Dr. Candace Johnson was appointed Deputy Director for the Institute in 2008. She is also the Chair of the Department of Pharmacology and Therapeutics and the Robert Lew and Anne Wallace Chair for Translational Research. She joined the faculty of Roswell Park Cancer Institute in February 2002, after serving as the Deputy Director of Basic Research at the University of Pittsburgh Cancer Institute, and Professor of Pharmacology and Medicine at the University of Pittsburgh School of Medicine.
Dr. Johnson earned her doctoral degree in Immunology from Ohio State University, Columbus, in 1977. From 1977 to 1981, she completed research and postdoctoral fellowships in Immunology/Cell Biology at the Michigan Cancer Foundation, Detroit.
Dr. Johnson’s research interests include translational research to facilitate the efficient application of promising laboratory findings in clinical studies; preclinical design and development of more effective therapeutic approaches to cancer using highly characterized tumor models; and mechanisms of vitamin D mediated antiproliferative effects either alone or in combination with other cytotoxic agents.
Dr. Johnson is a member of the National Institutes of Health Reviewers Reserve and has served as a member of the National Cancer Institute Review Group Subcommittee A Cancer Center (Parent Committee) and of the Experimental Therapeutics Study Section (2) for 2 terms. She also is a member of many professional and scientific societies, Senior Editor of Molecular Cancer Therapeutics, Associate Editor of Molecular and Cellular Differentiation, Oncology, and Molecular Pharmacology, and a member of the editorial board of Oncology Reports and Molecular Pharmacology.
Dr. Johnson has authored or coauthored more than 130 journal publications, book chapters and abstracts, and has been issued patents on the "Use of Pretreatment Chemicals to Enhance Efficacy of Cytotoxic Agents" and “Endothelial Specific Targeting.”
Program
Vitamin D, novel agents, prostate cancer, and experimental therapeutics
Studies are focused on the pre-clinical development and design of more effective therapeutic approaches to cancer using mouse tumor model systems. Project areas include the mechanisms of vitamin D-mediated anti-proliferative effects either alone or in combination with conventional cytotoxic agents; the effect of vitamin D on cell cycle control and apoptosis in prostate model systems; the effect of glucocorticoids on vitamin D-mediated anti-tumor and hypercalcemic effects through the vitamin D receptor (VDR); the isolation and characterization of tumor-derived endothelial cells with the potential to target for therapeutic intervention; and elucidating the mechanisms involved in the differential response of tumor-derived endothelial cells to vitamin D and steroids with therapeutic implications. Dr. Johnson has a wide variety of highly characterized and readily available murine syngeneic and human xenograft tumor models to evaluate therapeutic efficacy as well as to examine potential mechanisms of action. In addition, Dr. Johnson provides the basic science interface to a number of clinical studies based on these studies in collaboration with Dr. Donald L. Trump, President and CEO, Roswell Park Cancer Institute.
Progress
Studies in our laboratory demonstrate that calcitriol (vitamin D or 1,25 dihydroxycholecalciferol), a central factor in bone and mineral metabolism, has significant antitumor activity in vitro and in vivo in a number of murine syngeneic and human xenograft tumor model systems. Calcitriol induces cell cycle arrest, decreases survival signaling molecules and induces modulators of apoptosis in various tumor types. Clinically in phase I studies, we have determined the MTD of calcitriol alone and in combination with a number of cytotoxic agents and/or glucocorticoids and we have completed a phase II trial in androgen-independent prostate cancer where the combination of calcitriol and dexamethasone resulted in an enhanced anti-tumor effect. Induction of CYP24, the enzyme primarily responsible for calcitriol catabolism, may be a factor in bioavailability, calcitriol exposure and the anti-proliferative activity pre-clinically and clinically. In addition, the endothelial cells in tumors are sensitive to calcitriol and uniquely modulate CYP24 expression through epigenetic changes.
Epigenetic events affect gene expression without alteration in DNA gene sequence and lead to transcriptional gene silencing and inactivation of tumor suppressor genes in human cancer. While many studies document epigenetic changes in tumor cells, only limited data support a role for epigenetic changes in the “normal” cells found in the tumor microenvironment. Epigenetic changes are found in the stromal fibroblasts from normal human breast tissue and breast carcinoma and in the tumor stroma and endothelium of localized human prostate cancer. We developed a model system for isolation of endothelial cells freshly from tumor and demonstrate that CYP24, the catabolic enzyme involved in calcitriol signaling, becomes epigenetically silenced selectively in tumor-derived endothelial cells (TDEC). Pertinent to the studies proposed here, calcitriol also inhibits proliferation of endothelial cells and can inhibit angiogenesis in a number of tumor model systems. TDEC maintains phenotypic characteristics which are distinct from endothelial cells isolated from normal tissues and from Matrigel plugs (MDEC). In TDEC, calcitriol induces G0/G1 arrest, modulates p27 and p21, and induces apoptotic cell death and decreases P-Erk and P-Akt. In contrast, endothelial cells isolated from normal tissues and MDEC are unresponsive to calcitriol-mediated anti-proliferative effects despite intact signaling through the vitamin D receptor (VDR). Differences may be due to the over-expression of CYP24 in MDEC and in these cells, mRNA, protein and enzymatic activity for CYP24 are markedly increased. In TDEC, which is sensitive to calcitriol, the CYP24 promoter is hypermethylated in two CpG island regions located at the 5'end, which may contribute to gene silencing of CYP24. The extent of methylation in these two regions is significantly less in MDEC. Treatment of TDEC with the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine, restores calcitriol-mediated induction of CYP24 and resistance to calcitriol. Similar differences between the tumor and normal microenvironments are observed in endothelial cells from other syngeneic, transgenic and xenograft tumor systems and in endothelial cells isolated from normal mouse tissues. In addition, methylation of the CYP24 promoter as measured by methylation-specific PCR (MSP) was significantly increased in endothelial cells isolated by expression microdissection (xMD) from human prostate tumors. Lastly, when MDEC are incubated with conditioned media from tumor cells for 14-21 days, these cells regain sensitivity to the antiproliferative effects of calcitriol, CYP24 induction is silenced and regions 1 and 2 of the CYP24 promoter are hypermethylated. The characteristics of these cells are similar to the endothelial cells found in tumors or TDEC.
Therefore, we are testing the overall hypothesis that in tumors “epigenetic silencing of gene expression in endothelial cells from different microenvironments impact signaling pathways and ultimately therapeutic application”. We propose here to utilize a unique model system where differences exist in the epigenetic silencing of calcitriol-induced CYP24 gene expression in endothelial cells from the tumor and normal microenvironments and based on these data, we will elucidate the epigenetic signal transduction mechanism(s) that lead to the epigenetic silencing of CYP24; determine whether epigenetic silencing of CYP24 occurs in human endothelial cell and tumor cell populations isolated from human prostate cancer tumors; and identify other potential targets of DNA methylation in TDEC vs MDEC.
Calcitriol significantly enhances the in vitro and in vivo antitumor efficacy of the platinum analogues, cisplatin and carboplatin as well as the taxanes, paclitaxel and docetaxel. Enhancement of drug-mediated apoptosis by calcitriol is associated with an increase in PARP-, MEK- and caspase-cleavage and MEKK-1 with a decrease in P-Erk and P-Akt. In addition, the expression of the p53 homolog, p73, is strongly induced by calcitriol and p73 can sensitize tumor cells to the cytotoxic effects of platinum and taxanes suggesting a central role for p73 in calcitriol/cisplatin-mediated apoptosis. While calcitriol does not increase total intracellular platinum content or formation of GG or AG adducts, calcitriol pre-treatment reduces the cellular capacity to repair cisplatin damaged DNA. In addition, we have established a correlation between the ability of calcitriol to decrease expression of p53 and p21 and increase cisplatin cytotoxicity. Therefore, calcitriol-mediated suppression of p53 and its downstream targets may compromise repair of platinum: DNA adducts and enhance cisplatin cytotoxicity. Based on these pre-clinical data, we performed two phase I clinical trials of calcitriol with either carboplatin or paclitaxel and administered higher doses of calcitriol than previously reported without toxicity.
Therefore, calcitriol has significant pro-apoptotic effects and can synergize with other cytotoxic modalities that potentially share the same targets, P-Akt, P-Erk, p21 and/or p73. Based on this data, we propose to examine the potential efficacy and mechanisms of calcitriol in combination with cisplatin and gemcitabine both pre-clinically and clinically and we will determine the role of p73 in calcitriol enhancement of cisplatin-mediated antitumor activity; examine whether a relationship exists between modulation of these effects in vitro on tumor cells and a significant antitumor response in vivo in a rat bladder tumor model system; and evaluate through the conduct of a neoadjuvant phase II clinical trial, the effect of calcitriol (phase I dose, D1, 2), cisplatin (75mg/m2, D2 every 28 days) and gemcitabine (800mg/m2, D2 weekly) for 2 cycles before cystectomy in muscle-invading transitional cell bladder cancer.
Publications
Below are links to Pub Med for Dr. Johnson’s publications while at Roswell Park Cancer Institute (2002 – present) and earlier.
