Initial testing (stage 1) of the curaxin CBL0137 by the pediatric preclinical testing program

Identification of curaxin as a potential new therapeutic for JAK2 V617F mutant patients

Myelofibrosis is a myeloproliferative neoplasm (MPN) which typically results in reduced length and quality of life due to systemic symptoms and blood count changes arising from fibrotic changes in the bone marrow. While the JAK2 inhibitor ruxolitinib provides some clinical benefit, there remains a substantial unmet need for novel targeted therapies to better modify the disease process or eradicate the cells at the heart of myelofibrosis pathology. Repurposing drugs bypasses many of the hurdles present in drug development, such as toxicity and pharmacodynamic profiling. To this end we undertook a re-analysis of our pre-existing proteomic data sets to identify perturbed biochemical pathways and their associated drugs/inhibitors to potentially target the cells driving myelofibrosis. This approach identified CBL0137 as a candidate for targeting Jak2 mutation-driven malignancies. CBL0137 is a drug derived from curaxin targeting the Facilitates Chromatin Transcription (FACT) complex. It is reported to trap the FACT complex on chromatin thereby activating p53 and inhibiting NF-kB activity. We therefore assessed the activity of CBL0137 in primary patient samples and murine models of Jak2-mutated MPN and found it preferentially targets CD34+ stem and progenitor cells from myelofibrosis patients by comparison with healthy control cells. Further we investigate its mechanism of action in primary haemopoietic progenitor cells and demonstrate its ability to reduce splenomegaly and reticulocyte number in a transgenic murine model of myeloproliferative neoplasms.

Curaxin CBL0137 inhibits endothelial inflammation and atherogenesis via suppression of the Src-YAP signalling axis

BACKGROUND AND PURPOSE

Atherosclerotic vascular disease is the leading cause of mortality and morbidity worldwide. Our previous study uncovered that endothelium-specific knockdown of YAP suppresses atherogenesis, suggesting that YAP is a promising therapeutic target against atherosclerotic vascular disease. We established a drug screening platform, which aimed to identify new YAP inhibitors for anti-atherosclerotic treatment.

EXPERIMENTAL APPROACH

Drug screening was performed by a luciferase reporter gene assay. RNA sequencing was performed to acquire the transcriptomic profile of CBL0137-treated endothelial cells. We assessed and validated the inhibitory effect of CBL0137 on YAP activity and inflammatory response in HUVECs and HAECs. We evaluated the vasoprotective effect of CBL0137 in vivo against plaque formation in ApoE^-/- mice, using both disturbed flow-induced and chronic western diet-induced atherosclerotic models.

KEY RESULTS

We identified CBL0137 as a novel YAP inhibitor from an FDA drug library. CBL0137 inhibited YAP activity by restraining its phosphorylation at Y357. CBL0137 inhibited YAP activity to repress endothelial inflammation. Mechanistically, CBL0137 suppressed YAP phosphorylation at Y357 via the tyrosine-protein kinase Src. Furthermore, administration of CBL0137 ameliorated endothelial inflammation and the atherogenesis induced by disturbed flow and consumption of an atherogenic diet in ApoE^-/- mice.

CONCLUSION AND IMPLICATIONS

To our knowledge, this is the first study to identify CBL0137 as a novel YAP inhibitor. We have demonstrated that pharmacologically targeting YAP by CBL0137 inhibits atherogenesis. The present results suggest that CBL0137 holds promise as a new drug for the treatment of atherosclerotic vascular disease.

Recent progress and novel approaches to treating atypical teratoid rhabdoid tumor

Atypical teratoid rhabdoid tumors (AT/RT) are malignant central nervous system (CNS) tumors that occur mostly in young children and have historically carried a very poor prognosis. While recent clinical trial results show that this tumor is curable, outcomes are still poor compared to other central nervous system embryonal tumors. We here review prior AT/RT clinical trials and highlight promising pre-clinical results that may inform novel clinical approaches to this aggressive cancer.

Targeting Features of Curaxin CBL0137 on Hematological Malignancies In Vitro and In Vivo

The anticancer activity of Curaxin CBL0137, a DNA-binding small molecule with chromatin remodulating effect, has been demonstrated in different cancers. Herein, a comparative evaluation of CBL0137 activity was performed in respect to acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia and multiple myeloma (MM) cultured in vitro. MTT assay showed AML and MM higher sensitivity to CBL0137's cytostatic effect comparatively to other hematological malignancy cells. Flow cytometry cell cycle analysis revealed an increase in subG1 and G2/M populations after CBL0137 cell treatment, but the prevalent type of arrest varied. Apoptosis activation by CBL0137 measured by Annexin-V/PI dual staining was more active in AML and MM cells. RT2 PCR array showed that changes caused by CBL0137 in signaling pathways involved in cancer pathogenesis were more intensive in AML and MM cells. On the murine model of AML WEHI-3, CBL0137 showed significant anticancer effects in vivo, which were evaluated by corresponding changes in spleen and liver. Thus, more pronounced anticancer effects of CBL0137 in vitro were observed in respect to AML and MM. Experiments in vivo also indicated the perspective of CBL0137 use for AML treatment. This in accordance with the frontline treatment approach in AML using epigenetic drugs.

TP53 loss‑of‑function mutations reduce sensitivity of acute leukaemia to the curaxin CBL0137

The presence of a TP53 mutation is a predictor of poor outcome in leukaemia, and efficacious targeted therapies for these patients are lacking. The curaxin CBL0137 has demonstrated promising antitumour activities in multiple cancers such as glioblastoma, acting through p53 activation, NF‑κB inhibition and chromatin remodelling. In the present study, it was revealed using Annexin‑V/7‑AAD apoptosis assays that CBL0137 has efficacy across several human acute leukaemia cell lines with wild‑type TP53, but sensitivity is reduced in TP53‑mutated subtypes. A heterozygous TP53 loss‑of‑function mutation in the KMT2A‑AFF1 human RS4;11 cell line was generated, and it was demonstrated that heterozygous TP53 loss‑of‑function is sufficient to cause a significant reduction in CBL0137 sensitivity. To the best of our knowledge, this is the first evidence to suggest a clinically significant role for functional p53 in the efficacy of CBL0137 in acute leukaemia. Future CBL0137 clinical trials should include TP53 mutation screening, to establish the clinical relevance of TP53 mutations in CBL0137 efficacy.

Kidney cancer biomarkers and targets for therapeutics: survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, p53, KRAS and AKT in renal cell carcinoma

The incidence of renal cell carcinoma (RCC) is increasing worldwide with an approximate 20% mortality rate. The challenge in RCC is the therapy-resistance. Cancer resistance to treatment employs multiple mechanisms due to cancer heterogeneity with multiple genetic and epigenetic alterations. These changes include aberrant overexpression of (1) anticancer cell death proteins (e.g., survivin/BIRC5), (2) DNA repair regulators (e.g., ERCC6) and (3) efflux pump proteins (e.g., ABCG2/BCRP); mutations and/or deregulation of key (4) oncogenes (e.g., MDM2, KRAS) and/or (5) tumor suppressor genes (e.g., TP5/p53); and (6) deregulation of redox-sensitive regulators (e.g., HIF, NRF2). Foci of tumor cells that have these genetic alterations and/or deregulation possess survival advantages and are selected for survival during treatment. We will review the significance of survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, TP5/p53, KRAS and AKT in treatment resistance as the potential therapeutic biomarkers and/or targets in RCC in parallel with our analized RCC-relevant TCGA genetic results from each of these gene/protein molecules. We then present our data to show the anticancer drug FL118 modulation of these protein targets and RCC cell/tumor growth. Finally, we include additional data to show a promising FL118 analogue (FL496) for treating the specialized type 2 papillary RCC.

Histone chaperone FACT complex inhibitor CBL0137 interferes with DNA damage repair and enhances sensitivity of medulloblastoma to chemotherapy and radiation

Medulloblastoma (MB) is a malignant pediatric brain tumor with a poor prognosis. Post-surgical radiation and cisplatin-based chemotherapy have been a mainstay of treatment, which often leads to substantial neurocognitive impairments and morbidity, highlighting the need for a novel therapeutic target to enhance the sensitivity of MB tumors to cytotoxic therapies. We performed a comprehensive study using a cohort of 71 MB patients' samples and pediatric MB cell lines and found that MB tumors have elevated levels of nucleosome remodeling FACT (FAcilitates Chromatin Transcription) complex and DNA repair enzyme AP-endonuclease1 (APE1). FACT interacts with APE1 and facilitates recruitment and acetylation of APE1 to promote repair of radiation and cisplatin-induced DNA damage. Further, levels of FACT and acetylated APE1 both are correlate strongly with MB patients' survival. Targeting FACT complex with CBL0137 inhibits DNA repair and alters expression of a subset of genes, and significantly improves the potency of cisplatin and radiation in vitro and in MB xenograft. Notably, combination of CBL0137 and cisplatin significantly suppressed MB tumor growth in an intracranial orthotopic xenograft model. We conclude that FACT complex promotes chemo-radiation resistance in MB, and FACT inhibitor CBL0137 can be used as a chemo-radiation sensitizer to augment treatment efficacy and reduce therapy-related toxicity in high-risk pediatric patients.

Stimulation of an anti-tumor immune response with "chromatin-damaging" therapy

Curaxins are small molecules that bind genomic DNA and interfere with DNA-histone interactions leading to the loss of histones and decondensation of chromatin. We named this phenomenon 'chromatin damage'. Curaxins demonstrated anti-cancer activity in multiple pre-clinical tumor models. Here, we present data which reveals, for the first time, a role for the immune system in the anti-cancer effects of curaxins. Using the lead curaxin, CBL0137, we observed elevated expression of several group of genes in CBL0137-treated tumor cells including interferon sensitive genes, MHC molecules, some embryo-specific antigens suggesting that CBL0137 increases tumor cell immunogenicity and improves recognition of tumor cells by the immune system. In support of this, we found that the anti-tumor activity of CBL0137 was reduced in immune deficient SCID mice when compared to immune competent mice. Anti-tumor activity of CBL0137 was abrogated in CD8+ T cell depleted mice but only partially lost when natural killer or CD4+ T cells were depleted. Further support for a key role for the immune system in the anti-tumor activity of CBL0137 is evidenced by an increased antigen-specific effector CD8+ T cell and NK cell response, and an increased ratio of effector T cells to Tregs in the tumor and spleen. CBL0137 also elevated the number of CXCR3-expressing CTLs in the tumor and the level of interferon-γ-inducible protein 10 (IP-10) in serum, suggesting IP-10/CXCR3 controls CBL0137-elicited recruitment of effector CTLs to tumors. Our collective data underscores a previously unrecognized role for both innate and adaptive immunity in the anti-tumor activity of curaxins.

Dual Targeting of Chromatin Stability By The Curaxin CBL0137 and Histone Deacetylase Inhibitor Panobinostat Shows Significant Preclinical Efficacy in Neuroblastoma

PURPOSE

We investigated whether targeting chromatin stability through a combination of the curaxin CBL0137 with the histone deacetylase (HDAC) inhibitor, panobinostat, constitutes an effective multimodal treatment for high-risk neuroblastoma.

EXPERIMENTAL DESIGN

The effects of the drug combination on cancer growth were examined in vitro and in animal models of MYCN-amplified neuroblastoma. The molecular mechanisms of action were analyzed by multiple techniques including whole transcriptome profiling, immune deconvolution analysis, immunofluorescence, flow cytometry, pulsed-field gel electrophoresis, assays to assess cell growth and apoptosis, and a range of cell-based reporter systems to examine histone eviction, heterochromatin transcription, and chromatin compaction.

RESULTS

The combination of CBL0137 and panobinostat enhanced nucleosome destabilization, induced an IFN response, inhibited DNA damage repair, and synergistically suppressed cancer cell growth. Similar synergistic effects were observed when combining CBL0137 with other HDAC inhibitors. The CBL0137/panobinostat combination significantly delayed cancer progression in xenograft models of poor outcome high-risk neuroblastoma. Complete tumor regression was achieved in the transgenic Th-MYCN neuroblastoma model which was accompanied by induction of a type I IFN and immune response. Tumor transplantation experiments further confirmed that the presence of a competent adaptive immune system component allowed the exploitation of the full potential of the drug combination.

CONCLUSIONS

The combination of CBL0137 and panobinostat is effective and well-tolerated in preclinical models of aggressive high-risk neuroblastoma, warranting further preclinical and clinical investigation in other pediatric cancers. On the basis of its potential to boost IFN and immune responses in cancer models, the drug combination holds promising potential for addition to immunotherapies.

Proteomic Analysis of an Induced Pluripotent Stem Cell Model Reveals Strategies to Treat Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm of early childhood with a poor survival rate, thus there is a requirement for improved treatment strategies. Induced pluripotent stem cells offer the ability to model disease and develop new treatment strategies. JMML is frequently associated with mutations in PTPN11. Children with Noonan syndrome, a development disorder, have an increased incidence of JMML associated with specific germline mutations in PTPN11. We undertook a proteomic assessment of myeloid cells derived from induced pluripotent stem cells obtained from Noonan syndrome patients with PTPN11 mutations, either associated or not associated with an increased incidence of JMML. We report that the proteomic perturbations induced by the leukemia-associated PTPN11 mutations are associated with TP53 and NF-Kκb signaling. We have previously shown that MYC is involved in the differential gene expression observed in Noonan syndrome patients associated with an increased incidence of JMML. Thus, we employed drugs to target these pathways and demonstrate differential effects on clonogenic hematopoietic cells derived from Noonan syndrome patients, who develop JMML and those who do not. Further, we demonstrated these small molecular inhibitors, JQ1 and CBL0137, preferentially extinguish primitive hematopoietic cells from sporadic JMML patients as opposed to cells from healthy individuals.

Challenges and Opportunities for Childhood Cancer Drug Development

Cancer in children is rare with approximately 15,700 new cases diagnosed in the United States annually. Through use of multimodality therapy (surgery, radiation therapy, and aggressive chemotherapy), 70% of patients will be "cured" of their disease, and 5-year event-free survival exceeds 80%. However, for patients surviving their malignancy, therapy-related long-term adverse effects are severe, with an estimated 50% having chronic life-threatening toxicities related to therapy in their fourth or fifth decade of life. While overall intensive therapy with cytotoxic agents continues to reduce cancer-related mortality, new understanding of the molecular etiology of many childhood cancers offers an opportunity to redirect efforts to develop effective, less genotoxic therapeutic options, including agents that target oncogenic drivers directly, and the potential for use of agents that target the tumor microenvironment and immune-directed therapies. However, for many high-risk cancers, significant challenges remain.

Potent antileukemic activity of curaxin CBL0137 against MLL-rearranged leukemia

Around 10% of acute leukemias harbor a rearrangement of the MLL/KMT2A gene, and the presence of this translocation results in a highly aggressive, therapy-resistant leukemia subtype with survival rates below 50%. There is a high unmet need to identify safer and more potent therapies for MLL-rearranged (MLL-r) leukemia that can be combined with established chemotherapeutics to decrease treatment-related toxicities. The curaxin, CBL0137, has demonstrated nongenotoxic anticancer and chemopotentiating effects in a number of preclinical cancer models and is currently in adult Phase I clinical trials for solid tumors and hematological malignancies. The aim of our study was to investigate whether CBL0137 has potential as a therapeutic and chemopotentiating compound in MLL-r leukemia through a comprehensive analysis of its efficacy in preclinical models of the disease. CBL0137 decreased the viability of a panel of MLL-r leukemia cell lines (n = 12) and xenograft cells derived from patients with MLL-r acute lymphoblastic leukemia (ALL, n = 3) in vitro with submicromolar IC50s. The small molecule drug was well-tolerated in vivo and significantly reduced leukemia burden in a subcutaneous MV4;11 MLL-r acute myeloid leukemia model and in patient-derived xenograft models of MLL-r ALL (n = 5). The in vivo efficacy of standard of care drugs used in remission induction for pediatric ALL was also potentiated by CBL0137. CBL0137 exerted its anticancer effect by trapping Facilitator of Chromatin Transcription (FACT) into chromatin, activating the p53 pathway and inducing an Interferon response. Our findings support further preclinical evaluation of CBL0137 as a new approach for the treatment of MLL-r leukemia.

SSRP1 promotes colorectal cancer progression and is negatively regulated by miR-28-5p

In this study, microarray data analysis, real‐time quantitative PCR and immunohistochemistry were used to detect the expression levels of SSRP1 in colorectal cancer (CRC) tissue and in corresponding normal tissue. The association between structure‐specific recognition protein 1 (SSRP1) expression and patient prognosis was examined by Kaplan‐Meier analysis. SSRP1 was knocked down and overexpressed in CRC cell lines, and its effects on proliferation, cell cycling, migration, invasion, cellular energy metabolism, apoptosis, chemotherapeutic drug sensitivity and cell phenotype‐related molecules were assessed. The growth of xenograft tumours in nude mice was also assessed. MiRNAs that potentially targeted SSRP1 were determined by bioinformatic analysis, Western blotting and luciferase reporter assays. We showed that SSRP1 mRNA levels were significantly increased in CRC tissue. We also confirmed that this upregulation was related to the terminal tumour stage in CRC patients, and high expression levels of SSRP1 predicted shorter disease‐free survival and faster relapse. We also found that SSRP1 modulated proliferation, metastasis, cellular energy metabolism and the epithelial‐mesenchymal transition in CRC. Furthermore, SSRP1 induced apoptosis and SSRP1 knockdown augmented the sensitivity of CRC cells to 5‐fluorouracil and cisplatin. Moreover, we explored the molecular mechanisms accounting for the dysregulation of SSRP1 in CRC and identified microRNA‐28‐5p (miR‐28‐5p) as a direct upstream regulator of SSRP1. We concluded that SSRP1 promotes CRC progression and is negatively regulated by miR‐28‐5p.

Current Strategies for Elimination of HIV-1 Latent Reservoirs Using Chemical Compounds Targeting Host and Viral Factors

Since the implementation of combination antiretroviral therapy (cART), rates of HIV type 1 (HIV-1) mortality, morbidity, and newly acquired infections have decreased dramatically. In fact, HIV-1-infected individuals under effective suppressive cART approach normal life span and quality of life. However, long-term therapy is required because the virus establish a reversible state of latency in memory CD4⁺ T cells. Two principle strategies, namely "shock and kill" approach and "block and lock" approach, are currently being investigated for the eradication of these HIV-1 latent reservoirs. Actually, both of these contrasting approaches are based on the use of small-molecule compounds to achieve the cure for HIV-1. In this review, we discuss the recent progress that has been made in designing and developing small-molecule compounds for both strategies.

Identifying novel therapeutic agents using xenograft models of pediatric cancer

In the USA, the overall cure rate for all childhood cancers is seventy percent, and in many patients that ultimately fail curative therapy, initial responses to current multimodality treatments (surgery, radiation therapy and chemotherapy) is good, with overall 5-year event-free survival approaching 80 %. However, current approaches to curative therapy result in significant morbidity and long-term sequelae, including cardiac dysfunction and cognitive impairment. Furthermore, dose-intensive chemotherapy with conventional agents has not significantly improved outcomes for patients that present with advanced or metastatic disease. Classical cytotoxic agents remain the backbone for curative therapy of both hematologic and solid tumors of childhood. While 'molecularly' targeted agents have shown some clinical activity, responses are often modest and of short duration; hence, there is a need to identify new classes of cytotoxic agent that are effective in patients at relapse and that have reduced or different toxicity profiles to normal tissues. Here we review the pediatric preclinical testing program experience of testing novel agents, and the value and limitations of preclinical xenograft models and genetically engineered mouse models for developing novel agents for treatment of childhood cancer.