Modulation of parathyroid hormone- related protein levels (PTHrP) in anaplastic thyroid cancer Alan Dackiw, MD, PhD, a Jingxuan Pan, MD, Phd, b Guangpu Xu, MD, Phd, b and Sai-Ching J. Yeung, MD, b,c Baltimore, Md, and Houston, Tex Background. Studies have demonstrated that manumycin, a farnesyltransferase inhibitor, enhances the cytotoxic effect of paclitaxel in anaplastic thyroid cancer cells and in xenografts, but the mechanism of this effect is unknown. Parathyroid hormone--related protein (PTHrP) may function as an oncoprotein that inhibits apoptosis and enhances cell proliferation, in addition to its role as the mediator of humoral hypercalcemia of malignancy. We hypothesized that this protein might have a novel role in anaplastic thyroid cancer. Methods. Five anaplastic thyroid cancer cell lines (ARO, DRO, KAT-4, Hth-74, C-643) were examined for PTHrP expression in vitro by immunohistochemistry (IHC), radioimmunoassay, and Western blot (IP/WB) analyses. PTHrP expression was also examined in an in vivo xenograft model. The effects of manumycin and paclitaxel on PTHrP expression were studied. Results. All 5 ATC cell lines were found to robustly express PTHrP by IHC of fixed cells and radioimmunoassay of cell lysates and conditioned culture media (range, 468 ± 55 to 1410 ± 195 pg/mg cellular protein). Manumycin (54 lmol/L), but not paclitaxel (22 lmol/L), decreased the amount of PTHrP. Further, PTHrP was decreased in KAT-4 xenografts in nude mice that had been treated for 3 weeks with biweekly intraperitoneal injections of manumycin (7.5 mg/kg), compared with control mice by IHC. On Western blot analyses, fractionation of radiolabeled proteins showed that manumycin decreased synthesis of PTHrP in cytoplasm, with the amount of newly synthesized PTHrP in the nucleus and increased ubiquitination of PTHrP suggesting increased degradation of PTHrP through the proteasome pathway. Conclusions. Manumycin inhibits cell proliferation and decreases PTHrP levels in anaplastic thyroid cancer cells in vitro and in vivo and decreases the PTHrP level in the nucleus where PTHrP may function as an oncoprotein. These data suggest that PTHrP has a novel role in anaplastic thyroid cancer and that modulation of PTHrP levels may be of therapeutic benefit in this lethal malignancy. (Surgery 2005;138:456-63.) From the Department of Surgery, Division of Endocrine and Oncologic Surgery, Johns Hopkins Hospital, a Baltimore, Md; The Department of Endocrine Neoplasia and Hormonal Disorders b and General Internal Medicine, c The University of Texas M. D. Anderson Cancer Center, Houston PARATHYROID HORMONE–RELATED PROTEIN (PTHrP) is involved in the regulation of bone resorption, the increased renal excretion of phosphorus, and reabsorption of calcium, smooth muscle relaxation, regulation of the fetal calcium level, milk production during lactation, mammary gland development, and cell growth. PTHrP also is re- sponsible for mediating hypercalcemia of malig- nancy, which was first described in 1941 by Albright. 1 PTHrP also may play a significant role in growth of cancer cells. Specifically, studies performed have shown a role for PTHrP in delaying apopto- sis, shortening cell-doubling time, and promoting tumor growth. 2 It also has been shown that an acti- vated ras oncogene can induce PTHrP promoter activity in the presence of a mutation in the tumor suppressor gene p53. 3 Conversely, suppression of PTHrP gene expression by antisense RNA 4 or antisense deoxynucleotides 5 has been shown to have an antitumor effect. These collective findings indicate that PTHrP may be a target for anticancer therapy. Presented at the 66th Annual Meeting of the Society of Univer- sity Surgeons, Nashville, Tennessee, February 9-12, 2005. Supported by a grant from the Physician Referral Service of The University of Texas M. D. Anderson Cancer Center and a grant RPG-99-154-01-CDD from the American Cancer Society (S.J.Y.). Reprint requests: Alan Dackiw MD, PhD, Department of Sur- gery, Division of Endocrine and Oncologic Surgery, Johns Hop- kins, 600 North Wolfe St., Blalock 657, Baltimore, MD 21287. E-mail: adackiw1@jhmi.edu. Sai-Ching Jim Yeung, Division of Internal Medicine, Unit 437, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030. E-mail: syeung@mdanderson.org. 0039-6060/$ - see front matter Ó 2005 Mosby, Inc. All rights reserved. doi:10.1016/j.surg.2005.06.033 456 SURGERY