Selective but not pan-CDK inhibition abrogates 5-FU-driven tissue factor upregulation in colon cancer

Thromboembolic events are complications in cancer patients and hypercoagulability has been linked to the tissue factor (TF) pathway, making this an attractive target. Here, we investigated the effects of chemotherapeutics and CDK inhibitors (CDKI) abemaciclib/palbociclib (CDK4/6), THZ-1 (CDK7/12/13), and dinaciclib (CDK1/2/5/9) alone and in combination regimens on TF abundance and coagulation. The human colorectal cancer (CRC) cell line HROC173 was treated with 5-FU or gemcitabine to stimulate TF expression. TF+ cells were sorted, recultured, and re-analyzed. The effect of treatment alone or in combination was assessed by functional assays. Low-dose chemotherapy induced a hypercoagulable state and significantly upregulated TF, even after reculture without treatment. Cells exhibited characteristics of epithelial-mesenchymal transition, including high expression of vimentin and mucin. Dinaciclib and THZ-1 also upregulated TF, while abemaciclib and palbociclib downregulated it. Similar results were observed in coagulation assays. The same anticoagulant activity of abemaciclib was seen after incubation with peripheral immune cells from healthy donors and CRC patients. Abemaciclib reversed 5-FU-induced TF upregulation and prolonged clotting times in second-line treatment. Effects were independent of cytotoxicity, senescence, and p27kip1 induction. TF-antibody blocking experiments confirmed the importance of TF in plasma coagulation, with Factor XII playing a minor role. Short-term abemaciclib counteracts 5-FU-induced hypercoagulation and eventually even prevents thromboembolic events.

p16 overexpression identifies oncogenic high-risk HPV infection in non-oropharyngeal squamous cell carcinoma of the head and neck

BACKGROUND

Human papillomavirus (HPV) is an increasing risk factor for cancer. HPV-associated oropharyngeal squamous cell carcinoma (OPSCC) is associated with a favorable outcome. Blockstaining for p16 is a surrogate marker for HPV+ OPSCC. In oral and laryngeal squamous cell carcinoma (OSCC/LSCC), the relevance of p16 immunohistochemistry, alone or in combination with other cell cycle-related proteins, to identify HPV-driven non-OPSCC is less well understood.

METHODS

We stained for p16, pRb, cyclin D1, and p53 in 327 HNSCC. In 310 OPSCC, HPV-status was assessed by HPV DNA PCR. In 119 non-OPSCC, RNA in situ hybridization was additionally performed. HPV-status was correlated with staining patterns, p53 and clinical data.

RESULTS

The OPSCC showed blockstaining for p16 in 36%, 8% were equivocal. Of these, HPV-testing was performed in 57%, and 53% were positive for HPV DNA. HPV-association correlated with absence of pRb and cyclin D1 and favorable outcome. In non-OPSCC, 18% showed p16-blockstaining, and 13% showed E6/E7 RNA. Six of seven HPV+ OSCC and 8/8 LSCC lost pRb and cyclin D1. Compared to HPV-negative counterparts, patients with HPV+ cancers had lower rates of alcohol consumption and keratinizing morphology. HPV-positive OSCC had a longer overall survival (p < 0.05). HPV subtype 16 was the most common.

CONCLUSIONS

We conclude that HPV-positive non-OPSCC are associated with p16 overexpression and low levels of pRb and cyclin D1. High expression of pRb and cyclin D1 indicates HPV-negativity.

Knockdown of coagulation factor VII has potential anticoagulant and anti-inflammatory effects in a mouse model of group A streptococcal sepsis

Infections originating from subcutaneous tissues are among the most common invasive infections caused by group A streptococcus (GAS) and associated with systemic coagulation activation. The role of intrinsic coagulation factors on GAS virulence has recently been determined, but the role of the extrinsic coagulation factor VII is unknown. Using a mouse model, in which GAS-sepsis emerges from a subcutaneous infection, we show that FVII is a negative acute phase protein. F7 knockdown using antisense oligonucleotides resulted in an attenuated systemic coagulation activation and inflammatory response in septic animals. The findings indicate FVII's ability to modify the host response.

Molecular Determinants of Calcitriol Signaling and Sensitivity in Glioma Stem-like Cells

Glioblastoma is the most common primary brain cancer in adults and represents one of the worst cancer diagnoses for patients. Suffering from a poor prognosis and limited treatment options, tumor recurrences are virtually inevitable. Additionally, treatment resistance is very common for this disease and worsens the prognosis. These and other factors are hypothesized to be largely due to the fact that glioblastoma cells are known to be able to obtain stem-like traits, thereby driving these phenotypes. Recently, we have shown that the in vitro and ex vivo treatment of glioblastoma stem-like cells with the hormonally active form of vitamin D3, calcitriol (1α,25(OH)2-vitamin D3) can block stemness in a subset of cell lines and reduce tumor growth. Here, we expanded our cell panel to over 40 different cultures and can show that, while half of the tested cell lines are sensitive, a quarter can be classified as high responders. Using genetic and proteomic analysis, we further determined that treatment success can be partially explained by specific polymorphism of the vitamin D3 receptor and that high responders display a proteome suggestive of blockade of stemness, as well as migratory potential.

Establishing safe high hydrostatic pressure devitalization thresholds for autologous head and neck cancer vaccination and reconstruction

High hydrostatic pressure specifically devitalizes cells and tissues without major changes in their molecular structure. Hence, high hydrostatic pressure may enhance the development of whole-cell anti-tumor vaccines, representing tumor heterogeneity and thus (neo-) antigen diversity. Moreover, safe devitalization of tumor-infiltrated supporting tissue may facilitate reimplantation for functional reconstruction. However, precise high hydrostatic pressure thresholds for safe cancer cell killing are unknown. Here, we show that high hydrostatic pressure of at least 450 MPa is necessary to safely devitalize head and neck squamous cell cancer. A pressure of 300 MPa, which has been used frequently in cancer vaccine preparation, resulted in partial devitalization with 27% live cells in flow cytometry and 4% remaining autofluorescence in cell culture after one week. The remaining cells could form vital tumors in the chorioallantoic membrane assay. In contrast, 450 MPa killed all cells in vitro and prevented tumor outgrowth in ovo. The effectiveness of 450 MPa was attributed to the induction of DNA double-strand breaks, independent of apoptosis, autophagy, or methuosis. Furthermore, 450 MPa continued to induce immunogenic cell death. Our results demonstrate that 450 MPa of high hydrostatic pressure induces safe and sustained devitalization of head and neck cancer cells and tissues. Because of the heterogeneity in pressure resistance, we propose our approach as a starting point for determining the precise thresholds for other cancer entities. Further studies on head and neck cancer should focus on immunological co-cultures, combinations of immune checkpoint inhibition, and accurate anatomical reconstruction with pressure-treated autografts.

Short-term immune-checkpoint inhibition partially rescues perturbed bone marrow hematopoiesis in mismatch-repair deficient tumors

Wide-spread cancer-related immunosuppression often curtails immune-mediated antitumoral responses. Immune-checkpoint inhibitors (ICIs) have become a state-of-the-art treatment modality for mismatch repair-deficient (dMMR) tumors. Still, the impact of ICI-treatment on bone marrow perturbations is largely unknown. Using anti-PD1 and anti-LAG-3 ICI treatments, we here investigated the effect of bone marrow hematopoiesis in tumor-bearing Msh2loxP/loxP;TgTg(Vil1-cre) mice. The OS under anti-PD1 antibody treatment was 7.0 weeks (vs. 3.3 weeks and 5.0 weeks, control and isotype, respectively). In the anti-LAG-3 antibody group, OS was 13.3 weeks and thus even longer than in the anti-PD1 group (p = 0.13). Both ICIs induced a stable disease and reduced circulating and splenic regulatory T cells. In the bone marrow, a perturbed hematopoiesis was identified in tumor-bearing control mice, which was partially rescued by ICI treatment. In particular, B cell precursors and innate lymphoid progenitors were significantly increased upon anti-LAG-3 therapy to levels seen in tumor-free control mice. Additional normalizing effects of ICI treatment were observed for lin-c-Kit+IRF8+ hematopoietic stem cells, which function as a "master" negative regulator of the formation of polymorphonuclear-myeloid-derived suppressor cell generation. Accompanying immunofluorescence on the TME revealed significantly reduced numbers of CD206+F4/80+ and CD163+ tumor-associated M2 macrophages and CD11b+Gr1+ myeloid-derived suppressor cells especially upon anti-LAG-3 treatment. This study confirms the perturbed hematopoiesis in solid cancer. Anti-LAG-3 treatment partially restores normal hematopoiesis. The interference of anti-LAG-3 with suppressor cell populations in otherwise inaccessible niches renders this ICI very promising for subsequent clinical application.

Chemotherapeutics Used for High-Risk Neuroblastoma Therapy Improve the Efficacy of Anti-GD2 Antibody Dinutuximab Beta in Preclinical Spheroid Models

Anti-disialoganglioside GD2 antibody ch14.18/CHO (dinutuximab beta, DB) improved the outcome of patients with high-risk neuroblastoma (HR-NB) in the maintenance phase. We investigated chemotherapeutic compounds used in newly diagnosed patients in combination with DB. Vincristine, etoposide, carboplatin, cisplatin, and cyclophosphamide, as well as DB, were used at concentrations achieved in pediatric clinical trials. The effects on stress ligand and checkpoint expression by neuroblastoma cells and on activation receptors of NK cells were determined by using flow cytometry. NK-cell activity was measured with a CD107a/IFN-γ assay. Long-term cytotoxicity was analyzed in three spheroid models derived from GD2-positive neuroblastoma cell lines (LAN-1, CHLA 20, and CHLA 136) expressing a fluorescent near-infrared protein. Chemotherapeutics combined with DB in the presence of immune cells improved cytotoxic efficacy up to 17-fold compared to in the controls, and the effect was GD2-specific. The activating stress and inhibitory checkpoint ligands on neuroblastoma cells were upregulated by the chemotherapeutics up to 9- and 5-fold, respectively, and activation receptors on NK cells were not affected. The CD107a/IFN-γ assay revealed no additional activation of NK cells by the chemotherapeutics. The synergistic effect of DB with chemotherapeutics seems primarily attributed to the combined toxicity of antibody-dependent cellular cytotoxicity and chemotherapy, which supports further clinical evaluation in frontline induction therapy.

CDK4/6 blockade provides an alternative approach for treatment of mismatch-repair deficient tumors

Mismatch repair-deficient (dMMR) tumors show a good response toward immune checkpoint inhibitors (ICI), but developing resistance impairs patients’ outcomes. Here, we compared the therapeutic potential of an α-PD-L1 antibody with the CDK4/6 inhibitor abemaciclib in two preclinical mouse models of dMMR cancer, focusing on immune-modulatory effects of either treatment. Abemaciclib monotherapy significantly prolonged overall survival of Mlh1^−/− and Msh2^{loxP/loxP;TgTg(Vil1-cre)} mice (Mlh1^−/−: 14.5 wks vs. 9.0 wks (α-PD-L1), and 3.5 wks (control); Msh2^{loxP/loxP;TgTg(Vil1-cre)}: 11.7 wks vs. 9.6 wks (α-PD-L1), and 2.0 wks (control)). The combination was not superior to either monotherapy. PET/CT imaging revealed individual response profiles, with best clinical responses seen with abemaciclib mono- and combination therapy. Therapeutic effects were accompanied by increasing numbers of tumor-infiltrating CD4⁺/CD8⁺ T-cells and lower numbers of M2-macrophages. Levels of T cell exhaustion markers and regulatory T cell counts declined. Expression analysis identified higher numbers of dendritic cells and neutrophils within tumors together with high expression of DNA damage repair genes as part of the global stress response. In Mlh1^−/− tumors, abemaciclib suppressed the PI3K/Akt pathway and led to induction of Mxd4/Myc. The immune-modulatory potential of abemaciclib renders this compound ideal for dMMR patients not eligible for ICI treatment.

Procoagulant Activity of Blood and Microvesicles Is Disturbed by Pneumococcal Pneumolysin, Which Interacts with Coagulation Factors

The coagulation and contact systems are parts of the innate immune system as they prevent bleeding and dissemination of pathogens and also contribute to microbial killing by inflammatory reactions and the release of antimicrobial peptides. Here, we investigated the influence of Streptococcus pneumoniae on the coagulation and contact system. S. pneumoniae (pneumococci), but no other investigated streptococcal species, impairs coagulation of blood by autolysis and release of pneumolysin. Defective blood coagulation results from the lysis of tissue factor-producing mononuclear cells and their procoagulant microvesicles, which are the main trigger for blood coagulation during sepsis. In addition, pneumolysin binds coagulation and contact system factors, but this does not result in activation. Thus, pneumococci modulate activation of the coagulation system by releasing pneumolysin, which could potentiate lung injury during pneumonia.

Global metabolic alterations in colorectal cancer cells during irinotecan-induced DNA replication stress

BACKGROUND

Metabolic adaptations can allow cancer cells to survive DNA-damaging chemotherapy. This unmet clinical challenge is a potential vulnerability of cancer. Accordingly, there is an intense search for mechanisms that modulate cell metabolism during anti-tumor therapy. We set out to define how colorectal cancer CRC cells alter their metabolism upon DNA replication stress and whether this provides opportunities to eliminate such cells more efficiently.

METHODS

We incubated p53-positive and p53-negative permanent CRC cells and short-term cultured primary CRC cells with the topoisomerase-1 inhibitor irinotecan and other drugs that cause DNA replication stress and consequently DNA damage. We analyzed pro-apoptotic mitochondrial membrane depolarization and cell death with flow cytometry. We evaluated cellular metabolism with immunoblotting of electron transport chain (ETC) complex subunits, analysis of mitochondrial mRNA expression by qPCR, MTT assay, measurements of oxygen consumption and reactive oxygen species (ROS), and metabolic flux analysis with the Seahorse platform. Global metabolic alterations were assessed using targeted mass spectrometric analysis of extra- and intracellular metabolites.

RESULTS

Chemotherapeutics that cause DNA replication stress induce metabolic changes in p53-positive and p53-negative CRC cells. Irinotecan enhances glycolysis, oxygen consumption, mitochondrial ETC activation, and ROS production in CRC cells. This is connected to increased levels of electron transport chain complexes involving mitochondrial translation. Mass spectrometric analysis reveals global metabolic adaptations of CRC cells to irinotecan, including the glycolysis, tricarboxylic acid cycle, and pentose phosphate pathways. P53-proficient CRC cells, however, have a more active metabolism upon DNA replication stress than their p53-deficient counterparts. This metabolic switch is a vulnerability of p53-positive cells to irinotecan-induced apoptosis under glucose-restricted conditions.

CONCLUSION

Drugs that cause DNA replication stress increase the metabolism of CRC cells. Glucose restriction might improve the effectiveness of classical chemotherapy against p53-positive CRC cells. The topoisomerase-1 inhibitor irinotecan and other chemotherapeutics that cause DNA damage induce metabolic adaptations in colorectal cancer (CRC) cells irrespective of their p53 status. Irinotecan enhances the glycolysis and oxygen consumption in CRC cells to deliver energy and biomolecules necessary for DNA repair and their survival. Compared to p53-deficient cells, p53-proficient CRC cells have a more active metabolism and use their intracellular metabolites more extensively. This metabolic switch creates a vulnerability to chemotherapy under glucose-restricted conditions for p53-positive cells.

Implementation of a combined CDK inhibition and arginine-deprivation approach to target arginine-auxotrophic glioblastoma multiforme cells

Constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy are hallmarks of Glioblastoma multiforme (GBM). The latter metabolic defect renders tumor cells vulnerable to arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards SpyADI as well as CDK inhibitors (CDKis). To improve therapeutic effects, we here applied a combined approach based on SpyADI and CDKis (dinaciclib, abemaciclib). Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D and effects of this combined SpyADI/CDKi approach were analyzed in-depth. All CDKi/SpyADI combinations yielded synergistic antitumoral effects, especially when given sequentially (SEQ), i.e., CDKi in first-line and most pronounced in the 3D models. SEQ application demonstrated impaired cell proliferation, invasiveness, and viability. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate and extracellular acidification rate after SpyADI/abemaciclib monotherapy or its combination regimens. The combined treatment even induced autophagy in target cells (abemaciclib/SpyADI > dinaciclib/SpyADI). By contrast, the unfolded protein response and p53/p21 induced senescence played a minor role. Transmission electron microscopy confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2 and induced expression changes of genes involved in cellular/cytoskeletal integrity. This study highlights the strong antitumoral potential of a combined arginine deprivation and CDK inhibition approach via complex effects on mitochondrial dysfunction, invasiveness as well as DNA-damage response. This provides a good starting point for further in vitro and in vivo proof-of-concept studies to move forward with this strategy.

HGG-13. Combined CDK inhibition and arginine-deprivation as targeted therapy for arginine-auxotrophic glioblastoma multiforme cells

INTRODUCTION/BACKGROUND: Glioblastoma multiforme show constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy. This renders tumor cells vulnerable towards arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards administration of SpyADI as well as CDK inhibitors (CDKis). To improve effects, we applied a sequential (SEQ) CDKi/SpyADI approach to examine mechanistic insights and drug susceptibility. MATERIALS AND METHODS: Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D (spheres and glioma stem-like cells (GSC)) and effects of this combined CDKi/SpyADI approach were analyzed. This included viability staining via Calcein AM in 2D and 3D-Glo in 3D culture and cell death analysis via flow cytometry. Therapy-induced morphological changes were identified with transmission electron microscopy (TEM). Besides, 3D-invasiveness, cellular stress, and DNA damage responses were measured. RESULTS: All SEQ-CDKi/SpyADI combinations yielded synergistic antitumoral effects, characterized by impaired cell proliferation, invasiveness, and viability. Notably, this SEQ-CDKi/SpyADI approach was most effective in 3D models. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate along with extracellular acidification rate after abemaciclib/SpyADI monotherapy or its combination regimens. TEM confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and SEQ- CDKi/SpyADI combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2. CONCLUSION: This study highlights the antitumoral potential of a combined SpyADI/CDKi approach. We show that sequential application of these substances has complex effects on mitochondrial dysfunction, invasiveness, and DNA-damage response. This provides a good starting point for further proof-of-concept studies to move forward with this strategy.

Preclinical Head and Neck Squamous Cell Carcinoma Models for Combined Targeted Therapy Approaches

This study aimed to refine combined targeted approaches on well-characterized, low-passage tumor models. Upon in vivo xenografting in immunodeficient mice, three cell lines from locally advanced or metastatic HNSCC were established. Following quality control and basic characterization, drug response was examined after therapy with 5-FU, Cisplatin, and cyclin-dependent kinase inhibitors (abemaciclib, THZ1). Our cell lines showed different in vitro growth kinetics, morphology, invasive potential, and radiosensitivity. All cell lines were sensitive to 5-FU, Cisplatin, and THZ1. One cell line (HNSCC48 P0 M1) was sensitive to abemaciclib. Here, Cyto-FISH revealed a partial CDKN2a deletion, which resulted from a R58* mutation. Moreover, this cell line demonstrated chromosome 12 polysomy, accompanied by an increase in CDK4-specific copy numbers. In HNSCC16 P1 M1, we likewise identified polysomy-associated CDK4-gains. Although not sensitive to abemaciclib per se, the cell line showed a G1-arrest, an increased number of acidic organelles, and a swollen structure. Notably, intrinsic resistance was conquered by Cisplatin because of cMYC and IDO-1 downregulation. Additionally, this Cisplatin-CDKI combination induced HLA-ABC and PD-L1 upregulation, which may enhance immunogenicity. Performing functional and molecular analysis on patient-individual HNSCC-models, we identified CDK4-gains as a biomarker for abemaciclib response prediction and describe an approach to conquer intrinsic CDKI resistance.

PEGylation increases antitumoral activity of arginine deiminase of Streptococcus pyogenes

Abstract

Arginine auxotrophy is a metabolic defect that renders tumor cells vulnerable towards arginine-depleting substances, such as arginine deiminase (ADI) from Streptococcus pyogenes (SpyADI). Previously, we confirmed SpyADI susceptibility on patient-derived glioblastoma multiforme (GBM) models in vitro and in vivo. For application in patients, serum half-life of the enzyme has to be increased and immunogenicity needs to be reduced. For this purpose, we conjugated the S. pyogenes-derived SpyADI with 20 kDa polyethylene glycol (PEG20) moieties, achieving a PEGylation of seven to eight of the 26 accessible primary amines of the SpyADI. The PEGylation reduced the overall activity of the enzyme by about 50% without affecting the Michaelis constant for arginine. PEGylation did not increase serum stability of SpyADI in vitro, but led to a longer-lasting reduction of plasma arginine levels in mice. Furthermore, SpyADI-PEG20 showed a higher antitumoral capacity towards GBM cells in vitro than the native enzyme.

Key points

• PEGylation has no effect on the affinity of SpyADI for arginine

• PEGylation increases the antitumoral effects of SpyADI on GBM in vitro

• PEGylation prolongs plasma arginine depletion by SpyADI in mice

Long-term survivor of metastatic squamous-cell head and neck carcinoma with occult primary after cetuximab-based chemotherapy: A case report

BACKGROUND

Cancer of unknown primary (CUP) is a histological proven malignant tumor whose origin cannot be detected despite careful examination. Most cervical lymph node metastases in CUP (80%) will originate from head and neck sites, and 15% show infiltration of squamous carcinoma cells. The survival rates of CUP are poor: The 5-year-survival rate ranges from 10% to 15%. First-line treatment recommendation for advanced, inoperable squamous cell carcinoma of head/neck (HNSCC) was cetuximab plus platinum-fluorouracil chemotherapy until recently, when checkpoint inhibitors proved clinically beneficial therapies.

CASE SUMMARY

Here, we report a case of a 42-year-old female patient with cervical and abdominal lymph node and distant bone metastases of an occult primary of the head and neck (squamous cell carcinoma, human papillomavirus positive). The cancer was diagnosed during pregnancy 10 years ago, and after giving birth, the patient was treated with cetuximab plus platinum-fluorouracil chemotherapy achieving complete remission (CR). CR lasted 26 mo when new metastases (abdominal lymph node, lumbar vertebral body) emerged. Both manifestations were irradiated. From then on, the patient has not received any further treatment, and her disease has remained controlled. Ten years after the initial cancer diagnosis, the patient is still alive and in good health, representing an exceptional case of HNSCC.

CONCLUSION

This case illustrates the exceptional clinical course and benefits of combined therapy approaches in advanced metastatic HNSCC with occult primary.

Establishment and characterization of patient-derived head and neck cancer models from surgical specimens and endoscopic biopsies

Background

Head and neck squamous cell carcinoma (HNSCC) is heterogeneous in etiology, phenotype and biology. Patient-derived xenografts (PDX) maintain morphology and molecular profiling of the original tumors and have become a standard “Avatar” model for human cancer research. However, restricted availability of tumor samples hindered the widespread use of PDX. Most PDX-projects include only surgical specimens because reliable engraftment from biopsies is missing. Therefore, sample collection is limited and excludes recurrent and metastatic, non-resectable cancer from preclinical models as well as future personalized medicine.

Methods

This study compares the PDX-take rate, -growth, histopathology, and molecular characteristics of endoscopic specimens with surgical specimens. HNSCC samples (n = 55) were collected ad hoc, fresh frozen and implanted into NOD.Cg-Prkdc^scidIl2rg^tm1Wjl/SzJ mice.

Results

Engraftment was successful in both sample types. However, engraftment rate was lower (21 vs. 52%) and growth delayed (11.2 vs. 6.7 weeks) for endoscopic biopsies. Following engraftment, growth kinetic was similar. Comparisons of primary tumors and corresponding PDX models confirmed preservation of histomorphology (HE histology) and molecular profile (Illumina Cancer Hotspot Panel) of the patients’ tumors. Accompanying flow cytometry on primary tumor specimens revealed a heterogeneous tumor microenvironment among individual cases and identified M2-like macrophages as positive predictors for engraftment. Vice versa, a high PD-L1 expression (combined positive score on tumor/immune cells) predicted PDX rejection.

Conclusion

Including biopsy samples from locally advanced or metastatic lesions from patients with non-surgical treatment strategies, increases the availability of PDX for basic and translational research. This facilitates (pre-) clinical studies for individual response prediction based on immunological biomarkers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02047-w.

The Individual Effects of Cyclin-Dependent Kinase Inhibitors on Head and Neck Cancer Cells-A Systematic Analysis

Cyclin-dependent kinase inhibitors (CDKi´s) display cytotoxic activity against different malignancies, including head and neck squamous cell carcinomas (HNSCC). By coordinating the DNA damage response, these substances may be combined with cytostatics to enhance cytotoxicity. Here, we investigated the influence of different CDKi´s (palbociclib, dinaciclib, THZ1) on two HNSCC cell lines in monotherapy and combination therapy with clinically-approved drugs (5-FU, Cisplatin, cetuximab). Apoptosis/necrosis, cell cycle, invasiveness, senescence, radiation-induced γ-H2AX DNA double-strand breaks, and effects on the actin filament were studied. Furthermore, the potential to increase tumor immunogenicity was assessed by analyzing Calreticulin translocation and immune relevant surface markers. Finally, an in vivo mouse model was used to analyze the effect of dinaciclib and Cisplatin combination therapy. Dinaciclib, palbociclib, and THZ1 displayed anti-neoplastic activity after low-dose treatment, while the two latter substances slightly enhanced radiosensitivity. Dinaciclib decelerated wound healing, decreased invasiveness, and induced MHC-I, accompanied by high amounts of surface-bound Calreticulin. Numbers of early and late apoptotic cells increased initially (24 h), while necrosis dominated afterward. Antitumoral effects of the selective CDKi palbociclib were weaker, but combinations with 5-FU potentiated effects of the monotherapy. Additionally, CDKi and CDKi/chemotherapy combinations induced MHC I, indicative of enhanced immunogenicity. The in vivo studies revealed a cell line-specific response with best tumor growth control in the combination approach. Global acting CDKi's should be further investigated as targeting agents for HNSCC, either individually or in combination with selected drugs. The ability of dinaciclib to increase the immunogenicity of tumor cells renders this substance a particularly interesting candidate for immune-based oncological treatment regimens.

Cyclin-dependent kinase inhibitors exert distinct effects on patient-derived 2D and 3D glioblastoma cell culture models

Current therapeutic approaches have met limited clinical success for glioblastoma multiforme (GBM). Since GBM harbors genomic alterations in cyclin-dependent kinases (CDKs), targeting these structures with specific inhibitors (CDKis) is promising. Here, we describe the antitumoral potential of selective CDKi on low-passage GBM 2D- and 3D models, cultured as neurospheres (NSCs) or glioma stem-like cells (GSCs). By applying selective CDK4/6i abemaciclib and palbociclib, and the more global CDK1/2/5/9-i dinaciclib, different effects were seen. Abemaciclib and dinaciclib significantly affected viability in 2D- and 3D models with clearly visible changes in morphology. Palbociclib had weaker and cell line-specific effects. Motility and invasion were highly affected. Abemaciclib and dinaciclib additionally induced senescence. Also, mitochondrial dysfunction and generation of mitochondrial reactive oxygen species (ROS) were seen. While autophagy was predominantly visible after abemaciclib treatment, dinaciclib evoked γ-H2AX-positive double-strand breaks that were boosted by radiation. Notably, dual administration of dinaciclib and abemaciclib yielded synergistic effects in most cases, but the simultaneous combination with standard chemotherapeutic agent temozolomide (TMZ) was antagonistic. RNA-based microarray analysis showed that gene expression was significantly altered by dinaciclib: genes involved in cell-cycle regulation (different CDKs and their cyclins, SMC3), mitosis (PLK1, TTK), transcription regulation (IRX3, MEN1), cell migration/division (BCAR1), and E3 ubiquitination ligases (RBBP6, FBXO32) were downregulated, whereas upregulation was seen in genes mediating chemotaxis (CXCL8, IL6, CCL2), and DNA-damage or stress (EGR1, ARC, GADD45A/B). In a long-term experiment, resistance development was seen in 1/5 cases treated with dinaciclib, but this could be prevented by abemaciclib. Vice versa, adding TMZ abrogated therapeutic effects of dinaciclib and growth was comparable to controls. With this comprehensive analysis, we confirm the therapeutic activity of selective CDKi in GBM. In addition to the careful selection of individual drugs, the timing of each combination partner needs to be considered to prevent resistance.

Cyclin-dependent kinase inhibitors in head and neck cancer and glioblastoma-backbone or add-on in immune-oncology?

Cyclin-dependent kinases (CDK) control the cell cycle and play a crucial role in oncogenesis. Pharmacologic inhibition of CDK has contributed to the recent clinical approval of dual CDK4/6 inhibitors for the treatment of breast and small cell lung cancer. While the anticancer cell effects of CDK inhibitors are well-established, preclinical and early clinical studies describe additional mechanisms of action such as chemo- and radiosensitization or immune stimulation. The latter offers great potential to incorporate CDK inhibitors in immune-based treatments. However, dosing schedules and accurate timing of each combination partner need to be respected to prevent immune escape and resistance. In this review, we provide a detailed summary of CDK inhibitors in the two solid cancer types head and neck cancer and glioblastoma multiforme; it describes the molecular mechanisms of response vs. resistance and covers strategies to avoid resistance by the combination of immunotherapy or targeted therapy.

HGG-07. CYCLIN-DEPENDENT KINASES AS TARGET STRUCTURES FOR CANCER THERAPY – A COMPARATIVE IN VITRO ANALYSIS ON PATIENT-DERIVED GLIOBLASTOMA CELL CULTURE MODELS

INTRODUCTION

Current therapeutic approaches have limited clinical success for Glioblastoma patients, making novel strategies urgent. Cyclin-dependent kinases (CDK) are crucial in cell cycle, oncogenic transcription, DNA repair, and stem-cell renewal. Glioma cells frequently show genomic alterations in CDKs. Here, we evaluated the antitumoral activity of selective CDK inhibitors (CDKI) abemaciclib (CDK4/6), palbociclib (CDK4/6), and dinaciclib (CDK1/2/5/9) alone and in combination with chemo-/radiotherapy. MATERIALS/

METHODS

Low passage glioblastoma cell lines (N=5) with different molecular characteristics were cultured in 2D and 3D (neurospheroids (NSPs), glioma stem-cells (GSCs). The impact of CDKI alone or in combination with TMZ and radiation (2Gy) was examined. Viability was measured using Calcein-AM and 3D-Glo assays; DNA double-strand breaks by γ-H2AX immunofluorescence. Functional analyses were performed from a 2D culture (72h treatment).

RESULTS

Dinaciclib significantly affected viability of GBM cell lines even shortly after low-dose treatment. CDK 4/6 inhibitors were less effective. Abemaciclib and dinaciclib acted radio-sensitizing. Dinaciclib combined with different substances (72h, dose: IC₂₀), synergistically potentiated antitumoral effects. In a scratch assay, abemaciclib decelerated wound healing; dinaciclib even induced cell death. Microarray analysis revealed altered gene expression: Genes mediating cell adhesion, division, DNA-binding, apoptosis (Casp3,Casp8), senescence (ASF1A,CENPA,FBXO31), and autophagy (ATG4D,ATG2A,SOGA1) were upregulated. Chemotaxis-mediating (CXCL8,CCL20) and proto-oncogenes like JUNB and FOS were strongly down-regulated. Long-term treatment induced dinaciclib resistance in 1/5 cases, and none abemaciclib-treated cells. This was reversed when dinaciclib was combined with TMZ.

CONCLUSION

Our results demonstrate strong anti-GBM activity of dinaciclib and abemaciclib, with additive effects of chemotherapy and radiosensitization, encouraging to move forward this strategy.

In vivo vaccination with cell line-derived whole tumor lysates: neoantigen quality, not quantity matters

BACKGROUND

Cancer vaccines provide a complex source of neoantigens. Still, increasing evidence reveals that the neoantigen quality rather than the quantity is predictive for treatment outcome.

METHODS

Using the preclinical Mlh1^-/- tumor model, we performed a side-by side comparison of two autologous cell-line derived tumor lysates (namely 328 and A7450 T1 M1) harboring different tumor mutational burden (TMB; i.e. ultra-high: 328; moderate-high: A7450 T1 M1). Mice received repetitive prophylactic or therapeutic applications of the vaccine. Tumor incidence, immune responses and tumor microenvironment was examined.

RESULTS

Both tumor cell lysates delayed tumor formation in the prophylactic setting, with the A7450 T1 M1 lysate being more effective in decelerating tumor growth than the 328 lysate (median overall survival: 37 vs. 25 weeks). Comparable results were achieved in therapeutic setting and could be traced back to antigen-driven immune stimulation. Reactive T cells isolated from A7450 T1 M1-treated mice recognized autologous Mlh1^-/- tumor cells in IFNγ ELISpot, but likewise YAC-1 cells, indicative for stimulation of both arms of the immune system. By deciphering local effects, vaccines shaped the tumor microenvironment differently. While A7450 T1 M1 prophylactically vaccinated tumors harbored low numbers of myeloid-derived suppressor cells (MDSC) and elevated CD8-T cell infiltrates, vaccination with the 328 lysate evoked MDSC infiltration. Similar effects were seen in the therapeutic setting with stable disease induction only upon A7450 T1 M1 vaccination. Untangling individual response profiles revealed strong infiltration with LAG3⁺ and PD-L1⁺ immune cells when treatments failed, but almost complete exclusion of checkpoint-expressing lymphocytes in long-term survivors.

CONCLUSIONS

By applying two tumor cell lysates we demonstrate that neoantigen quality outranks quantity. This should be considered prior to designing cancer vaccine-based combination approaches.

Kininogen supports inflammation and bacterial spreading during Streptococccus Pyogenes Sepsis

BACKGROUND

High-molecular-weight kininogen is a cofactor of the human contact system, an inflammatory response mechanism that is activated during sepsis. It has been shown that high-molecular-weight kininogen contributes to endotoxemia, but is not critical for local host defense during pneumonia by Gram-negative bacteria. However, some important pathogens, such as Streptococcus pyogenes, can cleave kininogen by contact system activation. Whether kininogen causally affects antibacterial host defense in S. pyogenes infection, remains unknown.

METHODS

Kininogen concentration was determined in course plasma samples from septic patients. mRNA expression and degradation of kininogen was determined in liver or plasma of septic mice. Kininogen was depleted in mice by treatment with selective kininogen directed antisense oligonucleotides (ASOs) or a scrambled control ASO for 3 weeks prior to infection. 24 h after infection, infection parameters were determined.

FINDINGS

Data from human and mice samples indicate that kininogen is a positive acute phase protein. Lower kininogen concentration in plasma correlate with a higher APACHE II score in septic patients. We show that ASO-mediated depletion of kininogen in mice indeed restrains streptococcal spreading, reduces levels of proinflammatory cytokines such as IL-1β and IFNγ, but increased intravascular tissue factor and fibrin deposition in kidneys of septic animals.

INTERPRETATION

Mechanistically, kininogen depletion results in reduced plasma kallikrein levels and, during sepsis, in increased intravascular tissue factor that may reinforce immunothrombosis, and thus reduce streptococcal spreading. These novel findings point to an anticoagulant and profibrinolytic role of kininogens during streptococcal sepsis.

FUNDING

Full details are provided in the Acknowledgements section.

High mutational burden in colorectal carcinomas with monoallelic POLE mutations: absence of allelic loss and gene promoter methylation

Hypermutator-type colorectal carcinomas are microsatellite-stable and have point mutations of the exonuclease domain of the DNA polymerase ε or δ genes (POLE and POLD1, respectively), and an ultrahigh tumor mutational burden (TMB). These tumors may be associated with enhanced antitumor immunity and preferentially afflict younger patients, but this notion awaits validation by accrual of further cases for detailed correlative phenotypic and molecular study. We performed POLE and POLD1 exonuclease domain Sanger sequencing of 271 unselected colorectal carcinomas. We identified two microsatellite-stable tumors with somatic POLE p.P286R variants, both with ultrahigh TMBs as demonstrated by whole exome sequencing. A POLE p.V411L was found in another two microsatellite-stable tumors with ultrahigh TMBs. Two of these four tumors were from young patients (<50 years old, nonsyndromic), and there was seen a prominent T-cell infiltration in three of them. Furthermore, a somatic POLE p.A465T was found in a Lynch-associated tumor, which, hypothetically, might have enhanced TMB (which was the highest of all). In two tumors, a somatic POLE p.V411L and a POLD1 p.E279K, respectively, were found only focally, and TMBs were low. It is commonly assumed that compromise of one allele is sufficient, but this has not been specifically addressed. Therefore, resequencing of the POLE or POLD1 mutations was done with DNA from tumor cells isolated by laser-capture microdissection. This demonstrated that the mutations were monoallelic, and there was no evidence of a "second hit", neither by allelic loss (allelotyping with polymorphic microsatellite markers), nor by promoter methylation (Pyromark CpG assays). Taken together, including at least the more common DNA polymerase mutations in NGS panels allows for straightforward identification of hypermutator-type colorectal carcinomas which often may be "immunoreactive". This is important at least in young patients or when a metastasizing stage of disease has been reached and immune-checkpoint therapy enters deliberation.

Streptococcus gallolyticus abrogates anti-carcinogenic properties of tannic acid on low-passage colorectal carcinomas

The tannase-producing Gram-positive bacterial species Streptococcus gallolyticus subsp. gallolyticus (Sgg) is an opportunistic pathogen of the human gut and strongly associated with colorectal cancer (CRC). A unique feature of Sgg is its ability to degrade tannic acids (TA). TA constitute an important part of the human diet with known anti-tumorigenic properties. Here, we examined whether Sgg is able to protect tumor cells from the toxic effect of TA and thus drive tumorigenesis indirectly. Human CRC cell lines (n = 8) were treated with increasing concentrations of TA. We confirmed the cytotoxic activity of TA in a dose-dependent manner. In virtually all cell lines, viability decreased significantly (>60% inhibition). Moreover, pyrogallol, the degradation product of TA, had no effect on the tested cell lines. This suggests a specific effect of TA. Cytotoxicity was due to necrosis and induction of senescence in residual cells. Finally, when TA was degraded by Sgg, the cytotoxic effect could be abolished. Tumor cells even responded with boosted cell proliferation, highlighting the impact of Sgg on CRC progression. We here provide another piece of evidence for the active interplay between Sgg and cancer preventive components. These data will help to move forward in designing concepts for therapeutic and eventually also prophylactic approaches to combat gastrointestinal malignancies.

Activation of the Kynurenine Pathway in Human Malignancies Can Be Suppressed by the Cyclin-Dependent Kinase Inhibitor Dinaciclib

Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO2) are the key enzymes of tryptophan (TRP) metabolism in the kynurenine pathway (KP). Both enzymes function as indicators of immunosuppression and poor survival in cancer patients. Direct or indirect targeting of either of these substances seems thus reasonable to improve therapy options for patients. In this study, glioblastoma multiforme (GBM) as well as head and neck squamous cell carcinomas (HNSCC) were examined because of their different mechanisms of spontaneous and treatment-induced immune escape. Effects on gene expression and protein levels were examined. Accompanying assessment of TRP metabolites from treated GBM cell culture supernatants was conducted. Our results show a heterogeneous and inversely correlated expression profile of TRP-metabolizing genes among GBM and HNSCC cells, with low, but inducible IDO1 expression upon IFNγ treatment. TDO2 expression was higher in GBM cells, while genes encoding kynurenine aminotransferases were mainly confined to HNSCC cells. These data indicate that the KP is active in both entities, with however different enzymes involved in TRP catabolism. Upon treatment with Temozolomide, the standard of care for GBM patients, IDO1 was upregulated. Comparable, although less pronounced effects were seen in HNSCC upon Cetuximab and conventional drugs (i.e., 5-fluorouracil, Gemcitabine). Here, IDO1 and additional genes of the KP (KYAT1, KYAT2, and KMO) were induced. Vice versa, the novel yet experimental cyclin-dependent kinase inhibitor Dinaciclib suppressed KP in both entities. Our comprehensive data imply inhibition of the TRP catabolism by Dinaciclib, while conventional chemotherapeutics tend to activate this pathway. These data point to limitations of conventional therapy and highlight the potential of targeted therapies to interfere with the cells' metabolism more than anticipated.

NSG mice as hosts for oncological precision medicine

Patient-derived xenograft (PDX) models have been rediscovered as meaningful research tool. By using severely immunodeficient mice, high-engraftment rates can be theoretically achieved, permitting clinical stratification strategies. Apart from engraftment efficacy, tolerability towards certain cytostatic drugs varies among individual mouse strains thus impeding large-scale screenings. Here, we aimed at optimizing an in vivo treatment schedule using the widely applied cytostatic drug 5-fluoruracil (5-FU) for exemplary response prediction in colorectal cancer (CRC) PDX models. Four different individual CRC PDX models were engrafted into NOD.Cg-Prkdc^scidIl2rg^tm1Wjl (NSG) mice. Mice with established PDX were allocated to different treatment groups, receiving 5-FU, the oral prodrug Capecitabine, or 5-FU/leucovorin (LV) at different doses. Body weight, tumor size, and general behavior were assessed during therapy. Ex vivo analyses were done from blood samples, liver, as well as tumor resection specimen. Engraftment efficacy was high as expected in NSG mice, yielding stable PDX growth for therapy stratification. However, overall tolerability towards 5-FU was unexpectedly low, whereas the prodrug Capecitabine as well as the combination of 5-FU/LV at low doses were well tolerated. Accompanying plasma level determination of DYPD, the rate-limiting enzyme for 5-FU-mediated toxicity, revealed reduced activity in NSG mice compared with other common laboratory mouse strains, offering a likely explanation for the drug incompatibility. Also, the De Ritis quotient was highly elevated in treated mice, reflecting overall organ injury even at low doses. Summarizing these findings, NSG mice are ideal hosts for in vivo engraftment studies. However, the complex immunodeficiency reduces tolerance to certain drugs, thus making those mice especially sensitive. Consequently, such dose finding and tolerance tests constitute a necessity for similar cancer precision medicine approaches.

Unraveling the Heterogeneous Mutational Signature of Spontaneously Developing Tumors in MLH1-/- Mice

Mismatch repair deficient (MMR-D) tumors exemplify the prototypic hypermutator phenotype. Owing to the high mutation rates, plenty of neo-antigens are present on the tumor cells' surface, ideally shared among different cancer types. The MLH1 knock out mouse represents a preclinical model that resembles features of the human MMR-D counterpart. While these mice develop neoplasias in a sequential twin-peaked manner (lymphomas > gastrointestinal tumors (GIT)) we aimed at identification of underlying molecular mechanisms. Using whole-genome sequencing, we focused on (I) shared and (II) mutually exclusive mutations and describe the process of ongoing mutational events in tumor-derived cell cultures. The landscape of MLH1^-/- tumors is heterogeneous with only a few shared mutations being detectable among different tumor entities (ARID1A and IDH2). With respect to coding microsatellite analysis of MMR-D-related target genes, partial overlap was detectable, yet recognizing shared antigens. The present study is the first reporting results of a comparison between spontaneously developing tumors in MMR-D driven tumorigenesis. Additionally to identifying ARID1A as potential causative mutation hotspot, this comprehensive characterization of the mutational landscape may be a good starting point to refine therapeutic concepts.

The contact system proteases play disparate roles in streptococcal sepsis

Sepsis causes an activation of the human contact system, an inflammatory response mechanism against foreign surfaces, proteins and pathogens. The serine proteases of the contact system, factor XII and plasma kallikrein, are decreased in plasma of septic patients, which was previously associated with an unfavorable outcome. However, the precise mechanisms and roles of contact system factors in bacterial sepsis are poorly understood. We, therefore, studied the physiological relevance of factor XII and plasma kallikrein in a mouse model of experimental sepsis. We show that decreased plasma kallikrein concentration in septic mice is a result of reduced mRNA expression plasma prekallikrein gene, indicating that plasma kallikrein belong to negative acute phase proteins. Investigations regarding the pathophysiological function of contact system proteases during sepsis revealed different roles for factor XII and plasma kallikrein. In vitro, factor XII decelerated bacteria induced fibrinolysis, whereas plasma kallikrein supported it. Remarkably, depletion of plasma kallikrein (but not factor XII) by treatment with antisense-oligonucleotides, dampens bacterial dissemination and growth in multiple organs in the mouse sepsis model. These findings identify plasma kallikrein as a novel host pathogenicity factor in Streptococcus pyogenes sepsis.

Novel Isoquinolinamine and Isoindoloquinazolinone Compounds Exhibit Antiproliferative Activity in Acute Lymphoblastic Leukemia Cells

Nitrogen-containing heterocycles such as quinoline, quinazolinones and indole are scaffolds of natural products and have broad biological effects. During the last years those structures have been intensively synthesized and modified to yield new synthetic molecules that can specifically inhibit the activity of dysregulated protein kinases in cancer cells. Herein, a series of newly synthesized isoquinolinamine (FX-1 to 8) and isoindoloquinazolinone (FX-9, FX-42, FX-43) compounds were evaluated in regards to their anti-leukemic potential on human B- and T-acute lymphoblastic leukemia (ALL) cells. Several biological effects were observed. B-ALL cells (SEM, RS4;11) were more sensitive against isoquinolinamine compounds than T-ALL cells (Jurkat, CEM). In SEM cells, metabolic activity decreased with 10 μM up to 26.7% (FX-3), 25.2% (FX-7) and 14.5% (FX-8). The 3-(p-Tolyl) isoquinolin-1-amine FX-9 was the most effective agent against B- and T-ALL cells with IC50 values ranging from 0.54 to 1.94 μM. None of the tested compounds displayed hemolysis on erythrocytes or cytotoxicity against healthy leukocytes. Anti-proliferative effect of FX-9 was associated with changes in cell morphology and apoptosis induction. Further, influence of FX-9 on PI3K/AKT, MAPK and JAK/STAT signaling was detected but was heterogeneous. Functional inhibition testing of 58 kinases revealed no specific inhibitory activity among cancer-related kinases. In conclusion, FX-9 displays significant antileukemic activity in B- and T-ALL cells and should be further evaluated in regards to the mechanisms of action. Further compounds of the current series might serve as templates for the design of new compounds and as basic structures for modification approaches.

Suspected Hereditary Cancer Syndromes in Young Patients: Heterogeneous Clinical and Genetic Presentation of Colorectal Cancers

Colorectal cancer (CRC) is rare in young patients without a confirmed family history of cancer. Reports of an increased prevalence of POLD1/POLE mutations in young patients with colorectal cancer have raised awareness and support routine genetic testing for patients with early-onset tumors. In cases of CRC without proven MMR-germline mutation, molecular analyses are warranted to confirm or rule out other familial CRC syndromes. This article describes the cases of two young male patients, who presented with locally advanced and metastatic CRC, and reports the results of the germline mutational analyses done for both patients. These cases demonstrate the importance of special care and molecular diagnostic procedures for young patients with CRC. KEY POINTS: Patients with colorectal cancer who are younger than 50 years at initial diagnosis (early onset) should routinely undergo genetic testing.Early- and very-early-onset patients (younger than 40 years) with absence of microsatellite instability should be considered for tumor mutation burden testing and/or DNA polymerase proofreading mutation.The mutational signature of HSP110 within mismatch repair deficiency-related tumors may help to identify patients likely to benefit from 5-fluorouracil-based chemotherapy.Intensified, maintained, and specific surveillance may help to reduce secondary tumor progression.

Chemo-immunotherapy improves long-term survival in a preclinical model of MMR-D-related cancer

Background

Mismatch Repair Deficiency (MMR-D)-related tumors are highly immunogenic and constitute ideal vaccination targets. In a proof-of-concept study delayed tumorigenesis and prolonged survival has been shown in a clinically-relevant mouse model for MMR-D-related diseases (=MLH1 knock out mice). To refine this approach, vaccination was combined with immune modulatory low-dose chemotherapy to polarize immune regulatory subtypes.

Methods

Mice (prophylactic: 8–10 weeks; therapeutic: > 36 weeks) received a single injection of cyclophosphamide (CPX, 120 mg/kg bw, i.p.) or gemcitabine (GEM, 100 mg/kg bw, i.p.) prior to vaccination (lysate of a gastrointestinal tumor allograft, 10 mg/kg bw, n = 9 mice/group). The vaccine was given repetitively (10 mg/kg bw, s.c., 4 x / once a week, followed by monthly boosts) until tumor formation or progression. Tumor growth ([¹⁸F] FDG PET/CT imaging) and immune responses were monitored (flow cytometry, IFNγ ELISpot). The microenvironment was analyzed by immunofluorescence.

Results

Prophylactic application of GEM + lysate delayed tumorigenesis compared to lysate monotherapy and CPX-pre-treatment (median time of onset: 53 vs. 47 vs. 48 weeks). 33% of mice even remained tumor-free until the experimental endpoint (= 65 weeks). This was accompanied by long-term effect on cytokine plasma levels; splenic myeloid derived suppressor cells (MDSC) as well as regulatory T cell numbers. Assessment of tumor microenvironment from GEM + lysate treated mice revealed low numbers of MDSCs, but enhanced T cell infiltration, in some cases co-expressing PD-L1. Therapeutic chemo-immunotherapy (GEM + lysate) had minor impact on overall survival (median time: 12 (GEM + lysate) vs. 11.5 (lysate) vs. 3 weeks (control)), but induced complete remission in one case. Dendritic and T cell infiltrates increased in both treatment groups. Reactive T cells specifically recognized MLH1^−/− tumor cells in IFNγ ELISpot, but lacked response towards NK cell targets YAC-1.

Conclusions

Combined chemo-immunotherapy impairs tumor onset and growth likely attributable to modulation of immune responses. Depleting or ‘re-educating’ immunosuppressive cell types, such as MDSC, may help moving a step closer to combat cancer.

Arginine-Depleting Enzymes - An Increasingly Recognized Treatment Strategy for Therapy-Refractory Malignancies

Arginine auxotrophy occurs in certain tumor types and is usually caused by the silencing of argininosuccinate synthetase 1 or arginine lyase genes. Such tumors are often associated with an intrinsic chemoresistance and thus a poor prognosis. Arginine auxotrophy however renders these tumors vulnerable to treatment with arginine-degrading enzymes. Among the most frequently applied arginine-degrading agents are bacterial arginine deiminases (ADI). The anti-cancerous effects of ADI derived from different bacteria were extensively studied in numerous preclinical cell culture and xenograft models. Mycoplasma-derived ADI-PEG20 is most commonly used and is currently under clinical investigation as a single agent therapeutic as well as in combination with different antineoplastic compounds. Mechanistically, ADI is capable of reducing metabolic activity in tumor cells, contributing to autophagy, senescence and apoptosis in arginine auxotrophic cells. Although clinical trials are promising, the resistance development upon initial treatment response is an increasing challenge. Furthermore, interference of ADI with the tumor microenvironment is poorly understood. In the present review, we outline recent experimental ADI-based treatment approaches and their translation into the clinic. Furthermore, we summarize new insights into the molecular mechanisms underlying the anti-cancer effects of ADI that might facilitate the refinement of ADI-based combination therapy approaches.

Murine Endogenous Retroviruses Are Detectable in Patient-Derived Xenografts but Not in Patient-Individual Cell Lines of Human Colorectal Cancer

Endogenous retroviruses are remnants of retroviral infections. In contrast to their human counterparts, murine endogenous retroviruses (mERV) still can synthesize infectious particles and retrotranspose. Xenotransplanted human cells have occasionally been described to be mERV infected. With genetic engineered mice and patient-derived xenografts (PDXs) on the rise as eminent research tools, we here systematically investigated, if different tumor models harbor mERV infections. Relevant mERV candidates were first preselected by next generation sequencing (NGS) analysis of spontaneous lymphomas triggered by colorectal cancer (CRC) PDX tissue. Two primer systems were designed for each of these candidates (AblMLV, EcoMLV, EndoPP, MLV, and preXMRV) and implemented in an quantitative real-time (RT-qPCR) screen using murine tissues (n = 11), PDX-tissues (n = 22), PDX-derived cell lines (n = 13), and patient-derived tumor cell lines (n = 14). The expression levels of mERV varied largely both in the PDX samples and in the mouse tissues. No mERV signal was, however, obtained from cDNA or genomic DNA of CRC cell lines. Expression of EcoMLV was higher in PDX than in murine tissues; for EndoPP it was the opposite. These two were thus further investigated in 40 additional PDX. In addition, four patient-derived cell lines free of any mERV expression were subcutaneously injected into immunodeficient mice. Outgrowing cell-derived xenografts barely expressed EndoPP. In contrast, the expression of EcoMLV was even higher than in surrounding mouse tissues. This expression gradually vanished within few passages of re-cultivated cells. In summary, these results strongly imply that: (i) PDX and murine tissues in general are likely to be contaminated by mERV, (ii) mERV are expressed transiently and at low level in fresh PDX-derived cell cultures, and (iii) mERV integration into the genome of human cells is unlikely or at least a very rare event. Thus, mERVs are stowaways present in murine cells, in PDX tissues and early thereof-derived cell cultures. We conclude that further analysis is needed concerning their impact on results obtained from studies performed with PDX but also with murine tumor models.

The mutational profile and infiltration pattern of murine MLH1-/- tumors: concurrences, disparities and cell line establishment for functional analysis

Mice lines homozygous negative for one of the four DNA mismatch repair (MMR) genes (MLH1, MSH2, PMS2, MSH6) were generated as models for MMR deficient (MMR-D) diseases. Clinically, hereditary forms of MMR-D include Lynch syndrome (characterized by a germline MMR gene defect) and constitutional MMR-D, the biallelic form. MMR-D knockout mice may be representative for both diseases. Here, we aimed at characterizing the MLH1^-/- model focusing on tumor-immune microenvironment and identification of coding microsatellite mutations in lymphomas and gastrointestinal tumors (GIT).

All tumors showed microsatellite instability (MSI) in non-coding mononucleotide markers. Mutational profiling of 26 coding loci in MSI⁺ GIT and lymphomas revealed instability in half of the microsatellites, two of them (Rfc3 and Rasal2) shared between both entities. MLH1^-/- tumors of both entities displayed a similar phenotype (high CD71, FasL, PD-L1 and CTLA-4 expression). Additional immunofluorescence verified the tumors’ natural immunosuppressive character (marked CD11b/CD200R infiltration). Vice versa, CD3⁺ T cells as well as immune checkpoints molecules were detectable, indicative for an active immune microenvironment. For functional analysis, a permanent cell line from an MLH1^-/- GIT was established. The newly developed MLH1^-/- A7450 cells exhibit stable in vitro growth, strong invasive potential and heterogeneous drug response. Moreover, four additional MSI target genes (Nktr1, C8a, Taf1b, and Lig4) not recognized in the primary were identified in this cell line.

Summing up, molecular and immunological mechanisms of MLH1^-/- driven carcinogenesis correlate well with clinical features of MMR-D. MLH1^-/- knockout mice combine characteristics of Lynch syndrome and constitutional MMR-D, making them suitable models for preclinical research aiming at MMR-D related diseases.

Cellular vaccination of MLH1-/- mice - an immunotherapeutic proof of concept study

Mismatch-repair deficiency (MMR-D) is closely linked to hypermutation and accordingly, high immunogenicity. MMR-D-related tumors thus constitute ideal vaccination targets for both therapeutic and prophylactic approaches. Herein, the prophylactic and therapeutic impact of a cellular vaccine on tumor growth and tumor-immune microenvironment was studied in a murine MLH1^-/- knockout mouse model. Prophylactic application of the lysate (+/- CpG ODN 1826) delayed tumor development, accompanied by increased levels of circulating T cell numbers. Therapeutic application of the vaccine prolonged overall survival (median time: 11.5 (lysate) and 12 weeks (lysate + CpG ODN) vs. 3 weeks (control group), respectively) along with reduced tumor burden, as confirmed by PET/CT imaging and immune stimulation (increased CD3⁺CD8⁺ T - and NK cell numbers, reduced levels of TIM-3⁺ cells in both treatment groups). Coding microsatellite analysis of MMR-D-related target genes revealed increased mutational load upon vaccination (total mutation frequency within 28 genes: 28.6% vaccine groups vs. 14.9% control group, respectively). Reactive immune cells recognized autologous tumor cells, but also NK cells target YAC-1 in IFNγ ELISpot and, even more importantly, in functional kill assays. Assessment of tumor microenvironment revealed infiltration of CD8⁺ T-cells and granulocytes, but also upregulation of immune checkpoint molecules (LAG-3, PD-L1). The present study is the first reporting in vivo results on a therapeutic cellular MMR-D vaccine. Vaccination-induced prolonged survival was achieved in a clinically-relevant mouse model for MMR-D-related diseases by long-term impairment of tumor growth and this could be attributed to re-activated immune responses.

Colorectal carcinoma tumour budding and podia formation in the xenograft microenvironment

Tumour budding and podia formation are well-appreciated in surgical pathology as an aggressive invasion phenotype of colorectal carcinoma cells that is attained in the microenvironment of the invasive margin. In this study, we addressed how tumour budding and podia formation feature in xenografts. Primary colorectal carcinomas (N = 44) of various molecular types (sporadic standard type, high-degree microsatellite-unstable, CpG island methylator phenotype) were transplanted subcutaneously into T and B cell-deficient NSG mice, making possible immunohistochemistry with routine surgical pathology antibodies. Tumor budding and podia formation were both appreciably present in the xenografts. Quantitative evaluations of cytokeratin immunostains of primaries and their corresponding xenografts showed a reduction of tumour buds in the xenografts. Furthermore, in xenografts tumour cells were completely negative by pSTAT3 immunohistochemistry, indicating absence of cytokine/chemokine signalling, but nuclear β-catenin and SMAD4 immunostainings as read-out of wnt and BMP pathway activation, respectively, were maintained. Carcinoma cells in most xenografts retained immunostaining of at least some nuclei by immunohistochemistry with antibodies against pERK1/2. K-ras/B-raf mutational status did not correlate with tumour budding or podia formation in the xenografts. Our results indicate that tumour budding and podia formation can be modelled by xenografting, and in NSG mice it can be studied with the same immunohistochemical methods as used for primaries in surgical pathology. Dysregulation of wnt and BMP signalling appears to be transferred into the xenograft microenvironment, but not cytokine/chemokine signalling.

Deciphering molecular mechanisms of arginine deiminase-based therapy - Comparative response analysis in paired human primary and recurrent glioblastomas

Arginine auxotrophy constitutes the Achilles' heel for several tumors, among them glioblastoma multiforme (GBM). Hence, arginine-depleting enzymes such as arginine deiminase (ADI) from Streptococcus pyogenes are promising for treatment of primary and maybe even refractory GBM. Based on our previous study in which ADI-susceptibility was shown on a panel of patient-derived GBM cell lines, we here aimed at deciphering underlying molecular mechanisms of ADI-mediated growth inhibition. We found that ADI (35 mU/mL) initially induces a cellular stress-response that is characterized by upregulation of genes primarily belonging to the heat-shock protein family. In addition to autophagocytosis, we show for the first time that senescence constitutes another cellular response mechanism upon ADI-treatment and that this bacterial enzyme is able to act as radiosensitizer (¼ cases). Long-term treatment schedules revealed no resistance development, with treated cells showing morphological signs of cell stress. Next, several combination strategies were employed to optimize ADI-based treatment. Simultaneous and sequential S. pyogenes ADI-based combinations included substances acting at different molecular pathways (curcumin, resveratrol, quinacrine, and sorafenib, 2 × 72 h treatment). Adding drugs to GBM cell lines (n = 4, including a matched pair of primary and recurrent GBM in one case) accelerated and potentiated ADI-mediated cytotoxicity. Autophagy was identified as the main cause of tumor growth inhibition. Of note, residual cells again showed classical signs of senescence in most combinations. Our results suggest an alternative treatment regimen for this fatal cancer type which circumvents many of the traditional barriers. Using the metabolic defect in GBM thus warrants further (pre-) clinical evaluation.

Application of in vivo imaging techniques to monitor therapeutic efficiency of PLX4720 in an experimental model of microsatellite instable colorectal cancer

OBJECTIVES

Patient-derived tumor cell lines are a powerful tool to analyze the sensitivity of individual tumors to specific therapies in mice. An essential prerequisite for such an approach are reliable quantitative techniques to monitor tumor progression in vivo.

METHODS

We have employed HROC24 cells, grown heterotopically in NMRI Foxn1^nu mice, as a model of microsatellite instable colorectal cancer to investigate the therapeutic efficiencies of 5'-fluorouracil (5'-FU) and the mutant BRAF inhibitor PLX4720, a vemurafenib analogue, by three independent methods: external measurement by caliper, magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-(¹⁸F)fluoro-D-glucose (¹⁸F-FDG).

RESULTS

Repeated measure ANOVA by a general linear model revealed that time-dependent changes of anatomic tumor volumes measured by MRI differed significantly from those of anatomic volumes assessed by caliper and metabolic volumes determined by PET/CT. Over the investigation period of three weeks, neither 5'-FU, PLX4720 nor a combination of both drugs affected the tumor volumes. Also, there was no drug effect on the apparent diffusion constant (ADC) value as detected by MRI. Interestingly, however, PET/CT imaging showed that PLX4720-containing therapies transiently reduced the standardized uptake value (SUV), indicating a temporary response to treatment.

CONCLUSIONS

5'-FU and PLX4720 were largely ineffective with respect to HROC24 tumor growth. Tumoral uptake of ¹⁸F-FDG, as expressed by the SUV, proved as a sensitive indicator of small therapeutic effects. Metabolic imaging by ¹⁸F-FDG PET/CT is a suitable approach to detect effects of tumor-directed therapies early and even in the absence of morphological changes.

Frameshift mutational target gene analysis identifies similarities and differences in constitutional mismatch repair-deficiency and Lynch syndrome

Mismatch-repair deficient (MMR-D) malignancies include Lynch Syndrome (LS), which is secondary to germline mutations in one of the MMR genes, and the rare childhood-form of constitutional mismatch repair-deficiency (CMMR-D); caused by bi-allelic MMR gene mutations. A hallmark of LS-associated cancers is microsatellite instability (MSI), characterized by coding frameshift mutations (cFSM) in target genes. By contrast, tumors arising in CMMR-D patients are thought to display a somatic mutation pattern differing from LS. This study has the main goal to identify cFSM in MSI target genes relevant in CMMR-D and to compare the spectrum of common somatic mutations, including alterations in DNA polymerases POLE and D1 between LS and CMMR-D. CMMR-D-associated tumors harbored more somatic mutations compared to LS cases, especially in the TP53 gene and in POLE and POLD1, where novel mutations were additionally identified. Strikingly, MSI in classical mononucleotide markers BAT40 and CAT25 was frequent in CMMR-D cases. MSI-target gene analysis revealed mutations in CMMR-D-associated tumors, some of them known to be frequently hit in LS, such as RNaseT2, HT001, and TGFβR2. Our results imply a general role for these cFSM as potential new drivers of MMR-D tumorigenesis.

Functional Characterization and Drug Response of Freshly Established Patient-Derived Tumor Models with CpG Island Methylator Phenotype

Patient-individual tumor models constitute a powerful platform for basic and translational analyses both in vitro and in vivo. However, due to the labor-intensive and highly time-consuming process, only few well-characterized patient-derived cell lines and/or corresponding xenografts exist. In this study, we describe successful generation and functional analysis of novel tumor models from patients with sporadic primary colorectal carcinomas (CRC) showing CpG island methylator phenotype (CIMP). Initial DNA fingerprint analysis confirmed identity with the patient in all four cases. These freshly established cells showed characteristic features associated with the CIMP-phenotype (HROC40: APC^wt, TP53^mut, KRAS^mut; 3/8 marker methylated; HROC43: APC^mut, TP53^mut, KRAS^mut; 4/8 marker methylated; HROC60: APC^wt, TP53^mut, KRAS^wt; 4/8 marker methylated; HROC183: APC^mut, TP53^mut, KRAS^mut; 6/8 marker methylated). Cell lines were of epithelial origin (EpCAM⁺) with distinct morphology and growth kinetics. Response to chemotherapeutics was quite individual between cells, with stage I-derived cell line HROC60 being most susceptible towards standard clinically approved chemotherapeutics (e.g. 5-FU, Irinotecan). Of note, most cell lines were sensitive towards “non-classical” CRC standard drugs (sensitivity: Gemcitabin > Rapamycin > Nilotinib). This comprehensive analysis of tumor biology, genetic alterations and assessment of chemosensitivity towards a broad range of (chemo-) therapeutics helps bringing forward the concept of personalized tumor therapy.

Host defense peptides for treatment of colorectal carcinoma - a comparative in vitro and in vivo analysis

Host defense peptides (HDP) constitute effector molecules of the innate immune system. Besides acting against microbia and fungi, they exhibit broad and selective oncolytic activity. The underlying mechanism is at least partially attributable to elevated surface-exposed levels of phosphatidylserine (PS) on tumor targets. In this study, comprehensive analysis of NK-2-based derivatives (C7A, C7A-D21K, and C7A-Δ) was done on patient-derived ultra-low passage colorectal carcinoma (CRC) cell lines. Peptides were designed to improve antitumoral potential. Mellitin was used as positive control and a non-toxic peptide (NK11) served as negative control. Subsequently, effectiveness of local HDP application was determined in xenopatients.

Generally, CRC lines displayed a heterogeneous pattern of surface-exposed PS, which was usually below standard CRC cells. Of note, five out of seven cell lines were susceptible towards HDP-mediated lysis (lytic activity of peptides: C7A-D21K > C7A-Δ= C7A). Oncolytic activity correlated mostly with surface-exposed PS levels. Apoptosis as well as necrosis were involved in killing. In an in vivo experiment, substantial growth inhibition of HROC24 xenografts was observed after HDP therapy and, surprisingly, also after NK11 treatment.

These promising data underline the high potential of HDPs for oncolytic therapies and may provide a rationale for optimizing preclinical treatment schedules based on NK-2.

Arginine deprivation by arginine deiminase of Streptococcus pyogenes controls primary glioblastoma growth in vitro and in vivo

Arginine auxotrophy constitutes a weak point of several tumors, among them glioblastoma multiforme (GBM). Hence, those tumors are supposed to be sensitive for arginine-depleting substances, such as arginine deiminase (ADI). Here we elucidated the sensitivity of patient-individual GBM cell lines toward Streptococcus pyogenes-derived ADI. To improve therapy, ADI was combined with currently established and pre-clinical cytostatic drugs. Additionally, effectiveness of local ADI therapy was determined in xenopatients. Half of the GBM cell lines tested responded well toward ADI monotherapy. In those cell lines, viability decreased significantly (up to 50%). Responding cell lines were subjected to combination therapy experiments to test if any additive or even synergistic effects may be achieved. Such promising results were obtained in 2/3 cases. In cell lines HROG02, HROG05 and HROG10, ADI and Palomid 529 combinations were most effective yielding more than 70% killing after 2 rounds of treatment. Comparable boosted antitumoral effects were observed after adding chloroquine to ADI (>60% killing). Apoptosis, as well as cell cycle dysregulation were found to play a minor role. In some, but clearly not all cases, (epi-) genetic silencing of arginine synthesis pathway genes (argininosuccinate synthetase 1 and argininosuccinate lyase) explained obtained results. In vivo, ADI as well as the combination of ADI and SAHA efficiently controlled HROG05 xenograft growth, whereas adding Palomid 529 to ADI did not further increase the strong antitumoral effect of ADI. The cumulative in vitro and in vivo results proved ADI as a very promising candidate therapeutic, especially for development of adjuvant GBM combination treatments.

Establishment and characterization of cell lines from chromosomal instable colorectal cancer

AIM: To generate novel tumor models for preclinical validation of biomarkers that allow drug response prediction and individual therapeutic decisions.

METHODS: Cell line establishment was conducted by both direct in vitro culturing and in vivo xenografting followed by in vitro culturing procedure. A comprehensive characterization was subsequently performed. This included quality control, consisting of the confirmation of human and colorectal cancer (CRC) origin by DNA fingerprint and epithelial cell adhesion molecule (EpCAM) staining, as well as mycoplasma and human virus testing. Phenotypic analysis was done by light microscopy and multicolor flow cytometry. Histopathological examination (β-catenin and cytokeratin staining) was conducted in direct comparison to parental tumor tissues. Extensive molecular-pathological profiling included mutation analysis for CRC-associated driver mutations, assessment of chromosomal and microsatellite instability, and the grade of CpG island methylation. Additionally, an array-based comparative genomic hybridization analysis was performed. Drug responsiveness was assessed for a panel of classical and novel substances in clinical use for the treatment of solid cancers. Finally, tumorigenicity of the cell lines was tested by xenografting into immunocompromised nude mice.

RESULTS: Herein we describe the establishment of three ultra-low passage cell lines from two individual patients suffering from sporadic CRC. One cell line was derived directly from an early stage case (HROC18), whereas two cell lines could be established both direct from patient material and after xenografting from a late stage tumor (HROC32). All cell lines were free of contaminating mycoplasma and viruses. Molecular-pathological analysis allowed all cell lines to be classified as chromosomal instable (CIN⁺). They were aneuploid, with CpG island promoter methylation and microsatellite instability being absent. The following mutational profile was observed both in the cell lines and the parental tumor tissue: HROC18: APC^mut, p53^mut, K-ras^wt; HROC32: APC^wt, p53^mut, K-ras^mut. All cell lines were characterized as epithelial (EpCAM⁺) cells, showing distinct morphology and migration speed, but comparable growth kinetics. The cell lines showed different patterns of response towards clinically approved and novel drugs, with HROC18 being more resistant than HROC32 cells. Finally, in vivo tumorigenicity was demonstrated.

CONCLUSION: We successfully established and characterized novel ultra-low passage patient-derived CRC models as useful instruments for analyzing biological characteristics associated with the CIN⁺ phenotype.

Tumor-infiltrating B cells: The ignored players in tumor immunology

B cells infiltrating into solid tumors are poorly investigated despite their described positive prognostic value. Whether this antitumor potential comes from either the antigen presentation or the antibody production capacity of B cells, or both, is unknown. Our recently published method on tumor-infiltrating B lymphocyte cloning may prove helpful in unraveling the actual relevance of these cells for tumor development and response to therapy.

Mistletoe lectin has a shiga toxin-like structure and should be combined with other Toll-like receptor ligands in cancer therapy

Mistletoe extract (ME) is applied as an adjuvant treatment in cancer therapy in thousands of patients each year in Europe. The main immunostimulating component of mistletoe extract, mistletoe lectin, recently has been shown to be a pattern recognition receptor ligand and hence is binding to an important class of pathogen-sensing receptors. Pattern recognition receptor ligands are potent activators of dendritic cells. This activation is a prerequisite for a full-blown T-cell response against cancer cells. Pattern recognition receptor ligands are increasingly recognized as important players in cancer immunotherapy. We collect evidence from case studies on spontaneous regression, from epidemiology, from experiments in a mouse cancer model, and from protein structure comparisons to argue that a combination of mistletoe therapy with other pattern recognition receptor ligand substances leads to an increased immune stimulatory effect. We show that mistletoe lectin is a plant protein of bacterial origin with a 3D structure very similar to shiga toxin from Shigella dysenteriae, which explains the remarkable immunogenicity of mistletoe lectin. Secondly, we show that a combination of pattern recognition receptor ligands applied metronomically in a cancer mouse model leads to complete remission, while single pattern recognition receptor ligands slowed tumor growth. Taken together, we propose to combine mistletoe drugs with other pattern recognition receptor ligand drugs to increase its efficacy in adjuvant or even primary cancer therapy.

Microsatellite instability in hematological malignancies: Hypermutation vs. immune control-who is challenging who?

The genome of colorectal carcinomas displaying pronounced microsatellite instability codes for an extraordinarily high number of mutated proteins that elicit tumor-specific cellular immune responses. We have recently demonstrated that leukemic cells are also vulnerable to T cells specific for tumor-associated antigens produced in the context of microsatellite instability. This finding extends our understanding of secondary and therapy-related leukemogenesis, linking it to the mutual interaction between immune control and escape.