Induction and rejoining of DNA double-strand breaks in bladder tumor cells

The induction and rejoining of radiation-induced double-strand breaks (DSBs) in cells of six bladder tumor cell lines (T24, UM-UC3, TCC-SUP, RT112, J82, HT1376) were measured using the neutral comet assay. Radiation dose-response curves (0-60 Gy) showed damage (measured as mean tail moment) for five of the cell lines in the same rank order as cell survival (measured over 0-10 Gy), with the least damage in the most radioresistant cell line. Damage induction correlated well with clonogenic survival at high doses (SF10) for all six cell lines. At the clinically relevant dose of 2 Gy, correlation was good for four cell lines but poor for two (TCC-SUP and T24), The rejoining process had a fast and slow component for all cell lines. The rate of these two components of DNA repair did not correlate with cell survival. However, the time taken to reduce the amount of DNA damage to preirradiated control levels correlated positively with cell survival at 10 Gy but not 2 Gy; radioresistant cells rejoined the induced DSBs to preirradiation control levels more quickly than the radiosensitive cells. Although the results show good correlation between SF10 and DSBs for all six cell lines, the lack of correlation with SF2 for TCC-SUP and T24 cells would suggest that a predictive test should be carried out at the clinically relevant dose. At present the neutral comet assay cannot achieve this. (C) 2000 by Radiation Research Society.

Antibody Targeting of Camptothecin-Loaded PLGA Nanoparticles to Tumor Cells

Antibody targeting of drug substances can improve the efficacy of the active molecule, improving distribution and concentration of the drug at the site of injury/disease. Encapsulation of drug substances into polymeric nanoparticles can also improve the therapeutic effects of such compounds by protecting the molecule until its action is required. In this current study, we have brought together these two rationales to develop a novel immunonanoparticle with improved therapeutic effect against colorectal tumor cells. This nanoparticle comprised a layer of peripheral antibodies (Ab) directed toward the Fas receptor (CD95/Apo-1) covalently attached to poly(lactide-co-glycolide) nanoparticles (NP) loaded with camptothecin. Variations in surface carboxyl density permitted up to 48.5 mu g coupled Ab per mg of NP and analysis of nanoparticulate cores showed efficient camptothecin loading. Fluorescence visualization studies confirmed internalization of nanoconstructs into endocytic compartments of HCT 116 cells, an effect not evident in NP without superficial Ab. Cytotoxicity studies were then carried out against HCT116 cells. After 72 h, camptothecin solution resulted in an IC50 of 21.8 ng mL(-1). Ab-directed delivery of NP-encapsulated camptothecin was shown to be considerably more effective with an IC50 of 0.37 ng mL(-1). Calculation of synergistic ratios for these nanoconstructs demonstrated synergy of pharmacological relevance. Indeed, the results in this paper suggest that the attachment of anti-Fas antibodies to camptothecin-loaded nanoparticles may result in a therapeutic strategy that could have potential in the treatment of tumors expressing death receptors.

Cancer-related ectopic expression of the bone-related transcription factor RUNX2 in non-osseous metastatic tumor cells is linked to cell proliferation and motility

Introduction: Metastatic breast cancer cells frequently and ectopically express the transcription factor RUNX2, which normally attenuates proliferation and promotes maturation of osteoblasts. RUNX2 expression is inversely regulated with respect to cell growth in osteoblasts and deregulated in osteosarcoma cells.

Repression of NHE1 Expression by PPAR gamma Activation Is a Potential New Approach for Specific Inhibition of the Growth of Tumor Cells In vitro and In vivo

Ligand-induced activation of peroxisome proliferator-activated receptor gamma (PPAIR gamma) inhibits proliferation in cancer cells in vitro and in vivo; however, the downstream targets remain undefined. We report the identification of a peroxisome proliferator response element in the promoter region of the Na+/ H transporter gene NHE1, the overexpression of which has been associated with carcinogenesis. Exposure of breast cancer cells expressing high levels of PPAR gamma to its natural and synthetic agonists resulted in downregulation of NHE1 transcription as well as protein expression. Furthermore, the inhibitory effect of activated PPAR gamma on tumor colony-forming ability was abrogated on overexpression of NHE1, whereas small interfering RNA-mediated gene silencing of NHE1 significantly increased the sensitivity of cancer cells to growth-inhibitory stimuli. Finally, histopathologic analysis of breast cancer biopsies obtained from patients with type II diabetes treated with the synthetic agonist rosiglitazone showed significant repression of NHE1 in the tumor tissue. These data provide evidence for tumor-selective downregulation of NHE1 by activated PPAR gamma in vitro and in pathologic specimens from breast cancer patients and could have potential implications for the judicious use of low doses of PPAR gamma ligands in combination chemotherapy regimens for an effective therapeutic response. [Cancer Res 2009;69(22):8636-44]

Targeting Human Gastrointestinal Stromal Tumor Cells with a Quadruplex-Binding Small Molecule

Most of human gastrointestinal stromal tumors (GIST) are driven by activating mutations in the protooncogene KIT, a tyrosine kinase receptor. Clinical treatment with imatinib targets the kinase domain of KIT, but tumor regrowth occurs as a result of them development of resistant mutations in the kinase active site. An alternative small-molecule approach to GIST therapy is described, in which the KIT gene is directly targeted, and thus, kinase resistance may be circumvented. A naphthalene diimide derivative has been used to demonstrate the concept of dual quadruplex targeting. This compound strongly stabilizes both telomeric quadruplex DNA and quadruplex sites in the KIT promoter in vitro. It is shown here that the compound is a potent inducer of growth arrest in a patient-derived GIST cell line at a concentration (similar to 1 mu M) that also results in effective inhibition of telomerase activity and almost complete suppression of KIT mRNA and KIT protein expression. Molecular modeling studies with a telomeric quadruplex have been used to rationalize aspects of the experimental quadruplex melting data.

Mechanistic Rationale to Target PTEN-Deficient Tumor Cells with Inhibitors of the DNA Damage Response Kinase ATM

Ataxia telangiectasia mutated (ATM) is an important signaling molecule in the DNA damage response (DDR). ATM loss of function can produce a synthetic lethal phenotype in combination with tumor-associated mutations in FA/BRCA pathway components. In this study, we took an siRNA screening strategy to identify other tumor suppressors that, when inhibited, similarly sensitized cells to ATM inhibition. In this manner, we determined that PTEN and ATM were synthetically lethal when jointly inhibited. PTEN-deficient cells exhibited elevated levels of reactive oxygen species, increased endogenous DNA damage, and constitutive ATM activation. ATM inhibition caused catastrophic DNA damage, mitotic cell cycle arrest, and apoptosis specifically in PTEN-deficient cells in comparison with wild-type cells. Antioxidants abrogated the increase in DNA damage and ATM activation in PTEN-deficient cells, suggesting a requirement for oxidative DNA damage in the mechanism of cell death. Lastly, the ATM inhibitor KU-60019 was specifically toxic to PTEN mutant cancer cells in tumor xenografts and reversible by reintroduction of wild-type PTEN. Together, our results offer a mechanistic rationale for clinical evaluation of ATM inhibitors in PTEN-deficient tumors.

Disseminated tumor cells and their prognostic significance in nonmetastatic prostate cancer patients

Detection of pretreatment disseminated cells (pre-DTC) reflecting its homing to bone marrow (BM) in prostate cancer (PCa) might improve the current model to predict recurrence or survival in men with nonmetastatic disease despite of primary treatment. Thereby, pre-DTC may serve as an early prognostic biomarker. Post-treatment DTCs (post-DTC) finding may supply the clinician with additional predictive information about the possible course of PCa. To assess the prognostic impact of DTCs in BM aspirates sampled before initiation of primary therapy (pre-DTC) and at least 2 years after (post-DTC) to established prognostic factors and survival in patients with PCa. Available BM of 129 long-term follow-up patients with T1-3N0M0 PCa was assessed in addition to 100 BM of those in whom a pretreatment BM was sampled. Patients received either combined therapy [n = 81 (63%)], radiotherapy (RT) with different duration of hormone treatment (HT) or monotherapy with RT or HT alone [n = 48 (37%)] adapted to the criteria of the SPCG-7 trial. Mononuclear cells were deposited on slides according to the cytospin methodology and DTCs were identified by immunocytochemistry using the pancytokeratin antibodies AE1/AE3. The median age of men at diagnosis was 64.5 years (range 49.5-73.4 years). The median long-term follow-up from first BM sampling to last observation was 11 years. Categorized clinically relevant factors in PCa showed only pre-DTC status as the statistically independent parameter for survival in the multivariate analysis. Pre-DTCs homing to BM are significantly associated with clinically relevant outcome independent to the patient's treatment at diagnosis with nonmetastatic PCa.