Hyperthermia increases the susceptibility of chondro- and osteosarcoma cells to natural killer cell-mediated lysis

As an adjuvant to chemotherapy hyperthermia has proven to be successful as a treatment for osteo- and chondrosarcoma patients. The aim of this study was to investigate whether hyperthermia could increase cellular expression of heat-shock-protein 72 in human osteo- and chondrosarcoma cells and how heat treatment would affect their susceptibility to natural killer cell (NK-cell)-mediated lysis. About 5 - 10 % of the peripheral mononuclear blood cells (PBMC) in the human peripheral blood are natural killer cells (NK-cells). Natural cytotoxicity, mediated by NK-cells, is believed to play an important role in host defense against cancer. The exact mechanisms of recognition of target cells and subsequent NK- cell activation are not yet known. NK-cells, isolated from the peripheral blood of healthy donors, were enriched by magnetic cell-separation to a purity of 85 - 97 %, assessed by FACS-analysis. The susceptibility of heat-treated (42.5degreesC, 90 minutes) and untreated osteosarcoma (MG63) and chondrosarcoma (HTB94) cell lines to NK-killing was determined by a release assay of lactate dehydrogenase (LDH). Lysis by NK-cells was increased by heat treatment of the target cells from 16 6 % + 4.5 % to 33 % + 15 %, p = 0.035, for osteosarcoma cells, (E/T ratio of 5:1) and from 13.7% + 3.1% to 27.9% + 169%, p=0.021, (E/T ratio of 20:1) for chondrosarcoma cells. An increased expression of HSP72 of chondro- and osteosarcoma cells after heat treatment was detected by the Western blot technique. The results of this study show that hyperthermia increases HSP72 expression in osteo- and chondrosarcoma cells and their susceptibility to NK-cell-mediated lysis. These findings may lead to new therapeutic strategies, using hyperthermia to improve immunological defense against chondro- and osteosarcoma cells.