Daniel P. Griswold

Evaluation of single agents and combinations of chemotherapeutic agents in mouse colon carcinomas.

Single agents and combinations of agents were tested for antitumor activity against four transplantable colon tumors in mice. The most impressive anti‐tumor activity was obtained with anguidine and the combination of anguidine + 5‐FU against colon adenocarcinoma No. 38. Antitumor potentiation was obtained when the combination was injected simultaneously on a Q7d schedule (two experiments), but not on an alternating schedule of administration (3 or 4 days separating injections of the two agents). Anguidine was highly active only in a colon tumor that was very responsive to 5‐FU. The correlation between high 5‐FU sensitivity and high anguidine sensitivity may be coincidental or could be of predictive value. Other active single agents and combinations of agents against one or more of the colon tumors include 5‐FU, 5‐FUdR, MeCCNU, BCNU, homoharringtonine, ara‐C, Cis‐Pt‐II, dianhydrogalactitol, piperazinedione, cyclophosphamide; MeCCNU + 5‐FU; Adriamycin + 5‐FU; Adriamycin + cyclophosphamide; Adriamycin + palmO‐ara‐C; cyclophosphamide + procarbazine; and 5‐FU + palmO‐ara‐C. (The combination of 5‐FU + palmO‐ara‐C was potentiating only on an alternating schedule.) The results of surgery‐chemotherapy adjuvant treatment of metastatic colon tumors established that if an agent or a combination was highly active against moderately advanced tumor masses, this treatment was also highly active after surgery against residual metastatic disease. The converse was also true. That is, if the agent or combination was inactive or marginally active against moderately advanced disease, the treatment was also relatively ineffectual after surgery against residual metastatic disease. Based on surgical‐adjuvant experiments with colon tumor No. 26, the following agents and combinations are conditionally recommended: MeCCNU + 5‐FU; MeCCNU + Ara‐C; cyclophosphamide + Ara‐C; BCNU+ 5‐FU and MeCCNU. It is also assumed that those agents active against the advanced disease are likely to be active after surgery against residual metastatic cells. Thus, agents highly active against advanced‐stage colon adenocarcinoma No. 38 are possible candidates for adjuvant therapy. On this basis, anguidine and anguidine + 5‐FU are recommended.

A colon tumor model for anticancer agent evaluation.

Colon tumors of mice were induced with 1, 2‐dimethylhydrazine, N‐nitroso‐N‐methylurethane, methylnitrosourea, and 4‐methyl‐N′‐nitro‐N‐nitrosoguanidine. Of 82 transplantation attempts, four were successful, and the four tumors have been maintained as distinct tumor lines by subcutaneous transplantation. The tumors graded from II, adenocarcinoma, to IV, undifferentiated carcinoma. Volume‐doubling times varied over a three‐fold range, and metastatic potential ranged from 5 to about 100%. The tumors responded to treatment with some of the same agents found to be active in man. These included cyclophosphamide, 5‐fluorouracil, and certain nitrosoureas. Preliminary evidence suggests that these tumor lines may be useful as experimental models.

Cell cycle effects of trimetrexate (CI-898)

SummaryThe cell cycle phase specificity of trimetrexate (CI-898) was examined. CHO cells synchronized by mitotic selection were exposed to 50 μM trimetrexate for 2 h at various time points after release from Colcemid block. Only S phase cells were sensitive to trimetrexate when survival was measured by a cloning assay. Comparison of plateau phase and log phase cultures indicated that plateau phase CHO cells were relatively insensitive to 5 μM trimetrexate. Exponentially growing L1210 cells were continuously exposed to either 30 nM or 3 nM trimetrexate and analyzed by DNA flow cytometry. Incubation with 30 nM trimetrexate produced cell cycle arrest in late G1 or early S phase, while exposure to 3 nM trimetrexate caused only a delay in progression through S phase. In an in vivo schedule dependence study with mice bearing approximately 3×106 P388 leukemia cells, trimetrexate was most effective with frequent administration. Mice treated on the optimal schedule, every 3 h×8 on days 1, 5, and 9 after tumor implant, had life-span increases in excess of 100%.

THE CELL POPULATION KINETICS AND RESPONSE TO AN S‐PHASE SPECIFIC AGENT OF THREE TRANSPLANTABLE COLON TUMOR LINES

The relative cell population kinetics of three transplantable murine colon tumor lines (Colon 26, 36 and 38) with different histological and metastatic characteristics were studied in relation to the response of each line to an S‐phase specific agent. The mean doubling times for the three lines between 0·1 and 1·0 g are similar (4·2 days) but marked differences are apparent in times to tumor appearance (0·1 g) and in median days to death. The length of the cell cycle is about one day and the length of the S‐phase 10–11 hr for Colon 36 and 38. The length of the cell cycle in Colon 26 is difficult to estimate by conventional methods but probably exceeds 24 hr and the S‐phase is 10–11 hr; [3H]TdR pulse labeling indices for Colon 36 and 38 decrease with time and tumor size from about 0·45 in 0·1 to 0·2 g tumors to about 0·33 at 3 g. The decrease in the [3H]TdR labeling index for Colon 26 is more pronounced (from about 0·38 at 0·1 g to 0·21 at 1·0 g). The shapes of the PLM curves and the [3H]TdR labeling index data are consistent with the observed sensitivity to an S‐phase specific agent (Palmo‐AraC, NSC 135962) in Colon 36 and the minimal response observed in Colon 26. Colon 38 is intermediate between Colon 36 and Colon 26 in kinetic properties and in response to the S‐phase agent.

Use of Experimental Models in the Study of Approaches to Treatment of Colorectal Cancer

Animal tumors have been widely used as models in studies of the etiology, behavior, and treatment of cancer of man. It is the last consideration that is of concern here, i.e., the development of optimal approaches to therapy through the use of experimental models. Many questions of the clinical oncologist cannot be answered from therapeutic trials in man because of the limitations imposed by ethics that preclude the use of certain controls and assay procedures. If, then, a totally empirical approach is to be avoided, the answers to those questions must come through the use of likely relevant animal tumors. Yet relevancy can often be determined only in retrospect. Nevertheless, experimentalists as well as clinicians have already recognized the need for better tumor models. It is hoped that their use will lead to improved therapeutic results as well as a better understanding of the nature of cancer growth and spread.