Percutaneous transcatheter embolization procedures involve the selective occlusion of blood vessels. Occlusive agents, referred to as embolics, vary in material characteristics including chemical composition, mechanical properties, and the ability to concurrently deliver drugs. Commercially available polymeric embolics range from gelatin foam to synthetic polymers such as poly(vinyl alcohol). Current systems under investigation include tunable, bioresorbable microspheres composed of chitosan or poly(ethylene glycol) derivatives, in situ gelling liquid embolics with improved safety profiles, and radiopaque embolics that are trackable in vivo. This article reviews commercially available materials used for embolization as well as polymeric materials that are under investigation.

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting – such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes – are addressed.

Locoregional therapies for cancer are minimally invasive procedures in which the treatment is administered directly into cancerous tissue. Transarterial chemoembolization (TACE) is used to treat intermediate stage hepatocellular carcinoma (HCC). TACE uses an embolic material to block blood flow while coadministering a chemotherapeutic to the neoplastic tissue. Liquid embolics capable of drug loading are at the forefront of development as they allow for deeper permeation of tumor vasculature, increase neoplasm exposure to therapeutics, and resist revascularization by occupying both large and small diameter vessels. In this work, two chemotherapeutics used in the treatment of HCC, doxorubicin and sorafenib, were incorporated into the in situ gelling liquid embolic composed of a silk-elastinlike protein polymer (SELP-815 K). The base forms of the drugs had no significant effect on the viscosity, the gelation kinetics, and the gel stiffness of the SELP: all properties essential for the successful performance of an injectable liquid embolic. In vitro release studies indicated that the SELP liquid embolic delivered doxorubicin and sorafenib, either alone or in combination, at therapeutically relevant concentrations for a minimum of 14 and 30 days, respectively.

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