Zinc-binding compounds induce cancer cell death via distinct modes of action

Metal-binding compounds have been shown to have anticancer activity and are being evaluated clinically as anticancer agents. We have recently found that a zinc-binding compound, 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), kills cancer cells by transporting zinc into the cells. We therefore compared the action of clioquinol with two other cytotoxic zinc-binding compounds, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and pyrrolidine dithiocarbamate (PDTC). We demonstrate that metal-binding compounds can be subclassified based upon the reversibility of their cytotoxicity by metal supplementation and their modes of action. Understanding the mechanisms whereby metal-binding compounds affect cell behavior may aid in their optimization for clinical use.     

HDAC inhibitor SNDX-275 enhances efficacy of trastuzumab in erbB2-overexpressing breast cancer cells and exhibits potential to overcome trastuzumab resistance

Trastuzumab (or Herceptin), as the first erbB2-targeted therapy, has been successfully used to treat breast cancer patients with erbB2-overexpressing tumors. However, resistances to trastuzumab frequently occur, and novel strategies/agents are urgently needed to abrogate the resistant phenotype. Our current study explores the potential of SNDX-275, a class I HDAC inhibitor, to overcome trastuzumab resistance and investigates the combinational effects of SNDX-275 and trastuzumab on both sensitive and resistant breast cancer cells. Cell proliferation assays showed that SNDX-275 significantly enhanced trastuzumab-induced growth inhibition in trastuzumab-sensitive, erbB2-overexpressing breast cancer cells. Importantly, SNDX-275 at its therapeutic range re-sensitized trastuzumab-resistant cells to trastuzumab-mediated growth inhibition. SNDX-275 in combination with trastuzumab resulted in a dramatic reduction of erbB3 and its phosphorylation (P-erbB3), and inhibition of Akt signaling. Apoptotic-ELISA and western blot analyses confirmed that the combinations of SNDX-275 and trastuzumab as compared to SNDX-275 alone significantly enhanced DNA fragmentation and induced more PARP cleavage and caspase-3 activation in both trastuzumab-sensitive and -resistant breast cancer cells. Furthermore, co-immunoprecipitation assays revealed that SNDX-275 mainly attenuated the interactions of erbB2 and erbB3 receptors, but had no significant effect on erbB2/IGF-1R or erbB3/IGF-1R associations in the trastuzumab-resistant breast cancer cells. These data indicated that SNDX-275 enhanced trastuzumab efficacy against erbB2-overexpressing breast cancer cells, and exhibited potential to overcome trastuzumab resistance via disrupting erbB2/erbB3 interactions and inactivating PI-3K/Akt signaling. SNDX-275 may be included in erbB2-targeted regimen as a novel strategy to treat breast cancer patients whose tumors overexpress erbB2.     

Enhanced anti-tumor activity by the combination of TRAIL/Apo-2L and combretastatin A-4 against human colon cancer cells via induction of apoptosis in vitro and in vivo

The present study indicated that the combination of TRAIL/Apo-2L and CA-4 exerted synergistic anti-proliferative effect against human colon carcinoma cells including SW-620 and HCT-116 in vitro. Moreover, the increased anti-tumor efficacy of TRAIL/Apo-2L combined with CA-4 was further validated on SW-620 xenograft model in nude mice. These enhanced anti-cancer activities were accompanied by caspase-mediated apoptosis. Furthermore, it was identified that NF-κB as the major determinant of TRAIL/Apo-2L resistance could be blocked in cytoplasm by TRAIL/Apo-2L plus CA-4 treatment. Taken together, these findings build the rationale for further (pre)clinical development of TRAIL/Apo-2L and CA-4 against colorectal cancer.     

Efficient induction of apoptosis by doxorubicin coupled to cell-penetrating peptides compared to unconjugated doxorubicin in the human breast cancer cell line MDA-MB 231

Doxorubicin (Dox) is a commonly used drug to treat various types of cancers. Previously, we demonstrated that coupling Dox to cell-penetrating peptides (CPPs) represent a valuable strategy to overcome drug resistance in MDA-MB 231 breast cancer cells. In the present study, we evaluated the properties of these Dox conjugates (Dox–CPPs) in terms of apoptosis induction. Dox–CPPs were found to induce apoptotic death in MDA-MB 231 cells at a lower dose than that needed for unconjugated Dox. Cell death induction was associated with Bax oligomerisation, release of cytochrome c, caspase activation, chromatin condensation and internucleosomal degradation. However, whereas Bcl-2 overexpression was very potent in inhibiting apoptosis triggered by Dox, this anti-apoptotic protein was largely inefficient in preventing Dox–CPPs-induced apoptosis. These observations suggest that mitochondrial disruption is the main event in Dox-induced apoptotic signaling but that Dox–CPPs are probably able to trigger additional apoptotic pathways independent of mitochondrial events. Thus, the higher efficacy of Dox conjugated to CCPs in apoptosis induction might not be due exclusively to increased drug accumulation but also to the activation of multiple apoptotic pathways.     

Inhibition of tumor cell migration and metastasis by the proton-sensing GPR4 receptor

GPR4 is a member of the proton-sensing G protein-coupled receptor family. Within tumor microenvironments, the interstitial acidic pH may activate GPR4 to regulate the behavior of tumor cells. Mouse B16F10 melanoma cells and TRAMP-C1 prostate cancer cells, genetically engineered to overexpress GPR4 or the control vector, were subject to a series of cell migration, invasion and metastasis assays. Upon GPR4 overexpression and activation in an acidic pH, the migration of B16F10 and TRAMP-C1 cells was substantially inhibited in comparison to the vector control. Similar results were observed in the Matrigel invasion and transendothelial invasion assays. At the molecular level, stimulation of GPR4 by acidosis induced the activation of RhoA and the formation of actin stress fibers. In addition, treating B16F10 cells with the known Rho activator CN01 (calpeptin) strongly inhibited cell migration, recapitulating the acidosis/GPR4-induced motility inhibition phenotype. To examine the biological effects in vivo, B16F10 melanoma cells were intravenously injected into syngeneic C57BL/6 mice and pulmonary metastasis was inhibited by approximately 80% in GPR4-overexpressing B16F10 cells in comparison to the vector control. Upon treatment with the Rho activator CN01, the phenotype of the B16F10 vector cells paralleled that of the GPR4-overexpressing cells in cell migration and metastasis assays. These findings suggest that GPR4 activation by an acidic pH inhibits tumor cell migration and invasion, and the Rho GTPase is at least partly responsible for this phenotype.     

Long-term exposure to sorafenib of liver cancer cells induces resistance with epithelial-to-mesenchymal transition,increased invasion and risk of rebound growth

Sorafenib leads to a survival benefit in patients with advanced hepatocellular carcinoma but its use is hampered by the occurrence of drug resistance. To investigate the molecular mechanisms involved we developed five resistant human liver cell lines in which we studied morphology, gene expression and invasive potential. The cells changed their appearance, lost E-cadherin and KRT19 and showed high expression of vimentin, indicating epithelial-to-mesenchymal transition. Resistant cells showed reduced adherent growth, became more invasive and lost liver-specific gene expression. Furthermore, following withdrawal of sorafenib, the resistant cells showed rebound growth, a phenomenon also found in patients. This cell model was further used to investigate strategies for restoration of sensitivity to sorafenib.