Douglas D. Fang

An allosteric PRC2 inhibitor targeting the H3K27me3 binding pocket of EED

Polycomb repressive complex 2 (PRC2) consists of three core subunits, EZH2, EED and SUZ12, and plays pivotal roles in transcriptional regulation. The catalytic subunit EZH2 methylates histone H3 lysine 27 (H3K27), and its activity is further enhanced by the binding of EED to trimethylated H3K27 (H3K27me3). Small-molecule inhibitors that compete with the cofactor S-adenosylmethionine (SAM) have been reported. Here we report the discovery of EED226, a potent and selective PRC2 inhibitor that directly binds to the H3K27me3 binding pocket of EED. EED226 induces a conformational change upon binding EED, leading to loss of PRC2 activity. EED226 shows similar activity to SAM-competitive inhibitors in blocking H3K27 methylation of PRC2 target genes and inducing regression of human lymphoma xenograft tumors. Interestingly, EED226 also effectively inhibits PRC2 containing a mutant EZH2 protein resistant to SAM-competitive inhibitors. Together, we show that EED226 inhibits PRC2 activity via an allosteric mechanism and offers an opportunity for treatment of PRC2-dependent cancers.

Synergistic Effect of the γ-Secretase Inhibitor PF-03084014 and Docetaxel in Breast Cancer Models

Notch signaling mediates breast cancer cell survival and chemoresistance. In this report, we aimed to evaluate the antitumor efficacy of PF‐03084014 in combination with docetaxel in triple‐negative breast cancer models. The mechanism of action was investigated. PF‐03084014 significantly enhanced the antitumor activity of docetaxel in multiple xenograft models including HCC1599, MDA‐MB‐231Luc, and AA1077. Docetaxel activated the Notch pathway by increasing the cleaved Notch1 intracellular domain and suppressing the endogenous Notch inhibitor NUMB. PF‐03084014 used in combination with docetaxel reversed these effects and demonstrated early‐stage synergistic apoptosis. Docetaxel elicited chemoresistance by elevating cytokine release and expression of survivin and induced an endothelial mesenchymal transition (EMT) phenotype by increasing the expressions of Snail, Slug, and N‐cadherin. When reimplanted, the docetaxel‐residual cells not only became much more tumorigenic, as evidenced by a higher fraction of tumor‐initiating cells (TICs), but also showed higher metastatic potential compared with nontreated cells, leading to significantly shortened survival. In contrast, PF‐03084014 was able to suppress expression of survivin and MCL1, reduce ABCB1 and ABCC2, upregulate BIM, reverse the EMT phenotype, and diminish the TICs. Additionally, the changes to the ALDH+ and CD133+/CD44+ subpopulations following therapy corresponded with the TIC self‐renewal assay outcome. In summary, PF‐03084014 demonstrated synergistic effects with docetaxel through multiple mechanisms. This work provides a strong preclinical rationale for the clinical utility of PF‐03084014 to improve taxane therapy.

HIP1–ALK, A Novel ALK Fusion Variant that Responds to Crizotinib

Introduction: The aim of this study was to identify anaplastic lymphoma kinase (ALK) rearrangements in lung cancer patient-derived xenograft (PDX) models and to explore their responses to crizotinib. Methods: Screening of 99 lung cancer PDX models by the NanoString ALK fusion assay identified two ALK-rearranged non–small-cell lung cancer (NSCLC) tumors, including one harboring a previously known echinoderm microtubule-associated protein-like 4 (EML4)–ALK fusion and another containing an unknown ALK fusion variant. Expression array, RNA-Seq, reverse transcription polymerase chain reaction, and direct sequencing were then conducted to confirm the rearrangements and to identify the novel fusion partner in the xenograft and/or the primary patient tumor. Finally, pharmacological studies were performed in PDX models to evaluate their responses to ALK inhibitor crizotinib. Results: Two ALK-rearranged NSCLC PDX models were identified: one carried a well-known EML4–ALK variant 3a/b and the other harbored a novel huntingtin interacting protein 1 (HIP1)–ALK fusion gene. Exon 28 of the HIP1 gene located on chromosome 7 was fused to exon 20 of the ALK gene located on chromosome 2. Both cases were clinically diagnosed as squamous cell carcinoma. Compared with the other lung cancer PDX models, both ALK-rearranged models displayed elevated ALK mRNA expression. Furthermore, in vivo efficacy studies demonstrated that, similar to the EML4–ALK-positive model, the HIP1–ALK-containing PDX model was sensitive to treatment with crizotinib. Conclusions: Discovery of HIP1 as a fusion partner of ALK in NSCLC is a novel finding. In addition, the HIP1–ALK-rearranged tumor is sensitive to treatment with crizotinib in vivo, implicating HIP1–ALKas an oncogenic driver of lung tumorigenesis. Collectively, our results indicate that HIP1–ALK-positive NSCLC may benefit from clinical applications of crizotinib.

Discovery of First-in-Class, Potent, and Orally Bioavailable Embryonic Ectoderm Development (EED) Inhibitor with Robust Anticancer Efficacy

Overexpression and somatic heterozygous mutations of EZH2, the catalytic subunit of polycomb repressive complex 2 (PRC2), are associated with several tumor types. EZH2 inhibitor, EPZ-6438 (tazemetostat), demonstrated clinical efficacy in patients with acceptable safety profile as monotherapy. EED, another subunit of PRC2 complex, is essential for its histone methyltransferase activity through direct binding to trimethylated lysine 27 on histone 3 (H3K27Me3). Herein we disclose the discovery of a first-in-class potent, selective, and orally bioavailable EED inhibitor compound 43 (EED226). Guided by X-ray crystallography, compound 43 was discovered by fragmentation and regrowth of compound 7, a PRC2 HTS hit that directly binds EED. The ensuing scaffold hopping followed by multiparameter optimization led to the discovery of 43. Compound 43 induces robust and sustained tumor regression in EZH2MUT preclinical DLBCL model. For the first time we demonstrate that specific and direct inhibition of EED can be effective as an anticancer strategy.

Antitumor Efficacy of the Dual PI3K/mTOR Inhibitor PF-04691502 in a Human Xenograft Tumor Model Derived from Colorectal Cancer Stem Cells Harboring a PIK3CA Mutation

PIK3CA (phosphoinositide-3-kinase, catalytic, alpha polypeptide) mutations can help predict the antitumor activity of phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway inhibitors in both preclinical and clinical settings. In light of the recent discovery of tumor-initiating cancer stem cells (CSCs) in various tumor types, we developed an in vitro CSC model from xenograft tumors established in mice from a colorectal cancer patient tumor in which the CD133+/EpCAM+ population represented tumor-initiating cells. CD133+/EpCAM+ CSCs were enriched under stem cell culture conditions and formed 3-dimensional tumor spheroids. Tumor spheroid cells exhibited CSC properties, including the capability for differentiation and self-renewal, higher tumorigenic potential and chemo-resistance. Genetic analysis using an OncoCarta™ panel revealed a PIK3CA (H1047R) mutation in these cells. Using a dual PI3K/mTOR inhibitor, PF-04691502, we then showed that blockage of the PI3K/mTOR pathway inhibited the in vitro proliferation of CSCs and in vivo xenograft tumor growth with manageable toxicity. Tumor growth inhibition in mice was accompanied by a significant reduction of phosphorylated Akt (pAKT) (S473), a well-established surrogate biomarker of PI3K/mTOR signaling pathway inhibition. Collectively, our data suggest that PF-04691502 exhibits potent anticancer activity in colorectal cancer by targeting both PIK3CA (H1047R) mutant CSCs and their derivatives. These results may assist in the clinical development of PF-04691502 for the treatment of a subpopulation of colorectal cancer patients with poor outcomes.

Combined gemcitabine and CHK1 inhibitor treatment induces apoptosis resistance in cancer stem cell-like cells enriched with tumor spheroids from a non-small cell lung cancer cell line

Evaluating the effects of novel drugs on appropriate tumor models has become crucial for developing more effective therapies that target highly tumorigenic and drug-resistant cancer stem cell (CSC) populations. In this study, we demonstrate that a subset of cancer cells with CSC properties may be enriched into tumor spheroids under stem cell conditions from a non-small cell lung cancer cell line. Treating these CSC-like cells with gemcitabine alone and a combination of gemcitabine and the novel CHK1 inhibitor PF-00477736 revealed that PF-00477736 enhances the anti-proliferative effect of gemcitabine against both the parental and the CSC-like cell populations. However, the CSC-like cells exhibited resistance to gemcitabine-induced apoptosis. Collectively, the spheroid-forming CSC-like cells may serve as a model system for understanding the mechanism underlying the drug resistance of CSCs and for guiding the development of better therapies that can inhibit tumor growth and eradicate CSCs.

Abstract 4504: PF-04449913, a small molecule inhibitor of Hedgehog signaling, is effective in inhibiting tumor growth in preclinical models

Aberrant activation of the Hedgehog (Hh) signaling pathway has been implicated in several human cancers. Mutations in the Patched (PTCH1) gene are responsible for basal cell nevus syndrome, and are commonly found in sporadic basal cell carcinoma and in medulloblastoma. In this study we evaluated PF-04449913, an inhibitor of the Hh signaling pathway, in a Ptch1+/-p53 mouse model of medulloblastoma and in human patient derived xenograft models. Treatment of Ptch1+/-p53+/- or Ptch1+/-p53-/- medulloblastoma allografts with PF-04449913 produced potent dose-dependent inhibition of Hh pathway activity resulting in stable tumor regression. Using Gli1 transcript levels as a surrogate for Hh pathway activity, the pharmacodynamic effects of PF-04449913 were evaluated in medulloblastoma allografts following single dose and multi dose administrations of compound. PF-04449913 treated medulloblastoma allografts had reduced levels of Gli1 gene expression and down regulation of genes linked to the Hh signaling pathway. PF-04449913 was also effective when combined with a chemotherapeutic agent in a colon patient derived xenograft model and a pancreatic patient derived xenograft model, resulting in 63% and 73% tumor growth inhibition respectively. Collectively, our study demonstrates the therapeutic efficacy of a small molecule inhibitor of Hh pathway in preclinical models of multiple cancer types in either single or combination treatments. 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 4504. doi:10.1158/1538-7445.AM2011-4504

Identification of cancer stem cells provides novel tumor models for drug discovery

Cancer stem cells (CSCs) have received considerable attention from the research community since they were first reported in human acute myeloid leukemia 15 years ago. Accumulating evidence suggests that CSCs are responsible for tumor initiation and progression, drug resistance, and metastasis in both liquid and solid tumors. These findings lead to the development of novel compounds targeting CSC populations that is becoming increasingly important for eradicating CSCs in heterogeneous tumor masses and to cure the cancer. Since 2003, we have participated in CSC studies and encountered crucial early events in the field. This article reviews the history of CSC biology, clarifies the term and its definition, and further addresses the issue of how to utilize CSCs in therapeutic target discovery and drug development based on our substantial experience.

Abstract 3492: γ-secretase inhibitor PF-03084014 diminishes the tumor-initiating cells and demonstrates synergy with docetaxel in breast cancer xenograft models

Notch signaling is known to be a survival pathway for tumor-initiating cells. In this report, we demonstrate that the γ-secretase inhibitor PF-03084014 significantly enhances the antitumor activity of docetaxel in multiple xenograft models of triple-negative breast cancer. Mechanistic evaluation revealed that PF-03084014 perturbs the Notch signaling pathway and suppresses the function of tumor initiating cells (TIC). In MDA-MB-231Luc model, treatment of docetaxel led to a significant increase of CD133+/CD44+ and ALDH+ subpopulations by FACS analysis. In combination with PF-03084014, these two unique cell subpopulations were significantly diminished. Correspondingly, the functional analyses by tumor re-implant and mammosphere-forming efficiency assays revealed that docetaxel-therapy promoted the tumor initiating capability of the remaining cells, in which an increased stem cell property and Notch pathway activation were observed through gene signature changes. In contrast, PF-03084014 co-treatment with docetaxel substantially hampered the self-renewal ability of these cells. Notch target gene analysis demonstrated the biological relevance of PF-03084014-induced activity. To characterize the function of CD133+/CD44+ subpopulation, MDA-MB-231Luc tumors were de-bulked by the treatment with docetaxel. Subsequently, the CD133+/CD44+ and CD133-/CD44- subpopulatons were isolated and re-implanted in SCID-bg mice using a limiting dilution approach. The results showed that CD133+/CD44+ cells gave rise to tumors with a 100 % take rate (10/10), whereas CD133-/CD44- cells were not tumorgenic (0/10). In addition, CD133+/CD44+ cells exhibited much higher tumorigenicity compared with the respective adherent parental cell line. PF-03084014 treatment caused a significant delay of CD133+/CD44+ tumor growth. The ability of PF-03084014 to suppress TICs was also observed in other breast cancer xenografts, including patient derived models. This data suggests that anti-TIC is one of the contributing mechanisms for the synergistic activities of PF-03084014 in combination with docetaxel. Our work provides potential therapeutic opportunities for PF-03084014 to improve conventional cytotoxic therapy by inhibiting Notch signaling in tumor-initiating cells and other bulk tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3492. doi:1538-7445.AM2012-3492

Abstract 307: Targeting BCL-2 and BCL-xL with a novel dual inhibitor APG-1252 triggers cell death and inhibits tumor growth in small cell lung cancer models

Small cell lung cancer (SCLC) is one of the most deadly diseases with a dismal five year survival rate less than 7%. Even though most SCLC patients respond to the initial platinum-based cytotoxic or radiation therapies, they inevitably relapse and succumb to the disease. Anti-apoptotic proteins BCL-2 and BCL-xL, which are highly expressed in 40-60% of SCLCs and play a critical role in tumorigenesis and drug resistance, have been emerging as a promising target for therapeutic intervention. We have recently developed a novel dual BCL-2/BCL-xL inhibitor APG-1252 for cancer therapy. In this study, the effect of APG-1252 was evaluated in a panel of SCLC cell lines for discovery of indications and predictive biomarkers. The results show that the sensitivity of SCLC cell lines with sub-µM or nM IC50 values are correlated with the higher expression levels of BCL-2/BCL-xL, BIM and/or PUMA but lower levels of MCL-1. Conversely, the resistant cell lines either lack of BCL-2/BCL-xL protein, or exhibit higher level of MCL-1 protein. In xenograft tumor models, consistent with in vitro results, APG-1252 exhibits antitumor activities in the models derived from the sensitive cells but not in those from the resistant cells. Interestingly, while ABT-263 failed to inhibit H146 xenograft tumor growth, despite of its similar in vitro killing ability as APG-1252, APG-1252 showed potent antitumor activity in the xenograft model. To overcome the drug resistance conferred by MCL-1 in the resistant cells, we explore the combination therapy with other targeted agents. We found that our novel MDM2 inhibitor APG-115 was able to overcome the intrinsic resistance and sensitize those cells to APG-1252 in vitro, suggesting that reducing the apoptotic threshold by inhibiting other anti-death proteins like MCL-1 or increasing apoptotic function through p53 can enhance SCLC sensitivity to APG-1252. Collectively, APG-1252 represents a novel opportunity that can neutralize the protection from BCL-2/BCL-xL and trigger cell death and inhibit tumor growth in SCLC models. With the significance of these preclinical data, APG-1252 has been granted for phase 1 clinical trials in USA (NCT03080311) and China. Citation Format: GuangFeng Wang, Ping Min, MiaoYi Wu, Shuo Dang, ChuanYan Tang, Fei Zhang, Ming Guo, Shaomeng Wang, Jing Deng, Douglas D. Fang, DaJun Yang, YiFan Zhai. Targeting BCL-2 and BCL-xL with a novel dual inhibitor APG-1252 triggers cell death and inhibits tumor growth in small cell lung cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 307.