APR-246 exhibits anti-leukemic activity and synergism with conventional chemotherapeutic drugs in acute myeloid leukemia cells

Ferroptosis: Potential therapeutic targets and prognostic predictions for acute myeloid leukemia (Review)

Ferroptosis is a relatively recently discovered type of regulated cell death that is induced by iron-dependent lipid peroxidation. The key contributing factors to ferroptosis are the loss of glutathione peroxidase 4 which is required for reversing lipid peroxidation, the buildup of redox-active iron and the oxidation of phospholipids containing polyunsaturated fatty acids. Ferroptosis has been associated with a number of diseases, including cancers such as hepatocellular carcinoma, breast cancer, acute renal damage and neurological disorders such as Alzheimer's disease and Alzheimer's disease, and there may be an association between ferroptosis and acute myeloid leukemia (AML). The present review aims to describe the primary regulatory pathways of ferroptosis, and the relationship between ferroptosis and the occurrence and development of AML. Furthermore, the present review comprehensively summarizes the latest advances in the treatment and prognosis of ferroptosis in AML.

Unmet Horizons: Assessing the Challenges in the Treatment of TP53-Mutated Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains a challenging hematologic malignancy. The presence of TP53 mutations in AML poses a therapeutic challenge, considering that standard treatments face significant setbacks in achieving meaningful responses. There is a pressing need for the development of innovative treatment modalities to overcome resistance to conventional treatments attributable to the unique biology of TP53-mutated (TP53mut) AML. This review underscores the role of TP53 mutations in AML, examines the current landscape of treatment options, and highlights novel therapeutic approaches, including targeted therapies, combination regimens, and emerging immunotherapies, as well as agents being explored in preclinical studies according to their potential to address the unique hurdles posed by TP53mut AML.

The Metabolic Landscape of Breast Cancer and Its Therapeutic Implications

Breast cancer is the most common malignant tumor globally as of 2020 and remains the second leading cause of cancer-related death among female individuals worldwide. Metabolic reprogramming is well recognized as a hallmark of malignancy owing to the rewiring of multiple biological processes, notably, glycolysis, oxidative phosphorylation, pentose phosphate pathway, as well as lipid metabolism, which support the demands for the relentless growth of tumor cells and allows distant metastasis of cancer cells. Breast cancer cells are well documented to reprogram their metabolism via mutations or inactivation of intrinsic factors such as c-Myc, TP53, hypoxia-inducible factor, and the PI3K/AKT/mTOR pathway or crosstalk with the surrounding tumor microenvironments, including hypoxia, extracellular acidification and interaction with immune cells, cancer-associated fibroblasts, and adipocytes. Furthermore, altered metabolism contributes to acquired or inherent therapeutic resistance. Therefore, there is an urgent need to understand the metabolic plasticity underlying breast cancer progression as well as to dictate metabolic reprogramming that accounts for the resistance to standard of care. This review aims to illustrate the altered metabolism in breast cancer and its underlying mechanisms, as well as metabolic interventions in breast cancer treatment, with the intention to provide strategies for developing novel therapeutic treatments for breast cancer.

Understanding the Continuum between High-Risk Myelodysplastic Syndrome and Acute Myeloid Leukemia

Myelodysplastic syndrome (MDS) is a clonal hematopoietic neoplasm characterized by bone marrow dysplasia, failure of hematopoiesis and variable risk of progression to acute myeloid leukemia (AML). Recent large-scale studies have demonstrated that distinct molecular abnormalities detected at earlier stages of MDS alter disease biology and predict progression to AML. Consistently, various studies analyzing these diseases at the single-cell level have identified specific patterns of progression strongly associated with genomic alterations. These pre-clinical results have solidified the conclusion that high-risk MDS and AML arising from MDS or AML with MDS-related changes (AML-MRC) represent a continuum of the same disease. AML-MRC is distinguished from de novo AML by the presence of certain chromosomal abnormalities, such as deletion of 5q, 7/7q, 20q and complex karyotype and somatic mutations, which are also present in MDS and carry crucial prognostic implications. Recent changes in the classification and prognostication of MDS and AML by the International Consensus Classification (ICC) and the World Health Organization (WHO) reflect these advances. Finally, a better understanding of the biology of high-risk MDS and the mechanisms of disease progression have led to the introduction of novel therapeutic approaches, such as the addition of venetoclax to hypomethylating agents and, more recently, triplet therapies and agents targeting specific mutations, including FLT3 and IDH1/2. In this review, we analyze the pre-clinical data supporting that high-risk MDS and AML-MRC share the same genetic abnormalities and represent a continuum, describe the recent changes in the classification of these neoplasms and summarize the advances in the management of patients with these neoplasms.

Targeting p53 pathways: mechanisms, structures, and advances in therapy

The TP53 tumor suppressor is the most frequently altered gene in human cancers, and has been a major focus of oncology research. The p53 protein is a transcription factor that can activate the expression of multiple target genes and plays critical roles in regulating cell cycle, apoptosis, and genomic stability, and is widely regarded as the "guardian of the genome". Accumulating evidence has shown that p53 also regulates cell metabolism, ferroptosis, tumor microenvironment, autophagy and so on, all of which contribute to tumor suppression. Mutations in TP53 not only impair its tumor suppressor function, but also confer oncogenic properties to p53 mutants. Since p53 is mutated and inactivated in most malignant tumors, it has been a very attractive target for developing new anti-cancer drugs. However, until recently, p53 was considered an "undruggable" target and little progress has been made with p53-targeted therapies. Here, we provide a systematic review of the diverse molecular mechanisms of the p53 signaling pathway and how TP53 mutations impact tumor progression. We also discuss key structural features of the p53 protein and its inactivation by oncogenic mutations. In addition, we review the efforts that have been made in p53-targeted therapies, and discuss the challenges that have been encountered in clinical development.

Drugging p53 in cancer: one protein, many targets

Mutations in the TP53 tumour suppressor gene are very frequent in cancer, and attempts to restore the functionality of p53 in tumours as a therapeutic strategy began decades ago. However, very few of these drug development programmes have reached late-stage clinical trials, and no p53-based therapeutics have been approved in the USA or Europe so far. This is probably because, as a nuclear transcription factor, p53 does not possess typical drug target features and has therefore long been considered undruggable. Nevertheless, several promising approaches towards p53-based therapy have emerged in recent years, including improved versions of earlier strategies and novel approaches to make undruggable targets druggable. Small molecules that can either protect p53 from its negative regulators or restore the functionality of mutant p53 proteins are gaining interest, and drugs tailored to specific types of p53 mutants are emerging. In parallel, there is renewed interest in gene therapy strategies and p53-based immunotherapy approaches. However, major concerns still remain to be addressed. This Review re-evaluates the efforts made towards targeting p53-dysfunctional cancers, and discusses the challenges encountered during clinical development.

Clinical features of complex karyotype in newly diagnosed acute myeloid leukemia

Complex karyotype acute myeloid leukemia (CK-AML) has been classified as an adverse-risk subtype. Although a few reports have further classified CK-AML as typical (including monosomy of chromosomes 5, 7 and 17 or deletion of 5q, 7q and/or 17p) or atypical, the clinical features of these subtypes in Japanese patients remain unclear. We retrospectively analyzed a total of 115 patients with CK-AML, including 77 with typical CK-AML and 38 with atypical CK-AML. Median overall survival (OS) was significantly shorter in patients with typical CK-AML than atypical CK-AML (143 days vs. 369 days, P = 0.009). Among patients with typical CK-AML, those with monosomy 17 or deletion of 17p had significantly shorter OS than patients without such abnormalities (105 days vs. 165 days, P = 0.033). TP53 mutations were more predominant in patients with typical CK-AML than in patients with atypical CK-AML (69.7% vs. 32.4%, P < 0.001). Patients with typical CK-AML had a poor prognosis regardless of TP53 mutation status. Among patients with atypical CK-AML, however, prognosis was worse for those with the TP53 mutation than those without the mutation. In conclusion, prognosis is extremely poor for both typical CK-AML and atypical CK-AML with TP53 mutation.

TP-0903 Is Active in Preclinical Models of Acute Myeloid Leukemia with TP53 Mutation/Deletion

Acute myeloid leukemia (AML) with mutations in the tumor suppressor gene TP53 confers a dismal prognosis with 3-year overall survival of <5%. While inhibition of kinases involved in cell cycle regulation induces synthetic lethality in a variety of TP53 mutant cancers, this strategy has not been evaluated in mutant TP53 AML. Previously, we demonstrated that TP-0903 is a novel multikinase inhibitor with low nM activity against AURKA/B, Chk1/2, and other cell cycle regulators. Here, we evaluated the preclinical activity of TP-0903 in TP53 mutant AML cell lines, including a single-cell clone of MV4-11 containing a TP53 mutation (R248W), Kasumi-1 (R248Q), and HL-60 (TP 53 null). TP-0903 inhibited cell viability (IC50, 12−32 nM) and induced apoptosis at 50 nM. By immunoblot, 50 nM TP-0903 upregulated pChk1/2 and pH2AX, suggesting induction of DNA damage. The combination of TP-0903 and decitabine was additive in vitro, and in vivo significantly prolonged median survival compared to single-agent treatments in mice xenografted with HL-60 (vehicle, 46 days; decitabine, 55 days; TP-0903, 63 days; combination, 75 days) or MV4-11 (R248W) (51 days; 62 days; 81 days; 89 days) (p < 0.001). Together, these results provide scientific premise for the clinical evaluation of TP-0903 in combination with decitabine in TP53 mutant AML.

Amplified EPOR/JAK2 Genes Define a Unique Subtype of Acute Erythroid Leukemia

Acute erythroid leukemia (AEL) is a unique subtype of acute myeloid leukemia characterized by prominent erythroid proliferation whose molecular basis is poorly understood. To elucidate the underlying mechanism of erythroid proliferation, we analyzed 121 AEL using whole-genome, whole-exome, and/or targeted-capture sequencing, together with transcriptome analysis of 21 AEL samples. Combining publicly available sequencing data, we found a high frequency of gains and amplifications involving EPOR/JAK2 in TP53-mutated cases, particularly those having >80% erythroblasts designated as pure erythroid leukemia (10/13). These cases were frequently accompanied by gains and amplifications of ERG/ETS2 and associated with a very poor prognosis, even compared with other TP53-mutated AEL. In addition to activation of the STAT5 pathway, a common feature across all AEL cases, these AEL cases exhibited enhanced cell proliferation and heme metabolism and often showed high sensitivity to ruxolitinib in vitro and in xenograft models, highlighting a potential role of JAK2 inhibition in therapeutics of AEL.

SIGNIFICANCE

This study reveals the major role of gains, amplifications, and mutations of EPOR and JAK2 in the pathogenesis of pure erythroleukemia. Their frequent response to ruxolitinib in patient-derived xenograft and cell culture models highlights a possible therapeutic role of JAK2 inhibition for erythroleukemia with EPOR/JAK2-involving lesions. This article is highlighted in the In This Issue feature, p. 369.

TP53 copy number and protein expression inform mutation status across risk categories in acute myeloid leukemia

Mutant TP53 is an adverse risk factor in acute myeloid leukemia (AML), but large-scale integrated genomic-proteomic analyses of TP53 alterations in patients with AML remain limited. We analyzed TP53 mutational status, copy number (CN), and protein expression data in AML (N = 528) and provide a compilation of mutation sites and types across disease subgroups among treated and untreated patients. Our analysis shows differential hotspots in subsets of AML and uncovers novel pathogenic variants involving TP53 splice sites. In addition, we identified TP53 CN loss in 70.2% of TP53-mutated AML cases, which have more deleterious TP53 mutations, as well as copy neutral loss of heterozygosity in 5/32 (15.6%) AML patients who had intact TP53 CN. Importantly, we demonstrate that mutant p53 protein expression patterns by immunohistochemistry evaluated using digital image-assisted analysis provide a robust readout that integrates TP53 mutation and allelic states in patients with AML. Expression of p53 by immunohistochemistry informed mutation status irrespective of TP53 CN status. Genomic analysis of comutations in TP53-mutant AML shows a muted landscape encompassing primarily mutations in genes involved in epigenetic regulation (DNMT3A and TET2), RAS/MAPK signaling (NF1, KRAS/NRAS, PTPN11), and RNA splicing (SRSF2). In summary, our data provide a rationale to refine risk stratification of patients with AML on the basis of integrated molecular and protein-level TP53 analyses.

Are We Moving the Needle for Patients with TP53-Mutated Acute Myeloid Leukemia?

The currently available therapeutic options for patients with TP53-mutated acute myeloid leukemia (AML) are insufficient, as they translate to a median overall of only 6-9 months, and less than 10% of patients undergoing the most aggressive treatments, such as intensive induction therapy and allogeneic hematopoietic stem cell transplantation, will be cured. The lack of clear differences in outcomes with different treatments precludes the designation of a standard of care. Recently, there has been growing attention on this critical area of need by way of better understanding the biology of TP53 alterations and the disparities in outcomes among patients in this molecular subgroup, reflected in the development and testing of agents with novel mechanisms of action. Promising preclinical and efficacy data exist for therapies that are directed at the p53 protein rendered dysfunctional via mutation or that inhibit the CD47/SIRPα axis or other immune checkpoints such as TIM-3. In this review, we discuss recently attractive and emerging therapeutic agents, their preclinical rationale and the available clinical data as a monotherapy or in combination with the currently accepted backbones in frontline and relapsed/refractory settings for patients with TP53-mutated AML.

SOHO State of the Art Updates and Next Questions:Harnessing Apoptosis in AML

The treatment landscape for acute myeloid leukemia has expanded significantly in the past 5 years with the approval of several therapeutic small molecules. While agents such as FLT3 inhibitors and IDH inhibitors are restricted for patients with specific mutations, the selective BCL-2 inhibitor venetoclax combined with a hypomethylating agent or low-dose cytarabine was approved after demonstrating frontline efficacy across a molecularly heterogenous group of patients. Currently, venetoclax is being investigated in combination with multiple other therapies as the role of the intrinsic apoptotic pathway in acute myeloid leukemia continues to be explored.

APR-246 induces early cell death by ferroptosis in acute myeloid leukemia

APR-246 is a promising new therapeutic agent that targets p53 mutated proteins in myelodysplastic syndromes and in acute myeloid leukemia (AML). APR-246 reactivates the transcriptional activity of p53 mutants by facilitating their binding to DNA target sites. Recent studies in solid cancers have found that APR-246 can also induce p53-independent cell death. In this study, we demonstrate that AML cell death occurring early after APR-246 exposure is suppressed by iron chelators, lipophilic antioxidants and inhibitors of lipid peroxidation, and correlates with the accumulation of markers of lipid peroxidation, thus fulfilling the definition of ferroptosis, a recently described cell death process. The capacity of AML cells to detoxify lipid peroxides by increasing their cystine uptake to maintain major antioxidant molecule glutathione biosynthesis after exposure to APR-246 may be a key determinant of sensitivity to this compound. The association of APR-246 with induction of ferroptosis (either by pharmacological compounds, or genetic inactivation of SLC7A11 or GPX4) had a synergistic effect on the promotion of cell death, both in vivo and ex vivo.

Opportunities for Ferroptosis in Cancer Therapy

A critical hallmark of cancer cells is their ability to evade programmed apoptotic cell death. Consequently, resistance to anti-cancer therapeutics is a hurdle often observed in the clinic. Ferroptosis, a non-apoptotic form of cell death distinguished by toxic lipid peroxidation and iron accumulation, has garnered substantial attention as an alternative therapeutic strategy to selectively destroy tumours. Although there is a plethora of research outlining the molecular mechanisms of ferroptosis, these findings are yet to be translated into clinical compounds inducing ferroptosis. In this perspective, we elaborate on how ferroptosis can be leveraged in the clinic. We discuss a therapeutic window for compounds inducing ferroptosis, the subset of tumour types that are most sensitive to ferroptosis, conventional therapeutics that induce ferroptosis, and potential strategies for lowering the threshold for ferroptosis.

New Treatment Options for Older Patients with Acute Myeloid Leukemia

OPINION STATEMENT

The treatment of acute myeloid leukemia (AML) has evolved considerably over the past several years. Advances in the field have historically benefited younger patients; however, a growing understanding of the molecular basis of leukemogenesis has brought multiple targeted agents to the clinic for patients of all ages. These therapies have expanded the therapeutic landscape for elderly patients from more than best supportive care and low-intensity monotherapy. In general, we currently utilize a backbone regimen of a hypomethylating agent (HMA) or low-intensity chemotherapy with the BCL-2 inhibitor venetoclax for the majority of elderly patients with newly diagnosed AML. For patients with targetable mutations, we employ a doublet/triplet strategy of HMA + a targeted inhibitor +/- venetoclax, often in the context of a clinical trial. CPX-351 is reserved for patients with secondary or therapy-related AML. In this review, we will outline our approach to the treatment of elderly patients with AML, with particular emphasis on recently approved agents and emerging novel therapies.

Antitumor Effects of PRIMA-1 and PRIMA-1Met (APR246) in Hematological Malignancies: Still a Mutant P53-Dependent Affair?

Because of its role in the regulation of the cell cycle, DNA damage response, apoptosis, DNA repair, cell migration, autophagy, and cell metabolism, the TP53 tumor suppressor gene is a key player for cellular homeostasis. TP53 gene is mutated in more than 50% of human cancers, although its overall dysfunction may be even more frequent. TP53 mutations are detected in a lower percentage of hematological malignancies compared to solid tumors, but their frequency generally increases with disease progression, generating adverse effects such as resistance to chemotherapy. Due to the crucial role of P53 in therapy response, several molecules have been developed to re-establish the wild-type P53 function to mutant P53. PRIMA-1 and its methylated form PRIMA-1^Met (also named APR246) are capable of restoring the wild-type conformation to mutant P53 and inducing apoptosis in cancer cells; however, they also possess mutant P53-independent properties. This review presents the activities of PRIMA-1 and PRIMA-1^Met/APR246 and describes their potential use in hematological malignancies.

Apoptosis targeted therapies in acute myeloid leukemia: an update

Introduction: Management of acute myeloid leukemia (AML) continues to be a therapeutic challenge despite significant recent advancements. Dysregulation of several components of apoptotic pathways has been identified as potential driver in AML. Areas covered: Overexpression of anti-apoptotic proteins, B-cell lymphoma 2 (BCL2), BCL-XL, and myeloid cell leukemia-1 (MCL1), has been associated with worse outcome in AML. Dysfunction of p53 pathway (often through mouse double minute 2 homolog (MDM2)) and high expression of inhibitor of apoptosis proteins (IAP) constitute other disruptions of apoptotic machinery. Significant antileukemic activity of BCL2 inhibitors (particularly venetoclax) in preclinical models has translated into improved objective response and overall survival in combination with hypomethylating agents in AML. Addition of MCL1, BCL-XL, or MDM2 inhibitors could potentially overcome resistance to BCL2 inhibition. Authors conducted a thorough review of available literature on therapeutic options targeting apoptosis in AML, using PubMed, MEDLINE, meeting abstracts, and ClinicalTrials.gov. Expert opinion: While venetoclax remains the core component of targeting apoptosis, ongoing clinical trials should help find ideal combination regimens in different AML subgroups. Future research should focus on overcoming resistance to BCL2 inhibition, optimal management of adverse events, and development of biomarkers to identify patients most likely to benefit from apoptosis-targeted therapies.

Precision medicine in acute myeloid leukemia: where are we now and what does the future hold?

INTRODUCTION

Precision medicine has revolutionized the diagnostic and therapeutic management of acute myeloid leukemia (AML), from standardized schemes based on chemotherapy to tailored approaches according to molecular and genetic profile and targeted therapy.

AREAS COVERED

The main topics of precision medicine in AML were reviewed in MEDLINE, EMBASE, and Cochrane Central Register databases, and future directions in this therapeutic area were addressed. This review included targeted therapies, drug-sensitivity tests and predictive biomarkers, and genetic studies employing pharmacogenetic and deep sequencing strategies.

EXPERT OPINION

Precision medicine has opened the door to personalized therapy for specific AML patient populations with promising results. Several targeted therapies have been approved or are being tested for specific mutations (i.e. FLT3, IDH, BCL-2, TP53), obtaining improvements in clinical outcomes and less toxicity as compared with intensive treatment, allowing potential combination therapy. Ongoing trials and real data will establish the role of these molecules in monotherapy or combined in different AML settings (front-line, relapsed/refractory, or post-transplant). Experience in drug-sensitivity predictors and pharmacogenetic biomarkers is encouraging and could be useful tools in the next years, but we need a better understanding of AML biology and pathogenesis as well as confirmatory studies to demonstrate the utility in clinical practice.

An expert overview of emerging therapies for acute myeloid leukemia: novel small molecules targeting apoptosis, p53, transcriptional regulation and metabolism

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive malignancy of clonal myeloid precursor cells. Curative therapy has classically involved the use of intensive induction chemotherapy followed by consolidation with additional chemotherapy or allogeneic hematopoietic stem cell transplant. For many patients, such an approach is prohibitive because of high treatment-related toxicities. Advancements in the molecular understanding of AML have led to the introduction of new targeted therapies that are changing the treatment landscape for AML.

AREAS COVERED

We review emerging small molecule inhibitors that have shown preclinical efficacy for the treatment of AML. The compounds discussed affect apoptosis, p53-mediated interactions, transcriptional regulation, and cellular metabolism. We performed a literature search of PubMed and primarily included relevant sources published from 2000 to the present, though earlier sources are also referenced.

EXPERT OPINION

Most clinical trials for AML currently employ novel targeted therapies that demonstrate promising activity in preclinical models. We anticipate that new small molecule inhibitors will continue to enter the clinical realm and alter the treatment paradigm for AML. In a field where clinical advancement was comparatively slow for many years, it appears that we are now starting to see the rapid growth borne out of the deepening molecular understanding of AML.

Myelodysplastic syndromes: a review of therapeutic progress over the past 10 years

INTRODUCTION

Myelodysplastic syndromes (MDS) represent a range of bone marrow disorders, with patients affected by cytopenias and risk of progression to AML. There are limited therapeutic options available for patients, including hypomethylating agents (azacitidine/decitabine), growth factor support, lenalidomide, and allogeneic stem cell transplant.

AREAS COVERED

This review provides an overview of the progress made over the past decade for emerging therapies for lower- and higher-risk MDS (MDS-HR). We also cover advances in prognostication, supportive care, and use of allogeneic SCT in MDS.

EXPERT OPINION

While there have been no FDA-approved therapies for MDS in the past decade, we anticipate the approval of luspatercept based on results from the MEDALIST trial for patients with lower-risk MDS (MDS-LR) and ringed sideroblasts who have failed or are ineligible for erythropoiesis stimulating agents (ESAs). With growing knowledge of the biologic and molecular mechanisms underlying MDS, it is anticipated that new therapies will be approved in the coming years.

From Bench to Bedside and Beyond: Therapeutic Scenario in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of clonal disorders characterized by abnormal proliferation of undifferentiated myeloid progenitors, impaired hematopoiesis, and variable response to therapy. To date, only about 30% of adult patients with AML become long-term survivors and relapse and/or disease refractoriness are the major cause of treatment failure. Thus, this is an urgent unmet clinical need and new drugs are envisaged in order to ameliorate disease survival outcomes. Here, we review the latest therapeutic approaches (investigational and approved agents) for AML treatment. A specific focus will be given to molecularly targeted therapies for AML as a representation of possible agents for precision medicine. We will discuss experimental and preclinical data for FLT3, IDH1, BCL-2, Hedgehog pathway inhibitors, and epitherapy.

Small Molecules Targeting Mutant P53: A Promising Approach for Cancer Treatment

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More than half of all human tumors express mutant forms of p53, with the ovary, lung, pancreas, and colorectal cancers among the tumor types that display the highest prevalence of p53 mutations. In addition, the expression of mutant forms of p53 in tumors is associated with poor prognosis due to increased chemoresistance and invasiveness. Therefore, the pharmacological restoration of wild-type-like activity to mutant p53 arises as a promising therapeutic strategy against cancer. This review is focused on the most relevant mutant p53 small molecule reactivators described to date. Despite some of them have entered into clinical trials, none has reached the clinic, which emphasizes that new pharmacological alternatives, particularly with higher selectivity and lower adverse toxic side effects, are still required.

PRIMA-1MET cytotoxic effect correlates with p53 protein reduction in TP53-mutated chronic lymphocytic leukemia cells

TP53 gene defects represent the most unfavorable prognostic factor in chronic lymphocytic leukemia (CLL). Although recently introduced small-molecule B-cell receptor signalling inhibitors have revolutionized CLL treatment, data for ibrutinib still point to impaired prognosis for TP53-affected patients. Among cancer-associated TP53 mutations, missense substitutions predominate and typically result in a high mutated-p53 protein level. Therefore, rescuing the p53 tumor suppressor function through specific small molecules restoring p53 wild-type (wt) conformation represents an attractive therapeutic strategy for cancer patients with TP53 missense mutations. We tested the effect of mutated-p53 reactivating molecule PRIMA-1^MET in 62 clinical CLL samples characterized for TP53 mutations and p53 protein level. At the subtle PRIMA-1^MET concentrations (1-4 μM), most samples manifested concentration-dependent viability decrease and, conversely, apoptosis induction, with the response being similar in both the TP53-mutated and TP53-wt groups, as well as in the TP53-mutated samples with p53 protein stabilization and without it. PRIMA-1^MET was able to reduce mutated p53 protein in a proportion of TP53-mutated CLL samples, and this reduction correlated with a significantly stronger viability decrease and apoptosis induction than samples with stable p53 levels. CLL cells are mostly sensitive to PRIMA-1^MET apart from those with stable mutated p53.

PRIMA-1MET Induces Cellular Senescence and Apoptotic Cell Death in Cholangiocarcinoma Cells

BACKGROUND/AIM

This study examined the in vitro effects of the bile duct cancer drug PRIMA-1^MET on cholangiocarcinoma (CCA) cell growth to determine its potential usefulness in CCA therapy.

MATERIALS AND METHODS

The effect of this drug on the expression of senescent markers (p16^INK4A and p21) and the phosphorylation of p53 was investigated, as was the association between senescent markers and the patients' clinicopathological data.

RESULTS

PRIMA-1^MET inhibited CCA cell growth with the half maximal-inhibitory concentration (IC₅₀) values of 21.9-40.8 μM. PRIMA-1^MET induced phospho-p53, p16^INK4A and p21 triggering cellular senescence and apoptosis. High expressions of p16^INK4A and p21 were associated with a high survival rate of patients with CCA.

CONCLUSION

PRIMA-1^MET may potentially be an alternative anticancer agent that might lead to a better prognosis in patients with CCA.

Abnormal accumulation of p53 predicts radioresistance leading to poor survival in patients with endometrial carcinoma

Type II endometrial carcinoma mainly originates from p53 aberration. However, the detailed prognostic significance of p53 aberration in endometrial carcinoma remains to be clarified. In the present study, abnormal p53 accumulation was analyzed using immunohistochemical techniques in endometrial carcinoma samples derived from 221 consecutive patients. The expression levels of p53 were associated with clinicopathological parameters and patient survival. P53 overexpression was observed in 37/221 patients (17%), and was associated with non-endometrioid histology, post-menopause and advanced tumor stage (III/IV; P=0.0006, P=0.03 and P=0.025, respectively). Survival analysis indicated that patients with p53-overexpressing tumors exhibited poor overall survival (OS) compared with patients without p53 overexpression (P<0.000001). Univariate and multivariate analyses demonstrated that the parameters p53 overexpression, age ≥70, non-endometrioid histology and advanced stage were significant and independent prognostic factors for poor OS (P=0.00012, P=0.00048, P=0.0027 and P=0.0015, respectively). Additionally, adjuvant radiotherapy was associated with increased OS in patients without p53 overexpression. This finding was not observed for patients with adjuvant chemotherapy. In contrast to patients without p53 overexpression, patients with p53 overexpression exhibited no association with OS (P=0.02 vs. P=0.40). Notably, adjuvant radiotherapy was identified to be a significant prognostic factor for favorable OS in the subset of patients that did not exhibit p53 overexpression and received post-operative treatment (P=0.026). The findings suggested that abnormal p53 accumulation may influence patient survival via unfavorable biological tumor properties, including rapid progression and radioresistance. The present study offered valuable insights for the genome-directed management of endometrial carcinoma.

Synergistic effects of PRIMA-1Met (APR-246) and 5-azacitidine in TP53-mutated myelodysplastic syndromes and acute myeloid leukemia

Myelodysplastic syndromes and acute myeloid leukemia with TP53 mutations are characterized by frequent relapses, poor or short responses, and poor survival with the currently available therapies including chemotherapy and 5-azacitidine (AZA). PRIMA-1^Met(APR-246,APR) is a methylated derivative of PRIMA-1, which induces apoptosis in human tumor cells through restoration of the transcriptional transactivation function of mutant p53. Here we show that low doses of APR on its own or in combination with AZA reactivate the p53 pathway and induce an apoptosis program. Functionally, we demonstrate that APR exerts these activities on its own and that it synergizes with AZA in TP53-mutated myelodysplastic syndromes (MDS)/acute myeloid leukemia (AML) cell lines and in TP53-mutated primary cells from MDS/AML patients. Low doses of APR on its own or in combination with AZA also show significant efficacy in vivo Lastly, using transcriptomic analysis, we found that the APR + AZA synergy was mediated by downregulation of the FLT3 pathway in drug-treated cells. Activation of the FLT3 pathway by FLT3 ligand reversed the inhibition of cell proliferation by APR + AZA. These data suggest that TP53-mutated MDS/AML may be better targeted by the addition of APR-246 to conventional treatments.

Immunotherapy in Hodgkin Lymphoma: Present Status and Future Strategies

Although classical Hodgkin lymphoma (cHL) is usually curable, 20-30% of the patients experience treatment failure and most of them are typically treated with salvage chemotherapy and autologous stem cell transplantation (autoSCT). However, 45-55% of that subset further relapse or progress despite intensive treatment. At the advanced stage of the disease course, recently developed immunotherapeutic approaches have provided very promising results with prolonged remissions or disease stabilization in many patients. Brentuximab vedotin (BV) has been approved for patients with relapsed/refractory cHL (rr-cHL) who have failed autoSCT, as a consolidation after autoSCT in high-risk patients, as well as for patients who are ineligible for autoSCT or multiagent chemotherapy who have failed ≥ two treatment lines. However, except of the consolidation setting, 90-95% of the patients will progress and require further treatment. In this clinical setting, immune checkpoint inhibitors (CPIs) have produced impressive results. Both nivolumab and pembrolizumab have been approved for rr-cHL after autoSCT and BV failure, while pembrolizumab has also been licensed for transplant ineligible patients after BV failure. Other CPIs, sintilimab and tislelizumab, have been successfully tested in China, albeit in less heavily pretreated populations. Recent data suggest that the efficacy of CPIs may be augmented by hypomethylating agents, such as decitabine. As a result of their success in heavily pretreated disease, BV and CPIs are moving to earlier lines of treatment. BV was recently licensed by the FDA for the first-line treatment of stage III/IV Hodgkin lymphoma (HL) in combination with AVD (only stage IV according to the European Medicines Agency (EMA)). CPIs are currently being evaluated in combination with AVD in phase II trials of first-line treatment. The impact of BV and CPIs was also investigated in the setting of second-line salvage therapy. Finally, combinations of targeted therapies are under evaluation. Based on these exciting results, it appears reasonable to predict that an improvement in survival and a potential increase in the cure rates of cHL will soon become evident.

Current status and new treatment approaches in TP53 mutated AML

Mutations in the essential tumor suppressor gene, TP53, are observed in only 5-10% of acute myeloid leukemia (AML) cases, but are highly associated with therapy-related AML and cases with complex karyotype. The mutational status of TP53 is a critical prognostic indicator, with dismal outcomes consistently observed across studies. Response rates to traditional cytotoxic chemotherapy are poor and long-term survival after allogeneic hematopoietic stem cell transplant is rare. Therapy with hypomethylating agents has resulted in a modest improvement in outcomes over intensive chemotherapy, but durable responses are seldom observed. In view of the intrinsic resistance to standard chemotherapies conferred by mutations in TP53, novel treatment approaches are required. In this review, we examine the current treatment landscape in TP53 mutated AML and discuss emerging therapeutic approaches currently under clinical investigation.

Molecular Approaches to Treating Pediatric Leukemias

Over the past decades, striking progress has been made in the treatment of pediatric leukemia, approaching 90% overall survival in children with acute lymphoblastic leukemia (ALL) and 75% in children with acute myeloid leukemia (AML). This has mainly been achieved through multiagent chemotherapy including CNS prophylaxis and risk-adapted therapy within collaborative clinical trials. However, prognosis in children with refractory or relapsed leukemia remains poor and has not significantly improved despite great efforts. Hence, more effective and less toxic therapies are urgently needed. Our understanding of disease biology, molecular drivers, drug resistance and, thus, the possibility to identify children at high-risk for treatment failure has significantly improved in recent years. Moreover, several new drugs targeting key molecular pathways involved in leukemia development, cell growth, and proliferation have been developed and approved. These striking achievements are linked to the great hope to further improve survival in children with refractory and relapsed leukemia. This review gives an overview on current molecularly targeted therapies in children with leukemia, including kinase, and proteasome inhibitors, epigenetic and enzyme targeting, as well as apoptosis regulators among others.

Knockdown of LncRNA-UCA1 suppresses chemoresistance of pediatric AML by inhibiting glycolysis through the microRNA-125a/hexokinase 2 pathway

Dysregulation of lncRNAs is implicated in chemoresistance in varieties of tumor including acute myeloid leukemia (AML). LncRNA urothelial carcinoma-associated 1 (UCA1) was reported to play an oncogenic role in AML. However, whether UCA1 was involved in chemoresistance in pediatric AML remains unclear. UCA1 expression in AML patients after adriamycin (ADR)-based chemotherapy and ADR-resistant AML cells was examined by qRT-PCR. The effects of UCA1 on the cytotoxicity of ADR and glycolysis were evaluated by MTT assay and measuring the glucose consumption and lactate production in HL60 and HL60/ADR cells, repectively. The protein levels of hypoxia-inducible factor 1α (HIF-1α) and hexokinase 2 (HK2) were determined by Western blot. Luciferase reporter assay and RNA immunoprecipitation (RIP) assay were used to confirm the relationships between UCA1, HK2, and miR-125a. We found that UCA1 expression was upregulated following ADR-based chemotherapy. Knockdown of UCA1 increased the cytotoxic effect of ADR and inhibited HIF-1α-dependent glycolysis in ADR-resistant AML cells. Additionally, UCA1 functioned as a ceRNA of miR-125a by directly binding to miR-125a. HK2, a target of miR-125a, was positively regulated by UCA1 in HL60 and HL60/ADR cells. More notably, UCA1 overexpression overturned miR-125-mediated inhibition on HIF-1α-dependent glycolysis in HL60 and HL60/ADR cells. Furthermore, 2-deoxy-glucose (2-DG) exposure inhibited HIF-1α-dependent glycolysis, and attenuated UCA1-induced increase of chemoresistance in HL60 and HL60/ADR cells. We conclude that knockdown of UCA1 plays a positive role in overcoming the chemoresistance of pediatric AML, through suppressing glycolysis by the miR-125a/HK2 pathway, contributing to a better understanding of the molecular mechanism of chemoresistance in AML.

Targeting mutant p53 for efficient cancer therapy

The tumour suppressor gene TP53 is the most frequently mutated gene in cancer. Wild-type p53 can suppress tumour development by multiple pathways. However, mutation of TP53 and the resultant inactivation of p53 allow evasion of tumour cell death and rapid tumour progression. The high frequency of TP53 mutation in tumours has prompted efforts to restore normal function of mutant p53 and thereby trigger tumour cell death and tumour elimination. Small molecules that can reactivate missense-mutant p53 protein have been identified by different strategies, and two compounds are being tested in clinical trials. Novel approaches for targeting TP53 nonsense mutations are also underway. This Review discusses recent progress in pharmacological reactivation of mutant p53 and highlights problems and promises with these strategies.

MicroRNA-103 confers the resistance to long-treatment of adriamycin to human leukemia cells by regulation of COP1

Adriamycin (ADR) is an anti-cancer drug which offers improvement in survival for acute myeloid leukemia (AML) patients. However, the drug resistance is almost inevitable. Increasing evidences suggested that microRNAs (miRNAs) were associated with cancer chemo-resistance. Here, we aimed to explore the possible mechanism of miR-103 affected resistance to ADR in AML cells. Different concentrations of ADR were used to induce K562 and KASUMI-1 cells, and miR-103 mimic, inhibitor were transfected into K562 and KASUMI-1 cells. Cell viability and proliferation were determined by trypan blue staining and MTT assays for evaluating K562 and KASUMI-1 cells drug resistance. The relationship of miR-103 and COP1, Trib1, and C/EBPα were analyzed by qRT-PCR and Western blot. Cell proliferation, viability were detected again. Besides, the expressions of main factors of cell cycle and PI3K/AKT signal pathway were analyzed by Western blot. Results showed that ADR inhibited cell viability and proliferation in K562 and KASUMI-1 cells. However, K562 and KASUMI-1 cells appeared drug resistance for 50 passages at 0.8 µM of ADR. In addition, miR-103 expression was up-regulated in ADR-resistant K562 cells (K562/ADR) and overexpression of miR-103 increased K562 cells drug resistance via promoting cell viability and cell cycle-related factors expressions. COP1 was positively regulated by miR-103, suppression of miR-103 recovered K562/ADR cells drug resistance by regulation of COP1, Trib1, and C/EBPα. Besides, miR-103 blocked PI3K/AKT signal pathway by regulation of COP1. These data indicated that miR-103 was up-regulated in drug resistant cells and it may regulate ADR-resistance by regulation of COP1 in AML cells.

PRIMA-1 and PRIMA-1Met (APR-246): From Mutant/Wild Type p53 Reactivation to Unexpected Mechanisms Underlying Their Potent Anti-Tumor Effect in Combinatorial Therapies

p53 protects cells from genetic assaults by triggering cell-cycle arrest and apoptosis. Inactivation of p53 pathway is found in the vast majority of human cancers often due to somatic missense mutations in TP53 or to an excessive degradation of the protein. Accordingly, reactivation of p53 appears as a quite promising pharmacological approach and, effectively, several attempts have been made in that sense. The most widely investigated compounds for this purpose are PRIMA-1 (p53 reactivation and induction of massive apoptosis )and PRIMA-1^Met (APR-246), that are at an advanced stage of development, with several clinical trials in progress. Based on publications referenced in PubMed since 2002, here we review the reported effects of these compounds on cancer cells, with a specific focus on their ability of p53 reactivation, an overview of their unexpected anti-cancer effects, and a presentation of the investigated drug combinations.

Mutant p53 as a therapeutic target for the treatment of triple-negative breast cancer: Preclinical investigation with the anti-p53 drug, PK11007

The identification of a targeted therapy for patients with triple-negative breast cancer (TNBC) is one of the most urgent needs in breast cancer therapeutics. The p53 gene is mutated in approximately 80% of patients with TNBC, and is a potential therapeutic target for patients with this form of breast cancer. The 2-sulfonylpyrimidine compound, PK11007, preferentially decreases viability in p53-compromised cancer cell lines. We investigated PK11007 as a potential new treatment for TNBC. IC₅₀ values for inhibition of proliferation in a panel of 17 breast cell lines by PK11007 ranged from 2.3 to 42.2 μM. There were significantly lower IC₅₀ values for TNBC than for non-TNBC cell lines (p = 0.03) and for p53-mutated cell lines compared with p53 WT cells (p = 0.003). Response to PK11007 however, was independent of the estrogen receptor (ER) or HER2 status of the cell lines. In addition to inhibiting cell proliferation, PK11007 induced apoptosis in p53 mutant cell lines. Using RNAseq and gene ontology analysis, we found that PK11007 altered the expression of genes enriched in pathways involved in regulated cell death, regulation of apoptosis, signal transduction, protein refolding and locomotion. The observations that PK11007 inhibited cell proliferation, induced apoptosis and altered genes involved in cell death are all consistent with the ability of PK11007 to reactivate mutant p53. Based on our data, we conclude that targeting mutant p53 with PK11007 is a potential approach for treating p53-mutated breast cancer, including the subgroup with TN disease.

Mutant p53 as a target for cancer treatment

TP53 (p53) is the single most frequently altered gene in human cancers, with mutations being present in approximately 50% of all invasive tumours. However, in some of the most difficult-to-treat cancers such as high-grade serous ovarian cancers, triple-negative breast cancers, oesophageal cancers, small-cell lung cancers and squamous cell lung cancers, p53 is mutated in at least 80% of samples. Clearly, therefore, mutant p53 protein is an important candidate target against which new anticancer treatments could be developed. Although traditionally regarded as undruggable, several compounds such as p53 reactivation and induction of massive apoptosis-1 (PRIMA-1), a methylated derivative and structural analogue of PRIMA-1, i.e. APR-246, 2-sulfonylpyrimidines such as PK11007, pyrazoles such as PK7088, zinc metallochaperone-1 (ZMC1), a third generation thiosemicarbazone developed by Critical Outcome Techonologies Inc. (COTI-2) as well as specific peptides have recently been reported to reactive mutant p53 protein by converting it to a form exhibiting wild-type properties. Consistent with the reactivation of mutant p53, these compounds have been shown to exhibit anticancer activity in preclinical models expressing mutant p53. To date, two of these compounds, i.e. APR-246 and COTI-2 have progressed to clinical trials. A phase I/IIa clinical trial with APR-246 reported no major adverse effect. Currently, APR-246 is undergoing a phase Ib/II trial in patients with advanced serous ovarian cancer, while COTI-2 is being evaluated in a phase I trial in patients with advanced gynaecological cancers. It remains to be shown however, whether any mutant p53 reactivating compound has efficacy for the treatment of human cancer.

PRIMA-1met (APR-246) inhibits growth of colorectal cancer cells with different p53 status through distinct mechanisms

PRIMA-1^met (APR-246) is a methylated derivative and structural analog of PRIMA-1 (p53 re-activation and induction of massive apoptosis). PRIMA-1^met has been reported to restore both the wild type (wt) structure and function of mutant p53. Here, we show that PRIMA-1^met is highly effective at limiting the growth of CRC cells regardless of p53 status. However, PRIMA-1^met induces robust apoptosis only in CRC cells with mutant p53. Upregulation of Noxa, a proapoptotic molecule, is crucial for PRIMA-1^met mediated activity. In human xenograft model of disease, PRIMA-1^met effectively suppresses CRC tumor growth. Our results uncover distinct mechanisms of PRIMA-1^met in CRC with different p53 status, thus providing a mechanistic rationale to evaluate the clinical efficacy of PRIMA-1^met in CRC patients with different p53 status.

PRIMA-1MET induces apoptosis through accumulation of intracellular reactive oxygen species irrespective of p53 status and chemo-sensitivity in epithelial ovarian cancer cells

There is an intensive need for the development of novel drugs for the treatment of epithelial ovarian cancer (EOC), the most lethal gynecologic malignancy due to the high recurrence rate. TP53 mutation is a common event in EOC, particularly in high-grade serous ovarian cancer, where it occurs in more than 90% of cases. Recently, PRIMA-1 and PRIMA‑1MET (p53 reactivation and induction of massive apoptosis and its methylated form) were shown to have an antitumor effect on several types of cancer. Despite that PRIMA-1MET is the first compound evaluated in clinical trials, the antitumor effects of PRIMA-1MET on EOC remain unclear. In this study, we investigated the therapeutic potential of PRIMA-1MET for the treatment of EOC cells. PRIMA-1MET treatment of EOC cell lines (n=13) resulted in rapid apoptosis at various concentrations (24 h IC50 2.6-20.1 µM). The apoptotic response was independent of the p53 status and chemo-sensitivity. PRIMA‑1MET treatment increased intracellular reactive oxygen species (ROS), and PRIMA-1MET-induced apoptosis was rescued by an ROS scavenger. Furthermore, RNA expression analysis revealed that the mechanism of action of PRIMA‑1MET may be due to inhibition of antioxidant enzymes, such as Prx3 and GPx-1. In conclusion, our results suggest that PRIMA-1MET represents a novel therapeutic strategy for the treatment of ovarian cancer irrespective of p53 status and chemo-sensitivity.

Anti-leukaemic effects induced by APR-246 are dependent on induction of oxidative stress and the NFE2L2/HMOX1 axis that can be targeted by PI3K and mTOR inhibitors in acute myeloid leukaemia cells

The small molecule APR-246 (PRIMA-1(MET) ) is a novel drug that restores the activity of mutated and unfolded TP53 protein. However, the mechanisms of action and potential off-target effects are not fully understood. Gene expression profiling in TP53 mutant KMB3 acute myeloid leukaemia (AML) cells showed that genes which protected cells from oxidative stress to be the most up-regulated. APR-246 exposure also induced reactive oxygen species (ROS) formation and depleted glutathione in AML cells. The genes most up-regulated by APR-246, confirmed by quantitative real time polymerase chain reaction, were heme oxygenase-1 (HMOX1, also termed HO-1), SLC7A11 and RIT1. Up-regulation of HMOX1, a key regulator of cellular response to ROS, was independent of TP53 mutational status. NFE2L2 (also termed Nrf2), a master regulator of HMOX1 expression, showed transcriptional up-regulation and nuclear translocation by APR-246. Down-regulation of NFE2L2 by siRNA in AML cells significantly increased the antitumoural effects of APR-246. The PI3K inhibitor wortmannin and the mTOR inhibitor rapamycin inhibited APR-246-induced nuclear translocation of NFE2L2 and counteracted the protective cellular responses to APR-246, resulting in synergistic cell killing together with APR-246. In conclusion, ROS induction is important for antileukaemic activities of APR-246 and inhibiting the protective response of the Nrf-2/HMOX1 axis using PI3K inhibitors, enhances the antileukaemic effects.

APR-246 (PRIMA-1(MET)) strongly synergizes with AZD2281 (olaparib) induced PARP inhibition to induce apoptosis in non-small cell lung cancer cell lines

APR-246 (PRIMA-1(Met)) is able to bind mutant p53 and restore its normal conformation and function. The compound has also been shown to increase intracellular ROS levels. Importantly, the poly-[ADP-ribose] polymerase-1 (PARP-1) enzyme plays an important role in the repair of ROS-induced DNA damage. We hypothesize that by blocking this repair with the PARP-inhibitor AZD2281 (olaparib), DNA damage would accumulate in the cell leading to massive apoptosis. We observed that APR-246 synergistically enhanced the cytotoxic response of olaparib in TP53 mutant non-small cell lung cancer cell lines, resulting in a strong apoptotic response. In the presence of wild type p53 a G2/M cell cycle block was predominantly observed. NOXA expression levels were significantly increased in a TP53 mutant background, and remained unchanged in the wild type cell line. The combined treatment of APR-246 and olaparib induced cell death that was associated with increased ROS production, accumulation of DNA damage and translocation of p53 to the mitochondria. Out data suggest a promising targeted combination strategy in which the response to olaparib is synergistically enhanced by the addition of APR-246, especially in a TP53 mutant background.

PRIMA-1Met induces apoptosis in Waldenström's Macroglobulinemia cells independent of p53

PRIMA-1Met has shown promising preclinical activity in various cancer types. However, its effect on Waldenström's Macroglobulinemia (WM) cells as well as its exact mechanism of action is still elusive. In this study, we evaluated the anti- tumor activity of PRIMA-1Met alone and in combination with dexamethasone or bortezomib in WM cell lines and primary samples. Treatment of WM cells with PRIMA-1Met resulted in induction of apoptosis, inhibition of migration and suppression of colony formation. Upon PRIMA-1Met treatment, p73 was upregulated and Bcl-xL was down-regulated while no significant change in expression of p53 was observed. Furthermore, siRNA knockdown of p53 in WM cell line did not influence the PRIMA-1Met-induced apoptotic response whereas silencing of p73 inhibited latter response in WM cells. Importantly, combined treatment of BCWM-1 cells with PRIMA-1Met and dexamethasone or bortezomib induced synergistic reduction in cell survival. Our study provides insights into the mechanisms of anti-WM activity of PRIMA-1Met and supports further clinical evaluation of PRIMA-1Met as a potential novel therapeutic intervention in WM.

Targeting of Mutant p53 and the Cellular Redox Balance by APR-246 as a Strategy for Efficient Cancer Therapy

TP53 is the most frequently mutated gene in cancer. The p53 protein activates transcription of genes that promote cell cycle arrest or apoptosis, or regulate cell metabolism, and other processes. Missense mutations in TP53 abolish specific DNA binding of p53 and allow evasion of apoptosis and accelerated tumor progression. Mutant p53 often accumulates at high levels in tumor cells. Pharmacological reactivation of mutant p53 has emerged as a promising strategy for improved cancer therapy. Small molecules that restore wild type activity of mutant p53 have been identified using various approaches. One of these molecules, APR-246, is a prodrug that is converted to the Michael acceptor methylene quinuclidinone (MQ) that binds covalently to cysteines in p53, leading to refolding and restoration of wild type p53 function. MQ also targets the cellular redox balance by inhibiting thioredoxin reductase (TrxR1) and depleting glutathione. This dual mechanism of action may account for the striking synergy between APR-246 and platinum compounds. APR-246 is the only mutant p53-targeting compound in clinical development. A phase I/IIa clinical trial in hematological malignancies and prostate cancer showed good safety profile and clinical effects in some patients. APR-246 is currently tested in a phase Ib/II trial in patients with high-grade serous ovarian cancer.

Inactivation of the p53-KLF4-CEBPA Axis in Acute Myeloid Leukemia

PURPOSE

In acute myeloid leukemia (AML), the transcription factors CEBPA and KLF4 as well as the universal tumor suppressor p53 are frequently deregulated. Here, we investigated the extent of dysregulation, the molecular interactions, and the mechanisms involved.

EXPERIMENTAL DESIGN

One hundred ten AML patient samples were analyzed for protein levels of CEBPA, KLF4, p53, and p53 modulators. Regulation of CEBPA gene expression by KLF4 and p53 or by chemical p53 activators was characterized in AML cell lines.

RESULTS

We found that CEBPA gene transcription can be directly activated by p53 and KLF4, suggesting a p53-KLF4-CEBPA axis. In AML patient cells, we observed a prominent loss of p53 function and concomitant reduction of KLF4 and CEBPA protein levels. Assessment of cellular p53 modulator proteins indicated that p53 inactivation in leukemic cells correlated with elevated levels of the nuclear export protein XPO1/CRM1 and increase of the p53 inhibitors MDM2 and CUL9/PARC in the cytoplasm. Finally, restoring p53 function following treatment with cytotoxic chemotherapy compounds and p53 restoring non-genotoxic agents induced CEBPA gene expression, myeloid differentiation, and cell-cycle arrest in AML cells.

CONCLUSIONS

The p53-KLF4-CEBPA axis is deregulated in AML but can be functionally restored by conventional chemotherapy and novel p53 activating treatments.

PRIMA-1Met induces myeloma cell death independent of p53 by impairing the GSH/ROS balance

The aim of this study was to assess the efficiency of p53 reactivation and induction of massive apoptosis (PRIMA-1(Met)) in inducing myeloma cell death, using 27 human myeloma cell lines (HMCLs) and 23 primary samples. Measuring the lethal dose (LD50) of HMCLs revealed that HMCLs displayed heterogeneous sensitivity, with an LD50 ranging from 4 μM to more than 200 μM. The sensitivity of HMCLs did not correlate with myeloma genomic heterogeneity or TP53 status, and PRIMA-1(Met) did not induce or increase expression of the p53 target genes CDKN1A or TNFRSF10B/DR5. However, PRIMA-1(Met) increased expression of NOXA in a p53-independent manner, and NOXA silencing decreased PRIMA1(Met)-induced cell death. PRIMA-1(Met) depleted glutathione (GSH) content and induced reactive oxygen species production. The expression of GSH synthetase correlated with PRIMA-1(Met) LD50 values, and we showed that a GSH decrease mediated by GSH synthetase silencing or by and L-buthionine sulphoximine, an irreversible inhibitor of γ-glutamylcysteine synthetase, increased PRIMA-1(Met)-induced cell death and overcame PRIMA-1(Met) resistance. PRIMA-1(Met) (10 μM) induced cell death in 65% of primary cells independent of the presence of del17p; did not increase DR5 expression, arguing against an activation of p53 pathway; and synergized with L-buthionine sulphoximine in all samples. Finally, we showed in mouse TP53(neg) JJN3-xenograft model that PRIMA-1(Met) inhibited myeloma growth and synergized with L-buthionine sulphoximine in vivo.

The clinical development of p53-reactivating drugs in sarcomas - charting future therapeutic approaches and understanding the clinical molecular toxicology of Nutlins

INTRODUCTION

The majority of human sarcomas, particularly soft tissue sarcomas, are relatively resistant to traditional cytotoxic therapies. The proof-of-concept study by Ray-Coquard et al., using the Nutlin human double minute (HDM)2-binding antagonist RG7112, has recently opened a new chapter in the molecular targeting of human sarcomas.

AREAS COVERED

In this review, the authors discuss the challenges and prospective remedies for minimizing the significant haematological toxicities of the cis-imidazole Nutlin HDM2-binding antagonists. Furthermore, they also chart the future direction of the development of p53-reactivating (p53-RA) drugs in 12q13-15 amplicon sarcomas and as potential chemopreventative therapies against sarcomagenesis in germ line mutated TP53 carriers. Drawing lessons from the therapeutic use of Imatinib in gastrointestinal tumours, the authors predict the potential pitfalls, which may lie in ahead for the future clinical development of p53-RA agents, as well as discussing potential non-invasive methods to identify the development of drug resistance.

EXPERT OPINION

Medicinal chemistry strategies, based on structure-based drug design, are required to re-engineer cis-imidazoline Nutlin HDM2-binding antagonists into less haematologically toxic drugs. In silico modelling is also required to predict toxicities of other p53-RA drugs at a much earlier stage in drug development. Whether p53-RA drugs will be therapeutically effective as a monotherapy remains to be determined.

PRIMA-1Met/APR-246 displays high antitumor activity in multiple myeloma by induction of p73 and Noxa

Targeting p53 by the small-molecule PRIMA-1(Met)/APR-246 has shown promising preclinical activity in various cancer types. However, the mechanism of PRIMA-1(Met)-induced apoptosis is not completely understood and its effect on multiple myeloma cells is unknown. In this study, we evaluated antitumor effect of PRIMA-1(Met) alone or its combination with current antimyeloma agents in multiple myeloma cell lines, patient samples, and a mouse xenograft model. Results of our study showed that PRIMA-1(Met) decreased the viability of multiple myeloma cells irrespective of p53 status, with limited cytotoxicity toward normal hematopoietic cells. Treatment of multiple myeloma cells with PRIMA-1(Met) resulted in induction of apoptosis, inhibition of colony formation, and migration. PRIMA-1(Met) restored wild-type conformation of mutant p53 and induced activation of p73 upregulating Noxa and downregulating Mcl-1 without significant modulation of p53 level. siRNA-mediated silencing of p53 showed a little effect on apoptotic response of PRIMA-1(Met), whereas knockdown of p73 led to substantial attenuation of apoptotic activity in multiple myeloma cells, indicating that PRIMA-1(Met)-induced apoptosis is, at least in part, p73-dependent. Importantly, PRIMA-1(Met) delayed tumor growth and prolonged survival of mice bearing multiple myeloma tumor. Furthermore, combined treatment of PRIMA-1(Met) with dexamethasone or doxorubicin displayed synergistic effects in both multiple myeloma cell lines and primary multiple myeloma samples. Consistent with our in vitro observations, cotreatment with PRIMA-1(Met) and dexamethasone resulted in enhanced antitumor activity in vivo. Our study for the first time shows antimyeloma activity of PRIMA-1(Met) and provides the rationale for its clinical evaluation in patients with multiple myeloma, including the high-risk group with p53 mutation/deletion.