Abstract 4624: Profiling antitumor activity, immune cell infiltration, pharmokinetics, and receptor occupancy in a murine colon cancer model following immune checkpoint blockade

Clinical success of immune checkpoint blocking antibodies has accelerated the evaluation of immune-related targets for novel anti-cancer therapies. Preclinical testing of immune-targeted oncology agents requires preclinical models with functional immune systems. Utilization of murine syngeneic tumor models provides a robust system to evaluate anti-tumor activity and mechanism of action. This study evaluates the anti-tumor activity and immune response of different immune-oncology therapies in the CT26.WT murine colon cancer model. In addition, an anti-PD-1 pharmacokinetic profile was established and receptor occupancy evaluated.

For this study, C57BL/6JOlaHsd mice were subcutaneously inoculated with CT26.WT cells. Tumor bearing mice were administered anti-CTLA-4, anti-PD-1, anti-PD-L1, anti-OX40, or anti-LAG3 monotherapy twice weekly for 3 weeks. Tumor volume was used to assess anti-tumor activity. Immune response to checkpoint blockade was monitored in a subset of tumors, and lymphocyte and myeloid populations were analyzed following two weeks of dosing. In addition, an anti-PD-1 pharmacokinetic profile experiment was performed using LC-MS/MS on mouse plasma from multiple time points. PD-1 receptor occupancy was also determined by flow cytometry utilizing a saturation/detection method.

Following 3 weeks of monotherapy treatment all immune checkpoint blocking therapies, anti-CTLA4, anti-PD-1, anti-PD-L1, anti-OX40, and anti-LAG3, resulted in significant antitumor response in CT26.WT derived tumors. Phenotypes of tumor infiltrating lymphocytes (TILs) resident in tumors were profiled across check point inhibitor treatments: CD45+ lymphocytes were analyzed for populations of cytotoxic lymphocytes (CTLs, CD8+ cells), T-helper cells (CD4+ cells), regulatory T-cells (T-regs, CD4+/CD25+/FoxP3+ cells). The immune cell responses to checkpoint inhibitors were distinct and varied across immune checkpoint blocking antibodies. Furthermore, an empirical exposure-response analysis of anti-PD-1 in the CT26.WT colon model was demonstrated using a novel LC/MS-MS method of detection. Dose dependent occupancy of PD-1 receptors by anti-PD-1 in CT26.WT tumors was also observed.

Our results demonstrate a significant anti-tumor response across five immune checkpoint blocking antibodies in the CT26.WT colon cancer model; however, immune response profiles are notably different across these blocking antibodies. Importantly, a novel LC/MS-MS method was developed specifically in mouse plasma to determine exposure response. Utilizing these multiple data sets will allow for PK/PD modeling to generate expectations for future dose response. This type of comprehensive analysis constitutes a highly-relevant tool to evaluate efficacy and mechanism of action for novel immune-targeted therapies for oncology.

Citation Format: Patrick Allison, Hua-Chen Chang, Paul Trampont, Lindsey Standarski, Lauren Urisic, Jennifer Rusk, Jaydeep Mehta, Joshua Fohey, Eric Thomas, Karan Agrawal, Brandy Wilkinson. Profiling antitumor activity, immune cell infiltration, pharmokinetics, and receptor occupancy in a murine colon cancer model following immune checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4624.

ShcA and c-Abl provide a new signaling axis regulating beta-selection (63.8)

Progression of immature CD4-CD8- thymocytes through β selection checkpoint is determined by signals from the pre-T cell receptor (pre-TCR) along with signals from Notch. Knockout of the adapter protein ShcA, or transgenic expression of a phosphorylation-defective mutant of ShcA (ShcFFF) leads to a severe block at β selection. Our studies to mechanistically understand the ShcA function showed that ShcA acts upstream of ERK, and the transcription factors Egr-1 and Egr-3 during β selection; however, phospho-ShcA also appeared to be linked to other signaling pathways. We performed a yeast three-hybrid screen, using as bait ShcA that was phosphorylated by Lck. This screen identified binding of c-Abl (via its SH2 domain) to phosphorylated ShcA. During pre TCR dependent signaling, phosphorylation of ShcA was required for optimal c-Abl phosphorylation. Using mice deficient either in c-Abl and/or its homologue Arg, we show that ShcA and c-Abl regulate DN thymocyte proliferation, and the proper localization of DN thymocytes near the thymic cortex. Ectopic expression of a constitutive active c-Abl allowed thymocytes to resume proliferation, differentiation, and CXCR4 dependent migration to SDF-1α. Collectively, these data reveal a previously unappreciated ShcA::c-Abl signaling axis that appears to critically influence thymic β selection.

ShcA mediates the dominant pathway to extracellular signal-regulated kinase activation during early thymic development

During thymic development, the beta selection checkpoint is regulated by pre-T-cell receptor-initiated signals. Progression through this checkpoint is influenced by phosphorylation and activation of the serine/threonine kinases extracellular signal-regulated kinase 1 (ERK1) and ERK2, but the in vivo relevance of specific upstream players leading to ERK activation is not known. Here, using mice with a conditional loss of the shc1 gene or expressing mutants of ShcA, we demonstrate that the adapter protein ShcA is responsible for up to 70% of ERK activation in double-negative (DN) thymocytes in vivo and ex vivo. We also identify two specific tyrosines on ShcA that promote ERK phosphorylation in vivo, and mice expressing ShcA with mutations of these tyrosines show impaired DN thymocyte development. This work provides the first in vivo demonstration of the relative requirement of upstream adapters in controlling ERK activation during beta selection and suggests a dominant role for ShcA.

The placental-umbilical unit in sickle cell disease pregnancy: A model for studying in vivo functional adjustments to hypoxia in humans

The placental-umbilical unit in sickle cell disease (SCD) pregnancy was used to explore hypoxia in vivo, an important factor in the pathophysiology of this disease. Gross examination and microscopic analysis of the placentas, taken immediately after delivery, indicate good concordance between maturity and term as controls, but higher frequency of vascular injuries such as excess syncytial knots, excess fibrin deposits, congestion and villous necroses. Unexpectedly, neither leukocyte recruitment nor alteration in extraplacental membrane was observed, suggesting the absence of inflammation. Additionally, interleukin (IL)-6 and IL-8 concentrations, measured by enzyme-linked immunosorbent assay (ELISA), were similar in the placental maternal blood from controls and SCD. There were also no significant differences found in IL-6 vein blood concentrations between controls and SCD, IL-8 being not detected. Immunostaining of umbilical vein endothelium in SCD pregnancies showed redistribution of PECAM-1 (CD31), von Willebrand factor (vWF), and P-selectin to the cell surface, controls exhibiting the classical pattern. Staining quantification indicated increases in vWF (+36.2%; P=.006) and vascular endothelial growth factor (VEGF) expression (+96.0%; P=.006) over control, but a reduction in endothelial nitric oxide synthase (eNOS) (-45.5%; P=.029). These results document, for the first time, direct functional adjustments in response to hypoxia in human in vivo. The mechanism for these changes has not been clearly established, but it may reflect increased tolerance to SCD hypoxic conditions and hypoxia in general.

Hypermethylation of metallothionein-3 CpG island in gastric carcinoma

The expression of metallothionein (MT)-3 is often markedly reduced in gastric carcinoma (GC). The molecular mechanism of this MT-3 downregulation is unknown. Transcriptional silencing of MT-3 by methylation of CpG island was investigated by nucleotide sequencing and denaturing high performance liquid chromatography (DHPLC) analyses. We found that normal brain tissue and a xenografted GC that expressed MT-3 mRNA had unmethylated regions of the CpG island in intron1 of this gene. On the other hand, gastric cancer cell lines AGS and MKN445, a xenografted GC, and a representative primary gastric cancer that had no expression of MT-3 mRNA demonstrated hypermethylation of the MT-3 intron1 CpG island. Treatment of the gastric cancer cell lines with 5-azacytidine resulted in new expression of MT-3 mRNA in these cells. A quantifying DHPLC assay was developed to determine the methylation status of this specific region of the MT-3 gene. Fifty-eight primary GC and their corresponding normal gastric epithelial tissues, and 34 normal gastric mucosa were analyzed for MT-3 methylation by DHPLC in the region of methylation abnormalities initially identified. Our DHPLC analyses of the methylated MT-3 product demonstrated that the primary gastric cancers have an average methylation percentage of 6.3% per tumor compared with 2.4% in normal gastric tissues (P < 0.05). The MT-3 was not methylated in all of eight P53-positive GCs and hypermethylated in eight of 13 P53-negative cases by immunohistochemistry staining (P = 0.007). In conclusion, the CpG island in the MT-3 intron1 are abnormally hypermethylated in many gastric carcinomas and may account for the downregulation of MT-3 in gastric carcinogenesis.

Apoptosis of immature thymocytes mediated by E2/CD99

E2/CD99 is a 32-kDa transmembrane molecule that does not belong to any known family of proteins. It appears to regulate adhesion properties of T cells as previously reported, in particular, the induction of homotypic adhesion in CD4+ CD8+ thymocytes. Apoptosis induced via E2/CD99 displays characteristic morphologic features, but includes early mitochondrial alterations and phosphatidylserine exposure at the outer leaflet of the plasma membrane. It is not followed by detectable DNA fragmentation, and its time course is much longer than apoptosis induced via the Fas/CD95 pathway. It requires 18 h for completion. E2/CD99-induced apoptosis does not require any RNA or protein synthesis and still occurs following blockage of the Fas pathway. It is, however, dependent on CPP32 and IL-1beta-converting enzyme-type cysteine proteases, as shown by blockade with their respective specific inhibitors. This effect is restricted to double-positive thymocytes carrying an intermediate density of CD3 and including all CD69+ cells. Thus, E2/CD99 apears to mediate a distinctive apoptotic signal at a critical stage of thymocyte differentiation, i.e., when positive selection is known to occur.

Apoptosis of immature thymocytes mediated by E2/CD99

E2/CD99 is a 32-kDa transmembrane molecule that does not belong to any known family of proteins. It appears to regulate adhesion properties of T cells as previously reported, in particular, the induction of homotypic adhesion in CD4+ CD8+ thymocytes. Apoptosis induced via E2/CD99 displays characteristic morphologic features, but includes early mitochondrial alterations and phosphatidylserine exposure at the outer leaflet of the plasma membrane. It is not followed by detectable DNA fragmentation, and its time course is much longer than apoptosis induced via the Fas/CD95 pathway. It requires 18 h for completion. E2/CD99-induced apoptosis does not require any RNA or protein synthesis and still occurs following blockage of the Fas pathway. It is, however, dependent on CPP32 and IL-1beta-converting enzyme-type cysteine proteases, as shown by blockade with their respective specific inhibitors. This effect is restricted to double-positive thymocytes carrying an intermediate density of CD3 and including all CD69+ cells. Thus, E2/CD99 apears to mediate a distinctive apoptotic signal at a critical stage of thymocyte differentiation, i.e., when positive selection is known to occur.

Chemoembolization: principles and perspectives

Chemoembolization is the injection of active-principle-bearing microparticles via selective catheterization. The authors discuss the advantages and the possibilities of this method in relation to selective catheterization and to the various time periods required for microparticle biodegradation and the kinetics of drug release. Particular attention is paid to intra-arterial chemoperfusion, chemoembolization and chemoinfusion with microparticles.

[A study in dogs of micropellets for use in angiographic therapeutic procedures (author's transl)]

A study was conducted in dogs to evaluate the effect on the organism of a new embolisation material: carnauba wax micropellets. The ultimate objective was to study the possible use of micropellets containing an active product for therapy in situ. Renal embolisation was performed by selective or highly selective arterial catheterisation in dogs. Pathological examination demonstrated that only mild foreign body reactions occurred at the embolisation site. Overall tolerance was good. The micropellets were shown to possess some biodegradation properties and to be susceptible to deformation. An attempt is made to define the ideal micropellet from the point of view of size, kinetic features, and biodegradation properties.