Apparent convergence (at 2-monoacylglycerol level) of phosphatidic acid and 2-monoacylglycerol pathways of synthesis of chylomicron triacylglycerols

Dietary fats are converted into chylomicron triacylglycerols via the 2-monoacylglycerol and phosphatidic acid pathways of acylglycerol formation. In view of the known positional and fatty acid specificity of the acyltransferases, the triacylglycerol structures resulting from the two pathways would be expected to differ, but this has not been demonstrated. We have performed stereospecific analyses on the chylomicron triacylglycerols from rats fed menhaden oil and the corresponding fatty acid alkyl esters, which would be expected to be assimilated via the monoacylglycerol and the phosphatidic acid pathways, respectively. The results show a remarkable similarity between the two triacylglycerol types in the fatty acid composition of the sn-1 and sn-3 positions, along with marked differences in the composition of the sn-2 positions. The triacylglycerols from rats fed oil retained about 85% of the original fatty acids in the sn-2 position, including a high proportion of the long chain polyunsaturates (e.g., 5-7% 20:5 and 4-5% 22:6). The triacylglycerols from rats fed the alkyl ester contained large amounts of endogenous fatty acids in the sn-2 position (e.g., 18% 16:1, 14% 18:1, 14% 18:2, and 2.5% 20:4), which approximated the composition of the sn-2 position of the presumed phosphatidic acid intermediates. The sn-1 position contained a much higher proportion of polyunsatured fatty acids (e.g., 12-13% 20:5, 5-6% 22:6) than the sn-2 position (e.g. 2-3% 20:5, 0-0.6% 22:6) of triacylglycerols from rats fed the ester. We conclude that the chylomicron triacylglycerols arising via the 2-monoacylglycerol and the phosphatidic acid pathways differ mainly in the composition of the fatty acids in the sn-2 position. The similarity in the acids of the sn-1 and sn-3 positions of the chylomicron triacylglycerols from rats fed oil or ester is consistent with a hydrolysis of the acylglycerol products of the phosphatidic acid pathway to 2-monoacylglycerols prior to reconversion to triacylglycerols via the monoacylglycerol pathway and secretion as chylomicrons.

Heterogeneous effects of interferon on antitumor agents' cytotoxicities to human colon carcinoma cell lines

Six established human colon carcinoma cell lines that segregated into three groups with different degrees of differentiation were treated using three subclasses of interferons as single agents and in combination with either 5-fluorouracil, cis-platinum, or adriamycin. The cytotoxicities of the combination treatments were heterogeneous and did not relate to the cell's levels of differentiation. Our data suggest that the optimal combinations of interferons and chemotherapeutic agents are independent of the differentiation state of the colon cancer cells.

Surface array proteins of Campylobacter fetus block lectin-mediated binding to type A lipopolysaccharide

Campylobacter fetus strains with type A lipopolysaccharide (LPS) and a surface array protein layer (S+) have been found to be pathogenic in humans and animals. Spontaneous laboratory mutants that lack surface array proteins (S-) are sensitive to the bactericidal activity of normal human serum. The ability of lectins to determine the presence of the S-layer and differentiate LPS type was assessed. We screened 14 lectins and found 3 (wheat germ agglutinin, Bandeiraea simplicifolia II, and Helix pomatia agglutinin) that agglutinated S- C. fetus strains with type A LPS but not S- strains with type B or type C LPS or S+ strains. However, the S+ type A strains were agglutinated after sequential water extraction, heat, or pronase treatment, all of which remove the S-layer, whereas there was no effect on the control strains. Specific carbohydrates for each lectin and purified LPS from a type A C. fetus strain specifically inhibited agglutination of an S- type A strain. In a direct enzyme-linked lectin assay, binding to the S- type A LPS strain was significantly greater than binding to the S+ strain (P = 0.01) or to a Campylobacter jejuni strain (P = 0.008). Consequently, these results indicate that the three lectins bind to the O side chains of C. fetus type A LPS but that the presence of the S-layer on intact cells blocks binding.

Biological characterization of multidrug-resistant human colon carcinoma sublines induced/selected by two methods

Two independent multidrug-resistant (MDR) sublines, AdR1.2 and SRA1.2, were developed from the established human colon carcinoma cell line LoVo. AdR1.2 was developed by a long-term continuous exposure of LoVo cells to Adriamycin in stepwise increments of concentration; SRA1.2 was selected/induced by pulse treatments by using a single concentration of Adriamycin. The two resistant sublines were cross-resistant and cross-sensitive to a similar spectrum of cytotoxic agents. However, AdR1.2 was most resistant to Adriamycin among the nine agents tested, and SRA1.2 was most resistant to Vinca alkaloids. Although SRA1.2 had biological characteristics similar to those of LoVo, AdR1.2 had remarkably altered biological properties, including no detectable carcinoembryonic antigen secretion, a smaller proportion of proliferating cells and a lower growth rate, lower fraction of cells in S phase, a lower colony-forming ability, and smaller colonies. In addition, the resistant phenotype of AdR1.2 was reversed when the cells were grown in a drug-free medium, whereas SRA1.2 maintained its resistance for at least 10 months under similar conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the plasma membrane proteins demonstrated overproduction of an Mr 130,000 protein in both the resistant sublines. The Mr 130,000 protein was not immunoreactive with C219 monoclonal antibody against p170, but the absence of Mr 130,000 protein in an AdR1.2 revertant and the parental LoVo suggests that it is an MDR-related plasma membrane protein. The absence of a 46-kDa cytosolic protein and the presence of a Mr 150,000 plasma membrane protein were found in AdR1.2 but not in SRA1.2. This Mr 150,000 protein immunoreacted with C219. This protein was also present, although in a reduced amount, in an AdR1.2 revertant that retained three times the MDR of LoVo cells and was thus comparable to SRA1.2. The two MDR sublines thus may represent two independent subclones which may serve as two different models for the study of multidrug resistance in human colon cancer.

Intestinal absorption of menhaden and rapeseed oils and their fatty acid methyl and ethyl esters in the rat

The relative cellular uptake and incorporation into prechylomicrons and chylomicrons was investigated for the menhaden and rapeseed oil fatty acids, when given by stomach tube as the original oils or the corresponding methyl and ethyl esters. The intermediates and final products of cellular acylation were determined by chromatographic methods at various times over a period of 1-24 h. There was little selectivity in the uptake among the oligo- and poly-unsaturated fatty acids of menhaden oil, when either oil or esters were fed. In contrast, the long-chain saturated and monounsaturated fatty acids of rapeseed oil were discriminated against during both cellular uptake and reacylation (60% overall reduction in utilization). Also, there was detectable discrimination against the long-chain polyunsaturated monoacylglycerols of menhaden oil and against the long-chain saturated and monounsatured monoacylglycerols of rapeseed oil during both cellular uptake and reacylation (30% overall reduction in utilization). Evidence was obtained for an indiscriminate cellular uptake of variable amounts (4-22%) of intact dietary methyl and ethyl esters of fatty acids, which, however, appeared in the chylomicrons only to a very limited extent (0.1-1.0% of total lipid). During peak absorption the cellular and lymphatic appearance of fatty acids from the digestion and absorption of the alkyl esters was nearly 50% lower than that from the corresponding triacylglycerols. The slower absorption of the fatty acids from the alkyl ester feeding is hypothetically attributed to a lower efficiency of the phosphatidic acid pathway, which is required in the absence of dietary 2-monoacylglycerols, but other mechanisms cannot be excluded.

Lipolysis of menhaden oil triacylglycerols and the corresponding fatty acid alkyl esters by pancreatic lipase in vitro: a reexamination

In order to distinguish between possible fatty acid differences during lumenal lipolysis and cellular absorption, we have reinvestigated the in vitro hydrolysis of menhaden oil and its alkyl esters by pancreatic lipase. For this purpose we incubated menhaden oil or its fatty acid methyl and ethyl esters with porcine pancreatic lipase in the presence of bile salts and determined the composition of the released free fatty acids, monoacylglycerols, diacylglycerols, and residual triacylglycerols, or the free fatty acids and residual alkyl esters, respectively, by thin-layer and gas-liquid chromatography. There was significant discrimination against the delta 4- to delta 7-unsaturated fatty acids of both medium and long chain lengths during the hydrolysis of menhaden oil and its fatty acid ethyl esters. In general, the ethyl esters were hydrolyzed 10-50 times more slowly than the corresponding glyceryl esters, depending on the exact ratio of the two substrate types. None of the triacylglycerols or ethyl esters, however, was completely resistant to hydrolysis resulting in an eventual cleavage of all the alkyl esters and presumably all the primary ester bonds in the triacylglycerol molecules. Since the rate of release of the least resistant fatty acid exceeded that of the most resistant acid by only a factor of 6, it is concluded that in the presence of a large excess of lipase the liberated fatty acids would approach the composition of the dietary alkyl or glyceryl esters, as observed during lumenal lipolysis (Yang, L.-Y., A. Kuksis, and J. J. Myher. 1989. Biochem. Cell Biol. 67: 192-204).

Metronidazole enhances the cytotoxic synergism produced by the combination of 1-beta-arabinofuranosylcytosine and cis-diamminedichloroplatinum

Metronidazole (MZ) was evaluated as a single agent or in combination with CDDP and araC for its cytotoxic effects on five established human colon carcinoma cell lines. MZ alone produced little cytotoxicity at 1 h drug incubation. The cytotoxicity was detectable only after 2 h incubation and increased as a function of duration of treatment, suggesting a time-dependent rather than a dose-dependent cytotoxic effect. MZ had no effect on CDDP- or araC-induced cytotoxicity, whereas MZ enhanced the synergism resulting from the combination of two antitumor agents on the human colon tumor cell lines tested. Such enhancement was more pronounced on cells growing in stationary rather than in exponential phase. MZ not only produced a reversible S-phase arrest but also lessened the CDDP-produced inhibition on the incorporation of araC into DNA. However, it did not enhance CDDP-induced DNA cross-linkings, with or without araC. Our results indicated that MZ enhanced the synergism produced by two antitumor drugs in combination and that enhancement was accompanied by an increase in S-phase population and of the incorporation of araC into nucleic acids.

Lumenal hydrolysis of menhaden and rapeseed oils and their fatty acid methyl and ethyl esters in the rat

Simple alkyl (ethyl) esters of polyunsaturated fish oil fatty acids have been proposed as dietary supplements, but their relative efficiency of digestion and absorption have not been determined. Using stomach tubes, we gave rats menhaden or rapeseed oils, or the corresponding methyl and ethyl esters, and determined by chromatographic methods the lipid classes and molecular species recovered from the lumen of the jejunum during the first 1 to 2.5 h of digestion. Hydrolysis of menhaden oil resulted in a preferential retention of a high proportion of the polyunsaturated long chain acids in the sn-2-monoacylglycerols and in the residual triacyglycerols, while digestion of rapeseed oil led to a preferential release of free long chain monounsaturated fatty acids. In contrast, hydrolysis of the alkyl (methyl and ethyl) esters of the fatty acids of either menhaden or rapeseed oil resulted in a composition of free fatty acids which was much more representative of the original esters. It was therefore concluded that the differential lumenal liberation of the long chain and polyunsaturated (three or more double bonds) fatty acids from fish and rapeseed oil is largely due to their characteristic distribution between the primary and secondary positions in the glycerol molecule, and to a much lesser extent to a chain length discrimination by pancreatic lipase. This study also shows that the methyl and ethyl esters are hydrolyzed about 4 times more slowly than the corresponding triacylglycerols, which is sufficient to maintain a saturated micellar solution of fatty acids in the intestinal lumen during absorption.

Synergism of 1-beta-D-arabinofuranosylcytosine and cis-diamminedichloroplatinum in their lethal efficacies against seven established cancer cell lines of gastrointestinal origin

We previously reported that the combination of cis-diamminedichloroplatinum (CDDP) and 1-beta-D-arabinofuranosylcytosine (ara-C) induced a remarkable synergistic killing effect on an established human colon carcinoma cell line, LoVo. The current study investigated whether this effect was LoVo specific or could be extended to other colon cancer cell lines as well as to cell lines of different histological origins, including an estrogen receptor-positive breast cancer cell line (MCF7), an ovarian cancer cell line (OV1225), and an esophageal cancer cell line (Hcu18). The six human colorectal cancer cell lines included in this study represent three biological groups with distinct phenotypic properties. Group 1 (well-differentiated) consisted of LoVo and SW48; group 2 (intermediately differentiated) comprised SW480 and SW620; and group 3 (undifferentiated) was represented by SW403 and SW1116. No significant synergistic cytotoxicity was noted after the breast and ovarian cancer cells were treated. However, synergistic lethal effects were observed in all of the six colon cancer cell lines as well as the esophageal cancer cell line. The synergistic effect on the gastrointestinal cancer cell lines was related to the concentration of ara-C and CDDP during treatment. Our results suggest that the cytotoxic synergism between ara-C and CDDP may be tissue-type specific and that synergism may depend on the histological origin of the cancer.

Increased cytotoxicity and reversal of resistance to cis-diamminedichloro-platinum(II) with entrapment of cis-Bis-neodecanoato-trans-R,R-1,2-diaminocyclohexaneplatinum (II) in multilamellar lipid vesicles

The role of liposome entrapment in modulating the cytotoxicity of a lipophilic cisplatin derivative was assessed. cis-Bis-neodecanoato-trans-R,R-1,2-diaminocyclohexaneplatinum++ +(II) (NDDP) was tested in suspension (free NDDP) or entrapped in multilamellar vesicles composed of dimyristoylphosphatidyl choline and dimyristoylphosphatidyl glycerol (L-NDDP). Against LoVo colon carcinoma cells sensitive to cisplatin, L-NDDP was two times more cytotoxic in vitro than free NDDP and cisplatin (Do 7 microM for L-NDDP, 15 microM for free NDDP, and 16 microM for cisplatin). Against LoVo cells resistant to a concentration of 3 micrograms/ml of cisplatin, L-NDDP was three times more cytotoxic than free NDDP and cisplatin (Do 14 microM for L-NDDP, 45 microM for free NDDP, and 48 microM for cisplatin). In in vivo studies, free NDDP was less potent and less active than L-NDDP against i.p. L-1210 leukemia (free NDDP, optimum %T/C 148 at a dose of 75 mg/kg; L-NDDP, optimum %T/C 185 at a dose of 25 mg/kg) and i.p. L1210/PDD leukemia (free NDDP, optimum %T/C 128 at a dose of 50 mg/kg on Days 1, 5, and 9; L-NDDP, optimum %T/C 200 at a dose of 12.5 mg/kg on Days 1, 5, and 9). Free NDDP administered i.v. was inactive against liver metastases of M5076 reticulosarcoma (%T/C 102) while L-NDDP showed significant activity (%T/C 140). The single dose i.v. LD50 in mice of free NDDP and L-NDDP were similar (79.4 mg/kg for free NDDP and 64.5 mg/kg for L-NDDP). These studies show that NDDP is a liposome-dependent drug since it can only be satisfactorily formulated in the liposomal form and since the liposomal carrier plays a crucial role in determining its antitumor activity.

The heterogenous cytotoxic response of colon cancer cells is unrelated to phenotypic differentiation characteristics

Six colon cancer cell lines segregated into three groups with distinct biological properties (i.e., morphological differentiation, DNA content, carcinoembryonic antigen production, etc.) were treated with ten antitumor drugs. Cytotoxic responses were heterogenous and not associated to biological grouping, in fact, for some drugs, the response of one member of the group resembled that of a member of another group rather than its group counterpart. Thus the most common phenotypic characteristics that identify colon cancer cells did not predict the cytotoxic response and do not appear useful for stratifying patients into categories with distinct responses to currently available chemotherapeutic agents.

Stereochemical course of intestinal absorption and transport of mustard-seed oil triacylglycerols in the rat

Male rats with thoracic duct cannulae were intubated with mustard-seed oil or the corresponding fatty acid methyl esters and the lymph was collected over 0-24 h. The chylomicron and very low density lipoprotein fractions were obtained by conventional ultracentrifugation. The triacylglycerols and glycerophospholipids were isolated and the positional distribution and molecular association of fatty acids were determined by stereospecific and chromatographic methods. The oleic, linoleic, and linolenic acids were recovered in the lymph in the proportion in which they occurred in the fat fed, while eicosenoic, erucic, and lignoceric acids were rejected to about the same extent by the two pathways of intestinal triacylglycerol biosynthesis. It is shown that the lymph triacylglycerols arising via the monoacylglycerol or the phosphatidic acid pathway possess structures that are closely similar to each other and to that of the original mustard-seed oil. It is proposed that this is a result of comparable fatty acid and positional specificity of the acyltransferases associated with the acylglycerol synthesis in the animal and plant tissues and the wide range of fatty acid chain lengths in the mustard-seed oil.

Size and composition of lymph chylomicrons following feeding corn oil or its fatty acid methyl esters

Male rats with thoracic duct cannulae were intubated with corn oil or fatty acid methyl esters and the lymph was collected over the next 2-72 h. The apoprotein (apo) composition of the chylomicrons, isolated by conventional ultracentrifugation, was determined by sodium dodecyl sulfate - polyacrylamide - glycerol gel electrophoresis and isoelectric focusing. The lipid content and composition was assessed by gas--liquid chromatography. The particle size was obtained by calculation and confirmed by electron microscopy. The study demonstrates that both the monoacylglycerol (corn oil feeding) and the phosphatidic acid (methyl ester feeding) pathways of triacylglycerol biosynthesis yield chylomicrons with closely similar apoprotein profiles representing apo B-48, apo A-IV, apo E, apo A-I, and the apo C components. A protein band corresponding to apo B-100 was occasionally observed as a minor component of the chylomicrons from both groups of animals. The chylomicrons from corn oil feeding had about two times larger diameters than those from methyl ester feeding. There were no significant differences in the composition of the apoproteins, although the smaller particles had two times higher apoprotein/triacylglycerol ratios. It was calculated that the amount of apo B per lipid particle for the ester fed rats ranged from one to eight molecules and was closely correlated with the particle size. The corn oil fed rats yielded about three molecules apo B per lipid particle regardless of the particle size. It is concluded that the pathway of intestinal triacylglycerol biosynthesis has a significant effect on the apoprotein mass and to a lesser extent on the apoprotein and lipid composition of the chylomicrons. The phosphatidic acid pathway produces smaller particles and transfers to the bloodstream twice as much apoprotein per gram of fat than the monoacylglycerol pathway, which yields the larger particles. Possible variations in the site and rate of biosynthesis of the triacylglycerols could not be entirely excluded as contributing factors.

Ligands of second generation platinum analogs decrease both platinum-induced DNA cross-linking and its ability to interact with 1-beta-D-arabinofuranosyl cytosine to potentiate cytotoxic efficacy

We evaluated the cytotoxic and DNA cross-linking (CL) ability of four second generation platinum coordination complexes (TNO-6, JM-89, JM-8 and JM-9) delivered alone or in combination with 1-beta-D-arabinofuranosyl cytosine (ara-C) to human colon cancer cells (LoVo). Cell survival varied markedly as a function of the particular substitution moiety. JM-8 and JM-9 were virtually ineffective, even at concentrations as high as 50 micrograms/ml. At that concentration cis-diamminedichloroplatinum(II) (cis-DDP) killed greater than 99.99% of the cells. JM-82 was slightly more active while TNO-6 was the only derivative with appreciably higher cytotoxic activity due to an abrogation of the shoulder region of the type C survival curve. The highest CL effect was observed for cis-DDP followed closely by TNO-6. Very little CL effects were demonstrated for the other three analogs JM-82, JM-8 and JM-9 when measured 6 h after treatment. The combination of cis-DDP and ara-C augmented 10-fold the cytotoxic activity of cis-DDP alone, an effect accompanied by an almost 2-fold increase in CL; every other analog failed to interact in a potentiating manner (either cytotoxicity, or CL at 6 h) with the antimetabolite. Thus, it appears clear that the associated moieties of the Pt coordination complex play a fundamental role in reducing the interaction of the analogs with DNA (as reflected by the decreased CL and cytotoxic effects produced by each agent alone) and in totally preventing their interaction with ara-C to yield a potentiating lethal effect.

New monoclonal antibodies against colon cancer-associated antigens

Established human colon cancer cells with distinct degrees of differentiation (LoVo, well-differentiated; SW620, intermediate differentiation; and SW1116, poorly differentiated) were used to produce monoclonal antibodies (MoAbs) by standard hybridoma techniques. Specificity was tested by an enzyme-linked immunosorbent assay against human foreskin cells, 7 established human colon cancer lines, a panel of 17 established human tumor lines of different histological origins, purified carcinoembryonic antigen, panels of red blood cells, and a suspension of lymphocytes obtained from 30 random normal donors. MoAb LoVo-F4 3E4/1A1/2E10 (MoAb F4/2E10) reacted with five colon cancer lines and only slightly with MCF-7 cells (estrogen receptor positive breast carcinoma). MoAb LoVo-F4 3E4/1A1/5C10 also reacted with the previous five colon cancer lines and with two gastric cancer lines. A MoAb obtained with a LoVo 3 M KCl membrane extract reacted exclusively with LoVo cells. MoAb SW620-F1 4E5/1A3 reacted with only three colon cancer cell lines and an estrogen receptor negative breast cancer line. MoAb SW1116-F2 1E3/1A1 reacted with four colon carcinoma cell lines, one gastric cancer line, MCF-7 cells, and a lung cancer line. MoAb SW1116-F2 1F3/1B1 reacted intensely with purified carcinoembryonic antigen and with every carcinoembryonic antigen-producing cell line available in our laboratory. Further studies concentrated on the immunoglobulin G1 MoAb F4/2E10. We demonstrated that the purified MoAb did not inhibit binding of MoAb CA19-9 to any colon Ca lines and reacted with fresh human colon carcinoma specimens regardless of whether they were processed by cryostat or paraffin embedding after fixation in formalin for 24 through 96 h. Using the peroxidase-antiperoxidase technique, MoAb F4/2E10 did not react with 23 normal adult and 18 fetal (less than 3 months old) human tissue specimens. When tested on 312 specimens of diverse histological origins and diseases, the MoAb was positive in 57 of 62 colorectal cancers, in 12 of 19 villous adenomas, in 5 of 7 adenomatous polyps, and in 10 of 12 cases of ulcerative colitis. With the exception of 2 of 15 cases of Crohn's disease that were slightly positive, all tissues from nonmalignant diseases (regardless of histological origin) were consistently negative. There was only weak reactivity in 2 of 18 breast cancers, 7 of 21 squamous cell carcinomas, 4 of 27 lung tumors, 1 of 13 kidney carcinomas and in 7 miscellaneous tumors.(ABSTRACT TRUNCATED AT 400 WORDS)

Peplomycin and bleomycin effects on human colon cancer cells

The lethal effects of peplomycin and bleomycin on cultured human colon cancer cells (LoVo) were compared by using the technique of inhibition of colony formation. The survival of LoVo cells after treatment for 1 h with either peplomycin or bleomycin was characterized by a biphasic exponential curve. When the exposure time was extended to 24 h, both drugs produced much greater cytotoxic effects, with survival decreased to less than 0.10% for bleomycin and less than 0.02% for peplomycin. Both peplomycin and bleomycin, in a dose-dependent manner, inhibited the incorporation of thymidine into cells. On an equal-weight basis, the cytotoxicity of peplomycin (24-h exposure) was similar to that of bleomycin. Both agent also inhibited the incorporation of leucine and uridine after 24 h of drug exposure, but to a lesser extent than inhibition of thymidine incorporation. However, after 1 h of exposure, such inhibitory effects were minimal. These results demonstrate that prolonged peplomycin or bleomycin exposure produces greater cell-kill than shorter drug exposure. Schedules with continuous drug administration should be explored clinically.

The activity of flavone acetic acid (NSC 347512) on human colon cancer cells in vitro

Flavone acetic acid (FAA) was incubated for 1 to 48 hr with 3 established human colon cancer cell lines endowed with distinct degrees of phenotypic properties. All 3 lines responded to FAA in almost identical fashion; when incubated with the drug for only 1 hr, an initial decrease in survival was observed for concentrations of 250 micrograms/ml but no further increments in cytotoxicity were elicited when the concentration of FAA was augmented. Increasing the length of treatment yielded relatively modest increments (about 1 log) in cell killing only after an interval of 48 hr and only at the highest concentration (1000 micrograms/ml). Because of these relatively poor cytotoxic effects and because the therapeutic range of FAA is so narrow, we conclude that this agent will not be a valuable contribution to the antitumor arsenal, at least for colon cancer.

Cellular basis for the inefficacy of 5-FU in human colon carcinoma

Five established human colorectal carcinoma cell lines with distinct phenotypic properties were exposed to different concentrations of 5-FU for varying time intervals. Effects were measured by sequential cell counts and by inhibition of colony formation. Treatment for 1 hr with 1 microgram/ml barely decreased survival of all cell lines as measured by colony formation; at a concentration of 100 microgram/ml, survival was modestly reduced for all cell lines, and for concentrations of 1000 microgram/ml, survival was decreased by greater than 50%. Extending the length of the treatment interval markedly increased the degree of cell kill for all concentrations of 5-FU. Treatment for greater than 24 hrs resulted in almost complete extermination of colony-forming cells, even for relatively resistant cell lines. The effect of 5-FU treatment on cell number was more complex and depended on drug concentration, length of treatment, and type of cell line. In general, decrements in cell numbers were somewhat related to both drug concentration and length of treatment interval, especially if performed 7 days after terminating drug treatment. Earlier cell counts were inconclusive and the same result could be obtained for different drug concentrations or treatment intervals. Furthermore, these results would change on a daily basis. More important, cell count results never correlated with the survival endpoint measured by inhibition of colony formation. Our results suggest that enhancement of the currently poor performance of 5-FU in the treatment of human colon carcinoma could originate from changing the administration modality to long-term infusion.

The synergistic lethal interaction of cis-diamminedichloroplatinum and natural nucleosides is related to increased DNA cross-links

Human tumor cells were treated in vitro with combinations of cis- or trans-dichlodiammineplatinum (DDP) and natural nucleosides (thymidine, uridine, cytidine and adenosine). Effects were measured by inhibition of colony-formation (cell survival) and DNA alkaline elution (DNA cross-links). No increments in cell lethality or DNA cross-links were elicited by any combination of trans-DDP and nucleosides. In contrast, every combination of cis-DDP and nucleoside was eminently synergistic with 5- and 10-fold increases in cell lethality over the predicted sum of each agent alone. These increments in cell kill correlated linearly with increases in DNA crosslinks suggesting that the nucleosides interact with cis-DDP to enhance its cytotoxic crosslinking mode of action.

Cytotoxic efficacy of reconstituted and stored antitumor agents

The stability of the cell-killing efficacy of 10 antitumor drugs stored at different temperatures and concentrations was evaluated on an established human colon carcinoma cell line using the colony formation technique. Drugs were reconstituted in the appropriate solvent, further diluted in 0.9% NaCl solution to obtain the desired storage concentration, and stored at 4 degrees C, -20 degrees C, and -70 degrees C for periods of up to 3 weeks. Cytotoxic efficacy was tested weekly by exposing the cells to the final drug dilution for 1 h at 37 degrees C. Stability of cytotoxic potency depended on the particular drug, and the duration, concentration, and temperature of storage but, in general, most drugs remained efficacious only within limited periods of time (at most, 2 weeks). These results suggest that the conditions of drug storage following reconstitution are critical factors with respect to lethal efficacy. Therefore, analysis of in vitro cytotoxic efficacy can be meaningful only when storage conditions are specified in order to avoid false-negative results in the human tumor clonogenic assay.

Comparative cytotoxicity between cisplatin and second generation platinum analogs

The cytotoxic activity of cis-DDP and four second generation platinum coordination complexes (TNO-6; JM-82; JM-8; and JM-9) was compared on six established human colon carcinoma cell lines with different degrees of differentiation. Cytotoxicity was evaluated by the inhibition of colony formation technique. Cis-DDP was uniformily active against all lines. JM-8 and JM-9 were virtually ineffective for all cell lines, even at concentrations as high as 50 micrograms/ml. JM-82 was slightly more active although (with the exception of LoVo cells) still about 10-fold less efficacious than cis-DDP. TNO-6 was the only derivative with appreciable cytotoxic activity although about 2 to 5-fold less than cis-DDP for lines SW48, 620, 480, and 1116. For LoVo and SW403, TNO-6 was slightly more active than cis-DDP. In both such instances, increased efficacy resulted from abrogation of the shoulder region of the survival curve while the slope remained essentially intact. Thus any enhancement in therapeutic efficacy with these second generation analogues can only be expected from possible decreases in toxic effects but not from superior tumor cell kill activity.

Cellular discriminants for a biological classification of human colon carcinoma

We categorized established human colon carcinoma cell lines into three biological groups. Our studies were performed on six colorectal cancer lines representing the proposed three groups. Group I consisted of two lines designated LoVo and SW 48; Group II comprised two lines called SW 480 and SW 620; and Group III was represented by lines SW 403 and SW 1116. Group I consisted of the most differentiated cells. This differentiation encompassed morphological markers, gland and signet ring formation, and ciliary development. The outstanding morphological characteristic of Group III was the development of numerous multinucleated giant cells. The range and modal chromosome number increased from Group I to Group III, a change reflected by the higher DNA content of these cells as measured by flow cytometry. Carcinoembryonic antigen synthesis was maximal for Group III and virtually absent for Group II. The number of clonogenic cells decreased from Group I to Group III, while the proportion of nonproliferating cells calculated both by experiments using continuous labeling with tritiated thymidine, and by the primer-available alpha-DNA polymerase index, increased from Group I through Group III. Another important cytokinetic difference was that Group I had an exponential cell cycle stage distribution not seen for the other groups. Cells in Group I were easily propagated in athymic (nude) rats by s.c. injection; cells in Group II injected s.c. grew for about 30 days and then regressed spontaneously. Cells in Group III could only be grown when inoculated intracerebrally. Thus, our studies have now confirmed and extended the hypothesis that cultured human colorectal carcinomas can be separated into at least three groups on the basis of morphological differentiation, chromatin distribution, carcinoembryonic antigen production, cytokinetic properties, and xenograft propagation. Perhaps this classification is just the tip of the iceberg, and future studies will determine the existence of additional groups or subgroups on the basis of other markers. However, at present it appears established that malignant cells with a common histological origin in the gut express their phenotypic potential in a sufficiently discrete manner as to permit their classification into distinct biological groups. Thus, the stage is set for extrapolating this in vitro classification for an in vivo segregation of human colorectal tumors into categories with specific properties and diverse prognosis.

Cultured human tumour cells may be arrested in all stages of the cycle during stationary phase: demonstration of quiescent cells in G1, S and G2 phase

Six human colon carcinoma cell lines were induced to enter stationary phase of growth by nutrient deprivation and cell crowding. Growth kinetics parameters (cell number, flow cytometric analysis of DNA distribution, and labelling and mitotic indices) were measured sequentially for all lines during the various stages of in vitro growth. Our results demonstrated that a substantial fraction of cells (9-18%) were located in G2 phase when they changed from an exponential to a stationary mode of growth. Moreover, a large number of cells in stationary phase of growth had an S-phase DNA content, as determined by flow cytometry, but failed to incorporate radioactive DNA precursors (up to 15-fold difference). To substantiate these findings, cells in stationary phase of growth were induced to enter exponential growth by re-seeding in fresh medium at a lower density. Subsequently observed changes in DNA-compartment distribution, and in labelling and mitotic indices were those expected from cells that had been arrested at different stages of the cycle during their previous stationary phase. Thus, the non-proliferating quiescent state (Q), traditionally located 'somewhere' in G1 phase, appears to be composed also of cells that can be arrested at other stages of the cycle (Qs and QG2). Although the proportion of such cells is rather small, their contribution to the growth kinetics behaviour of human in vivo tumours will become apparent following 'recruiting' or 'synchronizing' clinical manoeuvres and will prevent the formation of a clear-cut wave of synchronized cells.