A Small Molecule RAS-Mimetic Disrupts RAS Association with Effector Proteins to Block Signaling.

Oncogenic activation of RAS genes via point mutations occurs in 20%-30% of human cancers. The development of effective RAS inhibitors has been challenging, necessitating new approaches to inhibit this oncogenic protein. Functional studies have shown that the switch region of RAS interacts with a large number of effector proteins containing a common RAS-binding domain (RBD). Because RBD-mediated interactions are essential for RAS signaling, blocking RBD association with small molecules constitutes an attractive therapeutic approach. Here, we present evidence that rigosertib, a styryl-benzyl sulfone, acts as a RAS-mimetic and interacts with the RBDs of RAF kinases, resulting in their inability to bind to RAS, disruption of RAF activation, and inhibition of the RAS-RAF-MEK pathway. We also find that ribosertib binds to the RBDs of Ral-GDS and PI3Ks. These results suggest that targeting of RBDs across multiple signaling pathways by rigosertib may represent an effective strategy for inactivation of RAS signaling.

Cryo-EM structures of cancer-specific helical and kinase domain mutations of PI3Kα.

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that perform multiple and important cellular functions. The protein investigated here belongs to class IA of the PI3Ks; it is a dimer consisting of a catalytic subunit, p110α, and a regulatory subunit, p85α, and is referred to as PI3Kα. The catalytic subunit p110α is frequently mutated in cancer. The mutations induce a gain of function and constitute a driving force in cancer development. About 80% of these mutations lead to single-amino-acid substitutions in one of three sites of p110α: two in the helical domain of the protein (E542K and E545K) and one at the C-terminus of the kinase domain (H1047R). Here, we report the cryo-electron microscopy structures of these mutants in complex with the p110α-specific inhibitor BYL-719. The H1047R mutant rotates its sidechain to a new position and weakens the kα11 activation loop interaction, thereby reducing the inhibitory effect of p85α on p110α. E542K and E545K completely abolish the tight interaction between the helical domain of p110α and the N-terminal SH2 domain of p85α and lead to the disruption of all p85α binding and a dramatic increase in flexibility of the adaptor-binding domain (ABD) in p110α. Yet, the dimerization of PI3Kα is preserved through the ABD-p85α interaction. The local and global structural features induced by these mutations provide molecular insights into the activation of PI3Kα, deepen our understanding of the oncogenic mechanism of this important signaling molecule, and may facilitate the development of mutant-specific inhibitors.

Nanobodies and chemical cross-links advance the structural and functional analysis of PI3Kα.

Nanobodies and chemical cross-linking were used to gain information on the identity and positions of flexible domains of PI3Kα. The application of chemical cross-linking mass spectrometry (CXMS) facilitated the identification of the p85 domains BH, cSH2, and SH3 as well as their docking positions on the PI3Kα catalytic core. Binding of individual nanobodies to PI3Kα induced activation or inhibition of enzyme activity and caused conformational changes that could be correlated with enzyme function. Binding of nanobody Nb3-126 to the BH domain of p85α substantially improved resolution for parts of the PI3Kα complex, and binding of nanobody Nb3-159 induced a conformation of PI3Kα that is distinct from known PI3Kα structures. The analysis of CXMS data also provided mechanistic insights into the molecular underpinning of the flexibility of PI3Kα.

Cryo-EM structures of PI3Kα reveal conformational changes during inhibition and activation.

Phosphoinositide 3-kinases (PI3Ks) are lipid kinases essential for growth and metabolism. Their aberrant activation is associated with many types of cancers. Here we used single-particle cryoelectron microscopy (cryo-EM) to determine three distinct conformations of full-length PI3Kα (p110α-p85α): the unliganded heterodimer PI3Kα, PI3Kα bound to the p110α-specific inhibitor BYL-719, and PI3Kα exposed to an activating phosphopeptide. The cryo-EM structures of unbound and of BYL-719-bound PI3Kα are in general accord with published crystal structures. Local deviations are presented and discussed. BYL-719 stabilizes the structure of PI3Kα, but three regions of low-resolution extra density remain and are provisionally assigned to the cSH2, BH, and SH3 domains of p85. One of the extra density regions is in contact with the kinase domain blocking access to the catalytic site. This conformational change indicates that the effects of BYL-719 on PI3Kα activity extend beyond competition with adenosine triphosphate (ATP). In unliganded PI3Kα, the DFG motif occurs in the "in" and "out" positions. In BYL-719-bound PI3Kα, only the DFG-in position, corresponding to the active conformation of the kinase, was observed. The phosphopeptide-bound structure of PI3Kα is composed of a stable core resolved at 3.8 Å. It contains all p110α domains except the adaptor-binding domain (ABD). The p85α domains, linked to the core through the ABD, are no longer resolved, implying that the phosphopeptide activates PI3Kα by fully releasing the niSH2 domain from binding to p110α. The structures presented here show the basal form of the full-length PI3Kα dimer and document conformational changes related to the activated and inhibited states.

A Statewide Randomized Controlled Trial to Compare Three Models for Implementing Parent Child Interaction Therapy.

OBJECTIVE: This study (NIMH RO1 MH095750; ClinicalTrials.gov Identifier: NCT02543359) evaluated the effectiveness of three training models to implement a well-established evidence-based treatment, Parent-Child Interaction Therapy (PCIT). METHOD: Fifty licensed outpatient clinics, including 100 clinicians, 50 supervisors, and 50 administrators were randomized to one of three training conditions: 1) Learning Collaborative (LC), 2) Cascading Model (CM) or 3) Distance Education (DE). Data to assess training and implementation outcomes were collected at 4 time points coinciding with the training period: baseline, 6- (mid), 12- (post), and 24-months (1-year follow-up). RESULTS: Multi-level hierarchical linear growth modeling was used to examine changes over time in training outcomes. Results indicate that clinicians in CM were more likely to complete training, reported high levels of training satisfaction and better learning experiences compared to the other training conditions. However, supervisors in the LC condition reported greater learning experiences, higher levels of knowledge, understanding of treatment, and satisfaction compared to supervisors in other conditions. Although clinicians and supervisors in the DE condition did not outperform their counterparts on any outcomes, their performance was comparable to both LC and CM in terms of PCIT use, supervisor perceived acceptability, feasibility, system support, and clinician satisfaction. CONCLUSIONS: Through the use of a randomized controlled design and community implementation, this study contributes to the current understanding of the impact of training design on implementation of PCIT. Results also indicate that although in-person training methods may produce more positive clinician and supervisor outcomes, training is not a one-size-fits-all model, with DE producing comparable results on some variables.

An MXD1-derived repressor peptide identifies noncoding mediators of MYC-driven cell proliferation.

MYC controls the transcription of large numbers of long noncoding RNAs (lncRNAs). Since MYC is a ubiquitous oncoprotein, some of these lncRNAs probably play a significant role in cancer. We applied CRISPR interference (CRISPRi) to the identification of MYC-regulated lncRNAs that are required for MYC-driven cell proliferation in the P493-6 and RAMOS human lymphoid cell lines. We identified 320 noncoding loci that play positive roles in cell growth. Transcriptional repression of any one of these lncRNAs reduces the proliferative capacity of the cells. Selected hits were validated by RT-qPCR and in CRISPRi competition assays with individual GFP-expressing sgRNA constructs. We also showed binding of MYC to the promoter of two candidate genes by chromatin immunoprecipitation. In the course of our studies, we discovered that the repressor domain SID (SIN3-interacting domain) derived from the MXD1 protein is highly effective in P493-6 and RAMOS cells in terms of the number of guides depleted in library screening and the extent of the induced transcriptional repression. In the cell lines used, SID is superior to the KRAB repressor domain, which serves routinely as a transcriptional repressor domain in CRISPRi. The SID transcriptional repressor domain is effective as a fusion to the MS2 aptamer binding protein MCP, allowing the construction of a doxycycline-regulatable CRISPRi system that allows controlled repression of targeted genes and will facilitate the functional analysis of growth-promoting lncRNAs.

Sexual Offense Disclosure Assessment in Youth Referred to Community Treatment: A Latent Class Analysis.

This study seeks to extend research evaluating tools to assess the disclosure of sexually abusive behavior. The subjects were 239 male youth (ages 10-20 years) who were court-ordered to participate in a community-based collaborative intervention for sexual offending that includes outpatient and probationary services. All youth participated in an interview to capture referral incident details about admission, responsibility, empathy, and remorse at intake, during intervention, and at discharge. Intake, treatment, discharge, and recidivism measures were also collected from multiple sources. Latent class analysis identified three classes based on the intake interview: Empathetic Admitters (22%), Unempathetic Admitters (38%), and Unempathetic Deniers (40%). Significant class differences were found on intake (e.g., use of physical force, caregiver denial of youth responsibility), treatment (e.g., any sanctions/violations), and discharge measures (e.g., successful treatment, probation officer ratings), but not in recidivism rates. The findings extend efforts to identify and target different disclosure patterns whose clinical monitoring may support a comprehensive intervention.

How do the working lives of general practitioners in rural areas compare with elsewhere in Scotland? Cross-sectional analysis of the Scottish School of Primary Care Survey.

INTRODUCTION: The shortage of GPs in Scotland is concerning, particularly in rural areas. There are many reasons why GPs are leaving general practice; however, satisfaction with working life is an important predictor of GP retention. The aim of this study was to compare the working lives and intentions to reduce work participation of rural GPs and GPs working elsewhere in Scotland. METHODS: Quantitative analysis of responses from a nationally representative survey of GPs in Scotland. GPs were classified as 'non-rural' or 'rural' and these groups were compared using univariate and multivariate statistical analysis on four domains of working lives (job satisfaction, job stressors and positive and negative job attributes) and four intentions to reduce work participation (reducing working hours, working abroad, leaving direct patient care and leaving medical work entirely). RESULTS: There were significant differences in characteristics between rural and non-rural GPs. After controlling for these differences, GP age and gender, rural GPs reported higher job satisfaction, lower job stressors, higher positive job attributes, and lower negative job attributes than GPs elsewhere. A significant interaction between gender and rurality was found for job satisfaction, indicating that it was rural female GPs who were more satisfied. Rural GPs were, however, more likely to intend to work abroad and leave medical work entirely within 5 years than other GPs. DISCUSSION: These findings corroborate research from around the world and have serious implications for the future care of patients in rural areas. Further research is urgently required to understand the drivers of these findings.

A Randomized Pilot of a Tailored Smoking Cessation Quitline Intervention for Individuals Who Smoke and Vape.

INTRODUCTION: Although e-cigarettes are not a federally approved tobacco cessation aid in the United States, many smokers use them to quit or cut down on smoking. Tailored behavioral support could improve rates of complete smoking cessation for those individuals. AIMS AND METHODS: A novel behavioral treatment to help dual cigarette and e-cigarette users quit smoking was tested in a randomized pilot with a state tobacco quitline. Ninety-six dual users of cigarettes and e-cigarettes were recruited from incoming state quitline callers and randomized to receive enhanced e-cigarette coaching (EEC) or quitline treatment as usual (TAU) to examine EEC feasibility and acceptability. Outcomes at 3 months were treatment satisfaction, engagement, beliefs, and smoking cessation. This pilot was not powered to detect differences in quit rates. RESULTS: Sixty-nine percent responded to the 3-month survey. EEC treatment satisfaction was noninferior to TAU: 93.8% (30/32) of EEC and 73.5% (25/34) of TAU reported being "very satisfied" or "satisfied" with treatment, respectively. EEC participants completed more coaching calls than TAU (M = 3.4 vs. M = 2.7, p = .03), and the majority in both groups elected to receive nicotine replacement therapy (EEC: 100%, TAU: 94%, p = .24). With missing data imputed as smoking, intent-to-treat 7-day point prevalence smoking abstinence rates were 41.3% (19/46) for EEC and 28.0% (14/50) for TAU (p = .20). CONCLUSIONS: The EEC quitline intervention for dual cigarette and e-cigarette users demonstrated high levels of treatment satisfaction and engagement. This pilot was not powered to detect significant differences in smoking cessation; however, cessation rates were promising and warrant evaluation in a fully powered trial. IMPLICATIONS: If this scalable behavioral treatment to help dual cigarette and e-cigarette users quit smoking proves to be effective in a larger trial, quitlines could implement this harm reduction approach to improve outcomes for callers who already use e-cigarettes and are planning to use them while quitting smoking.

How do the working lives of general practitioners in rural areas compare with elsewhere in Scotland? Cross-sectional analysis of the Scottish School of Primary Care National GP Survey.

INTRODUCTION: Like many countries around the world, Scotland faces a shortage of general practitioners (GPs) due to both recruitment and retention issues. Such workforce shortages are of particular concern in rural areas. There are many reasons why GPs are leaving general practice; however, satisfaction with working life is an important predictor of GP retention. It is important, therefore, to understand working life satisfaction of rural GPs. The purpose of this study was to compare the working lives and intentions to reduce work participation of rural GPs and GPs working elsewhere in Scotland. METHODS: This study was a quantitative analysis of survey data from the Scottish School of Primary Care national working lives survey. GPs were classified as working in 'non-rural' or 'rural' practices based on the Scottish Government's rural binary classification system, and were compared using univariate and multivariate statistical analysis on four domains of working lives: job satisfaction, job stressors, positive and negative job attributes, and four intentions to reduce work participation: reducing working hours, working abroad, leaving direct patient care and leaving medical work entirely. RESULTS: A total of 2465 GPs returned the survey, giving a response rate of 56%. Three-hundred and forty seven GPs who returned the survey worked in practices in rural areas (14.1%). Rural GPs were more likely to do out-of-hours work (p<0.001), to have worked in their practice for fewer years (p=0.014), to work in single-GP partnerships (p<0.001), and to work in practices with smaller list sizes (p<0.001), than GPs in non-rural settings. Compared with GPs elsewhere, rural GPs reported higher mean job satisfaction (5.23 v 5.39, respectively; p<0.005), lower mean job stressors (3.58 v 3.29; p<0.001) and lower mean negative job attributes (4.08 vs 3.78; p<0.001). These differences remained highly significant after controlling for potential confounders (age, gender and the differences in work practices shown above). In regression analysis, a significant interaction was found between gender and rurality for job satisfaction (p=0.008), which indicated that rural female GPs' higher job satisfaction mainly accounted for rural GPs' increased job satisfaction. No significant interaction was found between gender and rurality for the other domains of working lives. Compared with GPs elsewhere, however, rural GPs were more likely to intend to work abroad (mean 1.39 v 1.55; p=0.013) and leave medical work entirely within 5 years (mean 2.15 v 2.36; p=0.039). These intentions remained significant after controlling for potential confounders. No significant interaction was found between gender and rurality for variables for intentions to reduce work participation. CONCLUSION: Rural GPs in Scotland are more satisfied with their working lives than GPs working elsewhere in Scotland, which is mainly due to higher job satisfaction in female GPs in rural areas. Despite this, rural GPs as a whole have a higher intention to leave their job in the next 5 years than their non-rural counterparts. Although some of these differences are small, they may signal serious implications for the future care of patients in rural areas and require further research to understand the drivers of this.

Synthetic fluorescent MYC probe: Inhibitor binding site elucidation and development of a high-throughput screening assay.

We report the discovery of a fluorescent small molecule probe. This probe exhibits an emission increase in the presence of the oncoprotein MYC that can be attenuated by a competing inhibitor. Hydrogen-deuterium exchange mass spectrometry analysis, rationalized by induced-fit docking, suggests it binds to the "coiled-coil" region of the leucine zipper domain. Point mutations of this site produced functional MYC constructs resistant to inhibition in an oncogenic transformation assay by compounds that displace the probe. Utilizing this probe, we have developed a high-throughput assay to identify MYC inhibitor scaffolds. Screening of a diversity library (N = 1408, 384-well) and a library of pharmacologically active compounds (N = 1280, 1536-well) yielded molecules with greater drug-like properties than the probe. One lead is a potent inhibitor of oncogenic transformation and is specific for MYC relative to resistant mutants and transformation-inducing oncogenes. This method is simple, inexpensive, and does not require protein modification, DNA binding, or the dimer partner MAX. This assay presents an opportunity for MYC inhibition researchers to discover unique scaffolds.

Absence of Decussation in Optic Pathway Inflammation in Neuromyelitis Optica and Its Implications for Astrocyte Localization.

ABSTRACT: A 39-year-old woman presented with acute visual loss in her right eye. Brain and orbit MRI demonstrated T2 hyperintensity along a long section of her right optic nerve, chiasm, and tract with no evidence of decussation of the inflammation. Subsequent seropositivity for the aquaporin 4 antibody confirmed a diagnosis of neuromyelitis optica. Posterior pathway involvement is typical in neuromyelitis optica and supports the hypothesis that the condition is an astrocytopathy. Furthermore, the absence of decussation in the condition may be a function of astrocyte localization within the chiasm.

Making Implementation Last: The Impact of Training Design on the Sustainability of an Evidence-Based Treatment in a Randomized Controlled Trial.

Although advances have been made in facilitating the implementation of evidence-based treatments, little is known about the most effective way to sustain their use over time. The current study examined the sustainability of one evidence-based treatment, Parent-Child Interaction Therapy (PCIT), following a statewide implementation trial testing three training methods: Cascading Model, Learning Collaborative, and Distance Education. Participants included 100 clinicians and 50 administrators from 50 organizations across Pennsylvania. Clinicians and administrators reported on sustainability at 24-months, as measured by the number of clients receiving PCIT and the continued use of the PCIT protocol. Multi-level path analysis was utilized to examine the role of training on sustainability. Clinicians and administrators reported high levels of sustainability at 24-months. Clinicians in the Cascading Model reported greater average PCIT caseloads at 24-months, whereas clinicians in the Learning Collaborative reported greater full use of the PCIT protocol at 24-months. Attending consultation calls was associated with delivering PCIT to fewer families. Implications for the sustainable delivery of PCIT beyond the training year as well as for the broader field of implementation science are discussed.

Hereditary vs Familial Pancreatic Cancer: Associated Genetic Syndromes and Clinical Perspective.

Pancreatic ductal adenocarcinoma (PDAC) is a disease marked by high rates of mortality; it is mostly incurable at the time of diagnosis. Only about 7% of patients survive 5 years after diagnosis. Diagnosis at a late stage and rapid progression with minimal response to available treatments are the main reasons for this poor outcome. It is crucial to identify individuals at high risk of developing PDAC so preventive and early detection measures can be employed. Approximately 10% to 15% of PDAC cases have a hereditary or familial basis. In the majority of PDAC cases, no main causative gene has been identified, but several known germline pathogenic mutations have been shown to be related to an increased risk of this cancer. The presence of 2 or more patients with pancreatic cancer within the circle of first-degree relatives, without the presence of a causative germline mutation, is defined as familial pancreatic cancer; this accounts for 4% to 10% of PDAC. Based on the growing evidence supporting the benefit of germline genetic testing in patients with PDAC, both the American Society of Clinical Oncology and the National Comprehensive Cancer Network recently updated their guidelines to include recommendations around genetic testing for patients with pancreatic cancer. However, there is no general consensus on the group of patients and individuals who should be studied and screened. We present a demonstrative case and review the available data on hereditary and familial PDAC.

tsRNA signatures in cancer.

Small, noncoding RNAs are short untranslated RNA molecules, some of which have been associated with cancer development. Recently we showed that a class of small RNAs generated during the maturation process of tRNAs (tRNA-derived small RNAs, hereafter "tsRNAs") is dysregulated in cancer. Specifically, we uncovered tsRNA signatures in chronic lymphocytic leukemia and lung cancer and demonstrated that the ts-4521/3676 cluster (now called "ts-101" and "ts-53," respectively), ts-46, and ts-47 are down-regulated in these malignancies. Furthermore, we showed that tsRNAs are similar to Piwi-interacting RNAs (piRNAs) and demonstrated that ts-101 and ts-53 can associate with PiwiL2, a protein involved in the silencing of transposons. In this study, we extended our investigation on tsRNA signatures to samples collected from patients with colon, breast, or ovarian cancer and cell lines harboring specific oncogenic mutations and representing different stages of cancer progression. We detected tsRNA signatures in all patient samples and determined that tsRNA expression is altered upon oncogene activation and during cancer staging. In addition, we generated a knocked-out cell model for ts-101 and ts-46 in HEK-293 cells and found significant differences in gene-expression patterns, with activation of genes involved in cell survival and down-regulation of genes involved in apoptosis and chromatin structure. Finally, we overexpressed ts-46 and ts-47 in two lung cancer cell lines and performed a clonogenic assay to examine their role in cell proliferation. We observed a strong inhibition of colony formation in cells overexpressing these tsRNAs compared with untreated cells, confirming that tsRNAs affect cell growth and survival.

Synthetic molecules for disruption of the MYC protein-protein interface.

MYC is a key transcriptional regulator involved in cellular proliferation and has established roles in transcriptional elongation and initiation, microRNA regulation, apoptosis, and pluripotency. Despite this prevalence, functional chemical probes of MYC function at the protein level have been limited. Previously, we discovered 5a, that binds to MYC with potency and specificity, downregulates the transcriptional activities of MYC and shows efficacy in vivo. However, this scaffold posed intrinsic pharmacokinetic liabilities, namely, poor solubility that precluded biophysical interrogation. Here, we developed a screening platform based on field-effect transistor analysis (Bio-FET), surface plasmon resonance (SPR), and a microtumor formation assay to analyze a series of new compounds aimed at improving these properties. This blind SAR campaign has produced a new lead compound of significantly increased in vivo stability and solubility for a 40-fold increase in exposure. This probe represents a significant advancement that will not only enable biophysical characterization of this interaction and further SAR, but also contribute to advances in understanding of MYC biology.

The butterfly effect in cancer: a single base mutation can remodel the cell.

We have compared the proteome, transcriptome, and metabolome of two cell lines: the human breast epithelial line MCF-10A and its mutant descendant MCF-10A-H1047R. These cell lines are derived from the same parental stock and differ by a single amino acid substitution (H1047R) caused by a single nucleotide change in one allele of the PIK3CA gene, which encodes the catalytic subunit p110α of PI3K (phosphatidylinositol 3-kinase). They are considered isogenic. The H1047R mutation of PIK3CA is one of the most frequently encountered somatic cancer-specific mutations. In MCF-10A, this mutation induces an extensive cellular reorganization that far exceeds the known signaling activities of PI3K. The changes are highly diverse, with examples in structural protein levels, the DNA repair machinery, and sterol synthesis. Gene set enrichment analysis reveals a highly significant concordance of the genes differentially expressed in MCF-10A-H1047R cells and the established protein and RNA signatures of basal breast cancer. No such concordance was found with the specific gene signatures of other histological types of breast cancer. Our data document the power of a single base mutation, inducing an extensive remodeling of the cell toward the phenotype of a specific cancer.

Potent and Targeted Activation of Latent HIV-1 Using the CRISPR/dCas9 Activator Complex.

HIV-1 provirus integration results in a persistent latently infected reservoir that is recalcitrant to combined antiretroviral therapy (cART) with lifelong treatment being the only option. The "shock and kill" strategy aims to eradicate latent HIV by reactivating proviral gene expression in the context of cART treatment. Gene-specific transcriptional activation can be achieved using the RNA-guided CRISPR-Cas9 system comprising single guide RNAs (sgRNAs) with a nuclease-deficient Cas9 mutant (dCas9) fused to the VP64 transactivation domain (dCas9-VP64). We engineered this system to target 23 sites within the long terminal repeat promoter of HIV-1 and identified a "hotspot" for activation within the viral enhancer sequence. Activating sgRNAs transcriptionally modulated the latent proviral genome across multiple different in vitro latency cell models including T cells comprising a clonally integrated mCherry-IRES-Tat (LChIT) latency system. We detected consistent and effective activation of latent virus mediated by activator sgRNAs, whereas latency reversal agents produced variable activation responses. Transcriptomic analysis revealed dCas9-VP64/sgRNAs to be highly specific, while the well-characterized chemical activator TNFα induced widespread gene dysregulation. CRISPR-mediated gene activation represents a novel system which provides enhanced efficiency and specificity in a targeted latency reactivation strategy and represents a promising approach to a "functional cure" of HIV/AIDS.

Oncogenic activity of the regulatory subunit p85ß of phosphatidylinositol 3-kinase (PI3K).

Expression of the regulatory subunit p85ß of PI3K induces oncogenic transformation of primary avian fibroblasts. The transformed cells proliferate at an increased rate compared with nontransformed controls and show elevated levels of PI3K signaling. The oncogenic activity of p85ß requires an active PI3K-TOR signaling cascade and is mediated by the p110α and p110ß isoforms of the PI3K catalytic subunit. The data suggest that p85ß is a less effective inhibitor of the PI3K catalytic subunit than p85α and that this reduced level of p110 inhibition accounts for the oncogenic activity of p85ß.

Inhibitor of MYC identified in a Kröhnke pyridine library.

In a fluorescence polarization screen for the MYC-MAX interaction, we have identified a novel small-molecule inhibitor of MYC, KJ-Pyr-9, from a Kröhnke pyridine library. The Kd of KJ-Pyr-9 for MYC in vitro is 6.5 ± 1.0 nM, as determined by backscattering interferometry; KJ-Pyr-9 also interferes with MYC-MAX complex formation in the cell, as shown in a protein fragment complementation assay. KJ-Pyr-9 specifically inhibits MYC-induced oncogenic transformation in cell culture; it has no or only weak effects on the oncogenic activity of several unrelated oncoproteins. KJ-Pyr-9 preferentially interferes with the proliferation of MYC-overexpressing human and avian cells and specifically reduces the MYC-driven transcriptional signature. In vivo, KJ-Pyr-9 effectively blocks the growth of a xenotransplant of MYC-amplified human cancer cells.