Preclinical characterization and clinical trial of CFI-400945, a polo-like kinase 4 inhibitor, in patients with relapsed/refractory acute myeloid leukemia and higher-risk myelodysplastic neoplasms

CFI-400945 is a selective oral polo-like kinase 4 (PLK4) inhibitor that regulates centriole duplication. PLK4 is aberrantly expressed in patients with acute myeloid leukemia (AML). Preclinical studies indicate that CFI-400945 has potent in vivo efficacy in hematological malignancies and xenograft models, with activity in cells harboring TP53 mutations. In this phase 1 study in very high-risk patients with relapsed/refractory AML and myelodysplastic syndrome (MDS) (NCT03187288), 13 patients were treated with CFI-400945 continuously in dose escalation from 64 mg/day to 128 mg/day. Three of the 9 efficacy evaluable AML patients achieved complete remission (CR). Two of 4 AML patients (50%) with TP53 mutations and complex monosomal karyotype achieved a CR with 1 patient proceeding to allogenic stem cell transplant. A third patient with TP53 mutated AML had a significant reduction in marrow blasts by > 50% with an improvement in neutrophil and platelet counts. Responses were observed after 1 cycle of therapy. Dose-limiting toxicity was enteritis/colitis. A monotherapy and combination therapy study with a newer crystal form of CFI-400945 in patients with AML, MDS and chronic myelomonocytic leukemia (CMML) is ongoing (NCT04730258).

Polo-like kinase 4 inhibitor CFI-400945 suppresses liver cancer through cell cycle perturbation and eliciting antitumor immunity

BACKGROUND AND AIMS

Prognosis of HCC remains poor due to lack of effective therapies. Immune checkpoint inhibitors (ICIs) have delayed response and are only effective in a subset of patients. Treatments that could effectively shrink the tumors within a short period of time are idealistic to be employed together with ICIs for durable tumor suppressive effects. HCC acquires increased tolerance to aneuploidy. The rapid division of HCC cells relies on centrosome duplication. In this study, we found that polo-like kinase 4 (PLK4), a centrosome duplication regulator, represents a therapeutic vulnerability in HCC.

APPROACH AND RESULTS

An orally available PLK4 inhibitor, CFI-400945, potently suppressed proliferating HCC cells by perturbing centrosome duplication. CFI-400945 induced endoreplication without stopping DNA replication, causing severe aneuploidy, DNA damage, micronuclei formation, cytosolic DNA accumulation, and senescence. The cytosolic DNA accumulation elicited the DEAD box helicase 41-stimulator of interferon genes-interferon regulatory factor 3/7-NF-κβ cytosolic DNA sensing pathway, thereby driving the transcription of senescence-associated secretory phenotypes, which recruit immune cells. CFI-400945 was evaluated in liver-specific p53/phosphatase and tensin homolog knockout mouse HCC models established by hydrodynamic tail vein injection. Tumor-infiltrated immune cells were analyzed. CFI-400945 significantly impeded HCC growth and increased infiltration of cluster of differentiation 4-positive (CD4 + ), CD8 + T cells, macrophages, and natural killer cells. Combination therapy of CFI-400945 with anti-programmed death-1 showed a tendency to improve HCC survival.

CONCLUSIONS

We show that by targeting a centrosome regulator, PLK4, to activate the cytosolic DNA sensing-mediated immune response, CFI-400945 effectively restrained tumor progression through cell cycle inhibition and inducing antitumor immunity to achieve a durable suppressive effect even in late-stage mouse HCC.

The spindle assembly checkpoint is a therapeutic vulnerability of CDK4/6 inhibitor-resistant ER+ breast cancer with mitotic aberrations

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) are standard first-line treatments for metastatic ER⁺ breast cancer. However, acquired resistance to CDK4/6i invariably develops, and the molecular phenotypes and exploitable vulnerabilities associated with resistance are not yet fully characterized. We developed a panel of CDK4/6i-resistant breast cancer cell lines and patient-derived organoids and demonstrate that a subset of resistant models accumulates mitotic segregation errors and micronuclei, displaying increased sensitivity to inhibitors of mitotic checkpoint regulators TTK and Aurora kinase A/B. RB1 loss, a well-recognized mechanism of CDK4/6i resistance, causes such mitotic defects and confers enhanced sensitivity to TTK inhibition. In these models, inhibition of TTK with CFI-402257 induces premature chromosome segregation, leading to excessive mitotic segregation errors, DNA damage, and cell death. These findings nominate the TTK inhibitor CFI-402257 as a therapeutic strategy for a defined subset of ER⁺ breast cancer patients who develop resistance to CDK4/6i.

Abstract 5394: Uterine leiomyosarcoma with homologous recombination deficiency is highly sensitive to polo-like kinase 4 inhibitor

INTRODUCTION: Uterine leiomyosarcoma (LMS) is rare and aggressive and without a well-established cancer-driver. Treatment is mainly surgical because most other therapies have limited benefits. Polo-like kinase 4 (PLK4) is a modulator of centriole duplication that is essential for proper cell division. Its inhibition by the PLK4 inhibitor, CFI-400945 resulted in centriole dysregulation, increased in double-strand DNA damage, and ultimately, mitotic catastrophe and cell death. Recent genomic studies have identified a subset of LMS with homologous recombination (HR) repair deficiency. We hypothesize that HR-deficient LMS is highly sensitive to CFI-400945.

METHODS: Gene knockouts (KO) were done by CRISPR-Cas9 system. Plasmids encoding the BRCA1- and BRCA2-targeting guide RNA, Cas9 protein, and selection markers were generated and were transfected into SK-UT-1 and SKN followed by selection with antibiotics. The KO and wild-type cell lines were treated with CFI-400945 in vitro. Percentage apoptosis was evaluated by Annexin V-PI staining and cell proliferation was examined by sulforhodamine B assay. To determine whether BRCA1- and BRCA2-KO had any effects on double-strand DNA damage, the γH2AX foci were studied by immunofluorescence staining.

RESULTS: CFI-400945 caused a greater degree of apoptosis and less cell viability in the KO than in the wild-type cell lines. In SK-UT-1, quantity of apoptotic cells for BRCA2-KO and BRCA1-KO were 77% and 34%, respectively, versus 27% in the wild-type cell line (p<0.05). Less dramatic findings were observed in SKN with respective percentages of 20% and 25% versus 15% (p<0.05). In SK-UT-1, the mean IC50 for BRCA2-KO and BRCA1-KO were 3.4 nM and 5.5 nM, respectively, versus 7.8 nM in the wild-type cell line (p<0.05). Similar observations were noted in SKN, with respective mean IC50 of 6.5 nM and 7.1 nM versus 10.0 nM (p<0.05). After CFI-400945 treatment, the γH2AX/Hoechst 33342 staining intensity ratio was 0.40 in SK-UT-1 BRAC2-KO and 0.44 in BRCA1-KO, where both were higher than in the corresponding wild-type cell line with 0.29 (p<0.05). Similarly, the intensities in the two SKN KO cell lines were 0.29 and 0.31, respectively, and higher than in the wild-type cell line with 0.19 (p <0.05).

CONCLUSIONS: PLK4 inhibitor induced DNA double-strand breaks in LMS and the repair of these breakages was dependent on HR repair. In vitro, LMS with BRCA1 or BRCA2 deficiencies were more sensitive to the effect of PLK4 inhibitor.

Citation Format: Tsz Yan Chong, Horace HY Lee, Judy WP Yam, Kin Long Chow, Ho Shing Wong, Ka Yu Tse, Mark R. Bray, Tak Wah Mak, Philip PC Ip. Uterine leiomyosarcoma with homologous recombination deficiency is highly sensitive to polo-like kinase 4 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5394.

TWT-203: Phase 1b/2 dose-confirming study of CFI-402257 as a single agent in advanced solid tumors and in combination with fulvestrant in patients with ER+/HER2- advanced breast cancer after disease progression on prior CDK4/6 and endocrine therapy

TPS1123

Background: TTK (Threonine Tyrosine Kinase also known as Monopolar spindle 1 [Mps1]), is a dual-specificity serine-threonine kinase critical for anaphase promoting complex/cyclosome inhibition at the spindle assembly checkpoint, and is required for chromosome alignment and error correction. Inhibition of TTK causes cells to prematurely exit mitosis with unattached chromosomes, resulting in aneuploidy and cell death. Higher TTK tumor levels correlate with worse prognosis and may contribute to the survival and proliferation of aneuploid cells. CFI-402257, a potent and selective inhibitor of TTK inhibits the growth of a variety of human cancer-derived cell lines with IC50 of 8-40 nM. A first-in-human phase 1 study of CFI-402257 administered orally as a single agent, demonstrated a tolerable safety profile and evidence of clinical activity in patients with advanced solid tumors. The MTD was 168 mg daily, and the study expanded to 3 cohorts: solid tumors, HER2-negative breast cancer, and hormone receptor positive (HR+/HER2-) breast cancer in combination with fulvestrant. The dose limiting toxicity was manageable and reversible dose-dependent neutropenia. Investigator-confirmed partial responses (cPR) were observed in 5 patients (10.6%) with 25 (53.2%) exhibiting disease control. In the HR+/HER2- breast cancer population previously treated with cyclin dependent kinase 4/6 inhibitors (CDK4/6i) and aromatase inhibitors, there were 4 cPR’s with a median duration of response of 256 days, with responses emerging after 2 cycles of therapy. Responses were observed with CFI-402257 as a single agent and in combination with fulvestrant. Based on these data, study TWT-203 will focus on advanced solid tumors and advanced HR+/HER2- breast cancers in combination with an approved endocrine therapy. Methods: Safety and clinical activity of CFI-402257 monotherapy will be evaluated in patients with advanced solid tumors (Part A) or in combination with fulvestrant in patients with HR+/HER2- advanced breast cancer (Part B). Part A will confirm the RP2D using a 3+3 design with a starting dose of 126 mg daily. Part B evaluates CFI-402257 in combination with fulvestrant in patients with HR+/HER2- advanced breast cancer following progression on prior CDK4/6i and endocrine therapy. Initially 6 patients will be treated with CFI-402257 and fulvestrant, and safety, tolerability, and PK evaluated, with further expansion to confirm the RP2D and characterize CFI-402257 activity. Efficacy endpoints include overall response rate and disease control rate. Safety endpoints include incidence of treatment emergent adverse events. Exploratory objectives include characterization of protein and molecular alterations relevant to the cell cycle and CFI-402257 response.

Abstract 4130: Improvement of drug efficacy of polo-like kinase 4 inhibitor in the treatment of uterine leiomyosarcoma

Introduction: Uterine leiomyosarcoma (Ut-LMS) is aggressive. Recurrence usually develops in 50 - 70% of patients and effective chemotherapy regime are limited. Polo-like kinase 4 (PLK4) is vital modulator of centriole duplication and cell mitotic progression. Inhibition of PLK4 disrupts mitosis, which leads to polyploidy, further genomic instability, mitotic catastrophe, and cell death. Recently, CFI-400945, a PLK4 inhibitor, has been found effective in preclinical studies in the treatment of several malignancies but its effectiveness on Ut-LMS has not been investigated. In phase I studies, CFI-400945 was well tolerated although toxicity, primarily reversible neutropenia, was observed at higher doses. Ataxia-telangiectasia mutated (ATM) is a key kinase in the DNA damage response pathway. AZD0156, an ATM kinase inhibitor, has recently been proposed to be used with other DNA damaging agents in cancer treatments. We explored the effectiveness of a combined approach with CFI-400945 and AZD0156 in Ut-LMS.

Methods: Ut-LMS cell lines SK-UT-1, SKN and SK-LMS-1 cultured in-vitro were treated with CFI-400945 and AZD0156. PLK4 gene expression in these cell lines was also determined by RT-qPCR assays. Cell proliferation was examined using the sulforhodamine B (SRB) assay while apoptosis was examined by Annexin V-PI and caspase 3/7 assays. Immunofluorescence confocal centrosome quantification and flow cytometry PI cell cycle analysis were used to detect centrosome overduplication and generation of aneuploidy cells. The effect of gene expression in normal uterine smooth muscle cells and Ut-LMS cell lines treated with CFI-400945 was performed by RNA-Seq. DNA damage was detected using neutral comet assay.

Results: Ut-LMS cell lines expressed high levels of PLK4 and were highly sensitive (IC50 in nM range) to CFI-400945. Centrosome overduplication, aneuploidy cells, and cell growth inhibition were observed in a dose-dependent manner, and prominent apoptosis was observed at 48 hours after drug treatment. Gene set enrichment analysis on RNA-Seq data indicated that cells were under genotoxic stress after CFI-400945 treatment while comet assay verified DNA damage. Cell arrest and apoptosis with CFI-400945 was further enhanced by the addition of AZD0156. Combined treatment of CFI-400945 and AZD0156 produced synergistic antineoplastic effects in all three Ut-LMS cell lines, with combination indices <1. DNA damage was also enhanced in the combined treatment group versus the single treatment group.

Conclusion: The PLK4 inhibitor CFI-400945 was a potent treatment for Ut-LMS in vitro. This effect was further augmented when combined with the DNA damage response pathway inhibitor AZD0156. The synergistic effect of these agents is promising, and should be investigated further in the treatment of Ut-LMS

Citation Format: Hok Yeung Horace Lee, Kin Long Chow, Ho Shing Wong, Tsz Yan Chong, Ka Yu Tse, Mark R. Bray, Tak Wah Mak, Philip PC Ip. Improvement of drug efficacy of polo-like kinase 4 inhibitor in the treatment of uterine leiomyosarcoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4130.

Abstract PD2-03: CDK4/6 inhibitor-resistant ER+ breast cancer cell lines are hypersensitive to TTK inhibition

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i), in combination with hormonal therapies, have become standard of care for the treatment of estrogen receptor-positive (ER+)/HER2-negative metastatic breast cancer. Despite demonstrating significant improvements in progression-free survival, acquired resistance to these inhibitors invariably develops. Recent analyses of clinical samples have identified emergent genomic alterations conferring acquired resistance to CDK4/6i, and begin to define the biology of this new clinical entity. Discovery of vulnerabilities of CDK4/6i-resistant tumours is imperative to improve the survival of this group of patients. We modeled CDK4/6i resistance in ER+ breast cancer cell lines using two complementary approaches: (1) spontaneous development of resistance upon continuous exposure to the palbociclib for 6-9 months, and (2) genetic engineering of RB1 loss of function. In both cases, palbociclib resistance was confirmed by colony formation and cell proliferation assays. To identify potential therapeutic strategies for CDK4/6i-resistant cells, we tested the in vitro activity of novel cell cycle inhibitors using sulforhodamine B (SRB) cytotoxicity assays. CFI-402257, a selective TTK inhibitor now in Phase I testing, induced significantly increased cytotoxicity in different CDK4/6i-resistant models compared to parental cell lines, including but not exclusively those with RB1 loss. CFI-402257 treatment caused defects in cell cycle progression and increased DNA damage and genomic instability in CDK4/6i-resistant cells, while these effects were mild in parental, CDK4/6i-sensitive cell lines. In some cases, these phenotypes were accompanied by an increase in apoptotic signaling. Analysis of the molecular determinants of these effects are being evaluated (additional results will be presented). In xenografts derived from MCF7 cells, CFI-402257 treatment completely abrogated the growth of RB1-KO tumours and had a much less pronounced effect on wild-type tumours. In summary, our results nominate the TTK inhibitor CFI-402257 as a promising therapeutic strategy for breast cancer patients who progress after CDK4/6 inhibition. A clinical trial testing this strategy is being launched.

Citation Format: Isabel Soria Bretones, Kelsie L Thu, Jennifer Silvester, Reza Kiarash, Graham C Fletcher, Jennifer Cruickshank, Mark R Bray, Tak W Mak, David W Cescon. CDK4/6 inhibitor-resistant ER+ breast cancer cell lines are hypersensitive to TTK inhibition [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr PD2-03.

Safety and tolerability of CFI-400945, a first-in-class, selective PLK4 inhibitor in advanced solid tumours: a phase 1 dose-escalation trial

Background

CFI-400945 is a first-in-class oral inhibitor of polo-like kinase 4 (PLK4) that regulates centriole duplication. Primary objectives of this first-in-human phase 1 trial were to establish the safety and tolerability of CFI-400945 in patients with advanced solid tumours. Secondary objectives included pharmacokinetics, pharmacodynamics, efficacy, and recommended phase 2 dose (RP2D).

Methods

Continuous daily oral dosing of CFI-400945 was evaluated using a 3+3 design guided by incidence of dose-limiting toxicities (DLTs) in the first 28-day cycle. Safety was assessed by CTCAE v4.0. ORR and CBR were evaluated using RECIST v1.1.

Results

Forty-three patients were treated in dose escalation from 3 to 96 mg/day, and 9 were treated in 64 mg dose expansion. After DLT occurred at 96 and 72 mg, 64 mg was established as the RP2D. Neutropenia was a common high-grade (19%) treatment-related adverse event at ≥ 64 mg. Half-life of CFI-400945 was 9 h, with C_max achieved 2–4 h following dosing. One PR (45 cycles, ongoing) and two SD ≥ 6 months were observed (ORR = 2%; CBR = 6%).

Conclusions

CFI-400945 is well tolerated at 64 mg with dose-dependent neutropenia. Favourable pharmacokinetic profiles were achieved with daily dosing. Response rates were low without biomarker pre-selection. Disease-specific and combination studies are ongoing.

Trial Registration

Clinical Trials Registration Number – NCT01954316 (Oct 1st, 2013)

Abstract 3935: PLK4 inhibition as a strategy for non-small cell lung cancer radiosensitization

Background/Purpose: Lung cancer remains the leading cause of cancer-related death. Concurrent chemoradiation is the standard of care for locally advanced non-small cell lung cancer (NSCLC). Despite advancements in treatment, local control remains an issue and survival is suboptimal, highlighting the need for novel therapeutic approaches. Polo-like kinase 4 (PLK4) is a serine/threonine kinase that controls centriole duplication. PLK4 is highly expressed in multiple malignancies including lung cancer. CFI-400945 is a specific PLK4 inhibitor currently undergoing clinical trial evaluation. As radiation causes cell death primarily via a mitotic death, we hypothesized that disruption of the mitotic machinery by inhibition of PLK4 would enhance the effects of radiation.

Methods: The effects of CFI-400945 on cell survival and radiation sensitivity were examined using the clonogenic survival assay in two KRAS-mutant lung cancer cell lines (H460 and A549). Confocal microscopy was utilized to determine the effects of PLK4 inhibition on radiation-induced mitotic catastrophe (defined as the presence of 2 or more distinct nuclear lobes within a single cell). Cell cycle distribution by flow cytometry was determined after treatment with CFI-400945 and radiation.

Results: Exposure of H460 and A549 lung cancer cell lines to 10nM CFI-400945 for 48h reduced clonogenic survival to 63.9% and 83.1% respectively. CFI-400945 treatment of H460 and A549 cells resulted in radiosensitization of both cell lines with dose enhancement factors (DEF) of 1.60 and 1.31. To understand the mechanism of enhanced radiosensitivity with CFI-400945 treatment the effects on radiation-induced mitotic catastrophe were determined. In both H460 and A549 cells the combination of radiation and PLK4 inhibition enhanced the proportion of cells undergoing mitotic catastrophe. The combination of CFI-400945 and radiation resulted in increased G2/M arrest and appearance of >4N populations by flow cytometric analysis when compared to drug or radiation treatment alone.

Conclusion: PLK4 inhibition with CFI-400945 enhances the radiosensitivity of lung cancer cell lines via mitotic catastrophe and G2/M arrest and these data support additional pre-clinical testing.

Citation Format: Thomas J. Hayman, Mark R. Bray, Jacqueline M. Mason, Tak W. Mak, Joseph N. Contessa. PLK4 inhibition as a strategy for non-small cell lung cancer radiosensitization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3935.

Phase I study of CFI-402257, an oral TTK inhibitor, in patients with advanced solid tumors

TPS2619

Background: TTK (MPS1), a dual-specificity serine-threonine kinase, is critical for the spindle assembly checkpoint (SAC), chromosome alignment and error correction in mitosis. Inhibition of TTK causes premature mitotic exit with unattached chromosomes, resulting in chromosomal missegregation, aneuploidy and cell death. TTK is overexpressed in several tumor types, which may contribute to survival and proliferation of aneuploid cells, and higher expression correlates with adverse outcomes. The Campbell Family Therapeutics Group at the University Health Network (UHN) has developed CFI-402257, a potent (Ki = 0.09 nM, IC50 = 1.2 nM), highly selective and orally active inhibitor of TTK, with negligible activity towards 265 other kinases. Robust suppression of tumor growth was achieved upon oral dosing of single agent CFI-402257 at tolerated doses in several cell line (breast, colorectal) and patient-derived (ovarian) xenograft models. Pharmacodynamic effects including reduction in phospho-histone H3 were observed. In syngeneic mouse colorectal cancer models, CFI-402257 + PD-1 immune checkpoint blockade demonstrated greater activity than either agent alone, and resulted in tumor regressions and immunity to rechallenge. Methods: This multi-center Phase I dose escalation study (3+3 design) will determine the safety, tolerability and maximum tolerated dose (MTD) of CFI-402257 administered as daily continuous oral treatment. Secondary and correlative endpoints include plasma PK, antitumor activity, and molecular features associated with response or clinical benefit. An expansion cohort (n = 12) will be enrolled at the MTD. Key inclusion criteria: adult patients with advanced solid tumors, measurable disease (RECIST 1.1), adequate organ function and performance status (ECOG 0-1). Exclusion criteria: uncontrolled medical illness, CNS metastases (unless stable x 3 months). CFI-402257 will be dosed once daily on a continuous schedule in 28-day cycles, beginning at 5 mg/day with planned escalation to 56 mg/day. DL1 completed enrolment 01/2017 and accrual is ongoing. Phase II studies are planned (Stand Up to Cancer Canada Breast Cancer Dream Team). Funding: UHN, CIRM. Clinical trial information: NCT02792465.

Abstract CT066: First-in-human phase I trial of the oral PLK4 inhibitor CFI-400945 in patients with advanced solid tumors

Background: CFI-400945 is a first-in-class, potent, selective, orally active inhibitor of Polo-like kinase 4 (PLK4) (Ki = 0.26 nM), a conserved master regulator of centriole duplication that is important for maintenance of genomic integrity. In preclinical studies, CFI-400945 demonstrated robust anti-tumor activity, including durable complete tumor regression, in a large number of patient-derived xenograft models from multiple tumor types (breast, ovarian, pancreas, prostate carcinomas; some derived from heavily pre-treated patients). The objectives of this first-in-human phase I trial are to establish safety, tolerability, pharmacokinetics, and recommended phase II dose (RP2D) of CFI-400945.

Methods: Patients with advanced solid tumors age >18 years, with ECOG performance status of 0-1, adequate organ function and RECIST-measurable disease progressing on standard treatments are eligible. Dose escalation follows a standard 3+3 design, with a starting dose of 3mg once daily continuous oral dosing based upon preclinical data and a severely toxic dose to 10 percent (STD10) in rats of 3 mg/kg. The primary endpoint is the incidence of dose limiting toxicities (DLTs) during the first cycle. Safety assessments using CTCAE version 4.03 criteria are performed weekly during the first three cycles and then every two weeks. Response assessments are performed every two cycles.

Results: From April/14 to December/15, 31 patients were enrolled across eight pre-defined dose levels (3, 6, 11, 16, 24, 32, 48 and 72 mg). No DLT events have been observed. Dose escalation at 96mg is currently ongoing. The most frequent treatment-related adverse events (trAEs) include fatigue (24%), diarrhea (17.2%), nausea (17.2%), decreased appetite (13.8%) and vomiting (6.9%). All trAEs were grade 1 or grade 2. Fifteen serious adverse events (SAEs) have occurred in 9 patients, all considered unrelated to CFI-400945 treatment. Preliminary PK results estimate a half-life of about 10 hours, with Cmax and AUC showing dose proportionality. Two patients enrolled at the 48 mg dose level have completed >6 cycles, including a patient with KRAS mutant colorectal cancer who achieved 24% reduction in target lesions and >50% reduction in serum CEA levels.

Conclusions: CFI-400945 is well tolerated at doses up to 72mg with a favorable PK profile. Preliminary evidence of anti-tumor activity has been observed. Exploration of 96mg daily dosing is ongoing and once the RP2D has been established exploration of anti-tumor activity in biomarker-driven expansion arms of CFI-400945 in indications including advanced breast cancer is planned. Updated results of this ongoing trial will be presented at the meeting.

Citation Format: Philippe L. Bedard, David W. Cescon, Graham Fletcher, Trish Denny, Richard Brokx, Peter Sampson, Mark R. Bray, Dennis J. Slamon, Tak W. Mak, Zev A. Wainberg. First-in-human phase I trial of the oral PLK4 inhibitor CFI-400945 in patients with advanced solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT066.

Discovery of Pyrazolo[1,5-a]pyrimidine TTK Inhibitors: CFI-402257 is a Potent, Selective, Bioavailable Anticancer Agent

This work describes a scaffold hopping exercise that begins with known imidazo[1,2-a]pyrazines, briefly explores pyrazolo[1,5-a][1,3,5]triazines, and ultimately yields pyrazolo[1,5-a]pyrimidines as a novel class of potent TTK inhibitors. An X-ray structure of a representative compound is consistent with 1(1)/2 type inhibition and provides structural insight to aid subsequent optimization of in vitro activity and physicochemical and pharmacokinetic properties. Incorporation of polar moieties in the hydrophobic and solvent accessible regions modulates physicochemical properties while maintaining potency. Compounds with enhanced oral exposure were identified for xenograft studies. The work culminates in the identification of a potent (TTK K i = 0.1 nM), highly selective, orally bioavailable anticancer agent (CFI-402257) for IND enabling studies.

A phase I trial of the aurora kinase inhibitor, ENMD-2076, in patients with relapsed or refractory acute myeloid leukemia or chronic myelomonocytic leukemia

ENMD-2076 is a novel, orally-active molecule that inhibits Aurora A kinase, as well as c-Kit, FLT3 and VEGFR2. A phase I study was conducted to determine the maximum tolerated dose (MTD), recommended phase 2 dose (RP2D) and toxicities of ENMD-2076 in patients with acute myeloid leukemia (AML) and chronic myelomonocytic leukemia (CMML). Patients received escalating doses of ENMD-2076 administered orally daily [225 mg (n = 7), 375 mg (n = 6), 325 mg (n = 9), or 275 mg (n = 5)]. Twenty-seven patients were treated (26 AML; 1 CMML-2). The most common non-hematological toxicities of any grade, regardless of association with drug, were fatigue, diarrhea, dysphonia, dyspnea, hypertension, constipation, and abdominal pain. Dose-limiting toxicities (DLTs) consisted of grade 3 fatigue, grade 3 typhilitis, grade 3 syncope and grade 3 QTc prolongation). Of the 16 evaluable patients, one patient achieved a complete remission with incomplete count recovery (CRi), three experienced a morphologic leukemia-free state (MLFS) with a major hematologic improvement in platelets (HI-P), and 5 other patients had a reduction in marrow blast percentage (i.e. 11-65 %). The RP2D in this patient population is 225 mg orally once daily.

Targeting Mitosis in Cancer: Emerging Strategies

The cell cycle is an evolutionarily conserved process necessary for mammalian cell growth and development. Because cell-cycle aberrations are a hallmark of cancer, this process has been the target of anti-cancer therapeutics for decades. However, despite numerous clinical trials, cell-cycle-targeting agents have generally failed in the clinic. This review briefly examines past cell-cycle-targeted therapeutics and outlines how experience with these agents has provided valuable insight to refine and improve anti-mitotic strategies. An overview of emerging anti-mitotic approaches with promising pre-clinical results is provided, and the concept of exploiting the genomic instability of tumor cells through therapeutic inhibition of mitotic checkpoints is discussed. We believe this strategy has a high likelihood of success given its potential to enhance therapeutic index by targeting tumor-specific vulnerabilities. This reasoning stimulated our development of novel inhibitors targeting the critical regulators of genomic stability and the mitotic checkpoint: AURKA, PLK4, and Mps1/TTK.

Functional characterization of CFI-400945, a Polo-like kinase 4 inhibitor, as a potential anticancer agent

PLK4 was identified as a promising therapeutic target through a systematic approach that combined RNAi screening with gene expression analysis in human breast cancers and cell lines. A drug discovery program culminated in CFI-400945, a potent and selective PLK4 inhibitor. Cancer cells treated with CFI-400945 exhibit effects consistent with PLK4 kinase inhibition, including dysregulated centriole duplication, mitotic defects, and cell death. Oral administration of CFI-400945 to mice bearing human cancer xenografts results in the significant inhibition of tumor growth at doses that are well tolerated. Increased antitumor activity in vivo was observed in PTEN-deficient compared to PTEN wild-type cancer xenografts. Our findings provide a rationale for the clinical evaluation of CFI-400945 in patients with solid tumors, in particular those deficient in PTEN.

Abstract C265: Significant in vivo activity of ENMD-2076, a novel multi-targeted kinase inhibitor, towards xenograft models of human hepatocellular carcinomas

Background: Hepatocellular carcinoma (HCC) is a primary malignancy of the liver. It represents the third leading cause of cancer deaths worldwide, with over 500,000 people affected each year. The incidence of HCC is particularly high in China, accounting for more than 50% of the global incidences. The development of targeted anticancer agents effective against HCC for patients who do not tolerate, or have failed or relapsed from sorafenib treatment would meet a major unmet medical need. ENMD-2076 is an orally bioavailable small molecule inhibitor of Aurora A and angiogenic kinases including VEGFR 2 and FGFR 1 with pro-apoptotic, antiproliferative and angiogenic activities against a variety of human cancers. ENMD-2076 has been tested in multiple Phase I and II clinical trials, with partial responses (PR) and prolonged progression free survival (PFS) observed in multiple cancers including liver cancer.

Objective: This in vivo study was designed to compare the efficacy of ENMD-2076 with that of standard of care agents including sorafenib, doxorubicin, and 5-FU in 3 different cell-line derived human HCC xenograft models. The tolerability and efficacy of combinations of ENMD-2076 with doxorubicin or 5-FU were also determined.

Experimental Design: Three different human HCC cell lines, SMMC-7721, QGY-7703 and HepG 2 were used for establishing subcutaneous tumor xenograft models in nude mice. After tumors grew to more than 100 mm3, mice were randomly assigned into one of the groups receiving vehicle, sorafenib, ENMD-2076 alone or in combination with chemotherapy agents, including doxorubicin or 5-FU, respectively, for 20 days. Results: In all HCC models tested, ENMD-2076 induced tumor growth inhibition significantly greater than that of sorafenib. When treated with ENMD-2076 at 100 mg/kg, the tumor growth inhibition (TGI) rates were 73.67%, 76.59% or 80.12% in the SMMC-7721, QGY-7703 or HepG 2 models, respectively, which were significantly higher than those observed in sorafenib treated groups (48.63%, 51.43%, or 57.60%, respectively;P<0.01 in all three models). Tumor growth inhibition rates were similarly higher in the ENMD-2076 treated groups than in groups treated with doxorubicin at 1 mg/kg and 5-FU at 30 mg/kg. The combined treatment of ENMD-2076 with either doxorubicin or 5-FU was well tolerated. Higher TGI rates were observed in combination groups compared to single agents of chemotherapies but were not statistically different.

Conclusion: ENMD-2076 showed robust antitumor activity against three cell line-derived xenograft models of HCC superior to that of sorafenib, doxorubicin, and 5FU, supporting clinical investigation of this agent in HCC patients who do not tolerate, or have failed or relapsed from other systemic treatment such as sorafenib, doxorubicin or 5 FU.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C265.

Citation Format: Peipei Yin, Hongqi Lu, Mark R. Bray, Bingsheng Li, Ken Ren. Significant in vivo activity of ENMD-2076, a novel multi-targeted kinase inhibitor, towards xenograft models of human hepatocellular carcinomas . [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C265.

Predictive biomarkers of sensitivity to the aurora and angiogenic kinase inhibitor ENMD-2076 in preclinical breast cancer models

PURPOSE

The Aurora kinases are a family of conserved serine-threonine kinases with key roles in mitotic cell division. As with other promising anticancer targets, patient selection strategies to identify a responsive subtype will likely be required for successful clinical development of Aurora kinase inhibitors. The purpose of this study was to evaluate the antitumor activity of the Aurora and angiogenic kinase inhibitor ENMD-2076 against preclinical models of breast cancer with identification of candidate predictive biomarkers.

EXPERIMENTAL DESIGN

Twenty-nine breast cancer cell lines were exposed to ENMD-2076 and the effects on proliferation, apoptosis, and cell-cycle distribution were evaluated. In vitro activity was confirmed in MDA-MB-468 and MDA-MB-231 triple-negative breast cancer xenografts. Systematic gene expression analysis was used to identify up- and downregulated pathways in the sensitive and resistant cell lines, including within the triple-negative breast cancer subset.

RESULTS

ENMD-2076 showed antiproliferative activity against breast cancer cell lines, with more robust activity against cell lines lacking estrogen receptor expression and those without increased HER2 expression. Within the triple-negative breast cancer subset, cell lines with a p53 mutation and increased p53 expression were more sensitive to the cytotoxic and proapoptotic effects of ENMD-2076 exposure than cell lines with decreased p53 expression.

CONCLUSIONS

ENMD-2076 exhibited robust anticancer activity against models of triple-negative breast cancer and the candidate predictive biomarkers identified in this study may be useful in selecting patients for Aurora kinase inhibitors in the future.

P3-01-08: In Vitro and In Vivo Antitumor Activity of the Aurora and Angiogenic Kinase Inhibitor ENMD-2076 in Triple-Negative Breast Cancer Models

Background

Triple-negative breast cancer (TNBC) is an aggressive biologic subtype which lacks effective targeted anti-cancer agents and is characterized by a high mitotic index and dependence on angiogenesis. ENMD-2076 is a novel orally bioavailable Aurora and angiogenic kinase inhibitor currently in clinical development with favorable pharmacokinetics and a manageable toxicity profile. The purpose of this study was to use TNBC cell line-based in vitro and in vivo models to demonstrate the antitumor activity of ENMD-2076 towards this breast cancer subtype compared to the luminal and HER2−amplified subtypes. Additionally, we used baseline gene expression profiling and pathway analysis to explore molecular predictors of responsiveness to ENMD-2076 in TNBC.

Methods: Twenty-five breast cancer cell lines were exposed to ENMD-2076 and the effects on proliferation, apoptosis, and cell cycle distribution were evaluated. Proliferation was assessed using an SRB assay, apoptosis was analyzed using a caspase 3/7 assay and cell cycle was measured using flow cytometry. In vitro activity of ENMD-2076 was confirmed in 3-D cell culture and in MDA-MB-231 and MDA-MB-468 triple-negative breast cancer xenograft models and immunohistochemical analysis was performed for phosphor-histone H3 (pHH3). Gene array and gene set enrichment analysis (GSEA) was used to identify pathways differentially regulated in the sensitive and resistance cell lines, including within the triple-negative breast cancer subset.

Results: In vitro exposure to ENMD-2076 resulted in robust inhibition of proliferation in TNBC cell lines which was associated with a G2 cell cycle arrest and induction of caspase-dependent apoptosis. Of the TNBC cell lines screened, 1 of 10 had a mean IC50 value > 5 μmol/L and 7 of 10 had a mean IC50 ≤ 1 μmol/L (Fisher's exact test, p-value = 0.009). In comparison, only 1 luminal (ER+) and one UER2-amplified breast cancer cell line had an IC50 value < 1, whereas 7 and 5 resistant lines were luminal and HER2−amplified, respectively (Fisher's exact test, p-values = 0.02 and 0.11 for ER and HER2 status, respectively). ENMD-2076 exhibited antitumor activity towards MDA-MD-231 and MDA-MB-468 xenograft models of TNBC with statistically significant tumor growth inhibition compared to vehicle control (p< 0.05 and p< 0.01, respectively). A trend towards an increase in pHH3 staining cells in the MDA-MB-231 ENMD-2076 treated group compared to the vehicle control group was observed; however, this was not statistically significant (104.7 ± 36.2 positive cells/mm2 in treated vs. 79.9 ± 34.5 in control). Using significance of analysis of microarrays (SAM) analysis and GSEA, we identified Ran, a member of the mitotic spindle regulation pathway as upregulated in sensitive TNBC cell lines (p = 0.017). Interestingly, AURKA, the main target of ENMD-2076, is a core gene in this pathway.

Conclusions: ENMD-2076 exhibited robust anticancer activity towards preclinical models of TNBC, supporting future clinical investigations of this agent in TNBC with an emphasis on the continued development of biomarkers predictive of response in this breast cancer subset.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-01-08.

ENMD-2076 is an orally active kinase inhibitor with antiangiogenic and antiproliferative mechanisms of action

ENMD-2076 is a novel orally active, small molecule kinase inhibitor with a mechanism of action involving several pathways key to tumor growth and survival: angiogenesis, proliferation, and the cell cycle. ENMD-2076 has selective activity against the mitotic kinase Aurora A, as well as kinases involved in angiogenesis (VEGFRs, FGFRs). ENMD-2076 inhibited the growth in vitro of a wide range of human solid tumor and hematopoietic cancer cell lines with IC(50) values ranging from 0.025 to 0.7 μmol/L. ENMD-2076 was also shown to induce regression or complete inhibition of tumor growth in vivo at well-tolerated doses in tumor xenograft models derived from breast, colon, melanoma, leukemia, and multiple myeloma cell lines. Pharmacodynamic experiments in vivo showed that in addition to inhibiting Aurora A, single doses of ENMD-2076 had sustained inhibitory effects on the activation of Flt3 as well as the angiogenic tyrosine kinases, VEGFR2/KDR and FGFR1 and 2. ENMD-2076 was shown to prevent the formation of new blood vessels and regress formed vessels in vivo at doses equivalent to those that gave substantial activity in tumor xenograft models. These results indicate that ENMD-2076 is a well-tolerated, orally active multitarget kinase inhibitor with a unique antiangiogenic/antiproliferative profile and provides strong preclinical support for use as a therapeutic for human cancers. Several phase 1 studies involving ENMD-2076 have been recently completed, and the compound is currently being evaluated in a phase 2 clinical trial in patients with platinum-resistant ovarian cancer.

Phase I safety, pharmacokinetic, and pharmacodynamic study of ENMD-2076, a novel angiogenic and Aurora kinase inhibitor, in patients with advanced solid tumors

PURPOSE

ENMD-2076 is a unique orally bioavailable Aurora kinase and VEGFR inhibitor. The purpose of this phase 1 study of ENMD-2076 was to determine the MTD, pharmacokinetic, and pharmacodynamic profiles and preliminary antitumor activity.

EXPERIMENTAL DESIGN

Patients with refractory advanced solid malignancies were treated with ENMD-2076 orally with continuous once daily dosing. Doses from 60 to 200 mg/m(2) were evaluated using a standard 3 (to 4) + 3 design. Pharmacokinetic parameters were studied on days 1, 28, and 30 to 35 of cycle 1. Expanded MTD cohorts included patients with ovarian cancer, colorectal cancer, and refractory solid tumors.

RESULTS

A total of 67 patients (46 F, 21M; ages 30-76) entered the study. Dose levels of 60, 80, 120, 200, and 160 mg/m(2) were evaluated. Two patients experienced grade 3 hypertension at 200 mg/m(2), and additional grade 3 neutropenia events limited tolerability at this dose. An intermediate dose of 160 mg/m(2) was determined to be the MTD. The most common drug-related adverse events included hypertension, nausea/vomiting, and fatigue. The pharmacokinetics of ENMD-2076 were characterized by a rapid absorption phase (T(max) 3-7.8 hours), a t(1/2) of 27.3 to 38.3 hours after a single dose, and dose proportional exposure. Decreased plasma sVEGFR2 was observed posttreatment. Two patients with platinum refractory/resistant ovarian cancer had RECIST partial responses.

CONCLUSIONS

ENMD-2076 was well tolerated, had a linear pharmacokinetic profile, and showed promising antitumor activity, particularly in ovarian cancer. The recommended phase 2 dose of ENMD-2076 is 160 mg/m(2) administered orally once daily with continuous dosing.

Preclinical activity of a novel multiple tyrosine kinase and aurora kinase inhibitor, ENMD-2076, against multiple myeloma

ENMD-2076 is a novel, orally-active molecule that has been shown to have significant activity against aurora and multiple receptor tyrosine kinases. We investigated the activity of ENMD-2076 against multiple myeloma (MM) cells in vitro and in vivo. ENMD-2076 showed significant cytotoxicity against MM cell lines and primary cells, with minimal cytotoxicity to haematopoietic progenitors. ENMD-2076 inhibited the phosphoinositide 3-kinase/AKT pathway and downregulated survivin and X-linked inhibitor of apoptosis as early as 6 h after treatment. With longer treatment (24-48 h), ENMD-2076 also inhibited aurora A and B kinases, and induced G(2)/M cell cycle arrest. In non-obese diabetic/severe combined immunodeficient mice implanted with H929 human plasmacytoma xenografts, oral treatment with ENMD-2076 (50, 100, 200 mg/kg per day) resulted in a dose-dependent inhibition of tumour growth. Immunohistochemical staining of excised tumours showed significant reduction in phospho-Histone 3 (pH3), Ki-67, and angiogenesis, and also a significant increase in cleaved caspase-3 at all dose levels compared to tumours from vehicle-treated mice. In addition, a significant reduction in p-FGFR3 was observed on Western blot. ENMD-2076 shows significant activity against MM cells in vitro and in vivo, and acts on several pathways important for myeloma cell growth and survival. These results provide preclinical rationale for clinical investigation of ENMD-2076 in MM.

Assessment of the in vivo antitumor effects of ENMD-2076, a novel multitargeted kinase inhibitor, against primary and cell line-derived human colorectal cancer xenograft models

PURPOSE

This in vivo study was designed to investigate the efficacy of ENMD-2076, a small-molecule kinase inhibitor with activity against the Aurora kinases A and B, and several other tyrosine kinases linked to cancer, including vascular endothelial growth factor receptor 2, cKit, and fibroblast growth factor receptor 1, against murine xenograft models of human colorectal cancer (CRC).

EXPERIMENTAL DESIGN

HT-29 CRC cell line xenografts were treated with either vehicle or ENMD-2076 (100 or 200 mg/kg) orally daily for 28 days. Tumor growth inhibition, dynamic contrast-enhanced magnetic resonance imaging, and (18)FDG-positron emission tomography were conducted to assess the antiproliferative, antiangiogenic, and antimetabolic responses, respectively. Effects on proliferation were also analyzed by immunohistochemical methods. Additionally, three patient-derived xenografts from primary and metastatic sites were treated with ENMD-2076 (100 mg/kg) and assessed for tumor growth inhibition.

RESULTS

In the HT-29 xenograft model, ENMD-2076 induced initial tumor growth inhibition followed by regression. Treatment was associated with significant tumor blanching, indicating a loss of vascularity and substantial reductions in tumor vascular permeability and perfusion as measured by dynamic contrast-enhanced magnetic resonance imaging. Positron emission tomography scanning showed significant decreases in (18)FDG uptake at days 3 and 21 of treatment, which was associated with a marked reduction in proliferation as assessed by Ki-67. All three of the patient-derived xenografts tested were sensitive to treatment with ENMD 2076 as measured by tumor growth inhibition.

CONCLUSIONS

ENMD-2076 showed robust antitumor activity against cell line and patient-derived xenograft models of CRC that is detectable by functional imaging, supporting clinical investigation of this agent in CRC.

Abstract C75: A novel multi-targeted Aurora A and VEGFR2 kinase inhibitor, ENMD-2076, demonstrates synergistic antiproliferative and proapoptotic effects in combination with chemotherapy and trastuzumab in breast cancer cell lines

Introduction: ENMD-2076 is an orally bioavailable small molecule kinase inhibitor with antiproliferative activity via Aurora A kinase inhibition, and antiangiogenic activity via VEGFR2 inhibition. ENMD-2076 is being studied in a phase I clinical trial in advanced solid tumors and has demonstrated a tolerable side-effect profile. Due to the involvement of both Aurora A and angiogenic signaling pathways in breast cancer, we explored the combination of ENMD-2076 and chemotherapy or anti-HER2 therapy against a panel of breast cancer cell lines.

Methods: Breast cancer cell lines were exposed to varying submicromolar concentrations of ENMD-2076 alone and in combination with carboplatin, docetaxel, or trastuzumab (HER2-overexpressing cell lines only). Proliferation was assessed using an SRB assay and analyzed using the Calcusyn program, whereby synergy was defined as a Combination Index of less than 1. FISH was performed to assess Aurora A gene amplification, VEGF concentrations were measured by ELISA, and apoptosis was analyzed using a caspase 3/7 assay.

Results: The combination of ENMD-2076 and carboplatin resulted in synergistic inhibition of proliferation in both HER2 + (BT-474, SKBr3, ZR-75-30) and in triple negative (MDA 231, MDA 468) breast cancer cell lines. Likewise, ENMD-2076 and trastuzumab resulted in robust synergistic growth inhibition in HER2 + breast cancer cell lines. Synergy was not observed with the ENMD-2076 and docetaxel combination. FISH analysis demonstrated that tumor cells were sensitive to ENMD-2076 regardless of levels of Aurora A amplification. An increase in apoptosis that was maximal at 72 hours was observed with single agent ENMD-2076 and the combinations with carboplatin or trastuzumab. Similarly, VEGF concentrations were decreased in response to treatment with ENMD-2076 alone or in combination with the other agents.

Discussion: These in vitro results demonstrate that ENMD-2076 acts synergistically with carboplatin to inhibit proliferation of triple negative breast cancer cell lines, and with both carboplatin and trastuzumab towards HER2+ breast cancer cell lines. This activity is associated with induction of cell death and reduction of VEGF secretion. These data are being confirmed in vivo using both trastuzumab-sensitive and trastuzumab-resistant xenograft models.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C75.

Abstract A156: Mechanisms of resistance to Aurora kinase B inhibitors in leukemia: Development and characterization of in vitro models

Aurora kinase inhibitors are generating great interest as new mitosis targeting drugs in cancer chemotherapy. Whilst these new agents are progressing through clinical trials against both solid and haematological malignancies, knowledge of the molecular factors that influence sensitivity and resistance remains limited. Development of optimal treatment modalities and the design of next generation Aurora inhibitors requires an understanding of processes and pathways of drug sensitivity mechanisms. In this study we report the development and characterisation of an in vitro derived leukaemia model of resistance to the Aurora B inhibitor ZM447439. CCRF-CEM cells were selected for resistance in 4uM ZM447439 and designated CEM/AKB4 cells. Cytotoxicity assays showed that CEM/AKB4 cells were 13.2 fold resistant to ZM44739 compared to parental CEM cells. Resistance was not associated with the multi-drug resistance phenotype and CEM/AKB4 cells showed no cross-resistance to a number of tubulin-targeting mitotic poisons or DNA-damaging agents. The CEM/AKB4 cells remained sensitive to the Aurora kinase A inhibitor, ENMD-2076. Cell cycle analysis revealed that exposure of CEM cells to ZM447439 (0.4–4 uM) caused extensive cell cycle disruption and cell death. In contrast, the cell cycle profiles of CEM/AKB4 cells at the same concentrations of drug were barely altered. Full length sequencing of the Aurora B gene revealed a single point mutation in the kinase domain corresponding to a G160E amino acid substitution. Molecular modelling of drug binding in Aurora B containing this mutation suggested that resistance is mediated by the glutamate substitution preventing formation of an active binding motif for Aurora B inhibitors. Moreover molecular docking of an Aurora B inhibitor with a novel binding motif was unchanged in the mutant enzyme suggesting this drug may abrogate resistance. Aurora kinase B inhibitor resistant cells are a valuable tool for identifying resistance mechanisms and the design of new kinase inhibitors active against Aurora kinase B mutations.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A156.

Design and synthesis of thiazole-5-hydroxamic acids as novel histone deacetylase inhibitors

We have designed and synthesized a series of structurally novel hydroxamic acid-based histone deacetylase (HDAC) inhibitors characterized by a zinc chelating head group attached directly to a thiazole ring. The thiazole ring connects to a piperazine spacer, which is capped with a sulfonamide group. These novel molecules potently inhibit an HDAC enzyme mixture derived from HeLa cervical carcinoma cells and show potent antiproliferative activity against the breast cancer cell line MCF7.

DJ-1, a novel regulator of the tumor suppressor PTEN

The phosphatidylinositol 3' kinase (PI3'K) pathway, which regulates cell survival, is antagonized by the PTEN tumor suppressor. The regulation of PTEN is unclear. A genetic screen of Drosophila gain-of-function mutants identified DJ-1 as a suppressor of PTEN function. In mammalian cells, DJ-1 underexpression results in decreased phosphorylation of PKB/Akt, while DJ-1 overexpression leads to hyperphosphorylation of PKB/Akt and increased cell survival. In primary breast cancer samples, DJ-1 expression correlates negatively with PTEN immunoreactivity and positively with PKB/Akt hyperphosphorylation. In 19/23 primary non-small cell lung carcinoma samples, DJ-1 expression was increased compared to paired nonneoplastic lung tissue, and correlated positively with relapse incidence. DJ-1 is thus a key negative regulator of PTEN that may be a useful prognostic marker for cancer.

Soluble Interleukin-13Rα2 Decoy Receptor Inhibits Hodgkin’s Lymphoma Growth in Vitro and in Vivo

Recent studies have demonstrated that the malignant Reed-Sternberg cells of Hodgkin's lymphoma (HL) secrete and are responsive to interleukin (IL)-13. We hypothesized that overexpression of a soluble IL-13 decoy receptor (sIL-13Ralpha2) via adenoviral-mediated gene transfer would inhibit IL-13-induced Reed-Sternberg cell proliferation. Western blot and ELISA analysis verified expression of sIL-13Ralpha2 in cell lysates and supernatants of AdsIL-13Ralpha2-transduced COS-7 cells. Treatment of two IL-13-responsive HL-derived cell lines, HDLM-2 and L-1236, with AdsIL-13Ralpha2-conditioned medium, resulted in the inhibition of cell proliferation, and down-regulated the phosphorylation of signal transducer and activator of transcription 6 (STAT6), an important mediator of IL-13 signaling. i.v. delivery of AdsIL-13Ralpha2 in NOD/SCID mice with s.c. implanted HDLM-2 cells delayed tumor onset and growth while enhancing survival compared with control mice. Intratumoral administration of AdsIL-13Ralpha2 led to the regression or stabilization of established tumors and was associated with diminished STAT6 phosphorylation. Our data demonstrate that AdsIL-13Ralpha2 can suppress HL growth in vitro and in vivo.

The B7 family member B7-H3 preferentially down-regulates T helper type 1-mediated immune responses

We investigated the in vivo function of the B7 family member B7-H3 (also known as B7RP-2) by gene targeting. B7-H3 inhibited T cell proliferation mediated by antibody to T cell receptor or allogeneic antigen-presenting cells. B7-H3-deficient mice developed more severe airway inflammation than did wild-type mice in conditions in which T helper cells differentiated toward type 1 (T(H)1) rather than type 2 (T(H)2). B7-H3 expression was consistently enhanced by interferon-gamma but suppressed by interleukin 4 in dendritic cells. B7-H3-deficient mice developed experimental autoimmune encephalomyelitis several days earlier than their wild-type littermates, and accumulated higher concentrations of autoantibodies to DNA. Thus, B7-H3 is a negative regulator that preferentially affects T(H)1 responses.

Overexpression of AKT2/protein kinase Bbeta leads to up-regulation of beta1 integrins, increased invasion, and metastasis of human breast and ovarian cancer cells

To determine how AKT2 might contribute to tumor cell progression, a full-length, wild-type, human AKT2/protein kinase B (PKB)beta cDNA was transfected into a panel of eight human breast and ovarian cancer cells. AKT2 transfectants demonstrated increased adhesion and invasion through collagen IV because of up-regulation of beta1 integrins. In addition, AKT2 cells were more metastatic than control cells in vivo. Increased invasion by AKT2 was blocked by preincubation with an anti-beta1 integrin function blocking antibody, exposure to wortmannin, and by expression of phosphatase and tensin homologue tumor suppressor (PTEN). Confocal microscopy performed on transfected human breast cancer cells showed that unlike AKT1, AKT2 protein predominantly localized adjacent to the collagen IV matrix during cellular attachment. Overexpression of AKT2, but not AKT1 or AKT3, was sufficient to duplicate the invasive effects of phosphoinositide 3-OH kinase (PI3-K) transfected in breast cancer cells. Furthermore, expression of kinase dead AKT2(181 amino acid methionine [M]), and not kinase dead AKT1(179M) or AKT3(177M), was capable of blocking invasion induced by either human epidermal growth factor receptor-2 (HER-2) overexpression or by activation of PI3-K. Taken together, these data indicate that AKT2 mediates PI3-K-dependent effects on adhesion, motility, invasion, and metastasis in vivo.

Fusion of the CH1 domain of IgG1 to epidermal growth factor (EGF) prolongs its retention in the blood but does not increase tumor uptake

An expression vector (pJW4) for a human epidermal growth factor (hEGF)-CH1 fusion protein was constructed by fusing the gene for hEGF with the gene for CH1 of murine IgG1 with/without a peptide linker sequence [(GGGGS)3] and inserting the recombinant gene into vector pGEX2T. Expression vector pGEX2T was transfected into E. coli (BL-21) and hEGF-CH1 expressed by induction of the lac Iq promotor with 50 microM isopropyl beta-D-thiogalactopyranoside (IPTG). hEGF- CH1 fused to glutathione S-transferase (GST) was isolated and purified by affinity chromatography. GST was cleaved using thrombin. SDS-PAGE demonstrated a protein with the expected M(r) (18 kDa) positive for hEGF by Western blot. hEGF-linker-CH1 exhibited preserved binding to A431 (2-3 x 10(6) EGFR/cell) and MDA-MB-468 breast cancer cells (1-2 x 10(6) EGFR/cell). hEGF-CH1 without the linker exhibited poor receptor binding. hEGF-linker-CH1 also exhibited strong binding to soluble EGFR equivalent to that of hEGF. The tumor and normal tissue distribution of hEGF-linker-CH1 labeled with 123I was compared with 123 I-hEGF at 24 h after i.v. injection to mice implanted with s.c. MDA-MB-468 xenografts. Fusion of hEGF with CH1 increased its retention in the blood 14-fold but did not significantly increase tumor uptake. Tumor/blood ratios were higher for hEGF than for hEGF-linker-CH1. We conclude that hEGF is more attractive than hEGF-linker-CH1 for imaging EGFR-positive tumors.

Probing the surface of eukaryotic cells using combinatorial toxin libraries

The success of proteomics hinges in part on the development of approaches able to map receptors on the surface of cells. One strategy to probe a cell surface for the presence of internalized markers is to make use of Shiga-like toxin 1 (SLT-1), a ribosome-inactivating protein that kills eukaryotic cells [1, 2]. SLT-1 binds to the glycolipid globotriaosylceramide [3, 4], which acts as a shuttle, allowing the toxin to be imported and routed near ribosomes. We investigated the use of SLT-1 as a structural template to create combinatorial libraries of toxin variants with altered receptor specificity. Since all SLT-1 variants retain their toxic function, this property served as a search engine enabling us to identify mutants from these libraries able to kill target cells expressing internalizable receptors. Random mutations were introduced in two discontinuous loop regions of the SLT-1 receptor binding subunit. Minimal searches from screening 600 bacterial colonies randomly picked from an SLT-1 library identified toxin mutants able to kill cell lines resistant to the wild-type toxin. One such mutant toxin was shown to bind to a new receptor on these cell lines by flow cytometry. Toxin libraries provide a strategy to delineate the spectrum of receptors on eukaryotic cells.

Analysis of binding of the family 2a carbohydrate-binding module from Cellulomonas fimi xylanase 10A to cellulose: specificity and identification of functionally important amino acid residues

The family 2a carbohydrate-binding module (CBM2a) of xylanase 10A from Cellulomonas fimi binds to the crystalline regions of cellulose. It does not share binding sites with the N-terminal family 4 binding module (CBM4-1) from the cellulase 9B from C.fimi, a module that binds strictly to soluble sugars and amorphous cellulose. The binding of CBM2a to crystalline matrices is mediated by several residues on the binding face, including three prominent, solvent-exposed tryptophan residues. Binding to crystalline cellulose was analyzed by making a series of conservative (phenylalanine and tyrosine) and non-conservative substitutions (alanine) of each solvent-exposed tryptophan (W17, W54 and W72). Other residues on the binding face with hydrogen bonding potential were substituted with alanine. Each tryptophan plays a different role in binding; a tryptophan is essential at position 54, a tyrosine or tryptophan at position 17 and any aromatic residue at position 72. Other residues on the binding face, with the exception of N15, are not essential determinants of binding affinity. Given the specificity of CBM2a, the structure of crystalline cellulose and the dynamic nature of the binding of CBM2a, we propose a model for the interaction between the polypeptide and the crystalline surface.

Shiga-like toxin-1 receptor on human breast cancer, lymphoma, and myeloma and absence from CD34(+) hematopoietic stem cells: implications for ex vivo tumor purging and autologous stem cell transplantation

The ribosome-inactivating protein, Shiga-like toxin-1 (SLT-1), targets cells that express the glycolipid globotriaosylceramide (CD77) on their surface. CD77 and/or SLT-1 binding was detected by flow cytometry and immunocytochemistry on lymphoma and breast cancer cells recovered from biopsies of primary human cancers as well as on B cells or plasma cells present in blood/bone marrow samples of multiple myeloma patients. Breast cancer cell lines also expressed receptors for the toxin and were sensitive to SLT-1. Treatment of primary B lymphoma, B-cell chronic lymphocytic leukemia, and myeloma B or plasma cells with SLT-1-depleted malignant B cells by 3- to 28-fold, as measured by flow cytometry. Depletion of myeloma plasma cells was confirmed using a cellular limiting dilution assay followed by reverse transcriptase-polymerase chain reaction analysis of clonotypic IgH transcripts, which showed a greater than 3 log reduction in clonotypic myeloma cells after SLT-1 treatment. Receptors for the toxin were not detected on human CD34(+) hematopoietic progenitor cells (HPC). HPC were pretreated with a concentration of SLT-1 known to purge primary malignant B cells and cultured for 6 days. The number of HPC was comparable in toxin-treated and untreated cultures. HPC were functionally intact as well. Colony-forming units (CFU) were present at an identical frequency in untreated and SLT-1 pretreated cultures, confirming that CFU escape SLT-1 toxicity. The results suggest the ex vivo use of SLT-1 in purging SLT-1 receptor-expressing malignant cells from autologous stem cell grafts of breast cancer, lymphoma, and myeloma patients.

Probing the role of tryptophan residues in a cellulose-binding domain by chemical modification

The cellulose-binding domain (CBDCex) of the mixed function glucanase-xylanase Cex from Cellulomonas fimi contains five tryptophans, two of which are located within the beta-barrel structure and three exposed on the surface (Xu GY et al., 1995, Biochemistry 34:6993-7009). Although all five tryptophans can be oxidized by N-bromosuccinimide (NBS), stopped-flow measurements show that three tryptophans react faster than the other two. NMR analysis during the titration of CBDCex with NBS shows that the tryptophans on the surface of the protein are fully oxidized before there is significant reaction with the two buried tryptophans. Additionally, modification of the exposed tryptophans does not affect the conformation of the backbone of CBDCex, whereas complete oxidation of all five tryptophans denatures the polypeptide. The modification of the equivalent of one and two tryptophans by NBS reduces binding of CBDCex to cellulose by 70% and 90%, respectively. This confirms the direct role of the exposed aromatic residues in the binding of CBDCex to cellulose. Although adsorption to cellulose does afford some protection against NBS, as evidenced by the increased quantity of NBS required to oxidize all of the tryptophan residues, the polypeptide can still be oxidized completely when adsorbed. This suggests that, whereas the binding appears to be irreversible overall [Ong E et al., 1989, Bio/Technology 7:604-607], each of the exposed tryptophans interacts reversibly with cellulose.

A Density Functional Study of Active Site Models for Xanthine Oxidase

The suggestion that hydroxide is coordinated to the oxidised molybdenum site in xanthine oxidase (XnO) is tested theoretically by computing the structures of a range of four-, five-, and six-coordinate active site models. The local density approximation of density functional theory has been used with the two experimentally verified singly bonded sulfur ligands modeled by both dithiolene, [SRCCRS](2-) (R = H and CH(3)), and thiolate, [CH(3)S](-) groups. Both ligand types give virtually identical results for analogous species. Based on a comparison of the computed M-L distances and those reported in recent EXAFS studies, it is concluded that both four- and six-coordination are unlikely since the optimized Mo-S contacts are too short or too long respectively. Of the five-coordinate MoOS(SR)(2)X models, the ones with X = [OH](-) give computed M-L bond lengths in excellent agreement with the reported EXAFS data while X = H(2)O, NH(3), [CH(3)S](-), and O(2-) give relatively poor agreement. The theoretical results imply that the active site represents a stable, preferred geometry rather than some imposed entatic state.

Identification of an essential tyrosyl residue in the binding site of Schizophyllum commune xylanase A

Ultraviolet difference spectroscopy studies with the Schizophyllum commune xylanase in the presence of inhibitors and substrates indicated the participation of one or more tyrosyl residues in the binding of substrates to xylanase. Chemical modification experiments with group-specific reagents in the absence and presence of substrates confirmed the essential role of a tyrosyl residue in substrate binding while discounting the participation of tryptophan. A fourth-derivative absorbance spectroscopic method was developed to facilitate the quantitation of modified tyrosyl and tryptophanyl residues. This analysis showed that two tyrosyl residues of the xylanase are modified by tetranitromethane in the absence of substrate with the concomitant loss of catalytic activity. Protection of the xylanase with xylooligosaccharides resulted in the nitration of only one residue, and such enzyme derivatives retained 94% catalytic activity. Differential modification of the xylanase with tetranitromethane generated an enzyme derivative with the characteristic absorbance at 428 nm of 3-nitrotyrosine. Amino acid analysis and N-terminal sequencing of peptides with strong absorbance at 428 nm isolated from the protease-digested modified enzyme by reverse-phase HPLC identified the essential residue as Tyr97. Alignment of the S. commune xylanase amino acid sequence with those of the 18 other known family G xylanases revealed that Tyr97 is a conserved aromatic residue, further suggesting its essential role in substrate binding.

Quantitation of tryptophan and tyrosine residues in proteins by fourth-derivative spectroscopy

A method for quantitation of tryptophan and tyrosine residues in proteins by fourth-derivative ultraviolet spectroscopy is described. The direct quantitation of tryptophan is based on measurement of a tryptophan-specific trough at 292 nm in the fourth derivative of a protein's ultraviolet absorption spectrum. A peak overlapping the tryptophan and tyrosine signatures at A282 is used to quantify tyrosine content. The procedure is accomplished by adding back known quantities of tyrosine to the sample and subtracting the contribution of tryptophan to the A282 peak to obtain an internal calibration curve. This curve is linear, with the ordinate axis intercept relating the quantity (residues/mole) of tyrosine present in the protein. This nondestructive and facile method was used to successfully predict the tryptophan and tyrosine content of a variety of well-characterized proteins. The utility of this method was further demonstrated by resolving the number of tryptophan and tyrosine residues in proteins oxidized by N-bromosuccinimide.

Identification of a glutamate residue at the active site of xylanase A from Schizophyllum commune

The xylanase A (endo-1,4-beta-D-xylan xylanhydrolase) of the basidiomycete Schizophyllum commune was treated with the powerful carboxylate-modifying reagent 1-(4-azonia-4,4-dimethyl-pentyl)-3-ethylcarbodiimide iodide (EAC) in the presence of substrate. This treatment was followed by complete inactivation of the enzyme with [14c]EAC after the removal of excess reagent and protecting ligand. The inactivated enzyme was digested with endoproteinase Arg-C or trypsin, and peptides were separated and purified using reverse-phase high-performance liquid chromatography. Following sub-digestion of individual radioactive peptides with staphylococcal V8 protease and endoproteinase Lys-C, amino acid composition analysis and sequencing analysis revealed that the [14C]EAC label was bound exclusively to Glu87. Comparison of the primary sequences of related xylanase with that of xylanase A revealed that Glu87 is a highly conserved residue. Based on this similarity and the mechanism of carbodiimide action, Glu87 is proposed to act as the nucleophile in the catalytic mechanism of xylanase A. The possible environment of the putative catalytic glutamate residue was explored using hydrophobic-cluster analysis and secondary-structure prediction based on the primary sequence of xylanase.

Action pattern of xylo-oligosaccharide hydrolysis by Schizophyllum commune xylanase A

The endo-1,4-beta-xylanase of the basidiomycete Schizophyllum commune, designated xylanase A, was studied to determine its action pattern, rates of reaction and bond-cleavage frequencies on xylo-oligomer and xylo-alditol substrates ranging in degree of polymerization (Dp) from xylotriose (X3) to xyloheptaose (X7). An HPLC method using a Dionex HPLC and Carbopac PA1 ion-exchange column with pulsed amperometric detection was developed to quantify both substrate loss and increase of products. Xylanase A had no detectable activity on xylobiose (X2) and low activity on xylotriose and xylotetraose (X4) but cleaved X5-X7 rapidly with X2 and X3 as major products. Initial rate data from hydrolyses of individual oligomers at 25 degrees C and pH 5.81 indicated that the Michaelis constant (Km) decreased with increasing chain length (n) of oligomer. Turnover number (kcat) increased with chain length up to n = 7 suggesting that the specificity region of xylanase A spans about seven xylose units. Bond-cleavage frequencies obtained from xylanase A hydrolysis of xylo-alditols indicated a strong preference for internal linkages of the xylose chain. The action pattern of xylanase A on reduced substrates suggests that the catalytic site is located assymetrically within the binding cleft of the enzyme.