Tipping Growth Inhibition into Apoptosis by Combining Treatment with MDM2 and WIP1 Inhibitors in p53WT Uterine Leiomyosarcoma

Harnessing p53 for targeted cancer therapy: new advances and future directions

The transcription factor p53 is the most frequently impaired tumor suppressor in human cancers. In response to various stress stimuli, p53 activates transcription of genes that mediate its tumor-suppressive functions. Distinctive characteristics of p53 outlined here enable a well-defined program of genes involved in cell cycle arrest, apoptosis, senescence, differentiation, metabolism, autophagy, DNA repair, anti-viral response, and anti-metastatic functions, as well as facilitating autoregulation within the p53 network. This versatile, anti-cancer network governed chiefly by a single protein represents an immense opportunity for targeted cancer treatment, since about half of human tumors retain unmutated p53. During the last two decades, numerous compounds have been developed to block the interaction of p53 with the main negative regulator MDM2. However, small molecule inhibitors of MDM2 only induce a therapeutically desirable apoptotic response in a limited number of cancer types. Moreover, clinical trials of the MDM2 inhibitors as monotherapies have not met expectations and have revealed hematological toxicity as a characteristic adverse effect across this drug class. Currently, combination treatments are the leading strategy for enhancing efficacy and reducing adverse effects of MDM2 inhibitors. This review summarizes efforts to identify and test therapeutics that work synergistically with MDM2 inhibitors. Two main types of drugs have emerged among compounds used in the following combination treatments: first, modulators of the p53-regulated transcriptome (including chromatin modifiers), translatome, and proteome, and second, drugs targeting the downstream pathways such as apoptosis, cell cycle arrest, DNA repair, metabolic stress response, immune response, ferroptosis, and growth factor signaling. Here, we review the current literature in this field, while also highlighting overarching principles that could guide target selection in future combination treatments.

Targeting MDM2-mediated suppression of p53 with idasanutlin: a promising therapeutic approach for acute lymphoblastic leukemia

Despite available treatments for acute lymphoblastic leukemia (ALL), the disease's high clinical variability necessitates new therapeutic strategies, particularly for patients with high-risk features. The tumor suppressor protein p53, encoded by the TP53 gene and known as the guardian of the genome, plays a crucial role in preventing tumor development. Over 90% of ALL cases initially harbor wild-type TP53. Reactivation of p53, which is encoded from the wild type TP53 but lost its function for several reasons, is an attractive therapeutic approach in cancer treatment. p53 can be activated in a non-genotoxic manner by targeting its primary repressor, the MDM2 protein. Clinical trials involving MDM2 inhibitors are currently being conducted in a growing body of investigation, reflecting of the interest in incorporating these treatments into cancer treatment strategies. Early-phase clinical trials have demonstrated the promise of idasanutlin (RG7388), one of the developed compounds. It is a second-generation MDM2-p53 binding antagonist with enhanced potency, selectivity, and bioavailability. The aim of this study is to evaluate the efficacy of RG7388 as a therapeutic strategy for ALL and to investigate its potential impact on improving treatment outcomes for high-risk patients. RG7388 potently decreased the viability in five out of six ALL cell lines with diverse TP53 mutation profiles, whereas only one cell line exhibited high resistance. RG7388 induced a pro-apoptotic gene expression signature with upregulation of p53-target genes involved in the intrinsic and extrinsic pathways of apoptosis. Consequently, RG7388 led to a concentration-dependent increase in caspase-3/7 activity and cleaved poly (ADP-ribose) polymerase. In this research, RG7388 was investigated with pre-clinical methods in ALL cells as a novel treatment strategy. This study suggests further functional research and in-vivo evaluation, and it highlights the prospect of treating p53-functional ALL with MDM2 inhibitors.

WIP1-mediated regulation of p38 MAPK signaling attenuates pyroptosis in sepsis-associated acute kidney injury

Wild-Type p53-Induced Phosphatase 1 (WIP1/PPM1D) is a serine/threonine phosphatase that plays a significant role in various physiological processes. However, the involvement of WIP1 in kidney remains unclear. Lipopolysaccharide (LPS) was administered to induce acute injury in mice and human kidney 2 (HK2) cells in the study. The WIP1 inhibitor, CCT007093, was administered both in vitro and in vivo to assess its effect on kidney. The single-cell sequencing (scRNA-seq) data revealed that Ppm1d mRNA reached peak on day 2 following unilateral ischemia-reperfusion injury (uni-IRI) in mice, especially in the proximal renal tubules during repair phase. Compared to the control group, WIP1 protein exhibited a significant increase in renal tubules of patients with acute tubular injury (ATI) and mice with LPS-induced acute kidney injury (AKI), as well as in LPS-injured HK2 cells. In vitro experiments showed that CCT007093 increased the protein levels of NLRP3, cleaved-Caspase1, GSDMD-N and IL-1β in HK2 cells and further reduced the viability of LPS-stimulated HK2 cells. In vivo experiments showed that inhibition of WIP1 activity with CCT007093 further increased cleaved-Caspase1, GSDMD-N protein levels in kidney tissue from mice with LPS-induced AKI. In addition, LPS induces phosphorylation of p38 MAPK, a key regulator of pyroptosis, which is further activated by CCT007093. In conclusion, inhibition of WIP1 activity acts as a positive regulator of renal tubular pyroptosis mainly through the mediation of phospho-p38 MAPK.

Extracellular Signal-Regulated Kinase Inhibitor SCH772984 Augments the Anti-Cancer Effects of Gemcitabine in Nanoparticle Form in Pancreatic Cancer Models

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a poor response to the limited treatment options currently available. Hence, there is a need to identify new agents that could enhance the efficacy of existing treatments. This study investigated a combination therapy using gemcitabine (GEM) and SCH772984, an extracellular signal-regulated kinase (ERK) inhibitor, in both free form and nanoparticle-encapsulated form for PDAC treatment. Cell viability and Matrigel growth assays were used to determine the anti-proliferative and cytotoxic effects of GEM and SCH772984 on PDAC cells. Additionally, western blotting was used to determine the degree to which SCH772984 engaged ERK in PDAC cells. Lastly, immunohistochemistry and hematoxylin and eosin (H&E) staining were used to determine how GEM and SCH772984 affected expression of Ki-67 cell proliferation marker in PDX (patient derived xenograft) PDAC tissues. PDAC cell lines (MIA PaCa-2 and PANC-1) treated with the combination of free GEM and SCH772984 showed reduction in cell viability compared to cells treated with free GEM or SCH772984 administered as a single agent. Encapsulated forms of GEM and SCH772984 caused a greater reduction in cell viability than the free forms. Interestingly, co-administration of GEM and SCH772984 in separate nanoparticle (NP) systems exhibited the highest reduction in cell viability. Western blotting analysis confirmed ERK signaling was inhibited by both free and encapsulated SCH772984. Importantly, GEM did not interfere with the inhibitory effect of SCH772984 on phosphorylated ERK (pERK). Collectively, our studies suggest that combination therapy with GEM and SCH772984 effectively reduced PDAC cell viability and growth, and co-administration of NP encapsulated GEM and SCH772984 in separate NP systems is an effective treatment strategy for PDAC.

SF3B1 Mutations Are Associated with Resistance to Non-Genotoxic MDM2 Inhibition in Chronic Lymphocytic Leukemia

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.

Splicing Modulation Results in Aberrant Isoforms and Protein Products of p53 Pathway Genes and the Sensitization of B Cells to Non-Genotoxic MDM2 Inhibition

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 TP53^WT cells. It was especially noteworthy that a novel p21^WAF1 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.

Venetoclax Drug Increases the Apoptosis of T and B Acute Lymphoblastic Leukemia Cells by Reducing the Expression of BCL-2

Venetoclax, a specific inhibitor of the BCL2 protein, is administered for the treatment of acute lymphoblastic leukemia. However, despite being utilized in conjunction with chemotherapy, the drug exhibits instances of resistance. The exact mechanisms responsible for this resistance remain relatively obscure. Within the context of this investigation, the study aimed to explore the involvement of anti- and pro-apoptotic proteins as one of the potential mechanisms underlying this resistance phenomenon. Blast cells were extracted from patients diagnosed with B&T acute lymphoid leukemia. Subsequently, these cells were subjected to a cultivation process. Following the cultivation, treatment with the Venetoclax drug was administered to both groups of B&T cells. Additionally, one group from each cell type was designated as a control. The relative expression levels of genes BCL-2, MCL-1, and BIM were assessed in comparison to the control group. Annexin V-fluorescein isothiocyanate and propidium iodide staining was done to check cell apoptosis. The results showed a significant increase in the expression of BIM gene and a significant decrease in BCL-2 gene compared to the control group, but the change in the expression of MCL-1 gene was not significant. Also, an increase in apoptosis was observed in the treatment groups compared to the control. Although it was shown that changes in the expression of pro- and anti-apoptotic genes can lead to an increase in cell apoptosis and a decrease in the number of blast cells, more studies are needed to investigate the simultaneous effect of Venetoclax drug with other drugs and also in the form of a clinical trial.

In vitro and in vivo study of GSK2830371 and RG7388 combination in liver adenocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is an adenocarcinoma arising from the intrahepatic bile duct and accounts for the second highest incidence of primary liver cancers after hepatocellular carcinoma. The lack of effective treatment leads to a poor prognosis for advanced iCCA, so new targeted therapy is needed. The impairment of wild-type (WT) p53 tumor suppressor function by its negative regulators frequently occurs in iCCA. Therefore, restoration of WT p53 function by inhibiting its negative regulators is a therapeutic strategy being explored for cancer treatment. Combining an MDM2 inhibitor (MDM2i, RG7388) to stabilize p53 and a WIP1 inhibitor (WIP1i, GSK2830371) to increase p53 phosphorylation enhances p53 function. The combination of MDM2 and WIP1 inhibitors has been reported in several cancer types but in vivo studies are lacking. In the current study, liver adenocarcinoma cell lines, RBE and SK-Hep-1, were treated with RG7388 alone and in combination with GSK2830371. Cell proliferation, clonogenicity, protein and mRNA expressions, and cell cycle distribution were performed to investigate the effect and mechanism of growth suppression. To evaluate the antitumor efficacy of RG7388 and GSK2830371 in vivo, SK-Hep-1 xenografts in NOD-SCID mice were treated with combination therapy for two weeks. The combination of MDM2i and WIP1i significantly increased the growth inhibition, cytotoxicty, p53 protein expression, and phosphorylation (Ser15), leading to transactivation of downstream targets (p21^WAF1 and MDM2). The in vivo results demonstrated that the combination treatment can significantly inhibit tumor growth. In this study, the liver adenocarcinoma cell lines responded to combination treatment via reactivation of p53 function evidenced by increased p53 expression, phosphorylation and expression of its downstream targets. This efficacy was also demonstrated in vivo. The current research provides a novel strategy for targeting the p53 pathway in liver adenocarcinoma that warrants further investigation.

p53 as a biomarker and potential target in gastrointestinal stromal tumors

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.