P53 activation inhibits all types of hematopoietic progenitors and all stages of megakaryopoiesis

Nanoencapsulation of MDM2 Inhibitor RG7388 and Class-I HDAC Inhibitor Entinostat Enhances their Therapeutic Potential Through Synergistic Antitumor Effects and Reduction of Systemic Toxicity

Inhibitors of the p53-MDM2 interaction such as RG7388 have been developed to exploit latent tumor suppressive properties in p53 in 50% of tumors in which p53 is wild-type. However, these agents for the most part activate cell cycle arrest rather than death, and high doses in patients elicit on-target dose-limiting neutropenia. Recent work from our group indicates that combination of p53-MDM2 inhibitors with the class-I HDAC inhibitor Entinostat (which itself has dose-limiting toxicity issues) has the potential to significantly augment cell death in p53 wild-type colorectal cancer cells. We investigated whether coencapsulation of RG7388 and Entinostat within polymeric nanoparticles (NPs) could overcome efficacy and toxicity limitations of this drug combination. Combinations of RG7388 and Entinostat across a range of different molar ratios resulted in synergistic increases in cell death when delivered in both free drug and nanoencapsulated formats in all colorectal cell lines tested. Importantly, we also explored the in vivo impact of the drug combination on murine blood leukocytes, showing that the leukopenia induced by the free drugs could be significantly mitigated by nanoencapsulation. Taken together, this study demonstrates that formulating these agents within a single nanoparticle delivery platform may provide clinical utility beyond use as nonencapsulated agents.

The Role of p53 in Nanoparticle-Based Therapy for Cancer

p53 is arguably one of the most important tumor suppressor genes in humans. Due to the paramount importance of p53 in the onset of cell cycle arrest and apoptosis, the p53 gene is found either silenced or mutated in the vast majority of cancers. Furthermore, activated wild-type p53 exhibits a strong bystander effect, thereby activating apoptosis in surrounding cells without being physically present there. For these reasons, p53-targeted therapy that is designed to restore the function of wild-type p53 in cancer cells seems to be a very appealing therapeutic approach. Systemic delivery of p53-coding DNA or RNA using nanoparticles proved to be feasible both in vitro and in vivo. In fact, one p53-based therapeutic (gendicine) is currently approved for commercial use in China. However, the broad use of p53-based therapy in p53-inactivated cancers is severely restricted by its inadequate efficacy. This review highlights the current state-of-the-art in this area of biomedical research and also discusses novel approaches that may help overcome the shortcomings of p53-targeting nanomedicine.

Targeting apoptosis dysregulation in myeloid malignancies - The promise of a therapeutic revolution

In recent years, the therapeutic landscape of myeloid malignancies has been completely revolutionized by the introduction of several new drugs, targeting molecular alterations or pathways crucial for leukemia cells survival. Particularly, many agents targeting apoptosis have been investigated in both pre-clinical and clinical studies. For instance, venetoclax, a pro-apoptotic agent active on BCL-2 signaling, has been successfully used in the treatment of acute myeloid leukemia (AML). The impressive results achieved in this context have made the apoptotic pathway an attractive target also in other myeloid neoplasms, translating the experience of AML. Therefore, several drugs are now under investigation either as single or in combination strategies, due to their synergistic efficacy and capacity to overcome resistance. In this paper, we will review the mechanisms of apoptosis and the specific drugs currently used and under investigation for the treatment of myeloid neoplasia, identifying critical research necessities for the upcoming years.

Single-cell multi-omics identifies chronic inflammation as a driver of TP53-mutant leukemic evolution

Understanding the genetic and nongenetic determinants of tumor protein 53 (TP53)-mutation-driven clonal evolution and subsequent transformation is a crucial step toward the design of rational therapeutic strategies. Here we carry out allelic resolution single-cell multi-omic analysis of hematopoietic stem/progenitor cells (HSPCs) from patients with a myeloproliferative neoplasm who transform to TP53-mutant secondary acute myeloid leukemia (sAML). All patients showed dominant TP53 'multihit' HSPC clones at transformation, with a leukemia stem cell transcriptional signature strongly predictive of adverse outcomes in independent cohorts, across both TP53-mutant and wild-type (WT) AML. Through analysis of serial samples, antecedent TP53-heterozygous clones and in vivo perturbations, we demonstrate a hitherto unrecognized effect of chronic inflammation, which suppressed TP53 WT HSPCs while enhancing the fitness advantage of TP53-mutant cells and promoted genetic evolution. Our findings will facilitate the development of risk-stratification, early detection and treatment strategies for TP53-mutant leukemia, and are of broad relevance to other cancer types.

Neurons and glial cells acquire a senescent signature after repeated mild traumatic brain injury in a sex-dependent manner

Mild traumatic brain injury (mTBI) is an important public health issue, as it can lead to long-term neurological symptoms and risk of neurodegenerative disease. The pathophysiological mechanisms driving this remain unclear, and currently there are no effective therapies for mTBI. In this study on repeated mTBI (rmTBI), we have induced three mild closed-skull injuries or sham procedures, separated by 24 h, in C57BL/6 mice. We show that rmTBI mice have prolonged righting reflexes and astrogliosis, with neurological impairment in the Morris water maze (MWM) and the light dark test. Cortical and hippocampal tissue analysis revealed DNA damage in the form of double-strand breaks, oxidative damage, and R-loops, markers of cellular senescence including p16 and p21, and signaling mediated by the cGAS-STING pathway. This study identified novel sex differences after rmTBI in mice. Although these markers were all increased by rmTBI in both sexes, females had higher levels of DNA damage, lower levels of the senescence protein p16, and lower levels of cGAS-STING signaling proteins compared to their male counterparts. Single-cell RNA sequencing of the male rmTBI mouse brain revealed activation of the DNA damage response, evidence of cellular senescence, and pro-inflammatory markers reminiscent of the senescence-associated secretory phenotype (SASP) in neurons and glial cells. Cell-type specific changes were also present with evidence of brain immune activation, neurotransmission alterations in both excitatory and inhibitory neurons, and vascular dysfunction. Treatment of injured mice with the senolytic drug ABT263 significantly reduced markers of senescence only in males, but was not therapeutic in females. The reduction of senescence by ABT263 in male mice was accompanied by significantly improved performance in the MWM. This study provides compelling evidence that senescence contributes to brain dysfunction after rmTBI, but may do so in a sex-dependent manner.

Molecular Targeting of the Most Functionally Complex Gene in Precision Oncology: p53

While chemotherapy is a key treatment strategy for many solid tumors, it is rarely curative, and most tumor cells eventually become resistant. Because of this, there is an unmet need to develop systemic treatments that capitalize on the unique mutational landscape of each patient's tumor. The most frequently mutated protein in cancer, p53, has a role in nearly all cancer subtypes and tumorigenesis stages and therefore is one of the most promising molecular targets for cancer treatment. Unfortunately, drugs targeting p53 have seen little clinical success despite promising preclinical data. Most of these drug compounds target specific aspects of p53 inactivation, such as through inhibiting negative regulation by the mouse double minute (MDM) family of proteins. These treatment strategies fail to address cancer cells' adaptation mechanisms and ignore the impact that p53 loss has on the entire p53 network. However, recent gene therapy successes show that targeting the p53 network and cellular dysfunction caused by p53 inactivation is now possible and may soon translate into successful clinical responses. In this review, we discuss p53 signaling complexities in cancer that have hindered the development and use of p53-targeted drugs. We also describe several current therapeutics reporting promising preclinical and clinical results.

Targeting Cellular Senescence for Age-Related Diseases: Path to Clinical Translation

SUMMARY

Beyond the palliative reach of today's medicines, medical therapies of tomorrow aim to treat the root cause of age-related diseases by targeting fundamental aging mechanisms. Pillars of aging include, among others, genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, dysregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. The unitary theory of fundamental aging processes posits that by targeting one fundamental aging process, it may be feasible to impact several or all others given its interdependence. Indeed, pathologic accumulation of senescent cells is implicated in chronic diseases and age-associated morbidities, suggesting that senescent cells are a good target for whole-body aging intervention. Preclinical studies using senolytics, agents that selectively eliminate senescent cells, and senomorphics, agents that inhibit production or release of senescence-associated secretory phenotype factors, show promise in several aging and disease preclinical models. Early clinical trials using a senolytic combination (dasatinib and quercetin), and other senolytics including flavonoid, fisetin, and BCL-xL inhibitors, illustrate the potential of senolytics to alleviate age-related dysfunction and diseases including wound healing. Translation into clinical applications requires parallel clinical trials across institutions to validate senotherapeutics as a vanguard for delaying, preventing, or treating age-related disorders and aesthetic aging.

Identification of a small-molecule RPL11 mimetic that inhibits tumor growth by targeting MDM2-p53 pathway

BACKGROUND

Targeting ribosome biogenesis to activate p53 has recently emerged as a therapeutic strategy in human cancer. Among various ribosomal proteins, RPL11 centralizes the nucleolar stress-sensing pathway by binding MDM2, leading to MDM2 inactivation and p53 activation. Therefore, the identification of MDM2-binding RPL11-mimetics would be valuable for anti-cancer therapeutics.

METHODS

Based on the crystal structure of the interface between RPL11 and MDM2, we have identified 15 potential allosteric modulators of MDM2 through the virtual screening.

RESULTS

One of these compounds, named S9, directly binds MDM2 and competitively inhibits the interaction between RPL11 and MDM2, leading to p53 stabilization and activation. Moreover, S9 inhibits cancer cell proliferation in vitro and in vivo. Mechanistic study reveals that MDM2 is required for S9-induced G2 cell cycle arrest and apoptosis, whereas p53 contributes to S9-induced apoptosis.

CONCLUSIONS

Putting together, S9 may serve as a lead compound for the development of an anticancer drug that specifically targets RPL11-MDM2-p53 pathway.

Results from a First-in-Human Phase I Study of Siremadlin (HDM201) in Patients with Advanced Wild-Type TP53 Solid Tumors and Acute Leukemia

PURPOSE

This phase I, dose-escalation study investigated the recommended dose for expansion (RDE) of siremadlin, a p53-MDM2 inhibitor, in patients with wild-type TP53 advanced solid or hematologic cancers.

PATIENTS AND METHODS

Initial dosing regimens were: 1A (day 1; 21-day cycle; dose 12.5-350 mg) and 2A (days 1-14; 28-day cycle; dose 1-20 mg). Alternative regimens included 1B (days 1 and 8; 28-day cycle) and 2C (days 1-7; 28-day cycle). The primary endpoint was incidence of dose-limiting toxicities (DLT) during cycle 1.

RESULTS

Overall, 115 patients with solid tumors and 93 with hematologic malignancies received treatment. DLTs occurred in 8/92 patients with solid tumors and 10/53 patients with hematologic malignancies. In solid tumors, an RDE of 120 mg was defined in 1B. In hematologic tumors, RDEs were defined in 1A: 250 mg, 1B: 120 mg, and 2C: 45 mg. More patients with hematologic malignancies compared with solid tumors experienced grade 3/4 treatment-related adverse events (71% vs. 45%), most commonly resulting from myelosuppression. These were more frequent and severe in patients with hematologic malignancies; 22 patients exhibited tumor lysis syndrome. Overall response rates at the RDEs were 10.3% [95% confidence interval (CI), 2.2-27.4] in solid tumors and 4.2% (95% CI, 0.1-21.1), 20% (95% CI, 4.3-48.1), and 22.2% (95% CI, 8.6-42.3) in acute myeloid leukemia (AML) in 1B, 1A, and 2C, respectively.

CONCLUSIONS

A common safety profile was identified and preliminary activity was noted, particularly in AML. Comprehensive investigation of dosing regimens yielded recommended doses/regimens for future combination studies.

The Y14-p53 regulatory circuit in megakaryocyte differentiation and thrombocytopenia

Thrombocytopenia-absent radius (TAR) syndrome is caused by RBM8A insufficiency. We generated megakaryocyte-specific Rbm8a knockout (Rbm8aKO^MK) mice that exhibited marked thrombocytopenia, internal hemorrhage, and splenomegaly, providing evidence that genetic deficiency of Rbm8a causes a disorder of platelet production. Rbm8aKO^MK mice accumulated low-ploidy immature megakaryocytes in the bone marrow and exhibited defective platelet activation and aggregation. Accordingly, depletion of Y14 (RBM8A) in human erythroleukemia (HEL) cells compromised phorbol-ester-induced polyploidization. Notably, Y14/RBM8A deficiency induced both p53 and p21 in megakaryocytes and HEL cells. Treatment with a p53 inhibitor restored ex vivo differentiation of Rbm8aKO^MK megakaryocytes and unexpectedly activated Y14 expression in HEL cells. Trp53 knockout partially restored megakaryocyte differentiation by reversing cell-cycle arrest and increased platelet counts of Rbm8aKO^MK, indicating that excess p53 in part accounts for thrombocytopenia in TAR syndrome. This study provides evidence for the role of the Y14-p53 circuit in platelet production and a potential therapeutic strategy.

Phase 1 Trial of ALRN-6924, a Dual Inhibitor of MDMX and MDM2, in Patients with Solid Tumors and Lymphomas Bearing Wild-type TP53

PURPOSE

We describe the first-in-human dose-escalation trial for ALRN-6924, a stabilized, cell-permeating peptide that disrupts p53 inhibition by mouse double minute 2 (MDM2) and MDMX to induce cell-cycle arrest or apoptosis in TP53-wild-type (WT) tumors.

PATIENTS AND METHODS

Two schedules were evaluated for safety, pharmacokinetics, pharmacodynamics, and antitumor effects in patients with solid tumors or lymphomas. In arm A, patients received ALRN-6924 by intravenous infusion once-weekly for 3 weeks every 28 days; arm B was twice-weekly for 2 weeks every 21 days.

RESULTS

Seventy-one patients were enrolled: 41 in arm A (0.16-4.4 mg/kg) and 30 in arm B (0.32-2.7 mg/kg). ALRN-6924 showed dose-dependent pharmacokinetics and increased serum levels of MIC-1, a biomarker of p53 activation. The most frequent treatment-related adverse events were gastrointestinal side effects, fatigue, anemia, and headache. In arm A, at 4.4 mg/kg, dose-limiting toxicities (DLT) were grade 3 (G3) hypotension, G3 alkaline phosphatase elevation, G3 anemia, and G4 neutropenia in one patient each. At the MTD in arm A of 3.1 mg/kg, G3 fatigue was observed in one patient. No DLTs were observed in arm B. No G3/G4 thrombocytopenia was observed in any patient. Seven patients had infusion-related reactions; 3 discontinued treatment. In 41 efficacy-evaluable patients with TP53-WT disease across both schedules the disease control rate was 59%. Two patients had confirmed complete responses, 2 had confirmed partial responses, and 20 had stable disease. Six patients were treated for >1 year. The recommended phase 2 dose was schedule A, 3.1 mg/kg.

CONCLUSIONS

ALRN-6924 was well tolerated and demonstrated antitumor activity.

Cellular Senescence in Lung Fibrosis

Fibrosing interstitial lung diseases (ILDs) are chronic and ultimately fatal age-related lung diseases characterized by the progressive and irreversible accumulation of scar tissue in the lung parenchyma. Over the past years, significant progress has been made in our incomplete understanding of the pathobiology underlying fibrosing ILDs, in particular in relation to diverse age-related processes and cell perturbations that seem to lead to maladaptation to stress and susceptibility to lung fibrosis. Growing evidence suggests that a specific biological phenomenon known as cellular senescence plays an important role in the initiation and progression of pulmonary fibrosis. Cellular senescence is defined as a cell fate decision caused by the accumulation of unrepairable cellular damage and is characterized by an abundant pro-inflammatory and pro-fibrotic secretome. The senescence response has been widely recognized as a beneficial physiological mechanism during development and in tumour suppression. However, recent evidence strengthens the idea that it also drives degenerative processes such as lung fibrosis, most likely by promoting molecular and cellular changes in chronic fibrosing processes. Here, we review how cellular senescence may contribute to lung fibrosis pathobiology, and we highlight current and emerging therapeutic approaches to treat fibrosing ILDs by targeting cellular senescence.

Senolytic drugs: from discovery to translation

Senolytics are a class of drugs that selectively clear senescent cells (SC). The first senolytic drugs Dasatinib, Quercetin, Fisetin and Navitoclax were discovered using a hypothesis-driven approach. SC accumulate with ageing and at causal sites of multiple chronic disorders, including diseases accounting for the bulk of morbidity, mortality and health expenditures. The most deleterious SC are resistant to apoptosis and have up-regulation of anti-apoptotic pathways which defend SC against their own inflammatory senescence-associated secretory phenotype (SASP), allowing them to survive, despite killing neighbouring cells. Senolytics transiently disable these SCAPs, causing apoptosis of those SC with a tissue-destructive SASP. Because SC take weeks to reaccumulate, senolytics can be administered intermittently - a 'hit-and-run' approach. In preclinical models, senolytics delay, prevent or alleviate frailty, cancers and cardiovascular, neuropsychiatric, liver, kidney, musculoskeletal, lung, eye, haematological, metabolic and skin disorders as well as complications of organ transplantation, radiation and cancer treatment. As anticipated for agents targeting the fundamental ageing mechanisms that are 'root cause' contributors to multiple disorders, potential uses of senolytics are protean, potentially alleviating over 40 conditions in preclinical studies, opening a new route for treating age-related dysfunction and diseases. Early pilot trials of senolytics suggest they decrease senescent cells, reduce inflammation and alleviate frailty in humans. Clinical trials for diabetes, idiopathic pulmonary fibrosis, Alzheimer's disease, COVID-19, osteoarthritis, osteoporosis, eye diseases and bone marrow transplant and childhood cancer survivors are underway or beginning. Until such studies are done, it is too early for senolytics to be used outside of clinical trials.

Targeting p53-MDM2 Interaction Using Small Molecule Inhibitors and the Challenges Needed to be Addressed

MDM2 protein is the core negative regulator of p53 that maintains the cellular levels of p53 at a low level in normal cells. Mutation of the TP53 gene accounts for 50% of all human cancers. In the remaining malignancies with wild-type TP53, p53 function is inhibited through other mechanisms. Recently, synthetic small molecule inhibitors have been developed which target a small hydrophobic pocket on MDM2 to which p53 normally binds. Given that MDM2-p53 antagonists have been undergoing clinical trials for different types of cancer, this review illustrates different aspects of these new cancer targeted therapeutic agents with the focus on the major advances in the field. It emphasizes on the p53 function, regulation of p53, targeting of the p53-MDM2 interaction for cancer therapy, and p53-dependent and -independent effects of inhibition of p53-MDM2 interaction. Then, representatives of small molecule MDM2-p53 binding antagonists are introduced with a focus on those entered into clinical trials. Furthermore, the review discusses the gene signatures in order to predict sensitivity to MDM2 antagonists, potential side effects and the reasons for the observed hematotoxicity, mechanisms of resistance to these drugs, their evaluation as monotherapy or in combination with conventional chemotherapy or with other targeted therapeutic agents. Finally, it highlights the certainly intriguing questions and challenges which would be addressed in future studies.

MDM2 inhibition: an important step forward in cancer therapy

Targeting the interaction between tumor suppressor p53 and the E3 ligase MDM2 represents an attractive treatment approach for cancers with wild-type or functional TP53. Indeed, several small molecules have been developed and evaluated in various malignancies. We provide an overview of MDM2 inhibitors under preclinical and clinical investigation, with a focus on molecules with ongoing clinical trials, as indicated by ClinicalTrials.gov . Because preclinical and clinical exploration of combination strategies is underway, data supporting these combinations are also described. We identified the following molecules for inclusion in this review: RG7112 (RO5045337), idasanutlin (RG7388), AMG-232 (KRT-232), APG-115, BI-907828, CGM097, siremadlin (HDM201), and milademetan (DS-3032b). Information about each MDM2 inhibitor was collected from major congress records and PubMed using the following search terms: each molecule name, "MDM2"and "HDM2." Only congress records were limited by date (January 1, 2012-March 6, 2020). Special attention was given to available data in hematologic malignancies; however, available safety data in any indication are reported. Overall, targeting MDM2 is a promising treatment strategy, as evidenced by the increasing number of MDM2 inhibitors entering the clinic. Additional clinical investigation is needed to further elucidate the role of MDM2 inhibitors in the treatment of human cancers.

Dedifferentiated Liposarcoma: Systemic Therapy Options

OPINION STATEMENT

Over the last several years, the systemic treatment landscape for dedifferentiated liposarcoma (DDLPS) has notably expanded. Historically, systemic therapy options have been limited to cytotoxic chemotherapy agents, including doxorubicin, ifosfamide, gemcitabine, and docetaxel, that were shown to have efficacy in unselected populations of patients with soft tissue sarcomas. More recently, however, there have been phase II and III trials establishing clinical benefit of the cytotoxic agents trabectedin and eribulin along with the tyrosine kinase inhibitor pazopanib in patients with advanced liposarcoma and DDLPS. Additionally, there are several investigational targeted therapies that have incorporated advances in the understanding of DDLPS disease biology, exploiting the fact that nearly all such tumors include highly amplified expression of MDM2 and CDK4. Recent clinical trials have supported the benefit of the CDK4 inhibitor abemaciclib and the nuclear export inhibitor selinexor and support continued development of anti-MDM2 therapies, with particular attention to the bone marrow toxicity and resultant thrombocytopenia that has thus far limited their use. In contrast, the checkpoint inhibitors pembrolizumab and nivolumab remain of questionable benefit, although these immunotherapy drugs may have a role when combined with other therapeutic agents. Ongoing phase III trials will clarify the role of these novel agents. Future directions include directly comparing current standard-of-care options and newer therapies, developing synergistic combinations of novel agents, and evaluating their role in patients with localized DDLPS.

MDM2-p53 Interaction Inhibitors: The Current State-of-Art and Updated Patent Review (2010-Present)

Background:

Mouse Double Minute 2 protein (MDM2) is a cellular regulator of p53 tumor suppressor (p53). Inhibition of the interaction between MDM2 and p53 proteins is a promising anticancer therapy.

Objective:

This updated patent review is an attempt to compile the research and achievements of the various researchers working on small molecule MDM2 inhibitors from 2010 to date. We provide an outlook into the future for therapy based on MDM2 inhibition by presenting an overview of the most relevant patents which have recently appeared in the literature.

Methods:

Literature and recent patents focusing on the anticancer potential of MDM2-p53 interaction inhibitors and its applications have been analyzed. We put the main emphasis on the most perspective compounds which are or were examined in clinical trials.

Results:

Literature data indicated that MDM2 inhibitors are therapeutically effective in specific types of cancer or non-cancer diseases. A great number of patents and research work around new MDM2- p53 interaction inhibitors, possible combinations, new indications, clinical regimens in previous years prove that this targeted therapy is in the scope of interest for many business and academic research groups.

Conclusion:

Novel MDM2 inhibitors thanks to higher potency and better ADME properties have shown effectiveness in preclinical and clinical development however the final improvement of therapeutic potential for MDM2 inhibitors might depend on the useful combination therapy and exploring new cancer and non-cancer indications.

Induction of differentiation of human stem cells ex vivo: Toward large-scale platelet production

Platelet transfusion is one of the most reliable strategies to cure patients suffering from thrombocytopenia or platelet dysfunction. With the increasing demand for transfusion, however, there is an undersupply of donors to provide the platelet source. Thus, scientists have sought to design methods for deriving clinical-scale platelets ex vivo. Although there has been considerable success ex vivo in the generation of transformative platelets produced by human stem cells (SCs), the platelet yields achieved using these strategies have not been adequate for clinical application. In this review, we provide an overview of the developmental process of megakaryocytes and the production of platelets in vivo and ex vivo, recapitulate the key advances in the production of SC-derived platelets using several SC sources, and discuss some strategies that apply three-dimensional bioreactor devices and biochemical factors synergistically to improve the generation of large-scale platelets for use in future biomedical and clinical settings.

Megakaryocyte polyploidization: role in platelet production

Mammal megakaryocytes (MK) undergo polyploidization during their differentiation. This process leads to a marked increase in the MK size and of their cytoplasm. Contrary to division by classical mitosis, ploidization allows an economical manner to produce platelets as they arise from the fragmentation of the MK cytoplasm. The platelet production in vivo correlates to the entire MK cytoplasm mass that depends both upon the number of MKs and their size. Polyploidization occurs by several rounds of DNA replication with at the end of each round an aborted mitosis at late phase of cytokinesis. As there is also a defect in karyokinesis, MKs are giant cells with a single polylobulated nucleus with a 2^xN ploidy. However, polyploidization per se does not increase platelet production because it requires a parallel development of MK organelles such as mitochondria, granules and the demarcation membrane system. MK polyploidization is regulated by extrinsic factors, more particularly by thrombopoietin (TPO), which during a platelet stress increases first polyploidization before enhancing the MK number and by transcription factors such as RUNX1, GATA1, and FLI1 that regulate MK differentiation explaining why polyploidization and cytoplasmic maturation are intermingled. MK polyploidization is ontogenically regulated and is markedly altered in malignant myeloid disorders such as acute megakaryoblastic leukemia and myeloproliferative disorders as well as in hereditary thrombocytopenia, more particularly those involving transcription factors or signaling pathways. In addition, MKs arising from progenitors in vitro have a much lower ploidy in vitro than in vivo leading to a low yield of platelet production in vitro. Thus, it is tempting to find approaches to increase MK polyploidization in vitro. However, these approaches require molecules that are able to simultaneously increase MK polyploidization and to induce terminal differentiation. Here, we will focus on the regulation by extrinsic and intrinsic factors of MK polyploidization during development and pathological conditions.

Senolytics decrease senescent cells in humans: Preliminary report from a clinical trial of Dasatinib plus Quercetin in individuals with diabetic kidney disease

Background

Senescent cells, which can release factors that cause inflammation and dysfunction, the senescence-associated secretory phenotype (SASP), accumulate with ageing and at etiological sites in multiple chronic diseases. Senolytics, including the combination of Dasatinib and Quercetin (D + Q), selectively eliminate senescent cells by transiently disabling pro-survival networks that defend them against their own apoptotic environment. In the first clinical trial of senolytics, D + Q improved physical function in patients with idiopathic pulmonary fibrosis (IPF), a fatal senescence-associated disease, but to date, no peer-reviewed study has directly demonstrated that senolytics decrease senescent cells in humans.

Methods

In an open label Phase 1 pilot study, we administered 3 days of oral D 100 mg and Q 1000 mg to subjects with diabetic kidney disease (N = 9; 68·7 ± 3·1 years old; 2 female; BMI:33·9 ± 2·3 kg/m²; eGFR:27·0 ± 2·1 mL/min/1·73m²). Adipose tissue, skin biopsies, and blood were collected before and 11 days after completing senolytic treatment. Senescent cell and macrophage/Langerhans cell markers and circulating SASP factors were assayed.

Findings

D + Q reduced adipose tissue senescent cell burden within 11 days, with decreases in p16^INK4A-and p21^CIP1-expressing cells, cells with senescence-associated β-galactosidase activity, and adipocyte progenitors with limited replicative potential. Adipose tissue macrophages, which are attracted, anchored, and activated by senescent cells, and crown-like structures were decreased. Skin epidermal p16^INK4A+ and p21^CIP1+ cells were reduced, as were circulating SASP factors, including IL-1α, IL-6, and MMPs-9 and −12.

Interpretation

“Hit-and-run” treatment with senolytics, which in the case of D + Q have elimination half-lives <11 h, significantly decreases senescent cell burden in humans.

Fund

NIH and Foundations.

ClinicalTrials.gov Identifier: NCT02848131. Senescence, Frailty, and Mesenchymal Stem Cell Functionality in Chronic Kidney Disease: Effect of Senolytic Agents.

Anti-tumor activity of the MDM2-TP53 inhibitor BI-907828 in dedifferentiated liposarcoma patient-derived xenograft models harboring MDM2 amplification

PURPOSE

Dedifferentiated liposarcoma (DDLPS) is a soft tissue malignancy characterized by amplification of the mouse double minute 2 homolog (MDM2) gene. MDM2 is a negative regulator of tumor protein 53 (TP53). We tested the in vivo efficacy of BI-907828, a small molecule inhibitor of the MDM2-TP53 interaction, in two DDLPS patient-derived xenografts (PDX).

METHODS

Partially immunodeficient mice were bilaterally engrafted with UZLX-STS3 (n = 24) and UZLX-STS5 (n = 24) human DDLPS tissue harboring MDM2 amplifications. Mice were grouped as follows: (a) vehicle (0.5% hydroxyethylcellullose) 10 ml/kg daily per os (p.o.); (b) doxorubicin 5 mg/kg weekly intraperitoneally (i.p.); (c) BI-907828 2.5 mg/kg daily p.o. and (d) BI-907828 10 mg/kg daily p.o. The treatment lasted for 15 days, all mice treated with BI-907828 were followed for 37 days post-treatment. Efficacy was assessed by tumor volume and histopathological evaluation.

RESULTS

The 15-day treatment with 2.5 mg/kg and 10 mg/kg BI-907828 significantly inhibited tumor growth in UZLX-STS5 and -STS3 (p < 0.0001 compared to control for both models). All UZLX-STS5 and -STS3 tumors treated with BI-907828 decreased in size during treatment, and BI-907828-treated UZLX-STS5 tumors even disappeared completely. During the follow-up period, no tumor regrowth was observed in the UZLX-STS5 model and both doses of BI-907828 led to a pathological complete response, whereas a dose-dependent regrowth was seen in the UZLX-STS3 model.

CONCLUSION

BI-907828 showed significant anti-tumor activity in DDLPS PDX harboring MDM2 amplifications, providing a strong rationale for early clinical testing of BI-907828 in a DDLPS patient population.

MDM2 antagonists as a novel treatment option for acute myeloid leukemia: perspectives on the therapeutic potential of idasanutlin (RG7388)

Acute myeloid leukemia (AML) is a clonal heterogenous malignancy of the myeloid cells with a poor prognosis lending itself to novel treatment strategies. TP53 is a critical tumor suppressor and plays an essential role in leukemogenesis. Although TP53 is relatively unusual in de novo AML, inactivation of wild-type p53 (WT-p53) is a common event. Murine double minute 2 (MDM2) is a key negative regulator of p53 and its expression; inhibition of MDM2 is postulated to reactivate WT-p53 and its tumor suppressor functions. Nutlins were the first small molecule inhibitors that bind to MDM2 and target its interaction with p53. RG7388 (idasanutlin), a second-generation nutlin, was developed to improve upon the potency and toxicity profile of earlier nutlins. Preliminary data from early phase trials and ongoing studies suggest clinical response with RG7388 (idasanutlin) both in monotherapy and combination strategies in AML. We herein briefly discuss currently approved therapies in AML and review the clinical data for RG7388 (idasanutlin) and MDM2 inhibition as novel treatment strategies in AML. We further describe efficacy and toxicity profile data from completed and ongoing trials of RG7388 (idasanutlin) and other MDM2-p53 inhibitors in development. Many targeted therapies have been approved recently in AML, with a focus on the older and unfit population for intensive induction therapy and in relapsed/refractory disease. The "nutlins", including RG7388 (idasanutlin), merit continued investigation in such settings.

A phase I study of the HDM2 antagonist SAR405838 combined with the MEK inhibitor pimasertib in patients with advanced solid tumours

BACKGROUND

This phase I, open-label, dose-escalation study evaluated the safety, pharmacokinetics and pharmacodynamics of combination therapy with the HDM2 inhibitor SAR405838 and the MEK1/2 inhibitor pimasertib administered orally once daily (QD) or twice daily (BID) in locally advanced or metastatic solid tumours (NCT01985191).

METHODS

Patients with locally advanced or metastatic solid tumours with documented wild-type TP53 and RAS or RAF mutations were enroled. A 3 + 3 dose-escalation design was employed. The primary objective was to assess maximum tolerated dose (MTD).

RESULTS

Twenty-six patients were treated with SAR405838 200 or 300 mg QD plus pimasertib 60 mg QD or 45 mg BID. The MTD was SAR405838 200 mg QD plus pimasertib 45 mg BID. The most common dose-limiting toxicity was thrombocytopenia. The most frequently occurring treatment-related adverse events were diarrhoea (81%), increased blood creatine phosphokinase (77%), nausea (62%) and vomiting (62%). No significant drug-drug interactions were observed. The biomarkers MIC-1 and pERK were, respectively, upregulated and downregulated in response to study treatment. In 24 efficacy-evaluable patients, one patient (4%) had a partial response and 63% had stable disease.

CONCLUSIONS

The safety profile of SAR405838 and pimasertib combined was consistent with the safety profiles of both drugs. Preliminary antitumour activity was observed.

Epigenetic regulation of megakaryocytic and erythroid differentiation by PHF2 histone demethylase

Plant homeodomain finger 2 (PHF2) is a JmjC family histone demethylase that demethylates H3K9me2, a repressive gene marker. PHF2 was found to play a role in the differentiation of several tissue types such as osteoblast and adipocyte differentiation. We report here that PHF2 plays a role in the epigenetic regulation of megakaryocytic (MK) and erythroid differentiation. We investigated PHF2 expression during MK and erythroid differentiation in K562 and human CD34⁺ progenitor (hCD34⁺ ) cells. Our data demonstrate that PHF2 expression is down-regulated during megakaryopoiesis and erythropoiesis. PHF2 has a negative role in MK and erythroid differentiation of K562 cells; knockdown of PHF2 promotes MK and erythroid differentiation of hCD34⁺ cells. Similarly, we found that p53 expression is also down-regulated during MK and erythroid differentiation, which parallels PHF2 expression. PHF2 binds to the p53 promoter and regulates the expression of p53 by demethylating H3K9me2 in the promoter region of p53. Taken together, our data show that PHF2 is a negative epigenetic regulator of MK and erythroid differentiation, and that one of the pathways through which PHF2 affects MK and erythroid differentiation is via regulation of p53 expression.

miR-144/451 represses the LKB1/AMPK/mTOR pathway to promote red cell precursor survival during recovery from acute anemia

The microRNAs miR-144 and -451 are encoded by a bicistronic gene that is strongly induced during red blood cell formation (erythropoiesis). Ablation of the miR-144/451 gene in mice causes mild anemia under baseline conditions. Here we show that miR-144/451^−/− erythroblasts exhibit increased apoptosis during recovery from acute anemia. Mechanistically, miR-144/451 depletion increases the expression of the miR-451 target mRNA Cab39, which encodes a co-factor for the serine-threonine kinase LKB1. During erythropoietic stress, miR-144/451^−/− erythroblasts exhibit abnormally increased Cab39 protein, which activates LKB1 and its downstream AMPK/mTOR effector pathway. Suppression of this pathway via drugs or shRNAs enhances survival of the mutant erythroblasts. Thus, miR-144/451 facilitates recovery from acute anemia by repressing Cab39/AMPK/mTOR. Our findings suggest that miR-144/451 is a key protector of erythroblasts during pathological states associated with dramatically increased erythropoietic demand, including acute blood loss and hemolytic anemia.

Identification of key microRNAs associated with diffuse large B-cell lymphoma by analyzing serum microRNA expressions

PURPOSE

This study aimed to investigate the molecular mechanism underlying diffuse large B-cell lymphoma (DLBCL).

METHODS

Serum miRNA expression analysis for the serum samples of patients with DLBCL and those of controls was performed using the Illumina sequencing technology. Differentially expressed miRNAs (DEMs) were identified on the basis of the sequencing data. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses and protein-protein interaction (PPI) network construction for the target genes of DEMs were also conducted. Moreover, the selected DEMs were verified using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

Fifty-one DEMs were identified between DLBCL disease and control groups, of which two were upregulated and 49 were downregulated. In total, 3631 target genes of DEMs were obtained, and hsa-miR-34a-5p had the most target genes. Among the 51 DEMs, 19 were significantly enriched in 41 KEGG pathways. hsa-miR-34a-5p was enriched in 15 pathways such as the p53 signaling pathway. hsa-miR-323b-3p was enriched in four pathways such as pathways in cancer. The PPI network revealed that hsa-miR-34a-5p had the most target genes such as tumor protein p53 (TP53), and hsa-miR-431-5p regulated tyrosine protein kinase Fyn (FYN). Furthermore, qRT-PCR results showed that hsa-miR-34a-5p was upregulated, whereas hsa-miR-323b-3p and hsa-miR-431-5p were downregulated.

CONCLUSION

hsa-miR-34a-5p may be directly regulated by TP53 and may be involved in DLBCL development via the p53 signaling pathway. Furthermore, hsa-miR-323b-3p may be related to DLBCL by participating in pathways in cancer. hsa-miR-431-5p may also play a role in DLBCL by regulating FYN.

MDM2/X inhibitors under clinical evaluation: perspectives for the management of hematological malignancies and pediatric cancer

The two murine double minute (MDM) family members MDM2 and MDMX are at the center of an intense clinical assessment as molecular target for the management of cancer. Indeed, the two proteins act as regulators of P53, a well-known key controller of the cell cycle regulation and cell proliferation that, when altered, plays a direct role on cancer development and progression. Several evidence demonstrated that functional aberrations of P53 in tumors are in most cases the consequence of alterations on the MDM2 and MDMX regulatory proteins, in particular in patients with hematological malignancies where TP53 shows a relatively low frequency of mutation while MDM2 and MDMX are frequently found amplified/overexpressed. The pharmacological targeting of these two P53-regulators in order to restore or increase P53 expression and activity represents therefore a strategy for cancer therapy. From the discovery of the Nutlins in 2004, several compounds have been developed and reported with the ability of targeting the P53-MDM2/X axis by inhibiting MDM2 and/or MDMX. From natural compounds up to small molecules and stapled peptides, these MDM2/X pharmacological inhibitors have been extensively studied, revealing different biological features and different rate of efficacy when tested in in vitro and in vivo experimental tumor models. The data/evidence coming from the preclinical experimentation have allowed the identification of the most promising molecules and the setting of clinical studies for their evaluation as monotherapy or in therapeutic combination with conventional chemotherapy or with innovative therapeutic protocols in different tumor settings. Preliminary results have been recently published reporting data about safety, tolerability, potential side effects, and efficacy of such therapeutic approaches. In this light, the aim of this review is to give an updated overview about the state of the art of the clinical evaluation of MDM2/X inhibitor compounds with a special attention to hematological malignancies and to the potential for the management of pediatric cancers.

Rapamycin and bafilomycin A1 alter autophagy and megakaryopoiesis

Autophagy is an effective strategy for cell development by recycling cytoplasmic constituents. Genetic deletion of autophagy mediator Atg7 in hematopoietic stem cells (HSCs) can lead to failure of megakaryopoiesis and enhanced autophagy has been implicated in various hematological disorders such as immune thrombocytopenia and myelodysplastic syndrome. Here, we examined the hypothesis that optimal autophagy is essential for megakaryopoiesis and thrombopoiesis by altering autophagy using pharmacological approaches. When autophagy was induced by rapamycin or inhibited by bafilomycin A1 in fetal liver cells, we observed a significant decrease in high ploidy megakaryocytes, a reduction of CD41 and CD61 co-expressing cells, and less proplatelet or platelet formation. Additionally, reduced cell size was shown in megakaryocytes derived from rapamycin, but not bafilomycin A1-treated mouse fetal liver cells. However, when autophagy was altered in mature megakaryocytes, we observed no significant change in proplatelet formation, which was consistent with normal platelet counts, megakaryocyte numbers, and ploidy in Atg7^flox/flox PF4-Cre mice with megakaryocyte- and platelet-specific deletion of autophagy-related gene Atg7. Therefore, our findings suggest that either induction or inhibition of autophagy in the early stage of megakaryopoiesis suppresses megakaryopoiesis and thrombopoiesis.

Uncoupling of the Hippo and Rho pathways allows megakaryocytes to escape the tetraploid checkpoint

Megakaryocytes are naturally polyploid cells that increase their ploidy by endomitosis. However, very little is known regarding the mechanism by which they escape the tetraploid checkpoint to become polyploid. Recently, it has been shown that the tetraploid checkpoint was regulated by the Hippo-p53 pathway in response to a downregulation of Rho activity. We therefore analyzed the role of Hippo-p53 pathway in the regulation of human megakaryocyte polyploidy. Our results revealed that Hippo-p53 signaling pathway proteins are present and are functional in megakaryocytes. Although this pathway responds to the genotoxic stress agent etoposide, it is not activated in tetraploid or polyploid megakaryocytes. Furthermore, Hippo pathway was observed to be uncoupled from Rho activity. Additionally, polyploid megakaryocytes showed increased expression of YAP target genes when compared to diploid and tetraploid megakaryocytes. Although p53 knockdown increased both modal ploidy and proplatelet formation in megakaryocytes, YAP knockdown caused no significant change in ploidy while moderately affecting proplatelet formation. Interestingly, YAP knockdown reduced the mitochondrial mass in polyploid megakaryocytes and decreased expression of PGC1α, an important mitochondrial biogenesis regulator. Thus, the Hippo pathway is functional in megakaryocytes, but is not induced by tetraploidy. Additionally, YAP regulates the mitochondrial mass in polyploid megakaryocytes.