Non-cytotoxic and Sublethal Paclitaxel Treatment Potentiates the Sensitivity of Cultured Ovarian Tumor SKOV-3 Cells to Lysis by Lymphokine-activated Killer Cells

Background: The standard treatment of epithelial ovarian cancer is tumor debulking by surgery, followed by six cycles of chemotherapy consisting of cisplatinum and paclitaxel. However, this therapy protocol is not satisfactory, since about 50% of the treated patients eventually experience recurrence within a few years of follow-up. Thus, a more innovative treatment modality is urgently needed for patients with this malignancy. We hypothesized that pretreatment of ovarian cancer SKOV-3 cells at a non-cytotoxic to sublethal dose range of paclitaxel would result in increased sensitivity to LAK-mediated killing. Materials and Methods: MTT and trypan blue dye exclusion were used to determine the non- cytotoxic to sublethal range of paclitaxel against SKOV-3 cells. A 4-h 51 Cr release cytotoxicity assay was used to evaluate the sensitivity of paclitaxel-treated and untreated SKOV-3 cells. Immunofluorescence/flow cytometric analysis was used for phenotypic changes of cells with or without paclitaxel treatment. Results: Our results with trypan blue dye exclusion and MTT assays showed that the non-cytotoxic to sublethal range was between 0.001 IM and 0.01 IM. Pretreatment of SKOV-3 cells with paclitaxel at these doses for 72 h revealed significantly enhanced LAK-mediated killing against SKOV-3 cells with the highest sensitivity achieved with cells treated with 0.001 IM paclitaxel, as compared with the baseline killing of untreated cells using LAK cell alone (p<0.05). The enhanced sensitivity of LAK-mediated killing appeared to be in part due to paclitaxel-induced expression of ICAM-1 on SKOV-3 cells. Conclusion: This treatment approach may be useful for further development of an effective therapeutic mode for patients with ovarian cancer. Human epithelial ovarian cancer is the fourth most lethal cancer in women with 75% of the patients presenting at an advanced stage of the disease (1). The standard treatment of advanced epithelial ovarian cancer is comprehensive tumor debulking, followed by six cycles of chemotherapy consisted of cisplatinum and taxanes. A second look operation is usually scheduled to determine the effectiveness of the treatments. However, the value of this second look surgery is controversial, since nearly 50% of treated patients with the so-called "pathologically tumor-negative findings" will experience recurrence within a few years of follow-up. Thus a more novel treatment modality is urgently needed for patients with advanced ovarian cancer. Taxanes are cancer therapeutic agents such as paclitaxel (taxol) with potent antitumor activity against a number of human cancer types, including human ovarian cancer, breast, cervical, endometrial, esophageal, gastric, colon, bladder and lung (2). Paclitaxel was found in 1969 and was extracted from the western yew, Taxus breviflolia. Wani et al. (3) identified the chemical structure of paclitaxel and demonstrated its cytotoxic effect. The major mechanism of its antineoplastic action is the promotion of polymerization of tubulin dimers to form microtubules and stabilization of the microtubles by preventing depolymerization. Moreover, paclitaxel blocks the cell cycle at the metaphase/anaphase transition, causing inhibition of cell proliferation (4). Recently, paclitaxel has also been shown to induce apoptosis in an ovarian cancer cell line and its paclitaxel-resistant clone (5, 6). IL-2 has been demonstrated to be able to augment the cytolysis capability of lymphokine-activated killer (LAK) cells both in vitro and in vivo against tumor cells (7-9). The