Menin inhibitor MI-3454 induces remission in MLL1-rearranged and NPM1-mutated models of leukemia.

The protein-protein interaction between menin and mixed lineage leukemia 1 (MLL1) plays a critical role in acute leukemias with translocations of the MLL1 gene or with mutations in the nucleophosmin 1 (NPM1) gene. As a step toward clinical translation of menin-MLL1 inhibitors, we report development of MI-3454, a highly potent and orally bioavailable inhibitor of the menin-MLL1 interaction. MI-3454 profoundly inhibited proliferation and induced differentiation in acute leukemia cells and primary patient samples with MLL1 translocations or NPM1 mutations. When applied as a single agent, MI-3454 induced complete remission or regression of leukemia in mouse models of MLL1-rearranged or NPM1-mutated leukemia, including patient-derived xenograft models, through downregulation of key genes involved in leukemogenesis. We also identified MEIS1 as a potential pharmacodynamic biomarker of treatment response with MI-3454 in leukemia, and demonstrated that this compound is well tolerated and did not impair normal hematopoiesis in mice. Overall, this study demonstrates, for the first time to our knowledge, profound activity of the menin-MLL1 inhibitor as a single agent in clinically relevant PDX models of leukemia. These data provide a strong rationale for clinical translation of MI-3454 or its analogs for leukemia patients with MLL1 rearrangements or NPM1 mutations.

Development of combination therapies to maximize the impact of KRAS-G12C inhibitors in lung cancer.

KRAS represents an excellent therapeutic target in lung cancer, the most commonly mutated form of which can now be blocked using KRAS-G12C mutant-specific inhibitory trial drugs. Lung adenocarcinoma cells harboring KRAS mutations have been shown previously to be selectively sensitive to inhibition of mitogen-activated protein kinase kinase (MEK) and insulin-like growth factor 1 receptor (IGF1R) signaling. Here, we show that this effect is markedly enhanced by simultaneous inhibition of mammalian target of rapamycin (mTOR) while maintaining selectivity for the KRAS-mutant genotype. Combined mTOR, IGF1R, and MEK inhibition inhibits the principal signaling pathways required for the survival of KRAS-mutant cells and produces marked tumor regression in three different KRAS-driven lung cancer mouse models. Replacing the MEK inhibitor with the mutant-specific KRAS-G12C inhibitor ARS-1620 in these combinations is associated with greater efficacy, specificity, and tolerability. Adding mTOR and IGF1R inhibitors to ARS-1620 greatly improves its effectiveness on KRAS-G12C mutant lung cancer cells in vitro and in mouse models. This provides a rationale for the design of combination treatments to enhance the impact of the KRAS-G12C inhibitors, which are now entering clinical trials.

KRAS G12C NSCLC Models Are Sensitive to Direct Targeting of KRAS in Combination with PI3K Inhibition.

PURPOSE: KRAS-mutant lung cancers have been recalcitrant to treatments including those targeting the MAPK pathway. Covalent inhibitors of KRAS p.G12C allele allow for direct and specific inhibition of mutant KRAS in cancer cells. However, as for other targeted therapies, the therapeutic potential of these inhibitors can be impaired by intrinsic resistance mechanisms. Therefore, combination strategies are likely needed to improve efficacy.Experimental Design: To identify strategies to maximally leverage direct KRAS inhibition we defined the response of a panel of NSCLC models bearing the KRAS G12C-activating mutation in vitro and in vivo. We used a second-generation KRAS G12C inhibitor, ARS1620 with improved bioavailability over the first generation. We analyzed KRAS downstream effectors signaling to identify mechanisms underlying differential response. To identify candidate combination strategies, we performed a high-throughput drug screening across 112 drugs in combination with ARS1620. We validated the top hits in vitro and in vivo including patient-derived xenograft models. RESULTS: Response to direct KRAS G12C inhibition was heterogeneous across models. Adaptive resistance mechanisms involving reactivation of MAPK pathway and failure to induce PI3K-AKT pathway inactivation were identified as likely resistance events. We identified several model-specific effective combinations as well as a broad-sensitizing effect of PI3K-AKT-mTOR pathway inhibitors. The G12Ci+PI3Ki combination was effective in vitro and in vivo on models resistant to single-agent ARS1620 including patient-derived xenografts models. CONCLUSIONS: Our findings suggest that signaling adaptation can in some instances limit the efficacy of ARS1620 but combination with PI3K inhibitors can overcome this resistance.

The reactivity-driven biochemical mechanism of covalent KRASG12C inhibitors.

Activating mutations in KRAS are among the most common tumor driver mutations. Until recently, KRAS had been considered undruggable with small molecules; the discovery of the covalent KRASG12C inhibitors ARS-853 and ARS-1620 has demonstrated that it is feasible to inhibit KRAS with high potency in cells and animals. Although the biological activity of these inhibitors has been described, the biochemical mechanism of how the compounds achieve potent inhibition remained incompletely understood. We now show that the activity of ARS-853 and ARS-1620 is primarily driven by KRAS-mediated catalysis of the chemical reaction with Cys12 in human KRASG12C, while the reversible binding affinity is weak, in the hundreds of micromolar or higher range. The mechanism resolves how an induced, shallow and dynamic pocket not expected to support high-affinity binding of small molecules can nevertheless be targeted with potent inhibitors and may be applicable to other targets conventionally considered undruggable.

Targeting KRAS Mutant Cancers with a Covalent G12C-Specific Inhibitor.

KRASG12C was recently identified to be potentially druggable by allele-specific covalent targeting of Cys-12 in vicinity to an inducible allosteric switch II pocket (S-IIP). Success of this approach requires active cycling of KRASG12C between its active-GTP and inactive-GDP conformations as accessibility of the S-IIP is restricted only to the GDP-bound state. This strategy proved feasible for inhibiting mutant KRAS in vitro; however, it is uncertain whether this approach would translate to in vivo. Here, we describe structure-based design and identification of ARS-1620, a covalent compound with high potency and selectivity for KRASG12C. ARS-1620 achieves rapid and sustained in vivo target occupancy to induce tumor regression. We use ARS-1620 to dissect oncogenic KRAS dependency and demonstrate that monolayer culture formats significantly underestimate KRAS dependency in vivo. This study provides in vivo evidence that mutant KRAS can be selectively targeted and reveals ARS-1620 as representing a new generation of KRASG12C-specific inhibitors with promising therapeutic potential.

Phosphorylation of Nonmuscle Myosin Light Chain Promotes Endothelial Injury in Hyperlipidemic Rats Through a Mechanism Involving Downregulation of Dimethylarginine Dimethylaminohydrolase 2.

Suppression of dimethylarginine dimethylaminohydrolase (DDAH) activation is related to endothelial dysfunction in hyperlipidemia, and nonmuscle myosin regulatory light chain (nmMLC20) has been show to exert transcriptional function in regulation of gene expression. This study aims to explore whether the suppression of DDAH activation promotes endothelial injury under the condition of hyperlipidemia and whether nmMLC20 can regulate DDAH expression in a phosphorylation-dependent manner. The rats were fed with high-fat diet for 8 weeks to establish a hyperlipidemic model, which showed an increase in plasma lipids and endothelial injury, accompanied by an elevation in myosin light chain kinase (MLCK) activity, phosphorylated nmMLC20 (p-nmMLC20) level, and asymmetric dimethylarginine (ADMA) content as well as a reduction in DDAH2 expression, DDAH activity, and nitric oxide (NO) content. Next, human umbilical vein endothelial cells (HUVECs) were incubated with oxidized low-density lipoprotein (ox-LDL; 100 µg/mL) for 24 hours to establish a cellular injury model in vitro. Consistent with the finding in vivo, ox-LDL induced HUVECs injury (apoptosis and necrosis) concomitant with an increase in MLCK activity, p-nmMLC20 level (in total or nuclear proteins), and ADMA content as well as a reduction in DDAH2 expression, DDAH activity, and NO content; these phenomena were attenuated by MLCK inhibitor. Either in hyperlipidemic rats or in ox-LDL-treated HUVECs, there was not significant change in DDAH1 expression. Based on these observations, we conclude that the suppression of DDAH2 expression might account for, at least partially, the vascular endothelial dysfunction in hyperlipidemia, and nmMLC20 plays a role in suppression of DDAH2 expression in a phosphorylation-dependent manner.

Allele-specific inhibitors inactivate mutant KRAS G12C by a trapping mechanism.

It is thought that KRAS oncoproteins are constitutively active because their guanosine triphosphatase (GTPase) activity is disabled. Consequently, drugs targeting the inactive or guanosine 5'-diphosphate-bound conformation are not expected to be effective. We describe a mechanism that enables such drugs to inhibit KRAS(G12C) signaling and cancer cell growth. Inhibition requires intact GTPase activity and occurs because drug-bound KRAS(G12C) is insusceptible to nucleotide exchange factors and thus trapped in its inactive state. Indeed, mutants completely lacking GTPase activity and those promoting exchange reduced the potency of the drug. Suppressing nucleotide exchange activity downstream of various tyrosine kinases enhanced KRAS(G12C) inhibition, whereas its potentiation had the opposite effect. These findings reveal that KRAS(G12C) undergoes nucleotide cycling in cancer cells and provide a basis for developing effective therapies to treat KRAS(G12C)-driven cancers.

Selective Inhibition of Oncogenic KRAS Output with Small Molecules Targeting the Inactive State.

UNLABELLED: KRAS gain-of-function mutations occur in approximately 30% of all human cancers. Despite more than 30 years of KRAS-focused research and development efforts, no targeted therapy has been discovered for cancers with KRAS mutations. Here, we describe ARS-853, a selective, covalent inhibitor of KRAS(G12C) that inhibits mutant KRAS-driven signaling by binding to the GDP-bound oncoprotein and preventing activation. Based on the rates of engagement and inhibition observed for ARS-853, along with a mutant-specific mass spectrometry-based assay for assessing KRAS activation status, we show that the nucleotide state of KRAS(G12C) is in a state of dynamic flux that can be modulated by upstream signaling factors. These studies provide convincing evidence that the KRAS(G12C) mutation generates a "hyperexcitable" rather than a "statically active" state and that targeting the inactive, GDP-bound form is a promising approach for generating novel anti-RAS therapeutics. SIGNIFICANCE: A cell-active, mutant-specific, covalent inhibitor of KRAS(G12C) is described that targets the GDP-bound, inactive state and prevents subsequent activation. Using this novel compound, we demonstrate that KRAS(G12C) oncoprotein rapidly cycles bound nucleotide and responds to upstream signaling inputs to maintain a highly active state.

PI3K-δ and PI3K-γ inhibition by IPI-145 abrogates immune responses and suppresses activity in autoimmune and inflammatory disease models.

Phosphoinositide-3 kinase (PI3K)-δ and PI3K-γ are preferentially expressed in immune cells, and inhibitors targeting these isoforms are hypothesized to have anti-inflammatory activity by affecting the adaptive and innate immune response. We report on a potent oral PI3K-δ and PI3K-γ inhibitor (IPI-145) and characterize this compound in biochemical, cellular, and in vivo assays. These studies demonstrate that IPI-145 exerts profound effects on adaptive and innate immunity by inhibiting B and T cell proliferation, blocking neutrophil migration, and inhibiting basophil activation. We explored the therapeutic value of combined PI3K-δ and PI3K-γ blockade, and IPI-145 showed potent activity in collagen-induced arthritis, ovalbumin-induced asthma, and systemic lupus erythematosus rodent models. These findings support the hypothesis that inhibition of immune function can be achieved through PI3K-δ and PI3K-γ blockade, potentially leading to significant therapeutic effects in multiple inflammatory, autoimmune, and hematologic diseases.

Selective inhibition of phosphoinositide 3-kinase p110α preserves lymphocyte function.

Class IA phosphoinositide 3-kinase (PI3K) is essential for clonal expansion, differentiation, and effector function of B and T lymphocytes. The p110δ catalytic isoform of PI3K is highly expressed in lymphocytes and plays a prominent role in B and T cell responses. Another class IA PI3K catalytic isoform, p110α, is a promising drug target in cancer but little is known about its function in lymphocytes. Here we used highly selective inhibitors to probe the function of p110α in lymphocyte responses in vitro and in vivo. p110α inhibition partially reduced B cell receptor (BCR)-dependent AKT activation and proliferation, and diminished survival supported by the cytokines BAFF and IL-4. Selective p110δ inhibition suppressed B cell responses much more strongly, yet maximal suppression was achieved by targeting multiple PI3K isoforms. In mouse and human T cells, inhibition of single class IA isoforms had little effect on proliferation, whereas pan-class I inhibition did suppress T cell expansion. In mice, selective p110α inhibition using the investigational agent MLN1117 (previously known as INK1117) did not disrupt the marginal zone B cell compartment and did not block T cell-dependent germinal center formation. In contrast, the selective p110δ inhibitor IC87114 strongly suppressed germinal center formation and reduced marginal zone B cell numbers, similar to a pan-class I inhibitor. These findings show that although acute p110α inhibition partially diminishes AKT activation, selective p110α inhibitors are likely to be less immunosuppressive in vivo compared with p110δ or pan-class I inhibitors.

[A primary observation of the long-term effect of modified crown lengthening procedure].

OBJECTIVE: To observe the effect of modified surgical crown lengthening procedure and discuss the factors which could affect the periodontal health of the operated teeth. METHODS: Seventeen patients, a total of 20 teeth, who received the modified crown lengthening surgery were recruited in a retrospective study (1 - 6 years). The periodontal status of the operated teeth was compared with the adjacent and the contralateral natural teeth respectively. RESULTS: One out of seventeen patients appeared root fracture after surgery, one patient wasn't satisfied with the color of the molar's metal crown, other fifteen patients were satisfied with the esthetics and function of the teeth. The sites where probing depth was 4 mm just accounted for 4% (5/120) of the operated teeth, and the probing depth of the other sites was less than or equal to 3 mm. Although 83% (33/40) of buccal and lingual sites of the teeth exhibited various degrees of bleeding index, the periodontal indices of the operated teeth and the adjacent teeth. The position of the crown margin had a significantly negative correlation with the bleeding index (r = -0.742), and the plaque index was moderately correlated with the bleeding index (r = 0.480). CONCLUSIONS: The modified surgical crown lengthening indicated a good effect, which could be an alternative method to save the residual crown and root. The position of crown margin might be the main factor which influences the periodontal health of the teeth.

Discovery of tricyclic 5,6-dihydro-1H-pyridin-2-ones as novel, potent, and orally bioavailable inhibitors of HCV NS5B polymerase.

A novel series of non-nucleoside small molecules containing a tricyclic dihydropyridinone structural motif was identified as potent HCV NS5B polymerase inhibitors. Driven by structure-based design and building on our previous efforts in related series of molecules, we undertook extensive SAR studies, in which we identified a number of metabolically stable and very potent compounds in genotype 1a and 1b replicon assays. This work culminated in the discovery of several inhibitors, which combined potent in vitro antiviral activity against both 1a and 1b genotypes, metabolic stability, good oral bioavailability, and high C(12) (PO)/EC(50) ratios.

5,5'- and 6,6'-dialkyl-5,6-dihydro-1H-pyridin-2-ones as potent inhibitors of HCV NS5B polymerase.

The discovery of 5,5'- and 6,6'-dialkyl-5,6-dihydro-1H-pyridin-2-ones as potent inhibitors of the HCV RNA-dependent RNA polymerase (NS5B) is described. Several of these agents also display potent antiviral activity in cell culture experiments (EC50 <0.10 microM). In vitro DMPK data for selected compounds as well as crystal structures of representative inhibitors complexed with the NS5B protein are also disclosed.

5,6-Dihydro-1H-pyridin-2-ones as potent inhibitors of HCV NS5B polymerase.

5,6-Dihydro-1H-pyridin-2-one analogs were discovered as a novel class of inhibitors of genotype 1 HCV NS5B polymerase. Among these, compound 4ad displayed potent inhibitory activities in biochemical and replicon assays (IC(50) (1b)<10nM; IC(50) (1a)<25nM, EC(50) (1b)=16nM), good in vitro DMPK properties, as well as moderate oral bioavailability in monkeys (F=24%).

Studies toward the duocarmycin prodrugs for the antibody prodrug therapy approach.

A tricyclic precursor for the synthesis of the prodrugs of pro-1,2,9,9a-tetrahydrocyclopropa[c]benz-[e]indole-4-one tetramethoxyindolecarboxamide (CBI-TMI) was prepared using the ring-closing metathesis approach. The tricyclic intermediate was converted to an advanced precursor of a CBI-TMI prodrug equipped with a linker presumably suitable for activation using the aldolase catalytic antibody 38C2. An attempted 38C2-catalyzed two-step activation of the hydroxy-pro-CBI intermediate involving retro-aldol and the ß-elimination reactions was also examined.

Novel HCV NS5B polymerase inhibitors derived from 4-(1',1'-dioxo-1',4'-dihydro-1'lambda(6)-benzo[1',2',4']thiadiazin-3'-yl)-5-hydroxy-2H-pyridazin-3-ones. Part 5: Exploration of pyridazinones containing 6-amino-substituents.

The synthesis of 4-(1',1'-dioxo-1',4'-dihydro-1'lambda(6)-benzo[1',2',4']thiadiazin-3'-yl)-5-hydroxy-2H-pyridazin-3-ones bearing 6-amino substituents as potent inhibitors of the HCV RNA-dependent RNA polymerase (NS5B) is described. Several of these agents also display potent antiviral activity in cell culture experiments (EC(50)<0.10 microM). In vitro DMPK data (microsome t(1/2), Caco-2 P(app)) for many of the compounds are also disclosed, and a crystal structure of a representative inhibitor complexed with the NS5B protein is discussed.

4-(1,1-Dioxo-1,4-dihydro-1lambda6-benzo[1,4]thiazin-3-yl)-5-hydroxy-2H-pyridazin-3-ones as potent inhibitors of HCV NS5B polymerase.

4-(1,1-Dioxo-1,4-dihydro-1lambda(6)-benzo[1,4]thiazin-3-yl)-5-hydroxy-2H-pyridazin-3-one analogs were discovered as a novel class of inhibitors of HCV NS5B polymerase. Structure-based design led to the identification of compound 3a that displayed potent inhibitory activities in biochemical and replicon assays (1b IC(50)<10 nM; 1b EC(50)=1.1 nM) as well as good stability toward human liver microsomes (HLM t(1/2)>60 min).

Pyrrolo[1,2-b]pyridazin-2-ones as potent inhibitors of HCV NS5B polymerase.

Pyrrolo[1,2-b]pyridazin-2-one analogs were discovered as a novel class of inhibitors of genotype 1 HCV NS5B polymerase. Structure-based design led to the discovery of compound 3 k, which displayed potent inhibitory activities in biochemical and replicon assays (IC(50) (1b)<10nM; EC(50) (1b)=12 nM) as well as good stability towards human liver microsomes (HLM t(1/2)>60 min).

Novel HCV NS5B polymerase inhibitors derived from 4-(1',1'-dioxo-1',4'-dihydro-1'lambda(6)-benzo[1',2',4']thiadiazin-3'-yl)-5-hydroxy-2H-pyridazin-3-ones. Part 3: Further optimization of the 2-, 6-, and 7'-substituents and initial pharmacokinetic assessments.

5-Hydroxy-3(2H)-pyridazinone derivatives were investigated as inhibitors of genotype 1 HCV NS5B polymerase. Lead optimization led to the discovery of compound 3a, which displayed potent inhibitory activities in biochemical and replicon assays [IC(50) (1b)<10nM; IC(50) (1a)=22 nM; EC(50) (1b)=5nM], good stability toward human liver microsomes (HLM t(1/2)>60 min), and high ratios of liver to plasma concentrations 12h after a single oral administration to rats.

Novel HCV NS5B polymerase inhibitors derived from 4-(1',1'-dioxo-1',4'-dihydro-1'lambda6-benzo[1',2',4']thiadiazin-3'-yl)-5-hydroxy-2H-pyridazin-3-ones: Part 4. Optimization of DMPK properties.

5-Hydroxy-3(2H)-pyridazinone derivatives were investigated as potent inhibitors of genotype 1 HCV NS5B polymerase focusing on the optimization of their drug metabolism and pharmacokinetics (DMPK) profiles. This investigation led to the discovery of potent inhibitors with improved DMPK properties.