Anti-tumor activity of the beta-adrenergic receptor antagonist propranolol in neuroblastoma.

Neuroblastoma (NB) is a pediatric tumor of the sympathetic nervous system, which is often associated with elevated catecholamines. More than half of patients with metastatic NB relapse and survival is extremely poor with current therapies. In a high-throughput screen of FDA-approved drugs we identified anti-NB activity for the nonselective ß-adrenergic receptor antagonist propranolol hydrochloride. Propranolol inhibited growth of a panel of fifteen NB cell lines irrespective of MYCN status, and treatment induced apoptosis and decreased proliferation. Activity was dependent on inhibition of the ß2, and not ß1, adrenergic receptor, and treatment resulted in activation of p53 and p73 signaling in vitro. The majority of NB cell lines and primary tumors express ß2 adrenergic receptor and higher mRNA levels correlate with improved patient survival, but expression levels did not correlate with in vitro sensitivity to propranolol. Furthermore, propranolol is synergistic with the topoisomerase I inhibitor SN-38 and propranolol inhibits growth of NB xenografts in vivo at doses similar to those used to treat infants with hemangiomas and hypertension. Taken together, our results suggest that propranolol has activity against NB and thus should be considered in combination treatments for patients with relapsed and refractory NB.

Eukaryotic translation elongation factor 1-alpha 1 inhibits p53 and p73 dependent apoptosis and chemotherapy sensitivity.

The p53 family of transcription factors is a key regulator of cell proliferation and death. In this report we identify the eukaryotic translation elongation factor 1-alpha 1 (eEF1A1) to be a novel p53 and p73 interacting protein. Previous studies have demonstrated that eEF1A1 has translation-independent roles in cancer. We report that overexpression of eEF1A1 specifically inhibits p53-, p73- and chemotherapy-induced apoptosis resulting in chemoresistance. Short-interfering RNA-mediated silencing of eEF1A1 increases chemosensitivity in cell lines bearing wild type p53, but not in p53 null cells. Furthermore, silencing of eEF1A1 partially rescues the chemoresistance observed in response to p53 or p73 knockdown, suggesting that eEF1A1 is a negative regulator of the pro-apoptotic function of p53 and p73. Thus, in the context of p53-family signaling, eEF1A1 has anti-apoptotic properties. These findings identify a novel mechanism of regulation of the p53 family of proteins by eEF1A1 providing additional insight into potential targets to sensitize tumors to chemotherapy.

SATB2 augments ΔNp63α in head and neck squamous cell carcinoma.

ΔNp63α is a critical pro-survival protein overexpressed in 80% of head and neck squamous cell carcinomas (HNSCCs) where it inhibits TAp73ß transcription of p53-family target genes, which is thought to increase HNSCC resistance to chemotherapy-induced cell death. However, the mechanisms governing ΔNp63α function are largely unknown. In this study, we identify special AT-rich-binding protein 2 (SATB2) as a new ΔNp63α-binding protein that is preferentially expressed in advanced-stage primary HNSCC and show that SATB2 promotes chemoresistance by enhancing ΔNp63α-mediated transrepression by augmenting ΔNp63α engagement to p53-family responsive elements. Furthermore, SATB2 expression positively correlates with HNSCC chemoresistance, and RNA interference-mediated knockdown of endogenous SATB2 re-sensitizes HNSCC cells to chemotherapy- and γ-irradiation-induced apoptosis, irrespective of p53 status. These findings unveil SATB2 as a pivotal modulator of ΔNp63α that governs HNSCC cell survival.

Expression of p53 in renal carcinoma cells is independent of pVHL.

Renal clear-cell carcinoma (RCC) is the predominant form of kidney cancer and is highly refractory to conventional anti-cancer therapies. The status of p53 tumor suppressor gene has been correlated with the efficacy of radio- and chemotherapies, where presence of mutant p53 is associated with reduced responsiveness to treatment. However, p53 itself is rarely mutated in RCC, rather suggesting that the p53 pathway might be compromized in RCC cells. In support of this notion, the transactivation property of normal p53 was shown to be repressed in various transformed kidney epithelial cells via an unknown dominant-negative mechanism. Mutation of the von Hippel-Lindau (VHL) gene causes familial VHL disease, which includes predisposition to RCC. Moreover, biallelic inactivation of VHL has been observed in the vast majority of sporadic RCC. Recently, the expression of pVHL in RCC cells was demonstrated to elevate the expression of p53 by inducing the binding of RNA-stabilizing protein HuR to the 3'untranslated region of p53 mRNA. Contrary to this finding, we report here that the reconstitution of a variety of VHL(-/-) RCC lines including 786-O, RCC4, and A498 or non-RCC cells with wild-type pVHL does not influence the expression of p53 and fails to induce p53-responsive gene p21CIP1/WAF1 or p53-responsive reporters. These results suggest that the expression of p53 in RCC cells is independent of pVHL.

Chemosensitivity linked to p73 function.

Most chemotherapeutic agents induce DNA damage, leading to p53 accumulation and apoptosis. The factors that determine chemosensitivity in p53-defective tumor cells are poorly understood. We found that the p53 family member p73 is induced by a wide variety of chemotherapeutic drugs. Blocking p73 function with a dominant-negative mutant, siRNA, or homologous recombination led to chemoresistance of human tumor cells and engineered transformed cells, irrespective of p53 status. Mutant p53 can inactivate p73 and downregulation of mutant p53 enhanced chemosensitivity. These findings indicate that p73 is a determinant of chemotherapeutic efficacy in humans.