Numerous human tumor types, including ovarian cancer, display a significant expression of the CD44 family of cell surface proteoglycans. To develop tumor-targeted drugs, we have initially evaluated whether the CD44 ligand hyaluronic acid (HA) could serve as a backbone for paclitaxel (TXL) prodrugs. HA-TXL was prepared by modification of previous techniques. The in vitro cytotoxicity of HA-TXL against the CD44(+) human ovarian carcinoma cell lines SKOV-3ip and NMP-1 could be significantly blocked by preincubation with a molar excess of free HA. Female nude mice bearing intraperitoneal implants of NMP-1 cells were treated intraperitoneally with a single sub-maximum tolerated dose dose of HA-TXL or with multiple-dose regimens of paclitaxel (Taxol; Mead Johnson, Princeton, NJ) to determine the effects of these regimens on host survival and intraperitoneal tumor burden, with the latter being assessed by magnetic resonance imaging. NMP-1 xenografts were highly resistant to Taxol regimens, as host survival was only nominally improved compared to controls (T//C approximately 120), whereas single-dose HA-TXL treatment significantly improved survival in this model (T//C approximately 140; P = .004). In both NMP-1 and SKOV-3ip models, MR images of abdomens of HA-TXL-treated mice obtained shortly before controls required humane sacrifice revealed markedly reduced tumor burdens compared to control mice. This study is among the first to demonstrate that HA-based prodrugs administered locoregionally have antitumor activity in vivo.

The structure of human transmembrane pro-TNF-alpha was studied both in intact cell systems and in an in vitro translation system. In intact cell systems (LPS-induced THP-1 and TNF cDNA-transfected COS-7), a trimer of pro-TNF was detected after chemical cross-linking based on its molecular weight in Western blotting analysis. The trimer was shown to be a TNF-specific protein and could be partially cleaved to 26-kDa pro-TNF monomers by cleaving the cross-linkers. The trimeric structure was assembled intracellularly, because it could be detected in both the in vitro microsomal translation system and in THP-1 cells coincident with the appearance of pro-TNF in the cell lysate, prior to secretion of mature TNF. To further analyze the relationship between the trimeric structure and the biological activity of pro-TNF, we characterized several noncleavable pro-TNF deletion mutants. We observed a correlation between expression of TNF cytotoxicity in a juxtacrine fashion and detection of trimer. Thus, human pro-TNF-alpha, like the secreted mature TNF-alpha, has trimeric structure which is assembled intracellularly before transport to the cell surface and is apparently required for mediating its biologic activity.

The future should see development of drug targeting approaches that exploit CD44 expression on CSCs/TICs, including applications to cytotoxic agents currently in the clinic.

CD44, the primary receptor for hyaluronic acid, plays an important role in tumor growth and metastasis. CD44-hyaluronic acid interactions can be exploited for targeted delivery of anti-cancer agents specifically to cancer cells. Although various splicing variants of CD44 are expressed on the plasma membrane of cancer cells, the hyaluronic acid binding domain (HABD) is highly conserved among the CD44 splicing variants. Using a novel two-step process, we have identified monothiophosphate-modified aptamers (thioaptamers) that specifically bind to the CD44’s HABD with high affinities. Binding affinities of the selected thioaptamers for the HABD were in the range of 180–295 nM, significantly higher affinity than that of hyaluronic acid (Kd > μM range). The selected thioaptamers bound to CD44 positive human ovarian cancer cell lines (SKOV3, IGROV, and A2780), but failed to bind CD44 negative NIH3T3 cell line. Our results indicated that thio substitution at specific positions of the DNA phosphate backbone result in specific and high affinity binding of thioaptamers to CD44. The selected thioaptamers will be of great interest for further development as a targeting or imaging agent to deliver therapeutic payloads for cancer tissues.