Abstract 1658: ADT-007 binds RAS and inhibits RAS signaling

RAS is a critically important oncogenic protein that is mutated in approximately 1/3 of cancers resulting in aberrant activation of downstream signaling, which drives malignant transformation. Current molecular targeted therapeutics, and several in development, inhibit only specific mutant alleles (G12C, G12D). In addition, compounds which directly inhibit RAS via proteolytic degradation or inhibit RAS activation by SOS1 are in preclinical development and are referred to as Pan-KRAS inhibitors. Previously investigators have reported that the NSAID, sulindac, can selectively inhibit RAS mutant tumorigenesis by a cyclooxygenase (COX)-independent mechanism. Sulindac, and more potent analogs have also previously been reported to inhibit RAS-mediated transformation and directly bind RAS. Here we describe an ultra-potent non-COX inhibitory derivative of sulindac, ADT-007, which binds to and inhibits RAS nucleotide binding and RAS-effector association.

ADT-007 binding to KRAS was evaluated by Micro-Tag cell target engagement and by Cellular Thermal Shift Assay (CETSA) which demonstrated a potency of target engagement (EC50) value in the subnanomolar range. Consistent with molecular docking studies, HSQC NMR spectroscopy using recombinant KRAS revealed that ADT-007 interacted with KRAS after Mg2+ chelation to obtain a nucleotide free (NF) state, resulting in chemical shift changes and signal attenuation of residues in the P-loop and nucleotide binding domain. Similarly, biochemical assays confirmed that ADT-007 prevented MANT-GTP binding to recombinant NF KRAS but did not compete with bound GTP. Functional assays also showed that KRAS binding to RAF-RBD(GST) was inhibited by ADT-007. The compound inhibited constitutive RAS activation (RAF-RBD pulldown) in serum starved MiaPaCa-2 pancreatic cancer cells harboring a KRAS-G12C mutation and demonstrated Pan-RAS inhibition in serum- or EGF-stimulated cells. Further, ADT-007 inhibited AKT phosphorylation and EGF-stimulated downstream ERK1/2 phosphorylation. Finally, ADT-007 demonstrated RAS-selective growth inhibition in isogenic pancreatic and colorectal cancer cell pairs (BxPC-3, HT29). Together, these experiments support further development of ADT-007 and related analogs for treatment of RAS-driven cancers.

Citation Format: Adam B. Keeton, Xi Chen, Jacob Valiyaveettil, Chung-Hui Huang, Tyler E. Mattox, Khalda Fadlalla, Jeremy B. Foote, Donald J. Buchsbaum, Kristy L. Berry, Elmar Nurmemmedov, Ivan Babic, Vadim Gaponenko, Gregory Gorman, Lori Coward, Yulia Y. Maxuitenko, Forrest T. Smith, Gary A. Piazza. ADT-007 binds RAS and inhibits RAS signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1658.

Enhancing anticancer activity of checkpoint immunotherapy by targeting RAS

Approximately 30% of human cancers harbor a gain‐in‐function mutation in the RAS gene, resulting in constitutive activation of the RAS protein to stimulate downstream signaling, including the RAS‐mitogen activated protein kinase pathway that drives cancer cells to proliferate and metastasize. RAS‐driven oncogenesis also promotes immune evasion by increasing the expression of programmed cell death ligand‐1, reducing the expression of major histocompatibility complex molecules that present antigens to T‐lymphocytes and altering the expression of cytokines that promote the differentiation and accumulation of immune suppressive cell types such as myeloid‐derived suppressor cells, regulatory T‐cells, and cancer‐associated fibroblasts. Together, these changes lead to an immune suppressive tumor microenvironment that impedes T‐cell activation and infiltration and promotes the outgrowth and metastasis of tumor cells. As a result, despite the growing success of checkpoint immunotherapy, many patients with RAS‐driven tumors experience resistance to therapy and poor clinical outcomes. Therefore, RAS inhibitors in development have the potential to weaken cancer cell immune evasion and enhance the antitumor immune response to improve survival of patients with RAS‐driven cancers. This review highlights the potential of RAS inhibitors to enhance or broaden the anticancer activity of currently available checkpoint immunotherapy.

Exploiting RAS Nucleotide Cycling as a Strategy for Drugging RAS-Driven Cancers

Oncogenic mutations in RAS genes result in the elevation of cellular active RAS protein levels and increased signal propagation through downstream pathways that drive tumor cell proliferation and survival. These gain-of-function mutations drive over 30% of all human cancers, presenting promising therapeutic potential for RAS inhibitors. However, many have deemed RAS “undruggable” after nearly 40 years of failed drug discovery campaigns aimed at identifying a RAS inhibitor with clinical activity. Here we review RAS nucleotide cycling and the opportunities that RAS biochemistry presents for developing novel RAS inhibitory compounds. Additionally, compounds that have been identified to inhibit RAS by exploiting various aspects of RAS biology and biochemistry will be covered. Our current understanding of the biochemical properties of RAS, along with reports of direct-binding inhibitors, both provide insight on viable strategies for the discovery of novel clinical candidates with RAS inhibitory activity.

Abstract 4822: Targeting RAS and downstream signaling in high-grade serous ovarian carcinoma with novel RAS inhibitors

High grade serous ovarian carcinoma (HGSOC), which accounts for 70-80% of ovarian cancer deaths, is characterized by TP53 mutations and about half of these tumors present defects in homologous recombination DNA repair pathway genes. PARP inhibitors have now become FDA-approved for the treatment of recurrent and BRCA-associated ovarian cancer. Despite providing a major advance in ovarian cancer treatment in recent years, resistance to PARP inhibitors is often encountered and new treatment strategies must be devised. Oncogenic RAS and constitutively active RAS signaling regulate multiple downstream cascades to increase cell proliferation, survival, and malignant transformation. Despite the absence of RAS mutations, upregulation in the RAS pathway is prevalent in HGSOC, suggesting that these represent key, yet under-explored, inhibition targets for the treatment of ovarian cancer. Further bolstering the importance of RAS pathway inhibition are reports on cytotoxic synergistic effects for the combination of MEK and PARP inhibitors in ovarian cancer. The development of inhibitors directly targeting RAS has been hindered by the lack of suitable surfaces on the protein for small molecule binding and its high affinity for GTP binding. We developed a novel series of indene derivatives that showed highly selective growth inhibitory activity in tumor cells harboring constitutively active RAS vs. cells with low levels of active RAS. Chemical optimization led to a series of compounds that potently and selectively inhibit RAS-dependent tumor cell growth by blocking GTP binding to RAS. Here we examined the effects of RAS inhibition by two novel compounds, MCI-059 and MCI-062, in a panel of HGSOC cell lines with variable baseline levels of active RAS. We observed potent growth inhibitory activity for these novel inhibitors in most of the 15 ovarian cancer cell lines tested (IC50s ~25nM and 7nM for MCI-059 and MCI-062, respectively), with the lesser sensitivity in OV-90 cells correlating with its lowest basal levels of active RAS measured by a pull down assay using GST-RAF1-RBD/ glutathione agarose beads. Time-course experiments revealed that MCI-062 induces apoptosis beginning at 18-24 hours. Furthermore, both MCI-059 and MCI-062 inhibited: i) RAS-RAF1-RBD binding in GTPγS loaded recombinant human KRAS; ii) RAS-RAF1-RBD binding in OVCAR8 and SKOV3ip cells under normal culture growth conditions or under serum starvation followed by EGF-stimulation; iii) EGF-stimulated activation of the RAF-MEK-ERK and PI3K-AKT cascades in OVCAR-8 and SKOV3ip cells. We also confirmed that MCI-062 decreases several components of the RAS downstream signaling pathway via RPPA analysis. In summary, our results demonstrate that MCI-059 and MCI-062 inhibit HGSOC cell growth by blocking RAS-effector interactions, and support further evaluation of our novel RAS inhibitors for the treatment of ovarian cancer.

Citation Format: Tyler E. Mattox, Tiffany S. Norton, Adam B. Keeton, Antonio B. Ward, Yulia Y. Maxuitenko, Kristy L. Berry, Bing Zhu, Alla Musiyenko, Elaine Gavin, Veronica Ramirez-Alcantara, Xi Chen, Jacob Valiyaveettil, Jennifer Scalici, Rodney P. Rocconi, Gary A. Piazza, Luciana Madeira da Silva. Targeting RAS and downstream signaling in high-grade serous ovarian carcinoma with novel RAS inhibitors [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 4822.

Abstract B54: Targeting constitutively active RAS signaling in high-grade serous ovarian carcinoma (HGSOC) with ADT-006, a novel small molecule that blocks RAS-effector interactions

Gain-of-function mutations in RAS genes occur at high frequency in several types of cancer, including pancreatic, colorectal, and lung adenocarcinomas. Such driver mutations result in constitutive activation of RAS and its downstream signaling pathways, promoting tumor cell proliferation, survival, and metastasis. The development of drugs directly targeting RAS has been hindered due to the lack of suitable surfaces on the protein for small-molecule binding, as well as its high affinity for GTP binding. We recently identified a novel series of indene derivatives that showed highly selective growth inhibitory activity in tumor cells harboring constitutively active RAS versus tumor cells with low levels of active RAS. Chemical optimization resulted in series of compounds that potently and selectively inhibit RAS-dependent tumor cell growth by blocking RAS-effector interactions. High-grade serous ovarian carcinoma (HGSOC) is invariably characterized by the key driver mutation in TP53, but other mutational drivers, such as mutations or altered methylation of BRCA1 and BRCA2, cyclin E1, PIK3CA and AKT1/2 amplifications, and loss of NF1, RB1 and PTEN, are also commonly found. Conversely, RAS mutations are usually associated with low-grade serous ovarian carcinoma (LGSOC) and mucinous ovarian tumors. Here we show that 5 (OVCAR5, OVCAR8, ES2, KURAMOCHI, and IGROV1) out of 12 ovarian cancer cell lines tested have high levels of constitutive RAS activation as measured by the active RAS pull-down assay, comparable or higher than those of MIA PaCa-2 pancreatic cancer cells, which harbors the activating mutation G12C on KRAS. The 7 remainder cell lines tested (A2780, SKOV3ip, CAOV3, OVCAR4, OVCAR3, OVSAHO, and OV90) had levels of active RAS comparable or lower than BxPC-3 pancreatic cells, which lacks constitutively active RAS. Interestingly, most ovarian cancer cell lines were highly sensitive to ADT-006 (IC50 ~20 nM) in vitro, with the exception of OV-90 cells, which showed IC50 ~300 nM and the lowest level of active RAS measured by the pull-down assay. Treatment of intact SKOV3ip and OVCAR8 cells with ADT-006 inhibited RAF/MAPK and PI3K/AKT phosphorylation within the same concentration range as the growth inhibitory activity of this compound. Xenograft studies performed with SKOV3ip cells implanted intraperitoneally in athymic nude mice and treated twice daily with ADT-006 i.p. at the dose of 10 mg/kg for two weeks showed significant antitumor activity with no discernible toxicity. Our results demonstrate that ADT-006 inhibits HGSOC cell growth by blocking RAS-effector interactions, and supports further evaluation of our novel RAS inhibitors for the treatment of ovarian cancer.

Citation Format: Luciana Madeira da Silva, Tyler E. Mattox, Adam B. Keeton, Bing Zhu, Kristy L. Berry, Alla Musiyenko, Elaine Gavin, Kevin Lee, Veronica Ramirez-Alcantara, Yulia Y. Maxuitenko, Xi Chen, Jacob Valiyaveettil, Michael R. Boyd, Jennifer Scalici, Rodney Rocconi, Gary A. Piazza. Targeting constitutively active RAS signaling in high-grade serous ovarian carcinoma (HGSOC) with ADT-006, a novel small molecule that blocks RAS-effector interactions [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr B54.

Abstract 2778: Tumor target vs. tissue of tumor origin: cluster analysis of genomic profile of 42 human tumor in vitro and in vivo models

Traditionally, drug development has relied upon testing cancer drug candidates in cell lines. Active drugs are then tested in human tumor xenograft models, usually selected based upon the cell lines in which the drug showed activity. The majority of drugs fail at this stage as they do not show activity in the xenograft models chosen. We performed Affymetrix genomic analysis on 42 human tumor xenograft models and the original cell lines from which they were established. The genomic profiles obtained underwent Unsupervised Hierarchical Cluster Analysis to ascertain which cell lines and xenograft models had similar genomic profiles and which did not. The analysis showed that only 24 of 42 human tumor xenograft models clustered side-by-side with the cell line from which they were established. All 6 human leukemia/lymphoma xenograft models clustered very well with the cell lines from which they were established, and they clustered perfectly according to histological class. Five out of six human colon tumor xenograft models clustered well with the cell lines from which they were established and according to histotype. Of the 18 xenograft/cell line pairs that did not cluster side-by-side, 10 pairs remained in the same general cluster, whereas the partners of 8 other pairs were dispersed across different major clusters. Ovarian, breast, melanoma, and pancreatic human tumor xenograft models did not cluster according to histotype. Our data may explain why some drugs that show in vitro activity in some cell lines are not active in other cell lines of the same histological type, and also why some drugs that show activity in vitro then fail in xenograft models. In our laboratory, the PANC-1 cell line is very often chosen as a model of pancreatic cancer. A drug showing activity in the PANC-1 cell line would next be tested in other in vitro models of pancreatic cancer (e.g., MIA PaCa-2, CFPAC-1, and BxPC-3). However, none of these other pancreatic models have a similar genetic profile to PANC-1. Based upon our data, the cell line showing most similarity to the PANC-1 cell line is the breast cancer cell line MDA-MB-231. It is our suggestion that a drug showing activity in the PANC-1 cell line should be tested in other cell lines showing similar genetic profiles, not in cell lines based on histotype. Another example from our analysis is the LOX-IMV1 melanoma cell line. Not only does this cell line not cluster with its corresponding LOX-IMV1 xenograft model, it clusters most closely with the NCI/ADR-RES ovarian cell line. In summary, the genomic profiles of approximately 57% of the tumor xenograft models analyzed closely associate with the cell line from which they were established. Some of the tumor xenograft models show very little similarity to the cell lines from which they were established. Additionally, many of the models (both xenografts and cell lines), do not cluster according to their tissue of origin.

Citation Format: Michael J. Roberts, Michael S. Koratich, Murray Stackhouse, Richard D. May, Andrew D. Penman, Tommie A. Gamble, Kristy L. Berry, Joseph F. Murphy, Robert J. Rooney, Yulia Y. Maxuitenko. Tumor target vs. tissue of tumor origin: cluster analysis of genomic profile of 42 human tumor in vitro and in vivo models. [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 2778. doi:10.1158/1538-7445.AM2013-2778

Abstract 3114: Effects of tumor-stromal interactions on gene expression in panel of mouse tumor models

Tumor growth is not determined solely by the tumor cells but is governed by interactions between tumor cells and host stromal cells, including endothelial cell activation and fibroblastic stroma response. Tumor stroma profoundly influences many steps of tumor progression. In many human cancers, such as breast, prostate, and colon, the stroma comprises the majority of the tumor mass, as a hallmark of the clinical feature called desmoplasia. Numerous studies have showed that tumor-stromal cell interactions play crucial roles in supporting cancer progression and in promoting anticancer drug resistance by alternating gene expression profiles in both tumor and stromal cells through network tumor-stromal interactions in the tumor microenvironments. It has been challenging to obtain separate gene profiles for tumor and stroma with human tumor samples as both tumor and stromal cells share the same genome. In xenograft mouse tumor models, human tumor cells are supported by mouse host stromal microenvironment. Therefore, effects of tumor stromal integrations on gene expression can be profiled separately by taking advantage of this heterogeneous genetic makeup. To understand the underlying biological process of stroma in cancer and select relevant in vitro and in vivo model systems for various targeted anticancer drug discovery and development projects, we selected a panel of 30 commonly used xenograft tumor mouse models that are derived from human tumor cell lines of various cancer histotypes and conducted analyses of differential gene expression in both human cancer cells and mouse host stromal cells before and after their interactions in vivo by using quantitative PCR with mouse and human specific primers. Growing the human tumors as a continuous in vivo passage subcutaneously in immunodeficient mice permits stroma infiltration over a long time. We have examined a number of anticancer target genes involved in different signaling pathways, such as tumor angiogenesis, apoptosis and survival (Akt/mTOR signaling pathway). Our study results have demonstrated that tumor stromal interactions significantly regulate expression levels of various genes important in tumor progression and development of resistance to treatment in both tumor and stromal cells. Tumor animal models play a critical role in translating the bench science to the bedside medical care of cancer patients. Decisions for moving new anticancer agents into costly clinical investigations are mostly based on the preclinical results using xenograft mouse models. The results of this gene profiling approach could provide tools for studying tumor microenvironment and tumor stromal interactions in vivo to advance anticancer drug development.

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 3114. doi:10.1158/1538-7445.AM2011-3114

Abstract 5154: Serotonin signaling as a novel target of tumor angiogenesis

Angiogenesis is a well-controlled process that is regulated by multiple factors that are secreted by the cancer cells as well as other cells within the tumor microenvironment. Angiogenesis inhibitors are showing therapeutic efficacy in an increasing number of human cancers. However, in both preclinical and clinical settings, the benefits are transitory and are followed by resistance and a restoration of tumor growth and progression. Therefore, novel anti-angiogenic strategies with complementary mechanisms are needed to maximize efficacy and minimize resistance to current angiogenesis inhibitors. Activation of platelets and blood coagulation frequently occurs in cancer patients. Apart from VEGF, platelets contain several other angiogenic growth factors and inhibitors that are released upon activation and promote tumor neoangiogenesis. Although considerable attention has been focused on platelet peptide growth factors, little is known about the mitogenic effects of nonpeptide platelet products such s serotonin (5-HT), considering that 99% of 5-HT in blood is found in platelets and is released at blood clotting sites. In previous studies, we have shown that endothelial cells express 5-HT receptors and 5-HT has growth stimulatory effcts on multiple types of endothelial cells. We have also demonstrated that 5-HT binds to inhibitory type of G-protein coupled receptors and stimulates the phosphorylation of PYK2/PI3K/AKT/mTOR signaling pathway, the same signaling pathway, which has been activated by most angiogenic factors, including VEGF. In our recent studies, we explored angiogenic promoting activity of 5-HT in the mouse matrigel plug assay (in vivo angiogenesis model system) and antiangiogenic potential of antagonists against 5-HT receptors in xenograft-CAM assay (ex vivo tumor angiogenesis model system). The most importantly, an antagonist against a specific 5-HT receptor demonstrated the synergistic effect in blocking tumor-induced new blood vessel formation when it was applied in combination with Sutent, a FDA approved antiangiogenic drug against VEGF receptor. The results of this study suggest that 5-HT signaling pathway constitute a novel target of tumor angiogenesis in anticancer therapeutic development.

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 5154. doi:10.1158/1538-7445.AM2011-5154

Abstract 3943: Affymetrix whole genome microarray analysis of 51 human tumor cell lines representative of 16 different tissues of origin: Unsupervised hierarchical clustering

The total mRNA for each sample of 51 human tumor cell lines representative of 16 different tissues of origin was split into 3 replicates, and analyzed against the entire human genome using standard Affx WT procedures. Approximately 50% of the samples (25 out of the 51 cell lines tested) exhibited low-level clustering related to their tissue of origin. The remaining 50% (26 out of the 51 cell lines tested) did not cluster with other samples of the same tissue of origin. These data reveal the importance of testing potential anticancer agents in multiple models representative of several different tumors of origin, as there is a 50% chance that the model chosen is not actually representative of the intended tissue of origin. This analysis also showed that the pancreatic cancer cell line CFPAC-1 did not cluster with any other cell line tested, revealing the unique genetic profile of this cell line. Interestingly, the reported lung cancer cell lines NCI-H69 and NCI-H82 clustered more closely with leukemic lines than with lung or any other solid tumor. This is particularly interesting as these lines are known to grow/behave more like a suspension culture than a monolayer. The NCI recently published its genetic analysis of their 60-panel, and they revealed that the MDA-MB-435 cell line, traditionally thought to be a breast cancer cell line, more closely resembled a melanoma line; hence, it was re-classified as a melanoma (likely a metastasized melanoma that was taken from the breast site). Our analysis reveals that another traditional breast cancer cell line, UISO-BCA-1, also clusters more closely with the melanomas (including the MDA-MB-435 cell line), suggesting that this cell line also may have been misclassified. Based on these data, we suggest that any potential anticancer agent showing activity in a particular cell line should be tested in other cell lines that cluster with the active line, and not merely in other lines supposedly representative of the same tissue of origin. Furthermore, in early stage testing, it would be more prudent to test several cell lines from different clusters, rather than several cell lines from different tissues of origin. It follows that by testing orphan drugs against several cell lines from each cluster, it would be possible to significantly narrow (and possibly identify), the likely drug target.

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 3943. doi:10.1158/1538-7445.AM2011-3943

Abstract 4418: Affymetrix whole genome microarray analysis of 24 human tumor xenograft models and the cell lines from which they were developed: Clustering of targets vs tumor tissue of origin

The NCI recently performed microarray expression analysis on its 60-panel of human tumor cell lines. This revealed important information, with some cell lines shown to be from a different tissue of origin than originally believed. Traditionally, potential anti-cancer agents have been evaluated in these in vitro models, and then moved into the corresponding in vivo xenograft model(s) based on the in vitro results. It has been shown that drugs which are effective in vitro are not necessarily effective in vivo and vice versa. Systematic microarray analysis of traditional xenograft models in conjunction with their in vitro counterparts has not been performed. The development of a human tumor xenograft in a mouse might be expected to lead to changes in gene expression, and this could account, in some instances, for the disconnect in results observed between in vitro and in vivo models. Our aim was to perform a genetic analysis against the entire human genome using 24 cell lines from 11 differing tissues of origin that were implanted into immune-deficient mice to establish a xenograft model for each. Once the tumors reached approximately 1 cm3 in size, the tumors were removed, cut into approx. 2-3 mm3 fragments, and an in vivo tumor passage was established. Microarray expression in fragments of those xenografted tumors was compared to microarray expression in the cell line from which they were developed. The total mRNA for each sample was split into 3 replicates, and analyzed against the entire human genome using standard Affx WT procedures. The results showed that over 60% (15 of 24) of the xenograft samples clustered with the cell line from which it was developed, whereas approximately 40% (9 of 24) did not, revealing that major changes in gene expression had occurred in 40% of these xenograft samples. Furthermore, when analyzed alone, these particular 24 cell line samples clustered according to their tissue of origin, whereas the tumor fragment samples did not appear to cluster. On the basis of these data we are currently performing the same analysis on an additional 25 tumor fragments and their corresponding matched cell lines to allow for a more accurate, in-depth cluster analysis. These data strongly suggest that although precedent exists to select in vitro models on the basis of their tissue of origin, no such precedent exists for in vivo models. In vivo models should be more carefully selected to ensure that the model chosen is still representative of the tissue to be tested. It follows that a drug candidate effective in a particular in vitro model might be expected to show activity in other in vitro lines from the same tissue of origin. However, a drug candidate effective in a particular in vivo model representative of a tissue of origin should not be expected to show efficacy in other in vivo models representing the same tissue type.

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 4418. doi:10.1158/1538-7445.AM2011-4418

Abstract 1865: Colon cancer chemopreventive properties of a non-cyclooxygenase inhibitory amide derivative of sulindac

Previous studies have concluded that the mechanism responsible for the antineoplastic properties of NSAIDs is cyclooxygenase (COX) independent, which suggests that more selective drugs can be developed for cancer chemoprevention by targeting such mechanisms. With this paradigm, we are synthesizing novel sulindac derivatives that have reduced COX inhibitory activity, but enhanced tumor cell growth inhibitory activity. A prototypic dimethylethyl amide derivative referred to as sulindac sulfide amide (SSA) was previously reported to lack COX-1 or COX-2 inhibitory activity, yet have improved potency to inhibit tumor cell growth in vitro. For example, SSA inhibited the growth of human HT-29 colon tumor cells with IC50 values of 1-2 µM compared with 70-90 µM for sulindac sulfide (SS), a non-selective COX inhibitor. SSA was also appreciably more effective than SS in inhibiting HT-29 colon tumor cell growth using a 3-dimensional in vitro tumor cell model. SSA induced apoptosis of HT-29 carcinoma cells, but normal human colonocytes were insensitive to treatment, suggesting an element of tumor selectivity. The mechanism of SSA induced apoptosis is associated with cGMP phosphodiesterase (PDE) inhibition, elevation of intracellular cGMP, and activation of protein kinase G, which also appears to be an important off-target effect of SS. SSA inhibited the growth of a variety of histologically diverse tumor cell lines, an effect that is consistent with studies showing the overexpression of PDE5 in various tumor types, including colorectal adenomas and carcinomas. SSA was well tolerated in the FCCC Min mouse model in which oral administration reduced colon tumor multiplicity by approximately 80% and tumor incidence by 50%. SSA also inhibited tumor growth in the human HT-29 colon mouse xenograft model by approximately 60%, while sulindac at its maximum tolerated dose was marginally effective. The antitumor activity of SSA in the HT-29 model was accompanied by decreased numbers of proliferating cells and increased numbers of apoptotic cells as determined by immunohistochemistry. Pharmacokinetic studies in mice bearing HT-29 xenografts revealed that plasma and tumor levels of SSA from a tolerated dose of SSA appreciably exceeded the in vitro IC50 value for growth inhibition. In contrast, sulindac generated plasma and tumor levels of SS that were appreciably less than the IC50 value for tumor cell growth inhibition. These results support the feasibility of chemically modifying sulindac to design out COX associated toxicities, while increasing anticancer efficacy. Newer sulindac derivatives with higher potency and target selectivity, as well as formulations to improve oral bioavailability are being developed for colon cancer chemoprevention. Funding provided by NIH/NCI grants CA131378 and CA148817.

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 1865. doi:10.1158/1538-7445.AM2011-1865

Colon tumor cell growth-inhibitory activity of sulindac sulfide and other nonsteroidal anti-inflammatory drugs is associated with phosphodiesterase 5 inhibition

Nonsteroidal anti-inflammatory drugs (NSAID) display promising antineoplastic activity, but toxicity resulting from cyclooxygenase (COX) inhibition limits their clinical use for chemoprevention. Studies suggest that the mechanism may be COX independent, although alternative targets have not been well defined. Here, we show that the NSAID sulindac sulfide (SS) inhibits cyclic guanosine 3',5'-monophosphate (cGMP) phosphodiesterase (PDE) activity in colon tumor cell lysates at concentrations that inhibit colon tumor cell growth in vitro and in vivo. A series of chemically diverse NSAIDs also inhibited cGMP hydrolysis at concentrations that correlate with their potency to inhibit colon tumor cell growth, whereas no correlation was observed with COX-2 inhibition. Consistent with its selectivity for inhibiting cGMP hydrolysis compared with cyclic AMP hydrolysis, SS inhibited the cGMP-specific PDE5 isozyme and increased cGMP levels in colon tumor cells. Of numerous PDE isozyme-specific inhibitors evaluated, only the PDE5-selective inhibitor MY5445 inhibited colon tumor cell growth. The effects of SS and MY5445 on cell growth were associated with inhibition of β-catenin-mediated transcriptional activity to suppress the synthesis of cyclin D and survivin, which regulate tumor cell proliferation and apoptosis, respectively. SS had minimal effects on cGMP PDE activity in normal colonocytes, which displayed reduced sensitivity to SS and did not express PDE5. PDE5 was found to be overexpressed in colon tumor cell lines as well as in colon adenomas and adenocarcinomas compared with normal colonic mucosa. These results suggest that PDE5 inhibition, cGMP elevation, and inhibition of β-catenin transcriptional activity may contribute to the chemopreventive properties of certain NSAIDs.

Abstract 563: Novel role of VEGF and neuropilin-1 in breast cancer tumor-stromal interactions

Human breast cancers contain high levels of fibroblastic stroma as a critical feature of desmoplasia. The complex interactions between tumor and stromal cells play important roles in tumor growth, metastasis and resistance to anticancer treatments. Our previous in vivo studies showed that increased levels of tumor-released VEGF were associated with increased desmoplastic responses and resulted in a hormonal resistance phenotype of ER+ breast tumor. Based on our findings, a clinical trial conducted at UAB with a new combinational treatment targeting both ER and VEGF signalings has achieved significant objective response in ER+ breast cancer patients. In our current studies, we further studied the role of VEGF in mediating tumor-stromal interactions and initiation of desmoplasia. Our results have shown that tumor released VEGF interacts with stromal fibroblasts which express VEGF receptors R1, R2 and Neuropilin-1 (NRP1), thereby stimulating their infiltration to promote desmoplastic response. Down regulation of NRP1 expression by siRNA significantly abolished the fibroblast chemo-attractive motility towards VEGF, while the VEGFR1 and VEGFR2 blocking antibodies had no effects on their migration mobility, suggesting that NRP1 expressed in fibroblast is involved in tumor-stroma cell interactions in breast cancer. Our studies using breast cancer xenograft mouse model with regulated tumor VEGF expression revealed that tumor VEGF expression was positively correlated with expression of NRP1 and alpha smooth muscle actin (α-SMA, a transformed/myo fibroblast marker) in the tumor stroma. In addition, levels of tumor VEGF, stromal NRP1 and α-SMA were all positively correlated with level of tumor stromal content and tumor growth. Blocking tumor VEGF with a neutralizing antibody (Avastin) as a treatment modality in xenograft mice reversed the VEGF increased desmoplasia. Our study results reveal a novel role of VEGF and NRP1 in tumor-stromal interactions and desmoplasia, indicating NRP1 can be a therapeutic target for breast cancer 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 563.

A novel sulindac derivative that does not inhibit cyclooxygenases but potently inhibits colon tumor cell growth and induces apoptosis with antitumor activity

Nonsteroidal anti-inflammatory drugs such as sulindac have shown promising antineoplastic activity, although toxicity from cyclooxygenase (COX) inhibition and the suppression of prostaglandin synthesis limits their use for chemoprevention. Previous studies have concluded that the mechanism responsible for their antineoplastic activity may be COX independent. To selectively design out the COX inhibitory activity of sulindac sulfide (SS), in silico modeling studies were done that revealed the crucial role of the carboxylate moiety for COX-1 and COX-2 binding. These studies prompted the synthesis of a series of SS derivatives with carboxylate modifications that were screened for tumor cell growth and COX inhibitory activity. A SS amide (SSA) with a N,N-dimethylethyl amine substitution was found to lack COX-1 and COX-2 inhibitory activity, yet potently inhibit the growth of human colon tumor cell lines, HT-29, SW480, and HCT116 with IC(50) values of 2 to 5 micromol/L compared with 73 to 85 micromol/L for SS. The mechanism of growth inhibition involved the suppression of DNA synthesis and apoptosis induction. Oral administration of SSA was well-tolerated in mice and generated plasma levels that exceeded its in vitro IC(50) for tumor growth inhibition. In the human HT-29 colon tumor xenograft mouse model, SSA significantly inhibited tumor growth at a dosage of 250 mg/kg. Combined treatment of SSA with the chemotherapeutic drug, Camptosar, caused a more sustained suppression of tumor growth compared with Camptosar treatment alone. These results indicate that SSA has potential safety and efficacy advantages for colon cancer chemoprevention as well as utility for treating malignant disease if combined with chemotherapy.

Sorafenib is efficacious and tolerated in combination with cytotoxic or cytostatic agents in preclinical models of human non-small cell lung carcinoma

PURPOSE

Sorafenib tosylate (sorafenib, BAY 43-9006, Nexavar) is a multi-kinase inhibitor that targets tumor cell proliferation and angiogenesis. These studies evaluated the efficacy and tolerability of combinations of sorafenib plus agents used to treat non-small cell lung cancer (NSCLC) using preclinical models of that disease.

METHODS

Intravenous (iv) vinorelbine and interperitoneal (ip) cisplatin were administered intermittently (q4d x 3) in combination with sorafenib administered orally (po) once daily for 9 days starting on the same day as the standard agent. In studies with sorafenib and gefitinib, both agents were administered po daily for 10 days starting on the same day. Treatment in all studies was initiated against established sc tumors, and each study was conducted in duplicate. Efficacy was assessed as the delay in tumor growth to a specified size (TGD).

RESULTS

Vinorelbine (6.7 mg/kg) and sorafenib (40 mg/kg) produced TGDs of 2.4 and 7.8 days, respectively, in the NCI-H460 NSCLC model. Combination therapy produced a 10.0-day TGD with no increase in toxicity. Combination therapy in the NCI-H23 NSCLC model with the highest evaluated dose levels of sorafenib plus cisplatin was well tolerated and produced TGDs equivalent to those produced by cisplatin alone. Lower dose levels of each agent produced approximately additive TGD's. Combination therapy in the A549 NSCLC model with sorafenib and gefitinib produced TGDs equivalent to that produced by sorafenib alone with no toxicity. Tumor growth in the MDA-MB-231 mammary tumor model, that contains mutations in signal transduction proteins downstream of the EGF receptor (the target of gefitinib) was also inhibited by sorafenib, but not by gefitinib.

CONCLUSION

Concurrent administration of sorafenib and vinorelbine, cisplatin or gefitinib was at least as efficacious as the individual agents alone and was well tolerated. These results support the inclusion of sorafenib in clinical trials in NSCLC employing combinations of both cytotoxic and cytostatic agents.

Identification of dithiolethiones with better chemopreventive properties than oltipraz

Oltipraz and related dithiolethiones are an important class of chemopreventive agents. Studies were undertaken to identify cancer chemopreventive dithiolethiones more active than oltipraz. Largely based upon enzyme induction activities in vitro, 17 dithiolethiones, including oltipraz, were analyzed for their ability to induce hepatic phase II enzyme activities in vivo. Of these compounds, 15 produced greater induction of NAD(P)H:quinone reductase and 11 yielded greater induction of glutathione S-transferase than oltipraz. All 17 dithiolethiones were then tested for their ability to inhibit acute hepatotoxicity by aflatoxin B1 (AFB1), which previously has been shown to be an intermediate predictor of chemopreventive activity. Rats were pretreated with dithiolethiones (0.3 mmol/kg body wt, three times a week per os) and challenged with two acutely toxic doses of AFB1 (0.5 mg/kg body wt, once daily for two successive days per os). Inhibition of hepatotoxicity was measured by changes in body weight gain during AFB1 challenge, reduction in levels of hepatic enzymes in serum and diminution of bile duct cell proliferation. Nine dithiolethiones spanning a range of responses in this toxicity screen were further tested for their ability to prevent AFB1-induced tumorigenicity, as assessed by a reduction in hepatic burden of putative preneoplastic foci. Six dithiolethiones were found to be considerably more effective than oltipraz in preventing AFB1-induced tumorigenesis. In general, dithiolethiones that were very effective in inhibition of acute hepatotoxicity were also found to be effective in prevention of hepatic tumorigenesis.

Urinary taurine as a non-invasive marker of aflatoxin B1-induced hepatotoxicity: success and failure

The usefulness of urinary taurine as a non-invasive measure of hepatotoxicity of aflatoxin B1 (AFB1) was evaluated: changes in urinary taurine were characterized in a dose-response, acute toxicity experiment and in two sub-chronic, low dose exposure experiments. Urine of young, male, F344 rats was collected for 4 days prior to, and for 3 days after, the treatment with AFB1. Rats received a single p.o. dose of 0, 0.25, 0.5, 1, 2 or 3 mg AFB1/kg body wt. A transient increase in urinary taurine was noted with doses of 1, 2 or 3 mg AFB1/kg. In two sub-chronic exposure experiments, rats were gavaged with 25 microg AFB1/day for 5 successive days per week for 1 or 2 weeks (approximately 0.25 mg/kg/day). In the first experiment, only a transient increase in urinary taurine during 5 successive doses of AFB1 was observed, while in the second experiment, urinary taurine rose continuously during the 2 weeks of the AFB1 treatment. An explanation for these differing results is not obvious. Urinary taurine appeared to be a useful, non-invasive marker when hepatotoxicity was extensive. Unfortunately, at the low doses of AFB1 (0.25-0.5 mg/kg) as used in carcinogenesis experiments (10 doses of 25 microg/rat), urinary taurine appeared to be an insensitive measure of hepatic damage.

Protection against aflatoxin B1-induced hepatic toxicity as short-term screen of cancer chemopreventive dithiolethiones

Dithiolethiones are an important class of cancer chemopreventive agents. More than 50 new dithiolethione analogs were synthesized for structure-activity studies. Using selected dithiolethiones, studies were designed to measure protection against the hepatotoxicity of aflatoxin B1 (AFB1) and relate it to the protection against carcinogenicity. Young male F344 rats were pretreated with 0.1 or 0.3 mmol dithiolethiones/kg body wt and challenged with toxic doses of AFB1 (50 micrograms/100 g rat/day) on 2 successive days. One day later, the protection from hepatotoxicity was assessed by measuring serum hepatic enzymes, hepatic necrosis, and degree of bile duct cell proliferation. The ability of these dithiolethiones to prevent AFB1-induced tumorigenicity was assessed by quantifying the hepatic burden of putative preneoplastic lesions [placental glutathione S-transferase (GST-P)-positive foci]. Significant correlations (p < 0.01) were observed between these toxicological indices and GST-P focal burden (alanine aminotransferase, r = 0.943; sorbitol dehydrogenase, r = 0.897; histological index, r = 0.893; bile duct cell proliferation, r = 0.933). These results imply that inhibition of hepatotoxicity affords protection against hepatocarcinogenicity. The extent of protection from acute hepatotoxicity offers a simple, short-term biological endpoint to screen dithiolethiones and related compounds for their chemopreventive properties.

Evaluation of the post-initiation effects of oltipraz on aflatoxin B1-induced preneoplastic foci in a rat model of hepatic tumorigenesis

Previous studies have demonstrated that ingestion of 5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione (oltipraz) during the aflatoxin B1 (AFB1) treatment phase completely prevented hepatic cancer. In this study we evaluated the effect of feeding oltipraz during the post-AFB1 treatment phase. Fifty-five male F344 rats were divided into five groups. All rats were gavaged with 25 micrograms AFB1/rat, five times a week for two successive weeks. The rats were fed the oltipraz-supplemented diet according to three different feeding regimes: during the AFB1 treatment phase (1 week prior to, during and 1 week after the last gavage with AFB1); during the post-treatment phase; or throughout the entire time of the experiment. Phenobarbital-supplemented diet was fed during post-treatment phase to one group and this was used as a positive control for the promotion of AFB1-induced focal growth. The burden of putative, preneoplastic, hepatic glutathione S-transferase P-positive foci was evaluated at 13 weeks after the AFB1 treatment phase. As seen previously, oltipraz fed during the AFB1 treatment phase significantly inhibited focal development, i.e. the volume percent of the liver occupied with foci was reduced by 87%. Oltipraz when fed during the post-treatment phase neither inhibited nor enhanced focal development.

Transient intervention with oltipraz protects against aflatoxin-induced hepatic tumorigenesis

Oltipraz [5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione] protects against aflatoxin B1-induced hepatocarcinogenesis in rats when fed before and during carcinogen exposure; however, such an exposure-chemoprotection intervention paradigm is not directly relevant to most human populations. To model and assess the possible efficacy of short term interventions targeted at individuals at risk for sustained exposure to aflatoxins, 175-g male F344 rats were treated daily with 25 micrograms of aflatoxin B1, p.o., for 28 days. One week after the start of aflatoxin B1 exposure, half of the animals were fed a diet supplemented with 0.075% oltipraz for 10 days; these rats were then restored to the unsupplemented AIN-76A diet for the remainder of the experimental period. Livers were analyzed 2 or 3 months after the last aflatoxin B1 dose for burden of glutathione S-transferase P (GST-P)-positive foci, as an index of presumptive preneoplastic tumors. The transient intervention with oltipraz reduced the volume percent of hepatic GST-P-positive foci by 54% (P = 0.047) and 72% (P = 0.004) at 2 and 3 months, respectively. A strong positive correlation was also observed between the extent of fibrosis in the livers of these animals and the hepatic burden of GST-P-positive foci, implying that cytotoxicity is associated with the tumorigenic process. This protection may reflect alterations in the metabolism and disposition of aflatoxin B1 induced by oltipraz. Glutathione S-transferase catalyze the detoxication of aflatoxin-8,9-oxide and were found to be rapidly induced in the livers of animals after the beginning of the oltipraz intervention. Glutathione S-transferase activity remained significantly (P < 0.05) higher until 9 days after the end of the oltipraz intervention. In contrast, levels of hepatic aflatoxin-DNA adducts were not significantly reduced until 4 days after the beginning of the intervention but remained significantly (P < 0.05) lower up to 11 days after the end of the intervention. The cumulative reduction in levels of hepatic aflatoxin-DNA adducts (approximately 25%) by the oltipraz intervention underestimated the reduction in the hepatic burden of GST-P-positive foci. The significant protection against presumptive preneoplastic tumors, despite the delay of intervention, suggests that oltipraz may exert substantial activity against the cytotoxic and autopromoting action of repeated exposures to aflatoxin B1 and supports the utility of intervention trials with oltipraz in individuals chronically consuming aflatoxin B1-contaminated foods, particularly in regions with high incidences of liver cancer.