A Novel Pan-RAS Inhibitor with a Unique Mechanism of Action Blocks Tumor Growth in Mouse Models of GI Cancer

Here we characterize a novel pan-RAS inhibitor, ADT-007, that potently and selectively inhibited the growth of histologically diverse cancer cell lines with mutant or activated RAS irrespective of the RAS mutation or isozyme. Growth inhibition was dependent on activated RAS and associated with reduced GTP-RAS levels and MAPK/AKT signaling. ADT-007 bound RAS in lysates from sensitive cells with sub-nanomolar EC 50 values but did not bind RAS in lysates from insensitive cells with low activated RAS. Insensitivity to ADT-007 was attributed to metabolic deactivation by UGT-mediated glucuronidation, providing a detoxification mechanism to protect normal cells from pan-RAS inhibition. Molecular modeling and experiments using recombinant RAS revealed that ADT-007 binds RAS in a nucleotide-free conformation to block GTP activation. Local injection of ADT-007 strongly inhibited tumor growth in syngeneic immune competent and xenogeneic immune deficient mouse models of colorectal and pancreatic cancer and activated innate and adaptive immunity in the tumor microenvironment.

SIGNIFICANCE

ADT-007 is a novel pan-RAS inhibitor with a unique mechanism of action having potential to circumvent resistance to mutant-specific KRAS inhibitors and activate antitumor immunity. The findings support further development of ADT-007 analogs and/or prodrugs with oral bioavailability as a generalizable monotherapy or combined with immunotherapy for RAS mutant cancers.

BACKGROUND

It is projected that colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDA) will cause 52,580 and 49,830 deaths in the US in 2023, respectively (1). The 5-year survival rates for CRC and PDA are 65% and 12%, respectively (1). Over 50% of CRC and 90% of PDA patients harbor mutations in KRAS genes that are associated with poor prognosis, making the development of novel KRAS inhibitors an urgent unmet medical need (2).

PDE5 and PDE10 inhibition activates cGMP/PKG signaling to block Wnt/β-catenin transcription, cancer cell growth, and tumor immunity

Although numerous reports conclude that nonsteroidal anti-inflammatory drugs (NSAIDs) have anticancer activity, this common drug class is not recommended for long-term use because of potentially fatal toxicities from cyclooxygenase (COX) inhibition. Studies suggest the mechanism responsible for the anticancer activity of the NSAID sulindac is unrelated to COX inhibition but instead involves an off-target, phosphodiesterase (PDE). Thus, it might be feasible develop safer and more efficacious drugs for cancer indications by targeting PDE5 and PDE10, which are overexpressed in various tumors and essential for cancer cell growth. In this review, we describe the rationale for using the sulindac scaffold to design-out COX inhibitory activity, while improving potency and selectivity to inhibit PDE5 and PDE10 that activate cGMP/PKG signaling to suppress Wnt/β-catenin transcription, cancer cell growth, and tumor immunity.

Abstract 2707: A novel RAS inhibitor, MCI-062, inhibits colon tumor growth in vivo and activates antitumor immunity

Approximately 45% of colorectal cancers harbor mutations in the KRAS gene, resulting in constitutive activation of RAS signaling through effector proteins, primarily RAF and PI3K. Members of the RAS family are GTPases that function as a molecular switch, cycling between inactive (GDP-bound) and active (GTP-bound) states in cells to regulate proliferation and survival. Constitutive signaling from mutant RAS drives tumorigenesis, in part, by deregulation of the cell cycle, resulting in increased proliferation (mitosis) and decreased apoptosis of tumor cells. From an extensive medicinal chemistry/screening campaign, we identified a novel compound class that potently and selectively inhibits the growth of tumor cell lines harboring constitutively activated RAS by a mechanism involving the disruption of RAS nucleotide loading, blockage of effector activation, and consequent inhibition of signaling. A prototype of the class, MCI-062, inhibits the growth of KRAS-driven (HCT-116) colon tumor cells with low nanomolar IC50 values, while RAS-independent (HT-29) colon tumor cells harboring the BRAF V600E mutation, are essentially insensitive. A strong correlation was measured among a larger panel of tumor cell lines between potency to inhibit tumor cell growth and levels of activated RAS. The growth inhibitory effects of MCI-062 were sustained and irreversible as demonstrated by colony formation and apoptosis assays. MCI-062 treatment of HCT-116 colon tumor cells reduced levels of activated RAS and RAS-mediated signaling as measured by GST-RBD pulldown assays and phospho-specific immunoblotting. Within the same concentration range, MCI-062 induced mitotic arrest as measured by cell cycle analysis of DNA content and phospho-histone H3B immunofluorescence. Further analysis revealed that MCI-062 interfered with localization of the mitosis-inducing protein, PLK1 to kinetochores and decreased nuclear localization of its substrate, Cdc25C, a downstream target of RAS-RAF signaling involved in both mitotic entry and exit checkpoints. In vivo testing of MCI-062 in a syngeneic mouse model of KRAS-driven colon cancer (CT-26) demonstrated that MCI-062 engages its molecular target, depleting GTP-RAS and suppressing activation of the MAPK signal transduction pathway, and inhibiting tumor growth. MCI-062 also suppresses PD-L1 expression and activates anti-tumor immunity, which may contribute to its antitumor activity and suggests potential benefits of combining with immunotherapy. From these studies, we have identified a novel class of RAS inhibitors that potently and selectively inhibits RAS-driven tumor growth by disrupting downstream signaling, leading to cell cycle arrest and apoptosis. These findings support further development of MCI-062 for treatment of RAS-driven colorectal and other cancers. Funding provided by NCI grants R01CA131378, R01CA148817, R01CA197147, and R01CA155638.

Citation Format: Adam B. Keeton, Antonio Ward, Xi Chen, Jacob Valiyaveettil, Bing Zhu, Veronica Ramirez-Alcantara, Yulia Maxuitenko, Kristy Berry, Tyler E. Mattox, Michael R. Boyd, Gary A. Piazza. A novel RAS inhibitor, MCI-062, inhibits colon tumor growth in vivo and activates antitumor immunity [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 2707.

Abstract 2731: A novel PDE10/beta-catenin inhibitor, MCI-048, suppresses lung tumorigenesis to block metastasis

We previously reported that phosphodiesterase 10A (PDE10) is overexpressed during early stages of lung cancer and is essential for lung tumor cell growth. Here we characterize a novel PDE10 inhibitor, MCI-048, that was identified by screening a library of indene compounds. MCI-048 potently inhibited the growth and induced apoptosis of multiple human lung cancer cell lines expressing PDE10, while normal human airway epithelial cells lacking PDE10 expression were appreciably less sensitive. The mechanism of action of MCI-048 involves PDE10 inhibition, cGMP elevation, PKG activation, and phosphorylation of β-catenin at key residues that induce ubiquitination and proteosomal degradation of the oncogenic pool of β-catenin in cytoplasm to suppress the translocation of active β-catenin to the nucleus and Lef/Tcf-mediated transcription of genes encoding for proteins such as c-myc, cyclin D, and survivin, which are essential for tumor cell proliferation and survival. Pharmacokinetic and tissue distribution studies revealed a unique feature of MCI-048 to accumulate at high concentrations in lungs relative to plasma and other tissues. To assess the potential of MCI-048 for the treatment of lung cancer and blocking metastasis, we tested the drug in two mouse models of lung cancer involving either orthotopic implantation of KRAS mutant A549 lung tumor cells or the chemical carcinogen, urethane. Oral administration of MCI-048 significantly inhibited tumor growth and extended survival in the orthotopic model using two different protocols to either treat the primary tumor or metastasis. Similarly, MCI-048 significantly reduced tumor burden as measured by both surface counting and histopathological analysis in the urethane-induced model of lung tumorigenesis. Biochemical analysis showed that MCI-048 reduced levels of urethane-induced active Ras-GTP and PDE10 levels, as well as other oncogenic markers, including pEGFR and c-Myc. Both mouse models revealed that MCI-048 was well tolerated with no discernable toxicity, thus supporting preclinical development for the treatment of lung cancer. Funding provided by NCI grants R21CA182941, R01CA131378, R01CA148817, R01CA197147, and R01CA155638.

Citation Format: Bing Zhu, Veronica Ramirez-Alcantara, Antonio Ward, Kristy Berry, Adam B. Keeton, Michael R. Boyd, Yulia Maxuitenko, Xi Chen, Gary A. Piazza. A novel PDE10/beta-catenin inhibitor, MCI-048, suppresses lung tumorigenesis to block metastasis [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 2731.

Abstract 3864: A novel PDE10/β-catenin pathway inhibitor, MCI-030, for the treatment of colorectal cancer

Over 90% of colorectal cancers harbor mutations in β-catenin or pathway components (e.g. APC) that stabilize β-catenin, causing nuclear translocation and constitutive Tcf-mediated transcription of genes encoding proteins essential for the proliferation and survival of tumor cells. We recently reported that the cyclic nucleotide degrading phosphodiesterase (PDE) isozyme PDE10 is overexpressed in colorectal cancers relative to normal tissue. Its expression and enzymatic activity are essential for colon tumor cell growth, as evidenced by knockdown of PDE10 expression using siRNA or inhibition of enzyme activity using known inhibitors such as PF-2545920. PDE10 inhibition in tumor cells expressing high levels of PDE10 causes increased intracellular cGMP levels to activate PKG and phosphorylate β-catenin, which induces ubiquitination and proteasomal degradation to suppress nuclear translocation and Tcf transcriptional activity. Conversely, ectopic expression of PDE10 in normal colonocytes or precancerous adenoma cells causes increased levels of β-catenin and the expression of proteins (e.g. cyclin D and survivin) essential for the proliferation and survival of tumor cells. To identify novel antitumor PDE10 inhibitors, we screened a chemically diverse library of indenes for PDE10 and tumor cell growth inhibitory activity. Following extensive chemical optimization, MCI-030 emerged as a potent and selective inhibitor of tumor cell growth. Similar to PF-2545920, but with appreciably greater potency and tumor cell selectivity, MCI-030 inhibited colon tumor cell growth by activating cGMP/PKG signaling to phosphorylate and induce β-catenin degradation. MCI-030 also inhibited colon tumor cell spheroid formation and reduced spheroid size and growth at concentrations that inhibit PDE10. Oral administration of MCI-030 significantly inhibited colon tumor formation in the Apc+/min-FCCC mouse model without discernable toxicity. Importantly, unlike PDE10 inhibitors developed to cross the blood-brain barrier for the treatment of CNS disorders, MCI-030 lacks the sedation side effects. Together, these findings support preclinical development of MCI-030 for the treatment of colorectal cancer as a novel PDE10 inhibitor capable of selectively inhibiting the growth of tumors harboring β-catenin or APC mutations. Funding provided by NCI grants R01CA131378, R01CA148817, R01CA197147, and R01CA155638.

Citation Format: Antonio B. Ward, Xi Chen, Jacob Valiyaveettil, Kevin Lee, Wen-Chi L. Chang, Yulia Maxuitenko, Veronica Ramirez-Alcantara, Kristy Berry, Luciana Madeira da Silva, Bing Zhu, Tyler Mattox, Michael R. Boyd, Adam B. Keeton, Margie L. Clapper, Harry S. Cooper, Gary A. Piazza. A novel PDE10/β-catenin pathway inhibitor, MCI-030, for the treatment of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3864.

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 B23: DC070-547, a novel Ras inhibitor potently and selectivity inhibits colon tumor growth in vitro and in vivo

Introduction: Activating mutations in Ras oncogenes play a critical role in the development of colorectal cancer and are an indicator of poor prognosis. Constitutive activation of Ras proteins is also associated with resistance to chemotherapy and radiation in which treatment options are limited. Despite extensive efforts, no drugs have been successfully developed that target these aberrant gene products, in part because of the high affinity of Ras binding to GTP, which is essential for Ras activation. Using a phenotypic screening assay designed to select for Ras inhibitors and follow-up chemical optimization, a novel Ras inhibitor, DC070-547 was identified, which potently and selectively inhibits the growth of colon tumor cells with activated Ras in vitro and in vivo.

Methods: Tumor cell growth inhibitory activity of DC070-547 was measured in a panel of human colon tumor cell lines using the CellTiter Glo assay following 72 h of treatment. Ras activation levels were measured by precipitating GTP-bound Ras from human colon tumor cell lysates with GST-Raf1-RBD/GSH Sepharose followed by western blotting using anti-Ras antibody. Isogenic cell lines were established by transfecting Ras wild-type HT-29 colon tumor cells with mutant H-Ras. Disruption of Ras-Raf binding was determined by pre-incubating cell lysates or intact cells in the presence of DC070-547 for 30 or 45 min followed by Ras pull-down with GST-Raf beads and western blotting using anti-Ras or an anti-GST antibody as a loading control. Cell cycle arrest and apoptosis were measured by DNA content and annexin V levels, respectively. Antitumor activity was determined in a mouse xenograft model subcutaneously implanted with mutant K-Ras HCT-116 colon tumor cells. Mice were treated with DC070-547 administered i.p. for 14 days at a dose of 2.5 mg/kg bid in a co-solvent formulation.

Results: DC070-547 potently inhibits the growth of mutant K-Ras HCT-116 and other colon tumor cell lines having constitutively activated Ras with IC50 values as low as 2 nM and selectivity indices of approximately 100-fold for HT-29 and other colon tumor cells lacking activated Ras. Among a panel of six colon tumor cell lines, a strong correlation was measured between IC50 values for growth inhibition and the level of Ras activation, suggesting that activated Ras is the primary target. Isogenic cell line pairs involving transfecting Ras wild-type cells with mutant H-Ras confirmed that sensitivity to DC070-547 required activated Ras. DC070-547 also blocked Ras-Raf binding in cell lysates and intact cells at concentrations that inhibit the growth of tumor cells with activated Ras. The mechanism of growth inhibition by DC070-547 appears to involve mitotic arrest and apoptosis. Moreover, cells obtained from normal colon mucosa were essentially refractory to treatment with DC070-547. In a mouse xenograft model involving mutant K-Ras human HCT-116 colon tumors, DC070-547 was well tolerated and caused a sustained inhibition of tumor growth in which there was complete tumor regression in 3 of 7 mice.

Conclusions: DC070-547 potently and selectively inhibits the growth of colon tumor cells with constitutively activated Ras by disrupting Ras-effector interactions and represents a first-in-class drug development candidate for the treatment of Ras-driven colorectal cancer.

Citation Format: Veronica Ramirez-Alcantara, Adam B. Keeton, Bing Zhu, Kevin J. Lee, Joshua Canzoneri, Ashley S. Lindsey, Luciana Madeira da Silva Barnes, Kristy Berry, Jacob Valiyaveettil, Xi Chen, Michael R. Boyd, Gary Piazza. DC070-547, a novel Ras inhibitor potently and selectivity inhibits colon tumor growth in vitro and in vivo. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr B23.

Abstract 326: Discovery and in vitro and in vivo characterization of a novel, small-molecule Ras inhibitor class

Introduction: Mutations in ras genes that result in constitutive activation of Ras proteins are key drivers of oncogenesis, but no effective drugs have been developed that target these aberrant gene products. Through iterative screening and chemical optimization using a phenotypic assay designed to select for Ras inhibitors, we identified a novel series of compounds that potently and selectively inhibit the growth of tumor cells harboring activated Ras relative to cells lacking activated Ras. Several compounds in the series have favorable drug-like properties with strong antitumor activity in a mouse K-Ras mutant tumor model.

Methods: Viable cell number was measured using a luminescent indicator of ATP. Disruption of Ras-Raf binding was determined by pre-incubating GST-Raf beads with cell lysates in the presence of test compounds for 30 min. Ras activation was measured by Ras pull-down and western blotting using an anti-Ras antibody. Cell cycle arrest was measured by DNA content. Antitumor activity was determined in a subcutaneous mouse tumor model involving K-Ras mutant HCT116 colon tumors. Mice were treated with Ras inhibitors administered ip for 14 days bid at a dose of 2.5 or 5 mg/kg.

Results: Low nanomolar concentrations of DC070-547 inhibited the growth of multiple tumor cell lines harboring activated K-Ras, N-Ras or H-Ras with a selectivity index greater than 100-fold over cells lacking activated Ras. Ras selectivity was confirmed by transfecting human HT29 colon and H322 lung tumor cells that lack activated Ras with mutant H-Ras, thus inducing sensitivity to DC070-547. The compound also inhibited Ras-Raf binding as evident by Ras-pull down assays of lysates from tumor cells treated with DC070-0547 at concentrations that inhibit tumor cell growth. DC070-547 caused G2 phase cell cycle arrest and induced apoptosis selectively in tumor cells containing activated Ras. Cultured epithelial cells derived from normal colon, mammary, and lung tissues were essentially refractory to treatment.The Ras inhibitors were evaluated for antitumor activity in a subcutaneous mouse model involving K-Ras mutant human HCT116 colon tumors. Treatments were well tolerated and completely suppressed tumor growth with the effect being sustained for at least six weeks after treatment was discontinued. Complete tumor regression was also apparent in some of the treated mice.

Conclusion: While Ras is widely considered to be non-druggable, we have identified a novel series of compounds that potently and selectivity inhibit the growth of tumor cells harboring activated Ras. With promising drug-like properties, these compounds represent a first in class series of Ras inhibitors from which several prospective drug development candidates have been identified.. These results support further preclinical development and future Phase I/II clinical evaluation in patients with Ras-driven cancers.

Citation Format: Adam B. Keeton, Bing Zhu, Kevin J. Lee, Joshua C. Canzoneri, Sara C. Sigler, Ashley S. Lindsey, Veronica Ramirez-Alcantara, Luciana Barnes, Tyler E. Mattox, Kate McConnell, Kristy L. Berry, Jacob Valiyaveettil, Xi Chen, Michael R. Boyd, Gary A. Piazza. Discovery and in vitro and in vivo characterization of a novel, small-molecule Ras inhibitor class. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 326.

Abstract 1238: A novel Ras inhibitor potently and selectively suppresses lung tumor cell growth by blocking Ras-Raf binding

Mutations in ras genes that result in constitutive activation of Ras proteins are key drivers of oncogenesis, but no effective drugs have been developed that target these aberrant gene products. Screening using a phenotypic assay designed to select for Ras inhibitors and iterative chemical synthesis, identified a preclinical drug development candidate with attractive drug-like properties designated as DC070-547. Here we evaluated the sensitivity of non-small cell lung cancer (NSCLC) cell lines to DC070-547. The compound potently suppresses the growth of human A549, H460, HOP62, H1299, H1975 lung tumor cells having high levels of activated Ras with low nanomolar IC50 values. By contrast, normal human airway epithelial cells (NHAECs) and H322 lung tumor cells with low levels of activated Ras displayed IC50 values in the mid micromolar range. The Ras selectivity of DC070-547 was confirmed by ectopic expression of mutant H-Ras-G12V (H-Rasm) in H322 cells using a retroviral construct, in which the IC50 value of DC070-547 for growth inhibition was reduced approximately 2,500 fold compared with vector control cells. To study the mechanism of action, Ras activation status was measured by Ras-Raf pull-down assays using GTP-bound Ras from cell lysates with GST-Raf1-RBD/GSH sepharose and followed by western blotting with Ras antibodies. Direct binding to Ras was apparent by the ability of DC070-547 to inhibit Ras-Raf binding at concentrations that inhibit Ras-dependent tumor cell growth. Pull-down assays also showed a dose-dependent inhibition of Ras-GTP levels in intact H-Rasm-H322 cells treated with DC070-547 at the same concentration range. Western blot analysis of Ras-immunoprecipitated proteins revealed that DC070-547 also attenuated high levels of EGFR phosphorylation at Y1068 in H-Rasm-H322 cells but not in control cells. These results demonstrate novel Ras inhibitory activities of DC070-547 in NSCLC cell lines. DC070-547 and its pipeline analogs are being evaluated for antitumor efficacy in preclinical mouse models of lung cancers.

Citation Format: Bing Zhu, Xi Chen, Veronica Ramirez-Alcantara, Kevin Lee, Jacob Valiyaveettil, Joshua Canzoneri, Sara Sigler, Kristy Berry, Ashley Lindsey, Adam Keeton, Michael R. Boyd, Gary A. Piazza. A novel Ras inhibitor potently and selectively suppresses lung tumor cell growth by blocking Ras-Raf binding. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1238.

Abstract A140: Novel drug development candidate potently and selectively inhibits growth of tumor cells harboring activated Ras

Introduction: Mutations in ras genes that result in constitutive activation of Ras proteins are key drivers of oncogenesis, but no effective drugs have been developed that target these aberrant gene products. Through iterative chemical synthesis and screening using a phenotypic assay designed to select for Ras inhibitors, we identified a small-molecule lead compound that was then optimized for potency and selectivity to inhibit the growth of tumor cells harboring activated Ras relative to cells lacking activated Ras.

Materials and methods: Viable cell number was measured using the CellTiter-Glo® ATP assay (Promega) following 72 hr of treatment. Ras activation status was measured by precipitating GTP-bound Ras from cell lysates with GST-Raf1-RBD/GSH sepharose followed by western blotting using anti-Ras antibody. Ras binding was determined by pre-incubating cell lysates with GST-Raf1-RBD/GSH sepharose, treating with test compounds for 30 min, followed by western blotting using anti-Ras antibody. Cell cycle distribution was measured by DNA content following DyeCycle Green labeling.

Results: Low nanomolar concentrations of DC070-547 inhibited the growth of multiple tumor cell lines harboring activated K-Ras, N-Ras or H-Ras with selectivity indices greater than 100-fold over cells lacking activated Ras. By surveying a large panel of human colon, breast, and lung tumor cell lines, a strong correlation was measured between potency to inhibit tumor cell growth and Ras activation status. Ras selectivity was confirmed by transfecting human H322 lung tumor cells that lack activated Ras with mutant H-Ras and inducing sensitivity to DC070-547. The compound inhibited Ras-Raf binding as shown by Ras-pull down in cell lysates following treatment with DC070-547 at concentrations that inhibit tumor cell growth. DC070-547 also caused cell cycle arrest in the G2 phase selectively in tumor cells containing activated Ras. Interestingly, cultured epithelial cells derived from normal colon, mammary, and lung tissues were essentially refractory to treatment.

Conclusion: While Ras is widely considered to be non-druggable, we have identified a series of compounds that potently and selectively inhibit the growth of tumor cells harboring activated Ras. With promising drug-like properties, DC070-547 has been selected from this series as a prospective drug development candidate that is being evaluated for anti-tumor efficacy and toxicity in preclinical models.

Citation Format: Gary A. Piazza, Bing Zhu, Kevin Lee, Joshua Canzoneri, Sara Sigler, Ashley Lindsey, Veronica Ramirez-Alcantara, Luciana Madeira da Silva, Haddon Mullins, Alisa Trinh, Kristy Berry, Jacob Valiyaveettil, Adam B. Keeton, Xi Chen, Michael R. Boyd. Novel drug development candidate potently and selectively inhibits growth of tumor cells harboring activated Ras. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A140.

Abstract 4360: Validation of phosphodiesterase 10A as a cancer target

Phosphodiesterase 10A (PDE10) is a cAMP and cGMP degrading PDE isozyme that is highly expressed in the brain striatum where it plays an important role in cognition and psychomotor activity. PDE10 inhibitors are being developed for the treatment of schizophrenia and Huntington's disease and are generally well tolerated, likely because of low expression levels in peripheral tissues. We recently reported high levels of PDE10 in tumors and that genetic silencing by siRNA inhibits tumor cell growth with a high degree of selectivity over normal cells (Li et al., Oncogene 2014). These observations suggest that PDE10 may have an unrecognized role in tumorigenesis and represents a novel cancer target. To further test this possibility, we studied the effects of a highly specific PDE10 inhibitor, Pf-2545920 (MP-10) on colon tumor cell growth. Here we show that Pf-2545920 selectively inhibits tumor cell growth, causes G1 cell cycle arrest, and induces apoptosis. The concentration range by which Pf-2545920 inhibits tumor cell growth parallels the concentration range required to increase intracellular cyclic nucleotide levels and activate PKA and PKG. Moreover, PDE10 knockdown by siRNA reduces the sensitivity of tumor cells to the growth inhibitory activity of Pf-2545920. Using the crystal structure of PDE10 to design novel inhibitors, a series of compounds were synthesized and screened for tumor cell growth inhibitory activity and PDE10 isozyme specificity. A lead compound, ADT-030 was found to inhibit tumor cell growth and PDE10 enzymatic activity with IC50 values in the nanomolar range, but did not significantly affect the growth of normal cells. Unlike Pf-2545920, ADT-030 exhibits high selectivity for activating PKG signaling without affecting PKA signaling. Inhibitors of PKA and PKG were used to confirm that the tumor cell growth inhibitory activity associated with PDE10 inhibition involves PKG activation, while PKA activation appears to be ancillary. These findings serve to validate PDE10 as a cancer target, whereby novel inhibitors can be designed to specifically activate cGMP/PKG signaling with a high degree of tumor cell selectivity. Supported by NIH grants 1R01CA155638 and 1R01CA131378 (Piazza).

Citation Format: Kevin Lee, Nan Li, Xi Chen, Bing Zhu, Larry Yet, Luciana Madeira da Silva, Suzanne Russo, Adam B. Keeton, Michael R. Boyd, Gary A. Piazza. Validation of phosphodiesterase 10A as a cancer target. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4360. doi:10.1158/1538-7445.AM2015-4360

Abstract 701: A novel class of Ras selective inhibitors

Despite the fact that activating mutations in the various forms of Ras were identified as driving factors in oncogenesis over thirty years ago, there are still no effective therapeutics which act on this target. We recently synthesized and characterized a novel class of compounds that show striking potency and selectivity to inhibit the growth of tumor cells with mutant Ras. Through iterative structure-activity studies, we selected for and optimized Ras selectivity to achieve high potency with IC50 values in the low nanomolar range and selectivity indices of nearly 100-fold. For example, ADT-062 inhibited the growth of human HCT116 colon tumor cells that harbor mutant K-Ras with an IC50 value of 8.4 + 3.6 nM,. In contrast, human HT29 colon tumor cells that have wild type Ras displayed an IC50 value of 521 + 253 nM in response to ADT-062 treatment. When surveying a larger panel of colon tumor cell lines, we observed a direct correlation between potency and Ras activation status. Further, ADT-062 induced cell cycle arrest only in the Ras-mutant cell line. To study the mechanism by which this class of compounds selectively inhibits the growth of tumor cells with mutant K-Ras, we profiled lysates from treated HCT116 and HT29 colon tumor cells using high resolution LC-MS/MS. Over 100 ions were identified that were differentially affected by treatment with ADT-062 at its IC50 value in the respective cell line. Among the ions of interest, a component of the purine biosynthetic pathway, 5′-phosphoribosyl-N-formylglycinamide (FGAR), was found to be induced 200-fold (p = .0031) in K-Ras mutant cells compared with Ras wild type cells. Together, these findings suggest that this compound may cause a Ras selective disruption of purine metabolism and cell cycle progression which contributes to the selectivity by which this novel class of compounds inhibit the growth of tumor cells with mutant Ras. These findings may enable us to develop this compound class as a novel therapeutic which targets Ras driven tumors and tumors which may become resistant to other targeted therapeutics through secondary Ras mutations.

Citation Format: Joshua C. Canzoneri, Xi Chen, Adam B. Keeton, Kevin Lee, Bernard Gary, Ethan B. Butler, William E. Grizzle, Landon Wilson, Stephen Barnes, Michael R. Boyd, Gary A. Piazza. A novel class of Ras selective inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 701. doi:10.1158/1538-7445.AM2015-701

Effects of inducers and inhibitors on drug-metabolizing enzymes and on drug toxicity in extrahepatic tissues

When a compound that is removed from the body by metabolism produces toxicity in extrahepatic organs directly, rather than via active metabolites, induction or inhibition of the drug-metabolizing enzymes simply will decrease or enhance, respectively, the toxic effects of the compound. On the other hand, the effects of chemicals whose toxicity depends on their activation by metabolism may be modified in a complex way by pretreatment with inducers or inhibitors of the enzymes; it may, therefore, be impossible to predict the effect of pretreatment on the metabolism and toxicity of a given compound. The major sources of such complexity are that (a) inducers and inhibitors can have multiple effects on pathways of drug toxification or detoxification, both in the liver and in extrahepatic tissues, (b) active metabolites can be formed both in the liver and at extrahepatic sites, and they may not be sufficiently stable for transport from one site to another, and (c) regardless of the effect of pretreatment on pathways of extrahepatic metabolism, the accompanying effects on hepatic metabolism may determine the extrahepatic distribution and site of metabolism (in vivo) of a protoxin or its active metabolite(s). A review of studies on pulmonary toxicity produced by three agents--monocrotaline, bromobenzene, and 4-ipomeanol--illustrates several of these problems, and also shows the value of using inducers and inhibitors in the experimental analysis of extrahepatic toxicity produced by reactive metabolites.

Influenza A (H1N1) virus resistance to cyanovirin-N arises naturally during adaptation to mice and by passage in cell culture in the presence of the inhibitor

Influenza A/New Caledonia/20/99 (H1N1) virus was studied for development of resistance to cyanovirin-N (CVN). CVN neutralizes virus infectivity by binding to specific high-mannose oligosaccharides on the viral haemagglutinin 1 (HA1) subunit. During virus adaptation to mice in the absence of CVN treatment the virus became resistant to CVN (CVN-MR virus), as did virus passaged in cell culture in the presence of CVN (CVN-R virus). The CVN-R virus possessed a single amino acid change at position 94a (Asn94aAsp) of HA1 that eliminated this glycosylation site. The CVN-MR virus at mouse passage 7 was a mixture of clones, consisting of a single mutation (Asp225Gly) and double mutations (Asn63Ser+Asp225Gly or Asn94a+Asp225Gly), eliminating glycosylation sites. CVN did not bind well to the CVN-R and CVN-MR viruses. Propagating these viruses in cells treated with 1 mM deoxymannojirimycin (dMJ, mannosidase inhibitor) increased sensitivity to CVN, suggesting that glycans attached at other sites on HA1 that typically are not high-mannosidic became so due to dMJ treatment. Further evaluation showed that the Asp225Gly mutant virus was sensitive to the inhibitor and did not kill mice or induce weight loss. The CVN-R virus was also avirulent to mice. The double-mutant CVN-MR viruses were resistant to CVN and caused deaths and severe weight loss in mice. CVN-R virus subjected to mouse adaptation acquired the 225 mutation and a lethal phenotype. Thus, the 225 mutation in the HA receptor-binding site in combination with a loss of glycan at Asn (63 or 94a) are important for mouse adaptation in this virus. The mutations reported here causing resistance to CVN are consistent with its known mode of action.

Ethnobotany and drug discovery: the experience of the US National Cancer Institute

Between 1960 and 1981 the National Cancer Institute (NCI) screened 114,000 extracts of 35,000 plants, mainly collected in temperate regions. Of the three clinically active anticancer drugs so far discovered in that programme, none was isolated from a plant collected on an ethnobotanical basis, though various Taxus species, which are the source of taxol, are reported to have been used medicinally. Since 1986, the NCI has focused its collections in tropical and subtropical regions worldwide; collections cover a broad taxonomic range, though priority is given to medicinal plants when relevant information is available. As of August 1993, 21,881 extracts derived from over 10,500 samples had been tested in a screen for activity against the human immunodeficiency virus (HIV); 2320 of these extracts were of medicinal plant origin. Approximately 18% of both the total number of extracts and the medicinal plant-derived extracts showed significant anti-HIV activity; in each instance about 90% of the active extracts were aqueous. The activity of the aqueous extracts has been attributed mainly to the presence of polysaccharides or tannins. Four plant-derived compounds are in preclinical development at the NCI; only one of the four sources plants, obtained from a noncontract source, was collected on an ethnobotanical basis. At this stage the results indicate that the current NCI collection policy offers the best chances for the discovery and development of agents for the treatment of AIDS (acquired immune deficiency syndrome) and cancer.

Candidaspongiolides, distinctive analogues of tedanolide from sponges of the genus Candidaspongia

Fractionation of cytotoxic extracts of specimens of a newly described sponge genus, Candidaspongia, has yielded the candidaspongiolides (3), a complex mixture of acyl esters of a macrolide related to tedanolide. The general structure of the candidaspongiolides was determined by analyses of various 2D NMR and MS data sets. The acyl ester components were identified by GC-MS analysis of the derived fatty acid methyl esters. The mixture could be selectively converted to the deacylated macrolide core (4) by enzymolysis with immobilized porcine lipase, with the structure of the candidaspongiolide core then secured by NMR and MS analysis. The candidaspongiolide mixture was potently cytotoxic, exhibiting a mean panel 50% growth inhibition (GI50) of 14 ng/mL in the National Cancer Institute's 60-cell-line in vitro antitumor screen.

Bioengineering lactic acid bacteria to secrete the HIV-1 virucide cyanovirin

An urgent need exists to prevent the sexual transmission of HIV-1. With prevalence rates exceeding 35% in parts of sub-Saharan Africa, increasing attention has been placed on developing and testing microbicidal agents capable of preventing virus transmission at mucosal sites. HIV-1 microbicides must meet several requirements before their widespread use. The drugs must be able to neutralize a diversity of HIV-1 strains, not induce mucosal inflammation, be associated with minimal side effects, and be effective for a prolonged period after a single application. Recent work has demonstrated the utility of recombinant lactic acid bacteria (LAB) as agents of mucosal drug delivery. Here, we describe the bioengineering of strains of LAB to secrete the prototypic virucidal compound cyanovirin (CV-N) and demonstrate the anti-HIV-1 activity of secreted CV-N. Our results suggest that recombinant LAB may serve as effective microbicidal compounds and deserve in vivo testing in simian immunodeficiency virus models of mucosal virus transmission.

Antitumor activity and distribution of pyrroloiminoquinones in the sponge genus Zyzzya

A detailed analysis of four different collections of the sponge genus Zyzzya yielded nine pyrroloiminoquinones of the makaluvamine, batzelline, and isobatzelline/damirone classes. Dereplication analyses of additional Zyzzya extracts did not disclose more potent or additional new compounds. Comparative testing of these compounds in the National Cancer Institute's 60 cell line human tumor screen revealed varying levels of potency and differential cytotoxicity, apparently related to the unsaturation levels in and substitution patterns on the core ring system. Further studies on the topoisomerase II-mediated DNA cleavage were conducted. Reductive activation of the pyrroloiminoquinones led to DNA damage in vitro, which correlated with half wave potentials and reversibility parameters. DNA damage could be abrogated by ascorbate. Fluorescence displacement was used to measure intercalation with DNA; intercalation efficiency did not correlate with DNA-damaging proficiency. Makaluvamine H (5) emerged as the most potent and differential of our isolates, roughly comparable to makaluvamines C (in vitro) and I (in vivo). 3,7-Dimethyl guanine was isolated from one of the Zyzzya collections and from the sponge Latrunculia purpurea.

Isolation and characterization of griffithsin, a novel HIV-inactivating protein, from the red alga Griffithsia sp

Griffithsin (GRFT), a novel anti-HIV protein, was isolated from an aqueous extract of the red alga Griffithsia sp. The 121-amino acid sequence of GRFT has been determined, and biologically active GRFT was subsequently produced by expression of a corresponding DNA sequence in Escherichia coli. Both native and recombinant GRFT displayed potent antiviral activity against laboratory strains and primary isolates of T- and M- tropic HIV-1 with EC50 values ranging from 0.043 to 0.63 nM. GRFT also aborted cell-to-cell fusion and transmission of HIV-1 infection at similar concentrations. High concentrations (e.g. 783 nM) of GRFT were not lethal to any tested host cell types. GRFT blocked CD4-dependent glycoprotein (gp) 120 binding to receptor-expressing cells and bound to viral coat glycoproteins (gp120, gp41, and gp160) in a glycosylation-dependent manner. GRFT preferentially inhibited gp120 binding of the monoclonal antibody (mAb) 2G12, which recognizes a carbohydrate-dependent motif, and the (mAb) 48d, which binds to CD4-induced epitope. In addition, GRFT moderately interfered with the binding of gp120 to sCD4. Further data showed that the binding of GRFT to soluble gp120 was inhibited by the monosaccharides glucose, mannose, and N-acetylglucosamine but not by galactose, xylose, fucose, N-acetylgalactosamine, or sialic acid-containing glycoproteins. Taken together these data suggest that GRFT is a new type of lectin that binds to various viral glycoproteins in a monosaccharide-dependent manner. GRFT could be a potential candidate microbicide to prevent the sexual transmission of HIV and AIDS.

Development of a fluorescent microplate assay for determining cyanovirin-N levels in plasma

A sensitive immunosorbent competition assay was developed for quantitation of the anti-HIV protein cyanovirin-N (CV-N) in plasma using a 96-well plate format and a fluorescent endpoint. The assay is based on the binding of CV-N in plasma to plate-bound anti-CV-N antibodies, followed by removal of the plasma and addition of europium-labeled CV-N (Eu3+ -CV-N) to compete for the remaining antibody sites. Detection by addition of a dissociative fluorescence enhancement solution and time-resolved fluorescence measurements allowed correlation to the concentration of the native CV-N in plasma. A linear detection range of 1-100 nM (r2>0.99) was obtained for CV-N in mouse plasma. This assay was then utilized for analysis of plasma levels of CV-N samples following subcutaneous injection of CV-N into mice. The results of these studies confirmed the reliability and sensitivity of this assay and the feasibility of its use for pharmacokinetic studies in a variety of species.

Neamphamide A, a new HIV-inhibitory depsipeptide from the Papua New Guinea marine sponge Neamphius huxleyi

A new HIV-inhibitory cyclic depsipeptide, neamphamide A (2), was isolated from a Papua New Guinea collection of the marine sponge Neamphius huxleyi. Its structure was established through interpretation of spectroscopic data and by acid hydrolysis, derivatization of the free amino acids, and LC-MS analysis of the derivatives. Neamphamide A (2) contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethylheptanoic acid moiety. The amino acid constituents were identified as L-Leu, L-NMeGln, D-Arg, D- and L-Asn, two residues of D-allo-Thr, L-homoproline, (3S,4R)-3,4-dimethyl-L-glutamine, beta-methoxytyrosine, and 4-amino-7-guanidino-2,3-dihydroxyheptanoic acid. In a cell-based XTT assay, 2 exhibited potent cytoprotective activity against HIV-1 infection with an EC50 of approximately 28 nM.

Cytotoxic alkaloids from the marine sponge Thorectandra sp

Three beta-carboline alkaloids, Compound 1, 1-deoxysecofascaplysin A (2), and fascaplysin (3), were isolated from the aqueous and organic extracts of the marine sponge Thorectandra sp. The structures of 1 and 2 were determined on the basis of spectral data. Compound 1 inhibited the growth of MCF-7 (breast) with an IC50 of 5.9 microg/mL while Compound 2 inhibited the growth of MCF-7 as well as OVCAR-3 (ovarian) human tumor cell lines with IC50s of 1.5 and 2.2 microg/mL, respectively.

A Frameshift Mutation and Alternate Splicing in Human Brain Generate a Functional Form of the Pseudogene Cytochrome P4502D7 That Demethylates Codeine to Morphine

A frameshift mutation 138delT generates an open reading frame in the pseudogene, cytochrome P4502D7 (CYP2D7), and an alternate spliced functional transcript of CYP2D7 containing partial inclusion of intron 6 was identified in human brain but not in liver or kidney from the same individual. mRNA and protein of the brain variant CYP2D7 were detected in 6 of 12 human autopsy brains. Genotyping revealed the presence of the frameshift mutation 138delT only in those human subjects who expressed the brain variant CYP2D7. Genomic DNA analysis in normal volunteers revealed the presence of functional CYP2D7 in 4 of 8 individuals. In liver, the major organ involved in drug metabolism, a minor metabolic pathway mediated by CYP2D6 metabolizes codeine (pro-drug) to morphine (active drug), whereas norcodeine is the major metabolite. In contrast, when expressed in Neuro2a cells, brain variant CYP2D7 metabolized codeine to morphine with greater efficiency compared with the corresponding activity in cells expressing CYP2D6. Morphine binds to micro-opioid receptors in certain regions of the central nervous system, such as periaqueductal gray, and produces pain relief. The brain variant CYP2D7 and micro-opioid receptor colocalize in neurons of the periaqueductal gray area in human brain, indicating that metabolism of codeine to morphine could occur at the site of opioid action. Histio-specific isoforms of P450 generated by alternate splicing, which mediate selective metabolism of pro-drugs within tissues, particularly the brain, to generate active drugs may play an important role in drug action and provide newer insights into the genetics of metabolism.

Gymnangiamide, a Cytotoxic Pentapeptide from the Marine Hydroid Gymnangium regae

A cytotoxic aqueous extract from the marine hydroid Gymnangium regae provided a novel linear pentapeptide, designated gymnangiamide (1). The planar structure of 1 was elucidated by interpretation of spectral data as well as chemical degradation and derivatization studies. In addition to the amino acids isoleucine and phenylserine, this peptide contained N-desmethyldolaisoleuine, O-desmethyldolaproine, and alpha-guanidino serine, three residues that have not previously been reported in a natural product. The absolute configurations of the constituent amino/guanidino acids were determined by chemical degradation and derivatization, followed by HPLC and LC-MS comparison with authentic standards. Gymnangiamide (1) was moderately cytotoxic against a number of human tumor cell lines in vitro.

Cyclonellin, a new cyclic octapeptide from the marine sponge Axinella carteri

Cyclonellin (1), a new cyclic octapeptide, was isolated from an aqueous extract of the marine sponge Axinella carteri. Its structure was elucidated by interpretation of NMR spectral data of the intact compound and N-terminal Edman sequencing of linear peptide fragments obtained by partial hydrolysis of 1. The absolute configurations of the constituent amino acids were determined by acid hydrolysis, derivitization with FDAA, and LC-MS analyses.

Cyanovirin-N inhibits AIDS virus infections in vaginal transmission models

The cyanobacterial protein cyanovirin-N (CV-N) potently inactivates diverse strains of HIV-1 and other lentiviruses due to irreversible binding of CV-N to the viral envelope glycoprotein gp120. In this study, we show that recombinant CV-N effectively blocks HIV-1(Ba-L) infection of human ectocervical explants. Furthermore, we demonstrate the in vivo efficacy of CV-N gel in a vaginal challenge model by exposing CV-N-treated female macaques (Macaca fascicularis) to a pathogenic chimeric SIV/HIV-1 virus, SHIV89.6P. All of the placebo-treated and untreated control macaques (8 of 8) became infected. In contrast, 15 of 18 CV-N-treated macaques showed no evidence of SHIV infection. Further, CV-N produced no cytotoxic or clinical adverse effects in either the in vitro or in vivo model systems. Together these studies suggest that CV-N is a good candidate for testing in humans as an anti-HIV topical microbicide.

Identification of a new chondropsin class of antitumor compound that selectively inhibits V-ATPases

We identify a new naturally occurring class of inhibitor of vacuolar H+-ATPases (V-ATPases) isolated from vacuolar membranes of Neurospora crassa and from chromaffin granule membranes of Bos taurus. To date, the new class includes six chondropsins and poecillastrin A, large polyketide-derived macrolide lactams with 33-37 membered rings. In the National Cancer Institute's 60-cell screen the chondropsin class showed a tumor cell growth inhibitory fingerprint essentially indistinguishable from that of the bafilomycin/concanamycin and the salicylihalamide/lobatamide classes of well-established V-ATPase inhibitors. Half-maximal inhibition of V-ATPase activity in vitro occurred at 0.04-0.7 microM for the fungal vacuolar V-ATPase and at 0.4 to >10 microM for the chromaffin granule V-ATPase. Thus, the new inhibitors are somewhat less potent than the other two classes, which typically have Ki values of <10 nM for V-ATPases, and the new inhibitors differ from the other two classes in their specificity. The bafilomycin class inhibits all eucaryotic V-ATPases, the salicylihalamide class inhibits mammalian V-ATPases but not fungal V-ATPases, and the new chondropsin class inhibits the N. crassa V-ATPase better than the chromaffin granule V-ATPase. Two mutations in the N. crassa V-ATPase that affect the binding of bafilomycin had small but reproducible effects on the affinity of chondropsins for the V-ATPase, suggesting the possibility of a similar mechanism of inhibition.

Potent anti-influenza activity of cyanovirin-N and interactions with viral hemagglutinin

The novel antiviral protein cyanovirin-N (CV-N) was initially discovered based on its potent activity against the human immunodeficiency virus (HIV). Subsequent studies identified the HIV envelope glycoproteins gp120 and gp41 as molecular targets of CV-N. More recently, mechanistic studies have shown that certain high-mannose oligosaccharides (oligomannose-8 and oligomannose-9) found on the HIV envelope glycoproteins comprise the specific sites to which CV-N binds. Such selective, carbohydrate-dependent interactions may account, at least in part, for the unusual and unexpected spectrum of antiviral activity of CV-N described herein. We screened CV-N against a broad range of respiratory and enteric viruses, as well as flaviviruses and herpesviruses. CV-N was inactive against rhinoviruses, human parainfluenza virus, respiratory syncytial virus, and enteric viruses but was moderately active against some herpesvirus and hepatitis virus (bovine viral diarrhea virus) strains (50% effective concentration [EC(50)] = approximately 1 micro g/ml) while inactive against others. Remarkably, however, CV-N and related homologs showed highly potent antiviral activity against almost all strains of influenza A and B virus, including clinical isolates and a neuraminidase inhibitor-resistant strain (EC(50) = 0.004 to 0.04 micro g/ml). When influenza virus particles were pretreated with CV-N, viral titers were lowered significantly (>1,000-fold). Further studies identified influenza virus hemagglutinin as a target for CV-N, showed that antiviral activity and hemagglutinin binding were correlated, and indicated that CV-N's interactions with hemagglutinin involved oligosaccharides. These results further reveal new potential avenues for antiviral therapeutics and prophylaxis targeting specific oligosaccharide-comprised sites on certain enveloped viruses, including HIV, influenza virus, and possibly others.

Cyanovirin-N gel as a topical microbicide prevents rectal transmission of SHIV89.6P in macaques

Cyanovirin-N (CV-N), an 11-kDa cyanobacterial protein, potently inactivates diverse strains of HIV-1, HIV-2, and simian immunodeficiency virus (SIV) and also prevents virus-to-cell fusion, virus entry, and infection of cells in vitro. These properties make CV-N an attractive candidate for use as a topical microbicide to prevent the sexual transmission of HIV. We evaluated the efficacy of gel-formulated, recombinant CV-N gel asa topical microbicide in male macaques (Macaca fascicularis) that were rectally challenged with a chimeric SIV/HIV-1 virus known as SHIV89.6P. All of the untreated macaques were infected and experienced CD4+T cell depletion. In contrast, none of the macaques that received either 1% or 2% CV-N gel showed evidence of SHIV89.6P infection. Neither CV-N nor placebo gels produced any adverse effects in any macaque following the rectal application. These results indicate that CV-N gel as a topical microbicide can prevent rectal transmission of SHIV in macaques. These studies encourage clinical evaluation of CV-N as a topical microbicide to prevent sexual transmission of HIV in humans.

A potent novel anti-HIV protein from the cultured cyanobacterium Scytonema varium

A new anti-HIV protein, scytovirin, was isolated from aqueous extracts of the cultured cyanobacterium Scytonema varium. The protein displayed potent anticytopathic activity against laboratory strains and primary isolates of HIV-1 with EC50 values ranging from 0.3 to 22 nM. Scytovirin binds to viral coat proteins gp120, gp160, and gp41 but not to cellular receptor CD4 or other tested proteins. This unique protein consists of a single 95-amino acid chain with significant internal sequence duplication and 10 cysteines forming five intrachain disulfide bonds.

Cyanovirin-N binds to the viral surface glycoprotein, GP1,2 and inhibits infectivity of Ebola virus

Ebola virus (Ebo) causes severe hemorrhagic fever and high mortality in humans. There are currently no effective therapies. Here, we have explored potential anti-Ebo activity of the human immunodeficiency virus (HIV)-inactivating protein cyanovirin-N (CV-N). CV-N is known to potently inhibit the infectivity of a broad spectrum of HIV strains at the level of viral entry. This involves CV-N binding to N-linked high-mannose oligossacharides on the viral glycoprotein gp120. The Ebola envelope contains somewhat similar oligosaccharide constituents, suggesting possible susceptibility to inhibition by CV-N. Our initial results revealed that CV-N had both in vitro and in vivo antiviral activity against the Zaire strain of the Ebola virus (Ebo-Z). Addition of CV-N to the cell culture medium at the time of Ebo-Z infection inhibited the development of viral cytopathic effects (CPEs). CV-N also delayed the death of Ebo-Z-infected mice, both when given as a series of daily subcutaneous injections and when the virus was incubated ex vivo together with CV-N before inoculation into the mice. Furthermore, similar to earlier results with HIV gp120, CV-N bound with considerable affinity to the Ebola surface envelope glycoprotein, GP(1,2). Competition experiments with free oligosaccharides were consistent with the view that carbohydrate-mediated CV-N/GP(1,2) interactions involve oligosaccharides residing on the Ebola viral envelope. Overall, these studies broaden the range of viruses known to be inhibited by CV-N, and further implicate carbohydrate moieties on viral surface proteins as common viral molecular targets for this novel protein.

Multisite and multivalent binding between cyanovirin-N and branched oligomannosides: calorimetric and NMR characterization

Binding of the protein cyanovirin-N to oligomannose-8 and oligomannose-9 of gp120 is crucially involved in its potent virucidal activity against the human immunodeficiency virus (HIV). The interaction between cyanovirin-N and these oligosaccharides has not been thoroughly characterized due to aggregation of the oligosaccharide-protein complexes. Here, cyanovirin-N's interaction with a nonamannoside, a structural analog of oligomannose-9, has been studied by nuclear magnetic resonance and isothermal titration calorimetry. The nonamannoside interacts with cyanovirin-N in a multivalent fashion, resulting in tight complexes with an average 1:1 stoichiometry. Like the nonamannoside, an alpha1-->2-linked trimannoside substructure interacts with cyanovirin-N at two distinct protein subsites. The chitobiose and internal core trimannoside substructures of oligomannose-9 are not recognized by cyanovirin-N, and binding of the core hexamannoside occurs at only one of the sites on the protein. This is the first detailed analysis of a biologically relevant interaction between cyanovirin-N and high-mannose oligosaccharides of HIV-1 gp120.

Functional homologs of cyanovirin-N amenable to mass production in prokaryotic and eukaryotic hosts

Cyanovirin-N (CV-N) is under development as a topical (vaginal or rectal) microbicide to prevent sexual transmission of human immunodeficiency virus (HIV), and an economically feasible means for very large-scale production of the protein is an urgent priority. We observed that N-glycosylation of CV-N in yeast eliminated the anti-HIV activity, and that dimeric forms and aggregates of CV-N occurred under certain conditions, potentially complicating the efficient, large-scale manufacture of pure monomeric CV-N. We therefore expressed and tested CV-N homologs in which the glycosylation-susceptible Asn residue at position 30 was replaced with Ala, Gln, or Val, and/or the Pro at position 51 was replaced by Gly to eliminate potential conformational heterogeneity. All homologs exhibited anti-HIV activity comparable to wild-type CV-N, and the Pro51Gly homologs were significantly more stable proteins. These glycosylation-resistant, functional cyanovirins should be amenable to large-scale production either in bacteria or in eukaryotic hosts.

Thioltransferase (glutaredoxin) mediates recovery of motor neurons from excitotoxic mitochondrial injury

Mitochondrial dysfunction involving electron transport components is implicated in the pathogenesis of several neurodegenerative disorders and is a critical event in excitotoxicity. Excitatory amino acid L-beta-N-oxalylamino-L-alanine (L-BOAA), causes progressive corticospinal neurodegeneration in humans. In mice, L-BOAA triggers glutathione loss and protein thiol oxidation that disrupts mitochondrial complex I selectively in motor cortex and lumbosacral cord, the regions affected in humans. We examined the factors regulating postinjury recovery of complex I in CNS regions after a single dose of L-BOAA. The expression of thioltransferase (glutaredoxin), a protein disulfide oxidoreductase regulated through AP1 transcription factor was upregulated within 30 min of L-BOAA administration, providing the first evidence for functional regulation of thioltransferase during restoration of mitochondrial function. Regeneration of complex I activity in motor cortex was concurrent with increase in thioltransferase protein and activity, 1 hr after the excitotoxic insult. Pretreatment with alpha-lipoic acid, a thiol delivery agent that protects motor neurons from L-BOAA-mediated toxicity prevented the upregulation of thioltransferase and AP1 activation, presumably by maintaining thiol homeostasis. Downregulation of thioltransferase using antisense oligonucleotides prevented the recovery of complex I in motor cortex and exacerbated the mitochondrial dysfunction in lumbosacral cord, providing support for the critical role for thioltransferase in maintenance of mitochondrial function in the CNS.

Unusual sulfamate indoles and a novel indolo[3,2-a]carbazole from Ancorina sp

Four new indoles, ancorinolates A-C and bis-ancorinolate B, which contain sulfamate and sulfate groups, were isolated from the aqueous extract of the sponge Ancorina sp. In addition, ancorinazole, an indolo[3,2-a]carbazole also possessing sulfamate and sulfate groups, was isolated from two separate New Zealand collections of Ancorina sp. Ancorinazole is the first indolo[3,2-a]carbazole described as a natural product. Ancorinolates A (1) and C (3) showed weak HIV-inhibitory activity in the XTT-based, anticytopathicity assay.

Application of high-field NMR and cryogenic probe technologies in the structural elucidation of poecillastrin a, a new antitumor macrolide lactam from the sponge poecillastra species

Poecillastrin A (1), a new polyketide-derived macrolide lactam, was isolated from a deep-water collection of the marine sponge Poecillastra species. The structure of poecillastrin A (1) was assigned using NMR data acquired at 500 MHz with an inverse-detection cryogenic probe and at 800 MHz with a room-temperature probe.

Structures of the complexes of a potent anti-HIV protein cyanovirin-N and high mannose oligosaccharides

The development of anti-human immunodeficiency virus (HIV) microbicides for either topical or ex vivo use is of considerable interest, mainly due to the difficulties in creating a vaccine that would be active against multiple clades of HIV. Cyanovirin-N (CV-N), an 11-kDa protein from the cyanobacterium (blue-green algae) Nostoc ellipsosporum with potent virucidal activity, was identified in the search for such antiviral agents. The binding of CV-N to the heavily glycosylated HIV envelope protein gp120 is carbohydrate-dependent. Since previous CV-N-dimannose structures could not fully explain CV-N-oligomannose binding, we determined the crystal structures of recombinant CV-N complexed to Man-9 and a synthetic hexamannoside, at 2.5- and 2.4-A resolution, respectively. CV-N is a three-dimensional domain-swapped dimer in the crystal structures with two primary sites near the hinge region and two secondary sites on the opposite ends of the dimer. The binding interface is constituted of three stacked alpha1-->2-linked mannose rings for Man-9 and two stacked mannose rings for hexamannoside with the rest of the saccharide molecules pointing to the solution. These structures show unequivocally the binding geometry of high mannose sugars to CV-N, permitting a better understanding of carbohydrate binding to this potential new lead for the design of drugs against AIDS.

New dimeric macrolide glycosides from the marine sponge Myriastra clavosa

Clavosolides A-D (1-4), dimeric macrolides incorporating cyclopropyl, tetrahydropyranyl, and glycosidic ring systems, were isolated from the cytotoxic extract of a Philippines collection of the marine sponge Myriastra clavosa. The structures of the clavosolides, which occurred as only trace metabolites, were elucidated through extensive NMR spectroscopic analyses. Clavosolides A (1) and B (2) were recently reported metabolites from M. clavosa, while the unsymmetrical dimers clavosolides C (3) and D (4) had new structures.

Isolation and structure of pedilstatin from a republic of maldives Pedilanthus sp

A new cancer cell growth inhibitor designated pedilstatin (1) was isolated from a Republic of Maldives Pedilanthus sp. The structure was determined to be 13-O-acetyl-12-O-[2'Z,4'E-octadienoyl]-4alpha-deoxyphorbol on the basis of high-resolution mass spectral and 2D NMR assignments. Pedilstatin was found to significantly inhibit growth of the P388 lymphocytic leukemia cell line with an ED(50) of 0.28 microg/mL, to afford, at concentrations of 2-5 microM, protection (to 80%) of human-derived lymphoblastoid CEM-SS cells from infection and cell-killing by HIV-1, and to show inhibition of protein kinase C with a K(i) of 620 +/- 20 nM.

The microbicide cyanovirin-N expressed on the surface of commensal bacterium Streptococcus gordonii captures HIV-1

OBJECTIVE

To explore the feasibility of expressing the potent HIV-inactivating protein, cyanovirin-N (CV-N), in the human commensal bacterium Streptococcus gordonii, as a possible approach for local delivery of CV-N to prevent sexual transmission of HIV-1.

DESIGN AND METHODS

To express CV-N in S. gordonii, we used the host-vector system we had previously developed. CV-N was expressed as a fusion protein both attached to the bacterial surface and secreted in soluble form in the supernatant of liquid cultures. The soluble form of recombinant CV-N was tested for gp120-binding activity in an enzyme-linked immunosorbent assay, whereas S. gordonii strain expressing CV-N on the surface was analyzed in an in vitro HIV capturing assay.

RESULTS

Two recombinant S. gordonii strains secreting or displaying CV-N on the bacterial surface were constructed and the expression of CV-N was confirmed by immunoblot and flow-cytometric analysis. The secreted form of recombinant CV-N exhibited a concentration-dependent binding to the envelope glycoprotein gp120 of HIV-1, whereas CV-N displayed on the bacterial surface was able to capture HIV virions efficiently.

CONCLUSION

The anti-HIV protein CV-N in S. gordonii was expressed in a biologically active form. This represents a first step in the development of a system to deliver and maintain an effective concentration of a microbicide in the vaginal mucosa.

Constitutive expression and localization of the major drug metabolizing enzyme, cytochrome P4502D in human brain

Cytochrome P4502D6, an important isoform of cytochrome P450, mediates the metabolism of several psychoactive drugs in liver. Quantitatively, liver is the major drug metabolizing organ, however metabolism of drugs in brain could modulate pharmacological and pharmacodynamic effects of psychoactive drugs at their site of action and explain some of the variation typically seen in patient population. We have measured cytochrome P450 content and examined constitutive expression of CYP2D mRNA and protein in human brain regions by reverse transcription polymerase chain reaction, Northern and immunoblotting and localized it by in situ hybridization and immunohistochemistry. CYP2D mRNA was expressed constitutively in neurons of cerebral cortex, Purkinje and granule cell layers of cerebellum, reticular neurons of midbrain and pyramidal neurons of CA1, CA2 and CA3 subfields of hippocampus. Immunoblot studies demonstrated the presence of cytochrome P4502D protein in cortex, cerebellum, midbrain, striatum and thalamus of human brain. Immunohistochemical localization showed the predominant presence of cytochrome P4502D not only in neuronal soma but also in dendrites of Purkinje and cortical neurons. These studies demonstrate constitutive expression of cytochrome P4502D in neuronal cell population in human brain, indicating its possible role in metabolism of psychoactive drugs directly at or near their site of action, in neurons, in human brain.

Domain-swapped structure of a mutant of cyanovirin-N

Cyanovirin-N (CV-N) is a potent 11 kDa HIV-inactivating protein that binds with high affinity to the HIV surface envelope protein gp120. A double mutant P51S/S52P of CV-N was engineered by swapping two critical hinge-region residues Pro51 and Ser52. This mutant has biochemical and biophysical characteristics equivalent to the wild-type CV-N and its structure resembles that of wild-type CV-N. However, the mutant shows a different orientation in the hinge region that connects two domains of the protein. The observation that this double mutant crystallizes under a wide variety of conditions challenges some of the current hypotheses on domain swapping and on the role of hinge-region proline residues in domain orientation. The current structure contributes to the understanding of domain swapping in cyanovirins, permitting rational design of domain-swapped CV-N mutants.