CDK4/6-MEK Inhibition in MPNSTs Causes Plasma Cell Infiltration, Sensitization to PD-L1 Blockade, and Tumor Regression

Triple Combination of MEK, BET, and CDK Inhibitors Significantly Reduces Human Malignant Peripheral Nerve Sheath Tumors in Mouse Models

PURPOSE

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive soft-tissue sarcoma that develops sporadically or in patients with neurofibromatosis type 1 (NF1). Its development is marked by the inactivation of specific tumor suppressor genes (TSG): NF1, CDKN2A, and SUZ12/EED (polycomb repressor complex 2). Each TSG loss can be targeted by particular drug inhibitors, and we aimed to systematically combine these inhibitors, guided by TSG inactivation status, to test their precision medicine potential for MPNSTs.

EXPERIMENTAL DESIGN

We performed a high-throughput screening in 3 MPNST cell lines testing 14 MEK inhibitors (MEKi), 11 cyclin-dependent kinase 4/6 inhibitors (CDKi), and 3 bromodomain inhibitors (BETi) as single agents and 147 pairwise co-treatments. Best combinations were validated in nine MPNST cell lines, and three were tested in one sporadic and one NF1-associated patient-derived orthotopic xenograft (PDOX) MPNST mouse model. A final combination of the three inhibitor classes was tested in the same PDOX models.

RESULTS

A high degree of redundancy was observed in the effect of compounds of the same inhibitory class, individually or in combination, and responses matched with TSG inactivation status. The MEKi-BETi (ARRY-162 + I-BET151) co-treatment triggered a reduction in half of the NF1-related MPNST PDOXs and all the sporadic tumors, reaching 65% reduction in tumor volume in the latter. Remarkably, this reduction was further increased in both models combining the three inhibitor classes, reaching 85% shrinkage on average in the sporadic MPNST.

CONCLUSIONS

Our results strongly support precision therapies for MPNSTs guided by TSG inactivation status. MEKi-BETi CDKi triple treatment elicits a significant reduction of human MPNST PDOXs.

A Sequencing Overview of Malignant Peripheral Nerve Sheath Tumors: Findings and Implications for Treatment

Malignant peripheral nerve sheath tumors (MPNSTs) are rare but aggressive malignancies with a low 5-year survival rate despite current treatments. MPNSTs frequently harbor mutations in key genes such as NF1, CDKN2A, TP53, and PRC2 components (EED or SUZ12) across different disease stages. With the rapid advancement of high-throughput sequencing technologies, the molecular characteristics driving MPNST development are becoming clearer. This review summarizes recent sequencing studies on peripheral nerve sheath tumors, including plexiform neurofibromas (PNs), atypical neurofibromatous neoplasm with uncertain biologic potential (ANNUBP), and MPNSTs, highlighting key mutation events in tumor progression from the perspectives of epigenetics, transcriptomics, genomics, proteomics, and metabolomics. We also discuss the therapeutic implications of these genomic findings, focusing on preclinical and clinical trials targeting these alterations. Finally, we conclude that overcoming tumor resistance through combined targeted therapies and personalized treatments based on the molecular characteristics of MPNSTs will be a key direction for future treatment strategies.

UBR5 in Tumor Biology: Exploring Mechanisms of Immune Regulation and Possible Therapeutic Implications in MPNST

Malignant peripheral nerve sheath tumor (MPNST) is a rare but aggressive soft-tissue sarcoma characterized by poor response to therapy. The primary treatment remains surgical resection with negative margins. Nonetheless, in the setting of neurofibromatosis type 1 (NF1), the five-year survival rate is at 20-50%, with recurrence occurring in up to 50% of individuals. For patients with metastatic and unresectable disease, current treatment options include cytotoxic chemotherapy, which offers minimal benefit, and most patients die within five years of diagnosis. Despite advances in targeted therapy focusing on inhibiting Ras signaling and its downstream effectors, clinical trials report minimal clinical benefit, highlighting the need to explore alternative pathways in MPNST pathogenesis. Here, we discuss the role of the E3 ubiquitin ligase, UBR5, in cancer progression and immune modulation across various malignancies, including breast, lung, and ovarian cancer. We focus on mechanisms by which UBR5 contributes to tumorigenesis, focusing on its influence on tumor microenvironment and immune modulation. Additionally, we explore UBR5's roles in normal tissue function, DNA damage response, metastasis, and therapeutic resistance, illustrating its multifaceted contribution to cancer biology. We discuss evidence implicating UBR5 in immune evasion and highlight its potential as a therapeutic target to enhance the efficacy of immune checkpoint blockade (ICB) therapy in MPNST, a tumor typically characterized by an immune cold microenvironment. We outline current immune-based strategies and challenges in MPNST management, ongoing efforts to shift the immune landscape in MPNST, and ultimately, we suggest that targeting UBR5 could be a novel strategy to potentiate ICB therapy-mediated anti-tumor immune response and clinical outcomes, particularly in MPNST patients with inoperable or metastatic disease.

Multidimensional Immunotyping of Human NF1-Associated Peripheral Nerve Sheath Tumors Uncovers Tumor-Associated Macrophages as Key Drivers of Immune Evasion in the Tumor Microenvironment

PURPOSE

Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft-tissue sarcomas and the leading cause of mortality in individuals with neurofibromatosis type 1 (NF1). Despite many clinical trials, outcomes for patients with MPNST have remained stagnant, and most succumb to their disease; thus, novel therapeutic approaches are needed. A better understanding of the MPNST immune ecosystem will aid in the development of strategies to activate the immune system against the tumor. In this study, we profile the tumor immune microenvironment (TIME) in NF1-associated peripheral nerve sheath tumors (PNST) to discover insights on the role played by tumor-infiltrating immune cells in malignant transformation.

EXPERIMENTAL DESIGN

Using fresh and formalin-fixed paraffin-embedded tissue from patients diagnosed with NF1-PNST, we dissected the TIME through IHC, multiparameter flow cytometry, and comparative transcriptomic studies.

RESULTS

Immunophenotyping confirmed increased immune cell infiltration during malignant progression, with a predominance of infiltrating myeloid cells, particularly CD163+ tumor-associated macrophages (TAM). The T cells within MPNST exhibited signs of tumor activation, characterized by high programmed cell death 1 expression. Additionally, MPNST specimens demonstrated elevated levels of immunosuppressive TAM, with heightened PD-L1 expression. The proportion of CD163+ myeloid cells within the TIME correlated with poorer progression-free survival. Notably, loss of H3K27 trimethylation correlated with low immune cell infiltration in MPNST.

CONCLUSIONS

Malignant transformation of NF1-PNST is characterized by an immunosuppressive microenvironment comprising TAM with high expression of PD-L1, which is associated with inferior outcomes. These findings suggest the clinical potential of immune-modulating therapeutics that can unleash an antitumor immune response.

[Analysis of clinical features, treatment methods, and prognostic influence factors in patients with malignant peripheral nerve sheath tumor]

Objective

To investigate the clinical features, treatment methods, and prognostic influence factors of patients with malignant peripheral nerve sheath tumor (MPNST).

Methods

A retrospective analysis was conducted on 96 MPNST patients treated between January 1, 2015 and December 31, 2021. There were 46 males and 50 females, aged between 15 and 87 years (mean, 48.2 years). The tumors were located in the trunk in 50 cases, extremities in 39 cases, and head and neck in 7 cases. The maximum tumor diameter was <5 cm in 49 cases, ≥5 cm in 32 cases, with 15 cases missing data. Tumor depth was deep in 77 cases and superficial in 19 cases. The Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) histological grading was G1 in 9 cases, G2 in 12 cases, and G3 in 34 cases, with 41 cases missing data. There were 37 recurrent MPNST cases, 32 cases with neurofibromatosis type 1 (NF1), and 26 cases in stage Ⅳ. Postoperative adjuvant radiotherapy was administered to 25 patients, perioperative chemotherapy to 45 patients, and anlotinib-targeted therapy to 30 patients. R 0 resection was achieved in 73 cases. Patients were divided into groups based on the presence or absence of NF1, and baseline data between the two groups were compared. Kaplan-Meier curves were generated to assess disease-free survival (DFS) and overall survival (OS) based on various factors (age, gender, presence of NF1, recurrent MPNST, stage Ⅳ MPNST, FNCLCC grade, R 0 resection, tumor location, tumor size, tumor depth, perioperative chemotherapy, postoperative adjuvant radiotherapy, and anlotinib-targeted therapy), and differences between survival curves were analyzed using the Log-Rank test. Multivariate COX proportional hazards regression was used to identify independent prognostic factors for MPNST.

Results

Patients with NF1 had a significantly higher proportion of superficial tumors and lower FNCLCC grade compared to those without NF1 ( P<0.05); no significant difference was found for other variables ( P<0.05). Kaplan-Meier analysis showed that recurrent MPNST, stage Ⅳ MPNST, FNCLCC grade, R 0 resection, perioperative chemotherapy, and anlotinib-targeted therapy were factors influencing 1-year DFS ( P<0.05), while stage Ⅳ MPNST, FNCLCC grade, and perioperative chemotherapy were factors affecting 3-year OS ( P<0.05). Multivariate COX proportional hazards regression analysis revealed that recurrent MPNST and high-grade FNCLCC (G3) were independent prognostic factors for 1-year DFS ( P<0.05), while stage Ⅳ MPNST, superficial tumor depth, age over 60 years, postoperative adjuvant radiotherapy, and anlotinib-targeted therapy were independent prognostic factors for 3-year OS ( P<0.05).

Conclusion

MPNST patients with NF1 tend to have more superficial tumors and lower FNCLCC grades. FNCLCC grade, R 0 resection, and adjuvant therapies, including radiotherapy and anlotinib-targeted therapy, are closely associated with MPNST prognosis. Complete surgical resection should be prioritized in clinical management, along with adjuvant treatments such as radiotherapy and targeted therapy of anlotinib to improve patient outcomes.

Linking FOXM1 and PD-L1 to CDK4/6-MEK targeted therapy resistance in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, Ras-driven sarcomas characterized by loss of the NF1 tumor suppressor gene and hyperactivation of MEK and CDK4/6 kinases. MPNSTs lack effective therapies. We recently demonstrated remarkable efficacy of dual CDK4/6-MEK inhibition in mice with de novo MPNSTs, which was heightened by combined targeting of the immune checkpoint protein, PD-L1. The triple combination therapy targeting CDK4/6, MEK, and PD-L1 led to extended MPNST regression and improved survival, although most tumors eventually acquired drug resistance. Here, we consider the immune activation phenotype caused by CDK4/6-MEK inhibition in MPNSTs that uniquely involved intratumoral plasma cell accumulation. We discuss how PD-L1 and FOXM1, a tumor-promoting transcription factor, are functionally linked and may be key mediators of resistance to CDK4/6-MEK targeted therapies. Finally, the role of FOXM1 in suppressing anti-tumor immunity and potentially thwarting immune-based therapies is considered. We suggest that future therapeutic strategies targeting the oncogenic network of CDK4/6, MEK, PD-L1, and FOXM1 represent exciting future treatment options for MPNST patients.

The NF1+/- Immune Microenvironment: Dueling Roles in Neurofibroma Development and Malignant Transformation

Neurofibromatosis type 1 (NF1) is a common genetic disorder resulting in the development of both benign and malignant tumors of the peripheral nervous system. NF1 is caused by germline pathogenic variants or deletions of the NF1 tumor suppressor gene, which encodes the protein neurofibromin that functions as negative regulator of p21 RAS. Loss of NF1 heterozygosity in Schwann cells (SCs), the cells of origin for these nerve sheath-derived tumors, leads to the formation of plexiform neurofibromas (PNF)-benign yet complex neoplasms involving multiple nerve fascicles and comprised of a myriad of infiltrating stromal and immune cells. PNF development and progression are shaped by dynamic interactions between SCs and immune cells, including mast cells, macrophages, and T cells. In this review, we explore the current state of the field and critical knowledge gaps regarding the role of NF1(Nf1) haploinsufficiency on immune cell function, as well as the putative impact of Schwann cell lineage states on immune cell recruitment and function within the tumor field. Furthermore, we review emerging evidence suggesting a dueling role of Nf1+/- immune cells along the neurofibroma to MPNST continuum, on one hand propitiating PNF initiation, while on the other, potentially impeding the malignant transformation of plexiform and atypical neurofibroma precursor lesions. Finally, we underscore the potential implications of these discoveries and advocate for further research directed at illuminating the contributions of various immune cells subsets in discrete stages of tumor initiation, progression, and malignant transformation to facilitate the discovery and translation of innovative diagnostic and therapeutic approaches to transform risk-adapted care.

FOXM1, MEK, and CDK4/6: New Targets for Malignant Peripheral Nerve Sheath Tumor Therapy

Malignant peripheral nerve sheath tumors (MPNSTs) are deadly sarcomas, which desperately need effective therapies. Half of all MPNSTs arise in patients with neurofibromatosis type I (NF1), a common inherited disease. NF1 patients can develop benign lesions called plexiform neurofibromas (PNFs), often in adolescence, and over time, some PNFs, but not all, will transform into MPNSTs. A deeper understanding of the molecular and genetic alterations driving PNF-MPNST transformation will guide development of more targeted and effective treatments for these patients. This review focuses on an oncogenic transcription factor, FOXM1, which is a powerful oncogene in other cancers but little studied in MPNSTs. Elevated expression of FOXM1 was seen in patient MPNSTs and correlated with poor survival, but otherwise, its role in the disease is unknown. We discuss what is known about FOXM1 in MPNSTs relative to other cancers and how FOXM1 may be regulated by and/or regulate the most commonly altered players in MPNSTs, particularly in the MEK and CDK4/6 kinase pathways. We conclude by considering FOXM1, MEK, and CDK4/6 as new, clinically relevant targets for MPNST therapy.

Analysis of treatment sequence and outcomes in patients with relapsed malignant peripheral nerve sheath tumors

Background

Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas originating from cellular components within the nerve sheath. The incidence of MPNST is highest in people with neurofibromatosis type 1 (NF1), and MPNST is the leading cause of death for these individuals. Complete surgical resection is the only curative therapeutic option, but is often unfeasible due to tumor location, size, or presence of metastases. Evidence-based choices of chemotherapy for recurrent/refractory MPNST remain elusive. To address this gap, we conducted a retrospective analysis of our institutional experience in treating patients with relapsed MPNST in order to describe patient outcomes related to salvage regimens.

Methods

We conducted a retrospective electronic health record analysis of patients with MPNST who were treated at Johns Hopkins Hospital from January 2010 to June 2021. We calculated time to progression (TTP) based on salvage chemotherapy regimens.

Results

Sixty-five patients were included in the analysis. Upfront therapy included single or combined modalities of surgery, chemotherapy, or radiotherapy. Forty-eight patients received at least 1 line of chemotherapy, which included 23 different regimens (excluding active clinical studies). Most patients (n = 42, 87.5%) received a combination of doxorubicin, ifosfamide, or etoposide as first-line chemotherapy. Salvage chemotherapy regimens and their TTP varied greatly, with irinotecan/temozolomide-based regimens having the longest average TTP (255.5 days, among 4 patients).

Conclusions

Patients with advanced or metastatic MPNST often succumb to their disease despite multiple lines of therapy. These data may be used as comparative information in decision-making for future patients and clinical trials.