Development of an in vitro chemo-radiation response assay for cervical carcinoma.
OBJECTIVE
To determine if synergistic effects of radiation (RT) and chemotherapy (chemo) on human cervical carcinoma cell lines and fresh tumor explants could be determined using an in vitro assay.


METHODS
In vitro radiation response was determined for 4 cell lines and 26 fresh tumor explants in an agar-based assay. Cells were exposed to increasing doses of RT with or without cisplatin (CDDP), carmustine (BCNU), buthionine sulfoximine (BSO), or paclitaxel (Tax). Cell suspensions were cultured for 5 days, with [(3)H]thymidine added on day 3 and proliferation was measured. Results were reported as the fraction of proliferation compared to control (FC). For each combination of irradiation and drug, synergy was tested using the Chou analysis, where a combination index (CI) <1 indicated synergistic interaction. In simple correlation analysis, an R value of >0.7 indicated cross-resistance.


RESULTS
RT dose-dependent proliferation inhibition was observed for 2 of the 4 cell lines, and for all but 1 of the fresh specimens. Significant heterogeneity of tumor response to RT was seen. Four specimens that were 1 standard deviation below the median FC response after exposure to 300 cGy were classified as extremely radiation resistant. Twenty-one tumors were evaluated for synergistic response using the combination of chemo and RT with a median FC of 0.27 (+/-0.27) for 6.0 Gy of RT alone, 0.22 (+/-0.21) for CDDP alone, and 0.05 (+/-0.08) for the combination. A CI of 0.35 and an R value of 0.09 demonstrated synergy between chemo and RT without cross-resistance. Similar synergy without cross-resistance was found for RT in combination with BCNU, BSO, and TAX.


CONCLUSIONS
Heterogeneous RT dose-response relationships in the in vitro assay were demonstrated. Explants were more sensitive to RT than cell lines. Unlike cell lines, fresh tumor cells consistently displayed synergy with RT and chemo. The synergy between RT and BSO suggests that glutathione depletion may enhance the effect of RT. The assay was feasible for examining fresh tumors and may be an important tool for studying RT or drug resistance. Clinical trials to evaluate this assay are indicated.
Monk
Bradley J
BJ
Department of Obstetrics and Gynecology, Division of Gynecologic Oncology, University of California, Irvine, Orange, California 92868, USA.
Burger
Robert A
RA
Parker
Ricardo
R
Radany
Eric H
EH
Redpath
Leslie
L
Fruehauf
John P
JP
D000970:Antineoplastic Agents / Q000494:pharmacology*; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D002330:Carmustine / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002945:Cisplatin / Q000494:pharmacology; D003131:Combined Modality Therapy; D004307:Dose-Response Relationship, Radiation; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006801:Humans; D017239:Paclitaxel / Q000494:pharmacology; D010865:Pilot Projects; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*
D000970:Antineoplastic Agents; D011838:Radiation-Sensitizing Agents; D019328:Buthionine Sulfoximine; D017239:Paclitaxel; D002945:Cisplatin; D002330:Carmustine