Selective Disruption of Rb–Raf-1 Kinase Interaction Inhibits Pancreatic Adenocarcinoma Growth Irrespective of Gemcitabine Sensitivity

Abstract

Inactivation of the Retinoblastoma tumor suppressor protein, (Rb), is widespread in human cancers. Inactivation of Rb is thought to be initiated by association with Raf-1 (C-Raf) kinase, and here we determined how RRD-251, a disruptor of the Rb-Raf-1 interaction, affects pancreatic tumor progression. Assessment of phospho-Rb levels in resected human pancreatic tumor specimens by immunohistochemistry (n=95) showed that increased Rb phosphorylation correlated with increasing grade of resected human pancreatic adenocarcinomas (p=0.0272), which correlated with reduced overall patient survival (p=0.0186). To define the anti-tumor effects of RRD-251 (50μM), cell-cycle analyses, senescence, cell viability, cell migration, anchorage-independent growth, angiogenic tubule formation and invasion assays were performed on gemcitabine sensitive and resistant pancreatic cancer cells. RRD-251 prevented S-phase entry, induced senescence and apoptosis, and inhibited anchorage-independent growth and invasion (p< 0.01). Drug efficacy on subcutaneous and orthotopic xenograft models was tested by intraperitoneal injections of RRD-251 (50mpk) alone or in combination with gemcitabine (250mg/kg). RRD-251 significantly reduced tumor growth in vivo accompanied by reduced Rb phosphorylation and lymph node and liver metastasis (p<0.01). Combination of RRD-251 with gemcitabine demonstrated cooperative effect on tumor growth (p< 0.01). In conclusion, disruption of the Rb-Raf-1 interaction significantly reduces the malignant properties of pancreatic cancer cells irrespective of their gemcitabine sensitivity. Selective targeting of Rb-Raf-1 interaction might be a promising strategy targeting pancreatic cancer.

Cell Cycle Protein Expression in Neuroendocrine Tumors

“…Our observations are consistent with other studies, which have found that high expression of phospho-RB1 is associated with an increasing degree of tumor aggressiveness in a variety tumors, including pancreatic adenocarcinoma, 39 breast and ovarian cancer, 40 synovial sarcoma, 41 head and neck squamous cell carcinoma. 12 High expression of CDK4/CDK6 and/or high expression of CCND1 were also found to be associated with more aggressive behavior and/or poor survival in breast cancer, 42,43 primary ovarian serous carcinomas, 13 papillary carcinoma, 44 meningiomas, 45 periampullary adenocarcinoma, 14 extremity soft-tissue sarcomas, 15 laryngeal squamous cell carcinomas, 46 esophageal adenocarcinoma, 47 and lung adenocarcinoma.…”

Nicotine Reduces Survival via Augmentation of Paracrine HGF–MET Signaling in the Pancreatic Cancer Microenvironment

“…The L3.6pl pancreatic cancer cell metastatic variant was derived as previously described (19, 20). The selection of L3.6pl GemRes gemcitabine-resistant pancreatic cancer cells was conducted as previously described (12, 21). Cells were maintained in culture with Dulbecco’s Modified Eagle’s Medium/F12 (DMEM/F12) with 10% fetal bovine serum (FBS) (Atlanta Biologicals, Atlanta, GA) and 0.6% penicillin/streptomycin and 5% CO2/95% air at 37°C.…”

Downstream mediators of the intratumoral interferon response suppress antitumor immunity, induce gemcitabine resistance and associate with poor survival in human pancreatic cancer

“…L3.6pl metastatic variant was derived as previously described [17, 18]. The selection of L3.6pl GemRes gemcitabine-resistant pancreatic cancer cells was conducted as previously described [19]. All human PC cell lines were authenticated within 6 months by short tandem repeat (STR) analysis.…”