mTOR inhibition sensitizes ONC201-induced anti-colorectal cancer cell activity

Mammalian integrated stress responses in stressed organelles and their functions

The integrated stress response (ISR) triggered in response to various cellular stress enables mammalian cells to effectively cope with diverse stressful conditions while maintaining their normal functions. Four kinases (PERK, PKR, GCN2, and HRI) of ISR regulate ISR signaling and intracellular protein translation via mediating the phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α) at Ser51. Early ISR creates an opportunity for cells to repair themselves and restore homeostasis. This effect, however, is reversed in the late stages of ISR. Currently, some studies have shown the non-negligible impact of ISR on diseases such as ischemic diseases, cognitive impairment, metabolic syndrome, cancer, vanishing white matter, etc. Hence, artificial regulation of ISR and its signaling with ISR modulators becomes a promising therapeutic strategy for relieving disease symptoms and improving clinical outcomes. Here, we provide an overview of the essential mechanisms of ISR and describe the ISR-related pathways in organelles including mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Meanwhile, the regulatory effects of ISR modulators and their potential application in various diseases are also enumerated.

Roles of Rictor alterations in gastrointestinal tumors (Review)

Gastrointestinal tumors account for five of the top 10 causes of mortality from all cancers (colorectal, liver, stomach, esophageal and pancreatic cancer). Mammalian target of rapamycin (mTOR) signaling is commonly dysregulated in various human cancers. As a core component of the mTOR complex 2 (mTORC2), Rictor is a key effector molecule of the PI3K/Akt pathway. A high alteration rate of Rictor has been observed in gastrointestinal tumors, and such Rictor alterations are often associated with resistance to chemotherapy and related adverse clinical outcomes. However, the exact roles of Rictor in gastrointestinal tumors remain elusive. The aim of the present study was to critically discuss the following: i) Mutation and biological characteristics of Rictor in tumors with a detailed overview of Rictor in cell proliferation, angiogenesis, apoptosis, autophagy and drug resistance; ii) the role of Rictor in tumors of the digestive system, particularly colorectal, hepatobiliary, gastric, esophageal and pancreatic cancer and cholangiocarcinoma; and iii) the current status and prospects of targeted therapy for Rictor by inhibiting Akt activation. Despite the growing realization of the importance of Rictor/mTORC2 in cancer, the underlying mechanistic details remain poorly understood; this needs to change in order for the development of efficient targeted therapies and re‑sensitization of therapy‑resistant cancers to be made possible.

ONC201/TIC10 enhances durability of mTOR inhibitor everolimus in metastatic ER+ breast cancer

The mTOR inhibitor, everolimus, is an important clinical management component of metastatic ER+ breast cancer (BC). However, most patients develop resistance and progress on therapy, highlighting the need to discover strategies that increase mTOR inhibitor effectiveness. We developed ER+ BC cell lines, sensitive or resistant to everolimus, and discovered that combination treatment of ONC201/TIC10 with everolimus inhibited cell growth in 2D/3D in vitro studies. We confirmed increased therapeutic response in primary patient cells progressing on everolimus, supporting clinical relevance. We show that ONC201/TIC10 mechanism in metastatic ER+ BC cells involves oxidative phosphorylation inhibition and stress response activation. Transcriptomic analysis in everolimus resistant breast patient tumors and mitochondrial functional assays in resistant cell lines demonstrated increased mitochondrial respiration dependency, contributing to ONC201/TIC10 sensitivity. We propose that ONC201/TIC10 and modulation of mitochondrial function may provide an effective add-on therapy strategy for patients with metastatic ER+ BCs resistant to mTOR inhibitors.

Therapeutic targeting of TRAIL death receptors

The discovery of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) along with its potent and selective antitumor effects initiated a decades-long search for therapeutic strategies to target the TRAIL pathway. First-generation approaches were focused on the development of TRAIL receptor agonists (TRAs), including recombinant human TRAIL (rhTRAIL) and TRAIL receptor-targeted agonistic antibodies. While such TRAIL pathway-targeted therapies showed promise in preclinical data and clinical trials have been conducted, none have advanced to FDA approval. Subsequent second-generation approaches focused on improving upon the specific limitations of first-generation approaches by ameliorating the pharmacokinetic profiles and agonistic abilities of TRAs as well as through combinatorial approaches to circumvent resistance. In this review, we summarize the successes and shortcomings of first- and second-generation TRAIL pathway-based therapies, concluding with an overview of the discovery and clinical introduction of ONC201, a compound with a unique mechanism of action that represents a new generation of TRAIL pathway-based approaches. We discuss preclinical and clinical findings in different tumor types and provide a unique perspective on translational directions of the field.

IMP075 targeting ClpP for colon cancer therapy in vivo and in vitro

ONC201 is a well-known caseinolytic protease (ClpP)activator with established benefits against multiple tumors, including colorectal cancer (CRC). In this study, we investigated the anticancer effects and associated mechanisms of the ClpP agonist IMP075, derived from ONC201. Acute toxicity and CCK-8 assayswere employed to determine the safety of IMP075. The effectiveness of IMP075 was investigated in HCT116 cells and a mouse xenograft tumor model. Additionally, the properties of IMP075 were evaluated by pharmacokinetic,CYP inhibition, and hERG inhibition assays. Finally, isothermal titration calorimetry (ITC), differential scanning fluorimetry (DSF), cellular thermal shift assay (CETSA), molecular dynamics simulations, point mutations, and shRNA experiments were employed to elucidate the potential mechanism of IMP075. Compared with ONC201, IMP075 exhibited similar toxicity and improved antitumor effects in vitro and in vivo. Interestingly, the affinity and agonistic effects of IMP075 on ClpP were superior to ONC201, which allowed IMP075 to disrupt respiratory chain integrity at lower doses in HCT116 cells, leading to mitochondrial dysfunction. Furthermore, molecular dynamics simulations demonstrate that IMP075 forms two pairs of hydrogen bonds with ClpP, maintaining ClpP in an agonistic state. Importantly, the antiproliferative activity of IMP075 significantly decreased following ClpP knockdown. Our findings substantiate that IMP075 exerts excellent antitumor effects against CRC by activating ClpP-mediated impairment of mitochondrial function. Due to its superior properties, IMP075 appears to be have huge prospects for application.

Mechanisms of imipridones in targeting mitochondrial metabolism in cancer cells

ONC201 is the first member of the imipridone family of anticancer drugs to enter the clinic for the treatment of diverse solid and hematologic cancers. A subset of pediatric and adult patients with highly aggressive brain tumors has shown remarkable clinical responses to ONC201, and recently, the more potent derivative ONC206 entered clinical trials as a single agent for the treatment of central nervous system (CNS) cancers. Despite the emerging clinical interest in the utility of imipridones, their exact molecular mechanisms are not fully described. In fact, the existing literature points to multiple pathways (e.g. tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) signaling, dopamine receptor antagonism, and mitochondrial metabolism) as putative drug targets. We have performed a comprehensive literature review and highlighted mitochondrial metabolism as the major target of imipridones. In support of this, we performed a meta-analysis of an ONC201 screen across 539 human cancer cell lines and showed that the mitochondrial caseinolytic protease proteolytic subunit (ClpP) is the most significant predictive biomarker of response to treatment. Herein, we summarize the main findings on the anticancer mechanisms of this potent class of drugs, provide clarity on their role, and identify clinically relevant predictive biomarkers of response.

Targeting multiple signaling pathways: the new approach to acute myeloid leukemia therapy

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults and the second most common form of acute leukemia in children. Despite this, very little improvement in survival rates has been achieved over the past few decades. This is partially due to the heterogeneity of AML and the need for more targeted therapeutics than the traditional cytotoxic chemotherapies that have been a mainstay in therapy for the past 50 years. In the past 20 years, research has been diversifying the approach to treating AML by investigating molecular pathways uniquely relevant to AML cell proliferation and survival. Here we review the development of novel therapeutics in targeting apoptosis, receptor tyrosine kinase (RTK) signaling, hedgehog (HH) pathway, mitochondrial function, DNA repair, and c-Myc signaling. There has been an impressive effort into better understanding the diversity of AML cell characteristics and here we highlight important preclinical studies that have supported therapeutic development and continue to promote new ways to target AML cells. In addition, we describe clinical investigations that have led to FDA approval of new targeted AML therapies and ongoing clinical trials of novel therapies targeting AML survival pathways. We also describe the complexity of targeting leukemia stem cells (LSCs) as an approach to addressing relapse and remission in AML and targetable pathways that are unique to LSC survival. This comprehensive review details what we currently understand about the signaling pathways that support AML cell survival and the exceptional ways in which we disrupt them.

ONC201 and imipridones: Anti-cancer compounds with clinical efficacy

ONC201 was originally discovered as TNF-Related Apoptosis Inducing Ligand (TRAIL)-inducing compound TIC10. ONC201 appears to act as a selective antagonist of the G protein coupled receptor (GPCR) dopamine receptor D2 (DRD2), and as an allosteric agonist of mitochondrial protease caseinolytic protease P (ClpP). Downstream of target engagement, ONC201 activates the ATF4/CHOP-mediated integrated stress response leading to TRAIL/Death Receptor 5 (DR5) activation, inhibits oxidative phosphorylation via c-myc, and inactivates Akt/ERK signaling in tumor cells. This typically results in DR5/TRAIL-mediated apoptosis of tumor cells; however, DR5/TRAIL-independent apoptosis, cell cycle arrest, or antiproliferative effects also occur. The effects of ONC201 extend beyond bulk tumor cells to include cancer stem cells, cancer associated fibroblasts and immune cells within the tumor microenvironment that can contribute to its efficacy. ONC201 is orally administered, crosses the intact blood brain barrier, and is under evaluation in clinical trials in patients with advanced solid tumors and hematological malignancies. ONC201 has single agent clinical activity in tumor types that are enriched for DRD2 and/or ClpP expression including specific subtypes of high-grade glioma, endometrial cancer, prostate cancer, mantle cell lymphoma, and adrenal tumors. Synergy with radiation, chemotherapy, targeted therapy and immune-checkpoint agents has been identified in preclinical models and is being evaluated in clinical trials. Structure-activity relationships based on the core pharmacophore of ONC201, termed the imipridone scaffold, revealed novel potent compounds that are being developed. Imipridones represent a novel approach to therapeutically target previously undruggable GPCRs, ClpP, and innate immune pathways in oncology.

Development of Novel Anticancer Agents with a Scaffold of Tetrahydropyrido[4,3-d]pyrimidine-2,4-dione

ONC201 is a small molecular anticancer agent currently in multiple Phase II clinical trials. Based on the pharmacophore of ONC201, a series of small molecular compounds with a core structure of tetrahydropyrido[4,3-d]pyrimidine-2,4-dione were designed and synthesized. Preliminary mechanism studies of these compounds indicated that they can inhibit the phosphorylation of AKT and ERK, induce the dephosphorylation of Foxo3a, and promote the expression of TRAIL and the enhancement of activating transcription factor 4 (ATF4) in PC-3 cells. Structure-activity relationship (SAR) studies indicated that modifications of the substituted groups on the core structure can significantly improve the cellular activities of these compounds. The most potent compounds are over 100 times more potent than ONC201 in inhibition of cell growth in a panel of different types of human cancer cell lines.

Ferrocene-Containing Impiridone (ONC201) Hybrids: Synthesis, DFT Modelling, In Vitro Evaluation, and Structure⁻Activity Relationships

Inspired by the well-established clinical evidence about the interplay between apoptotic TRAIL (tumour necrosis factor-related apoptosis-inducing ligand) mechanism and reactive oxygen species (ROS)-mediated oxidative stress, a set of novel ONC201 hybrids containing the impiridone core and one or two differently positioned ferrocenylalkyl groups were synthesised in our present work. These two types of residues have been implicated in the aforementioned mechanisms associated with cytotoxic activity. A straightforward, primary amine-based synthetic approach was used allowing the introduction of a variety of N-substituents into the two opposite regions of the heterocyclic skeleton. Reference model compounds with benzyl and halogenated benzyl groups were also synthesised and tested. The in vitro assays of the novel impiridones on five malignant cell lines disclosed characteristic structure-activity relationship (SAR) featuring significant substituent-dependent activity and cell-selectivity. A possible contribution of ROS-mechanism to the cytotoxicity of the novel metallocenes was suggested by density functional theory (DFT)studies on simplified models. Accordingly, unlike the mono-ferrocenylalkyl-substituted products, the compounds containing two ferrocenylalkyl substituents in the opposite regions of the impiridone core display a much more pronounced long-term cytotoxic effect against A-2058 cell line than do the organic impiridones including ONC201 and ONC212. Furthermore, the prepared bis-metallocene derivatives also present substantial activity against COLO-205- and EBC-1 cell lines.

Dose intensification of TRAIL-inducing ONC201 inhibits metastasis and promotes intratumoral NK cell recruitment

ONC201 is a first-in-class, orally active antitumor agent that upregulates cytotoxic TRAIL pathway signaling in cancer cells. ONC201 has demonstrated safety and preliminary efficacy in a first-in-human trial in which patients were dosed every 3 weeks. We hypothesized that dose intensification of ONC201 may impact antitumor efficacy. We discovered that ONC201 exerts dose- and schedule-dependent effects on tumor progression and cell death signaling in vivo. With dose intensification, we note a potent anti-metastasis effect and inhibition of cancer cell migration and invasion. Our preclinical results prompted a change in ONC201 dosing in all open clinical trials. We observed accumulation of activated NK+ and CD3+ cells within ONC201-treated tumors and that NK cell depletion inhibits ONC201 efficacy in vivo, including against TRAIL/ONC201-resistant Bax-/- tumors. Immunocompetent NCR1-GFP mice, in which NK cells express GFP, demonstrated GFP+ NK cell infiltration of syngeneic MC38 colorectal tumors. Activation of primary human NK cells and increased degranulation occurred in response to ONC201. Coculture experiments identified a role for TRAIL in human NK-mediated antitumor cytotoxicity. Preclinical results indicate the potential utility for ONC201 plus anti-PD-1 therapy. We observed an increase in activated TRAIL-secreting NK cells in the peripheral blood of patients after ONC201 treatment. The results offer what we believe to be a unique pathway of immune stimulation for cancer therapy.

ONC201 Targets AR and AR-V7 Signaling, Reduces PSA, and Synergizes with Everolimus in Prostate Cancer

Androgen receptor (AR) signaling plays a key role in prostate cancer progression, and androgen deprivation therapy (ADT) is a mainstay clinical treatment regimen for patients with advanced disease. Unfortunately, most prostate cancers eventually become androgen-independent and resistant to ADT with patients progressing to metastatic castration-resistant prostate cancer (mCRPC). Constitutively activated AR variants (AR-V) have emerged as mediators of resistance to AR-targeted therapy and the progression of mCRPC, and they represent an important therapeutic target. Out of at least 15 AR-Vs described thus far, AR-V7 is the most abundant, and its expression correlates with ADT resistance. ONC201/TIC10 is the founding member of the imipridone class of small molecules and has shown anticancer activity in a broad range of tumor types. ONC201 is currently being tested in phase I/II clinical trials for advanced solid tumors, including mCRPC, and hematologic malignancies. There has been promising activity observed in patients in early clinical testing. This study demonstrates preclinical single-agent efficacy of ONC201 using in vitro and in vivo models of prostate cancer. ONC201 has potent antiproliferative and proapoptotic effects in both castration-resistant and -sensitive prostate cancer cells. Furthermore, the data demonstrate that ONC201 downregulates the expression of key drivers of prostate cancer such as AR-V7 and downstream target genes including the clinically used biomarker PSA (KLK3). Finally, the data also provide a preclinical rationale for combination of ONC201 with approved therapeutics for prostate cancer such as enzalutamide, everolimus (mTOR inhibitor), or docetaxel.Implications: The preclinical efficacy of ONC201 as a single agent or in combination, in hormone-sensitive or castration-resistant prostate cancer, suggests the potential for immediate clinical translation. Mol Cancer Res; 16(5); 754-66. ©2018 AACR.

Identification of DNA-PKcs as a primary resistance factor of TIC10 in hepatocellular carcinoma cells

The current study tested the anti-hepatocellular carcinoma (HCC) cell activity of TIC10, a first-in-class small-molecule tumor necrosis (TNF)-related apoptosis-inducing ligand (TRAIL) inducer. TIC10 exerted potent anti-proliferative and pro-apoptotic actions in primary and established human HCC cells. TIC10 blocked Akt-Erk activation, leading to Foxo3a nuclear translocation, as well as TRAIL and death receptor-5 (DR5) transcription in HCC cells. We propose that DNA-PKcs is a major resistance factor of TIC10 possibly via inhibiting Foxo3a nuclear translocation. DNA-PKcs inhibition, knockdown or mutation facilitated TIC10-induced Foxo3a nuclear translocation, TRAIL/DR5 expression and cell apoptosis. Reversely, exogenous DNA-PKcs over-expression inhibited above actions by TIC10. In vivo, oral administration of TIC10 significantly inhibited HepG2 tumor growth in nude mice, which was further potentiated with Nu7026 co-administration. Thus, TIC10 shows promising anti-HCC activity, alone or together with DNA-PKcs inhibitors.

Anti-tumor effects of ONC201 in combination with VEGF-inhibitors significantly impacts colorectal cancer growth and survival in vivo through complementary non-overlapping mechanisms

Background

Small molecule ONC201 is an investigational anti-tumor agent that upregulates intra-tumoral TRAIL expression and the integrated stress response pathway. A Phase I clinical trial using ONC201 therapy in advanced cancer patients has been completed and the drug has progressed into Phase II trials in several cancer types. Colorectal cancer (CRC) remains one of the leading causes of cancer worldwide and metastatic disease has a poor prognosis. Clinical trials in CRC and other tumor types have demonstrated that therapeutics targeting the vascular endothelial growth factor (VEGF) pathway, such as bevacizumab, are effective in combination with certain chemotherapeutic agents.

Methods

We investigated the potential combination of VEGF inhibitors such as bevacizumab and its murine-counterpart; along with other anti-angiogenic agents and ONC201 in both CRC xenograft and patient-derived xenograft (PDX) models. We utilized non-invasive imaging and immunohistochemistry to determine potential mechanisms of action.

Results

Our results demonstrate significant tumor regression or complete tumor ablation in human xenografts with the combination of ONC201 with bevacizumab, and in syngeneic MC38 colorectal cancer xenografts using a murine VEGF-A inhibitor. Imaging demonstrated the impact of this combination on decreasing tumor growth and tumor metastasis. Our results indicate that ONC201 and anti-angiogenic agents act through distinct mechanisms while increasing tumor cell death and inhibiting proliferation.

Conclusion

With the use of both a murine VEGF inhibitor in syngeneic models, and bevacizumab in human cell line-derived xenografts, we demonstrate that ONC201 in combination with anti-angiogenic therapies such as bevacizumab represents a promising approach for further testing in the clinic for the treatment of CRC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0671-0) contains supplementary material, which is available to authorized users.

Anti-pancreatic cancer activity of ONC212 involves the unfolded protein response (UPR) and is reduced by IGF1-R and GRP78/BIP

Pancreatic cancer is chemo-resistant and metastasizes early with an overall five-year survival of ∼8.2%. First-in-class imipridone ONC201 is a small molecule in clinical trials with anti-cancer activity. ONC212, a fluorinated-ONC201 analogue, shows preclinical efficacy in melanoma and hepatocellular-cancer models. We investigated efficacy of ONC201 and ONC212 against pancreatic cancer cell lines (N=16 including 9 PDX-cell lines). We demonstrate ONC212 efficacy in 4 in-vivo models including ONC201-resistant tumors. ONC212 is active in pancreatic cancer as single agent or in combination with 5-fluorouracil, irinotecan, oxaliplatin or RTK inhibitor crizotinib. Based on upregulation of pro-survival IGF1-R in some tumors, we found an active combination of ONC212 with inhibitor AG1024, including in vivo. We show a rationale for targeting pancreatic cancer using ONC212 combined with targeting the unfolded-protein response and ER chaperones such as GRP78/BIP. Our results lay the foundation to test imipridones, anti-cancer agents, in pancreatic cancer, that is refractory to most drugs.