Further evaluation of the antitumor potential of natural
products identified from molecular target or traditional cellbased
assays requires the use of in vivo assays. The NCI
uses the Hollow Fiber Assay as a relatively inexpensive in vivo prescreen to prioritize compounds for testing in the
more definitive human tumor xenograft models.199 Traditionally,
xenograft models were not employed until the bioactive
components had been obtained in pure form. Currently, both
the Hollow Fiber Assay and xenograft models are being
utilized for the prioritization of natural product extracts for
fractionation at NCI. Information on the regular in vivo
assays currently used by the NCI, including a detailed
description of the protocol used in the Hollow Fiber Assay,
can be obtained from the following URL: http://dtp.nci.nih.gov/screening.html