AKR lymphoma malignancy variants differing at late phase of metastasis

Release from apoptosis correlates with tumor progression in the AKR lymphoma

Disturbance of apoptosis is an established factor in tumorigenesis. The role of apoptosis in tumor progression is not yet clear. In the present study we compared the tendency to spontaneous apoptosis (and the proliferative capacity) of tumor cells derived from primary (PT) and metastatic tumor (MT) cells of several AKR lymphoma variants. Apoptosis-related gene expression was also compared. Our results indicate that release from apoptosis has a role in the tumor progression of this T cell lymphoma. At the cellular level, a markedly lower apoptotic tendency was observed in MT than in PT cells. The existence of macrophages only in PT also supports the presence of apoptotic cells in local but not in MTs. By contrast, proliferative capacity does not determine tumor aggressiveness in this system. At the molecular level, we found a higher staining intensity for bcl-2 in MT than in PT cells, suggesting that bcl-2 might be responsible for the reduced apoptosis in MT compared to PT cells. Evidence for p53 overexpression was found in the MT cells of one of the variants but in none of the PT. Comparison of Fas receptor, unexpectedly showed an increased expression in MT versus PT cells, possibly indicating resistance to Fas-induced apoptosis in the MT cells.

Comparison of growth rate of two B16 melanomas differing in metastatic potential in young versus middle-aged mice

The rise of cancer frequency as a function of age is a well-established fact. The aspect of the host age-tumor progression relationship, namely the slower metastatic spread in aged patients, has been investigated to a lesser extent. In the present study, we examined whether host-age-dependent growth rate varies with metastatic capacity of the tumor. The parental B16 and the B16/Col/R, a highly metastatic variant, were employed. A more pronounced growth of both tumors in young as compared to middle-aged mice was found. However, the differential growth in middle-aged versus young mice was more evident in the highly metastatic variant. According to the tumor size data, a sixfold growth reduction in middle-aged mice was observed with B16/Col/R and an only twofold growth reduction was seen with the B16 melanoma. The data might eventually contribute to the finding of more appropriate treatment modalities for the middle-aged cancer patient.

Role of immune response as determinant of tumor progression in function of host age in the B16 melanoma

Aging constitutes the major cause for the development of most neoplastic diseases. However, tumors in aged people present with a lower degree of aggressiveness than in young patients. The reasons for this paradoxical behavior are not clear. We attempted to verify whether the immune system has a role in the relation between host age, immune response and tumor progression. We compared the growth rate of B16 melanoma and a highly malignant variant, the B16/Col/R, in young and aged mice that have or have not undergone splenectomy. The following results were obtained: (1) Splenectomy stimulated growth in the parental melanoma in both young and aged mice, indicating a protective role of the spleen against this tumor at all ages; (2) Spleen ablation provoked inhibition of the highly-metastatic variant growth in young mice, suggesting a stimulatory role of the spleen in this case; (3) By contrast, in aged mice inoculated with the B16/Col/R variant, splenectomy enhanced tumor growth, indicating a defensive role of the spleen. Age favors a positive host response against the aggressive clone of the melanoma. Differential host response in young versus aged mice can explain, in this tumor system, the difference in tumor progression rate as a function of age.

Correlation between malignancy level of AKR lymphoma variants and sensitivity to hyperthermia

The tumor progression process has been found to be accompanied by various cell membrane modifications. This cell organelle may therefore be considered as a target for drugs directed against tumor cells of advanced cancer. Hyperthermia acts on tumor cells largely, although not only, via an effect on the cell membrane. In the present study, the in vitro effect of hyperthermia on the tumorigenicity of cells derived from two AKR lymphoma variants of malignancy, TAU-39 of low (LM) and TAU-38 of high-malignancy (HM), was compared. The cells of the HM variant were markedly more sensitive to hyperthermic treatment than those of the LM one. Pretreatment of cells at 41 degrees C or 43 degrees C resulted in a more marked delay in tumor appearance in mice injected with the HM than in those inoculated with the LM variant. Moreover, in mice inoculated with cells pretreated at 45 degrees C, long term survivors were found only in those inoculated with the HM variant. These results corroborate our previous data regarding the effect of hyperthermia on metastatic and primary tumor cells of AKR lymphoma as well as the F1 and F10 variants of B16 melanoma.