Oncogenic KRAS mutations found in 20% to 30% of all non–small cell lung cancers (NSCLC) are associated with chemoresistance and poor prognosis. Here we demonstrate that activation of the cell protective stress response gene NRF2 by KRAS is responsible for its ability to promote drug resistance. RNAi-mediated silencing of NRF2 was sufficient to reverse resistance to cisplatin elicited by ectopic expression of oncogenic KRAS in NSCLC cells. Mechanistically, KRAS increased NRF2 gene transcription through a TPA response element (TRE) located in a regulatory region in exon 1 of NRF2. In a mouse model of mutant KrasG12D-induced lung cancer, we found that suppressing the NRF2 pathway with the chemical inhibitor brusatol enhanced the antitumor efficacy of cisplatin. Cotreatment reduced tumor burden and improved survival. Our findings illuminate the mechanistic details of KRAS-mediated drug resistance and provide a preclinical rationale to improve the management of lung tumors harboring KRAS mutations with NRF2 pathway inhibitors. Cancer Res; 74(24); 1–12. ©2014 AACR.

Oncogenic KRAS mutations found in 20-30% of all non-small cell lung cancers (NSCLC) are associated with chemoresistance and poor prognosis. Here we demonstrate that activation of the cell protective stress response gene NRF2 by KRAS is responsible for its ability to promote drug resistance. RNAi-mediated silencing of NRF2 was sufficient to reverse resistance to cisplatin elicited by ectopic expression of oncogenic KRAS in NSCLC cells. Mechanistically, KRAS increased NRF2 gene transcription through a TPA response element (TRE) located in the NRF2 promoter. In a mouse model of mutant KrasG12D-induced lung cancer, we found that suppressing the NRF2 pathway with the chemical inhibitor brusatol enhanced the antitumor efficacy of cisplatin. Co-treatment reduced tumor burden and improved survival. Our findings illuminate the mechanistic details of KRAS-mediated drug resistance and provide a preclinical rationale to improve the management of lung tumors harboring KRAS mutations with NRF2 pathway inhibitors.

Modeling the hematogenous spread of cancer cells to distant organs poses one of the greatest challenges in the study of human metastasis. Both tumor cell–intrinsic properties as well as interactions with reactive stromal cells contribute to this process, but identification of relevant stromal signals has been hampered by the lack of models allowing characterization of the metastatic niche. Here, we describe an implantable bioengineered scaffold, amenable to in vivo imaging, ex vivo manipulation, and serial transplantation for the continuous study of human metastasis in mice. Orthotopic or systemic inoculation of tagged human cancer cells into the mouse leads to the release of circulating tumor cells into the vasculature, which seed the scaffold, initiating a metastatic tumor focus. Mouse stromal cells can be readily recovered and profiled, revealing differential expression of cytokines, such as IL1β, from tumor-bearing versus unseeded scaffolds. Finally, this platform can be used to test the effect of drugs on suppressing initiation of metastatic lesions. This generalizable model to study cancer metastasis may thus identify key stromal-derived factors with important implications for basic and translational cancer research. Cancer Res; 74(24); 1–10. ©2014 AACR.

Modeling the hematogenous spread of cancer cells to distant organs poses one of the greatest challenges in the study of human metastasis. Both tumor-cell intrinsic properties as well as interactions with reactive stromal cells contribute to this process, but identification of relevant stromal signals has been hampered by the lack of models allowing characterization of the metastatic niche. Here we describe an implantable bioengineered scaffold, amenable to in vivo imaging, ex vivo manipulation and serial transplantation for the continuous study of human metastasis in mice. Orthotopic or systemic inoculation of tagged human cancer cells into the mouse leads to the release of circulating tumor cells (CTCs) into the vasculature, which seed the scaffold, initiating a metastatic tumor focus. Mouse stromal cells can be readily recovered and profiled, revealing differential expression of cytokines, such as IL-1β, from tumor-bearing versus unseeded scaffolds. Finally, this platform can be used to test the effect of drugs on suppressing initiation of metastatic lesions. This generalizable model to study cancer metastasis may thus identify key stromal-derived factors with important implications for basic and translational cancer research.

Few studies have examined associations between plasma choline metabolites and risk of colorectal cancer. Therefore, we investigated associations between plasma biomarkers of choline metabolism [choline, betaine, dimethylglycine, and trimethylamine N-oxide (TMAO)] and colorectal cancer risk among postmenopausal women in a case–control study nested within the Women’s Health Initiative Observational Study. We selected 835 matched case–control pairs, and cases were further stratified by tumor site (proximal, distal, or rectal) and stage (local/regional or metastatic). Colorectal cancer was assessed by self-report and confirmed by medical records over the mean of 5.2 years of follow-up. Baseline plasma choline metabolites were measured by LC/MS-MS. In multivariable-adjusted conditional logistic regression models, plasma choline tended to be positively associated with rectal cancer risk [OR (95% confidence interval, CI)highest vs. lowest quartile = 2.44 (0.93–6.40); P trend = 0.08], whereas plasma betaine was inversely associated with colorectal cancer overall [0.68 (0.47–0.99); P trend = 0.01] and with local/regional tumors [0.64 (0.42–0.99); P trend = 0.009]. Notably, the plasma betaine:choline ratio was inversely associated with colorectal cancer overall [0.56 (0.39–0.82); P trend = 0.004] as well as with proximal [0.66 (0.41–1.06); P trend = 0.049], rectal [0.27 (0.10–0.78); P trend = 0.02], and local/regional [0.50 (0.33–0.76); P trend = 0.001] tumors. Finally, plasma TMAO, an oxidative derivative of choline produced by intestinal bacteria, was positively associated with rectal cancer [3.38 (1.25–9.16); P trend = 0.02] and with overall colorectal cancer risk among women with lower (vs. higher) plasma vitamin B12 levels (P interaction = 0.003). Collectively, these data suggest that alterations in choline metabolism, which may arise early in disease development, may be associated with higher risk of colorectal cancer. The positive association between plasma TMAO and colorectal cancer risk is consistent with an involvement of the gut microbiome in colorectal cancer pathogenesis. Cancer Res; 74(24); 1–11. ©2014 AACR.