Nab-paclitaxel, a nanoparticle conjugate of paclitaxel to human albumin, exhibits efficacy in pancreatic cancer, non–small cell lung cancer and breast cancer. However, there is a lack of predictive biomarkers to identify patients who might benefit most from its administration. This study addresses this gap in knowledge by identifying that caveolin-1 (Cav-1) is a candidate mechanism-based biomarker. Caveolae are small membrane invaginations important for transendothelial albumin uptake. Cav-1, the principal structural component of caveolae, is overexpressed in the cancers noted above that respond to nab-paclitaxel. Thus, we hypothesized that Cav-1 may be critical for albumin uptake in tumors and perhaps determine their response to this drug. Cav-1 protein levels correlated positively with nab-paclitaxel sensitivity. RNAi-mediated attenuation of Cav-1 expression reduced uptake of albumin and nab-paclitaxel in cancer cells and rendered them resistant to nab-paclitaxel–induced apoptosis. Conversely, Cav-1 overexpression enhanced sensitivity to nab-paclitaxel. Selection for cellular resistance to nab-paclitaxel in cell culture correlated with a loss of Cav-1 expression. In mouse xenograft models, cancer cells, where Cav-1 was attenuated, exhibited resistance to the antitumor effects of nab-paclitaxel therapy. Overall, our findings suggest Cav-1 as a predictive biomarker for the response to nab-paclitaxel and other albumin-based cancer therapeutic drugs. Cancer Res; 77(21); 5925–37. ©2017 AACR.

The efficacy of neoadjuvant therapy (NT) versus surgery first (SF) for pancreatic ductal adenocarcinoma (PDAC) remains controversial. A random-effects meta-analysis of only prospective randomized controlled trials (RCTs) comparing NT versus SF for potentially resectable (PR) or borderline resectable (BR) PDAC was performed. Among six RCTs including 850 patients, 411 (48.3%) received NT and 439 (51.6%) SF. In all included trials, NT was gemcitabine-based: four using chemoradiation and two chemotherapy alone. Based on an intention-to-treat analysis, NT resulted in improved overall survival (OS) compared to SF (HR 0.73, 95% CI 0.61–0.86). This effect was independent of anatomic classification (PR: hazard ratio (HR) 0.73, 95% CI 0.59–0.91; BR: HR 0.51 95% CI 0.28–0.93) or NT type (chemoradiation: HR 0.77, 95% CI 0.61–0.98; chemotherapy alone: HR 0.68, 95% CI 0.54–0.87). Overall resection rate was similar (risk ratio (RR) 0.93, 95% CI 0.82–1.04, I² = 39.0%) but NT increased the likelihood of a margin-negative (R0) resection (RR 1.51, 95% CI 1.18–1.93, I² = 0%) and having negative lymph nodes (RR 2.07, 95% CI 1.47–2.91, I² = 12.3%). In this meta-analysis of prospective RCTs, NT significantly improved OS in an intention-to-treat fashion, compared with SF for localized PDAC. Randomized controlled trials using contemporary multi-agent chemotherapy will be needed to confirm these findings and to define the optimal NT regimen.

Caveolin-1 (Cav-1) is a 21 kDa protein enriched in caveolae and has been implicated in oncogenic cell transformation, tumorigenesis and metastasis. We explored roles for Cav-1 in pancreatic cancer (PC) prognostication, tumor progression, resistance to therapy and whether targeted downregulation could lead to therapeutic sensitization. Cav-1 expression was assessed in cell lines, mouse models and patient samples and knocked down in order to compare changes in proliferation, invasion, migration, response to chemotherapy and radiation and tumor growth. We found Cav-1 is overexpressed in human PC cell lines, mouse models and human pancreatic tumors and is associated with worse tumor grade and clinical outcomes. In PC cell lines, disruption/depletion of caveolae/Cav-1 reduces proliferation, colony formation and invasion. Radiation and chemotherapy up-regulate Cav-1 expression, while Cav-1 depletion induces both chemosensitization and radiosensitization through altered apoptotic and DNA repair signaling. In vivo, Cav-1 depletion significantly attenuates tumor initiation and growth. Finally, Cav-1 depletion leads to altered JAK/STAT, JNK and Src signaling in PC cells. Together, higher Cav-1 expression is correlated with worse outcomes, is essential for tumor growth and invasion (both in vitro and in vivo), is responsible for promoting resistance to therapies and may serve as a prognostic/predictive biomarker and target in PC.

KRAS-activating mutations are oncogenic drivers and are correlated with radioresistance of multiple cancers, including colorectal cancer, but the underlying precise molecular mechanisms remain elusive. Herein we model the radiosensitivity of isogenic HCT116 and SW48 colorectal cancer cell lines bearing wild-type or various mutant KRAS isoforms. We demonstrate that KRAS mutations indeed lead to radioresistance accompanied by reduced radiotherapy-induced mitotic catastrophe and an accelerated release from G2/M arrest. Moreover, KRAS mutations result in increased DNA damage response and upregulation of 53BP1 with associated increased non-homologous end-joining (NHEJ) repair. Remarkably, KRAS mutations lead to activation of NRF2 antioxidant signaling to increase 53BP1 gene transcription. Furthermore, genetic silencing or pharmacological inhibition of KRAS, NRF2 or 53BP1 attenuates KRAS mutation-induced radioresistance, especially in G1 phase cells. These findings reveal an important role for a KRAS-induced NRF2-53BP1 axis in the DNA repair and survival of KRAS-mutant tumor cells after radiotherapy, and indicate that targeting NRF2, 53BP1 or NHEJ may represent novel strategies to selectively abrogate KRAS mutation-mediated radioresistance.

There is an urgent need for the development of novel therapies to treat pancreatic cancer, which is among the most lethal of all cancers. KRAS-activating mutations, which are found in more than 90% of pancreatic adenocarcinomas, drive tumor dependency on the Ras/MAPK and Akt signaling pathways. Radiation is currently being explored as a component of the standard treatment regimen for pancreatic cancer. This study's purpose was to test the hypothesis that MAP kinase kinase (MEK or MAP2K) inhibitors will offer clear therapeutic benefit when integrated into radiotherapy treatment regimens for treatment of this disease. We explored the activation of the mitogen-activated protein kinase (MAPK) and Akt pathways in response to radiation in multiple pancreatic tumor cell lines. Small molecule inhibitors of MEK (PD0325901) and Akt (API-2) were subsequently evaluated for their radiosensitizing potential alone and in combination. In vivo efficacy was tested in subcutaneous MIA-PaCa2 xenografts. Phosphorylated levels of extracellular signal–regulated kinase (ERK)-1/2 and Akt were found to increase in response to radiation treatment in our pancreatic tumor cell line panel. MEK inhibitor–induced radiosensitization was observed in vitro and in vivo. The further addition of an Akt inhibitor to the MEK inhibitor/radiation regimen resulted in enhanced therapeutic gain as determined by increased radiosensitization and tumor cell death. In conclusion, MEK inhibition results in growth arrest, apoptosis, and radiosensitization of multiple preclinical pancreatic tumor models, and the effects can be enhanced by combination with an Akt inhibitor. These results provide rationale for further testing of a treatment regimen in pancreatic cancer that combines MEK inhibition with radiation, optimally in conjunction with Akt inhibition. Mol Cancer Ther; 11(5); 1193–202. ©2012 AACR.