Nechama Haran-Ghera

Erythropoietin induces tumor regression and antitumor immune responses in murine myeloma models

Recombinant human erythropoietin (rHuEpo) has been used successfully in the treatment of cancer-related anemia. Clinical observations with several patients with multiple-myeloma treated with rHuEpo has shown, in addition to the improved quality of life, a longer survival than expected, considering the poor prognostic features of these patients. Based on these observations, we evaluated the potential biological effects of rHuEpo on the course of tumor progression by using murine myeloma models (MOPC-315-IgAλ2 and 5T33 MM-IgG2b). Here we report that daily treatment of MOPC-315 tumor-bearing mice with rHuEpo for several weeks induced complete tumor regression in 30–60% of mice. All regressors that were rechallenged with tumor cells rejected tumor growth, and this resistance was tumor specific. The Epo-triggered therapeutic effect was shown to be attributed to a T cell-mediated mechanism. Serum Ig analysis indicated a reduction in MOPC-315 λ light chain in regressor mice. Intradermal inoculation of 5T33 MM tumor cells followed by Epo treatment induced tumor regression in 60% of mice. The common clinical manifestation of myeloma bone disease in patients with multiple-myeloma was established in these myeloma models. Epo administration to these tumor-bearing mice markedly prolonged their survival and reduced mortality. Therefore, erythropoietin seems to act as an antitumor therapeutic agent in addition to its red blood cell-stimulating activity.

Skin initiating action and lung carcinogenesis by derivatives of urethane (ethyl carbamate) and related compounds

Abstract The possibility that a metabolite might be implicated in the carcinogenic action of urethane on the lungs, and in its limited “initiating” action in the case of skin carcinogenesis, prompted the testing of a number of derivatives and analogues of urethane for both lung carcinogenesis and skin initiation in mice. The modifications in molecular structure of urethane involved (i) changes in the carbamyl portion, (ii) changes in its carboethoxy portion, (iii) phosphorylated derivatives, and (iv) addition compounds with keto and amino acids. Most of the compounds tested proved inactive, and among those that did give positive results, the effects were weak ; thus indicating that none of them represented the sought-for metabolite. Some tentative implications of the results are discussed as pointers for further enquiry.

Induction of Leukemia in Mice by Irradiation and Radiation Leukemia Virus Variants

Publisher Summary This chapter reviews the experimental data concerning pathways involved in the development of leukemias in the C57BL strain induced by exposure to fractionated whole-body irradiation or by inoculating one of the different radiation leukemia virus variants available. In the absence of cofactors, these virus variants differ in their leukemogenic potential. The target organ for the overt development of most spontaneous or induced murine lymphoid leukemias is the thymus. The thymus is considered by many investigators because of the site of neoplastic transformation and proliferation. Potential leukemic cells are identified in the bone marrow of most mice treated with leukemogenic agents irrespective of the ultimate overt leukemia development expressed mostly in the thymus. The development pathways during leukemogenesis involve two fundamental phases preceding the overt expression of a tumor: (1) the transformation of normal stem cells or prothymocytes into preleukemic cells and (2) the differentiation and proliferation of the transformed cells into autonomously growing malignant cells. The leukemogenic potential of the different leukemogenic agents is determined by different tumor cell-host relationships. The presence of an intact thymus leads to the establishment and proliferation of preleukemic cells induced by the radiation leukemia virus (RadLV) variants.

The role of thymus subpopulations in “T” leukemia development☆

Abstract Based on antigenic properties of the cell surface of mouse thymocytes, spontaneous (AKR mice) and induced T leukemias (C57BL/6 mice) were shown to have characteristics of the minor thymus subpopulation, namely, low levels of θ and high levels of H-2. Leukemogenic agents (fractionated irradiation or inoculation of radiation leukemia virus) were shown to induce a transient or permanent change in thymus population patterns. Within several weeks following leukemogenic treatment there was a relative enrichment of thymocytes bearing low levels of θ and high levels of H-2 and partially resistant to hydrocortisone and capable of induceing a graft versus host response. Transplantation bioassays carried out indicated the lack of demonstrable leukemic cells in the thymus within several weeks following the leukemogenic treatment. Similar spontaneous age-related changes in the pattern of the nonleukemic AKR thymus, namely, increase in the high H-2 thymus subpopulation and a gradual decrease in the percentage of θ-bearing cells was observed from 5 months onwards. The relationship between the availability of certain thymus subpopulations and the ultimate overt leukemia development was indicated.

Chemoimmunotherapy Reduces the Progression of Multiple Myeloma in a Mouse Model

Multiple myeloma (MM) is a B-cell malignancy characterized by clonal proliferation of malignant plasma cells in the bone marrow. Recently, we showed a correlation between increased ratios of functional regulatory T cells (Treg) and disease progression in a unique mouse model that mimics the human disease. Cyclophosphamide (CYC) is a cytotoxic alkylating agent widely used in chemotherapeutic regimens. Low-dose CYC was previously reported to selectively reduce Treg levels and to contribute to immunostimulation. Our objectives were (a) to determine whether treatment using a low-dose CYC could reduce MM progression and (b) to further characterize the modes of action underlying these effects. We found that both low- and high-dose CYC given to sick mice with hind limb paralysis resulted in the disappearance of the paralysis, the replacement of plasma tumor cells in the bone marrow by normal cell populations, and a significant prolongation of survival. However, only low-dose CYC treatment decreased the incidence of MM. Low-dose CYC rendered Tregs susceptible to apoptosis because of the downregulation of Bcl-xL and CTLA-4 in these cells, and a decreased production of interleukin 2 by effector CD4 cells. Moreover, using this treatment, we noted the recovery of IFN-γ–producing natural killer T cells and maturation of dendritic cells. Treatment of tumor-bearing mice with repeated administrations of low-dose CYC at longer time intervals (coinciding with the blocked renewal of Tregs) resulted in reduced tumor load, and the prevention or delay of disease recurrence, thereby breaking immune tolerance against MM tumor cells. Cancer Prev Res; 3(10); 1265–76. ©2010 AACR.

Genetic resistance to murine leukemia induced by different radiation leukemia virus variants; a comparative study on the role of the H-2 complex.

Association of resistance to leukemogenesis with theH-2 complex was investigated. Three variants of the radiation leukemia virus: D-RadLV, RadLV and RS-RadLV were tested. Using congenic and recombinant mouse strains, the region includingH-2K andI-A/B was found to be involved with resistance to all three viruses. In addition,H-2D-region linked resistance was found in leukemogenesis in two of the three passages. The phenotypic expression of resistance associated withH-2D seemed to depend on the simultaneous presence ofH-2K-H-21-linked resistance alleles. TheH-2 haplotypes associated with resistance or sensitivity to the different RadLV variants were different for each passage, suggesting that there is a large degree of heterogeneity both inH-2-linked resistance and between the radiation-induced leukemia viruses.

A Leukemogenic Filtrable Agent from Chemically-Induced Lymphoid Leukemia in C57BL Mice

Summary Thymic lymphomas were induced in 60% of C57BL mice fed with 7, 12-dimethylbenz (a) anthracene dissolved in polyethylene glycol 400, the mean latent period from the start of the DMBA feedings being 176 days. Three series of cell-free filtrates prepared from the DMBA-induced lymphomas were leukemogenic, producing 15-27% lymphomas in the tested mice. Serial cell-free passages of the original filtrate-induced lymphomas revealed a similar leukemogenic activity of 10-30%.

Increased Regulatory versus Effector T Cell Development Is Associated with Thymus Atrophy in Mouse Models of Multiple Myeloma

CD4+CD25+Foxp3+ regulatory T cells (Tregs) play a central role in cancer tolerance. However, mechanisms leading to their accumulation in cancer remain unknown. Although the thymus is the main site of Treg development, thymic contribution to Treg expansion in cancer has not been directly examined. Herein, we used two murine models of multiple myeloma (MM), 5T2 MM and 5T33 MM, to examine Treg accumulation in peripheral lymphoid organs, including spleen, lymph nodes, bone marrow, and blood, and to explore thymic Treg development during malignancy. We found that peripheral ratios of suppressive-functional Tregs increased in both models of MM-inflicted mice. We found that thymic ratios of Treg development in MM increased, in strong association with thymus atrophy and altered developmental processes in the thymus. The CD4+CD8+ double-positive population, normally the largest thymocyte subset, is significantly decreased, whereas the CD4−CD8− double-negative population is increased. Administration of thymocytes from MM-inflicted mice compared with control thymocytes resulted in increased progression of the disease, and this effect was shown to be mediated by Tregs in the thymus of MM-inflicted mice. Our data suggest that increased ratios of Treg development in the thymus may contribute to disease progression in MM-inflicted mice.

Dependent and autonomous phases during leukemogenesis

Abstract Preleukemic cells could be identified mainly among bone marrow cells of C57B1/6 mice shortly after intrathymic inoculation of radiation leukemia virus variants inducing high or low overt leukemia development. Mice were shown to carry preleukemic cells without necessarily developing overt leukemia. The presence of the intact thymus was essential to initiating the proliferation of preleukemic cells. Two fundamental phases, affected by tumor cell-host relationships, were observed during the latent period: (1) Dependent phase—the proliferation of preleukemic cells being dependent on specific host environments and (2) Autonomous phase—involving tumor cell proliferation irrespective of host conditions. The occurrence of the “autonomous” variant seemed to be a prerequisite for overt leukemia expression.

Role of pineal melatonin and melatonin-induced-immuno-opioids in murine leukemogenesis

The relationship between the pineal gland, melatonin and melatonin-induced-immuno-opioids with the response of C57BI/6 mice to A-RadLV induced T cell lymphomas was investigated. Mice were injected at day 0 with A-RadLV and from day 10 they were treated chronically with melatonin 4 mg/kg body weight, naltrexone 1 mg/kg or phosphate buffered saline, throughout the experiment. In another protocol, groups of mice were a) surgical pinealectomized at day-14, b) functional pinealectomized (24:24 hours light) from day -20 and c) sham pinealectomized. At day 0 each group was inoculated intrathymically with A-RadLV. The results show that melatonin accelerated (p < 0.005) leukemogenesis whereas the surgical pinealectomy and the functional pinealectomy delayed it (p < 0.005 andp < 0.01). Moreover, the action of melatonin was blocked by naltrexone (p < 0.005), indicating the involvement of melatonin-induced-immuno-opioids in the development of the lymphomas.