Efficient Encapsulation of Etoposide in Amphiphilic Glycolchitsoan Nano-carriers

A. Raza*, I.F. Uchegbu**, A.G. Schatzlein**

*Nuclear Medicines, Oncology and Radiotherapy Institute, Islamabad, Pakistan

abida_rao@yahoo.com

**The School of Pharmacy, University of London, London, United Kingdom

Abstract

Etoposide, a lipophilic epipodophyllotoxine derivative, acts by forming ternary complex with topoisomerase II and DNA, which lead to DNA strand breaks and subsequent cancer cell apoptosis. It is extensively used in anticancer therapy, both of solid tumors and hematological malignancies. Current etoposide formulations are highly problematic as they are associated with adverse side effects such as hypotension, anaphylaxis, bronchospasm, etc .  We have previously demonstrated that amphiphilic glycol chitosan can be engineered to form nanoparticulate clusters that efficiently encapsulate hydrophobic drug molecules and increase bioavailability e.g. in the gut or across the blood-brain-barrier (Qu, X., et al. (2006) Biomacromolecules 7(12): 3452-9).  Here we demonstrate that suitably modified derivatives of glycol chitosan tailored using varying ratios of hydrophobic (palmitoylation) and hydrophilic (quareternisation) modifications are able to efficiently solubilise etoposide. Two variants of quarternary palmitoyl glycolchitosans GCPQ1 (21.9 ± 0.62 palmitoylation, 24.3 ± 1.8 quaternization) and GCPQ2 (34.2 ± 5.1 palmitoylation, 8.2 ± 2.4 quaternization) were synthesised. The molecular weight was determined by GPC/MALS as 13.72 ± 1.39 kDa for GCPQ1 and 10.13 ± 0.63 kDa for GCPQ2, respectively. The more hydrophobic GCPQ2 polymer is able to solubilise 10.98 ± 0.23 mg of etoposide per 5mg/ml of polymer as compared to the less hydrophobic polymer which can solubilise 6.09 ± 0.16 mg of etoposide per 5mg/ml of polymer. The micelles size was found 21.2 ± 0.3 nm and 142 ± 20.5 nm with a positive zeta potential in the range of 47.7 ± 0.9 at pH 3.88 ± 0.005and 62.7 ± 7.7 at pH 4.13 ± 0.002 respectively. Formulations were found to be quite stable on storage at 4^oC over three months with size only changing by 5%. Formulation consistency in upper, lower and whole formulation after shaking was found quite good using the photon correlation spectroscopy i.e. 31.0 ± 0.3, 27.6 ± 0.1 and 28.6 ± 0.3 nm respectively, after 24 hrs at 4C. Furthermore, we found that freeze dried formulations also have excellent stability and are easily reconstituted to give particles of 33.16 ± 2.177 nm with a positive zeta potential value of 43.5 ± 1.2 as compared to 22.5 ± 1.05 nm and zeta potential of 43.7 ± 1.1 before freeze drying. In vitro evaluation of nanoparticulate etoposide with different cell lines showed a lower IC 50 value than the commercial formulation. For Mda-mbk 231 cell lines IC 50 found was 2.1µM as compared to 9.33 µM with the eposin. In vivo evaluation of the nanoparticulate formulation is still to be studied. But preliminary data shows that modified glycol chitosan  can be a better tool for solubilising the hydrophobic drugs which are negligibly soluble in aqueous media.

Key words: Etoposide, glycol chitosan, nanocarriers, encapsulation, solubility

Full name:       Dr Abida Raza

Contact:          Dr Abida Raza

Senior Scientist

Molecular Diagnostics and Research Labs, NORI

G-8/3, Islamabad, Pakistan

Affiliation:      Nuclear Medicines, Oncology and Radiotherapy Institute (NORI), Islamabad, Pakistan

Tel No.: 0092-51-9260611 ext 295

Fax No.: 0092-51-9260616

E.mail:                        abida_rao@yahoo.com