Comparative cytotoxicity of bisantrene, mitoxantrone, ametantrone, dihydroxyanthracenedione, dihydroxyanthracenedione diacetate, and doxorubicin on human cells in vitro

The cytotoxic efficacies of several substituted anthraquinones, ametantrone, dihydroxyanthracenedione, dihydroxyanthracenedione diacetate, mitoxantrone, bisantrene, and doxorubicin, were evaluated on an established human colon adenocarcinoma cell line by the method of inhibition of colony formation. The concentration-dependent survival curve following treatment for 1 hr was biphasic exponential for all agents. At concentrations below 1 microgram/ml, mitoxantrone was about twice as active as both hydroxyl-substituted anthracenediones and doxorubicin, about 14 times more efficacious than ametantrone, and about 22 times more powerful than bisantrene. At higher concentrations, these differences in efficacy became even more pronounced. Treatment in stationary phase decreased the lethal efficacy of doxorubicin but not that of the other agents. No recovery of potentially lethal or sublethal damage was noted for any agent, but for anthracenedione derivatives, there was a small but statistically significant increase in cell kill during fractionated exposure. Continuous treatment with mitoxantrone or bisantrene resulted in marked degrees of cell killing, reaching 99.95 and 99.5%, respectively, after 24 hr. For doxorubicin, cell kill efficacy declined after 4 hr. Mitoxantrone was 10-fold more active on cells in G2 phase than on those in mid- to late-S phase. Sensitivity in G1 phase was intermediate. Thus, mitoxantrone appears as the most active compound while bisantrene and ametantrone are the least active agents. The cytotoxic efficacy of bisantrene increases during prolonged continuous exposure, while that of mitoxantrone increases in fractionated administration. These characteristics could be exploited in clinical strategies designed to improve the performance of these agents.

The lethal activity and repair inhibition capacity of 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-1-nitrosourea (NSC 95466, PCNU), a nitrosourea with low carbamoylating activity

The survival response of human colorectal carcinoma cells treated in vitro for 1 h with PCNU was characterized by a threshold exponential curve, Dq = 8 micrograms/ml (1 h) and Do = 22 micrograms/ml (1 h). Continuous treatment induced decreasing degrees of cell kill although PCNU was biologically stable in solution for at least 24 h. Cells treated with PCNU were unable to recover from potentially lethal damage but were quite capable of repairing PCNU-induced sublethal damage. Thus, PCNU with different alkylating and carbamoylating than other nitrosourea congeners had similar cytotoxic and repair inhibition capacities. Any therapeutic gain in the clinical use of PCNU must derive only from its lipophilic properties and not from its superior activity at the cellular level.

Lethal activity and kinetic response of cultured human cells to 4'-(9-acridinylamino)methanesulfon-m-anisidine

Cytotoxic and cytokinetic effects of 4'-(9-acridinylamino)methanesulfon-m-anisidine (m-AMSA) were studied on a cultured human colon carcinoma and on a human lymphoma (T1) cell line. Proliferating cells were more susceptible (10-fold) to the cytotoxic effect of m-AMSA than were nonproliferating cells. The agent had minimal effects on DNA synthesis. At comparable exposure doses on m-AMSA, the degree of lethal cell damage exceeded inhibition of DNA synthesis by 4-fold. Cells synchronized in different stages of the cell cycle were equally sensitive to the cytotoxic effects of the drug, although the major cytokinetic effect was a block in G2. A greater killing effect was obtained by fractionated delivery than by a comparable dose delivered at one. These results suggest that superior antitumor results may be achieved by adequately spaced low doses of m-AMSA in the treatment of sensitive human tumors.

Differential killing efficacy of twenty antitumor drugs on proliferating and nonproliferating human tumor cells

The lethal effects of a 1-hr treatment with 20 antitumor drugs on proliferating and nonproliferating cultured human colon carcinoma cells (line LoVo) were analyzed quantitatively by the colony-forming technique. Proliferating cells were obtained from exponentially growing cultures, while nonproliferating cells were from cultures in a stationary phase of growth. The 1-hr treatment was intended to approximate serum peak levels after bolus administration. Two agents, cis-platinum and vindesine, were more effective on nonproliferating than on proliferating cells. Mitomycin C, nitrosourea, and dihydroxybisalkylanthracenedione were equally effective on proliferating and nonproliferating cells. The low lethal activity (less than 1 log) of methylglyoxal bis(guanylhydrazone), hycanthone, and vinblastine was similar in proliferating and nonproliferating cells. For most drugs (Adriamycin, rubidazone, bleomycin, maytansine, vincristine, epipodophyllotoxin, fluorouracil, hydroxyurea, methotrexate, and transplantinum) cytotoxicity was significantly less pronounced (or even totally absent) in nonproliferating than in proliferating cells. These results demonstrate the significance of cellular proliferation kinetics in determining sensitivity to antitumor therapy. Nonproliferating human cells have decreased sensitivity to most antitumor agents. An occasional agent may present increased activity to nonproliferating cells; but at best, few agents can be expected to be as effective on nonproliferating as on proliferating cells.

A method to measure carcinoembryonic antigen neosynthesis by cultured colon carcinoma cells

A double-antibody radioimmunoprecipitation assay was used to measure the rate of incorporation of radioactive precursors into carcinoembryonic antigen (CEA) newly synthesized by cultured human colon carcinoma (LoVo) cells. Mixtures of 125I-labeled CEA and standard CEA were used to construct titration curves as a function of concentration, time of incubation, and temperature for goat anti-CEA serum and rabbit antigoat serum. In contrast to the zirconyl phosphate gel method, the double-antibody technique did not precipitate compounds with low molecular weights. Similar slopes were observed when standard CEA was used to inhibit immunoprecipitation of 125I-labeled CEA by both the zirconyl phosphate gel and the double-antibody techniques. When CEA produced by the colon carcinoma cells (CEA-LoVo) was used to inhibit immunoprecipitation of radioactive 125 I-labeled CEA, the curve was superimposed upon that elicited for standard CEA. CEA-LoVo incorporated significant amounts of [N-acetyl-3H]glucosamine, and chromatography of the 3H-labeled CEA-LoVo eluted with a peak superimposed upon that of the First British Standard for CEA. This method was subsequently used to estimate changes in the rate of CEA neosynthesis by LoVo cells as a function of culture age. The rate of incorporation of [N-acetyl-3H]glucosamine into CEA of LoVo cells in stationary phase was about three times that measured for cells in exponential growth. The technique described in this report has the advantage that labeling of CEA results from actual metabolic cellular activity. Therefore, it provides a tracer method to study the localization and kinetics of CEA synthesis by cultured colon cells.

Serum CEA levels in a human colonic adenocarcinoma (LOVO) xenograft system

The relationship between tumor size and circulating CEA titers was examined for a human colonic adenocarcinoma xenografted in Balb/C athymic mice. Xenograft material was derived from line LoVo, which produces moderate amounts of CEA, both in vitro and in vivo. No correlation was found between tumor size and serum CEA levels.

Treatment of cultured human colon carcinoma cells with fluorinated pyrimidines

The shape of the initial part of the dose-dependent response curve of LoVo cells, an established human colon carcinoma cell line, exposed for 1 hr to graded concentrations of 5-FU depended on the medium supplement, i.e., fetal calf serum (FCS), in which the cells were treated and subsequently incubated for colony-formation. At concentrations of 50--100 micrograms/ml (equivalent to peak plasma levels following an in vivo bolus dose of 15 mg/kg) cell kill was completely prevented by FCS. The serum did not contain thymidine (TdR) but had significant amounts of uridine (UR). When 5-FU was delivered in dialyzed FCS, concentrations of 50--100 micrograms/ml achieved only a modest 15% cell kill after 1 hour treatment. Regardless of medium supplement, the killing effect of 5-FU did not increase beyond concentrations greater than 2,000 micrograms/ml. Increasing the exposure interval dramatically increased the killing of LoVo cells by 5-FU, although the effects of medium supplement on the degree of cell survival persisted for about 12 hours. Virtually all of the incorporated 5-FU was transformed into 5-FUR, and a very small proportion eventually was incorporated into nucleic acids, suggesting that the killing effect of 5-FU on LoVo cells is mediated mostly by ribosidation and not by conversion into the deoxyribonucleoside. This conclusion is supported by the failure of 5-FUdR to kill LoVo cells after a treatment interval of one hour, even at concentrations of 5000 micrograms/ml; yet after the same exposure interval, 5-FUR effectively killed cells at concentrations of 50--100 micrograms/ml. TdR afforded no protection from cell kill by 5-FU. In contrast, UR was capable of protecting LoVo cells from the lethal effects of both 5-FU and 5-FUR even at concentrations as low as 10 micrograms/ml. Ftorafur exposed to LoVo cells for 1 hour had a slight killing effect (about 20--25%) at concentrations ranging up to 2000 micrograms/ml. Although the lethal effect of ftorafur was slightly increased after longer periods of incubation, it failed to reach 90% even after intervals of 48 hours. The results on cellular sensitivity that we obtained for LoVo cells treated with various fluorinated pyrimidines differ substantially from those of other investigators who used different methods to assess cell killing on nonhuman and noncolonic cell systems. The predictive relevance of these data as compared to those obtained in other systems is justified by the suboptimal results with these agents in clinical practice.

Observations on the synthesis of carcinoembryonic antigen by an established human colonic carcinoma cell line

Some properties and kinetics of synthesis of the carcinoembryonic antigen (CEA-LoVo) produced by an established human colon carcinoma cell line were analyzed. CEA-LoVo was assayed by the method of Chu and Reynoso which was standardized against the activity of the First British Standard for CEA. CEA-LoVo was stable at -20 and 4 degrees C. At 37 degrees C, CEA-LoVo degraded at the rate of 1.4%/day in cell-free supernatants, and at the rate of 6.6%/day in the supernatants of monolayer cultures. CEA-LoVo was sensitive to enzymatic treatment with trypsin (approximately 55% loss)) and extraction of PCA (> 70% loss). The elution profile of CEA-LoVo in Concanavalin A-Sepharose B coincided with that of the First British Standard for CEA. No A or B blood group antigenic activity was noted. Studies employing immunofluorescent and horseradish peroxidase-labeled antibody techniques demonstrated heavy membrane and moderate intracytoplasmic localization. The greatest amount of net synthesis occurred for cells in the stationary phase while CEA-LoVo release occurred maximally in the lag phase.

Observations on the synthesis of carcinoembryonic antigen by an established human colonic carcinoma cell line

Some properties and kinetics of synthesis of the carcinoembryonic antigen (CEA-LoVo) produced by an established human colon carcinoma cell line were analyzed. CEA-LoVo was assayed by the method of Chu and Reynoso which was standardized against the activity of the First British Standard for CEA. CEA-LoVo was stable at -20 and 4 degrees C. At 37 degrees C, CEA-LoVo degraded at the rate of 1.4%/day in cell-free supernatants, and at the rate of 6.6%/day in the supernatants of monolayer cultures. CEA-LoVo was sensitive to enzymatic treatment ( approximately 55% loss) and extraction of PCA (greater than 70% loss). The elution profile of CEA-LoVo in concanavalin A-Sepharose B coincided with that of the First British Standard for CEA. No A or B blood group antigenic activity was noted. Studies employing immunofluorescent and horseradish peroxidase-labeled antibody techniques demonstrated heavy membrane and moderate intracytoplasmic localization. The greatest amount of net synthesis occurred for cells in stationary phase while CEA-LoVo release occurred maximally in lag phase.

Establishment of a human carcinoembryonic antigen-producing colon adenocarcinoma cell line

A human carcinoembryonic antigen-producing colon carcinoma cell line has been established. The cells form acinar structures and signet ring cells. The lumen of the acini presents microvilli and a glycocalyx. Neighboring cells show desmosomes and terminal bars. The cells present an aneuploid karyotype with a modal number of 49. No marker chromosomes are found, although a significant proportion of cells show an altered A2 chromosome and an extra B. Exponentially growing cultures produce 54 ng of carcinoembryonic antigen/10(6) cells. Kinetic parameters are as follows: doubling time, 37 hr; mitotic index, 0.8%; labeling index, 31%; generation time, 30 hr; G1 phase, 7 hr; S phase, 18 hr; G2 phase, 5 hr; growth fraction 90%. This cell line, designated line LoVo, represents an in vitro model for human colon carcinoma.