Designing a broad-spectrum integrative approach for cancer prevention and treatment

Targeted therapies and the consequent adoption of "personalized" oncology have achieved notable successes in some cancers; however, significant problems remain with this approach. Many targeted therapies are highly toxic, costs are extremely high, and most patients experience relapse after a few disease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistant immortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are not reliant upon the same mechanisms as those which have been targeted). To address these limitations, an international task force of 180 scientists was assembled to explore the concept of a low-toxicity "broad-spectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspects of relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a wide range of high-priority targets (74 in total) that could be modified to improve patient outcomes. For these targets, corresponding low-toxicity therapeutic approaches were then suggested, many of which were phytochemicals. Proposed actions on each target and all of the approaches were further reviewed for known effects on other hallmark areas and the tumor microenvironment. Potential contrary or procarcinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixed evidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of the relationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. This novel approach has potential to be relatively inexpensive, it should help us address stages and types of cancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for future research is offered.

Cholesterol Depletion Alters Cardiomyocyte Subcellular Signaling and Increases Contractility

Membrane cholesterol levels play an important factor in regulating cell function. Sarcolemmal cholesterol is concentrated in lipid rafts and caveolae, which are flask-shaped invaginations of the plasma membrane. The scaffolding protein caveolin permits the enrichment of cholesterol in caveolae, and caveolin interactions with numerous proteins regulate their function. The purpose of this study was to determine whether acute reductions in cardiomyocyte cholesterol levels alter subcellular protein kinase activation, intracellular Ca²⁺ and contractility. Methods: Ventricular myocytes, isolated from adult Sprague Dawley rats, were treated with the cholesterol reducing agent methyl-β-cyclodextrin (MβCD, 5 mM, 1 hr, room temperature). Total cellular cholesterol levels, caveolin-3 localization, subcellular, ERK and p38 mitogen activated protein kinase (MAPK) signaling, contractility, and [Ca²⁺]i were assessed. Results: Treatment with MβCD reduced cholesterol levels by ~45 and shifted caveolin-3 from cytoskeleton and triton-insoluble fractions to the triton-soluble fraction, and increased ERK isoform phosphorylation in cytoskeletal, cytosolic, triton-soluble and triton-insoluble membrane fractions without altering their subcellular distributions. In contrast the primary effect of MβCD was on p38 subcellular distribution of p38α with little effect on p38 phosphorylation. Cholesterol depletion increased cardiomyocyte twitch amplitude and the rates of shortening and relaxation in conjunction with increased diastolic and systolic [Ca²⁺]i. Conclusions: These results indicate that acute reductions in membrane cholesterol levels differentially modulate basal cardiomyocyte subcellular MAPK signaling, as well as increasing [Ca²⁺]_i and contractility.

Measurement of 1,5-anhydroglucitol in blood and saliva: from non-targeted metabolomics to biochemical assay

Background

Diabetes testing using saliva, rather than blood and urine, could facilitate diabetes screening in public spaces. We previously identified 1,5-anhydro-d-glucitol (1,5-AG) in saliva as a diabetes biomarker. The Glycomark™ assay kit is FDA approved for 1,5-AG measurement in blood. Here we evaluated its applicability for 1,5-AG quantification in saliva.

Methods

Using pooled saliva samples, we validated Glycomark™ assay use with a RX Daytona⁺ clinical chemistry analyser. We then used this set-up to analyse 82 paired blood and saliva samples from a diabetes case–control study, for which broad mass spectrometry-based characterization of the blood and saliva metabolome was also available. Osmolality was measured to account for potential variability in saliva samples.

Results

The technical variability of the read-outs for the pooled saliva samples (CV = 2.05 %) was comparable to that obtained with manufacturer-provided blood surrogate quality controls (CV = 1.38–1.8 %). We found a high correlation between Glycomark assay and mass spectrometry measurements of serum 1,5-AG (r² = 0.902), showing reproducibility of the non-targeted metabolomics results. The significant correlation between the osmolality measurements performed at two independent platforms with the time interval of 2 years (r² = 0.887), also indicates the sample integrity. The assay read-out for saliva was not correlated with the mass spectrometry-based 1,5-AG saliva measurements. Comparison with the full saliva metabolome revealed a high correlation of the saliva assay read-outs with galactose.

Conclusions

Glycomark™ assay read-outs for saliva were stable and replicable. However, the signal was dominated by galactose, which is biochemically similar to 1,5-AG and absent in blood. Adapting the 1,5-AG kit for saliva analysis will require enzymatic depletion of galactose. This should be feasible, since the assay already includes a similar step for glucose depletion from blood samples.

Bortezomib-mediated downregulation of S-phase kinase protein-2 (SKP2) causes apoptotic cell death in chronic myelogenous leukemia cells

Background

Proteasome inhibitors are attractive cancer therapeutic agents because they can regulate apoptosis-related proteins. Bortezomib also known as Velcade^®, a proteasome inhibitor that has been approved by the food and drug administration for treatment of patients with multiple myeloma, and many clinical trials are ongoing to examine to the efficacy of bortezomib for the treatment of other malignancies. Bortezomib has been shown to induce apoptosis and inhibit cell growth of many cancer cells. In current study, we determine whether bortezomib induces cell death/apoptosis in CML.

Methods

Cell viability was measured using MTT assays. Apoptosis was measured by annexin V/PI dual staining and DNA fragmentation assays. Immunoblotting was performed to examine the expression of proteins. Colony assays were performed using methylcellulose.

Results

Treatment of CML cells with bortezomib results in downregulation of S-phase kinase protein 2 (SKP2) and concomitant stabilization of the expression of p27Kip1. Furthermore, knockdown of SKP2 with small interference RNA specific for SKP2 caused accumulation of p27Kip1. CML cells exposed to bortezomib leads to conformational changes in Bax protein, resulting in loss of mitochondrial membrane potential and leakage of cytochrome c to the cytosol. In the cytosol, cytochrome c causes sequential activation of caspase-9, caspase-3, PARP cleavage and apoptosis. Pretreatment of CML cells with a universal inhibitor of caspases, z-VAD-fmk, prevents bortezomib-mediated apoptosis. Our data also demonstrated that bortezomib treatment of CML downregulates the expression of inhibitor of apoptosis proteins. Finally, inhibition of proteasome pathways by bortezomib suppresses colony formation ability of CML cells.

Conclusions

Altogether, these findings suggest that bortezomib suppresses the cell proliferation via induction of apoptosis in CML cells by downregulation of SKP2 with concomitant accumulation of p27Kip1, suggesting that proteasomal pathway may form novel therapeutic targets for better management of CML.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0823-y) contains supplementary material, which is available to authorized users.

F-BOX proteins in cancer cachexia and muscle wasting: Emerging regulators and therapeutic opportunities

Cancer cachexia is a debilitating metabolic syndrome accounting for fatigue, an impairment of normal activities, loss of muscle mass associated with body weight loss eventually leading to death in majority of patients with advanced disease. Cachexia patients undergoing skeletal muscle atrophy show consistent activation of the SCF ubiquitin ligase (F-BOX) family member Atrogin-1 (also known as MAFBx/FBXO32) alongside the activation of the muscle ring finger protein1 (MuRF1). Other lesser known F-BOX family members are also emerging as key players supporting muscle wasting pathways. Recent work highlights a spectrum of different cancer signaling mechanisms impacting F-BOX family members that feed forward muscle atrophy related genes during cachexia. These novel players provide unique opportunities to block cachexia induced skeletal muscle atrophy by therapeutically targeting the SCF protein ligases. Conversely, strategies that induce the production of proteins may be helpful to counter the effects of these F-BOX proteins. Through this review, we bring forward some novel targets that promote atrogin-1 signaling in cachexia and muscle wasting and highlight newer therapeutic opportunities that can help in the better management of patients with this devastating and fatal disorder.

Broad targeting of resistance to apoptosis in cancer

Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer.

Targeting the Nuclear Export Protein XPO1/CRM1 Reverses Epithelial to Mesenchymal Transition

Here we demonstrate for the first time that targeted inhibition of nuclear exporter protein exportin 1 (XPO1) also known as chromosome maintenance region 1 (CRM1) by Selective Inhibitor of Nuclear Export (SINE) compounds results in reversal of EMT in snail-transduced primary human mammary epithelial cells (HMECs). SINE compounds selinexor (KPT-330) and KPT-185, leptomycin B (LMB as +ve control) but not KPT-301 (-ve control) reverse EMT, suppress mesenchymal markers and consequently induce growth inhibition, apoptosis and prevent spheroid formation. SINE treatment resulted in nuclear retention of snail regulator FBXL5 that was concurrent with suppression of snail and down-regulation of mesenchymal markers. FBXL5 siRNA or transfection with cys528 mut-Xpo1 (lacking SINE binding site) markedly abrogated SINE activity highlighting an XPO1 and FBXL5 mediated mechanism of action. Silencing XPO1 or snail caused re-expression of FBXL5 as well as EMT reversal. Pathway analysis on SINE treated HMECs further verified the involvement of additional F-Box family proteins and confirmed the suppression of snail network. Oral administration of selinexor (15 mg/kg p.o. QoDx3/week for 3weeks) resulted in complete cures (no tumor rebound at 120 days) of HMLER-Snail xenografts. These findings raise the unique possibility of blocking EMT at the nuclear pore.

Airway surface liquid volume expansion induces rapid changes in amiloride-sensitive Na+ transport across upper airway epithelium-Implications concerning the resolution of pulmonary edema

During airway inflammation, airway surface liquid volume (ASLV) expansion may result from the movement of plasma proteins and excess liquid into the airway lumen due to extravasation and elevation of subepithelial hydrostatic pressure. We previously demonstrated that elevation of submucosal hydrostatic pressure increases airway epithelium permeability resulting in ASLV expansion by 500 μL cm⁻² h⁻¹. Liquid reabsorption by healthy airway epithelium is regulated by active Na⁺ transport at a rate of 5 μL cm⁻² h⁻¹. Thus, during inflammation the airway epithelium may be submerged by a large volume of luminal liquid. Here, we have investigated the mechanism by which ASLV expansion alters active epithelial Na⁺ transport, and we have characterized the time course of the change. We used primary cultures of tracheal airway epithelium maintained under air interface (basal ASLV, depth is 7 ± 0.5 μm). To mimic airway flooding, ASLV was expanded to a depth of 5 mm. On switching from basal to expanded ASLV conditions, short-circuit current (I_sc, a measure of total transepithelial active ion transport) declined by 90% with a half-time (t_1/2) of 1 h. 24 h after the switch, there was no significant change in ATP concentration nor in the number of functional sodium pumps as revealed by [³H]-ouabain binding. However, amiloride-sensitive uptake of ²²Na⁺ was reduced by 70% upon ASLV expansion. This process is reversible since after returning cells back to air interface, I_sc recovered with a t_1/2 of 5–10 h. These results may have important clinical implications concerning the development of Na⁺ channels activators and resolution of pulmonary edema.

Abstract 1424: F-box protein fbxl5 nuclear retention by specific inhibitors of nuclear export induces snail ubiquitination leading to reversal of EMT

Background: FBXL5 belonging to SKP1-cullin 1-F-box protein E3 ligase complexes (F-BOX) been shown to promote snail nuclear ubiquitination thereby regulating snail induced epithelial-to-mesenchymal transition (EMT) processes. However, cancer associated enhancement in the nuclear exporter Exportin1 (Xpo1) expression results in nuclear expulsion of FBXL5 causing snail stability and EMT. Here we demonstrate that Xpo1 inhibition by specific inhibitors of nuclear export (SINEs) results in nuclear retention FBXL5, causing nuclear degradation of SNAIL leading to reversal of mesenchymal phenotype to epithelial in HMLE-SNAIL models.

Methods: Molecular assays (MTT, Annexin V FITC, Histone DNA ELISA, Spheroid formation, Western Blotting, Confocal microscopy, Co-immunoprecipitation, Xpo1 site directed mutagenesis) and computational techniques (gene expression microarray, pathway analysis) were used. In vivo activity of Selinexor was evaluated in xenografts developed from HMLE-SNAIL cells in ICR-SCID mice.

Results: SINEs [Selinexor (KPT-330) and +ve controls KPT-185 and Leptomycin B (LMB)) not KPT-301 (-ve control)] reverse mesenchymal morphology, induce growth inhibition and apoptosis in HMLE-SNAIL and Kras-HMLE-SNAIL cells and prevent spheroid formation (IC50s ∼150 nM). Immunofluorescence analysis demonstrated that SINE treatment resulted in nuclear retention of FBXL5 that was concurrent with nuclear degradation of snail. Co-immunoprecipitation experiments showed nuclear ubiquitination of snail by SINEs. Western blotting analysis verified nuclear enhancement of FBXL5 that was consistent with down-regulation of EMT markers (Vimentin, snail, EpCAM) and enhancement of E-Cadherin. SiRNA against FBXL5 or transfecting cells with cys528 mut-Xpo1 that lacks SINE binding site markedly abrogated SINE activity thereby verifying the Xpo1 and FBXL5 mediated mechanisms of action. Pathways analysis of quadruplet microarray expression arrays from SINE treated HMLE-SNAIL cells demonstrated differential expression of F-Box family proteins [FBXO2, FBXL17, FBXO33, FBXO37, FBXW7 (p<0.001)] and suppression of snail network. Most significantly, oral administration of SINE (Selinexor at 15 mg/kg three times a week for three weeks) resulted in complete cure of HMLE-SNAIL tumors (tumor free at 120 days). SINE exposed animals showed normal spleen size and morphology in comparison to control animals that showed spleen enlargement (p<0.001). Quantitative sandwich ELISA of spleen tissue extracts showed suppression of snail expression in SINE treatment animals.

Conclusion: This is the first proof of concept study demonstrating that targeted inhibition of Xpo1 can inhibit EMT through nuclear retention of FBOX protein, particularly FBXL5 and consequent snail ubiquitination and degradation. Our findings open a unique possibility to block EMT at the nuclear pore.

Citation Format: Irfana Muqbil, Amro Aboukameel, Yosef Landesman, Michael Kauffman, Sharon Shacham, Ramzi M. Mohammad, Asfar S. Azmi. F-box protein fbxl5 nuclear retention by specific inhibitors of nuclear export induces snail ubiquitination leading to reversal of EMT. [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 1424. doi:10.1158/1538-7445.AM2015-1424

Abstract 1756: Preclinical activity in non-Hodgkin's lymphoma of Selinexor, a selective inhibitor of nuclear export (SINE), is enhanced through combination with standard-of-care therapies

The nuclear export protein Exportin 1 (XPO1) is overexpressed in diffuse large B-cell lymphoma (DLBCL), follicular small cell cleaved Lymphoma (FSCCL) and a wide variety of other cancers, which often correlates with poor prognosis. Selinexor is an oral SINE currently in Phase 1/2 clinical testing, which targets XPO1 to induce apoptosis across a broad spectrum of tumor types. This broad action is primarily due to forced nuclear retention and reactivation of tumor suppressor proteins (TSPs), resulting in selective tumor cell death. We have previously reported anti-lymphoma activity of selinexor in murine models of DLBCL, in spontaneous canine aggressive lymphomas and in preliminary results from B-cell lymphoma patients enrolled in a Phase 1 trial of hematological malignancies. One promising finding thus far is that efficacy of selinexor appears to be independent of the presence of the mutations in MYC and BCL2/6 found in “double-hit” DLBCL, which is typically resistant to standard treatments. Here we report combination studies involving Selinexor-Dexamethasone and Selinexor-mTOR inhibitor everolimus in Non Hodgkin's lymphoma relative to front-line standard of care.

Selinexor was found to be potently cytotoxic across a broad panel of B-cell lymphoma cell lines. Furthermore, combination of selinexor with dexamethasone (Dex) or the mTOR inhibitor everolimus resulted in synergistic cytotoxicity in the WSU-DLCL2 and WSU-FSCCL cell lines. The superior cytotoxicity observed in the combination was consistent with enhanced nuclear retention of different TSPs. In WSU-DLCL2 xenografts, analogs of selinexor KPT-251 and KPT-276 showed comparable efficacy to R-CHOP and in a model of disseminated follicular lymphoma using WSU-FSCCL cells, selinexor had similar efficacy to rituximab for extending survival. The combination of selinexor and Dex or selinexor and everolimus in both xenografts are ongoing.

B-cell lymphoma cells in culture are highly sensitive to selinexor. Furthermore, combination of selinexor with Dex or everolimus is synergistically toxic to DLBCL cells. This synergism is consistent with the mechanism of action of these drugs in that both selinexor and Dex antagonize NF-κB and mTOR is an XPO1 cargo protein. The comparable in vivo activity of selinexor and related SINE compounds relative standard of care is consistent with the observations of objective responses in B-cell lymphoma patients in Phase I clinical testing. Ongoing preclinical work is designed to extend comparisons of selinexor with other standard of care and broaden the characterization of combination therapies in an effort to provide a rational basis for studying specific combinations in B-cell lymphoma clinical trials.

Citation Format: Asfar S. Azmi, Amro Aboukameel, Robert O. Carlson, Sivan Elloul, Sharon Shacham, Michael Kauffman, Ran Frenkel, Ramzi M. Mohammad. Preclinical activity in non-Hodgkin's lymphoma of Selinexor, a selective inhibitor of nuclear export (SINE), is enhanced through combination with standard-of-care therapies. [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 1756. doi:10.1158/1538-7445.AM2015-1756

Abstract 4688: Overcoming drug resistance and stemness in oncogenic kras driven pancreatic ductal adenocarcinoma through PAK4 inhibition

Background: In spite of the established role of oncogenic Kras in the development and subsistence of Pancreatic Cancer (PC), no clinically viable agents have been developed to suppress this master regulator. Unlike other druggable proteins, Kras lacks the ideal binding pocket for small molecules. Therefore, there is an unmet need to identify novel druggable sites on Kras or to develop agents that target key effector proteins downstream. The p21-activated kinase 4 (PAK4) is a key effector downstream of Rho family GTPases. PAK4 is over-expressed in most PC cell lines tested but not in normal human pancreatic ductal epithelial cells (HPDE). Gene copy number amplification studies in PC patient cohorts confirmed PAK4 amplification. RNA interference of PAK4 suppresses PC cell proliferation making PAK4 an attractive therapeutic target. In collaboration with Karyopharm Therapeutics, we developed novel PAK4 allosteric modulators (PAMs; KPT-7189, KPT-9274, KPT-9307). Methods: Using multiple molecular biology techniques we tested PAMs activity (in the presence and absence of -ve and +ve controls) on a panel of PC cells lines, PAK4 over-expressing Gemcitabine resistant (GEM-R) PC models and highly resistant flow sorted cancer stem cells (CSC). Pancreatic CSC's are triple positive for CD133+CD44+EpCam+ and undergo epithelial-to-mesenchymal transition (EMT). The toxicity and efficacy of PAMs were evaluated in vitro and in sub-cutaneous mouse models of PC.

Results: The novel, orally bioavailable PAMs show anti-proliferative activity in vitro against different PC cell lines (AsPC-1, Colo-357, MiaPaCa-2, L3.6pl and HPAC IC50s <250nM) while sparing HPDE (IC50s 5 fold higher). Cell growth inhibition was concurrent with apoptosis induction and suppression of colony formation in 5 different PC cell lines (not in HPDE). PAMs reduced RNA and PAK4 protein levels along with the inhibition of proliferative and anti-apoptotic signals downstream of PAK4. Co-immunoprecipitation experiments showed disruption of PAK4 complexes (p65, Bcl-2 and vimentin). Confocal, western blot and RT-PCR analysis of PAM-treated CSC spheroids showed reversal of EMT and suppression of stem markers EpCAM, vimentin and snail with re-expression of epithelial phenotype promoter E-cadherin. Additionally PAMs synergize with Gemcitabine and oxaliplatin (CI<1) in vitro. KPT-9274, possesses desirable PK properties and is well tolerated in mice with the absence of any clinical signs of toxicity up to 200 mg/kg oral daily dose. Pre-clinical animal efficacy (as a single agent and in combination with gemcitabine) in a sub-cutaneous, orthotopic (from primary cells) and LSL-K-Ras G12D/+;LSL-Trp53R172H/+;Pdx-1-Cre transgenic mouse models are ongoing.

Conclusions: These proof of concept studies demonstrating the anti-proliferative effects of novel PAK4 allosteric modulators in pancreatic cancer warrant further clinical investigations.

Citation Format: Asfar S. Azmi, William Senapedis, Erkan Baloglu, Yosef Landesman, Michael Kauffman, Sharon Shacham, Jack Wu, Amro Aboukameel, Irfana Muqbil, Ramzi M. Mohammad. Overcoming drug resistance and stemness in oncogenic kras driven pancreatic ductal adenocarcinoma through PAK4 inhibition. [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 4688. doi:10.1158/1538-7445.AM2015-4688

Role of leptin and leptin receptors in hematological malignancies

Leptin is an adipose-derived cytokine that has an important role in bodyweight homeostasis and energy balance. There are a number of studies which have suggested that leptin and its receptors dysregulation play a critical role in the development of malignancies including hematological malignancies, mainly via activation of the JAK/STAT pathway which regulates downstream signaling pathways such as PI3K/AKT signaling and ERK1/2. In this review, current understandings of leptin/leptin receptors mediated pathogenesis in various lymphoid malignancies are described. Blocking of the leptin receptor might be a unique therapeutic approach for many hematological malignancies.

Regulation of KRAS-PAK4 axis by microRNAs in cancer

MicroRNAs (miRNAs), often aberrantly expressed in cancer, have been implicated in the regulation of a number of critical cell survival pathways including the genes in the Kras signaling. Kras mutations are observed in more than half of cancers and its inhibition has been the focus of intense research for the past 30 years. However, Kras itself has proven to be non-druggable due in part to the absence of binding pockets for small molecule drugs. These hurdles resulted in researchers shifting their focus on targeting proteins downstream to Kras pathways. P21 activated kinase 4 (PAK4) belongs to the family of serine/threonine kinases comprising of 6 isoforms (PAK 1-6) and is considered as a key effector of Rho family of GTPases downstream of RAS. PAK4 controls critical processes such as cellular motility, proliferation and survival. Recently a number of small molecule PAK4 antagonists have been investigated in preclinical and clinical setting; albeit without any success. Emerging evidence shows that PAK is tightly regulated by a number of miRNAs that are also recognized to promote hyper-activation of oncogenic Kras signaling. Therefore, the understanding of the role of miRNAs in the regulation of PAK4 is critical to the development of therapies against this important player in the Kras pathway. Through this review, we bring forward mechanistic insights on PAK4 regulation by aberrantly expressed miRNAs in cancer and its implications on Kras signaling. We anticipate that enhanced knowledge of the miRNA-PAK4 interaction network will allow the development of successful therapies targeting this critical protein to ultimately rein in Kras.

Abstract 1771: Novel small molecule pak4 allosteric modulators with activity against pancreatic cancer

The p21-activated kinase 4 (PAK4) acts as a key effector of Rho family GTPases downstream of K-Ras and is found over-expressed in most of the available pancreatic cancer (PC) cell lines but not in normal human pancreatic ductal epithelial cells (HPDE). Gene copy number amplification studies in PC patient cohorts has shown amplification of PAK4. Most importantly, RNA interference of PAK4 suppresses PC cell proliferation making PAK4 an attractive therapeutic target within the K-Ras signaling network. Nevertheless, the previously developed PAK4 Type I ATP competitive inhibitor (PF-3758309; tested in non-pancreatic models) was evaluated in a Phase 1 study and showed undesirable pharmacokinetic properties as well as no objective responses and was subsequently discontinued. In order to fill this scientific void, we evaluated a new class of PAK4 allosteric modulators in PC. Using multiple molecular biology techniques we tested the Pak4 modulators' activities (in the presence and absence of -ve and +ve controls) in a panel of PC cells lines, PAK4 over-expressing Gemcitabine resistant (GEM-R) PC models and highly resistant flow sorted PC stem cells (CSC). CSC's are triple positive for CD133+CD44+EpCam+ and undergo epithelial-to-mesenchymal transition (EMT). The toxicity and efficacy of these PAK4 modulators were evaluated in sub-cutaneous mouse models of PC. The novel, orally available PAK4 allosteric modulators (KPT-7189, KPT-8752) show anti-proliferative activity against different PC cell lines (AsPC-1, Colo-357, MiaPaCa-2, L3.6pl and HPAC IC50s <250nM) sparing HPDE (IC50s 5 fold higher). Cell growth inhibition was concurrent with apoptosis induction and suppression of colony forming abilities in 5 different PC cell lines (not in HPDE). KPT-7189 reduced PAK4 protein levels along with the inhibition of proliferative and anti-apoptotic signals downstream of PAK4. Molecularly, PAK4 RNA interference enhanced KPT-7189 activity and co-immunoprecipitation experiments showed disruption of PAK4 complexes (p65, Bcl-2 and vimentin). KPT-7189 inhibited spheroid forming ability of CSCs and reversed the epithelial-to-mesenchymal (EMT) phenotype. Confocal, western blot and RT-PCR analysis of KPT-7189 treated CD33+CD44+EpCam+ spheroids showed suppression of EMT and CSC markers EpCAM, vimentin and snail with re-expression of epithelial phenotype promoter E-cadherin. A similar compound, KPT-8752, with desirable PK properties was well tolerated in mice with the absence of any clinical signs of toxicity up to 200 mg/kg oral daily dose. Pre-clinical animal efficacy trial in sub-cutaneous, orthotopic and LSL-K-Ras G12D/+;LSL-Trp53R172H/+;Pdx-1-Cre transgenic mouse models are ongoing. This is the first proof of concept study demonstrating the anti-proliferative effects of novel allosteric modulators of PAK4, a downstream effector of K-Ras, in pancreatic cancer that warrants further clinical investigations.

Citation Format: Asfar S. Azmi, William Senapedis, Yosef Landesman, Erkan Baloglu, Ori Kalid, Jack Wu, Bin Bao, Amro Aboukameel, Sharon Shacham, Michael Kauffman, Ramzi M. Mohammad. Novel small molecule pak4 allosteric modulators with activity against pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1771. doi:10.1158/1538-7445.AM2014-1771

Abstract LB-185: Novel activity of selective inhibitors of nuclear export in epithelial-to-mesenchymal transition models

Epithelial-to-mesenchymal transition (EMT) that confers tumors an aggressive phenotype is a fine tuned process regulated by a number of molecules that are strategically distributed in the nuclear and cytosolic compartments of cancer cells. Major EMT regulating proteins and transcription factors (TFs), such as wnt/βcatenin, notch, TGF-β, Twist and Snail are recognized to undergo nuclear-cytosolic shuttling using specialized transporters; karyopherins. The export of most of the EMT regulating TFs is mediated exclusively by Exportin1/XPO1/CRM1 through nuclear exclusion sequence (NES) recognition. These observations indicate that nuclear transport may play a critical role in the development of EMT. However, to date there have been no studies evaluating the impact of nuclear export inhibition on EMT. We have earlier developed Specific Inhibitors of Nuclear Export (SINEs) that block XPO1 leading to nuclear retention of various tumor suppressor proteins (TSPs) and TFs. This is the first report showing that XPO1 inhibition by SINEs induce global re-organization of proteins leading to reversal of EMT in Robert Weinberg's snail transduced immortalized human mammary epithelial (HMLE-Snail) cells. Snail is a NES carrying transcription factor that has been documented to regulate EMT from either the nucleus or cytosol. Exposure of HMLE-Snail cells to SINEs to clinically relevant concentration of 0-200 nM [i.e. KPT-185, its inactive analog KPT-TRANS, and clinical agent Selinexor (KPT-330)] resulted in reversal of cellular morphology from mesenchymal to epithelial (MET) that was concurrent with growth inhibition and apoptosis. KPT-185 treatment at 150 nM (IC50) concentration suppressed spheroid forming ability of HMLE-snail cells. Molecular analysis of KPT-185 treated HMLE-snail cells and corresponding spheroids showed suppression of key EMT markers including snail, Twist, vimentin and EpCAM. Co-immunoprecipitation studies verified the disruption of the pre-dominantly cytosolic snail-XPO1 interaction upon SINE treatment. In order to understand the mechanism of EMT reversal, RNA from quadruplet SINE treated HMLE-Snail cells were subjected to mRNA microarrays and systems biology analysis. KPT-185 treatment resulted in differential expression of 720 genes (fold change p<0.001). The statistically significant differentially expressed genes were subjected to pathway analysis (upstream and downstream regulator analysis and similarity analysis to known EMT gene networks), which showed downregulation in Snail, HDAC1 and Glucosamine (UDP-N-acetyl)-2-epimerase/N-acetylmannosamine kinase (GNE) networks. Conversely, the activated networks included apoptosis and p73 signaling. The network genes were validated at the expression level using, RT-PCR and western blotting. The anti-tumor activity of SINEs against HMLE-snail derived spheroids grown subcutaneously in mice is currently being evaluated. In conclusion, this is the first study demonstrating the role of XPO1 in EMT. Selinexor is currently being evaluated in 3 phase 1 studies in patients with advanced solid tumor and hematological malignancies. Therefore, in view of our results, XPO1 inhibition through SINEs can be a new form of therapy for highly aggressive and metastatic tumors that harbor EMT.

Citation Format: Asfar S. Azmi, Sharon Shacham, Michael Kauffman, Dilara McCauley, Amro Aboukameel, Ramzi M. Mohammad. Novel activity of selective inhibitors of nuclear export in epithelial-to-mesenchymal transition models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-185. doi:10.1158/1538-7445.AM2014-LB-185

Nuclear retention of Fbw7 by specific inhibitors of nuclear export leads to Notch1 degradation in pancreatic cancer

Chromosome maintenance region 1 (CRM1) also called Exportin 1 (Xpo1), a protein found elevated in pancreatic ductal adenocarcinoma (PDAC), blocks tumor suppressor protein (TSP) function through constant nuclear export. Earlier we had shown that targeting CRM1 by our newly developed specific inhibitors of nuclear export (SINE) leads to inhibition of pancreatic cancer cell proliferation and tumor growth arrest. In this paper we define the mechanism of SINE action. Our lead SINE KPT-185 inhibits PDAC cell growth, cell migration, tumor invasion and induces apoptosis and G2-M cell cycle arrest in low nano molar range (IC50s~150 nM). Mechanistically we demonstrate that the activity of KPT-185 is associated with nuclear retention of Fbw7; which degrades nuclear Notch-1 leading to decreased tumor promoting markers such as C-Myc, Cyclin-D1, Hes1 and VEGF. The orally bioavailable SINE (KPT-251) showed potent anti-tumor activity in a Colo-357 PDAC xenografts model; residual tumor analysis showed activation of Fbw7 concomitant with attenuation of Notch1 and its downstream genes. These results suggest that the antitumor activity of KPT-185 is in part due to nuclear retention of Fbw7 and consequent Notch1 degradation. The new CRM1 inhibitors, therefore, hold strong potential and warrant further clinical investigations for PDAC.

A novel small-molecule inhibitor of mcl-1 blocks pancreatic cancer growth in vitro and in vivo

Using a high-throughput screening (HTS) approach, we have identified and validated several small-molecule Mcl-1 inhibitors (SMI). Here, we describe a novel selective Mcl-1 SMI inhibitor, 2 (UMI-77), developed by structure-based chemical modifications of the lead compound 1 (UMI-59). We have characterized the binding of UMI-77 to Mcl-1 by using complementary biochemical, biophysical, and computational methods and determined its antitumor activity against a panel of pancreatic cancer cells and an in vivo xenograft model. UMI-77 binds to the BH3-binding groove of Mcl-1 with Ki of 490 nmol/L, showing selectivity over other members of the antiapoptotic Bcl-2 family. UMI-77 inhibits cell growth and induces apoptosis in pancreatic cancer cells in a time- and dose-dependent manner, accompanied by cytochrome c release and caspase-3 activation. Coimmunoprecipitation experiments revealed that UMI-77 blocks the heterodimerization of Mcl-1/Bax and Mcl-1/Bak in cells, thus antagonizing the Mcl-1 function. The Bax/Bak-dependent induction of apoptosis was further confirmed using murine embryonic fibroblasts that are Bax- and Bak-deficient. In an in vivo BxPC-3 xenograft model, UMI-77 effectively inhibited tumor growth. Western blot analysis in tumor remnants revealed enhancement of proapoptotic markers and significant decrease of survivin. Collectively, these promising findings show the therapeutic potential of Mcl-1 inhibitors against pancreatic cancer and warrant further preclinical investigations.

Comparative in vivo evaluations of curcumin and its analog difluorinated curcumin against cisplatin-induced nephrotoxicity

Curcumin, a polyphenol, has pharmacological effects including antioxidant, anti-inflammatory and anti-cancer features. In this study, we have performed comparative in vivo evaluations of CDF (curcumin difluorinated) and curcumin in cisplatin-induced nephrotoxicity in rats. Male Wistar rats were divided into four groups: (1) Control; (2) Cisplatin (7 mg/kg body wt, intraperitoneal as a single dose); (3) Cisplatin and CDF (50 mg/rat/day; for 12 days); (4) Cisplatin and curcumin (50 mg/rat/day), for 12 days). Cisplatin treated rats exhibited kidney injury manifested by increased serum N-urea and creatinine (P < 0.001). Kidney from cisplatin treated rats also exhibited significant increase in malondialdehyde (MDA) and 8-isoprostane levels (P < 0.001). Treatment with CDF and curcumin prevented the rise in serum N-urea, creatinine, MDA and 8-isoprostane as compared to experimental control group in kidney (P < 0.05). Compared to curcumin, CDF had greater potential in suppressing cisplatin-induced pro-inflammatory factors NF-κB and COX-2 as well as downstream markers Nrf2 and HO-1 (P < 0.05) in kidney. The analysis on anion transport markers (OAT1 and OAT3) showed a similar trend (CDF > curcumin). CDF could reduce the expression of multi-drug resistance markers OCT1, OCT2, MRP2 and MRP4 to a much greater extent than curcumin (P < 0.05). We also demonstrate that CDF influenced the expression of p-mTOR, p-p70S6K1, p-4E-BP1 and p-Akt. These data suggest that CDF can potentially be used to reduce the chemotherapy induced nephrotoxicity thereby enhancing the therapeutic window of cisplatin. The results also proved that compared to curcumin, CDF has superior protective effect in nephrotoxicity.

Novel PAK4 inhibitors for pancreatic cancer therapy

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Background: Pancreatic cancer (PC) is a deadly disease in urgent need of novel molecularly targeted drugs. Gene copy number amplification studies in PC patient cohorts has shown amplification of the p21-activated kinase (PAK) family member PAK4. PAK4 acts as a key effector of the Rho family GTPases downstream of Ras signaling. Moreover, PAK4 protein is over-expressed in PC cell lines but not in normal human pancreatic ductal epithelial (HPDE) cells. Most importantly, RNA interference of PAK4 has been shown to suppress PC cell proliferation. These studies clearly make PAK4 an attractive therapeutic target especially because direct targeting of Kras has been a failure. Methods: We have identified a new class of PAK4 allosteric modulators that show anti-proliferative activity against several PC cell lines (IC50s <250nM) while sparing normal HPDE (IC50s5 fold higher). Results: Cell growth inhibition is concurrent with apoptosis induction and suppression of colony formation in the PC cell lines (and not in HPDE cells). Our small molecule PAK4 allosteric modulator, KPT-7189, suppresses PAK4 protein expression and caused reversal of anti-apoptotic signaling. PAK4 RNA interference enhances KPT-7189 activity, and co-immunoprecipitation experiments showed disruption of PAK4 binding partners. KPT-7189 also inhibited spheroid forming ability of highly resistant PC cells carrying markers of cancer stem cells (CSCs;triple positive for CD33+CD44+EpCAM+) consistent with epithelial-to-mesenchymal (EMT) phenotype. Molecular analyses of KPT-7189 treated CD33+CD44+EpCAM+ spheroids showed suppression of EMT and CSC markers with re-expression of epithelial phenotype markers. Another potent PAK allosteric modulator in the same series, KPT-7651 showing good oral bioavailability (%F = 95%) was well tolerated by mice with a maximum tolerated dose of 60 mg/kg following oral administration. Pre-clinical animal efficacy trial in sub-cutaneous, orthotopic and LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre transgenic mice model is currently under investigation. Conclusions: This is the first proof of concept study demonstrating the development of a PAK4-targeted drug for the treatment of PC, and thus further pre-clinical and clinical investigations are warranted.

Understanding XPO1 target networks using systems biology and mathematical modeling

The nuclear transport protein Exportin 1 (XPO1), also called chromosome region maintenance 1 (CRM1), is over-expressed 2- 4 fold in cancer. XPO1 is one of seven nuclear exporter proteins, and is solely responsible for the transport of the major tumor suppressor proteins (TSPs) from the nucleus to the cytoplasm. XPO1 exports any protein that carries a leucine-rich, hydrophobic nuclear export sequence (NES). A number of inhibitors have been discovered that block XPO1 function and thereby restore TSPs to the nucleus of both malignant and normal cells. However, natural product, irreversible XPO1 antagonists such as leptomycin B (LMB) have proven toxic in both preclinical models and in the clinic. Recently, orally bioavailable, drug-like small molecule, potent and selective inhibitors of XPO1 mediated nuclear export ("SINE") have been designed and are undergoing clinical evaluations in both humans and canines with cancer. The breadth of clinical applicability and long-term viability of an XPO1 inhibition strategy requires a deeper evaluation of the consequence of global re-organization of proteins in cancer and normal cells. Unfortunately, most of the studies on XPO1 inhibitors have focused on evaluating a limited number of TSPs or other proteins. Because XPO1 carries ~220 mammalian proteins out of the nucleus, such reductionism has not permitted a global understanding of cellular behavior upon drug-induced disruption of XPO1 function. The consequence of XPO1 inhibition requires holistic investigations that consider the entire set of XPO1 targets and their respective pathways modulated without losing key details. Systems biology is one such holistic approach that can be applied to understand XPO1 regulated proteins along with the downstream players involved. This review provides comprehensive evaluations of the different computational tools that can be utilized in the better understanding of XPO1 and its target. We anticipate that such holistic approaches can allow for the development of a clinically successful XPO1 targeted therapeutic strategy against cancer.