Chemical remodeling of a cellular chaperone to target the active state of mutant KRAS

The discovery of small-molecule inhibitors requires suitable binding pockets on protein surfaces. Proteins that lack this feature are considered undruggable and require innovative strategies for therapeutic targeting. KRAS is the most frequently activated oncogene in cancer, and the active state of mutant KRAS is such a recalcitrant target. We designed a natural product-inspired small molecule that remodels the surface of cyclophilin A (CYPA) to create a neomorphic interface with high affinity and selectivity for the active state of KRASG12C (in which glycine-12 is mutated to cysteine). The resulting CYPA:drug:KRASG12C tricomplex inactivated oncogenic signaling and led to tumor regressions in multiple human cancer models. This inhibitory strategy can be used to target additional KRAS mutants and other undruggable cancer drivers. Tricomplex inhibitors that selectively target active KRASG12C or multiple RAS mutants are in clinical trials now (NCT05462717 and NCT05379985).

Abstract 3598: A first-in-class tri-complex KRASG13C(ON) inhibitor validates therapeutic targeting of KRASG13Cand drives tumor regressions in preclinical models

The clinical activity of KRASG12C(OFF) inhibitors has validated KRASG12C as an oncogenic driver in human cancers and demonstrated the power of targeting cysteine mutations with covalent inhibitors. A second oncogenic RAS cysteine mutation, KRASG13C, is found predominantly in non-small cell lung cancer (NSCLC), with > 2,700 new cases reported in the USA in 2020 but relatively little is known about the biochemical and cellular properties of KRASG13C. KRASG12C-selective inhibitors are not active against KRASG13C and currently there are no direct, targeted inhibitors available for patients with KRASG13C-driven cancers. We report the development of a potent, selective, orally bioavailable tri-complex inhibitor of KRASG13C. Using chemical and genetic approaches, we describe unique properties of KRASG13C and their influence on oncogenic signaling and the co-mutational landscape of KRASG13C mutant tumors. These insights provide the basis for targeting KRASG13C NSCLC in the clinic and shape future combination strategies.

RM-041 is a potent and selective covalent inhibitor of KRASG13C(ON) with attractive drug-like properties. RM-041 forms a tri-complex between KRASG13C(ON) and cyclophilin A (CypA), a highly abundant intracellular chaperone protein. The assembled non-covalent tri-complex rapidly prevents KRASG13C(ON) signaling via steric blockade of RAS effector binding, and covalent engagement with Cys-13 converts the inactive assembly into an irreversibly inhibited complex. In cells, RM-041 covalently modifies KRASG13C(ON), drives deep suppression of RAS pathway signaling, and inhibits cell proliferation in KRASG13C mutant cancer cell lines. In KRASG13C xenograft tumor models, oral administration of RM-041 produces deep and durable suppression of RAS pathway activity and induces tumor regressions in vivo at well-tolerated doses.

Compared to KRASG12C, KRASG13C exhibits a higher rate of spontaneous nucleotide exchange, reducing its dependence on GEF reloading and sensitivity to upstream inhibitors (e.g., SHP2 and SOS1) and underscoring the need for direct KRASG13C inhibition. In addition, KRASG13C is uniquely sensitive to select GAPs, including NF1. In line with this observation, an analysis of the co-mutational landscape of KRASG13C patient tumor samples revealed a high prevalence of NF1LOF mutation, likely resulting in enhanced wild-type RAS signaling. Our preclinical combination data support a therapeutic strategy of mutant selective KRASG13C inhibition with RM-041 and co-targeting an upstream node, such as SHP2, to attenuate cooperative wild-type RAS signaling. In summary, RM-041 is a first-in-class, mutant-selective, oral, tricomplex inhibitor of KRASG13C(ON) with the potential to address an unmet need in patients with KRASG13C mutant cancer, supporting the advancement of RM-041 towards clinical evaluation.

Citation Format: Christopher J. Schulze, Jim Cregg, Kyle J. Seamon, Yu Chi Yang, Zhican Wang, Lindsay S. Garrenton, Alun Bermingham, John E. Knox, Aidan Tomlinson, Kang-Jye Chou, Shaoling Li, David P. Wildes, Mallika Singh, Elena S. Koltun, Adrian L. Gill, Robert J. Nichols, Jacqueline A. Smith. A first-in-class tri-complex KRASG13C(ON) inhibitor validates therapeutic targeting of KRASG13Cand drives tumor regressions in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3598.

Abstract 1261: A next generation tri-complex KRASG12C(ON) inhibitor directly targets the active, GTP-bound state of mutant RAS and may overcome resistance to KRASG12C(OFF) inhibition

The KRASG12C mutation is found in 11% of non-small cell lung cancers and 4% of colorectal cancers. Recently, a class of KRASG12C(OFF) inhibitors has shown promising activity in patients whose cancers bear KRASG12C. These data validate KRASG12C as an oncogenic driver, as well the mechanism of action of the KRASG12C(OFF) inhibitor class – sequestration of inactive, GDP-bound KRASG12C(OFF) proteins. Previous work has demonstrated this mechanism of action is vulnerable to adaptive tumor cell responses that activate KRASG12C by increasing upstream signaling and driving the cellular pool of KRASG12C towards the RAS(ON) state. These escape mechanisms, in which KRASG12C can be reactivated in the presence of a KRASG12C(OFF) inhibitor, highlight the potential for an inhibitor that directly targets and disables the KRASG12C(ON) form.

Using structure-based drug design, we have discovered RM-032, a potent covalent inhibitor of KRASG12C(ON) that forms a tri-complex between KRASG12C(ON) and cyclophilin A (CypA), a highly abundant immunophilin. The assembled tri-complex prevents KRASG12C(ON) from signaling via steric blockade of RAS effector binding. In cells, kinetic analyses demonstrate near-immediate disruption of RAS effector binding and extinction of KRASG12C(ON) signaling. RM-032 is dual selective for KRASG12C(ON) and NRASG12C(ON).

In vitro, RM-032 drives increased durability of inhibition of both RAS pathway signaling and cell proliferation in KRASG12C tumor cells compared with KRASG12C(OFF) inhibition. RM-032 displays attractive drug-like properties including cross-species oral bioavailability, and is predicted to achieve adequate exposures following oral dosing in humans. Oral administration of RM-032 produces deep and durable suppression of RAS pathway activity in KRASG12C tumor models and drives profound tumor regressions in vivo at well-tolerated doses. Across multiple tumor xenograft models, advanced KRASG12C(ON) inhibitors, including RM-032, appear to outperform KRASG12C(OFF) inhibitors.

RM-032 permits a broad array of combination opportunities for treating KRASG12C mutant cancer types where single agent KRASG12C(ON) inhibition may be insufficient, for example with agents targeting nodes both upstream (e.g., SHP2 and SOS1) and downstream (e.g., MEK and ERK) of RAS, as well as parallel pathways (e.g., mTORC1). RM-032 is a next generation mutant-selective inhibitor of KRASG12C(ON) that may overcome liabilities of first-generation KRASG12C(OFF) inhibitors and provide additional benefit to patients by directly targeting the active form of this important oncogenic driver mutation.

Citation Format: Robert J. Nichols, Jim Cregg, Christopher J. Schulze, Zhican Wang, Kevin Yang, Jingjing Jiang, Daniel M. Whalen, Rich Hansen, Lindsay S. Garrenton, Alun Bermingham, John E. Knox, Tiffany Choy, Denise Reyes, Mayra Rios, Kyle Seamon, Michael Longhi, Kang-Jye Chou, Shaoling Li, David P. Wildes, Mallika Singh, Elena S. Koltun, Adrian L. Gill, Jacqueline A. M. Smith. A next generation tri-complex KRASG12C(ON) inhibitor directly targets the active, GTP-bound state of mutant RAS and may overcome resistance to KRASG12C(OFF) inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1261.

Shp1 Loss Enhances Macrophage Effector Function and Promotes Anti-Tumor Immunity

Shp1, encoded by the gene Ptpn6, is a protein tyrosine phosphatase that transduces inhibitory signals downstream of immunoreceptors in many immune cell types. Blocking Shp1 activity represents an exciting potential immunotherapeutic strategy for the treatment of cancer, as Shp1 inhibition would be predicted to unleash both innate and adaptive immunity against tumor cells. Antibodies blocking the interaction between CD47 on tumor cells and SIRPα on macrophages enhance macrophage phagocytosis, show efficacy in preclinical tumor models, and are being evaluated in the clinic. Here we found that Shp1 bound to phosphorylated peptide sequences derived from SIRPα and transduced the anti-phagocytic signal, as Shp1 loss in mouse bone marrow-derived macrophages increased phagocytosis of tumor cells in vitro. We also generated a novel mouse model to evaluate the impact of global, inducible Ptpn6 deletion on anti-tumor immunity. We found that inducible Shp1 loss drove an inflammatory disease in mice that was phenotypically similar to that seen when Ptpn6 is knocked out from birth. This indicates that acute perturbation of Shp1 in vivo could drive hyperactivation of immune cells, which could be therapeutically beneficial, though at the risk of potential toxicity. In this model, we found that Shp1 loss led to robust anti-tumor immunity against two immune-rich syngeneic tumor models that are moderately inflamed though not responsive to checkpoint inhibitors, MC38 and E0771. Shp1 loss did not promote anti-tumor activity in the non-inflamed B16F10 model. The observed activity in MC38 and E0771 tumors was likely due to effects of both innate and adaptive immune cells. Following Shp1 deletion, we observed increases in intratumoral myeloid cells in both models, which was more striking in E0771 tumors. E0771 tumors also contained an increased ratio of effector to regulatory T cells following Shp1 loss. This was not observed for MC38 tumors, though we did find increased levels of IFNγ, a cytokine produced by effector T cells, in these tumors. Overall, our preclinical data suggested that targeting Shp1 may be an attractive therapeutic strategy for boosting the immune response to cancer via a mechanism involving both innate and adaptive leukocytes.

Allosteric Inhibition of SHP2 Stimulates Antitumor Immunity by Transforming the Immunosuppressive Environment

The protein tyrosine phosphatase SHP2 binds to phosphorylated signaling motifs on regulatory immunoreceptors including PD-1, but its functional role in tumor immunity is unclear. Using preclinical models, we show that RMC-4550, an allosteric inhibitor of SHP2, induces antitumor immunity, with effects equivalent to or greater than those resulting from checkpoint blockade. In the tumor microenvironment, inhibition of SHP2 modulated T-cell infiltrates similar to checkpoint blockade. In addition, RMC-4550 drove direct, selective depletion of protumorigenic M2 macrophages via attenuation of CSF1 receptor signaling and increased M1 macrophages via a mechanism independent of CD8⁺ T cells or IFNγ. These dramatic shifts in polarized macrophage populations in favor of antitumor immunity were not seen with checkpoint blockade. Consistent with a pleiotropic mechanism of action, RMC-4550 in combination with either checkpoint or CSF1R blockade caused additive antitumor activity with complete tumor regressions in some mice; tumors intrinsically sensitive to SHP2 inhibition or checkpoint blockade were particularly susceptible. Our preclinical findings demonstrate that SHP2 thus plays a multifaceted role in inducing immune suppression in the tumor microenvironment, through both targeted inhibition of RAS pathway-dependent tumor growth and liberation of antitumor immune responses. Furthermore, these data suggest that inhibition of SHP2 is a promising investigational therapeutic approach. SIGNIFICANCE: Inhibition of SHP2 causes direct and selective depletion of protumorigenic M2 macrophages and promotes antitumor immunity, highlighting an investigational therapeutic approach for some RAS pathway-driven cancers.

Abstract PR10: Tri-complex inhibitors of the oncogenic, GTP-bound form of KRASG12C overcome RTK-mediated escape mechanisms and drive tumor regressions in vivo

RAS proteins are small GTPases that drive cell proliferation and survival when bound to GTP. Mutant RAS proteins are found in approximately one-third of human cancers, and exist predominantly in the GTP-bound state, leading to excessive downstream signaling via interaction with effectors such as RAF. A KRAS mutation in which glycine-12 is mutated to cysteine (KRASG12C) is found in 11-12% of non-small cell lung cancers. Recently, multiple potent, covalent inhibitors of KRASG12C have been reported that target the inactive, GDP-bound form of KRASG12C, and thus rely on the residual intrinsic hydrolysis of GTP to cycle KRASG12C proteins through the inactive, GDP-bound state. This mechanism is vulnerable to adaptive responses in cancer cells that can activate RAS by increasing upstream signaling and further increase the relative abundance of KRASG12C(GTP) over KRASG12C(GDP). An inhibitor that directly targets the active, GTP-bound form of KRASG12C would overcome this limitation. Drawing inspiration from natural products like cyclosporine and rapamycin, we have developed tri-complex inhibitors of KRASG12C(GTP) that promote a ternary complex between KRASG12C and the abundant immunophilin cyclophilin A (CypA). These sanglifehrin-inspired inhibitors exploit significant non-covalent interactions in the SWI/SWII region of KRAS combined with an electrophilic cysteine-targeted warhead to potently and irreversibly inhibit KRASG12C(GTP). The inhibitors selectively drive formation of KRASG12C-inhibitor-CypA ternary complexes that are sterically prevented from interacting with the RAS Binding Domain (RBD) of BRAF in biochemical studies. In cellular models, KRASG12C(GTP) inhibitors attenuate both RAS-MAPK signaling and cell viability in cancer cell lines bearing KRASG12C mutations, but not other mutations in RAS or other pathway oncoproteins. In vivo administration of a KRASG12C(GTP) inhibitor drives dose-dependent tumor regressions in the NCI-H358 KRASG12C NSCLC xenograft mouse model and is well-tolerated. Consistent with targeting the KRAS(GTP) state, inhibitory activity in vitro is unaffected by RTK activation, whereas the activity of first generation KRASG12C(GDP) inhibitors is significantly attenuated. In addition, proliferation of NCI-H358 and MIA PaCa-2 cells in vitro is suppressed for a significantly longer duration with KRASG12C(GTP) inhibitor treatment compared to KRASG12C(GDP) inhibitors. The combination of sub-maximal concentrations of a MEK inhibitor and a KRASG12C(GTP) inhibitor drove pronounced cell death. In contrast, the MEK and KRASG12C(GDP) inhibitor combination evoked a modest enhancement of the antiproliferative effects and does not cause cell death. Tri-complex inhibitors that target the active, GTP-bound form of KRAS thus represent a second generation of KRASG12C inhibitor. Chemical modulation of the non-covalent and covalent interactions of our tri-complex inhibitors provides an exciting opportunity to step beyond KRASG12C to target the GTP-bound state of additional RAS variants, and we demonstrate in vitro covalent inhibition of KRASG13C. By directly targeting active RAS-GTP, tri-complex inhibitors have the potential to overcome adaptive resistance mechanisms that emerge following inhibition of aberrant RAS-MAPK pathway activation.

Citation Format: Christopher J Schulze, Alun Bermingham, Tiffany J Choy, James J Cregg, Gert Kiss, Abby Marquez, Denise Reyes, Mae Saldajeno-Concar, Caroline E Weller, Daniel M Whalen, Yu C Yang, Elena S Koltun, Robert J Nichols, Mallika Singh, David Wildes, Adrian L Gill, Richard L Hansen, Steve Kelsey, Mark A Goldsmith, Jacqueline A.M. Smith. Tri-complex inhibitors of the oncogenic, GTP-bound form of KRASG12C overcome RTK-mediated escape mechanisms and drive tumor regressions in vivo [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr PR10. doi:10.1158/1535-7163.TARG-19-PR10

RAS nucleotide cycling underlies the SHP2 phosphatase dependence of mutant BRAF-, NF1- and RAS-driven cancers

Oncogenic alterations in the RAS/RAF/MEK/ERK pathway drive the growth of a wide spectrum of cancers. While BRAF and MEK inhibitors are efficacious against BRAFV600E-driven cancers, effective targeted therapies are lacking for most cancers driven by other pathway alterations, including non-V600E oncogenic BRAF, RAS GTPase-activating protein (GAP) NF1 (neurofibromin 1) loss and oncogenic KRAS. Here, we show that targeting the SHP2 phosphatase (encoded by PTPN11) with RMC-4550, a small-molecule allosteric inhibitor, is effective in human cancer models bearing RAS-GTP-dependent oncogenic BRAF (for example, class 3 BRAF mutants), NF1 loss or nucleotide-cycling oncogenic RAS (for example, KRASG12C). SHP2 inhibitor treatment decreases oncogenic RAS/RAF/MEK/ERK signalling and cancer growth by disrupting SOS1-mediated RAS-GTP loading. Our findings illuminate a critical function for SHP2 in promoting oncogenic RAS/MAPK pathway activation in cancers with RAS-GTP-dependent oncogenic BRAF, NF1 loss and nucleotide-cycling oncogenic KRAS. SHP2 inhibition is a promising molecular therapeutic strategy for patients with cancers bearing these oncogenic drivers.

Abstract 4877: Allosteric inhibition of SHP2 variants containing cancer-associated activating mutations

SHP2 (PTPN11) is a non-receptor protein tyrosine phosphatase and scaffold protein that functions in multiple signal transduction pathways. Genetic and pharmacologic evidence supports a role for SHP2 in driving the proliferation of cancer cells dependent upon a range of activated RTKs, certain RAS and BRAF mutations, and NF1 loss-of-function mutations. In addition, dominant activating mutations in PTPN11 fuel pathogenic RAS/MAPK signaling and underlie certain human RASopathies (40% of Noonan syndrome and 80% of LEOPARD syndrome) and cancers (35% of JMML and up to 5% of many other cancers). These mutants destabilize an autoinhibited conformation of SHP2, which can also be activated by binding to diphosphotyrosine motifs in vivo or to synthetic diphosphopeptides in vitro. Multiple selective, allosteric inhibitors that stabilize this autoinhibited state and potently inhibit wild-type (WT) SHP2 have recently been reported, but the impact of these inhibitors on mutant forms of the protein is less well established. Here we investigate the activity of a diverse set of over fifty allosteric SHP2 inhibitors on multiple cancer-associated activating mutants of SHP2, both in the presence and absence of an activating diphosphopeptide. The rank order of potencies of the inhibitors remains identical for all mutants, although a decrease in potency relative to WT is seen in some mutants, which is magnified further in the presence of activating peptide. These results conform to a simple equilibrium model, where inhibitors show a reduction in potency against activated mutants that is proportional to the energetic magnitude of the activating mutation. Surprisingly, some common activating mutations of SHP2 (e.g., D61G) have a relatively modest energetic effect, and exhibit similar sensitivity to allosteric inhibitors as WT SHP2. We follow up these biochemical results with cellular inhibition studies in HEK293 cells stably transfected with the respective SHP2 mutants. Collectively, these results suggest that potent allosteric SHP2 inhibitors will be effective at inhibiting the growth of cancers driven by a subset of activating mutations in SHP2.

Citation Format: David Wildes, Naing Aay, Andreas Buckl, Daphne Hsieh, Ashutosh S. Jogalekar, Gert Kiss, Elena S. Koltun, Abby Marquez, Kevin T. Mellem, Jason Romero, Mae Saldajeno-Concar, Christopher J. Schulze, Chris M. Semko, Walter Won, Robert J. Nichols, Carlos Stahlhut, Christos Tzitzilonis, Adrian L. Gill, Jacqueline A. Smith. Allosteric inhibition of SHP2 variants containing cancer-associated activating mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4877.

Evaluation of Doxycycline-Laden Oral Bait and Topical Fipronil Delivered in a Single Bait Box to Control Ixodes scapularis (Acari: Ixodidae) and Reduce Borrelia burgdorferi and Anaplasma phagocytophilum Infection in Small Mammal Reservoirs and Host-Seeking Ticks

A field trial was conducted on residential properties in a Lyme disease endemic area of New Jersey to determine the efficacy of Maxforce Tick Management System (TMS) bait boxes modified with doxycycline hyclate-laden bait to reduce the acarological risk of Lyme disease and the utility of galvanized steel shrouds to protect the bait boxes from squirrel depredation and ability to routinely service these devices. The strategy began with a 9-wk deployment against larvae followed by a 17-wk deployment against nymphs and larvae the second year. Passive application of fipronil reduced nymphal and larval tick burdens on small mammals by 76 and 77%, respectively, and nymphal tick abundance by 81% on treated properties. In addition, the percentage of infected small mammals recovered from intervention areas following treatment was reduced by 96% for Borrelia burgdorferi and 93% for Anaplasma phagocytophilum. Infection prevalence in host-seeking nymphal ticks for both B. burgdorferi and A. phagocytophilum were reduced by 93 and 61%, respectively. Results indicate that Maxforce TMS bait boxes fitted with doxycycline-impregnated bait is an effective means of reducing ticks and infection prevalence for B. burgdorferi and A. phagocytophilum in both rodent reservoirs and questing Ixodes scapularis Say ticks. The protective shroud allows the device to be routinely serviced and protect against squirrel depredation.

Design of Selective Substrates and Activity-Based Probes for Hydrolase Important for Pathogenesis 1 (HIP1) from Mycobacterium tuberculosis

Although serine proteases are important mediators of Mycobacterium tuberculosis (Mtb) virulence, there are currently no tools to selectively block or visualize members of this family of enzymes. Selective reporter substrates or activity-based probes (ABPs) could provide a means to monitor infection and response to therapy using imaging methods. Here, we use a combination of substrate selectivity profiling and focused screening to identify optimized reporter substrates and ABPs for the Mtb "Hydrolase important for pathogenesis 1" (Hip1) serine protease. Hip1 is a cell-envelope-associated enzyme with minimal homology to host proteases, making it an ideal target for probe development. We identified substituted 7-amino-4-chloro-3-(2-bromoethoxy)isocoumarins as irreversible inhibitor scaffolds. Furthermore, we used specificity data to generate selective reporter substrates and to further optimize a selective chloroisocoumarin inhibitor. These new reagents are potentially useful in delineating the roles of Hip1 during pathogenesis or as diagnostic imaging tools for specifically monitoring Mtb infections.

An in vivo multiplexed small-molecule screening platform

Phenotype-based small-molecule screening is a powerful method to identify molecules that regulate cellular functions. However, such screens are generally performed in vitro under conditions that do not necessarily model complex physiological conditions or disease states. Here, we use molecular cell barcoding to enable direct in vivo phenotypic screening of small-molecule libraries. The multiplexed nature of this approach allows rapid in vivo analysis of hundreds to thousands of compounds. Using this platform, we screened >700 covalent inhibitors directed toward hydrolases for their effect on pancreatic cancer metastatic seeding. We identified multiple hits and confirmed the relevant target of one compound as the lipase ABHD6. Pharmacological and genetic studies confirmed the role of this enzyme as a regulator of metastatic fitness. Our results highlight the applicability of this multiplexed screening platform for investigating complex processes in vivo.

Cysteine Cathepsin Inhibitors as Anti-Ebola Agents

The recent Ebola virus outbreak in western Africa highlights the need for novel therapeutics that target Ebola virus and other filoviruses. Filoviruses require processing by host cell-derived cysteine cathepsins for productive infection. Here we report the generation of a focused library of cysteine cathepsin inhibitors and subsequent screening to identify compounds with potent activity against viral entry and replication. Our top compounds show highly potent and broad-spectrum activity against cysteine cathepsins and were able to effectively block entry of Ebola and Marburg viruses. These agents are promising leads for development as antifilovirus therapeutics.

Genome-Directed Lead Discovery: Biosynthesis, Structure Elucidation, and Biological Evaluation of Two Families of Polyene Macrolactams against Trypanosoma brucei

Marine natural products are an important source of lead compounds against many pathogenic targets. Herein, we report the discovery of lobosamides A-C from a marine actinobacterium, Micromonospora sp., representing three new members of a small but growing family of bacterially produced polyene macrolactams. The lobosamides display growth inhibitory activity against the protozoan parasite Trypanosoma brucei (lobosamide A IC50 = 0.8 μM), the causative agent of human African trypanosomiasis (HAT). The biosynthetic gene cluster of the lobosamides was sequenced and suggests a conserved cluster organization among the 26-membered macrolactams. While determination of the relative and absolute configurations of many members of this family is lacking, the absolute configurations of the lobosamides were deduced using a combination of chemical modification, detailed spectroscopic analysis, and bioinformatics. We implemented a "molecules-to-genes-to-molecules" approach to determine the prevalence of similar clusters in other bacteria, which led to the discovery of two additional macrolactams, mirilactams A and B from Actinosynnema mirum. These additional analogs have allowed us to identify specific structure-activity relationships that contribute to the antitrypanosomal activity of this class. This approach illustrates the power of combining chemical analysis and genomics in the discovery and characterization of natural products as new lead compounds for neglected disease targets.

Borrelidin B: isolation, biological activity, and implications for nitrile biosynthesis

Borrelidin (1) is a nitrile-containing bacterially derived polyketide that is a potent inhibitor of bacterial and eukaryotic threonyl-tRNA synthetases. We now report the discovery of borrelidin B (2), a tetrahydro-borrelidin derivative containing an aminomethyl group in place of the nitrile functionality in borrelidin. The discovery of this new metabolite has implications for both the biosynthesis of the nitrile group and the bioactivity of the borrelidin compound class. Screening in the SToPS assay for tRNA synthetase inhibition revealed that the nitrile moiety is essential for activity, while profiling using our in-house image-based cytological profiling assay demonstrated that 2 retains biological activity by causing a mitotic stall, even in the absence of the nitrile motif.

A systematic analysis of biosynthetic gene clusters in the human microbiome reveals a common family of antibiotics

In complex biological systems, small molecules often mediate microbe-microbe and microbe-host interactions. Using a systematic approach, we identified 3,118 small-molecule biosynthetic gene clusters (BGCs) in genomes of human-associated bacteria and studied their representation in 752 metagenomic samples from the NIH Human Microbiome Project. Remarkably, we discovered that BGCs for a class of antibiotics in clinical trials, thiopeptides, are widely distributed in genomes and metagenomes of the human microbiota. We purified and solved the structure of a thiopeptide antibiotic, lactocillin, from a prominent member of the vaginal microbiota. We demonstrate that lactocillin has potent antibacterial activity against a range of Gram-positive vaginal pathogens, and we show that lactocillin and other thiopeptide BGCs are expressed in vivo by analyzing human metatranscriptomic sequencing data. Our findings illustrate the widespread distribution of small-molecule-encoding BGCs in the human microbiome, and they demonstrate the bacterial production of drug-like molecules in humans. PAPERCLIP:

"Function-first" lead discovery: mode of action profiling of natural product libraries using image-based screening

Cytological profiling is a high-content image-based screening technology that provides insight into the mode of action (MOA) for test compounds by directly measuring hundreds of phenotypic cellular features. We have extended this recently reported technology to the mechanistic characterization of unknown natural products libraries for the direct prediction of compound MOAs at the primary screening stage. By analyzing a training set of commercial compounds of known mechanism and comparing these profiles to those obtained from natural product library members, we have successfully annotated extracts based on MOA, dereplicated known compounds based on biological similarity to the training set, and identified and predicted the MOA of a unique family of iron siderophores. Coupled with traditional analytical techniques, cytological profiling provides an avenue for the creation of "function-first" approaches to natural products discovery.

Examining the fish microbiome: vertebrate-derived bacteria as an environmental niche for the discovery of unique marine natural products

Historically, marine invertebrates have been a prolific source of unique natural products, with a diverse array of biological activities. Recent studies of invertebrate-associated microbial communities are revealing microorganisms as the true producers of many of these compounds. Inspired by the human microbiome project, which has highlighted the human intestine as a unique microenvironment in terms of microbial diversity, we elected to examine the bacterial communities of fish intestines (which we have termed the fish microbiome) as a new source of microbial and biosynthetic diversity for natural products discovery. To test the hypothesis that the fish microbiome contains microorganisms with unique capacity for biosynthesizing natural products, we examined six species of fish through a combination of dissection and culture-dependent evaluation of intestinal microbial communities. Using isolation media designed to enrich for marine Actinobacteria, we have found three main clades that show taxonomic divergence from known strains, several of which are previously uncultured. Extracts from these strains exhibit a wide range of activities against both Gram-positive and Gram-negative human pathogens, as well as several fish pathogens. Exploration of one of these extracts has identified the novel bioactive lipid sebastenoic acid as an anti-microbial agent, with activity against Staphylococcus aureus, Bacillus subtilis, Enterococcus faecium, and Vibrio mimicus.

Elimination of Borrelia burgdorferi and Anaplasma phagocytophilum in rodent reservoirs and Ixodes scapularis ticks using a doxycycline hyclate-laden bait

A field trial was conducted in a Lyme disease-endemic area of New Jersey to determine the efficacy of a doxycyline hyclate rodent bait to prophylactically protect and cure small-mammal reservoirs and reduce infection rates in questing Ixodes scapularis ticks for Borrelia burgdorferi and Anaplasma phagocytophilum. The doxycycline-laden bait was formulated at a concentration of 500 mg/kg and delivered during the immature tick feeding season in rodent-targeted bait boxes. The percentage of infected small mammals recovered from treated areas after 2 years of treatment was reduced by 86.9% for B. burgdorferi and 74% for A. phagocytophilum. Infection rates in questing nymphal ticks for both B. burgdorferi and A. phagocytophilum were reduced by 94.3% and 92%, respectively. Results from this study indicate that doxycycline-impregnated bait is an effective means of reducing infection rates for B. burgdorferi and A. phagocytophilum in both rodent reservoirs and questing I. scapularis ticks.

Effectiveness of the 4-Poster passive topical treatment device in the control of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) in New Jersey

Twenty-five "4-Poster" feeders were placed throughout a 5.2 km(2) study area within a secured military facility situated in a hyperendemic area for Lyme disease in central Monmouth County, New Jersey. Calculated levels of control, relative to untreated areas, peaked at 82.7%, 77.3%, and 94.2% for of host-seeking Ixodes scapularis Say larvae, nymphs, and adults, respectively, within 5 years of deployment. Control of host-seeking Amblyomma americanum (L.) peaked at 99.2%, 89.5%, and 96.9% for larvae, nymphs, and adults, respectively, during the treatment period. Tick burdens on hunter-killed deer were significantly reduced on deer harvested from the treatment area and on deer that had consumed bait corn. Populations of subadult I. scapularis and A. americanum demonstrated some rebound effect following the removal of 4-Posters, but treatment area tick populations remained lower than control area populations 2 years following withdrawal of the 4-Posters. However, control of I. scapularis adults declined to 20.7% by the third fall activity period following removal of the 4-Posters. The posttreatment phase of the study was of insufficient duration to evaluate continued population rebound of adults and subadults during subsequent activity periods.

Ability of two natural products, nootkatone and carvacrol, to suppress Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) in a Lyme disease endemic area of New Jersey

We evaluated the ability of the natural, plant-derived acaricides nootkatone and carvacrol to suppress Ixodes scapularis Say and Amblyomma americanum (L.) (Acari: Ixodidae). Aqueous formulations of 1 and 5% nootkatone applied by backpack sprayer to the forest litter layer completely suppressed I. scapularis nymphs through 2 d. Thereafter, the level of reduction gradually declined to < or =50% at 28 d postapplication. Against A. americanum nymphs, 1% nootkatone was less effective, but at a 5% concentration, the level of control was similar or greater to that observed with I. scapularis through 21 d postapplication. Initial applications of 0.05% carvacrol were ineffective, but a 5% carvacrol formulation completely suppressed nymphs of both species through 2 d and resulted in significant reduction in I. scapularis and A. americanum nymphs through 28 and 14 d postapplication, respectively. Backpack sprayer applications of 5% nootkatone to the shrub and litter layers resulted in 100% control of I. scapularis adults through 6 d, but the level of reduction declined to 71.5% at 28 d postapplication. By contrast, high-pressure applications of 2% nootkatone to the litter layer resulted in 96.2-100% suppression of both I. scapularis and A. americanum nymphs through 42 d, whereas much lower control was obtained from the same formulation applied by backpack sprayer. Backpack sprayer application of a 3.1% nootkatone nanoemulsion resulted in 97.5-98.9 and 99.3-100% reduction in I. scapularis and A. americanum nymphs, respectively, at 1 d postapplication. Between 7 d and 35 d postapplication, the level of control varied between 57.1% and 92.5% for I. scapularis and between 78.5 and 97.1% for A. americanum nymphs. The ability of natural products to quickly suppress and maintain significant control of populations of these medically important ticks at relatively low concentrations may represent a future alternative to the use of conventional synthetic acaricides.

Precipitation and temperature as predictors of the local abundance of Ixodes scapularis (Acari: Ixodidae) nymphs

Populations of Ixodes scapularis Say nymphs were surveyed at a Lyme disease- endemic area for 8 consecutive yr (1998-2005) to characterize annual changes in abundance. Precipitation and temperature were also monitored over the period 1998-2004 to determine their potential value as predictors of tick abundance. Although both parameters showed annual variation, no statistical differences in the annual abundance of I. scapularis nymphs were observed over the 8-yr period. Our results suggest that precipitation and temperature were not predictive of the abundance of I. scapularis nymphs.

Suppression of Ixodes scapularis (Acari: Ixodidae) following annual habitat-targeted acaricide applications against fall populations of adults

Spring acaricide applications directed against nymphal Ixodes scapularis have been shown to be effective, but are perceived by the public as having significant adverse environmental impacts, particularly against nontarget organisms. Targeting the adult stage of I. scapularis in the fall would hypothetically result in indirect control of subsequent subadult stages while avoiding other arthropods that are typically inactive during this period. We demonstrate that single fall applications of deltamethrin for 3 consecutive years immediately reduced fall questing adults, while also rapidly reducing the abundance of all postembryonic stages. Deltamethrin applied to the shrub-layer vegetation resulted in levels of control between 97.1% and 100% at 7 days postapplication. Repeated applications against the reproductive stage of I. scapularis progressively reduced the abundance of larvae and nymphs in treated plots, reaching 91.4% and 100% by the conclusion of the study.

Integrated use of 4-Poster passive topical treatment devices for deer, targeted acaricide applications, and Maxforce TMS bait boxes to rapidly suppress populations of Ixodes scapularis (Acari: Ixodidae) in a residential landscape

In fall 2003, we began testing an integrated control strategy to rapidly achieve and sustain reduced numbers of Ixodes scapularis Say (Acari: Ixodidae) in a residential area. We combined two host-targeted technologies in conjunction with single, barrier acaricide applications to sequentially attack each postembryonic life stage of the tick. Granular deltamethrin applied to the lawn-forest interface of participant properties resulted in 100% control of host-seeking nymphs. Nymphal and larval tick burdens on targeted small mammal hosts at treated properties were reduced by 92.7 and 95.4%, respectively, after the first year (2004) of combined interventions. Over the same period, populations of host-seeking nymphs, larvae, and adults were reduced by 58.5, 24.8, and 77.8%, respectively. After interventions in 2005, tick burdens on small mammals were maintained at similar levels, whereas control of host-seeking nymphs, larvae, and adults increased to 94.3, 90.6, and 87.3%, respectively. Prospects for widespread use of these technologies to protect the public's health are discussed.

Host associations of Ixodes scapularis (Acari: Ixodidae) in residential and natural settings in a Lyme disease-endemic area in New Jersey

We live-trapped small mammals and flagged vegetation within wooded natural and residential landscapes to examine how any observed differences in small mammal species composition may influence Ixodes scapularis Say burdens and the abundance of host-seeking ticks. Two years of live trapping showed that Eastern chipmunks, Tamias striatus, were captured with significantly greater frequency in some residential areas than white-footed mice, Peromyscus leucopus, whereas the proportion of white-footed mouse captures was higher or similar to chipmunk captures in the undeveloped natural areas. Both mice and chipmunks seemed to adapt well to managed residential landscapes, with residential sites yielding similar or significantly greater numbers of captures compared with undeveloped sites. In areas where chipmunk captures outnumbered mice, larval tick burdens on mice were either higher or no different than in areas where few or no chipmunks were captured, in contrast to previous studies suggesting that alternate hosts should reduce larval burdens on mice. Chipmunks apparently play an important role in the Lyme disease transmission cycle in these residential settings.

Relative encounter frequencies and prevalence of selected Borrelia, Ehrlichia, and Anaplasma infections in Amblyomma americanum and Ixodes scapularis (Acari: Ixodidae) ticks from central New Jersey

To evaluate their relative importance in tick-borne disease transmission in New Jersey, host-seeking Amblyomma americanum (L.) and Ixodes scapularis Say adults and nymphs were collected during spring activity periods in 2003 and 2004 to determine relative frequencies at which these ticks were encountered from an area known to be hyperendemic for Lyme disease. Although similar numbers of the two species were encountered during early spring of both years, A. americanum were encountered more often later in the season and exhibited a longer activity period than I. scapularis. A. americanum nymphs were collected at frequencies between 2.6 and 7.3 times higher than I. scapularis nymphs. Polymerase chain reaction (PCR) analysis of 121 A. americanum adults yielded infection prevalences of 9.1% for Borrelia lonestari, 12.3% for Ehrlichia chaffeenensis, and 8.2% for E. ewingii, and coinfection prevalences of 4.1% for E. chaffeensis/E. ewingii and 0.8% for E. chaffeensis/B. lonestari. Infection prevalences in 147 I. scapularis adults were 50.3% for B. burgdorferi, 6.1% for Anaplasma (Ehrlichia) phagocytophilum, and 1.4% for a recently described novel Borrelia species, whereas the coinfection prevalences were 2.7% for B. burgdorferi/A. phagocytophilum, 0.7% for B. burgdorferi/novel Borrelia, and 0.7% for A. phagocytophilum/novel Borrelia. The B. burgdorferi infection prevalence in I. scapularis was considerably higher than that in A. americanum. However, the higher A. americanum encounter frequencies compared with I. scapularis may result in increased risk of acquiring exposure to A. americanum-transmitted pathogens. The potential public health implications of these results are discussed.

Surgical treatment of permanent atrial fibrillation using microwave energy ablation: a prospective randomized clinical trial

OBJECTIVE

Radiofrequency or the use of microwave energy in combination with atrial size reduction during open heart surgery have been reported to be effective in up to 75% in the treatment of permanent atrial fibrillation. However, no data from prospective randomized trials using microwave energy are available.

METHODS

Forty-three patients with permanent atrial fibrillation undergoing open-heart surgery were randomly stratified into treatment group receiving microwave ablation and atrial size reduction (n=24) or control group (n=19). Patients in either group were treated with amiodarone or sotalol for 3 months if sinus rhythm or any atrioventricular rhythm was successfully restored. Follow-up time points were at 3, 6 and 12 month after surgery.

RESULTS

In the treatment group 22 out of 24 patients (91,7%) were successfully converted to sinus rhythm by using intraoperative microwave ablation therapy whereas only six out of 19 (31.5%) patients converted to sinus rhythm directly after surgery. At 12-month follow-up there were still a significantly higher percentage of patients in the treatment group free from atrial fibrillation when compared to control (80 vs. 33.3%, P=0.036).

CONCLUSION

The preliminary data from this first prospectively randomized trial indicate that microwave ablation combined with atrial size reduction is a safe and highly efficient treatment in permanent atrial fibrillation.

[Surgical treatment of aortic valve disease in old age]

In terms of long-term survival and quality of life, excellent results with aortic valve replacement (AVR) can also be achieved in patients older than 70 years of age. An indication for this procedure is given in symptomatic patients with significant aortic valve stenosis, patients with severe acute aortic insufficiency (AI), those with signs of cardiac insufficiency but still normal left ventricular function, and asymptomatic AI patients with an ejection fraction of less than 50% and/or an end-diastolic LV diameter (EDD) of more than 75 mm or an end-systolic diameter (ESD) of more than 55 mm. Many patients with a heart defect in need of surgical treatment also have CAD as well, in which case a bypass should be performed at the same time. For AVR, both mechanical and biological prostheses are available, the latter being regarded as the method of choice in patients aged over 70. The mechanical variant requires life-long anticoagulation therapy with phenprocoumon.

Continuous transesophageal echocardiographic (TEE) monitoring during port-access cardiac surgery

BACKGROUND

Since the introduction of the closed-chest minimally invasive heart surgery using the Port-Access system a variety of monitoring techniques including fluoroscopy, transesophageal echocardiography (TEE) and invasive pressure measurements have been described. We investigated whether or not single TEE is feasible for perioperative monitoring of the placement, localization and proper function of the endovascular cardiopulmonary bypass (CPB) devices.

METHODS

Fifty-one patients (35 mitral valve repair or replacement [MVR], 8 coronary artery bypass grafting [CABG], 5 atrial septal defects [ASD] and 3 left atrial myxoma) were subjected to Port-Access surgery (PAS). Intraoperative Omniplane-TEE (2D- and color-flow Doppler techniques) was used as the leading monitoring device for correct positioning of the endopulmonary vent catheter and the venous cannula, and for the visualization of the guide wire and the endoaortic occlusion catheter (Endoclamp). After balloon inflation, its proper positioning and function during endo-aortic occlusion, sufficient delivery of cardioplegia into the coronary ostia, absence of leakage flow and adequate venting were controlled. Left and right radial artery catheters as well as aortic root pressure measurements served as controls. Additional fluoroscopy was used as standby device.

RESULTS

In 46 patients (90.1%) sufficient perioperative monitoring was provided by single TEE. In five cases additional intermittent fluoroscopy was necessary for correct positioning of the guide wire (CABG) and the Endoclamp (three MVR and one ASD). Dislocation of the Endoclamp into the left ventricle was observed once but was successfully corrected by TEE guidance. Weaning from CPB and de-airing were easily guided with TEE. We did not observe balloon-mediated aortic injury or aortic valve dysfunction, and myocardial recovery from CPB was uneventful. All cases of MVRs showed sufficient results (68% without evidence of regurgitation, 32% showed residual mitral valve incompetence of less than grade II). Neither perivalvular leakage (MV-replacement) nor shunt- (residual ASD) flow were detectable.

CONCLUSIONS

We recommend single TEE as a safe and effective on-line imaging device for monitoring the endovascular CPB system during PAS. Fluoroscopy with its potential risk for the patients and the staff due to x-ray exposure should only be used in the presence of peripheral vascular disease or when echocardiographic imaging is insufficient.

Clinical relevance of accuracy of pedicle screw placement. A computed tomographic-supported analysis

STUDY DESIGN

The location of pedicle screws (n = 244) and the increase in the pedicle diameter were determined by computed tomography after screw removal in 50 patients with 360 degrees lumbar fusions. The neurologic findings were examined before and after surgery.

OBJECTIVES

To evaluate the correlation between the accuracy of pedicle screw placement and preoperative and postoperative neurologic findings.

SUMMARY OF BACKGROUND DATA

Incorrect placement of pedicle screws that was detected by computed tomography has been published in several studies. Simultaneous pathologic neurologic deficits are thought to be created by an eccentric screw track.

METHODS

Two observers controlled the screw tracts and pedicle diameters. The results were compared with preoperative and postoperative neurologic findings.

RESULTS

Fifty-nine percent (144 of 244) of screws were placed centrally in the pedicle. More than half of the eccentric screws (100, 41%; medial 79, 32.4%; lateral 21, 8.6%) penetrated the pedicle wall less than 2 mm (51; 20.9%). In only one patient (0.5%) a radicular irritation was found without objective electrophysiologic correlation when the screw was more than 6 mm medial to the pedicle wall. After screw removal, an insignificant increase in the size of the pedicle diameter in L1-S1 was noted.

CONCLUSIONS

Experienced surgeons implant pedicle screws with an accuracy of approximately 80%. The accuracy could be improved by using image-guided insertion equipment. The neurologic symptoms are rarely influenced by an eccentric pedicle screw tract even if penetration of the pedicle wall is more than 6 mm. The results stress the importance of preoperative planning (pedicle diameter, pedicle angle, screw length) when implanting transpedicular fixators.

Exogenous lumbar spondylodiscitis following a stabwound injury and vertebral fracture. A case report and review of the literature

Exogenous spondylodiscitis is a rare event and is usually iatrogenic. Non-iatrogenic exogenous spondylodiscitis has been described in the literature following transabdominal gunshot wounds associated with injury to the intestines and spine. Several cases of traumatic meningitis and one of a traumatic meningocele following an injury of the spinal sac have been reported. No report of exogenous spondylodiscitis complicating a stabwound has been published. This is a report of exogenous spondylodiscitis following a paravertebral stabwound with a knife in association with a superior wedge fracture of L2.