FURTHER STUDIES OF ANTIGENIC COMPETITION : III. A MODEL TO ACCOUNT FOR THE PHENOMENON BASED ON A DEFICIENCY OF CELL-TO-CELL INTERACTION IN IMMUNE LYMPHOID CELL POPULATIONS

A striking correlation between the capacity of an antigen to nonspecifically suppress humoral immune responses of subsequently administered antigens which are non-cross-reacting, i.e. to manifest antigenic competition and produce enlargement of spleen size through cell proliferation, was found. Increase in spleen size was always accompanied by a drop in the normal proportion of thymus-derived cells to non-thymus-derived cells. Various means of altering the immune response to the initial antigen, and hence, the capacity of that antigen to suppress in a model of antigenic competition were performed and correlated with changes in spleen size and in the proportion of θ-positive cells in the spleen. In all instances, when the experimental condition reduced or abolished antigenic competition, the increase in spleen size and reduction in the proportion of θ-positive cells in the spleen was reduced or abolished. Furthermore, under conditions in which the suppressive capacity of the initial antigen was unaltered, the increase in spleen size and reduction in θ-proportion occurred normally. Finally, the better the suppression in a model of antigenic competition, the greater the increase in spleen size and reduction in the proportion of θ-positive cells. On the basis of these observations, it appears that there is a relationship between spleen enlargement through clonally restricted cell proliferation and the expression of antigenic competition; one cannot have the latter without the former. It is postulated that the immunological lesion associated with antigenic competition resides at the level of interference with cell interaction between thymus-derived antigen-reactive cells and marrow-derived antibody-forming cells. This occurs as a result of a relative "diluting out" of cells of both populations carrying antigenic specificity differing from the one(s) which induced the dilution effect in the first place. The net effect of this is to decrease the chance of a "hit" or interaction between a marrow-derived and thymus-derived cell of the same specificities. This mechanism, which is compatible with theories of clonal selection, and which in fact is dependent upon them, supports the view that the term "antigenic competition" is a misnomer; there is no competition by the antigens for anything. The term "antigen-induced suppression" is suggested as a more suitable alternative

Antiadhesive antibodies targeting E-cadherin sensitize multicellular tumor spheroids to chemotherapy <i>in vitro</i>

Abstract Multicellular resistance, a subtype of therapeutic resistance manifested in cancer cells grown as three-dimensional multicellular masses, such as spheroids in vitro and solid tumors in vivo, occurs with respect to a variety of anticancer treatment strategies including chemotherapy, ionizing radiation, and even host-mediated antibody-dependent cellular cytotoxicity. Previous studies from our laboratory have shown that multicellular resistance to chemotherapy demonstrated by aggregates of EMT-6 murine mammary carcinoma cells can be overcome by using hyaluronidase to disrupt intercellular adhesive interactions and associated patterns of protein expression. In this proof of principle study, we explored the concept of antiadhesive chemosensitization in the context of human cancer cells by using a monoclonal antibody to disrupt E-cadherin-mediated cell-cell interactions in multicellular spheroids of HT29 human colorectal adenocarcinoma. In so doing, we found that disruption of E-cadherin-mediated adhesion sensitizes multicellular spheroids of HT29 in vitro to treatment with 5-fluorouracil, paclitaxel, vinblastine, and etoposide but not cisplatin. Furthermore, we have found that antibody-mediated blockage of E-cadherin function leads to decreased expression and activity of protein kinase C α and β1, both of which have previously been implicated in chemoresistance exhibited by HT29 cells; however, we have found that the chemosensitization effects of the anti-E-cadherin antibody are independent of its influence on protein kinase C β1

Potent efficacy of metronomic topotecan and pazopanib combination therapy in preclinical models of primary or late stage metastatic triple-negative breast cancer

Metronomic chemotherapy has shown promising activity in numerous preclinical studies and also some phase II clinical studies involving various tumor types, and is currently undergoing phase III trial evaluation. Triple-negative breast cancer (TNBC) is an aggressive histological subtype with limited treatment options and very poor prognosis following progression after standard chemotherapeutic regimens. Herein, we evaluated the potential therapeutic impact and molecular mechanisms of topotecan administered in a continuous low-dose metronomic (LDM) manner, alone or in concurrent combination with pazopanib, an antiangiogenic tyrosine kinase inhibitor (TKI), in a triple-negative, primary and metastatic breast cancer orthotopic model; potential molecular mechanisms of efficacy were also studied, especially the impact of hypoxic conditions. The combination of metronomic topotecan and pazopanib significantly enhanced antitumor activity compared to monotherapy with either drug and prolonged survival, even in the advanced metastatic survival setting, with a marked decrease in tumor vascularity, proliferative index, and the induction of apoptosis. Significant changes in tumor angiogenesis, cancer cell proliferation, apoptosis, HIF1α levels, HIF-1 target genes and ABCG2 were found both in vitro and in tumor tissue. Notably, the pazopanib and metronomic topotecan combination treatment inhibited expression of HIF1α and ABCG2 genes in cells grown under hypoxic conditions, and this was associated with an increased intracellular concentration of the active form of topotecan. Our results suggest a potential novel therapeutic option for the treatment of metastatic triple-negative breast cancer patients

CLASSIFICATION OF THYMUS-DERIVED AND MARROW-DERIVED LYMPHOCYTES BY DEMONSTRATION OF THEIR ANTIGEN-BINDING CHARACTERISTICS

Antigen-binding cells of T and B origin can readily be determined by quantitating the number of sheep erythrocytes per rosette after glutaraldehyde fixation. The T1 and T2 populations have low antigen-binding properties and are very unstable without fixation. The B1 and B2 populations are stable and correlate with precursor and secretory cells. Fixation of rosettes permits a sensitive test for studying differentiation of T and B cells

Impact of Metronomic UFT/Cyclophosphamide Chemotherapy and Antiangiogenic Drug Assessed in a New Preclinical Model of Locally Advanced Orthotopic Hepatocellular Carcinoma

AbstractHepatocellular carcinoma (HCC) is an intrinsically chemotherapy refractory malignancy. Development of effective therapeutic regimens would be facilitated by improved preclinical HCC models. Currently, most models consist of subcutaneous human tumor transplants in immunodeficient mice; however, these do not reproduce the extensive liver disease associated with HCC or metastasize. To address this deficiency, we developed an orthotopic model. Human HCC cells were transfected with the gene encoding secretable β-subunit human choriogonadotropin (β-hCG), which was used as a surrogate marker of tumor burden. The HCC cells were implanted into the left liver lobe of severe combined immunodeficient (SCID) mice, after which the efficacy of different therapies was evaluated on established, but liver-confined human Hep3B cell line HCC. Treatments included sorafenib or metronomic chemotherapy using cyclophosphamide (CTX), UFT, an oral 5-fluorouracil prodrug, or doxorubicin either alone or in various combinations, with or without an antiangiogenic agent, DC101, an anti-vascular endothelial growth factor receptor-2 antibody. Sorafenib inhibited tumor growth in a dose-dependent manner but caused severe weight loss in SCID mice, thus necessitating use of DC101 in subsequent experiments. Although less toxicity was observed using either single or doublet metronomic chemotherapy without any added antiangiogenic agent, none, provided survival benefit. In contrast, significantly improved overall survival was observed using various combinations of metronomic chemotherapy regimens such as UFT + CTX with DC101. In conclusion, using this model of liver-confined but advanced HCC suggests that the efficacy of a targeted antiangiogenic drug or metronomic chemotherapy can be mutually enhanced by concurrent combination treatment

Id1 Restrains p21 Expression to Control Endothelial Progenitor Cell Formation

Loss of Id1 in the bone marrow (BM) severely impairs tumor angiogenesis resulting in significant inhibition of tumor growth. This phenotype has been associated with the absence of circulating endothelial progenitor cells (EPCs) in the peripheral blood of Id1 mutant mice. However, the manner in which Id1 loss in the BM controls EPC generation or mobilization is largely unknown. Using genetically modified mouse models we demonstrate here that the generation of EPCs in the BM depends on the ability of Id1 to restrain the expression of its target gene p21. Through a series of cellular and functional studies we show that the increased myeloid commitment of BM stem cells and the absence of EPCs in Id1 knockout mice are associated with elevated p21 expression. Genetic ablation of p21 rescues the EPC population in the Id1 null animals, re-establishing functional BM-derived angiogenesis and restoring normal tumor growth. These results demonstrate that the restraint of p21 expression by Id1 is one key element of its activity in facilitating the generation of EPCs in the BM and highlight the critical role these cells play in tumor angiogenesis

Cyclophosphamide "metronomic" chemotherapy for palliative treatment of a young patient with advanced epithelial ovarian cancer

BACKGROUND: Evaluation of the clinical efficacy and tolerance of metronomic chemotherapy as salvage therapy in a young patient with advanced, platinum resistant, ovarian carcinoma and bad performance status. CASE PRESENTATION: We tried palliative chemotherapy with daily low dose oral cyclophosphamide with a patient suffering from stage IIIC ovarian cancer that responded to daily cyclophosphamide (CTX) after no response to chemotherapy with paclitaxel and carboplatin as first line and progression after second line with topotecan. The progression-free survival time on daily low dose oral cyclophosphamide treatment was 65 months without side effects. She was well during the chemotherapy and lived a normal working and social life. CONCLUSION: We think that use of low dose of oral CTX should be investigated further as a strategy against tumour progression after standard chemotherapy in patients who are platinum resistant with poor performance status