Subcapsular renal transplantation of neurogenic tumors and tumor spheroids. A comparative study of RN6 and RG2 tumor clones after syngeneic and allogeneic transplantation.

The subcapsular renal transplantation tumor model was explored to standardize the growth of rat RN6 neurinoma and RG2 glioma nitrosourea-induced clonal cell lines in syngeneic and allogeneic systems. Growth of RN6 and RG2 tumor spheroids was compared with that of solid subcutaneous tumor pieces transplanted under the renal capsule. Two morphometrical methods were applied to evaluate growth rates. Tumor specimens were examined histologically with regard to their morphology, extent of immune reactions, and development of tumor necroses. The take rate was 98%. In the syngeneic system linear progressive tumor growth was found, while in preirradiated allogeneic rats this was only the case up to 21 to 25 days post transplantation (p.t.). Strong rejection reactions in the allogeneic RN6 tumors were noted from 4 to 7 days p.t. resulting in total tumor rejection after 10 to 14 days. Both kinds of tumors, especially in the first days of growth, were characterized by strong desmoplastic reaction with rich reticulin fiber formation. However, after 10 days, in the center of RG2 subcapsular renal tumors (SRT) this kind of reaction was found only in the vicinity of tumor vessels, while RN6 SRT demonstrated reticulin fibers around tumor cells in all cases studied. The transplantation experiments revealed that the malignant RN6 and RG2 spheroids represent a suitable tool to study three-dimensional early tumor growth in both in vivo and in vitro cultures. The model of spheroid transplantation under the renal capsule is simple to handle and well reproducible. Compared with subcutaneous tumors the SRT model has advantages in early stages of tumor growth because the tumors are clearly visible grossly and can be easily submitted to adequate morphometry, indicating that this model may be suitable for experimental chemotherapy and radiotherapy studies.