Targeted Drug Delivery - Nanomaterials for Medical Applications - page 189

malignant disorders. I.v. infusion of conventional cisplatin formulation has low
bioavailability to the target organ, and in addition, it has been shown to have
significant side effects, like ototoxicity and nephrotoxicity. Drug encapsulation
measured by ultraviolet spectroscopy varied from 30 to 80% for different ratios
of cisplatin and protein. In vitro release kinetics showed that the NP-based for-
mulation had biphasic release kinetics and was capable of sustained release
compared with the free drug (80% release in 45h). The study exhibited the fea-
sibility of the albumin-based cisplatin NP formulation as a sustained release
vehicle of cisplatin.
5.4.2 Attachment of the Drug on the NM Surface
Drug may be loaded on the surface instead of the interior of an NP. To do this,
there must be functional groups on the NP surface ( Figure 5.1 B) that allows any
of the following processes: covalent, charge-charge, or HI between the drug
and the NP.
5.4.2.1 Attachment with Covalent Interaction
Common covalent coupling methods involve formation of a disulfide bond,
cross-linking between two primary amines, reaction between a carboxylic acid
and primary amine, reaction between maleimide and thiol, reaction between
hydrazide and aldehyde, and reaction between a primary amine and free alde-
hyde. 72 Attachment of drugs to the NMs is discussed in the succeeding sections.
Procedure for covalent attachment of drugs on NMs
(1) Take 1 mg of carboxyl-surface-modified NM and disperse in buffer that has
been optimized for the NM.
(2) Take drug that has available amine or hydroxyl group for covalent conjuga-
tion and dissolve at 0.1-2 mg/mL depending upon the loading of the drug
required.
(3) Add 0.050 M borate buffer at pH 5 (or manufacturer's recommended buf-
fer) to the NPs.
(4) Add 50 µL of 0.02 M ethyl-aminopropyl-carbodiimide hydrochloride (EDC)
and 25 µL of 0.8 mM N -hydroxy succinamide (NHS) and mix well for 1-5 min
(optimize the conditions depending upon the NMs and drug to be loaded).
(5) Add the drug that has been dissolved in the buffer that is appropriate for the
NM.
(6) Incubate with shaking for 1-2 h at RT.
(7) Remove excess drug by centrifugation, dialysis, or magnetization for mag-
netic NMs. The centrifugation speed needs to be optimized depending upon
the size of the NMs. The MW cutoff of the dialysis tubing also needs to be
chosen based on the size of the NMs. Magnetization is recommended for
≥25 nm but not for < 25 nm because the process may take more than 24 h.
(8) Resuspend the NMs in the recommended buffer and refrigerate until use.