Vitamin D analogs, a new treatment for retinoblastoma: The first Ellsworth Lecture.
OBJECTIVE
This lecture honors the memory of Dr. Robert M. Ellsworth, an important figure in the development of current treatments of retinoblastoma (RB), and reviews our studies of vitamin D analogs as treatments for retinoblastoma in two experimental mouse models. We identified vitamin D receptors in retinoblastoma and examined the effectiveness and mechanism of action of these analogs.


METHODS
Reverse-transcriptase polymerase chain reaction (RT-PCR) amplification was used to detect vitamin D receptor mRNAs in human and mouse retinoblastomas. The effectiveness and toxicity of vitamin D(2), calcitriol, and synthetic analogs were studied in the athymic/Y-79 xenograft and transgenic mouse models of RB. Dosing was 5X/week for five weeks. Dose-response studies focused on tumor inhibition; toxicity studies investigated survival and serum calcium. The mechanism of action of vitamin D was investigated using terminal transferase dUTP labeling 3'-overhang ligation to measure apoptosis; immunohistochemistry measured p53-dependent gene expression and cell proliferation.


RESULTS
Vitamin D receptor mRNAs were detectable in Y-79 RB cells, LH beta-Tag tumors, and human RB specimens using RT-PCR. Calcitriol inhibited cell growth in vitro. Calcitriol and vitamin D(2) inhibited in vivo growth in xenograft and transgenic models, but therapeutic levels were toxic due to hypercalcemia. Two analogs, 16,23-D(3) and 1 alpha-OH-D( 2), inhibited tumors in animal models of RB with reduced toxicity. The mechanism of action appears related to increased p53-related gene expression resulting in increased apoptosis.


CONCLUSIONS
16,23-D(3) and 1 alpha-OH-D(2) are effective in tumor reduction in two mouse models of RB with low toxicity. These results warrant initiating phase 1 and phase 2 clinical studies in children.
D000818:Animals; D017209:Apoptosis; D002117:Calcitriol / Q000627:therapeutic use*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004195:Disease Models, Animal; D004872:Ergocalciferols / Q000627:therapeutic use*; D006801:Humans; D007124:Immunoenzyme Techniques; D019394:Ki-67 Antigen / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008822:Mice, Transgenic; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000235:genetics; D019572:Retinal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D012175:Retinoblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051028:bcl-2-Associated X Protein
C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D017931:DNA Primers; D004872:Ergocalciferols; D019394:Ki-67 Antigen; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D002117:Calcitriol