Antitumor effect of 22-oxa-calcitriol, a noncalcemic analogue of calcitriol, in athymic mice implanted with human breast carcinoma and its synergism with tamoxifen.
The antitumor effect of 22-oxa-calcitriol (OCT), a newly developed noncalcemic analogue of calcitriol, was examined in vivo in athymic mice implanted with human breast carcinoma with or without estrogen receptor (ER). In ER-positive MCF-7 tumor, the growth of which was dependent on exogenous estrogen, administration p.o. of OCT as well as the antiestrogen tamoxifen five times a week for 4 weeks suppressed tumor growth in a dose-related fashion. The antitumor effect of 1.0 microgram/kg body weight (BW) OCT (mean +/- SEM of tumor weight in 6 mice: 28 +/- 4% of vehicle-treated group) was comparable to that of 2.0 mg/kg BW tamoxifen (25 +/- 6% of control group). In addition, a synergistic antitumor effect of submaximal doses of OCT and tamoxifen was observed in MCF-7 tumor in vivo as well as in ER-positive breast carcinoma cell lines (MCF-7 and ZR-75-1) in vitro. Administration of OCT p.o. three times a week for 4 weeks also suppressed the growth of ER-negative MX-1 tumor in a dose-dependent manner without raising serum calcium concentrations. The antitumor effect of 1.0 microgram/kg BW OCT (mean +/- SEM of tumor weight in 10 mice: 44 +/- 6% of vehicle-treated group) was greater than that of 500 micrograms/kg BW Adriamycin (71 +/- 6% of control group). These results indicate that OCT suppresses the growth of ER-negative as well as ER-positive breast carcinoma in vivo without causing hypercalcemia and that the antitumor effect of OCT can be enhanced by tamoxifen in an ER-positive tumor. It is suggested that OCT may provide a new strategy, either alone or in combination with other anticancer drugs, for systemic adjuvant therapy of breast carcinoma regardless of ER status.
Abe-Hashimoto
J
J
Research Laboratories, Chugai Pharmaceutical Co., Ltd., Tokyo, Japan.
Kikuchi
T
T
Matsumoto
T
T
Nishii
Y
Y
Ogata
E
E
Ikeda
K
K
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy*; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy; D011960:Receptors, Estrogen; D013629:Tamoxifen / Q000627:therapeutic use*; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D011960:Receptors, Estrogen; D013629:Tamoxifen; D002117:Calcitriol; C051883:maxacalcitol