title: Potentiation of cisplatin antitumor activity using a vitamin D analogue in a murine squamous cell carcinoma model system.
abstract: In a murine squamous cell carcinoma (SCC) model, we have demonstrated that both 1,25-dihydroxycholecalciferol (1,25-D3) and the analogue 1,25-dihydroxy-16-ene-23-yne-cholecalciferol (Ro23-7553) have significant in vitro and in vivo antitumor activity. We have examined here the cell cycle effect of 1,25-D3 and Ro23-7553 on SCCVII/SF tumor cells by quantitating nuclear DNA using a detergent-trypsin method via flow cytometry analysis. Both 1,25-D3 and Ro23-7553 resulted in a significant increase of cells in G0-G1, with an accompanying decrease of cells in S phase. The ability to arrest cells in G0-G1 has been exploited by combining Ro23-7553 with the cytotoxic agent cisplatin (cis-diamminodichloroplatinum; cDDP). Using the in vitro clonogenic assay, pretreatment with Ro23-7553 for 24-48 h significantly enhanced cDDP-mediated tumor cell kill as compared to concurrent treatment with Ro23-7553 and cDDP or cDDP alone. To examine the effect of Ro23-7553 and cDDP in vivo, C3H/HeJ mice with 9-14-day SCC tumors were treated either for 3 days with varying i.p. doses of Ro23-7553 or for 7 days continuously through the use of Alzet pumps, and on the last day of Ro23-7553 treatment, cDDP (1-6 mg/kg) was administered. Using the in vivo excision tumor cell clonogenic assay, in which tumors were removed from animals 24 h after cDDP treatment and plated in a clonogenic assay, pretreatment with Ro23-7553 markedly enhanced cDDP-mediated clonogenic tumor cell kill, even at low doses of cDDP as compared to cDDP treatment alone. Similarly, a significant decrease in fractional tumor volume and increase in tumor regrowth delay was observed when animals were pretreated before cDDP with Ro23-7553 as compared to either agent alone. These results demonstrate a significant enhanced antitumor effect with Ro23-7553 pretreatment before cDDP both in vitro and in vivo and suggest that Ro23-7553 may potentiate cDDP cytotoxicity through effects on cell cycle progression.
authors.affiliation: Department of Otolaryngology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pennsylvania 15213, USA.
authors.forename: B W
authors.initials: BW
authors.lastname: Light
authors.forename: W D
authors.initials: WD
authors.lastname: Yu
authors.forename: M C
authors.initials: MC
authors.lastname: McElwain
authors.forename: D M
authors.initials: DM
authors.lastname: Russell
authors.forename: D L
authors.initials: DL
authors.lastname: Trump
authors.forename: C S
authors.initials: CS
authors.lastname: Johnson
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects*; D002945:Cisplatin / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005260:Female; D051379:Mice; D008809:Mice, Inbred C3H
chemical_list: D000970:Antineoplastic Agents; D002117:Calcitriol; C064183:Ro 23-7553; D002945:Cisplatin