Target In Human Cancer Research Articles

Subunits of human condensins are potential therapeutic targets for cancers

The main role of condensins is to regulate chromosome condensation and segregation during cell cycles. Recently, it has been suggested in the literatures that subunits of condensin I and condensin II are involved in some human cancers. This paper will first briefly discuss discoveries of human condensins, their components and structures, and their multiple cellular functions. This will be followed by reviews of most recent studies on subunits of human condensins and their dysregulations or mutations in human cancers. It can be concluded that many of these subunits have potentials to be novel targets for cancer therapies. However, hCAP-D2, a subunit of human condensin I, has not been directly documented to be associated with any human cancers to date. This review hypothesizes that hCAP-D2 can also be a potential therapeutic target for human cancers, and therefore that all subunits of human condensins are potential therapeutic targets for human cancers.

Challenges in validating candidate therapeutic targets in cancer.

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.

Indoleamine 2,3-dioxygenase (IDO1), PD-L1, and overall survival (OS) of patients diagnosed with esophageal cancer.

50 Background: Immune checkpoint inhibition of PD-L1 is emerging as an important therapeutic target for patients with advanced esophageal cancer. However, response rates to therapy remain low. IDO1 is a rate-limiting immunosuppressive enzyme that has emerged as an important immunotherapeutic target in human cancer. The role, expression pattern, and relevance of IDO1 in esophageal cancer are currently unknown. Here, we utilize gene expression analysis of the cancer genome atlas and quantitative immunohistochemistry (IHC) to understand whether IDO1 contributes to a poor esophageal cancer patient prognosis. Methods: mRNA expression was assessed using Hi-RNA sequencing in an esophageal squamous cell carcinoma (SCC) cohort of 87 patients and an adenocarcinoma (AC) cohort of 97 patients. Survival data was obtained from the Cancer Genome Atlas. Patient survival was analyzed by the Kaplan-Meier Method. IHC for a second cohort of 93 cases of esophageal SCC were stained for IDO1, PD-L1, and CD3ε, followed by light microscopic immunoscoring analysis. Correlation between markers was analyzed using Fisher’s exact test. Results: The median OS for high versus low IDO1 mRNA levels was 15.9 months vs 41.5 months, respectively (p =0.02) in the SCC cohort. The median OS was 20.1 months and 58.6 months in the high vs low IDO1 mRNA levels, respectively (p = 0.036) in the esophageal AC cohort. High co-expression for IDO1 and PD-L1 vs low co-expression of these markers, demonstrated a median OS of 15.1 months and 41.5 months, respectively, in the SCC cohort, and 13.7 months and 41.5 months, respectively, in the AC cohort. IHC for IDO1 SCC showed a significant correlation with PD-L1 (p = < 0.0001) and CD3ε (p = < 0.0001). PD-L1 expression also significantly correlated with CD3ε expression (p = < 0.0001). Conclusions: Esophageal cancer with high IDO1 and PD-L1 levels is associated with significantly decreased survival. The expression of IDO1 and PD-L1 is significantly enhanced by the coincident intratumoral increase of T cells. These data suggest that combinatorial approaches for combination therapies that simultaneously inhibit IDO1 and PD-(L)1 may enhance T-cell mediated control of esophageal cancer in patients.

Disruption of the anaphase-promoting complex confers resistance to TTK inhibitors in triple-negative breast cancer

TTK protein kinase (TTK), also known as Monopolar spindle 1 (MPS1), is a key regulator of the spindle assembly checkpoint (SAC), which functions to maintain genomic integrity. TTK has emerged as a promising therapeutic target in human cancers, including triple-negative breast cancer (TNBC). Several TTK inhibitors (TTKis) are being evaluated in clinical trials, and an understanding of the mechanisms mediating TTKi sensitivity and resistance could inform the successful development of this class of agents. We evaluated the cellular effects of the potent clinical TTKi CFI-402257 in TNBC models. CFI-402257 induced apoptosis and potentiated aneuploidy in TNBC lines by accelerating progression through mitosis and inducing mitotic segregation errors. We used genome-wide CRISPR/Cas9 screens in multiple TNBC cell lines to identify mechanisms of resistance to CFI-402257. Our functional genomic screens identified members of the anaphase-promoting complex/cyclosome (APC/C) complex, which promotes mitotic progression following inactivation of the SAC. Several screen candidates were validated to confer resistance to CFI-402257 and other TTKis using CRISPR/Cas9 and siRNA methods. These findings extend the observation that impairment of the APC/C enables cells to tolerate genomic instability caused by SAC inactivation, and support the notion that a measure of APC/C function could predict the response to TTK inhibition. Indeed, an APC/C gene expression signature is significantly associated with CFI-402257 response in breast and lung adenocarcinoma cell line panels. This expression signature, along with somatic alterations in genes involved in mitotic progression, represent potential biomarkers that could be evaluated in ongoing clinical trials of CFI-402257 or other TTKis.

Synthesis, Radiosynthesis and Metabolism of 131I-Y-c(CGRRAGGSC).

The formation of the complex interleukin-11(IL-11) and IL-11 receptor (IL-11R) is closely related with tumor progression. Binding of IL-11 to the IL-11 receptor α-chain (IL-11Rα) has been suggested as a target for human cancer. The cyclic peptide c(CGRRAGGSC) is a mimic of IL-11. To explore 131I-Y-c(CGRRAGGSC) synthesis and radiosynthesis, and metabolism in SKOV3 tumorbearing mice. In this study, 131I labeled c(CGRRAGGSC) was designed and characterized. For radiolabeling, tyrosine was used as a linker to connect c(CGRRAGGSC) and 131I. Balb/c nude mice bearing SKOV3 human ovarian carcinoma were used for in vivo studies. Uptake of 131I-cyclic nonapeptide by the tumor was visualized by single photon emission computerized tomography (SPECT). The entire labeling process, which took 15 min by chloramine-T method, resulted in a high labeling yield (93.03±6.78%), and high radiochemical purity (RCP) (>95%). SPECT imaging showed that accumulation of the probe in the tumor was close to background levels. In addition, biodistribution studies showed that the accumulation of 131I-Y-c(CGRRAGGSC) in normal mice was similar to that of Na131I. Tyrosine is a suitable chelating agent for the use of radioiodine labeling, however the bioactivity of the conjugate needs further investigation.

The E3 Ligase RING1 Targets p53 for Degradation and Promotes Cancer Cell Proliferation and Survival.

As a component of the transcriptional repression complex 1 (PRC1), the ring finger protein RING1 participates in the epigenetic regulation in cancer. However, the contributions of RING1 to cancer etiology or development are unknown. In this study, we report that RING1 is a critical negative regulator of p53 homeostasis in human hepatocellular and colorectal carcinomas. RING1 acts as an E3 ubiquitin (Ub) ligase to directly interact with and ubiquitinate p53, resulting in its proteasome-dependent degradation. The RING domain of RING1 was required for its E3 Ub ligase activity. RING1 depletion inhibited the proliferation and survival of the p53 wild-type cancer cells by inducing cell-cycle arrest, apoptosis, and senescence, with only modest effects on p53-deficient cells. Its growth inhibitory effect was partially rescued by p53 silencing, suggesting an important role for the RING1-p53 complex in human cancer. In clinical specimens of hepatocellular carcinoma, RING1 upregulation was evident in association with poor clinical outcomes. Collectively, our results elucidate a novel PRC1-independent function of RING1 and provide a mechanistic rationale for its candidacy as a new prognostic marker and/or therapeutic target in human cancer.Significance: These results elucidate a novel PRC1-independent function of RING1 and provide a mechanistic rationale for its candidacy as a new prognostic marker and/or therapeutic target in human cancer. Cancer Res; 78(2); 359-71. ©2017 AACR.

Therapeutic relevance of the PP2A-B55 inhibitory kinase MASTL/Greatwall in breast cancer.

PP2A is a major tumor suppressor whose inactivation is frequently found in a wide spectrum of human tumors. In particular, deletion or epigenetic silencing of genes encoding the B55 family of PP2A regulatory subunits is a common feature of breast cancer cells. A key player in the regulation of PP2A/B55 phosphatase complexes is the cell cycle kinase MASTL (also known as Greatwall). During cell division, inhibition of PP2A-B55 by MASTL is required to maintain the mitotic state, whereas inactivation of MASTL and PP2A reactivation is required for mitotic exit. Despite its critical role in cell cycle progression in multiple organisms, its relevance as a therapeutic target in human cancer and its dependence of PP2A activity is mostly unknown. Here we show that MASTL overexpression predicts poor survival and shows prognostic value in breast cancer patients. MASTL knockdown or knockout using RNA interference or CRISPR/Cas9 systems impairs proliferation of a subset of breast cancer cells. The proliferative function of MASTL in these tumor cells requires its kinase activity and the presence of PP2A-B55 complexes. By using a new inducible CRISPR/Cas9 system in breast cancer cells, we show that genetic ablation of MASTL displays a significant therapeutic effect in vivo. All together, these data suggest that the PP2A inhibitory kinase MASTL may have both prognostic and therapeutic value in human breast cancer.

Abstract 1127: Aberrant nuclear expression of GSK-3beta in human head and neck carcinoma

Abstract Background: Recurrent/metastatic head and neck squamous cell carcinoma (SCCHN) and salivary gland malignancies are difficult to treat with limited standard of care options at the present time. Glycogen Synthase Kinase-3beta (GSK-3beta), a serine/threonine protein kinase, has been implicated as a potential therapeutic target in human cancer. Our in vivo studies demonstrated that our novel GSK-3 inhibitors significantly potentiated the effects of conventional chemotherapy in patient-derived xenograft models of glioblastoma and breast cancer leading to regression of tumors. In order to develop a rationale to test our novel GSK-3 inhibitors in head and neck (H&N) malignancies, we evaluated the expression pattern of GSK-3beta in human H&N benign tissue and malignant tumors. Methods: We used immunohistochemical staining of H&N tumor tissue Microarray (TMA), 48 total cases (20 benign tissues, 28 malignant), to study the expression pattern of GSK-3beta. GSK-3beta nuclear accumulation was defined as positive staining of more than 50% of cancer cell nuclei throughout the tumor regardless of cytoplasmic staining. Results: Of the 20 malignant H&N samples (15 SCCHN, 1 nasopharyngeal and 5 other histology), 13 (65%) were found to have aberrant nuclear accumulation of GSK-3beta. Amongst SCCHN, 73% (11 of 15 samples) had aberrant nuclear accumulation of GSK-3beta. In contrast, none (0%) of the 11 benign non-salivary H&N tissue showed detectable expression of GSK-3beta. Of interest, 60% of salivary adenoid cystic carcinoma specimens and 44% of benign salivary gland tissue showed GSK-3beta expression. Conclusions: Our results demonstrate for the first time, that there is aberrant nuclear expression of GSK-3beta in SCCHN. This finding supports further exploring of our novel GSK-3beta inhibitor as a potential therapeutic target for recurrent/metastatic SCCHN and also, as a potential prognostic and predictive biomarker for risk of recurrent disease and chemo- or radio-resistance. Its role in salivary gland malignancies requires further studying. Citation Format: Maria Matsangou, Andrey Ugolkov, Timothy J. Taxter, Sandeep Samant, Andrew P. Mazar, Francis J. Giles. Aberrant nuclear expression of GSK-3beta in human head and neck carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1127. doi:10.1158/1538-7445.AM2017-1127

Abstract 5074: Therapeutic targeting of bromodomain and extra-terminal proteins degradation in triple-negative breast cancer

Abstract Triple negative breast cancer represents the most clinically challenging subtypes of breast cancer for which targeted therapeutics are still lacking. BET proteins have emerged as new therapeutic targets for human cancer and other diseases.We have developed a highly potent BET degrader, BETd-246, with an exceptional selectivity based upon a new class of BET inhibitor, BETi-211, and investigated its therapeutic potential and mechanisms of action in TNBC. BETd-246 induces degradation of BET proteins at low nanomolar concentrations within 1 hour, leading to potent anti-proliferative activity and strong apoptosis induction in the majority of TNBC cell lines, and is much more effective than the BETi-211 treatment. RNA-seq analysis reveals that degradation of BET proteins by BETd-246 elicits distinct transcriptional response than BET BD inhibition in TNBC cell lines. Transcriptomic analysis also shows a number of proliferation and survival-related genes were differentially regulated by BETd-246 and BETi-211 which were confirmed by quantitative RT-PCR. Mechanistically, down-regulation of MCL1 by BETd-246 plays a key role in the robust apoptosis induction in TNBC cell lines. In in vivo models, BETd-246 effectively degrades BET proteins and suppresses MCL1 expression in xenograft tumor tissues and exhibits a strong antitumor activity at well-tolerated dose-schedules in mice. Our data strongly suggest that targeting BET protein degradation is an exciting therapeutic strategy for TNBC. Citation Format: Longchuan Bai, Bing Zhou, Chao-Yie Yang, Jiao Ji, Donna McEachern, Sally Przybranowski, Shaomeng Wang. Therapeutic targeting of bromodomain and extra-terminal proteins degradation in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5074. doi:10.1158/1538-7445.AM2017-5074

LSD1 demethylates HIF1α to inhibit hydroxylation and ubiquitin-mediated degradation in tumor angiogenesis.

Lysine-specific demethylase 1 (LSD1), which has been considered as a potential therapeutic target in human cancer, has been known to regulate many biological functions through its non-histone substrates. Although LSD1-induced hypoxia-inducible factor alpha (HIF1α) demethylation has recently been proposed, the effect of LSD1 on the relationship between HIF1α post-translational modifications (PTMs) and HIF1α-induced tumor angiogenesis remains to be elucidated. Here, we identify a new methylation site of the HIF1α protein antagonized by LSD1 and the interplay between HIF1α protein methylation and other PTMs in regulating tumor angiogenesis. LSD1 demethylates HIF1α at lysine (K) 391, which protects HIF1α against ubiquitin-mediated protein degradation. LSD1 also directly suppresses PHD2-induced HIF1α hydroxylation, which has a mutually dependent interplay with Set9-mediated HIF1α methylation. Moreover, the HIF1α acetylation that occurs in a HIF1α methylation-dependent manner is inhibited by the LSD1/NuRD complex. HIF1α stabilized by LSD1 cooperates with CBP and MTA1 to enhance vascular endothelial growth factor (VEGF)-induced tumor angiogenesis. Thus, LSD1 is a key regulator of HIF1α/VEGF-mediated tumor angiogenesis by antagonizing the crosstalk between PTMs involving HIF1α protein degradation.

Targeting of human cancers by miRNAs delivered by mesenchymal stem cell derived microparticles.

e14062 Background: Recent data has shown that several oncogenic and tumor suppressor kinases that are deregulated in human cancers can be targeted via specific miRNA sequences. miRNAs can inhibit oncogenic kinase activity as well as upregulate tumor suppressor kinases in cancer cells, leading to inhibition of tumor processes such as invasion, migration and resistance to apoptosis. Examples include the inhibition of PLK1 activity that is overexpressed in breast, ovarian, pancreatic and colorectal cancers by the ectopic expression of miR-10b, miR-100 or miR-593, and the targeting of the increased FAK expression in breast cancer cells by miR-7. Methods: In this study, we have employed preclinical models of cancer disease and have utilized advanced genomics technologies in combination with innovative in vivo imaging techniques to conduct pharmacokinetics and pharmacodynamics studies as well as safety and efficacy studies in order to establish a mechanism of action and demonstrate that miRNA-loaded microparticles can interfere with tumor promoting kinase activity in vivo Results: Our results demonstrate that delivering specific miRNAs targeted against aberrant protein kinase activity may potentially be a novel approach to selectively inhibit cancer cell processes. Conclusions: We report the development of a new microRNA-based approach to target cancer cells by potentially interfering in multiple signaling pathways that are mediated by kinase-dependent mechanisms. We propose that therapeutic miRNA sequences can be delivered to cancer cells via microparticles (MPs) derived from umbilical cord mesenchymal stem cells (MSCs). The engineered MPs home selectively to tumor sites via specific chemokine receptors, fuse with the cell membrane and incorporate miRNA directly into the target cancer cells.

AKT Inhibition in Solid Tumors With AKT1 Mutations.

Purpose AKT1 E17K mutations are oncogenic and occur in many cancers at a low prevalence. We performed a multihistology basket study of AZD5363, an ATP-competitive pan-AKT kinase inhibitor, to determine the preliminary activity of AKT inhibition in AKT-mutant cancers. Patients and Methods Fifty-eight patients with advanced solid tumors were treated. The primary end point was safety; secondary end points were progression-free survival (PFS) and response according to Response Evaluation Criteria in Solid Tumors (RECIST). Tumor biopsies and plasma cell-free DNA (cfDNA) were collected in the majority of patients to identify predictive biomarkers of response. Results In patients with AKT1 E17K-mutant tumors (n = 52) and a median of five lines of prior therapy, the median PFS was 5.5 months (95% CI, 2.9 to 6.9 months), 6.6 months (95% CI, 1.5 to 8.3 months), and 4.2 months (95% CI, 2.1 to 12.8 months) in patients with estrogen receptor-positive breast, gynecologic, and other solid tumors, respectively. In an exploratory biomarker analysis, imbalance of the AKT1 E17K-mutant allele, most frequently caused by copy-neutral loss-of-heterozygosity targeting the wild-type allele, was associated with longer PFS (hazard ratio [HR], 0.41; P = .04), as was the presence of coincident PI3K pathway hotspot mutations (HR, 0.21; P = .045). Persistent declines in AKT1 E17K in cfDNA were associated with improved PFS (HR, 0.18; P = .004) and response ( P = .025). Responses were not restricted to patients with detectable AKT1 E17K in pretreatment cfDNA. The most common grade ≥ 3 adverse events were hyperglycemia (24%), diarrhea (17%), and rash (15.5%). Conclusion This study provides the first clinical data that AKT1 E17K is a therapeutic target in human cancer. The genomic context of the AKT1 E17K mutation further conditioned response to AZD5363.

CYP4A in tumor-associated macrophages promotes pre-metastatic niche formation and metastasis

Tumor-associated macrophages (TAMs) play an essential role in metastasis. However, what enables TAMs to have a superior capacity to establish pre-metastatic microenvironment in distant organs is unclear. Here we have begun to uncover the effects of cytochrome P450 (CYP) 4A in TAMs on lung pre-metastatic niche formation and metastasis. CYP4A+ TAM infiltration was positively associated with metastasis, pre-metastatic niche formation and poor prognosis in breast cancer patients. The pharmacological inhibition of CYP4A reduced lung pre-metastatic niche formation (evidenced by a decrease in vascular endothelial growth factor receptor 1 positive (VEGFR1+) myeloid cell recruitment and pro-metastatic protein expression) and metastatic burden, accompanied with TAM polarization away from the M2 phenotype in spontaneous metastasis models of 4T1 breast cancer and B16F10 melanoma. Co-implantation of 4T1 cells with CYP4A10high macrophages promoted lung pre-metastatic niche formation and metastasis. Depletion of TAMs disrupted lung pre-metastatic niches and thereby prevented metastasis. Treatment with the CM from CYP4A10high M2 macrophages (M2) increased pre-metastatic niche formation and metastatic burden in the lungs, whereas CYP4A inhibition attenuated these effects. In vitro TAM polarization away from the M2 phenotype induced by CYP4A inhibition decreased VEGFR1+ myeloid cell migration and fibronectin expression, accompanied with downregulation of STAT3 signaling. Conversely, overexpression of CYP4A or exogenous addition of 20-hydroxyeicosatetraenoic acid promoted M2 polarization and cytokine production of macrophages and thereby enhanced migration of VEGFR1+ myeloid cells, which were reversed by siRNA or pharmacological inhibition of STAT3. Importantly, a combined blocking M2 macrophage-derived factors TGF-β, VEGF and SDF-1 abolished VEGFR1+ myeloid cell migration and fibroblast activation induced by CYP4A. In summary, CYP4A in TAMs is crucial for lung pre-metastatic niche formation and metastasis, and may serve as a potential therapeutic target in human cancer.

Anti-helminthic niclosamide inhibits Ras-driven oncogenic transformation via activation of GSK-3.

Despite the importance of Ras oncogenes as a therapeutic target in human cancer, their ‘undruggable’ tertiary structures limit the effectiveness of anti-Ras drugs. Canonical Wnt signaling contributes to Ras activity by glycogen synthase kinase 3 (GSK-3)-dependent phosphorylation at the C-terminus and subsequent degradation. In the accompanying report, we show that the anti-helminthic niclosamide directly binds to GSK-3 and inhibits Axin functions in colon cancer cells, with reversion of Snail-mediated epithelial-mesenchymal transition. In this study, we report that niclosamide effectively suppresses Ras and nuclear NFAT activities regardless of the mutational status of Ras at nM levels. Mechanistically, niclosamide increased endogenous GSK-3 activity, shortening the half-life of mutant Ras. Further, niclosamide activates Raf-1 kinase inhibitory protein, a downstream target of Snail repressor. Niclosamide treatment attenuates Ras-induced oncogenic potential in vitro and in vivo. These findings provide a clinically available repositioned Ras inhibitor as well as a novel strategy for inhibiting the Ras via GSK-3.

Promising therapeutic role of miR-27b in tumor.

MicroRNAs are small nonprotein-encoding RNAs ranging from 18 to 25 nucleotides in size and regulate multiple biological pathways via directly targeting a variety of associated genes in cancers. MicroRNA-27b is a highly conserved MicroRNA throughout vertebrates and there are two homologs (hsa-miR-27a and hsa-miR-27b) in humans. MicroRNA-27b is an intragenic microRNA located on chromosome 9q22.1 within the C9orf3 gene, clustering with miR-23b and miR-24-1 in human. As a frequently dysregulated microRNA in human cancers, microRNA-27b could function as a tumor suppressor or an oncogenic microRNA. More and more studies indicate that microRNA-27b is involved in affecting various biological processes, such as angiogenesis, proliferation, metastasis, and drug resistance, and thus may act as a promising therapeutic target in human cancers. In this review, we discuss the role of microRNA-27b in detail and offer novel insights into molecular targeting therapy for cancers.

Long noncoding RNA activated by transforming growth factor-β promotes cancer development and is a prognostic marker in cervical cancer.

Long noncoding RNAs (lncRNAs) have been highlighted as crucial elements in cancer biology. LncRNA activated by transforming growth factor-β (ATB) was identified to promote the development of multiple cancers and may serve as a potential therapeutic target in human cancers. However, to the best of our knowledge, the functional role of ATB in cervical cancer has not been verified yet. The expression of lncRNA ATB was evaluated by quantitative reverse transcriptase-polymerase chain reaction assay in cervical cancer cell lines and clinical specimens. The clinical significance of ATB was statistically evaluated by analyzing the relationship between ATB overexpression and the clinicopathological characteristics of cervical cancer patients. Moreover, Kaplan-Meier analysis and log-rank test were conducted to investigate the role of ATB in the overall survival (OS) and progression-free survival (PFS) of cervical cancer patients or subgroup patients. Furthermore, univariate and multivariate analyses were adopted to identify the risk factors of OS and PFS of cervical cancer patients. LncRNA ATB was upregulated in cervical cancer cell lines and tissues (P < 0.05). Statistical analysis revealed that ATB overexpression was correlated with higher squamous cell carcinoma antigen level, larger tumor size, lymph node metastasis, and more advanced International Federation of Gynecology and Obstetrics (FIGO) stage of cervical cancer patients (P < 0.05). In addition, survival analysis showed that ATB upregulation was associated with poorer OS in cervical cancer patients and in subgroup patients without/with lymph node metastasis and with FIGO Stage I/II (P < 0.05). Furthermore, high ATB expression was defined as an independent risk factor of poorer OS and early recurrence of cervical cancer patients (P < 0.05). LncRNA ATB correlates with the malignant phenotypes and poor prognosis of cervical cancer. ATB may serve as a promising prognostic marker and therapeutic target of cervical cancer patients.

PRL2 Phosphatase Is a Key Mediator of Oncogenic Cytokine Signaling in Leukemia Stem Cells

Acute myeloid leukemia (AML) is a heterogeneous disease with multiple signaling pathways contributing to its pathogenesis. Mutations in receptor tyrosine kinase KIT and FLT3 are found in approximately 40% of AML patients and targeted therapies for inhibiting KIT and FLT3 have failed, thus new targets for therapeutic intervention need to be identified. The phosphatase of regenerating liver (PRL) family of phosphatases, consisting of PRL1, PRL2, and PRL3, represents an intriguing group of proteins being validated as biomarkers and therapeutic targets in human cancer. While PRL2 is highly expressed in some subtypes of human AML, including AML1-ETO+ AML and AML with mixed lineage leukemia (MLL) translocations, its role in AML is largely unknown. To determine the role of PRL2 in the pathogenesis of AML, we utilized two murine models of human AML induced by transducing mouse HSCs with AML1-ETO or MLL-AF9. We found that PRL2 is important for the progression and maintenance of leukemia induced by AML1-ETO or MLL-AF9 through enhancing leukemia stem cell (LSC) self-renewal. To elucidate the mechanisms by which PRL2 promotes LSC maintenance, we performed genome wide RNA-seq analysis of MLL-AF9+ LSCs. Gene Set Enrichment Analysis (GESA) indicates that PRL2 deficiency alters the MLL-AF9 signature essential for LSC self-renewal.We have recently identified PRL2 to be important for the proliferation and self-renewal of hematopoietic stem cells (HSCs) through the regulation of KIT signaling. Notably, PRL2 null hematopoietic progenitor cells showed decreased KIT phosphorylation as well as ERK phosphorylation following SCF stimulation, suggesting that PRL2 is important for KIT activation. Given that KIT inactivation could be mediated by removal from the cell surface and intracellular degradation, we reasoned that PRL2 may regulate KIT receptor internalization and stability. That was indeed the case. We found that the KIT protein half-life in PRL2 null hematopoietic progenitor cells (Kit+) was significantly decreased compared to WT cells. Furthermore, PRL2 null progenitor cells showed enhanced KIT ubiquitination compared to WT cells and less KIT was found on the surface of PRL2 null progenitor cells compared to WT cells following SCF stimulation. We also found that loss of PRL2 in human AML cells resulted in enhanced internalization of KIT. These observations demonstrate that PRL2 deficiency results in less KIT on the cell surface and a lower global KIT level in the cell.Upon SCF stimulation, KIT binds to and induces the phosphorylation of CBL proteins, which in turn act as E3 ligases, mediating the ubiquitination and degradation of KIT. To understand how PRL2 modulates the turnover of KIT in hematopoietic cells, we performed GST-pulldown assays and found that the substrate-trapping mutant PRL2/CS-DA showed an increased association with KIT and CBL compared to wild-type PRL2 in Kasumi-1 cells, suggesting that KIT and CBL may be PRL2 substrates. Furthermore, we found that PRL2/CS-DA mutant showed enhanced association with FLT3 and CBL compared to wild-type PRL2 in MV4-11 cells. Our data suggest that PRL2 dephosphorylates CBL and inhibits CBL activity toward KIT and FLT3, leading to sustained activation of downstream signaling pathways.To determine the functional significance of PRL2 in human AML with KIT and FLT3 mutations, we utilized two well-established murine model of myeloproliferative neoplasms (MPN) induced by KITD814V or FLT3-ITD. We found that loss of Prl2 decreased the ability of oncogenic KITD814V and FLT3-ITD to promote mouse hematopoietic stem and progenitor cell (HSPC) proliferation in vitro andthe development of MPN in vivo. Furthermore, we found that genetic and pharmacological inhibition of PRL2 decreased the proliferation and survival of human AML cells bearing KIT or FLT3 mutations.Taken together, we demonstrate that PRL2 promotes leukemia stem cell (LSC) self-renewal and maintenance through sustaining the activity of oncogenic KIT and FLT3 signals. Our findings suggest that pharmacological inhibition of PRL2 holds potential as a novel therapy for acute myeloid leukemia, and might also be applicable to the treatment of other human cancers. DisclosuresNo relevant conflicts of interest to declare.

Discovery of potent NEK2 inhibitors as potential anticancer agents using structure-based exploration of NEK2 pharmacophoric space coupled with QSAR analyses.

High expression of Nek2 has been detected in several types of cancer and it represents a novel target for human cancer. In the current study, structure-based pharmacophore modeling combined with multiple linear regression (MLR)-based QSAR analyses was applied to disclose the structural requirements for NEK2 inhibition. Generated pharmacophoric models were initially validated with receiver operating characteristic (ROC) curve, and optimum models were subsequently implemented in QSAR modeling with other physiochemical descriptors. QSAR-selected models were implied as 3D search filters to mine the National Cancer Institute (NCI) database for novel NEK2 inhibitors, whereas the associated QSAR model prioritized the bioactivities of captured hits for in vitro evaluation. Experimental validation identified several potent NEK2 inhibitors of novel structural scaffolds. The most potent captured hit exhibited an [Formula: see text] value of 237 nM.

PinX1: structure, regulation and its functions in cancer.

PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) is a novel cloned gene located at human chromosome 8p23, playing a vital role in maintaining telomeres length and chromosome stability. It has been demonstrated to be involved in tumor genesis and progression in most malignancies. However, some researches showed opposing molecular status of PinX1 gene and its expression patterns in several other types of tumors. The pathogenic mechanism of PinX1 expression in human malignancy is not yet clear. Moreover, emerging evidence suggest that PinX1 (especially its TID domain) might be a potential new target cancer treatment. Therefore, PinX1 may be a new potential diagnostic biomarker and therapeutic target for human cancers, and may play different roles in different human cancers. The functions and the mechanisms of PinX1 in various human cancers remain unclear, suggesting the necessity of further extensive works of its role in tumor genesis and progression.

152. Tumor Inhibition by Using Chitosan:siRNA PDGFR-β in Breast Cancer Model of Rat

Platelet-derived-growth factors (PDGFs) may represent a novel target in human cancer because they regulate many cellular processes, including cell proliferation, transformation, apoptosis and angiogenesis. PDGF-D's exert their cellular effects by two receptors PDGFR-α and PDGFR-β. Moreover PDGF ligands and receptors are proto-oncogenes that can be activated by various types of alternatives in cancer cells. Breast cancer is the most common and fatal type of cancer. The PDGF pathway is essential in tumor angiogenesis. It is known that the expression of PDGF receptors is altered and upregulated in breast cancer. Delivery is very important for success in gene therapy. Among the different non-viral gene delivery system, chitosan has very useful properties as a gene carrier. In this study; we investigated the effect of chitosan:siRNA complexes on tumor angiogenesis in breast tumor models of rats. Firstly chitosan:siRNA complexes (1/5-1/20 rate) targeting to PDGFR-β were prepared and characterized in vitro. Transfection efficiency of these nanoplexes in breast cancer cells such MCF-7, MDA-MB-231 and MDA-MB-435 was assayed. In in vitro transfection studies, 54%-65% of PDGFR-β inhibition was measured. Then these chitosan:siRNA complexes were injected intratumorally to tumor bearing Sprague Dawley rats. After tumor reached to constant size, complexes (20/1) were injected (40µg siRNA) and tumor volumes were measured periodically. After sacrification of animals, tissue and blood samples were taken and investigated histologically and immuno-histochemically. Expression levels of PDGFR-β determined by ELISA, mRNA levels were measured by RT-PCR also. Nanoplexes having 207 ± 3.5 nm size and 14.2 mV surface charge were used in this study. Tumor volume of nanoplex treated rats decreased at 92.49% at the end of the experiment (28th day). After free siRNA treatment, however, tumor volume increased very slowly until 21 days (68.1 % of decreasing value) then went up fastly. RT-PCR, Western-blot studies and immuno-histochemical data showed similarity with tumor volume measurements. Similar IFN response with tumor (untreated) was obtained after nanoplex administration. In conclusion, chitosan can be complexed with siRNA targeting PDGFR-β and chitosan:siRNA PDGFR-β nanocomplexes may be useful alternative in the treatment of breast cancer. The receptors of PDGF may be also suitable target in breast cancer.