Dear Nicholas Heimann, 

The following recent publication covers the answer to your question:

Invest New Drugs. 2016 Mar 9. [Epub ahead of print]

Convection-enhancement delivery of liposomal formulation of oxaliplatin shows less toxicity than oxaliplatin yet maintains a similar median survival time in F98 glioma-bearing rat model.

Shi M1, Fortin D2, Paquette B3, Sanche L1.

Author information

Abstract

Results of clinical trials with oxaliplatin in treating glioblastoma are dismal. Previous works showed that intravenous (i.v.) delivery of oxaliplatin did not increase the survival of F98 glioma-bearing Fisher rats. Low accumulation of the drug in tumor cells is presumed to be responsible for the lack of antitumor effect. In the present study, convection-enhanced delivery (CED) was used to directly inject oxaliplatin in brain tumor implanted in rats. Since CED can led to severe toxicity, the liposomal formulation of oxaliplatin (Lipoxal™) was also assessed. The maximum tolerated dose (MTD) of oxaliplatin was 10 μg, while that of Lipoxal™ was increased by 3-times reaching 30 μg. Median survival time (MeST) of F98 glioma-bearing rats injected with 10 μg oxaliplatin by CED was 31 days, 7.5 days longer than untreated control (p = 0.0002); while CED of 30 μg Lipoxal™ reached the same result. Compared to previous study on i.v. delivery of these drugs, their injection by CED significantly increased their tumoral accumulations as well as MeSTs in the F98 glioma bearing rat model. The addition of radiotherapy (15 Gy) to CED of oxaliplatin or Lipoxal™ increased the MeST by 4.0 and 3.0 days, respectively. The timing of radiotherapy (4 h or 24 h after CED) produced similar results. However, the treatment was better tolerated when radiotherapy was performed 24 h after CED. In conclusion, a better tumoral accumulation was achieved when oxaliplatin and Lipoxal™ were injected by CED. The liposomal encapsulation of oxaliplatin reduced its toxic, while maintaining its antitumor potential.

http://www.ncbi.nlm.nih.gov/pubmed/26961906

Hoping this will be helpful,

Rafik

Every compound has a relative solubility in Oil and water as the solution media. It is important to discern how much a compound tends to dissolve in a media. Hence, Scientists have defined parameters to explain it, like hyrophilic-lipophilic balance or octanol-to water index. For small drugs remained in water, liposomal formulations  consist of long and saturated carbon chains phospholipids bearing net negative charge and PEG-DSPEs provides a high loading of drug with long sustained release in body systemic circulation, No matter if your drug has a positive or negative charge.

Liposome with high positive charge interacts to whole blood cells, being eliminated rapidly from serum. liposomes with high negative charges provide better avoidance with blood cells, but can be subjected to stimulate humoral system. 

For small lipophylic drugs, other nano-vehicles like PLGA are more suitable than liposomes as they provide  a large matrix and a lot of hydrophobic surfaces on the surfaces of the pores for drug to anchor and being not washed.