Comparison of pH, bloodflow, and antigenicity in a heat-sensitive (EMT6) and a heat-resistant (RIF) tumor

The authors studied 2 transplantable murine tumors that have different heat sensitivities. Exposure to 430/1h results in 100% cure of EMT6 tumors as opposed to no cure in RIF tumors. They saw little difference between the heat sensitivities of the 2 tumor lines in vitro at either pH 7.4 or 6.7. Measurement of pH in vivo was performed immediately before and 1 and 6h after heating. There was no significant change at 1h after heating, although at 6h after heating there was a reduction in pH of the EMT6 tumor, which was not mirrored in the RIF tumor. Bloodflow data were inferred from measurements of intravascular volume. Bloodflow was reduced to 10% of control values at 12h after heating, but gradually recovered to approximately 50% of control values by 48h in both tumors. The EMT6 tumor displays a more rapid decrease in bloodflow but also recovers faster than the RIF tumor. The authors also performed experiments to establish the degree of antigenicity of the two cell lines. TD/sub 50/ rose from 5-10 cells in controls to over 2000 cells in pre-immunized animals with the EMT6 tumor. No change in TD/sub 50/ was seen when RIF cells were employed. The results suggest that the combination of the increased acidity of heated EMT6 tumors and its antigenicity are responsible for the difference in cure rates between the two tumor lines