Abstract 262: Inhibition of the novel immune checkpoint CEACAM1 enhances antitumor immunological activity

Blockade of co-inhibitory immune receptors has become a promising approach for the activation of anti-tumor immunity. CEACAM1, a recently characterized immune checkpoint, is a member of the Ig superfamily expressed by activated effector lymphocytes and cancer cells. Expression of CEACAM1 on cancer cells induces a co-inhibitory signal to T and NK cells through homophilic CEACAM1 interactions. CEACAM1 is expressed across multiple tumor types and its presence is independent of PD-L1 expression.

CM-24 is a humanized anti-CEACAM1 IgG4 antibody with high affinity and selectivity for CEACAM1. We investigated the activity of CM-24 and its ability to reverse CEACAM1-induced immune evasion alone and in combination with other checkpoint inhibitors. CM-24 was demonstrated to be a potent blocker of intercellular CEACAM1-CEACAM1 interactions and reversed inhibition of activated lymphocytes by restoring the phosphorylation signal of ZAP70. CM-24 enhanced the cytotoxic activity of cytotoxic T cell and NK cells against various cancer types, which was accompanied by higher secretion of Granzyme B and IFNγ. In addition, a synergistic activity with various immune checkpoint blockers was observed, including ones that target the PD-1 pathway. Various in vivo tumor xenograft models demonstrated that CM-24 has clear anti-tumor activity accompanied by an increase in immunological activity of T cells within the tumor. Collectively, preclinical data show that CM-24 has effective anti-tumor activity in various in vitro and in vivo models and demonstrate that CM-24 has the potential to enhance the cytotoxic activity of lymphocytes against malignant cells. CM-24 is now moving towards phase 1 clinical study.

Citation Format: Gal Markel, Ilana Mandel, Yair Sapir, Motti Hakim, Sharon Hashmueli, Tehila Ben-Moshe. Inhibition of the novel immune checkpoint CEACAM1 enhances antitumor immunological activity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 262. doi:10.1158/1538-7445.AM2015-262

Preclinical and first-in-human evaluation of PRX-105, a PEGylated, plant-derived, recombinant human acetylcholinesterase-R

PRX-105 is a plant-derived recombinant version of the human 'read-through' acetylcholinesterase splice variant (AChE-R). Its active site structure is similar to that of the synaptic variant, and it displays the same affinity towards organophosphorus (OP) compounds. As such, PRX-105 may serve as a bio-scavenger for OP pesticides and chemical warfare agents. To assess its potential use in prophylaxis and treatment of OP poisoning we conducted several preliminary tests, reported in this paper. Intravenous (IV) PRX-105 was administered to mice either before or after exposure to an OP toxin. All mice who received an IV dose of 50nmol/kg PRX-105, 2min before being exposed to 1.33×LD50 and 1.5×LD50 of toxin and 10min after exposure to 1.5×LD50 survived. The pharmacokinetic and toxicity profiles of PRX-105 were evaluated in mice and mini-pigs. Following single and multiple IV doses (50 to 200mg/kg) no deaths occurred and no significant laboratory and histopathological changes were observed. The overall elimination half-life (t½) in mice was 994 (±173) min. Additionally, a first-in-human study, to assess the safety, tolerability and pharmacokinetics of the compound, was conducted in healthy volunteers. The t½ in humans was substantially longer than in mice (average 26.7h). Despite the small number of animals and human subjects who were assessed, the fact that PRX-105 exerts a protective and therapeutic effect following exposure to lethal doses of OP, its favorable safety profile and its relatively long half-life, renders it a promising candidate for treatment and prophylaxis against OP poisoning and warrants further investigation.

Survival function of the FADD-CASPASE-8-cFLIP(L) complex

Caspase-8, the initiator caspase of the death receptor pathway of apoptosis, its adapter molecule, FADD, required for caspase-8 activation, and cFLIPL, a caspase-8-like protein that lacks a catalytic site and blocks caspase-8-mediated apoptosis, are each essential for embryonic development. Animals deficient in any of these genes present with E10.5 embryonic lethality. Recent studies have shown that development in caspase-8-deficient mice is rescued by ablation of RIPK3, a kinase that promotes a form of programmed, necrotic cell death. Here, we show that FADD, RIPK3 double-knockout mice develop normally but that the lethal effects of cFLIP deletion are not rescued by RIPK3 deficiency. Remarkably, in mice lacking FADD, cFLIP, and RIPK3, embryonic development is normal. This can be explained by the convergence of two cell processes: the enzymatic activity of the FADD-caspase-8-cFLIPL complex blocks RIPK3-dependent signaling (including necrosis), whereas cFLIPL blocks RIPK3-independent apoptosis promoted by the FADD-caspase-8 complex.

Novel immunotherapy for malignant melanoma with a monoclonal antibody that blocks CEACAM1 homophilic interactions

CEACAM1 (biliary glycoprotein-1, CD66a) was reported as a strong clinical predictor of poor prognosis in melanoma. We have previously identified CEACAM1 as a tumor escape mechanism from cytotoxic lymphocytes. Here, we present substantial evidence in vitro and in vivo that blocking of CEACAM1 function with a novel monoclonal antibody (MRG1) is a promising strategy for cancer immunotherapy. MRG1, a murine IgG1 monoclonal antibody, was raised against human CEACAM1. It recognizes the CEACAM1-specific N-domain with high affinity (K(D) ~ 2 nmol/L). Furthermore, MRG1 is a potent inhibitor of CEACAM1 homophilic binding and does not induce any agonistic effect. We show using cytotoxicity assays that MRG1 renders multiple melanoma cell lines more vulnerable to T cells in a dose-dependent manner, only following antigen-restricted recognition. Accordingly, MRG1 significantly enhances the antitumor effect of adoptively transferred, melanoma-reactive human lymphocytes using human melanoma xenograft models in severe combined immunodeficient/nonobese diabetic (SCID/NOD) mice. A significant antibody-dependent cell cytotoxicity response was excluded. It is shown that MRG1 reaches the tumor and is cleared within a week. Importantly, approximately 90% of melanoma specimens are CEACAM1(+), implying that the majority of patients with melanoma could be amenable to MRG1-based therapy. Normal human tissue microarray displays limited binding to luminal epithelial cells on some secretory ducts, which was weaker than the broad normal cell binding of other anticancer antibodies in clinical use. Importantly, MRG1 does not directly affect CEACAM1(+) cells. CEACAM1 blockade is different from other immunomodulatory approaches, as MRG1 targets inhibitory interactions between tumor cells and late effector lymphocytes, which is thus a more specific and compartmentalized immune stimulation with potentially superior safety profile.

Adaptive alternative splicing correlates with less environmental risk of parkinsonism

BACKGROUND/OBJECTIVE

Environmental exposure to anti-acetylcholinesterases (AChEs) aggravates the risk of Parkinsonism due to currently unclear mechanism(s). We explored the possibility that the brain's capacity to induce a widespread adaptive alternative splicing response to such exposure may be involved.

METHODS

Following exposure to the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), brain region transcriptome profiles were tested.

RESULTS

Changes in transcript profiles, alternative splicing patterns and splicing-related gene categories were identified. Engineered mice over-expressing the protective AChE-R splice variant showed less total changes but more splicing-related ones than hypersensitive AChE-S over-expressors with similarly increased hydrolytic activities. Following MPTP exposure, the substantia nigra and prefrontal cortex (PFC) of both strains showed a nuclear increase in the splicing factor ASF/SF2 protein. Furthermore, intravenous injection with highly purified recombinant human AChE-R changed transcript profiles in the striatum.

CONCLUSIONS

Our findings are compatible with the working hypothesis that inherited or acquired alternative splicing deficits may promote parkinsonism, and we propose adaptive alternative splicing as a strategy for attenuating its progression.

Accelerated carcinogenesis following liver regeneration is associated with chronic inflammation-induced double-strand DNA breaks

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and is considered to be the outcome of chronic liver inflammation. Currently, the main treatment for HCC is surgical resection. However, survival rates are suboptimal partially because of tumor recurrence in the remaining liver. Our aim was to understand the molecular mechanisms linking liver regeneration under chronic inflammation to hepatic tumorigenesis. Mdr2-KO mice, a model of inflammation-associated cancer, underwent partial hepatectomy (PHx), which led to enhanced hepatocarcinogenesis. Moreover, liver regeneration in these mice was severely attenuated. We demonstrate the activation of the DNA damage-response machinery and increased genomic instability during early liver inflammatory stages resulting in hepatocyte apoptosis, cell-cycle arrest, and senescence and suggest their involvement in tumor growth acceleration subsequent to PHx. We propose that under the regenerative proliferative stress induced by liver resection, the genomic unstable hepatocytes generated during chronic inflammation escape senescence and apoptosis and reenter the cell cycle, triggering the enhanced tumorigenesis. Thus, we clarify the immediate and long-term contributions of the DNA damage response to HCC development and recurrence.

Caspase-8 serves both apoptotic and nonapoptotic roles

Knockout of caspase-8, a cysteine protease that participates in the signaling for cell death by receptors of the TNF/nerve growth factor family, is lethal to mice in utero. To explore tissue-specific roles of this enzyme, we established its conditional knockout using the Cre/loxP recombination system. Consistent with its role in cell death induction, deletion of caspase-8 in hepatocytes protected them from Fas-induced caspase activation and death. However, application of the conditional knockout approach to investigate the cause of death of caspase-8 knockout embryos revealed that this enzyme also serves cellular functions that are nonapoptotic. Its deletion in endothelial cells resulted in degeneration of the yolk sac vasculature and embryonal death due to circulatory failure. Caspase-8 deletion in bone-marrow cells resulted in arrest of hemopoietic progenitor functioning, and in cells of the myelomonocytic lineage, its deletion led to arrest of differentiation into macrophages and to cell death. Thus, besides participating in cell death induction by receptors of the TNF/nerve growth factor family, caspase-8, apparently independently of these receptors, also mediates nonapoptotic and perhaps even antiapoptotic activities.

vFLIP protects PC-12 cells from apoptosis induced by Sindbis virus: implications for the role of TNF-alpha

Sindbis virus (SV) is an alphavirus used as a model for studying the pathogenesis of viral encephalitis. In this study we examined the effects and the mechanisms involved in the apoptosis induced by SV in PC-12 cells, and the role of a vFLIP in this process. Infection of PC-12 cells with a neurovirulent strain of SV, SVNI, induced cell apoptosis. Overexpression of vFLIP encoded by the HHV-8 or treatment with a caspase-8 inhibitor inhibited cell apoptosis. SVNI induced an increase in the expression of tumor necrosis factor alpha (TNF-alpha), and pre-treatment of the cells with an anti-TNF-alpha blocking antibody or with soluble TNF-alpha receptor abrogated the apoptotic effect of SVNI. Moreover, TNF-alpha R1 knockout mice were more resistant to the cytopathic effects of the virus as compared to control animals. Our results indicate that the apoptosis induced by SVNI is mediated by activation of caspase-8, and that TNF-alpha plays an important role in the apoptotic response.

Differential regulation of Bcl-2 and Bax expression in cells infected with virulent and nonvirulent strains of sindbis virus

Sindbis virus is an alphavirus that infects cells in either lytic or persistent infection. In this study we examined the effects of Sindbis virus on cell apoptosis and on the expression of Bcl-2 and Bax. Of the two strains studied, SVA and SVNI, only the neurovirulent strain, SVNI, induced apoptosis of astrocytes and PC-12 cells. SVA, which infects cells in a persistent manner, induced up-regulation of bcl-2 mRNA and Bcl-2 protein, whereas SVNI induced an increase in Bax levels. Our results indicate a differential regulation of Bcl2 and Bax expression by SVA and SVNI, which may be associated with the apoptotic potential of the viruses.