Structure-Activity Relationship of the Dimeric and Oligomeric Forms of a Cytotoxic Biotherapeutic Based on Diphtheria Toxin.

Protein aggregation is a well-recognized problem in industrial preparation, including biotherapeutics. These low-energy states constantly compete with a native-like conformation, which is more pronounced in the case of macromolecules of low stability in the solution. A better understanding of the structure and function of such aggregates is generally required for the more rational development of therapeutic proteins, including single-chain fusion cytotoxins to target specific receptors on cancer cells. Here, we identified and purified such particles as side products of the renaturation process of the single-chain fusion cytotoxin, composed of two diphtheria toxin (DT) domains and interleukin 13 (IL-13), and applied various experimental techniques to comprehensively understand their molecular architecture and function. Importantly, we distinguished soluble purified dimeric and fractionated oligomeric particles from aggregates. The oligomers are polydisperse and multimodal, with a distribution favoring lower and even stoichiometries, suggesting they are composed of dimeric building units. Importantly, all these oligomeric particles and the monomer are cystine-dependent as their innate disulfide bonds have structural and functional roles. Their reduction triggers aggregation. Presumably the dimer and lower oligomers represent the metastable state, retaining the native disulfide bond. Although significantly reduced in contrast to the monomer, they preserve some fraction of bioactivity, manifested by their IL-13RA2 receptor affinity and selective cytotoxic potency towards the U-251 glioblastoma cell line. These molecular assemblies probably preserve structural integrity and native-like fold, at least to some extent. As our study demonstrated, the dimeric and oligomeric cytotoxin may be an exciting model protein, introducing a new understanding of its monomeric counterpart's molecular characteristics.

4-(Methylthio)butyl isothiocyanate inhibits the proliferation of breast cancer cells with different receptor status.

BACKGROUND: Epidemiological studies indicate that the consumption of Brassicaceae plants, a rich source of biologically active isothiocyanates (ITCs), may effectively reduce cancer risk. In the current study, we evaluated the anticancer potential of 4-(methylthio)butyl ITC (erucin, ERN) against three phenotypically different breast cancer cell lines: MDA-MB-231, SKBR-3 and T47D. METHODS: The effect of ERN on the viability of breast cancer cells was evaluated using sulforhodamine B and clonogenic assays, and acridine orange/ethidium bromide staining. Cell cycle was investigated using flow cytometry. The status of signaling molecules was examined by western blot analysis. RESULTS: ERN decreased the viability of all tested cancer cell lines in a concentration-dependent manner; this effect was much weaker in normal breast cells (MCF-10A). ERN induced cell cycle arrest in the G2/M phase, down-regulated the phosphorylation of S6 ribosomal protein in all tested breast cancer cell lines, and reduced HER2 receptor levels in SKBR-3 cells. A 24-h treatment with lower concentrations of ERN (5-20µM) induced apoptosis; higher ERN concentrations (40µM) induced necrosis. The latter also irreversibly inhibited the proliferative potential of cancer cells. CONCLUSION: ERN effectively inhibits proliferation of breast cancer cells irrespectively of their receptor status.

Combination of lapatinib with isothiocyanates overcomes drug resistance and inhibits migration of HER2 positive breast cancer cells.

BACKGROUND: Lapatinib is a commonly used drug that interrupts signaling from the epidermal growth factor receptors, EGFR and HER2/neu. Long-term exposure to lapatinib during therapy eliminates cells that are sensitive to the drug; however, at the same time it increases probability of lapatinib-resistant cell selection. The aim of this study was to verify whether combinations of lapatinib with one of isothiocyanates (sulforaphane, erucin or sulforaphene), targeting different levels of HER2 signaling pathway, exert stronger cytotoxic effect than therapy targeting the receptor only, using heterogeneous populations consisting of lapatinib-sensitive and lapatinib-resistant breast cancer cells. METHODS: Lapatinib-sensitive HER2 overproducing SKBR-3 breast cancer cells and their lapatinib-resistant derivatives were combined at different proportions to simulate enrichment of cancer cell population in a drug-resistant fraction during lapatinib therapy. Effects of treatments on cell survival (MTT), apoptosis induction (PARP cleavage), prosurvival signaling (p-Akt, p-S6) as well as cell motility (wound healing assay) and invasion (Boyden chamber assay) were investigated. RESULTS: Combination of lapatinib with any of isothiocyanates significantly decreased cell viability and inhibited migration of populations consisting of different amounts of drug-sensitive and drug-resistant cells. In case of population entirely composed of lapatinib-resistant cells the most effective was combination of lapatinib with erucin which decreased cell viability and motility, phosphorylation of Akt, S6 and VEGF level more efficiently than each agent alone. CONCLUSIONS: Combination of lapatinib and isothiocyanates, especially erucin, might be considered as an effective treatment reducing metastatic potential of breast cancer cells, even these with the drug resistance phenotype.

Sensitization of HER2 Positive Breast Cancer Cells to Lapatinib Using Plants-Derived Isothiocyanates.

Nearly 25% of all breast cancer is characterized by overexpression of HER2 (human epidermal growth factor receptor 2) which leads to overactivation of prosurvival signal transduction pathways, especially through Akt-mTOR-S6K kinases, and results in enhanced proliferation, migration, induction of angiogenesis, and apoptosis inhibition. Anti-HER2 targeted therapies, such as specific monoclonal antibodies or small-molecule tyrosine kinase inhibitors, even in combination, still seem to be insufficient due to incidence of primary or acquired resistance and prevalence of serious side-effects of these drugs. We assumed that combination of compounds that target different levels of the above-mentioned signal transduction pathway might be more effective in eradication of breast cancer cells. In our in vitro research we used a commercially available drug, lapatinib, acting at the level of the receptor in combination with 1 of the plant-derived isothiocyanates: sulforaphane, erucin, or sulforaphene, as it has been shown previously that sulforaphane inhibits Akt-mTOR-S6K1 pathway in breast cancer cells. We used 2 HER2 overexpressing breast cancer cell lines, SKBR-3 and BT-474. Combinations of the drug and isothiocyanates considerably decreased their viability. This action was synergistic and was accompanied by a decrease in phosphorylation of HER2, Akt, and S6. Combined treatment induced apoptosis more efficiently than either agent alone; however the most effective was a combination of lapatinib with erucin. These findings might support the optimization of therapy based on lapatinib treatment.

Sulforaphane inhibits growth of phenotypically different breast cancer cells.

PURPOSE: Cancer development and resistance to chemotherapy correlates with aberrant activity of mitogenic pathways. In breast cancers, pro-survival PI3K-Akt-mTOR-S6K1 [corrected] signaling pathway is often hyperactive due to overexpression of genes coding for growth factors or estrogen receptors, constitutive activation of PI3K or Akt and loss of PTEN, a negative regulator of the pathway. Since epidemiologic as well as rodent tumor studies indicate that sulforaphane (SFN), a constituent of many edible cruciferous vegetables, might be a potent inhibitor of mammary carcinogenesis, we analyzed the response of four breast cancer cell lines representing different abnormalities in ErbB2/ER-PI3K-Akt-mTOR-S6K1[corrected] signaling pathway to this compound. METHODS: Four different breast cancer cell lines were used: MDA MB 231, MCF-7, SKBR-3 and MDA MB 468. Cell viability and ultrastructure, protein synthesis, autophagy induction and phosphorylation status of Akt and S6K1 kinases upon SFN treatment were determined. RESULTS: We observed that all four cell lines are similarly sensitive to SFN. SFN decreased phosphorylation of Akt and S6K1 kinases and at higher concentrations induced autophagy in all studied cell lines. Moreover, global protein synthesis was inhibited by SFN in investigated cell lines in a dose-dependent manner. CONCLUSION: These results indicate that SFN is a potent inhibitor of the viability of breast cancer cells representing different activity of the ErbB2/ER-PI3K-Akt-mTOR-S6K1 [corrected] pro-survival pathway and suggest that it targets downstream elements of the pathway.