Liposome loading with metal ions

1. A method of loading at least one therapeutic agent into a liposome in a liposome composition, the method comprising:

i) providing a composition comprising liposomes, said liposomes lacking an ionophore, in an external solution, the liposomes containing an internal solution comprising encapsulated copper ions;

ii) adding at least one therapeutic agent to the external solution; and

iii) maintaining the agent in the external solution for sufficient time to load the agent into the liposomes.

2. The method of claim 1 , wherein the internal solution comprises a copper compatible solution.

3. The method of claim 1 , wherein the external solution and external surfaces of the liposome contain substantially no uncomplexed copper ions.

4. The method of claim 3 , wherein the external solution comprises a copper chelating agent.

5. The method of claim 3 , wherein uncomplexed copper ions are removed, from the external solution prior to step (ii) by chromatography or by extensive solution exchange or dialysis.

6. The method of claim 1 , wherein the internal solution and the external solution have substantially the same pH.

7. The method of claim 1 , wherein the liposomes have less than 20 mol % cholesterol.

8. The method of claim 1 , wherein the pH of the internal solution is in the range of about 6.0 to about 8.5.

9. The method of claim 1 , wherein the liposomes comprise one or more lipids that are negatively charged at physiological pH.

10. The method of claim 9 , wherein the one or more negatively charged lipids are selected from PG and PI.

11. The method of claim 1 , wherein a second therapeutic agent is loaded by means of a transmembrane gradient established with an ionophore supplied to the liposomes after step (iii).

12. A method of loading at least one therapeutic agent into a liposome in a liposome composition, the method comprising:

i) providing a composition comprising liposomes in an external solution, the liposomes containing an internal solution comprising encapsulated copper ions;

ii) adding at least one therapeutic agent to the external solution; and

iii) maintaining the agent in the external solution for sufficient time to load the agent into the liposomes, and

wherein the liposomes do not at any time during said loading comprise an ionophore.

13. A method of loading at least one therapeutic agent into a liposome in a liposome composition, the method comprising:

i) providing a composition comprising liposomes in an external solution, the liposomes containing an internal solution comprising encapsulated copper ions;

ii) adding at least one therapeutic agent to the external solution; and

iii) maintaining the agent in the external solution for sufficient time to load the agent into the liposomes, and

wherein said loading is conducted in the absence of ionophore.