Bispecific PD1-IL2v and anti-PD-L1 break tumor immunity resistance by enhancing stem-like tumor-reactive CD8+ T cells and reprogramming macrophages

Immunotherapies have shown remarkable, albeit tumor-selective, therapeutic benefits in the clinic. Most patients respond transiently at best, highlighting the importance of understanding mechanisms underlying resistance. Herein, we evaluated the effects of the engineered immunocytokine PD1-IL2v in a mouse model of de novo pancreatic neuroendocrine cancer that is resistant to checkpoint and other immunotherapies. PD1-IL2v utilizes anti-PD-1 as a targeting moiety fused to an immuno-stimulatory IL-2 cytokine variant (IL2v) to precisely deliver IL2v to PD-1⁺ T cells in the tumor microenvironment. PD1-IL2v elicited substantial infiltration by stem-like CD8⁺ T cells, resulting in tumor regression and enhanced survival in mice. Combining anti-PD-L1 with PD1-IL2v sustained the response phase, improving therapeutic efficacy both by reprogramming immunosuppressive tumor-associated macrophages and enhancing T cell receptor (TCR) immune repertoire diversity. These data provide a rationale for clinical trials to evaluate the combination therapy of PD1-IL2v and anti-PD-L1, particularly in immunotherapy-resistant tumors infiltrated with PD-1⁺ stem-like T cells.

Aberrant hyperexpression of the RNA binding protein FMRP in tumors mediates immune evasion

Many human cancers manifest the capability to circumvent attack by the adaptive immune system. In this work, we identified a component of immune evasion that involves frequent up-regulation of fragile X mental retardation protein (FMRP) in solid tumors. FMRP represses immune attack, as revealed by cancer cells engineered to lack its expression. FMRP-deficient tumors were infiltrated by activated T cells that impaired tumor growth and enhanced survival in mice. Mechanistically, FMRP’s immunosuppression was multifactorial, involving repression of the chemoattractant C-C motif chemokine ligand 7 (CCL7) concomitant with up-regulation of three immunomodulators—interleukin-33 (IL-33), tumor-secreted protein S (PROS1), and extracellular vesicles. Gene signatures associate FMRP’s cancer network with poor prognosis and response to therapy in cancer patients. Collectively, FMRP is implicated as a regulator that orchestrates a multifaceted barrier to antitumor immune responses.

Cancer cell autophagy, reprogrammed macrophages, and remodeled vasculature in glioblastoma triggers tumor immunity

Glioblastoma (GBM) is poorly responsive to therapy and invariably lethal. One conceivable strategy to circumvent this intractability is to co-target distinctive mechanistic components of the disease, aiming to concomitantly disrupt multiple capabilities required for tumor progression and therapeutic resistance. We assessed this concept by combining vascular endothelial growth factor (VEGF) pathway inhibitors that remodel the tumor vasculature with the tricyclic antidepressant imipramine, which enhances autophagy in GBM cancer cells and unexpectedly reprograms immunosuppressive tumor-associated macrophages via inhibition of histamine receptor signaling to become immunostimulatory. While neither drug is efficacious as monotherapy, the combination of imipramine with VEGF pathway inhibitors orchestrates the infiltration and activation of CD8 and CD4 T cells, producing significant therapeutic benefit in several GBM mouse models. Inclusion up front of immune-checkpoint blockade with anti-programmed death-ligand 1 (PD-L1) in eventually relapsing tumors markedly extends survival benefit. The results illustrate the potential of mechanism-guided therapeutic co-targeting of disparate biological vulnerabilities in the tumor microenvironment.

Abstract 71: The immunocytokine PD1-IL2v overcomes immune checkpoint resistance, and combination with an anti-PD-L1 antibody further enhances its anti-tumor activity

Cancer immunotherapies have shown therapeutic benefits in the clinic, but treatments involving immuno-stimulatory agents such as interleukin 2 (IL-2) are typically accompanied by severe adverse events. One strategy to limit the systemic toxicity of IL-2 is to target it specifically to the tumor microenvironment. Here we evaluated the therapeutic efficacy of the bi-specific immunocytokine PD1-IL2v in the genetically engineered, spontaneous RIP1-Tag5 (RT5) mouse model of pancreatic neuroendocrine tumors (PanNETs). PD1-IL2v is a bi-specific molecule based on a bivalent PD-1 antibody to which a single IL2 variant (IL2v) is fused. PD-1 serves as a targeting moiety to deliver IL2v in cis to PD-1-positive T cells located in the immune tumor microenvironment, and IL2v has been engineered to lack binding to CD25 in order to selectively expand effector T cells but not immuno-suppressive regulatory T cells (Tregs). Although RT5 mice are capable of mounting an adaptive immune response against the tumor-driving oncoprotein, PanNETs developing in RT5 are resistant to immune checkpoint inhibitors. In comparing the untargeted version of IL2v combined with an anti-PD-1 antibody vs. the PD-1 targeted immunocytokine PD1-IL2v, we found that PD1-IL2v, but not the mixture, produced significant anti-tumor activity. PD1-IL2v treatment resulted in a substantial infiltration of CD8+ T cells into the pancreatic islet tumors, which in the context of sustained treatment with PD1-IL2v resulted in tumor regression. Interestingly, following tumor shrinkage, the PanNETs appeared to stabilize and eventually relapsed. Notably, we identified up-regulation of PD-L1 on the tumor vasculature in relapsing tumors as a potential factor in the observed adaptive resistance, which encouraged combining an anti-PD-L1 antibody with PD1-IL2v, leading to enhanced therapeutic benefit. The data obtained in this spontaneous de novo tumor model motivate consideration of evaluating the PD1-IL2v/anti-PD-L1 combination therapy in the clinical setting, in particular in anti-PD-1/anti-PD-L1 resistant tumors infiltrated with PD1+CD8+ T cells.

Citation Format: Stephan Wullschleger, Mélanie Tichet, Laura Codarri-Deak, Pablo Umana, Christian Klein, Douglas Hanahan. The immunocytokine PD1-IL2v overcomes immune checkpoint resistance, and combination with an anti-PD-L1 antibody further enhances its anti-tumor activity [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 71.

ALK7 Signaling Manifests a Homeostatic Tissue Barrier That Is Abrogated during Tumorigenesis and Metastasis

Herein, we report that the TGFß superfamily receptor ALK7 is a suppressor of tumorigenesis and metastasis, as revealed by functional studies in mouse models of pancreatic neuroendocrine and luminal breast cancer, complemented by experimental metastasis assays. Activation in neoplastic cells of the ALK7 signaling pathway by its principal ligand activin B induces apoptosis. During tumorigenesis, cancer cells use two different approaches to evade this barrier, either downregulating activin B and/or downregulating ALK7. Suppressing ALK7 expression additionally contributes to the capability for metastatic seeding. ALK7 is associated with shorter relapse-free survival of various human cancers and distant-metastasis-free survival of breast cancer patients. This study introduces mechanistic insights into primary and metastatic tumor development, in the form of a protective barrier that triggers apoptosis in cells that are not "authorized" to proliferate within a particular tissue, by virtue of those cells expressing ALK7 in a tissue microenvironment bathed in its ligand.

Myeloid Cells Orchestrate Systemic Immunosuppression, Impairing the Efficacy of Immunotherapy against HPV+ Cancers

Cancers induced by human papillomaviruses (HPV) should be responsive to immunotherapy by virtue of expressing the immunogenic oncoproteins E6/E7. However, advanced forms of cervical cancer, driven by HPV, are poorly responsive to immune response-enhancing treatments involving therapeutic vaccination against these viral neoantigens. Leveraging a transgenic mouse model of HPV-derived cancers, K14HPV16/H2b, we demonstrated that a potent nanoparticle-based E7 vaccine, but not a conventional "liquid" vaccine, induced E7 tumor antigen-specific CD8+ T cells in cervical tumor-bearing mice. Vaccination alone or in combination with anti-PD-1/anti-CTLA4 did not elicit tumor regression nor increase CD8+ T cells in the tumor microenvironment (TME), suggesting the presence of immune-suppressive barriers. Patients with cervical cancer have poor dendritic cell functions, have weak cytotoxic lymphocyte responses, and demonstrate an accumulation of myeloid cells in the periphery. Here, we illustrated that myeloid cells in K14HPV16/H2b mice possess potent immunosuppressive activity toward antigen-presenting cells and CD8+ T cells, dampening antitumor immunity. These immune-inhibitory effects inhibited synergistic effects of combining our oncoprotein vaccine with immune checkpoint-blocking antibodies. Our data highlighted a link between HPV-induced cancers, systemic amplification of myeloid cells, and the detrimental effects of myeloid cells on CD8+ T-cell activation and recruitment into the TME. These results established immunosuppressive myeloid cells in lymphoid organs as an HPV+ cancer-induced means of circumventing tumor immunity that will require targeted abrogation to enable the induction of efficacious antitumor immune responses.

Cancer cell-derived long pentraxin 3 (PTX3) promotes melanoma migration through a toll-like receptor 4 (TLR4)/NF-κB signaling pathway

Cutaneous melanoma is one of the most aggressive cancers characterized by a high plasticity, a propensity for metastasis, and drug resistance. Melanomas are composed of phenotypically diverse subpopulations of tumor cells with heterogeneous molecular profiles that reflect intrinsic invasive abilities. In an attempt to identify novel factors of the melanoma invasive cell state, we previously investigated the nature of the invasive secretome by using a comparative proteomic approach. Here, we have extended this analysis to show that PTX3, an acute phase inflammatory glycoprotein, is one such factor secreted by invasive melanoma to promote tumor cell invasiveness. Elevated PTX3 production was observed in the population of MITFlow invasive cells but not in the population of MITFhigh differentiated melanoma cells. Consistently, MITF knockdown increased PTX3 expression in MITFhigh proliferative and poorly invasive cells. High levels of PTX3 were found in tissues and blood of metastatic melanoma patients, and in BRAF inhibitor-resistant melanoma cells displaying a mesenchymal invasive MITFlow phenotype. Genetic silencing of PTX3 in invasive melanoma cells dramatically impaired migration and invasion in vitro and in experimental lung extravasation assay in xenografted mice. In contrast, addition of melanoma-derived or recombinant PTX3, or expression of PTX3 enhanced motility of low migratory cells. Mechanistically, autocrine production of PTX3 by melanoma cells triggered an IKK/NFκB signaling pathway that promotes migration, invasion, and expression of the EMT factor TWIST1. Finally, we found that TLR4 and MYD88 knockdown inhibited PTX3-induced melanoma cell migration, suggesting that PTX3 functions through a TLR4-dependent pathway. Our work reveals that tumor-derived PTX3 contributes to melanoma cell invasion via targetable inflammation-related pathways. In addition to providing new insights into the biology of melanoma invasive behavior, this study underscores the notion that secreted PTX3 represents a potential biomarker and therapeutic target in a subpopulation of MITFlow invasive and/or refractory melanoma.

Nanoparticle Conjugation of Human Papillomavirus 16 E7-long Peptides Enhances Therapeutic Vaccine Efficacy against Solid Tumors in Mice

Treatment of patients bearing human papillomavirus (HPV)-related cancers with synthetic long-peptide (SLP) therapeutic vaccines has shown promising results in clinical trials against premalignant lesions, whereas responses against later stage carcinomas have remained elusive. We show that conjugation of a well-documented HPV-E7 SLP to ultra-small polymeric nanoparticles (NP) enhances the antitumor efficacy of therapeutic vaccination in different mouse models of HPV⁺ cancers. Immunization of TC-1 tumor-bearing mice with a single dose of NP-conjugated E7LP (NP-E7LP) generated a larger pool of E7-specific CD8⁺ T cells with increased effector functions than unconjugated free E7LP. At the tumor site, NP-E7LP prompted a robust infiltration of CD8⁺ T cells that was not accompanied by concomitant accumulation of regulatory T cells (Tregs), resulting in a higher CD8⁺ T-cell to Treg ratio. Consequently, the amplified immune response elicited by the NP-E7LP formulation led to increased regression of large, well-established tumors, resulting in a significant percentage of complete responses that were not achievable by immunizing with the non-NP-conjugated long-peptide. The partial responses were characterized by distinct phases of regression, stable disease, and relapse to progressive growth, establishing a platform to investigate adaptive resistance mechanisms. The efficacy of NP-E7LP could be further improved by therapeutic activation of the costimulatory receptor 4-1BB. This NP-E7LP formulation illustrates a "solid-phase" antigen delivery strategy that is more effective than a conventional free-peptide ("liquid") vaccine, further highlighting the potential of using such formulations for therapeutic vaccination against solid tumors. Cancer Immunol Res; 6(11); 1301-13. ©2018 AACR.

Targeting the Proteasome-Associated Deubiquitinating Enzyme USP14 Impairs Melanoma Cell Survival and Overcomes Resistance to MAPK-Targeting Therapies

Advanced cutaneous melanoma is one of the most challenging cancers to treat because of its high plasticity, metastatic potential, and resistance to treatment. New targeted therapies and immunotherapies have shown remarkable clinical efficacy. However, such treatments are limited to a subset of patients and relapses often occur, warranting validation of novel targeted therapies. Posttranslational modification of proteins by ubiquitin coordinates essential cellular functions, including ubiquitin-proteasome system (UPS) function and protein homeostasis. Deubiquitinating enzymes (DUB) have been associated to multiple diseases, including cancer. However, their exact involvement in melanoma development and therapeutic resistance remains poorly understood. Using a DUB trap assay to label cellular active DUBs, we have observed an increased activity of the proteasome-associated DUB, USP14 (Ubiquitin-specific peptidase 14) in melanoma cells compared with melanocytes. Our survey of public gene expression databases indicates that high expression of USP14 correlates with melanoma progression and with a poorer survival rate in metastatic melanoma patients. Knockdown or pharmacologic inhibition of USP14 dramatically impairs viability of melanoma cells irrespective of the mutational status of BRAF, NRAS, or TP53 and their transcriptional cell state, and overcomes resistance to MAPK-targeting therapies both in vitro and in human melanoma xenografted mice. At the molecular level, we find that inhibition of USP14 rapidly triggers accumulation of poly-ubiquitinated proteins and chaperones, mitochondrial dysfunction, ER stress, and a ROS production leading to a caspase-independent cell death. Our results provide a rationale for targeting the proteasome-associated DUB USP14 to treat and combat melanomas. Mol Cancer Ther; 17(7); 1416-29. ©2018 AACR.

Cellular endogenous NAD(P)H fluorescence as a label-free method for the identification of erythrocytes and reticulocytes

Reticulocytes and erythrocytes are the ultimate differentiated stages of erythropoiesis. In addition to being anucleate cells, they are characterized by the clearance of their mitochondrial pool or lack thereof. Given that for most research-oriented flow cytometry experiments erythrocytes and reticulocytes are often undesirable cell types, their identification and exclusion from analyses can be essential. Here, we describe a flow cytometric method based on cellular NAD(P)H-related autofluorescence, whose localization is mainly associated with mitochondria. By increasing the sensitivity of the specific NAD(P)H-fluorescence detector, we discovered a population with weak levels of NAD(P)H fluorescence signals whose immunophenotypical and physiological characterization in mouse bone marrow led to its identification as both erythrocytes and reticulocytes. Our method showed comparable sensitivity and specificity to the detection of red blood cells based on the absorption of light by oxyhemoglobin. This NAD(P)H-based approach consistently identified over 95% of the total pool of erythrocytes and reticulocytes in bone marrow samples and revealed robust as over 93% of these two erythropoietic subsets were identified in melanoma tumor samples with the same method. The measurement of cellular endogenous NAD(P)H fluorescence, therefore, offers a reliable and straightforward alternative to identify erythrocytes and reticulocytes without additional immunostaining or the need to modify the cytometer's optical configuration. © 2018 International Society for Advancement of Cytometry.

SIGMAR1 Regulates Membrane Electrical Activity in Response to Extracellular Matrix Stimulation to Drive Cancer Cell Invasiveness

The sigma 1 receptor (Sig1R) is a stress-activated chaperone that regulates ion channels and is associated with pathologic conditions, such as stroke, neurodegenerative diseases, and addiction. Aberrant expression levels of ion channels and Sig1R have been detected in tumors and cancer cells, such as myeloid leukemia and colorectal cancer, but the link between ion channel regulation and Sig1R overexpression during malignancy has not been established. In this study, we found that Sig1R dynamically controls the membrane expression of the human voltage-dependent K(+) channel human ether-à-go-go-related gene (hERG) in myeloid leukemia and colorectal cancer cell lines. Sig1R promoted the formation of hERG/β1-integrin signaling complexes upon extracellular matrix stimulation, triggering the activation of the PI3K/AKT pathway. Consequently, the presence of Sig1R in cancer cells increased motility and VEGF secretion. In vivo, Sig1R expression enhanced the aggressiveness of tumor cells by potentiating invasion and angiogenesis, leading to poor survival. Collectively, our findings highlight a novel function for Sig1R in mediating cross-talk between cancer cells and their microenvironment, thus driving oncogenesis by shaping cellular electrical activity in response to extracellular signals. Given the involvement of ion channels in promoting several hallmarks of cancer, our study also offers a potential strategy to therapeutically target ion channel function through Sig1R inhibition.

Tumour-derived SPARC drives vascular permeability and extravasation through endothelial VCAM1 signalling to promote metastasis

Disruption of the endothelial barrier by tumour-derived secreted factors is a critical step in cancer cell extravasation and metastasis. Here, by comparative proteomic analysis of melanoma secretomes, we identify the matricellular protein SPARC as a novel tumour-derived vascular permeability factor. SPARC deficiency abrogates tumour-initiated permeability of lung capillaries and prevents extravasation, whereas SPARC overexpression enhances vascular leakiness, extravasation and lung metastasis. SPARC-induced paracellular permeability is dependent on the endothelial VCAM1 receptor and p38 MAPK signalling. Blocking VCAM1 impedes melanoma-induced endothelial permeability and extravasation. The clinical relevance of our findings is highlighted by high levels of SPARC detected in tumour from human pulmonary melanoma lesions. Our study establishes tumour-produced SPARC and VCAM1 as regulators of cancer extravasation, revealing a novel targetable interaction for prevention of metastasis.

Metformin blocks melanoma invasion and metastasis development in AMPK/p53-dependent manner

Metformin was reported to inhibit the proliferation of many cancer cells, including melanoma cells. In this report, we investigated the effect of metformin on melanoma invasion and metastasis development. Using different in vitro approaches, we found that metformin inhibits cell invasion without affecting cell migration and independently of antiproliferation action. This inhibition is correlated with modulation of expression of proteins involved in epithelial-mesenchymal transition such as Slug, Snail, SPARC, fibronectin, and N-cadherin and with inhibition of MMP-2 and MMP-9 activation. Furthermore, our data indicate that this process is dependent on activation of AMPK and tumor suppressor protein p53. Finally, we showed that metformin inhibits melanoma metastasis development in mice using extravasation and metastasis models. The presented data reinforce the fact that metformin might be a good candidate for clinical trial in melanoma treatment.

The p53/p21Cip1/ Waf1 pathway mediates the effects of SPARC on melanoma cell cycle progression

Secreted protein acidic and rich in cysteine (SPARC), or osteonectin, belongs to the family of matricellular proteins that modulate cell-matrix interactions and cellular functions. SPARC is highly expressed in melanoma, and we reported that SPARC promotes epithelial/mesenchymal-like changes and cell migration. Here, we used siRNA and conditional shRNA to investigate the contribution of tumor-derived SPARC to melanoma cell growth in vitro and in vivo. We found that depletion of SPARC induces G2/M cell cycle arrest and tumor growth inhibition with activation of p53 and induction of p21(Cip1/Waf1) acting as a checkpoint, preventing efficient mitotic progression. In addition, we demonstrate that reduced mesenchymal features and the invasive potential of SPARC-silenced cells are independent of p21(Cip1/Waf1) induction and cell cycle arrest. Importantly, overexpression of SPARC reduces p53 protein levels and leads to an increase in cell number during exponential growth. Our findings indicate that in addition to its well-known function as a mediator of melanoma cell migration and tumor-host interactions, SPARC regulates, in a cell-autonomous manner, cell cycle progression and proliferation through the p53/p21(Cip1/Waf1) pathway.