of rodents than from the alveoli of humans because rodents lack bronchioles. However, additional studies are required to determine whether this difference influences the deposition of aerosolised particles in the lungs (Phalen et al., 2008). Total aerosol deposition is better in nasal breathing humans than in oral breathing humans. Upper respiratory tract deposition is similar in nasal breathing humans and in dogs, hamsters, and rabbits. However, pulmonary deposition in nasal breathing humans is comparable to that of dogs and monkeys, but lower than in hamsters and rats. The peak particle size for pulmonary deposition is larger in

humans than in dogs, guinea pigs, monkeys, and rats (Phalen et al., 2008)

of cetuximab to bind to EGFR or its inhibitory activity.

**4. Airways delivery in preclinical studies 4.1 Animal models for aerosol delivery in cancer 4.1.1 Animal model for assessing lung deposition** 

Great care should be taken when administering anticancer agent *via* the pulmonary route. Anticancer agents are potentially toxic for the lung and may impair the pulmonary function in some patients, but most of them are not very toxic when the inhalation procedure is standardized and the dose well defined. The safety of healthcare workers should be considered. Aerosolised chemotherapy should be delivered in a well-ventilated room with an efficient air filtering system (Gagnadoux et al., 2007). Wittgen et al demonstrated the advantages of combining a mobile HEPA (High Efficiency Particulate Air) filter air cleaning system with a demistifier tent to prevent aerosol propagation during inhalation of nebulised liposomal cisplatin (Wittgen et al., 2006).
