The selective PI3Kα inhibitor BYL719 as a novel therapeutic option for neuroendocrine tumors: Results from multiple cell line models

Concomitant inhibition of PI3K/mTOR signaling pathways boosts antiproliferative effects of lanreotide in bronchopulmonary neuroendocrine tumor cells

Introduction: Somatostatin analogues (SSAs) are commonly used in the treatment of hormone hypersecretion in neuroendocrine tumors (NETs), however the extent to which they inhibit proliferation is much discussed. Objective: We studied the antiproliferative effects of novel SSA lanreotide in bronchopulmonary NETs (BP-NETs). We focused on assessing whether pretreating cells with inhibitors for phosphatidylinositol 3-kinase (PI3K) and mammalian target for rapamycin (mTOR) could enhance the antiproliferative effects of lanreotide. Methods: BP-NET cell lines NCI-H720 and NCI-H727 were treated with PI3K inhibitor BYL719 (alpelisib), mTOR inhibitor everolimus and SSA lanreotide to determine the effect on NET differentiation markers, cell survival, proliferation and alterations in cancer-associated pathways. NT-3 cells, previously reported to express somatostatin receptors (SSTRs) natively, were used as control for SSTR expression. Results: SSTR2 was upregulated in NCI-H720 and NT-3 cells upon treatment with BYL719. Additionally, combination treatment consisting of BYL719 and everolimus plus lanreotide tested in NCI-H720 and NCI-H727 led to diminished cell proliferation in a dose-dependent manner. Production of proteins activating cell death mechanisms was also induced. Notably, a multiplexed gene expression analysis performed on NCI-H720 revealed that BYL719 plus lanreotide had a stronger effect on the downregulation of mitogens than lanreotide alone. Discussion/Conclusion: We report a widespread analysis of changes in BP-NET cell lines at the genetic/protein expression level in response to combination of lanreotide with pretreatment consisting of BYL719 and everolimus. Interestingly, SSTR expression reinduction could be exploited in therapeutic and diagnostic applications. The overall results of this study support the evaluation of combination-based therapies using lanreotide in preclinical studies to further increase its antiproliferative effect and ultimately facilitate its use in high-grade tumors.

Dual inhibition of atypical PKC signaling and PI3K/Akt signaling dysregulates c-Myc to induce apoptosis in clear cell Renal Cell Carcinoma

Background

Renal Cell Carcinoma (RCC) is the most common type of kidney cancer (85%). 75% of the RCC cases involve conventional clear cell RCC (ccRCC). Approximately, 39% of late-stage patients (stage IV) are treated with chemotherapeutic agents. Phosphatidylinositol-3-kinase (PI3K) and Mitogen-Activated Protein Kinase Kinase (MEK)/extracellular signal-regulated kinase (ERK1/2) pathways are frequently activated in RCC. In addition, atypical PKCs (PKC-ί and PKC ζ) are overexpressed in most cancer cells, and they play a central role in tumor progression and the metastasis of different types of cancers. Our goal is to establish the role of aPKCs in the regulation of multiple key activated pathways in ccRCC. In this study, we also established a novel therapeutic regimen for dual inhibition of key activated pathways.

Method

In this study, 786-0 and Caki-1 cells were studied and subjected to cell viability assay, western blot analysis, scratch & wound healing assay, transwell invasion assay, immunofluorescence, immunoprecipitation, flow cytometry, and quantitative real-time polymerase chain reaction. We used combination of PI3K inhibitor- Alpelisib (BYL719) and ICA-1 (a PKC-ι-specific 5-amino-1-2,3-dihydroxy-4-(methylcyclopentyl)-1H-imidazole-4-carboxamide). In addition to drug treatment, small interfering RNA (siRNA) technology was used to further confirm the experimental outcome of the drug treatment.

Results

Our results suggest that treatment of ccRCC cells with a combination of ICA-1 (aPKC inhibitor) and BYL719 (PI3K inhibitor) downregulates PKC-ί and causes downstream inhibition of c-Myc. Inhibition of the PKCί also reduces activation of MEK/ERK1/2. It is observed that treatment with ICA-1 disrupts the level of the aPKC-Akt1 association. ICA-1 treatment also shows a reduced level of association between aPKC and c-Myc. The inhibition of aPKCs and downstream effector proteins by combination therapy is more pronounced compared to a single therapy. These effects contribute to reduced cell growth, and eventually, the induction of apoptosis. The decreased level of N-cadherin, p-vimentin, and vimentin and the increased level of E-cadherin confirm reduced malignancy.

Conclusion

Therefore, implementing a combination of Alpelisib and a PKC-ι inhibitor is an effective approach to reducing cell proliferation, and invasion that eventually induces apoptosis and may be considered as a potential therapeutic option in ccRCC.

Improving susceptibility of neuroendocrine tumors to radionuclide therapies: personalized approaches towards complementary treatments

Radionuclide therapies are an important tool for the management of patients with neuroendocrine neoplasms (NENs). Especially [131I]MIBG and [177Lu]Lu-DOTA-TATE are routinely used for the treatment of a subset of NENs, including pheochromocytomas, paragangliomas and gastroenteropancreatic tumors. Some patients suffering from other forms of NENs, such as medullary thyroid carcinoma or neuroblastoma, were shown to respond to radionuclide therapy; however, no general recommendations exist. Although [131I]MIBG and [177Lu]Lu-DOTA-TATE can delay disease progression and improve quality of life, complete remissions are achieved rarely. Hence, better individually tailored combination regimes are required. This review summarizes currently applied radionuclide therapies in the context of NENs and informs about recent advances in the development of theranostic agents that might enable targeting subgroups of NENs that previously did not respond to [131I]MIBG or [177Lu]Lu-DOTA-TATE. Moreover, molecular pathways involved in NEN tumorigenesis and progression that mediate features of radioresistance and are particularly related to the stemness of cancer cells are discussed. Pharmacological inhibition of such pathways might result in radiosensitization or general complementary antitumor effects in patients with certain genetic, transcriptomic, or metabolic characteristics. Finally, we provide an overview of approved targeted agents that might be beneficial in combination with radionuclide therapies in the context of a personalized molecular profiling approach.

Synergistic therapeutic potential of alpelisib in cancers (excluding breast cancer): Preclinical and clinical evidences

The phosphoinositide 3-kinase (PI3K) signaling pathway is well-known for its important role in cancer growth, proliferation and migration. The activation of PI3K pathway is always connected with endocrine resistance and poor prognosis in cancers. Alpelisib, a selective inhibitor of PI3K, has been demonstrated to be effective in combination with endocrine therapy in HR+ PIK3CA-mutated advanced breast cancer in preclinical and clinical trials. Recently, the synergistic effects of alpelisib combined with targeted agents have been widely reported in PIK3CA-mutated cancer cells, such as breast, head and neck squamous cell carcinoma (HNSCC), cervical, liver, pancreatic and lung cancer. However, previous reviews mainly focused on the pharmacological activities of alpelisib in breast cancer. The synergistic therapeutic potential of alpelisib in other cancers has not yet been well reviewed. In this review, an extensive study of related literatures (published until December 20, 2022) regarding the anti-cancer functions and synergistic effects of alpelisib was carried out through the databases. Useful information was extracted. We summarized the preclinical and clinical studies of alpelisib in combination with targeted anti-cancer agents in cancer treatment (excluding breast cancer). The combinations of alpelisib and other targeted agents significantly improved the therapeutic efficacy both in preclinical and clinical studies. Unfortunately, synergistic therapies still could not effectively avoid the possible toxicities and adverse events during treatment. Finally, some prospects for the combination studies in cancer treatment were provided in the paper. Taken together, this review provided valuable information for alpelisib in preclinical and clinical applications.

Carcinoid Syndrome: Preclinical Models and Future Therapeutic Strategies

Carcinoid syndrome represents a debilitating paraneoplastic disease, caused by the secretion of several substances, occurring in about 10-40% of patients with well-differentiated neuroendocrine tumors (NETs). The main signs and symptoms associated with carcinoid syndrome are flushing, diarrhea, hypotension, tachycardia, bronchoconstriction, venous telangiectasia, dyspnea and fibrotic complications (mesenteric and retroperitoneal fibrosis, and carcinoid heart disease). Although there are several drugs available for the treatment of carcinoid syndrome, the lack of therapeutic response, poor tolerance or resistance to drugs are often reported. Preclinical models are indispensable tools for investigating the pathogenesis, mechanisms for tumor progression and new therapeutic approaches for cancer. This paper provides a state-of-the-art overview of in vitro and in vivo models in NETs with carcinoid syndrome, highlighting the future developments and therapeutic approaches in this field.

Hydrophobic Bile Salts Induce Pro-Fibrogenic Proliferation of Hepatic Stellate Cells through PI3K p110 Alpha Signaling

Bile salts accumulating during cholestatic liver disease are believed to promote liver fibrosis. We have recently shown that chenodeoxycholate (CDC) induces expansion of hepatic stellate cells (HSCs) in vivo, thereby promoting liver fibrosis. Mechanisms underlying bile salt-induced fibrogenesis remain elusive. We aimed to characterize the effects of different bile salts on HSC biology and investigated underlying signaling pathways. Murine HSCs (mHSCs) were stimulated with hydrophilic and hydrophobic bile salts. Proliferation, cell mass, collagen deposition, and activation of signaling pathways were determined. Activation of the human HSC cell line LX 2 was assessed by quantification of α-smooth muscle actin (αSMA) expression. Phosphatidyl-inositol-3-kinase (PI3K)-dependent signaling was inhibited both pharmacologically and by siRNA. CDC, the most abundant bile salt accumulating in human cholestasis, but no other bile salt tested, induced Protein kinase B (PKB) phosphorylation and promoted HSC proliferation and subsequent collagen deposition. Pharmacological inhibition of the upstream target PI3K-inhibited activation of PKB and pro-fibrogenic proliferation of HSCs. The PI3K p110α-specific inhibitor Alpelisib and siRNA-mediated knockdown of p110α ameliorated pro-fibrogenic activation of mHSC and LX 2 cells, respectively. In summary, pro-fibrogenic signaling in mHSCs is selectively induced by CDC. PI3K p110α may be a potential therapeutic target for the inhibition of bile salt-induced fibrogenesis in cholestasis.

Lysosomal Changes in Mitosis

The recent discovery demonstrating that the leakage of cathepsin B from mitotic lysosomes assists mitotic chromosome segregation indicates that lysosomal membrane integrity can be spatiotemporally regulated. Unlike many other organelles, structural and functional alterations of lysosomes during mitosis remain, however, largely uncharted. Here, we demonstrate substantial differences in lysosomal proteome, lipidome, size, and pH between lysosomes that were isolated from human U2OS osteosarcoma cells either in mitosis or in interphase. The combination of pharmacological synchronization and mitotic shake-off yielded ~68% of cells in mitosis allowing us to investigate mitosis-specific lysosomal changes by comparing cell populations that were highly enriched in mitotic cells to those mainly in the G1 or G2 phases of the cell cycle. Mitotic cells had significantly reduced levels of lysosomal-associated membrane protein (LAMP) 1 and the active forms of lysosomal cathepsin B protease. Similar trends were observed in levels of acid sphingomyelinase and most other lysosomal proteins that were studied. The altered protein content was accompanied by increases in the size and pH of LAMP2-positive vesicles. Moreover, mass spectrometry-based shotgun lipidomics of purified lysosomes revealed elevated levels of sphingolipids, especially sphingomyelin and hexocylceramide, and lysoglyserophospholipids in mitotic lysosomes. Interestingly, LAMPs and acid sphingomyelinase have been reported to stabilize lysosomal membranes, whereas sphingomyelin and lysoglyserophospholipids have an opposite effect. Thus, the observed lysosomal changes during the cell cycle may partially explain the reduced lysosomal membrane integrity in mitotic cells.

Canine insulinoma as a model for human malignant insulinoma research: Novel perspectives for translational clinical studies

Insulinomas are considered rare indolent neuroendocrine neoplasms in human medicine, however when metastases occur no curative treatment is available thus, novel therapies are needed. Recently advances have been made in unraveling the pathophysiology of malignant insulinoma still major challenges hinder the development of a functional model to study them. Canine malignant insulinoma have similar recurrence and a poor prognosis as human malignant insulinoma. Additionally, both human and canine patients share extensively the same environment, tend to develop insulinoma seemingly spontaneously with an etiological role for hormones, at a similar incidence and stage of lifespan, with metastasis commonly to liver and regional lymph nodes, which are unresponsive to current therapies. However, the occurrence of metastases in dogs is as high as 95% compared with only 5-16% in human studies. From a comparative oncology perspective, the shared features with human insulinoma but higher incidence of metastasis in canine insulinoma suggests the latter as a model for human malignant insulinomas. With the common purpose of increasing survival rates of human and veterinary patients, in this review we are going to compare and analyze clinical, pathological and molecular aspects of canine and human insulinomas to evaluate the suitability of the canine model for future translational clinical studies.

Everolimus-induced somatostatin receptor overexpression in a rectal neuroendocrine tumor patient may promote somatostatin receptor-guided radionuclide therapy (peptide receptor radiotherapy) as an additional treatment option

We present a case of Grade II, well-differentiated rectal neuroendocrine tumor in a 39-year-old patient. Following different sequential treatment modalities, the disease progressed both on metabolic (18F-fluorodeoxyglucose positron emission tomography-computed tomography [¹⁸F-FDG PET/CT]) and somatostatin receptor (SSTR)-imaging (⁶⁸Ga-DOTA-Tyr3-octreotate [⁶⁸Ga-DOTATATE] PET/CT), and the patient received three cycles of peptide receptor radiotherapy (PRRT). Two years later, upon new progression due to the appearance of metabolically active, ⁶⁸Ga-DOTATATE PET/CT-negative liver lesions, targeted treatment with everolimus was introduced. Further morphologic and metabolic progression occurred 4 months after everolimus initiation, however, this time liver lesions demonstrated increased SSTR-expression on⁶⁸Ga-DOTATATE PET/CT. Thus, the patient became eligible for a second PRRT course.

Cross-talk among MEN1, p53 and Notch regulates the proliferation of pancreatic neuroendocrine tumor cells by modulating INSM1 expression and subcellular localization

Genomic analysis of Pancreatic Neuroendocrine Tumors (PanNETs) has revealed that these tumors often lack mutations in typical cancer-related genes such as the tumor suppressor gene p53. Instead, PanNET tumorigenesis usually involves mutations in specific PanNET-related genes, such as tumor suppressor gene MEN1. Using a PanNET mouse model, human tissues and human cell lines, we studied the cross-talk among MEN1, p53 and Notch signaling pathways and their role in PanNETs. Here, we show that reactivation of the early developmental program of islet cells underlies PanNET tumorigenesis by restoring the proliferative capacity of PanNET cells. We investigated the role of INSM1, a transcriptional regulator of islet cells' development, and revealed that its expression and subcellular localization is regulated by MEN1 and p53. Both human and mouse data show that loss of MEN1 in a p53 wild-type genetic background results in increased nuclear INSM1 expression and cell proliferation. Additionally, inhibition of Notch signaling in a p53 wild-type background reduces the proliferation of PanNET cells, due to repression of INSM1 transcription and nuclear localization. Our study elucidates the molecular mechanisms governing the interactions of INSM1 with MEN1, p53 and Notch and their roles in PanNET tumorigenesis, suggesting INSM1 as a key transcriptional regulator of PanNET cell proliferation.

The role of different PI3K protein subtypes in the metastasis, angiogenesis and clinical prognosis of hepatocellular carcinoma

BACKGROUND AND OBJECTIVES

Abnormal activation of the PI3K/AKT pathway is closely related to tumor occurrence, development and angiogenesis. PI3K, as a key protein in the PI3K/Akt pathway, has different subtypes that play diverse roles in various tumors. The aim of this study was to examine the roles of different PI3K protein subtypes (PI3Kp110α, PI3Kp110β, and PI3Kp110δ) in the metastasis, angiogenesis and prognosis of hepatocellular carcinoma (HCC).

METHODS

The roles of different PI3K protein subtypes in the metastasis, angiogenesis and prognosis of HCC were assessed by immunohistochemical staining of 97 HCC tissues and the STRING database.

RESULTS

Our results showed that PI3Kp110α and PI3Kp110δ were associated with HCC metastasis and angiogenesis. Patients with high expression of PI3Kp110α and PI3Kp110δ had a worse prognosis and shorter survival time, respectively, than those with low expression, whereas these effects were not observed for PI3Kp110β. Cox regression analysis showed that PI3Kp110α and clinical stage were independent risk factors for the overall survival of HCC patients.

CONCLUSIONS

PI3Kp110α and PI3Kp110δ promoted HCC metastasis and angiogenesis via the PI3K/AKT pathway, and PI3Kp110α was an independent risk factor for HCC patients. These findings provide valuable insights for the prognosis evaluation and the selection of subtype inhibitors of HCC patients.

Transcriptomic analysis by RNA sequencing characterises malignant progression of canine insulinoma from normal tissue to metastatic disease

Insulinomas (INS) are the most common human and canine functioning pancreatic neuroendocrine tumours. The long-term prognosis for malignant INS is poor, because micrometastases are frequently missed during surgery. As human and canine malignant INS share clinical and histopathological features, dogs have been proposed as models for INS research. Using RNA-sequencing, we conducted a pilot study to better understand the underlying molecular mechanisms of canine INS. Normal canine pancreas and lymph node control tissues were compared with primary INS and INS-metastatic lymph nodes, revealing more than 3,000 genes differentially expressed in normal pancreas compared to primary INS. Only 164 genes were differentially expressed between primary INS and INS-metastatic lymph nodes. Hierarchical clustering analysis demonstrated similar genetic profiles in normal pancreas and early clinical stage primary INS, whereas late clinical stage primary INS resembled the genetic profile of INS-metastatic lymph nodes. These findings suggest that markers of malignant behaviour could be identified at the primary site of the disease. Finally, using the REACTOME pathways database, we revealed that an active collagen metabolism, extracellular matrix remodelling, beta-cell differentiation and non-beta-cell trans-differentiation might cause disease progression and hyperinsulinism in INS, identifying major pathways worthy of future research in this currently poorly controlled disease.

Synergistic Highly Potent Targeted Drug Combinations in Different Pheochromocytoma Models Including Human Tumor Cultures

There are no officially approved therapies for metastatic pheochromocytomas apart from ultratrace 131I-metaiodbenzylguanidine therapy, which is approved only in the United States. We have, therefore, investigated the antitumor potential of molecular-targeted approaches in murine pheochromocytoma cell lines [monocyte chemoattractant protein (MPC)/monocyte chemoattractant protein/3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)], immortalized mouse chromaffin Sdhb-/- cells, three-dimensional pheochromocytoma tumor models (MPC/MTT spheroids), and human pheochromocytoma primary cultures. We identified the specific phosphatidylinositol-3-kinase α inhibitor BYL719 and the mammalian target of rapamycin inhibitor everolimus as the most effective combination in all models. Single treatment with clinically relevant doses of BYL719 and everolimus significantly decreased MPC/MTT and Sdhb-/- cell viability. A targeted combination of both inhibitors synergistically reduced MPC and Sdhb-/- cell viability and showed an additive effect on MTT cells. In MPC/MTT spheroids, treatment with clinically relevant doses of BYL719 alone or in combination with everolimus was highly effective, leading to a significant shrinkage or even a complete collapse of the spheroids. We confirmed the synergism of clinically relevant doses of BYL719 plus everolimus in human pheochromocytoma primary cultures of individual patient tumors with BYL719 attenuating everolimus-induced AKT activation. We have thus established a method to assess molecular-targeted therapies in human pheochromocytoma cultures and identified a highly effective combination therapy. Our data pave the way to customized combination therapy to target individual patient tumors.

Overexpression of somatostatin receptor type 2 in neuroendocrine tumors for improved Ga68-DOTATATE imaging and treatment

BACKGROUND

Neuroendocrine tumors are found throughout the body, including the pancreas. These tumors are phenotypically and genetically heterogeneous and can be difficult to accurately image using current imaging standards. However, positron emission tomography/computed tomography with radiolabeled somatostatin analogs has shown clinical success because many neuroendocrine tumors overexpress somatostatin receptor subtype 2. Unfortunately, patients with poorly differentiated neuroendocrine tumors often have a diminished level of somatostatin receptor subtype 2. We found that histone deacetylase inhibitors can upregulate the functional expression of somatostatin receptor subtype 2.

METHODS

We evaluated the effect of histone deacetylase inhibitors on somatostatin receptor subtype 2 expression at the mRNA and protein level in neuroendocrine tumor cell lines. The effect of histone deacetylase inhibitors on surface somatostatin receptor subtype 2 was also investigated by fluorescence-activated cell sorting analysis. Changes in somatostatin receptor subtype 2 expression in neuroendocrine tumor xenografts after treatment were imaged using Ga68-DOTATATE positron emission tomography/computed tomography.

RESULTS

The functional increase of somatostatin receptor subtype 2 in neuroendocrine tumors after histone deacetylase inhibitor treatment was confirmed through in vitro experiments and small animal Ga68-DOTATATE positron emission tomography/computed tomography imaging. Histone deacetylase inhibitors increased somatostatin receptor subtype 2 transcription and protein expression in neuroendocrine tumor cell lines. Small animal Ga68-DOTATATE positron emission tomography/computed tomography imaging confirmed the enhancement of radiopeptide uptake after histone deacetylase inhibitor administration.

CONCLUSION

This study demonstrates a new method to potentially improve imaging and treatments that target somatostatin receptor subtype 2 in neuroendocrine tumors.

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

The mammalian target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling. The PI3K/Akt/mTOR pathway has a pivotal role in the oncogenesis of neuroendocrine tumors (NETs). In addition, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) drive angiogenesis in NETs and therefore contributes to neuroendocrine tumor development. Hence, mTOR and angiogenesis inhibitors have been developed. Everolimus, a first-generation mTOR inhibitor, has shown significant survival benefit in advanced gastroenteropancreatic NETs. Sunitinib, a pan-tyrosine kinase inhibitor that targets the VEGF receptor, has proven to increase progression-free survival in advanced pancreatic NETs. Nevertheless, primary and acquired resistance to rapalogs and sunitinib has limited the clinical benefit for NET patients. Despite the identification of multiple molecular mechanisms of resistance, no predictive biomarker has made it to the clinic. This review is focused on the mTOR signaling and angiogenesis in NET, the molecular mechanisms of primary and acquired resistance to everolimus and sunitinib and how to overcome this resistance by alternative drug compounds.

Simultaneous inhibition of PI3Kα and CDK4/6 synergistically suppresses KRAS-mutated non-small cell lung cancer

Objective

Activating KRAS mutations are the most common drivers in the development of non-small cell lung cancer (NSCLC). However, unsuccess of treatment by direct inhibition of KRAS has been proven. Deregulation of PI3K signaling plays an important role in tumorigenesis and drug resistance in NSCLC. The activity of PI3Kα-selective inhibition against KRAS-mutated NSCLC remains largely unknown.

Methods

Cell proliferation was detected by sulforhodamine B assay. Cell cycle distribution and apoptosis were measured by flow cytometry. Cell signaling was assessed by Western blot and immunohistochemistry. RNA interference was used to down-regulate the expression of cyclin D1. Human NSCLC xenografts were employed to detect therapeutic efficacy in vivo.

Results

CYH33 possessed variable activity against a panel of KRAS-mutated NSCLC cell lines. Although CYH33 blocked AKT phosphorylation in all tested cells, Rb phosphorylation decreased in CYH33-sensitive, but not in CYH33-resistant cells, which was consistent with G1 phase arrest in sensitive cells. Combined treatment with the CDK4/6 inhibitor, PD0332991, and CYH33 displayed synergistic activity against the proliferation of both CYH33-sensitive and CYH33-resistant cells, which was accompanied by enhanced G1-phase arrest. Moreover, down-regulation of cyclin D1 sensitized NSCLC cells to CYH33. Reciprocally, CYH33 abrogated the PD0332991-induced up-regulation of cyclin D1 and phosphorylation of AKT in A549 cells. Co-treatment with these two drugs demonstrated synergistic activity against A549 and H23 xenografts, with enhanced inhibition of Rb phosphorylation.

Conclusions

Simultaneous inhibition of PI3Kα and CDK4/6 displayed synergistic activity against KRAS-mutated NSCLC. These data provide a mechanistic rationale for the combination of a PI3Kα inhibitor and a CDK4/6 inhibitor for the treatment of KRAS-mutated NSCLC.

Effect of combined treatment with a pan-PI3K inhibitor or an isoform-specific PI3K inhibitor and everolimus on cell proliferation in GH-secreting pituitary tumour in an experimental setting

PURPOSE

PI3K/Akt/mTOR pathway activation is common in GH-secreting pituitary tumours, and a target for treatment with mTOR inhibitors, including everolimus (EVE). The current study aimed to evaluate the efficacy of two PI3K inhibitors (PI3Ki), NVP-BKM120 and NVP-BYL719, alone and in combination with EVE in rat GH-secreting pituitary tumour cell line (GH3) and human GH-secreting pituitary tumour cell cultures.

METHODS

In GH3 cell line and in six GH-secreting tumour cell cultures, the effects of PI3Ki and EVE, as single agents and in combination, were tested on cell viability and colony survival, by MTT and clonogenic assay, respectively, whereas western blot was performed to evaluate the underlying intracellular signalling pathways.

RESULTS

PI3Ki and EVE showed a dose-dependent inhibition of cell viability in GH3 cell line, with PI3Ki displaying a synergistic effect when combined with EVE. PI3Ki and EVE inhibited colony survival in GH3 cell line with no further improvement in combination. In GH-secreting pituitary tumour cell cultures PI3Ki are effective in inhibiting cell viability increasing the slight and non significant inhibition induced by EVE as single agent, generally showing a synergistic effect. Despite in both GH3 cell line and GH-secreting pituitary tumour cell cultures combination of PI3Ki enhanced EVE effect, the study of intracellular signalling pathways revealed a different regulation of PI3K/Akt/mTOR and MAPK between the two models.

CONCLUSIONS

The results of the current study demonstrated that PI3Ki, especially in combination with EVE, are effective in inhibiting cell proliferation, therefore representing a promising therapeutic tool for the treatment of aggressive GH-secreting pituitary tumours, not responsive to standard medical therapies.

Molecular features and translational outlook for Epstein-Barr virus-associated gastric cancer

Epstein-Barr Virus (EBV) was the first discovered human tumor virus and is the etiological agent of B cell lymphomas and also epithelial cancers. Indeed, nearly 10% of gastric cancers worldwide are EBV-positive and display unique molecular, epigenetic, and clinicopathological features. EBV-positive gastric cancers display the highest rate of host genome methylation of all tumor types studied and harbor recurrent mutations activating PI3Kα, silencing ARID1A, and amplifying PD-L1. While EBV infection of B cells can be studied efficiently, de novo epithelial cell infection is much more difficult. We propose that new culture models including 3D-based gastric organoids and xenografts can bring new insight into EBV-induced gastric carcinogenesis and will lead to improved precision medicine-based therapies for patients with EBV-positive gastric cancer.

The role of GSK3 and its reversal with GSK3 antagonism in everolimus resistance

Pancreatic neuroendocrine tumors (panNETs) are often inoperable at diagnosis. The mTORC1 inhibitor everolimus has been approved for the treatment of advanced NETs. However, the regular development of resistance to everolimus limits its clinical efficacy. We established two independent everolimus-resistant panNET (BON1) cell lines (BON1 RR1, BON1 RR2) to find potential mechanisms of resistance. After 24 weeks of permanent exposure to 10 nM everolimus, BON1 RR1 and BON1 RR2 showed stable resistance with cellular survival rates of 96.70% (IC₅₀ = 5200 nM) and 92.30% (IC₅₀ = 2500 nM), respectively. The control cell line showed sensitivity to 10 nM everolimus with cellular survival declining to 54.70% (IC₅₀ = 34 nM). Both resistant cell lines did not regain sensitivity over time and showed persistent stable resistance after a drug holiday of 13 weeks. The mechanisms of resistance in our cell line model included morphological adaptations, G1 cell cycle arrest associated with reduced CDK1(cdc2) expression and decreased autophagy. Cellular migration potential was increased and indirectly linked to c-Met activation. GSK3 was over-activated in association with reduced baseline IRS-1 protein levels. Specific GSK3 inhibition strongly decreased BON1 RR1/RR2 cell survival. The combination of everolimus with the PI3Kα inhibitor BYL719 re-established everolimus sensitivity through GSK3 inhibition and restoration of autophagy. We suggest that GSK3 over-activation combined with decreased baseline IRS-1 protein levels and decreased autophagy may be a crucial feature of everolimus resistance, and hence, a possible therapeutic target.

Context-dependent expression of a conditionally-inducible form of active Akt

Akt kinases are key signaling components in proliferation-competent and post-mitotic cells. Here, we sought to create a conditionally-inducible form of active Akt for both in vitro and in vivo applications. We fused a ligand-responsive Destabilizing Domain (DD) derived from E. coli dihydrofolate reductase to a constitutively active mutant form of Akt1, Akt(E40K). Prior work indicated that such fusion proteins may be stabilized and induced by a ligand, the antibiotic Trimethoprim (TMP). We observed dose-dependent, reversible induction of both total and phosphorylated/active DD-Akt(E40K) by TMP across several cellular backgrounds in culture, including neurons. Phosphorylation of FoxO4, an Akt substrate, was significantly elevated after DD-Akt(E40K) induction, indicating the induced protein was functionally active. The induced Akt(E40K) protected cells from apoptosis evoked by serum deprivation and was neuroprotective in two cellular models of Parkinson's disease (6-OHDA and MPP⁺ exposure). There was no significant protection without induction. We also evaluated Akt(E40K) induction by TMP in mouse substantia nigra and striatum after neuronal delivery via an AAV1 adeno-associated viral vector. While there was significant induction in striatum, there was no apparent induction in substantia nigra. To explore the possible basis for this difference, we examined DD-Akt(E40K) induction in cultured ventral midbrain neurons. Both dopaminergic and non-dopaminergic neurons in the cultures showed DD-Akt(E40K) induction after TMP treatment. However, basal DD-Akt(E40K) expression was 3-fold higher for dopaminergic neurons, resulting in a significantly lower induction by TMP in this population. Such findings suggest that dopaminergic neurons may be relatively inefficient in protein degradation, a property that could relate to their lack of apparent DD-Akt(E40K) induction in vivo and to their selective vulnerability in Parkinson's disease. In summary, we generated an inducible, biologically active form of Akt. The degree of inducibility appears to reflect cellular context that will inform the most appropriate applications for this and related reagents.

Co-administration of iRGD with peptide HPRP-A1 to improve anticancer activity and membrane penetrability

To improve the specificity and penetration of anticancer peptides against tumors, in this study, we examined the effects of co-administration of the membrane-active peptide HPRP-A1 and the tumor homing/penetrating peptide iRGD. iRGD peptide is widely recognized as an efficient cell membrane penetration peptide targeting to αvβ3 integrins and neuropilin-1 (NRP-1) receptors, which show high expression in many tumor cells. The anticancer activity, cancer specificity and penetration activity in vitro and in vivo of the co-administered peptides were examined on 2D monolayer cells, 3D multi-cellular spheroids (MCS) and xenograft nude mice. Co-administration of iRGD and HPRP-A1 exhibited stronger anticancer activity and tumor specificity against A549 non-small cell lung cancer cells with NRP-1 receptor overexpression compared with HPRP-A1 alone. A549 cells showed uptake of the peptide combination and destruction of the integrity of the cell membrane, as well as adherence to the mitochondrial net, resulting in induction of apoptosis by a caspase-dependent pathway. The iRGD peptide dramatically increased the penetration depth of HPRP-A1 on A549 MCS and anticancer efficacy in an A549 xenograft mouse model. Our results suggest that the co-administration strategy of anticancer and penetrating peptides could be a potential therapeutic approach for cancer treatment in clinical practice.

Targeted therapy of gastroenteropancreatic neuroendocrine tumours: preclinical strategies and future targets

Molecular targeted therapy of advanced neuroendocrine tumours (NETs) of the gastroenteropancreatic (GEP) system currently encompasses approved therapy with the mammalian target of rapamycin (mTOR) inhibitor everolimus and the multi-tyrosinkinase inhibitor sunitinib. However, clinical efficacy of these treatment strategies is limited by low objective response rates and limited progression-free survival due to tumour resistance. Further novel strategies for molecular targeted therapy of NETs of the GEP system are needed. This paper reviews preclinical research models and signalling pathways in NETs of the GEP system. Preclinical and early clinical data on putative novel targets for molecular targeted therapy of NETs of the GEP system are discussed, including PI3K, Akt, mTORC1/mTORC2, GSK3, c-Met, Ras-Raf-MEK-ERK, embryogenic pathways (Hedgehog, Notch, Wnt/beta-catenin, TGF-beta signalling and SMAD proteins), tumour suppressors and cell cycle regulators (p53, cyclin-dependent kinases (CDKs) CDK4/6, CDK inhibitor p27, retinoblastoma protein (Rb)), heat shock protein HSP90, Aurora kinase, Src kinase family, focal adhesion kinase and epigenetic modulation by histone deacetylase inhibitors.