Murine Double Minute 2 Overexpression Research Articles

Ubiquitin ligase MDM2 mediates endothelial inflammation in Kawasaki disease vasculitis development.

Kawasaki disease (KD) often complicates coronary artery lesions (CALs). Despite the established significance of STAT3 signaling during the acute phase of KD and signal transducer and activator of transcription 3 (STAT3) signaling being closely related to CALs, it remains unknown whether and how STAT3 was regulated by ubiquitination during KD pathogenesis. Bioinformatics and immunoprecipitation assays were conducted, and an E3 ligase, murine double minute 2 (MDM2) was identified as the ubiquitin ligase of STAT3. The blood samples from KD patients before and after intravenous immunoglobulin (IVIG) treatment were utilized to analyze the expression level of MDM2. Human coronary artery endothelial cells (HCAECs) and a mouse model were used to study the mechanisms of MDM2-STAT3 signaling during KD pathogenesis. The MDM2 expression level decreased while the STAT3 level and vascular endothelial growth factor A (VEGFA) level increased in KD patients with CALs and the KD mouse model. Mechanistically, MDM2 colocalized with STAT3 in HCAECs and the coronary vessels of the KD mouse model. Knocking down MDM2 caused an increased level of STAT3 protein in HCAECs, whereas MDM2 overexpression upregulated the ubiquitination level of STAT3 protein, hence leading to significantly decreased turnover of STAT3 and VEGFA. MDM2 functions as a negative regulator of STAT3 signaling by promoting its ubiquitination during KD pathogenesis, thus providing a potential intervention target for KD therapy.

Xinnaotongluo liquid protects H9c2 cells from H/R-induced damage by regulating MDM2/STEAP3.

Xinnaotongluo liquid has been used to improve the clinical symptoms of patients with myocardial infarction. However, the molecular mechanism of Xinnaotongluo liquid is not completely understood. H9c2 cells exposed to hypoxia/reoxygenation (H/R) was used to simulate damage to cardiomyocytes in myocardial infarction in vitro. The biological indicators of H9c2 cells were measured by cell counting kit-8, enzyme linked immunoabsorbent assay, and western blot assay. In H/R-induced H9c2 cells, a markedly reduced murine double minute 2 (MDM2) was observed. However, the addition of Xinnaotongluo liquid increased MDM2 expression in H/R-induced H9c2 cells. And MDM2 overexpression strengthened the beneficial effects of Xinnaotongluo liquid on H9c2 cells from the perspective of alleviating oxidative damage, cellular inflammation, apoptosis and ferroptosis of H/R-induced H9c2 cells. Moreover, MDM2 overexpression reduced the protein expression of p53 and Six-Transmembrane Epithelial Antigen of Prostate 3 (STEAP3). Whereas, STEAP3 overexpression hindered the function of MDM2-overexpression in H/R-induced H9c2 cells. Our results insinuated that Xinnaotongluo liquid could protect H9c2 cells from H/R-induced damage by regulating MDM2/STEAP3, which provide a potential theoretical basis for further explaining the working mechanism of Xinnaotongluo liquid.

Abstract P6-10-10: Genetic alterations in breast cancer associated with MDM2 dependency and sensitivity to the MDM2 inhibitor milademetan

Abstract Background: Murine double minute 2 (MDM2), a potent negative regulator of p53, promotes tumorigenesis if dysregulated. MDM2 dysregulation occurs via different mechanisms, including MDM2 gene amplification, MDM2 overexpression, and loss of cyclin-dependent kinase inhibitor 2A (CDKN2A), which encodes the MDM2 regulator p14ARF. Combined inactivation of MDM2 and GATA3 in hormone receptor-positive (HR+) breast cancer is lethal to the cell. Pharmacologic inhibition of MDM2 is a rational therapeutic strategy for MDM2-dependent, TP53 wildtype (WT) tumors, including tumors with MDM2 amplification or CDKN2A loss, and GATA3-mutant HR+ breast cancers. We determined the frequency and associated characteristics of genetic alterations of MDM2-dependent breast cancers, and evaluated sensitivity of these tumors to the small-molecule MDM2 inhibitor milademetan (RAIN-32). Methods: Genomic data were obtained from three datasets: METABRIC; TCGA PanCancer Atlas, GDC v23.0 (April 2020); AACR Genie, v11. Among TP53 WT breast cancer samples from each dataset, the frequency of GATA3 frameshift mutations, MDM2 amplification (copy number [CN] ≥12), and CDKN2A homozygous loss was determined individually and as co-alterations. The antitumoral activity of milademetan was evaluated in a GATA3-mutant, TP53 WT HR+ breast cancer cell line (MCF7 GATA3 G336fs*17), a breast xenograft model (MCF7 GATA3 G335fs), and ex vivo in MDM2-amplified patient-derived breast cancer organoids (CTG-2810, ER+/PR+/HER2–, MDM2 CN 8). Results: Genetic alteration frequencies in TP53 WT breast cancers by dataset are shown in the Table. GATA3 frameshift mutations (7.3–11.7%), MDM2 amplification (0.3–1.1%), and CDKN2A loss (0.2–1.2%) occurred across breast tumors, but were found with highest frequencies in HR+ tumors. Co-alteration frequencies in TP53 WT breast cancers across the aforementioned datasets were < 1%: GATA3 mutations/MDM2 CN ≥12 (0.2–0.3%); GATA3 mutations/CDKN2A loss (0.1–0.2%); MDM2 CN ≥12/CDKN2A loss (0%). Mean MDM2 expression (log2 (TPM+1)) in HR+ breast cancers (TCGA) were: GATA3 mutations, 5.12; CDKN2A loss, 5.88; MDM2 CN ≥12, 8.13, TP53 WT without these alterations, 4.78; mutant TP53, 4.35. A GATA3-mutant ER+ breast cancer cell line was sensitive to milademetan in vitro (IC50 126 nM). Milademetan 100 mg/kg displayed antitumor activity in GATA3-mutant HR+ breast xenograft and PDX models (p< 0.05 vs. vehicle). Milademetan also displayed activity in MDM2-amplified HR+ breast cancer organoids (IC50 0.2 μM). In a phase I study (NCT01877382), a patient with heavily pretreated MDM2-amplified breast cancer (MDM2 CN 16.8) had tumor shrinkage (18.2%) and PFS of 7.3 months with milademetan (orally 260 mg 3/14 days). Conclusions: The frequency of genetic alterations potentially targetable by MDM2 inhibition among TP53 WT breast cancers (i.e., GATA3 mutations, MDM2 amplification, and CDKN2A loss) is greatest in the HR+ subset, and these genetic biomarkers are associated with higher MDM2 expression. Preclinical data show that the MDM2 inhibitor milademetan has antitumor activity in GATA3-mutant and MDM2-amplified HR+ breast cancers, and support the clinical evaluation of milademetan in these tumors. Two clinical trials of milademetan – MANTRA-2 (Phase 2 basket study in solid tumors with TP53 WT and MDM2 CN ≥12; NCT05012397) and MANTRA-4 (Phase 1 study of milademetan + atezolizumab in solid tumors with CDKN2A loss) – are enrolling patients or in planning. Table. Citation Format: Francois-Clement Bidard, Diana Bello Roufai, Arielle J. Medford, Vijaya Tirunagaru, Robert C. Doebele, Aditya Bardia. Genetic alterations in breast cancer associated with MDM2 dependency and sensitivity to the MDM2 inhibitor milademetan [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-10-10.

CircMCTP2 (has-circ-0000658) facilitates the proliferation and metastasis of bladder carcinoma through modulating the miR-498/murine double minute-2 axis

ABSTRACT CircMCTP2 is a novel circRNA, which is associated with various kinds of malignant tumors progression, such as gastric cancer. However, the function of circMCTP2 in bladder carcinoma (BC) has no idea. The purpose of this study was tantamount to functionally dissect circMCTP2 in the progression of BC. In our study, circMCTP2 expression was strongly increased in BC tissues and cell lines. High expression of circMCTP2 predicted a poor prognosis of BC patients. CircMCTP2 deficiency impaired the cell growth, migration as well as invasive ability of BC cell lines (J82 and T24). In vivo, circMCTP2 deficiency cut the tumor growth rates and the tumor weight. In BC cells, circMCTP2 deficiency enhanced the translation of E-cadherin, while diminishing the translation of N-cadherin, Vimentin, and Snail. Moreover, circMCTP2 acted as a sponge of miR-498 to regulate murine double minute-2 (MDM2) expression. In BC tissues, a negative correlation was observed between the expression levels of circMCTP2 and miR-498. Additionally, either miR-498 silencing or MDM2 over-expression augmented the carcinogenic action of circMCTP2 on BC. In conclusion, our study showed that circMCTP2 regulates the expression of MDM2 by sponging miR-498 to promote the development of BC. These findings offer a new strategy for early diagnosis of BC and its therapeutics.

Interruption of MDM2 signaling augments MDM2-targeted T cell-based antitumor immunotherapy through antigen-presenting machinery.

Identification of immunogenic tumor antigens, their corresponding T cell epitopes and the selection of effective adjuvants are prerequisites for developing effective cancer immunotherapies such as therapeutic vaccines. Murine double minute 2 (MDM2) is an E3 ubiquitin-protein ligase that negatively regulates tumor suppressor p53. Because MDM2 overexpression serves as a poor prognosis factor in various types of tumors, it would be beneficial to develop MDM2-targeted cancer vaccines. In this report, we identified an MDM2-derived peptide epitope (MDM232-46) that elicited antigen-specific and tumor-reactive CD4+ T cell responses. These CD4+ T cells directly killed tumor cells via granzyme B. MDM2 is expressed in head and neck cancer patients with poor prognosis, and the T cells that recognize this MDM2 peptide were present in these patients. Notably, Nutlin-3 (MDM2-p53 blocker), inhibited tumor cell proliferation, was shown to augment antitumor T cell responses by increasing MDM2 expression, HLA-class I and HLA-DR through class II transactivator (CIITA). These results suggest that the use of this MDM2 peptide as a therapeutic vaccine combined with MDM2 inhibitors could represent an effective immunologic strategy to treat cancer.

An Open-Label, Global, Multicenter, Phase 1b/2 Study of KRT-232, a First-in-Class, Oral Small-Molecule Inhibitor of Murine Double Minute 2 (MDM2), Combined with Ruxolitinib in Patients Who Have Myelofibrosis and a Suboptimal Response to Ruxolitinib

An Open-Label, Global, Multicenter, Phase 1b/2 Study of KRT-232, a First-in-Class, Oral Small-Molecule Inhibitor of Murine Double Minute 2 (MDM2), Combined with Ruxolitinib in Patients Who Have Myelofibrosis and a Suboptimal Response to Ruxolitinib

A Phase 1 Dose Escalation Study of Milademetan in Combination with 5-Azacitidine (AZA) in Patients with Acute Myeloid Leukemia (AML) or High-Risk Myelodysplastic Syndrome (MDS)

A Phase 1 Dose Escalation Study of Milademetan in Combination with 5-Azacitidine (AZA) in Patients with Acute Myeloid Leukemia (AML) or High-Risk Myelodysplastic Syndrome (MDS)

P53/MDM2 Co-Expression in Laryngeal Squamous Cell Carcinoma Based on Digital Image Analysis.

P53 is a key regulator of genomic stability and function, acting as a tumor suppressor protein. Our aim was to correlate P53 expression with murine double minute 2 (MDM2), a proto-oncogene that interacts with P53 and forms an auto-regulatory pathway, in laryngeal squamous cell carcinoma (LSCC). A total of 50 LSCC cases were included in the study. Immunohistochemistry was applied by using antibodies to P53 and MDM2 in the corresponding tissue sections. Protein expression levels for both molecules were measured by implementing a digital image analysis assay (immunostaining intensity levels, densitometric evaluation). Overexpression of P53 protein was observed in 16/50 (32%) LSCC cases, while 22/50 (44%) cases strongly expressed MDM2 protein. Interestingly, in 13/50 (26%) cases, combined overexpression of P53/MDM2 was detected. Overall P53 was strongly positively correlated with MDM2 expression (p=0.001). Both P53 and MDM2 overexpression were significantly correlated with advanced stage of LSCC (p=0.032 and p=0.001, respectively). Additionally, MDM2 was found to be associated with poorer survival of patients (p=0.046). Aberrant co-expression of P53 and MDM2 is associated with advanced stage in LSCC. Furthermore, MDM2 overexpression is a frequent and critical genetic event in LSCC and seems to negatively affect survival.

CP‑31398 attenuates endometrial cancer cell invasion, metastasis and resistance to apoptosis by downregulating MDM2 expression.

Endometrial cancer (EC) is one of the most common malignancies of the female reproductive system, and metastasis is a major cause of mortality. In this study, we aimed to explore the role of CP-31398 in the migration, invasion and apoptosis of EC cells by its regulation of the expression of the murine double minute 2 (MDM2) gene. For this purpose, EC tissues and adjacent normal tissues were collected, and the positive expression rate of MDM2 in these tissues was assessed. Subsequently, the cellular 50% inhibitory concentration (IC50) of CP-31398 was measured. The EC RL95-2 and KLE cell lines had a higher MDM2 expression and were thus selected for use in subsequent experiments. The EC cells were then treated with CP-31398 (2 µg/ml), and were transfected with siRNA against MDM2 or an MDM2 overexpression plasmid in order to examine the effects of CP-31398 and MDM2 on EC cell activities. The expression of p53, p21, Bad, Bax, B-cell lymphoma-2 (Bcl-2), cytochrome c (Cyt-c), caspase-3, Cox-2, matrix metalloproteinase (MMP)-2 and MMP-9 was measured to further confirm the effects of CP-31398 on cell migration, invasion and apoptosis. Our results indicated that MDM2 was highly expressed in EC tissues. Notably, EC cell viability decreased with the increasing concentrations of CP-31398. The EC cells treated with CP-31398 or siRNA against MDM2 exhibited an increased apoptosis and a suppressed migration and invasion, corresponding to an increased expression of p53, p21, Bad, Bax, Cyt-c and caspase-3, as well as to a decreased expression of Bcl-2, Cox-2, MMP-2 and MMP-9. Moreover, treatment with CP-31398 and siRNA against MDM2 further enhanced these effects. Taken together, the findings of this study indicate that the CP-31398-mediated downregulation of MDM2 may suppress EC progression via its inhibitory role in EC cell migration, invasion and resistance to apoptosis. Therefore, treatment with CP-31398 may prove to be possible therapeutic strategy for EC.

MDM2 Overexpression Modulates the Angiogenesis-Related Gene Expression Profile of Prostate Cancer Cells.

The Murine Double Minute 2 (MDM2) amplification or overexpression has been found in many tumors with high metastatic and angiogenic ability. Our experiments were designed to explore the impact of MDM2 overexpression, specifically on the levels of angiogenesis-related genes, which can also play a major role in tumor propagation and increase its metastatic potential. In the present study, we have used the human angiogenesis RT2 profiler PCR array to compare the gene expression profile between LNCaP and LNCaP-MST (MDM2 transfected) prostate cancer cells, along with LNCaP-MST cells treated with Nutlin-3, an MDM2 specific inhibitor. As a result of the overexpression of MDM2 gene in LNCaP-MST (10.3-fold), Thrombospondin 1 (THBS1), Tumor necrosis factor alpha (TNF-α) and Matrix metallopeptidase 9 (MMP9) were also found to be significantly up-regulated while genes such as Epiregulin (EREG), Tissue inhibitor of metalloproteinases 1 (TIMP1) were down-regulated. Also, we determined the total MMP activity and MMP9 expression in LNCaP, LNCaP-MST and SJSA-1 cells. Our results indicated that MDM2 level is positively correlated with MMP activity and MMP9 secretion. Our findings offer strong supporting evidence that MDM2 can impact growth and metastatic potential of cancer cells through tilting the balance towards pro-angiogenic mechanisms.

MDM2 is implicated in high-glucose-induced podocyte mitotic catastrophe via Notch1 signalling.

Podocyte injury and depletion are essential events involved in the pathogenesis of diabetic nephropathy (DN). As a terminally differentiated cell, podocyte is restricted in ‘post‐mitosis’ state and unable to regenerate. Re‐entering mitotic phase will cause podocyte disastrous death which is defined as mitotic catastrophe (MC). Murine double minute 2 (MDM2), a cell cycle regulator, is widely expressed in renal resident cells including podocytes. Here, we explore whether MDM2 is involved in podocyte MC during hyperglycaemia. We found aberrant mitotic podocytes with multi‐nucleation in DN patients. In vitro, cultured podocytes treated by high glucose (HG) also showed an up‐regulation of mitotic markers and abnormal mitotic status, accompanied by elevated expression of MDM2. HG exposure forced podocytes to enter into S phase and bypass G2/M checkpoint with enhanced expression of Ki67, cyclin B1, Aurora B and p‐H3. Genetic deletion of MDM2 partly reversed HG‐induced mitotic phase re‐entering of podocytes. Moreover, HG‐induced podocyte injury was alleviated by MDM2 knocking down but not by nutlin‐3a, an inhibitor of MDM2‐p53 interaction. Interestingly, knocking down MDM2 or MDM2 overexpression showed inhibition or activation of Notch1 signalling, respectively. In addition, genetic silencing of Notch1 prevented HG‐mediated podocyte MC. In conclusion, high glucose up‐regulates MDM2 expression and leads to podocyte MC. Notch1 signalling is an essential downstream pathway of MDM2 in mediating HG‐induced MC in podocytes.

Synergistic targeting of malignant pleural mesothelioma cells by MDM2 inhibitors and TRAIL agonists.

Malignant Pleural Mesothelioma (MPM) is a chemoresistant tumor characterized by low rate of p53 mutation and upregulation of Murine Double Minute 2 (MDM2), suggesting that it may be effectively targeted using MDM2 inhibitors. In the present study, we investigated the anticancer activity of the MDM2 inhibitors Nutlin 3a (in vitro) and RG7112 (in vivo), as single agents or in combination with rhTRAIL.In vitro studies were performed using MPM cell lines derived from epithelioid (ZL55, M14K), biphasic (MSTO211H) and sarcomatoid (ZL34) MPMs. In vivo studies were conducted on a sarcomatoid MPM mouse model.In all the cell lines tested (with the exception of ZL55, which carries a biallelic loss-of-function mutation of p53), Nutlin 3a enhanced p21, MDM2 and DR5 expression, and decreased survivin expression. These changes were associated to cell cycle arrest but not to a significant induction of apoptosis. A synergistic pro-apoptotic effect was obtained through the association of rhTRAIL in all the cell lines harboring functional p53. This synergistic interaction of MDM2 inhibitor and TRAIL agonist was confirmed using a mouse preclinical model. Our results suggest that the combined targeting of MDM2 and TRAIL might provide a novel therapeutic option for treatment of MPM patients, particularly in the case of sarcomatoid MPM with MDM2 overexpression and functional inactivation of wild-type p53.

Molecular Markers of Fibro-Osseous Lesions and Osteosarcomas of the Craniofacial Complex—Current Situation and Recent Advances

Fibro-osseous lesions share clinical, radiological, and pathological features, particularly in the craniofacial complex, a location where diagnosing these lesions is challenging. Some molecular markers involved in the pathogenesis of these lesions offer significant diagnostic support. Guanine nucleotide-binding protein/alpha subunit (GNAS) mutations are specific to fibrous dysplasias and are not encountered in ossifying fibromas (including juvenile variants), or in low-grade and high-grade osteosarcomas of the jaw. Low-grade and dedifferentiated osteosarcomas show murine double-minute 2 (MDM2) amplification, with overexpression of MDM2, abnormalities not encountered in fibrous dysplasia, or in ossifying fibroma. No recurrent cytogenetic or molecular abnormality has been reported to date in conventional ossifying fibromas. The juvenile variants of ossifying fibroma exhibit MDM2/RAS protein activator like-1 (RASAL1) co-amplification, without MDM2 overexpression, abnormalities also observed in certain aggressive osteosarcomas of the jaw, which may derive from juvenile ossifying fibroma. MDM2/RASAL1 co-amplification may constitute an early molecular marker of aggressive juvenile ossifying fibroma and may indicate a need for closer follow-up and more radical treatment.

MDM2 gene amplification in esophageal carcinoma.

Esophageal cancer (EC) is one of the most common malignancies diagnosed in the Western world with an increasing incidence noted for esophageal adenocarcinoma (EAC). Despite improvements in staging, surgical procedures and postoperative treatments, the overall survival of patients with EC remains low. Murine double minute‑2 (MDM2) acts as an oncogene by inducing the degradation of the tumor‑suppressor protein TP53. In order to evaluate the MDM2 gene amplification status in EAC and squamous cell carcinoma (SCC), we established a quantitative PCR (qPCR) assay, screening a total of 127 esophageal carcinoma cases for MDM2 amplification. Esophageal carcinoma cases with enhanced MDM2 gene copy numbers were further analyzed by fluorescence in situ hybridisation (FISH) and MDM2 immunostaining. Among a total of 23 specimens (18%), identified by qPCR to possess elevated MDM2 gene copy numbers, one third (6.3%) showed a cluster‑like fluorescence pattern by FISH analyses and marked MDM2 protein immunostaining. MDM2 gene amplifications did not correlate with the occurrence of TP53 mutations. Due to the high therapeutic relevance of MDM2 overexpression, but the high cost of FISH, we suggest a primary screening of MDM2 copy number variations by qPCR, followed by detailed FISH analysis of the identified ECs.

The E3 ubiquitin protein ligase MDM2 dictates all-trans retinoic acid-induced osteoblastic differentiation of osteosarcoma cells by modulating the degradation of RARα

Retinoic acid receptor alpha (RARα) has a critical role in the differentiation process of osteosarcoma cells induced by all-trans retinoic acid (ATRA). However, degradation of RARα through ubiquitin proteasome pathway weakens the differentiation efficiency of osteosarcoma cells. In this study, we discover that murine double minute-2 (MDM2) acts as an E3 ubiquitin ligase to target RARα for degradation. We observe that MDM2 is required for RARα polyubiquitination and proteasomal degradation because downregulation of MDM2 by short hairpin RNA results in the accumulation of RARα, and MDM2 overexpression promotes the degradation of RARα. We also demonstrate that the N-terminal domain of MDM2 (amino acids 1-109) is the major RARα-binding site. Importantly, endogenous MDM2 levels are not only upregulated in human primary osteosarcoma blasts but are also inversely correlated with the level of osteopontin, which is a marker of bone differentiation. Moreover, MDM2 impairs the ATRA-induced osteoblastic differentiation of osteosarcoma cells, whereas an inhibitor of the MDM2 ubiquitin ligase synergizes with ATRA to enhance the differentiation of osteosarcoma cells and primary osteosarcoma blasts. Therefore, our study indicates that MDM2 serves as an E3 ubiquitin ligase to regulate the degradation of RARα and suggests that MDM2 is a novel therapeutic target for ATRA-based differentiation therapeutic approaches in osteosarcoma.

Abstract B155: The E3 ubiquitin protein ligase MDM2 dictates all-trans retinoic acid induced osteoblastic differentiation of osteosarcoma cells by modulating the degradation of RARα

Abstract Retinoic acid receptor alpha (RARα) plays a critical role in the differentiation process of osteosarcoma cells induced by all-trans retinoic acid (ATRA). However, degradation of RARα through ubiquitin proteasome pathway weakens the differentiation efficiency of osteosarcoma cells. In this study, we discover that murine double minute-2 (MDM2) acts as an E3 ubiquitin ligase to target RARα for degradation. We observe that MDM2 is required for RARα polyubiquitination and proteasomal degradation because downregulation of MDM2 by shRNA results in the accumulation of RARα, and MDM2 overexpression promotes the degradation of RARα. We also demonstrate that the N-terminal domain of MDM2 (amino acids 1-109) is the major RARα-binding site. Importantly, endogenous MDM2 levels are not only upregulated in human primary osteosarcoma blasts, but they are also inversely correlated with the level of OPN, which is a marker of bone differentiation. Moreover, MDM2 impairs the ATRA-induced osteoblastic differentiation of osteosarcoma cells, whereas an inhibitor of the MDM2 ubiquitin ligase synergises with ATRA to enhance the differentiation of osteosarcoma cells and primary osteosarcoma blasts. Therefore, our study indicates that MDM2 serves as an E3 ubiquitin ligase to regulate the degradation of RARα and suggests that MDM2 is a novel therapeutic target for ATRA-based differentiation therapeutic approaches in osteosarcoma. Citation Format: Meidan Ying, Qian Zhou, Xuejing Shao, Ji Cao, Hong Zhu, Bo Yang, Qiaojun He. The E3 ubiquitin protein ligase MDM2 dictates all-trans retinoic acid induced osteoblastic differentiation of osteosarcoma cells by modulating the degradation of RARα. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B155.

Abstract 80: Analysis of the regulation of angiogenesis pathway by inhibiting MDM2 function in LNCaP-MST prostate cancer cells using PCR array

Abstract Interfering with angiogenesis is a well-known strategy for cancer treatment due the fact that this process is essential for promoting cancer growth and metastatic spread by providing adequate supply of oxygen and nutrients to the tumor cells. The process of angiogenesis is highly regulated by both activator and inhibitor genes through their corresponding proteins. One of the suspected promoters of angiogenesis is MDM2 (Murine Double Minute 2 gene). The overexpression of MDM2 has been found in many cancer types and also correlated well with poor prognosis of certain cancers. In addition to some of the newly emerging mechanistic abilities, MDM2 is well known to regulate p53 levels and its functions by dual mechanisms, which plays a major role in many cellular processes such as cell cycle control and apoptosis. However, the role for MDM2 in regulating angiogenesis is slowly evolving which can explain the potential metastatic status of the cancer where there is no p53 mutation. In this connection, to further understand its role in tumor angiogenesis, the status of MMP9 (Matrix metallopeptidase 9 also called gelatinase B), THSB1 (Thrombospondin 1), TGB1 (Transforming growth factor-beta 1) were studied, by inhibiting MDM2. The ultimate goal of our study was to determine how the angiogenesis pathway is regulated by the overexpression of MDM2. To explore the possible mechanisms, LNCaP (prostate cancer cells), and LNCaP-MST (MDM2 transfected prostate cancer cells) cells were treated with Nutlin-3 (20 uM for 24 hours). Indeed LNCaP-MST cells are known to show 10 times higher expression of MDM2 compared to LNCaP cells. Therefore, Nutlin-3 treatment was expected to inhibit the interaction between p53 and MDM2 in these cells and thereby impact the expression of angiogenesis pathway related genes. When we analyzed the gene expression profile using a PCR array that was designed to explore the above mentioned pathway we were able to confirm that MDM2 overexpression could positively regulate MMP9, THSB1, and TGB1 levels in a highly significant manner. Interestingly, the genes expression profile that was found to be elevated in LNCaP-MST cells was reversed after Nutlin-3 treatment confirming that some of these angiogenesis related genes are positively regulated by MDM2 overexpression. In Conclusion, we are proposing that targeting MDM2 can effectively control the pro-angiogenesis mechanisms that can be found activated in MDM2 positive cancer types. We are conducting further studies to fully unravel the role of MDM2 in promoting tumor angiogenesis and metastatic ability (The financial support from the Royal Dames of Cancer Research Inc., Ft. Lauderdale is gratefully acknowledged). Citation Format: Ali Alaseem, Thiagarajan Venkatesan, Khalid Alhazzani, Appu Rathinavelu. Analysis of the regulation of angiogenesis pathway by inhibiting MDM2 function in LNCaP-MST prostate cancer cells using PCR array. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 80. doi:10.1158/1538-7445.AM2015-80

Triptolide induces apoptosis of gastric cancer cells via inhibiting the overexpression of MDM2.

Triptolide has been reported to exhibit antitumor effects in several cancers. This study investigates the mechanism by which triptolide induces apoptosis of gastric cancer cells. Gastric biopsies were collected for histological evaluation and detection of murine double minute 2 (MDM2) expression. Gastric cancer cells were cultured and treated with different concentrations of triptolide at indicated time points. The expression of MDM2, p53 protein, and target proteins including p21, PUMA, and X-linked inhibitor of apoptosis protein (XIAP) was detected. Apoptosis of cells treated with or without triptolide was evaluated. Our results showed that MDM2 protein was overexpressed in gastric cancer (p < 0.01, resp.). Triptolide induced significant apoptosis of gastric cancer cells in a dose- and time-dependent manner (p < 0.05). In addition, treatment with triptolide strongly inhibited the overexpression of MDM2 in gastric cancer cells, and this MDM2 inhibition led to increased levels of p53 protein and inhibition of XIAP (p < 0.05). However, triptolide failed to increase the expression of p53 target protein p21 and PUMA (p > 0.05). In conclusion, triptolide may induce apoptosis of gastric cancer cells via the inhibition of MDM2 overexpression in a p53-independent manner.

Abstract 2603: Specific growth suppression of wild-type p53 tumor cells by DNA-modified siRNA sequences targeting MDM2

Abstract Background: Murine double minute 2 (MDM2) is an oncoprotein that inactivates p53 tumor suppressor protein by ubiquitination and subsequent proteasomal degradation. MDM2 is overexpressed in 10%-20% of human cancers, most of which carry wild-type (wt) p53. Synthetic siRNAs silence gene expression by RNA interference. However, siRNAs also suppress the expression of unintended targets containing complementary sequences to as short as 6 bases of the seed region of siRNA (off-target effects). Such nonspecific effects can be avoided by nucleotide modifications, including DNA replacement in the seed region. Aim: We conducted this study to select canonical and DNA-modified siRNAs possessing high silencing activity for MDM2 with less nonspecific effects. In addition, we examined the validity of the MDM2-p53 interaction as a target for RNAi cancer therapy. Methods: Twenty-four siRNA sequences targeting MDM2 were newly selected using the siDifect software. In total, 33 siRNAs, including 9 previously reported sequences, were chemically synthesized. Effective siRNAs were converted to double-stranded RNA-DNA chimera (dsRDC), which had a DNA replacement in the 5′ region of the guide strand (nucleotide 1-6 from the 5′ end) and its complementary sequence of the passenger strand, including the adjacent 2-b overhang. Three cell lines, SJSA-1 osteosarcoma (high MDM2 expression, wt p53), NUGC3 gastric cancer (mutant p53), and Kato-III gastric cancer (mutant p53), were used. MDM2 protein and mRNA levels were examined using Western blotting and real-time RT-PCR, respectively. Cell viability was measured using WST-8 assay. siRNA and dsRDC were transfected using Lipofectamine RNAiMAX (Invitrogen) according to the manufacturer's instructions. Results: Among the 33 siRNAs examined, 7 siRNAs (2 previously reported and 5 newly designed) at 1 nM suppressed MDM2 mRNA expression and cell viability of SJSA-1 cells by 72%-86% and 51%-75%, respectively. These effective siRNAs were converted to dsRDC-modified form. Two of them demonstrated MDM2 knockdown and growth suppression of wt p53 tumor cells as efficiently as the unmodified forms. Further, in comparison with the unmodified forms, the modified forms showed less nonspecific growth suppression of cells carrying mutant p53. These 2 dsRDC-modified siRNAs were both newly selected sequences. Conclusions: Our 2 newly selected dsRDC-modified siRNAs had high knockdown activity and less nonspecific cytotoxicity. Thus, they represent potent therapeutic agents against cancers carrying wt p53 with MDM2 overexpression. Citation Format: Mitsuaki Hirose, Kenji Yamato, Rie Saito, Takunori Ueno, Sachiko Hirai, Hideo Suzuki, Shinji Endo, Ichinosuke Hyodo. Specific growth suppression of wild-type p53 tumor cells by DNA-modified siRNA sequences targeting MDM2. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2603. doi:10.1158/1538-7445.AM2014-2603

Murine double minute-2 expression in B-cell chronic lymphocytic leukemia: correlation with apoptosis and disease outcome

Introduction B-cell chronic lymphocytic leukemia (B-CLL) is characterized by accumulation of quiescent monoclonal CD5+ B cells, which arise from undefined defects in apoptotic cell death. murine double minute-2 (MDM2) oncoprotein exists in an autoregulatory feedback loop with the tumor suppressor protein p53 and block p53-mediated transactivation and apoptosis. Aim of this work The aim of the study was to evaluate the overexpression of MDM2 in B-CLL patients and correlate it with apoptosis using annexin-V expression and disease outcome. Patients and methods This study was conducted on 55 patients including 45 patients with typical B-CLL; their ages ranged from 55 to 72 years, with a mean age of 58.55 ± 3.9 years. Ten age-matched and sex-matched apparently healthy individuals were included as the control group. The diagnosis of B-CLL was based on clinical, hematological, immunophenotypic, and cytogenetic criteria. Annexin-V and MDM2 oncoprotein expression was assessed by flow cytometric analysis. Results Our study revealed that MDM2 was overexpressed in 53% of B-CLL cases and it was significantly elevated in comparison with the control group (P < 0.001). There was an inverse correlation between MDM2 overexpression and apoptosis (P < 0.001). The mean level of MDM2 expression was significantly reduced after therapy compared with the pretreatment level in the responder group (P < 0.001), whereas there was no significant difference (P>0.05) in the nonresponder group. The expression of MDM2 significantly correlated with the percentage of CD38 expression, LDH level, and B2M level (P < 0.001, P < 0.001, and P < 0.001, respectively) and patients who had responded to treatment showed a significant increase in the level of annexin-V (P < 0.001). MDM2 expression, percentage of CD38 expression, and LDH and B2M levels were significantly higher in the high-risk patients compared with low-risk and intermediate-risk patients (P < 0.001, P < 0.01, P < 0.05, and P < 0.001, respectively).Conclusion MDM2 expression was inversely correlated with apoptosis, with decreased MDM2 expression in responder patients.