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 trans-endothelial albumin uptake. Cav-1, the principal structural component of caveolae, is overexpressed in the cancers noted above which 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.

Purpose: Activating BRAF mutations, most commonly BRAF V600E , are a major oncogenic driver of many cancers. We explored whether BRAF V600E promotes radiation resistance and whether selectively targeting BRAF V600E with a BRAF inhibitor (vemurafenib, BRAFi) sensitizes BRAF V600E thyroid cancer cells to radiotherapy. Experimental Design: Immunoblotting, neutral comet, immunocytochemistry, functional reporter, and clonogenic assays were used to analyze the outcome and molecular characteristics following radiotherapy with or without BRAF V600E or vemurafenib in thyroid cancer cells. Results: BRAF V600E thyroid cancer cell lines were associated with resistance to ionizing radiation (IR), and expression of BRAF V600E into wild-type BRAF thyroid cancer cells led to IR resistance. BRAFi inhibited ERK signaling in BRAF V600E mutants, but not BRAF wild-type thyroid cancer cell lines. BRAFi selectively radiosensitized and delayed resolution of IRinduced gH2AX nuclear foci in BRAF V600E cells. Moreover, BRAFi impaired global DNA repair and altered the resolution of 53BP1 and RAD51 nuclear foci in BRAF V600E cells following IR. BRAF V600E mutants displayed enhanced nonhomologous end-joining (NHEJ) repair activity, which was abolished by BRAFi. Intriguingly, BRAF V600E mutation led to upregulation of XLF, a component of NHEJ, which was prevented by BRAFi. Importantly, BRAFi in combination with radiotherapy resulted in marked and sustained tumor regression of BRAF V600E thyroid tumor xenografts. Conclusions: BRAF V600E mutation promotes NHEJ activity leading to radioresistance and BRAFi selectively radiosensitizes BRAF V600E thyroid cancer cells through inhibiting NHEJ. Our findings suggest that combining BRAFi and radiation may improve the therapeutic outcome of patients with BRAF V600Emutant thyroid cancer.

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.

Patient and Methods: Stage II/III rectal cancer patients were enrolled on a phase I study with 3+3 study design, with an expansion cohort of 9 patients at the maximum tolerated dose (MTD).Following a 5-day trametinib lead-in, with pre-and post-treatment tumor biopsies, patients received trametinib and CRT, surgery, and adjuvant chemotherapy. Trametinib was given orally daily at 3 dose levels: 0.5 mg, 1 mg, and 2 mg. CRT consisted of infusional 5FU 225 mg/m 2 /day and 28 daily fractions of 1.8 Gy (total 50.4Gy). The primary endpoint was to identify the MTD and recommended phase 2 dose. Immunohistochemistry (IHC) staining for phosphorylated -ERK (pERK) and genomic profiling was performed on the tumor samples.Results: Patients were enrolled to all dose levels, and 18 patients were evaluable for toxicities and responses. Treatment was well-tolerated, and there was one dose-limiting toxicity of diarrhea, which was attributed to CRT rather than trametinib. At the 2 mg dose level, 25% had pathological complete response. IHC staining confirmed dose-dependent decrease in pERK with increasing trametinib doses. Conclusions:The combination of trametinib with 5FU-CRT is safe and well-tolerated, and may warrant additional study in a phase II trial, perhaps in a RAS/RAF-mutant selected population.

In recent years, human serum albumin (HSA) has been characterized as an ideal drug carrier in the cancer arena. Caveolin-1 (Cav-1) has been established as the principal structural protein of caveolae and, thus, critical for caveolae-mediated endocytosis. Cav-1 has been shown to be overexpressed in cancers of the lung and pancreas, among others. We found that Cav-1 expression plays a critical role in both HSA uptake and response to albumin-based chemotherapies. As such, developing a novel albumin-based chemotherapy that is more selective for tumors with high Cav-1 expression or high levels of caveolar-endocytosis could have significant implications in biomarker-directed therapy. Herein, we present the development of a novel and effective HSA-SN-38 conjugate (SSH20). We find that SSH20 uptake decreases significantly by immunofluorescence assays and western blotting after silencing of Cav-1 expression through RNA interference. Decreased drug sensitivity occurs in Cav-1-depleted cells using cytotoxicity assays. Importantly, we find significantly reduced sensitivity to SSH20 in Cav-1-silenced tumors compared to Cav-1-expressing tumors in vivo . Notably, we show that SSH20 is significantly more potent than irinotecan in vitro and in vivo . Together, we have developed a novel HSA-conjugated chemotherapy that is potent, effective, safe, and demonstrates improved efficacy in high Cav-1-expressing tumors.

Resectable pancreatic adenocarcinoma (PC) is generally managed with surgery followed by chemotherapy, but the role of postoperative chemoradiation (pCRT) is controversial. We sought to identify a microRNA (miRNA) expression profile associated with higher risk for local-regional recurrence (LRR), which might help identify patients that may benefit from pCRT. Total RNA was isolated from viable tumor from 88 patients who underwent PC resection with or without chemotherapy, but did not receive radiation. Digital miRNA expression profiling was performed and risk scores were calculated based on the expression levels of the four most significantly correlated miRNAs, and dichotomized about the median to detect correlations between risk group, LRR and overall survival (OS). Two cohorts from The Cancer Genome Atlas (TCGA) and Seoul National University (SNU) were used for validation. Patients with high-risk scores had significantly worse LRR (p = 0.001) and worse OS (p = 0.034). Two-year OS rates for the high-and low-risk groups were 27.7% and 52.2%, respectively. On multivariable analysis, the risk score remained significantly associated with LRR (p = 0.018). When validated on TCGA data, a high-risk score was associated with worse OS on univariate (p = 0.03) and multivariable analysis (p = 0.017). When validated on the SNU cohort, a high-risk score was likewise associated with worse OS (p = 0.042). We have developed a 4-miRNA molecular signature that is associated with risk of LRR and OS after PC resection and validated on two separate cohorts. This signature has the potential to select patients most likely to benefit from pCRT, and should be tested further.

Purpose: Concurrent gemcitabine and nab-paclitaxel treatment is one of the preferred chemotherapy regimens for metastatic and locally advanced pancreatic ductal adenocarcinoma (PDAC). Previous studies demonstrate that caveolin-1 (Cav-1) expression is critical for nab-paclitaxel uptake into tumors and correlates with response. Gemcitabine increases nab-paclitaxel uptake by increasing Cav-1 expression. Thus, we hypothesized that pretreatment with gemcitabine would further enhance the sensitivity of PDAC to nab-paclitaxel by increasing Cav-1 expression and nab-paclitaxel uptake. Experimental Design: We investigated the sensitivity of different gemcitabine and nab-paclitaxel treatment regimens in a panel of PDAC cell lines and orthotopic xenograft models. The sensitivity of different treatment regimens was compared with the standard concurrent treatment. Results: Pretreatment with gemcitabine before nab-paclitaxel increased Cav-1 and albumin uptake and significantly decreased proliferation and clonogenicity compared with concurrent treatment, which correlated with increased levels of apoptosis. Cav-1 silencing reduced the uptake of albumin, and therapeutic advantage was observed when cells were pretreated with gemcitabine prior to nab-paclitaxel. In addition, we observed that pretreatment with gemcitabine resulted in partial synchronization of cells in the G2–M-phase at the time of nab-paclitaxel treatment, providing another mechanism for the benefit of altered scheduling. In heterotopic and orthotopic xenograft models, the altered schedule of gemcitabine prior to nab-paclitaxel significantly delayed tumor growth compared with concurrent delivery without added toxicity. Conclusions: Pretreatment with gemcitabine significantly increased nab-paclitaxel uptake and correlated with an increased treatment efficacy and survival benefit in preclinical models, compared with standard concurrent treatment. These results justify preclinical and clinical testing of this altered scheduling combination.

BRAF activating mutations act as oncogenic drivers and are highly prevalent in thyroid cancer, occurring in about 60% of papillary thyroid cancer (PTC) as well as 30-40% anaplastic thyroid cancer (ATC). MAPK signaling and treatment resistance is driven by BRAF mutations in thyroid cancer. Among the most common of these mutations is BRAFV600E, which can be selectively inhibited by vemurafenib. Using a panel of PTC and ATC cell lines we assessed how the presence/absence of BRAFV600E impacts radiation sensitivity. We used radiation clonogenics, comet assays, nuclear foci formation, immunoblotting, and mouse xenografts models to determine the effect of vemurafenib on PTC and ATC cells. Analysis of radiation clonogenics implicated higher radioresistance in cell lines containing the BRAFV600E mutation as compared to wild-type BRAF. Additionally, forced expression of BRAFV600E in a wild-type thyroid cancer cell line induced radioresistance. Vemurafenib inhibited MAPK signaling in V600E mutant cell lines, but showed no effect in BRAF wild-type cell lines. Vemurafenib pretreatment selectively radiosensitized BRAFV600E mutants in vitro, as assessed by radiation clonogenic assays. Comet assays revealed impairment of DNA repair in BRAFV600E lines when treated with vemurafenib and radiation. Additionally, γ-H2A.x westerns and nuclear foci staining indicated that vemurafenib pretreatment decreases the tumor cell’s ability to repair DNA double-strand breaks (DSB) in BRAFV600E cell lines. Vemurafenib also appeared to alter the kinetics of formation and resolution of 53BP1 and Rad51 nuclear foci in these cell lines. Evaluation of DSB functional repair using GFP reporter constructs, suggests that BRAFV600E induces NHEJ repair, which can be attenuated by vemurafenib treatment. Finally, vemurafenib effectively increases radiosensitivity of BRAF V600E tumors in vivo. From our results, BRAF activating mutation appears to be associated with radioresistance. Vemurafenib selectively radiosensitizes both PTC and ATC cells through inhibition of DNA repair mechanisms. Combining vemurafenib and radiation may improve therapeutic control for BRAFV600E mutant thyroid cancers. Citation Format: Ryan N. Robb, Linlin Yang, Terence Williams. Vemurafenib selectively radiosensitizes BRAF V600E mutant papillary and anaplastic thyroid carcinoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5186. doi:10.1158/1538-7445.AM2017-5186