John Frederick Boylan

Phase I Study of RO4929097, a Gamma Secretase Inhibitor of Notch Signaling, in Patients With Refractory Metastatic or Locally Advanced Solid Tumors

PURPOSE To determine the maximum-tolerated dose (MTD) and assess safety, pharmacokinetics, pharmacodynamics, and evidence of antitumor activity of RO4929097, a gamma secretase inhibitor of Notch signaling in patients with advanced solid malignancies. PATIENTS AND METHODS Patients received escalating doses of RO4929097 orally on two schedules: (A) 3 consecutive days per week for 2 weeks every 3 weeks; (B) 7 consecutive days every 3 weeks. To assess reversible CYP3A4 autoinduction, the expanded part of the study tested three dosing schedules: (B) as above; modified A, 3 consecutive d/wk for 3 weeks; and (C) continuous daily dosing. Positron emission tomography scans with [(18)F]fluorodeoxyglucose (FDG-PET) were used to assess tumor metabolic effects. RESULTS Patients on schedule A (n = 58), B (n = 47), and C (n = 5; expanded cohort) received 302 cycles of RO4929097. Common grade 1 to 2 toxicities were fatigue, thrombocytopenia, fever, rash, chills, and anorexia. Transient grade 3 hypophosphatemia (dose-limiting toxicity, one patient) and grade 3 pruritus (two patients) were observed at 27 mg and 60 mg, respectively; transient grade 3 asthenia was observed on schedule A at 80 mg (one patient). Tumor responses included one partial response in a patient with colorectal adenocarcinoma with neuroendocrine features, one mixed response (stable disease) in a patient with sarcoma, and one nearly complete FDG-PET response in a patient with melanoma. Effect on CYP3A4 induction was observed. CONCLUSION RO4929097 was well tolerated at 270 mg on schedule A and at 135 mg on schedule B; the safety of schedule C has not been fully evaluated. Further studies are warranted on the basis of a favorable safety profile and preliminary evidence of clinical antitumor activity.

Preclinical Profile of a Potent γ-Secretase Inhibitor Targeting Notch Signaling with In vivo Efficacy and Pharmacodynamic Properties

Notch signaling is an area of great interest in oncology. RO4929097 is a potent and selective inhibitor of gamma-secretase, producing inhibitory activity of Notch signaling in tumor cells. The RO4929097 IC50 in cell-free and cellular assays is in the low nanomolar range with >100-fold selectivity with respect to 75 other proteins of various types (receptors, ion channels, and enzymes). RO4929097 inhibits Notch processing in tumor cells as measured by the reduction of intracellular Notch expression by Western blot. This leads to reduced expression of the Notch transcriptional target gene Hes1. RO4929097 does not block tumor cell proliferation or induce apoptosis but instead produces a less transformed, flattened, slower-growing phenotype. RO4929097 is active following oral dosing. Antitumor activity was shown in 7 of 8 xenografts tested on an intermittent or daily schedule in the absence of body weight loss or Notch-related toxicities. Importantly, efficacy is maintained after dosing is terminated. Angiogenesis reverse transcription-PCR array data show reduced expression of several key angiogenic genes. In addition, comparative microarray analysis suggests tumor cell differentiation as an additional mode of action. These preclinical results support evaluation of RO4929097 in clinical studies using an intermittent dosing schedule. A multicenter phase I dose escalation study in oncology is under way.

Identification of the MEK1(F129L) Activating Mutation as a Potential Mechanism of Acquired Resistance to MEK Inhibition in Human Cancers Carrying the B-RafV600E Mutation

Although targeting the Ras/Raf/MEK pathway remains a promising anticancer strategy, mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors in clinical development are likely to be limited in their ability to produce durable clinical responses due to the emergence of acquired drug resistance. To identify potential mechanisms of such resistance, we established MEK inhibitor-resistant clones of human HT-29 colon cancer cells (HT-29R cells) that harbor the B-RafV600E mutation. HT-29R cells were specifically resistant to MEK inhibition in vitro and in vivo, with drug-induced elevation of MEK/ERK and their downstream targets primarily accountable for drug resistance. We identified MEK1(F129L) mutation as a molecular mechanism responsible for MEK/ERK pathway activation. In an isogenic cell system that extended these findings into other cancer cell lines, the MEK1(F129L) mutant exhibited higher intrinsic kinase activity than wild-type MEK1 [MEK1(WT)], leading to potent activation of ERK and downstream targets. The MEK1(F129L) mutation also strengthened binding to c-Raf, suggesting an underlying mechanism of higher intrinsic kinase activity. Notably, the combined use of Raf and MEK inhibitors overcame the observed drug resistance and exhibited greater synergy in HT-29R cells than the drug-sensitive HT-29 parental cells. Overall, our findings suggested that mutations in MEK1 can lead to acquired resistance in patients treated with MEK inhibitors and that a combined inhibition of Raf and MEK may be potentially useful as a strategy to bypass or prevent drug resistance in the clinic.

BRAFV600E Negatively Regulates the AKT Pathway in Melanoma Cell Lines

Cross-feedback activation of MAPK and AKT pathways is implicated as a resistance mechanism for cancer therapeutic agents targeting either RAF/MEK or PI3K/AKT/mTOR. It is thus important to have a better understanding of the molecular resistance mechanisms to improve patient survival benefit from these agents. Here we show that BRAFV600E is a negative regulator of the AKT pathway. Expression of BRAFV600E in NIH3T3 cells significantly suppresses MEK inhibitor (RG7167) or mTORC1 inhibitor (rapamycin) induced AKT phosphorylation (pAKT) and downstream signal activation. Treatment-induced pAKT elevation is found in BRAF wild type melanoma cells but not in a subset of melanoma cell lines harboring BRAFV600E. Knock-down of BRAFV600E in these melanoma cells elevates basal pAKT and downstream signals, whereas knock-down of CRAF, MEK1/2 or ERK1/2 or treatment with a BRAF inhibitor have no impact on pAKT. Mechanistically, we show that BRAFV600E interacts with rictor complex (mTORC2) and regulates pAKT through mTORC2. BRAFV600E is identified in mTORC2 after immunoprecipitation of rictor. Knock-down of rictor abrogates BRAFV600E depletion induced pAKT. Knock-down of BRAFV600E enhances cellular enzyme activity of mTORC2. Aberrant activation of AKT pathway by PTEN loss appears to override the negative impact of BRAFV600E on pAKT. Taken together, our findings suggest that in a subset of BRAFV600E melanoma cells, BRAFV600E negatively regulates AKT pathway in a rictor-dependent, MEK/ERK and BRAF kinase-independent manner. Our study reveals a novel molecular mechanism underlying the regulation of feedback loops between the MAPK and AKT pathways.

The novel gamma secretase inhibitor RO4929097 reduces the tumor initiating potential of melanoma.

Several reports have demonstrated a role for aberrant NOTCH signaling in melanoma genesis and progression, prompting us to explore if targeting this pathway is a valid therapeutic approach against melanoma. We targeted NOTCH signaling using RO4929097, a novel inhibitor of gamma secretase, which is a key component of the enzymatic complex that cleaves and activates NOTCH. The effects of RO4929097 on the oncogenic and stem cell properties of a panel of melanoma cell lines were tested both in vitro and in vivo, using xenograft models. In human primary melanoma cell lines, RO4929097 decreased the levels of NOTCH transcriptional target HES1. This was accompanied by reduced proliferation and impaired ability to form colonies in soft agar and to organize in tridimensional spheres. Moreover, RO4929097 affected the growth of human primary melanoma xenograft in NOD/SCID/IL2gammaR-/- mice and inhibited subsequent tumor formation in a serial xenotransplantation model, suggesting that inhibition of NOTCH signaling suppresses the tumor initiating potential of melanoma cells. In addition, RO4929097 decreased tumor volume and blocked the invasive growth pattern of metastatic melanoma cell lines in vivo. Finally, increased gene expression of NOTCH signaling components correlated with shorter post recurrence survival in metastatic melanoma cases. Our data support NOTCH inhibition as a promising therapeutic strategy against melanoma.

High tumor levels of IL6 and IL8 abrogate preclinical efficacy of the γ-secretase inhibitor, RO4929097

Interest continues to build around the early application of patient selection markers to prospectively identify patients likely to show clinical benefit from cancer therapies. Hypothesis generation and clinical strategies often begin at the preclinical stage where responder and nonresponder tumor cell lines are first identified and characterized. In the present study, we investigate the drivers of in vivo resistance to the γ‐secretase inhibitor RO4929097. Beginning at the tissue culture level, we identified apparent IL6 and IL8 expression differences that characterized tumor cell line response to RO4929097. We validated this molecular signature at the preclinical efficacy level identifying additional xenograft models resistant to the in vivo effects of RO4929097. Our data suggest that for IL6 and IL8 overexpressing tumors, RO4929097 no longer impacts angiogenesis or the infiltration of tumor associated fibroblasts. These preclinical data provide a rationale for preselecting patients possessing low levels of IL6 and IL8 prior to RO4929097 dosing. Extending this hypothesis into the clinic, we monitored patient IL6 and IL8 serum levels prior to dosing with RO4929097 during Phase I. Interestingly, the small group of patients deriving some type of clinical benefit from RO4929097 presented with low baseline levels of IL6 and IL8. Our data support the continued investigation of this patient selection marker for RO4929097 and other types of Notch inhibitors undergoing early clinical evaluation.

Inactivation of Mirk/Dyrk1B Kinase Targets Quiescent Pancreatic Cancer Cells

A major problem in the treatment of cancer arises from quiescent cancer cells that are relatively insensitive to most chemotherapeutic drugs and radiation. Such residual cancer cells can cause tumor regrowth or recurrence when they reenter the cell cycle. Earlier studies showed that levels of the serine/theronine kinase Mirk/dyrk1B are elevated up to 10-fold in quiescent G0 tumor cells. Mirk uses several mechanisms to block cell cycling, and Mirk increases expression of antioxidant genes that decrease reactive oxygen species (ROS) levels and increase quiescent cell viability. We now show that a novel small molecule Mirk kinase inhibitor blocked tumor cells from undergoing reversible arrest in a quiescent G0 state and enabled some cells to exit quiescence. The inhibitor increased cycling in Panc1, AsPc1, and SW620 cells that expressed Mirk, but not in HCT116 cells that did not. Mirk kinase inhibition elevated ROS levels and DNA damage detected by increased phosphorylation of the histone protein H2AX and by S-phase checkpoints. The Mirk kinase inhibitor increased cleavage of the apoptotic proteins PARP and caspase 3, and increased tumor cell kill several-fold by gemcitabine and cisplatin. A phenocopy of these effects occurred following Mirk depletion, showing drug specificity. In previous studies Mirk knockout or depletion had no detectable effect on normal tissue, suggesting that the Mirk kinase inhibitor could have a selective effect on cancer cells expressing elevated levels of Mirk kinase. Mol Cancer Ther; 10(11); 2104–14. ©2011 AACR.

Identification of novel, potent and selective inhibitors of Polo-like kinase 1.

A series of pyrimidodiazepines was identified as potent Polo-like kinase 1 (PLK1) inhibitors. The synthesis and SAR are discussed. The lead compound 7 (RO3280) has potent inhibitory activity against PLK1, good selectivity against other kinases, and excellent in vitro cellular potency. It showed strong antitumor activity in xenograft mouse models.

Abstract B130: BRAFV600E negatively regulates the PI3K/AKT pathway in melanoma cell lines.

The BRAFV600E mutation is frequently found in human cancers (∼ 8%), with the highest incidence in melanoma (60–70%). Small molecules targeting BRAFV600E or MEK have shown significant clinical activity in melanoma patients carrying the BRAFV600E mutation. However, rapid acquisition of drug resistance is an emerging problem that limits patient survival benefits from these agents. MEK inhibition abrogates the intrinsic negative feedback on both RAS/RAF/MEK and PI3K/AKT pathways leading to induction of MEK and AKT phosphorylation. Induction of MEK and AKT phosphorylation may confer resistance and limit the clinical activity of MEK inhibitors. In this study, we investigated the molecular mechanisms of crosstalk between the two pathways. In NIH3T3 cells, engineered expression of BRAFV600E activates the MEK/ERK pathway leading to a significant growth advantage compared to control cells both in vitro and in vivo. MEK inhibition in NIH3T3 control cells strongly induces AKT phosphorylation (Thr308 and Ser473) and downstream signalling, whereas in NIH3T3 cells expressing BRAFV600E the AKT phosphorylation is significantly reduced. Knockdown of BRAFV600E restores MEK inhibition-induced elevation of AKT phosphorylation (pAKT). In the melanoma cell line with wild-type BRAF, MEK inhibition also induces pAKT (Thr308 and Ser473), whereas in the melanoma cell lines harbouring BRAFV600E, MEK inhibition-induced pAKT is not seen. Knockdown of BRAFV600E in those melanoma cell lines significantly elevates basal pAKT levels. These results suggest that BRAFV600E negatively regulates AKT pathway activation. In BRAFV600E melanoma cell lines, knockdown of MEK1/2 or ERK1/2 and inhibition of BRAF by RAF inhibitor have minimal effects on pAKT, suggesting that BRAFV600E suppresses AKT activation independent of the MEK/ERK downstream signals and its kinase activity. Furthermore, the elevation of pAKT(Thr308 and Ser473) caused by BRAFV600E knockdown can be abolished by Rictor, but not Raptor, knockdown, suggesting that the pAKT induction is Rictor dependent. Lack of pAKT induction in cells carrying BRAFV600E is associated with co-purification of Rictor-mTOR and Raptor-mTOR complexes, which is rarely seen in cells with wild type BRAF. Taken together, our data demonstrate that in BRAFV600E melanoma cells, BRAFV600E negatively regulates AKT phosphorylation in a Rictor-dependent, MEK/ERK and kinase-independent manner, possibly via altering Rictor-mTOR complex formation. This study reveals a novel molecular mechanism of crosstalk between the RAF/MEK and the PI3K/AKT pathways, suggesting an underlying mechanism whereby a subset of BRAFV600E melanoma cells are exquisitely sensitive to MEK inhibition. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B130.

Abstract 5036: Activating MEK1(F129L) mutation as a potential mechanism of acquired resistance to MEK inhibition in human cancers carrying the B-RafV600E mutation

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Targeting the Ras/Raf/MEK pathway represents a promising anticancer strategy. The clinical development of MEK inhibitors, similar to other highly selective targeted agents, is expected to have limited durable clinical response due to the emergence of drug acquired resistance. To identify potential mechanisms underlying such resistance, we established MEK inhibitor-resistant clones (HT-29R) from a human colorectal cancer cell line HT-29 harboring the B-Raf V600E mutation. HT-29R are resistant to MEK inhibition under both in vitro and in vivo growth conditions. Drug-induced feedback activation of MEK/ERK and downstream targets were found primarily accountable for the resistance. Moreover, we identified the MEK1(F129L) mutation as a molecular mechanism responsible for pathway activation. In an isogenic cell system and extending into other cancer cell lines, the MEK1(F129L) mutant exhibits higher intrinsic kinase activity than wild type (WT) MEK1, leading to a significant activation of ERK and downstream targets confering resistance to MEK inhibition. The MEK1(F129L) mutation showed stronger binding to c-Raf which suggests an underlying mechanism of the higher kinase activity of the MEK1(F129L). Importantly, the combination of Raf and MEK inhibitors overcame resistance and exhibited greater synergy in HT-29R as compared to HT-29S. This study suggests MEK1 mutation could be a potential mechanism of drug acquired resistance emerging in MEK inhibitor-treated cancer patients and should be monitored in the clinic. Combined inhibition of Raf and MEK represents a potential therapeutic strategy to overcome the resistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5036. doi:10.1158/1538-7445.AM2011-5036