(483f) Cathepsin B Degradable Peptidic Dendrimers for Drug Delivery

INTRODUCTION: Polymers are widely used as drug delivery vehicles due to their ability to accumulate passively in tumor.  Polymers can also be functionalized to achieve active targeting. Dendrimers offer several advantages over other conventional polymers. Here we report the use of peptidic dendrimers as drug delivery vehicles. These dendrimers are designed to degrade in the presence of an enzyme cathepsin B which is overexpressed at tumor site. A tetrapeptide glycyl-phenylalanyl-leucyl-glycine (GFLG) is used as a building block.  The tetrapeptide GFLG is known to be recognized by cathepsin B. Two polymers with positive and negative surface charge were synthesized and characterized for their degradation profile in the presence of cathepsin B.  By conjugation of a model drug 2-methoxyestradiol (2ME) to these polymers we show that peptidic dendrimers have the potential to be used as drug delivery vehicles.

EXPERIMENTAL METHODS: Positively and negatively charged peptidic dendrimers were synthesized using a convergent approach where tetrapeptide (GFLG) was added to the central core having four arms.  Degradation profile of these polymers in the presence of enzyme cathepsin B and stability in the presence of PBS and acetate buffer was evaluated using HPLC. Glycine derivative of 2ME was attached to the tetrapeptide (GFLG) followed by conjugation of this unit (GFLGG2ME) to the central core to yield 2ME containing peptidic dendrimer. The activity of monomer and the polymer was evaluated by performing cytotoxicity studies using breast cancer cell line MDA-MB-231.

RESULTS AND DISCUSSION: Both positively and negatively charged peptidic dendrimers showed time dependant degradation in the presence of cathepsin B. Negatively charged dendrimer showed faster rate of degradation compared to positively charged amine terminated dendrimer. Polymers were stable in the presence of PBS and acetate buffer for 24 h.  GI₅₀ values (concentration to inhibit cellular growth by 50 %) for free drug 2ME, monomer GFLGG2ME were 0.89 µM and 7.6 µM respectively. Drug containing polymer (38 % wt/wt of drug) showed GI₅₀ value of 8.5 µM while control polymer did not show any cytotoxicity. At equivalent drug concentrations, peptidic dendrimers were at least 8 times more active than N-(2-hydroxypropylmethacrylamide) (HPMA) copolymers containing 2ME (GI₅₀ value of 114 µM).  

CONCLUSION: Peptidic dendrimer has the potential to be used as carrier for 2-methoxyestradiol for breast cancer treatment.

ACKNOWLEDGEMENTS: This research was supported by Department of Biopharmaceutical Sciences, University of Illinois Chicago and Department of Defense (Breast Cancer Research) concept award (W81XWH-09-1-0687) to R. Kolhatkar.