Poly(amidoamine) Dendrimer-Doxorubicin Conjugates: In Vitro Characteristics and Pseudosolution Formulation in Pressurized Metered-Dose Inhalers

Lung cancers are the leading cause of cancer death for both men and women. A series of PEGylated poly(amidoamine) dendrimer-based doxorubicin (DOX) nanocarriers (G3NH(2)-mPEG-nDOX) were synthesized and their chemistry tailored for the development of novel pseudosolution formulations in propellant-based metered dose inhalers (pMDIs) with enhanced aerosol characteristics. A pH-labile bond was used to conjugate DOX to dendrimer for controlled intracellular release. We employed a two-step PEGylation strategy to cover a range of DOX loading and PEGylation density. We investigated the impact of pH, PEGylation density, and DOX payload on the release of DOX from the conjugate. We also determined the cellular internalization of the conjugate, the intracellular release kinetics of DOX from the conjugate, and their ability to kill human alveolar carcinoma cells (A549). The acid-labile conjugates sustained the release of DOX in acidic medium, and also intracellularly, as determined by nuclear colocalization studies with confocal microscopy. Meanwhile, DOX was retained in the conjugate at extracellular physiological conditions, indicating their potential to achieve spatial and temporal controlled release profiles. We also observed that the kinetics of cellular entry of the conjugates with DOX increased significantly compared to free DOX. Due to controlled release, the G3NH2-mPEG-nDOX conjugates showed time dependent cell kill, but their cell kill ability was comparable to free DOX, which suggests their potential in vivo as compared to free DOX. The conjugates were formulated in pMDIs as pseudosolution formulations, with the help of a minimum amount of cosolvent (ethanol; <0.4%; v/v). The physical stability and aerosol characteristics of the conjugates were controlled by the PEGylation density of the carriers: the higher the PEG density, the better the dispersibility and the better the deep lung deposition of the conjugates (fine particle fraction up to ca. 80%).