Novel MEK inhibitor trametinib and other retinoblastoma gene (RB)-reactivating agents enhance efficacy of 5-fluorouracil on human colon cancer cells

Establishment and characterization of patient-derived xenograft of a rare pediatric anaplastic pleomorphic xanthoastrocytoma (PXA) bearing a CDC42SE2-BRAF fusion

Pleomorphic xanthoastrocytoma (PXA) is a rare subset of primary pediatric glioma with 70% 5-year disease free survival. However, up to 20% of cases present with local recurrence and malignant transformation into more aggressive type anaplastic PXA (AXPA) or glioblastoma. The understanding of disease etiology and mechanisms driving PXA and APXA are limited, and there is no standard of care. Therefore, development of relevant preclinical models to investigate molecular underpinnings of disease and to guide novel therapeutic approaches are of interest. Here, for the first time we established, and characterized a patient-derived xenograft (PDX) from a leptomeningeal spread of a patient with recurrent APXA bearing a novel CDC42SE2-BRAF fusion. An integrated -omics analysis was conducted to assess model fidelity of the genomic, transcriptomic, and proteomic/phosphoproteomic landscapes. A stable xenoline was derived directly from the patient recurrent tumor and maintained in 2D and 3D culture systems. Conserved histology features between the PDX and matched APXA specimen were maintained through serial passages. Whole exome sequencing (WES) demonstrated a high degree of conservation in the genomic landscape between PDX and matched human tumor, including small variants (Pearson's r = 0.794-0.839) and tumor mutational burden (~ 3 mutations/MB). Large chromosomal variations including chromosomal gains and losses were preserved in PDX. Notably, chromosomal gain in chromosomes 4-9, 17 and 18 and loss in the short arm of chromosome 9 associated with homozygous 9p21.3 deletion involving CDKN2A/B locus were identified in both patient tumor and PDX sample. Moreover, chromosomal rearrangement involving 7q34 fusion; CDC42SE-BRAF t (5;7) (q31.1, q34) (5:130,721,239, 7:140,482,820) was identified in the PDX tumor, xenoline and matched human tumor. Transcriptomic profile of the patient's tumor was retained in PDX (Pearson r = 0.88) and in xenoline (Pearson r = 0.63) as well as preservation of enriched signaling pathways (FDR Adjusted P < 0.05) including MAPK, EGFR and PI3K/AKT pathways. The multi-omics data of (WES, transcriptome, and reverse phase protein array (RPPA) was integrated to deduce potential actionable pathways for treatment (FDR < 0.05) including KEGG01521, KEGG05202, and KEGG05200. Both xenoline and PDX were resistant to the MEK inhibitors trametinib or mirdametinib at clinically relevant doses, recapitulating the patient's resistance to such treatment in the clinic. This set of APXA models will serve as a preclinical resource for developing novel therapeutic regimens for rare anaplastic PXAs and pediatric high-grade gliomas bearing BRAF fusions.

Predictive biomarkers for response to trametinib in non-small cell lung cancer

BACKGROUND

Non-small cell lung cancer (NSCLC) is a leading cause of cancer deaths. Current companion diagnostics use driver mutation sequencing to select patients for molecularly targeted agents (MTA), even though most patients lack actionable mutations. These diagnostics utilize static biomarkers, ignoring real-time tumor cell biology.

OBJECTIVE

Trametinib is FDA-approved in combination with dabrafenib for BRAF V600E-positive NSCLC, however, it has plausible utility beyond these patients. We sought to identify novel biomarkers for maximizing trametinib application.

METHODS

Trametinib responses were evaluated in 12 EGFR/BRAF wild-type (WT) NSCLC cell lines with diverse RAS mutational status. We identified three response categories by colony assay. Trametinib-induced molecular dynamics were studied using immunoassays and apoptosis/necrosis assays, to identify predictive response biomarkers.

RESULTS

p27 accumulation and cyclin D1 downregulation suggested universal cell cycle arrest with trametinib. However, 4 cell lines showed PARP cleavage and 8 showed increased phospho-4E-BP1, suggesting varied cellular outcomes from apoptosis, necrosis, senescence to autophagy. Cleaved PARP, phospho-4E-BP1 and phospho-AKT expression can predict these outcomes.

CONCLUSIONS

Trametinib monotherapy outcome may depend upon cellular context more than oncogenic mutation status. In BRAF WT NSCLC, trametinib may be best suited for combination therapy and dynamic biomarkers could select combinations and predict responses.

Molecular-Targeted Therapy for Tumor-Agnostic Mutations in Acute Myeloid Leukemia

Comprehensive genomic profiling examinations (CGPs) have recently been developed, and a variety of tumor-agnostic mutations have been detected, leading to the development of new molecular-targetable therapies across solid tumors. In addition, the elucidation of hereditary tumors, such as breast and ovarian cancer, has pioneered a new age marked by the development of new treatments and lifetime management strategies required for patients with potential or presented hereditary cancers. In acute myeloid leukemia (AML), however, few tumor-agnostic or hereditary mutations have been the focus of investigation, with associated molecular-targeted therapies remaining poorly developed. We focused on representative tumor-agnostic mutations such as the TP53, KIT, KRAS, BRCA1, ATM, JAK2, NTRK3, FGFR3 and EGFR genes, referring to a CGP study conducted in Japan, and we considered the possibility of developing molecular-targeted therapies for AML with tumor-agnostic mutations. We summarized the frequency, the prognosis, the structure and the function of these mutations as well as the current treatment strategies in solid tumors, revealed the genetical relationships between solid tumors and AML and developed tumor-agnostic molecular-targeted therapies and lifetime management strategies in AML.

A chemoproteoinformatics approach demonstrates that aspirin increases sensitivity to MEK inhibition by directly binding to RPS5

MEK inhibitors are among the most successful molecularly targeted agents used as cancer therapeutics. However, to treat cancer more efficiently, resistance to MEK inhibitor-induced cell death must be overcome. Although previous genetic approaches based on comprehensive gene expression analysis or RNAi libraries led to the discovery of factors involved in intrinsic resistance to MEK inhibitors, a feasible combined treatment with the MEK inhibitor has not yet been developed. Here, we show that a chemoproteoinformatics approach identifies ligands overcoming the resistance to cell death induced by MEK inhibition as well as the target molecule conferring this resistance. First, we used natural products, perillyl alcohol and sesaminol, which induced cell death in combination with the MEK inhibitor trametinib, as chemical probes, and identified ribosomal protein S5 (RPS5) as their common target protein. Consistently, trametinib induced cell death in RPS5-depleted cancer cells via upregulation of the apoptotic proteins BIM and PUMA. Using molecular docking and molecular dynamics (MD) simulations, we then screened FDA- and EMA-approved drugs for RPS5-binding ligands and found that acetylsalicylic acid (ASA, also known as aspirin) directly bound to RPS5, resulting in upregulation of BIM and PUMA and induction of cell death in combination with trametinib. Our chemoproteoinformatics approach demonstrates that RPS5 confers resistance to MEK inhibitor-induced cell death, and that aspirin could be repurposed to sensitize cells to MEK inhibition by binding to RPS5.

CDK Inhibition Reverses Acquired 5-Fluorouracil Resistance in Hepatocellular Carcinoma Cells

Background. 5-Fluorouracil (5-FU) has been widely applied in treating cancers. However, its usage is largely limited in hepatocellular carcinoma (HCC), due to acquired resistance. Here, we aim to identify target proteins and investigate their roles in 5-FU sensitivity of HCC cells. Methods. Mass spectrometry (MS) proteomics was performed on 5-FU-resistant cell line (BEL7402/5-FU) and its parental cell line (BEL7402) with 5-FU treatment. In order to identify potential targets, we compared the proteomics between two cell line groups and used bioinformatics tools to select hub proteins from all differentially expressed proteins. Results. We finally focused on a group of cell cycle-related kinases (CDKs). By CCK8 assay, we confirmed that the CDK inhibitor significantly decreased the IC50 of 5-FU-resistant cells. Conclusions. Our study verified that CDK inhibition can reverse 5-FU resistance of HCC cells.

An Update on the Potential Roles of E2F Family Members in Colorectal Cancer

Colorectal cancer (CRC) is a major health burden worldwide, and thus, optimised diagnosis and treatments are imperative. E2F transcription factors (E2Fs) are a family of transcription factors consisting of eight genes, contributing to the oncogenesis and development of CRC. Importantly, E2Fs control not only the cell cycle but also apoptosis, senescence, DNA damage response, and drug resistance by interacting with multiple signaling pathways. However, the specific functions and intricate machinery of these eight E2Fs in human CRC remain unclear in many respects. Evidence on E2Fs and CRC has been scattered on the related regulatory genes, microRNAs (miRNAs), and competing endogenous RNAs (ceRNAs). Accordingly, some drugs targeting E2Fs have been transferred from preclinical to clinical application. Herein, we have systemically reviewed the current literature on the roles of various E2Fs in CRC with the purpose of providing possible clinical implications for patient diagnosis and prognosis and future treatment strategy design, thereby furthering the understanding of the E2Fs.

Rabdosianone I, a Bitter Diterpene from an Oriental Herb, Suppresses Thymidylate Synthase Expression by Directly Binding to ANT2 and PHB2

Simple Summary

In the present study, we found the novel pleiotropic regulation of the oncogene product thymidylate synthase (TS) by a chemical biology approach to identify rabdosianone I-binding proteins. Rabdosianone I, which is extracted from a traditional Asian herb Isodon japonicus Hara for longevity, suppressed TS expression at mRNA and protein levels. We immobilized rabdosianone I onto nano-magnetic beads and identified two mitochondrial proteins, adenine nucleotide translocase 2 (ANT2) and prohibitin 2 (PHB2), as the direct targets of rabdosianone I in cancer cells. Mechanistically, the knockdown of ANT2 or PHB2 promoted proteasomal degradation of the TS protein. In addition, PHB2 reduced TS mRNA levels. Thus, we provide previously unknown mechanisms of TS regulation by ANT2 and PHB2 and propose the possibility of rabdosianone I as a promising lead compound for the discovery of a novel TS suppressor.

Abstract

Natural products have numerous bioactivities and are expected to be a resource for potent drugs. However, their direct targets in cells often remain unclear. We found that rabdosianone I, which is a bitter diterpene from an oriental herb for longevity, Isodon japonicus Hara, markedly inhibited the growth of human colorectal cancer cells by downregulating the expression of thymidylate synthase (TS). Next, using rabdosianone I-immobilized nano-magnetic beads, we identified two mitochondrial inner membrane proteins, adenine nucleotide translocase 2 (ANT2) and prohibitin 2 (PHB2), as direct targets of rabdosianone I. Consistent with the action of rabdosianone I, the depletion of ANT2 or PHB2 reduced TS expression in a different manner. The knockdown of ANT2 or PHB2 promoted proteasomal degradation of TS protein, whereas that of not ANT2 but PHB2 reduced TS mRNA levels. Thus, our study reveals the ANT2- and PHB2-mediated pleiotropic regulation of TS expression and demonstrates the possibility of rabdosianone I as a lead compound of TS suppressor.

Overexpression of sortilin is associated with 5-FU resistance and poor prognosis in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer worldwide. Even if 5-fluorouracil (5-FU) is used as the first-line chemotherapeutic drug, responsiveness is only 20-30%. Acquired resistance to 5-FU contributes to both poor patient prognosis and relapse, emphasizing the need to identify biomarkers. Sortilin, a vacuolar protein sorting 10 protein (Vps10p), implicated in protein trafficking, is over expressed in CRC cell lines cultured 72 hours in presence of 5-FU. This overexpression was also observed in 5-FU-resistant cells derived from these cell lines as well as in CRC primary cultures (or patients derived cell lines). A significantly higher expression of sortilin was observed in vivo, in 5-FU-treated tumours engrafted in Nude mice, as compared with non-treated tumour. A study of transcriptional regulation allowed identifying a decrease in ATF3 expression, as an explanation of sortilin overexpression following 5-FU treatment. In silico analysis revealed SORT1 expression correlation with poor prognosis. Moreover, sortilin expression was found to be positively correlated with CRC tumour grades. Collectively, our findings identify sortilin as a potential biomarker of 5-FU resistance associated with poor clinical outcomes and aggressiveness in CRC. As a new prognostic factor, sortilin expression could be used to fight against CRC.

MEK Inhibitor Augments Antitumor Activity of B7-H3-Redirected Bispecific Antibody

Targeting cancer antigens by T cell-engaging bispecific antibody (BiAb) or chimeric antigen receptor T cell therapy has achieved successes in hematological cancers, but attempts to use it to fight solid cancers have been disappointing, in part due to antigen escape. MEK inhibitor had limited activity as a single agent, but enhanced antitumor activity when combined with other therapies, such as targeted drugs or immunotherapy agents. This study aimed to analyze the expression of B7-H3 in non-small-cell lung cancer (NSCLC) and bladder cancer (BC) and to evaluate the combinatorial antitumor effect of B7-H3 × CD3 BiAb with MEK inhibitor trametinib. We found B7-H3 was highly expressed in NSCLC and BC compared with normal samples and its increased expression was associated with poor prognosis. Treatment with trametinib alone could induce apoptosis in tumor cell, while has no effect on T cell proliferation, and a noticeable elevation of B7-H3 expression in tumor cells was also observed following treatment. B7-H3 × CD3 BiAb specifically and efficiently redirected their cytotoxicity against B7-H3 overexpressing tumor cells both in vitro and in xenograft mouse models. While trametinib treatment alone affected tumor growth, the combined therapy increased T cell infiltration and significantly suppressed tumor growth. Together, these data suggest that combination therapy with B7-H3 × CD3 BiAb and MEK inhibitor may serve as a new therapeutic strategy in the future clinical practice for the treatment of NSCLC and BC.

MEK blockade overcomes the limited activity of palbociclib in head and neck cancer

Head and neck cancer (HNC) is characterized with multiple aberrations in cell cycle pathways, including amplification of cyclin D1. Palbociclib (PAL), a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, has been reported to regulate cell cycle progression in HNC. However, recent studies have revealed the acquired resistance of certain cells to PAL through activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. Therefore, we investigated whether the inhibition of MEK/ERK pathway by trametinib (TRA) may overcome the limited efficacy of PAL in HNC. We evaluated the effect of PAL alone and in combination with TRA on the viability of HNC cells, and found that the combination treatment synergistically inhibited the proliferation of HNC cells. The combination treatment induced G0/G1 cell cycle arrest and apoptotic cell death. In particular, apoptosis mediated by the combination treatment was accompanied with an increase in caspase-3 activity and the number of TUNEL-positive apoptotic cells. These results were consistent with the decrease in cell cycle progression and mitogen-activated protein kinase (MAPK) pathway activation. In a xenograft mouse model of HNC, PAL and TRA synergistically inhibited tumor growth and enhanced tumor cell apoptosis, consistent with the increase in the number of TUNEL-positive cells. The anti-proliferative effects were evident in tumor tissues subjected to the combination treatment as compared with those treated with single drug. Taken together, our study demonstrates that the combination of PAL and TRA exerts synergistic anticancer effects and inhibits cell cycle check points and MEK/ERK pathway in HNC, suggestive of their potential application for HNC treatment.

Aberrant modulation of ribosomal protein S6 phosphorylation confers acquired resistance to MAPK pathway inhibitors in BRAF-mutant melanoma

BRAF and MEK inhibitors have shown remarkable clinical efficacy in BRAF-mutant melanoma; however, most patients develop resistance, which limits the clinical benefit of these agents. In this study, we found that the human melanoma cell clones, A375-DR and A375-TR, with acquired resistance to BRAF inhibitor dabrafenib and MEK inhibitor trametinib, were cross resistant to other MAPK pathway inhibitors. In these resistant cells, phosphorylation of ribosomal protein S6 (rpS6) but not phosphorylation of ERK or p90 ribosomal S6 kinase (RSK) were unable to be inhibited by MAPK pathway inhibitors. Notably, knockdown of rpS6 in these cells effectively downregulated G₁ phase-related proteins, including RB, cyclin D1, and CDK6, induced cell cycle arrest, and inhibited proliferation, suggesting that aberrant modulation of rpS6 phosphorylation contributed to the acquired resistance. Interestingly, RSK inhibitor had little effect on rpS6 phosphorylation and cell proliferation in resistant cells, whereas P70S6K inhibitor showed stronger inhibitory effects on rpS6 phosphorylation and cell proliferation in resistant cells than in parental cells. Thus regulation of rpS6 phosphorylation, which is predominantly mediated by BRAF/MEK/ERK/RSK signaling in parental cells, was switched to mTOR/P70S6K signaling in resistant cells. Furthermore, mTOR inhibitors alone overcame acquired resistance and rescued the sensitivity of the resistant cells when combined with BRAF/MEK inhibitors. Taken together, our findings indicate that RSK-independent phosphorylation of rpS6 confers resistance to MAPK pathway inhibitors in BRAF-mutant melanoma, and that mTOR inhibitor-based regimens may provide alternative strategies to overcome this acquired resistance.

MEK inhibitor enhanced the antitumor effect of oxaliplatin and 5‑fluorouracil in MEK1 Q56P‑mutant colorectal cancer cells

Mitogen‑activated protein kinase kinase (MEK) small molecule inhibitors have been investigated in preclinical or clinical trials for the treatment of cancer. In the present study the genetic test results of 120 patients with colorectal cancer (CRC) were screened and the mutation rate of MEK1 was identified to be 1.67%. MEK inhibition by U0126 significantly decreased the growth of SW48 cells that harbored the MEK1 Q56P mutation, although it did not evidently affect the growth of NCI‑H508 cells with MEK1 wild‑type. In addition, U0126 increased the sensitivity of SW48 cells to 5‑fluorouracil (5‑FU) and oxaliplatin by producing more γH2AX foci and decreasing the expression of excision repair cross‑complementation group 1 and thymidylate synthase. The results suggested that MEK inhibitors in combination with oxaliplatin/5‑FU may offer an improved therapeutic effect in patients with MEK‑mutant CRC.

Therapeutic potential of combined BRAF/MEK blockade in BRAF-wild type preclinical tumor models

Background

Mounting evidence suggests that RAF-mediated MEK activation plays a crucial role in paradox MAPK (re)activation, leading to resistance and therapeutic failure with agents hitting a single step along the MAPK cascade.

Methods

We examined the molecular and functional effects of single and combined BRAF (dabrafenib), pan-RAF (RAF265), MEK (trametinib) and EGFR/HER2 (lapatinib) inhibition, using Western Blot and conservative isobologram analysis to assess functional synergism, and explored genetic determinants of synergistic interactions. Immunoprecipitation based assays were used to detect the interaction between BRAF and CRAF. The Mann-Whitney U test was used for comparing quantitative variables.

Results

Here we demonstrated that a combination of MEK and BRAF inhibitors overcomes paradoxical MAPK activation (induced by BRAF inhibitors) in BRAF-wt/RAS-mut NSCLC and PDAC in vitro. This results in growth inhibitory synergism, both in vitro and in vivo, in the majority (65%) of the cellular models analyzed, encompassing cell lines and patient-derived cancer stem cells and organoids. However, RAS mutational status is not the sole determinant of functional synergism between RAF and MEK inhibitors, as demonstrated in KRAS isogenic tumor cell line models. Moreover, in EGFR-driven contexts, paradoxical MAPK (re)activation in response to selective BRAF inhibition was dependent on EGFR family signaling and could be offset by simultaneous EGFR/HER-2 blockade.

Conclusions

Overall, our data indicate that RAF inhibition-induced paradoxical MAPK activation could be exploited for therapeutic purposes by simultaneously targeting both RAF and MEK (and potentially EGFR family members) in appropriate molecular contexts. KRAS mutation per se does not effectively predict therapeutic synergism and other biomarkers need to be developed to identify patients potentially deriving benefit from combined BRAF/MEK targeting.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0820-5) contains supplementary material, which is available to authorized users.

RAS-MAPK Reactivation Facilitates Acquired Resistance in FGFR1-Amplified Lung Cancer and Underlies a Rationale for Upfront FGFR-MEK Blockade

The FGFR kinases are promising therapeutic targets in multiple cancer types, including lung and head and neck squamous cell carcinoma, cholangiocarcinoma, and bladder cancer. Although several FGFR kinase inhibitors have entered clinical trials, single-agent clinical efficacy has been modest and resistance invariably occurs. We therefore conducted a genome-wide functional screen to characterize mechanisms of resistance to FGFR inhibition in a FGFR1-dependent lung cancer cellular model. Our screen identified known resistance drivers, such as MET, and additional novel resistance mediators including members of the neurotrophin receptor pathway (NTRK), the TAM family of tyrosine kinases (TYRO3, MERTK, AXL), and MAPK pathway, which were further validated in additional FGFR-dependent models. In an orthogonal approach, we generated a large panel of resistant clones by chronic exposure to FGFR inhibitors in FGFR1- and FGFR3-dependent cellular models and characterized gene expression profiles employing the L1000 platform. Notably, resistant clones had enrichment for NTRK and MAPK signaling pathways. Novel mediators of resistance to FGFR inhibition were found to compensate for FGFR loss in part through reactivation of MAPK pathway. Intriguingly, coinhibition of FGFR and specific receptor tyrosine kinases identified in our screen was not sufficient to suppress ERK activity or to prevent resistance to FGFR inhibition, suggesting a redundant reactivation of RAS-MAPK pathway. Dual blockade of FGFR and MEK, however, proved to be a more powerful approach in preventing resistance across diverse FGFR dependencies and may represent a therapeutic opportunity to achieve durable responses to FGFR inhibition in FGFR-dependent cancers. Mol Cancer Ther; 17(7); 1526-39. ©2018 AACR.

Overexpression of Semaphorin-3E enhances pancreatic cancer cell growth and associates with poor patient survival

Semaphorin-3E (Sema3E) is a member of an axon guidance gene family, and has recently been reported to contribute to tumor progression and metastasis. However, its role in pancreatic cancer is yet unknown and uncharacterized. In this study, we showed that Sema3E is overexpressed in human pancreatic cancer, and that high Sema3E levels are associated with tumor progression and poor survival. Interestingly, we also observed Sema3E expression in the nucleus, even though Sema3E is reported to be a secreted protein. Overexpression of Sema3E in pancreatic cancer cells promoted cell proliferation and migration in vitro, and increased tumor incidence and growth in vivo. Conversely, knockout of Sema3E suppressed cancer cell proliferation and migration in vitro, and reduced tumor incidence and size in vivo. Moreover, Sema3E induced cell proliferation via acting through the MAPK/ERK pathway. Collectively, these results reveal an undiscovered role of Sema3E in promoting pancreatic cancer pathogenesis, suggesting that Sema3E may be a suitable prognostic marker and therapeutic target for pancreatic cancer.

The Level of TWIST1 expression determines the response of colon cancer cells to mitogen-activated protein kinases inhibitors

BACKGROUND/AIM

Currently, it has been proposed that combination of 5-fluorouracil (5FU) with inhibitors of the mitogen-activated protein kinases (MAPKs) signaling pathway might enhance the efficacy of 5FU-based chemotherapy in colon cancer. Our study aimed to investigate an impact of TWIST1 silencing on the sensitivity of cancer cells to 5FU and selected MAPK inhibitors.

MATERIALS AND METHODS

The suppression of TWIST1 expression in human colon cancer HT29 and HCT116 cell lines was achieved by transduction with lentiviral vector carrying the TWIST1 silencing sequence (pLL3.7-sh TWIST1). The statistical calculation was performed with analysis of variance or Dunnett's test for comparison to control group. Paired Student's t-test was performed when two groups were analyzed.

RESULTS

Suppression of TWIST1 reduced the proliferation rate of colon cancer cells and enhanced their sensitivity to 5FU and MAPKs inhibitors. The sensitivity of HT29 cells to examined compounds was more dependent on TWIST1 expression level compared to HCT116 cells. The most noticeable effect of TWIST1 suppression on sensitivity of both colon cancer cell lines to combined treatment of 5FU and the MAPKs inhibitors was observed for inhibitors of p38α/β and JNK1-3. We also noted that the suppression of TWIST1 significantly sensitized both cell lines to combined treatment of 5FU and Rac inhibitor.

CONCLUSIONS

Our observations point to TWIST1 expression level as a marker of colon cancer sensitivity to combined treatment of 5FU and MAPKs inhibitors.

Nitrilase 1 modulates lung tumor progression in vitro and in vivo

Uncovering novel growth modulators for non-small cell lung cancer (NSCLC) may lead to new therapies for these patients. Previous studies suggest Nit1 suppresses chemically induced carcinogenesis of the foregut in a mouse model. In this study we aimed to determine the role of Nit1 in a transgenic mouse lung cancer model driven by a G12D Kras mutation. Nit1 knockout mice (Nit1^−/−) were crossed with Kras^G12D/+ mice to investigate whether a G12D Kras mutation and Nit1 inactivation interact to promote or inhibit the development of NSCLC. We found that lung tumorigenesis was suppressed in the Nit1-null background (Nit1^−/−:Kras^G12D/+). Micro-CT scans and gross tumor measurements demonstrated a 5-fold reduction in total tumor volumes compared to Nit1^+/+Kras^G12D/+ (p<0.01). Furthermore, we found that Nit1 is highly expressed in human lung cancer tissues and cell lines and use of siRNA against Nit1 decreased overall cell survival of lung cancer cells in culture. In addition, cisplatin response was enhanced in human lung cancer cells when Nit1 was knocked down and Nit1^−/−:Kras^G12D/+ tumors showed increased sensitivity to cisplatin in vivo. Together, our data indicate that Nit1 may play a supportive role in the modulation of lung tumorigenesis and represent a novel target for NSCLCs treatment.

System identification of signaling dependent gene expression with different time-scale data

Cells decode information of signaling activation at a scale of tens of minutes by downstream gene expression with a scale of hours to days, leading to cell fate decisions such as cell differentiation. However, no system identification method with such different time scales exists. Here we used compressed sensing technology and developed a system identification method using data of different time scales by recovering signals of missing time points. We measured phosphorylation of ERK and CREB, immediate early gene expression products, and mRNAs of decoder genes for neurite elongation in PC12 cell differentiation and performed system identification, revealing the input-output relationships between signaling and gene expression with sensitivity such as graded or switch-like response and with time delay and gain, representing signal transfer efficiency. We predicted and validated the identified system using pharmacological perturbation. Thus, we provide a versatile method for system identification using data with different time scales.

MEK162 Enhances Antitumor Activity of 5-Fluorouracil and Trifluridine in KRAS-mutated Human Colorectal Cancer Cell Lines

BACKGROUND

Preclinical evidence demonstrates that mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway inhibition increases sensitivity to 5-fluorouracil (5-FU) in colorectal cancer (CRC) cell lines and xenografts. Here, we aimed to investigate how CRC cell sensitivity to this combination is correlated to Kirsten rat sarcoma (KRAS) and proto-oncogene B-rapidly accelerated fibrosarcoma (BRAF) mutation, that are common in CRC and often lead to resistance to chemotherapy.

MATERIALS AND METHODS

Wild-type and mutant KRAS/BRAF human CRC cell lines were treated with escalating doses of 5-FU or trifluridine with MEK162 (MEK1/2 inhibitor) for 72 h. Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and synergism expressed by the combination index was calculated using CalcuSyn.

RESULTS

Evidence of synergistic antitumor activity was observed for the majority of human CRC cell lines treated with MEK162 plus 5-FU (4/6) or trifluridine (7/9). Synergism was greater in KRAS- or BRAF-mutant cell lines compared to wild-type KRAS/BRAF CRC cell lines.

CONCLUSION

The combination of MEK inhibition and trifluridine is worthwhile advancing in clinical development, particularly for treatment-refractory KRAS- or BRAF-mutated metastatic CRC.

Coadministration of Trametinib and Palbociclib Radiosensitizes KRAS-Mutant Non-Small Cell Lung Cancers In Vitro and In Vivo

PURPOSE

To investigate the potential roles that p16 (CDKN2A) and RB activation have in sensitization to MEK inhibitor in resistant KRAS-mutant non-small cell lung cancer cells (NSCLC) in vitro and in vivo.

EXPERIMENTAL DESIGN

Cell viability was measured with MTS assays. Effects of administration of radiation and combination drug treatments were evaluated by clonogenic assay, flow cytometry, and Western blots. DNA repair was assessed using immunofluorescent analysis. Finally, lung cancer xenografts were used to examine in vivo effects of drug treatment and radiation therapy.

RESULTS

In this study, we showed that sensitivity to MEK inhibitor correlated to the RB/p16/CDK4 pathway and knockdown of RB induced resistance in cell lines sensitive to MEK inhibitor. Also, overexpression of p16 and inhibition of CDK4 had the ability to sensitize normally resistant cell lines. Our data indicated that the MEK inhibitor (trametinib, GSK112012) cooperated with the CDK4/6 inhibitor (palbociclib, PD0332991) to strongly reduce cell viability of KRAS-mutant NSCLCs that were resistant to the MEK inhibitor in vitro and in vivo. In addition, we report for the first time that resistance of KRAS-mutant NSCLCs to MEK inhibitor is, at least partly, due to p16 mutation status, and we described a drug combination that efficiently reactivates the RB tumor suppressor pathway to trigger radiosensitizing effects, apoptosis, and cell-cycle arrest.

CONCLUSIONS

Our findings suggest that MEK inhibitor in combination with CDK4/6 inhibitor has significant anti-KRAS-mutant NSCLC activity and radiosensitizing effect in preclinical models, potentially providing a novel therapeutic strategy for patients with advanced KRAS-mutant NSCLCs.

Targeted molecular profiling of rare genetic alterations in colorectal cancer using next-generation sequencing

Mutation frequencies of common genetic alterations in colorectal cancer have been in the spotlight for many years. This study highlights few rare somatic mutations, which possess the attributes of a potential CRC biomarker yet are often neglected. Next-generation sequencing was performed over 112 tumor samples to detect genetic alterations in 31 rare genes in colorectal cancer. Mutations were detected in 26/31 (83.9 %) uncommon genes, which together contributed toward 149 gene mutations in 67/112 (59.8 %) colorectal cancer patients. The most frequent mutations include KDR (19.6 %), PTEN (17 %), FBXW7 (10.7 %), SMAD4 (10.7 %), VHL (8 %), KIT (8 %), MET (7.1 %), ATM (6.3 %), CTNNB1 (4.5 %) and CDKN2A (4.5 %). RB1, ERBB4 and ERBB2 mutations were persistent in 3.6 % patients. GNAS, FGFR2 and FGFR3 mutations were persistent in 1.8 % patients. Ten genes (EGFR, NOTCH1, SMARCB1, ABL1, STK11, SMO, RET, GNAQ, CSF1R and FLT3) were found mutated in 0.9 % patients. Lastly, no mutations were observed in AKT, HRAS, MAP2K1, PDGFR and JAK2. Significant associations were observed between VHL with tumor site, ERBB4 and SMARCB1 with tumor invasion, CTNNB1 with lack of lymph node involvement and CTNNB1, FGFR2 and FGFR3 with TNM stage. Significantly coinciding mutation pairs include PTEN and SMAD4, PTEN and KDR, EGFR and RET, EGFR and RB1, FBXW7 and CTNNB1, KDR and FGFR2, FLT3 and CTNNB1, RET and RB1, ATM and SMAD4, ATM and CDKN2A, ERBB4 and SMARCB1. This study elucidates few potential colorectal cancer biomarkers, specifically KDR, PTEN, FBXW7 and SMAD4, which are found mutated in more than 10 % patients.

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.

Trametinib modulates cancer multidrug resistance by targeting ABCB1 transporter

Overexpression of adenine triphosphate (ATP)-binding cassette (ABC) transporters is one of the main reasons of multidrug resistance (MDR) in cancer cells. Trametinib, a novel specific small-molecule mitogen-activated extracellular signal-regulated kinase (MEK) inhibitor, is currently used for the treatment of melanoma in clinic. In this study, we investigated the effect of trametinib on MDR mediated by ABC transporters. Trametinib significantly potentiated the effects of two ABCB1 substrates vincristine and doxorubicin on inhibition of growth, arrest of cell cycle and induction of apoptosis in cancer cells overexpressed ABCB1, but not ABCC1 and ABCG2. Furthermore, trametinib did not alter the sensitivity of non-ABCB1 substrate cisplatin. Mechanistically, trametinib potently blocked the drug-efflux activity of ABCB1 to increase the intracellular accumulation of rhodamine 123 and doxorubicin and stimulates the ATPase of ABCB1 without alteration of the expression of ABCB1. Importantly, trametinib remarkably enhanced the effect of vincristine against the xenografts of ABCB1-overexpressing cancer cells in nude mice. The predicted binding mode showed the hydrophobic interactions of trametinib within the large drug binding cavity of ABCB1. Consequently, our findings may have important implications for use of trametinib in combination therapy for cancer treatment.

Fenofibrate increases radiosensitivity in head and neck squamous cell carcinoma via inducing G2/M arrest and apoptosis

Radiation therapy is an important treatment for head and neck squamous cell carcinoma (HNSCC). However, how to promote radiation sensitivity in HNSCC remains a challenge. This study aimed to investigate the radiosensitizing effects of fenofibrate on HNSCC and explore the underlying mechanisms. HNSCC cell lines CNE-2 and KB were subjected to ionizing radiation (IR), in the presence or absence of fenofibrate treatment. Cell growth and survival, apoptosis and cell cycle were evaluated. In addition, CNE-2 cells were xenografted into nude mice and subjected to IR and/ or fenofibrate treatment. The expression of cyclinB and CDK1 was detected by Western blotting. Our results showed that fenofibrate efficiently radiosensitized HNSCC cells and xenografts in mice, and induced apoptosis and G2/M arrest via reducing the activity of the CDK1/cyclinB1 kinase complex. These data suggest that fenofibrate could be a promising radiosensitizer for HNSCC radiotherapy.

Role of runt-related transcription factor 2 in signal network of tumors as an inter-mediator

Runt-related transcription factor 2 (RUNX2) is a member of the polyomavirus enhancer-binding protein 2/core-binding factor superfamily. RUNX2 is known for its contribution to osteoblast phenotype and bone formation. In recent years, increasing attention has been focused on the relationship of Runx2 with tumorigenesis. In different types of tumor cells, RUNX2 cooperates with its co-activators or co-inhibitors, and mediates the responses of cells to various signaling pathways that are hyperactive in tumors. Thus, several downstream target genes of RUNX2 are activated when RUNX2 interacts with its co-factors, leading to a variety of effects on tumor cells (epithelial-mesenchymal transition, metastasis, proliferation, and osteolytic lesion). This review focuses on the involvement of RUNX2 in tumor cells in the crosstalk of diverse signaling pathways and its multiple functions to develop optimal and feasible approaches for clinical treatment based on the functions of RUNX2.

Trametinib, a novel MEK kinase inhibitor, suppresses lipopolysaccharide-induced tumor necrosis factor (TNF)-α production and endotoxin shock

Lipopolysaccharide (LPS), one of the most prominent pathogen-associated molecular patterns (PAMPs), activates macrophages, causing release of toxic cytokines (i.e. tumor necrosis factor (TNF)-α) that may provoke inflammation and endotoxin shock. Here, we tested the potential role of trametinib, a novel and highly potent MAPK/ERK kinase (MEK) inhibitor, against LPS-induced TNF-α response in monocytes, and analyzed the underlying mechanisms. We showed that trametinib, at nM concentrations, dramatically inhibited LPS-induced TNF-α mRNA expression and protein secretion in transformed (RAW 264.7 cells) and primary murine macrophages. In ex-vivo cultured human peripheral blood mononuclear cells (PBMCs), this MEK inhibitor similarly suppressed TNF-α production by LPS. For the mechanism study, we found that trametinib blocked LPS-induced MEK-ERK activation in above monocytes, which accounted for the defective TNF-α response. Macrophages or PBMCs treated with a traditional MEK inhibitor PD98059 or infected with MEK1/2-shRNA lentivirus exhibited a similar defect as trametinib, and nullified the activity of trametinib. On the other hand, introducing a constitutively-active (CA) ERK1 restored TNF-α production by LPS in the presence of trametinib. In vivo, mice administrated with trametinib produced low levels of TNF-α after LPS stimulation, and these mice were protected from LPS-induced endotoxin shock. Together, these results show that trametinib inhibits LPS-induced TNF-α expression and endotoxin shock probably through blocking MEK-ERK signaling.

U0126 protects cells against oxidative stress independent of its function as a MEK inhibitor

U0126 is a potent and selective inhibitor of MEK1 and MEK2 kinases. It has been widely used as an inhibitor for the Ras/Raf/MEK/ERK signaling pathway with over 5000 references on the NCBI PubMed database. In particular, U0126 has been used in a number of studies to show that inhibition of the Raf/MEK/ERK pathway protects neuronal cells against oxidative stress. Here, we report that U0126 can function as an antioxidant that protects PC12 cells against a number of different oxidative-stress inducers. This protective effect of U0126 is independent of its function as a MEK inhibitor, as several other MEK inhibitors failed to show similar protective effects. U0126 reduces reactive oxygen species (ROS) in cells. We further demonstrate that U0126 is a direct ROS scavenger in vitro, and the oxidation products of U0126 exhibit fluorescence. Our finding that U0126 is a strong antioxidant signals caution for its future usage as a MEK inhibitor and for interpreting some previous results.

Biological and molecular effects of small molecule kinase inhibitors on low-passage human colorectal cancer cell lines

Low-passage cancer cell lines are versatile tools to study tumor cell biology. Here, we have employed four such cell lines, established from primary tumors of colorectal cancer (CRC) patients, to evaluate effects of the small molecule kinase inhibitors (SMI) vemurafenib, trametinib, perifosine, and regorafenib in an in vitro setting. The mutant BRAF (V600E/V600K) inhibitor vemurafenib, but also the MEK1/2 inhibitor trametinib efficiently inhibited DNA synthesis, signaling through ERK1/2 and expression of genes downstream of ERK1/2 in BRAF mutant cells only. In case of the AKT inhibitor perifosine, three cell lines showed a high or intermediate responsiveness to the drug while one cell line was resistant. The multikinase inhibitor regorafenib inhibited proliferation of all CRC lines with similar efficiency and independent of the presence or absence of KRAS, BRAF, PIK3CA, and TP53 mutations. Regorafenib action was associated with broad-range inhibitory effects at the level of gene expression but not with a general inhibition of AKT or MEK/ERK signaling. In vemurafenib-sensitive cells, the antiproliferative effect of vemurafenib was enhanced by the other SMI. Together, our results provide insights into the determinants of SMI efficiencies in CRC cells and encourage the further use of low-passage CRC cell lines as preclinical models.

Targeted biopharmaceuticals for cancer treatment

Cancer is a complex invasive genetic disease that causes significant mortality rate worldwide. Protein-based biopharmaceuticals have significantly extended the lives of millions of cancer patients. This article reviews the biological function and application of targeted anticancer biopharmaceuticals. We first discuss the specific antigens and core pathways that are used in the development of targeted cancer therapy. The innovative monoclonal antibodies, non-antibody proteins, and small molecules targeting these antigens or pathways are then reviewed. Finally, the current challenges in anticancer biopharmaceuticals development and the potential solutions to address these challenges are discussed.

Vitamin D analogs combined with 5-fluorouracil in human HT-29 colon cancer treatment

In the present study, we evaluated the antitumor effect of two synthetic analogs of vitamin D, namely PRI-2191 [(24R)-1,24-dihydroxyvitamin D₃] and PRI-2205 (5,6-trans calcipotriol), in combined human colon HT-29 cancer treatment with 5-fluorouracil (5-FU). Mice bearing HT-29 tumors transplanted subcutaneously or orthotopically were injected with vitamin D analogs and 5-FU in various schedules. A statistically significant inhibition of subcutaneous or orthotopic tumor growth was observed as a result of combined therapy. In HT-29 tumors and in cells from in vitro culture, we observed increased vitamin D receptor (VDR) expression after treatment with either PRI-2205 or 5-FU alone, or in combination. Moreover, PRI-2205 decreased the percentage of cells from intestinal tumors in G₂/M and S stages and increased sub-G₁. Increased VDR expression was also observed after combined treatment of mice with 5-FU and PRI-2191. Moreover, our docking studies showed that PRI-2205 has stronger affinity for VDR, DBP and CAR/RXR ligand binding domains than PRI-2191. PRI-2191 analog, used with 5-FU, increased the percentage of subcutaneous tumor cells in G₀/G₁ and decreased the percentage in G₂/M, S and sub-G₁ populations as compared to 5-FU alone. In in vitro studies, we observed increased expression of p21 and p-ERK1/2 diminution via use of both analogs as compared to use of 5-FU alone. Simultaneously, PRI-2191 antagonizes some pro-apoptotic activities of 5-FU in vitro. However, in spite of these disadvantageous effects in terms of apoptosis, the therapeutic effect expressed as tumor growth retardation by PRI-2191 is significant. Our results suggest that the mechanism of potentiation of 5-FU antitumor action by both analogs is realized via increased p21 expression and decreased p-ERK1/2 level which may lead to diminution of thymidylate synthase expression. Higher binding affinity for VDR, DBP, but also for CAR\RXR ligand binding domain of PRI-2205 may, in part, explain its very low toxicity with sustained anticancer activity.

Molecular pathways: the basis for rational combination using MEK inhibitors in KRAS-mutant cancers

Mutations in RAS oncogenes are frequently observed in human cancers, and the mutations result in activation of the RAS-RAF-MEK-ERK pathway, leading to cell proliferation and survival. The pathway is, therefore, a potent therapeutic target in the RAS-mutant cancers. MEK inhibitors can specifically block the pathway and are one of the key types of drugs for the treatment of the RAS-mutant cancers. As RAS proteins activate other downstream signaling proteins in addition to the RAS-RAF-MEK-ERK pathway, combination therapeutic approaches with MEK inhibitors are also being evaluated. Moreover, MEK inhibitors can arrest cancer cells in G1 phase and repress prosurvival Bcl2 family proteins such as MCL1 and BCL2/BCLXL, and increase expression of Bim, a proapoptotic BH3-only family protein. This mechanism may explain the efficacy of the combination of MEK inhibitors with cytotoxic agents or other targeted inhibitors. A better understanding of the pathway will help us with development of rational combinations for the treatment of the RAS-mutant cancers.

Targeted therapy in gastrointestinal malignancies

Increased understanding of cancer pathogenesis has identified several pathways that serve as potential targets for novel targeted agents in development. The selection of targeted cancer therapy based on biomarkers has instigated a new era of personalized medicine and changed the way we practice oncology. Many targeted agents are approved for treatment of gastrointestinal malignancies most targeting tumor angiogenesis, and many more are in different phases of development. Here we briefly summarize nine different targeted agents that are approved currently in the U.S. and several other agents currently being studied in various gastrointestinal cancers.

Trametinib: first global approval

Trametinib is an orally bioavailable mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor with antineoplastic activity. The compound specifically binds to MEK1 and MEK2, resulting in inhibition of growth factor-mediated cell signalling and cellular proliferation in various cancers. Originally developed by Japan Tobacco, GlaxoSmithKline has licensed exclusive worldwide rights to the compound and conducted development in a number of different cancer types. Trametinib, as a monotherapy, has been approved in the US for the treatment of unresectable or metastatic malignant melanoma with BRAF V600E or V600K mutations, as detected by an FDA-approved test. The compound, as a monotherapy, has also been submitted for regulatory review in the EU for BRAF mutation-positive malignant melanoma, and is in phase III development in Europe, Argentina, Canada and Oceania. Phase II development is underway for pancreatic cancer, non-small cell lung cancer and relapsed or refractory leukaemias. GlaxoSmithKline is also developing trametinib for use in combination with dabrafenib in BRAF V600 mutation-positive metastatic cutaneous melanoma; the combination is at the preregistration stage in the EU and a phase III clinical programme is underway worldwide. Phase II development for this combination is also underway in colorectal cancer. Several phase I trials have also been initiated to evaluate trametinib in combination with other drugs for the treatment of various solid tumours and haematological malignancies. A paediatric oral solution formulation has been assessed against the oral tablet formulation in a phase I trial. This article summarizes the milestones in the development of trametinib leading to this first approval for unresectable or metastatic BRAF mutation-positive malignant melanoma.