Drug affinity and targeted delivery: double functionalization of silk spheres for controlled doxorubicin delivery into Her2-positive cancer cells

BACKGROUND: The optimal drug delivery system should be biocompatible, biodegradable, and allow the sustained release of the drug only after it reaches the target cells. Silk, as a natural polymer, is a great candidate for building drug carriers. Genetically engineered silks offer the possibility of functionalization. Previously, we characterized bioengineered silk spheres that were functionalized with H2.1 peptide that selectively delivered a drug to Her2-positive cancer cells. However, drug leakage from the silk spheres showed the need for improved control. RESULTS: To control the drug loading and release, we designed and produced functional silk (DOXMS2) that contains a DOX peptide with an affinity for doxorubicin. The DOXMS2 spheres showed the decreased release of doxorubicin compared with MS2 particles. Next, the DOXMS2 silk was blended with the H2.1MS1 polymer to improve the control of doxorubicin binding and release into Her2-positive cancer cells. The H2.1MS1:DOXMS2 particles showed the highest doxorubicin-loading capacity and binding per cell, which resulted in the highest cytotoxic effect compared with that of other sphere variants. Since drug release at a pH of 7.4 from the blended H2.1MS1:DOXMS2 particles was significantly lower than from blended spheres without DOXMS2 silk, this indicated that such particles could control the release of the drug into the circulatory system before the carrier reached the tumor site. CONCLUSIONS: This strategy, which is based on the blending of silks, allows for the generation of particles that deliver drugs in a controlled manner.