Abstract 1476: A therapeutic antibody that inhibits CD73 activity by dual mechanisms

CD73 has a central role in dictating the adenosine concentration within the tumor as it is the final step in converting extracellular ATP to adenosine. Thus, substantial reduction of CD73 enzymatic activity has the potential to reduce immunosuppression of effector immune cells within the tumor. We present data describing an anti-human CD73 antibody that suppresses CD73 by two mechanisms: 1. direct inhibition of enzymatic activity upon binding to CD73 and 2. rapid, near-complete internalization of the enzyme. Durable reduction of cell-surface CD73 was observed in multiple tumor cell lines both in vitro and in vivo. The unique properties of this antibody are a result of the use of a human IgG2-IgG1 hybrid antibody with effector function eliminated by specific mutations of the Fc. The IgG2 sequence of this antibody drives superior internalization of CD73 and enhanced CD73 inhibition. Syngeneic tumor models demonstrate that CD73 contributes to resistance to anti-tumor therapy. Combination therapy with PD-1 blockade and a surrogate anti-mouse-CD73 antibody resulted in a better anti-tumor efficacy than either treatment alone. Finally, we demonstrate a novel technique for assessing CD73 enzymatic activity in situ that has potential for clinical application. These data support antibody-based anti-CD73 therapy in cancer and highlight a novel mechanism for inhibition of CD73 enzymatic activity.

Citation Format: Bryan C. Barnhart, Emanuela Sega, Aaron Yamniuk, Sandra Hatcher, Ming Lei, Haben Ghermazien, Anne Lewin, Xi-Tao Wang, Haichun Huang, Pingping Zhang, Alan Korman. A therapeutic antibody that inhibits CD73 activity by dual mechanisms. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1476.

FcγRs Modulate the Anti-tumor Activity of Antibodies Targeting the PD-1/PD-L1 Axis

Immune checkpoint blockade of the programmed cell death protein 1 (PD-1) pathway by monoclonal antibodies (Abs) has shown promising clinical benefit in the treatment of multiple cancer types. We elucidated the contribution of the fragment crystallizable (Fc) domains of anti-PD-1 and anti-PD-ligand 1 (L1) Abs for their optimal anti-tumor activity. We revealed that distinct Fcγ receptor (FcγRs) dependency and mechanisms account for the in vivo activity of anti-PD-1 versus anti-PD-L1 Abs. Anti-PD-1 Abs were found to be FcγR independent in vivo; the presence of FcγR-binding capacity compromises their anti-tumor activity. In contrast, the anti-PD-L1 Abs show augmented anti-tumor activity when activating FcγR binding is introduced into the molecules, altering myeloid subsets within the tumor microenvironment.

Receptor-mediated delivery of siRNAs by tethered nucleic acid base-paired interactions

We report a new strategy for cell-type-specific delivery of functional siRNAs into cells. The method involves the noncovalent attachment of siRNAs to ligand-conjugated oligodeoxynucleotides via nucleic acid base-paired interactions. The resulting complexes can be directly applied to cells, leading to specific cellular uptake and gene silencing. The method is simple, economical, and can be easily adapted for other cell surface receptors. Here we show the application of this method for the delivery of siRNAs to folate receptor-expressing cells.

Issues related to targeted delivery of proteins and peptides

While modern genomic and proteomic technology enables rapid screening of novel proteins and peptides as potential drug candidates, design of delivery systems for these biologics remains challenging especially to achieve site-specific pharmacological actions. This article discusses the issues associated with targeted delivery of protein and peptide drugs at physiochemical, physiological, and intracellular levels with a special focus on cancer therapy.

Folate receptor-targeted immunotherapy: Induction of humoral and cellular immunity against hapten-decorated cancer cells

We previously exploited the frequent overexpression of folate receptors on cancer cells to decorate malignant cell surfaces selectively with folate-hapten conjugates. In antihapten-immunized hosts, this targeted localization of foreign haptens to tumor cells led to rapid accumulation of autologous antihapten IgG, which in turn yielded potent antitumor activity upon stimulation with cytokines (IL-2, IFN-alpha). In an effort to understand the effector mechanisms responsible for tumor regression, we have now investigated the involvement of both humoral and cellular immune components in the tumor destruction process. We report that the dependence of therapeutic efficacy on folate-hapten concentration is bimodal, suggesting that the conjugate must bridge between a cell surface FR and an antihapten IgG in order to mediate killing. Studies with cancer cells in vitro further demonstrate that folate-fluorescein-marked tumor cells are killed primarily by antibody-dependent cellular cytotoxicity and phagocytosis, with no contribution from complement-dependent mechanisms. Investigations of specific immune cell involvement also reveal that asialo-GM1(+)-natural killer cells, macrophages, CD4+ T cells and CD8+ T cells contribute significantly to recognition/removal of the cancer mass, and that elimination of these cell types markedly compromises the therapy. Because the initial antibody-dependent stage of tumor cell killing is shown to lead to a long-term antibody-independent cellular immunity that involves both CD4+ and CD8+ T cells, we propose that F(c) receptor-expressing immune cells not only initiate destruction of the IgG-marked tumor cells, but also participate in presentation of endogenous tumor antigens in a manner that leads to long-term cellular immunity.

Folate receptor-targeted immunotherapy of cancer: mechanism and therapeutic potential

The vitamin, folic acid, has become a useful ligand for targeted cancer therapies because it binds to a tumor-associated antigen known as the folate receptor (FR). By linking folic acid to therapeutic agents, folate-targeted cancer therapies can deliver therapeutic drugs specifically to FR-positive tumor cells. This chapter provides a summary of a specific application of folate-targeted therapies whereby folic acid is exploited to carry an attached hapten (a highly antigenic molecule) to the surfaces of tumor cells for the purpose of rendering the tumors more immunogenic. The basic strategy is to (i) saturate (label) the surface of FR-positive tumor cells with a folate-hapten conjugate against which the cancer-bearing host already has a pre-existing or induced immunity, (ii) allow the surface bound haptens to attract anti-hapten antibodies to the tumor cell surface, and (iii) stimulate Fc receptor-bearing immune cells to mount an antitumor response against the anti-hapten antibody opsonized tumor cells. In immune competent murine tumor models, hapten-marked cancer cells have been shown to be quickly recognized by antibodies and the associated Fc receptor-expressing immune cells dedicated to eliminating antibody-coated target cells. Given the need for cancer cells to escape immune surveillance in order to proliferate and survive in vivo, folate-targeted immunotherapies that mark an otherwise immunologically "invisible" cancer cell as distinctively "non-self" may provide a key strategy for combating malignant disease.

Cardiac output assessed by arterial thermodilution during exsanguination and fluid resuscitation: experimental validation against a reference technique

BACKGROUND AND OBJECTIVE

The arterial thermodilution technique offers the ability to measure cardiac output using only central venous and arterial catheters. However, the technique has been reported to overestimate cardiac output because of a higher loss of cold indicator due to the increased distance between the sites of injection and measurement. In this study, the two techniques were compared with respect to conditions of low cardiac output in which a longer passage time may further increase loss of indicator.

METHODS

Seventeen anaesthetized dogs were studied during hypovolaemic shock and fluid resuscitation. Cardiac output measurements were carried out simultaneously by arterial and pulmonary artery thermodilution techniques.

RESULTS

One-hundred-and-two measurements were performed. The mean cardiac output was 2.28 +/- 1.4Lmin(-1) by the pulmonary arterial technique and 2.29 +/- 1.56Lmin(-1) by the arterial thermodilution technique. The correlation coefficient between the two measurements was 0.95, the precision -0.04 +/- 0.41 Lmin(-1) and the limits of agreement from -0.86 to 0.78Lmin(-1). The agreement was also consistent at low cardiac outputs.

CONCLUSIONS

The arterial thermodilution technique may serve as a less invasive cardiac output monitor in conditions of severe bleeding and shock.

Evaluation of carcinoembryonic antigen levels in gastric juice, stomach mucosa and plasma in high-risk and gastric cancer patients

The aim of this study is to compare the levels of carcinoembryonic antigen (CEA) in the gastric juice, stomach mucosa and plasma of gastrectomy patients at risk of developing cancer with those in normal controls and gastric cancer subjects. Blood samples, gastric juices and biopsy material were taken from 52 patients (8 normal, 10 gastric carcinomas, 24 gastroresected according to Billroth II and 10 according to Billroth I). No significant correlation was found between age, sex or smoking habits and CEA levels in plasma, gastric juice or stomach mucosa. A significant correlation between CEA levels in gastric secretion and those in tissue emerged from out data (n = 52; r = 0.67; p less than 0.01). A minor correlation was found between tissue and plasma CEA values (r = 0.34; p less than 0.05). The mean levels of CEA in plasma did not show significant differences between controls and neoplastic risk subjects. The average level of CEA in gastric secretions and in tissue were significantly lower in normal controls than in neoplastic and gastroresected patients; in this latter group, we have observed a correlation between the severity of the histological lesions and the levels of CEA in the biopsy specimens; no correlation was found with the type of operation (Billroth I or Billroth II). The level of CEA in gastric juices and in biopsy material, therefore, appears to be more useful than in plasma in recognizing cancer risk subjects.

Specific and aspecific immune responsiveness in lung cancer patients: cutaneous delayed hypersensitivity reactions to a lung cancer-associated antigen

The ability of a lung cancer-associated antigen (LCAA) to provoke specific cutaneous delayed-hypersensitivity reactions has been studied on a group of 59 lung cancer patients. Biological activity of LCAA, monitored by skin testing, was demonstrated in 32% (17 of 53) of lung cancer patients, in 48.0% with limited disease, and in 17.2% with extensive disease. All the responders were in the group of normal reactors to standard recall antigens, if three antigens were used (PPDSK-SD, candida). No correlation was found between biological activity of LCAA and level of immunocompetence evaluated by lymphocyte-blastic transformation with PHA and count of rosette E-forming cells. These studies on the capacity to evoke specific DTH reactions in lung-cancer patients will be extended to the use of assays in vitro in the perspective of a more significant evaluation of immunocompetence levels.

Specific blastogenic response of peripheral blood lymphocytes from lung cancer patients to a fetal lung antigen

A human lung tumor fetal-associated antigen (LTFA) has been purified from lung tumor tissue by a combination of salt precipitation and ion-exchange chromatography. The purification steps were monitored by double immunodiffusion with the use of a rabbit anti-LTFA-specific antiserum. The isolated protein was tested for its blastogenic properties toward peripheral blood lymphocytes (PBL) by [3H]thymidine incorporation. PBL obtained from 25 healthy individuals, 34 patients with tumors other than lung tumors, 13 patients with lung diseases other than lung tumors, and 51 lung tumor-bearing patients were tested. Only PBL with an in vitro positive response to phytohemagglutinin were employed. Whereas PBL of lung tumor patients showed a significant blastogenic response to the purified antigen in 14 of 22 patients tested (60%), PBL of other patients were completely unreactive (P less than 0.005). The present data suggested that a specific immune response toward an LTFA was present in patients with lung cancers.

Immunologic monitoring during combined radiochemoimmunotherapy in inoperable lung cancer

49 patients with advanced lung cancer underwent a combined treatment including radiochemoimmunotherapy. Before and at the end of the combined treatment, the immune status of the patients has been evaluated by testing the immunoreactivity to PPD in vivo and the phytohemagglutinin lymphocyte response and the rosette-forming cells in vitro. While the in vitro tests were not significantly modified by immunostimulation, as regards the immunoreactivity to PPD, we observed a positive conversion at the end of the treatment in 11 out of 25 patients who showed a negative reaction before therapy. All the patients who converted from negative to positive showed also a good response to therapy with regression or no progression of the tumor. Survival curves confirmed the prognostic value of PPD reactivity.

Partial characterization of a fetal lung antigen associated with human bronchogenic carcinoma

A human lung tumor-associated fetal antigen (LTFA) has been partially isolated and characterized. The antigen that differs in several immunochemical parameters from previously described lung cancer antigens was shared by fetal lung and liver tissue. The neoantigen migrated in immunoelectrophoresis as an alpha2-beta globulin, had an average molecular size of 7S, and was soluble in 50% saturated ammonium sulfate. Whereas LTFA was insensitive to both DNase and RNase treatment, its antigenicity was completely abolished by pronase. The biologic significance of this antigen and its possible clinical use were discussed.

Short-Term Results of Combined Radioimmunotherapy in Inoperable Lung Cancer

Fifty-three inoperable lung cancer patients were treated with radiotherapy combined with immunostimulation with BCG. A good response was obtained in 30 patients (56 %); the results were not significantly different than those obtained with a control group of 50 lung cancer patients matched by age, sex and stage of the disease (24 out of 50 = 46 %). These short-term results were compared with the immunologic « status » of patients evaluated before treatment by the parameters monitoring in vivo and in vitro delayed type hypersensitivity. The good response to therapy was documented in a higher percentage of patients with positive skin tests to recall and standard antigens and with normal values of lymphocyte transformation with PHA and Rosette E-forming cells, in comparison with patients with low levels of immunocompetence. An impairment of the cell-mediated immune response was found after combined therapy, presumably due to radiotherapy. BCG was not able to restore the patient's immunocompetence, no effect on host's immune reactivity was demonstrated. As regards humoral immunity, the patients with low levels of IgG before treatment (12/14) showed a good response.

Quantitation of estradiol receptors employing a sensitive radioimmunoassay

A method aimed at the identification and quantitation of estradiol receptors has been developed. The test is based on competitive binding reaction between solubilized cell receptors and anti-estradiol antibodies bound to acrylamide beads, for 3H-estradiol. The technique can be employed both for estradiol radioimmunoassay and quantitation of specific receptors in tissues and appears to be a sensitive, specific and reproducible method which can be applied to the evaluation of any hormone and its receptor.