Suppression of Moloney sarcoma virus immunity following sensitization with attenuated virus.
(1/982)
Murine sarcoma virus (Moloney strain) (MSV-M)-induced tumors are unusual in that they regularly appear less than 2 weeks after virus inoculation, progress for 1 to 2 weeks, and are rejected by normal adult BALB/c mice. Rejectio leaves the animals immune to tumor induction. In the present study, presensitization of normal adult BALB/c mice with attenuated MSV-M resulted in an altered pattern of tumor immunity. Injection of active MSV-M into the presensitized animals resulted in tumor induction and rejection similar to that observed in normal animals, but rejection failed to produce protection against the secondary inoculation with MSV-M. After the second inoculation with active MSV-M, tumors appeared and progressed but ultimately were rejected. Over 80% of the mice died, 25% after the primary challenge and the remainder after the secondary challenge. At death, all mice had histological evidence of leukemia which was the probable cause of death. The animals that died following the secondary challenge also had evidence of disseminated MSV-M. Solid tumor nodules were found in skeletal muscle distant from the original site of inoculation, and active MSV-M was isolated from spleen and lungs. The possibility that the results were produced by specific suppression of MSV-Moloney leukemia virus immunity is discussed. (+info)
Rapamycin causes poorly reversible inhibition of mTOR and induces p53-independent apoptosis in human rhabdomyosarcoma cells.
(2/982)
The mammalian target of rapamycin (mTOR) has been shown to link growth factor signaling and posttranscriptional control of translation of proteins that are frequently involved in cell cycle progression. However, the role of this pathway in cell survival has not been demonstrated. Here, we report that rapamycin, a specific inhibitor of mTOR kinase, induces G1 cell cycle arrest and apoptosis in two rhabdomyosarcoma cell lines (Rh1 and Rh30) under conditions of autocrine cell growth. To examine the kinetics of rapamycin action, we next determined the rapamycin sensitivity of rhabdomyosarcoma cells exposed briefly (1 h) or continuously (6 days). Results demonstrate that Rh1 and Rh30 cells were equally sensitive to rapamycin-induced growth arrest and apoptosis under either condition. Apoptosis was detected between 24 and 144 h of exposure to rapamycin. Both cell lines have mutant p53; hence, rapamycin-induced apoptosis appears to be a p53-independent process. To determine whether induction of apoptosis by rapamycin was specifically due to inhibition of mTOR signaling, we engineered Rh1 and Rh30 clones to stably express a mutant form of mTOR that was resistant to rapamycin (Ser2035-->Ile; designated mTOR-rr). Rh1 and Rh30 mTOR-rr clones were highly resistant (>3000-fold) to both growth inhibition and apoptosis induced by rapamycin. These results are the first to indicate that rapamycin-induced apoptosis is mediated by inhibition of mTOR. Exogenous insulin-like growth factor (IGF)-I protected both Rh1 and Rh30 from apoptosis, without reactivating ribosomal p70 S6 kinase (p70S6K) downstream of mTOR. However, in rapamycin-treated cultures, the response to IGF-I differed between the cell lines: Rh1 cells proliferated normally, whereas Rh30 cells remained arrested in G1 phase but viable. Rapamycin is known to inhibit synthesis of specific proteins but did not inhibit synthesis or alter the levels of mTOR. To examine the rate at which the mTOR pathway recovered, the ability of IGF-I to stimulate p70S6K activity was followed in cells treated for 1 h with rapamycin and then allowed to recover in medium containing > or =100-fold excess of FK506 (to prevent rapamycin from rebinding to its cytosolic receptor FKBP-12). Our results indicate that, in Rh1 cells, rapamycin dissociates relatively slowly from FKBP-12, with a t1/2 of approximately 17.5 h. in the presence of FK506, whereas there was no recovery of p70S6K activity in the absence of this competitor. This was of interest because rapamycin was relatively unstable under conditions of cell culture having a biological t1/2 of approximately 9.9 h. These results help to explain why cells are sensitive following short exposures to rapamycin and may be useful in guiding the use of rapamycin analogues that are entering clinical trials as novel antitumor agents. (+info)
GR-891: a novel 5-fluorouracil acyclonucleoside prodrug for differentiation therapy in rhabdomyosarcoma cells.
(3/982)
Differentiation therapy provides an alternative treatment of cancer that overcomes the undesirable effects of classical chemotherapy, i.e. cytotoxicity and resistance to drugs. This new approach to cancer therapy focuses on the development of specific agents designed to selectively engage the process of terminal differentiation, leading to the elimination of tumorigenic cells and recovery of normal cell homeostasis. A series of new anti-cancer pyrimidine acyclonucleoside-like compounds were designed and synthesized by structural modifications of 5-fluorouracil, a drug which causes considerable cell toxicity and morbidity, and we evaluated their applicability for differentiation therapy in human rhabdomyosarcoma cells. We tested the pyrimidine derivative GR-891, (RS)-1-[[3-(2-hydroxyethoxy)-1-isopropoxy]propyl]-5-fluorouracil, an active drug which shows low toxicity in vivo and releases acrolein which is an aldehyde with anti-tumour activity. Both GR-891 and 5-fluorouracil caused time- and dose-dependent growth inhibition in vitro; however, GR-891 showed no cytotoxicity at low doses (22.5 micromol l(-1) and 45 micromol l(-1)) and induced terminal myogenic differentiation in RD cells (a rhabdomyosarcoma cell line) treated for 6 days. Changes in morphological features and in protein organization indicated re-entry in the pathway of muscular maturation. Moreover, GR-891 increased adhesion capability mediated by the expression of fibronectin, and did not induce overexpression of P-glycoprotein, the mdr1 gene product, implicated in multidrug resistance. New acyclonucleoside-like compounds such as GR-891 have important potential advantages over 5-fluorouracil because of their lower toxicity and their ability to induce myogenic differentiation in rhabdomyosarcoma cells. Our results suggest that this drug may be useful for differentiation therapy in this type of tumour. (+info)
Selective promoting activity of phorbol myristate acetate in experimental skin carcinogenesis.
(4/982)
Experiments were undertaken to study the effect of promotion treatment on epidermal tumour induction pattern in precancerous mouse skin. Swiss albino mice were given a single s.c. injection of 0-5 mg 20-methylcholanthrene in the right scapular region. Six weeks later, 1-83 nmol of phorbol myristate acetate (PMA) was applied biweekly on the reactive skin. Histopathology of the induced tumours showed early appearance of squamous cell carcinomas and rhabdomyosarcomas. Fibrosarcoma, the most common tumour type induced on MCA injection alone, was absent. Trichoepithelioma, a benign tumour, was induced in PMA-treated mice. This gives new evidence of the selective action of PMA, enhancing the induction of epithelial and muscle tumours, with concurrent inhibition of fibroblastic tumours. (+info)
Restoration of p16INK4A protein induces myogenic differentiation in RD rhabdomyosarcoma cells.
(5/982)
p16INK4A (p16) tumour suppressor induces growth arrest by inhibiting function of cyclin-dependent kinase (CDK)4 and CDK6. Homozygous p16 gene deletion is frequent in primary rhabdomyosarcoma (RMS) cells as well as derived cell lines. To confirm the significance of p16 gene deletion in tumour biology of RMS, a temperature-sensitive p16 mutant (E119G) gene was retrovirally transfected into the human RMS cell line RD, which has homozygous gene deletion of p16 gene. Decrease from 40 degrees C (restrictive) to 34 degrees C (permissive) culture temperature reduced CDK6-associated kinase activity and induced G1 growth arrest. Moreover, RD-p16 cells cultured under permissive condition demonstrated differentiated morphology coupled with expressions of myogenin and myosin light chain. These suggest that deletion of p16 gene may not only facilitate growth but also inhibit the myogenic differentiation of RD RMS cells. (+info)
Effective T cell regeneration following high-dose chemotherapy rescued with CD34+ cell enriched peripheral blood progenitor cells in children.
(6/982)
The ex vivo enrichment for the CD34+ cell fraction of PBPC, while it retains the capacity to restore haematopoiesis and potentially reduces a contamination by tumour cells, implements a depletion of T cells. To test whether such a setting adversely affects T cell reconstitution, we monitored T cells in four paediatric patients after CD34+ selected PBPC transplantation. The dose of CD34+ cells, which were enriched to 74%, median, was 7.1 x 10(6)/kg, median, that of T cells was 0.071 x 10(6)/kg, median. The patients were homogenous with respect to features with a potential to effect T cell reconstitution (low median age, (35 years); stage IV malignant tumours in first CR, uncomplicated post-treatment course). The results of sequential FACS analyses showed that by 9 months after treatment all four patients had recovered (1) a normal T cell count (CD3+ cells 1434/microl, median); (2) a normal CD4+ cell count (816/microl, median), while CD8+ cells were recovered (>330/microl) already by 3 months; (3) a normal CD4/CD8 ratio (1.8, median), as a result of an augmented growth of CD4+ cells between 3 and 6 months (increase of CD4+ cells 4.9-fold, median, CD8+ cells 1.1-fold, median). Expansion of cells with a CD45RA+ phenotype (thymus-derived T cells) predominated; from 3 to 6 months the increase of CD4+/CD45RA+ T cells was 130-fold, that of CD4+/CD45RO+ cells was 1.7-fold; CD8+/CD45RA+ cells increased 9-fold, CD8+/CD45RO+ cells increased 2.1-fold, indicating effective thymopoiesis. The findings demonstrate that in paediatric patients the setting of HD-CTX rescued with autologous CD34+ selected PBPC per se is not predictive of an impaired T cell recovery. High thymic activity may be a key factor for the rapid restoration of T cells. (+info)
Improved survival of children with advanced tumors by myeloablative chemotherapy and autologous peripheral blood stem cell transplantation in complete remission.
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Five children with neuroblastoma (NB) stage IV and five children with rhabdomyosarcoma (RMS) stage III were treated with myeloablative chemotherapy and autologous peripheral blood stem cell transplantation (MCT/PBSCT) in the state of complete remission (CR) achieved by conventional therapy. PBSCs were collected in CR status using a cell separator with blood access through a double-lumen central venous catheter. PBSCs with 1.9+/-0.8x10(5) of CFU-GM per patient weights (kg) were infused following MCT after a period of conventional therapy for 11.1+/-2.1 or 9.7+/-0.9 months in NB or RMS patients, respectively. Regimen-related toxicity of MCT was tolerable and peripheral white blood cell count recovered beyond 1.0x10(3)/microl 10-12 days after infusion of PBSCs in all patients. All of RMS patients and three of five NB patients survived for an average of 31.6 months (ranged 10.8-58.1). The survival rate of these patients was improved as compared with our historical controls, and presumably, with that of conventional chemotherapy previously reported. Despite a limited number of patients, it appears that MCT/PBSCT may be effective in improving survival by preventing relapse which may occur thereafter if treated with conventional therapy alone. Furthermore, MCT/PBSCT reduced the duration of treatment, as compared with that of conventional chemo-therapy. Therefore, this study may suggest the feasibility and promise of the therapy including MCT/PBSCT for children with advanced stages of NB and RMS. (+info)
Rhabdomyosarcoma: an overview.
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Rhabdomyosarcoma (RMS) is a malignant tumor of mesenchymal origin thought to arise from cells committed to a skeletal muscle lineage. With approximately 250 cases diagnosed yearly in the United States, it is the third most common extracranial solid tumor of childhood after Wilms' tumor and neuroblastoma. Important epidemiologic, biologic, and therapeutic differences have been elucidated within the RMS family. Common sites of primary disease include the head and neck region, genitourinary tract, and extremities. A site-based tumor-nodes-metastasis staging system is being incorporated into use for assessing prognosis and assigning therapy in conjunction with the traditional surgicopathologic clinical grouping system. The development of intensive multimodality treatment protocols tested in large-scale international trials has resulted in significant improvements in outcome, especially for patients with local or locally extensive disease for whom a 60%-70% disease-free survival can be expected. Despite aggressive approaches incorporating surgery, dose-intensive combination chemotherapy, and radiation therapy, the outcome for patients with metastatic disease remains poor. Future challenges include the development of less toxic therapy for patients with localized disease and new approaches for patients with metastatic disease. (+info)