Preferential liver gene expression with polypropylenimine dendrimers

Area of Science:

• Biochemistry
• Nanotechnology
• Molecular Biology

Background:

• Polypropylenimine dendrimers (DAB) have demonstrated in vitro gene delivery capabilities.
• Previous studies focused on lower generation dendrimers for gene delivery.
• The impact of carrier-DNA interaction strength and in vivo activity of low molecular weight carriers remained to be fully elucidated.

Purpose of the Study:

• To investigate the effect of electrostatic interaction strength between dendrimers and DNA on gene transfer.
• To evaluate the in vivo gene transfer activity of non-amphiphilic, low molecular weight dendrimer carriers.
• To synthesize and characterize quaternary ammonium derivatives of polypropylenimine dendrimers for gene delivery.

Main Methods:

• Synthesis of methyl quaternary ammonium derivatives (Q4, Q8, Q16, Q32) from DAB dendrimers.
• Ethidium bromide exclusion assay and colloidal stability tests to assess DNA binding.
• In vitro biocompatibility and in vivo gene transfer studies following intravenous administration.

Main Results:

• Quaternization of DAB 8 significantly enhanced DNA binding and colloidal stability.
• Q8-DNA formulations exhibited excellent tolerability upon intravenous injection, unlike toxic DAB 8-DNA.
• Quaternization improved in vitro biocompatibility for higher generation dendrimers (DAB 16, DAB 32).
• Intravenous administration of DAB 16-DNA and Q8-DNA resulted in liver-targeted gene expression, contrasting with lung targeting of controls.

Conclusions:

• Polypropylenimine dendrimers are effective gene delivery systems with potential for liver targeting.
• Molecular modifications enhancing colloidal stability improve tolerability for intravenous gene delivery.
• Quaternization is a key modification for improving dendrimer-DNA complex stability and in vivo performance.
• A lung avoidance hypothesis is proposed for these dendrimer formulations in vivo.