R. Wallace Brockman

NMR study of in vivo RIF-1 tumors. Analysis of perchloric acid extracts and identification of 1H, 31P and 13C resonances

Perchloric acid extracts of radiation-induced fibrosarcoma (RIF-1) tumors grown in mice have been analyzed by multinuclear NMR spectroscopy and by various chromatographic methods. This analysis has permitted the unambiguous assignment of the 31P resonances observed in vivo to specific phosphorus-containing metabolites. The region of the in vivo spectra generally assigned to sugar phosphates has been found in RIF-1 tumors to contain primarily phosphorylethanolamine and phosphorylcholine rather than glycolytic intermediates. Phosphocreatine was observed in extracts of these tumor cells grown in culture as well as in the in vivo spectra, indicating that at least some of the phosphocreatine observed in vivo arises from the tumor itself and not from normal tissues. In the 31P-NMR spectra of the perchloric acid extract, resonances originating from purine and pyrimidine nucleoside di- and triphosphate were resolved. HPLC analyses of the nucleotide pool indicate that adenine derivatives were the most abundant components, but other nucleotides were present in significant amounts. The 1H and 13C resonance assignments of the majority of metabolites present in RIF-1 extracts have also been made. Of particular importance is the ability to observe lactate, the levels of which may provide a noninvasive measure of glycolysis in these cells in both the in vitro states. In addition, the aminosulfonic acid, taurine, was found in high levels in the tumor extracts.

Identification of metabolites of 9-β-d-arabinofuranosyl-2-fluoroadenine, an antitumor and antiviral agent

Analysis of blood from a dog given a 400 mg/m2 dose of 9-beta-D-arabinofuranosyl-2-fluoroadenine (2-F-araA) led to the identification of parent drug and a major metabolite, 9-beta-D-arabinofuranosyl-2-fluorohypoxanthine. 2-Fluoroadenine, a toxic derivative of 2-F-araA, was not detected in blood within the limits of detection, suggesting that parent drug was absorbed and distributed without systemic exposure to this toxic derivative. Parent drug, 2-fluoroadenine, and 9-beta-D-arabinofuranosyl-2-fluorohypoxanthine were identified in urine of dog, monkey, and mouse.

Retinoic acid‐binding protein in experimental and human colon tumors

Retinoic acid‐binding protein is present in metastatic murine colon tumors as well as in Lewis lung tumors and in lungs and brains of mice bearing these tumors; however, this protein is below the limits of detection in weakly‐metastatic carcinomas and in normal lung, colon, or brains. These observations are interesting since they concern the possibility of measuring the binding protein levels of colon tumors in clinical specimens as biochemical markers in human malignancy. A total of thirty‐three human colon tumors and related materials were analyzed for the presence of the binding protein. The interfering serum albumin, which nonspecifically binds retinoic acid, was eliminated by affinity chromatography. Of the twenty colon, cecum, and rectum tumors analyzed, 80% contained the binding protein in detectable amounts, and 20% showed nondetectable or marginally detectable amounts. Twenty‐two percent of the human colon segments isolated from patients suspected for colon tumors contained the binding protein in readily detectable amounts, whereas 78% revealed nondetectable to marginally detectable amounts. The retinoic acid‐binding protein of human colon tumor shared the same ligand specificity, thiol functions in ligand‐binding, and sedimentation coefficient as the binding protein isolated from chick embryo skin. However, the human protein exhibited altered isoelectric pH.

A convenient procedure for purification of thymidylate synthase from L1210 cells.

Abstract Several laboratories have described procedures for purification of thymidylate synthase (TMP synthase) that utilize folates or folate analogs covalently attached to a matrix. The principle of separation is the formation of a ternary complex between dUMP, TMP synthase, and the bound ligand and the subsequent elution of the enzyme with buffers that do not contain dUMP. We have successfully used 10-formylfolic acid as the bound ligand for the purification of TMP synthase. As compared to other ligands that have been used, 10-formylfolic acid has the advantages that it can be easily synthesized, it is stable, and the enzyme is eluted as a sharp peak. Application of this procedure to L1210 leukemia cells gave 1765-fold purification of TMP synthase with a recovery of 39%. The native enzyme had a molecular weight of 78,000, which is about the same as that reported.

Alterations in nucleotide pools induced by 3-deazaadenosine and related compounds role of adenylate deaminase

3-Deazaadenine, 3-deazaadenosine, and the carbocyclic analog of 3-deazaadenosine produced similar effects on nucleotide pools of L1210 cells in culture: each caused an increase in IMP and a decrease in adenine nucleotides and had no effect on nucleotides of uracil and cytosine. Concentrations of 50-100 microM were required to produce these effects. Although 3-deazaadenosine and carbocyclic 3-deazaadenosine are known to be potent inhibitors of adenosylhomocysteine hydrolase, the effects on nucleotide pools apparently are not mediated via this inhibition because they are also produced by the base, 3-deazaadenine, and because the concentrations required are higher than those required to inhibit the hydrolase. Cells grown in the presence of 3-deazaadenine or 3-deazaadenosine contained phosphates of 3-deazaadenosine (the mono- and triphosphates were isolated); from cells grown in the presence of the carbocyclic analog of 3-deazaadenosine, the monophosphate was isolated, but evidence for the presence of the triphosphate was not obtained. A cell-free supernatant fraction from L1210 cells supplemented with ATP catalyzed the formation of monophosphates from 3-deazaadenosine or carbocyclic 3-deazaadenosine, and a cell-free supernatant fraction supplemented with 5-phosphoribosyl 1-pyrophosphate (PRPP) catalyzed the formation of 3-deaza-AMP from 3-deazaadenine. Adenosine kinase apparently was not solely responsible for the phosphorylation of the nucleosides because a cell line that lacked this enzyme converted 3-deazaadenosine to phosphates. No evidence was obtained that the effects on nucleotide pools resulted from a block of the IMP-AMP conversion, but the results could be rationalized as a consequence of increased AMP deaminase activity. This explanation is supported by two observations: (a) coformycin, an inhibitor of AMP deaminase, prevented the effects on nucleotide pools, and (b) 3-deazaadenine decreased the conversion of carbocyclic adenosine to carbocyclic ATP and increased its conversion to carbocyclic GTP. The latter conversion requires the action of AMP deaminase and the observed effects can be rationalized by a nucleoside analog-mediated increase in AMP deaminase activity. Because these effects on nucleotide pools are produced only by concentrations higher than those required to inhibit adenosylhomocysteine hydrolase, they may not contribute significantly to the biological effects of 3-deazaadenosine or carbocyclic 3-deazaadenosine.(ABSTRACT TRUNCATED AT 400 WORDS)

Cross-resistance of drug-resistant murine leukemias to deoxyspergualin (NSC 356894) in vivo

SummaryDeoxyspergualin, the 15-deoxy derivative of the antibiotic spergualin, is a novel guanidino analog structurally related to spermine. Deoxyspergualin has significant activity in selected experimental tumor models, and clinical trials have been initiated. Described here are in vivo evaluations of the therapeutic activity of deoxyspergualin against murine leukemia lines specifically resistant to eight clinically useful antitumor drugs. These were P388 lines resistant to doxorubicin, vincristine, L-phenylalanine mustard, cisplatin, ara-C, and methotrexate and L1210 lines resistant to 5-FU, L-phenylalanine mustard, and cyclophosphamide. Sensitivity to deoxyspergualin was evaluated in parallel comparisons of each resistant leukemia to the sensitive line from which it had been derived. All experiments were repeated at least once for confirmation of results. Responses were quantitated in terms of the change in tumor cell numbers from the beginning of treatment to the end of treatment as estimated from the median survival times of dying mice. The results indicated that P388 leukemia resistant to cisplatin (P388/DDPt) was cross-resistant to deoxyspergualin. No cross-resistance was observed in leukemias resistant to doxorubicin, vincristine, ara-C, methotrexate, or cyclophosphamide. L1210 resistant to 5-FU (L1210/5-FU) was collaterally sensitive to deoxyspergualin. Although cross-resistance was also observed in P388/L-PAM, L1210/L-PAM retained sensitivity to deoxyspergualin. Total glutathione concentrations in P388/L-PAM and L1210/L-PAM provided no apparent explanation for this unexpected result. It may be tentatively concluded that resistance to cisplatin, L-PAM, or other DNA alkylators or cross-linkers may increase the potential for cross-resistance to deoxyspergualin. This conclusion requires verification with additional alkylating agents, with drug-resistant human tumor cell lines, and with prospective clinical studies. However, it has present implications for the mechanism(s) of deoxyspergualin activity, for the selection of patients for clinical trials of this investigational new drug, and for the design of noncross-resistant drug combinations.

COMPARISON OF THE ANTICYTOMEGALOVIRUS ACTIVITY OF A GROUP OF PYRIMIDINE ANALOGS

We have carried out extensive screening studies with a broad variety of chemical agents using human cytomegalovirus (CMV) in vitro as a test system. From these studies, certain classes of compounds have begun to emerge which apparently have significant activity against this virus. These anti-CMV compounds include purine analogsl, certain thiosemicarbazones (unpublished data), and pyrimidine analogs, with the latter compounds consistently having,the highest degree of activity against the virus. This paper presents the results of quantitative experiments designed to demonstrate comparative structure and antivirus activity relationships within the pyrimidines studied.