Radium-223 dichloride (radium-223, Xofigo), a targeted alpha therapy, is currently used for the treatment of patients with castration-resistant prostate cancer (CRPC) with bone metastases. This study ...examines the mode-of-action and antitumor efficacy of radium-223 in two prostate cancer xenograft models.
Mice bearing intratibial LNCaP or LuCaP 58 tumors were randomized into groups (
= 12-17) based on lesion grade and/or serum PSA level and administered radium-223 (300 kBq/kg) or vehicle, twice at 4-week intervals. X-rays and serum samples were obtained biweekly. Soft tissue tumors were observed macroscopically at sacrifice. Tibiae were analyzed by gamma counter, micro-CT, autoradiography and histology.
Radium-223 inhibited tumor-induced osteoblastic bone growth and protected normal bone architecture, leading to reduced bone volume in LNCaP and abiraterone-resistant LuCaP 58 models. Furthermore, radium-223 resulted in lower PSA values and reduced total tissue and tumor areas, indicating that treatment constrains prostate cancer growth in bone. In addition, radium-223 suppressed abnormal bone metabolic activity as evidenced by decreased number of osteoblasts and osteoclasts and reduced level of the bone formation marker PINP. Mode-of-action studies revealed that radium-223 was deposited in the intratumoral bone matrix. DNA double-strand breaks were induced in cancer cells within 24 hours after radium-223 treatment, and PSA levels were significantly lower 72 hours after treatment, providing further evidence of the antitumor effects.
Taken together, radium-223 therapy exhibits a dual targeting mode-of-action that induces tumor cell death and suppresses tumor-induced pathologic bone formation in tumor microenvironment of osseous CRPC growth in mice.
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Bone metastasis is a common clinical complication in several cancer types, and it causes a severe reduction in quality of life as well as lowering survival time. Bone metastases proceed through a ...vicious self-reinforcing cycle that can be osteolytic or osteoblastic in nature. The vicious cycle is characterized by cancer cells residing in bone releasing signal molecules that promote the differentiation of osteoclasts and osteoblasts either directly or indirectly. The increased activity of osteoclasts and osteoblasts then increases bone turnover, which releases growth factors that benefit metastatic cancer cells. In order to improve the prognosis of patients with bone metastases this cycle must be broken. Radium-223 dichloride (radium-223), the first targeted alpha therapy (TAT) approved, is an osteomimetic radionuclide that is incorporated into bone metastases where its high-linear energy transfer alpha radiation disrupts both the activity of bone cells and cancer cells. Therefore, radium-223 treatment has been shown preclinically to directly affect cancer cells in both osteolytic breast cancer and osteoblastic prostate cancer bone metastases as well as to inhibit the differentiation of osteoblasts and osteoclasts. Clinical studies have demonstrated an increase in survival in patients with metastatic castration-resistant prostate cancer. Due to the effectiveness and low toxicity of radium-223, several novel combination treatment strategies are currently eliciting considerable research interest.
Radium-223 dichloride and enzalutamide are indicated for metastatic castration-resistant prostate cancer and their combination is currently being investigated in a large phase 3 clinical trial. Here, ...we evaluated the antitumor efficacy of radium-223, enzalutamide, and their combination in the intratibial LNCaP model mimicking prostate cancer metastasized to bone.
experiments revealed that the combination of radium-223 and enzalutamide inhibited LNCaP cell proliferation and showed synergistic efficacy. The combination of radium-223 and enzalutamide also demonstrated enhanced
antitumor efficacy, as determined by measuring serum PSA levels in the intratibial LNCaP model. A decreasing trend in the total area of tumor-induced abnormal bone was associated with the combination treatment. The serum levels of the bone formation marker PINP and the bone resorption marker CTX-I were lowest in the combination treatment group and markedly decreased compared with vehicle group. Concurrent administration of enzalutamide did not impair radium-223 uptake in tumor-bearing bone or the ability of radium-223 to inhibit tumor-induced abnormal bone formation. In conclusion, combination treatment with radium-223 and enzalutamide demonstrated enhanced antitumor efficacy without compromising the integrity of healthy bone. The results support the ongoing phase 3 trial of this combination.
Osteolytic bone disease is a hallmark of multiple myeloma (MM) mediated by MM cell proliferation, increased osteoclast activity, and suppressed osteoblast function. The proteasome inhibitor ...bortezomib targets MM cells and improves bone health in MM patients. Radium-223 dichloride (radium-223), the first targeted alpha therapy approved, specifically targets bone metastases, where it disrupts the activity of both tumor cells and tumor-supporting bone cells in mouse models of breast and prostate cancer bone metastasis. We hypothesized that radium-223 and bortezomib combination treatment would have additive effects on MM. In vitro experiments revealed that the combination treatment inhibited MM cell proliferation and demonstrated additive efficacy. In the systemic, syngeneic 5TGM1 mouse MM model, both bortezomib and radium-223 decreased the osteolytic lesion area, and their combination was more effective than either monotherapy alone. Bortezomib decreased the number of osteoclasts at the tumor–bone interface, and the combination therapy resulted in almost complete eradication of osteoclasts. Furthermore, the combination therapy improved the incorporation of radium-223 into MM-bearing bone. Importantly, the combination therapy decreased tumor burden and restored body weights in MM mice. These results suggest that the combination of radium-223 with bortezomib could constitute a novel, effective therapy for MM and, in particular, myeloma bone disease.
An increased risk of non-pathological fractures in patients with prostate cancer and bone metastases has been associated with combination treatment with radium-223, abiraterone, and ...prednisone/prednisolone in the absence of bone-protecting agents. Here, we investigated possible mechanisms leading to this outcome using an intratibial LNCaP model mimicking prostate cancer bone metastases. Male NOD.scid mice were inoculated intratibially with LNCaP prostate cancer cells and treated with vehicle, radium-223, abiraterone, prednisone, zoledronic acid, or their combinations for 28 days. Serum TRACP 5b and PSA levels were measured. Bone structure, quality, and formation rate of non-tumor-bearing and tumor-bearing tibiae were analyzed by microCT, 3-point bending assay, and dynamic histomorphometry, respectively. Radium-223 incorporation into bone was also measured. Radium-223/abiraterone/prednisone combination treatment induced a transient increase in bone resorption indicated by elevated TRACP 5b levels, which was inhibited by concurrent treatment with zoledronic acid. Furthermore, radium-223/abiraterone/prednisone combination reduced periosteal and trabecular new bone formation and the number of osteoblasts, but bone structure or biomechanical quality were not affected. The abiraterone/prednisone treatment decreased radium-223 incorporation into tumor-bearing bone, possibly explaining the lack of additional antitumor efficacy. In conclusion, radium-223/abiraterone/prednisone combination increased bone resorption, which may have been one of the mechanisms leading to an increased fracture risk in patients with mCRPC.
Bone metastases are associated with increased morbidity and poor prognosis in breast cancer patients. Radium-223 dichloride is a calcium mimetic that localizes to bone, providing targeted therapy for ...skeletal metastasis.
We investigated the mode of action of radium-223 dichloride using breast cancer cell, osteoclast, and osteoblast cultures as well as a mouse model of breast cancer bone metastasis. A single dose of radium-223 dichloride was used in three different settings mimicking the prevention or treatment of bone metastasis. Disease progression was monitored using fluorescence and radiographic imaging and histological analyses. The effect of radium-223 dichloride alone and in combination with doxorubicin or zoledronic acid on survival of mice was analyzed by Kaplan-Meier methods. All statistical tests used were two-sided.
Radium-223 dichloride incorporated into bone matrix and inhibited proliferation of breast cancer cells and differentiation of osteoblasts and osteoclasts (all P values < .001) in vitro. In an established bone metastasis setting, radium-223 dichloride prevented tumor-induced cachexia (0/14 vs 7/14 control mice) and decreased osteolysis by 56% and tumor growth by 43% (all P values < .05). Radium-223 dichloride induced double-strand DNA breaks in cancer cells in vivo. Finally, radium-223 dichloride extended survival as a monotherapy (29.2 days, 95% confidence interval CI = 26.6 to 31.8 days, P = .039) and in combination with zoledronic acid (31.4 days, 95% CI = 28.8 to 34.0 days, P = .004) or doxorubicin (31.5 days, 95% CI = 29.5 to 33.5 days, P < .001) compared to the vehicle group (24.9 days, 95% CI = 23.4 to 26.4 days). Similar but even more pronounced effects were observed when radium-223 dichloride was administered in a preventive or micrometastatic setting.
Our findings strongly support the development of radium-223 dichloride for the treatment of breast cancer patients with or at high risk of developing bone metastases.
Bone metastases are prevalent in many common cancers such as breast, prostate, and lung cancers, and novel therapies for treating bone metastases are needed. Human immune system-engrafted models are ...used in immuno-oncology (IO) studies for subcutaneous cancer cell or patient-derived xenograft implantations that mimic primary tumor growth. Novel efficacy models for IO compounds on bone metastases need to be established. The study was performed using CIEA NOG (NOG) mice engrafted with human CD34+ hematopoietic stem cells (huNOG) and age-matched immunodeficient NOG mice. Bone phenotyping was performed to evaluate baseline differences. BT-474 human breast cancer cells were inoculated into the tibia bone marrow, and cancer-induced bone changes were monitored by X-ray imaging. Bone content and volume were analyzed by dual X-ray absorptiometry and microcomputed tomography. Tumor-infiltrating lymphocytes (TILs) and the expression of immune checkpoint markers were analyzed by immunohistochemistry. Bone phenotyping showed no differences in bone architecture or volume of the healthy bones in huNOG and NOG mice, but the bone marrow fat was absent in huNOG mice. Fibrotic areas were observed in the bone marrow of some huNOG mice. BT-474 tumors induced osteoblastic bone growth. Bone lesions appeared earlier and were larger, and bone mineral density was higher in huNOG mice. huNOG mice had a high number of human CD3-, CD4-, and CD8-positive T cells and CD20-positive B cells in immune-related organs. A low number of TILs and PD-1-positive cells and low PD-L1 expression were observed in the BT-474 tumors at the endpoint. This study reports characterization of the first breast cancer bone growth model in huNOG mice. BT-474 tumors represent a “cold” tumor with a low number of TILs. This model can be used for evaluating the efficacy of combination treatments of IO therapies with immune-stimulatory compounds or therapeutic approaches on bone metastatic breast cancer.
Abstract
When tumor cells home to bone microenvironment they secrete factors that stimulate osteoclast formation, which results in increased bone resorption. This in turn increases the release of ...factors from bone matrix that stimulate the growth of tumor cells, leading to a vicious cycle characterized by extensive bone loss and enhanced tumor growth in bone. Thus, factors that inhibit osteoclast formation or bone resorption activity of mature osteoclasts may have the potential to inhibit the vicious cycle. The RANKL inhibitor denosumab is approved for treatment of bone metastases from solid tumors, and the cathepsin K inhibitor odanacatib has been shown to suppress bone resorption in breast cancer patients with bone metastases. Human osteoclasts can be generated from bone marrow-derived CD34+ mesenchymal stem cells in the presence of M-CSF and RANKL. In this study we report optimization of separate in vitro culture systems for determining osteoclast differentiation and activity, and validation of denosumab and odanacatib as reference inhibitors of osteoclast differentiation and activity, respectively. CD34+ human osteoclast precursor cells were cultured on bovine bone slices for 7 days. Different concentrations of denosumab (0.01 - 10 μg/ml) were added in the cultures at day 0, and tartrate-resistant acid phosphatase isoform 5b activity (TRACP 5b) was measured from the culture medium collected at day 7 as an index of the number of formed osteoclasts. Osteoclast activity was studied by allowing the formed mature osteoclasts to resorb bone during an additional 3-day culture period. The culture medium was changed and different concentrations of odanacatib (0.001 - 1.0 μM) were added into the cultures at day 7, and the amount of C-terminal cross-linked telopeptides of type I collagen (CTX-I) was measured in the culture medium collected at day 10 to quantitate bone resorption during days 7-10. Denosumab and odanacatib showed strong concentration dependent inhibition of osteoclast differentiation and activity, respectively, with EC50 values of 0.124 μg/ml for denosumab and 0.0433 μM for odanacatib. We conclude that we have validated denosumab as a reference compound of osteoclast differentiation and odanacatib as a reference compound of osteoclast activity in a human in vitro osteoclast culture system. The culture system is a clinically reliable tool for identifying new compounds affecting the vicious cycle of osteolytic bone metastases, and clarifying if these active compounds target directly osteoclast differentiation or activity.
Citation Format: Jenni Bernoulli, Jussi M. Halleen, Mari I. Suominen, Johanna Tuomela, Jukka Rissanen, Katja M. Fagerlund. Validation of human osteoclast cultures for studying the mode-of-action and identification of new compounds with the potential of inhibiting the vicious cycle in osteolytic bone metastases. abstract. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 364.
Preclinical tumor growth experiments often result in heterogeneous datasets that include growing, regressing, or stable growth profiles in the treatment and control groups. Such confounding ...intertumor variability may mask the true treatment effects especially when less aggressive treatment alternatives are being evaluated.
We developed a statistical modeling approach in which the growing and poorly growing tumor categories were automatically detected by means of an expectation-maximization algorithm coupled within a mixed-effects modeling framework. The framework is implemented and distributed as an R package, which enables model estimation and statistical inference, as well as statistical power and precision analyses.
When applied to four tumor growth experiments, the modeling framework was shown to (i) improve the detection of subtle treatment effects in the presence of high within-group tumor variability; (ii) reveal hidden tumor subgroups associated with established or novel biomarkers, such as ERβ expression in a MCF-7 breast cancer model, which remained undetected with standard statistical analysis; (iii) provide guidance on the selection of sufficient sample sizes and most informative treatment periods; and (iv) offer flexibility to various cancer models, experimental designs, and treatment options. Model-based testing of treatment effect on the tumor growth rate (or slope) was shown as particularly informative in the preclinical assessment of treatment alternatives based on dietary interventions.
In general, the modeling framework enables identification of such biologically significant differences in tumor growth profiles that would have gone undetected or had required considerably higher number of animals when using traditional statistical methods.
Abstract
Background and objective: Bone is the most common site of metastasis in prostate cancer (PCa) and results in significant morbidity and poor prognosis. Disseminated PCa cells conquer ...hematopoietic stem cell niches, and during outgrowth they induce osteoblasts to form new, disorganized bone. Also osteoclasts are activated at a varying degree. PI3K activation has important role in survival and proliferation of PCa cells, mediating critical signaling pathways involving tumor and stromal cell interaction in the bone microenvironment. BAY 1082439 is a highly selective and potent PI3K inhibitor currently in Phase I, with equipotent activity against PI3Kα and PI3Kβ isoforms. Radium-223 dichloride (ra-223/Xofigo) is alpha-emitting calcium mimetic that via efficient osteoaffinity provides targeted radiation therapy against bone metastases. We have previously reported that BAY 1082439 and ra-223 showed synergistic anti-proliferative and apoptosis-inductive effects in vitro in LNCaP PCa cells (Suominen et al, AACR Annual Meeting 2014). Here, we investigated the effects of BAY 1082439 and ra-223 as single agents and in combination in the osteoblastic LNCaP tumors in tibia of male nod.scid mice.
Methods: Tumors were established 6 weeks after inoculation of LNCaP cells. Mice were randomized into four treatment groups (vehicle, ra-223; BAY 1082439 and ra-223 + BAY 1082439) based on serum PSA and bone lesion score. Treatments were continued for six weeks and the efficacy was assessed by the following endpoints biweekly and/or at the end of the study: PSA, bone formation marker PINP, bone lesions and bone volume (measured by microCT), and tumor and bone area by histological analysis.
Results: Both ra-223 and BAY 1082439 monotherapies inhibited tumor growth (reduction 67.9%, p = 0.029 and 67.4%, p = 0.009, respectively). Furthermore, BAY 1082439 monotherapy treatment group displayed 68.8% of necrotic tumor, compared to 6.5% in the control group (p = 0.009). In the combination group, tumor growth was further suppressed (tumor reduction 89%, p = 0.005) and it is noteworthy that 60% of animals had no detectable tumors in histology. All treatments inhibited the tumor-induced bone formation compared to vehicle, and the combination treatment inhibited progression of bone lesions nearly completely. In conclusion, BAY 1082439 and ra-223 as monotherapies decreased tumor burden and tumor-induced bone reaction, and the observed effects were further enhanced by the combination treatment.
Citation Format: Mari I. Suominen, Jukka Morko, Katja M. Fagerlund, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Jussi M. Halleen, Arne Scholz, Ningshu Liu. PI3K inhibitor BAY 1082439 and radium-223 dichloride decrease tumor burden and tumor-induced bone formation in an established bone metastatic prostate cancer model in mice. abstract. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 381.
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