Enzyme pathology and the histologic categorization of human lung tumors: the continuum of quantitative biochemical indices of neoplasticity

The purpose of the present enzymic and histologic analysis of pulmonary samples from 39 subjects was to discern a common, meaningful pattern which may underlie the biochemical heterogeneity of lung neoplasms. The distribution among the different tumors of thymidine kinase, uridine kinase, phosphoserine phosphatase, hexokinase and adenylate kinase was found to correlate with each other. By averaging their standardized units (normal lung = 0) an enzymic index of neoplasticity was calculated for each tumor and used (in increasing order) to rank all 39. The index, showing a significant positive correlation with mitotic frequency, encompassed a continuous 100-fold range. Poorly differentiated carcinomas ranked high while neoplasms with better differentiation and prognosis placed in the lower half of the range. The results indicate that enzymes showing coordinated variations over a broad spectrum of tumors could contribute objective criteria to the rating of any individual tumor against a continuous, quantitative scale of neoplasticity.     

Serum thymidine kinase as a tumor marker of colorectal carcinogenesis induced with 1,2-dimethylhydrazine in rats

Thymidine kinase is the key enzyme in salvage pathway for pyrimidine nucleotide synthesis. High activities of thymidine kinase have been found in rapidly proliferating normal, neoplastic tissues and sera from patients with various diseases including lymphoma, leukemias and small cell lung cancer. We investigated the serum thymidine kinase activities and the colorectal carcinomas in rats treated with 1,2-dimethylhydrazine. The positive correlations between serum thymidine kinase activities and numbers of total and large tumors were observed. These findings suggest the measurement of serum thymidine kinase activity may be clinically valuable in an early stage of the colonic carcinogenesis.     

Pyrimidine nucleotide metabolism in human colon carcinomas: Comparison of normal tissues,primary tumors and xenografts

The activities of 5 enzymes involved in the pyrimidine metabolism were measured in xenografts of 8 human colon adenocarcinomas and in the corresponding primary tumors and normal tissues. The enzymes studied were thymidine kinase, thymidine phosphorylase, uridine kinase, uridine phosphorylase and thymidylate synthase. With the exception of the phosphorylases in one tumor, all enzyme activities were higher in primary tumors than in the corresponding normal tissues. The average activities of thymidine kinase and thymidylate synthase were of the same order of magnitude in xenografts and in primary tumors. The uridine metabolizing enzymes tend to have a higher activity in xenografts than in primary tumors. The most consistent and significant change was a sharp decrease in thymidine phosphorylase activity in xenografts as compared to primary tumors. Whether or not the difference in thymidine phosphorylase activity between xenografts and primary tumors is related to the contribution of non-cancerous cells in primary tumors remains to be determined. However, these results raise questions concerning the representativeness of xenografts with reference to primary tumors and suggest that care should be taken in the application of this model.     

The undifferentiated enzymic composition of human fetal lung and pulmonary tumors.

The concentrations of 16 to 21 enzymes, representing various metabolic pathways, have been determined in human adult, fetal, and neoplastic lung. At midgestation, 12 enzymes (among them, several that metabolize amino acids) were above their adult values while 3 other enzymes were still at low concentrations. These signs of biochemical immaturity are contrasted and compared with those in fetal human liver and rat lung. The enzymic composition of the 11 human pulmonary tumors studied resembled that of the normal fetal lungs closely; the same 12 enzymes were elevated and the same 2 were decreased (compared to nonneoplastic adult lung) in both. The characteristic abnormality in the overall pattern of enzymes, in the concentrations of individual ones, and in the quality of pyrroline-5-carboxylate reductase was clearly evident in both primary and metastatic tumors. The mean concentrations of 10 enzymes in the tumors were significantly different (higher or lower) from those in the control lungs (p less than 0.001 to less than 0.05). The best markers of neoplasticity were thymidine kinase, peptidyl proline hydroxylase, phosphoserine phosphatase, hexokinase, and pyrroline-5-carboxylate reductase. The results demonstrate that quantification of a small battery of enzymes, none of them tissue specific, can distinguish adult human lung from its neoplasms.     

Activities of enzymes converting 5-fluorouracil to 5-fluorouridine-5' monophosphate and 5-fluorodeoxyuridine-5' monophosphate in subcultured cell lines and solid tumor tissues

The activities of five enzymes, orotate phosphoribosyltransferase (OPRTase), uridine kinase (UR kinase), thymidine kinase (TdR kinase), uridine phosphorylase (UR Prylase) and thymidine phosphorylase (TdR Prylase), were examined in subcultured human acute leukemia cell lines (HL-60, CCRF-CEM), subcultured human solid tumor cell lines (Colo-205, HeLa-S3) and human cancerous tissues with a view to compare the activation of 5-fluorouracil in them. There was no significant difference in the activity of any enzyme between HL-60 and CCRF-CEM, Colo-205 and HeLa-S3, and human lung cancerous tissue and human colon cancerous tissue. Compared between the acute leukemia cell lines and the solid tumor cell lines, the UR kinase activity was high in both cell lines. The OPRTase and UR Prylase activities were low in the solid tumor cell lines. In the cancerous tissues, both the UR kinase and TdR kinase activities were low, but the UR Prylase and TdR Prylase activities were markedly high. The results suggest that the intracellular activation of 5-fluorouracil varies with different human cancerous cells. When the anti-cancer activity of 5-fluorouracil is tested in vitro, the difference of fluoropyrimidine metabolism in subcultured cell lines from that in the cancerous tissue should be taken in account.     

Uridine kinase activity in human tumors.

The activity of uridine kinase, a key enzyme in the salvage pathway for pyrimidine bases and nucleosides and for the activation of the corresponding chemotherapeutic analogs, varied 10-fold in a series of human colon adenosarcomas; similar variations were observed with other tumor types. In contrast to the leukemias where only the adult isozyme appears to be present, both the adult and embryonic forms were present in the solid tumors examined. The qualitative and quantitative differences may account, in part, for differences in the innate (initial) sensitivity of the tumors to pyrimidine base and nucleoside analogs.     

Radiation, pool size and incorporation studies in mice with 5-chloro-2'-deoxycytidine

Bolus doses of 5-chlorodeoxycytidine (CldC) administered with modulators of pyrimidine metabolism, followed by X-irradiation, resulted in a 2-fold dose increase effect against RIF-1 tumors in C3H mice. Pool size studies of the fate of [14C]-CldC in BDF1 mice bearing Sarcoma-180 tumors, which demonstrated the rapid formation of 5-chlorodeoxycytidylate (CldCMP), and incorporation of CldC as such in RIF-1 tumor DNA, indicate that CldC is a substrate for deoxycytidine kinase, as our past Km studies have shown. Our data indicate that 5-chlorodeoxyuridine triphosphate (CldUTP) accumulates from both the cytidine deaminase-thymidine kinase pathway, as well as from the deoxycytidine kinase-dCMP deaminase pathway, in tumor tissue. As shown in a previous study, tetrahydrouridine (H4U), a potent inhibitor of cytidine deaminase, can effectively inhibit the enzyme in the normal tissues of BDF1 mice. When H4U was administered with the modulators N-(phosphonacetyl)-L-aspartic acid (PALA) and 5-fluorodeoxycytidine (FdC), the levels of CldC-derived RNA and DNA directed metabolites increased in tumor and decreased in normal tissues compared to when CldC was administered alone. These modulators inhibit the de novo pathway of thymidine biosynthesis, lowering thymidine triphosphate (TTP) levels, which compete with CldUTP for incorporation into DNA. 5-Benzylacyclouridine (BAU), an inhibitor of uridine phosphorylase, was also utilized. DNA incorporation studies using C3H mice bearing RIF-1 tumors showed that the extent of incorporation of 5-chlorodeoxyuridine (CldU) into DNA correlates with the levels of cytidine and dCMP deaminases; this is encouraging in view of their high activity in many human malignancies and the low activities in normal tissues, including those undergoing active replication. Up to 3.9% replacement of thymidine by CldU took place in RIF-1 tumors, whereas incorporation into bone marrow was below our limit of detection. CldC did not result in photosensitization under conditions in cell culture in which radiosensitization to X rays was obtained. Thus, the combination of CldC with modulators of its metabolism has potential as a modality of selective radiosensitization for ultimate clinical use in a wider range of tumors than those of the brain.     

Comparison of pyrimidine nucleotide synthetic enzymes involved in 5-fluorouracil metabolism between human adenocarcinomas and squamous cell carcinomas

The activities of orotate phosphoribosyltransferase (OPRT), cytidine triphosphate (CTP) synthetase, deoxycytidine monophosphate (dCMP) deaminase, thymidine monophosphate (dTMP) kinase, uridine (Urd) kinase, thymidine (dThd) kinase, Urd and dThd phosphorylases, and DNA polymerase were examined in the eight human lung squamous cell carcinomas and five lung adenocarcinomas, and five tumor-adjacent normal lung tissues. All of these enzymes are involved in pyrimidine nucleotide synthesis. The metabolism of 5-fluorouracil (5-FU) was determined. The levels of these enzymes, except for OPRT, were high in tumor tissues and almost the same between lung squamous cell carcinomas and adenocarcinomas, with no statistical difference. The activities for phosphorylation and degradation of 5-FU were similar in each tissue type of tumor. As 5-FU is incorporated into tumor cells and is metabolized actively to 5-FU nucleotides in squamous cell carcinoma tissues, at almost the same level seen in adenocarcinoma tissues, this drug should have a wide clinical application.     

Biochemical measure of the volume doubling time of human pulmonary neoplasms

The volume doubling time (DT) of human lung neoplasms, determined from sequential, presurgery roentgenograms, was compared with biochemical and histologic observations on biopsy samples of the same tumors obtained during surgery. The DTs of the 16 neoplasms ranged from 24 days in an oat cell carcinoma to over 500 in a pulmonary carcinoid tumor, and showed a statistically significant, inverse correlation to the TK (thymidine kinase) and the UK (uridine kinase) concentration of the biopsy samples per g wet weight or mg DNA. Log DT bore a linear relationship to log TK (r = 0.75, P = 0.0008) and to log UK (r = 0.69, P = 0.0067), and an even better fit to the straight line was found when plotting the log of the standardized average of the two enzymes against log DT. The results demonstrate the feasibility of a biochemical method for determining the unknown DT of the many tumors that are not amenable (on account of shape, location, or lack of prior chest x-rays) to the direct, radiologic determination of this useful, dynamic parameter of clinical malignancy.     

Effect of chemotherapy on the nucleoside phosphate kinase activity in experimental tumors

In animals with experimental transplantable tumors, an effective treatment with antitumor compounds brought about interrelated changes in nucleoside phosphate kinase activity. The decrease in thymidine phosphate kinase activity was as a rule matched by an increase in that of uridine phosphate kinase. Consequently, "thymidine kinase-uridine kinase" shunt responsible for thymidine-uridine interconversion was suggested, which is switched on when the homeostasis of tumor cells is disturbed. In treatment of tumor-bearing animals, the effective dosage of antitumor drugs was considerably decreased due to a combination of the said compounds (inhibiting nucleoside kinases) or with azauridine which inhibits uridine monophosphate synthesis from orotidine-5'-phosphate.     

Enhanced levels of deoxycytidine kinase and thymidine kinase 1 and 2 after pulsed low dose rate irradiation as an adaptive response to radiation.

After pulsed low dose rate irradiation the activities of deoxycytidine kinase and thymidine kinase 1 and 2 were increased 1.5-2-fold 6 h after treatment. Twenty-four hours after treatment the activities of these enzymes had returned to control levels. We presume that the increase of enzyme activities is part of an adaptive response to irradiation and that this increase could be an explanation for the increased survival in the initial part of the SW-1573 cell survival curve. The observation that not only S-phase specific thymidine kinase 1 but also mitochondrial thymidine kinase 2 increases, implies that both these enzymes play a role in an adaptive response of cells to irradiation.     

Enzyme activities and isozyme patterns in human lung tumors

The isozyme patterns and activities of six enzymes were determined in surgical biopsy samples of lung tumors and non-neoplastic pulmonary areas. Fetal lungs were also examined. No tissue differences were found in the isozyme pattern of hexokinase or alkaline phosphatase; small differences in pyruvate kinase isozyme proportions were observed. The tumors exhibited significant deviations with respect to the lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) isozyme patterns. Despite the diversity of cell types, the proportions of the M-subunit of LDH in each tumor and that of the mitochondrial isozyme of MDH in all but one tumor were higher than in control samples from the same lung. In contrast, the normal fetal lung showed a higher LDH-H proportion than did adult lung and a mature MDH isozyme pattern. The alpha-glycerophosphate dehydrogenase and adenylate kinase activities of the tumors were about one-tenth and one-fourth, respectively, of those of nonneoplastic adult lung. These lower activities (evident also in normal fetal lung) were accompanied by 3- to 5-fold increases in the LDH, MDH, pyruvate kinase, and hexokinase activities of the tumors; fetal lungs had lesser increases (2- to 3-fold) for the first 3 enzymes. The common features of tumors with different cell types and histological grade identified here point to several enzymes the quantitation or isozyme analysis of which may be of practical use in distinguishing cancerous from nonneoplastic human lung samples. A combination of different indicators, such as opposite changes in LDH and alpha-glycerophosphate dehydrogenase activity, coupled with elevated proportions of LDH-M, may be used to diagnose neoplasia most reliably.     

5'-Deoxy-5-fluorouridine enzymatic activation from the masked compound to 5-fluorouracil in human malignant tissues

It has been reported that 5'-DFUR is converted to 5-FU by uridine phosphorylase in experimental animal tumors. The conversion of thymidine, uridine and 5'-DFUR as substrates was studied in tumor and normal tissues of human and animals. A further series of studies was performed using 1-(2'-deoxy-beta-D-glucopyranosyl) thymine (GPT), a specific inhibitor of uridine phosphorylase. We found that this conversion in human tumors was catalyzed not by uridine phosphorylase but by thymidine phosphorylase. It was also confirmed that the enzyme activities in various human cancers were significantly several times higher than those in adjacent normal tissues. We succeeded in tried and isolating thymidine phosphorylase in a fairly pure form, from which enzyme Km values were calculated. After administration of 5'-DFUR intravenously or orally to patents, tissue and blood samples were collected by biopsy or surgical operation to determine the 5-FU level. The 5-FU levels were always higher in tumor tissues than in the blood or in normal tissues. Finally effective clinical efficacy was demonstrated by oral administration of 5'-DFUR.     

Tumor chemosensitivity conferred by inserted herpes thymidine kinase genes: paradigm for a prospective cancer control strategy

The lack of highly exploitable biochemical differences between normal tissues and some tumors can theoretically be circumvented by a strategy utilizing gene insertion prophylactically to create tissue mosaicism for drug sensitivity, thereby ensuring that any tumor arising clonally will differ from part of the normal cell population. Elements of the strategy were tested with neoplastic BALB/c murine cell lines bearing the herpes thymidine kinase gene. Exposure to the herpes thymidine kinase-specific substrate 9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine ablated the clonogenic potential of the cells in vitro, and administration of this drug to BALB/c mice bearing tumors produced by the cell lines uniformly induced complete regression of the tumors. The observed responses to therapy imply that the strategy may prove valuable when the genetic technology needed for its human implementation becomes available.     

Relationship between the expression of estrogen-regulated genes and estrogen-stimulated proliferation of MCF-7 mammary tumor cells

The growth of MCF-7 cells was arrested by 24 h of isoleucine deprivation. Following replenishment of the medium, the incorporation of uridine and thymidine into trichloroacetic acid-precipitable material began to increase slowly and gradually rose to the level of cycling cells. The addition of 5 X 10(-9) M estradiol to growth-arrested cells dramatically shortened the time of onset of macromolecular synthesis and increased the overall amount of precursor incorporation 2- to 4-fold over the level obtained by arrested control cells. The increase in uridine incorporation preceded the increase in thymidine incorporation by 6 h. Inhibition of protein synthesis with cycloheximide blocked the recovery of macromolecular synthesis in both control and estrogen-treated cells. Actinomycin D was ineffective in blocking the estrogen-stimulated recovery of macromolecular synthesis at concentrations known to inhibit pre-rRNA synthesis (10(-8) M). At higher concentrations, uridine and thymidine incorporation were inhibited in a dose-dependent manner. Inhibition of RNA polymerase II activity with alpha-amanitin similarly blocked both the recovery of the cells from isoleucine starvation and the potentiation of this by estradiol. Dihydrofolate reductase and thymidine kinase activities are both stimulated by estradiol in MCF-7 cells. In cycling cells, estrogen stimulates a 2-fold increase in their messenger RNAs (mRNAs) within 24 h. The level of dihydrofolate reductase mRNA is unaffected by isoleucine starvation, and estrogen caused no change in dihydrofolate reductase mRNA levels over a 24-h period following reversal of growth arrest. Similar results were observed for the 600-nucleotide pS2 mRNA that has been identified as an estrogen-induced RNA in MCF-7 cells. In contrast, thymidine kinase mRNA was found to be increased by estrogen at 24 h, but not at 12 h, following reversal of growth arrest. This increase correlates with increases in thymidine, but not uridine incorporation. These data indicate that the estrogen-stimulated increase in thymidine incorporation following release from growth arrest is dependent on new RNA synthesis. However, the hormone did not increase the levels of three estrogen-regulated mRNAs coordinately with the increases observed in uridine incorporation.     

HeLa cells resistant to bromodeoxyuridine and deficient in thymidine kinase activity

Mutant sublines of HeLa S3 cells resistant to growth inhibition by bromodeoxyuridine (BUdR) have been isolated. The resistant cell lines (HeLa BU-10, HeLa BU-15, HeLa BU-25, HeLa BU-50, and HeLa BU-100) proliferated in the presence of 10, 15, 25, 50, and 100 μg/ml BUdR, respectively. Extracts from HeLa BU-25, HeLa BU-50, and HeLa BU-100 cells exhibited 2–5 per cent of the thymidine-³H, deoxyuridine-³H, and bromodeoxyuridine-³H phosphorylating activities of parental HeLa S3 cells. HeLa BU-10 and HeLa BU-15 cell extracts were also deficient in thymidine kinase activity, yielding approximately 43 per cent and 8 per cent, respectively, the thymidine kinase activity of parental HeLa S3 cells. The deficiency in thymidine kinase activity of HeLa BU-100 cells was not due to negative feedback inhibition by high levels of BUdR or to interference with the thymidine kinase assay by inhibitors or competing enzymes in the HeLa BU-100 cell extracts. Following 5 weekly passages in media lacking BUdR, the HeLa BU-100 cells did not exhibit increased thymidine kinase activity. Moreover, mixtures of extracts from HeLa S3 and HeLa BU-100 cells displayed a thymidine kinase activity equivalent to the sum of the activities of extracts prepared, respectively, from the HeLa S3 and HeLa BU-100 cells. Radioautographic studies have shown that after HeLa S3 cells were incubated for 6 hours with thymidine-³H, 35–45 per cent of the nuclei were heavily labeled with radioactivity. However, fewer HeLa BU-100 cells displayed labeled nuclei and the nuclei were only lightly labeled. HeLa BU-100 cell extracts contained normal amounts of thymidylate synthetase, thymidylate kinase, and uridine kinase activities. Following infection by vaccinia virus, high levels of thymidine kinase activity were induced in HeLa BU-100 cells.     

Biochemical mechanisms for the scheduled synergism of (αS, 5S)-2 amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid and 5-fluorouracil in P388 leukemia

Summary A study was made of the in vivo effects of equitoxic doses of AT-125 and 5-FU combination, being administered either simultaneously (% ILS 152) or with a 6-h pretreatment with AT-125 (% ILS 184). To examine the biochemical basis for the scheduled synergism, measurements were made of the concentration of PRPP, the specific activities of CPS II, cytidine, thymidine, uridine, deoxyuridine kinases, and fluorinated nucleotide formation in P388 tumors and the small intestine. Two hours after in vivo simultaneous treatment of mice bearing tumors the concentration of PRPP increased 9- and 6-fold above baseline in the tumor and the small intestine, respectively. In the AT-125 pretreatment arm the concentration of PRPP increased 18- and 7-fold above baseline in the tumor and the small intestine, respectively. CPS II activity was reduced to 28%–18% of control in the tumors in the simultaneous and pretreatment groups, respectively, whereas it remained unchanged in the small intestine. Specific activities of cytidine kinase (5.5±1), thymidine kinase (4.0±1.6), uridine kinase (35.6±6.5), and deoxyuridine kinase (2.4±1.1) nmol/mg protein/h remained unchanged with treatment. In concert with the increased intratumor concentration of PRPP, fluorinated nucleotide formation was proportionally increased in the treatment arms. These results indicate the importance of drug scheduling of the above two agents in treating P388 leukemia.Abbreviation AT 125 - S,5S -amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid - 5-FU 5-fluorouracil - 5-FdUMP 5-fluorodeoxyuridine monophosphate - PRPP phosphoribosyl pyrophosphate - 5-FUMP 5-fluorouridine monophosphate - 5-FUDP 5-fluorouridine diphosphate - 5-FUTP 5-fluorouridine triphosphate - UMP uridine monophosphate - UDP uridine diphosphate - UTP uridine triphosphate - ATP adenosine triphosphate - CPS II carbamylphosphate synthetase II - PCA perchloric acid Presented in part at the Seventy-fourth Annual Meeting of the American Association for Cancer Research, San Diego, California, May 1983     

Cytofluorometric determination of thymidine kinase activity in a mixture of normal and neoplastic cells.

A cytofluorometric assay allowing the measurement of thymidine phosphorylation in single cells had been established (Hengstschläger & Wawra, 1993). This assay enables us to correlate intracellular thymidine kinase (TK) activity with the DNA content of single cells. Enzyme activity levels from neuroblastoma cells and normal fibroblasts derived from the same patient were determined. Using this cytofluorometric assay in a mixture of both cell types the neoplastic cells could be distinguished from the normal fibroblasts because of their higher TK level. A human lymphoblastoid cell line was compared with the cell line KG-1, derived from an acute myelogenous leukaemia, in the same way. The increased enzyme activity enabled us to detect KG-1 cells in a mixture with an 10,000-fold excess of Epstein Barr virus transformed lymphocytes.     

Correlations of dihydropyrimidine dehydrogenase, thymidine phosphorylase and thymidine kinase activities in strongly and weakly malignant cultured murine neuroblastoma cells

The C-1300 neuroblastoma tumor which arises spontaneously in the A/J mouse has been maintained in this mouse strain. Two different cell populations have been recognized in cultured C-1300 mouse neuroblastoma (MNB): (1) round, "neuroblast-like" cells, growing in suspension (poorly attached), that have a highly malignant behavior when injected into the A/J mouse (T1 cells); and (2) flat, "epithelioid" cells that attach well to surfaces and show low malignancy towards the inoculated animals (T2 cells). The specific activities of the pyrimidine metabolizing enzymes thymidine phosphorylase (TP), dihydropyrimidine dehydrogenase (DPD) and thymidine kinase (TK) were examined in both MNB cell lines by a new radiochromatographic method. Enzymatic activities of TP and DPD in the cytosols of T2 (weakly malignant) cells were up to 15 times higher than those of T1 (strongly malignant) cells, whereas the mean TP/DPD activity ratio was 16 in either cell line. TP and DPD activity levels increased with time of growth in culture in T2 cells while no such increase was seen in the T1 cells. Maximal TK activity was similar in both cell lines but dropped more rapidly in the T2 cells as cell densities increased. The enzymatic activity levels of TP and DPD but not of TK correlated inversely with neoplastic expression of MNB cells. The observed patterns of pyrimidine metabolizing enzymes in MNB cells could result in an increased thymidine pool in T1 cells whenever TK activity is suppressed, whereas such conditions would favor the generation of thymine in the T2 cells.     

Enzyme activities in human fetal and neoplastic tissues

The concentrations of ten or 12 enzymes involved in the metabolism of DNA, collagen, amino acids, or glucose have been determined in variants of human intestinal and pulmonary tissues. In comparison to nonneoplastic adult colon, normal fetal colon had elevated concentrations of thymidine kinase, peptidyl proline hydroxylase, phosphoserine phosphatase, ornithine transcarbamylase, gamma-glutamyl transpeptidase, and ornithine aminotransferase. Raised activities of the first five of these enzymes, and of hexokinase, glucose-6-phosphate dehydrogenase, and pyrroline-5-carboxylate reductase distinguishes neoplastic from nonneoplastic sections of adult colon. Study of a wide range of pulmonary specimens permitted comparisons of different types of tumors, and revealed some subtle differences between lungs of noncancer patients and nonneoplastic portions of host lungs. The concentrations of eight previously identified enzymic indicators were less in moderately or well differentiated than in poorly differentiated pulmonary adenocarcinomas. The latter differed from epidermoid carcinomas (also poorly differentiated) by containing lower concentrations of thymidine kinase (both soluble and particulate) and hexokinase.