The invention is directed to pharmaceutical compositions and methods for delivery of a therapeutic or diagnostic agent from one bodily compartment to one or more other bodily compartment by administering one of the following conjugates: a polymer having multiple functional groups at least one of which is covalently bound to a therapeutic or diagnostic agent, and at least one cell uptake promoter covalently bound to the therapeutic or diagnostic agent; or a polymer and at least one cell uptake promoter bound thereto; the polymer further comprising multiple functional groups at least one of which is covalently bound a therapeutic or diagnostic agent.