Stimulation of natural killer cells with small molecule inhibitors of CD38 for the treatment of neuroblastoma

High-risk neuroblastoma (NB) accounts for 15% of all pediatric cancer deaths. Refractory disease for high-risk NB patients is attributed to chemotherapy resistance and immunotherapy failure. The poor prognosis for high-risk NB patients demonstrates an unmet medical need for the development of new, more efficacious therapeutics. CD38 is an immunomodulating protein that is expressed constitutively on natural killer (NK) cells and other immune cells in the tumor microenvironment (TME). Furthermore, CD38 over expression is implicated in propagating an immunosuppressive milieu within the TME. Through virtual and physical screening, we have identified drug-like small molecule inhibitors of CD38 with low micromolar IC50 values. We have begun to explore structure activity relationships for CD38 inhibition through derivatization of our most effective hit molecule to develop a new compound with lead-like physicochemical properties and improved potency. We have demonstrated that our derivatized inhibitor, compound 2, elicits immunomodulatory effects in NK cells by increasing cell viability by 190 ± 36% in multiple donors and by significantly increasing interferon gamma. Additionally, we have illustrated that NK cells exhibited enhanced cytotoxicity toward NB cells (14% reduction of NB cells over 90 minutes) when given a combination treatment of our inhibitor and the immunocytokine ch14.18-IL2. Herein we describe the synthesis and biological evaluation of small molecule CD38 inhibitors and demonstrate their potential utility as a novel approach to NB immunotherapy. These compounds represent the first examples of small molecules that stimulate immune function for the treatment of cancer.

Secreted frizzled related-protein 2 is prognostic for human pancreatic cancer patient survival and is associated with fibrosis

Pancreatic adenocarcinoma (PDAC) is one of the deadliest cancers, with five-year survival rates of 9%. We hypothesized that secreted frizzled-related protein 2 (SFRP2) may influence stromal growth in pancreatic cancer, since it increases fibrosis and collagen production in non-neoplastic pathologies. We assessed SFRP2 value as a biomarker and assessed its function in PDAC. SFRP2 gene expression in patients with PDAC was analyzed using TCGA data. Disease free survival (DFS) was analyzed using Kaplan Meier test. The effect of KRAS inhibition on SFRP2 expression in PDAC cells was assessed. The associations of stromal content with SFPR2 mRNA and protein with fibrosis were analyzed. The role of SFRP2 in mesenchymal transformation was assessed by western blot in fibroblasts. Of all cancers in TCGA, SFRP2 levels were highest in PDAC, and higher in PDAC than normal tissues (n= 234, p= 0.0003). High SFRP2 levels correlated with decreased DFS (p= 0.0097). KRAS inhibition reduced SFRP2 levels. Spearman correlation was 0.81 between stromal RNA and SFRP2 in human PDAC, and 0.75 between fibrosis and SFRP2 levels in PDAC tumors. SFRP2-treated fibroblasts displayed mesenchymal characteristics. SFRP2 is prognostic for PDAC survival, regulated by KRAS, and associated with PDAC fibrosis.

PDI inhibitor LTI6426 enhances panobinostat efficacy in preclinical models of multiple myeloma

The histone deacetylase inhibitor (HDACi), panobinostat (Pano), is approved by the United States Food and Drug Administration (FDA) and European Medicines Agency (EMA) for treatment of relapsed/refractory multiple myeloma (MM). Despite regulatory approvals, Pano is used on a limited basis in MM due largely to an unfavorable toxicity profile. The MM treatment landscape continues to evolve, and for Pano to maintain a place in that paradigm it will be necessary to identify treatment regimens that optimize its effectiveness, particularly those that permit dose reductions to eliminate unwanted toxicity. Here, we propose such a regimen by combining Pano with LTI6426, a first-in-class orally bioavailable protein disulfide isomerase (PDI) inhibitor. We show that LTI6426 dramatically enhances the anti-MM activity of Pano in vitro and in vivo using a proteasome inhibitor resistant mouse model of MM and a low dose of Pano that exhibited no signs of toxicity. We go on to characterize a transcriptional program that is induced by the LTI6426/Pano combination, demonstrating a convergence of the two drugs on endoplasmic reticulum (ER) stress pathway effectors ATF3 (Activating Transcription Factor 3), DDIT3/CHOP (DNA Damage Inducible Transcript 3, a.k.a. C/EBP Homologous Protein), and DNAJB1 (DnaJ homolog subfamily B member 1, a.k.a. HSP40). We conclude that LTI6426 may safely enhance low-dose Pano regimens and that ATF3, DDIT3/CHOP, and DNAJB1 are candidate pharmacodynamic biomarkers of response to this novel treatment regimen.

Selective targeting of CD38 hydrolase and cyclase activity as an approach to immunostimulation

The ectoenzyme CD38 is highly expressed on the surface of mature immune cells, where they are a marker for cell activation, and also on the surface of multiple tumor cells such as multiple myeloma (MM). CD38-targeted monoclonal antibodies (MABs) such as daratumumab and isatuximab bind to CD38 and promote cancer cell death by stimulating the antitumor immune response. Although MABs are achieving unprecedented success in a percentage of cases, high rates of resistance limit their efficacy. Formation of the immunosuppressive intermediate adenosine is a major route by which this resistance is mediated. Thus there is an urgent need for small molecule agents that boost the immune response in T-cells. Importantly, CD38 is a dual-function enzyme, serving as a hydrolase and a nicotinamide adenine dinucleotide (NAD+) cyclase, and both of these activities promote immunosuppression. We have employed virtual and physical screening to identify novel compounds that are selective for either the hydrolase or the cyclase activity of CD38, and have demonstrated that these compounds activate T cells in vitro. We are currently optimizing these inhibitors for use in immunotherapy. These small molecule inhibitors of the CD38-hydrolase or cyclase activity can serve as chemical probes to determine the mechanism by which CD38 promotes resistance to MAB therapy, and could become novel and effective therapeutic agents that produce immunostimulatory effects. Our studies have identified the first small molecule inhibitors of CD38 specifically for use as immunostimulants.

ATF3 Coordinates Antitumor Synergy between Epigenetic Drugs and Protein Disulfide Isomerase Inhibitors

Histone deacetylase inhibitors (HDACi) are largely ineffective in the treatment of solid tumors. In this study, we describe a new class of protein disulfide isomerase (PDI) inhibitors that significantly and synergistically enhance the antitumor activity of HDACi in glioblastoma and pancreatic cancer preclinical models. RNA-sequencing screening coupled with gene silencing studies identified ATF3 as the driver of this antitumor synergy. ATF3 was highly induced by combined PDI and HDACi treatment as a result of increased acetylation of key histone lysine residues (acetylated histone 3 lysine 27 and histone 3 lysine 18) flanking the ATF3 promoter region. These chromatin marks were associated with increased RNA polymerase II recruitment to the ATF3 promoter, a synergistic upregulation of ATF3, and a subsequent apoptotic response in cancer cells. The HSP40/HSP70 family genes DNAJB1 and HSPA6 were found to be critical ATF3-dependent genes that elicited the antitumor response after PDI and HDAC inhibition. In summary, this study presents a synergistic antitumor combination of PDI and HDAC inhibitors and demonstrates a mechanistic and tumor suppressive role of ATF3. Combined treatment with PDI and HDACi offers a dual therapeutic strategy in solid tumors and the opportunity to achieve previously unrealized activity of HDACi in oncology. SIGNIFICANCE: This study uses a first-in-class PDI inhibitor entering clinical development to enhance the effects of epigenetic drugs in some of the deadliest forms of cancer.

Tuning isoform selectivity and bortezomib sensitivity with a new class of alkenyl indene PDI inhibitor

Protein disulfide isomerase (PDI, PDIA1) is an emerging therapeutic target in oncology. PDI inhibitors have demonstrated a unique propensity to selectively induce apoptosis in cancer cells and overcome resistance to existing therapies, although drug candidates have not yet progressed to the stage of clinical development. We recently reported the discovery of lead indene compound E64FC26 as a potent pan-PDI inhibitor that enhances the cytotoxic effects of proteasome inhibitors in panels of Multiple Myeloma (MM) cells and MM mouse models. An extensive medicinal chemistry program has led to the generation of a diverse library of indene-containing molecules with varying degrees of proteasome inhibitor potentiating activity. These compounds were generated by a novel nucleophilic aromatic ring cyclization and dehydration reaction from the precursor ketones. The results provide detailed structure activity relationships (SAR) around this indene pharmacophore and show a high degree of correlation between potency of PDI inhibition and bortezomib (Btz) potentiation in MM cells. Inhibition of PDI leads to ER and oxidative stress characterized by the accumulation of misfolded poly-ubiquitinated proteins and the induction of UPR biomarkers ATF4, CHOP, and Nrf2. This work characterizes the synthesis and SAR of a new chemical class and further validates PDI as a therapeutic target in MM as a single agent and in combination with proteasome inhibitors.

Syrbactin proteasome inhibitor TIR-199 overcomes bortezomib chemoresistance and inhibits multiple myeloma tumor growth in vivo

Multiple myeloma (MM) and mantle cell lymphoma (MCL) are blood cancers that respond to proteasome inhibitors. Three FDA-approved drugs that block the proteasome are currently on the market, bortezomib, carfilzomib, and ixazomib. While these proteasome inhibitors have demonstrated clinical efficacy against refractory and relapsed MM and MCL, they are also associated with considerable adverse effects including peripheral neuropathy and cardiotoxicity, and tumor cells often acquire drug resistance. TIR-199 belongs to the syrbactin class, which constitutes a novel family of irreversible proteasome inhibitors. In this study, we compare TIR-199 head-to-head with three FDA-approved proteasome inhibitors. We demonstrate that TIR-199 selectively inhibits to varying degrees the sub-catalytic proteasomal activities (C-L/β1, T-L/β2, and CT-L/β5) in three actively dividing MM cell lines, with Ki₅₀ (CT-L/β5) values of 14.61 ± 2.68 nM (ARD), 54.59 ± 10.4 nM (U266), and 26.8 ± 5.2 nM (MM.1R). In most instances, this range was comparable with the activity of ixazomib. However, TIR-199 was more effective than bortezomib, carfilzomib, and ixazomib in killing bortezomib-resistant MM and MCL cell lines, as judged by a low resistance index (RI) between 1.7 and 2.2, which implies that TIR-199 indiscriminately inhibits both bortezomib-sensitive and bortezomib-resistant MM and MCL cells at similar concentrations. Importantly, TIR-199 reduced the tumor burden in a MM mouse model (p < 0.01) confirming its potency in vivo. Given the fact that there is still no cure for MM, the further development of TIR-199 or similar molecules that belong to the syrbactin class of proteasome inhibitors is warranted.

Abstract 3840: ATF3 drives synergy between protein disulfide isomerase (PDI) inhibitors and epigenetic cancer therapy

The clinical potential of epigenetic cancer therapy has not been fully realized. Histone deacetylase inhibitors (HDACi), for example, only benefit a minor fraction of all cancer patients despite thousands of preclinical studies demonstrating their antitumor effects. In this study we show that a new structural class of protein disulfide isomerase (PDI) that was discovered by our lab dramatically enhances the antitumor effects of HDACi and select other epigenetic modifiers. We set out to identify synergistic interactions between our lead PDI inhibitor, E64FC26, and FDA-approved drugs in the NCI Approved Oncology Drug Set VIII of ~130 marketed drugs. We identified robust and previously uncharacterized synergy with all four HDACi in the set (i.e., panobinostat, romidepsin, vorinostat, and belinostat) in a broad range of solid and heme-malignancies. For example, E64FC26 potentiated panobinostat-induced cytotoxicity by 240-fold in PANC-1 pancreatic cancer cells and by 20-fold in T98G glioblastoma cells. Synergy with HDACi involved an apoptotic response measured by the activation of caspase 3, 8, 9 and the cleavage of the caspase 3 substrate PARP. PDI mediates proper protein folding, and western blotting and confocal microscopy confirmed the accumulation of misfolded poly-ubiquitinated protein aggregates in treated cells, which we showed was a critical component underlying the synergistic effects of the combination. To further understand the mechanism, we profiled the transcriptomes of combination treated cells using comparative RNA-Seq. These experiments revealed a convergence on ATF3 and DDIT3, two candidates in the ER stress pathway. RNA-Seq results were confirmed by qPCR and western blotting analysis in a range of tumor types. ATF3 played an apparent dominant role in driving the synergy between PDI and HDAC inhibitors, as knockdown of ATF3 completely ameliorated synergy between the two drug classes. We further clarified this molecular mechanism to show that PDI inhibition induces an ER stress response that leads to the induction of ATF3, which is further potentiated in the presence of HDACi, leading to the synergistic effects of the drug combination. These effects were not limited to HDACi, as similar results were observed in combinations with other epigenetic targeted therapies. We went on to characterize the efficacy and tolerability of PDI and HDAC inhibitor combinations in multiple mouse models, including pancreatic and glioblastoma xenograft models as well as multiple myeloma xenotransplant models. In summary, this study presents the potent antitumor combination of PDI and HDAC inhibitors and demonstrates a key mechanistic role of the ATF3 transcription factor. The combination of our developmental PDI inhibitor and HDACi offers a new dual therapeutic strategy and the opportunity to amplify and rescue previously unrealized activity of epigenetic therapy in oncology.

Citation Format: Ravyn M. Duncan, Leticia Reyes, Katelyn Moats, Reeder M. Robinson, Holly A. Stessman, Nathan G. Dolloff. ATF3 drives synergy between protein disulfide isomerase (PDI) inhibitors and epigenetic cancer therapy [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 3840.

Discovery platform for inhibitors of IgH gene enhancer activity

Immunoglobulin heavy chain (IgH) translocations are common and early oncogenic events in B cell and plasma cell malignancies including B cell non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). IgH translocations bring oncogenes into close proximity with potent enhancer elements within the IgH locus, leading to oncogene up-regulation. As IgH enhancer activity is tightly controlled by B cell lineage-specific signaling and transcriptional networks, we hypothesized that IgH enhancers are potentially druggable targets/elements. To test this, we developed a molecular imaging-based high-throughput screening platform for discovering inhibitors of IgH enhancer-driven transcriptional activity. As proof of concept, we identified a low micromolar potency molecule (compound 30666) that inhibited immunoglobulin production by MM cells and blocked expression of an array of IgH translocation-induced oncogenes (CCND1, FGFR3/MMSET, and MYC) in MM and NHL cell lines. Prolonged exposure to 30666 significantly reduced the viability of IgH translocation-positive NHL and MM cells, but was less effective against cells lacking IgH translocations. Compound 30666 exhibited suitable pharmacological properties, including metabolic stability in liver microsomes and oral bioavailability in mice, and demonstrated preclinical anti-MM activity in a plasmacytoma mouse model. Our work suggests that IgH enhancers are attractive and potentially druggable targets for IgH translocation driven malignancies.

Glutaminase inhibitor CB-839 synergizes with carfilzomib in resistant multiple myeloma cells

Curative responses in the treatment of multiple myeloma (MM) are limited by the emergence of therapeutic resistance. To address this problem, we set out to identify druggable mechanisms that convey resistance to proteasome inhibitors (PIs; e.g., bortezomib), which are cornerstone agents in the treatment of MM. In isogenic pairs of PI sensitive and resistant cells, we observed stark differences in cellular bioenergetics between the divergent phenotypes. PI resistant cells exhibited increased mitochondrial respiration driven by glutamine as the principle fuel source. To target glutamine-induced respiration in PI resistant cells, we utilized the glutaminase-1 inhibitor, CB-839. CB-839 inhibited mitochondrial respiration and was more cytotoxic in PI resistant cells as a single agent. Furthermore, we found that CB-839 synergistically enhanced the activity of multiple PIs with the most dramatic synergy being observed with carfilzomib (Crflz), which was confirmed in a panel of genetically diverse PI sensitive and resistant MM cells. Mechanistically, CB-839 enhanced Crflz-induced ER stress and apoptosis, characterized by a robust induction of ATF4 and CHOP and the activation of caspases. Our findings suggest that the acquisition of PI resistance involves adaptations in cellular bioenergetics, supporting the combination of CB-839 with Crflz for the treatment of refractory MM.

Emerging Therapeutic Strategies for Overcoming Proteasome Inhibitor Resistance

The debut of the proteasome inhibitor bortezomib (Btz; Velcade®) radically and immediately improved the treatment of multiple myeloma (MM), an incurable malignancy of the plasma cell. Therapeutic resistance is unavoidable, however, and represents a major obstacle to maximizing the clinical potential of the drug. To address this challenge, studies have been conducted to uncover the molecular mechanisms driving Btz resistance and to discover new targeted therapeutic strategies and combinations that restore Btz activity. This review discusses the literature describing molecular adaptations that confer Btz resistance with a primary disease focus on MM. Also discussed are the most recent advances in therapeutic strategies that overcome resistance, approaches that include redox-modulating agents, murine double minute 2 inhibitors, therapeutic monoclonal antibodies, and new epigenetic-targeted drugs like bromodomain and extra terminal domain inhibitors.

Dual inactivation of Akt and ERK by TIC10 signals Foxo3a nuclear translocation, TRAIL gene induction, and potent antitumor effects

Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an antitumor protein that is in clinical trials as a potential anticancer therapy but suffers from drug properties that may limit efficacy such as short serum half-life, stability, cost, and biodistribution, particularly with respect to the brain. To overcome such limitations, we identified TRAIL-inducing compound 10 (TIC10), a potent, orally active, and stable small molecule that transcriptionally induces TRAIL in a p53-independent manner and crosses the blood-brain barrier. TIC10 induces a sustained up-regulation of TRAIL in tumors and normal cells that may contribute to the demonstrable antitumor activity of TIC10. TIC10 inactivates kinases Akt and extracellular signal-regulated kinase (ERK), leading to the translocation of Foxo3a into the nucleus, where it binds to the TRAIL promoter to up-regulate gene transcription. TIC10 is an efficacious antitumor therapeutic agent that acts on tumor cells and their microenvironment to enhance the concentrations of the endogenous tumor suppressor TRAIL.

Abstract P6-02-01: Elucidating the change of TRAIL sensitivity in basal like TNBC cell lines by lapatinib, and further therapeutic implication

Triple negative breast cancer (TNBC) comprises 15-20% of breast cancer, and carries a poor prognosis. Recently, efforts to understand this heterogeneous group of cancers have led to recognition of different subtypes of TNBC by Dr. Pietenpol et al based on genetic and functional signature. So far, the only targeting agent for TNBC still remains as androgen receptor inhibitor for LAR group. Thus, other strategies in therapeutic development for TNBCs are necessary. TRAIL (Tumor Necrosis Factor-related apoptosis inducing ligand), a member of the TNF-alpha family of death receptor ligands, induces apoptosis by binding death receptors (DR4 and DR5), could be a good strategy in therapeutic development in TNBC. Unfortunately, majority of breast cancer cell lines are resistant to TRAIL targeted therapy especially basal like group of cells, as previously shown in the work of Lipkowitz at the NCI. Lapatinib, a well known as erbB 1 and 2 inhibitor had been found to have off target activity inducing JNK, an important activator of nuclear transcription of death receptor, and mitochondrial mediated intrinsic apoptosis pathway. Interestingly, study of combination therapy with lapatinib and TRAIL not only confirmed baseline poor sensitivity to TRAIL induced apoptosis in “basal like” HCC 1937 and MDA-MB-468 cell lines, but also revealed an unexpected difference in sensitization to TRAIL induced apoptosis by Lapatinib pre-treatment between these two cell lines. When treated with 48hrs Lapatinib high–dose treatment, HCC 1937 showed increased sensitization whereas MDA-MB-468 did not. Both HCC 1937 and MDA-MB-468 are in the same basal like 1(BL1) group by Dr. Pietenpol's analysis, and their baseline sensitivity to TRAIL inducing apoptosis are the same. In terms of apoptosis - there are two big categories of cells. Type I cells are independent of mitochondria for the induction of Fas death receptor mediated apoptosis, where as type II cells are mitochrondria-dependent. Thus we hypothesized that this difference in lapatinib induced TRAIL sensitization between two cell lines is due to difference in one being type I vs the other being type II cell, and this type of apoptosis is not likely equal in same subgroup of TNBC. If this hypothesis is correct, targeting apoptosis pathway in TNBC should incorporate the recognition of apoptosis cell types rather than functional/genetic based subtypes. We will further elucidate our hypothesis by studying JNK, caspase 3 and 9 activity and downstream of both intrinsic, extrinsic apoptosis pathway.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-02-01.

CDK1 stabilizes HIF-1α via direct phosphorylation of Ser668 to promote tumor growth

Hypoxia-inducible factor 1 (HIF-1) is a major mediator of tumor physiology, and its activation is correlated with tumor progression, metastasis, and therapeutic resistance. HIF-1 is activated in a broad range of solid tumors due to intratumoral hypoxia or genetic alterations that enhance its expression or inhibit its degradation. As a result, decreasing HIF-1α expression represents an attractive strategy to sensitize hypoxic tumors to anticancer therapies. Here, we show that cyclin-dependent kinase 1 (CDK1) regulates the expression of HIF-1α, independent of its known regulators. Overexpression of CDK1 and/or cyclin B1 is sufficient to stabilize HIF-1α under normoxic conditions, whereas inhibition of CDK1 enhances the proteasomal degradation of HIF-1α, reducing its half-life and steady-state levels. In vitro kinase assays reveal that CDK1 directly phosphorylates HIF-1α at a previously unidentified regulatory site, Ser668. HIF-1α is stabilized under normoxic conditions during G 2/M phase via CDK1-mediated phosphorylation of Ser668. A phospho-mimetic construct of HIF-1α at Ser668 (S668E) is significantly more stable under both normoxic and hypoxic conditions, resulting in enhanced transcription of HIF-1 target genes and increased tumor cell invasion and migration. Importantly, HIF-1α (S668E) displays increased tumor angiogenesis, proliferation, and tumor growth in vivo compared with wild-type HIF-1α. Thus, we have identified a novel link between CDK1 and HIF-1α that provides a potential molecular explanation for the elevated HIF-1 activity observed in primary and metastatic tumors, independent of hypoxia, and offers a molecular rationale for the clinical translation of CDK inhibitors for use in tumors with constitutively active HIF-1.

Abstract 2943: Lapatinib restores TRAIL-mediated apoptosis in TRAIL-resistant Triple Negative Breast Cancer (TNBC) through an off-target strategy that appears to be independent of increased death receptor expression

Triple negative breast cancer (TNBC) comprises 15-20% of breast cancer, and carries a poor prognosis. TRAIL (Tumor Necrosis Factor-related apoptosis inducing ligand), a member of the TNF-alpha family of death receptor ligands, induces apoptosis by binding death receptors (DR4 and DR5), and can be a good therapeutic target in TNBC based on the work of Lipkowitz at the NCI. Lapatinib, a dual HER2 and EGFR inhibitor has been shown to sensitize colon cancer and GBM cells to TRAIL-induced apoptosis through an off-target effect that involves JNK. In colon cancer cell lines, this sensitization was found to be due to increased DR4 and DR5 protein levels, and this was not affected by HER2 and EGFR dual specific inhibition. The majority of breast cancer cell lines including HCC 1937, a BRCA1-deficient TNBC cell line derived from a patient with BRCA1 mutation, are known to have constitutive death receptor endocytosis resulting in resistance to TRAIL. We hypothesized that treatment of TNBC cells with lapatinib may induce sensitization to TRAIL-induced apoptosis in normally TRAIL-resistant cell lines, but possibly not by increased death receptor protein expression since these cells have defective cell surface expression. MDA-MB-231 and HCC 1937 cell lines are both well-validated TNBC cell lines. MDA-MB-231 is known to be sensitive to TRAIL, whereas HCC 1937 is resistant to TRAIL. These two cell lines were pre-treated with 0-10 μM lapatinib for 48 hrs. Cells were then treated with His-tagged recombinant TRAIL (50 ng/mL) for 24 hr subsequently. Cell Titer Glo assay, and sub-G1 DNA content analysis by flow cytometry showed increments of apoptosis after lapatinib pre-treatment. This change was more prominent in HCC 1937, which is normally resistant to TRAIL-induced apoptosis. However western blotting did not show increased DR4/DR5 by pre-treatment with lapatinib in either MDA-MB-231 or HCC 1937. This result suggests that we may have identified an off-target effect of lapatinib in TNBC that appears to not involve increased death receptor expression. We are further exploring the previously described role for JNK in the off-target effect to further elucidate this TRAIL death receptor- and Her2/EGFR-independent mechanism of TRAIL sensitization by lapatinib that has implication for TNBC therapy.

Citation Format: Bora Lim, Nathan G. Dolloff, Joshua E. Allen, David T. Dicker, Wafik S. El-Deiry. Lapatinib restores TRAIL-mediated apoptosis in TRAIL-resistant Triple Negative Breast Cancer (TNBC) through an off-target strategy that appears to be independent of increased death receptor expression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2943. doi:10.1158/1538-7445.AM2013-2943

Abstract 1020: VRC2, a novel bortezomib re-sensitizing compound for the treatment of multiple myeloma

The development of novel agents including the proteasome inhibitor bortezomib (Btz) has significantly improved treatment outcomes in multiple myeloma (MM). Despite these advances, resistance to therapy invariably emerges and MM remains an incurable disease. The objective of this study was to identify new therapeutic agents and combinations with the ability to overcome resistance to Btz in MM cells. We developed a high throughput drug screening (HTS) assay system to discover small molecules that selectively target Btz resistant MM cells as single agents and/or re-sensitize resistant cells to Btz. For HTS we used isogenic pairs of Btz sensitive (595 P) and resistant (595 VR) cells derived from iMycCα/Bcl-xL transgenic mouse model of MM. Cell viability was the HTS assay read-out, and 3 treatment groups (595 P, 595 VR, and 595 VR + Btz) were included to identify compounds with selective activity against Btz resistant cells as single agents, and compounds that restore Btz sensitivity in the presence of Btz. Our screening of multiple publically-available compound libraries identified several chemical structures with selective activity against Btz resistant cells. One compound in particular showed modest but significant selectivity for Btz resistant cells as a single agent, and most notably, exhibited potent Btz re-sensitizing activity when the 2 drugs were combined. We named this compound Velcade Re-sensitizing Compound 2, or VRC-2 for short. The Btz re-sensitizing activity of VRC-2 was confirmed using multiple human and mouse cell lines that had been selected for Btz resistance in vitro. IC50s for VRC-2 in normal mouse and human fibroblasts were 100-fold higher than that observed in MM cells, suggesting it may have a low toxicity profile in vivo. We are currently evaluating the activity of VRC-2 in animal models of MM, alone and in combination with Btz, and conducting molecular studies to identify its precise mechanism of action. This study establishes the proof-of-principal for our HTS approach and demonstrates the potential of VRC-2 in Btz refractory MM.

Citation Format: Amriti Lulla, Holly Stessman, David Dicker, Brian Van Ness, Wafik El-Deiry, Nathan G. Dolloff. VRC2, a novel bortezomib re-sensitizing compound for the treatment of multiple myeloma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1020. doi:10.1158/1538-7445.AM2013-1020

Profiling bortezomib resistance identifies secondary therapies in a mouse myeloma model

Multiple myeloma is a hematologic malignancy characterized by the proliferation of neoplastic plasma cells in the bone marrow. Although the first-to-market proteasome inhibitor bortezomib (Velcade) has been successfully used to treat patients with myeloma, drug resistance remains an emerging problem. In this study, we identify signatures of bortezomib sensitivity and resistance by gene expression profiling (GEP) using pairs of bortezomib-sensitive (BzS) and bortezomib-resistant (BzR) cell lines created from the Bcl-XL/Myc double-transgenic mouse model of multiple myeloma. Notably, these BzR cell lines show cross-resistance to the next-generation proteasome inhibitors, MLN2238 and carfilzomib (Kyprolis) but not to other antimyeloma drugs. We further characterized the response to bortezomib using the Connectivity Map database, revealing a differential response between these cell lines to histone deacetylase (HDAC) inhibitors. Furthermore, in vivo experiments using the HDAC inhibitor panobinostat confirmed that the predicted responder showed increased sensitivity to HDAC inhibitors in the BzR line. These findings show that GEP may be used to document bortezomib resistance in myeloma cells and predict individual sensitivity to other drug classes. Finally, these data reveal complex heterogeneity within multiple myeloma and suggest that resistance to one drug class reprograms resistant clones for increased sensitivity to a distinct class of drugs. This study represents an important next step in translating pharmacogenomic profiling and may be useful for understanding personalized pharmacotherapy for patients with multiple myeloma.

Sangivamycin-like molecule 6 exhibits potent anti-multiple myeloma activity through inhibition of cyclin-dependent kinase-9

Despite significant treatment advances over the past decade, multiple myeloma (MM) remains largely incurable. In this study we found that MM cells were remarkably sensitive to the death-inducing effects of a new class of sangivamycin-like molecules (SLM). A panel of structurally related SLMs selectively induced apoptosis in MM cells but not other tumor or nonmalignant cell lines at submicromolar concentrations. SLM6 was the most active compound in vivo, where it was well tolerated and significantly inhibited growth and induced apoptosis of MM tumors. We determined that the anti-MM activity of SLM6 was mediated by direct inhibition of cyclin-dependent kinase 9 (CDK9), which resulted in transcriptional repression of oncogenes that are known to drive MM progression (MAF, CCND1, MYC, and others). Furthermore, SLM6 showed superior in vivo anti-MM activity more than the CDK inhibitor flavopiridol, which is currently in clinical trials for MM. These findings show that SLM6 is a novel CDK9 inhibitor with promising preclinical activity as an anti-MM agent.

Clinical features and outcomes of plasma cell leukemia: a single-institution experience in the era of novel agents

Plasma cell leukemia (PCL) is a rare hematologic malignancy with aggressive clinical and biologic features. Data regarding its prognosis with the use of the novel agents, i.e., the immunomodulatory drugs thalidomide and lenalidomide, and the proteasome inhibitor bortezomib, are limited. We retrospectively reviewed clinical outcomes, response to therapy, and survival of 17 patients seen at the Penn State Hershey Cancer Institute since the availability of novel agents (2006–2011). Twelve patients had primary PCL (pPCL), and 5 secondary PCL (sPCL). PCL was associated with aggressive clinicobiological features, such as high-risk cytogenetics, elevated serum beta-2-microglobulin and lactate dehydrogenase, International Staging System stage III, and rapid relapse after therapy. With the use of thalidomide, lenalidomide, and bortezomib in 53%, 53%, and 88% patients, respectively, median overall survival (OS) was 18 months in the whole group (95% confidence interval, 11–21 months), and 21 and 4 months in pPCL and sPCL, respectively (P=0.015). OS was inferior to that of 313 consecutive patients with multiple myeloma (MM) treated in the same period, even when compared with a subset of 47 MM with high-risk cytogenetics. Although our data are limited by the small sample size, we conclude that novel agents may modestly improve survival in patients with PCL, when compared to historical controls. Novel therapies do not seem to overcome the negative prognosis of PCL as compared with MM.

Retrospective analysis of second malignancies in patients with multiple myeloma

8090

Background: Recent data from patients with multiple myeloma (MM) enrolled in randomized clinical trials have shown an increased incidence of second malignancies after treatment with lenalidomide, but the prevalence of second malignancies in the overall MM population is uncertain. Methods: We retrospectively analyzed the medical records of 320 consecutive MM patients followed at the Penn State Hershey Cancer Institute between 2006 and 2010. We excluded from the analysis basocellular and squamocellular carcinomas of the skin. Results: Forty-three patients (13%) were found to have second malignancies, and 5 of them had a third cancer. One pt had 4 cancers. They included cancers of the prostate (8 pts), breast (8), MDS/leukemia (6), colon/rectum (5), melanoma (5), lung (4), uterus (4), bladder (3), kidneys (2), pancreas (2), testicle (1), myeloproliferative disorders (1), and sarcoma (1). Of 50 cancers, 36 (72%) developed before the diagnosis of MM, at a median of 65 months (range, 1-372), and 14 after that, at a median of 37 months (range, 3-104). Lenalidomide was used in 239 (75%) patients, and in 9 of 14 cases of post-MM second malignancies. Conclusions: Second malignancies usually develop before the diagnosis of MM, i.e., MM is the second malignancy for the majority of patients. The use of lenalidomide could not be indicated as a possible carcinogenic factor for the majority of MM patients with second malignancies.

Abstract 5665: Multiplexing markers of response to sorafenib/mapatumumab combination therapy in hepatocellular carcinoma circulating tumor cells

Hepatocellular carcinoma (HCC) accounts for approximately 600,000 deaths per year worldwide. Effective therapeutic strategies for advanced stage patients are lacking, and the median survival rate for patients who are not eligible for surgical resection is a mere 6 months. Circulating tumor cells (CTCs) are detectable in the peripheral blood of cancer patients, are accessible through a minimally invasive procedure, and may provide a source of tumor tissue for analyzing molecular markers of therapeutic response that may help guide treatment protocols. To demonstrate this potential, we developed a system for imaging and quantifying multiplexed molecular markers of response to sorafenib/mapatumumab combination therapy in an HCC CTC model. The sorafenib/mapatumumab combination regimen is currently in phase 2 clinical trials for the treatment of HCC, and molecular markers that mediate the synergistic anti-tumor activity of this combination have been identified. These markers include phospho-p42/44 MAPK (p-ERK), Mcl-1, c-IAP2, and apoptotic markers such as cleaved caspase-3. We developed a technical approach using MultiSpectral Imaging (MSI) to quantitatively measure multiplexed fluorescent signals from primary antibodies specific to phospho-ERK, Mcl-1, c-IAP-2, and cleaved caspase-3 that had been conjugated to quantum dots (Qdots) with distinct fluorescence emission spectra. We first confirmed the ability to modulate marker expression and uncouple multiplexed Qdot signals by MSI in cultured HCC cells that had been treated with sorafenib or sorafenib/mapatumumab combinations. We then applied this detection system to HCC cells that were spiked into human blood and recovered using FDA-approved CTC isolation technology (CellSearch CTC Test by Veridex). Our data demonstrate the potential for studying molecular markers of therapeutic response in CTCs. Information gained from this technology may be used to guide therapeutic decisions or serve as pharmacokinetic/pharmacodynamic endpoints in experimental clinical protocols.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5665. doi:1538-7445.AM2012-5665

Abstract C77: Sangivamycin-like molecule 6 (SLM6) exhibits potent and selective anti-multiple myeloma activity through inhibition of P-TEFb

We previously reported the anti-tumor and anti-angiogenic activity of a new class of sangivamycin-like molecules (SLMs). In this study we aimed to further the preclinical development of these compounds by identifying tumor types with the highest sensitivity to their cytotoxic effects. Of 35 tumor cell lines from 8 different tissues of origin that we screened, we found that multiple myeloma (MM) cells were approximately 3–10 times more sensitive to SLMs than other tumor types. SLM3 as well as SLM5, SLM6, and SLM7 reduced viability and induced apoptosis of MM cells at sub-micromolar concentrations in vitro. By contrast, SLMs induced negligible amounts of apoptosis in other tumor and normal cell lines. SLM6 exhibited the most potent activity in vivo where it significantly inhibited the growth of xenografted MM tumors. We found that SLM6 inhibited cyclin dependent kinase 9 (CDK9) resulting in hypophosphorylation of RNA polymerase II (Ser2) and transcriptional repression of oncogenes that are known to drive MM progression and resistance to therapy (c-Maf, cyclin D1, c-Myc, L-Myc, and Mcl-1). Furthermore, we found that SLM6 increased the cytotoxic activity of therapies that are currently approved for MM treatment (bortezomib, lenalidomide, dexamethasone, and doxorubicin). These findings suggest that CDK9 inhibition is a particularly effective targeted strategy for MM, and SLM6 is a promising CDK9-targeted agent, both as a single agent and in combination with currently approved therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C77.

High-resolution imaging and antitumor effects of GFP(+) bone marrow-derived cells homing to syngeneic mouse colon tumors

Bone marrow-derived cells (BMDCs) participate in the growth and spread of tumors of the breast, brain, lung, and stomach. To date, there are limited reports of bone marrow involvement in colon cancer pathogenesis, but such findings would have the potential to generate novel treatments for colon cancer patients. We have established a mouse model for imaging BMDCs from whole tumor to single-cell resolution, whereby the bone marrow of lethally irradiated host animals is reconstituted with EGFP-expressing bone marrow cells from matched TgActb(EGFP) donors. The BM transplants yield mice with fluorescently labeled bone marrow, and so BMDCs can subsequently be monitored within a tumor through optical imaging. Successful BM reconstitution was confirmed at 8 weeks after transplantation, when surviving BALB/c mice were injected with CT26 mouse colon cancer cells. We find that up to 45% of cells dissociated from the tumors are GFP(+) and approximately 50% of Lin(+), CD11b(+), and CD3(+) cells express high levels of GFP. Notably, tumor growth is reduced in BM transplanted animals, compared with untransplanted host mice or EGFP-expressing BM donor mice. A needed next step is to separate the molecular and cellular (eg, T cells, NK cells, macrophages) bases of the antitumor effect of the BMDCs from any protumorigenic effect that could be subverted for therapeutic gain.

Off-target lapatinib activity sensitizes colon cancer cells through TRAIL death receptor up-regulation

Lapatinib, a dual HER2/EGFR (human epidermal growth factor receptor 2/epidermal growth factor receptor) inhibitor, is a recently approved targeted therapy for metastatic breast cancer. Because lapatinib enhances the efficacy of the chemotherapeutic agent capecitabine in breast cancer patients, we tested whether lapatinib also enhances the activity of anticancer agents in colorectal cancer. We found that lapatinib improved the proapoptotic effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and two TRAIL receptor agonists, the antibodies mapatumumab and lexatumumab. Tumors from mice treated with a combination of lapatinib and TRAIL exhibited more immunostaining for cleaved caspase-8, a marker of the extrinsic cell death pathway, than did tumors from mice treated with lapatinib or TRAIL alone. Furthermore, combination therapy suppressed tumor growth more effectively than either agent alone. Lapatinib up-regulated the proapoptotic TRAIL death receptors DR4 and DR5, leading to more efficient induction of apoptosis in the presence of TRAIL receptor agonists. This activity of lapatinib was independent of EGFR and HER2. The off-target induction of DR5 by lapatinib resulted from activation of the c-Jun amino-terminal kinase (JNK)/c-Jun signaling axis. This activity of lapatinib on TRAIL death receptor expression and signaling may confer therapeutic benefit when increased doses of lapatinib are used in combination with TRAIL receptor-activating agents.

Spectral imaging-based methods for quantifying autophagy and apoptosis

Spectral imaging systems are capable of detecting and quantifying subtle differences in light quality. In this study we coupled spectral imaging with fluorescence and white light microscopy to develop new methods for quantifying autophagy and apoptosis. For autophagy, we employed multispectral imaging to examine spectral changes in the fluorescence of LC3-GFP, a chimeric protein commonly used to track autophagosome formation. We found that punctate autophagosome-associated LC3-GFP exhibited a spectral profile that was distinctly different from diffuse cytosolic LC3-GFP. We then exploited this shift in spectral quality to quantify the amount of autophagosome-associated signal in single cells. Hydroxychloroquine (CQ), an anti-malarial agent that increases autophagosomal number, significantly increased the punctate LC3-GFP spectral signature, providing proof-of-principle for this approach. For studying apoptosis, we employed the Prism and Reflector Imaging Spectroscopy System (PARISS) hyperspectral imaging system to identify a spectral signature for active caspase-8 immunostaining in ex vivo tumor samples. This system was then used to rapidly quantify apoptosis induced by lexatumumab, an agonistic TRAIL-R2/DR5 antibody, in histological sections from a preclinical mouse model. We further found that the PARISS could accurately distinguish apoptotic tumor regions in hematoxylin and eosin-stained sections, which allowed us to quantify death receptor-mediated apoptosis in the absence of an apoptotic marker. These spectral imaging systems provide unbiased, quantitative and fast means for studying autophagy and apoptosis and complement the existing methods in their respective fields.

Quinacrine synergizes with 5-fluorouracil and other therapies in colorectal cancer

Although treatments have improved patient prognosis in surgically resectable colorectal cancer, new effective drugs with improved safety profiles are needed to improve the currently poor outcomes of patients with recurrent or metastatic colorectal cancer. Quinacrine, a small molecule anti-malarial agent that has activity in giardiasis, lupus, prion disease, and used as a means of non-surgical sterilization, has shown cytotoxic activity across a broad range of cancers. Here, we evaluate the potential of adding quinacrine to anticancer chemotherapeutics and targeted agents as a potential novel combinatorial therapy for advanced colon cancer. We show that quinacrine synergizes with 5-fluorouracil and significantly enhances the cytotoxicity of sorafenib in a panel of 10 human colorectal cancer cell lines, including those with KRAS mutations protein gel blot analysis confirmed that quinacrine's anticancer activity partially arises from its ability to stabilize p53 and lower anti-apoptotic protein levels. In a series of in vivo studies, quinacrine monotherapy lowered the tumor load of nu/nu mice bearing human colorectal cancer xenografts. In combination, quinacrine and 5-Fluorouracil significantly delayed tumor growth of a variety of different xenografts, as compared to each agent administered alone. Our results suggest that the administration of quinacrine in combination with chemotherapeutic agents and targeted agents should be further explored in patients with recurrent, locally advanced, or metastatic colorectal cancer.

Quinacrine sensitizes hepatocellular carcinoma cells to TRAIL and chemotherapeutic agents

Quinacrine has been widely explored in treatment of malaria, giardiasis, and rheumatic diseases. We find that quinacrine stabilizes p53 and induces p53-dependent and independent cell death. Treatment by quinacrine alone at concentrations of 10-20 mM for 1-2 d cannot kill hepatocellular carcinoma cells, such as HepG2, Hep3B, Huh7, which are also resistant to TRAIL. However, quinacrine renders these cells sensitive to treatment by TRAIL. Co-treatment of these cells with quinacrine and TRAIL induces overwhelming cell death within 3-4 h. Levels of DR5, a pro-apoptotic death receptor of TRAIL, are increased upon treatment with quinacrine, while levels of Mcl-1, an anti-apoptotic member of the Bcl-2 family, are decreased. While the synergistic effect of quinacrine with TRAIL appears to be in part independent of p53, knockdown of p53 in HepG2 cells by siRNA results in more cell death after treatment by quinacrine and TRAIL. The mechanism by which quinacrine sensitizes hepatocellular carcinoma cells to TRAIL and chemotherapies, and the potential for clinical application currently are being further explored. Lastly, quinacrine synergizes with chemotherapeutics, such as adriamycin, 5-FU, etoposide, CPT11, sorafenib, and gemcitabine, in killing hepatocellular carcinoma cells in vitro and the drug enhances the activity of sorafenib to delay tumor growth in vivo.

Human colon cancer stem cells are enriched by insulin-like growth factor-1 and are sensitive to figitumumab

Cancer stem cells (CSCs) are recognized as contributors to cancer progression and therapeutic resistance in liquid and solid malignancies. We analyzed a panel of human colon cancer cell lines for CSC populations by side population and aldehyde dehydrogenase activity. IGF-1 enriches these putative colon CSC populations in a β-catenin-dependent manner. Chemical inhibition of Akt depletes SP cells, and conversely, the overexpression of a constitutively active mutant version of Akt is sufficient to enrich CSC populations. CP-751,871, a fully human antibody with specificity to the IGF-1 receptor, is currently being tested in clinical trials for a variety of solid tumors. CP-751,871 reduces CSC populations in colon cancer cell lines in vitro and reduces tumor growth in vivo. We have identified a novel role for IGF-1 in the enrichment of chemo-resistant CSC populations. Our results suggest that CP-751,871 has preferential activity against putative CSC populations and, therefore, may complement current standard chemotherapeutic regimens that target cycling cells.

Overcoming hypoxia-induced apoptotic resistance through combinatorial inhibition of GSK-3β and CDK1

Tumor hypoxia is an inherent impediment to cancer treatment that is both clinically significant and problematic. In this study, we conducted a cell-based screen to identify small molecules that could reverse the apoptotic resistance of hypoxic cancer cells. Among the compounds, we identified were a structurally related group that sensitized hypoxic cancer cells to apoptosis by inhibiting the kinases GSK-3β and cyclin-dependent kinase (CDK) 1. Combinatorial inhibition of these proteins in hypoxic cancer cells and tumors increased levels of c-Myc and decreased expression of c-IAP2 and the central hypoxia response regulator hypoxia-inducible factor (HIF) 1α. In mice, these compounds augmented the hypoxic tumor cell death induced by cytotoxic chemotherapy, blocking angiogenesis and tumor growth. Taken together, our findings suggest that combinatorial inhibition of GSK-3β and CDK1 augment the apoptotic sensitivity of hypoxic tumors, and they offer preclinical validation of a novel and readily translatable strategy to improve cancer therapy.

Abstract 674: Novel combinatorial quinacrine cancer therapies for advanced colon cancer

BACKGROUND: Although treatments have improved patient prognosis in early stages of colorectal cancer, new effective drugs with improved safety profiles are needed for improving the treatment of patients with advanced colon cancer. Quinacrine, a small molecule anti-malarial agent that has activity in giardiasis, lupus, prion disease, and used as a means of non-surgical sterilization, has shown cytotoxic activity across a broad range of cancers. The well characterized safety profile of quinacrine and its anticancer activity hold promise in novel combinatorial cancer therapies.

OBJECTIVES: To evaluate the potential of adding quinacrine to anticancer chemotherapeutics and targeted agents as a potential novel combinatorial therapy for advanced colon cancer and to detail the mechanism of action of quinacrine when combined with cancer chemotherapy and targeted agents.

METHODS: In vitro dose-response curves and isobolograms were constructed for single agent and dual agent therapies using quinacrine, 5-fluorouracil, gemcitabine, and sorafenib using the following colon cancer cell lines: HT-29, HT-29-luc, HCT-15, HCT-116, HCT-116 p53−/−, HCT-116 bax−/−, RKO, DLD-1, SW-480, and SW-620. Western blot analysis and flow cytometry were used to investigate potential mechanisms of action and to examine cell death. In vivo experiments were carried out to investigate toxicity and efficacy of combinatorial quinacrine chemotherapy in an athymic nu/nu mouse tumor xenograft model with human HT-29-luc cells.

RESULTS: Single-agent quinacrine demonstrates potent anticancer activity with an average IC50 of 5.79 ± 0.83 μM across all ten colon cancer cell lines screened. In combination, quinacrine enhanced the anticancer activity of 5-fluorouracil and gemcitabine while significantly synergizing with sorafenib. Western blot analysis revealed that quinacrine's anticancer activity partially arises from its ability to stabilize p53, elevate death receptor levels, and lower anti-apoptotic protein levels. Quinacrine, when combined with sorafenib, dramatically lowers levels of the anti-apoptotic protein MCL-1. In vivo studies have shown that quinacrine monotherapy at a daily dose of 150 mg/kg significantly lowers the tumor load of nu/nu mice.

CONCLUSIONS: Quinacrine is cytotoxic to a broad range of colon cancer cells lines and enhances the anticancer activity of chemotherapies such as 5-fluorouracil, gemcitabine, and sorafenib. The administration of quinacrine in combination with chemotherapy agents and targeted agents in patients with advanced colon cancer should be further explored in the clinic.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 674. doi:10.1158/1538-7445.AM2011-674

Abstract 4101: Off-target lapatinib activity up-regulates TRAIL death receptors in colon cancer cells

Lapatinib is a dual HER2/EGFR inhibitor that is FDA-approved for the treatment of HER2+ metastatic breast cancer when combined with capecitabine. Colon cancer cells express high levels of EGFR and to a lesser extent, HER2, and therefore, we set out to identify effective therapeutic combinations involving lapatinib in colon cancer. We screened for therapeutic partners of lapatinib using SW620 cells, a cell line that expresses mutant p53 and is resistant to various chemotherapies and apoptosis-inducing agents. We found that high concentrations of lapatinib (10 microM) failed to induce cell death as a single agent or in combination with chemotherapy. However, lapatinib significantly enhanced the pro-apoptotic effects of TRAIL, a finding that we confirmed in a panel of colon cancer cell lines. Lapatinib also sensitized colon cancer cells to the agonistic TRAIL receptor antibodies mapatumumab and lexatumumab. We then tested this novel combination in vivo, and found that tumors from mice treated with lapatinib/TRAIL combinations exhibited increased staining for cleaved caspase-8, a biomarker of death receptor activity, compared to lapatinib or TRAIL treatment alone. Furthermore, the combination therapy suppressed tumor growth, whereas single agent treatments had little effect. Mechanistically, we found that lapatinib up-regulates both pro-apoptotic TRAIL death receptors, DR4 and DR5. Lapatinib increased DR5 mRNA, but had no effects on DR5 protein stability, suggesting that lapatinib up-regulates death receptors through a pre-translational or translational mechanism. Interestingly, other EGFR and HER2 inhibitors, individually or in combination, failed to increase death receptor expression or TRAIL sensitivity, leading us to hypothesize that this activity of lapatinib was due to an off-target effect. In support of this idea, lapatinib induced death receptor up-regulation in SW620 cells, which lack EGFR expression and have undetectable levels of HER2 signaling. In addition, lower lapatinib concentrations, which completely inhibited EGFR and HER2, were failed to induce death receptor expression and increase TRAIL sensitivity, further demonstrating the off-target nature of this effect. High concentrations of lapatinib increased phosphorylation of c-Jun, extracellular signal related kinase (ERK) and c-Jun N-terminal kinase (JNK). RNAi-mediated knockdown experiments proved that c-Jun and JNK, but not ERK, were required for lapatinib-induced DR5 up-regulation. We conclude that high concentrations of lapatinib, through an EGFR/HER2-indpendent mechanism, up-regulate TRAIL death receptors and increase TRAIL sensitivity by a mechanism involving the JNK/c-Jun signaling pathway. From a clinical perspective, therapeutic benefit may be gained from this off-target activity by using high doses of lapatinib and introducing TRAIL receptor-activating agents into the treatment regimen.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4101. doi:10.1158/1538-7445.AM2011-4101

Prozone effect of serum IgE levels in a case of plasma cell leukemia

We describe a case of multiple myeloma (MM) and secondary plasma cell leukemia (PCL) secreting IgE-kappa immunoglobulin. To our knowledge, only 2 cases of IgE-producing secondary PCL have been reported in the medical literature. In our patient, the only tumor marker available for monitoring the therapeutic response to chemotherapy and allogeneic stem cell transplantation was the quantitative M component at serum protein electrophoresis (SPEP), because serum free light chains were in the normal range, Bence-Jones proteinuria was absent, and quantitative serum IgE levels provided inaccurate and erratic results, due to the prozone effect. This is a laboratory phenomenon that occurs when antigen excess interferes with antibody-based methods requiring immune complex formation for detection. It is important to recognize the presence of a prozone effect, because it can produce falsely normal results, and therefore it could lead clinicians to incorrect assessment of the response to therapy.

The p53 target Plk2 interacts with TSC proteins impacting mTOR signaling, tumor growth and chemosensitivity under hypoxic conditions

Tuberous sclerosis complex 1 (TSC1) inhibits mammalian target of rapamycin (mTOR), a central promotor of cell growth and proliferation. The protein product of the TSC1 gene, hamartin (referred to as TSC1) is known to interact with Polo-like kinase 1 (Plk1) in a cell cycle regulated, phosphorylation-dependent manner. We hypothesized that the p53 target gene, Plk2, is a tumor suppressor, mediating its tumor suppressor function through interactions with TSC1 that facilitate TSC1/2 restraint of mTOR under hypoxic stress. We found that human lung tumor cells deficient in Plk2 grew larger than control tumors, and that Plk2 interacts with endogenous TSC1 protein. Additionally, C-terminal Plk2-GST fusion protein bound both TSC1 and TSC2 proteins. TSC1 levels were elevated in response to Adriamycin and cells transiently overexpressing Plk2 demonstrated decreased phosphorylation of the downstream target of mTOR, ribosomal protein p70S6 kinase during hypoxia. Plk2 levels were inversely correlated with cytoplasmic p70S6K phosphorylation. Plk2 levels did not increase in response to DNA damage (Adriamycin, CPT -11) when HCT 116 and H460 cells were exposed to hypoxia. TSC1-deficient mouse embryonic fibroblasts with TSC1 added back demonstrated decreased S6K phosphorylation, which was further decreased when Plk2 was transiently overexpressed. Interestingly, under normoxia, Plk2 deficient tumor cells demonstrated increased apoptosis in response to various chemotherapeutic agents including CPT -11 but increased resistance to apoptotic death after CPT-11 treatment under hypoxia, and tumor xenografts comprised of these Plk2-deficient cells were resistant to CPT -11. Our results point to a novel Plk2-TSC1 interaction with effects on mTOR signaling during hypoxia, and tumor growth that may enable targeting Plk2 signaling in cancer therapy.

Abstract 4326: High-resolution imaging and antitumor effects of GFP(+) bone marrow-derived cells homing to syngeneic mouse colon tumors

Bone marrow-derived cells (BMDCs) are believed to play a significant role in the growth and spread of certain tumors, namely cancers of the breast, brain, lung, and stomach. To date there are limited reports of bone marrow involvement in colon cancer pathogenesis, but such findings have the potential to generate novel treatments for patients with colon cancer. We have established two mouse models (Balb/c and C57/BL6 backgrounds) for imaging BMDCs from whole tumor to single-cell resolution, whereby the bone marrow of lethally irradiated host animals is reconstituted with EGFP-expressing bone marrow cells from matched donors. The bone marrow transplants (BMTs) yield mice with fluorescently labeled bone marrow and BMDCs can subsequently be monitored within a tumor through optical imaging, as well as ex vivo techniques. We have confirmed successful BM reconstitution at six or more weeks following transplantation. At least six weeks after transplantation, surviving Balb/c and C57/BL6 transplanted mice were injected with CT26 mouse colon cancer cells and p53-deficient Ras/Myc-transformed colonocytes, respectively. We have found up to 45% of cells dissociated from the tumors are GFP-positive and we are currently working to identify the various BM lineages represented within these populations. Interestingly, we have found that tumor growth is reduced in BMT animals compared with untransplanted host mice, as well as EGFP-expressing BM donor mice. We are currently working to determine whether an immune response associated with the BMT might account for these apparent anti-tumor effects. It will clearly be important to separate the molecular and cellular (T cells, NK cells, macrophages, etc) basis of the anti-tumor effect of the BMDCs from any pro-tumorigenic effect that could be subverted for therapeutic gain. Additionally, as an extension of our model we are performing orthotopic cecal wall injections in order to determine whether microenvironmental nuances alter BM homing to the colon versus subcutaneous space. It is expected that the identified BMDCs will aid in the development of novel cancer therapeutic and delivery strategies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4326.

Abstract 5044: Dual GSK-3β/CDK inhibitors induce multiple myeloma cell death and eliminate putative cancer stem cell populations

Multiple myeloma (MM) is a plasma cell malignancy that recurs in 100% of patients despite high treatment response rates. The incurable nature of the disease and the low proliferative capacity of terminally differentiated MM plasma cells supports the existence of a cancer stem cell (CSC) component - a cell population with self-renewal and drug resistance properties capable of repopulating the disease after seemingly effective treatment and periods of undetectable disease. It is imperative to develop new therapies that target both terminally differentiated MM plasma cells and MM CSCs to extend disease-free survival and control the disease. We tested the ability of c-Myc-inducing compounds, such as GSK-3β and dual GSK-3β/CDK inhibitors, to enhance the activity of bortezomib against advanced MM cell lines (RPM-I8226 and NCI-H929). We have shown that this class of inhibitors has anti-tumor effects and sensitizes numerous solid malignancies to apoptosis-inducing agents (Mayes P.A., Dolloff N.G. et al., in revision). Moreover, c-Myc expression increases protein translation, and in doing so, enhances the cytotoxicity of proteasome inhibitors such as bortezomib (Nawrocki et al., 2008). We found that GSK-3β inhibitors (lithium choloride and sc-24020) failed to induce apoptosis or reduce viability of MM cell lines or to enhance the activity of bortezomib. By contrast, the dual GSK-3β/CDK inhibitors, alsterpaullone and the nucleoside analogue SLM3 (Mayes P.A., Dolloff, N.G. et al., in revision), were highly toxic to MM cells both alone and in combination with bortezomib. In addition to inducing massive apoptosis and reducing MM cell viability, alsterpaullone and SLM3 eliminated the presence of dye-effluxing side-populations, that have been shown to exhibit CSC behavior in vitro and in animal models of MM. By comparison, bortezomib, adriamycin and melphalan increased the percentage of MM side-population cells, suggesting that MM CSC cells are more resistant to these agents compared to their non-CSC counterparts. Interestingly, alsterpaullone and SLM3 eliminate a distinctly large sub-population of MM cells that are enriched in side-population cells, providing a further characterization of the MM CSC phenotype. We propose that using GSK-3β/CDK inhibitors may be effective therapies, as they target tumorigenic CSC populations, which are responsible for disease relapse. We are currently testing this hypothesis in mouse models of MM.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5044.

Abstract 673: Novel anti-tumor activity of lapatinib derives from off-target up-regulation of TRAIL death receptors

Lapatinib, a HER2/EGFR inhibitor, is the most recently approved targeted therapy for metastatic breast cancer. Based on clinical evidence that lapatinib enhances efficacy of capecitabine in breast cancer patients, we hypothesized that lapatinib could augment the anti-cancer activity of agents in other tumor types such as colon cancer. Using in vitro cell death and apoptosis assays, we found lapatinib to have minimal effect on chemotherapy-induced cytotoxicity in colon cancer cell lines. However, elevated concentrations of lapatinib (5-10μM) significantly enhanced the pro-apoptotic effects of TRAIL and agonistic TRAIL receptor antibodies. In vivo, xenografted colon tumors from mice treated with lapatinib/TRAIL combinations exhibited more immunostaining for cleaved caspase-8, an apical caspase in the extrinsic cell death pathway, compared to tumors from mice treated with lapatinib or TRAIL alone. Furthermore, the combination therapy suppressed tumor growth, whereas single agent treatments had little effect. Mechanistically, lapatinib up-regulated proapoptotic TRAIL death receptors, DR4 and DR5, leading to more efficient induction of apoptosis in the presence of TRAIL and agonistic TRAIL receptor antibodies. Lapatinib had no appreciable effects on death receptor protein stability, and DR5 - but not DR4 - mRNA levels were increased, suggesting that lapatinib transcriptionally up-regulates DR5. Interestingly, other EGFR and HER2 inhibitors, individually or in combination, failed to increase death receptor expression and TRAIL sensitivity, suggesting that this novel effect resulted from off-target activity. In support of this hypothesis, lapatinib induced death receptor up-regulation in SW620 cells, which lack EGFR expression and detectable levels of HER2 signaling. Lower lapatinib concentrations (1μM), which completely inhibited EGFR and HER2, were not sufficient to induce death receptor expression and increase TRAIL sensitivity, further demonstrating the off-target nature of this effect. High concentrations of lapatinib increased phosphorylation of c-Jun, extracellular signal related kinase (ERK) and c-Jun N-terminal kinase (JNK). RNAi-mediated knockdown experiments proved that c-Jun, but not ERK or JNK, were required for lapatinib-induced DR5 up-regulation. We conclude that high concentrations of lapatinib, through an EGFR/HER2-indpendent mechanism, stimulate c-Jun phosphorylation/transcriptional activity leading to DR5 up-regulation and increased TRAIL sensitivity. From a clinical perspective, therapeutic benefit may be gained from this off-target activity by using high doses of lapatinib in combination with TRAIL-receptor-activating agents. Secondly, death receptor induction and signaling may serve as a biomarker of response following lapatinib treatment to identify patients that have responded most favorably to treatment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 673.

The alpha-receptor for platelet-derived growth factor as a target for antibody-mediated inhibition of skeletal metastases from prostate cancer cells

Bone resorption by osteoclasts is thought to promote the proliferation of prostate cancer cells disseminated to the skeleton (Mundy, 2002). Using a mouse model of experimental metastasis, we found that although late-stage metastatic tumors were indeed surrounded by osteoclasts, these cells were spatially unrelated to the small foci of cancer cells in early-stage metastases. This is the first evidence that survival and growth of disseminated prostate cancer cells immediately after their extravasation may not depend on osteoclast involvement. Interestingly, prostate cancer cells expressing the alpha-receptor for platelet-derived growth factor (PDGFRalpha) progress during early-stages of skeletal dissemination, whereas cells expressing lower levels or lacking this receptor fail to survive after extravasation in the bone marrow. However, non-metastatic cells acquire bone-metastatic potential upon ectopic overexpression of PDGFRalpha. Finally, functional blockade of human PDGFRalpha on prostate cancer cells utilizing a novel humanized monoclonal antibody -- soon to undergo phase-II clinical trials -- significantly impairs the establishment of early skeletal metastases. In conclusion, our results strongly implicate PDGFRalpha in prostate cancer bone tropism through its promotion of survival and progression of early-metastatic foci, providing ground for therapeutic strategies aimed at preventing or containing the initial progression of skeletal metastases in patients affected by prostate adenocarcinoma.

Human bone marrow activates the Akt pathway in metastatic prostate cells through transactivation of the alpha-platelet-derived growth factor receptor

The factors regulating the bone tropism of disseminated prostate cancer cells are still vaguely defined. We report that prostate cancer cells that metastasize to the skeleton respond to human bone marrow with a robust stimulation of the phosphatidylinositol 3-kinase/Akt pathway, whereas prostate cells that lack bone-metastatic potential respond negligibly. The majority of this Akt activation is dependent on alpha-platelet-derived growth factor receptor (alpha-PDGFR) signaling, which was shown using the small-molecule inhibitor of PDGFR signaling AG1296. Low concentrations of PDGF-AA and PDGF-BB found in bone marrow aspirates, which were detected by ELISA, do not account for the high levels of alpha-PDGFR signaling. Additionally, neutralizing PDGF binding using a alpha-PDGFR-specific antibody (IMC-3G3) failed to produce a significant inhibition of bone marrow-induced Akt activation. However, the inhibitory effect of IMC-3G3 rivaled that of AG1296 when incubation was done under conditions that stimulated alpha-PDGFR internalization. We conclude that alpha-PDGFR is activated by multiple soluble factors contained within human bone marrow, in addition to its natural ligands, and this transactivation is dependent on receptor localization to the plasma membrane. Therefore, alpha-PDGFR expression may provide select prostate phenotypes with a growth advantage within the bone microenvironment.

Bone-metastatic potential of human prostate cancer cells correlates with Akt/PKB activation by alpha platelet-derived growth factor receptor

Prostate adenocarcinoma metastasizes to the skeleton more frequently than any other organ. An underlying cause of this phenomenon may be the ability of bone-produced factors to specifically select disseminated prostate cancer cells that are susceptible to their trophic effects. Platelet-derived growth factor (PDGF), a potent mitogen for both normal and tumor cells, is produced in several tissues including bone, where it is synthesized by both osteoblasts and osteoclasts. Here, we show that PDGF causes a significantly stronger activation of the Akt/PKB survival pathway in bone-metastatic prostate cancer cells compared to nonmetastatic cells. Normal prostate epithelial cells and DU-145 prostate cells, originally derived from a brain metastasis, are not responsive to PDGF. In contrast, epidermal growth factor stimulates Akt to the same extent in all prostate cells tested. This difference in PDGF responsiveness depends on the higher expression of alpha-PDGFR in bone-metastatic compared to nonmetastatic prostate cells and the lack of alpha-PDGFR expression in normal and metastatic prostate cells derived from tissues other than bone. Thus, alpha-PDGFR expression might identify prostate cancer cells with the highest propensity to metastasize to the skeleton.

CX3CR1-fractalkine expression regulates cellular mechanisms involved in adhesion, migration, and survival of human prostate cancer cells

Chemokines and their receptors might be involved in the selection of specific organs by metastatic cancer cells. For instance, the CXCR4-SDF-1alpha pair regulates adhesion and migration of breast as well as prostate cancer cells to metastatic sites. In this study, we present the first evidence for the expression of CX3CR1--the specific receptor for the chemokine fractalkine--by human prostate cancer cells, whereas human bone marrow endothelial cells and differentiated osteoblasts express fractalkine. The adhesion of prostate cancer cells to human bone marrow endothelial cells in flow conditions is significantly reduced by a neutralizing antibody against fractalkine, and they migrate toward a medium conditioned by osteoblasts, which secrete the soluble form of the chemokine. Finally, fractalkine activates the PI3K/Akt survival pathway in human prostate cancer cells.