Combining TIGIT blockage with MDSC inhibition hinders breast cancer bone metastasis by activating anti-tumor immunity

Bone is the most common site of breast cancer metastasis. Bone metastasis are incurable and are associated with severe morbidity. Utilizing an immunocompetent mouse model of spontaneous breast cancer bone metastasis, we profiled the immune transcriptome of bone metastatic lesions and peripheral bone marrow at distinct metastatic stages, revealing dynamic changes during the metastatic process. We show that crosstalk between granulocytes and T cells is central to shaping an immunosuppressive microenvironment. Specifically, we identified the PD-1 and TIGIT signaling axes and the pro-inflammatory cytokine IL1b as central players in the interactions between granulocytes and T cells. Targeting these pathways in vivo resulted in attenuated bone metastasis and improved survival, by reactivating anti-tumor immunity. Analysis of patient samples revealed that TIGIT and IL1b are prominent in human bone metastasis. Our findings suggest that co-targeting immunosuppressive granulocytes and dysfunctional T cells may be a promising novel therapeutic strategy to inhibit bone metastasis.

Potent antitumor activity of anti-HER2 antibody-topoisomerase I inhibitor conjugate based on self-immolative dendritic dimeric-linker

Antibody-drug conjugates (ADCs) are a rapidly expanding class of anticancer therapeutics, with 14 ADCs already approved worldwide. We developed unique linker technologies for the bioconjugation of drug molecules with controlled-release applications. We synthesized cathepsin-cleavable ADCs using a dimeric prodrug system based on a self-immolative dendritic scaffold, resulting in a high drug-antibody ratio (DAR) with the potential to reach 16 payloads due to its dendritic structure, increased stability in the circulation and efficient release profile of a highly cytotoxic payload at the targeted site. Using our novel cleavable linker technologies, we conjugated the anti-human epidermal growth factor receptor 2 (anti-HER2) antibody, trastuzumab, with topoisomerase I inhibitors, exatecan or belotecan. The newly synthesized ADCs were tested in vitro on mammary carcinoma cells overexpressing human HER2, demonstrating a substantial inhibitory effect on the proliferation of HER2-positive cells. Importantly, a single dose of our trastuzumab-based ADCs administered in vivo to mice bearing HER2-positive tumors, showed a dose-dependent inhibition of tumor growth and survival benefit, with the most potent antitumor effects observed at 10 mg/kg, which resulted in complete tumor regression and survival of 100% of the mice. Overall, our novel dendritic technologies using the protease-cleavable Val-Cit linker present an opportunity for the development of highly selective and potent controlled-released therapeutic payloads. This strategy could potentially lead to the development of novel and effective ADC technologies for patients diagnosed with HER2-positive cancers. Moreover, our proposed ADC linker technology can be implemented in additional medical conditions such as other malignancies as well as autoimmune diseases that overexpress targets, other than HER2.

Deoxyhypusine hydroxylase: A novel therapeutic target differentially expressed in short-term vs long-term survivors of glioblastoma

Glioblastoma (GB) is the most aggressive neoplasm of the brain. Poor prognosis is mainly attributed to tumor heterogeneity, invasiveness and drug resistance. Only a small fraction of GB patients survives longer than 24 months from the time of diagnosis (ie, long-term survivors [LTS]). In our study, we aimed to identify molecular markers associated with favorable GB prognosis as a basis to develop therapeutic applications to improve patients' outcome. We have recently assembled a proteogenomic dataset of 87 GB clinical samples of varying survival rates. Following RNA-seq and mass spectrometry (MS)-based proteomics analysis, we identified several differentially expressed genes and proteins, including some known cancer-related pathways and some less established that showed higher expression in short-term (<6 months) survivors (STS) compared to LTS. One such target found was deoxyhypusine hydroxylase (DOHH), which is known to be involved in the biosynthesis of hypusine, an unusual amino acid essential for the function of the eukaryotic translation initiation factor 5A (eIF5A), which promotes tumor growth. We consequently validated DOHH overexpression in STS samples by quantitative polymerase chain reaction (qPCR) and immunohistochemistry. We further showed robust inhibition of proliferation, migration and invasion of GB cells following silencing of DOHH with short hairpin RNA (shRNA) or inhibition of its activity with small molecules, ciclopirox and deferiprone. Moreover, DOHH silencing led to significant inhibition of tumor progression and prolonged survival in GB mouse models. Searching for a potential mechanism by which DOHH promotes tumor aggressiveness, we found that it supports the transition of GB cells to a more invasive phenotype via epithelial-mesenchymal transition (EMT)-related pathways.

Development of Chitosan Particles Loaded with siRNA for Cystatin C to Control Intracellular Drug-Resistant Mycobacterium tuberculosis

The golden age of antibiotics for tuberculosis (TB) is marked by its success in the 1950s of the last century. However, TB is not under control, and the rise in antibiotic resistance worldwide is a major threat to global health care. Understanding the complex interactions between TB bacilli and their host can inform the rational design of better TB therapeutics, including vaccines, new antibiotics, and host-directed therapies. We recently demonstrated that the modulation of cystatin C in human macrophages via RNA silencing improved the anti-mycobacterial immune responses to Mycobacterium tuberculosis infection. Available in vitro transfection methods are not suitable for the clinical translation of host-cell RNA silencing. To overcome this limitation, we developed different RNA delivery systems (DSs) that target human macrophages. Human peripheral blood-derived macrophages and THP1 cells are difficult to transfect using available methods. In this work, a new potential nanomedicine based on chitosan (CS-DS) was efficiently developed to carry a siRNA-targeting cystatin C to the infected macrophage models. Consequently, an effective impact on the intracellular survival/replication of TB bacilli, including drug-resistant clinical strains, was observed. Altogether, these results suggest the potential use of CS-DS in adjunctive therapy for TB in combination or not with antibiotics.

Abstract 3243: Modulating the brain immune system to fight cancer in 3 dimensions

Despite the remarkable efficiency of immune checkpoint modulators against primary and metastatic brain neoplasms, there is a low percentage of responders and clinical trials report severe immune-mediated side effects and disease relapse. An accumulated body of evidence show that non-tumor cells within the tumor microenvironment (TME), specifically the brain microenvironment (BME), including tumor vasculature and immune stromal cells, such as astrocytes, microglia and pericytes, dictate the overall therapeutic efficacy. We synthesized a biodegradable, off-the-shelf and cost-effective nano-sized polymeric platform that combines a cancer vaccine with the targeted inhibition of molecular and/or cellular immune suppressive players. These precision nano-sized medicines aim to re-educate and harness patient T-cell response against tumors, leading to an immunological memory able to control tumor relapse without any follow-up treatment. The design of these advanced peptide and RNA immunotherapeutics is guided by the identification of lead immune suppressor factors and tumor-specific antigens and proinflammatory cytokines using novel 3D bio-printed brain tumor-immune models developed in our lab. Using this unique model platform we identified P-selectin as a novel immune checkpoint in the brain regulating cancer cells-microglia and tumor-associated macrophages interactions. Combining a P-selectin inhibitor with our first nano-immunotherapy candidates sensitized brain malignancies mouse models to immune-checkpoint modulators, dramatically increasing disease-free survival rates.

Citation Format: Eilam Yeini, Daniella Vaskovich-Koubi, Ron Kleiner, Helena F. Florindo, Ronit Satchi-Fainaro. Modulating the brain immune system to fight cancer in 3 dimensions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3243.

3D bioprinted cancer models: from basic biology to drug development

Effort invested in the development of new drugs often fails to be translated into meaningful clinical benefits for patients with cancer. The development of more effective anticancer therapeutics and accurate prediction of their clinical merit remain urgent unmet medical needs. As solid cancers have complex and heterogeneous structures composed of different cell types and extracellular matrices, three-dimensional (3D) cancer models hold great potential for advancing our understanding of cancer biology, which has been historically investigated in tumour cell cultures on rigid plastic plates. Advanced 3D bioprinted cancer models have the potential to revolutionize the way we discover therapeutic targets, develop new drugs and personalize anticancer therapies in an accurate, reproducible, clinically translatable and robust manner. These ex vivo cancer models are already replacing existing in vitro systems and could, in the future, diminish or even replace the use of animal models. Therefore, profound understanding of the differences in tumorigenesis between 2D, 3D and animal models of cancer is essential. This Review presents the state of the art of 3D bioprinted cancer modelling, focusing on the biological processes that underlie the molecular mechanisms involved in cancer progression and treatment response as well as on proteomic and genomic signatures.

Polyglutamate-based nanoconjugates for image-guided surgery and post-operative melanoma metastases prevention

Rationale: Cutaneous melanoma is the most aggressive and deadliest of all skin malignancies. Complete primary tumor removal augmented by advanced imaging tools and effective post-operative treatment is critical in the prevention of tumor recurrence and future metastases formation. Methods: To meet this challenge, we designed novel polymeric imaging and therapeutic systems, implemented in a two-step theranostic approach. Both are composed of the biocompatible and biodegradable poly(α,L-glutamic acid) (PGA) nanocarrier that facilitates extravasation-dependent tumor targeting delivery. The first system is a novel, fluorescent, Turn-ON diagnostic probe evaluated for the precise excision of the primary tumor during image-guided surgery (IGS). The fluorescence activation of the probe occurs via PGA degradation by tumor-overexpressed cathepsins that leads to the separation of closely-packed, quenched FRET pair. This results in the emission of a strong fluorescence signal enabling the delineation of the tumor boundaries. Second, therapeutic step is aimed to prevent metastases formation with minimal side effects and maximal efficacy. To that end, a targeted treatment containing a BRAF (Dabrafenib - mDBF)/MEK (Selumetinib - SLM) inhibitors combined on one polymeric platform (PGA-SLM-mDBF) was evaluated for its anti-metastatic, preventive activity in combination with immune checkpoint inhibitors (ICPi) αPD1 and αCTLA4. Results: IGS in melanoma-bearing mice led to a high tumor-to-background ratio and reduced tumor recurrence in comparison with mice that underwent surgery under white light (23% versus 33%, respectively). Adjuvant therapy with PGA-SLM-mDBF combined with ICPi, was well-tolerated and resulted in prolonged survival and prevention of peritoneal and brain metastases formation in BRAF-mutated melanoma-bearing mice. Conclusions: The results reveal the great clinical potential of our PGA-based nanosystems as a tool for holistic melanoma treatment management.

MCP-1/CCR2 axis inhibition sensitizes the brain microenvironment against melanoma brain metastasis progression

Development of resistance to chemo- and immunotherapies often occurs following treatment of melanoma brain metastasis (MBM). The brain microenvironment (BME), particularly astrocytes, cooperate toward MBM progression by upregulating secreted factors, among which we found that monocyte chemoattractant protein-1 (MCP-1) and its receptors, CCR2 and CCR4, were overexpressed in MBM compared with primary lesions. Among other sources of MCP-1 in the brain, we show that melanoma cells altered astrocyte secretome and evoked MCP-1 expression and secretion, which in turn induced CCR2 expression in melanoma cells, enhancing in vitro tumorigenic properties, such as proliferation, migration, and invasion of melanoma cells. In vivo pharmacological blockade of MCP-1 or molecular knockout of CCR2/CCR4 increased the infiltration of cytotoxic CD8⁺ T cells and attenuated the immunosuppressive phenotype of the BME as shown by decreased infiltration of Tregs and tumor-associated macrophages/microglia in several models of intracranially injected MBM. These in vivo strategies led to decreased MBM outgrowth and prolonged the overall survival of the mice. Our findings highlight the therapeutic potential of inhibiting interactions between BME and melanoma cells for the treatment of this disease.

Therapeutic targeting of PD-1/PD-L1 blockade by novel small-molecule inhibitors recruits cytotoxic T cells into solid tumor microenvironment

Background

Inhibiting programmed cell death protein 1 (PD-1) or PD-ligand 1 (PD-L1) has shown exciting clinical outcomes in diverse human cancers. So far, only monoclonal antibodies are approved as PD-1/PD-L1 inhibitors. While significant clinical outcomes are observed on patients who respond to these therapeutics, a large proportion of the patients do not benefit from the currently available immune checkpoint inhibitors, which strongly emphasize the importance of developing new immunotherapeutic agents.

Methods

In this study, we followed a transdisciplinary approach to discover novel small molecules that can modulate PD-1/PD-L1 interaction. To that end, we employed in silico analyses combined with in vitro, ex vivo, and in vivo experimental studies to assess the ability of novel compounds to modulate PD-1/PD-L1 interaction and enhance T-cell function.

Results

Accordingly, in this study we report the identification of novel small molecules, which like anti-PD-L1/PD-1 antibodies, can stimulate human adaptive immune responses. Unlike these biological compounds, our newly-identified small molecules enabled an extensive infiltration of T lymphocytes into three-dimensional solid tumor models, and the recruitment of cytotoxic T lymphocytes to the tumor microenvironment in vivo, unveiling a unique potential to transform cancer immunotherapy.

Conclusions

We identified a new promising family of small-molecule candidates that regulate the PD-L1/PD-1 signaling pathway, promoting an extensive infiltration of effector CD8 T cells to the tumor microenvironment.

Abstract 266: Adaptation of colorectal cancer cells to the brain microenvironment: The role of IRS2

Colorectal cancer (CRC) reflects the fourth most frequent etiology of brain metastasis (BM), with rising incidence. Yet, molecular mechanisms supporting the formation of these lesions from CRC are unknown. We aimed to explore drivers enabling tropism and adaptation of CRC cells to the brain environment and decipher mechanisms facilitating the process. We analyzed the FoundationOne database, which contains genomic alterations data of cancer-related genes in over 16,000 human CRC primary and metastasis samples. Increased prevalence of IRS2 gene amplification was observed in 13% of BM, compared to only 3% of primary tumors or other metastatic sites. IRS2 is a cytoplasmic adaptor mediating effects of insulin and IGF-1 receptors and is involved in more aggressive behavior of different cancer types. In agreement with the genomic data, immunohistochemistry of human clinical samples showed increased expression of IRS2 protein in BM. We constructed an in vitro system mimicking the brain microenvironment using cultured human astrocytes or their conditioned media. Under these conditions, IRS2-overexpressed CRC cells survived better and formed larger 3D spheres. IRS2-silenced CRC cells showed a mirror image. Moreover, in an intracranial CRC BM mouse model, IRS2-overexpressed cells generated larger brain lesions, while silencing IRS2 dramatically decreased tumor outgrowth and extended survival. Interestingly, transcriptomic analysis revealed enrichment of oxidative phosphorylation (OXPHOS) and Wnt/β-catenin pathways by IRS2. Indeed, IRS2-expressing cells showed increased mitochondrial activity and glycolysis-independent viability. Furthermore, IRS2-expressing cells had increased β-catenin transcriptional activity. Interestingly, β-catenin inhibition (using ICG-001) or IRS2 inhibition (using NT219) in IRS2-expressing cells decreased their viability, β-catenin transcriptional activity, and mitochondrial activity, suggesting involvement of IRS2 in modulating OXPHOS through β-catenin. β-catenin is known to confer 5-FU resistance; consequently, we showed that combination of 5-FU and NT219 worked in synergy, inhibited the formation of BM, and extended animal survival. These data reveal, for the first time, the unique genomic profile of CRC BM and imply the IRS2 role in promoting CRC BM. These effects may be mediated, at least in part, by modulation of the β-catenin and OXPHOS pathway. Given the molecular signature described, the approach to patients with BM may be significantly impacted by agents such as NT219.

Citation Format: Inbal Greenberg, Anat Klein, Rachel Grossman, Ethan Sokol, Eilam Yeini, Paula Ofek, Ronit Satchi-Fainaro, Bertrand Liang, Hadas Reuveni, Tami Rubinek, Ido Wolf. Adaptation of colorectal cancer cells to the brain microenvironment: The role of IRS2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 266.

Abstract 3520: Designing a dendritic cell-targeted immunotherapy for the treatment of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death. Low response rate, acquired resistance, severe side effects, highly desmoplastic, and immunosuppressive microenvironment have limited the clinical outcomes of immunotherapy in PDAC. To overcome these hurdles, we set to design novel immunotherapy that would be safe, efficacious, and selective to PDAC. The failure of immunotherapies to yield clinical response in PDAC is partially attributed to the inefficient antigen presentation by dendritic cells (DC) which results in insufficient T cells stimulation despite their expression of tumor-associated antigens (TAA). DC have an important role in the initiation and regulation of the innate and adaptive immune system. By efficient presentation of antigens, DC elicit an antigen-specific immune response. Trp53R172H is among the most common TP53 mutations in human PDAC, and is known as one of PDAC TAA. Despite the poor clinical outcomes, longer survival time was observed in PDAC patients with tumors that express high number of TAA combined with an abundant presentation of CD8+ T cell. To that end, we designed a DC-targeted nanoparticle (NP) containing PDAC Trp53R172H TAA and immune potentiators, with the DC targeting moiety, mannose, that was covalently conjugated to the NP, to enhance TAA presentation on DC. Thus, promote specific activation of T cells against PDAC’s TAA. The therapeutic activity of the NP was evaluated in vitro by our newly established 3D PDAC spheroids model, which composed of freshly isolated murine stromal cells, therefore, better imitates the complex microenvironment found in PDAC in vitro. Along with an in vivo PDAC model, we evaluated the safety profile and therapeutic effect of our NP. The NP proposed herein successfully activated splenocytes and induced a specific cytotoxic reaction against PDAC cells ex vivo, which may result in an improved survival rate.

Citation Format: Daniella Vaskovich-Koubi, Ron kleiner, Anat Eldar-Boock, Sabina Pozzi, Dikla Dikla Ben-Shushan, Helena F. Florindo, Ronit Satchi-Fainaro. Designing a dendritic cell-targeted immunotherapy for the treatment of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3520.

Current hurdles to the translation of nanomedicines from bench to the clinic

The field of nanomedicine has significantly influenced research areas such as drug delivery, diagnostics, theranostics, and regenerative medicine; however, the further development of this field will face significant challenges at the regulatory level if related guidance remains unclear and unconsolidated. This review describes those features and pathways crucial to the clinical translation of nanomedicine and highlights considerations for early-stage product development. These include identifying those critical quality attributes of the drug product essential for activity and safety, appropriate analytical methods (physical, chemical, biological) for characterization, important process parameters, and adequate pre-clinical models. Additional concerns include the evaluation of batch-to-batch consistency and considerations regarding scaling up that will ensure a successful reproducible manufacturing process. Furthermore, we advise close collaboration with regulatory agencies from the early stages of development to assure an aligned position to accelerate the development of future nanomedicines.

Turn on chemiluminescence-based probes for monitoring tyrosinase activity in conjunction with biological thiols

We report a chemiluminescent probe (CLPT1) that permits the paired detection of tyrosinase (Tyr) and biological thiols. Tyr only leads to a poor chemiluminescence response, a finding ascribed to the formation of a stable o-benzoquinone intermediate. The addition of glutathione (GSH), or ascorbate to the o-benzoquinone intermediate results in thiol conjugation or reduction to this intermediate, respectively. This produces a strong chemiluminescence response. Thiol co-dependence was demonstrated in live cells using the cell permeable analogue, CLPT3. The present chemiluminescence-based strategy allows the concurrent detection of tyrosinase activity and biological thiols.

BSCI-03. Adaptation of colorectal cancer cells to the brain microenvironment: The role of IRS2

Colorectal cancer (CRC) reflects the fourth most frequent etiology of brain metastasis (BM). Yet, molecular mechanisms supporting it are unknown. We aimed to explore drivers enabling adaptation of CRC cells to the brain and decipher mechanisms facilitating the process.

We analyzed the FoundationOne database, which contains genomic alterations data of cancer-related genes in over 16,000 human CRC primary and metastasis samples. Increased prevalence of IRS2 gene amplification was observed in 13% of BM, compared to only 3% of primary tumors or other metastatic sites. IRS2 is a cytoplasmic adaptor mediating effects of insulin and IGF-1 receptors and is involved in more aggressive behavior of different cancer types. In agreement with the genomic data, immunohistochemistry of human clinical samples showed increased expression of IRS2 protein in BM. We constructed an in-vitro system mimicking the brain microenvironment using cultured human astrocytes or their conditioned media. Under these conditions, IRS2-overexpressed CRC cells survived better and formed larger 3D spheres. IRS2-silenced CRC cells showed a mirror image. Moreover, in an intracranial CRC BM mouse model, IRS2-overexpressed cells generated larger brain lesions, while silencing IRS2 dramatically decreased tumor outgrowth and extended survival. Interestingly, transcriptomic analysis revealed enrichment of oxidative phosphorylation (OXPHOS) and Wnt/β-catenin pathways by IRS2. Indeed, IRS2-expressing cells showed increased mitochondrial activity and glycolysis-independent viability. Furthermore, IRS2-expressing cells had increased β-catenin transcriptional activity. Interestingly, β-catenin or IRS2 inhibition (using NT219) in IRS2-expressing cells decreased their viability, β-catenin transcriptional activity, and OXPHOS gene expression, suggesting involvement of IRS2 in modulating OXPHOS through β-catenin. β-catenin is known to confer 5-FU resistance; consequently, we showed that combination of 5-FU and NT219 worked in synergy, inhibited the formation of BM, and extended animal survival.

These data reveal the unique genomic profile of CRC BM and suggest IRS2 inhibition as a novel target for treatment of these patients.

Microengineered perfusable 3D-bioprinted glioblastoma model for in vivo mimicry of tumor microenvironment

Many drugs show promising results in laboratory research but eventually fail clinical trials. We hypothesize that one main reason for this translational gap is that current cancer models are inadequate. Most models lack the tumor-stroma interactions, which are essential for proper representation of cancer complexed biology. Therefore, we recapitulated the tumor heterogenic microenvironment by creating fibrin glioblastoma bioink consisting of patient-derived glioblastoma cells, astrocytes, and microglia. In addition, perfusable blood vessels were created using a sacrificial bioink coated with brain pericytes and endothelial cells. We observed similar growth curves, drug response, and genetic signature of glioblastoma cells grown in our 3D-bioink platform and in orthotopic cancer mouse models as opposed to 2D culture on rigid plastic plates. Our 3D-bioprinted model could be the basis for potentially replacing cell cultures and animal models as a powerful platform for rapid, reproducible, and robust target discovery; personalized therapy screening; and drug development.

Meet me halfway: Are in vitro 3D cancer models on the way to replace in vivo models for nanomedicine development?

The complexity and diversity of the biochemical processes that occur during tumorigenesis and metastasis are frequently over-simplified in the traditional in vitro cell cultures. Two-dimensional cultures limit researchers' experimental observations and frequently give rise to misleading and contradictory results. Therefore, in order to overcome the limitations of in vitro studies and bridge the translational gap to in vivo applications, 3D models of cancer were developed in the last decades. The three dimensions of the tumor, including its cellular and extracellular microenvironment, are recreated by combining co-cultures of cancer and stromal cells in 3D hydrogel-based growth factors-inclusive scaffolds. More complex 3D cultures, containing functional blood vasculature, can integrate in the system external stimuli (e.g. oxygen and nutrient deprivation, cytokines, growth factors) along with drugs, or other therapeutic compounds. In this scenario, cell signaling pathways, metastatic cascade steps, cell differentiation and self-renewal, tumor-microenvironment interactions, and precision and personalized medicine, are among the wide range of biological applications that can be studied. Here, we discuss a broad variety of strategies exploited by scientists to create in vitro 3D cancer models that resemble as much as possible the biology and patho-physiology of in vivo tumors and predict faithfully the treatment outcome.

Abstract 2716: P-selectin axis plays a key role in microglia immunophenotype and glioblastoma progression

Glioblastoma (GB) is an aggressive type of brain cancer with high mortality rate. It is a highly angiogenic tumor exhibiting an extremely invasive nature. As such, its brain microenvironment plays a crucial role in its progression. Microglia are the brain resident immune cells which have been shown to facilitate GB cell invasion and immune suppression. The mechanism by which GB cells alter microglia behavior is yet to be fully understood. One proposed mechanism involves adhesion molecules such as the Selectins family of proteins which are expressed on the surface of endothelial and immune cells and are involved in immune modulation and cancer immunity. We have previously shown that P-Selectin (SELP) is expressed by GB cells. Here, we investigated the factional role of SELP in GB-microglia interactions. First, we found that microglia cells facilitate the expression and secretion of SELP by GB cells, and that GB cells facilitate the expression of P-Selectin ligand by microglia. We then showed that SELP mediates microglia-enhanced GB invasion and proliferation in 2D and 3D in vitro models and has a role in microglia activation state. These findings were validated in vivo, showing that inhibition or downregulation of SELP leads to reduced tumor growth, increased overall survival and improved immune response. Single-Cells RNA-seq analysis of the tumors revealed an increase in pro-inflammatory microglia signature, reduction in cancer cell tumorigenesis potential and improved T cell activation. Our results indicated that SELP has an important role in GB progression and microenvironment activation. This work can improve our understanding of tumor-associated microglia function and the mechanisms by which GB cells suppress the immune system and invade the brain tissue.

Citation Format: Eilam Yeini, Paula Ofek, Sabina Pozzi, Nitzan Albeck, Dikla Ben-Shushan, Galia Tiram, Sapir Golan, Ron Kleiner, Ron Sheinin, Shlomit Reich-Zeliger, Rachel Grossman, Zvi Ram, Henry Brem, Thomas Hyde, Prerna Magod, Dinorah Friedmann-Morvinski, Asaf Madi, Ronit Satchi-Fainaro. P-selectin axis plays a key role in microglia immunophenotype and glioblastoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2716.

Abstract 714: From cancer to COVID-19- development of a dendritic cell-targeted nano-vaccine for prevention and therapy of COVID-19

Dendritic cells (DC) are antigen-presenting cells with an important role in the initiation and regulation of the innate and adaptive arms of the immune system. By efficient presentation of antigens, DC elicit an antigen-specific immune response. Therefore, we previously established in our laboratory a melanoma-DC-targeted NP that was evaluated and validated against aggressive melanoma. Although DC-therapy is mainly exploited in the treatment of cancer, DC are becoming a key therapeutic target in other pathologies such as infectious diseases. Viral pathogens, similarly, to cancer, modulate the host defense mechanisms to their benefit. COVID-19, an ongoing pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally and is already infecting tens of millions of people worldwide. Historically, vaccines are among therapies with the greatest impact in health and constitute an unmet medical need against coronavirus disease-19 (COVID-19) pandemic. To that end, we repurposed our recently published melanoma-targeted NP to co-deliver modulators of host immune response and SARS-CoV-2 specific antigen epitopes discovered by a computational approach integrating 3D information with large-scale statistical analysis. The immune response kinetics in patients infected with SARS-CoV-2 is poorly understood, but recent reports show that germinal B cells and active follicular T-helper cells, IgM/IgG SARS-CoV-2 antibodies, in addition to an enhanced cellular immunity, are found in patients with mild-to-moderate SARS-CoV-2 infection. Our preliminary data demonstrated that our nano-vaccine was able to activate specific immune cell response of effector T cells and B cells and decrease the regulatory activity of T cells, compared to controls. Moreover, we found that our DC-targeted SARS-CoV-2 NP successfully induced antigen-specific secretion of IgM and IgG antibodies with high binding affinity to the antigens. Importantly, our nano-vaccine elicited specific neutralization of Spike virus like particles (VLPs) by sera of immunized mice. We hypothesize that implementing our novel nano-vaccine platform for COVID-19 will lead to a safe and efficacious COVID-19 vaccine ready for first-in-human clinical trials.

Citation Format: Daniella Vaskovich-Koubi, Ron Kleiner, Yulia Liubomirski, Eilam Yeini, Galia Tiram, Sabina Pozzi, Anat Eldar-Boock, Helena F. Florindo, Ronit Satchi-Fainaro. From cancer to COVID-19- development of a dendritic cell-targeted nano-vaccine for prevention and therapy of COVID-19 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 714.

Abstract 2854: Adaptation of colorectal cancer cells to the brain microenvironment: the role of IRS2

Colorectal cancer (CRC) reflects the fourth most frequent etiology of brain metastasis (BM), with rising incidence. Yet, molecular mechanisms supporting the formation of these lesions from CRC are unknown. We aimed to explore drivers enabling tropism and adaptation of CRC cells to the brain environment and decipher mechanisms facilitating the process. We analyzed the FoundationOne database, which contains genomic alterations data of cancer-related genes in over 16,000 human CRC primary and metastasis samples. Increased prevalence of insulin receptor substrate 2 (IRS2) gene amplification was noted in BMs relative to primary tumors and other metastatic sites. IRS2 is a cytoplasmic adaptor mediating effects of insulin and IGF-1 receptors and is known to be involved in more aggressive behavior of different cancer types. In agreement with the genomic data, immunohistochemistry of human clinical samples showed increased expression of IRS2 protein in BMs. We subsequently constructed an in vitro system mimicking the brain microenvironment using cultured human astrocytes or their conditioned media (CM). Under these conditions using InSphero system, IRS2-overexpressed CRC cells survived better and formed larger 3D spheres. IRS2-silenced CRC cells showed a mirror image. Moreover, in an intracranial CRC surgical implantation BMs mouse model, IRS2-overexpressed CRC cells generated larger brain lesions, while silencing IRS2 in IRS2-amplified CRC cells dramatically decreased tumor outgrowth and survival. Interestingly, transcriptomic analysis revealed significant enrichment of the oxidative phosphorylation pathway by IRS2. Indeed, IRS2-expressing CRC cells showed increased mitochondrial activity using Seahorse extracellular flux analysis and glycolysis-independent viability. Furthermore, IRS2-expressing cells showed enhanced AKT phosphorylation and inhibition of PI3K or AKT using Alpelisib or iAKT, respectively, slightly decreased their proliferation in CM, suggesting that mechanisms additional to the AKT pathway may mediate IRS2 activity. The Wnt/β-catenin pathway was among the most significantly enriched pathways in the transcriptome. Indeed, IRS2-expressing cells had increased transcriptional activity of the β-catenin. In addition, iAKT or Alpelisib, and most significantly the IRS2 inhibitor (NT219), decreased the transcriptional activity of β-catenin in IRS2-expressing CRC cells, suggesting relevance of IRS2 in activating β-catenin. Moreover, NT219 demonstrated significant and dose-dependent inhibition of CRC cells viability. These data reveal, for the first time, the unique genomic profile of CRC BMs and imply the IRS2 role in promoting CRC BMs. These effects may be mediated, at least in part, by modulation of the AKT and β-catenin pathway. Given the molecular signature described, the approach to patients with BMs may be significantly impacted by agents such as NT219.

Citation Format: Inbal Greenberg, Anat Klein, Rachel Grossman, Ethan Sokol, Eilam Yeini, Paula Ofek, Ronit Satchi-Fainaro, Bertrand Liang, Hadas Reuveni, Tami Rubinek, Ido Wolf. Adaptation of colorectal cancer cells to the brain microenvironment: the role of IRS2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2854.

Abstract 1746: Designing a dendritic cell-targeted immunotherapy for the treatment of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death. Low response rate, acquired resistance, severe side effects, highly desmoplastic and immunosuppressive microenvironment have limited the clinical outcomes of immunotherapy in PDAC. To overcome these hurdles, we set to design a novel immunotherapy that would be safe, efficacious, and selective to PDAC. The failure of immunotherapies to yield clinical response in PDAC is partially attributed to the inefficient antigen presentation by dendritic cells (DC) which results in insufficient T cells stimulation despite their expression of tumor-associated antigens (TAA). DC have an important role in the initiation and regulation of the innate and adaptive arms of the immune system. By efficient presentation of antigens, DC elicit an antigen-specific immune response. Trp53R172H is among the most common TP53 mutations in human PDAC, and is known as one of PDAC TAA. Despite the poor clinical outcomes, longer survival time was observed in PDAC patients with tumors that express high number of TAA combined with an abundant presentation of CD8+ T cell. To that end, we designed a DC-targeted nanoparticle (NP) containing PDAC Trp53R172H TAA and immune potentiators, with the DC targeting moiety, mannose, that was covalently conjugated to the NP, to enhance TAA presentation on DC. This approach led to specific activation of T cells against PDAC's TAA. The therapeutic activity of the NP was evaluated in vitro by our newly established 3D PDAC spheroids model, which is composed of freshly isolated murine stromal cells, therefore, better imitates the complex microenvironment found in PDAC. Along with an in vivo PDAC model, we evaluated the safety profile and therapeutic efficacy of our NP. The NP proposed herein successfully activated splenocytes and induced a specific cytotoxic reaction against PDAC cells ex vivo, which may result in improved survival rate.

Citation Format: Ron Kleiner, Daniella Vaskovich, Sabina Pozzi, Anat Eldar-Boock, Dikla Ben-Shushan, Helena Florindo, Ronit Satchi-Fainaro. Designing a dendritic cell-targeted immunotherapy for the treatment of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1746.

Abstract 2850: Astrocyte-breast cancer interactions facilitate brain metastasis

Diagnosis and treatment of breast cancer patients have been considerably improved, including those at the metastatic stage. However, brain metastasis still presents a major clinical challenge, and it is a leading cause of death. Unfortunately, there are no targeted therapies specific for this secondary tumor, and the current treatment modalities present limited clinical outcomes. Thus, better understanding of the pathways involved in the metastatic cascade, which lead to brain metastases colonization and progression, is essential. To that end, we investigated the mutual effects of astrocytes and breast cancer cells, using the traditional 2-dimensional (2D) cell-culture and a newly-established 3-dimensional (3D) model of multicellular breast cancer brain metastases spheroids. We found that astrocytes enhance the proliferation, migration and invasion of breast cancer cells, suggesting a supportive role for astrocytes in the metastatic process of breast cancer in the brain. Using a protein array, we identified several cytokines which were elevated following the co-culturing of breast cancer cells with astrocytes, suggesting them as potential key candidates involved in breast cancer-brain stroma interactions. One of these cytokines was MCP-1, which is a chemokine that is associated with poor prognosis in breast cancer patients. When it was functionally neutralized, breast cancer cell proliferation and migration rates were decreased, in addition to reduced invasion shown in our 3D-spheroid model. Considering these results, MCP-1 is proposed as one of the key factors promoting breast cancer brain metastasis. Although further validation using in vivo models is still required, this study deepens our understanding of the contribution of the metastatic breast cancer cells-brain microenvironment crosstalk to brain colonization. Taken together, our findings may be utilized to provide a novel therapeutic approach for the prevention of breast cancer brain metastasis following resection of the primary lesion.

Keywords: Breast Cancer, Brain Metastasis, Brain Microenvironment, Astrocytes, Cytokines, Chemokines, MCP-1, CCL2, 3D Tumor Spheroids.

Citation Format: Sahar Israeli Dangoor, Ori Hadad, Ronit Satchi-Fainaro. Astrocyte-breast cancer interactions facilitate brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2850.

P-selectin axis plays a key role in microglia immunophenotype and glioblastoma progression

Glioblastoma (GB) is a highly invasive type of brain cancer exhibiting poor prognosis. As such, its microenvironment plays a crucial role in its progression. Among the brain stromal cells, the microglia were shown to facilitate GB invasion and immunosuppression. However, the reciprocal mechanisms by which GB cells alter microglia/macrophages behavior are not fully understood. We propose that these mechanisms involve adhesion molecules such as the Selectins family. These proteins are involved in immune modulation and cancer immunity. We show that P-selectin mediates microglia-enhanced GB proliferation and invasion by altering microglia/macrophages activation state. We demonstrate these findings by pharmacological and molecular inhibition of P-selectin which leads to reduced tumor growth and increased survival in GB mouse models. Our work sheds light on tumor-associated microglia/macrophage function and the mechanisms by which GB cells suppress the immune system and invade the brain, paving the way to exploit P-selectin as a target for GB therapy.

Abstract PO-003: Adaptation of colorectal cancer cells to the brain microenvironment: The role of IRS2

Brain metastases (BMs) from colorectal cancer (CRC) are currently the fourths leading cause of BMs, and their incidence is on the rise. Yet, mechanisms mediating the formation of BMs from CRC are unknown. We aimed to explore genomic drivers enabling tropism and adaptation of CRC cells to the brain environment and decipher mechanisms facilitating the process. We analyzed FoundationOne database, which contains genomic alterations data of cancer-related genes in over 16,000 human CRC primary and metastasis samples. Increased prevalence was noted in the insulin receptor substrate 2 (IRS2) gene, which was significantly amplified in BMs relative to primary tumors and other metastatic sites. IRS2 is a cytoplasmic adaptor mediating effects of insulin and IGF-1 receptors and is known to be involved in more aggressive behavior of different cancer types. In agreement with the genomic data, immunohistochemistry of human clinical samples showed increased expression of IRS2 protein in BMs. Next, we created an in-vitro system mimicking the brain microenvironment using human astrocytes or their conditioned media (CM). Under these conditions, IRS2-overexpressed CRC cells survived better and formed larger 3D spheres. IRS2-silenced CRC cells showed a mirror image. Furthermore, IRS2-overexpressed CRC cells generated larger brain lesions in an intracranial CRC BMs mice model. Interestingly, a transcriptomic analysis revealed significant enrichment of the AKT and β-catenin pathways by IRS2. Indeed, IRS2-amplified cells showed enhanced AKT phosphorylation and inhibition of PI3K or AKT using Alpelisib or Akt1/2 kinase inhibitor, respectively, effectively decreased their proliferation in CM. Importantly, IRS2-amplified cells had increased expression and transcriptional activity of the β-catenin, and AKT pathway inhibitors or IRS2 inhibitor (NT-219) had a more pronounced effect on the activity of β-catenin on those cells. These data indicate, for the first time, the unique genomic profile of CRC BMs and imply the IRS2 role in promoting CRC BMs. These effects may be mediated, at least in part, by modulation of the AKT and β-catenin pathway. These findings may pave the way for the development of novel therapeutic strategies to prevent BMs formation.

Citation Format: Inbal Greenberg, Anat Klein, Rachel Grossman, Ethan Sokol, Eilam Yeini, Paula Ofek, Ronit Satchi-Fainaro, Hadas Reuveni, Tami Rubinek, Ido Wolf. Adaptation of colorectal cancer cells to the brain microenvironment: The role of IRS2 [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-003.

Spontaneous regression of micro-metastases following primary tumor excision: a critical role for primary tumor secretome

Background

Numerous case studies have reported spontaneous regression of recognized metastases following primary tumor excision, but underlying mechanisms are elusive. Here, we present a model of regression and latency of metastases following primary tumor excision and identify potential underlying mechanisms.

Results

Using MDA-MB-231^HM human breast cancer cells that express highly sensitive luciferase, we monitored early development stages of spontaneous metastases in BALB/c nu/nu mice. Removal of the primary tumor caused marked regression of micro-metastases, but not of larger metastases, and in vivo supplementation of tumor secretome diminished this regression, suggesting that primary tumor-secreted factors promote early metastatic growth. Correspondingly, MDA-MB-231^HM-conditioned medium increased in vitro tumor proliferation and adhesion and reduced apoptosis. To identify specific mediating factors, cytokine array and proteomic analysis of MDA-MB-231^HM secretome were conducted. The results identified significant enrichment of angiogenesis, growth factor binding and activity, focal adhesion, and metalloprotease and apoptosis regulation processes. Neutralization of MDA-MB-231^HM-secreted key mediators of these processes, IL-8, PDGF-AA, Serpin E1 (PAI-1), and MIF, each antagonized secretome-induced proliferation. Moreover, their in vivo simultaneous blockade in the presence of the primary tumor arrested the development of micro-metastases. Interestingly, in the METABRIC cohort of breast cancer patients, elevated expression of Serpin E1, IL-8, or the four factors combined predicted poor survival.

Conclusions

These results demonstrate regression and latency of micro-metastases following primary tumor excision and a crucial role for primary tumor secretome in promoting early metastatic growth in MDA-MB-231^HM xenografts. If generalized, such findings can suggest novel approaches to control micro-metastases and minimal residual disease.

Bone metastasis is associated with acquisition of mesenchymal phenotype and immune suppression in a model of spontaneous breast cancer metastasis

The most common site of breast cancer metastasis is the bone, occurring in approximately 70% of patients with advanced disease. Bone metastasis is associated with severe morbidities and high mortality. Therefore, deeper understanding of the mechanisms that enable bone-metastatic relapse are urgently needed. We report the establishment and characterization of a bone-seeking variant of breast cancer cells that spontaneously forms aggressive bone metastases following surgical resection of primary tumor. We characterized the modifications in the immune milieu during early and late stages of metastatic relapse and found that the formation of bone metastases is associated with systemic changes, as well as modifications of the bone microenvironment towards an immune suppressive milieu. Furthermore, we characterized the intrinsic changes in breast cancer cells that facilitate bone-tropism and found that they acquire mesenchymal and osteomimetic features. This model provides a clinically relevant platform to study the functional interactions between breast cancer cells and the bone microenvironment, in an effort to identify novel targets for intervention.

Immune-mediated approaches against COVID-19

The coronavirus disease-19 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The long incubation period of this new virus, which is mostly asymptomatic yet contagious, is a key reason for its rapid spread across the world. Currently, there is no worldwide-approved treatment for COVID-19. Therefore, the clinical and scientific communities have joint efforts to reduce the severe impact of the outbreak. Research on previous emerging infectious diseases have created valuable knowledge that is being exploited for drug repurposing and accelerated vaccine development. Nevertheless, it is important to generate knowledge on SARS-CoV-2 mechanisms of infection and its impact on host immunity, to guide the design of COVID-19 specific therapeutics and vaccines suitable for mass immunization. Nanoscale delivery systems are expected to play a paramount role in the success of these prophylactic and therapeutic approaches. This Review provides an overview of SARS-CoV-2 pathogenesis and examines immune-mediated approaches currently explored for COVID-19 treatments, with an emphasis on nanotechnological tools.

Collagenase Nanoparticles Enhance the Penetration of Drugs into Pancreatic Tumors

Overexpressed extracellular matrix (ECM) in pancreatic ductal adenocarcinoma (PDAC) limits drug penetration into the tumor and is associated with poor prognosis. Here, we demonstrate that a pretreatment based on a proteolytic-enzyme nanoparticle system disassembles the dense PDAC collagen stroma and increases drug penetration into the pancreatic tumor. More specifically, the collagozome, a 100 nm liposome encapsulating collagenase, was rationally designed to protect the collagenase from premature deactivation and prolonged its release rate at the target site. Collagen is the main component of the PDAC stroma, reaching 12.8 ± 2.3% vol in diseased mice pancreases, compared to 1.4 ± 0.4% in healthy mice. Upon intravenous injection of the collagozome, ∼1% of the injected dose reached the pancreas over 8 h, reducing the level of fibrotic tissue to 5.6 ± 0.8%. The collagozome pretreatment allowed increased drug penetration into the pancreas and improved PDAC treatment. PDAC tumors, pretreated with the collagozome followed by paclitaxel micelles, were 87% smaller than tumors pretreated with empty liposomes followed by paclitaxel micelles. Interestingly, degrading the ECM did not increase the number of circulating tumor cells or metastasis. This strategy holds promise for degrading the extracellular stroma in other diseases as well, such as liver fibrosis, enhancing tissue permeability before drug administration.

Immunization with mannosylated nanovaccines and inhibition of the immune-suppressing microenvironment sensitizes melanoma to immune checkpoint modulators

A low response rate, acquired resistance and severe side effects have limited the clinical outcomes of immune checkpoint therapy. Here, we show that combining cancer nanovaccines with an anti-PD-1 antibody (αPD-1) for immunosuppression blockade and an anti-OX40 antibody (αOX40) for effector T-cell stimulation, expansion and survival can potentiate the efficacy of melanoma therapy. Prophylactic and therapeutic combination regimens of dendritic cell-targeted mannosylated nanovaccines with αPD-1/αOX40 demonstrate a synergism that stimulates T-cell infiltration into tumours at early treatment stages. However, this treatment at the therapeutic regimen does not result in an enhanced inhibition of tumour growth compared to αPD-1/αOX40 alone and is accompanied by an increased infiltration of myeloid-derived suppressor cells in tumours. Combining the double therapy with ibrutinib, a myeloid-derived suppressor cell inhibitor, leads to a remarkable tumour remission and prolonged survival in melanoma-bearing mice. The synergy between the mannosylated nanovaccines, ibrutinib and αPD-1/αOX40 provides essential insights to devise alternative regimens to improve the efficacy of immune checkpoint modulators in solid tumours by regulating the endogenous immune response.

Novel Oligo-Guanidyl-PEG Carrier Forming Rod-Shaped Polyplexes

A novel unconventional supramolecular oligo-cationic structure (Agm₆-M-PEG-OCH₃) has been synthesized to yield high efficiency therapeutic oligonucleotide (ON) delivery. Agm₆-M-PEG-OCH₃ was obtained by a multistep protocol that included the conjugation of agmatine (Agm) moieties to maltotriose (M), which was further derivatized with one poly(ethylene glycol) (PEG) chain. Gel electrophoresis analysis showed that the 19 base pairs dsDNA model ON completely associates with Agm₆-M-PEG-OCH₃ at 3 N/P molar ratio, which is in agreement with the in silico molecular predictions. Isothermal titration calorimetry (ITC) analyses showed that the Agm₆-M-PEG-OCH₃/ON association occurs through a combination of mechanisms depending on the N/P ratios resulting in different nanostructures. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that the Agm₆-M-PEG-OCH₃/ON polyplexes have rod-shape structure with a mean diameter of 50-75 nm and aspect ratio depending on the N/P ratio. The polyplexes were stable over time in buffer, while a slight size increase was observed in the presence of serum proteins. Cell culture studies showed that neither Agm₆-M-PEG-OCH₃ nor polyplexes displayed cytotoxic effects. Cellular uptake depended on the cell line and polyplex composition: cellular internalization was higher in the case of MCF-7 and KB cells compared to MC3T3-E1 cells and polyplexes with smaller aspect ratio were taken-up by cells more efficiently than polyplexes with higher aspect ratio. Finally, preliminary studies showed that our novel carrier efficiently delivered ONs into cells providing gene silencing.

Light emission enhancement by supramolecular complexation of chemiluminescence probes designed for bioimaging

Chemiluminescence offers advantages over fluorescence for bioimaging, since an external light source is unnecessary with chemiluminescent agents. This report demonstrates the first encapsulation of chemiluminescence phenoxy-adamantyl-1,2-dioxetane probes with trimethyl β-cyclodextrin. Clear proof for the formation of a 1 : 1 host-guest complex between the adamantyl-1,2-dioxetane probe and trimethyl β-cyclodextrin was provided by mass spectroscopy and NMR experiments. The calculated association constant of this host-guest system, 253 M-1, indicates the formation of a stable inclusion complex. The inclusion complex significantly amplified the light emission intensity relative to the noncomplexed probe under physiological conditions. Complexation of adamantyl-dioxetane with fluorogenic dye-tethered cyclodextrin resulted in light emission through energy transfer to a wavelength that corresponds to the fluorescent emission of the conjugated dye. Remarkably, the light emission intensity of this inclusion complex was approximately 1500-fold higher than that of the non-complexed adamantyl-dioxetane guest. We present the first demonstration of microscopic cell images obtained using a chemiluminescence supramolecular dioxetane probe and demonstrate the utility of these supramolecular complexes by imaging of enzymatic activity and bio-analytes in vitro and in vivo. We anticipate that the described chemiluminescence supramolecular dioxetane probes will find use in various biological applications.

ortho-Chlorination of phenoxy 1,2-dioxetane yields superior chemiluminescent probes for in vitro and in vivo imaging

A recent methodology, developed by our group, has enabled a dramatic improvement in the emissive nature of the excited species, formed during the chemiexcitation of dioxetanes under physiological conditions. This approach has resulted in the discovery of distinct phenoxy-dioxetane luminophores that produce a chemiluminescence signal via a direct-mode of emission. Here, we show a significant pK_a effect of our new phenoxy-dioxetanes on their chemiexcitation and on their ability to serve as chemiluminescent turn-ON probes for biological applications. Using an appropriate phenoxy-dioxetane probe with a direct-mode of emission, we were able to image β-galactosidase activity, in cancer cells and in tumor-bearing mice. To the best of our knowledge, this is the first example to demonstrate in vitro and in vivo endogenous enzymatic chemiluminescence images obtained by a single-component phenoxy-dioxetane probe. We anticipate that our strategy, for the design and synthesis of such distinct luminophores, will assist in providing new effective turn-ON probes for non-invasive intravital chemiluminescence imaging techniques.

α-Galactosylceramide and peptide-based nano-vaccine synergistically induced a strong tumor suppressive effect in melanoma

α-Galactosylceramide (GalCer) is a glycolipid widely known as an activator of Natural killer T (NKT) cells, constituting a promising adjuvant against cancer, including melanoma. However, limited clinical outcomes have been obtained so far. This study evaluated the synergy between GalCer and major histocompatibility complex (MHC) class I and MHC class II melanoma-associated peptide antigens and the Toll-Like Receptor (TLR) ligands CpG and monophosphoryl lipid A (MPLA), which we intended to maximize following their co-delivery by a nanoparticle (NP). This is expected to improve GalCer capture by dendritic cells (DCs) and subsequent presentation to NKT cells, simultaneously inducing an anti-tumor specific T-cell mediated immunity. The combination of GalCer with melanoma peptides and TLR ligands successfully restrained tumor growth. The tumor volume in these animals was 5-fold lower than the ones presented by mice immunized with NPs not containing GalCer. However, tumor growth was controlled at similar levels by GalCer entrapped or in its soluble form, when mixed with antigens and TLR ligands. Those two groups showed an improved infiltration of T lymphocytes into the tumor, but only GalCer-loaded nano-vaccine induced a prominent and enhanced infiltration of NKT and NK cells. In addition, splenocytes of these animals secreted levels of IFN-γ and IL-4 at least 1.5-fold and 2-fold higher, respectively, than those treated with the mixture of antigens and adjuvants in solution. Overall, the combined delivery of the NKT agonist with TLR ligands and melanoma antigens via this multivalent nano-vaccine displayed a synergistic anti-tumor immune-mediated efficacy in B16F10 melanoma mouse model.

STATEMENT OF SIGNIFICANCE

Combination of α-galactosylceramide (GalCer), a Natural Killer T (NKT) cell agonist, with melanoma-associated antigens presented by MHC class I (Melan-A:26) and MHC class II (gp100:44) molecules, and Toll-like Receptor (TLR) ligands (MPLA and CpG), within nanoparticle matrix induced a prominent anti-tumor immune response able to restrict melanoma growth. An enhanced infiltration of NKT and NK cells into tumor site was only achieved when the combination GalCer, antigens and TLR ligands were co-delivered by the nanovaccine.

Reverting the molecular fingerprint of tumor dormancy as a therapeutic strategy for glioblastoma

Glioblastoma is an aggressive and invasive brain malignancy with high mortality rates despite current treatment modalities. In this study, we show that a 7-gene signature, previously found to govern the switch of glioblastomas from dormancy to aggressive tumor growth, correlates with improved overall survival of patients with glioblastoma. Using glioblastoma dormancy models, we validated the role of 2 genes from the signature, thrombospondin-1 ( TSP-1) and epidermal growth factor receptor ( EGFR), as regulators of glioblastoma dormancy and explored their therapeutic potential. EGFR up-regulation was reversed using EGFR small interfering RNA polyplex, antibody, or small-molecule inhibitor. The diminished function of TSP-1 was augmented via a peptidomimetic. The combination of EGFR inhibition and TSP-1 restoration led to enhanced therapeutic efficacy in vitro, in 3-dimensional patient-derived spheroids, and in a subcutaneous human glioblastoma model in vivo. Systemic administration of the combination therapy to mice bearing intracranial murine glioblastoma resulted in marginal therapeutic outcomes, probably due to brain delivery challenges, p53 mutation status, and the aggressive nature of the selected cell line. Nevertheless, this study provides a proof of concept for exploiting regulators of tumor dormancy for glioblastoma therapy. This therapeutic strategy can be exploited for future investigations using a variety of therapeutic entities that manipulate the expression of dormancy-associated genes in glioblastoma as well as in other cancer types.-Tiram, G., Ferber, S., Ofek, P., Eldar-Boock, A., Ben-Shushan, D., Yeini, E., Krivitsky, A., Blatt, R., Almog, N., Henkin, J., Amsalem, O., Yavin, E., Cohen, G., Lazarovici, P., Lee, J. S., Ruppin, E., Milyavsky, M., Grossman, R., Ram, Z., Calderón, M., Haag, R., Satchi-Fainaro, R. Reverting the molecular fingerprint of tumor dormancy as a therapeutic strategy for glioblastoma.

Image-guided surgery using near-infrared Turn-ON fluorescent nanoprobes for precise detection of tumor margins

Complete tumor removal during surgery has a great impact on patient survival. To that end, the surgeon should detect the tumor, remove it and validate that there are no residual cancer cells left behind. Residual cells at the incision margin of the tissue removed during surgery are associated with tumor recurrence and poor prognosis for the patient. In order to remove the tumor tissue completely with minimal collateral damage to healthy tissue, there is a need for diagnostic tools that will differentiate between the tumor and its normal surroundings. Methods: We designed, synthesized and characterized three novel polymeric Turn-ON probes that will be activated at the tumor site by cysteine cathepsins that are highly expressed in multiple tumor types. Utilizing orthotopic breast cancer and melanoma models, which spontaneously metastasize to the brain, we studied the kinetics of our polymeric Turn-ON nano-probes. Results: To date, numerous low molecular weight cathepsin-sensitive substrates have been reported, however, most of them suffer from rapid clearance and reduced signal shortly after administration. Here, we show an improved tumor-to-background ratio upon activation of our Turn-ON probes by cathepsins. The signal obtained from the tumor was stable and delineated the tumor boundaries during the whole surgical procedure, enabling accurate resection. Conclusions: Our findings show that the control groups of tumor-bearing mice, which underwent either standard surgery under white light only or under the fluorescence guidance of the commercially-available imaging agents ProSense® 680 or 5-aminolevulinic acid (5-ALA), survived for less time and suffered from tumor recurrence earlier than the group that underwent image-guided surgery (IGS) using our Turn-ON probes. Our "smart" polymeric probes can potentially assist surgeons' decision in real-time during surgery regarding the tumor margins needed to be removed, leading to improved patient outcome.

PEGylated dendritic polyglycerol conjugate targeting NCAM-expressing neuroblastoma: Limitations and challenges

Neural cell adhesion molecule (NCAM) is found to be a stem-cell marker in several tumor types and its overexpression is known to correlate with increased metastatic capacity. To combine extravasation- and ligand-dependent targeting to NCAM overexpressing-cells in the tumor microenvironment, we developed a PEGylated NCAM-targeted dendritic polyglycerol (PG) conjugate. Here, we describe the synthesis, physico-chemical characterization and biological evaluation of a PG conjugate bearing the mitotic inhibitor paclitaxel (PTX) and an NCAM-targeting peptide (NTP). PG-NTP-PTX-PEG was evaluated for its ability to inhibit neuroblastoma progression in vitro and in vivo as compared to non-targeted derivatives and free drug. NCAM-targeted conjugate inhibited the migration of proliferating endothelial cells, suggesting it would be able to inhibit tumor angiogenesis. The targeting conjugate provided an improved binding and uptake on IMR-32 cells compared to non-targeted control. However, these results did not translate to our in vivo model on orthotopic neuroblastoma bearing mice.

Amphiphilic poly(α)glutamate polymeric micelles for systemic administration of siRNA to tumors

RNAi therapeutics carried a great promise to the area of personalized medicine: the ability to target "undruggable" oncogenic pathways. Nevertheless, their efficient tumor targeting via systemic administration had not been resolved yet. Amphiphilic alkylated poly(α)glutamate amine (APA) can serve as a cationic carrier to the negatively-charged oligonucleotides. APA polymers complexed with siRNA to form round-shaped, homogenous and reproducible nano-sized polyplexes bearing ~50 nm size and slightly negative charge. In addition, APA:siRNA polyplexes were shown to be potent gene regulators in vitro. In light of these preferred physico-chemical characteristics, their performance as systemically-administered siRNA nanocarriers was investigated. Intravenously-injected APA:siRNA polyplexes accumulated selectively in tumors and did not accumulate in the lungs, heart, liver or spleen. Nevertheless, the polyplexes failed to induce specific mRNA degradation, hence neither reduction in tumor volume nor prolonged mice survival was seen.

Nanoparticulate vaccine inhibits tumor growth via improved T cell recruitment into melanoma and huHER2 breast cancer

Nanoparticulate vaccines are promising tools to overcome cancer immune evasion. However, a deeper understanding on nanoparticle-immune cell interactions and treatments regime is required for optimal efficacy. We provide a comprehensive study of treatment schedules and mode of antigen-association to nanovaccines on the modulation of T cell immunity in vivo, under steady-state and tumor-bearing mice. The coordinated delivery of antigen and two adjuvants (Monophosphoryl lipid A, oligodeoxynucleotide cytosine-phosphate-guanine motifs (CpG)) by nanoparticles was crucial for dendritic cell activation. A single vaccination dictated a 3-fold increase on cytotoxic memory-T cells and raised antigen-specific immune responses against B16.M05 melanoma. It generated at least a 5-fold increase on IFN-γ cytokine production, and presented over 50% higher lymphocyte count in the tumor microenvironment, compared to the control. The number of lymphocytes at the tumor site doubled with triple immunization. This lymphocyte infiltration pattern was confirmed in mammary huHER2 carcinoma, with significant tumor reduction.

Amphiphilic nanocarrier-induced modulation of PLK1 and miR-34a leads to improved therapeutic response in pancreatic cancer

The heterogeneity of pancreatic ductal adenocarcinoma (PDAC) suggests that successful treatment might rely on simultaneous targeting of multiple genes, which can be achieved by RNA interference-based therapeutic strategies. Here we show a potent combination of microRNA and siRNA delivered by an efficient nanocarrier to PDAC tumors. Using proteomic-microRNA profiles and survival data of PDAC patients from TCGA, we found a novel signature for prolonged survival. Accordingly, we used a microRNA-mimic to increase miR-34a together with siRNA to silence PLK1 oncogene. For in vivo dual-targeting of this combination, we developed a biodegradable amphiphilic polyglutamate amine polymeric nanocarrier (APA). APA-miRNA-siRNA polyplexes systemically administered to orthotopically inoculated PDAC-bearing mice showed no toxicity and accumulated at the tumor, resulting in an enhanced antitumor effect due to inhibition of MYC oncogene, a common target of both miR-34a and PLK1. Taken together, our findings warrant this unique combined polyplex's potential as a novel nanotherapeutic for PDAC.

Macrophage-Induced Lymphangiogenesis and Metastasis following Paclitaxel Chemotherapy Is Regulated by VEGFR3

While chemotherapy strongly restricts or reverses tumor growth, the response of host tissue to therapy can counteract its anti-tumor activity by promoting tumor re-growth and/or metastases, thus limiting therapeutic efficacy. Here, we show that vascular endothelial growth factor receptor 3 (VEGFR3)-expressing macrophages infiltrating chemotherapy-treated tumors play a significant role in metastasis. They do so in part by inducing lymphangiogenesis as a result of cathepsin release, leading to VEGF-C upregulation by heparanase. We found that macrophages from chemotherapy-treated mice are sufficient to trigger lymphatic vessel activity and structure in naive tumors in a VEGFR3-dependent manner. Blocking VEGF-C/VEGFR3 axis inhibits the activity of chemotherapy-educated macrophages, leading to reduced lymphangiogenesis in treated tumors. Overall, our results suggest that disrupting the VEGF-C/VEGFR3 axis not only directly inhibits lymphangiogenesis but also blocks the pro-metastatic activity of macrophages in chemotherapy-treated mice.

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Chemotherapy promotes macrophage colonization of tumors

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Macrophages induce lymphangiogenesis in chemotherapy-treated tumors

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Macrophages secrete cathepsins, VEGF-C, and heparanase in a VEGFR3-dependent manner

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Blocking VEGFR3 in macrophages inhibits lymphangiogenesis and subsequent metastasis

Co-targeting the tumor endothelium and P-selectin-expressing glioblastoma cells leads to a remarkable therapeutic outcome

Glioblastoma is a highly aggressive brain tumor. Current standard-of-care results in a marginal therapeutic outcome, partly due to acquirement of resistance and insufficient blood-brain barrier (BBB) penetration of chemotherapeutics. To circumvent these limitations, we conjugated the chemotherapy paclitaxel (PTX) to a dendritic polyglycerol sulfate (dPGS) nanocarrier. dPGS is able to cross the BBB, bind to P/L-selectins and accumulate selectively in intracranial tumors. We show that dPGS has dual targeting properties, as we found that P-selectin is not only expressed on tumor endothelium but also on glioblastoma cells. We delivered dPGS-PTX in combination with a peptidomimetic of the anti-angiogenic protein thrombospondin-1 (TSP-1 PM). This combination resulted in a remarkable synergistic anticancer effect on intracranial human and murine glioblastoma via induction of Fas and Fas-L, with no side effects compared to free PTX or temozolomide. This study shows that our unique therapeutic approach offers a viable alternative for the treatment of glioblastoma.