Embolic Polylactide-Co-Glycolide Microspheres for Image-Guided,Transcathter Delivery of Sorafenib to Hepatocellular Carcinoma

Introduction: Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer and most patients are not eligible for potentially curative treatments (resection, transplant) as the cancer is often diagnosed during later stages.  Therefore, these patients undergo palliative treatments such as transcatheter therapies.  These therapies involve having doctors place a catheter in the femoral artery and using image guidance to guide it to tumor feeding branches of the hepatic artery.  Once the catheter is placed, chemotherapy or radiation therapy is given along with embolic agents to help contain the therapy locally to the tumor as well as to prevent blood flow to the tumor to help starve it. The purpose of our studies is to develop a drug delivery system to allow for sorafenib to be delivered as part of a transcatheter therapy via an embolic polymer microsphere bead.  Additionally, we have added an iron oxide component to serve as a contrast agent to allow for magnetic resonance imaging (MRI) of the delivery.

A more recent therapy for HCC is sorafenib (brand name Nexavar), which is a multikinase inhibitor that was approved by the FDA in 2007.  It is currently formulated as an oral tablet, and therefore, the systemic administration is associated with severe side effects such as diarrhea, hand foot syndrome (severe rashes of the hands and feet), and hypertension.  Therefore, patients do not tolerate sorafenib well.  Re-formulating sorafenib for delivery using transcatheter techniques would improve patient tolerance.  Furthermore, it would also allow for increased does at the tumor and an added embolic effect to improve therapy.

Methods: We have chosen polylactide-co-glycolide (PLG) as our platform and we employed a single emulsion/solvent evaporation method to fabricate our microspheres to co-encapsulate the sorafenib and a hydrophobic iron oxide.  We then characterized the size and morphology using microscopy and Image J software analysis.   Sorafenib and iron oxide loading were characterized with high performance liquid chromatography and inductively coupled plasma mass spectroscopy, respectively.  Sorafenib and iron oxide release were also monitored using similar methods.   The contrast effect these microspheres have under MRI was monitored in vitro using a 7 Tesla MRI scanner.  Lastly, the microspheres were injected to tumor feeding arteries transcather in a rabbit VX2 animal model to mimic clinical delivery.  The rabbit was then imaged in the same 7 Tesla MRI scanner to visualize the distribution of the microspheres.  After imaging, the rabbit was sacrificed and sections of the liver, tumors, stomach and lungs were harvested and submitted for histology with Prussian blue staining for iron to confirm the microsphere biodistribution.

Results: The resulting microspheres were of an average diameter of 22.7 microns.  Iron oxide content and sorafenib content were 0.209% w/w) and 14.0% (w/w) respectively.  The release study indicated slow burst release whereas 2.27% of the loaded sorafenib released within 3 days.  In vitro MRI imaging showed that increasing concentrations of the microspheres from 0-20 mg/mL caused a reduction in T2* from 111 to 8.13 ms.  Lastly, after infusion of the microspheres into the rabbit, we were able to depict the microspheres under MRI as areas of darkening near the tumors.  Prussian blue histology to confirm microsphere biodistribution indicated that the tumors showed high staining at the tumors and minimal staining in the normal liver, stomach and lungs (stomach and lungs are of concern as microsphere distribution to those tissues can cause problems).

Conclusion: These rigorous characterization studies show that embolic PLG microspheres can co-encapsulate sorafenib and iron oxide.  These microspheres can also be delivered locally to liver tumors through a catheter to ultimately produce a therapeutic response.