In the original publication [...].

Outcomes for patients with relapsed acute lymphoblastic leukemia (ALL) are poor and there is a need for novel therapies to improve outcomes. Targeted inhibition of WEE1 with small-molecule inhibitor adavosertib (AZD1775) has emerged as a therapeutic strategy to sensitize cancer cells to DNA-damaging chemotherapeutics, particularly in the context of TP53-mutated tumors. However, WEE1 inhibition as a potential therapeutic strategy for patients with high-risk and relapsed ALL, including those with TP53 mutations, has not been definitively evaluated. Anti-leukemic effects of adavosertib were investigated using a relapsed TP53 isogenic cell model system, primary patient, and patient-derived ALL samples (n = 27) in an ex vivo co-culture model system with bone marrow-derived mesenchymal stem cells. Combination effects with drugs currently used for relapsed ALL were quantified by Excess over Bliss analyses. Investigations for alterations of cell cycle and apoptosis as well as related proteins were examined by flow cytometry and Western blot, respectively. Our study demonstrates the potent anti-leukemic activity of the clinically advanced WEE1 inhibitor adavosertib in a large majority (n = 18/27) of high-risk and relapsed ALL specimens at lower than clinically attainable concentrations, independent of TP53 mutation status. We show that treatment with adavosertib results in S-phase disruption even in the absence of DNA-damaging agents and that premature mitotic entry is not a prerequisite for its anti-leukemic effects. We further demonstrate that WEE1 inhibition additively and synergistically enhances the anti-leukemic effects of multiple conventional chemotherapeutics used in the relapsed ALL treatment setting. Particularly, we demonstrate the highly synergistic and cytotoxic combination of adavosertib with the nucleoside analog cytarabine and provide mechanistic insights into the combinational activity, showing preferential engagement of apoptotic cell death over cell cycle arrest. Our findings strongly support in vivo interrogation of adavosertib with cytarabine in xenograft models of relapsed and high-risk ALL. Together, our data emphasize the functional importance of WEE1 in relapsed ALL cells and show WEE1 as a promising p53-independent therapeutic target for the improved treatment of high-risk and relapsed ALL.

Background: Chronic lymphocytic leukemia (CLL) treatment has transitioned from traditional chemotherapy to more targeted therapies, but challenges such as resistance and suboptimal responses persist. This study aimed to evaluate HDM201, a second-generation MDM2-p53 binding antagonist, as a novel therapeutic strategy for CLL, with a focus on its effectiveness across different TP53 genetic contexts. Methods: We utilized a panel of B cell leukemia-derived cell lines with varying TP53 statuses, including TP53-knockout (KO) derivatives of the human B cell line Nalm-6, and assessed the impact of HDM201 on primary CLL samples with both TP53 wild-type and mutant backgrounds. Results: Our results revealed that TP53 wild-type and heterozygous TP53-KO Nalm-6 cells were sensitive to HDM201, whereas homozygous TP53-KO cells and B cells with TP53 mutations exhibited significant resistance. Resistance was also noted in primary CLL samples with TP53 mutations. HDM201 effectively stabilized p53 and induced apoptosis in TP53 wild-type cells but had limited efficacy in TP53 mutant cells. Conclusions: These findings indicate that HDM201 holds promise as an additional targeted therapy option for wild-type TP53 CLL. The results underline the importance of TP53 status in predicting treatment efficacy and highlight the potential of HDM201 as a valuable addition to explore in CLL therapy. Future research should focus on identifying additional biomarkers of response and exploring the optimal way to include HDM201 in combination therapies to improve treatment outcomes in CLL.

Abstract Aim We aimed to design an MDM2-p53 antagonist with a differentiated tolerability profile that could be used to treat patients with wild-type TP53 malignancies. As part of an alliance between Newcastle University, Astex Pharmaceuticals, and Cancer Research Horizons, we discovered ASTX295, a potent inhibitor of the MDM2-p53 interaction that is currently under clinical investigation in patients with solid tumors (NCT03975387). We selected ASTX295 as a compound with a predicted short plasma half-life, which we hypothesised would help to mitigate the dose-limiting neutropenia and thrombocytopenia observed with earlier MDM2-p53 antagonists in clinical studies. To examine this hypothesis in vitro, we determined time- and concentration-dependent responses to ASTX295 treatment in healthy volunteer-derived human bone marrow cells, megakaryocytes, and in a panel of human tumor cell lines. Methods Samples containing bone marrow cells from healthy patients undergoing hip surgery were obtained under the ethical approval of the Newcastle Biobank (REC 12/NE/0395). Following Lymphoprep™ separation, cells were treated ex vivo with ASTX295 and seeded for Granulocyte-macrophage (GM) colony-forming assays in methylcellulose. Megakaryocytes were obtained from in vitro differentiation of CD34+ stem/progenitor cells. Human tumor cell lines (including MDM2-amplified SJSA-1) were treated with ASTX295 in vitro and seeded at low density for colony-forming assays. Exposures of 6, 12, or 24h were examined, and the data plotted to calculate LC50 values. Results The clonogenic survival of tumor cells was time-dependent, with LC50 values (mean ± SEM) in SJSA1 cells being 238 ± 46nM and 75 ± 7nM respectively (n = 3-4), following a 12h or 24h exposure to ASTX295. Time-dependent effects were also evident in five human bone marrow samples but with LC50 values of 1.9, >3, >10, >10, and >10uM being achieved at 12h, and 860 ± 268nM at 24h. Megakaryocytes showed similar time-dependent sensitivities in which daily treatment of 2 or 6h over three days did not induce apoptosis while significant cell death was observed when the treatment time was extended to 16-24h daily. In contrast, short, daily pulse treatment of 2-6h in cell lines (MV4-11, MOLM-13, SJSA-1) over three days was sufficient to induce cell death. Conclusions ASTX295 is a potent antagonist of the MDM2-p53 interaction. Collectively, our in vitro data suggest that a shorter exposure to ASTX295 (up to 12h), may help to spare healthy bone marrow cells whilst killing tumor cells. Hence, intermittent exposure to an MDM2-p53 antagonist could favourably modulate its therapeutic index. The predicted short plasma half-life of ASTX295 should provide flexibility in controlling the duration of exposure in vivo, potentially enabling a more bone-marrow sparing approach to MDM2-p53 antagonism to be utilised. Citation Format: Elaine Willmore, Maria Ahn, Suzanne Kyle, Yan Zhao, Huw Thomas, Kenneth S. Rankin, Luke Bevan, Lynsey Fazal, Keisha Hearn, Nicola Wilsher, Justyna Kucia-Tran, Nicola Ferrari, Nicola Wallis, Neil Thompson, John Lyons, Duncan Miller, Celine Cano, Martin E. Noble, Ian R. Hardcastle, Steven Howard, Gianni Chessari, John Lunec, David R. Newell, Steve R. Wedge. Targeting the MDM2-p53 interaction: Time- and concentration-dependent studies in tumor and normal human bone marrow cells reveal strategies for an enhanced therapeutic index [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3333.

Abstract In response to cellular stress, the tumor suppressor p53 is activated to modulate cell cycle progression, DNA repair, and apoptosis. Inhibition of the MDM2-p53 interaction in tumors carrying wild-type p53 prevents its degradation and can reactivate p53 to elicit an anti-cancer effect. Targeting the p53-MDM2 interaction therefore remains a promising strategy for cancer therapy. However, development of first generation MDM2 antagonists has been challenged by dose-limiting, on-target bone marrow toxicities. Understanding of differential effects of p53 pathway activation in normal hematopoietic versus cancer cells (to be presented in a separate abstract) together with our expertise in structure-based drug design have led to the discovery of ASTX295, a potent MDM2 antagonist with differentiated pharmacokinetic profile aimed at sparing bone marrow toxicities and increasing the therapeutic index. Here, we present the first disclosure of the structure and pre-clinical characterisation of ASTX295. ASTX295 exhibits potent activity (IC50<1 nM) against MDM2 in an ELISA-based in vitro assay and induces significant growth reduction in p53 wild-type, MDM2-amplified SJSA-1 cells (GI50=27 nM). Antiproliferative activity of ASTX295 was further demonstrated in a panel of 219 p53 wild-type cell lines, with 143 cell lines showing GI50 values less than 1 μM and 50 showing values less than 0.1 μM. Effects of ASTX295 are shown in cell lines carrying functional p53 as confirmed in three p53 wild-type and mutant cell line pairs (SJSA1 and SN40R2, A2780 and A2780CP, HCT116 and HCT116 p53−/−). In addition to inhibiting cell cycle progression and cell proliferation, ASTX295 also potently induces apoptosis following 24-48 hour treatment. Further in vitro analyses of ASTX295 demonstrated an increase in the levels of p53 (EC50=10 nM after 2 hours) and its transcriptional targets such as p21 and MDM2. In vivo, ASTX295 shows robust induction of p53 and its target genes at 3 and 6 hours after oral administration together with dose-dependent inhibition of tumour growth in the SJSA-1 xenograft model. Importantly, ASTX295 exhibits optimised pharmacokinetic and pharmacodynamic profiles with relatively short duration of pathway modulation and a desired predicted human half-life of 2-8 hours. Based on our pre-clinical hypothesis on differential time-dependent sensitivities of normal versus cancer cells to p53 activation, achieving such a profile while maintaining potency may increase the therapeutic index. These data highlight the therapeutic potential of ASTX295, which is currently being tested in a Phase 1/2 clinical trial in advanced solid tumors with wild-type p53 (NCT03975387). We plan to present preliminary clinical data in a separate abstract at this meeting. Citation Format: Maria Ahn, Luke Bevan, Ildiko Buck, Celine Cano, Juan Castro, Ben Cons, Jane Endicott, Lynsey Fazal, Nicola Ferrari, Ian Hardcastle, Keisha Hearn, Rhian Holvey, Steven Howard, Chris Johnson, Claire Jennings, Justyna Kucia-Tran, Suzanne Kyle, John Lunec, John Lyons, Duncan Miller, David Rees, Martin Noble, David R. Newell, Judith Reeks, Harpreet Saini, Jeffrey St. Denis, Emiliano Tamanini, Huw Thomas, Neil Thompson, Mladen Vinkovic, George Ward, Nicola Wallis, Hugh Walton, Stephen Wedge, Pamela Williams, Elaine Willmore, Nicola Wilshire, Yan Zhao, Gianni Chessari. Discovery of ASTX295, a potent, next-generation small molecule antagonist of MDM2 with differentiated pharmacokinetic profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6588.

Chronic lymphocytic leukemia (CLL) is a genetically and clinically diverse hematological cancer affecting middle-aged and elderly individuals. Novel targeted therapy options are needed for patients who relapse following initial responses or who are intrinsically resistant to current treatments. There is a growing body of investigation currently underway on MDM2 inhibitors in clinical trials, reflecting the increasing interest in including these drugs in cancer treatment regimens. One of the developed compounds, idasanutlin (RG7388), has shown promise in early-stage clinical trials. It is a second-generation MDM2–p53-binding antagonist with enhanced potency, selectivity, and bioavailability. In addition to the TP53 status, which is an important determinant of the response, we have shown in our previous studies that the SF3B1 mutational status is also an independent predictive biomarker of the ex vivo CLL patient sample treatment response to RG7388. The objective of this study was to identify novel biomarkers associated with resistance to RG7388. Gene set enrichment analysis of differentially expressed genes (DEGs) between RG7388-sensitive and -resistant CLL samples showed that the increased p53 activity led to upregulation of pro-apoptosis pathway genes while DNA damage response pathway genes were additionally upregulated in resistant samples. Furthermore, differential expression of certain genes was detected, which could serve as the backbone for novel combination treatment approaches. This research provides preclinical data to guide the exploration of drug combination strategies with MDM2 inhibitors, leading to future clinical trials and associated biomarkers that may improve outcomes for CLL patients.

Due to the rarity of TP53 mutations in acute lymphoblastic leukemia (ALL), p53 re-activation by antagonism of the p53-MDM2 interaction represents a potential therapeutic strategy for the majority of ALL. Here, we demonstrate the potent antileukemic activity of the MDM2 antagonist idasanutlin in high-risk and relapsed ex vivo coculture models of TP53 wildtype ALL (n = 40). Insufficient clinical responses to monotherapy MDM2 inhibitors in other cancers prompted us to explore optimal drugs for combination therapy. Utilizing high-throughput combination screening of 1971 FDA-approved and clinically advanced compounds, we identified BCL-xL/BCL-2 inhibitor navitoclax as the most promising idasanutlin combination partner. The idasanutlin-navitoclax combination was synergistically lethal to prognostically-poor, primary-derived and primary patient blasts in ex vivo coculture, and reduced leukemia burden in two very high-risk ALL xenograft models at drug concentrations safely attained in patients; in fact, the navitoclax plasma concentrations were equivalent to those attained in contemporary “low-dose” navitoclax clinical trials. We demonstrate a preferential engagement of cell death over G1 cell cycle arrest, mechanistically implicating MCL-1-binding pro-apoptotic sensitizer NOXA. The proposed combination of two clinical-stage compounds independently under clinical evaluation for ALL is of high clinical relevance and warrants consideration for the treatment of patients with high-risk and relapsed ALL.

There is a growing body of investigation currently underway on MDM2 inhibitors in clinical trials, reflecting the increasing interest in including these drugs in cancer treatment regimens. One of the developed compounds, idasanutlin (RG7388), has shown promise in early-stage clinical trials. It is a second-generation MDM2-p53 binding antagonist with enhanced potency, selectivity, and bioavailability. In addition to TP53 status, which is an important determinant of the response, we have shown in our previous studies that SF3B1 mutational status is also an independent predictive biomarker of ex vivo CLL patient sample treatment response to RG7388. The objective of this study was to identify novel biomarkers associated with resistance to RG7388. Gene set enrichment analysis of differentially expressed genes (DEGs) between RG7388-sensitive and resistant CLL samples showed that the increased p53 activity led to upregulation of pro-apoptosis pathway genes while DNA damage response pathway genes were additionally up-regulated in resistant samples. Furthermore, differential expression of certain genes was detected, which could serve as the backbone for novel combination treatment approaches. This research provides preclinical data to guide the exploration of drug combination strategies with MDM2 inhibitors, leading to future clinical trials and associated biomarkers to improve outcome for CLL patients.

Supplementary Table S1: A & B) List of genes with significantly increased mRNA levels in NGP cells 4 hours following treatment with 75nm RG7388 (GI50 in NGP cells) + 2.5µM GSK2830371. Genes were ordered based on p-value following Benjamini-Hotchberg correction for multiple testing. OR: Odds ratio.

Background Molecular characterisation of hepatocellular carcinoma (HCC) is central to the development of novel therapeutic strategies for the disease. We have previously demonstrated mutagenic consequences of Long-Interspersed Nuclear Element-1 (LINE1s/L1) retrotransposition. However, the role of L1 in HCC, besides somatic mutagenesis, is not well understood. Methods We analysed L1 expression in the TCGA-HCC RNAseq dataset ( n = 372) and explored potential relationships between L1 expression and clinical features. The findings were confirmed by immunohistochemical (IHC) analysis of an independent human HCC cohort ( n = 48) and functional mechanisms explored using in vitro and in vivo model systems. Results We observed positive associations between L1 and activated TGFβ-signalling, TP53 mutation, alpha-fetoprotein and tumour invasion. IHC confirmed a positive association between pSMAD3, a surrogate for TGFβ-signalling status, and L1 ORF1p ( P < 0.0001, n = 32). Experimental modulation of L1 ORF1p levels revealed an influence of L1 ORF1p on key hepatocarcinogenesis-related pathways. Reduction in cell migration and invasive capacity was observed upon L1 ORF1 knockdown, both in vitro and in vivo. In particular, L1 ORF1p increased PIN1 cytoplasmic localisation. Blocking PIN1 activity abrogated L1 ORF1p-induced NF-κB-mediated inflammatory response genes while further activated TGFβ-signalling confirming differential alteration of PIN1 activity in cellular compartments by L1 ORF1p. Discussion Our data demonstrate a causal link between L1 ORF1p and key oncogenic pathways mediated by PIN1, presenting a novel therapeutic avenue.

Supplementary Figures 1-5 from p53 Is a Direct Transcriptional Target of MYCN in Neuroblastoma

Supplementary figure S3: A) The ratios pp53Ser15 band: total p53 band optical density values (OD) in Figure 4F (Left) and 3D (Right) quantified using Imagej software. B) Western blot showing changes in pp53Ser15, MDM2, and p21WAF1 expression 12 hours after different concentrations of wild-type p53 (Wt), p53 mutants Ser15Ala (S15A) and Ser15Asp (S15D) ectopic expression in HCT116-/- cells. C) The quantification of p21WAF1 and MDM2 band OD values based on the last three lanes in Supplementary figure S3B and Figure 4F. The OD values were normalised to the optical density value calculated from the same area in the pcDNA3.1 track on each image.

Supplementary figure S4: A) Time-course of cell cycle distribution changes over 72 hours of treatment using FACS analysis. NGP and SJSA-1 cells were treated either with DMSO solvent control (Black), 2.5µM GSK2830371 (Blue), (GI50) Nutlin-3 (Red) or Nutlin-3 + GSK2830371 combination (Purple). HCT116+/+ cells were treated with 0.5 × Nutlin-3 GI50 in single and in combination treatment. B) Representative cell cycle distribution histograms for NGP and SJSA-1 cells indicating the increase in the proportion of Sub-G1events in response to 72 hours of treatment with GSK2830371 (WIP1i), Nutlin-3 and their combination.

Chronic lymphocytic leukemia (CLL) is a genetically and clinically heterogeneous malignancy affecting older individuals. There are a number of current treatment options for CLL, including monoclonal antibodies, targeted drugs, chemotherapy, and different combinations of these. However, for those patients who are intrinsically treatment resistant, or relapse following initial responses, novel targeted therapies are still needed. Targeting the mouse double-minute-2 human homolog (MDM2), a primary negative regulator of p53, is an appealing therapeutic strategy for non-genotoxic reactivation of p53, since the TP53 gene is in its wild-type state at diagnosis in approximately 90% of patients. Mutated SF3B1 and TP53 are both associated with more aggressive disease, resistance to therapies and poorer overall survival for CLL. In this study, we performed a screen for SF3B1 and TP53 mutations and tested RG7388 (idasanutlin), a second-generation MDM2 inhibitor, in a cohort of CLL primary patient samples. SF3B1 mutations were detected in 24 of 195 cases (12.3%) and found associated with poor overall survival (hazard ratio [HR] 2.12, p = 0.032) and high CD38 expression (median CD38 (%) 32 vs. 5; p = 0.0087). The novel striking finding of this study was an independent link between SF3B1 mutational status and poor response to RG7388. Overall, SF3B1 mutations in CLL patient samples were associated with resistance to treatment with RG7388 ex vivo, and patients with the wild type for both SF3B1 and TP53 are more likely to benefit from treatment with MDM2 inhibitors.

Several molecular subtypes of cancer are highly dependent on splicing for cell survival. There is a general interest in the therapeutic targeting of splicing by small molecules. E7107, a first-in-class spliceosome inhibitor, showed strong growth inhibitory activities against a large variety of human cancer xenografts. Chronic lymphocytic leukaemia (CLL) is a clinically heterogeneous hematologic malignancy, with approximately 90% of cases being TP53 wild-type at diagnosis. An increasing number of studies are evaluating alternative targeted agents in CLL, including MDM2–p53 binding antagonists. In this study, we report the effect of splicing modulation on key proteins in the p53 signalling pathway, an important cell death pathway in B cells. Splicing modulation by E7107 treatment reduced full-length MDM2 production due to exon skipping, generating a consequent reciprocal p53 increase in TP53WT cells. It was especially noteworthy that a novel p21WAF1 isoform with compromised cyclin-dependent kinase inhibitory activity was produced due to intron retention. E7107 synergized with the MDM2 inhibitor RG7388, via dual MDM2 inhibition; by E7107 at the transcript level and by RG7388 at the protein level, producing greater p53 stabilisation and apoptosis. This study provides evidence for a synergistic MDM2 and spliceosome inhibitor combination as a novel approach to treat CLL and potentially other haematological malignancies.

Supplementary figure S1: A) Volcano plot generated from the Wellcome Trust Sanger Institute Cosmic database showing the most significant genetic mutational determinants of response to MDM2 inhibition by Nutlin-3a. The plot shows the effect that genetic events, in commonly mutated genes in cancer, have on the IC50 for Nutlin-3a across a large panel of cell lines. The Y axis represents the p-value from multivariate ANOVA of drug gene interaction on an inverted log10 scale. This shows TP53 genetic status to be by far the strongest determinant of response to MDM2 antagonists (p=1.26e-54 ; Note this is off the Y-axis scale). The size of the circle reflects the sample size. B) Box and whiskers plot showing all the data associated with the TP53 node on the volcano plot from Supplementary figure S1A illustrating the range of sensitivities to Nutlin-3a among TP53 wild-type cell lines as determined by their IC50 values.

Childhood acute lymphoblastic leukaemia responds to standard treatment, but more targeted drugs are needed. Patient-derived xenografts (PDX) more closely resemble patient cancers than cell lines. PDXs do not proliferate well ex vivo without mesenchymal stromal cells (MSC). High-content microscopy allows separation of the cell types to allow greater accuracy to filter down the best drug combinations, and may provide insight into patient drug responses observed in the clinic. PDX-MSC cells were analysed with combinations of targeted and chemotherapeutic agents in an ex vivo co-culture system with some combinations deemed to be particularly effective. Caspase assays demonstrated increased cell death when drugs were used in combination in PDXs with high-risk cytogenetics. Subsequent in vivo testing revealed a triple combination was required in order to decrease leukaemic burden of very high risk subtypes, though ultimately resistance to the combination was still observed. Analysis of triple combination treated samples retrieved from mice revealed complete resistance to only one of the three drugs, suggesting resistance could be transient, or related to the pharmacokinetics of the drug.

KIT and PDGFRA play a major role in the oncogenic process in gastrointestinal stroma tumors (GIST) and small molecules have been employed with great success to target the KIT and PDGFRA pathways in this cancer. However, approximately 10% of patients with GIST are resistant to current targeted drug therapy. There is a need to explore other potential targets. Although p53 alterations frequently occur in most cancers, studies regarding p53 in GIST have been limited. The CDKN2A/MDM2/p53 axis regulates cell cycle progression and DNA damage responses, which in turn control tumor growth. This axis is the major event required for transformation from low- to high-risk GIST. Generally, p53 mutation is infrequent in GIST, but p53 overexpression has been reported to be associated with high-risk GIST and unfavorable prognosis, implying that p53 should play a critical role in GIST. Also, Wee1 regulates the cell cycle and the antitumor activity of Wee1 inhibition was reported to be p53 mutant dependent. In addition, Wee1 was reported to have potential activity in GIST through the regulation of KIT protein and this mechanism may be dependent on p53 status. In this article, we review previous reports regarding the role of p53 in GIST and propose targeting the p53 pathway as a novel additional treatment strategy for GIST.