RAD001 (Everolimus) inhibits growth of prostate cancer in the bone and the inhibitory effects are increased by combination with docetaxel and zoledronic acid

Anti-Cancer Stem-Cell-Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second-most commonly diagnosed cancer in men around the world. It is treated using a risk stratification approach in accordance with the National Comprehensive Cancer Network (NCCN) in the United States. The main treatment options for early PCa include external beam radiation therapy (EBRT), brachytherapy, radical prostatectomy, active surveillance, or a combination approach. In those with advanced disease, androgen deprivation therapy (ADT) is considered as a first-line therapy. However, the majority of cases eventually progress while receiving ADT, leading to castration-resistant prostate cancer (CRPC). The near inevitable progression to CRPC has spurred the recent development of many novel medical treatments using targeted therapies. In this review, we outline the current landscape of stem-cell-targeted therapies for PCa, summarize their mechanisms of action, and discuss avenues of future development.

From Therapy Resistance to Targeted Therapies in Prostate Cancer

Prostate cancer (PCa) is the second most common malignancy among men worldwide. Although early-stage disease is curable, advanced stage PCa is mostly incurable and eventually becomes resistant to standard therapeutic options. Different genetic and epigenetic alterations are associated with the development of therapy resistant PCa, with specific players being particularly involved in this process. Therefore, identification and targeting of these molecules with selective inhibitors might result in anti-tumoral effects. Herein, we describe the mechanisms underlying therapy resistance in PCa, focusing on the most relevant molecules, aiming to enlighten the current state of targeted therapies in PCa. We suggest that selective drug targeting, either alone or in combination with standard treatment options, might improve therapeutic sensitivity of resistant PCa. Moreover, an individualized analysis of tumor biology in each PCa patient might improve treatment selection and therapeutic response, enabling better disease management.

Drug repositioning by merging active subnetworks validated in cancer and COVID-19

Computational drug repositioning aims at ranking and selecting existing drugs for novel diseases or novel use in old diseases. In silico drug screening has the potential for speeding up considerably the shortlisting of promising candidates in response to outbreaks of diseases such as COVID-19 for which no satisfactory cure has yet been found. We describe DrugMerge as a methodology for preclinical computational drug repositioning based on merging multiple drug rankings obtained with an ensemble of disease active subnetworks. DrugMerge uses differential transcriptomic data on drugs and diseases in the context of a large gene co-expression network. Experiments with four benchmark diseases demonstrate that our method detects in first position drugs in clinical use for the specified disease, in all four cases. Application of DrugMerge to COVID-19 found rankings with many drugs currently in clinical trials for COVID-19 in top positions, thus showing that DrugMerge can mimic human expert judgment.

Phase I Study of Docetaxel and Temsirolimus in Refractory Solid Tumors

INTRODUCTION

The mammalian target of rapamycin (mTOR) is a downstream mediator in the phosphatidylinositol 3-kinase/Akt signaling pathway, and plays a central role in cell proliferation, growth, differentiation, migration, and survival. Temsirolimus (CCI-779), a selective inhibitor of the mTOR, is an ester analog of rapamycin (sirolimus) with improved aqueous solubility and pharmacokinetic (PK) properties. Preclinical studies have confirmed additive and synergistic antitumor activity in cancer cell lines (breast, prostate cancer) with combinations of taxanes and mTOR inhibitors. We conducted a phase I open-label, dose-escalation study to determine the maximal tolerated dose (MTD) of docetaxel in combination with temsirolimus in patients with refractory solid tumors.

PATIENTS AND METHODS

Eligible patients had a diagnosis of a refractory solid malignancy, measurable disease, and adequate organ function. Patients were sequentially enrolled in 4 dose level intravenous combinations of docetaxel and temsirolimus. Temsirolimus was administered weekly with docetaxel administered every 3 weeks. Laboratory data for tumor markers and radiologic imaging were conducted prestudy and then after every 2 cycles of the treatment. Radiologic response was assessed by Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Blood samples for PK and pharmacodynamic analysis were planned to be drawn at MTD. Apart from the traditional 3+3 design, we also implemented Bayesian Optimal Interval design which uses isotonic regression method to select MTD. We proceeded with isotonic regression analysis by using 20% dose-limiting toxicity (DLT) rate as target.

RESULTS

Twenty-six patients were treated in this study in 4 cohorts and dose levels. Fourteen males and 12 females were enrolled with a median age of 50 years (range of 27 to 72 y) and median Eastern Cooperative Oncology Group performance score of 1. Tumor histologies included pancreas (6), colon (5), rectum (3), gallbladder (2), non-small cell lung (2), endometrium (1), neuroendocrine (1), esophagus (1), stomach (1), pharynx (1), small intestine (1), and duodenum (1). Stable disease was observed in 2/4 (50%), 3/7 (43%), 4/10 (40%), and 3/5 (60%) patients in cohorts 1, 2, 3, and 4, respectively. Dose escalation in cohorts 2, 3, and 4 was complicated by DLTs such as grade 4 neutropenia and grade 3 diarrhea and an inability for patients to tolerate treatments during and beyond cycle 1 without dose reductions. Therefore, we could not determine an MTD or recommended phase II dose using the traditional 3+3 study analysis. Blood samples for PK and pharmacodynamic analysis were not collected since MTD was not determined. By using 20% DLT rate closest to the target, isotonic regression analysis showed identical estimated DLT rates in dose -1 (docetaxel 50 mg/m2 and temsirolimus 15 mg/m2) and dose level 1 (docetaxel 60mg/m2 and temsirolimus 15 mg/m2).

CONCLUSIONS

Dose escalation of docetaxel and temsirolimus was limited by severe myelosuppressive toxicity in this phase I study. Most of the DLTs occurred after cycle 1 of therapy hence, we were unable to determine MTD or collect blood samples for PK and pharmacodynamic analysis. Our trial did not meet its objectives due to significant DLTs with this chemotherapy combination. Although our novel use of Bayesian Optimal Interval design using isotonic regression method to select MTD showed identical estimated DLT rates in dose levels 1 and -1, clinically our patients were not able to complete 2 cycles of this regimen without dose reductions due to myelosuppressive toxicity in either of these dose levels, and hence, escaped clinical validity. This combination regimen should not be studied further at the dose levels and schedules tested in our study.

Inhibitors of the PI3K/Akt/mTOR Pathway in Prostate Cancer Chemoprevention and Intervention

The phosphatidylinositol 3-kinase (PI3K)/serine-threonine kinase (Akt)/mammalian target of the rapamycin (mTOR)-signaling pathway has been suggested to have connections with the malignant transformation, growth, proliferation, and metastasis of various cancers and solid tumors. Relevant connections between the PI3K/Akt/mTOR pathway, cell survival, and prostate cancer (PC) provide a great therapeutic target for PC prevention or treatment. Recent studies have focused on small-molecule mTOR inhibitors or their usage in coordination with other therapeutics for PC treatment that are currently undergoing clinical testing. In this study, the function of the PI3K/Akt/mTOR pathway, the consequence of its dysregulation, and the development of mTOR inhibitors, either as an individual substance or in combination with other agents, and their clinical implications are discussed. The rationale for targeting the PI3K/Akt/mTOR pathway, and specifically the application and potential utility of natural agents involved in PC treatment is described. In addition to the small-molecule mTOR inhibitors, there are evidence that several natural agents are able to target the PI3K/Akt/mTOR pathway in prostatic neoplasms. These natural mTOR inhibitors can interfere with the PI3K/Akt/mTOR pathway through multiple mechanisms; however, inhibition of Akt and suppression of mTOR 1 activity are two major therapeutic approaches. Combination therapy improves the efficacy of these inhibitors to either suppress the PC progression or circumvent the resistance by cancer cells.

Cellular growth factors as prospective therapeutic targets for combination therapy in androgen independent prostate cancer (AIPC)

Cancer is the second leading cause of death worldwide, with prostate cancer, the second most commonly diagnosed cancer among men. Prostate cancer develops in the peripheral zone of the prostate gland, and the initial progression largely depends on androgens, the male reproductive hormone that regulates the growth and development of the prostate gland and testis. The currently available treatments for androgen dependent prostate cancer are, however, effective for a limited period, where the patients show disease relapse, and develop androgen-independent prostate cancer (AIPC). Studies have shown various intricate cellular processes such as, deregulation in multiple biochemical and signaling pathways, intra-tumoral androgen synthesis; AR over-expression and mutations and AR activation via alternative growth pathways are involved in progression of AIPC. The currently approved treatment strategies target a single cellular protein or pathway, where the cells slowly develop resistance and adapt to proliferate via other cellular pathways over a period of time. Therefore, an increased research aims to understand the efficacy of combination therapy, which targets multiple interlinked pathways responsible for acquisition of resistance and survival. The combination therapy is also shown to enhance efficacy as well as reduce toxicity of the drugs. Thus, the present review focuses on the signaling pathways involved in the progression of AIPC, comprising a heterogeneous population of cells and the advantages of combination therapy. Several clinical and pre-clinical studies on a variety of combination treatments have shown beneficial outcomes, yet further research is needed to understand the potential of combination therapy and its diverse strategies.

Role of Altered Metabolic Microenvironment in Osteolytic Metastasis

Metastatic bone disease is generally incurable and leads to pathological fractures, pain, hypercalcemia, spinal cord compression and decreased mobility. The skeleton is the major site of bone metastases from solid cancers, including breast and prostate carcinoma. Bone metastasis is facilitated by activation of bone-resorbing osteoclasts, terminally differentiated multinucleated cells formed by fusion from monocytic precursors. Cancer cells are known to produce specific factors that stimulate osteoclast differentiation and function. Of interest, cancer cells are also known to alter their own bioenergetics increasing the use of glycolysis for their survival and function. Such change in energy utilization by cancer cells would result in altered levels of cell-permeable metabolites, including glucose, lactate, and pyruvate. Osteoclast resorption is energy-expensive, and we have previously demonstrated that during differentiation osteoclasts actively adapt to their bioenergetics microenvironment. We hypothesize that altered bioenergetics state of cancer cells will also modify the bioenergetics substrate availability for the tissue-resident bone cells, potentially creating a favorable milieu for pathological osteolysis. The goals of this review are to analyze how metastasizing cancer cells change the availability of energy substrates in bone microenvironment; and to assess how the altered bioenergetics may affect osteoclast differentiation and activity.

Randomized phase II trial of neoadjuvant everolimus in patients with high-risk localized prostate cancer

Background Despite definitive local therapy, patients with high-risk prostate cancer have a significant risk for local and distant failure. To date, no systemic therapy given prior to surgery has been shown to improve outcomes. The phosphatidilinositol 3-kinase/AKT/mTOR pathway is commonly dysregulated in men with prostate cancer. We sought to determine the clinical efficacy and safety of the mTOR/TORC1 inhibitor everolimus in men with high-risk prostate cancer undergoing radical prostatectomy. Methods This is a randomized phase II study of everolimus at two different doses (5 and 10 mg daily) given orally for 8 weeks before radical prostatectomy in men with high-risk prostate cancer. The primary endpoint was the pathologic response (histologic P0, margin status, extraprostatic extension) and surgical outcomes. Secondary endpoints included changes in serum PSA level and treatment effects on levels of expression of mTOR, p4EBP1, pS6 and pAKT. Results Seventeen patients were enrolled: nine at 10 mg dose and eight at 5 mg dose. No pathologic complete responses were observed and the majority of patients (88%) had an increase in their PSA values leading to this study being terminated early due to lack of clinical efficacy. Treatment-related adverse events were similar to those previously reported with the use of everolimus in other solid tumors and no additional surgical complications were observed. A significant decrease in the expression of p4EBP1 was noted in prostatectomy samples following treatment. Conclusions Neoadjuvant everolimus given at 5 mg or 10 mg daily for 8 weeks prior to radical prostatectomy did not impact pathologic responses and surgical outcomes of patients with high-risk prostate cancer. Trial registration NCT00526591 .

Everolimus (RAD001) sensitizes prostate cancer cells to docetaxel by down-regulation of HIF-1α and sphingosine kinase 1

Resistance to docetaxel is a key problem in current prostate cancer management. Sphingosine kinase 1 (SK1) and phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathways have been implicated in prostate cancer chemoresistance. Here we investigated whether their combined targeting may re-sensitize prostate cancer cells to docetaxel.In hormone-insensitive PC-3 and DU145 prostate cancer cells the mTOR inhibitor everolimus (RAD001) alone did not lead to significant cell death, however, it strongly sensitized cells to low levels (5 nM) of docetaxel. We show that mTOR inhibition has led to a decrease in hypoxia-inducible factor-1α (HIF-1α) protein levels and SK1 mRNA. HIF-1α accumulation induced by CoCl2 has led to a partial chemoresistance to RAD001/docetaxel combination. SK1 overexpression has completely protected prostate cancer cells from RAD001/docetaxel effects. Using gene knockdown and CoCl2 treatment we showed that SK1 mRNA expression is downstream of HIF-1α. In a human xenograft model in nude mice single RAD001 and docetaxel therapies induced 23% and 15% reduction in prostate tumor volume, respectively, while their combination led to a 58% reduction. RAD001 alone or in combination with docetaxel has suppressed intratumoral mTOR and SK1 signaling, however as evidenced by tumor size, it required docetaxel for clinical efficacy. Combination therapy was well tolerated and had similar levels of toxicity to docetaxel alone.Overall, our data demonstrate a new mechanism of docetaxel sensitization in prostate cancer. This provides a mechanistic basis for further clinical application of RAD001/docetaxel combination in prostate cancer therapy.

Impact of Phosphoproteomics in the Era of Precision Medicine for Prostate Cancer

Prostate cancer is the most common malignancy in men in the United States. While androgen deprivation therapy results in tumor responses initially, there is relapse and progression to metastatic castration-resistant prostate cancer. Currently, all prostate cancer patients receive essentially the same treatment, and there is a need for clinically applicable technologies to provide predictive biomarkers toward personalized therapies. Genomic analyses of tumors are used for clinical applications, but with a paucity of obvious driver mutations in metastatic castration-resistant prostate cancer, other applications, such as phosphoproteomics, may complement this approach. Immunohistochemistry and reverse phase protein arrays are limited by the availability of reliable antibodies and evaluates a preselected number of targets. Mass spectrometry-based phosphoproteomics has been used to profile tumors consisting of thousands of phosphopeptides from individual patients after surgical resection or at autopsy. However, this approach is time consuming, and while a large number of candidate phosphopeptides are obtained for evaluation, limitations are reduced reproducibility, sensitivity, and precision. Targeted mass spectrometry can help eliminate these limitations and is more cost effective and less time consuming making it a practical platform for future clinical testing. In this review, we discuss the use of phosphoproteomics in prostate cancer and other clinical cancer tissues for target identification, hypothesis testing, and possible patient stratification. We highlight the majority of studies that have used phosphoproteomics in prostate cancer tissues and cell lines and propose ways forward to apply this approach in basic and clinical research. Overall, the implementation of phosphoproteomics via targeted mass spectrometry has tremendous potential to aid in the development of more rational, personalized therapies that will result in increased survival and quality of life enhancement in patients suffering from metastatic castration-resistant prostate cancer.

Bone-Targeted Therapies in Cancer-Induced Bone Disease

Cancer-induced bone disease is a major source of morbidity and mortality in cancer patients. Thus, effective bone-targeted therapies are essential to improve disease-free, overall survival and quality of life of cancer patients with bone metastases. Depending of the cancer-type, bone metastases mainly involve the modulation of osteoclast and/or osteoblast activity by tumour cells. To inhibit metastatic bone disease effectively, it is imperative to understand its underlying mechanisms and identify the target cells for therapy. If the aim is to prevent bone metastasis, it is essential to target not only bone metastatic features in the tumour cells, but also tumour-nurturing bone microenvironment properties. The currently available bone-targeted agents mainly affect osteoclasts, inhibiting bone resorption (e.g. bisphosphonates, denosumab). Some agents targeting osteoblasts begin to emerge which target osteoblasts (e.g. romosozumab), activating bone formation. Moreover, certain drugs initially thought to target only osteoclasts are now known to have a dual action (activating osteoblasts and inhibiting osteoclasts, e.g. proteasome inhibitors). This review will focus on the evolution of bone-targeted therapies for the treatment of cancer-induced bone disease, summarizing preclinical and clinical findings obtained with anti-resorptive and bone anabolic therapies.

Generation of Prostate Cancer Patient-Derived Xenografts to Investigate Mechanisms of Novel Treatments and Treatment Resistance

Treatment advances lead to survival benefits of patients with advanced prostate cancer. These treatments are highly efficacious in a subset of patients; however, similarly to other cancers, after initial responses the tumors develop resistance (acquired resistance) and the patients succumb to the disease. Furthermore, there is a subset of patients who do not respond to the treatment at all (de novo resistance). Preclinical testing using patient-derived xenografts (PDXs) has led to successful drug development, and PDXs will continue to provide valuable resources to generate clinically relevant data with translational potential. PDXs demonstrate tumor heterogeneity observed in patients, preserve tumor-microenvironment architecture, and provide clinically relevant treatment responses. In view of the evolving biology of the advanced prostate cancer associated with new treatments, PDXs representing these new tumor phenotypes are urgently needed for the study of treatment responses and resistance. In this chapter, we describe methodologies used to establish prostate cancer PDXs and use of these PDXs to study de novo and acquired resistance.

Gorham-Stout Disease Successfully Treated With Sirolimus and Zoledronic Acid Therapy

Gorham-Stout disease is a life-threatening disorder often manifested by lymphatic malformation and osteolysis. Unfortunately, available therapies are not uniformly effective and often carry substantial morbidity. We report an 18-year-old male with Gorham-Stout disease manifested by lytic rib lesions and an intractable pleural effusion that responded dramatically to the combination of the mammalian target of rapamycin (mTOR) inhibitor sirolimus and the aminobisphosphonate zoledronic acid after failing interferon therapy. This tolerable therapeutic combination has demonstrated synergism in preclinical cancer models and merits further study in vascular anomalies.

A phase I study of everolimus and docetaxel in patients with castration-resistant prostate cancer

BACKGROUND

The PTEN tumor suppressor is frequently lost in CRPC, with activation of Akt-mTOR signaling, driving growth. We conducted a phase I trial of the mTOR inhibitor, everolimus, and docetaxel in CRPC.

PATIENTS AND METHODS

Eligible patients had progressive, metastatic, chemotherapy-naive CRPC. Patients received everolimus 10 mg daily for 2 weeks and underwent a restaging FDG-PET/computed tomography scan. Patient cohorts were subsequently treated at 3 dose levels of everolimus with docetaxel: 5 mg to 60 mg/m(2), 10 mg to 60 mg/m(2), and 10 mg to 70 mg/m(2). The primary end point was the safety and tolerability of combination therapy.

RESULTS

Accrual was 4 patients at level 1, 3 patients at level 2, and 8 patients at level 3. Common toxicities were hematologic and fatigue. Serum concentrations of everolimus when administered with docetaxel were 1.5 to 14.8 ng/mL in patients receiving 5 mg everolimus and 4.5 to 55.4 ng/mL in patients receiving 10 mg everolimus. Four patients had partial metabolic response (PMR) using FDG-PET, 12 had stable metabolic disease, and 2 had progressive metabolic disease after a 2-week treatment with everolimus alone. Five of 12 evaluable patients experienced a prostate-specific antigen (PSA) reduction ≥ 50% during treatment with everolimus together with docetaxel. All 4 patients with a PMR according to PET imaging experienced a PSA reduction in response to everolimus with docetaxel, and 3 of 4 had PSA declines ≥ 50%.

CONCLUSION

Everolimus 10 mg daily and docetaxel 60 mg/m(2) was safe in CRPC patients and these were the recommended doses in combination. FDG-PET response might serve as a biomarker for target inhibition by mTOR inhibitors.

Non-invasive molecular imaging for preclinical cancer therapeutic development

Molecular and non-invasive imaging are rapidly emerging fields in preclinical cancer drug discovery. This is driven by the need to develop more efficacious and safer treatments, the advent of molecular-targeted therapeutics, and the requirements to reduce and refine current preclinical in vivo models. Such bioimaging strategies include MRI, PET, single positron emission computed tomography, ultrasound, and optical approaches such as bioluminescence and fluorescence imaging. These molecular imaging modalities have several advantages over traditional screening methods, not least the ability to quantitatively monitor pharmacodynamic changes at the cellular and molecular level in living animals non-invasively in real time. This review aims to provide an overview of non-invasive molecular imaging techniques, highlighting the strengths, limitations and versatility of these approaches in preclinical cancer drug discovery and development.

Everolimus and zoledronic acid--a potential synergistic treatment for lung adenocarcinoma bone metastasis

Non-small-cell lung cancer (NSCLC) frequently metastasizes to bone. It is known that zoledronic acid is cytostatic to tumors, and everolimus, the inhibitor for mammalian target of the rapamycin, could inhibit many types of cancer. Herein, we evaluated the effect of zoledronic acid alone and in combination with everolimus on treating lung adenocarcinoma bone metastasis in vitro and in vivo. Mice treated with zoledronic acid in combination with everolimus had more apoptotic lung cancer cells and more cells were arrested in the G1/G0 phase. The phosphorylation of p70S6K was inhibited in the combination treatment group. Lung cancer cell invasion was also significantly inhibited in the group with combination treatment in vitro. Bone nuclear scans revealed more metastatic lesions in controls compared with those in the combination treatment group. Bone scans and radiographic images indicated that combination therapy significantly reduced bone metastasis. The moderate survival rate suggested that the drug combination was synergistic, which can delay NSCLC bone metastasis and prolong survival in vivo.

Targeting bone metastatic cancer: Role of the mTOR pathway

One of the great challenges of cancer medicine is to develop effective treatments for bone metastatic cancer. Most patients with advanced solid tumors will develop bone metastasis and will suffer from skeletal related events associated with this disease. Although some therapies are available to manage symptoms derived from bone metastases, an effective treatment has not been developed yet. The mammalian target of rapamycin (mTOR) pathway regulates cell growth and survival. Alterations in mTOR signaling have been associated with pathological malignancies, including bone metastatic cancer. Inhibition of mTOR signaling might therefore be a promising alternative for bone metastatic cancer management. This review summarizes the current knowledge on mTOR pathway signaling in bone tissue and provides an overview on the known effects of mTOR inhibition in bone cancer, both in in vitro and in vivo models.

Phase II study of docetaxel in combination with everolimus for second- or third-line therapy of advanced non-small-cell lung cancer

We conducted a phase II study of docetaxel in combination with everolimus, a mammalian target of rapamycin (mTOR) inhibitor, for salvage therapy of advanced non-small-cell lung cancer (NSCLC) based on promising preclinical and early-phase clinical data. Patients with advanced-stage NSCLC treated with one or two previous systemic therapy regimens were given docetaxel (60 mg/m) and everolimus (5 mg orally once daily on days 1-19) every 3 weeks. Archived tumor specimens were evaluated for markers of mTOR pathway activation (total and phosphorylated mTOR, Akt, S6, eIF4e, and 4EBP1). Twenty-eight patients were enrolled (median age: 62 years; male: 13; Caucasians: 19; adenocarcinoma: 20; performance status 0, 3; performance status 1, 23; 1 previous regimen, 16). A median of 3.5 cycles of therapy was administered. Two patients experienced partial response and 15 had stable disease (clinical benefit rate, 70%). The 6-month progression-free survival rate was 5%, and the median overall survival was 9.6 months. Low pAkt expression correlated with clinical benefit rate (p = 0.01) but not with progression-free survival or overall survival. The combination of everolimus and docetaxel was tolerated well, but the efficacy was relatively modest in an unselected population of patients with NSCLC.

A phase II trial of temsirolimus in men with castration-resistant metastatic prostate cancer

BACKGROUND

Phosphatase and tensin homologue (PTEN) loss is common in advanced prostate cancer, leading to constitutive activation of the PI3 kinase pathway. Temsirolimus blocks mammalian target of rapamycin (mTOR)/target of rapamycin complex 1 (TORC1), a key signaling node in this pathway; its activity in men with advanced castration-resistant metastatic prostate cancer (mCRPC) is unknown.

METHODS

We conducted a single-arm trial of weekly intravenous temsirolimus administration in men with chemorefractory mCRPC who had ≥ 5 circulating tumor cells (CTCs) at baseline. The primary end point was the change in CTCs at 8 weeks; secondary end points were composite progression-free survival (PFS) (excluding prostate-specific antigen [PSA]), PSA and radiographic response rates, safety, and survival. At PSA/CTC progression, an anti-androgen could be added while continuing temsirolimus.

RESULTS

Eleven patients were accrued out of a planned 20; the trial was stopped prematurely because of lack of efficacy/feasibility. Median age was 61 years, with 55% African-Americans and 36% Caucasian patients. Median baseline PSA level was 390 ng/dL, median baseline number of CTCs was 14 cells; 50% of patients had pain, and 63% had undergone ≥ 2 previous chemotherapy regimens. Median CTC decline was 48% and 3 patients experienced decline in CTCs to < 5. However, 73% of men had a persistently unfavorable number of CTCs (≥ 5) and only 1 patient had a ≥ 30% PSA decline. Median PFS was 1.9 months (95% confidence interval [CI], 0.9-3.1) and median overall survival (OS) was 8.8 months (95% CI, 3.1-15.6). Toxicities included grade 4 hypophosphatemia and central nervous system (CNS) hemorrhage, and frequent grade 3 fatigue, anemia, stomatitis, hypokalemia, weakness, and hyperglycemia.

CONCLUSION

Temsirolimus lacked sufficient clinical activity in men with mCRPC, despite transient CTC improvements in some men. Future studies should focus on combination approaches or novel PI3K pathway inhibitors.

Targeting the PI3K/Akt/mTOR pathway in castration-resistant prostate cancer

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is a key signaling pathway that has been linked to both tumorigenesis and resistance to therapy in prostate cancer and other solid tumors. Given the significance of the PI3K/Akt/mTOR pathway in integrating cell survival signals and the high prevalence of activating PI3K/Akt/mTOR pathway alterations in prostate cancer, inhibitors of this pathway have great potential for clinical benefit. Here, we review the role of the PI3K/Akt/mTOR pathway in prostate cancer and discuss the potential use of pathway inhibitors as single agents or in combination in the evolving treatment landscape of castration-resistant prostate cancer.

Phase 2 trial of single-agent everolimus in chemotherapy-naive patients with castration-resistant prostate cancer (SAKK 08/08)

BACKGROUND

The phosphatase and tensin homolog (PTEN) tumor suppressor gene is deregulated in many advanced prostate cancers, leading to activation of the phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway and thus increased cell survival.

OBJECTIVE

To evaluate everolimus, an inhibitor of mTOR, in patients with metastatic castration-resistant prostate cancer (mCRPC), and to explore potentially predictive serum biomarkers by proteomics, the significance of PTEN status in tumor tissue, and the impact of everolimus on immune cell subpopulations and function.

DESIGN, SETTING, AND PARTICIPANTS

A total of 37 chemotherapy-naive patients with mCRPC and progressive disease were recruited to this single-arm phase 2 trial (ClinicalTrials.gov identifier NCT00976755).

INTERVENTION

Everolimus was administered continuously at a dose of 10mg daily.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary end point was progression-free survival (PFS) at 12 wk defined as the absence of prostate-specific antigen (PSA), radiographic progression, or clinical progression. Groups were compared using Wilcoxon rank-sum tests or Fisher exact tests for continuous and discrete variables, respectively. Time-to-event end points were analyzed using the Kaplan-Meier method and univariate Cox regression.

RESULTS AND LIMITATIONS

A total of 13 patients (35%; 95% confidence interval, 20-53) met the primary end point. Confirmed PSA response ≥50% was seen in two (5%), and four further patients (11%) had a PSA decline ≥30%. Higher serum levels of carboxypeptidase M and apolipoprotein B were predictive for reaching the primary end point. Deletion of PTEN was associated with longer PFS and response. Treatment was associated with a dose-dependent decrease of CD3, CD4, and CD8 T lymphocytes and CD8 proliferation and an increase in regulatory T cells. Small sample size was the major limitation of the study.

CONCLUSIONS

Everolimus activity in unselected patients with mCRPC is moderate, but PTEN deletion could be predictive for response. Several serum glycoproteins were able to predict PFS at 12 wk. Prospective validation of these potential biomarkers is warranted.

TRIAL REGISTRATION

This study is registered with ClinicalTrials.gov with the identifier NCT00976755. Results of this study were presented in part at the 47th Annual Meeting of the American Society of Clinical Oncology (June 3-7, 2011; Chicago, IL, USA) and the annual meeting of the German, Austrian, and Swiss Societies for Oncology and Hematology (September 30-October 4, 2011; Basel, Switzerland).

Recent advances in prostate development and links to prostatic diseases

The prostate is a branched ductal-acinar gland that is part of the male reproductive tract. Prostate development depends upon the integration of steroid hormone signals, paracrine interactions between the stromal and epithelial tissue layers, and the actions of cell autonomous factors. Several genes and signaling pathways are known to be required for one or more steps of prostate development including epithelial budding, duct elongation, branching morphogenesis, and/or cellular differentiation. Recent progress in the field of prostate development has included the application of genome-wide technologies including serial analysis of gene expression, expression profiling microarrays, and other large-scale approaches to identify new genes and pathways that are essential for prostate development. The aggregation of experimental results into online databases by organized multilab projects including the Genitourinary Developmental Molecular Atlas Project has also accelerated the understanding of molecular pathways that function during prostate development and identified links between prostate anatomy and molecular signaling. Rapid progress has also recently been made in understanding the nature and role of candidate stem cells in the developing and adult prostate. This has included the identification of putative prostate stem cell markers, lineage tracing, and organ reconstitution studies. However, several issues regarding their origin, precise nature, and possible role(s) in disease remain unresolved. Nevertheless, several links between prostatic developmental mechanisms and the pathogenesis of prostatic diseases including benign prostatic hyperplasia and prostate cancer have led to recent progress on targeting developmental pathways as therapeutic strategies for these diseases.

Everolimus combined with cisplatin has a potential role in treatment of urothelial bladder cancer

Cisplatin (CDDP)-based chemotherapy is a commonly treatment for advanced urothelial carcinoma. However, episodes of cisplatin resistance have been referenced. Recently it has been reported that everolimus (RAD001) could have an important role to play in bladder-cancer treatment and that mTOR inhibitors may restore chemosensitivity in resistant tumours. The aim of this study was to assess RAD001 in vitro ability to enhance CDDP cytotoxicity in three human bladder-cancer cell lines. Over the course of 72h, the cells were exposed to different concentrations of CDDP and RAD001, isolated or combined. Treatment with CDDP statistically (P<0.05) decreased cell proliferation in cell lines in a dose-dependent manner. The anti-proliferative activity of CDDP used in combination with RAD001 was statistically significant (P<0.05) in the cell lines at all concentrations tested. RAD001 had a therapeutic effect when used in combination with CDDP and could therefore be a useful anti-cancer drug combination for patients with bladder cancer.

Synergistic effects of histone deacetylase inhibitor in combination with mTOR inhibitor in the treatment of prostate carcinoma

The aim of this study was to elucidate whether the treatment of a prostate carcinoma cell line (LNCaP) and LNCaP-derived tumors with the histone deacetylase (HDAC) inhibitor valproate in combination with the mammalian target of rapamycin (mTOR) inhibitor temsirolimus resulted in synergistic effects on cell proliferation and tumor growth. LNCaP cells were treated with valproate, temsirolimus or a combination of both. The proliferation rates and the expression of key markers of tumorigenesis were evaluated. In in vivo experiments, LNCaP cells were implanted into immune-suppressed male nude mice. Mice were treated with valproate (per os), temsirolimus (intravenously) or with a combination of both. Tumor volumes were calculated and mRNA expression was quantified. The incubation of LNCaP cells with the combination of valproate and temsirolimus resulted in a decrease of cell proliferation with an additive effect of both drugs in comparison to the single treatment. In particular, the combined application of valproate and temsirolimus led to a significant upregulation of insulin-like growth factor-binding protein-3 (IGFBP-3), which mediates apoptosis and inhibits tumor cell proliferation. In the mouse model, we found no significant differences in tumor growth between the different treatment arms but immunohistological analyses showed that tumors treated with a combination of valproate and temsirolimus, but not with the single drugs alone, exhibited a significant lower proliferation capacity.

Safety and preliminary efficacy analysis of the mTOR inhibitor ridaforolimus in patients with taxane-treated, castration-resistant prostate cancer

BACKGROUND

Few options are available after taxane-based therapy in men with CRPC. Genetic alterations involving the mTOR pathway have been associated with CRPC development, raising the hypothesis that blocking mTOR signaling may be an effective targeted approach to treatment.

PATIENTS AND METHODS

In this open-label phase II study, the mTOR inhibitor Ridaforolimus was administered at a dose of 50 mg intravenous once weekly to 38 patients with taxane-treated CRPC. The primary end point was best overall response according to modified Response Evaluation Criteria in Solid Tumors guidelines. Serum prostate-specific antigen levels were prospectively monitored as a biomarker for cancer activity.

RESULTS

No objective responses were observed, but 18 patients (47.4%) had stable disease as their best response. Based on progression-free survival analysis, median time to progression with Ridaforolimus was 28 days (95% confidence interval, 27-29). Eight patients (21.1%) had stable disease as their best overall prostate-specific antigen response. The median number of days from first to last dose was 109.5 days (range, 1-442 days). Ridaforolimus was generally well tolerated, with a safety profile similar to that observed in patients with advanced malignancies. The most common side effects were typically mild or moderate in severity.

CONCLUSIONS

Ridaforolimus was generally well tolerated. Treatment did not produce objective responses, but stable disease was observed in some patients with taxane-treated CRPC. Alternative treatment regimens, such as combination therapy with a taxane or in a maintenance treatment paradigm, should be considered for further evaluation in this patient population.

Emerging targeted therapies for castration-resistant prostate cancer

Until recently, few therapeutic options were available for patients with castration-resistant prostate cancer (CRPC). Since 2010, four new molecules with a demonstrated benefit (sipuleucel-T, cabazitaxel, abiraterone, and denosumab) have been approved in this setting, and to-date several other agents are under investigation in clinical trials. The purpose of this review is to present an update of targeted therapies for CRPC. Presented data are obtained from literature and congress reports updated until December 2011. Targeted therapies in advanced phases of clinical development include novel androgen signaling inhibitors, inhibitors of alternative signaling pathways, anti-angiogenic agents, inhibitors that target the bone microenvironment, and immunotherapeutic agents. Radium-223 and MDV3100 demonstrated a survival advantage in phase III trials and the road for their introduction in clinical practice is rapidly ongoing. Results are also awaited for phase III studies currently underway or planned with new drugs given as monotherapy (TAK-700, cabozantinib, tasquinimod, PROSTVAC-VF, ipilimumab) or in combination with docetaxel (custirsen, aflibercept, dasatinib, zibotentan). The optimal timing, combination, and sequencing of emerging therapies remain unknown and require further investigation. Additionally, the identification of novel markers of response and resistance to these therapies may better individualize treatment for patients with CRPC.

mTOR is a selective effector of the radiation therapy response in androgen receptor-positive prostate cancer

Ionizing radiation (IR) is used frequently in the management of multiple tumor types, including both organ-confined and locally advanced prostate cancer (PCa). Enhancing tumor radiosensitivity could both reduce the amount of radiation required for definitive treatment and improve clinical outcome. Androgen suppression therapy improves clinical outcomes when combined with radiation therapy but is associated with significant acute and chronic toxicities; hence, there is a clear need for alternative means to increase the therapeutic window of radiotherapy. Herein, it is demonstrated that the mammalian target of rapamycin (mTOR) inhibitors rapamycin (sirolimus) and temsirolimus limit both hormone therapy (HT)-sensitive and castration-resistant PCa (CRPC) cell proliferation as single agents and have a profound radiosensitization effect when used in combination with IR. Importantly, the observed radiosensitization was influenced by the treatment schedule, in which adjuvant administration of mTOR inhibitors was most effective in limiting PCa cell population doubling. This schedule-dependent influence on in vitro treatment outcome was determined to be the result of relative effects on the cell cycle kinetics. Finally, adjuvant administration of either mTOR inhibitor tested after IR significantly decreased clonogenic cell survival of both HT-sensitive and CRPC cells compared with IR alone. Taken together, these data demonstrate that inhibition of mTOR confers a radiosensitization phenotype that is dependent on relative cell cycle kinetics and provide a foundation for clinical assessment.

Everolimus enhances gemcitabine-induced cytotoxicity in bladder-cancer cell lines

The purpose of this study was to determine whether everolimus, a rapamycin derivative, might significantly enhance the cytotoxicity of gemcitabine, an antitumor drug, in two human bladder-cancer cell lines. Human bladder-cancer T24 and 5637 cells were incubated with gemcitabine and everolimus in a range of concentrations either alone or in combination for 72 h. Flow cytometry, comet assay, MTT method and optical microscopy were used to assess cell proliferation, cell cycle, DNA damage, and morphological alterations. Gemcitabine exerted an inhibitory effect on T24 and 5637 cell proliferation, in a concentration-dependent manner. Everolimus significantly reduced proliferation of 5637 bladder cancer cells (IC₃₀) at 1 μM), whereas T24 demonstrated marked resistance to everolimus treatment. A significant antiproliferative effect was obtained combining gemcitabine (100 nM) with everolimus (0.05-2 μM) with an arrest of cell cycle at S phase. Furthermore, an increase in frequency of DNA damage, apoptotic bodies, and apoptotic cells was observed when T24 and 5637 cancer cells were treated simultaneously with both drugs. Data show that in vitro combination produced a more potent antiproliferative effect when compared with single drugs.

Emerging therapeutic approaches in the management of metastatic castration-resistant prostate cancer

Although treatment options for men with castration-resistant prostate cancer (CRPC) have improved with the recent and anticipated approvals of novel immunotherapeutic, hormonal, chemotherapeutic and bone-targeted agents, clinical benefit with these systemic therapies is transient and survival times remain unacceptably short. Thus, we devote the second section of this two-part review to discussing emerging therapeutic paradigms and research strategies that are entering phase II and III clinical testing for men with metastatic CRPC. We will discuss a range of emerging hormonal, immunomodulatory, antiangiogenic, epigenetic and cell survival pathway inhibitors in current clinical trials, with an emphasis on how these therapies may complement our existing treatment options.

Future directions in castrate-resistant prostate cancer therapy

Although several new therapies have recently become available for the treatment of castrate-resistant prostate cancer (CRPC), the disease remains universally incurable and demands novel therapeutic approaches. To this end, great strides have been made in our understanding of the biologic and molecular mechanisms driving prostate cancer growth and progression in the past few years, resulting in widespread clinical investigation of numerous new targeted therapies. This review will highlight some of the key therapeutic agents that (in the opinion of the authors) may have the largest effect on the future management of CRPC, with a focus on both molecular targets and clinical trial design. These agents include angiogenesis inhibitors, mTOR pathway inhibitors, apoptosis-inducing drugs, IGF pathway inhibitors, Src family inhibitors, Hedgehog pathway antagonists, epigenetic therapies, PARP inhibitors, and prodrug approaches. The future of CRPC therapy appears brighter than ever before.

Recent developments in prostate cancer biomarker research: therapeutic implications

This review aims to present an overview of recent clinical trials targeting biomarkers in advanced prostate cancer. We searched ClinicalTrials.gov for early phase clinical trials on treatments of prostate cancer that have been recently completed, are ongoing or are actively recruiting participants. Drug targets and their mechanism of actions were assessed and summarized. Trials were categorized according to prostate cancer biomarkers that have potential as therapeutic targets. A total of 19 new therapeutic agents for the treatment of prostate cancer are included in this review. Trials are summarized according to the targeted biomarkers and are categorized into five therapeutic approaches: prostate cancer vaccine, epigenetic therapy, pro-apoptotic agents, prostate cancer antibodies and anti-angiogenesis approach. Some of the therapeutic agents reviewed showed promising results, warranting further investigation in late phase clinical trials. Recent novel prostate cancer biomarkers that made it through clinical trials and their relevance as drug targets are summarized. This review emphasizes the importance of specific prostate cancer biomarkers and their potentials as targets of the disease. Some clinical trials of targeted treatments in prostate cancer show promising results. Better understanding of disease mechanisms should potentially lead to more specific treatments for individual patients.

Targeting autophagy during cancer therapy to improve clinical outcomes

Autophagy is a catabolic process that turns over long-lived proteins and organelles and contributes to cell and organism survival in times of stress. Current cancer therapies including chemotherapy and radiation are known to induce autophagy within tumor cells. This is therefore an attractive process to target during cancer therapy as there are safe, clinically available drugs known to both inhibit and stimulate autophagy. However, there are conflicting positive and negative effects of autophagy and no current consensus on how to manipulate autophagy to improve clinical outcomes. Careful and rigorous evaluation of autophagy with a focus on how to translate laboratory findings into relevant clinical therapies remains an important aspect of improving clinical outcomes in patients with malignant disease.

Castration-resistant prostate cancer: targeted therapies and individualized treatment

Various molecular mechanisms have been implicated in the progression from hormone-sensitive to castration-resistant prostate cancer (CRPC). Novel targeted agents to treat CRPC have been developed that inhibit either androgen receptor (AR)-mediated signaling (AR antagonists and inhibitors of androgen synthesis) or non-AR-mediated signaling (inhibitors of Src, mammalian target of rapamycin, chaperone proteins, insulin-like growth factor-1 receptor, vascular endothelial growth factor, and endothelin-A receptor) pathways. However, variable efficacy has been observed in clinical trials, most likely because of the biologic heterogeneity of CRPC. To account for potential differences in disease biology, a more individualized approach to treatment, based on genomic and/or proteomic analyses of individual tumors, is being investigated. By identifying tumors with a characteristic molecular subtype and assigning treatment accordingly, it is hoped that a higher proportion of patients will benefit from targeted therapy. Additionally, lessons learned through the application of these technologies to prostate cancer may subsequently influence therapeutic development in other solid tumors.

Methodology to investigate androgen-sensitive and castration-resistant human prostate cancer xenografts in preclinical setting

Understanding the biology of prostate cancer and the roles of androgen receptor in prostate cancer progression is essential to the development of novel therapeutic strategies to effectively attack and eradicate this disease. Preclinical, in vivo, studies are critical to further evaluate potential clinical relevance of in vitro findings. Ideally, in vivo studies should employ models that mimic characteristics of prostate cancer from early diagnosis through the period of castration-resistant metastases. In this chapter we describe methodologies used to grow human prostate cancer xenografts in mice. In this setting, roles of androgen receptor signaling in prostate cancer progression and efficacy of novel treatment modalities, including those affecting androgen receptor signaling, can be investigated.

Phase 1 and pharmacokinetic study of everolimus, a mammalian target of rapamycin inhibitor, in combination with docetaxel for recurrent/refractory nonsmall cell lung cancer

BACKGROUND

Everolimus is a novel inhibitor of the mammalian target of rapamycin pathway, which is aberrantly activated in nonsmall cell lung cancer (NSCLC). The authors conducted a phase 1 and pharmacokinetic study of everolimus and docetaxel for recurrent NSCLC.

METHODS

Patients with advanced stage NSCLC and progression after prior platinum-based chemotherapy were eligible. Sequential cohorts were treated with escalating doses of docetaxel (Day 1) and everolimus (orally daily, Days 1-19) every 3 weeks. Pharmacokinetic sampling of everolimus and docetaxel was done in Cycle 1. The primary endpoint was determination of the recommended phase 2 doses of the combination.

RESULTS

Twenty-four patients were enrolled (median age, 62 years; women, 11; number of prior regimens, 1 [n=13], 2 [n=6], >or=3 [n=5]; Eastern Cooperative Oncology Group performance status, 0 [n=6], 1 [n=17]). The dose-limiting toxicities (DLTs) were fever with grade 3/4 neutropenia, grade 3 fatigue, and grade 3 mucositis. None of the 7 patients treated at the recommended phase 2 dose (docetaxel 60 mg/m2 and everolimus 5 mg daily) experienced DLT. Everolimus area under the concentration time curve (AUC) was not different with 60 or 75 mg/m2 docetaxel. Mean+/-standard deviation AUC-based accumulation factors for everolimus on Days 8 and 15 were 1.16+/-0.37 and 1.42+/-0.42, respectively. Docetaxel Day 1 half-life was 9.4+/-3.4 hours. Among 21 patients evaluable, 1 had a partial response, and 10 had disease stabilization.

CONCLUSIONS

The recommended phase 2 doses of docetaxel and everolimus for combination therapy are 60 mg/m2 and 5 mg orally daily, respectively. Promising anticancer activity has been noted.

Biomarker Development for the Clinical Activity of the mTOR Inhibitor Everolimus (RAD001): Processes, Limitations, and Further Proposals

The mTOR inhibitor everolimus (RAD001, Afinitor) is an orally active anticancer agent. Everolimus demonstrates growth-inhibitory activity against a broad range of tumor cell histotypes in vitro and has the capacity to retard tumor growth in preclinical tumor models in vivo through mechanisms directed against both the tumor cell and the solid tumor stroma components. These properties have rendered it to be a clinically active drug, with subsequent registration in renal cell carcinoma (Motzer et al. [2008]. Lancet372, 449-456) as well as showing strong potential as a combination partner (André F et al. [2008]. J Clin Oncol26. Abstract 1003). Although everolimus has a high specificity for its molecular target, the ubiquitous nature of mTOR and the multifactorial influence that mTOR signaling has on cell physiology have made studies difficult on the identification and validation of a biomarker set to predict and monitor drug sensitivity for clinical use. In this review, a summary of the preclinical and clinical data relevant to biomarker development for everolimus is presented, and the advantages and problems of current biomarkers are reviewed. In addition, alternative approaches to biomarker development are proposed on the basis of examples of a combination of markers and functional noninvasive imaging. In particular, we show how basal levels of pAKT and pS6 together could, in principle, be used to stratify patients for likely response to an mTOR inhibitor.

The role of docetaxel based therapy for prostate cancer in the era of targeted medicine

Docetaxel based chemotherapy has been shown to modestly extend life, relieve pain and improve the quality of life in patients with metastatic castration-resistant prostate cancer. Current trials are attempting to build on the backbone of docetaxel by combining it with novel biological agents. Trials are also investigating the role of docetaxel for earlier stages of prostate cancer. No standard second-line systemic therapy exists and such patients are candidates for clinical trials. The increased understanding of the mechanisms of progressive castration-resistant prostate cancer is being translated into an increasing pipeline of novel therapies.

New developments in the medical management of prostate cancer

Prostate cancer is a substantial public health burden and a leading cause of cancer-related morbidity and mortality in the United States despite the observation that annual prostate cancer-specific mortality rates have been declining during the previous decade. Although the reasons for this positive development are unclear, a combination of factors may have contributed. This update will review ongoing developments and summarize therapeutic advances in prostate cancer treatment on the basis of the current understanding of prostate cancer biology. Literature for this review was selected in 2009 by searching PubMed for the following keywords: prostatic neoplasms, castration, androgen receptor, hormonal, and chemotherapy. Emphasis is placed on published clinical studies in advanced prostate cancer therapeutics in the past 5 to 10 years. Also included in the review are novel hormonal agents targeting the androgen receptor currently in development for the treatment of advanced prostate cancer.

Hyaluronic acid-based hydrogels as 3D matrices for in vitro evaluation of chemotherapeutic drugs using poorly adherent prostate cancer cells

The current investigation aimed to develop a biomimetic, three-dimensional (3D) culture system for poorly adherent bone metastatic prostate cancer cells (C4-2B) for use as an in vitro platform for anti-cancer drug screening. To this end, hyaluronic acid (HA) derivatives carrying complementary aldehyde (HAALD) and hydrazide (HAADH) groups were synthesized and characterized. In situ encapsulation of C4-2B cells was achieved by simple mixing of HAALD and HAADH in the presence of the cells. Unlike two-dimensional (2D) monolayer culture in which cells adopt an atypical spread morphology, cells residing in the HA matrix formed distinct clustered structures which grew and merged, reminiscent of real tumors. Anti-cancer drugs added to the media surrounding the cell/gel construct diffused into the gel and killed the embedded cells. The HA hydrogel system was used successfully to test the efficacy of anti-cancer drugs including camptothecin, docetaxel, and rapamycin, alone and in combination, including specificity, dose and time responses. Responses of cells to anti-neoplastics differed between the 3D HA hydrogel and 2D monolayer systems. We suggest that the data obtained from 3D HA systems is superior to that from conventional 2D monolayers as the 3D system better reflects the bone metastatic microenvironment of the cancer cells.

Dasatinib inhibits the growth of prostate cancer in bone and provides additional protection from osteolysis

Background:

Dasatinib is a small molecule kinase inhibitor that has recently been shown to inhibit Src family kinases (SFK) and also has activity against CaP. Of importance to metastatic CaP, which frequently metastasises to bone, SFK are also vital to the regulation of bone remodelling. We sought to determine the ability of dasatinib to inhibit growth of CaP in bone.

Methods:

C4-2B CaP cells were injected into tibiae of SCID mice and treated with dasatinib, alone or in combination with docetaxel. Serum prostate-specific antigen levels, bone mineral density, radiographs and histology were analysed.

Results:

Treatment with dasatinib alone significantly lowered sacrifice serum prostate-specific antigen levels compared to control, 2.3±0.4 vs 9.2±2.1 (P=0.004). Combination therapy improved efficacy over dasatinib alone (P=0.010). Dasatinib increased bone mineral density in tumoured tibiae by 25% over control tumoured tibiae (P<0.001).

Conclusion:

Dasatinib inhibits growth of C4-2B cells in bone with improved efficacy when combined with docetaxel. Additionally, dasatinib inhibits osteolysis associated with CaP. These data support further study of dasatinib in clinical trials for men with CaP bone metastases.

Targeted therapy for advanced prostate cancer: inhibition of the PI3K/Akt/mTOR pathway

A large number of novel therapeutics is currently undergoing clinical evaluation for the treatment of prostate cancer, and small molecule signal transduction inhibitors are a promising class of agents. These inhibitors have recently become a standard therapy in renal cell carcinoma and offer significant promise in prostate cancer. Through an understanding of the key pathways involved in prostate cancer progression, a rational drug design can be aimed at the molecules critical to cellular signaling. This may enable administration of selective therapies based on the expression of molecular targets, more appropriately individualizing treatment for prostate cancer patients. One pathway with a prominent role in prostate cancer is the PI3K/Akt/mTOR pathway. Current estimates suggest that PI3K/Akt/mTOR signaling is upregulated in 30-50% of prostate cancers, often through loss of PTEN. Molecular changes in the PI3K/Akt/mTOR signaling pathway have been demonstrated to differentiate benign from malignant prostatic epithelium and are associated with increasing tumor stage, grade, and risk of biochemical recurrence. Multiple inhibitors of this pathway have been developed and are being assessed in the laboratory and in clinical trials, with much attention focusing on mTOR inhibition. Current clinical trials in prostate cancer are assessing efficacy of mTOR inhibitors in combination with multiple targeted or traditional chemotherapies, including bevacizumab, gefitinib, and docetaxel. Completion of these trials will provide substantial information regarding the importance of this pathway in prostate cancer and the clinical implications of its targeted inhibition. In this article we review the data surrounding PI3K/Akt/mTOR inhibition in prostate cancer and their clinical implications.