PPM1D in Solid and Hematologic Malignancies: Friend and Foe?

Gain of chromosome 17 is an early genetic abnormality in neuroblastoma with PPM1D emerging as a strong candidate oncogene driving tumor progression

Segmental gain of chromosome 17q is the most common genetic aberration in high-risk neuroblastoma, but its role in disease progression is poorly understood. This study aims to address the contribution of 17q gain to neuroblastoma malignancy. We analyzed the genetic and transcriptional landscape of 417 neuroblastoma patients across various risk groups and clinical stages using multi-omic approaches. Single-cell RNA/DNA sequencing and SNP arrays were combined to characterize genomic aberrations, while evolutionary trajectories were mapped to explore the accumulation of genetic changes in patients with neuroblastoma. Additionally, DNA and RNA sequencing were used to assess mutational burden and gene expression patterns. Our findings suggest that chromosome 17 gain is an early genetic event acquired during neuroblastoma development, correlating with the accumulation of additional chromosomal aberrations and poor prognosis. Increased segmental gains of chromosome 17q were observed during clonal evolution, relapse disease and metastasis. We identified PPM1D, a p53-inducible Ser/Thr phosphatase located on chr17q22.3, as a key player activated by segmental 17q-gain, gene-fusion, or gain-of-function somatic and germline mutations, further promoting neuroblastoma development/progression. Gain of chromosome 17 is an early driver of genetic instability in neuroblastoma, with PPM1D emerging as a potential candidate gene implicated in high-risk disease progression.

PPM1D Mutation as a Distinct Feature of Myeloid Neoplasms in B-Cell Non-Hodgkin Lymphoma Patients: A Retrospective Analysis

BACKGROUND/OBJECTIVES

Myeloid neoplasms are the most common secondary blood cancer in B-cell non-Hodgkin lymphoma (BNHL) patients treated with cytotoxic therapies. We aimed to characterize the genetic and clinicopathologic features of myeloid neoplasms arising after B-cell non-Hodgkin lymphoma (MN-BNHL) by comparing their features with myeloid neoplasms developing after solid cancer (MN-SC).

METHODS

We retrospectively analyzed the clinicopathologic and genetic data of myeloid neoplasm patients diagnosed between 2008 and 2023, categorized as MN-BNHL or MN-SC. Further NGS analysis was performed on available bone marrow samples with missing genetic data. The genetic profiles of myeloid neoplasms between BNHL and solid cancer groups were compared.

RESULTS

Sixteen patients developed MN-BNHL. Among the 11 MN-BNHL patients undergoing NGS, all harbored tier 1 mutations. PPM1D mutations (PPM1Dms) were most frequent (73%), followed by DNMT3A (46%) and TP53 (36%). PPM1Dms were significantly more prevalent than in MN-SC (n = 21), where TP53 mutations were most common (64%) (p < 0.001). PPM1Dms often co-occurred with DNMT3A. They were associated with prior radioimmunotherapy (relative risk (RR): 3.3 and RR 3.57). MN-BNHL patients with PPM1Dms exhibited improved survival compared to those without (p = 0.0376), but this benefit was negated by the presence of TP53 mutations (p = 0.0049).

CONCLUSIONS

PPM1Dms are a prominent genetic feature in MN-BNHL, suggesting a distinct role in its development compared to MN-SC. Further investigation is needed to elucidate the precise contribution of PPM1D and its interaction with other mutations in BNHL-related myeloid neoplasm development and prognosis.

Identification of small molecule inhibitors of PPM1D using an integrated drug discovery platform

PPM1D is a serine/threonine phosphatase recurrently activated in cancer, regulates the DNA damage response (DDR), and suppresses p53. Though PPM1D inhibition impairs tumor growth in cancer models and is the subject of multiple drug discovery efforts, no PPM1D inhibitors with clinical potential have been identified. We screened 600,000 compounds in a displacement assay and generated a hit series with nanomolar activity. We optimized our leads using internally developed assays to interrogate PPM1D, p53, and the DDR and defined important structure-activity relationships. Using an in vivo bioluminescent readout of p53 activation, we compared different DDR and p53 modulators and showed that despite having a distinct chemical structure, our lead compound had comparable in vivo activity to established PPM1D inhibitors. Our approach yielded multiple allosteric inhibitors of PPM1D, deepened our understanding of PPM1D as a drug target, and is highly amenable to studying other modulators of the DDR and p53.

The role of the PPM1D gene in tumor pathogenesis

The PPM1D gene and its protein product (serine-threonine protein phosphatase, PPM1D or Wip1) are involved in regulation of cell's DNA damage response, cell cycle control, and repair. Amplification, overexpression, or mutations of the PPM1D gene have a significant impact on cell responses to stress factors and genetic instability as well as impairments of processes of double-strand break repair, nucleotide excision repair, base excision repair, cell cycle, and apoptosis. PPM1D dephosphorylates and thus inactivates p53, proteins that respond to DNA strand integrity damage, cell cycle checkpoint proteins, and apoptotic proteins. This contributes to tumor development, growth, and maintenance of the tumor phenotype. In this review we consider data on the role of the PPM1D gene in the formation and maintenance of various oncological processes, including tumors of the mammary glands, ovaries, prostate gland, esophagus, stomach, intestines, liver and pancreas, hemoblastoses, and others.

Genomic mutation patterns and prognostic value in de novo and secondary acute myeloid leukemia: A multicenter study from China

Acute myeloid leukemia (AML) can manifest as de novo AML (dn-AML) or secondary AML (s-AML), with s-AML being associated with inferior survival and distinct genomic characteristics. The underlying reasons for this disparity remain to be elucidated. In this multicenter study, next-generation sequencing (NGS) was employed to investigate the mutational landscape of AML in 721 patients from June 2020 to May 2023.Genetic mutations were observed in 93.34% of the individuals, with complex variations (more than three gene mutations) present in 63.10% of them. TET2, ASXL1, DNMT3A, TP53 and SRSF2 mutations showed a higher prevalence among older individuals, whereas WT1 and KIT mutations were more commonly observed in younger patients. BCOR, BCORL1, ZRSR2, ASXL1 and SRSF2 exhibited higher mutation frequencies in males. Additionally, ASXL1, NRAS, PPMID, SRSF2, TP53 and U2AF1 mutations were more common in patients with s-AML, which PPM1D was more frequently associated with therapy-related AML (t-AML). Advanced age and hyperleukocytosis independently served as adverse prognostic factors for both types of AML; however, s-AML patients demonstrated a greater number of monogenic adverse prognostic factors compared to dn-AML cases (ASXL1, PPM1D, TP53 and U2AF1 in s-AML vs. FLT3, TP53 and U2AF1 in dn-AML). Age and sex-related gene mutations suggest epigenetic changes may be key in AML pathogenesis. The worse prognosis of s-AML compared to dn-AML could be due to the older age of s-AML patients and more poor-prognosis gene mutations. These findings could improve AML diagnosis and treatment by identifying potential therapeutic targets and risk stratification biomarkers.

Long-term breast cancer response to CDK4/6 inhibition defined by TP53-mediated geroconversion

Inhibition of CDK4/6 kinases has led to improved outcomes in breast cancer. Nevertheless, only a minority of patients experience long-term disease control. Using a large, clinically annotated cohort of patients with metastatic hormone receptor-positive (HR+) breast cancer, we identify TP53 loss (27.6%) and MDM2 amplification (6.4%) to be associated with lack of long-term disease control. Human breast cancer models reveal that p53 loss does not alter CDK4/6 activity or G1 blockade but instead promotes drug-insensitive p130 phosphorylation by CDK2. The persistence of phospho-p130 prevents DREAM complex assembly, enabling cell-cycle re-entry and tumor progression. Inhibitors of CDK2 can overcome p53 loss, leading to geroconversion and manifestation of senescence phenotypes. Complete inhibition of both CDK4/6 and CDK2 kinases appears to be necessary to facilitate long-term response across genomically diverse HR+ breast cancers.

PPM1D/Wip1 is amplified, overexpressed, and mutated in human non-Hodgkin's lymphomas

BACKGROUND

Wip1, is a p53-dependent Ser/Thr phosphatase involved in the timely termination of DDR. The PPM1D gene encoding Wip1 is deregulated and thus gained an oncogene character in common human solid tumors and cell lines. This study assessed the oncogenic potential of the PPM1D gene in human non- Hodgkin's lymphomas (NHL), the most common hematological malignancy worldwide.

METHODS AND RESULTS

FFPE human lymphoid hyperplasia (LH) (n = 17) and NHL tumor lymph node samples (n = 65) and human NHL cell lines were used to assess the oncogenic potential of the PPM1D gene in the present study. Copy number gain and mRNA expression analysis of the PPM1D/Wip1 gene were assessed by qRT-PCR analysis. Mutational analysis of Exon 6 of the PPM1D gene was performed by PCR amplification and Sanger sequencing. Expressions of Wip1 and p53 proteins were assessed by immunohistochemistry and Western blot analysis.

CONCLUSIONS

We found that PPM1D gained gene copy number in NHL tumors by 0.7-8 times compared to the control (p < 0.01). Increased PPM1D/Wip1 gene copy number was associated with higher mRNA and protein expression in human NHL samples (p < 0.01). Overexpression of Wip1 in NHL tumors and NHL cell lines was associated with amplification level and was unaffected by p53 status. Furthermore, a heterozygous type insertion mutation was detected in exon 6 (c.1553_1554insA) of the PPM1D gene particularly in DLBCL samples. Wip1 may have oncogenic potential, perhaps playing a role in the onset and progression of human NHL. The possible significance of Wip1 overexpression to chemotherapy response in NHL remains an intriguing question that requires more exploration.

Distinct landscape and clinical implications of therapy-related clonal hematopoiesis

Therapy-related clonal hematopoiesis (t-CH) is defined as clonal hematopoiesis detected in individuals previously treated with chemotherapy and/or radiation therapy. With the increased use of genetic analysis in oncological care, the detection of t-CH among cancer patients is becoming increasingly common. t-CH arises through the selective bottleneck imposed by chemotherapies and potentially through direct mutagenesis from chemotherapies, resulting in a distinct mutational landscape enriched with mutations in DNA damage-response pathway genes such as TP53, PPM1D, and CHEK2. Emerging evidence sheds light on the mechanisms of t-CH development and potential strategies to mitigate its emergence. Due to its unique characteristics that predominantly affect cancer patients, t-CH has clinical implications distinct from those of CH in the general population. This Review discusses the potential mechanisms of t-CH development, its mutational landscape, mutant-drug relationships, and its clinical significance. We highlight the distinct nature of t-CH and call for intensified research in this field.

Identification of Small Molecule Inhibitors of PPM1D Using a Novel Drug Discovery Platform

Protein phosphatase, Mg2+/Mn2+ dependent 1D (PPM1D), is a serine/threonine phosphatase that is recurrently activated in cancer, regulates the DNA damage response (DDR), and suppresses the activation of p53. Consistent with its oncogenic properties, genetic loss or pharmacologic inhibition of PPM1D impairs tumor growth and sensitizes cancer cells to cytotoxic therapies in a wide range of preclinical models. Given the therapeutic potential of targeting PPM1D specifically and the DDR and p53 pathway more generally, we sought to deepen our biological understanding of PPM1D as a drug target and determine how PPM1D inhibition differs from other therapeutic approaches to activate the DDR. We performed a high throughput screen to identify new allosteric inhibitors of PPM1D, then generated and optimized a suite of enzymatic, cell-based, and in vivo pharmacokinetic and pharmacodynamic assays to drive medicinal chemistry efforts and to further interrogate the biology of PPM1D. Importantly, this drug discovery platform can be readily adapted to broadly study the DDR and p53. We identified compounds distinct from previously reported allosteric inhibitors and showed in vivo on-target activity. Our data suggest that the biological effects of inhibiting PPM1D are distinct from inhibitors of the MDM2-p53 interaction and standard cytotoxic chemotherapies. These differences also highlight the potential therapeutic contexts in which targeting PPM1D would be most valuable. Therefore, our studies have identified a series of new PPM1D inhibitors, generated a suite of in vitro and in vivo assays that can be broadly used to interrogate the DDR, and provided important new insights into PPM1D as a drug target.

PPM1D activity promotes the replication stress caused by cyclin E1 overexpression

Oncogene-induced replication stress has been recognized as a major cause of genome instability in cancer cells. Increased expression of cyclin E1 caused by amplification of the CCNE1 gene is a common cause of replication stress in various cancers. Protein phosphatase magnesium-dependent 1 delta (PPM1D) is a negative regulator of p53 and has been implicated in termination of the cell cycle checkpoint. Amplification of the PPM1D gene or frameshift mutations in its final exon promote tumorigenesis. Here, we show that PPM1D activity further increases the replication stress caused by overexpression of cyclin E1. In particular, we demonstrate that cells expressing a truncated mutant of PPM1D progress faster from G1 to S phase and fail to complete licensing of the replication origins. In addition, we show that transcription-replication collisions and replication fork slowing caused by CCNE1 overexpression are exaggerated in cells expressing the truncated PPM1D. Finally, replication speed and accumulation of focal DNA copy number alterations caused by induction of CCNE1 expression was rescued by pharmacological inhibition of PPM1D. We propose that increased activity of PPM1D suppresses the checkpoint function of p53 and thus promotes genome instability in cells expressing the CCNE1 oncogene.

Ppm1d truncating mutations promote the development of genotoxic stress-induced AML

Hematopoietic stem cells (HSCs) ensure blood cell production during the life-time of an organism, and to do so they need to balance self-renewal, proliferation, differentiation, and migration in a steady state as well as in response to stress or injury. Importantly, aberrant proliferation of HSCs leads to hematological malignancies, and thus, tight regulation by various tumor suppressor pathways, including p53, is essential. Protein phosphatase magnesium-dependent 1 delta (PPM1D) is a negative regulator of p53 and promotes cell survival upon induction of genotoxic stress. Truncating mutations in the last exon of PPM1D lead to the production of a stable, enzymatically active protein and are commonly associated with clonal hematopoiesis. Using a transgenic mouse model, we demonstrate that truncated PPM1D reduces self-renewal of HSCs in basal conditions but promotes the development of aggressive AML after exposure to ionizing radiation. Inhibition of PPM1D suppressed the colony growth of leukemic stem and progenitor cells carrying the truncated PPM1D, and remarkably, it provided protection against irradiation-induced cell growth. Altogether, we demonstrate that truncated PPM1D affects HSC maintenance, disrupts normal hematopoiesis, and that its inhibition could be beneficial in the context of therapy-induced AML.

Associations Between Cancer Predisposition Mutations and Clonal Hematopoiesis in Patients With Solid Tumors

PURPOSE

Clonal hematopoiesis (CH), the expansion of clones in the hematopoietic system, has been linked to different internal and external features such as aging, genetic ancestry, smoking, and oncologic treatment. However, the interplay between mutations in known cancer predisposition genes and CH has not been thoroughly examined in patients with solid tumors.

METHODS

We used prospective tumor-blood paired sequencing data from 46,906 patients who underwent Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) testing to interrogate the associations between CH and rare pathogenic or likely pathogenic (P/LP) germline variants.

RESULTS

We observed an enrichment of CH-positive patients among those carrying P/LP germline mutations and identified a significant association between P/LP germline variants in ATM and CH. Germline and CH comutation patterns in ATM, TP53, and CHEK2 suggested biallelic inactivation as a potential mediator of clonal expansion. Moreover, we observed that CH-PPM1D mutations, similar to somatic tumor-associated PPM1D mutations, were depleted in patients with P/LP germline mutations in the DNA damage response (DDR) genes ATM, CHEK2, and TP53. Patients with solid tumors and harboring P/LP germline mutations, CH mutations, and mosaicism chromosomal alterations might be at an increased risk of developing secondary leukemia while germline variants in TP53 were identified as an independent risk factor (hazard ratio, 36; P < .001) for secondary leukemias.

CONCLUSION

Our results suggest a close relationship between inherited variants and CH mutations within the DDR genes in patients with solid tumors. Associations identified in this study might translate into enhanced clinical surveillance for CH and associated comorbidities in patients with cancer harboring these germline mutations.