Clinical Practices and Institutional Protocols on Prophylaxis, Monitoring, and Management of Selected Adverse Events Associated with Trastuzumab Deruxtecan.

The treatment of metastatic breast cancer (mBC) has evolved significantly in the past several years with the approval of new targeted agents. Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate with a topoisomerase I inhibitor payload, is a new addition to the class of therapies that target the human epidermal growth factor 2 (HER2) receptor. T-DXd was approved in the US in December 2019 for patients with HER2-positive metastatic or unresectable breast cancer who have received 2 or more prior anti-HER2-based regimens in the metastatic setting. In the DESTINY-Breast01 phase II trial (NCT03248492), T-DXd demonstrated high rates of durable responses in heavily pretreated patients with HER2-positive mBC, with a confirmed objective response rate of 62%, median duration of response of 18.2 months, and median progression-free survival of 19.4 months. In addition to efficacy, successful implementation of any new anticancer therapy includes learning how to prevent, monitor, and manage treatment-related adverse events. As T-DXd becomes more widely used, information can be gained from real-world clinical practices, institutional approaches, and the collaboration of multidisciplinary oncology teams who treat patients with T-DXd. This article reviews practical insights and management of nausea and vomiting, neutropenia, interstitial lung disease, risk of cardiotoxicity, and other adverse events associated with T-DXd administration from the perspective of health care providers who have experience utilizing T-DXd.

Management of Chemotherapy-Induced Nausea and Vomiting with Trastuzumab Deruxtecan: A Case Series.

INTRODUCTION: Trastuzumab deruxtecan is a monoclonal antibody linked to a chemotherapy moiety that was recently approved by the Food and Drug Administration (FDA) for the treatment of metastatic human epidermal growth factor receptor 2 (HER2) positive breast cancers. There are labeled black box warnings for interstitial lung disease (ILD)/pneumonitis and embryo-fetal toxicity. Additionally, chemotherapy-induced nausea and vomiting (CINV) was reported to be as high as 78% (∼8% grade 3 or higher) in phase I and II clinical trials. Clinical trial and package insert recommendations for the management of CINV are not available, making real-world management difficult. CASE PRESENTATION: We reviewed the first 10 patients who received trastuzumab deruxtecan at our hospital-based community cancer center to determine if CINV management was adequate. We found a rate of 28.9% CINV (all grade 1 and 2) despite treatment as a moderate emetic potential regimen. Interventions by the treatment team to manage trastuzumab deruxtecan as a high-risk emetic regimen resulted in reduced CINV and ongoing treatment for all patients. DISCUSSION AND CONCLUSION: This review indicates that management of CINV for patients receiving trastuzumab deruxtecan should follow recommendations for regimens with a high-risk emetic potential.

Remote Home Monitoring of Patients With Cancer During the COVID Pandemic: A Pilot Study.

PURPOSE: The COVID-19 pandemic has posed significant challenges in the care of patients with cancer, including how to manage outpatients who are COVID-positive but do not require hospitalization. We explored the use of a remote patient monitoring (RPM) program to care for such outpatients. METHODS: Consecutive patients who were tested for COVID-19 because of symptom onset but were clinically stable were offered enrollment into a pilot RPM program. Patients were provided equipment for vital sign measurements and a computer tablet to enter results three times per day. The results were monitored centrally by clinical staff. The goal was to closely monitor patients and escalate care as warranted. RESULTS: Between March and June of 2020, 29 patients were approached and 26 were enrolled. The mean age was 57 years old (range, 30-88), 14 were women, and patients remained in the program for an average of 16 days (range, 2-63). Twenty-four patients (83%) were on active anticancer therapy. During that time period, only one patient was admitted to the hospital for worsening respiratory symptoms. The percentage of days during which at least one set of data and all three sets of data were entered was 97.2% and 65.7%, respectively. There was no association between the demographic factors of age, sex, or the reason for being monitored with the level of engagement (P > .05). CONCLUSION: In this pilot study, patients with cancer were readily enrolled in a remote home monitoring program. Monitoring was feasible, and there was a high rate of engagement with the program. The role of RPM should be further tested as the COVID pandemic continues.

Primary Breast Carcinoma of the Vulva Metastatic to Lymph Nodes and Bones: A Case Report and Literature Review.

INTRODUCTION: Primary breast carcinoma can occur at ectopic sites. The axilla is the most common site of ectopic primary breast cancer, but presentation in the vulva is rare. We discuss a rare presentation of primary breast carcinoma of the vulva with distant lymph node and bone metastases in a premenopausal woman. CASE PRESENTATION: A vulvar malignancy consistent with adenocarcinoma of the mammary gland type was diagnosed in a 47-year-old premenopausal woman. The patient underwent radical vulvectomy with bilateral superficial and deep inguinal lymphadenectomy. The tumor was positive for estrogen receptor and negative for progesterone receptor and human epidermal growth factor receptor 2/neu on immunohistochemical findings. A positron emission tomography-computed tomography scan demonstrated lymph node and bone metastases. Her disease was treated as stage IV breast cancer with metastases to the bone. Palliative treatment with ovarian suppression, aromatase inhibitor, and cyclin-dependent kinase 4/6 inhibitor was recommended. DISCUSSION: For a diagnosis of primary breast cancer of the vulva, a thorough metastatic workup should be performed, with attention directed toward detecting a breast primary disease by results of the history, physical examination, and radiologic examination of the breasts mainly to help confirm that the vulvar lesion is the primary site as opposed to metastasis from a breast primary cancer and also for staging. Management of this rare entity is challenging because of a lack of specific guidelines, and treatment, therefore, is similar to that of breast cancer.Treatment should consist of an individualized combination of surgery, radiotherapy, chemotherapy, and antiestrogen hormonal therapy.

Upper-Extremity Deep Vein Thrombosis in Patients With Breast Cancer With Chest Versus Arm Central Venous Port Catheters.

Most of the patients undergoing treatment for cancer require placement of a totally implantable venous access device to facilitate safe delivery of chemotherapy. However, implantable ports also increase the risk of deep vein thrombosis and related complications in this high-risk population. The objective of this study was to assess the incidence of upper-extremity deep vein thrombosis (UEDVT) in patients with breast cancer to determine whether the risk of UEDVT was higher with chest versus arm ports, as well as to determine the importance of previously reported risk factors predisposing to UEDVT in the setting of active cancer. We retrospectively reviewed the medical records of 297 women with breast cancer who had ports placed in our institution between the dates of December 1, 2010, and December 31, 2016. The primary outcome was the development of radiologically confirmed UEDVT ipsilateral to the implanted port. Overall, 17 of 297 study subjects (5.7%) were found to have UEDVT. There was 1 documented case of associated pulmonary embolism. Fourteen (9.5%) of 147 subjects with arm ports experienced UEDVT compared with only 3 (2.0%) of 150 subjects with chest ports (P = .0056). Thus, implantation of arm ports as opposed to chest ports may be associated with a higher rate of UEDVT in patients with breast cancer.

Targeting tumor-associated carbohydrate antigens: a phase I study of a carbohydrate mimetic-peptide vaccine in stage IV breast cancer subjects.

Tumor-associated carbohydrate antigens (TACAs) support cell survival that could be interrupted by anti-TACA antibodies. Among TACAs that mediate cell survival signals are the neolactoseries antigen Lewis Y (LeY) and the ganglioside GD2. To induce sustained immunity against both LeY and GD2, we developed a carbohydrate mimicking peptide (CMP) as a surrogate pan-immunogen that mimics both. This CMP, referred to as P10s, is the N-terminal half of a peptide vaccine named P10s-PADRE, the C-terminal half of which (PADRE) is a Pan-T-cell epitope. A Phase I dose-escalation trial of P10s-PADRE plus adjuvant MONTANIDE™ ISA 51 VG was conducted in subjects with metastatic breast cancer to test 300 and 500 µg/injection in two cohorts of 3 subjects each. Doses of the P10s-PADRE vaccine were administered to research participants subcutaneously on weeks 1, 2, 3, 7 and 19. Antibody responses to P10s, GD2, and LeY were measured by ELISA. The P10s-PADRE vaccine induced antibodies specifically reactive with P10s, LeY and GD2 in all 6 subjects. Serum antibodies displayed Caspase-3-dependent apoptotic functionality against LeY or GD2 expressing breast cancer cell lines. Immunization with the P10s-PADRE vaccine was well-tolerated and induced functional antibodies, and the data suggest potential clinical benefit.

Managing Expectations in the Transition to Proof of Concept Studies.

BACKGROUND: As we move away from the traditional chemotherapy era to targeted therapy, the validity of old assessment paradigms associated with therapeutics are being raised in the context of immunotherapy. The old paradigm required elaborating on the toxicity assessment, with no expectation of efficacy in early phase trials. Safety data from Phase 1 and 2 studies with many immunotherapeutics show limited toxicities and draw attention to the need to demonstrate efficacy in the early evaluation of new agents. METHODS: Literature searches indicate that molecular oncology mechanistic-based agents are being linked with molecular disease status and clinical benefit. Biomarkers and other endpoints are being employed to accomplish this. Perspectives for a meaningful context of integrating biomarkers and clinical trial design are reviewed. RESULTS: The design and conduct of clinical trials have not been fully adjusted to the new era of personalized oncology, and so we are in transition. A part of this transition is the management of expectations and trial designs that need to be considered relative to preclinical experience in the development of therapeutics. For example, pathological complete response is now considered a surrogate marker for favorable prognosis in breast cancer patients who are treated in the neoadjuvant setting. This surrogate marker is tied to novel agents' mechanistic characteristics with no preclinical counterpart. CONCLUSION: The old paradigm considers patients equal with similar chances to respond to treatments, but the new paradigm considers patient's heterogeneity, a major fact that informs the design of clinical trials. By linking every treatment to a mechanism of action and to the presence of a specific biomarker, new trials are going to have more subjects who are likely to respond to the treatment.

Harnessing benefit from targeting tumor associated carbohydrate antigens.

Integrating additive or synergistic antitumor effects that focus on distinct elements of tumor biology are the most rational strategies for cancer treatment. Treatments for breast cancer have increased overall survival, but remain limited by lack of efficacy in a subset of breast cancer patients. The real challenge is to define what elements of tumor biology make the most sense to be integrated. An emerging strategy is to consider a systems biology approach to impact multiple interactions in networks as compare with hitting a specific protein-protein interaction target. In this review, we consider how targeting tumor associated carbohydrate antigens (TACA) that are fundamental to signal pathways might be tailored to harness benefit from combination therapy of sustained immunity with chemotherapy. An approach we are developing makes use of a carbohydrate mimetic peptide (CMP) to induce polyspecific antibodies, which by their nature have numerous on and off target effects. Linking multi-target TACA recognition with mechanisms affecting tumor growth in the context of network heterogeneity and concepts of immune surveillance to tumor cells and the type of breast cancer patients that would benefit from such an approach provides a novel integrative treatment.

Relevance of Pathological Complete Response after Neoadjuvant Therapy for Breast Cancer.

Breast cancer is a heterogeneous disease, and the different biological subtypes have different prognostic impacts. Neoadjuvant trials have recently become popular as they offer several advantages compared to traditional adjuvant trials. Studies have shown that patients who achieve pathological complete response (pCR) after neoadjuvant treatment have a better long-term outcome. Consequently, increasing the rate of pCR became the end point of neoadjuvant trials with the expectation of translation into improved survival. However, the definition of pCR has lacked uniformity, and the prognostic impact of achievement of pCR on survival in different breast cancer subtypes is uncertain. In this review, we present the controversies associated with the use of pCR as an end point in neoadjuvant trials.

Improving Communication on Intent of Chemotherapy Using QOPI Scores and PDSA Cycles.

Using the standardized ASCO Quality Oncology Practice Initiative (QOPI) guidelines for assessing quality cancer care, we identified communication about intent of chemotherapy as an area needing improvement in our program at the University of Arkansas for Medical Sciences (UAMS) and the Central Arkansas Veterans Healthcare System (CAVHS). We organized training in communications on intent of treatment (palliative vs curative) and added optional checkboxes to our electronic templates for progress notes. Afterwards, we conducted a retrospective review of electronic medical records of initially often randomly selected patient charts. The first 10 patient charts after 1 month of implementation showed intent of treatment in 80 % of charts compared to 74 % at baseline. We then changed checkboxes from mandatory to optional and reviewed 30 randomly selected patient charts. Intent of treatment was documented in 96.7 % of cases compared to 74 % at baseline. We also assessed patient satisfaction through surveys distributed in clinic. Patient satisfaction scores were close to 100 % for receiving clear information, understanding the reason for which they were receiving chemotherapy, and willingness of oncologists to listen carefully, to take time to answer questions, to explain things clearly, and to spend adequate time with them. In this study, we showed that training in communication of intent of chemotherapy and use of checkboxes in progress note templates could improve competency in communication of intent of therapy in cancer patients.

Defining and managing expectations for early immunotherapy cancer trials.

This review discusses the concept of expectations in assessing direct benefit to participants in phase I immunotherapy studies. With the push toward a faster assessment of clinical benefit or efficacy, limiting phase I studies to safety determination only is now viewed as obsolete and has been replaced by designs that draw attention to therapeutic benefit or efficacy. While this approach is touted as being more flexible in trial conduct, these designs are particularly problematic for immunotherapy studies. Defining and managing expectations is paramount on understanding the key axioms that emerge that include i) understanding bias in models and mechanistic results, ii) that no test is perfect, iii) it is difficult to select a good predictive biomarker in the absence of clinical data, even for targeted therapies, iv) markers predictive for monotherapy may not be predictive for combination therapy, and v) all about improved patient selection. Considering the heterogeneity of cancers and the immune response of the host, we think that immunotherapy should be developed in parallel with the identification of different clinico-pathological models of immune response to cancer. This approach would accomplish two important goals: 1) provide a biological understanding of the complete in vivo environment, thereby giving investigators the opportunity to optimize and maximize the effect of a specific immunotherapy agent and 2) addressing host environment issues simultaneously so that safety data and perceived benefit can be achieved more quickly.

Moving a Carbohydrate Mimetic Peptide into the clinic.

Tumor-Associated Carbohydrate Antigens (TACAs) are broad-spectrum targets for immunotherapy. Immunization with Carbohydrate Mimetic Peptides (CMPs) is a strategy to induce broad-spectrum TACA-reactive antibodies hypothesized to interfere with cellular pathways involved in tumor cell survival. A Phase I study was conducted with a first-in-man CMP referred to as P10s, conjugated to the Pan T cell carrier PADRE, along with MONTANIDE(™) ISA 51 VG as adjuvant over a course of 5 immunizations. While designed as a safety and tolerability study, the potential for therapeutic impact was observed in a subject with metastatic lesions as evaluated before and after vaccine treatment. The subject received Vinorelbine and Trastuzumab (VT) for two months prior to study eligibility. PET scans showed partial response in the lungs and complete resolution of a previously enlarged subpectoral lymph node. Immunization with P10s vaccine resulted in responses to P10s, with serum and plasma antibodies reactive with and cytotoxic to human breast cancer cells in vitro, including the Trastuzumab-resistant HCC1954 cell line. However, the patient developed cystic masses in the brain parenchyma with no apparent evidence of metastases. The subject was switched to Docetaxel, Pertuzumab and Trastuzumab a year later, and her last PET scan showed a complete response in the lungs and lymph nodes. Incubation of cancer cells with a combination of vaccine-induced serum and docetaxel suggests that the induced antibodies sensitize tumor cells for more efficient killing upon administration of docetaxel. The data suggest that P10s-PADRE induces anti-tumor antibody response that in combination with chemotherapy can affect metastatic lesions in breast cancer patients.

Role of Bruton's tyrosine kinase in myeloma cell migration and induction of bone disease.

Myeloma cells typically grow in bone, recruit osteoclast precursors and induce their differentiation and activity in areas adjacent to tumor foci. Bruton's tyrosine kinase (BTK), of the TEC family, is expressed in hematopoietic cells and is particularly involved in B-lymphocyte function and osteoclastogenesis. We demonstrated BTK expression in clinical myeloma plasma cells, interleukin (IL)-6- or stroma-dependent cell lines and osteoclasts. SDF-1 induced BTK activation in myeloma cells and BTK inhibition by small hairpin RNA or the small molecule inhibitor, LFM-A13, reduced their migration toward stromal cell-derived factor-1 (SDF-1). Pretreatment with LFM-A13 also reduced in vivo homing of myeloma cells to bone using bioluminescence imaging in the SCID-rab model. Enforced expression of BTK in myeloma cell line enhanced cell migration toward SDF-1 but had no effect on short-term growth. BTK expression was correlated with cell-surface CXCR4 expression in myeloma cells (n = 33, r = 0.81, P < 0.0001), and BTK gene and protein expression was more profound in cell-surface CXCR4-expressing myeloma cells. BTK was not upregulated by IL-6 while its inhibition had no effect on IL-6 signaling in myeloma cells. Human osteoclast precursors also expressed BTK and cell-surface CXCR4 and migrated toward SDF-1. LFM-A13 suppressed migration and differentiation of osteoclast precursors as well as bone-resorbing activity of mature osteoclasts. In primary myeloma-bearing SCID-rab mice, LFM-A13 inhibited osteoclast activity, prevented myeloma-induced bone resorption and moderately suppressed myeloma growth. These data demonstrate BTK and cell-surface CXCR4 association in myeloma cells and that BTK plays a role in myeloma cell homing to bone and myeloma-induced bone disease. Am. J. Hematol. 88:463-471, 2013. © 2013 Wiley Periodicals, Inc.

Human placenta-derived adherent cells prevent bone loss, stimulate bone formation, and suppress growth of multiple myeloma in bone.

Human placenta has emerged as a valuable source of transplantable cells of mesenchymal and hematopoietic origin for multiple cytotherapeutic purposes, including enhanced engraftment of hematopoietic stem cells, modulation of inflammation, bone repair, and cancer. Placenta-derived adherent cells (PDACs) are mesenchymal-like stem cells isolated from postpartum human placenta. Multiple myeloma is closely associated with induction of bone disease and large lytic lesions, which are often not repaired and are usually the sites of relapses. We evaluated the antimyeloma therapeutic potential, in vivo survival, and trafficking of PDACs in the severe combined immunodeficiency (SCID)-rab model of medullary myeloma-associated bone loss. Intrabone injection of PDACs into nonmyelomatous and myelomatous implanted bone in SCID-rab mice promoted bone formation by stimulating endogenous osteoblastogenesis, and most PDACs disappeared from bone within 4 weeks. PDACs inhibitory effects on myeloma bone disease and tumor growth were dose-dependent and comparable with those of fetal human mesenchymal stem cells (MSCs). Intrabone, but not subcutaneous, engraftment of PDACs inhibited bone disease and tumor growth in SCID-rab mice. Intratumor injection of PDACs had no effect on subcutaneous growth of myeloma cells. A small number of intravenously injected PDACs trafficked into myelomatous bone. Myeloma cell growth rate in vitro was lower in coculture with PDACs than with MSCs from human fetal bone or myeloma patients. PDACs also promoted apoptosis in osteoclast precursors and inhibited their differentiation. This study suggests that altering the bone marrow microenvironment with PDAC cytotherapy attenuates growth of myeloma and that PDAC cytotherapy is a promising therapeutic approach for myeloma osteolysis.

Consequences of daily administered parathyroid hormone on myeloma growth, bone disease, and molecular profiling of whole myelomatous bone.

BACKGROUND: Induction of osteolytic bone lesions in multiple myeloma is caused by an uncoupling of osteoclastic bone resorption and osteoblastic bone formation. Current management of myeloma bone disease is limited to the use of antiresorptive agents such as bisphosphonates. METHODOLOGY/PRINCIPAL FINDINGS: We tested the effects of daily administered parathyroid hormone (PTH) on bone disease and myeloma growth, and we investigated molecular mechanisms by analyzing gene expression profiles of unique myeloma cell lines and primary myeloma cells engrafted in SCID-rab and SCID-hu mouse models. PTH resulted in increased bone mineral density of myelomatous bones and reduced tumor burden, which reflected the dependence of primary myeloma cells on the bone marrow microenvironment. Treatment with PTH also increased bone mineral density of uninvolved murine bones in myelomatous hosts and bone mineral density of implanted human bones in nonmyelomatous hosts. In myelomatous bone, PTH markedly increased the number of osteoblasts and bone-formation parameters, and the number of osteoclasts was unaffected or moderately reduced. Pretreatment with PTH before injecting myeloma cells increased bone mineral density of the implanted bone and delayed tumor progression. Human global gene expression profiling of myelomatous bones from SCID-hu mice treated with PTH or saline revealed activation of multiple distinct pathways involved in bone formation and coupling; involvement of Wnt signaling was prominent. Treatment with PTH also downregulated markers typically expressed by osteoclasts and myeloma cells, and altered expression of genes that control oxidative stress and inflammation. PTH receptors were not expressed by myeloma cells, and PTH had no effect on myeloma cell growth in vitro. CONCLUSIONS/SIGNIFICANCE: We conclude that PTH-induced bone formation in myelomatous bones is mediated by activation of multiple signaling pathways involved in osteoblastogenesis and attenuated bone resorption and myeloma growth; mechanisms involve increased osteoblast production of anti-myeloma factors and minimized myeloma induction of inflammatory conditions.

The ephrinB2/EphB4 axis is dysregulated in osteoprogenitors from myeloma patients and its activation affects myeloma bone disease and tumor growth.

Myeloma bone disease is caused by uncoupling of osteoclastic bone resorption and osteoblastic bone formation. Bidirectional signaling between the cell-surface ligand ephrinB2 and its receptor, EphB4, is involved in the coupling of osteoblastogenesis and osteoclastogenesis and in angiogenesis. EphrinB2 and EphB4 expression in mesenchymal stem cells (MSCs) from myeloma patients and in bone cells in myelomatous bones was lower than in healthy counterparts. Wnt3a induced up-regulation of EphB4 in patient MSCs. Myeloma cells reduced expression of these genes in MSCs, whereas in vivo myeloma cell-conditioned media reduced EphB4 expression in bone. In osteoclast precursors, EphB4-Fc induced ephrinB2 phosphorylation with subsequent inhibition of NFATc1 and differentiation. In MSCs, EphB4-Fc did not induce ephrinB2 phosphorylation, whereas ephrinB2-Fc induced EphB4 phosphorylation and osteogenic differentiation. EphB4-Fc treatment of myelomatous SCID-hu mice inhibited myeloma growth, osteoclastosis, and angiogenesis and stimulated osteoblastogenesis and bone formation, whereas ephrinB2-Fc stimulated angiogenesis, osteoblastogenesis, and bone formation but had no effect on osteoclastogenesis and myeloma growth. These chimeric proteins had similar effects on normal bone. Myeloma cells expressed low to undetectable ephrinB2 and EphB4 and did not respond to the chimeric proteins. The ephrinB2/EphB4 axis is dysregulated in MM, and its activation by EphB4-Fc inhibits myeloma growth and bone disease.

Fenretinide inhibits myeloma cell growth, osteoclastogenesis and osteoclast viability.

Fenretinide (4HPR), a nontoxic analog of ATRA, has been investigated in various malignancies but not in multiple myeloma (MM), a plasma cell malignancy associated with induction of osteolytic bone disease. Here we show that 4HPR induces apoptosis through increased level of ROS and activation of caspase-8, 9 and 3, and inhibits growth of several MM cell lines in a dose-dependent manner. Serum or co-culture with the supportive osteoclasts partially protects MM cells from 4HPR-induced growth inhibition. Sphingosine-1 phosphate (S1P) significantly protects MM cells from 4HPR-induced apoptosis suggesting that as in other malignancies, this drug up-regulates ceramide in MM cells. 4HPR has no toxic effects on non-malignant cells such as blood mononucleated cells, mesenchymal stem cells and osteoblasts, but markedly reduces viability of endothelial cells and mature osteoclasts and inhibits differentiation of osteoclasts and MM-induced tube formation. 4HPR is a potential anti-MM agent, affecting MM cells and MM-induced bone disease and angiogenesis.

Inhibitor of DASH proteases affects expression of adhesion molecules in osteoclasts and reduces myeloma growth and bone disease.

Dipeptidyl peptidase (DPP) IV activity and/or structure homologues (DASH) are serine proteases implicated in tumourigenesis. We previously found that a DASH protease, fibroblast activation protein (FAP), was involved in osteoclast-induced myeloma growth. Here we further demonstrated expression of various adhesion molecules in osteoclasts cultured alone or cocultured with myeloma cells, and tested the effects of DASH inhibitor, PT-100, on myeloma cell growth, bone disease, osteoclast differentiation and activity, and expression of adhesion molecules in osteoclasts. PT-100 had no direct effects on viability of myeloma cells or mature osteoclasts, but significantly reduced survival of myeloma cells cocultured with osteoclasts. Real-time PCR array for 85 adhesion molecules revealed upregulation of 17 genes in osteoclasts after coculture with myeloma cells. Treatment of myeloma/osteoclast cocultures with PT-100 significantly downregulated 18 of 85 tested genes in osteoclasts, some of which are known to play roles in tumourigenesis and osteoclastogenesis. PT-100 also inhibited osteoclast differentiation and subsequent pit formation. Resorption activity of mature osteoclasts and differentiation of osteoblasts were not affected by PT-100. In primary myelomatous severe combined immunodeficient (SCID)-hu mice PT-100 reduced osteoclast activity, bone resorption and tumour burden. These data demonstrated that DASH proteases are involved in myeloma bone disease and tumour growth.

The proteasome inhibitor, bortezomib suppresses primary myeloma and stimulates bone formation in myelomatous and nonmyelomatous bones in vivo.

Multiple myeloma (MM), a hematologic malignancy of terminally differentiated plasma cells is closely associated with induction of osteolytic bone disease, induced by stimulation of osteoclastogenesis and suppression of osteoblastogenesis. The ubiquitin-proteasome pathway regulates differentiation of bone cells and MM cell growth. The proteasome inhibitor, bortezomib, is a clinical potent antimyeloma agent. The main goal of this study was to investigate the effect of bortezomib on myeloma-induced bone resorption and tumor growth in SCID-rab mice engrafted with MM cells from 16 patients. Antimyeloma response of bortezomib, which was evident in >50% of 16 experiments and resembled clinical response, was associated with significant increased bone mineral density (BMD) and osteoblast numbers, and reduced osteoclast numbers in myelomatous bones. This bone anabolic effect, which was also visualized on X-ray radiographs and confirmed by static and dynamic histomorphometric analyses, was unique to bortezomib and was not observed in hosts responding to melphalan, a chemotherapeutic drug widely used to treat MM. Bortezomib also increased BMD and osteoblasts number and reduced osteoclasts number in nonmyelomatous implanted bones. In vitro bortezomib directly suppressed human osteoclast formation and promoted maturation of osteoblasts. We conclude that bortezomib promotes bone formation in myelomatous and nonmyelomatous bones by simultaneously inhibiting osteoclastogenesis and stimulating osteoblastogenesis. As clinical and experimental studies indicate that bone disease is both a consequence and necessity of MM progression our results suggest and that bortezomib's effects on bone remodeling contribute to the antimyeloma efficacy of this drug.

Role of decorin in the antimyeloma effects of osteoblasts.

Building on our previous report that osteoblasts and increased bone formation have a negative impact on myeloma cell growth in a subset of patients, we investigated the role of decorin, the main small leucine-rich proteoglycan (SLRP) expressed and produced by osteoblasts, in the antimyeloma effects of osteoblasts. In coculture experiments with osteoblasts, primary myeloma cell survival was significantly higher when decorin expression in osteoblasts was knocked down by short-hairpin RNA. Coculture experiments of myeloma cells and supporting osteoclasts in the presence of osteoblast-conditioned medium showed reduced myeloma cell survival, an effect that was attenuated by decorin-neutralizing antibody. Decorin overexpression in mesenchymal stem cells or use of recombinant decorin in coculture with osteoclasts reduced the ability of osteoclasts to support primary myeloma cell survival. The antimyeloma effect of decorin involved direct induction of apoptosis and activation of p21(WAF). Decorin also inhibited myeloma cell-induced tube formation and osteoclast differentiation. Decorin expression was insignificantly lower in patients' than donors' osteoblasts and slightly increased by bortezomib. Certain SLRPs are involved in the antimyeloma effect of osteoblasts directly and indirectly through inhibition of angiogenesis and osteoclastogenesis; therefore, increasing endogenous or exogenous SLRPs in myelomatous bone may help control myeloma.