DNA-repair defects in pancreatic neuroendocrine tumors and potential clinical applications

Pathogenic Insights into DNA Mismatch Repair (MMR) Genes-Proteins and Microsatellite Instability: Focus on Adrenocortical Carcinoma and Beyond

DNA damage repair pathways, including mismatch repair (MMR) genes, are prone to carcinoma development in certain patients. The assessment of the MMR system is widely recognized as part of strategies concerning solid tumors (defective MMR cancers), especially MMR proteins (through immunohistochemistry), and molecular assays for microsatellite instability (MSI). We aim to highlight the status of MMR genes-proteins (including MSI) in the relationship with ACC (adrenocortical carcinoma) according to current knowledge. This is a narrative review. We included PubMed-accessed, full-length English papers published between January 2012 and March 2023. We searched studies on ACC patients for whom MMR status was assessed, respectively subjects harboring MMR germline mutations, namely Lynch syndrome (LS), who were diagnosed with ACC. MMR system assessments in ACCs involve a low level of statistical evidence. Generally, there are two main types of endocrine insights: 1. the role of MMR status as a prognostic marker in different endocrine malignancies (including ACC)-which is the topic of the present work, and 2. establishing the indication of immune checkpoint inhibitors (ICPIs) in selective, mostly highly aggressive, non-responsive to standard care forms upon MMR evaluation (which belongs to the larger chapter of immunotherapy in ACCs). Our one-decade, sample-case study (which, to our knowledge, it is the most comprehensive of its kind) identified 11 original articles (from 1 patient to 634 subjects per study diagnosed with either ACC or LS). We identified four studies published in 2013 and 2020 and two in 2021, three cohorts and two retrospective studies (the publication from 2013 includes a retrospective and a cohort distinct section). Among these four studies, patients already confirmed to have LS (N = 643, respective 135) were found to be associated with ACC (N = 3, respective 2), resulting in a prevalence of 0.0046%, with a respective of 1.4% being confirmed (despite not having a large amount of similar data outside these two studies). Studies on ACC patients (N = 364, respective 36 pediatric individuals, and 94 subjects with ACC) showed that 13.7% had different MMR gene anomalies, with a respective of 8.57% (non-germline mutations), while 3.2% had MMR germline mutations (N = 3/94 cases). Two case series included one family, with a respective four persons with LS, and each article introduced one case with LS-ACC. Another five case reports (between 2018 and 2021) revealed an additional five subjects (one case per paper) diagnosed with LS and ACC (female to male ratio of 4 to 1; aged between 44 and 68). Interesting genetic testing involved children with TP53-positive ACC and further MMR anomalies or an MSH2 gene-positive subject with LS with a concurrent germline RET mutation. The first report of LS-ACC referred for PD-1 blockade was published in 2018. Nevertheless, the use of ICPI in ACCs (as similarly seen in metastatic pheochromocytoma) is still limited. Pan-cancer and multi-omics analysis in adults with ACC, in order to classify the candidates for immunotherapy, had heterogeneous results, and integrating an MMR system in this larger and challenging picture is still an open issue. Whether individuals diagnosed with LS should undergo surveillance for ACC has not yet been proven. An assessment of tumor-related MMR/MSI status in ACC might be helpful. Further algorithms for diagnostics and therapy, also taking into consideration innovative biomarkers as MMR-MSI, are necessary.

Molecular and Functional Heterogeneity of Primary Pancreatic Neuroendocrine Tumors and Metastases

INTRODUCTION

Treatment response to the standard therapy is low for metastatic pancreatic neuroendocrine tumors (PanNETs) mainly due to the tumor heterogeneity. We investigated the heterogeneity between primary PanNETs and metastases to improve the precise treatment.

METHODS

The genomic and transcriptomic data of PanNETs were retrieved from the Genomics, Evidence, Neoplasia, Information, Exchange (GENIE), and Gene Expression Omnibus (GEO) database, respectively. Potential prognostic effects of gene mutations enriched in metastases were investigated. Gene set enrichment analysis was performed to investigate the functional difference. Oncology Knowledge Base was interrogated for identifying the targetable gene alterations.

RESULTS

Twenty-one genes had significantly higher mutation rates in metastases which included TP53 (10.3% vs. 16.9%, p = 0.035) and KRAS (3.7% vs. 9.1%, p = 0.016). Signaling pathways related to cell proliferation and metabolism were enriched in metastases, whereas epithelial-mesenchymal transition (EMT) and TGF-β signaling were enriched in primaries. Gene mutations were highly enriched in metastases that had significant unfavorable prognostic effects included mutation of TP53 (p < 0.001), KRAS (p = 0.001), ATM (p = 0.032), KMT2D (p = 0.001), RB1 (p < 0.001), and FAT1 (p < 0.001). Targetable alterations enriched in metastases included mutation of TSC2 (15.5%), ARID1A (9.7%), KRAS (9.1%), PTEN (8.7%), ATM (6.4%), amplification of EGFR (6.0%), MET (5.5%), CDK4 (5.5%), MDM2 (5.0%), and deletion of SMARCB1 (5.0%).

CONCLUSION

Metastases exhibited a certain extent of genomic and transcriptomic diversity from primary PanNETs. TP53 and KRAS mutation in primary samples might associate with metastasis and contribute to a poorer prognosis. A high fraction of novel targetable alterations enriched in metastases deserves to be validated in advanced PanNETs.

DAXX, ATRX, and MSI in PanNET and Their Metastases: Correlation with Histopathological Data and Prognosis

INTRODUCTION

Studies on pancreatic neuroendocrine tumors (PanNETs) regarding loss of ATRX, DAXX, or frequency of microsatellite instability (MSI) show inconclusive results. So far, data on corresponding metastaseshave not been published.

METHODS

We performed immunohistochemistry (IHC) of ATRX, DAXX, MSH2, MSH6, MLH1, and PMS2 on 74 PanNETs and 19 metastases. ATRX- and DAXX-negative PanNETs were further sequenced for mutations. We used polymerase chain reaction for MSI on cases with IHC loss of MSH2, MSH6, MLH1, and PMS2.

RESULTS

Immunohistochemical loss of DAXX and ATRX was observed in 8/74 (11%) and 6/74 (8%) PanNETs. Loss of DAXX immunoreactivity was statistically associated with higher tumor grade and showed a tendency toward a decreased overall survival. Sequencing of DAXX- (7/11 [64%]) and ATRX-negative (5/11 [45%]) PanNETs revealed a mutation in 6/7 (86%) and 2/5 (40%). The specificity of immunohistochemical loss of DAXX and ATRX for mutation was 80% and 67%, respectively. The expression status of DAXX compared to primary tumor differs in 2/12 (17%) lymph node metastases. We further identified 3/74 (4%) tumors as MSI, associated with a poor prognosis.

DISCUSSION/CONCLUSION

Our study supports the hypothesis that a loss of DAXX immunoreactivity can identify a more aggressive subtype of PanNET with high confidence, while ATRX loss is a weaker indicator. Our results also strengthen the role of DAXX immunolabeling as a prognostic marker. We could show that ATRX might be less suitable as a surrogate for sequencing. Our results indicate that IHC of DAXX and ATRX may identify PanNET subtypes as targets for more aggressive therapy.

Chemotherapy in Neuroendocrine Tumors

The role for cytotoxic chemotherapy in patients with well-differentiated neuroendocrine tumors (NETs) remains debated. Compared to patients with poorly differentiated neuroendocrine carcinomas (NECs) where chemotherapy is utilized ubiquitously, chemotherapy may play a more select role in patients with certain types of NETs (e.g., pancreatic tumors, higher grade tumors, and tumors possessing DNA damage repair defects). The primary types of chemotherapy that have been tested in patients with NETs include alkylating agent- and platinum agent-based combinations. Across regimens, chemotherapy appears to elicit greater antitumor activity in patients with pancreatic or grade 3 NETs. The role for chemotherapy in lower grade extra-pancreatic NETs remains undefined. Furthermore, while chemotherapy has demonstrated clinically meaningful benefit for patients in the systemic setting, its role in the adjuvant or neoadjuvant setting is as-of-yet undetermined. Finally, efforts to combine chemotherapy with targeted therapy and peptide receptor radionuclide therapy are ongoing, in hopes of improving the cytoreductive treatment options for patients with NETs.

Microsatellite Instability-High, Malignant Insulinoma With Brain Metastasis

Insulinomas are the most common type of functional pancreatic neuroendocrine tumor. Although insulinomas usually are noninvasive or benign, 10% are deemed invasive or malignant. The pathologic mechanisms that lead to the malignant phenotype are not well elucidated. In this case report, we present a patient with stage 4 malignant insulinoma with metastasis to the liver, bone, and brain. Genetic analysis of the tumor showed that the tumor was mismatch-repair deficient and had a high rate of microsatellite instability. There was loss of MLH1- and PMS2-encoded protein expression, and MLH1 and MEN1 variants were identified. Notably, the liver metastasis showed considerable tumor heterogeneity (well differentiated) compared with the brain metastasis (poorly differentiated).

Immunotherapeutics at the spearhead: current status in targeting neuroendocrine neoplasms

PURPOSE

Recent advances in the field of immunotherapy have significantly prolonged the survival of patients with aggressive carcinomas, but the role of immunotherapy in neuroendocrine neoplasms (NENs) remains to be elucidated.

METHODS AND RESULTS

We report a patient diagnosed with a well-differentiated grade 3 pancreatic NEN (pNEN) and type 3 liver metastases who received compassionate nivolumab as a fifth line treatment and achieved a durable partial response of more than 34 months. We have performed a systematic review to the literature on tumor microenvironment and potential biomarkers in the field of NEN including the tumor mutational burden, the tumor infiltrating lymphocytes, the programmed cell death ligand 1, and the mismatch repair system. The potential role of the immune system modulation together with a critical assessment of the recent phase II clinical studies in NEN including monotherapy with anti-PD-1/PD-L1 monoclonal antibodies, and combination therapies including anti-PD-1 along with anti-CTLA-4 monoclonal antibodies are also provided.

CONCLUSION

Immunotherapeutics are gaining a post in the field of NENs in cases progressing during the course of the disease, dictating urgently the identification of biomarkers that will enable selection of NEN patients who may benefit from this treatment.

Does the proteasome inhibitor bortezomib sensitize to DNA-damaging therapy in gastroenteropancreatic neuroendocrine neoplasms? - A preclinical assessment in vitro and in vivo

BACKGROUND

Well-differentiated gastroenteropancreatic neuroendocrine neoplasms are rare tumors with a slow proliferation. They are virtually resistant to many DNA-damaging therapeutic approaches, such as chemo- and external beam therapy, which might be overcome by DNA damage inhibition induced by proteasome inhibitors such as bortezomib.

METHODS AND RESULTS

In this study, we assessed several combined treatment modalities in vitro and in vivo. By cell-based functional analyses, in a 3D in ovo and an orthotopic mouse model, we demonstrated sensitizing effects of bortezomib combined with cisplatin, radiation and peptide receptor radionuclide therapy (PRRT). By gene expression profiling and western blot, we explored the underlying mechanisms, which resulted in an impaired DNA damage repair. Therapy-induced DNA damage triggered extrinsic proapoptotic signaling as well as the induction of cell cycle arrest, leading to a decreased vital tumor volume and altered tissue composition shown by magnetic resonance imaging and F-18-FDG-PET in vivo, however with no significant additional benefit related to PRRT alone.

CONCLUSIONS

We demonstrated that bortezomib has short-term sensitizing effects when combined with DNA damaging therapy by interfering with DNA repair in vitro and in ovo. Nevertheless, due to high tumor heterogeneity after PRRT in long-term observations, we were not able to prove a therapeutic advantage of bortezomib-combined PRRT in an in vivo mouse model.

The lipogenic LXR-SREBF1 signaling pathway controls cancer cell DNA repair and apoptosis and is a vulnerable point of malignant tumors for cancer therapy

Cancer cells are defective in DNA repair, so they experience increased DNA strand breaks, genome instability, gene mutagenesis, and tumorigenicity; however, multiple classic DNA repair genes and pathways are strongly activated in malignant tumor cells to compensate for the DNA repair deficiency and gain an apoptosis resistance. The mechanisms underlying this phenomenon in cancer are unclear. We speculate that a key DNA repair gene or signaling pathway in cancer has not yet been recognized. Here, we show that the lipogenic liver X receptor (LXR)-sterol response element binding factor-1 (SREBF1) axis controls the transcription of a key DNA repair gene polynucleotide kinase/phosphatase (PNKP), thereby governing cancer cell DNA repair and apoptosis. Notably, the PNKP levels were significantly reduced in 95% of human pancreatic cancer (PC) patients, particularly deep reduction for sixfold in all of the advanced-stage PC cases. PNKP is also deficient in three other types of cancer that we examined. In addition, the expression of LXRs and SREBF1 was significantly reduced in the tumor tissues from human PC patients compared with the adjacent normal tissues. The newly identified LXR-SREBF1-PNKP signaling pathway is deficient in PC, and the defect in the pathway contributes to the DNA repair deficiency in the cancer. Strikingly, further diminution of the vulnerable LXR-SREBF1-PNKP signaling pathway using a small molecule triptonide, a new LXR antagonist identified in this investigation, at a concentration of 8 nM robustly activated tumor-suppressor p53 and readily elevated cancer cell DNA strand breaks over an apoptotic threshold, and selectively induced PC cell apoptosis, resulting in almost complete elimination of tumors in xenograft mice without obvious complications. Our findings provide new insight into DNA repair and apoptosis in cancer, and offer a new platform for developing novel anticancer therapeutics.

Genetic analysis of the cooperative tumorigenic effects of targeted deletions of tumor suppressors Rb1, Trp53, Men1, and Pten in neuroendocrine tumors in mice

Genetic alterations of tumor suppressor genes (TSGs) are frequently observed to have cumulative or cooperative tumorigenic effects. We examined whether the TSGs Rb1, Trp53, Pten and Men1 have cooperative effects in suppressing neuroendocrine tumors (NETs) in mice. We generated pairwise homozygous deletions of these four genes in insulin II gene expressing cells using the Cre-LoxP system. By monitoring growth and examining the histopathology of the pituitary (Pit) and pancreas (Pan) in these mice, we demonstrated that pRB had the strongest cooperative function with PTEN in suppressing PitNETs and had strong cooperative function with Menin and TRP53, respectively, in suppressing PitNETs and PanNETs. TRP53 had weak cooperative function with PTEN in suppressing pituitary lesions. We also found that deletion of Pten singly led to prolactinomas in female mice, and deletion of Rb1 alone led to islet hyperplasia in pancreas. Collectively, our data indicated that pRB and PTEN pathways play significant roles in suppressing PitNETs, while the Menin-mediated pathway plays a significant role in suppressing PanNETs. Understanding the molecular mechanisms of these genes and pathways on NETs will help us understand the molecular mechanisms of neuroendocrine tumorigenesis and develop effective preclinical murine models for NET therapeutics to improve clinical outcomes in humans.

Two well-differentiated pancreatic neuroendocrine tumor mouse models

Multiple endocrine neoplasia type 1 (MEN1) is a genetic syndrome in which patients develop neuroendocrine tumors (NETs), including pancreatic neuroendocrine tumors (PanNETs). The prolonged latency of tumor development in MEN1 patients suggests a likelihood that other mutations cooperate with Men1 to induce PanNETs. We propose that Pten loss combined with Men1 loss accelerates tumorigenesis. To test this, we developed two genetically engineered mouse models (GEMMs)-MPR (Men1^flox/flox Pten^flox/flox RIP-Cre) and MPM (Men1^flox/flox Pten^flox/flox MIP-Cre) using the Cre-LoxP system with insulin-specific biallelic inactivation of Men1 and Pten. Cre in the MPR mouse model was driven by the transgenic rat insulin 2 promoter while in the MPM mouse model was driven by the knock-in mouse insulin 1 promoter. Both mouse models developed well-differentiated (WD) G1/G2 PanNETs at a much shorter latency than Men1 or Pten single deletion alone and exhibited histopathology of human MEN1-like tumor. The MPR model, additionally, developed pituitary neuroendocrine tumors (PitNETs) in the same mouse at a much shorter latency than Men1 or Pten single deletion alone as well. Our data also demonstrate that Pten plays a role in NE tumorigenesis in pancreas and pituitary. Treatment with the mTOR inhibitor rapamycin delayed the growth of PanNETs in both MPR and MPM mice, as well as the growth of PitNETs, resulting in prolonged survival in MPR mice. Our MPR and MPM mouse models are the first to underscore the cooperative roles of Men1 and Pten in cancer, particularly neuroendocrine cancer. The early onset of WD PanNETs mimicking the human counterpart in MPR and MPM mice at 7 weeks provides an effective platform for evaluating therapeutic opportunities for NETs through targeting the MENIN-mediated and PI3K/AKT/mTOR signaling pathways.

Dictating genomic destiny: Epigenetic regulation of pancreatic neuroendocrine tumours

Pancreatic neuroendocrine tumours are a diverse group of neoplasms with an increasingly well-defined genomic basis. Despite this, much of what drives this disease is still unknown and epigenetic influences represent the next tier of gene, and hence disease modifiers that are of unquestionable importance. Moreover, they are of arguably more significance than the genes themselves given their malleable nature and potential to be exploited for not only diagnosis and prognosis, but also therapy. This review summarises what is known regarding the key epigenetic modifiers of disease through the domains of diagnosis, prognosis and treatment.

WOMEN IN CANCER THEMATIC REVIEW: Systemic therapies in neuroendocrine tumors and novel approaches toward personalized medicine

Neuroendocrine tumors (NETs) are a group of heterogenous neoplasms. Evidence-based treatment options for antiproliferative therapy include somatostatin analogues, the mTOR inhibitor everolimus, the multiple tyrosine kinase inhibitor sunitinib and peptide receptor radionuclide therapy with 177-Lu-octreotate. In the absence of definite predictive markers, therapeutic decision making follows clinical and pathological criteria. As objective response rates with targeted drugs are rather low, and response duration is limited in most patients, numerous combination therapies targeting multiple pathways have been explored in the field. Upfront combination of drugs, however, is associated with increasing toxicity and has shown little benefit. Major advancements in the molecular understanding of NET based on genomic, epigenomic and transcriptomic analysis have been achieved with prognostic and therapeutic impact. New insight into molecular alterations has paved the way to biomarker-driven clinical trials and may facilitate treatment stratification toward personalized medicine in the near future. However, an improved understanding of the complexity of pathway interactions is required for successful treatment. A systems biology approach is one of the tools that may help to achieve this endeavor.

Ki-67 index and response to chemotherapy in patients with neuroendocrine tumours

Chemotherapy (CT) is widely used for neuroendocrine tumours (NETs), but there are no validated biomarkers to predict response. The Ki-67 proliferation index has been proposed as a means of selecting patients for CT, but robust data are lacking. The aim of this study was to investigate the relationship between response to chemotherapy and Ki-67 in NET. We reviewed data from 222 NET patients treated with CT. Tumours were graded according to Ki-67 index: G1 ≤2%, G2 3-20% and G3 >20%. Response was assessed according to RECIST and survival calculated from start of chemotherapy to death. To explore Ki-67 as a marker of response, we calculated the likelihood ratio and performed receiver operating characteristic analysis. Overall, 193 patients had a documented Ki-67 index, of which 173 were also evaluable for radiological response: 10% were G1, 46% G2 and 43% G3; 46% were pancreatic NET (PNET). Median overall survival was 22.1 months. Overall response rate was 30% (39% in PNET vs 22% in non-PNET) and 43% of patients had stable disease. Response rate increased with grade: 6% in G1 tumours, 24% in G2 and 43% in G3. However, maximum likelihood ratio was 2.3 at Ki-67=35%, and the area under the ROC curve was 0.60. As reported previously, a high Ki-67 was an adverse prognostic factor for overall survival. In conclusion, response to CT increases with Ki-67 index, but Ki-67 alone is an unreliable means to select patients for CT. Improved methods to stratify patients for systemic therapy are required.