The addition of chemotherapy to radiation therapy has the potential to sterilize micrometastases and tumor foci adjacent and peripheral to the treatment field, so as to enhance local control of malignancy and improve primary and salvage therapy. Studies were done to investigate the effects of combining cisplatin (CP), the most active single agent in squamous-cell cancer of the cervix, with irradiation and the addition of a protein kinase C (PKC) inhibitor. This initial report of these studies describes our experience in exposing human cervical carcinoma (HeLa-S3) cells grown in culture as multicellular tumor spheroids to continuous CP combined with radiation in an attempt to mimic both clinically achievable serum concentrations of CP and a weekly fractionated-dose environment. Radiation- dose-dependent delays of spheroid growth were not significantly increased in the presence of the PKC inhibitor 7-OH-staurosporine (UCN-01) at 1.0 nM and 10.0 nM concentrations. When dose comparisons at 8 Gy alone (2 Gy X 4 fractions) were made for combined therapy with either CP alone (1.0 μg/ml) or UCN-01 alone, absolute delays in spheroid growth at the highest concentrations used were comparable (range: 37-41 days). Although these data alone would not support minimal chemotherapeutic interaction, it appears that the overall effects observed for combination therapy were predominately radiation-dose dependent. The combination of UCN-01 plus CP (0.5 and 1.0 μ/ml, respectively) was effective in increasing the cytostatic and cytotoxic effects of irradiation at 4 Gy (2 Gy X 2 fractions). Observations made as early as day 4 and day 7 posttreatment were indicative of ≤40% and 60%, respectively, of morphological damage. Spheroid growth was essentially static at these doses over the evaluation time of 60 days. Intracellular junctions were disorganized, and spheroid swelling was evident and contributed to the modest dimensional changes observed after treatment. No surviving fractions could be generated from spheroids that were mechanically disrupted, trypsinized, and plated at day 7 after the initiation of treatment. At 2 months, 88% (14/16) and 94% (15/16) of the multimodality treatment groups (4 Gy + UCN-01 + CP [0.5 and 1.0 μ/ml], respectively) had sterilized spheroids, indicating that the CP concentration dependence may not be a sole determinant of efficacy. Our therapeutic strategy for combining irradiation with CP was based on the contemporary use of CP as the most successful agent in producing high survival rates in gynecological malignancy. The combination of UCN-01 with CP and irradiation may, however, represent a more effective strategy for enhancing future cisplatin-based chromatography regimens.
ASJC Scopus subject areas
- Cancer Research