Anti-tumor activity of N-thiolated beta-lactam antibiotics.

An ongoing strategy for cancer treatment is selective induction of apoptosis in cancer over normal cells. N-thiolated beta-lactams were found to induce DNA damage, growth arrest and apoptosis in cultured human cancer cells. However, whether these compounds have a similar effect in vivo has not been studied. We report here that treatment with the beta-lactam L-1 caused a significant inhibition of tumor growth in a breast cancer xenograft mouse model, associated with induction of DNA damage and apoptosis in vivo. These results suggest that the synthetic antibiotic N-thiolated beta-lactams hold great potential to be developed as novel anti-cancer drugs.

Geranylgeranyltransferase I inhibitors target RalB to inhibit anchorage-dependent growth and induce apoptosis and RalA to inhibit anchorage-independent growth.

Geranylgeranyltransferase I inhibitors (GGTIs) are presently undergoing advanced preclinical studies and have been shown to disrupt oncogenic and tumor survival pathways, to inhibit anchorage-dependent and -independent growth, and to induce apoptosis. However, the geranylgeranylated proteins that are targeted by GGTIs to induce these effects are not known. Here we provide evidence that the Ras-like small GTPases RalA and RalB are exclusively geranylgeranylated and that inhibition of their geranylgeranylation mediates, at least in part, the effects of GGTIs on anchorage-dependent and -independent growth and tumor apoptosis. To this end, we have created the corresponding carboxyl-terminal mutants that are exclusively farnesylated and verified that they retain the subcellular localization and signaling activities of the wild-type geranylgeranylated proteins and that Ral GTPases do not undergo alternative prenylation in response to GGTI treatment. By expressing farnesylated, GGTI-resistant RalA and RalB in Cos7 cells and human pancreatic MiaPaCa2 cancer cells followed by GGTI-2417 treatment, we demonstrated that farnesylated RalB, but not RalA, confers resistance to the proapoptotic and anti-anchorage-dependent growth effects of GGTI-2417. Conversely, farnesylated RalA but not RalB expression renders MiaPaCa2 cells less sensitive to inhibition of anchorage-independent growth. Furthermore, farnesylated RalB, but not RalA, inhibits the ability of GGTI-2417 to suppress survivin and induce p27(Kip1) protein levels. We conclude that RalA and RalB are important, functionally distinct targets for GGTI-mediated tumor apoptosis and growth inhibition.

Structure-activity relationships of synthetic analogs of (-)-epigallocatechin-3-gallate as proteasome inhibitors.

BACKGROUND: Cancer-related molecular targets of green tea polyphenols, such as (-)-epigallocatechin-3-gallate [(-)-EGCG], remain unknown. We previously showed that (-)-EGCG is a potent and specific inhibitor of the proteasomal chymotrypsin-like activity in vitro and in vivo. MATERIALS AND METHODS: EGCG amides and five simple analogs were prepared by enantioselective synthesis. Proteasome inhibition in vitro was measured by fluorogenic substrate assay and in vivo by accumulation of proteasome target proteins (p27, IkappaB-alpha and Bax). Inhibition of tumor cell proliferation was determined by G1 arrest, DNA fragmentation and colony formation inhibition. RESULTS: EGCG analogs with modifications in the A-ring, C-ring or ester bond inhibit the chymotrypsin-like activity of purified 20S proteasome with altered potencies. However, these compounds were able to potently inhibit the proteasome activity in vivo and also suppress colony formation of prostate cancer LNCaP cells. Some compounds caused G1 arrest and DNA fragmentation in leukemia Jurkat T cells. However, these EGCG analogs caused no or little proteasome inhibition in normal or nontransformed cells. CONCLUSION: The A-ring and gallate ester/amide bond are essential for the proteasome-inhibitory function of (-)-EGCG.