Autophagy in malignant transformation and cancer progression.

Autophagy plays a key role in the maintenance of cellular homeostasis. In healthy cells, such a homeostatic activity constitutes a robust barrier against malignant transformation. Accordingly, many oncoproteins inhibit, and several oncosuppressor proteins promote, autophagy. Moreover, autophagy is required for optimal anticancer immunosurveillance. In neoplastic cells, however, autophagic responses constitute a means to cope with intracellular and environmental stress, thus favoring tumor progression. This implies that at least in some cases, oncogenesis proceeds along with a temporary inhibition of autophagy or a gain of molecular functions that antagonize its oncosuppressive activity. Here, we discuss the differential impact of autophagy on distinct phases of tumorigenesis and the implications of this concept for the use of autophagy modulators in cancer therapy.

A diphtheria toxin-epidermal growth factor fusion protein is cytotoxic to human glioblastoma multiforme cells.

The cytotoxicity of a diphtheria toxin-human epidermal growth factor fusion protein (DAB(389)EGF) was tested against 14 human glioma cell lines. After cells were cultured for 48 h with various concentrations of DAB(389)EGF, the percentage reduction in thymidine incorporation was determined. For 13 of 14 cell lines, potent cytotoxicity was observed, with IC(50)s of 0.4-50 pM. The epidermal growth factor receptor (EGFR) density of these cell lines was determined by immunofluorescence microscopy, flow cytometry, and radioligand binding. These assays correlated well with each other and demonstrated EGFR levels of 15,000-230,000/cell for 13 of 14 cell lines. The cell line U138MG, which lacked EGFR, was the only cell line insensitive to DAB(389)EGF. Linear regression analysis showed a good correlation between EGFR density and DAB(389)EGF sensitivity (P < 0.001) and between results of flow cytometry and radiolabeled binding assays of EGFR density (P = 0.01). DAB(389)EGF may have potential for intracranial therapy of EGFR-positive glioblastomas.

Preclinical and clinical estimates of the basal apoptotic rate of a cancer predict the amount of apoptosis induced by subsequent proapoptotic stimuli.

PURPOSE: We hypothesized that the basal apoptotic rate (BAR) of a cancer would predict sensitivity to subsequent proapoptotic stimuli. To explore this, preclinical and clinical BAR assays were developed measuring cumulative apoptotic events through ELISAs for soluble caspase-cleaved cytokeratin 18 (M30) normalized to either cell number increase or total tumor volume, respectively. EXPERIMENTAL DESIGN: The BARs of A549, HCC44, and SW1573 non-small cell lung carcinoma cell lines were measured following different pro/antiapoptotic manipulations. In isogenic wild-type and stable knockdown (KD) series, pretreatment BARs were correlated with response to proapoptotic stimuli and compared with established apoptosis assays. Pretreatment and posttreatment serum was available from stereotactic body radiation therapy patients. RESULTS: Caspase inhibition and p53 KDs reduced the BAR, whereas serum deprivation, XIAP, or Bcl2 KDs increased the BAR. The nontreated BAR rank ordering of the XIAP series recapitulated that with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and caspase-3/7 activity assays, and predicted each line's sensitivity to TRAIL or irradiation. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, however, underestimated basal apoptosis during increased apoptotic stress, and caspase-3/7 activity detected minimal death in the media. P53 KDs with lower nontreated BARs were less sensitive to TRAIL and cisplatinum than wild-type. Stereotactic body radiation therapy increased serum M30 values, and the pretreatment clinical BAR strongly correlated with fold change in M30 on treatment (r = 0.93). CONCLUSIONS: M30-based BAR assays reflect apoptosis accurately and are more amenable to clinical application than existing apoptosis assays. The pretreatment BAR correlates with cell and/or tumor sensitivity to extrinsic and intrinsic apoptotic pathway stimulation. Prospective clinical exploration is warranted.