Poly – (L) – glutamic acid drug delivery system for the intravesical therapy of bladder cancer using WGA as targeting moiety
In the management of bladder cancer, surgical resection of the tumour is usually followed by intravesical instillation of immunomodulatives and/or chemotherapeutics. The purpose of this local intravesical therapy is to eliminate residual malignant cells after surgical intervention. The main limitation of a localised adjuvant therapy is the insufficient concentration of the active pharmaceutical ingredient (API) in malignant cells due to the unique structure of the human urothelium making it an exclusively hard to overcome barrier in the human body. Different strategies such as electromotive drug administration or local hyperthermia are employed to ameliorate intravesical drug uptake. Previous studies on biorecognitive targeting showed promising results for lectin-, especially wheat germ agglutinin (WGA), mediated drug delivery. Here, we present a targeted conjugate that provides enough binding sites for a possible API as well as high cytoadhesive and cytoinvasive potential. The conjugate should comprise the following components: First WGA, as the targeting moiety, second poly-L-glutamic acid (PGA) as a polymeric backbone providing more than 300 possible binding sites for an API and third fluorescein cadaverine (Fc), a fluorescent dye we coupled to PGA rendering the conjugate traceable. After purification via size exclusion chromatography (SEC) the WGA containing and therefore binding conjugate was isolated from the reaction mix. In flow-cytometric and fluorimetric experiments with single cells and cell monolayers, respectively, binding and internalisation of the conjugate representing a high molecular weight (>100 kDa) could be demonstrated. Fluorescent PGA without the WGA component showed neither binding nor internalisation potential. Microscopic colocalization studies with cell monolayers and single cells confirmed the cytoadhesive and cytoinvasive potential of the WGA containing conjugate. In accordance with the results of specificity studies the interaction between the conjugate and the cell surface depended solely on the WGA component of the conjugate.
With the help of this targeted drug delivery system limiting factors of intravesical adjuvant therapy could eventually be overcome and thereby treatment efficacy of instillative chemotherapy could be improved. In addition, traceable drug conjugates might bear interesting advantages for theranostic purposes in the treatment of bladder cancer.