Biological and Cell Kinetic Properties of a Human Colonic Adenocarcinoma (LoVo) Grown in Athymic Mice

Abstract In the present study, the human colonic adenocarcinoma cell line LoVo was established as a xenograft system in BALB/c athymic mice, and its biological and cell kinetic properties were examined. Line LoVo produced a 100% tumor incidence with inocula of 10 5 to 10 8 cells i.p. or 10 7 to 10 8 cells s.c., while inocula of 10 6 cells s.c. produced tumors in 50% of the cases. No tumor development was noted following i.v. inoculations of 10 3 to 10 8 cells after 120 days. Tumors arising i.p. grew as discrete nodules without ascitic fluid near vascular sources throughout the peritoneal cavity but did not induce new vascularization. Tumors arising s.c. grew with a typical Gompertzian pattern with growth characteristics reported previously for surgically derived colonic xenograft material. Tumor-doubling times ( T d 9s) were 7 days for 10 7 and 10 8 inocula between days 10 to 40 increasing to >13 days thereafter. Inocula of 10 6 cells grew slower ( T d = 13 days) and did not exhibit a significant plateau region. Tumors arising s.c. were extensively vascularized from the murine epidermis with no encapsulation by the host connective tissue. Using lethally irradiated cells or brain extract, the tumor growth pattern did not exhibit a Revesz effect. All tumors exhibited a well-differentiated morphology with extensive glandular formations. Focal necrosis was evident in early tumors, which coalesced to form a central mass at larger sizes. No metastatic involvement was noted in any normal tissues, including the proximal lymph nodes. Tumors arising s.c. from 10 7 cells were classified as early (0.4 to 0.6 cu cm) or late (1.4 to 1.6 cu cm). The cell kinetic profiles were determined using the percentage of labeled mitoses and in vitro [ 3 H]- and [ 14 C]thymidine-labeling procedures, as well as the primer-available DNA polymerase assay to estimate tumor growth fraction. Results indicated a slowly proliferating nature for early LoVo xenografts (growth fraction, 34%) with a characteristic human generation time [cell cycle time (T C ), ∼65 hr; S-phase duration (T S ), 18 hr] and a low cell loss factor (10%). With increasing tumor size, the major kinetic changes noted were a reduced growth fraction (23%) and an increased cell loss factor (63%). A colony formation assay was established using collagenase (150 IU/ml) and mechanical manipulations to achieve single-cell suspensions. Mean plating efficiency was 18.9% and was linear between 100 and 1000 cells. These results suggest that LoVo xenografts possess many properties expected for human colonic adenocarcinomas in situ and may provide an in vivo screening system for potential antitumor agents.