Edward M. Chan

Efficacy and Safety of Abemaciclib, an Inhibitor of CDK4 and CDK6, for Patients with Breast Cancer, Non-Small Cell Lung Cancer, and Other Solid Tumors.

UNLABELLED We evaluated the safety, pharmacokinetic profile, pharmacodynamic effects, and antitumor activity of abemaciclib, an orally bioavailable inhibitor of cyclin-dependent kinases (CDK) 4 and 6, in a multicenter study including phase I dose escalation followed by tumor-specific cohorts for breast cancer, non-small cell lung cancer (NSCLC), glioblastoma, melanoma, and colorectal cancer. A total of 225 patients were enrolled: 33 in dose escalation and 192 in tumor-specific cohorts. Dose-limiting toxicity was grade 3 fatigue. The maximum tolerated dose was 200 mg every 12 hours. The most common possibly related treatment-emergent adverse events involved fatigue and the gastrointestinal, renal, or hematopoietic systems. Plasma concentrations increased with dose, and pharmacodynamic effects were observed in proliferating keratinocytes and tumors. Radiographic responses were achieved in previously treated patients with breast cancer, NSCLC, and melanoma. For hormone receptor-positive breast cancer, the overall response rate was 31%; moreover, 61% of patients achieved either response or stable disease lasting ≥6 months. SIGNIFICANCE Abemaciclib represents the first selective inhibitor of CDK4 and CDK6 with a safety profile allowing continuous dosing to achieve sustained target inhibition. This first-in-human experience demonstrates single-agent activity for patients with advanced breast cancer, NSCLC, and other solid tumors. Cancer Discov; 6(7); 740-53. ©2016 AACR.See related commentary by Lim et al., p. 697This article is highlighted in the In This Issue feature, p. 681.

Semi-Mechanistic Pharmacokinetic/Pharmacodynamic Modeling of the Antitumor Activity of LY2835219, a New Cyclin-Dependent Kinase 4/6 Inhibitor, in Mice Bearing Human Tumor Xenografts

Purpose: Selective inhibition of cyclin-dependent kinases 4 and 6 (CDK4/6) represents a promising therapeutic strategy. However, despite documented evidence of clinical activity, limited information is available on the optimal dosing strategy of CDK4/6 inhibitors. Here, we present an integrated semi-mechanistic pharmacokinetic/pharmacodynamic model to characterize the quantitative pharmacology of LY2835219, a CDK4/6 inhibitor, in xenograft tumors. Experimental Design: LY2835219 plasma concentrations were connected to CDK4/6 inhibition and cell-cycle arrest in colo-205 human colorectal xenografts by incorporating the biomarkers, phospho-(ser780)-Rb, topoisomerase II α, and phosphohistone H3, into a precursor-dependent transit compartment model. This biomarker model was then connected to tumor growth inhibition (TGI) by: (i) relating the rate of tumor growth to mitotic cell density, and (ii) incorporating a concentration-dependent mixed cytostatic/cytotoxic effect driving quiescence and cell death at high doses. Model validation was evaluated by predicting LY2835219-mediated antitumor effect in A375 human melanoma xenografts. Results: The model successfully described LY2835219-mediated CDK4/6 inhibition, cell-cycle arrest, and TGI in colo-205, and was validated in A375. The model also demonstrated that a chronic dosing strategy achieving minimum steady-state trough plasma concentrations of 200 ng/mL is required to maintain durable cell-cycle arrest. Quiescence and cell death can be induced by further increasing LY2835219 plasma concentrations. Conclusions: Our model provides mechanistic insight into the quantitative pharmacology of LY2835219 and supports the therapeutic dose and chronic dosing strategy currently adopted in clinical studies. Clin Cancer Res; 20(14); 3763–74. ©2014 AACR.

The CDK4/6 Inhibitor LY2835219 Overcomes Vemurafenib Resistance Resulting from MAPK Reactivation and Cyclin D1 Upregulation

B-RAF selective inhibitors, including vemurafenib, were recently developed as effective therapies for melanoma patients with B-RAF V600E mutation. However, most patients treated with vemurafenib eventually develop resistance largely due to reactivation of MAPK signaling. Inhibitors of MAPK signaling, including MEK1/2 inhibitor trametinib, failed to show significant clinical benefit in patients with acquired resistance to vemurafenib. Here, we describe that cell lines with acquired resistance to vemurafenib show reactivation of MAPK signaling and upregulation of cyclin D1 and are sensitive to inhibition of LY2835219, a selective inhibitor of cyclin-dependent kinase (CDK) 4/6. LY2835219 was demonstrated to inhibit growth of melanoma A375 tumor xenografts and delay tumor recurrence in combination with vemurafenib. Furthermore, we developed an in vivo vemurafenib-resistant model by continuous administration of vemurafenib in A375 xenografts. Consistently, we found that MAPK is reactivated and cyclin D1 is elevated in vemurafenib-resistant tumors, as well as in the resistant cell lines derived from these tumors. Importantly, LY2835219 exhibited tumor growth regression in a vemurafenib-resistant model. Mechanistic analysis revealed that LY2835219 induced apoptotic cell death in a concentration-dependent manner in vemurafenib-resistant cells whereas it primarily mediated cell-cycle G1 arrest in the parental cells. Similarly, RNAi-mediated knockdown of cyclin D1 induced significantly higher rate of apoptosis in the resistant cells than in parental cells, suggesting that elevated cyclin D1 activity is important for the survival of vemurafenib-resistant cells. Altogether, we propose that targeting cyclin D1–CDK4/6 signaling by LY2835219 is an effective strategy to overcome MAPK-mediated resistance to B-RAF inhibitors in B-RAF V600E melanoma. Mol Cancer Ther; 13(10); 2253–63. ©2014 AACR.

Abstract CT232: Clinical activity of LY2835219, a novel cell cycle inhibitor selective for CDK4 and CDK6, in patients with metastatic breast cancer

LY2835219 is a novel cell cycle inhibitor selective for the cyclin-dependent kinases CDK4 and CDK6 (CDK4/6), which act in a protein complex with D-type cyclins to enable G1 to S cell cycle progression. Preclinical models indicate this complex plays a critical role in breast cancer. We conducted a phase I study with expansion cohorts to evaluate the safety, pharmacokinetics, and antitumor activity of LY2835219 in 5 different tumor types: glioblastoma; melanoma; and cancers of the lung, colon/rectum and breast. In the expansion cohorts, LY2835219 was administered continuously at 150-200mg orally every 12 hours on Days 1-28 of a 28-day cycle. RECIST v1.1 was used to assess tumor response. The most common possibly related treatment-emergent adverse events across the expansion cohorts (n=132) included diarrhea (5% G3/4), nausea (3% G3/4), fatigue (2% G3/4), vomiting (2% G3/4) and neutropenia (11% G3/4). In the metastatic breast cancer (MBC) cohort, 47 patients with a median of 7 prior systemic regimens received therapy with LY2835219. Across all MBC patients, 9 achieved a best overall response of confirmed partial response (PR), 24 achieved stable disease (SD), 11 had progressive disease (PD), and 3 were not evaluable for response. Among the 36 HR+ patients, there were 9 confirmed partial responses for an ORR of 25%. In addition, 20 of these 36 HR+ patients (56%) had SD: 7 patients had SD Citation Format: Amita Patnaik, Lee S. Rosen, Sara M. Tolaney, Anthony W. Tolcher, Jonathan W. Goldman, Leena Gandhi, Kyriakos P. Papadopoulos, Muralidhar Beeram, Drew W. Rasco, Scott P. Myrand, Palaniappan Kulanthaivel, Lily Li, Martin Frenzel, Damien M. Cronier, Edward M. Chan, Keith T. Flaherty, Patrick Y. Wen, Geoffrey I. Shapiro. Clinical activity of LY2835219, a novel cell cycle inhibitor selective for CDK4 and CDK6, in patients with metastatic breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr CT232. doi:10.1158/1538-7445.AM2014-CT232

Characterization of LY2228820 Dimesylate, a Potent and Selective Inhibitor of p38 MAPK with Antitumor Activity

p38α mitogen-activated protein kinase (MAPK) is activated in cancer cells in response to environmental factors, oncogenic stress, radiation, and chemotherapy. p38α MAPK phosphorylates a number of substrates, including MAPKAP-K2 (MK2), and regulates the production of cytokines in the tumor microenvironment, such as TNF-α, interleukin-1β (IL-1β), IL-6, and CXCL8 (IL-8). p38α MAPK is highly expressed in human cancers and may play a role in tumor growth, invasion, metastasis, and drug resistance. LY2228820 dimesylate (hereafter LY2228820), a trisubstituted imidazole derivative, is a potent and selective, ATP-competitive inhibitor of the α- and β-isoforms of p38 MAPK in vitro (IC50 = 5.3 and 3.2 nmol/L, respectively). In cell-based assays, LY2228820 potently and selectively inhibited phosphorylation of MK2 (Thr334) in anisomycin-stimulated HeLa cells (at 9.8 nmol/L by Western blot analysis) and anisomycin-induced mouse RAW264.7 macrophages (IC50 = 35.3 nmol/L) with no changes in phosphorylation of p38α MAPK, JNK, ERK1/2, c-Jun, ATF2, or c-Myc ≤ 10 μmol/L. LY2228820 also reduced TNF-α secretion by lipopolysaccharide/IFN-γ–stimulated macrophages (IC50 = 6.3 nmol/L). In mice transplanted with B16-F10 melanoma, tumor phospho-MK2 (p-MK2) was inhibited by LY2228820 in a dose-dependent manner [threshold effective dose (TED)70 = 11.2 mg/kg]. Significant target inhibition (>40% reduction in p-MK2) was maintained for 4 to 8 hours following a single 10 mg/kg oral dose. LY2228820 produced significant tumor growth delay in multiple in vivo cancer models (melanoma, non–small cell lung cancer, ovarian, glioma, myeloma, breast). In summary, LY2228820 is a p38 MAPK inhibitor, which has been optimized for potency, selectivity, drug-like properties (such as oral bioavailability), and efficacy in animal models of human cancer. Mol Cancer Ther; 13(2); 364–74. ©2013 AACR.

Increased c-Jun expression and reduced GATA2 expression promote aberrant monocytic differentiation induced by activating PTPN11 mutants.

ABSTRACT Juvenile myelomonocytic leukemia (JMML) is characterized by myelomonocytic cell overproduction and commonly bears activating mutations in PTPN11. Murine hematopoietic progenitors expressing activating Shp2 undergo myelomonocytic differentiation, despite being subjected to conditions that normally support only mast cells. Evaluation of hematopoietic-specific transcription factor expression indicates reduced GATA2 and elevated c-Jun in mutant Shp2-expressing progenitors. We hypothesized that mutant Shp2-induced Ras hyperactivation promotes c-Jun phosphorylation and constitutive c-Jun expression, permitting, as a coactivator of PU.1, excessive monocytic differentiation and reduced GATA2. Hematopoietic progenitors expressing activating Shp2 demonstrate enhanced macrophage CFU (CFU-M) compared to that of wild-type Shp2-expressing cells. Treatment with the JNK inhibitor SP600125 or cotransduction with GATA2 normalizes activating Shp2-generated CFU-M. However, cotransduction of ΔGATA2 (lacking the C-terminal zinc finger, needed to bind PU.1) fails to normalize CFU-M. NIH 3T3 cells expressing Shp2E76K produce higher levels of luciferase expression directed by the macrophage colony-stimulating factor receptor (MCSFR) promoter, which utilizes c-Jun as a coactivator of PU.1. Coimmunoprecipitation demonstrates increased c-Jun-PU.1 complexes in mutant Shp2-expressing hematopoietic progenitors, while chromatin immunoprecipitation demonstrates increased c-Jun binding to the c-Jun promoter and an increased c-Jun-PU.1 complex at the Mcsfr promoter. Furthermore, JMML progenitors express higher levels of c-JUN than healthy controls, substantiating the disease relevance of these mechanistic findings.

Abstract B233: Identification and characterization of LY2835219: A potent oral inhibitor of the cyclin-dependent kinases 4 and 6 (CDK4/6) with broad in vivo antitumor activity.

Dysregulation of the cell cycle, which normally regulates cell proliferation in response to mitogenic signaling and other extracellular stimuli, is a hallmark of cancer. The G1 restriction point is a primary mechanism controlling cell cycle progression and is controlled by the CDK4/6 pathway (CDK4/6-cyclin D1-Rb-CDKN2). The importance of this pathway is highlighted by inactivation of restriction point control in a majority of human tumors. Transition through the restriction point requires phosphorylation of Rb by CDK4/6, and these kinases are considered highly validated cancer drug targets. We have identified and characterized a potent and selective dual CDK4/6 inhibitor, LY2835219. Preclinical characterization was performed with the monomesylate salt (LY2835219-MsOH), which inhibits these kinases with a IC50 of 2 and 10 nM for CDK4 and CDK6, respectively. In vitro, LY2835219-MsOH is a potent inhibitor of Rb phosphorylation resulting in a G1 arrest, and its activity is specific for tumors that have functional Rb protein. In a multiplexed in vivo target inhibition assay (IVTI), LY2835219-MsOH is a potent inhibitor of Rb phosphorylation and induces complete cell cycle arrest 24 hrs after a single dose. In tumor-bearing mice, oral administration of LY2835219-MsOH inhibits tumor growth in a dose-dependent manner in colon (colo-205), glioblastoma (U87MG), acute myeloid leukemia (MV4–11), mantle cell lymphoma (Jeko-1), and lung (H460) xenografts. LY2835219-MsOH may be administered up to 56 days without adverse events or tumor outgrowth. LY2835219-MsOH enhances the in vivo activity of cytotoxic drugs, suggesting that this novel CDK4/6 inhibitor can be used in combination with these anti-neoplastic agents. In summary, we have identified an oral small molecule inhibitor of CDK4/6 that may provide therapeutic benefit to cancer patients with tumors that have functional Rb protein. 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 B233.

A First-in-Human Phase I Study of the Oral p38 MAPK Inhibitor, Ralimetinib (LY2228820 Dimesylate), in Patients with Advanced Cancer

Purpose: p38 MAPK regulates the production of cytokines in the tumor microenvironment and enables cancer cells to survive despite oncogenic stress, radiotherapy, chemotherapy, and targeted therapies. Ralimetinib (LY2228820 dimesylate) is a selective small-molecule inhibitor of p38 MAPK. This phase I study aimed to evaluate the safety and tolerability of ralimetinib, as a single agent and in combination with tamoxifen, when administered orally to patients with advanced cancer. Experimental Design: The study design consisted of a dose-escalation phase performed in a 3+3 design (Part A; n = 54), two dose-confirmation phases [Part B at 420 mg (n = 18) and Part C at 300 mg (n = 8)], and a tumor-specific expansion phase in combination with tamoxifen for women with hormone receptor–positive metastatic breast cancer refractory to aromatase inhibitors (Part D; n = 9). Ralimetinib was administered orally every 12 hours on days 1 to 14 of a 28-day cycle. Results: Eighty-nine patients received ralimetinib at 11 dose levels (10, 20, 40, 65, 90, 120, 160, 200, 300, 420, and 560 mg). Plasma exposure of ralimetinib (Cmax and AUC) increased in a dose-dependent manner. After a single dose, ralimetinib inhibited p38 MAPK–induced phosphorylation of MAPKAP-K2 in peripheral blood mononuclear cells. The most common adverse events, possibly drug-related, included rash, fatigue, nausea, constipation, pruritus, and vomiting. The recommended phase II dose was 300 mg every 12 hours as monotherapy or in combination with tamoxifen. Although no patients achieved a complete response or partial response,19 patients (21.3%) achieved stable disease with a median duration of 3.7 months, with 9 of these patients on study for ≥6 cycles. Conclusions: Ralimetinib demonstrated acceptable safety, tolerability, and pharmacokinetics for patients with advanced cancer. Clin Cancer Res; 22(5); 1095–102. ©2015 AACR.

Abstract P5-19-13: Clinical activity of abemaciclib, an oral cell cycle inhibitor, in metastatic breast cancer

Background: Abemaciclib, a small molecule inhibitor with selectivity against cyclin-dependent kinases 4 and 6 (CDK4/6), induces G1 arrest in Rb-proficient human breast cancers. In an early phase clinical trial, the safety and antitumor activity of abemaciclib (LY2835219) were evaluated in 2 cohorts of patients with metastatic breast cancer (mBC). One cohort evaluated single-agent abemaciclib in an unselected population of patients with mBC [Part D], while the combination of abemaciclib plus fulvestrant was evaluated in patients with hormone receptor positive (HR+) mBC [Part G]. We previously reported early results for these 2 cohorts of patients with mBC treated with either single-agent abemaciclib or the combination of abemaciclib plus fulvestrant (Patnaik et al, ASCO 2014). In the single-agent cohort, 47 patients with previously treated mBC were enrolled (36 HR+). All patients with >30% tumor reduction had HR+ mBC (13 of 36 patients). In this group of 13 patients with HR+ mBC, 9 patients had confirmed response for an objective response rate of 25%, and 4 patients had unconfirmed response. This study was ongoing with 14 of 36 HR+ mBC patients on treatment at time of analysis (range 238-471 days). Patients continuing on single-agent abemaciclib included 4 patients with unconfirmed response and 6 patients with confirmed response. For the combination of abemaciclib plus fulvestrant, 18 patients with HR+ mBC enrolled and 13 patients (72%) were still on treatment (range 31-143 days) at the time of analysis. Methods: In the single-agent cohort, patients with mBC were treated with abemaciclib at 150 or 200mg orally every 12 hours on a continuous schedule. In the combination cohort, patients with HR+ mBC (n=18) were treated with the combination of abemaciclib plus fulvestrant. Patients received abemaciclib at 200mg orally every 12 hours on a continuous schedule. Patients also received fulvestrant at 500mg intramuscularly every month. NCI CTCAE v4.0 was used to grade adverse events (AEs) and RECIST v1.1 was used to assess tumor response. Results: In the single-agent cohort, patients began enrolling in May 2012 with the last patient enrolled in March 2013. Patients had a median of 7 prior systemic therapies and 81% of patients had ≥2 metastatic sites. In the combination cohort, patients began enrolling in September 2013 with the last patient enrolled in January 2014. Patients in the combination cohort had a median of 4 prior systemic therapies and 67% of patients had ≥2 metastatic sites. An updated analysis will be presented for objective response rate, duration of treatment and clinical benefit rate and will include an additional 6 months of information for both the single-agent and combination cohorts. New analyses will include time to response, duration of response, change in tumor size over time, and characteristics of responders. In addition, safety data will include longer term follow-up through approximately September 2014. Conclusions: Abemaciclib is an oral cell cycle inhibitor that demonstrates single-agent activity against mBC, especially for HR+ disease. Based on its safety and efficacy profile, abemaciclib warrants further clinical investigation in confirmatory studies, both as a single agent and in combination with endocrine therapy. Citation Format: Sara M Tolaney, Lee S Rosen, Muralidhar Beeram, Jonathan W Goldman, Leena Gandhi, Anthony W Tolcher, Kyriakos P Papadopoulos, Drew W Rasco, Scott P Myrand, Palaniappan Kulanthaivel, Joan M Andrews, Martin Frenzel, Damien M Cronier, Edward M Chan, Keith T Flaherty, Patrick Y Wen, Geoffrey I Shapiro, Amita Patnaik. Clinical activity of abemaciclib, an oral cell cycle inhibitor, in metastatic breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-19-13.

Abstract LB-122: LY2835219, a selective inhibitor of CDK4 and CDK6, inhibits growth in preclinical models of human cancer.

Cell growth is regulated by the activity of certain cyclin-dependent kinases (CDKs), including CDK4 and CDK6 (hereafter CDK4/6), which specifically regulate cell cycle progression through the G1 restriction point. These CDKs act with the D-type cyclins to phosphorylate and inactivate the retinoblastoma (Rb) tumor suppressor protein, which in turn enables cell cycle progression from G1 to S phase. LY2835219 is a selective inhibitor of CDK4/6 with IC50 of 2 and 10 nM for CDK4 and CDK6, respectively. The current study evaluates the activity of LY2835219 in preclinical models of human cancer including non-small cell lung cancer (NSCLC), melanoma, mantle cell lymphoma (MCL), and ovarian cancer. A secondary focus of this study is to identify potential predictive biomarkers for response to LY2835219 in NSCLC, melanoma, and other cancers. For NSCLC, increased sensitivity to LY2835219 is associated both in vitro and in vivo with KRAS mutations. For established melanoma cell lines, similar levels of in vitro sensitivity are observed in different genetic subtypes. Accordingly, LY2835219 shows single-agent activity in the A375 melanoma xenograft model with daily oral dosing at 45 or 90 mg/kg. For MCL, durable growth inhibition of subcutaneously implanted xenografts is achieved with daily oral dosing at 50mg/kg. Finally, in an intra-peritoneal model that recapitulates clinical features of human ovarian cancer, LY2835219 not only inhibits tumor growth but also increases survival. These studies suggest that LY2835219 may have potential therapeutic application in the treatment of human cancers with specific molecular alterations. Citation Format: Jack A. Dempsey, Edward M. Chan, Teresa F. Burke, Richard P. Beckmann. LY2835219, a selective inhibitor of CDK4 and CDK6, inhibits growth in preclinical models of human cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-122. doi:10.1158/1538-7445.AM2013-LB-122