KRAS-mutant Pancreatic Cancer Research Articles

Aphanin, a triterpenoid from Amoora rohituka inhibits K-Ras mutant activity and STAT3 in pancreatic carcinoma cells.

Mutations of the K-Ras gene occur in over 90% of pancreatic carcinomas, and to date, no targeted therapies exist for this genetically defined subset of cancers. STAT3 plays a critical role in KRAS-driven pancreatic tumorigenesis, suggesting its potential as a therapeutic target in this cancer. Therefore, finding novel and potential drugs to inhibit oncogenic K-Ras is a major challenge in cancer therapy. In an attempt to develop novel anti-KRAS mutant chemotherapeutics, we isolated three novel triterpenoids from Amoora rohituka stem and their chemical structures were characterized by extensive 1H-NMR, 13C-NMR, Mass, IR spectroscopic studies and chemical transformations. Aphanin (3 alpha-angeloyloxyolean-12-en-28-oic acid) is one of the isolated novel triterpenoid compounds. We found aphanin exhibited antiproliferative effects, caused G0-G1 cell cycle arrest, inhibits K-Ras G12D mutant activity by decreased STAT3, p-STAT3, Akt, p-Akt, cyclin D1 and c-Myc expressions, and induced apoptosis in pancreatic cancer HPAF-II (ΔKRAS G12D ) cells. The apoptosis proceeded through depletion of GSH with a concomitant increase in the reactive oxygen species production. The results of our study have important implications for the development of aphanin as potential novel agent for the treatment of K-Ras mutant pancreatic cancer, and STAT3-cMyc-cyclinD1 axis may serve as an important predictive biomarker for the therapeutic efficacy.

A recombinant chimeric protein specifically induces mutant KRAS degradation and potently inhibits pancreatic tumor growth.

Pancreatic cancer is one of the most lethal human diseases, with an all-stage 5-year survival rate below 5%. To date, no effective and specific therapy is available for this disease. Mutations in KRAS are frequently reported in pancreatic and many other cancers; thus, KRAS is an attractive therapeutic target. Our objective was to specifically eliminate mutant KRAS and induce cell death of tumors expressing this mutant protein. We thus constructed several chimeric proteins by connecting the C-terminal domains of several adaptor proteins of E3 ubiquitin ligases such as CBL, CHIP, E6AP, and VHL, as well as VIF encoded by human immunodeficiency virus type 1 (HIV-1), to the Ras binding domain (RBD) of Raf. Although all of these chimeric proteins caused the degradation of mutant KRAS and the death of KRAS-mutant-tumor cell lines, the RBD-VIF with a protein transduction domain (PTD), named PTD-RBD-VIF, had the strongest tumor-killing effect. Intraperitoneally administered recombinant PTD-RBD-VIF potently inhibited the growth of xenografted KRAS-mutant pancreatic cancer cells. Our findings indicate that recombinant PTD-RBD-VIF, a chimeric protein with a combined cellular-viral origin, could be further developed for the treatment of various tumors harboring mutant or over-activated KRAS, especially for cases presenting with pancreatic cancer recurrence after surgery.

K-Ras mutation detection in liquid biopsy and tumor tissue as prognostic biomarker in patients with pancreatic cancer: a systematic review with meta-analysis.

K-Ras gene mutations have been found in most pancreatic cancers; however, conflicting data on the prognostic value of K-Ras mutations in pancreatic cancer have been published. We conducted a meta-analysis to assess its prognostic significance. Literature searches of PubMed, EMBASE, Cochrane Library, Web of Science and Google Scholar were performed through December 2015 to identify publications exploring the association of K-Ras mutation with overall survival. Forty eligible studies involving 3427 patients with pancreatic cancer were included in the present meta-analysis. Our analysis showed a hazard ratio (HR) of negative association with survival of 1.61 [95% confidence interval (CI) 1.36-1.90; p<0.01] in K-Ras mutant pancreatic cancer patients. In subgroup analyses, K-Ras mutations detected in tumor tissues and in liquid biopsies had HRs of 1.37 (95% CI 1.20-1.57; p<0.01) and 3.16 (95% CI 2.1-4.71; p<0.01), respectively. In addition, the HR was higher when K-Ras mutations were detected in fresh frozen samples (HR=2.01, 95% CI 1.28-3.16, p=0.002) than in formalin-fixed, paraffin-embedded (FFPE) samples (HR=1.29, 95% CI 1.12-1.49, p<0.01). Though K-Ras alterations are more frequent among non-East Asian individuals than East Asian individuals, there were no significant differences in HRs of survival between the two ethnic subgroups. In conclusion, this meta-analysis suggests that K-Ras mutations are associated with a worse overall survival in pancreatic cancer patients, especially when mutations are detected in liquid biopsies or fresh frozen tumor tissue samples.

KRAS Mutant Pancreatic Cancer: No Lone Path to an Effective Treatment.

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest cancers with a dismal 7% 5-year survival rate and is projected to become the second leading cause of cancer-related deaths by 2020. KRAS is mutated in 95% of PDACs and is a well-validated driver of PDAC growth and maintenance. However, despite comprehensive efforts, an effective anti-RAS drug has yet to reach the clinic. Different paths to inhibiting RAS signaling are currently under investigation in the hope of finding a successful treatment. Recently, direct RAS binding molecules have been discovered, challenging the perception that RAS is an “undruggable” protein. Other strategies currently being pursued take an indirect approach, targeting proteins that facilitate RAS membrane association or downstream effector signaling. Unbiased genetic screens have identified synthetic lethal interactors of mutant RAS. Most recently, metabolic targets in pathways related to glycolytic signaling, glutamine utilization, autophagy, and macropinocytosis are also being explored. Harnessing the patient’s immune system to fight their cancer is an additional exciting route that is being considered. The “best” path to inhibiting KRAS has yet to be determined, with each having promise as well as potential pitfalls. We will summarize the state-of-the-art for each direction, focusing on efforts directed toward the development of therapeutics for pancreatic cancer patients with mutated KRAS.

Cetuximab delivery and antitumor effects are enhanced by mild hyperthermia in a xenograft mouse model of pancreatic cancer.

Even with current promising antitumor antibodies, their antitumor effects on stroma‐rich solid cancers have been insufficient. We used mild hyperthermia with the intent of improving drug delivery by breaking the stromal barrier. Here, we provide preclinical evidence of cetuximab + mild hyperthermia therapy. We used four in vivo pancreatic cancer xenograft mouse models with different stroma amounts (scarce, MIAPaCa‐2; moderate, BxPC‐3; and abundant, Capan‐1 and Ope‐xeno). Cetuximab (1 mg/kg) was given systemically, and the mouse leg tumors were concurrently heated using a water bath method for 30 min at three different temperatures, 25°C (control), 37°C (intra‐abdominal organ level), or 41°C (mild hyperthermia) (n = 4, each group). The evaluated variables were the antitumor effects, represented by tumor volume, and in vivo cetuximab accumulation, indirectly quantified by the immunohistochemical fluorescence intensity value/cell using antibodies against human IgG Fc. At 25°C, the antitumor effects were sufficient, with a cetuximab accumulation value (florescence intensity/cell) of 1632, in the MIAPaCa‐2 model, moderate (1063) in the BxPC‐3 model, and negative in the Capan‐1 and Ope‐xeno models (760, 461). By applying 37°C or 41°C heat, antitumor effects were enhanced shown in decreased tumor volumes. These enhanced effects were accompanied by boosted cetuximab accumulation, which increased by 2.8‐fold (2980, 3015) in the BxPC‐3 model, 2.5‐ or 4.8‐fold (1881, 3615) in the Capan‐1 model, and 3.2‐ or 4.2‐fold (1469, 1922) in the Ope‐xeno model, respectively. Cetuximab was effective in treating even stroma‐rich and k‐ras mutant pancreatic cancer mouse models when the drug delivery was improved by combination with mild hyperthermia.

KRAS Mutant Pancreatic Cancer: No Lone Path to an Effective Treatment

KRAS Mutant Pancreatic Cancer: No Lone Path to an Effective Treatment

Long-Term ERK Inhibition in KRAS-Mutant Pancreatic Cancer Is Associated with MYC Degradation and Senescence-like Growth Suppression

Induction of compensatory mechanisms and ERK reactivation has limited the effectiveness of Raf and MEK inhibitors in RAS-mutant cancers. We determined that direct pharmacologic inhibition of ERK suppressed the growth of a subset of KRAS-mutant pancreatic cancer cell lines and that concurrent phosphatidylinositol 3-kinase (PI3K) inhibition caused synergistic cell death. Additional combinations that enhanced ERK inhibitor action were also identified. Unexpectedly, long-term treatment of sensitive cell lines caused senescence, mediated in part by MYC degradation and p16 reactivation. Enhanced basal PI3K-AKT-mTOR signaling was associated with de novo resistance to ERK inhibitor, as were other protein kinases identified by kinome-wide siRNA screening and a genetic gain-of-function screen. Our findings reveal distinct consequences of inhibiting this kinase cascade at the level of ERK.

Abstract A44: Inhibition of Foxm1 transcription factor diminished Kras-mutated tumor development

Abstract Increased expression level of the Forkhead Box M1 (FOXM1) transcription factor is found in multiple types of cancers, and its expression is correlated with poor prognosis in patients with cancers, including non-small cell lung cancers and pancreatic cancers. We and others have shown that FoxM1 transcriptionally regulates a variety of genes essential for cell cycle progression, inflammation, angiogenesis, tumor cell invasiveness and survival. Published studies demonstrated that genetic deletion of Foxm1 gene from SPC-rtTA/tetO-KrasG12D/Foxm1 fl/fl mouse lung epithelial cells conferred resistance to tumorigenesis caused by oncogenic KrasG12D, indicating Foxm1 is a critical regulator of Kras signaling pathway during lung cancer initiation. When treated SPC-rtTA/tetO-KrasG12D/tetO-FOXM1 mice with Doxycycline, lung epithelial cell-specific expressed transgenic FOXM1 and Kras cooperate to promote tumor growth in mouse lungs. In the present study, we determine whether expression of FoxM1 affects proliferation of human cancer cells harboring oncogenic Kras. Here, we show that depletion of FOXM1 expression using inducible shFOXM1 diminished proliferation of Kras-mutated human non-small cell adenocarcinoma (A549 and NCI-H23) and pancreatic cancer (PANC-1 and AsPC-1) cell lines. In contrast, increased expression of FOXM1 caused increased proliferation of Kras mutated cancer cells. Scratch wound healing assay demonstrated that FOXM1 stimulates the migration of these cells, which is associated with elevated epithelial-mesenchymal transition (EMT) markers. Our studies demonstrate that FOXM1 transcription factor is required for Kras mutated human cancer cells proliferation during tumor progression. Citation Format: I-Ching Wang, Hsin Chih Chien, Sheng-Yang Chao, Chien-Cheng Li. Inhibition of Foxm1 transcription factor diminished Kras-mutated tumor development. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A44.

K-Ras Promotes Tumorigenicity through Suppression of Non-canonical Wnt Signaling

K-Ras and H-Ras share identical effectors and have similar properties; however, the high degree of tumor-type specificity associated with K-Ras and H-Ras mutations suggests that they have unique roles in oncogenesis. Here, we report that oncogenic K-Ras, but not H-Ras, suppresses non-canonical Wnt/Ca(2+) signaling, an effect that contributes strongly to its tumorigenic properties. K-Ras does this by binding to calmodulin and so reducing CaMKii activity and expression of Fzd8. Restoring Fzd8 in K-Ras mutant pancreatic cells suppresses malignancy, whereas depletion of Fzd8 in H-Ras(V12)-transformed cells enhances their tumor initiating capacity. Interrupting K-Ras-calmodulin binding using genetic means or by treatment with an orally active protein kinase C (PKC)-activator, prostratin, represses tumorigenesis in K-Ras mutant pancreatic cancer cells. These findings provide an alternative way to selectively target this "undruggable" protein.

Abstract B48: Pancreatic cancer cells exhibit heterogeneous glucose and glutamine metabolic dependencies

Abstract Pancreatic cancer cells demonstrate altered metabolism that is consistent with amplified aerobic glycolysis, fueled by increased glucose uptake. Concurrently, additional studies have established an enhanced dependence on glutamine to power anabolic processes. Recently, there has been a renewed interest in understanding the altered metabolic requirements of cancer cells with the goal of targeting differential nutrient dependencies for therapeutic gain. We screened a panel of twelve well established and widely studied KRAS mutant pancreatic tumor-derived cell lines, as well as seven low passage KRAS mutant pancreatic patient-derived xenograft (PDX)-established tumor cell lines for the ability to proliferate in growth media deficient in glucose and/or glutamine. While 11 of 12 established cell lines were unable to proliferate in these nutrient-depleted conditions, we identified one (Capan-2) that was capable of proliferation in the complete absence of glucose. By comparison, of the seven PDX-derived cell lines screened, four demonstrated complete glucose or glutamine dependency, whereas one was capable of proliferation in the absence of glutamine and two proliferated in the absence of glucose. Our ongoing studies are focused on elucidating the mechanistic basis for glucose or glutamine independent growth. Defining these mechanisms may identify pharmacologic approaches that target metabolic pathways for the treatment of KRAS mutant pancreatic cancer. Citation Format: Kirsten L. Bryant, Anirban Maitra, Channing J. Der. Pancreatic cancer cells exhibit heterogeneous glucose and glutamine metabolic dependencies. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B48.

A MEK/PI3K/HDAC inhibitor combination therapy for KRAS mutant pancreatic cancer cells.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive, metastatic disease with limited treatment options. Factors contributing to the metastatic predisposition and therapy resistance in pancreatic cancer are not well understood. Here, we used a mouse model of KRAS-driven pancreatic carcinogenesis to define distinct subtypes of PDAC metastasis: epithelial, mesenchymal and quasi-mesenchymal. We examined pro-survival signals in these cells and the therapeutic response differences between them. Our data indicate that the initiation and maintenance of the transformed state are separable, and that KRAS dependency is not a fundamental constant of KRAS-initiated tumors. Moreover, some cancer cells can shuttle between the KRAS dependent (drug-sensitive) and independent (drug-tolerant) states and thus escape extinction. We further demonstrate that inhibition of KRAS signaling alone via co-targeting the MAPK and PI3K pathways fails to induce extensive tumor cell death and, therefore, has limited efficacy against PDAC. However, the addition of histone deacetylase (HDAC) inhibitors greatly improves outcomes, reduces the self-renewal of cancer cells, and blocks cancer metastasis in vivo. Our results suggest that targeting HDACs in combination with KRAS or its effector pathways provides an effective strategy for the treatment of PDAC.

Rational combination of MEK inhibitor and the STAT3 pathway modulator for the therapy in K-Ras mutated pancreatic and colon cancer cells.

K-Ras mutations are frequently detected in pancreatic and colon cancers, which are associated with the resistance to MEK inhibitors targeting the Ras pathway. Identifying the underlying mechanisms for the acquired resistance is essential for the future clinical development of MEK inhibitors. Here, we identified that Signal Transducer and Activator of Transcription 3 (STAT3) was significantly activated following the MEK inhibition using AZD6244, PD98059 and Trametinib in K-Ras mutant pancreatic and colon cancer cells. The STAT3 activation may be important for the MEK inhibitor resistance in these K-Ras mutant cancer cells. We have shown that dual inhibition of STAT3 and MEK using the STAT3 inhibitor LY5 and MEK inhibitor Trametinib exerts significant anti-tumor cell efficacy in K-Ras mutant pancreatic and colon cancer cells in vitro. In addition, Trametinib showed increased suppression on tumor growth in vivo in STAT3 knockdown pancreatic cancer cells compared with tumor growth of control cells without STAT3 knockdown. Taken together, our results suggest the induced STAT3 activation as a possible mechanism for the resistance to MEK inhibitor and demonstrate the potentials of a combination therapy using MEK and STAT3 inhibitors in pancreatic and colon cancers harboring K-Ras mutant proteins.

Piperlongumine Enhances Chemotherapy‐Induced Pancreatic Cancer Cell Death

Pancreatic cancer is one of the most deadly cancers with a nearly 95% mortality rate. The large majority of pancreatic cancer patients have mutations in the K‐ras oncogene which contribute to uncontrolled cell proliferation. The poor response of K‐ras mutant tumors to currently available chemotherapy and the extremely low survival rate of pancreatic cancer patients point to a critical need for alternative therapeutic strategies. The use of reactive oxygen species (ROS)‐inducing agents has emerged as an innovative and effective strategy to treat K‐ras mutant cancers. We investigated the effects of a known ROS inducer, piperlongumine (PPLGM), a bioactive agent found in long peppers, alone and in combination with chemotherapeutic agents (gemcitabine and erlotinib) on pancreatic cancer cell viability, survival, and apoptosis. MIA PaCa‐2, PANC‐1 (K‐ras mutant), and BxPC‐3 (wild‐type K‐ras) cells were treated with PPLGM, erlotinib, gemcitabine, and their combinations. Cell survival and apoptosis were assessed by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT), clonogenic survival, and histone‐DNA ELISA assays. The combination of PPLGM, erlotinib, and gemcitabine resulted in a greater reduction in cell viability and induction of apoptosis in all three pancreatic cancer cell lines when compared to any agent alone. These results suggest that the use of PPLGM in combination with chemotherapeutic agents could be a successful strategy for achieving better treatment outcomes in K‐ras mutant pancreatic cancer patients.

Abstract A25: Evaluating a role for Rac1-PAK1 signaling in promoting the growth of KRAS-mutant pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is an extremely lethal cancer characterized by a high frequency of activating mutations in the KRAS oncogene (95%), which is a well-validated driver of PDAC growth. With limited treatment options for this disease, there is an urgent need to better understand the aberrant signaling that occurs in order to better design therapeutic strategies. However, to date, no successful anti-K-Ras therapies have been developed. Current efforts have focused on inhibition of effectors of K-Ras signaling, in particular the Raf and PI3K effector signaling pathways. However, inhibitors targeting components of these pathways, when used as monotherapy or in combination, have been ineffectual for long-term treatment of KRAS mutant cancers. The lack of success of these inhibitors is due, in part, to the importance of other effectors in K-Ras-dependent cancer growth and the upregulation of compensatory signaling programs that overcome inhibitor activity. Consequently, in order to design effective combinatorial-targeted therapies, there is a pressing need to better understand the role of other effector signaling events that support mutant K-Ras-driven PDAC growth. The small GTPase Rac1 has a known role in driving K-Ras mutant cancers, but the specific effectors through which Rac1 promotes tumor growth have not been defined. We hypothesize that the PAK1 serine/threonine kinase, and related isoforms, PAK2 and PAK3, are key components downstream of Rac1 in mutant K-Ras PDAC. In support of this, we found that PAK1 RNA and protein levels are overexpressed in pancreatic cancer cell lines and in patient tumor samples when compared to normal tissues. Additionally we determined that stable shRNA-mediated suppression of PAK1 protein expression inhibited PDAC anchorage-independent and –dependent growth and Matrigel invasion in vitro. Further, knockdown of K-Ras in PDAC cell lines resulted in reduced phospho-PAK1 (T423) levels, indicating a decrease in PAK1 activity. We also found that a pharmacologic inhibitor of PAK1 and other Group I PAK isoforms (PAK2 and PAK3) inhibited PDAC growth. Additionally, in an RNAi kinome library screen, we identified PAK3 as a driver of resistance to pharmacologic inhibition of ERK. These observations then prompted our studies to evaluate a possible role for PAK2 and PAK3 in PDAC. Finally, our ongoing studies are evaluating the ability of Group I PAK inhibitors in combination with inhibitors of PI3K, mTORC1/2, and MEK1/2 to effectively block KRAS effector signaling and PDAC growth. Citation Format: Nicole M. Baker, Janine LoBello, Haiyong Han, Holly Yin, Jen Jen Yeh, Channing J. Der. Evaluating a role for Rac1-PAK1 signaling in promoting the growth of KRAS-mutant pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A25. doi: 10.1158/1557-3125.RASONC14-A25

Abstract B05: Thymidylate synthase cooperates with oncogenic KRAS to markedly accelerate pancreatic cancer progression in a novel KrasG12D/+ mouse model

Abstract Oncogenic KRAS is a key initiator in the development of pancreatic cancer; however, other aberrations are necessary for the progression into advanced metastatic disease. Our lab was the first to show that overexpression of Thymidylate Synthase (TS), an essential DNA synthesis and repair enzyme that is elevated in many common adult cancers, plays a direct role in promoting tumorigenesis. These findings suggest that TS is not a passive marker of proliferation, but rather an important oncogenic driver in cancer. To determine whether TS enhances the neoplastic effects of oncogenic KRAS, we established a novel animal model for pancreatic ductal adenocarcinoma (PDAC) by generating conditional KrasG12D mutant mice that express high levels of human TS (hTS) in the pancreas. We discovered that overexpression of hTS in the pancreas of Pdx1-cre-KrasG12D/+ mice significantly reduced survival of the hTS/KrasG12D/+ mice. Median survival of hTS/KrasG12D/+ mice was reduced by 50% as compared to KrasG12D/+ mice (112.5 vs 222 days, p=0.0005). To test whether TS accelerates the development of preneoplastic pancreatic ductal lesions and tumors, hTS/KrasG12D/+ and KrasG12D/+ mice were euthanized at 1 month intervals from 1.0 – 6.0 months of age and the percentage of ducts displaying normal, murine pancreatic intraepithelial neoplasia (mPanIN), or invasive PDAC was scored by a masked veterinary pathologist using world health organization (WHO) criteria. We found that hTS/KrasG12D/+ mice displayed a 10 fold increase in mPanIN2 and mPanIN3 lesions at 2 months of age as compared to KrasG12D/+ mice alone. At 3 months of age the hTS/KrasG12D/+ mice showed a 10 fold increase in PDAC formation as compared to KrasG12D/+ mice alone. To determine whether TS enhances the metastatic potential of oncogenic KRAS, lung and liver tissues were harvested from these mice and analyzed for the presence of metastasis. We found that hTS/KrasG12D/+ mice developed lung metastasis as early as 2 months of age, while KrasG12D/+ mice did not develop lung metastasis until 4 months of age. In addition, 60% of hTS/KrasG12D/+ mice in the 4 month age group displayed liver metastasis compared to 20% of KrasG12D/+ mice. Taken together, our data demonstrate that hTS overexpression in the pancreas 1) enhances the initiation of preneoplastic pancreatic ductal lesions, 2) accelerates pancreatic ductal adenocarcinoma development, 3) reduces survival, and 4) increases metastasis in hTS/KrasG12D/+ mice. These data demonstrate that hTS cooperates with oncogenic KRAS to accelerate the progression of pancreatic cancer. Therefore, we predict that combined inhibition of TS and KRAS signaling will maximize tumor regression. Our lab has identified 4 new TS allosteric inhibitors (provisional patent filed in 2013), which inhibit the catalytic activity of TS through a different binding site than 5-fluorouracil (5-FU). These lead allosteric inhibitors display mid-nanomolar to low micromolar activity in KRAS-mutant pancreatic cancer cell lines. Our goal is to combine these allosteric TS inhibitors with inhibitors of KRAS effectors, such as PI3K/AKT/mTOR and RAF/MEK/ERK pathways. Given the frequency of aberrant KRAS activation in pancreatic cancer and the striking effect of TS to enhance KRAS driven tumors in our hTS/KrasG12D/+ model, this combination strategy will be an important step in identifying novel treatments for pancreatic cancer. Citation Format: Rony A. Francois, Akbar Nawab, Min Chen, Mary K. Reinhard, Frederic J. Kaye, Maria Zajac-Kaye. Thymidylate synthase cooperates with oncogenic KRAS to markedly accelerate pancreatic cancer progression in a novel KrasG12D/+ mouse model. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B05. doi: 10.1158/1557-3125.RASONC14-B05

Abstract 803: A vertical combination strategy hitting multiple steps along the MAPK cascade: Molecular mechanisms of action and putative genetic determinants of synergism

Abstract Preclinical evidence shows that hitting a single point along the RAF/MEK/ERK cascade disrupts intra-pathway negative feedback loop, may cause paradoxical pathway activation and may lead to functional resistance. Thus, the “vertical” combination of agents simultaneously inhibiting RAF and MEK has been proposed as a strategy to synergistically inhibit tumor growth and delay resistance. Experimental procedures: Molecular and functional effects of single and combined MEK (using trametinib, T), BRAF (using dabrafenib, D), and RAF (using the pan-RAF inhibitor, RAF265, R) inhibition were dissected by WB analysis and conservative isobologram analysis to assess functional synergism, using a fixed dose-ratio experimental design. Summary data: We examined the in vitro molecular and functional consequences of D and T, alone or in combination, in a panel of different human BRAFV600E melanoma cell lines; both drugs inhibited cell growth and inactivated the MAPK pathway, but little or no synergistic growth inhibition was observed with their combination (CI: 0.7 - 1.3x106). Conversely, combined D+T suppressed malignant growth with highly synergistic effects in KRAS-mutant lung (2/5 cell lines tested) and pancreatic (4/6 cell lines tested) cancer models (CI: 0.1 - 0.7), in which selective BRAF inhibition induced hyperphosphorylation of MEK, ERK, and p90RSK (paradox effect). At concentrations inhibiting both BRAF and CRAF, R did not induce paradox MAPK activation and did not result in growth inhibitory synergism when combined with T. To define the role of RAS gene status in determining sensitivity/resistance to single and combined RAF and MEK blockade, we analyzed two isogenic tumor cell line models: H1299 expressing individual codon 12 KRAS mutants and isogenic HCT116 clones differing for the presence of a homo or heterozygous G13D KRAS mutation. Conversely, in lung cancer models driven by either EGFR mutations (HCC827, H1650) or HER-2 overexpression (Calu-3), selective BRAF inhibition also induced a paradox MAPK activation, which could be blocked using a reversible EGFR/HER-2 inhibitor (Lapatinib); in this context, combination (D+T) resulted in a non-synergic growth inhibitory effects. Conclusions: Overall, our data indicate that, in appropriate cellular contexts, vertical RAF/MEK inhibition-based combination strategies exert highly synergistic antitumor effects across different cancer models. Citation Format: Anais Del Curatolo, Ursula Cesta Incani, Ludovica Ciuffreda, Italia Falcone, Senji Shirasawa, Massimo Broggini, Isabella Sperduti, Adriana Eramo, Ruggero De Maria, Francesco Cognetti, Michele Milella. A vertical combination strategy hitting multiple steps along the MAPK cascade: Molecular mechanisms of action and putative genetic determinants of synergism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 803. doi:10.1158/1538-7445.AM2014-803

Abstract 657: Simultaneous inhibition of HER-family receptors by Pan-HER antibody mixture prevents compensatory HER-family receptor upregulation and induces cell death in a broad range of tumor models

Abstract Deregulation of HER family receptors plays an important role in the development and progression of human cancer. Although EGFR and HER2 receptors have proven to be clinically valuable targets, increasing evidence suggests substantial cross-talk between HER family members, and thus compensatory signaling may lead to resistance upon therapies targeting one receptor only. Targeting multiple receptors is more efficacious than single-targeted therapies, and is frequently able to overcome acquired resistance to inhibition of a single receptor. We have previously demonstrated that Pan-HER (Sym013) a mixture of monoclonal antibodies specifically targeting EGFR, HER2, and HER3 displays potent growth inhibition in a broad range of cancer cell lines. Growth-inhibiting activity persisted in the presence of EGFR and HER3 ligands, indicating that Pan-HER may overcome acquired resistance due to increased ligand production. In vitro findings further translated into in vivo model systems, where Pan-HER displayed efficacious tumor growth suppression across a broad range of cancer models, including KRAS-mutated patient-derived pancreatic cancer models, and was frequently able to overcome resistance to other HER family targeted therapies. Mechanistic studies confirm that Pan-HER treatment significantly decreases viability and induces apoptosis more effectively than single-receptor targeted therapies. Pan-HER treatment induces internalization and degradation of all three receptors in vitro, followed by subsequent downstream effects in essential growth and survival pathways. Compensatory receptor up-regulation and/or activation is frequently the downside of single-receptor targeted treatments. However, such receptor up-regulation is effectively prevented by Pan-HER. Histological assessment of Pan-HER-treated patient-derived xenograft tumors revealed that they largely consist of stromal cells, whereas tumor cells are sparse. Further immunohistochemical staining has also shown that these tumors have markedly lower EGFR, HER2, and HER3 receptor expression than tumors treated with single-receptor targeting regimens. We present here further evidence of Pan-HER superiority over single-receptor targeted regimens. Overall, Pan-HER represents a novel strategy to address tumor heterogeneity andtumor plasticity. Citation Format: Anna Dahlman, Helle J. Jacobsen, Thomas T. Poulsen, Paolo Conrotto, Mikkel W. Pedersen, Ivan D. Horak, Michael Kragh, Johan Lantto. Simultaneous inhibition of HER-family receptors by Pan-HER antibody mixture prevents compensatory HER-family receptor upregulation and induces cell death in a broad range of tumor models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 657. doi:10.1158/1538-7445.AM2014-657

Evaluating TBK1 as a therapeutic target in cancers with activated IRF3.

TBK1 (TANK-binding kinase 1) is a noncanonical IκB protein kinase that phosphorylates and activates downstream targets such as IRF3 and c-Rel and, mediates NF-κB activation in cancer. Previous reports demonstrated synthetic lethality of TBK1 with mutant KRAS in non-small cell lung cancer (NSCLC); thus, TBK1 could be a novel target for treatment of KRAS-mutant NSCLC. Here, the effect of TBK1 on proliferation in a panel of cancer cells by both genetic and pharmacologic approaches was evaluated. In KRAS-mutant cancer cells, reduction of TBK1 activity by knockdown or treatment with TBK1 inhibitors did not correlate with reduced proliferation in a two-dimensional viability assay. Verification of target engagement via reduced phosphorylation of S386 of IRF3 (pIRF3(S386)) was difficult to assess in NSCLC cells due to low protein expression. However, several cell lines were identified with high pIRF3(S386) levels after screening a large panel of cell lines, many of which also harbor KRAS mutations. Specifically, a large subset of KRAS-mutant pancreatic cancer cell lines was uncovered with high constitutive pIRF3(S386) levels, which correlated with high levels of phosphorylated S172 of TBK1 (pTBK1(S172)). Finally, TBK1 inhibitors dose-dependently inhibited pIRF3(S386) in these cell lines, but this did not correlate with inhibition of cell growth. Taken together, these data demonstrate that the regulation of pathways important for cell proliferation in some NSCLC, pancreatic, and colorectal cell lines is not solely dependent on TBK1 activity. TBK1 has therapeutic potential under certain contexts and phosphorylation of its downstream target IRF3 is a biomarker of TBK1 activity.

Novel synthetic oleanane triterpenoid AMR-MeOAc inhibits K-Ras through ERK, Akt and survivin in pancreatic cancer cells

K-Ras activating mutations are a major problem that drives aggressive tumor growth and metastasis in pancreatic cancer. Currently, there are no effective targeted therapies for this genetically defined subset of cancers harboring oncogenic K-Ras mutations that confer drug resistance, aggressive tumor growth, metastasis and poor clinical outcome. We identified a novel synthetic oleanane triterpenoid compound designated AMR-MeOAc that effectively kills K-Ras mutant pancreatic cancer HPAF-II cells. The cytotoxic effects correlated with apoptosis induction, as was evidenced by increase of apoptosis cells upon the treatment of AMR-MeOAc in HPAF-II cells. Our studies revealed that AMR-MeOAc treatment inhibits cancer associated survival gene survivin. Moreover, AMR-MeOAc also led to down regulation of Akt, ERK1/2 and survivin protein levels. Our results indicate that AMR-MeOAc or its active analogs could be a novel class of anticancer agents against K-Ras driven human pancreatic cancer.

Synergistic killing in pancreatic cancer cell lines of the combination of a MEK inhibitor and DNA methylation inhibitor.

e15025 Background: A growing body of evidence implicates aberrant DNA methylation in the etiology of a number of cancers, including pancreatic. Previous reports link defective ERK signaling with reduced DNA methylation via DNMT1. Here, we examined the ability of the MEK inhibitor U0126 to alter expression of DNMTs in k-RAS mutant and wild type pancreatic cancer cell lines and assess additive cytotoxicity of U0126, the hypomethylating agent 5-Azacytidine and two HDAC inhibitors. Methods: DNMT levels were quantified in AsPC1 and BxPC3 lines 2 days after adding 25 umolar U0126 using real-time RT-PCR. Significance was calculated using a Student t-test. For survival, agents were added singly and in combination: U0126, 25 umol; 5-Aza, 10 umol; Valproic acid 1 mmol and Trichostatin-A 5 umol. Survival was assessed using a colorimetric MTS method at 1, 2, 3, and 4 days. Expected cell survival and synergism were calculated via relative risk ratios, and significance via a Student t-test. Results: U0126 treatment reduced expression of DNMT1 significantly in AsPC1: 2.06 ± 0.3 vs. 1.09 ± 0.08, p = 0.004 (mean ± S.D., arbitrary units). No change was seen in BxPC3. Increased expression of de novo DNMT3a and DNMT3b was seen: AsPC1 1.28 ± 0.3 vs. 3.13 ± 0.8, p = 0.02; BxPC3 1.78 ± 0.3 vs. 4.14 ± 1, p = 0.02; AsPC1 1.26 ± 0.3 vs. 2.66 ± 0.4, p = 0.006, respectively. DNMT3b in BxPC3 was not altered significantly. U0126 and 5-Aza were individually cytotoxic in both cell lines, and synergism was observed in combination. In AsPC1, the observed vs. expected combination survival was 13% ± 3% vs. 29% ± 2%, p = 0.001; for BxPC3, 7% ± 2% vs. 62% ± 3%, p = 0.002, both at 4d. No synergism was found when adding Valproic acid or Trichostatin-A. Conclusions:Treatment of k-RAS mutant pancreatic cancer cell lines with the MEK inhibitor U0126 results in significantly reduced expression of DNMT1 and increased DNMT3a and DNMT3b. U0126 combined with 5-Aza produced synergistic cytotoxicity, which may be due to enhanced hypomethylation activity. Although no significant change in expression of DNMT1 was found in the BxPC3 cells, we noted synergistic cytotoxicity when treated with both U0126 and 5-Aza.