Bisphosphonates as anticancer agents in early breast cancer: preclinical and clinical evidence

Benefit of adjuvant bisphosphonates in early breast cancer treated with contemporary systemic therapy: A meta-analysis of randomized control trials

Background

The absolute and relative benefits of adjuvant bisphosphonates on disease-free survival and overall survival in patients receiving contemporary systemic therapy for early breast cancer is uncertain.

Methods

Data from randomized trials of adjuvant bisphosphonates that recruited patients exclusively after 2000 and reported disease free survival and overall survival was utilized. Five-year disease-free survival and overall survival in bisphosphonates and control group along with associated hazard ratios were extracted. Absolute data were weighted by sample size and hazard ratios were pooled using inverse variance and random effects modelling. Meta-regression comprising linear regression weighted by sample size (mixed effects) was performed to explore association between disease and treatment related factors and absolute differences in benefit from bisphosphonates.

Results

Eleven trials comprising 24023 patients were included in the analysis. For disease free survival, pooled hazard ratio was 0.89 (0.81-0.97, p = 0.008) with a 1.5 % weighted mean difference favoring bisphosphonates over control. There was no significant overall survival benefit (0.92, 0.82-1.03, p = 0.16). Among patients receiving anthracycline and taxane based chemotherapy, there were no differences in either disease free survival (0.95, 0.80-1.12) or overall survival (1.04, 0.81-1.32). Meta-regression showed lower benefits in higher risk patients (node-positive, larger tumor size, estrogen receptor-, grade 3 or those receiving chemotherapy). Overall, 1 % (95 % CI 0.75-1.15) of patients experienced osteonecrosis of jaw related to zoledronic acid.

Conclusions

Compared to the Early Breast Cancer Trialist's Collaborative Group meta-analysis, benefit from adjuvant bisphosphonates is lower in recent trials especially in higher risk patients receiving contemporary chemotherapy. The balance between benefits and risks of adjuvant bisphosphonates should be considered in individual patients.

Synthesis of the biologically important dideuterium-labelled adenosine triphosphate analogue ApppI(d2)

The chemical synthesis of the dideuterium-labelled ATP analogue 1-adenosin-5’-yl-3-(3-methylbut-3-en-1,1-d₂-1-ol) triphosphoric acid diester (ApppI(d₂)) is described. ApppI has been reported to be an important mevalonate pathway metabolite, induced by nitrogen-containing bisphosphonates used for the treatment of several diseases related to the calcium metabolism, of which osteoporosis is the most well-known. The availability of ApppI(d₂) opens possibilities to quantitative measurements of ApppI in biological samples by mass spectrometry. The synthesized target compound ApppI(d₂) was purified by high-performance counter current chromatography and characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy as well as high-resolution mass spectrometry.

Rapid Flow Synthesis of a Biomimetic Carbonate Apatite as an Effective Drug Carrier

A facile synthesis of apatite nanocrystals analogous to bioapatites with increased biocompatibility and biodegradability can remedy the shortcomings of the widely applied synthetic hydroxyapatite (HAp) for bone defect treatment. Here, we propose an expeditious synthesis method to develop a biomimetic B-type carbonate apatite (CAp) with a simple capillary microfluidic device at room temperature. The process not only eliminates fluctuations with the addition of carbonate but also produces safe CAp drug carriers through simultaneous alendronate incorporation to the CAp structure. CAp displayed superior mineralization on osteoblast-like MG-63 cells when compared with HAp and HAp drug carriers that were produced using identical methods. Furthermore, alendronate-incorporated CAp drug carriers potentially displayed higher cancer cell suppression when applied to breast cancer cells attached to the bone tissue model, which signifies enhanced cancer metastasis to bone suppression due to the likelihood of increased alendronate release of CAp owing to its faster dissolution. Overall, our results may provide promising opportunities for enhanced clinical CAp application for bone defect treatment, particularly for bone loss and cancer to bone metastasis.

Recent Advances in the Development of Tetrazine Ligation Tools for Pretargeted Nuclear Imaging

Tetrazine ligation has gained interest as a bio-orthogonal chemistry tool within the last decade. In nuclear medicine, tetrazine ligation is currently being explored for pretargeted approaches, which have the potential to revolutionize state-of-the-art theranostic strategies. Pretargeting has been shown to increase target-to-background ratios for radiopharmaceuticals based on nanomedicines, especially within early timeframes. This allows the use of radionuclides with short half-lives which are more suited for clinical applications. Pretargeting bears the potential to increase the therapeutic dose delivered to the target as well as reduce the respective dose to healthy tissue. Combined with the possibility to be applied for diagnostic imaging, pretargeting could be optimal for theranostic approaches. In this review, we highlight efforts that have been made to radiolabel tetrazines with an emphasis on imaging.

The optimized drug delivery systems of treating cancer bone metastatic osteolysis with nanomaterials

Some cancers such as human breast cancer, prostate cancer, and lung cancer easily metastasize to bone, leading to osteolysis and bone destruction accompanied by a complicated microenvironment. Systemic administration of bisphosphonates (BP) or denosumab is the routine therapy for osteolysis but with non-negligible side effects such as mandibular osteonecrosis and hypocalcemia. Thus, it is imperative to exploit optimized drug delivery systems, and some novel nanotechnology and nanomaterials have opened new horizons for scientists. Targeted and local drug delivery systems can optimize biodistribution depending on nanoparticles (NPs) or microspheres (MS) and implantable biomaterials with the controllable property. Drug delivery kinetics can be optimized by smart and sustained/local drug delivery systems for responsive delivery and sustained delivery. These delicately fabricated drug delivery systems with special matrix, structure, morphology, and modification can minimize unexpected toxicity caused by systemic delivery and achieve desired effects through integrating multiple drugs or multiple functions. This review summarized recent studies about optimized drug delivery systems for the treatment of cancer metastatic osteolysis, aimed at giving some inspiration in designing efficient multifunctional drug delivery systems.

A Review on Re-Packaging of Bisphosphonates Using Biomaterials

The need for bone repair and insight into new regeneration therapies as well as improvement of existing regeneration routes is constantly increasing as a direct consequence of the rise in the number of trauma victims, musculoskeletal disorders, and increased life expectancy. Bisphosphonates (BPs) have emerged as a class of drugs with proven efficacy against many bone disorders. The most recent ability of this class of drugs is being explored in its anti-cancer ability. However, despite the pharmacological success, there are certain shortcomings that have circumvented this class of the drug. The mediation of biomaterials in delivering bisphosphonates has greatly helped in overcoming some of these shortcomings. This article is focused on reviewing the benefits the bisphosphonates have provided upon getting delivered via the use of biomaterials. Furthermore, the role of bisphosphonates as a potent anticancer agent is also accounted. It is witnessed that employing engineering tools in combination with therapeutics has the potential to provide solutions to bone loss from degenerative, surgical, or traumatic processes, and also aid in accelerating the healing of large bone fractures and problematic non-union fractures. The role of nanotechnology in enhancing the efficacy of the bisphosphonates is also reviewed and innovative approaches are identified.

PharmaNet: Pharmaceutical discovery with deep recurrent neural networks

The discovery and development of novel pharmaceuticals is an area of active research mainly due to the large investments required and long payback times. As of 2016, the development of a novel drug candidate required up to $ USD 2.6 billion in investment for only 10% rate of approval by the FDA. To help decreasing the costs associated with the process, a number of in silico approaches have been developed with relatively low success due to limited predicting performance. Here, we introduced a machine learning-based algorithm as an alternative for a more accurate search of new pharmacological candidates, which takes advantage of Recurrent Neural Networks (RNN) for active molecule prediction within large databases. Our approach, termed PharmaNet was implemented here to search for ligands against specific cell receptors within 102 targets of the DUD-E database, which contains 22886 active molecules. PharmaNet comprises three main phases. First, a SMILES representation of the molecule is converted into a raw molecular image. Second, a convolutional encoder processes the data to obtain a fingerprint molecular image that is finally analyzed by a Recurrent Neural Network (RNN). This approach enables precise predictions of the molecules' target on the basis of the feature extraction, the sequence analysis and the relevant information filtered out throughout the process. Molecule Target prediction is a highly unbalanced detection problem and therefore, we propose that an adequate evaluation metric of performance is the area under the Normalized Average Precision (NAP) curve. PharmaNet largely surpasses the previous state-of-the-art method with 97.7% in the Receiver Operating Characteristic curve (ROC-AUC) and 65.5% in the NAP curve. We obtained a perfect performance for human farnesyl pyrophosphate synthase (FPPS), which is a potential target for antimicrobial and anticancer treatments. We decided to test PharmaNet for activity prediction against FPPS by searching in the CHEMBL data set. We obtained three (3) potential inhibitors that were further validated through both molecular docking and in silico toxicity prediction. Most importantly, one of this candidates, CHEMBL2007613, was predicted as a potential antiviral due to its involvement on the PCDH17 pathway, which has been reported to be related to viral infections.

Disease recurrence and oncological outcome of patients treated surgically with curative intent for estrogen receptor positive, lymph node negative breast cancer

BACKGROUND

The molecular era has identified four breast cancer subtypes. Luminal A breast cancer (LABC) is defined by estrogen-receptor positive (ER+), progesterone-receptor positive (PgR+) and human epidermal growth factor receptor-2 negative (HER2-) tumours; these cancers are the most common and carry favourable prognoses.

AIMS

To describe clinicopathologic features, oncological outcome and relapse patterns in LABC.

METHODS

Consecutive female patients diagnosed with ER/PgR+/HER2-, lymph node negative (LN-) breast cancer between 2005 and 2015 were included. Clinicopathological and recurrence data was recorded using descriptive statistics. Oncological outcome was determined using Kaplan-Meier and Cox-regression analyses.

RESULTS

Analysis was performed for 849 patients with median follow-up of 102.1 months. Mean disease-free (DFS) and overall survival (OS) were 85.8% and 91.8%. Seventy patients died during this study (8.2%), while 58 patients had recurrence; 7 had local recurrence (0.8%) and 51 had distant recurrence (DDR) (6.0%). Patients developing DDR were likely to be postmenopausal (P = 0.028), present symptomatically (P < 0.001) and have larger tumours (P < 0.001). The mean time to DDR was 65.7 months, with fatal recurrence occurring in 66.6% of patients with DDR (34/51). Systemic chemotherapy prescription did not influence DDR (P = 0.053). Age >65 (hazards ratio (HR):1.66, 95% Confidence Interval (CI):1.07-2.55, P = 0.022), presenting symptomatically (HR:2.28, 95%CI:1.21-4.29, P = 0.011) and tumour size >20 mm (HR:1.81, 95%CI:1.25-2.62, P = 0.002) predicted DFS, while age>65 (HR:2.60, 95%CI:1.49-4.53, P = 0.001) and being postmenopausal at diagnosis (HR:3.13, 95%CI:1.19-8.22, P = 0.020) predicted OS.

CONCLUSION

Our series demonstrated excellent survival outcomes for patients diagnosed with LN- LABC after almost a decade of follow-up. However, following DDR, fatal progression is often imminent.

Bisphosphonates and Cancer: A Relationship Beyond the Antiresorptive Effects

Bisphosphonates (BPs) are stable analogues of the Inorganic Pyrophosphate (PPi), an endogenous regulator of bone mineralization, which can resist the hydrolysis in the gastrointestinal tract. Their conformation allows targeting the bone as a result of their three-dimensional structure, which makes them primary agents against osteoclast-mediated bone loss. They are used in many bone pathological conditions, like bone metastasis, because of its ability to modulate bone metabolism into a less favorable place to cancer cell growth, through the inhibition of osteoclastogenesis and bone resorption. This review is focused on the mechanisms of action through which BPs affect the cellular activity and survival, mainly on their antitumoral effects. In conclusion, BPs are considered the primary therapy for skeletal disorders due to its high affinity for bone, but now they are also considered as potential antitumor agents due to its ability to induce tumor cell apoptosis, inhibition of cell adhesion, invasion and proliferation, modulation of the immune system to target and eliminate cancer cells as well as affect the angiogenic mechanisms. Like any other drug, they also have some adverse effects, but the most common, the acute phase reaction, can be minimized with the intake of calcium and vitamin D.

Bone-Modifying Agents in Early-Stage and Advanced Breast Cancer

PURPOSE OF REVIEW

Bone-modifying agents have an important role in the treatment of patients with bone mineral density loss, early-stage breast cancer to reduce risk of recurrence, and metastatic breast cancer with bone involvement. Here we review mechanisms of action of these agents and clinical indications for their use.

RECENT FINDINGS

The meta-analysis undertaken by the Early Breast Cancer Trialists' Collaborative Group showed that the use of bisphosphonates was associated with a decreased risk of breast cancer recurrence.

SUMMARY

The effect of bisphosphonates and receptor activator of nuclear factor kappa-B ligand inhibitors on bone health provides an opportunity to decrease the incidence of skeletal-related events and improve cancer outcomes in certain subsets of patients.

Kadsurenone is a useful and promising treatment strategy for breast cancer bone metastases by blocking the PAF/PTAFR signaling pathway

Breast cancer (BC) is characterized by high incidences of bone metastases. Current treatment strategies for BC bone metastases primarily focused on breaking the ‘vicious osteolytic cycle’. Platelet-activating factor (PAF) is a potent phospholipid mediator, which has previously reported biological activities in BC progression and osteoclast differentiation by activating its receptor PAF receptor (PTAFR). However, the role of PAF in the mediation of BC bone metastases remains elusive. In the present study, it was revealed that the upregulation of PTAFR was associated with an increased incidence of bone metastases. It was also revealed that PAF significantly enhanced the processes of BC cell migration and BC mediated osteoclastogenesis. These results suggest that PAF serves a promotion role in BC bone metastases. It was further demonstrated that the natural PAF antagonist Kadsurenone may effectively attenuate each process by partially blocking the PAF/PTAFR signaling pathway. Therefore, targeting PAF/PTAFR by Kadsurenone may be a promising treatment strategy for BC bone metastases.

In Silico-Based Repositioning of Phosphinothricin as a Novel Technetium-99m Imaging Probe with Potential Anti-Cancer Activity

l-Phosphinothricin (glufosinate or 2-amino-4-((hydroxy(methyl) phosphinyl) butyric acid ammonium salt (AHPB)), which is a structural analog of glutamate, is a recognized herbicide that acts on weeds through inhibition of glutamine synthetase. Due to the structural similarity between phosphinothricin and some bisphosphonates (BPs), this study focuses on investigating the possibility of repurposing phosphinothricin as a bisphosphonate analogue, particularly in two medicine-related activities: image probing and as an anti-cancer drug. As BP is a competitive inhibitor of human farnesyl pyrophosphate synthase (HFPPS), in silico molecular docking and dynamic simulations studies were established to evaluate the binding and stability of phosphinothricin with HFPPS, while the results showed good binding and stability in the active site of the enzyme in relation to alendronate. For the purpose of inspecting bone-tissue accumulation of phosphinothricin, a technetium (^99mTc)–phosphinothricin complex was developed and its stability and tissue distribution were scrutinized. The radioactive complex showed rapid, high and sustained uptake into bone tissues. Finally, the cytotoxic activity of phosphinothricin was tested against breast and lung cancer cells, with the results indicating cytotoxic activity in relation to alendronate. All the above results provide support for the use of phosphinothricin as a potential anti-cancer drug and of its technetium complex as an imaging probe.

The good and bad of targeting cancer-associated extracellular matrix

The maintenance of tissue homeostasis requires extracellular matrix (ECM) remodeling. Immune cells actively participate in regenerating damaged tissues contributing to ECM deposition and shaping. Dysregulated ECM deposition characterizes fibrotic diseases and cancer stromatogenesis, where a chronic inflammatory state sustains the ECM increase. In cancer, the ECM fosters several steps of tumor progression, providing pro-survival and proliferative signals, promoting tumor cell dissemination via collagen fibers or acting as a barrier to impede drug diffusion. Interfering with processes leading to chronic ECM deposition, as occurring in cancer, might allow the simultaneous targeting of both primary tumors and metastatic lesions. However, a note of caution comes from data showing that defective ECM deposition is associated with an exacerbated inflammatory and autoimmune phenotype and to lymphomagenesis. Immune cells display ITIM-inhibitory receptors recognizing collagens as counter ligands, which negatively regulate the immune response. This is in line with the idea that ECM components can provide homeostatic signals to immune cells to regulate and prevent unwanted activation, a concept particularly relevant in cancer where these mechanisms could be in place to keep infiltrating immune cells in a suppressive pro-tumoral state. In this context, the pharmacological targeting of myeloid cells, for which both direct and indirect roles in ECM deposition have been shown, can be a relevant option to this purpose.

Synthesis of a Biologically Important Adenosine Triphosphate Analogue, ApppD

The chemical synthesis of a adenosine triphosphate analogue, 1-adenosin-5'-yl 3-(3-methylbut-2-enyl) triphosphoric acid diester (ApppD), is described. ApppD is known to be an active metabolite of the mevalonate pathway in the human body like its structural isomer isopentenyl ester of ATP (ApppI). Very recently, ApppI has been found to possess novel function(s); now it will also be possible to examine the effects of ApppD more precisely because it can be synthesized in reasonable amounts. 1-Adenosin-5'-yl 3-(3-methylbut-2-enyl) diphosphoric acid diester (AppD; a adenosine diphosphate analogue) was also isolated from the synthesis mixture. Both ApppD and AppD were characterized by ¹H, ¹³C, ³¹P NMR and mass spectrometry methods.

Therapeutic Bone-Modifying Agents in the Nonmetastatic Breast Cancer Setting: The Controversy and a Value Assessment

Clinical trials and meta-analyses investigating bisphosphonates as an adjuvant breast cancer therapy have shown a consistent trend, with postmenopausal women and women receiving ovarian suppression with gonadotropin-releasing hormone therapy gaining improved breast cancer outcomes with the use of adjuvant bisphosphonate therapy. The interpretation of these data is controversial, because the primary endpoints of the majority of adjuvant bisphosphonate studies have been negative. Pros and cons as well as the value of adjuvant bisphosphonate therapy are discussed here.

Bisphosphonate-Functionalized Imaging Agents, Anti-Tumor Agents and Nanocarriers for Treatment of Bone Cancer

Bone metastases result from the invasion of primary tumors to bone. Current treatment modalities include local treatments such as surgery and radiotherapy, while systemic treatments include chemotherapy and (palliative) treatment of skeletal metastases. Nevertheless, once bone metastases have been established they remain incurable leading to morbidity and mortality. Bisphosphonates are a well-established class of drugs, which are increasingly applied in the treatment of bone cancers owing to their effective inhibition of tumor cells and suppression of bone metastases. The increased understanding of the mechanism of action of bisphosphonates on bone and tumor cells has prompted the development of novel bisphosphonate-functionalized imaging and therapeutic agents. This review provides an update on the preclinical efficacy of bisphosphonate-functionalized fluorophore, anti-tumor agents and nanocarriers for the treatment of bone metastases. After an overview of the general characteristics of bisphosphonates and their mechanisms of action, an outline is provided on the various conjugation strategies that have become available to functionalize imaging agents, anti-tumor agents and nanocarriers with bisphosphonates. Finally, the efficacy of these bisphosphonate-modified agents and carriers in preclinical studies is evaluated by reviewing their potential to target tumors and inhibit tumor growth in clinically relevant animal models for the treatment of bone cancer.

A Bone-Seeking trans-Cyclooctene for Pretargeting and Bioorthogonal Chemistry: A Proof of Concept Study Using 99mTc- and 177Lu-Labeled Tetrazines

A high yield synthesis of a novel, small molecule, bisphosphonate-modified trans-cyclooctene (TCO-BP, 2) that binds to regions of active bone metabolism and captures functionalized tetrazines in vivo, via the bioorthogonal inverse electron demand Diels-Alder (IEDDA) cycloaddition, was developed. A ^99mTc-labeled derivative of 2 demonstrated selective localization to shoulder and knee joints in a biodistribution study in normal mice. Compound 2 reacted rapidly with a ¹⁷⁷Lu-labeled tetrazine in vitro, and pretargeting experiments in mice, using 2 and the ¹⁷⁷Lu-labeled tetrazine, yielded high activity concentrations in shoulder and knee joints, with minimal uptake in other tissues. Pretargeting experiments with 2 and a novel ^99mTc-labeled tetrazine also produced high activity concentrations in the knees and shoulders. Critically, both radiolabeled tetrazines showed negligible uptake in the skeleton and joints when administered in the absence of 2. Compound 2 can be utilized to target functionalized tetrazines to bone and represents a convenient reagent to test novel tetrazines for use with in vivo bioorthogonal pretargeting strategies.

Oral Bisphosphonates and Improved Survival of Breast Cancer

Purpose: Bisphosphonates are used for treatment or prevention of osteoporosis and of bone metastases. The use of oral bisphosphonates was suggested to be associated with reduced risk of developing breast cancer, and their positive influence on breast cancer survival was only demonstrated with third-generation bisphosphonates. We studied the association of use of oral bisphosphonates after breast cancer diagnosis on overall and breast cancer survival.Experimental Design: A nested case-control analysis was performed using data from the population-based Breast Cancer in Northern Israel Study (BCINIS). Participants were postmenopausal women with newly diagnosed breast cancer insured by Clalit. Use of second-generation bisphosphonates (alendronate and/or risedronate) was identified using computerized prescription records. The analysis was restricted to women who did not use bisphosphonates prior to diagnosis.Results: In a cohort of 3,731 postmenopausal women with breast cancer, followed up for an average of 70 months, there were 799 cases of death which were matched to 15,915 control periods of living breast cancer cases. Use of bisphosphonates after diagnosis for at least 18 months was significantly more common among survivors than among their matched controls who died, adjusted for tumor stage/grade (overall survival: OR = 0.63, 0.41-0.96, P = 0.03; breast cancer-specific survival: OR = 0.28, 0.09-0.91, P = 0.035). A similar advantageous effect, but statistically underpowered, was found in estrogen receptor (ER)-positive, ER-negative, and HER2neu-positive tumors.Conclusions: The use of oral bisphosphonates, by postmenopausal, probably osteoporotic, women initiated after diagnosis of breast cancer was associated with a significant improvement in overall and breast-specific odds of survival. Clin Cancer Res; 23(7); 1684-9. ©2016 AACR.

The anti-metastatic micro-environment of the bone: Importance of osteocyte Cx43 hemichannels

Bone metastases of tumor cells are a common and life-threatening feature of a variety of late-stage cancers, including breast cancers. However, until now, much less has been known about the intrinsic anti-metastatic properties of the bones and how these could be exploited to prevent or treat bone metastases. Very recently, native Cx43 hemichannels present in osteocytes have been identified as important anti-metastatic signaling complexes by establishing high local extracellular ATP levels. Moreover, bisphosphonate drugs, applied as adjuvant therapies in the treatment of breast cancer patients and bone diseases, are known to display anti-metastatic properties. Now, it became clear that these compounds exert their effects through osteocyte Cx43 hemichannels, thereby triggering their opening and promoting ATP release in the extracellular micro-environment. Hence, endogenous osteocyte Cx43 hemichannels emerge as important and promising therapeutic targets for the prevention of bone metastases and/or clinical treatment of bone-metastasized breast cancers.

Bone targeted therapy for preventing skeletal-related events in metastatic breast cancer

Cancer cells can alter physiological mechanisms within bone resulting in high bone turnover, and consequently in skeletal-related events (SREs), causing severe morbidity in affected patients. The goals of bone targeted therapy, as bisphosphonates and denosumab, are the reduction of incidence and the delay in occurrence of the SREs, to improve quality of life and pain control. The toxicity profile is similar between bisphosphonates and denosumab, even if pyrexia, bone pain, arthralgia, renal failure and hypercalcemia are more common with bisphosphonates, while hypocalcemia and toothache are more frequently reported with denosumab. Osteonecrosis of the jaw (ONJ) occurred infrequently without statistically significant difference. The present review aims to provide an assessment on bone targeted therapies for preventing the occurrence of SREs in bone metastatic breast cancer patients, critically analyzing the evidence available so far on their effectiveness, in light of the different mechanisms of action. Thus, we try to provide tools for the most fitting treatment of bone metastatic breast cancer patients. We also provide an overview on the usefulness of bone turnover markers in clinical practice and new molecules currently under study for the treatment of bone metastatic disease.