Small cell lung cancer (SCLC) is an aggressive malignancy distinct from non-small cell lung cancer (NSCLC) in its metastatic potential and treatment response. Using an integrative proteomic and transcriptomic analysis, we investigated molecular differences contributing to the distinct clinical behavior of SCLC and NSCLC. SCLC demonstrated lower levels of several receptor tyrosine kinases and decreased activation of PI3K and Ras/MEK pathways, but significantly increased levels of E2F1-regulated factors including EZH2, thymidylate synthase, apoptosis mediators, and DNA repair proteins. Additionally, poly (ADP-ribose) polymerase 1 (PARP1), a DNA repair protein and E2F1 co-activator, was highly expressed at the mRNA and protein levels in SCLC. SCLC growth was inhibited by PARP1 and EZH2 knockdown. Furthermore, SCLC was significantly more sensitive to PARP inhibitors than NSCLC, and PARP inhibition downregulated key components of the DNA repair machinery and enhanced the efficacy of chemotherapy.

Purpose Mortality of patients with head and neck squamous cell carcinoma (HNSCC) is primarily driven by tumor cell radioresistance leading to locoregional recurrence (LRR). In this study, we use a classification of TP53 mutation (disruptive vs. nondisruptive) and examine impact on clinical outcomes and radiation sensitivity. Experimental Design Seventy-four patients with HNSCC treated with surgery and postoperative radiation and 38 HNSCC cell lines were assembled; for each, TP53 was sequenced and in vitro radioresistance measured using clonogenic assays. p53 protein expression was inhibited using shRNA and over-expressed using a retrovirus. Radiation-induced apoptosis, mitotic cell death, senescence, and ROS assays were performed. The effect of the drug metformin on overcoming mutant p53-associated radiation resistance was examined in vitro as well as in vivo, using an orthotopic xenograft model. Results Mutant TP53 alone was not predictive of LRR; however, disruptive TP53 mutation strongly predicted LRR (p=0.03). Cell lines with disruptive mutations were significantly more radioresistant (p<0.05). Expression of disruptive TP53 mutations significantly decreased radiation-induced senescence, as measured by SA-beta-gal staining, p21 expression, and release of reactive oxygen species (ROS). The mitochondrial agent metformin potentiated the effects of radiation in the presence of a disruptive TP53 mutation partially via senescence. Examination of our patient cohort showed that LRR was decreased in patients taking metformin. Conclusions Disruptive TP53 mutations in HNSCC tumors predicts for LRR, due to increased radioresistance via the inhibition of senescence. Metformin can serve as a radiosensitizer for HNSCC with disruptive TP53, presaging the possibility of personalizing HNSCC treatment.

No abstract

TP53 is the most frequently altered gene in head and neck squamous cell carcinoma (HNSCC) with mutations occurring in over two third of cases, but the prognostic significance of these mutations remains elusive. In the current study, we evaluated a novel computational approach termed Evolutionary Action (EAp53) to stratify patients with tumors harboring TP53 mutations as high or low risk, and validated this system in both in vivo and in vitro models. Patients with high risk TP53 mutations had the poorest survival outcomes and the shortest time to the development of distant metastases. Tumor cells expressing high risk TP53 mutations were more invasive and tumorigenic and they exhibited a higher incidence of lung metastases. We also documented an association between the presence of high risk mutations and decreased expression of TP53 target genes, highlighting key cellular pathways that are likely to be dysregulated by this subset of p53 mutations which confer particularly aggressive tumor behavior. Overall, our work validated EAp53 as a novel computational tool that may be useful in clinical prognosis of tumors harboring p53 mutations.

This regimen appears effective and has acceptable toxicity. The primary end point (1-year overall survival rate > 45%) was met, with encouraging survival duration. Smad4(Dpc4) immunostaining correlated with the pattern of disease progression. Prospective validation of Smad4(Dpc4) expression in cytology specimens as a predictive biomarker is warranted and may lead to personalized treatment strategies for patients with localized pancreatic cancer.

The p53-binding protein 1 (53BP1) is a well-known DNA damage response (DDR) factor, which is recruited to nuclear structures at the site of DNA damage and forms readily visualized ionizing radiation (IR) induced foci. Depletion of 53BP1 results in cell cycle arrest in G2/M phase as well as genomic instability in human as well as mouse cells. Within the DNA damage response mechanism, 53BP1 is classified as an adaptor/mediator, required for processing of the DNA damage response signal and as a platform for recruitment of other repair factors. More recently, specific 53BP1 contributions to DSB repair pathway choice have been recognized and are being characterized. In this review, we have summarized recent advances in understanding the role of 53BP1 in regulating DNA DSBs repair pathway choice, variable diversity joining [V(D)J] recombination and class-switch recombination (CSR).

Ionizing radiation (IR) is a key therapeutic regimen for many head and neck cancers (HNCs). However, the 5-year overall survival rate for locally-advanced HNCs is ∼50% and better therapeutic efficacy is needed. NAD(P)H:quinone oxidoreductase 1 (NQO1) is over-expressed in many cancers, and β-lapachone (β-lap), an unique NQO1 bioactivatable drug, exploits this enzyme to release massive reactive oxygen species (ROS) levels that synergizes with IR to kill by programmed necrosis. β-Lap represents a novel therapeutic opportunity in HNC leading to tumor-selective lethality that will enhance the efficacy of ionizing radiation. Immunohistochemical staining and western blot assays were used to assess the expression levels of NQO1 in HNC cells and tumors. Forty-five percent of endogenous HNCs express elevated NQO1 levels. In addition, multiple HNC cell lines and tumors demonstrated elevated levels of NQO1 expression and activity and were tested for anticancer lethality and radiosensitization by β-lap using long-term survival assays. The combination of nontoxic β-lap doses and IR significantly enhanced NQO1-dependenttumor cell lethality, increased ROS, TUNEL positive cells, DNA damage, NAD+ and adenosine triphosphate (ATP) consumption, and resulted in significantantitumor efficacy and prolonged survival in two xenograft murine HNC models, demonstrating β-Lap radiosensitization of HNCs through a NQO1-dependent mechanism. This translational study offers a potential biomarker-driven strategy using NQO1 expression to select tumors susceptible to β-lap-induced radiosensitization.

Thromboxane synthase (TXAS) is one of the enzymes downstream from cyclooxygenase-2 and catalyzes the synthesis of thromboxane A 2 (TXA 2 ). TXAS was among the genes we identified based on its overexpression in invasive bladder tumors. TXAS is overexpressed in common forms of bladder tumors: 69 of 97 (71.1%) transitional cell carcinoma (TCC), 38 of 53 (71.6%) squamous cell carcinoma, and 5 of 11 (45.5%) adenocarcinoma relative to nontumor tissue. Overall, 112 of 161 (69.5%) invasive tumors exhibited elevated expression. Significantly, patients with tumors having >4-fold levels of TXAS expression showed significant statistical evidence of lower overall survival expressed by the estimated hazard ratio of 2.74 with P = 0.009 in Cox's regression analysis. TXAS mRNA expression was found to be an independent prognostic marker for patients with bladder cancer. Treatment of bladder cancer cell lines (T24 and TCC-SUP) with TXAS inhibitors and TXA 2 (TP) receptor antagonists reduced cell growth, migration, and invasion, whereas TP agonists stimulated cell migration and invasion. The positive correlation between elevated TXAS expression and shorter patient survival supports a potential role for TXAS-regulated pathways in tumor invasion and metastases and suggests that modulation of the TXAS pathway may offer a novel therapeutic approach. (Cancer Res 2005; 65(24): 11581-7)