Shark cartilage as source of antiangiogenic compounds: from basic to clinical research.

The discovery that angiogenesis is a key condition for the growth of a tumor beyond a millimeter or two, brings about a new approach in the treatment of tumors using drugs able to inhibit the formation of new blood vessels. Also, it has been realized that antiangiogenic drugs can be useful in the treatment of other pathological processes, now classified as angiogenesis-dependent diseases. Initially, cartilage was considered as a possible natural source of antiangiogenic compounds due to its known avascular nature. To date, a number of in vitro and in vivo studies have suggested the existence of antiangiogenic and antitumor compounds in bovine and shark cartilage. However, the potential usefulness of shark cartilage in the treatment of cancer and other angiogenesis-dependent diseases have not been totally accepted due to (i) unsatisfactory patient outcome in clinical trials that have used shark cartilage in cancer patients, (ii) the lack of data that correlates bioavailability with pharmacological effects using oral shark cartilage. Thus, the objective of this review is to describe the main basic and clinical investigations reported in the literature, in which the antiangiogenic and/or antitumor properties of shark cartilage or of its extracts were evaluated. Possible explanations for conflicting results are discussed as well.