Abstract 4600: Potent and selective C-C chemokine receptor (CCR4) antagonists potentiate anti-tumor immune responses by inhibiting regulatory T cells (Treg)

Naturally suppressive CD4+ Foxp3+ Treg are essential for immune tolerance. Although Treg-mediated suppression of effector cells is important to control inflammation and prevent autoimmune diseases, the presence of Treg in the tumor microenvironment (TME) has been shown to dampen anti-tumor immune responses. Human Treg express CCR4, the receptor for the chemokines CCL17 and CCL22. These chemokines are produced by tumor cells, tumor-associated macrophages and dendritic cells, as well as by effector T cells (Teff). Preclinical and clinical data supports a role for CCR4-mediated recruitment and accumulation of Treg in the TME which can be associated with poor prognosis. Further, recent longitudinal studies in patients receiving IO agents demonstrate an influx of Treg in responding patients which may dampen optimal anti-tumor responses. Therefore, CCR4 is an ideal target to selectively block Treg recruitment into the TME.

We have developed structurally unique series of small molecule antagonists of CCR4. These antagonists have cellular potencies in multiple assays (e.g. chemotaxis of primary human Treg in 100% serum) in the low double-digit nM range. Representative compounds are selective against other chemokine receptors, GPCRs and ion channels, including the hERG channel, and lack inhibition of common human CYP450 enzymes. Moreover, compounds have excellent in vitro and in vivo ADME properties, consistent with convenient oral dosing. In preclinical syngeneic tumor models, these CCR4 antagonists block Treg migration and support expansion of activated Teff. In contrast to the non-selective approach of depleting anti-CCR4 antibodies, our compounds reduce Treg in the tumor, but not in peripheral tissues such as blood, spleen or skin. In preclinical efficacy studies, CCR4 antagonists potentiate the anti-tumor effects of various checkpoint inhibitors and immune stimulators such as anti-PD-L1 and anti-CD137 antibodies. We observe enhanced tumor growth inhibition and increased tumor regressions when these agents are combined with CCR4 antagonists, without any gross toxicity. Further characterization of these CCR4 antagonists and their anti-tumor effects will be described.

Citation Format: Oezcan Talay, Lisa Marshall, Cesar Meleza, Maureen K. Reilly, Omar Robles, Mikhail Zibisky, Abood Okal, Lisa Seitz, Jenny McKinnell, Scott Jacobson, Erin Riegler, Emily Karbaz, David Chian, Angela Wadsworth, Paul Kassner, David Wustrow, Jordan S. Fridman. Potent and selective C-C chemokine receptor (CCR4) antagonists potentiate anti-tumor immune responses by inhibiting regulatory T cells (Treg) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4600. doi:10.1158/1538-7445.AM2017-4600

INCB24360 (Epacadostat), a Highly Potent and Selective Indoleamine-2,3-dioxygenase 1 (IDO1) Inhibitor for Immuno-oncology

A data-centric medicinal chemistry approach led to the invention of a potent and selective IDO1 inhibitor 4f, INCB24360 (epacadostat). The molecular structure of INCB24360 contains several previously unknown or underutilized functional groups in drug substances, including a hydroxyamidine, furazan, bromide, and sulfamide. These moieties taken together in a single structure afford a compound that falls outside of “drug-like” space. Nevertheless, the in vitro ADME data is consistent with the good cell permeability and oral bioavailability observed in all species (rat, dog, monkey) tested. The extensive intramolecular hydrogen bonding observed in the small molecule crystal structure of 4f is believed to significantly contribute to the observed permeability and PK. Epacadostat in combination with anti-PD1 mAb pembrolizumab is currently being studied in a phase 3 clinical trial in patients with unresectable or metastatic melanoma.

Abstract 4290: Potent and selective next generation inhibitors of indoleamine-2,3-dioxygenase (IDO1) for the treatment of cancer

The IDO1 pathway has been proposed to mediate immunosuppressive effects in the tumor microenvironment through its role in the catabolism of tryptophan, resulting in effects on the differentiation and proliferation of T cells. IDO1 inhibition has shown promising clinical benefit as well as exacerbated toxicity in the treatment of melanoma, when combined with the anti-CTLA-4 antibody ipilimumab.

We have discovered a novel class of highly selective small molecule inhibitors of IDO1 which surpass the potency of the compounds currently in clinical development. These compounds potently inhibit IDO1 activity in IFN-γ stimulated HeLa cells with single digit nM potency. Importantly, they also retain their potency in the presence of human serum, with IC50 values ranging between 5 and 15 nM in this more physiologically relevant media. Consistent with the role of IDO1+ dendritic cells in the suppression of T cell proliferation, this series of molecules is capable of restoring the proliferative capacity of human T cells (which is inhibited by allogeneic IDO1+ dendritic cells) with EC50 values of 2-3 nM. The molecules exhibit preclinical PK characteristics that are suitable for assessing the contribution of IDO1 to tumor growth in murine models, both alone and in combination with other therapeutic agents. The compounds have high metabolic stability against cultured human hepatocytes and exhibit preclinical PK and ADME characteristics consistent with once-daily dosing in humans. The full preclinical profile of one of these molecules, selected for clinical evaluation, will be the focus of this presentation.

In conclusion, we have discovered a novel class of small molecule inhibitors of IDO1, which provides a preclinical basis for the clinical evaluation of a next generation IDO1 inhibitor in combination with other therapeutic agents.

Citation Format: Jay P. Powers, Matthew J. Walters, Rajkumar Noubade, Stephen W. Young, Lisa Marshall, Jan Melom, Adam Park, Nick Shah, Pia Bjork, Jordan S. Fridman, Hilary P. Beck, David Chian, Jenny V. McKinnell, Maksim Osipov, Maureen K. Reilly, Hunter P. Shunatona, James R. Walker, Mikhail Zibinsky, Juan C. Jaen. Potent and selective next generation inhibitors of indoleamine-2,3-dioxygenase (IDO1) for the treatment of cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4290. doi:10.1158/1538-7445.AM2015-4290

Abstract 787: FLX925 (AMG 925) is a rationally designed FLT3, CDK4/6 inhibitor that retains potency against clinically relevant secondary resistance mutations in FLT3

Acquired secondary resistance mutations to clinically active kinase inhibitors remains a key obstacle between valid therapeutic hypotheses and meaningful patient benefit. In AML, evidence suggests that inhibition of FLT3 (particularly in FLT3-ITD mutated cancers) can be efficacious; however, relapse from complete remission is common and often rapid. As with other cancers driven by key oncogenic kinase mutations (e.g. BCR-ABL in CML), a primary mechanism of resistance is the acquisition of secondary resistance mutations in the oncogenic kinase themselves. Multiple strategies have been pursued to address such resistance, including the development of kinase inhibitors that either bind their respective targets differently or by targeting multiple important pathways simultaneously. Herein we describe a rationally conceived next generation FLT3 inhibitor, FLX925 (previously AMG 925), that was prospectively designed to address or avoid common resistance mechanism to earlier FLT3 inhibitors with its unique binding mode and potent activity against CDK4/CDK6.

FLX925 is a potent and selective type 1 inhibitor of FLT3 that retains its cellular potency against clinically relevant secondary resistance mutations in FLT3 occurring with quizartinib or sorafenib treatment (FLX925 IC50: MOLM13ITD, 15 nM; MOLM13ITD/D835, 28 nM; MV4-11ITD, 16 nM; MV4-11ITD/D835, 19 nM; MV4-11ITD/N841, 16 nM; MV4-11ITD/F691, 73 nM). Indeed, while compounds currently in the clinic became more than 200-fold less potent against a number of mutants, FLX925 remained relatively equipotent (+/- 5-fold the parental cell line IC50) in these same resistant clones. This is in stark contrast to the striking cross-resistance observed with quizartinib in sorafenib resistant cells. Moreover, the few clones that grew out of a screen for resistance to FLX925 displayed a ‘persistence’ phenotype with modestly reduced sensitivity to FLX925 (∼5-fold IC50 shift) that was rapidly reversible. This persistence was associated with higher FLT3 protein levels and no detectable secondary mutations in FLT3.

In addition to its suppression of FLT3 signaling, FLX925 potently inhibits CDK4/CDK6, central components of the cell cycle machinery. This unique profile may reduce the likelihood of emergent resistant clones and extends the therapeutic potential of FLX925 to other malignancies dependent on these pathways (e.g. MCL). Indeed, the addition of PD0332991 (a selective CDK4/6 inhibitor) to a relatively selective FLT3 inhibitor reduced the frequency of acquired resistance in a cell based screen, relative to a FLT3 inhibitor alone. These data suggest the unique profile of FLX925 makes it an ideal inhibitor for the treatment of cancers driven by FLT3 signaling, such as AML. A phase I clinical trial evaluating the safety, tolerability pharmacokinetics and pharmacodynamics effects of FLX925 in patients with AML is ongoing.

Citation Format: Cong Li, Lingming Liang, Liqin Liu, Zhen Xia, Zhihong Li, Xianghong Wang, Lawrence McGee, Angus Sinclair, Sasha Kamb, Dineli Wickramasinghe, Sachie Marubayashi, Juan C. Jaen, Jordan S. Fridman, Kang Dai. FLX925 (AMG 925) is a rationally designed FLT3, CDK4/6 inhibitor that retains potency against clinically relevant secondary resistance mutations in FLT3. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 787. doi:10.1158/1538-7445.AM2015-787

JAK-STAT pathway activation in malignant and nonmalignant cells contributes to MPN pathogenesis and therapeutic response

The identification of JAK2/MPL mutations in patients with myeloproliferative neoplasms (MPN) has led to the clinical development of JAK kinase inhibitors, including ruxolitinib. Ruxolitinib reduces splenomegaly and systemic symptoms in myelofibrosis and improves overall survival; however, the mechanism by which JAK inhibitors achieve efficacy has not been delineated. Patients with MPN present with increased levels of circulating proinflammatory cytokines, which are mitigated by JAK inhibitor therapy. We sought to elucidate mechanisms by which JAK inhibitors attenuate cytokine-mediated pathophysiology. Single-cell profiling demonstrated that hematopoietic cells from myelofibrosis models and patient samples aberrantly secrete inflammatory cytokines. Pan-hematopoietic Stat3 deletion reduced disease severity and attenuated cytokine secretion, with similar efficacy as observed with ruxolitinib therapy. In contrast, Stat3 deletion restricted to MPN cells did not reduce disease severity or cytokine production. Consistent with these observations, we found that malignant and nonmalignant cells aberrantly secrete cytokines and JAK inhibition reduces cytokine production from both populations.

SIGNIFICANCE

Our results demonstrate that JAK-STAT3-mediated cytokine production from malignant and nonmalignant cells contributes to MPN pathogenesis and that JAK inhibition in both populations is required for therapeutic efficacy. These findings provide novel insight into the mechanisms by which JAK kinase inhibition achieves therapeutic efficacy in MPNs.

Selective inhibition of ADAM metalloproteases blocks HER-2 extracellular domain (ECD) cleavage and potentiates the anti-tumor effects of trastuzumab

The HER-2 receptor tyrosine kinase is an important regulator of cell proliferation and survival, and it is a clinically validated target of therapeutic intervention for HER-2 positive breast cancer patients. Its extracellular domain (ECD) is frequently cleaved by protease(s) in HER-2 overexpressing breast cancer patients, rendering the remaining membrane-bound portion (p95) a constitutively activated kinase. The presence of both serum ECD and cellular p95 protein has been linked to poor clinical outcome as well as reduced effectiveness of some therapeutic treatments. We have identified a series of potent, selective small molecule inhibitors of ADAM proteases, exemplified here by INCB003619, and demonstrate that these inhibitors effectively block HER-2 cleavage in HER-2 overexpressing human breast cancer cell lines. Intriguingly, when used in combination, INCB003619 dramatically enhances the antiproliferative activity of suboptimal doses of the anti-HER-2 antibody, trastuzumab, in HER-2 overexpressing/shedding breast cancer cell lines, accompanied by reduced ERK and AKT phosphorylation. Furthermore, INCB003619, in combination with trastuzumab, augments the pro-apoptotic and antiproliferative effects of the chemotherapeutic agent paclitaxel. Consistent with these in vitro data, INCB003619 reduces serum ECD levels and enhances the antitumor effect of trastuzumab in a xenograft tumor model derived from the HER-2 overexpressing BT-474 breast cancer cell line. Collectively, these findings suggest that blocking HER-2 cleavage with selective ADAM inhibitors may represent a novel therapeutic approach for treating HER-2 overexpressing breast cancer patients.

The interplay between inhibition of JAK2 and HSP90

A recent article by Weigert et al. published in The Journal of Experimental Medicine described the in vitro generation of synthetic mutations in Janus kinase 2 (JAK 2) that decreased the potency of JAK2 (or JAK1/JAK2) inhibitors in artificial systems. The authors found that heat shock protein 90 (HSP90) inhibitors circumvented the potency shift and suggested that HSP90 inhibition may abrogate JAK inhibitor resistance in these experimental systems. However, the clinical relevance of these laboratory-generated JAK2 mutations, which have not been identified to-date in patients treated with JAK inhibitors, and the therapeutic potential of HSP90 inhibitors in diseases involving aberrant JAK-STAT signaling remain to be determined.

Targeting JAK1/2 and mTOR in murine xenograft models of Ph-like acute lymphoblastic leukemia

CRLF2 rearrangements, JAK1/2 point mutations, and JAK2 fusion genes have been identified in Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL), a recently described subtype of pediatric high-risk B-precursor ALL (B-ALL) which exhibits a gene expression profile similar to Ph-positive ALL and has a poor prognosis. Hyperactive JAK/STAT and PI3K/mammalian target of rapamycin (mTOR) signaling is common in this high-risk subset. We, therefore, investigated the efficacy of the JAK inhibitor ruxolitinib and the mTOR inhibitor rapamycin in xenograft models of 8 pediatric B-ALL cases with and without CRLF2 and JAK genomic lesions. Ruxolitinib treatment yielded significantly lower peripheral blast counts compared with vehicle (P < .05) in 6 of 8 human leukemia xenografts and lower splenic blast counts (P < .05) in 8 of 8 samples. Enhanced responses to ruxolitinib were observed in samples harboring JAK-activating lesions and higher levels of STAT5 phosphorylation. Rapamycin controlled leukemia burden in all 8 B-ALL samples. Survival analysis of 2 representative B-ALL xenografts demonstrated prolonged survival with rapamycin treatment compared with vehicle (P < .01). These data demonstrate preclinical in vivo efficacy of ruxolitinib and rapamycin in this high-risk B-ALL subtype, for which novel treatments are urgently needed, and highlight the therapeutic potential of targeted kinase inhibition in Ph-like ALL.

A novel kinase inhibitor, INCB28060, blocks c-MET-dependent signaling, neoplastic activities, and cross-talk with EGFR and HER-3

PURPOSE

The c-MET receptor tyrosine kinase plays important roles in the formation, progression, and dissemination of human cancer and presents an attractive therapeutic target. This study describes the preclinical characterization of INCB28060, a novel inhibitor of c-MET kinase.

EXPERIMENTAL DESIGN

Studies were conducted using a series of in vitro and in vivo biochemical and biological experiments.

RESULTS

INCB28060 exhibits picomolar enzymatic potency and is highly specific for c-MET with more than 10,000-fold selectivity over a large panel of human kinases. This inhibitor potently blocks c-MET phosphorylation and activation of its key downstream effectors in c-MET-dependent tumor cell lines. As a result, INCB28060 potently inhibits c-MET-dependent tumor cell proliferation and migration and effectively induces apoptosis in vitro. Oral dosing of INCB28060 results in time- and dose-dependent inhibition of c-MET phosphorylation and tumor growth in c-MET-driven mouse tumor models, and the inhibitor is well tolerated at doses that achieve complete tumor inhibition. In a further exploration of potential interactions between c-MET and other signaling pathways, we found that activated c-MET positively regulates the activity of epidermal growth factor receptors (EGFR) and HER-3, as well as expression of their ligands. These effects are reversed with INCB28060 treatment. Finally, we confirmed that circulating hepatocyte growth factor levels are significantly elevated in patients with various cancers.

CONCLUSIONS

Activated c-MET has pleiotropic effects on multiple cancer-promoting signaling pathways and may play a critical role in driving tumor cell growth and survival. INCB28060 is a potent and selective c-MET kinase inhibitor that may have therapeutic potential in cancer treatment.

Safety and efficacy of INCB018424, a JAK1 and JAK2 inhibitor, in myelofibrosis

BACKGROUND

Myelofibrosis is a Philadelphia chromosome–negative myeloproliferative neoplasm associated with cytopenias, splenomegaly, poor quality of life, and shortened survival. About half of patients with myelofibrosis carry a gain-of-function mutation in the Janus kinase 2 gene (JAK2 V617F) that contributes to the pathophysiology of the disease. INCB018424 is a potent and selective Janus kinase 1 (JAK1) and JAK2 inhibitor.

METHODS

We conducted a phase 1−2 trial of INCB018424 in patients with JAK2 V617F−positive or JAK2 V617F−negative primary myelofibrosis, post–essential thrombocythemia myelofibrosis, or post–polycythemia vera myelofibrosis.

RESULTS

A total of 153 patients received INCB018424 for a median duration of more than 14.7 months. The initial dose-escalation phase established 25 mg twice daily or 100 mg once daily as maximum tolerated doses, on the basis of reversible thrombocytopenia. A dose-dependent suppression of phosphorylated signal transducer and activator of transcription 3 (STAT3), a marker of JAK signaling, was demonstrated in patients with wild-type JAK2 and in patients with the JAK2 V617F mutation. We studied additional doses and established that a 15-mg twice-daily starting dose, followed by individualized dose titration, was the most effective and safest dosing regimen. At this dose, 17 of 33 patients (52%) had a rapid objective response (≥50% reduction of splenomegaly) lasting for 12 months or more, and this therapy was associated with grade 3 or grade 4 adverse events (mainly myelosuppression) in less than 10% of patients. Patients with debilitating symptoms, including weight loss, fatigue, night sweats, and pruritus, had rapid improvement. Clinical benefits were associated with a marked diminution of levels of circulating inflammatory cytokines that are commonly elevated in myelofibrosis.

CONCLUSIONS

INCB018424 was associated with marked and durable clinical benefits in patients with myelofibrosis for whom no approved therapies existed. (Funded by Incyte; ClinicalTrials.gov number, NCT00509899.)

Selective inhibition of JAK1 and JAK2 is efficacious in rodent models of arthritis: preclinical characterization of INCB028050

Inhibiting signal transduction induced by inflammatory cytokines offers a new approach for the treatment of autoimmune diseases such as rheumatoid arthritis. Kinase inhibitors have shown promising oral disease-modifying antirheumatic drug potential with efficacy similar to anti-TNF biologics. Direct and indirect inhibition of the JAKs, with small molecule inhibitors like CP-690,550 and INCB018424 or neutralizing Abs, such as the anti-IL6 receptor Ab tocilizumab, have demonstrated rapid and sustained improvement in clinical measures of disease, consistent with their respective preclinical experiments. Therefore, it is of interest to identify optimized JAK inhibitors with unique profiles to maximize therapeutic opportunities. INCB028050 is a selective orally bioavailable JAK1/JAK2 inhibitor with nanomolar potency against JAK1 (5.9 nM) and JAK2 (5.7 nM). INCB028050 inhibits intracellular signaling of multiple proinflammatory cytokines including IL-6 and IL-23 at concentrations <50 nM. Significant efficacy, as assessed by improvements in clinical, histologic and radiographic signs of disease, was achieved in the rat adjuvant arthritis model with doses of INCB028050 providing partial and/or periodic inhibition of JAK1/JAK2 and no inhibition of JAK3. Diminution of inflammatory Th1 and Th17 associated cytokine mRNA levels was observed in the draining lymph nodes of treated rats. INCB028050 was also effective in multiple murine models of arthritis, with no evidence of suppression of humoral immunity or adverse hematologic effects. These data suggest that fractional inhibition of JAK1 and JAK2 is sufficient for significant activity in autoimmune disease models. Clinical evaluation of INCB028050 in RA is ongoing.

Hydroxyamidine inhibitors of indoleamine-2,3-dioxygenase potently suppress systemic tryptophan catabolism and the growth of IDO-expressing tumors

Malignant tumors arise, in part, because the immune system does not adequately recognize and destroy them. Expression of indoleamine-2,3-dioxygenase (IDO; IDO1), a rate-limiting enzyme in the catabolism of tryptophan into kynurenine, contributes to this immune evasion. Here we describe the effects of systemic IDO inhibition using orally active hydroxyamidine small molecule inhibitors. A single dose of INCB023843 or INCB024360 results in efficient and durable suppression of Ido1 activity in the plasma of treated mice and dogs, the former to levels seen in Ido1-deficient mice. Hydroxyamidines potently suppress tryptophan metabolism in vitro in CT26 colon carcinoma and PAN02 pancreatic carcinoma cells and in vivo in tumors and their draining lymph nodes. Repeated administration of these IDO1 inhibitors impedes tumor growth in a dose- and lymphocyte-dependent fashion and is well tolerated in efficacy and preclinical toxicology studies. Substantiating the fundamental role of tumor cell-derived IDO expression, hydroxyamidines control the growth of IDO-expressing tumors in Ido1-deficient mice. These activities can be attributed, at least partially, to the increased immunoreactivity of lymphocytes found in tumors and their draining lymph nodes and to the reduction in tumor-associated regulatory T cells. INCB024360, a potent IDO1 inhibitor with desirable pharmaceutical properties, is poised to start clinical trials in cancer patients.

Combined inhibition of Janus kinase 1/2 for the treatment of JAK2V617F-driven neoplasms: selective effects on mutant cells and improvements in measures of disease severity

PURPOSE

Deregulation of the Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway is a hallmark for the Philadelphia chromosome-negative myeloproliferative diseases polycythemia vera, essential thrombocythemia, and primary myelofibrosis. We tested the efficacy of a selective JAK1/2 inhibitor in cellular and in vivo models of JAK2-driven malignancy.

EXPERIMENTAL DESIGN

A novel inhibitor of JAK1/2 was characterized using kinase assays. Cellular effects of this compound were measured in cell lines bearing the JAK2V617F or JAK1V658F mutation, and its antiproliferative activity against primary polycythemiavera patient cells was determined using clonogenic assays. Antineoplastic activity in vivo was determined using a JAK2V617F-driven xenograft model, and effects of the compound on survival, organomegaly, body weight, and disease-associated inflammatory markers were measured.

RESULTS

INCB16562 potently inhibited proliferation of cell lines and primary cells from PV patients carrying the JAK2V617F or JAK1V658F mutation by blocking JAK-STAT signaling and inducing apoptosis. In vivo, INCB16562 reduced malignant cell burden, reversed splenomegaly and normalized splenic architecture, improved body weight gains, and extended survival in a model of JAK2V617F-driven hematologic malignancy. Moreover, these mice suffered from markedly elevated levels of inflammatory cytokines, similar to advanced myeloproliferative disease patients, which was reversed upon treatment.

CONCLUSIONS

These data showed that administration of the dual JAK1/2 inhibitor INCB16562 reduces malignant cell burden, normalizes spleen size and architecture, suppresses inflammatory cytokines, improves weight gain, and extends survival in a rodent model of JAK2V617F-driven hematologic malignancy. Thus, selective inhibitors of JAK1 and JAK2 represent a novel therapy for the patients with myeloproliferative diseases and other neoplasms associated with JAK dysregulation.

Compelling P1 substituent affect on metalloprotease binding profile enables the design of a novel cyclohexyl core scaffold with excellent MMP selectivity and HER-2 sheddase inhibition

A serendipitous discovery that the metalloprotease binding profile of a novel class of 2-carboxamide-3-hydroxamic acid piperidines could be significantly attenuated by the modification of the unexplored P1 substituent enabled the design and synthesis of a novel 2-carboxamide-1-hydroxamic acid cyclohexyl scaffold core that exhibited excellent HER-2 potency and unprecedented MMP-selectivity that we believe would not have been possible via conventional P1' perturbations.

Janus kinase inhibitor INCB20 has antiproliferative and apoptotic effects on human myeloma cells in vitro and in vivo

Protein tyrosine kinases of the Janus kinase (JAK) family are associated with many cytokine receptors, which, on ligand binding, regulate important cellular functions such as proliferation, survival, and differentiation. In multiple myeloma, JAKs may be persistently activated due to a constant stimulation by interleukin (IL)-6, which is produced in the bone marrow environment. INCB20 is a synthetic molecule that potently inhibits all members of the JAK family with a 100- to 1,000-fold selectivity for JAKs over >70 other kinases. Treatment of multiple myeloma cell lines and patient tumor cells with INCB20 resulted in a significant and dose-dependent inhibition of spontaneous as well as IL-6-induced cell growth. Importantly, multiple myeloma cell growth was inhibited in the presence of bone marrow stromal cells. The IL-6 dependent cell line INA-6 was particularly sensitive to the drug (IC50<1 micromol/L). Growth suppression of INA-6 correlated with an increase in the percentage of apoptotic cells and inhibition of signal transducer and activator of transcription 3 phosphorylation. INCB20 also abrogated the protective effect of IL-6 against dexamethasone by blocking phosphorylation of SHP-2 and AKT. In contrast, AKT phosphorylation induced by insulin-like growth factor-I remained unchanged, showing selectivity of the compound. In a s.c. severe combined immunodeficient mouse model with INA-6, INCB20 significantly delayed INA-6 tumor growth. Our studies show that disruption of JAKs and downstream signaling pathways may both inhibit multiple myeloma cell growth and survival and overcome cytokine-mediated drug resistance, thereby providing the preclinical rationale for the use of JAK inhibitors as a novel therapeutic approach in multiple myeloma.

Conversion of an MMP-potent scaffold to an MMP-selective HER-2 sheddase inhibitor via scaffold hybridization and subtle P1' permutations

A series of beta-sulfonamide piperidine hydroxamates were prepared and shown to be potent inhibitors of the human epidermal growth factor receptor-2 (HER-2) sheddase with excellent selectivity against MMP-1, -2, -3, and -9. This was achieved by exploiting subtle differences within the otherwise highly conserved S(1)(') binding pocket of the active sites within the metalloprotease family. In addition, it was discovered that the introduction of polarity to the P(1) and P(1)(') groups reduced the projected human clearance.

Design and identification of selective HER-2 sheddase inhibitors via P1' manipulation and unconventional P2' perturbations to induce a molecular metamorphosis

In an effort to obtain a MMP selective and potent inhibitor of HER-2 sheddase (ADAM-10), the P1' group of a novel class of (6S,7S)-7-[(hydroxyamino)carbonyl]-6-carboxamide-5-azaspiro[2.5]octane-5-carboxylates was attenuated and the structure-activity relationships (SAR) will be discussed. In addition, it was discovered that unconventional perturbation of the P2' moiety could confer MMP selectivity, which was hypothesized to be a manifestation of the P2' group effecting global conformational changes.

Selective inhibition of ADAM metalloproteases as a novel approach for modulating ErbB pathways in cancer

PURPOSE

ErbB receptor signaling pathways are important regulators of cell fate, and their dysregulation, through (epi)genetic alterations, plays an etiologic role in multiple cancers. ErbB ligands are synthesized as membrane-bound precursors that are cleaved by members of the ADAM family of zinc-dependent metalloproteases. This processing, termed ectodomain shedding, is essential for the functional activation of ErbB ligands. Recent studies suggest that elevated levels of ErbB ligands may circumvent the effectiveness of ErbB-targeted therapeutics. Here, we describe the discovery and preclinical development of potent, selective inhibitors of ErbB ligand shedding.

EXPERIMENTAL DESIGN

A series of biochemical and cell-based assays were established to identify selective inhibitors of ErbB ligand shedding. The therapeutic potential of these compounds was assessed in multiple in vivo models of cancer and matrix metalloprotease-related toxicity.

RESULTS

INCB3619 was identified as a representative selective, potent, orally bioavailable small-molecule inhibitor of a subset of ADAM proteases that block shedding of ErbB ligands. Administration of INCB3619 to tumor-bearing mice reduced ErbB ligand shedding in vivo and inhibited ErbB pathway signaling (e.g., phosphorylation of Akt), tumor cell proliferation, and survival. Further, INCB3619 synergized with clinically relevant cancer therapeutics and showed no overt or compounding toxicities, including fibroplasia, the dose-limiting toxicity associated with broad-spectrum matrix metalloprotease inhibitors.

CONCLUSIONS

Inhibition of ErbB ligand shedding offers a potentially novel and well-tolerated therapeutic strategy for the treatment of human cancers and is currently being evaluated in the clinic.

Discovery of a potent, selective, and orally active human epidermal growth factor receptor-2 sheddase inhibitor for the treatment of cancer

The design, synthesis, evaluation, and identification of a novel class of (6S,7S)-N-hydroxy-6-carboxamide-5-azaspiro[2.5]octane-7-carboxamides as the first potent and selective inhibitors of human epidermal growth factor receptor-2 (HER-2) sheddase is described. Several compounds were identified that possess excellent pharmacodynamic and pharmacokinetic properties and were shown to decrease tumor size, cleaved HER-2 extracellular domain plasma levels, and potentiate the effects of the humanized anti-HER-2 monoclonal antibody (trastuzumab) in vivo in a HER-2 overexpressing cancer murine xenograft model.

Targeting ADAM-mediated ligand cleavage to inhibit HER3 and EGFR pathways in non-small cell lung cancer

We describe here the existence of a heregulin-HER3 autocrine loop, and the contribution of heregulin-dependent, HER2-mediated HER3 activation to gefitinib insensitivity in non-small cell lung cancer (NSCLC). ADAM17 protein, a major ErbB ligand sheddase, is upregulated in NSCLC and is required not only for heregulin-dependent HER3 signaling, but also for EGFR ligand-dependent signaling in NSCLC cell lines. A selective ADAM inhibitor, INCB3619, prevents the processing and activation of multiple ErbB ligands, including heregulin. In addition, INCB3619 inhibits gefitinib-resistant HER3 signaling and enhances gefitinib inhibition of EGFR signaling in NSCLC. These results show that ADAM inhibition affects multiple ErbB pathways in NSCLC and thus offers an excellent opportunity for pharmacological intervention, either alone or in combination with other drugs.

Loss of p53 impedes the antileukemic response to BCR-ABL inhibition

Targeted cancer therapies exploit the continued dependence of cancer cells on oncogenic mutations. Such agents can have remarkable activity against some cancers, although antitumor responses are often heterogeneous, and resistance remains a clinical problem. To gain insight into factors that influence the action of a prototypical targeted drug, we studied the action of imatinib (STI-571, Gleevec) against murine cells and leukemias expressing BCR-ABL, an imatinib target and the initiating oncogene for human chronic myelogenous leukemia (CML). We show that the tumor suppressor p53 is selectively activated by imatinib in BCR-ABL-expressing cells as a result of BCR-ABL kinase inhibition. Inactivation of p53, which can accompany disease progression in human CML, impedes the response to imatinib in vitro and in vivo without preventing BCR-ABL kinase inhibition. Concordantly, p53 mutations are associated with progression to imatinib resistance in some human CMLs. Our results identify p53 as a determinant of the response to oncogene inhibition and suggest one way in which resistance to targeted therapy can emerge during the course of tumor evolution.

ADAM proteases, ErbB pathways and cancer

A disintegrin and metalloproteases (ADAMs) are zinc-dependent trans-membrane metalloproteases that shed the extracellular domains of membrane-bound growth factors, cytokines and receptors. Key functions of ADAMs have emerged in ErbB signalling pathways as being sheddases for multiple ErbB ligands. As the ErbB pathway is a validated target for anti-cancer drugs, the upstream activators of ErbB ligands, their sheddases, now enter the spotlight as new drug targets in the ErbB pathway. ADAMs are involved not only in tumour cell proliferation but also in angiogenesis and metastasis. Therefore, strategies targeting ADAMs might be an important complement to existing anti-ErbB approaches.

Survival signalling by Akt and eIF4E in oncogenesis and cancer therapy

Evading apoptosis is considered to be a hallmark of cancer, because mutations in apoptotic regulators invariably accompany tumorigenesis. Many chemotherapeutic agents induce apoptosis, and so disruption of apoptosis during tumour evolution can promote drug resistance. For example, Akt is an apoptotic regulator that is activated in many cancers and may promote drug resistance in vitro. Nevertheless, how Akt disables apoptosis and its contribution to clinical drug resistance are unclear. Using a murine lymphoma model, we show that Akt promotes tumorigenesis and drug resistance by disrupting apoptosis, and that disruption of Akt signalling using the mTOR inhibitor rapamycin reverses chemoresistance in lymphomas expressing Akt, but not in those with other apoptotic defects. eIF4E, a translational regulator that acts downstream of Akt and mTOR, recapitulates Akt's action in tumorigenesis and drug resistance, but is unable to confer sensitivity to rapamycin and chemotherapy. These results establish Akt signalling through mTOR and eIF4E as an important mechanism of oncogenesis and drug resistance in vivo, and reveal how targeting apoptotic programmes can restore drug sensitivity in a genotype-dependent manner.

Control of apoptosis by p53

The p53 tumor suppressor acts to integrate multiple stress signals into a series of diverse antiproliferative responses. One of the most important p53 functions is its ability to activate apoptosis, and disruption of this process can promote tumor progression and chemoresistance. p53 apparently promotes apoptosis through transcription-dependent and -independent mechanisms that act in concert to ensure that the cell death program proceeds efficiently. Moreover, the apoptotic activity of p53 is tightly controlled, and is influenced by a series of quantitative and qualitative events that influence the outcome of p53 activation. Interestingly, other p53 family members can also promote apoptosis, either in parallel or in concert with p53. Although incomplete, our current understanding of p53 illustrates how apoptosis can be integrated into a larger tumor suppressor network controlled by different signals, environmental factors, and cell type. Understanding this network in more detail will provide insights into cancer and other diseases, and will identify strategies to improve their therapeutic treatment.

Tumor promotion by Mdm2 splice variants unable to bind p53

The Mdm2 oncoprotein physically associates with p53 and antagonizes its tumor suppressor functions. Previous studies indicate that some tumors express alternatively or aberrantly spliced Mdm2 variants that are unable to bind p53, but whether these actively contribute to carcinogenesis or are a byproduct of cancer progression has been unclear. In this study, we examined the ability of full-length Mdm2 and several tumor-derived splice variants to modulate tumor development in E micro -myc transgenic mice. We report that several tumor-derived Mdm2 splice variants promote tumorigenesis in a manner that is comparable with full-length Mdm2. Our results imply that the current paradigm for understanding Mdm2 action during oncogenesis is incomplete, and its splice variants contribute to human cancer.

An epi-allelic series of p53 hypomorphs created by stable RNAi produces distinct tumor phenotypes in vivo

The application of RNA interference (RNAi) to mammalian systems has the potential to revolutionize genetics and produce novel therapies. Here we investigate whether RNAi applied to a well-characterized gene can stably suppress gene expression in hematopoietic stem cells and produce detectable phenotypes in mice. Deletion of the Trp53 tumor suppressor gene greatly accelerates Myc-induced lymphomagenesis, resulting in highly disseminated disease. To determine whether RNAi suppression of Trp53 could produce a similar phenotype, we introduced several Trp53 short hairpin RNAs (shRNAs) into hematopoietic stem cells derived from E(mu)-Myc transgenic mice, and monitored tumor onset and overall pathology in lethally irradiated recipients. Different Trp53 shRNAs produced distinct phenotypes in vivo, ranging from benign lymphoid hyperplasias to highly disseminated lymphomas that paralleled Trp53-/- lymphomagenesis in the E(mu)-Myc mouse. In all cases, the severity and type of disease correlated with the extent to which specific shRNAs inhibited p53 activity. Therefore, RNAi can stably suppress gene expression in stem cells and reconstituted organs derived from those cells. In addition, intrinsic differences between individual shRNA expression vectors targeting the same gene can be used to create an 'epi-allelic series' for dissecting gene function in vivo.

A senescence program controlled by p53 and p16INK4a contributes to the outcome of cancer therapy

p53 and INK4a/ARF mutations promote tumorigenesis and drug resistance, in part, by disabling apoptosis. We show that primary murine lymphomas also respond to chemotherapy by engaging a senescence program controlled by p53 and p16(INK4a). Hence, tumors with p53 or INK4a/ARF mutations-but not those lacking ARF alone-respond poorly to cyclophosphamide therapy in vivo. Moreover, tumors harboring a Bcl2-mediated apoptotic block undergo a drug-induced cytostasis involving the accumulation of p53, p16(INK4a), and senescence markers, and typically acquire p53 or INK4a mutations upon progression to a terminal stage. Finally, mice bearing tumors capable of drug-induced senescence have a much better prognosis following chemotherapy than those harboring tumors with senescence defects. Therefore, cellular senescence contributes to treatment outcome in vivo.

Dissecting p53 tumor suppressor functions in vivo

Although the p53 tumor suppressor acts in a plethora of processes that influence cellular proliferation and survival, it remains unclear which p53 functions are essential for tumor suppression and, as a consequence, are selected against during tumor development. Using a mouse model harboring primary, genetically modified myc-driven lymphomas, we show that disruption of apoptosis downstream of p53 by Bcl2 or a dominant-negative caspase 9 confers-like p53 loss-a selective advantage, and completely alleviates pressure to inactivate p53 during lymphomagenesis. Despite their p53-null-like aggressive phenotype, apoptosis-defective lymphomas that retain intact p53 genes do not display the checkpoint defects and gross aneuploidy that are characteristic of p53 mutant tumors. Therefore, apoptosis is the only p53 function selected against during lymphoma development, whereas defective cell-cycle checkpoints and aneuploidy are mere byproducts of p53 loss.

Cytochrome c depletion upon expression of Bcl-XS

We have shown previously that Bcl-XS causes acute cell death in 3T3 cells without activating caspases (Fridman, J. S., Benedict, M. A., and Maybaum, J. (1999) Cancer Res. 59, 5999-6004). In this study, we determined that the explanation for lack of caspase activation is the cellular depletion of cytochrome c. Electron microscopy revealed gross structural changes in the mitochondria of Bcl-XS-expressing cells; however, cytochrome c was not detected in cytosolic fractions from these cells. Surprisingly, it was determined that cellular cytochrome c levels decreased as Bcl-XS expression levels increased. Experiments performed to eliminate other possible explanations for the lack of caspase activation showed that these 3T3 cells have a functional cytoplasmic apoptosome, a complex of proteins that form a functional trigger capable of activating the proximal caspase in an apoptotic pathway Chinnaiyan, A. M. (1999) Neoplasia 1, 5-15, as cytosolic extracts from these cells were capable of cleaving pro-caspase-9. These cells were also able to release cytochrome c from their mitochondria after appropriate stimulation, other than Bcl-XS expression (i.e. withdrawal from serum for 24 h), and initiate a cell death that is inhibited by a dominant negative caspase-9. We conclude that lack of caspase activation is due to a Bcl-XS-induced depletion of active cytochrome c, a phenomenon that represents an alternative cell death effector pathway and/or a novel mechanism for regulating caspase activation.

bcl-X(S)-induced cell death in 3T3 cells does not require or induce caspase activation

Using a tetracycline-regulated expression system, we have shown that expression of bcl-X(s) is sufficient to induce acute cell death in 3T3 cells, and that the manner in which these cells die is both morphologically and biochemically different from Fas/CD95-induced apoptosis. bcl-X(s) expression causes loss of the inner mitochondrial membrane potential (deltapsim) but does not induce caspase activation. Loss of viability, as determined by mitochondrial function and ethidium bromide exclusion, was not inhibited by the broad-spectrum caspase inhibitor zVAD-fmk or by expression of a dominant negative caspase 9 (9DN). However, zVAD-fmk was efficacious in inhibiting cell death triggered by an activating anti-Fas/CD95 antibody. In addition, bcl-X(s) does not possess the 5th and 6th alpha-helices (thought to be the membrane-spanning domains in bcl-2, bcl-X(L), and bax) and, therefore, should not be able to form membrane channels, thus eliminating this possible mechanism of action. The finding that bcl-X(s) kills 3T3 cells without caspase activation, along with the absence of membrane spanning domains in bcl-X(s), may, therefore, represent a novel cell death pathway for the pro-death bcl-2 family members.

Expression of Bcl-XS alters cytokinetics and decreases clonogenic survival in K12 rat colon carcinoma cells

bcl-XS, a member of the bcl-2 family, has been shown to induce and/or sensitize some cells to undergo programmed cell death, and to negate the anti-apoptotic activity of bcl-XL and bcl-2 by mechanisms which are still uncertain. To help understand these mechanisms we have established stable derivatives of the K12 rat colon carcinoma cell line that express bcl-XS in a tetracycline-regulated manner, using an autoregulatory retroviral cassette. When bcl-XS expression is induced, we observe two phenotypic responses. A small fraction of cells appear to undergo spontaneous apoptosis while the majority of cells undergo a form of cytostasis. In the latter case, the cells stop dividing (or divide a limited number of times at a retarded rate) and swell to many times their original size. These cells can take on a ghostlike appearance and subsequently detach from the culture plates and die or they may remain intact in a hindered state of proliferation. Doubling times were calculated to be 31.4 h in the presence of tetracycline and 50.4 h without tetracycline, bcl-XS expression also causes dramatic alterations in the cell cycle distribution of K12 cells manifesting as a substantial decrease (approximately 50%) in the fraction of S phase cells with a concomitant increase in the G1 population. Continuous expression of bcl-XS, at levels approximately equal to that of bcl-XL, decreased the viability of K12 cells as demonstrated by a log decline in clonogenic survival. This decrease occurred without considerable apoptosis or a compensatory increase in the level of bcl-XL. None of these phenotypes were present in control cells expressing beta-galactosidase in a similar retroviral cassette. These observations demonstrate that bcl-XS can have substantial cytokinetic effects under circumstances that produce relatively little apoptosis.