Targeting of Lysosomes as a Therapeutic Target in Cancer.

Emerging Role of Semaphorins as Major Regulatory Signals and Potential Therapeutic Targets in Cancer

The 26S proteasome is a large intracellular adenosine 5'-triphosphate-dependent protease that identifies and degrades proteins tagged for destruction by the ubiquitin system. The orderly degradation of cellular proteins is critical for normal cell cycling and function, and inhibition of the proteasome pathway results in cell-cycle arrest and apoptosis. Dysregulation of this enzymatic system may also play a role in tumor progression, drug resistance, and altered immune surveillance, making the proteasome an appropriate and novel therapeutic target in cancer. Bortezomib (formerly known as PS-341) is the first proteasome inhibitor to enter clinical practice. It is a boronic aid dipeptide that binds directly with and inhibits the enzymatic complex. Bortezomib has recently shown significant preclinical and clinical activity in several cancers, confirming the therapeutic value of proteasome inhibition in human malignancy. It was approved in 2003 for the treatment of advanced multiple myeloma (MM), with approximately one third of patients with relapsed and refractory MM showing significant clinical benefit in a large clinical trial. Its mechanism of action is partly mediated through nuclear factor-kappa B inhibition, resulting in apoptosis, decreased angiogenic cytokine expression, and inhibition of tumor cell adhesion to stroma. Additional mechanisms include c-Jun N-terminal kinase activation and effects on growth factor expression. Several clinical trials are currently ongoing in MM as well as several other malignancies. This article discusses proteasome inhibition as a novel therapeutic target in cancer and focuses on the development, mechanism of action, and current clinical experience with bortezomib.

Lung cancer is the leading cause of cancer deaths worldwide. Since the number of patients responding well to current standard therapies is still small, further development of new anti-cancer drugs with minimum risk of adverse event is urgently awaited. To screen oncoantigens which could be used for the development of new diagnostic biomarkers and molecular targeted drugs, we have established a screening system as follows; i) To identify overexpressed genes in 120 lung cancers by genome-wide screening using the microarray representing 27,648 genes and pure populations of tumor cells taken from cancer tissues by laser microdissection, ii) To verify the candidate genes for their very low or absent expression in normal tissues by northern-blotting, iii) To validate the clinicopathological significance of their expression with tissue microarray covering hundreds of archived lung cancers, iv) To verify whether the target genes are essential for the growth or survival of cancer cells by RNAi and cell growth assays. During this process, we selected dozens of druggable oncoproteins with various enzymatic activities, and identified overexpression of Serine/Threonine phosphatase LAPP1 (lung cancer-associated protein phosphatase 1) in the majority of lung cancers and its scarce expression in normal tissues except testis. Strong LAPP1 expression was an independent prognostic factor for lung cancer patients who underwent curative surgery (P<0.0001). We identified EF-1δ (a cadmium-responsive proto-oncogene) as a LAPP1-interacting protein that was also over-expressed in cancer cells. Knock-down of LAPP1 or EF-1δ expression by siRNAs inhibited cell growth, whereas exogenous expression of LAPP1 in EF-1δ(+) cells enhanced the dephosphorylation of EF-1δ(+), and subsequent increase in the levels of active phospho-AKT. Inhibition of interaction between LAPP1 and EF-1δ by a cell-permeable peptide corresponding to a leucine zipper motif in EF-1δ, resulted in the destabilization of EF-1δ and inhibited cancer cell growth and invasion. LAPP1 is likely to be a prognostic biomarker and a potential therapeutic target for lung cancer. Citation Format: Yataro Daigo, Atsushi Takano, Yusuke Nakamura. Characterization of serine/threonine phosphatase LAPP1 as a diagnostic and therapeutic target for lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 690. doi:10.1158/1538-7445.AM2015-690

Background and aim - Through our functional proteomics screening efforts, we recently identified hornerin (HRNR) as a protein expressed on the cell surface of both cancer and cancer blood vessels. Hornerin is a member of the S100 family of proteins, a group of calcium binding proteins involved in the maintenance of calcium homeostasis, as well other fundamental cellular processes and signaling cascades. Several family members have been implicated in a variety of cancers, with evidence demonstrating that altered expression of S100 proteins was associated with tumor progression and prognosis. Therefore, we hypothesized that HRNR may represent an important therapeutic target for cancer. Method - De-identified human tumor microarray specimens underwent standard immunohistochemistry (IHC) procedure to determine HRNR expression in various type of cancer. Standard westernblot were also used to assess HRNR expression in eleven epithelial PDAC cell lines. Analysis of HRNR expression in cellular compartments was performed after differential centrifugation of PDAC cell lysates. Cell surface HRNR expression was further validated by immunofluorescence on non-permeabilized cells. Additionally, cells from 4 different renal carcinoma (RCC) PDX models were infected with human HRNR shRNA lentiviral particles in order to silence HRNR expression. Those cells were then injected subcutaneously into immunocompromised nude mice and assessed for tumor growth. Molecular mechanism of HRNR was evaluated via western blot. Effect of blocking HRNR on cancer in vitro and in vivo using a HRNR specific antibody was determined. Results - Based on IHC scoring, HRNR expression has been observed in twenty-one different types of cancer among which are PDAC and renal cancer. Expression of HRNR in tumor cells and on the cell surface of cancer was confirmed through cell fractionation and immunofluorescence. Validation of HRNR as an important cancer therapeutic target was demonstrated through siRNA knockout studies. PDX models of renal cancer that were devoid of HRNR expression were unable to form tumors in vivo. As members of the S100 family have been shown to activate signaling pathways important for proliferation and migration, we hypothesized that HRNR would be able to activate proteins in these signaling cascades. Western blot analysis of cells treated with recombinant HRNR revealed the activation of AKT and ERK and the stabilization of EGFR. Therefore, we evaluated the efficacy of a HRNR targeted antibody as a therapeutic. Treatment with the HRNR targeted antibody resulted in a decrease in cell proliferation and complete cell death that was HRNR specific. Conclusion - HRNR plays an important role in cancer and represents a novel therapeutic target. Citation Format: Julien Dimastromatteo, Kimberly A. Kelly. Hornerin as a novel therapeutic target for pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3049.

In the last few decades, the endocannabinoid system has attracted a great deal of interest in terms of its applications to clinical medicine. In particular, its applications in cancer probably represent one of the therapeutic areas with most promise. On the one hand, expression of the endocannabinoid system is altered in numerous types of tumours, compared to healthy tissue, and this aberrant expression has been related to cancer prognosis and disease outcome, suggesting a role of this system in tumour growth and progression that depends on cancer type. On the other hand, cannabinoids exert an anticancer activity by inhibiting the proliferation, migration and/or invasion of cancer cells and also tumour angiogenesis. However, some cannabinoids, at lower concentrations, may increase tumour proliferation, inducing cancer growth. Enough data has been provided to consider the endocannabinoid system as a new therapeutic target in cancer, although further studies to fully establish the effect of cannabinoids on tumour progression are still needed.

Over 85% of colorectal cancers is driven by aberrations in the Wnt-signaling pathway. Thus, identifying druggable targets in this pathway can be beneficial for optimizing colorectal cancer treatment. Within this context, a member of the RNA helicase gene family, DDX3, has been identified to exhibit oncogenic properties in breast and lung carcinomas as well as medulloblastomas. Notably, recent studies have identified DDX3 as a multilevel activator of Wnt-signaling in both normal and transformed cells without activating mutations in the Wnt signaling pathway. In this study, we evaluated whether DDX3 also plays a role in the constitutionally activated Wnt-signaling that drives colorectal cancer and therefore could be a potential therapeutic target in this cancer type. To determine if DDX3 is expressed in colorectal cancers, we immunohistochemically stained a cohort of 303 Dutch and German colorectal cancer patients. We found 40.4% of these tumors to overexpress DDX3 in comparison to the surrounding normal tissue. DDX3 expression was found predominantly in the cytoplasm and occasionally in the nucleus. High cytoplasmic DDX3 expression correlated with nuclear Beta-catenin expression, a marker of activated Wnt-signaling. The presence of nuclear DDX3 expression correlated with shorter overall survival (HR = 2.38, 95% CI 1.45-3.93, p < 0.001). Functionally, we validated these findings in vitro and found that inhibition of DDX3 with siRNA resulted in reduced proliferation and a G1-arrest in the HCT116 and HT29 colorectal cancer cell lines. This finding further supports the potential oncogenic role of DDX3 in colorectal cancer. With respect to targeting DDX3, we developed a small molecule inhibitor of DDX3, referred to as RK-33. RK-33 is designed to bind to the ATP-binding site of DDX3 and abrogate its functional activity. As proof of principle, we demonstrated that RK-33 binds preferentially to DDX3 and not to DDX5 and DDX17, other members of the RNA helicase family. Moreover, RK-33 inhibited the helicase activity in an in vitro assay. Furthermore, treatment of colorectal cancer cell lines and patient derived 3D- tumor cell cultures indicated that RK-33 inhibits growth and promotes cell death with IC-50 values ranging from 2.5 to 8 uM. To further elucidate the mechanism of RK-33, we studied if inhibition of DDX3 with RK-33 could cause inhibition of Wnt-signaling in colorectal cancer cell lines. Treatment with RK-33 indeed resulted in reduced TCF-reporter activity and lowered the mRNA expression levels of the Wnt-signaling downstream target genes AXIN-2, C-MYC, CCND1 and BIRC5A. Overall, we conclude that DDX3 has an oncogenic role in colorectal cancer. Inhibition of DDX3 with the small molecule inhibitor RK-33 causes potent inhibition of Wnt-signaling and is a promising future treatment strategy in colorectal cancer. Citation Format: Marise R. Heerma van Voss, Farhad Vesuna, Kari Trumpi, Justin Brilliant, Liudmila L. Kodach, Folkert H.M. Morsink, G. Johan A. Offerhaus, Horst Buerger, Elsken van der Wall, Paul J. van Diest, Venu Raman. Identification of the DEAD box RNA helicase DDX3 as a therapeutic target in colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3570. doi:10.1158/1538-7445.AM2015-3570

Phosphorylation of Ephrin-B1 Regulates Dissemination of Gastric Scirrhous Carcinoma

Oncogenicity of lncRNA FOXD2-AS1 and its molecular mechanisms in human cancers

Urokinase type plasminogen activator (uPA) is a 53-kDa serine protease initially synthesized as a catalytically inactive single chain polypeptide. Inactive-uPA is subject to proteolytic cleavage, which results in the two-chain active protein. uPA plays key roles in the enhancement of cell malignancy during tumor progression. The main objective of this review was to analyze and describe the main molecular mechanisms involved in the regulation of uPA expression in cancer Methods: Searching literature to evaluate and define the relevant information regarding to the state of the arts on uPA functionality and regulation in cancer, including intracellular signaling regulation, tumor progression, invasion, epigenetic mechanism, and finally uPA as therapeutic target in cancer. uPA expression is dysregulated in tumor cells, which results in increased cellular invasion capacities reflecting changes in uPA activity and expression during tumor progression. In this review we discuss the main aspects of uPA, from its capacity to activate plasminogen to plasmin, to the main intracellular signal transduction mechanisms as well as the epigenetic mechanisms involved in the regulation of uPA expression, including regulation by microRNAs. As well as, the current therapeutic methodologies targeting uPA for cancer treatment are described. Although, uPA is dysregulate in tumor progression, its expression is finely regulated at both enzymatic activity and at protein expression as well, which allow cancer cells efficiently survive, proliferate, and spread into neighbouring tissues and distant organs. Moreover, since uPA implications in tumor development and cancer cell invasion and metastasis, it is an attractive target for cancer chemotherapies.

The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. Cancer Res; 77(2); 434-47. ©2016 AACR.

<div>Abstract<p>The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. <i>Cancer Res; 77(2); 434–47. ©2016 AACR</i>.</p></div>

<div>Abstract<p>The polo family serine threonine kinase Plk4 has been proposed as a therapeutic target in advanced cancers based on increased expression in primary human cancers, facilitation of tumor growth in murine xenograft models, and centrosomal amplification induced by its overexpression. However, both the causal link between these phenomena and the feasibility of selective Plk4 inhibition remain unclear. Here we characterize Plk4-dependent cancer cell migration and invasion as well as local invasion and metastasis of cancer xenografts. Plk4 depletion suppressed cancer invasion and induced an epithelial phenotype in poorly differentiated breast cancer cells. In an unbiased BioID screen for Plk4 interactors, we identified members of the Arp2/3 complex and confirmed a physical and functional interaction between Plk4 and Arp2 in mediating Plk4-driven cancer cell movement. This interaction is mediated through the Plk4 Polo-box 1-Polo-box 2 domain and results in phosphorylation of Arp2 at the T237/T238 activation site, which is required for Plk4-driven cell movement. Our results validate Plk4 as a therapeutic target in cancer patients and reveal a new role for Plk4 in regulating Arp2/3-mediated actin cytoskeletal rearrangement. <i>Cancer Res; 77(2); 434–47. ©2016 AACR</i>.</p></div>

The majority of new drug approvals for cancer are based on existing therapeutic targets. One approach to the identification of novel targets is to perform high-throughput RNA interference (RNAi) cellular viability screens. We describe a novel approach combining RNAi screening in multiple cell lines with gene expression and genomic profiling to identify novel cancer targets. We performed parallel RNAi screens in multiple cancer cell lines to identify genes that are essential for viability in some cell lines but not others, suggesting that these genes constitute key drivers of cellular survival in specific cancer cells. This approach was verified by the identification of PIK3CA, silencing of which was selectively lethal to the MCF7 cell line, which harbours an activating oncogenic PIK3CA mutation. We combined our functional RNAi approach with gene expression and genomic analysis, allowing the identification of several novel kinases, including WEE1, that are essential for viability only in cell lines that have an elevated level of expression of this kinase. Furthermore, we identified a subset of breast tumours that highly express WEE1 suggesting that WEE1 could be a novel therapeutic target in breast cancer. In conclusion, this strategy represents a novel and effective strategy for the identification of functionally important therapeutic targets in cancer.

The chromatin remodeling SWI/SNF complex is mutated in 20% of all cancers and ARID1A is the most frequently mutated subunit. However, the tumor suppressive functions of ARID1A are not fully understood and no feasible therapeutic strategies are available for ARID1A-mutant cancers. Recent studies found that loss of ARID1A is associated with increased phosphorylation of AKT. We found that from a study that analyzed data from Project Achilles, a broad shRNA screening project, PIK3CA is the number 2 gene essential for survival of ARID1A-mutant cell lines compared to ARID1A-wildtype cell lines (P = 7.37 × 10-6, FDR < 0.001). Based on these findings, we hypothesized that the PI3K pathway is a potential therapeutic target in ARID1A-mutant cancers. We analyzed the Cancer Genome Atlas (TCGA) datasets and found that mutations in the PI3K pathway co-occur with ARID1A mutations. In addition, the number of co-existing PI3K pathway mutations in the same sample is higher when ARID1A is mutated. We knocked down PIK3CA in ARID1A-wildtype cells (RMG1 and OVCAR3) and ARID1A-mutant cells (OVAS and HCH-1). We found that proliferation was impaired more profoundly in ARID1A-mutant cells. Interestingly, HCH-1 cells are wildtype in PIK3CA, PTEN, PIK3R1 and KRAS, but are still sensitive to PIK3CA depletion. For an unbiased approach, we analyzed the Genomics of Drug Sensitivity in Cancer datasets, which contain drug responses of a large cancer cell line panel to 138 anti-cancer drugs. We compared the drug responses of 49 cell lines harboring inactivating ARID1A-mutations with 266 ARID1A-wildtype cell lines. We found that the presence of inactivating ARID1A mutations is highly associated with sensitivity to mTOR inhibitor AZD8055 (ranked 2nd, P = 2.00 × 10-3) and AKT inhibitor MK2206 (ranked 4th, P = 7.98 × 10-3). This association is still significant for MK2206 when we removed cell lines with PIK3CA, KRAS, PTEN, PIK3R1 and TSC1 alterations (P = 1.32 × 10-2). Finally, we investigated how ARID1A loss can directly increase PI3K/mTOR activity. Using microarray analysis, we found that knockdown of ARID1A up-regulated MYC and MYC target genes, including SLC7A5, an amino-acid transporter required for mTOR activation. Analysis of TCGA datasets showed that MYC amplification and ARID1A mutations are mutual exclusive events, suggesting that overexpression of MYC and loss of ARID1A may converge on the same pathway. In conclusion, we found that ARID1A-mutant cells are highly sensitive to PI3K/mTOR inhibition. Although ARID1A mutations frequently co-occur with PI3K pathway mutations, it is not the sole explanation of this specific sensitivity. ARID1A loss may increase mTOR signaling through MYC target gene SLC7A5. However, increase in PI3K/mTOR activity maybe a long term effect of ARID1A loss. Together, our data identified PI3K/mTOR signaling is essential for survival of ARID1A-mutant cancers and PI3K/mTOR inhibitors can be used as therapeutic strategies. Citation Format: Suet-Yan Kwan, Daisy I. Izaguirre, Xuanjin Cheng, Suet-Ying Kwan, Yvonne TM Tsang, Hoi-Shan Kwan, Kwong-Kwok Wong. The PI3K/mTOR pathway is a potential therapeutic target in cancers with ARID1A mutations. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4697. doi:10.1158/1538-7445.AM2015-4697

More than 30 published articles have suggested that a protein kinase called MELK is an attractive therapeutic target in human cancer, but three recent reports describe compelling evidence that it is not. These reports highlight the caveats associated with some of the research tools that are commonly used to validate candidate therapeutic targets in cancer research.