Arginine Depletion Therapy with ADI-PEG20 Limits Tumor Growth in Argininosuccinate Synthase-Deficient Ovarian Cancer, Including Small-Cell Carcinoma of the Ovary, Hypercalcemic Type.

PURPOSE: Many rare ovarian cancer subtypes, such as small-cell carcinoma of the ovary, hypercalcemic type (SCCOHT), have poor prognosis due to their aggressive nature and resistance to standard platinum- and taxane-based chemotherapy. The development of effective therapeutics has been hindered by the rarity of such tumors. We sought to identify targetable vulnerabilities in rare ovarian cancer subtypes. EXPERIMENTAL DESIGN: We compared the global proteomic landscape of six cases each of endometrioid ovarian cancer (ENOC), clear cell ovarian cancer (CCOC), and SCCOHT to the most common subtype, high-grade serous ovarian cancer (HGSC), to identify potential therapeutic targets. IHC of tissue microarrays was used as validation of arginosuccinate synthase (ASS1) deficiency. The efficacy of arginine-depriving therapeutic ADI-PEG20 was assessed in vitro using cell lines and patient-derived xenograft mouse models representing SCCOHT. RESULTS: Global proteomic analysis identified low ASS1 expression in ENOC, CCOC, and SCCOHT compared with HGSC. Low ASS1 levels were validated through IHC in large patient cohorts. The lowest levels of ASS1 were observed in SCCOHT, where ASS1 was absent in 12 of 31 cases, and expressed in less than 5% of the tumor cells in 9 of 31 cases. ASS1-deficient ovarian cancer cells were sensitive to ADI-PEG20 treatment regardless of subtype in vitro. Furthermore, in two cell line mouse xenograft models and one patient-derived mouse xenograft model of SCCOHT, once-a-week treatment with ADI-PEG20 (30 mg/kg and 15 mg/kg) inhibited tumor growth in vivo. CONCLUSIONS: Preclinical in vitro and in vivo studies identified ADI-PEG20 as a potential therapy for patients with rare ovarian cancers, including SCCOHT.

Hedgehog signaling in bone regulates whole-body energy metabolism through a bone-adipose endocrine relay mediated by PTHrP and adiponectin.

Bone plays a role in energy metabolism, but the interplay between bone and other organs in this process is not completely understood. Here, we show that upregulated Hh signaling in bones results in increased whole-body energy expenditure, white adipose tissue (WAT) browning, hypoglycemia and skeletal muscle atrophy. We found that Hh signaling induces PTHrP secretion from bones and causes WAT browning. Injection of PTHrP-neutralizing antibody attenuates WAT browning and improves the circulating blood glucose level while high-fat diet treatment only rescues hypoglycemia. Furthermore, bone-derived PTHrP stimulates adiponectin secretion in WAT and results in systemic increase of fatty acid oxidation and glucose uptake. Mechanistically, PTHrP activates both PKA/cAMP and Akt/Foxo pathways for Ucp1 expression in WAT. PTHrP couples adiponectin actions to activate the AMPK pathway in the skeletal muscles and liver, respectively, for fatty acid oxidation. Our findings establish a new bone-adipose hormonal relay that regulates whole-body energy metabolism.

Novel advances in the treatment of osteoporosis.

INTRODUCTION: Osteoporosis is a significant public health issue affecting over half of women aged over 50. With an aging population, its importance is set to increase further over time. Prevention of fragility fractures avoids significant mortality and morbidity as well as saving significant direct and indirect costs to the economy. In this review, we discuss existing treatments to contextualize the treatment landscape, and demonstrate how our understanding of bone pathophysiology has led to novel therapies-in the form of combinations and altered durations of existing treatments, as well as newer drug therapies. SOURCES OF DATA: PubMed and Embase were searched for randomized controlled trials of new therapies for osteoporosis. These searches were supplemented with material presented in abstract form at international meetings. AREAS OF AGREEMENT: New drugs that appear promising in the treatment of osteoporosis include the cathepsin K inhibitor, monoclonal antibodies against sclerostin and parathyroid hormone-related protein analog. AREAS OF CONTROVERSY: Separate to the development of novel drug therapies is the issue of how best to use agents that are currently available to us; specifically which agent to choose, alone or in combination; duration of therapy; how best to identify patients at highest risk of fracture, and to ensure the highest possible adherence to medication. Many of these issues have been addressed in other excellent review papers, and will not be considered in detail here. GROWING POINTS: As with all new treatments, we await results of long-term use and experience in 'real life' patient populations. AREAS TIMELY FOR DEVELOPING RESEARCH: As alluded to above, data are urgently required regarding the optimal duration of therapy; use of combination therapy; ordering of therapies for best therapeutic effect. As stratified medicine becomes more strongly considered in all areas of therapy, its merits in osteoporosis as in other musculoskeletal conditions, is timely and valuable.

PTHrP increases RANKL expression by stromal cells from giant cell tumor of bone.

Giant cell tumor of bone (GCT) presents with numerous osteoclast-like multinucleated giant cells that are principally responsible for the extensive bone resorption by the tumor. Although the precise etiology of GCT remains uncertain, the accumulation of giant cells is partially due to the high expression of the receptor activator of nuclear factor-κB ligand (RANKL) from the neoplastic stromal cells. Here, we have investigated whether parathyroid hormone-related protein (PTHrP) plays a role in the pathogenesis of GCT. Immunohistochemistry results revealed PTHrP expression in the stromal cells of the tumor, and that its receptor, the parathyroid hormone type 1 receptor (PTH1R), is expressed by both the stromal cells and giant cells. PCR and Western blot analyses confirmed the expression of PTHrP and PTH1R by isolated stromal cells from five patients presenting with GCT. Treatment of GCT stromal cells with varying concentrations of PTHrP (1-34) significantly increased both RANKL gene expression and the number of multinucleated cells formed from RAW 264.7 cells in co-culture experiments, whereas inhibition of PTHrP with a neutralizing antibody decreased RANKL gene expression. These results suggest that PTHrP is expressed within GCT by the stromal cells and can contribute to the abundant RANKL expression and giant cell formation within the tumor.

PTHrP drives breast tumor initiation, progression, and metastasis in mice and is a potential therapy target.

Parathyroid hormone-related protein (PTHrP) is a secreted factor expressed in almost all normal fetal and adult tissues. It is involved in a wide range of developmental and physiological processes, including serum calcium regulation. PTHrP is also associated with the progression of skeletal metastases, and its dysregulated expression in advanced cancers causes malignancy-associated hypercalcemia. Although PTHrP is frequently expressed by breast tumors and other solid cancers, its effects on tumor progression are unclear. Here, we demonstrate in mice pleiotropic involvement of PTHrP in key steps of breast cancer - it influences the initiation and progression of primary tumors and metastases. Pthrp ablation in the mammary epithelium of the PyMT-MMTV breast cancer mouse model caused a delay in primary tumor initiation, inhibited tumor progression, and reduced metastasis to distal sites. Mechanistically, it reduced expression of molecular markers of cell proliferation (Ki67) and angiogenesis (factor VIII), antiapoptotic factor Bcl-2, cell-cycle progression regulator cyclin D1, and survival factor AKT1. PTHrP also influenced expression of the adhesion factor CXCR4, and coexpression of PTHrP and CXCR4 was crucial for metastatic spread. Importantly, PTHrP-specific neutralizing antibodies slowed the progression and metastasis of human breast cancer xenografts. Our data identify what we believe to be new functions for PTHrP in several key steps of breast cancer and suggest that PTHrP may constitute a novel target for therapeutic intervention.

Expression of tumor invasion factors determines systemic engraftment and induction of humoral hypercalcemia in a mouse model of adult T-cell leukemia.

Infection with human T-cell leukemia virus type 1 (HTLV-1) leads sometimes to the development of adult T-cell lymphoma/leukemia (ATL), which is invariably fatal and often associated with humoral hypercalcemia of malignancy. The transformation of infected CD4 T cells and the pathogenesis of leukemia have been studied with great limitation in tissue culture and patients. To better understand the pathogenesis and perform preclinical drug studies, animal models of ATL are urgently needed. In mice, inoculation of HTLV-1 cell lines mostly leads to development of localized lymphomas. To develop an ATL animal model with leukemic spread of ATL cells, mouse strains with different well-defined immune deficiencies were inoculated intraperitoneally with different HTLV-1-infected cell lines (ACH.2, C8166, MT-2, MET-1). Inoculation of MET-1 cells into NOD/SCID mice provided the best model system for slowly developing T-cell leukemia with multiple organ involvement. In leukemic mice, an increase in serum calcium levels correlated with expression of receptor activator of nuclear factor kappa-light-chain-enhancer of activated B cells ligand on leukemic cells and secretion of parathyroid hormone-related protein and interleukin-6. In contrast to the other cell lines that did not spread systemically, MET-1 expressed both the adhesion molecules CD11a (LFA-1alpha) and CD49d (VLA-4alpha) and produced or induced expression of matrix metalloproteinases 1, 2, 3, and 9, thus underlining the importance of these molecules in the spread of adult T-cell leukemia cells. The MET-1/NOD/SCID model will be useful for developing interventions against invasion and spread of leukemic cells and subsequent humoral hypercalcemia of malignancy.

Intensification therapy with anti-parathyroid hormone-related protein antibody plus zoledronic acid for bone metastases of small cell lung cancer cells in severe combined immunodeficient mice.

Bone metastases occur in more than one-third of patients with advanced lung cancer and are difficult to treat. We showed previously the therapeutic effect of a third-generation bisphosphonate, minodronate, and anti-parathyroid hormone-related protein (PTHrP) neutralizing antibody on bone metastases induced by the human small cell lung cancer cell line, SBC-5, in natural killer cell-depleted severe combined immunodeficient mice. The purpose of our current study was to examine the effect of the combination of PTHrP antibody and zoledronic acid, which has been approved to treat bone metastases, against bone metastases produced by SBC-5 cells expressing PTHrP. Treatment with PTHrP antibody and/or zoledronic acid did not affect the proliferation of SBC-5 cells in vitro. Repeated treatments with either PTHrP antibody or zoledronic acid inhibited the formation of osteolytic bone metastases of SBC-5 cells but had no effect on metastases to visceral organs. Importantly, combined treatment with PTHrP antibody and zoledronic acid further inhibited the formation of bone metastases. Histologic assays showed that, compared with either PTHrP antibody or zoledronic acid alone, their combination decreased the number of tumor-associated osteoclasts and increased the number of apoptotic tumor cells. These findings suggest that this novel dual-targeting therapy may be useful for controlling bone metastases in a subpopulation of small cell lung cancer patients.

[Bony lesion with prostate cancer].

Bone metastases of prostate cancer usually have an underlying osteoclastic component. Bone metastasis is incurable and contributes significantly to disease-specific morbidity and mortality. Management of bone metabolism in patients is a clinically significant issue. Several key factors have been found to be important in tumor-induced promotion of osteoclast activity. Receptor activator of nuclear factor-kappa B ligand (RANKL) is produced by bone metastasis of prostate cancer, enabling these metastasis to induce osteolysis through osteoclast activation. Matrix metalloproteinases (MMPs) are secreted by prostate cancer cells and promote osteolysis primarily through degradation of bone matrix. In this way, many factors derived from prostate cancer metastases can promote osteolysis, and these factors may serve as therapeutic targets. The new agents are targeted to osteoclasts (i.e.: zoledronic acid, anti-RANKL monoclonal antibody, cathepsin K inhibitor, and anti-PTHrP monoclonal antibody), are considered to be standard management in the care of bone metastasis patients in combination with chemotherapy and hormone therapy. In this review, we summarized the current understanding and therapy of bone metastasis in prostate cancer.

[PTHrP and cancer cachexia].

Parathyroid hormone-related peptide (PTHrP) was discovered to be a causative factor of humoral hypercalcemia of malignancy (HHM) . It also causes cachexia including reduced food intake, body weight loss, and decreased locomotor activity by a mechanism that is independent of hypercalcemia and proinflammatory cytokine actions. PTHrP-induced cachexia is not associated with the repression of orexigenic peptides or induction of anorexigenic peptides ; unexpectedly, the expression of orexigenic peptides was increased and that of anorexigenic peptides was decreased in animals that developed PTHrP-induced cachexia. A neutralizing antibody against PTHrP rapidly restored food intake, body weight, and locomotor activity and also normalized the expression of orexigenic and anorexigenic peptides. Thus, PTHrP induces cachexia by mechanisms other than directly affecting the hypothalamic feeding regulated peptides.

The assembly of single domain antibodies into bispecific decavalent molecules.

Bispecific antibodies present unique opportunities in terms of new applications for engineered antibodies. However, designing ideal bispecific antibodies remains a challenge. Here we describe a novel bispecific antibody model in which five single domain antibodies (sdAbs) are fused via a linker sequence to the N-terminus of the verotoxin B (VTB) subunit, a pentamerization domain, and five sdAbs are fused via a linker sequence to the VTB C-terminus. Fifteen such decavalent bispecific molecules, termed decabodies, were constructed and characterized for the purpose of identifying an optimal decabody design. One of the fifteen molecules existed in a non-aggregated decavalent form. In conjunction with the isolation of sdAbs with the desired specificities from non-immune phage display libraries, the decabody strategy provides a means of generating high avidity bispecific antibody reagents, with good physical properties, relatively quickly.

Effects of anti-parathyroid hormone-related protein monoclonal antibody and osteoprotegerin on PTHrP-producing tumor-induced cachexia in nude mice.

We have previously demonstrated that parathyroid hormone-related protein (PTHrP) is a cachexia inducer, but it is still not known what PTHrP effects on target tissues induce the cachexia. Therefore, we examined the effects of anti-PTHrP antibody and osteoprotegerin (OPG) on PTHrP-producing tumor-induced cachexia. Nude mice bearing PTHrP-producing human lung cancer cells (HARA-B) exhibited cachexia with hypercalcemia 3-4 weeks after inoculation, accompanied by losses in body, adipose tissue, and muscle weight. OPG ameliorated hypercalcemia, as did neutralization of PTHrP with antibody; and it increased both body and adipose tissue weights. These increases in body and adipose tissue weight, however, were significantly less than those in mice treated with anti-PTHrP antibody. Simultaneous administration of OPG and anti-PTHrP antibody caused significant increases in body, adipose tissue, and muscle weight, along with an immediate decrease in blood ionized calcium levels. The increase in body weight was similar to that observed in mice treated with anti-PTHrP antibody alone, and the decrease in the blood ionized calcium levels was significantly greater than that in mice treated with OPG or anti-PTHrP antibody alone. These results suggest that an effect of PTHrP on target tissues other than hypercalcemia is involved in the development of cachexia. Expression of cachexia-inducing proinflammatory cytokines (interleukin-6 and leukemia inhibitory factor) is stimulated by PTHrP. This might be a mechanism by which PTHrP produces tumor-induced cachexia. It is also suggested that OPG and anti-PTHrP antibody synergistically act to ameliorate hypercalcemia, although the mechanism responsible for this is unclear.

Antitumor effect of parathyroid hormone-related protein neutralizing antibody in human renal cell carcinoma in vitro and in vivo.

Functional inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene occurs in 40-80% of human conventional renal cell carcinomas (RCCs). We showed recently that VHL-deficient RCCs expressed large amounts of parathyroid hormone-related protein (PTHrP), and that PTHrP, acting through the PTH1 receptor (PTH1R), plays an essential role in tumor growth. We also showed that PTHrP expression is negatively regulated by the VHL gene products (pVHL). Our goal was to determine whether blocking the PTHrP/PTH1R system might be of therapeutic value against RCC, independent of VHL status and PTHrP expression levels. The antitumor activity of PTHrP neutralizing antibody and of PTH1R antagonist were evaluated in vitro and in vivo in a panel of human RCC lines expressing or not pVHL. PTHrP is upregulated compared with normal tubular cells. In vitro, tumor cell growth and viability was decreased by up to 80% by the antibody in all cell lines. These effects resulted from apoptosis. Exogenously added PTHrP had no effect on cell growth and viability, but reversed the inhibitory effects of the antibody. The growth inhibition was reproduced by a specific PTH1R antagonist in all cell lines. In vivo, the treatment of nude mice bearing the Caki-1 RCC tumor with the PTHrP antibody inhibited tumor growth by 80%, by inducing apoptosis. Proliferation and neovascularization were not affected by the antiserum. Anti-PTHrP treatment induced no side effects as assessed by animal weight and blood chemistries. Current therapeutic strategies are only marginally effective against metastatic RCC, and adverse effects are common. This study provides a rationale for evaluating the blockade of PTHrP signaling as therapy for human RCC in a clinical setting.

Humanized monoclonal antibody against parathyroid hormone-related protein suppresses osteolytic bone metastasis of human breast cancer cells derived from MDA-MB-231.

BACKGROUND: Parathyroid hormone-related protein (PTHrP) has been implicated in bone metastasis. However, the effects on bone metastasis of blocking the PTHrP function have not been tested in the clinic. Here, the effects of a humanized anti-PTHrP monoclonal antibody (mAb) on bone metastasis in a human xenograft model are shown. MATERIALS AND METHODS: Subline MDA-5a, with high bone metastatic activity, was established from the human breast cancer cell line MDA-MB-231. Mice were injected with MDA-5a and an anti-PTHrP monoclonal antibody (mAb) raised against human PTHrP (1-34); bone metastasis was evaluated by X-ray photography. RESULTS: MDA-5a produced elevated levels of PTHrP, Interleukin 8 (IL-8), IL-6 and matrix metalloproteinase 1 (MMP-1) and frequently metastasized to the bone. Administration of the humanized anti-PTHrP mAb significantly suppressed osteolytic bone metastasis of MDA-5a and caused osteogenesis at the sites of metastasis. CONCLUSION: The humanized anti-PTHrP mAb was effective against bone metastasis by inducing osteogenesis and, therefore, will provide a new treatment option for bone metastasis in breast cancer.

Hypercalcemia in breast cancer: an echo of bone mobilization during lactation?

Hypercalcemia is a frequent complication of breast cancer which causes significant morbidity and mortality. Most commonly, it occurs in patients with multiple skeletal metastases. However, in a significant minority of patients, calcium levels become elevated in the absence of skeletal disease. In both instances, hypercalcemia is the result of pathological bone resorption caused by the secretion of cytokines that stimulate osteoclast differentiation and activity. One of these cytokines is parathyroid hormone-related protein (PTHrP). PTHrP is also secreted by normal breast cells during lactation to increase bone resorption and liberate skeletal calcium stores for the purposes of milk production. Therefore, the pathophysiology of hypercalcemia in breast cancer patients mimics the physiological processes that normally regulate calcium metabolism during lactation. Current therapy for hypercalcemia in breast cancer patients relies on the inhibition of bone resorption by a class of drugs known as bisphophonates. Newer therapies in development target cytokines involved in the recruitment and activation of osteoclasts by tumor cells.

Increased renal calcium reabsorption by parathyroid hormone-related protein is a causative factor in the development of humoral hypercalcemia of malignancy refractory to osteoclastic bone resorption inhibitors.

PURPOSE: Bisphosphonate and calcitonin lower blood calcium in humoral hypercalcemia of malignancy (HHM) by suppressing osteoclastic bone resorption, but repeated administration of these drugs often leads to relapse. In this study, we examined the roles of parathyroid hormone-related protein (PTHrP) in the development of bisphosphonate- and calcitonin-refractory HHM. EXPERIMENTAL DESIGN: Nude rats bearing the LC-6 JCK tumor xenograft (LC-6 rats) exhibited high bone turnover and HHM. Repeated administration of alendronate induced a sustained suppression of the bone resorption, but it caused only early and transient reduction of the blood calcium levels, leading to unresponsiveness to the drug. Because high blood levels of PTHrP were detected in the LC-6 rats, those that developed alendronate-refractory HHM were treated with an anti-PTHrP antibody. RESULTS: Administration of anti-PTHrP antibody to animals that received repeated administration of alendronate, thereby developing alendronate-refractory HHM, resulted in an increase in fractional excretion of calcium and a marked decrease of blood calcium level. Drug-refractory HHM was also observed in animals that received another osteoclast inhibitor, an eel calcitonin analogue elcatonin. The blood calcium level decreased after the initial administration of elcatonin, but it eventually became elevated during repeated administration. Administration of the anti-PTHrP antibody, but not of alendronate, effectively reduced the blood calcium of the animals that developed elcatonin-refractory HHM. CONCLUSION: High levels of circulating PTHrP and the resulting augmentation of renal calcium reabsorption is one of the major causes of the emergence of osteoclast inhibitor-refractory HHM. Thus, blockage of PTHrP functions by a neutralizing antibody against PTHrP would benefit patients who develop bisphosphonate- or calcitonin-refractory HHM.

[Acute hypercalcaemic crisis in the course of PTH-rP producing squamous cell carcinoma of the skin--a case report]. / Przelom hiperkalcemiczny w przebiegu raka plaskonablonkowego kolczystokomórkowego skóry wydzielajacego PTH-rP--opis przypadku.

Hypercalcemia is one of the most common paraneoplastic syndromes, where it may result from the presence of osteolytic metastases or from humoral effect of factors produced by tumor cells. One of such factors is the parathyroid hormone-related protein (PTH-rP). This protein is usually produced by solid tumors, especially by squamous cell carcinomas. In the case of squamous cell carcinoma of the skin hypercalcemia is very rare and symptomatic hypercalcemia is unusual. We present a case of acute hypercalcemic crisis as a consequence of overproduction of PTH-rP in a patient with spinocellular squamous cell carcinoma of the skin, which was proved by immunohistochemical staining of the tissue samples from the neoplastic lesion, metastases in bone and in lung, and also from kidney and liver.

New epitope peptides derived from parathyroid hormone-related protein which have the capacity to induce prostate cancer-reactive cytotoxic T lymphocytes in HLA-A2+ prostate cancer patients.

BACKGROUND: Parathyroid hormone-related protein (PTHrP) is produced by cancer cells and has been suggested to be responsible for malignancy-associated hypercalcemia and osteolysis after bone metatsases. Therefore, PTHrP is a promising target in the treatment of metastatic prostate cancer. METHODS: Seven PTHrP-derived peptides were prepared based on the HLA-A2 binding motif. These peptide candidates were screened by their ability to induce peptide-specific cytotoxic T lymphocytes (CTLs), and their ability to be recognized by immunoglobulin G (IgG). RESULTS: Both the PTHrP59-67 and PTHrP42-51 peptides were found to efficiently induce peptide-specific CTLs from peripheral blood mononuclear cells of HLA-A2+ prostate cancer patients with several HLA-A2 subtypes. These CTLs showed HLA-A2-restricted cytotoxicity toward prostate cancer cells. IgG reactive to the PTHrP42-51 peptide was frequently detected in prostate cancer patients. CONCLUSIONS: These results indicate that these two new PTHrP peptides will be useful in the peptide-based immunotherapy of HLA-A2+ prostate cancer patients, especially those with bone metastases.

Generation of a humanized monoclonal antibody against human parathyroid hormone-related protein and its efficacy against humoral hypercalcemia of malignancy.

A humanized monoclonal antibody against parathyroid hormone-related protein (PTHrP) was generated from the mouse monoclonal antibody raised against the peptide corresponding to the N-terminal 34 amino acids of the human PTHrP [(PTHrP(1-34)]. The humanized antibody interacted with the PTHrP(1-34) with a kD value of 1.90 x 10(-10) M, and the epitope resides between the amino acids 20 and 30 of the PTHrP. PTHrP(1-34) significantly increased the intracellular cAMP levels in the rat osteosarcoma cells that expressed PTHR1, and the 5 microg/mL or higher concentrations of the humanized antibody almost completely blocked the PTHrP-induced cAMP production even in the presence of 2 microg/mL PTHrP(1-34), demonstrating its ability to fully neutralize PTHrP function. There was no significant difference in the potency of the mouse, chimera, or the humanized antibodies to suppress the PTHrP-induced increase in the intracellular cAMP in ROS cells. Furthermore, at the same doses, the administration of the chimera or the humanized antibody was equally effective in reducing the blood ionized calcium levels of hypercalcemic mice bearing the PAN-7-JCK human pancreatic cancer xenograft or the LC-6-JCK human lung cancer xenograft that secreted PTHrP. Thus, humanized anti-PTHrP may be useful for the treatment of the humoral hypercalcemia of malignancy in humans.

Identification of parathyroid hormone-related protein-derived peptides immunogenic in human histocompatibility leukocyte antigen-A24+ prostate cancer patients.

Parathyroid hormone-related protein (PTHrP) is a key factor in the development of bone metastases, which are a major barrier in treating prostate cancer patients. In this study, we attempted to identify PTHrP-derived peptides immunogenic in human histocompatibility leukocyte antigen (HLA)-A24(+) prostate cancer patients. Among four different PTHrP peptides carrying the HLA-A24 binding motif, both the PTHrP(36-44) and PTHrP(102-111) peptides efficiently induced peptide-specific cytotoxic T lymphocytes from peripheral blood mononuclear cells (PBMCs) of HLA-A24(+) prostate cancer patients. Peptide-stimulated PBMCs showed cytotoxicity against prostate cancer cells in an HLA-A24-restricted manner. Experiments using antibodies and cold inhibition targets confirmed that their cytotoxicity was dependent on PTHrP peptide-specific and CD8(+) T cells. Immunoglobulin G reactive to the PTHrP(102-111) or PTHrP(110-119) peptide was frequently detected in the plasma of prostate cancer patients, suggesting that the PTHrP(102-111) peptide is able to elicit cellular and humoral immune responses in cancer patients. These results indicate that the PTHrP could be a promising target molecule for specific immunotherapy of HLA-A24(+) prostate cancer patients with metastases.