Evaluating dose-limiting toxicities of MDM2 inhibitors in patients with solid organ and hematologic malignancies: A systematic review of the literature

A first-in-human phase I study of a novel MDM2/p53 inhibitor alrizomadlin in advanced solid tumors

BACKGROUND

The mouse double minute 2 homolog (MDM2) oncogene exerts oncogenic activities in many cancers and represents a potential therapeutic target. This trial evaluated the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of alrizomadlin (APG-115), a novel MDM2/p53 inhibitor, in patients with advanced solid tumors.

PATIENTS AND METHODS

Patients with histologically confirmed advanced solid tumors who had progressed to standard treatment or lacked effective therapies were recruited. Alrizomadlin was administered once daily every other day for 21 days of a 28-day cycle until disease progression or intolerable toxicity.

RESULTS

A total of 21 patients were enrolled and treated with alrizomadlin; 57.1% were male and the median age was 47 (25-60) years. The maximum tolerated dose of alrizomadlin was 150 mg and the recommended phase II dose was 100 mg. One patient in the 200-mg cohort experienced dose-limiting toxicity of thrombocytopenia and febrile neutropenia. The most common grade 3/4 treatment-related adverse events were thrombocytopenia (33.3%), lymphocytopenia (33.3%), neutropenia (23.8%), and anemia (23.8%). Alrizomadlin demonstrated approximately linear pharmacokinetics (dose range 100-200 mg) and was associated with increased plasma macrophage inhibitory cytokine-1, indicative of p53 pathway activation. Of the 20 assessable patients, 2 [10%, 95% confidence interval (CI) 1.2% to 31.7%] patients achieved partial response and 10 (50%, 95% CI 27.2% to 72.8%) showed stable disease. The median progression-free survival was 6.1 (95% CI 1.7-10.4) months, which was significantly longer in patients with wild-type versus mutant TP53 (7.9 versus 2.2 months, respectively; P < 0.001). Among patients with MDM2 amplification and wild-type TP53, the overall response rate was 25% (2/8) and the disease control rate was 100% (8/8).

CONCLUSIONS

Alrizomadlin had an acceptable safety profile and demonstrated promising antitumor activity in MDM2-amplified and TP53 wild-type tumors. This study supports further exploration of alrizomadlin with recommended doses of 100 mg q.o.d. in 21 days on and 7 days off regimen.

Nanoencapsulation of MDM2 Inhibitor RG7388 and Class-I HDAC Inhibitor Entinostat Enhances their Therapeutic Potential Through Synergistic Antitumor Effects and Reduction of Systemic Toxicity

Inhibitors of the p53-MDM2 interaction such as RG7388 have been developed to exploit latent tumor suppressive properties in p53 in 50% of tumors in which p53 is wild-type. However, these agents for the most part activate cell cycle arrest rather than death, and high doses in patients elicit on-target dose-limiting neutropenia. Recent work from our group indicates that combination of p53-MDM2 inhibitors with the class-I HDAC inhibitor Entinostat (which itself has dose-limiting toxicity issues) has the potential to significantly augment cell death in p53 wild-type colorectal cancer cells. We investigated whether coencapsulation of RG7388 and Entinostat within polymeric nanoparticles (NPs) could overcome efficacy and toxicity limitations of this drug combination. Combinations of RG7388 and Entinostat across a range of different molar ratios resulted in synergistic increases in cell death when delivered in both free drug and nanoencapsulated formats in all colorectal cell lines tested. Importantly, we also explored the in vivo impact of the drug combination on murine blood leukocytes, showing that the leukopenia induced by the free drugs could be significantly mitigated by nanoencapsulation. Taken together, this study demonstrates that formulating these agents within a single nanoparticle delivery platform may provide clinical utility beyond use as nonencapsulated agents.

Proteasome Inhibition Sensitizes Liposarcoma to MDM2 Inhibition with Nutlin-3 by Activating the ATF4/CHOP Stress Response Pathway

Liposarcoma is the most commonly occurring soft-tissue sarcoma and is frequently characterized by amplification of chromosome region 12q13-15 harboring the oncogenes MDM2 and CDK4. This unique genetic profile makes liposarcoma an attractive candidate for targeted therapeutics. While CDK4/6 inhibitors are currently employed for treatment of several cancers, MDM2 inhibitors have yet to attain clinical approval. Here, we report the molecular characterization of the response of liposarcoma to the MDM2 inhibitor nutlin-3. Treatment with nutlin-3 led to upregulation of two nodes of the proteostasis network: the ribosome and the proteasome. CRISPR/Cas9 was used to perform a genome-wide loss of function screen that identified PSMD9, which encodes a proteasome subunit, as a regulator of response to nutlin-3. Accordingly, pharmacologic studies with a panel of proteasome inhibitors revealed strong combinatorial induction of apoptosis with nutlin-3. Mechanistic studies identified activation of the ATF4/CHOP stress response axis as a potential node of interaction between nutlin-3 and the proteasome inhibitor carfilzomib. CRISPR/Cas9 gene editing experiments confirmed that ATF4, CHOP, and the BH3-only protein, NOXA, are all required for nutlin-3 and carfilzomib-induced apoptosis. Furthermore, activation of the unfolded protein response using tunicamycin and thapsigargin was sufficient to activate the ATF4/CHOP stress response axis and sensitize to nutlin-3. Finally, cell line and patient-derived xenograft models demonstrated combinatorial effects of treatment with idasanutlin and carfilzomib on liposarcoma growth in vivo. Together, these data indicate that targeting of the proteasome could improve the efficacy of MDM2 inhibitors in liposarcoma.

SIGNIFICANCE

Targeting the proteasome in combination with MDM2 inhibition activates the ATF4/CHOP stress response axis to induce apoptosis in liposarcoma, providing a potential therapeutic approach for the most common soft-tissue sarcoma.

MDM2 Inhibition in the Treatment of Glioblastoma: From Concept to Clinical Investigation

Inhibition of the interaction between MDM2 and p53 has emerged as a promising strategy for combating cancer, including the treatment of glioblastoma (GBM). Numerous MDM2 inhibitors have been developed and are currently undergoing rigorous testing for their potential in GBM therapy. Encouraging results from studies conducted in cell culture and animal models suggest that MDM2 inhibitors could effectively treat a specific subset of GBM patients with wild-type TP53 or functional p53. Combination therapy with clinically established treatment modalities such as radiation and chemotherapy offers the potential to achieve a more profound therapeutic response. Furthermore, an increasing array of other molecularly targeted therapies are being explored in combination with MDM2 inhibitors to increase the effects of individual treatments. While some MDM2 inhibitors have progressed to early phase clinical trials in GBM, their efficacy, alone and in combination, is yet to be confirmed. In this article, we present an overview of MDM2 inhibitors currently under preclinical and clinical investigation, with a specific focus on the drugs being assessed in ongoing clinical trials for GBM patients.

Targeting USP2 regulation of VPRBP-mediated degradation of p53 and PD-L1 for cancer therapy

Since Mdm2 (Mouse double minute 2) inhibitors show serious toxicity in clinic studies, different approaches to achieve therapeutic reactivation of p53-mediated tumor suppression in cancers need to be explored. Here, we identify the USP2 (ubiquitin specific peptidase 2)-VPRBP (viral protein R binding protein) axis as an important pathway for p53 regulation. Like Mdm2, VPRBP is a potent repressor of p53 but VPRBP stability is controlled by USP2. Interestingly, the USP2-VPRBP axis also regulates PD-L1 (programmed death-ligand 1) expression. Strikingly, the combination of a small-molecule USP2 inhibitor and anti-PD1 monoclonal antibody leads to complete regression of the tumors expressing wild-type p53. In contrast to Mdm2, knockout of Usp2 in mice has no obvious effect in normal tissues. Moreover, no obvious toxicity is observed upon the USP2 inhibitor treatment in vivo as Mdm2-mediated regulation of p53 remains intact. Our study reveals a promising strategy for p53-based therapy by circumventing the toxicity issue.

Cellular Senescence in Hepatocellular Carcinoma: The Passenger or the Driver?

With the high morbidity and mortality, hepatocellular carcinoma (HCC) represents a major yet growing burden for our global community. The relapse-prone nature and drug resistance of HCC are regarded as the consequence of varying intracellular processes and extracellular interplay, which actively participate in tumor microenvironment remodeling. Amongst them, cellular senescence is regarded as a fail-safe program, leading to double-sword effects of both cell growth inhibition and tissue repair promotion. Particularly, cellular senescence serves a pivotal role in the progression of chronic inflammatory liver diseases, ultimately leading to carcinogenesis. Given the current challenges in improving the clinical management and outcome of HCC, senescence may exert striking potential in affecting anti-cancer strategies. In recent years, an increasing number of studies have emerged to investigate senescence-associated hepatocarcinogenesis and its derived therapies. In this review, we intend to provide an up-to-date understanding of liver cell senescence and its impacts on treatment modalities of HCC.

Senescence and the tumor-immune landscape: Implications for cancer immunotherapy

Cancer therapies, including conventional chemotherapy, radiation, and molecularly targeted agents, can lead to tumor eradication through a variety of mechanisms. In addition to their effects on tumor cell growth and survival, these regimens can also influence the surrounding tumor-immune microenvironment in ways that ultimately impact therapy responses. A unique biological outcome of cancer therapy is induction of cellular senescence. Senescence is a damage-induced stress program that leads to both the durable arrest of tumor cells and remodeling the tumor-immune microenvironment through activation of a collection pleiotropic cytokines, chemokines, growth factors, and proteinases known as the senescence-associated secretory phenotype (SASP). Depending on the cancer context and the mechanism of action of the therapy, the SASP produced following therapy-induced senescence (TIS) can promote anti-tumor immunity that enhances therapeutic efficacy, or alternatively chronic inflammation that leads to therapy failure and tumor relapse. Thus, a deeper understanding of the mechanisms regulating the SASP and components necessary for robust anti-tumor immune surveillance in different cancer and therapy contexts are key to harnessing senescence for tumor control. Here we draw a roadmap to modulate TIS and its immune-stimulating features for cancer immunotherapy.

Dedifferentiation in low-grade osteosarcoma: a Japanese Musculoskeletal Oncology Group (JMOG) study

BACKGROUND

Low-grade osteosarcomas, namely parosteal osteosarcoma (POS) and low-grade central osteosarcoma (LGCOS), occasionally dedifferentiate into high-grade malignancy, referred to as dedifferentiation in low-grade osteosarcoma (DLOS). This study aimed to elucidate the clinicopathologic features of DLOS, which are poorly described to date due to the extreme rarity of the disease.

METHODS

A total of 33 patients with DLOS were included. Clinical characteristics, including the diagnostic accuracy of tumor biopsy, multimodal treatments, and clinical course, were retrospectively reviewed. Univariate analysis was performed to identify prognostic factors associated with overall survival (OS) and metastasis-free survival (MFS).

RESULTS

The tumor subtypes comprised 10 cases (30.3%) of LGCOS and 23 cases (69.7%) of POS. The timing of dedifferentiation was synchronous in 25 (75.8%) and metachronous in 8 (24.2%) patients. The rates of preoperative diagnosis of DLOS were 40.0% and 65.4% for core needle biopsy and incisional biopsy, respectively. All patients underwent surgery and 25 patients received perioperative chemotherapy. Of the 13 patients who received neoadjuvant chemotherapy, 11 exhibited a poor histological response. The 5-year OS and MFS rates were 88.1% and 77.7%, respectively. Univariate analysis revealed that local recurrence was associated with poor OS (P < 0.01) and MFS (P < 0.01). Perioperative chemotherapy did not affect OS or MFS.

CONCLUSIONS

The diagnostic accuracy of tumor biopsy for DLOS was lower than that for bone sarcomas, as reported previously. In contrast to conventional osteosarcomas with high chemosensitivity, both histological responses and survival analysis revealed low efficacy of chemotherapy for DLOS.

Milademetan is a highly potent MDM2 inhibitor in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma of the skin with 2 etiologies. Merkel cell polyomavirus (MCPyV) integration is present in about 80% of all MCC. Virus-positive MCC (MCCP) tumors have few somatic mutations and usually express WT p53 (TP53). By contrast, virus-negative MCC (MCCN) tumors present with a high tumor mutational burden and predominantly UV mutational signature. MCCN tumors typically contain mutated TP53. MCCP tumors express 2 viral proteins: MCPyV small T antigen and a truncated form of large T antigen. MCPyV ST specifically activates expression of MDM2, an E3 ubiquitin ligase of p53, to inhibit p53-mediated tumor suppression. In this study, we assessed the efficacy of milademetan, a potent, selective, and orally available MDM2 inhibitor in several MCC models. Milademetan reduced cell viability of WT p53 MCC cell lines and triggered a rapid and sustained p53 response. Milademetan showed a dose-dependent inhibition of tumor growth in MKL-1 xenograft and patient-derived xenograft models. Here, along with preclinical data for the efficacy of milademetan in WT p53 MCC tumors, we report several in vitro and in vivo models useful for future MCC studies.

Comprehensive Analysis of Senescence Characteristics Defines a Novel Prognostic Signature to Guide Personalized Treatment for Clear Cell Renal Cell Carcinoma

Accumulating evidence has suggested the impact of senescence on tumor progression, but no report has yet described how senescence shapes the tumor microenvironment of clear cell renal cell carcinoma (ccRCC). The objective of this study was to delineate the senescence features of ccRCC and its role in shaping the tumor microenvironment through a comprehensive analysis of multiple datasets, including 2,072 ccRCC samples. Unsupervised consensus clustering identified three senescence subtypes, and we found that the senescence-activated subtype survived the worst, even in the condition of targeted therapy and immunotherapy. The activated senescence program was correlated to increased genomic instability, unbalanced PBMR1/BAP1 mutations, elevated immune cell infiltration, and enhanced immune inhibitory factors (cancer-associated fibroblasts, immune suppression, immune exclusion, and immune exhaustion signaling). A senescence score based on nine senescence-related genes (i.e., P3H1, PROX1, HJURP, HK3, CDKN1A, AR, VENTX, MAGOHB, and MAP2K6) was identified by adaptive lasso regression and showed robust prognostic predictive power in development and external validation cohorts. Notably, we found that the senescence score was correlated to immune suppression, and the low-score subgroup was predicted to respond to anti-PD-1 therapy, whereas the high-score subgroup was predicted to respond to Sunitinib/Everolimus treatment. Collectively, senescence acted as an active cancer hallmark of ccRCC, shaped the immune microenvironment, and profoundly affected tumor prognosis and drug treatment response.

Advancing targeted protein degradation for cancer therapy

The human proteome contains approximately 20,000 proteins, and it is estimated that more than 600 of them are functionally important for various types of cancers, including nearly 400 non-enzyme proteins that are challenging to target by traditional occupancy-driven pharmacology. Recent advances in the development of small-molecule degraders, including molecular glues and heterobifunctional degraders such as proteolysis-targeting chimeras (PROTACs), have made it possible to target many proteins that were previously considered undruggable. In particular, PROTACs form a ternary complex with a hijacked E3 ubiquitin ligase and a target protein, leading to polyubiquitination and degradation of the target protein. The broad applicability of this approach is facilitated by the flexibility of individual E3 ligases to recognize different substrates. The vast majority of the approximately 600 human E3 ligases have not been explored, thus presenting enormous opportunities to develop degraders that target oncoproteins with tissue, tumour and subcellular selectivity. In this Review, we first discuss the molecular basis of targeted protein degradation. We then offer a comprehensive account of the most promising degraders in development as cancer therapies to date. Lastly, we provide an overview of opportunities and challenges in this exciting field.

Safety and pharmacokinetics of milademetan, a MDM2 inhibitor, in Japanese patients with solid tumors: A phase I study

Milademetan (DS‐3032, RAIN‐32) is an orally available mouse double minute 2 (MDM2) antagonist with potential antineoplastic activity owing to increase in p53 activity through interruption of the MDM2‐p53 interaction. This phase I, dose‐escalating study assessed the safety, tolerability, efficacy, and pharmacokinetics of milademetan in 18 Japanese patients with solid tumors who relapsed after or were refractory to standard therapy. Patients aged ≥ 20 years received oral milademetan once daily (60 mg, n = 3; 90 mg, n = 11; or 120 mg, n = 4) on days 1 to 21 in a 28‐day cycle. Dose‐limiting toxicities, safety, tolerability, maximum tolerated dose, pharmacokinetics, and recommended dose for phase II were determined. The most frequent treatment‐emergent adverse events included nausea (72.2%), decreased appetite (61.1%), platelet count decreased (61.1%), white blood cell count decreased (50.0%), fatigue (50.0%), and anemia (50.0%). Dose‐limiting toxicities (three events of platelet count decreased and one nausea) were observed in the 120‐mg cohort. The plasma concentrations of milademetan increased in a dose‐dependent manner. Stable disease was observed in seven out of 16 patients (43.8%). Milademetan was well tolerated and showed modest antitumor activity in Japanese patients with solid tumors. The recommended dose for phase II was considered to be 90 mg in the once‐daily 21/28‐day schedule. Future studies would be needed to further evaluate the potential safety, tolerability, and clinical activity of milademetan in patients with solid tumors and lymphomas. The trial was registered with Clinicaltrials.jp: JapicCTI‐142693.