A phase I-II study of combination therapy with thymidine and cytosine arabinoside

Twenty-one patients with leukemia and lymphoma refractory to conventional therapy were treated with thymidine (dThd) at a dose of 75 g/m2/day for 48 h by continuous intravenous (IV) infusion, followed by cytosine arabinoside (ara-C) on an escalating dose schedule of 25-625 mg/m2/day for 48 h by continuous IV infusion. Toxicity included somnolence (1 patient), mucositis (2 patients), and myelosuppression (19 patients). One patient died prior to completion of therapy. Because of the patient population studied (mainly consisting of patients with leukemia refractory to conventional therapy) and the prevalence of myelosuppression prior to therapy, a median toxic dose was not evaluable. Therapeutic responses included a partial remission in a patient with acute myelogenous leukemia (AML) refractory to ara-C. An additional six patients with acute leukemia refractory to ara-C transiently cleared their peripheral blood of blasts, and a decrease in circulating blasts was noted in two other patients. Biochemical studies conducted on the peripheral blasts of two patients confirmed an enhancement by dThd of the incorporation of ara-C into the DNA of circulating blasts.

Radiolocalization of human mammary tumors in athymic mice by a monoclonal antibody

Monoclonal antibody B6.2 reacts with a protein found on the surface of primary and metastatic human mammary tumors. B6.2 immunoglobulin G (IgG) was purified, F(ab')2 and Fab' fragments were generated by pepsin digestion, and the IgG and its fragments were radiolabeled with 125I; all were successful in localizing human mammary tumors transplanted into athymic mice, with tumor:tissue ratios increasing over a 4-day period. The 125I-labeled IgG gave tumor:spleen, tumor:liver, and tumor:kidney ratios of greater than 10:1 and tumor:brain and tumor:muscle ratios of 50:1 to 110:1. The F(ab')2 fragment gave higher tumor:tissue ratios than did the IgG, with tumor:liver and tumor:spleen ratios of 15:1 to 20:1. No localization of the labeled B6.2 monoclonal antibody or its fragments was observed in athymic mice bearing a human melanoma or with isotype-identical control immunoglobulin or its fragments in athymic mice bearing the mammary tumors. Imaging experiments confirmed the ability of radiolabeled monoclonal antibody B6.2 and its fragments to detect the presence of transplanted human mammary tumor lesions of less than 0.4 cm without the aid of background subtraction manipulations.

Induction of differentiation of human myeloid leukemia cells by inhibitors of DNA synthesis

The HL-60 human leukemic promyelocyte can be induced to mature into terminally differentiated cells using certain nucleosides and chemotherapeutic agents. The mechanisms responsible for this induction of differentiation, however, remain unclear. We have monitored the effects of two specific inhibitors of DNA synthesis to determine whether slowing of DNA polymerization can induce HL-60 differentiation. The results demonstrate that cytosine arabinoside (ara-C) induces nonspecific esterase activity in HL-60 cells and increases surface expression of the monocyte antigen MY-4. The results also demonstrate that aphidicolin, an inhibitor of DNA polymerase which is not incorporated in DNA, induces similar phenotypic changes. The induction of differentiation by both agents was accompanied by loss of clonogenic potential as monitored by colony formation in methylcellulose. These observations suggest that terminal differentiation of HL-60 cells can be induced by drugs known to inhibit DNA synthesis.

Phase I trial of combination therapy with PALA and 5-FU

PALA is an inhibitor of de novo pyrimidine biosynthesis. Studies combining PALA with 5-FU in experimental models have demonstrated synergistic antitumor activity with only additive toxicity. The phase I study of PALA in combination with 5-FU is described. Sixteen patients received a total of 29 courses of PALA given as a 24-hour infusion daily for 5 days and 5-FU given by iv bolus at the end of each 24-hour PALA infusion. Cycles were repeated at 28-day intervals. Mucositis was dose-limiting when 940 mg/m3/day of PALA was given with 345 mg/m2/day of 5-FU. Diarrhea, skin rash, and myelosuppression (in decreasing order of frequency) occurred but were not dose-limiting. Alopecia occurred in all patients. Objective responses were seen in single patients with large cell carcinoma of the lung, fibrous histiocytoma, and adenocarcinoma of the colon refractory to prior 5-FU therapy. These studies support further phase II evaluation of the PALA and 5-FU combination.

Biological and biochemical evidence for an interaction between Marek's disease herpesvirus and avian leukosis virus in vivo

The DNA-containing Epstein-Barr herpesvirus has been implicated in the etiology of Burkitt's lymphoma, a malignant tumor of children in Africa. Recently, however, particles possessing four biochemical characteristics of RNA tumor viruses have also been identified in these tumors. The fact that both types of viruses are found suggests that an interaction between them may be playing a role in the etiology of Burkitt's lymphoma. To explore this possibility with a defined animal model, experiments were performed with the avian Marek's disease, a malignant lymphoproliferative disease associated with a herpesvirus. Controlled contact studies demonstrated that tumorigenesis in a line of isolator-derived, barrier-sustained, specific pathogen-free chickens requires exposure to both the Marek's disease herpesvirus and an avian leukosis virus, Rous-associated virus, type 2. Exposure to either agent alone did not result in tumors. Molecular hybridization experiments to cytoplasmic RNA from similarly contact-exposed conventional Cornell S-line chickens provided further evidence for the occurrence of an interaction between Marek's disease herpesvirus and the avian leukosis virus.

Burkitt's tumors contain particles encapsulating RNA-instructed DNA polymerase and high molecular weight virus-related RNA

Burkitt's lymphomas, linked by previous studies with the DNA-containing Epstein-Barr virus, contain an RNA related in sequence to that of Rauscher leukemia virus. The present study establishes that the viral-related RNA found in Burkitt's tumors is a 70S component encapsulated with RNA-instructed DNA polymerase in a particle possessing a density characteristic of RNA tumor viruses. Further, the DNA synthesized by the Burkitt particles hybridizes specifically to the RNA of Rauscher leukemia virus. Thus, four features characteristic of a known oncogenic RNA agent are also exhibited by particles found with a high (87%) frequency in Burkitt's tumors. The relation between the RNA particle and the Epstein-Barr virus and their etiological roles remains to be elucidated. However, relevant to these issues is the finding reported here that the presence of Epstein-Barr virus information in nonneoplastic cells does not lead to the production of the RNA particles that have been detected now in three different human neoplasias, including leukemias, breast cancer, and Burkitt's disease.

RNA related to that of a murine leukemia virus in Burkitt's tumors and nasopharyngeal carcinomas

RNA homologous to that of the Rauscher leukemia virus has been detected in Burkitt's lymphomas and nasopharyngeal carcinomas. Earlier excellent experimental evidence has linked these two human tumors with the Epstein-Barr virus, a DNA-containing agent.

Viral-related RNA in Hodgkins' disease and other human lymphomas

Molecular hybridization with radioactively labeled DNA complementary to the RNA of the Rauscher leukemia virus was used to probe for homologous RNA in human lymphomas. 22 of 32 specimens contained RNA possessing homology to the RNA of the mouse leukemia virus, but not to that of the unrelated viruses causing mammary tumors in mice or myeloblastosis in chickens. Normal adult and fetal tissues failed to show significant levels of the leukemia-specific RNA. It appears that human lymphomas contain RNA sequences homologous to those found in a viral agent known to cause leukemia and lymphomas in an experimental animal. The fact that human leukemias and sarcomas also contain this type of RNA further emphasizes a remarkable similarity between the corresponding neoplasias of murine and human origin.

RNA in human leukemic cells related to the RNA of a mouse leukemia virus (leukocytes-RNA-DNA hybridization-rauscher virus-polysomal RNA)

Molecular hybridization with radioactively labeled DNA complementary to the RNA of the Rauscher leukemia virus was used to probe for homologous RNA in the polysome fraction of human leukemic cells. The leukocytes of 24 out of 27 patients examined contained RNA possessing homology to that of the mouse leukemia agent, but not to that of the unrelated viruses causing mammary tumors in mice or myeloblastosis in chickens. Further, no control human leukocytes or other adult and fetal tissues showed significant levels of the leukemia-specific RNA. It would appear that human leukemic cells contain RNA sequences homologous to those found in a viral agent known to cause leukemia in an experimental animal. The fact that human sarcomas have also been shown to contain this type of RNA points to a remarkable parallelism in the leukemias and sarcomas of mice and men.

Human sarcomas contain RNA related to the RNA of a mouse leukemia virus

Labeled DNA complementary to the RNA of the Rauscher leukemia virus was hybridized with RNA from the polysome fraction of human sarcomas. Eighteen out of 25 specimens contained RNA possessing homology to the RNA of the mouse leukemia virus but not to that of the unrelated viruses causing mammary tumors in mice or myeloblastosis in chickens. Further, no normal adult or fetal tissues showed significant amounts of RNA specific to mouse leukemia virus. It appears that human sarcomas contain RNA sequences homologous to those found in an agent related to a virus known to cause sarcomas in mice.