Combination PI3K/MEK inhibition promotes tumor apoptosis and regression in PIK3CA wild-type, KRAS mutant colorectal cancer

Selective Eradication of Colon Cancer Cells Harboring PI3K and/or MAPK Pathway Mutations in 3D Culture by Combined PI3K/AKT/mTOR Pathway and MEK Inhibition

Colorectal cancer (CRC) is the second deadliest cancer in the world. Besides APC and p53 alterations, the PI3K/AKT/MTOR and MAPK pathway are most commonly mutated in CRC. So far, no treatment options targeting these pathways are available in routine clinics for CRC patients. We systematically analyzed the response of CRC cells to the combination of small molecular inhibitors targeting the PI3K and MAPK pathways. We used CRC cells in 2D, 3D spheroid, collagen gel cultures and freshly isolated organoids for drug response studies. Readout for drug response was spheroid or organoid growth, spheroid outgrowth, metabolic activity, Western blotting and immunofluorescence. We found profound tumor cell destruction under treatment with a combination of Torin 1 (inhibiting mTOR), MK2206 (targeting AKT) and selumetinib (inhibiting MEK) in 3D but not in 2D. Induction of cell death was due to apoptosis. Western blot analysis revealed efficient drug action. Gedatolisib, a dual PI3K/mTOR inhibitor, could replace Torin1/MK2206 with similar efficiency. The presence of PI3K and/or RAS-RAF-MAPK pathway mutations accounted for treatment responsiveness. Here, we identified a novel, efficient therapy, which induced proliferation stop and tumor cell destruction in vitro based on the genetic background. These preclinical findings show promise to further test this combi-treatment in vivo in mice and to potentially develop a mutation specific targeted therapy for CRC patients.

Pharmacologic Inhibition of SHP2 Blocks Both PI3K and MEK Signaling in Low-epiregulin HNSCC via GAB1

Preclinical and clinical studies have evidenced that effective targeted therapy treatment against receptor tyrosine kinases (RTKs) in different solid tumor paradigms is predicated on simultaneous inhibition of both the PI3K and MEK intracellular signaling pathways. Indeed, re-activation of either pathway results in resistance to these therapies. Recently, oncogenic phosphatase SHP2 inhibitors have been developed with some now reaching clinical trials. To expand on possible indications for SHP099, we screened over 800 cancer cell lines covering over 25 subsets of cancer. We found HNSCC was the most sensitive adult subtype of cancer to SHP099. We found that, in addition to the MEK pathway, SHP2 inhibition blocks the PI3K pathway in sensitive HNSCC, resulting in downregulation of mTORC signaling and anti-tumor effects across several HNSCC mouse models, including an HPV+ patient-derived xenograft (PDX). Importantly, we found low levels of the RTK ligand epiregulin identified HNSCCs that were sensitive to SHP2 inhibitor, and, adding exogenous epiregulin mitigated SHP099 efficacy. Mechanistically, epiregulin maintained SHP2-GAB1 complexes in the presence of SHP2 inhibition, preventing downregulation of the MEK and PI3K pathways. We demonstrate HNSCCs were highly dependent on GAB1 for their survival and knockdown of GAB1 is sufficient to block the ability of epiregulin to rescue MEK and PI3K signaling. These data connect the sensitivity of HNSCC to SHP2 inhibitors and to a broad reliance on GAB1-SHP2, revealing an important and druggable signaling axis. Overall, SHP2 inhibitors are being heavily developed and may have activity in HNSCCs, and in particular those with low levels of epiregulin.

KRASG12C inhibitor: combing for combination

Oncogenic mutation in KRAS is one of the most common alterations in human cancer. After decades of extensive research and unsuccessful drug discovery programs, therapeutic targeting of KRAS mutant tumour is at an exciting juncture. The discovery of mutation-specific inhibitors of KRASG12C and early positive findings from clinical trials has raised the hope of finally having a drug to treat a significant segment of KRAS mutant cancer patients. Crucially, it has also re-energized the RAS field to look beyond G12C mutation and find new innovative targeting opportunities. However, the early clinical trial data also indicates that there is significant variation in response among patients and that monotherapy treatment with KRASG12C inhibitors (G12Ci) alone is unlikely to be sufficient to elicit a sustained response. Understanding the molecular mechanism of variation in patient response and identifying possible combination opportunities, which could be exploited to achieve durable and significant responses and delay emergence of resistance, is central to the success of G12Ci therapy. Given the specificity of G12Ci, toxicity is expected to be minimal. Therefore, it might be possible to combine G12Ci with other targeted agents which have previously been explored to tackle KRAS mutant cancer but deemed too toxic, e.g. MEK inhibitor. Ongoing clinical trials will shed light on clinical resistance to G12C inhibitors, however extensive work is already ongoing to identify the best combination partners. This review provides an update on combination opportunities which could be explored to maximize the benefit of this new exciting drug.

Rigosertib elicits potent anti-tumor responses in colorectal cancer by inhibiting Ras signaling pathway

BACKGROUND

The therapeutic potency of Rigosertib (RGS) in the treatment of the myelodysplastic syndrome has been investigated previously, but little is known about its mechanisms of action.

METHODS

The present study integrates systems and molecular biology approaches to investigate the mechanisms of the anti-tumor effects of RGS, either alone or in combination with 5-FU in cellular and animal models of colorectal cancer (CRC).

RESULTS

The effects of RGS were more pronounced in dedifferentiated CRC cell types, compared to cell types that were epithelial-like. RGS inhibited cell proliferation and cell cycle progression in a cell-type specific manner, and that was dependent on the presence of mutations in KRAS, or its down-stream effectors. RGS increased both early and late apoptosis, by regulating the expression of p53, BAX and MDM2 in tumor model. We also found that RGS induced cell senescence in tumor tissues by increasing ROS generation, and impairing oxidant/anti-oxidant balance. RGS also inhibited angiogenesis and metastatic behavior of CRC cells, by regulating the expression of CD31, E-cadherin, and matrix metalloproteinases-2 and 9.

CONCLUSION

Our findings support the therapeutic potential of this potent RAS signaling inhibitor either alone or in combination with standard regimens for the management of patients with CRC.

Modeling Adaptive Resistance of KRAS Mutant Colorectal Cancer to MAPK Pathway Inhibitors with a Three-Dimensional Tumor Model

Single-agent drug treatment of KRAS^mut colorectal cancers is often ineffective because the activation of compensatory signaling pathways leads to drug resistance. To mimic cyclic chemotherapy treatments of patients, we showed that intermittent treatments of 3D tumor spheroids of KRAS^mut colorectal cancer cells with inhibitors of mitogen-activated protein kinase (MAPK) signaling pathway temporarily suppressed growth of spheroids. However, the efficacy of successive single-agent treatments was significantly reduced. Molecular analysis showed compensatory activation of PI3K/AKT and STAT kinases and EGFR family proteins. To overcome the adaptation of cancer cells to MAPK pathway inhibitors, we treated tumor spheroids with a combination of MEK and EGFR inhibitors. This approach significantly blocked signaling of MAPK and PI3K/AKT pathways and prevented the growth of spheroids, but it was not effective against STAT signaling. Although the combination treatment blocked the matrix invasion of DLD1 cells, additional treatments with STAT inhibitors were necessary to prevent invasiveness of HCT116 cells. Overall, our drug resistance model elucidated the mechanisms of treatment-induced growth and invasiveness of cancer cells and allowed design-driven testing and identifying of effective treatments to suppress these phenotypes.

Integrating Genome-Wide Association Studies and Gene Expression Profiles With Chemical-Genes Interaction Networks to Identify Chemicals Associated With Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer and has the second highest mortality rate in global cancer. Exploring the associations between chemicals and CRC has great significance in prophylaxis and therapy of tumor diseases. This study aims to explore the relationships between CRC and environmental chemicals on genetic basis by bioinformatics analysis. The genome-wide association study (GWAS) datasets for CRC were obtained from the UK Biobank. The GWAS data for colon cancer (category C18) includes 2,581 individuals and 449,683 controls, while that of rectal cancer (category C20) includes 1,244 individuals and 451,020 controls. In addition, we derived CRC gene expression datasets from the NCBI-GEO (GSE106582). The chemicals related gene sets were acquired from the comparative toxicogenomics database (CTD). Transcriptome-wide association study (TWAS) analysis was applied to CRC GWAS summary data and calculated the expression association testing statistics by FUSION software. We performed chemicals related gene set enrichment analysis (GSEA) by integrating GWAS summary data, mRNA expression profiles of CRC and the CTD chemical-gene interaction networks to identify relationships between chemicals and genes of CRC. We observed several significant correlations between chemicals and CRC. Meanwhile, we also detected 5 common chemicals between colon and rectal cancer, including methylnitronitrosoguanidine, isoniazid, PD 0325901, sulindac sulfide, and importazole. Our study performed TWAS and GSEA analysis, linked prior knowledge to newly generated data and thereby helped identifying chemicals related to tumor genes, which provides new clues for revealing the associations between environmental chemicals and cancer.

Overexpressed Hsp70 alleviated formaldehyde-induced apoptosis partly via PI3K/Akt signaling pathway in human bronchial epithelial cells

Formaldehyde (FA) is a ubiquitous environmental pollutant, which can induce apoptosis in lung cell and is related to the pathogenesis of asthma, pneumonia, and chronic obstructive pulmonary disease. Heat shock protein 70 (Hsp70) is an ATP-dependent molecular chaperone and exhibits an anti-apoptosis ability in a variety of cells. Previous studies reported that the expression of Hsp70 was induced when organisms were exposed to FA. Whether Hsp70 plays a role in the FA-induced apoptosis and the involved cell signaling pathway remain largely unknown. In this study, human bronchial epithelial cells with overexpressed Hsp70 and the control were exposed to different concentrations of FA (0, 40, 80, and 160 μmol/L) for 24 hours. Apoptosis and the expression levels of PI3K, Akt, p-Akt, MEK, p-MEK, and GLI2 were detected by Annexin-APC/7AAD double-labeled flow cytometry and western blot. The results showed that overexpression of Hsp70 decreased the apoptosis induced by FA and alleviated the decline of PI3k and p-Akt significantly. Inhibitor (LY 294002, a specific inhibitor of PI3K-Akt) test result indicated that PI3K-Akt signaling pathway was involved in the inhibition of FA-induced apoptosis by Hsp70 overexpression and also active in the maintenance of GLI2 level. However, it also suggested that other signaling pathways activated by overexpressed Hsp70 participated in this process, which was needed to be elucidated in further research.

Activation of WNT/β-catenin signaling results in resistance to a dual PI3K/mTOR inhibitor in colorectal cancer cells harboring PIK3CA mutations

PIK3CA is a frequently mutated gene in cancer, including about ~15 to 20% of colorectal cancers (CRC). PIK3CA mutations lead to activation of the PI3K/AKT/mTOR signaling pathway, which plays pivotal roles in tumorigenesis. Here, we investigated the mechanism of resistance of PIK3CA-mutant CRC cell lines to gedatolisib, a dual PI3K/mTOR inhibitor. Out of a panel of 29 CRC cell lines, we identified 7 harboring one or more PIK3CA mutations; of these, 5 and 2 were found to be sensitive and resistant to gedatolisib, respectively. Both of the gedatolisib-resistant cell lines expressed high levels of active glycogen synthase kinase 3-beta (GSK3β) and harbored the same frameshift mutation (c.465_466insC; H155fs*) in TCF7, which encodes a positive transcriptional regulator of the WNT/β-catenin signaling pathway. Inhibition of GSK3β activity in gedatolisib-resistant cells by siRNA-mediated knockdown or treatment with a GSK3β-specific inhibitor effectively reduced the activity of molecules downstream of mTOR and also decreased signaling through the WNT/β-catenin pathway. Notably, GSK3β inhibition rendered the resistant cell lines sensitive to gedatolisib cytotoxicity, both in vitro and in a mouse xenograft model. Taken together, these data demonstrate that aberrant regulation of WNT/β-catenin signaling and active GSK3β induced by the TCF7 frameshift mutation cause resistance to the dual PI3K/mTOR inhibitor gedatolisib. Cotreatment with GSK3β inhibitors may be a strategy to overcome the resistance of PIK3CA- and TCF7-mutant CRC to PI3K/mTOR-targeted therapies.

Targeting PP2A in cancer: Combination therapies

The serine/threonine phosphatase PP2A regulates a vast portion of the phosphoproteome including pathways involved in apoptosis, proliferation and DNA damage response and PP2A inactivation is a vital step in malignant transformation. Many groups have explored the therapeutic venue of combining PP2A reactivation with kinase inhibition to counteract the very changes in tumor suppressors and oncogenes that lead to cancer development. Conversely, inhibition of PP2A to complement chemotherapy and radiation-induced cancer cell death is also an area of active investigation. Here we review the studies that utilize PP2A targeted agents as combination therapy in cancer. A potential role for PP2A in tumor immunity is also highlighted.

Inhibitory effect of NVP-BKM120 on cholangiocarcinoma cell growth

Abnormal activation of the phosphatidylinositol 3-kinase (PI3K) pathway has been demonstrated in certain types of cancer, including cholangiocarcinoma (CCA). This pathway may therefore be a promising target for CCA treatment. The present study assessed the inhibitory effect of NVP-BKM120, a pan-class I PI3K inhibitor, on CCA cell growth. This inhibitory effect was determined using CCA cell lines and in CCA-inoculated mice. The result from sulforhodamine B (SRB) assay demonstrated that NVP-BKM120 treatment inhibited CCA cell growth in a dose-dependent manner, even at the lowest tested concentration. The in vivo study revealed that oral administration of NVP-BKM120 (10 or 30 mg/kg) to CCA-inoculated nude mice led to a reduction in tumor growth when compared with controls, which was indicated by an immunohistochemical assay for Ki67 expression. In addition, the result from TUNEL assay demonstrated that NVP-BKM120 induced cancer cell death without any signs of toxicity, which indicated by the body weight of mice (data not shown). Western blot analysis demonstrated that NVP-BKM120 inhibited CCA cell growth by suppressing RAC serine/threonine protein kinase/mechanistic target of rapamycin activation and inhibiting the phosphorylation of phosphatase and tensin homolog, which is the inactivation form of the negative regulator of this pathway. Therefore, the results of the present study indicated that NVP-BKM120 should be considered as a therapeutic agent against CCA that could be used to improve treatment.

LY3009120, a panRAF inhibitor, has significant anti-tumor activity in BRAF and KRAS mutant preclinical models of colorectal cancer

Activating mutations in the KRAS and BRAF genes, leading to hyperactivation of the RAS/RAF/MAPK oncogenic signaling cascade, are common in patients with colorectal cancer (CRC). While selective BRAF inhibitors are efficacious in BRAF^mut melanoma, they have limited efficacy in BRAF^mut CRC patients. In a RAS^mut background, selective BRAF inhibitors are contraindicated due to paradoxical activation of the MAPK pathway through potentiation of CRAF kinase activity. A way to overcome such paradoxical activation is through concurrent inhibition of the kinase activity of both RAF isoforms. Here, we further examined the effects of LY3009120, a panRAF and RAF dimer inhibitor, in human models of CRC with various mutational backgrounds. We demonstrate that LY3009120 induced anti-proliferative effects in BRAF^mut and KRAS^mut CRC cell lines through G1-cell cycle arrest. The anti-proliferative effects of LY3009120 in KRAS^mut CRC cell lines phenocopied molecular inhibition of RAF isoforms by simultaneous siRNA-mediated knockdown of ARAF, BRAF and CRAF. Additionally, LY3009120 displayed significant activity in in vivo BRAF^mut and KRAS^mut CRC xenograft models. Examination of potential resistance to LY3009120 demonstrated RAF-independent ERK and AKT activation in the KRAS^mut CRC cell line HCT 116. These findings describe the preclinical activity of a panRAF inhibitor in a BRAF^mut and KRAS^mut CRC setting.

Colonoscopy-based colorectal cancer modeling in mice with CRISPR-Cas9 genome editing and organoid transplantation

Most genetically engineered mouse models (GEMMs) of colorectal cancer are limited by tumor formation in the small intestine, a high tumor burden that limits metastasis, and the need to generate and cross mutant mice. Cell line or organoid transplantation models generally produce tumors in ectopic locations-such as the subcutaneous space, kidney capsule, or cecal wall-that do not reflect the native stromal environment of the colon mucosa. Here, we describe detailed protocols to rapidly and efficiently induce site-directed tumors in the distal colon of mice that are based on colonoscopy-guided mucosal injection. These techniques can be adapted to deliver viral vectors carrying Cre recombinase, CRISPR-Cas9 components, CRISPR-engineered mouse tumor organoids, or human cancer organoids to mice to model the adenoma-carcinoma-metastasis sequence of tumor progression. The colonoscopy injection procedure takes ∼15 min, including preparation. In our experience, anyone with reasonable hand-eye coordination can become proficient with mouse colonoscopy and mucosal injection with a few hours of practice. These approaches are ideal for a wide range of applications, including assessment of gene function in tumorigenesis, examination of tumor-stroma interactions, studies of cancer metastasis, and translational research with patient-derived cancers.

Synergistic anti-proliferative effects of mTOR and MEK inhibitors in high-grade chondrosarcoma cell line OUMS-27

Chondrosarcoma is a malignant bone tumor that produces cartilaginous neoplastic tissue. Owing to the absence of an effective adjuvant therapy, high-grade chondrosarcoma has a poor prognosis. Therefore, it is important to develop an effective adjuvant therapy to prevent the recurrence and metastasis. Mammalian target of rapamycin (mTOR), a central regulator of cell growth, metabolism, proliferation, and survival, is considered an important target for anticancer drug development. The mitogen activated protein kinase (MAPK) pathway is another highly implicated cellular pathway in cancer and is thought to have compensatory effects in response to the inhibition of the phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR signaling pathway. We investigated the mechanism of anti-proliferative effect of the mTOR inhibitor rapamycin and MAPK/ERK (MEK) inhibitor PD 0325901, and the combined effect of rapamycin and PD 0325901 on human chondrosarcoma cell line (OUMS-27). Combination therapy with rapamycin and PD 0325901 showed a stronger anti-proliferative effect on OUMS-27 cells than rapamycin monotherapy. We confirmed that the dual inhibition of the PI3K/Akt/mTOR and RAF/MEK/ERK signaling pathways had synergistic anti-proliferative effects in OUMS-27. Our results suggest that combination therapy of mTOR and MEK inhibitor could be an effective therapeutic approach against chondrosarcoma.

Synergistic antitumor effects of combination PI3K/mTOR and MEK inhibition (SAR245409 and pimasertib) in mucinous ovarian carcinoma cells by fluorescence resonance energy transfer imaging

The aim of this study was to clarify the synergistic effects of dual inhibition of the PI3K/mTOR and MAPK pathways in ovarian mucinous carcinoma (OMC) cells, using fluorescence resonance energy transfer (FRET) imaging. We exposed 6 OMC cell lines to a PI3K/mTOR inhibitor (voxtalisib, SAR245409) and/or a MEK inhibitor (pimasertib), and evaluated synergistic effects using the Chou-Talalay method. Then, S6K (PI3K pathway) and ERK (MAPK pathway) kinase activities, and their individual proliferative or cytotoxic effects were calculated by time-lapse FRET imaging. In combination with SAR245409, pimasertib (30 nM) synergistically inhibited cell growth (combination indexes: 0.03-0.5) and induced apoptosis in all 6 OMC cell lines. FRET-imaging results demonstrated that ERK inhibition induced both anti-proliferation and apoptosis in a dose-dependent manner in both MCAS and OAW42 cells. However, S6K inhibition suppressed proliferation in a threshold manner in both cell lines, although apoptosis was only induced in OAW42 cells. These results demonstrated that combined PI3K/mTOR and MEK inhibition exhibited synergistic antitumor effects in OMC cells and that FRET imaging is useful for analyzing kinase activities in live cells and elucidating their cytostatic and cytotoxic effects.

Acquired resistance to combination treatment through loss of synergy with MEK and PI3K inhibitors in colorectal cancer

Historically, understanding of acquired resistance (AQR) to combination treatment has been based on knowledge of resistance to its component agents. To test whether an altered drug interaction could be an additional factor in AQR to combination treatment, models of AQR to combination and single agent MEK and PI3K inhibitor treatment were generated. Combination indices indicated combination treatment of PI3K and MEK inhibitors remained synergistic in cells with AQR to single agent but not combination AQR cells. Differences were also observed between the models in cellular phenotypes, pathway signaling and drug cross-resistance. Genomics implicated TGFB2-EDN1 overexpression as candidate determinants in models of AQR to combination treatment. Supplementation of endothelin in parental cells converted synergism to antagonism. Silencing of TGFB2 or EDN1 in cells with AQR conferred synergy between PI3K and MEK inhibitor. These results highlight that AQR to combination treatment may develop through alternative mechanisms to those of single agent treatment, including a change in drug interaction.

PKM2 is not required for colon cancer initiated by APC loss

BACKGROUND

Cancer cells express the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2). PKM2 expression is not required for some cancers, and PKM2 loss can promote cancer progression; however, PKM2 has been reported to be essential in other tumor contexts, including a proposed non-metabolic role in β-catenin nuclear translocation. PKM2 is expressed in colon cancers where loss of the Apc tumor suppressor results in β-catenin nuclear translocation and aberrant activation of the canonical Wnt signaling pathway. Whether PKM2 is required in this colon cancer context has not been investigated.

RESULTS

Colon tumorigenesis was induced in mice harboring conditional Apc and Pkm2 alleles, and tumor progression was monitored by serial colonoscopy. PKM2 deletion had no effect on overall survival, the number of mice that developed tumors, or the number of tumors that developed per animal. Immunohistochemical analysis demonstrated PKM2 expression in wild-type tumors and the expected loss of PKM2 expression in tumors from Pkm2 conditional mice. Loss of PKM2 resulted in pyruvate kinase M1 expression but had no effect on nuclear β-catenin staining. These findings are consistent with tumor growth and activated Wnt signaling despite PKM2 loss in this model. We also found a large fraction of human colon cancers had very low or undetectable levels of PKM2 expression.

CONCLUSIONS

PKM2 is not required for Apc-deficient colon cancer or for nuclear translocation of β-catenin in Apc-null tumor cells. These findings suggest that PKM2 expression is not required for colon tumor formation or progression.

miR-363-3p inhibits tumor growth by targeting PCNA in lung adenocarcinoma

Increasing evidence suggests that microRNAs play key roles in lung cancer. Our previous study demonstrated that microRNA 363-3p (miR-363-3p) is downregulated in lung cancer tissues. In this study, we demonstrated that overexpression of miR-363-3p inhibits the proliferation and colony formation of A549 and H441 cells, while silencing of miR-363-3p has the converse effects. The anti-oncogenic function of miR-363-3p was verified in a mouse tumor xenograft model. Furthermore, cell cycle analysis showed miR-363-3p can induce S phase arrest by downregulating Cyclin-D1 and upregulating Cyclin-dependent kinase-2 in lung adenocarcinoma cells. Additionally, miR-363-3p enhances cell apoptosis, whereas miR-363-3p inhibitor prevents apoptosis and leads to downregulation of Bax and Bak expression. The anti-proliferative function of miR-363-3p toward lung cancer cells may be explained by its ability to inhibit the activation of the mTOR and ERK signaling pathways. Using target prediction software and luciferase reporter assays, we identified PCNA as a specific target of miR-363-3p. miR-363-3p can decreased the accumulation of endogenous PCNA in lung adenocarcinoma cells. Moreover, exogenous expression of PCNA relieve the inhibition of miR-363-3p on cell proliferation, colony formation and mTOR and ERK signaling pathways. Taken together, our data indicate that miR-363-3p suppresses tumor growth by targeting PCNA in lung adenocarcinoma.

Isolation of Circulating Tumor Cells in an Orthotopic Mouse Model of Colorectal Cancer

Despite the advantages of easy applicability and cost-effectiveness, subcutaneous mouse models have severe limitations and do not accurately simulate tumor biology and tumor cell dissemination. Orthotopic mouse models have been introduced to overcome these limitations; however, such models are technically demanding, especially in hollow organs such as the large bowel. In order to produce uniform tumors which reliably grow and metastasize, standardized techniques of tumor cell preparation and injection are critical. We have developed an orthotopic mouse model of colorectal cancer (CRC) which develops highly uniform tumors and can be used for tumor biology studies as well as therapeutic trials. Tumor cells from either primary tumors, 2-dimensional (2D) cell lines or 3-dimensional (3D) organoids are injected into the cecum and, depending on the metastatic potential of the injected tumor cells, form highly metastatic tumors. In addition, CTCs can be found regularly. We here describe the technique of tumor cell preparation from both 2D cell lines and 3D organoids as well as primary tumor tissue, the surgical and injection techniques as well as the isolation of CTCs from the tumor-bearing mice, and present tips for troubleshooting.

In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;KrasG12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5+ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

Differentiated exophytic vulvar intraepithelial lesions are genetically distinct from keratinizing squamous cell carcinomas and contain mutations in PIK3CA

Human papillomavirus-negative keratinizing vulvar cancers typically harbor TP53 mutations as do their precursors, differentiated vulvar intraepithelial neoplasia. However, atypical verruciform proliferations are also associated with these malignancies and their pathogenesis is poorly understood. This study compared 11 atypical verruciform lesions, including atypical verruciform hyperplasia, vulvar acanthosis with altered differentiation, and verruciform lichen simplex chronicus, with 14 human papillomavirus-negative keratinizing squamous cell carcinomas. Extracted tissue DNA was subjected to targeted massively parallel sequencing of the exonic regions of 300 genes. Eight (73%) and six (55%) of eleven atypical verruciform lesions contained mutations in PIK3CA and ARID2, respectively. No TP53 mutations were identified. Eleven (79%) and five (36%) of fourteen keratinizing squamous cell carcinomas tested contained TP53 and CDKN2A mutations, respectively. Keratinizing squamous cell carcinomas displayed the majority of copy number variations with some variations (7p gain and 8p loss) shared by some cases in both groups. One patient developed atypical verruciform lesions with PIK3CA mutations followed by a keratinizing carcinoma with mutations in both PIK3CA and TP53. This study, for the first time segregates atypical verruciform lesions by virtue of a unique genotype (PIK3CA mutant/TP53 wild type) illustrating an example of progression to a TP53-mutated keratinizing carcinoma. The findings indicate that although PIK3CA mutations are found in <10% of vulvar squamous cell carcinomas, they may be specific for a particular pathway involving atypical verruciform lesions, which could function as either a direct precursor or a risk factor for vulvar squamous cell carcinoma. Given the presence of a molecular signature, we propose the term 'differentiated exophytic vulvar intraepithelial lesion' for this group. Whether they function as direct precursors to a less common form of squamous cell carcinoma will require further study, but carcinomas associated with these lesions might warrant testing for PIK3CA mutations to address this question.

Translating genomic profiling to gastrointestinal cancer treatment

Next-generation sequencing enables faster, cheaper and more accurate whole-genome sequencing, allowing genome profiling and discovery of molecular features. As molecular targeted drugs are developed, treatment can be tailored according to molecular subtype. Gastric and colorectal cancers have each been divided into four subtypes according to molecular features. Profiling of the esophageal cancer genome is underway and its classification is anticipated. To date, identification of HER2 expression in gastric adenocarcinoma and KRAS, NRAS and BRAF mutations in colon cancer have proved essential for treatment decisions. However, to overcome therapy resistance and improve prognosis, further individualized therapy is required. Here, we summarize the treatment options for gastrointestinal cancer according to genomic profiling and discuss future directions.

Enhanced anti-tumour activity of the combination of the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037

PURPOSE

Tumours frequently have defects in multiple oncogenic pathways, e.g. MAPK and PI3K signalling pathways, and combinations of targeted therapies may be required for optimal activity. This study evaluated the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037, as single agents and in combination, in colorectal carcinoma cell lines and tumour xenograft-bearing mice.

METHODS

In vitro growth inhibition, survival and signal transduction were measured using the Sulforhodamine B, clonogenic and Western blotting assays, respectively, in HCT116 and HT29 cell lines. In vivo anti-tumour efficacy and pharmacokinetic properties were assessed in HCT116 and HT29 human colorectal cancer xenograft tumour-bearing mice.

RESULTS

The combination of WX-554 and WX-037 exhibited marked synergistic growth inhibition in vitro, which was associated with increased cytotoxicity and enhanced inhibition of ERK and S6 phosphorylation, compared to either agent alone. Pharmacokinetic analyses indicated that there was no PK interaction between the two drugs at low doses, but that at higher doses, WX-037 may delay the tumour uptake of WX-554. In vivo efficacy studies revealed that the combination of WX-037 and WX-554 was non-toxic and exhibited marked tumour growth inhibition greater than observed with either agent alone.

CONCLUSION

These studies show for the first time that combination treatment with the novel MEK inhibitor WX-554 and the novel PI3K inhibitor WX-037 can induce synergistic growth inhibition in vitro, which translates into enhanced anti-tumour efficacy in vivo.

MEK and TAK1 Regulate Apoptosis in Colon Cancer Cells with KRAS-Dependent Activation of Proinflammatory Signaling

MEK inhibitors have limited efficacy in treating RAS-RAF-MEK pathway-dependent cancers due to feedback pathway compensation and dose-limiting toxicities. Combining MEK inhibitors with other targeted agents may enhance efficacy. Here, codependencies of MEK, TAK1, and KRAS in colon cancer were investigated. Combined inhibition of MEK and TAK1 potentiates apoptosis in KRAS-dependent cells. Pharmacologic studies and cell-cycle analyses on a large panel of colon cancer cell lines demonstrate that MEK/TAK1 inhibition induces cell death, as assessed by sub-G₁ accumulation, in a distinct subset of cell lines. Furthermore, TAK1 inhibition causes G₂-M cell-cycle blockade and polyploidy in many of the cell lines. MEK plus TAK1 inhibition causes reduced G₂-M/polyploid cell numbers and additive cytotoxic effects in KRAS/TAK1-dependent cell lines as well as a subset of BRAF-mutant cells. Mechanistically, sensitivity to MEK/TAK1 inhibition can be conferred by KRAS and BMP receptor activation, which promote expression of NF-κB-dependent proinflammatory cytokines, driving tumor cell survival and proliferation. MEK/TAK1 inhibition causes reduced mTOR, Wnt, and NF-κB signaling in TAK1/MEK-dependent cell lines concomitant with apoptosis. A Wnt/NF-κB transcriptional signature was derived that stratifies primary tumors into three major subtypes: Wnt-high/NF-κB-low, Wnt-low/NF-κB-high and Wnt-high/NF-κB-high, designated W, N, and WN, respectively. These subtypes have distinct characteristics, including enrichment for BRAF mutations with serrated carcinoma histology in the N subtype. Both N and WN subtypes bear molecular hallmarks of MEK and TAK1 dependency seen in cell lines. Therefore, N and WN subtype signatures could be utilized to identify tumors that are most sensitive to anti-MEK/TAK1 therapeutics.

IMPLICATIONS

This study describes a potential therapeutic strategy for a subset of colon cancers that are dependent on oncogenic KRAS signaling pathways, which are currently difficult to block with selective agents. Mol Cancer Res; 14(12); 1204-16. ©2016 AACR.

PI3 Kinase Pathway and MET Inhibition is Efficacious in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer that is commonly associated with prior asbestos exposure. Receptor tyrosine kinases (RTKs) such as MET and its downstream target PI3K are overexpressed and activated in a majority of MPMs. Here, we studied the combinatorial therapeutic efficacy of the MET/ALK inhibitor crizotinib, with either a pan-class I PI3K inhibitor, BKM120, or with a PI3K/mTOR dual inhibitor, GDC-0980, in mesothelioma. Cell viability results showed that MPM cells were highly sensitive to crizotinib, BKM120 and GDC-0980 when used individually and their combination was more effective in suppressing growth. Treatment of MPM cells with these inhibitors also significantly decreased cell migration, and the combination of them was synergistic. Treatment with BKM120 alone or in combination with crizotinib induced G2-M arrest and apoptosis. Both crizotinib and BKM120 strongly inhibited the activity of MET and PI3K as evidenced by the decreased phosphorylation of MET, AKT and ribosomal S6 kinase. Using a PDX mouse model, we showed that a combination of crizotinib with BKM120 was highly synergetic in inhibiting MPM tumor growth. In conclusion our findings suggest that dual inhibition of PI3K and MET pathway is an effective strategy in treating MPM as compared to a single agent.

Combined inhibition of PI3K and PARP is effective in the treatment of ovarian cancer cells with wild-type PIK3CA genes

OBJECTIVE

Combined inhibition of PI3K and PARP has been shown to be effective in the treatment of preclinical models of breast cancer and prostate cancer independent of BRCA or PIK3CA mutational status. However, the knowledge about this combination treatment in ovarian cancer is limited. The aim of this study was to evaluate the therapeutic effect of PI3K inhibitor BKM120 and PARP inhibitor Olaparib on ovarian cancer cell lines bearing wild-type PIK3CA genes.

METHODS

We exposed three wild-type PIK3CA ovarian cancer cell lines to a PI3K inhibitor BKM120 and/or a PARP inhibitor Olaparib. The effect of BKM120 as a single-agent or in combination with Olaparib was evaluated by Cell Count Kit (CCK8) assay, immunoblotting, comet assay, flow cytometry and immunofluorescence staining assay. The combination indexes for synergistic effect on cell viability were calculated with the Chou-Talalay method. Ex vivo cultured ovarian cancer tissues from patients were analyzed by histological and immunohistochemical analyses.

RESULTS

Combined inhibition of PI3K and PARP effectively synergized to block the growth of three wild-type PIK3CA ovarian cancer cell lines and explants of a primary ovarian tumor specimen. Mechanistically, dual blockade of PI3K and PARP in these ovarian cancer cell lines resulted in substantially attenuated PI3K/AKT/mTOR signaling, impaired DNA damage response and deficient homologous recombination repair, with remarkable BRCA downregulation.

CONCLUSIONS

The combined use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib may be effective in ovarian cancers with a broader spectrum of cancer-associated genetic alterations but not limited to those with mutant PIK3CA or BRCA genes. BRCA downregulation may be a potential biomarker for the effective response to the proposed combination treatment.

Combined use of PI3K and MEK inhibitors synergistically inhibits lung cancer with EGFR and KRAS mutations

EGFR and KRAS mutations are the two most common driver mutations in non-small cell lung cancer (NSCLC). Molecular target-based therapy using small molecules such as gefitinib has been used for inhibiting EGFR with good initial responses; however, drug resistance is common when using a mono-targeting strategy. At present, KRAS remains an undruggable target. As such, the development of new drugs targeting the downstream of KRAS and EGFR and their crosstalk pathways is critically needed to effectively treat NSCLC. The present study aimed to elucidate the anticancer effects of PI3K (BKM120) and MEK (PD1056309) inhibitors on NSCLC cell lines with KRAS or EGFR mutations. Inhibition of the EGFR and KRAS downstream P13K pathway using BKM120 significantly inhibited the growth of NSCLC cell lines with either EGFR or KRAS mutations. In addition, significant cell cycle arrest and induction of apoptosis were observed following BKM120 treatment. Notably, although the A549 and H358 NSCLC cell lines harbor the same KRAS mutation, A549 cells were less sensitive than H358 cells in the response to BKM120 treatment. Similarly, PC-9 and H1650 cells harbor the same EGFR mutation, however, H1650 was less sensitive to BKM120. Different sensitivity between NSCLC cell lines with the same oncogenic mutation suggests that multiple crosstalk pathways exit. Combined usage of BKM120 and PD1056309 synergistically enhanced apoptosis in the A549 cells and mildly enhanced apoptosis in the H1650 and H358 cells, suggesting the crosstalk of the MEK pathway with the P13K/Akt pathways in these cell lines. Overall, our findings suggest that inhibition of EGFR and KRAS downstream with a P13K/Akt inhibitor could be useful for treating NSCLC. However, for NSCLC exhibiting crosstalk with other survival pathways, such as the MEK pathway, combination treatment is required.

Cytotoxicity of PEGylated liposomes co-loaded with novel pro-apoptotic drug NCL-240 and the MEK inhibitor cobimetinib against colon carcinoma in vitro

The overactivation of signaling pathways, such as the PI3K and MAPK, which are crucial to cell growth and survival, is a common feature in many cancer types. Though a number of advances have been made in the development of molecular agents targeting these pathways, their application as monotherapies has not significantly improved clinical outcome. A novel liposomal preparation was developed, co-loaded with NCL-240, a small-molecule inhibitor of the PI3K/mTOR pathway, along with cobimetinib, a MEK/ERK pathway inhibitor. This combination drug-loaded nanocarrier, (N+C)-LP, was able to significantly enhance the cytotoxicity of these drugs against colon carcinoma cells in vitro demonstrating a clear synergistic effect (combination index of 0.79). The (N+C)-LP was also able to induce cell cycle arrest of the cells, specifically in the G1 phase thereby preventing their progression to the S-phase, typical of the action of MEK inhibitors. Analyzing the apoptotic events, it was found that this effect on cell cycle regulation is followed by the induction of apoptosis. The quantified distribution of apoptotic events showed that the (N+C)-LP induced apoptosis significantly by over 3-4 fold (P<0.001) compared to other treatment groups. The co-loaded liposomal preparation was also targeted to the transferrin receptor of cancer cells by modifying the surface of the liposome with transferrin. FACS analysis showed that transferrin-mediated targeting enhanced the association of liposomes to HCT 116 cells by almost 5-fold. This could potentially allow for cancer cell-specific effects in vivo thereby minimizing any non-specific interactions of the liposomes with non-cancerous cells. Taken together, this study clearly shows that the combined inhibition of the PI3K and MEK pathways correlates with a significant anti-proliferative effect, due to cell-cycle regulation leading to the induction of apoptosis.

Dual Inhibition of MEK and PI3K Pathway in KRAS and BRAF Mutated Colorectal Cancers

Colorectal cancer (CRC) is a heterogeneous disease with multiple underlying causative genetic mutations. Genetic mutations in the phosphatidylinositol-3 kinase (PI3K) and the mitogen activated protein kinase (MAPK) pathways are frequently implicated in CRC. Targeting the downstream substrate MEK in these mutated tumors stands out as a potential target in CRC. Several selective inhibitors of MEK have entered clinical trial evaluation; however, clinical activity with single MEK inhibitors has been rarely observed and acquired resistance seems to be inevitable. Amplification of the driving oncogene KRAS(13D), which increases signaling through the ERK1/2 pathway, upregulation of the noncanonical wingless/calcium signaling pathway (Wnt), and coexisting PIK3CA mutations have all been implicated with resistance against MEK inhibitor therapy in KRAS mutated CRC. The Wnt pathway and amplification of the oncogene have also been associated with resistance to MEK inhibitors in CRCs harboring BRAF mutations. Thus, dual targeted inhibition of MEK and PI3K pathway effectors (mTOR, PI3K, AKT, IGF-1R or PI3K/mTOR inhibitors) presents a potential strategy to overcome resistance to MEK inhibitor therapy. Many clinical trials are underway to evaluate multiple combinations of these pathway inhibitors in solid tumors.

Colorectal cancer models for novel drug discovery

INTRODUCTION

Despite increased screening rates and advances in targeted therapy, colorectal cancer (CRC) remains the third leading cause of cancer-related mortality. CRC models that recapitulate key features of human disease are essential to the development of novel and effective therapeutics. Classic methods of modeling CRC such as human cell lines and xenograft mice, while useful for many applications, carry significant limitations. Recently developed in vitro and in vivo models overcome some of these deficiencies and thus can be utilized to better model CRC for mechanistic and translational research.

AREAS COVERED

The authors review established models of in vitro cell culture and describe advances in organoid culture for studying normal and malignant intestine. They also discuss key features of classic xenograft models and describe other approaches for in vivo CRC research, including patient-derived xenograft, carcinogen-induced, orthotopic transplantation and transgenic mouse models. We also describe mouse models of metastatic CRC.

EXPERT OPINION

No single model is optimal for drug discovery in CRC. Genetically engineered models overcome many limitations of xenograft models. Three-dimensional organoids can be efficiently derived from both normal and malignant tissue for large-scale in vitro and in vivo (transplantation) studies and are thus a significant advance in CRC drug discovery.

Dual pharmacological targeting of the MAP kinase and PI3K/mTOR pathway in preclinical models of colorectal cancer

BACKGROUND

The activation of the MAPK and PI3K/AKT/mTOR pathways is implicated in the majority of cancers. Activating mutations in both of these pathways has been described in colorectal cancer (CRC), thus indicating their potential as therapeutic targets. This study evaluated the combination of a PI3K/mTOR inhibitor (PF-04691502/PF-502) in combination with a MEK inhibitor (PD-0325901/PD-901) in CRC cell lines and patient-derived CRC tumor xenograft models (PDTX).

MATERIALS AND METHODS

The anti-proliferative effects of PF-502 and PD-901 were assessed as single agents and in combination against a panel of CRC cell lines with various molecular backgrounds. Synergy was evaluated using the Bliss Additivity method. In selected cell lines, we investigated the combination effects on downstream effectors by immunoblotting. The combination was then evaluated in several fully genetically annotated CRC PDTX models.

RESULTS

The in vitro experiments demonstrated a wide range of IC50 values for both agents against a cell line panel. The combination of PF-502 and PD-901 demonstrated synergistic anti-proliferative activity with Bliss values in the additive range. As expected, p-AKT and p-ERK were downregulated by PF-502 and PD-901, respectively. In PDTX models, following a 30-day exposure to PF-502, PD-901 or the combination, the combination demonstrated enhanced reduction in tumor growth as compared to either single agent regardless of KRAS or PI3K mutational status.

CONCLUSIONS

The combination of a PI3K/mTOR and a MEK inhibitor demonstrated enhanced anti-proliferative effects against CRC cell lines and PDTX models.

CDKN2A(p16) and HRAS are frequently mutated in vulvar squamous cell carcinoma

BACKGROUND

Two etiologic pathways of vulvar cancer are known, a human papillomavirus (HPV)- and a TP53-associated route, respectively, but other genetic changes may also play a role. Studies on somatic mutations in vulvar cancer other than TP53 are limited in number and size. In this study, we investigated the prevalence of genetic mutations in 107 vulvar squamous cell carcinomas (VSCCs).

METHODS

A total of 107 paraffin-embedded tissue samples of primarily surgically treated VSCCs were tested for HPV infection and screened for mutations in 14 genes (BRAF, CDKN2A(p16), CTNNB1, FBXW7, FGFR2, FGFR3, FOXL2, HRAS, KRAS, NRAS, PIK3CA, PPP2R1A, PTEN, and TP53) using Sanger sequencing and mass spectrometry.

RESULTS

Mutations were detected in 7 genes. Of 107 VSCCs, 66 tumors (62%) contained at least one mutation (TP53=58, CDKN2A(p16)=14, HRAS=10, PIK3CA=7, PPP2R1A=3, KRAS=1, PTEN=1). Mutations occurred most frequently in HPV-negative samples. Five-year survival was significantly worse for patients with a mutation (47% vs 59%, P=.035), with a large effect from patients carrying HRAS-mutations.

CONCLUSION

Somatic mutations were detected in 62% of VSCCs. As expected, HPV infection and TP53-mutations play a key role in the development of VSCC, but CDKN2A(p16), HRAS, and PIK3CA-mutations were also frequently seen in HPV-negative patients. Patients with somatic mutations, especially HRAS-mutations, have a significantly worse prognosis than patients lacking these changes, which could be of importance for the development of targeted therapy.