Microbubble mediated delivery of hydrophobic drugs using lipid oil nanodroplets

Introduction: Drug delivery to tumours is fundamental for effective treatment, however systemic delivery leads to a number of off-site toxicities. The pharmaceutical industry produces a substantial number of compounds that... [ view full abstract ]

Introduction:

Drug delivery to tumours is fundamental for effective treatment, however systemic delivery leads to a number of off-site toxicities. The pharmaceutical industry produces a substantial number of compounds that are hydrophobic and therefore intravenous delivery is difficult. Some of these compounds show excellent potential in vitro, however their hydrophobicity compromises their clinical use. There is therefore an unmet clinical need for the production of vehicles that will aid the delivery of hydrophobic drugs. We have produced Lipid Oil Nanodroplets (LONDs)¹, for encapsulating hydrophobic drugs. Through on-chip assembly LONDs were attached to lipid shelled, gas filled microbubbles (MBs). The MB-LOND construct exhibits the ultrasound imaging properties characteristic of MBs and the hydrophobic drug encapsulation potential of an oil-based nanodroplet.

Methods:

LONDs were produced in a two-step high pressure homogenisation process, in the size range of 100-300nm. The vascular disrupting agent Combretastatin A4 (CA4) was encapsulated in tripropionin LONDs. In vitro immunofluorescence for cell morphology, flow cytometry for cell cycle analysis and mass spectrometry to detect drug in tumour xenografts were all used to evaluate LONDs. VEGFR2 targeted MB-LOND constructs were injected intravenously, a low intensity ultrasound was used to burst the MBs and release LONDs near the tumour region. Following treatment the perfusion marker Hoechst 33342 was injected to assess tumour vascularisation.

Results & Discussion:

In vitro CA4 released and/or uptaken in endothelial cells leads to extensive cytoskeleton rearrangement, cell cycle arrest in mitosis and cell death. CA4 was detected by mass-spectrometry in human colorectal cancer xenografts following treatment with LONDs. Using Hoechst 33342 it was observed that treated tumours had significantly less perfused vessels compared to untreated. Our results show that LONDs enable hydrophobic drug encapsulation and effective in vitro and in vivo delivery, paving the way for other hydrophobic compounds. The further development and use of MB-LOND constructs has the potential to improve and enhance delivery, as well as the therapeutic index of previously undeliverable compounds.

References:

• Mico, V. et al. Evaluation of Lipid-Stabilised Tripropionin Nanodroplets as a Delivery Route for Combretastatin A4. Int J Pharm. (2017). 547-555