Calcitriol (1,25-dihydroxycholecalciferol) potentiates activity of mitoxantrone/dexamethasone in an androgen independent prostate cancer model.
OBJECTIVE
Mitoxantrone combined with glucocorticoids is widely used for androgen independent prostate cancer. It is well tolerated, reduces prostate specific antigen, diminishes pain and improves quality of life. Calcitriol (1,25-dihydroxycholecalciferol) inhibits proliferation, modulates cell cycle progression, induces apoptosis and potentiates the cytotoxic effects of a number of agents. Glucocorticoids potentiate the antitumor effects of calcitriol and blunt calcitriol induced hypercalcemia. Therefore, we investigated the effect of calcitriol on the antitumor efficacy of mitoxantrone and dexamethasone or mitoxantrone/dexamethasone in the PC-3 androgen independent prostate cancer model.


METHODS
We treated PC-3 cells in vitro with various concentrations of mitoxantrone/dexamethasone with and without calcitriol, and assessed growth inhibition by crystal violet assays. We similarly treated mice bearing PC-3 xenografts and performed excision clonogenic assays and tumor outgrowth studies to assess antitumor activity.


RESULTS
Calcitriol significantly increased mitoxantrone/dexamethasone mediated growth inhibition in PC-3 cells (p <0.05). Median dose effect analysis indicated that calcitriol is synergistic with mitoxantrone. Adding calcitriol to mitoxantrone/dexamethasone significantly reduced the surviving fraction per gm. tumor compared with mitoxantrone/dexamethasone or untreated controls (p <0.03). Calcitriol plus mitoxantrone/dexamethasone also caused significantly greater tumor regression in PC-3 xenografts compared with treatment with mitoxantrone/dexamethasone or untreated controls (p <0.02).


CONCLUSIONS
These preclinical data demonstrate that calcitriol increases the antitumor activity of mitoxantrone/dexamethasone in the PC-3 model system. This combination may be efficacious for prostate cancer.
Department of Medicine, University of Pittsburgh School of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania, USA.
Sharmila
S
Ahmed
Candace S
CS
Johnson
Robert M
RM
Rueger
Donald L
DL
Trump
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008942:Mitoxantrone / Q000494:pharmacology*; D009368:Neoplasm Transplantation; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000473:pathology; D014410:Tumor Stem Cell Assay
D003907:Dexamethasone; D008942:Mitoxantrone; D002117:Calcitriol