A phase II study of sorafenib in patients with chemo-naive castration-resistant prostate cancer

Evaluation of the therapeutic potential of masitinib and expression of its specific targets c-Kit, PDGFR-α, PDGFR-β, and Lyn in canine prostate cancer cell lines

Canine prostate cancer is classified into adenocarcinoma, transitional cell carcinoma with prostatic involvement, and mixed forms. Early metastatic spread leads to poor prognosis and limited treatment options. Masitinib is approved for the treatment of canine mast cell tumours and inhibits tyrosine kinase c-Kit, tyrosine-protein kinase Lyn (Lyn), and platelet-derived growth factor receptors alpha and beta (PDGFR-α, PDGFR-β), which are known to be expressed in canine prostate cancer. The aim of this study was to evaluate masitinib in an in vitro model consisting of cell lines from primary prostate adenocarcinoma, the associated lymph node metastasis of the same patient, and transitional cell carcinoma. To assess the suitability of the model system, the targets of masitinib were investigated by immunocytochemistry in the cell lines and by immunohistochemistry in the respective formalin-fixed, paraffin-embedded (FFPE) original neoplastic tissue. After exposure to masitinib, cell viability, cell count, apoptosis induction, and protein expression of c-Kit, Lyn, PDGFR-α, and PDGFR-β were assessed. To hedge the efficacy, two application protocols of masitinib (single application or 12-h double-dose regimen) were compared. Immunocytochemical and immunohistochemical analysis revealed increased Lyn, PDGFR-α, and PDGFR-β expression in cell lines and FFPE original neoplastic tissue compared to healthy prostate tissue. Masitinib exposure increased apoptosis, while the cell counts and cell viability decreased in a dose- and application interval-dependent manner, with increased impact in the 12-h double-dose regimen. These in vitro effects of masitinib in canine prostate cancer and associated metastasis support further in vivo research and modifications of the clinical treatment protocol in future studies.

Angiogenesis and Anti-Angiogenic Treatment in Prostate Cancer: Mechanisms of Action and Molecular Targets

Prostate cancer (PC) is the most common cancer in men and the second leading cause of cancer-related death worldwide. Many therapeutic advances over the last two decades have led to an improvement in the survival of patients with metastatic PC, yet the majority of these patients still succumb to their disease. Antiagiogenic therapies have shown substantial benefits for many types of cancer but only a marginal benefit for PC. Ongoing clinical trials investigate antiangiogenic monotherapies or combination therapies. Despite the important role of angiogenesis in PC, clinical trials in refractory castration-resistant PC (CRPC) have demonstrated increased toxicity with no clinical benefit. A better understanding of the mechanism of angiogenesis may help to understand the failure of trials, possibly leading to the development of new targeted anti-angiogenic therapies in PC. These could include the identification of specific subsets of patients who might benefit from these therapeutic strategies. This paper provides a comprehensive review of the pathways involved in the angiogenesis, the chemotherapeutic agents with antiangiogenic activity, the available studies on anti-angiogenic agents and the potential mechanisms of resistance.

Angiogenesis Inhibition in Prostate Cancer: An Update

Prostate cancer (PCa), like all other solid tumors, relies on angiogenesis for growth, progression, and the dissemination of tumor cells to other parts of the body. Despite data from in vitro and in vivo preclinical studies, as well as human specimen studies indicating the crucial role played by angiogenesis in PCa, angiogenesis inhibition in clinical settings has not shown significant benefits to patients, thus challenging the inclusion and usefulness of antiangiogenic agents for the treatment of PCa. However, one of the apparent reasons why these antiangiogenic agents failed to meet expectations in PCa can be due to the choice of the antiangiogenic agents, because the majority of these drugs target vascular endothelial growth factor-A (VEGFA) and its receptors. The other relevant causes might be inappropriate drug combinations, the duration of treatment, and the method of endpoint determination. In this review, we will first discuss the role of angiogenesis in PCa growth and progression. We will then summarize the different angiogenic growth factors that influence PCa growth dynamics and review the outcomes of clinical trials conducted with antiangiogenic agents in PCa patients and, finally, critically assess the current status and fate of antiangiogenic therapy in this disease.

Dose-dependent regulation of mitochondrial function and cell death pathway by sorafenib in liver cancer cells

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and the fourth most frequent cause of cancer-related death worldwide. Sorafenib is the first line recommended therapy for patients with locally advanced/metastatic HCC. The low response rate is attributed to intrinsic resistance of HCC cells to Sorafenib. The potential resistance to Sorafenib-induced cell death is multifactorial and involves all hallmarks of cancer. However, the presence of sub-therapeutic dose can negatively influence the antitumoral properties of the drug. In this sense, the present study showed that the sub-optimal Sorafenib concentration (10 nM) was associated with activation of caspase-9, AMP-activated protein kinase (AMPK), sustained autophagy, peroxisome proliferator-activated receptor-coactivator 1α (PGC-1α) and mitochondrial function in HepG2 cells. The increased mitochondrial respiration by Sorafenib (10 nM) was also observed in permeabilized HepG2 cells, but not in isolated rat mitochondria, which suggests the involvement of an upstream component in this regulatory mechanism. The basal glycolysis was dose dependently increased at early time point studied (6 h). Interestingly, Sorafenib increased nitric oxide (NO) generation that played an inhibitory role in mitochondrial respiration in sub-therapeutic dose of Sorafenib. The administration of sustained therapeutic dose of Sorafenib (10 µM, 24 h) induced mitochondrial dysfunction and dropped basal glycolysis derived acidification, as well as increased oxidative stress and apoptosis in HepG2. In conclusion, the accurate control of the administered dose of Sorafenib is relevant for the potential prosurvival or proapoptotic properties induced by the drug in liver cancer cells.

Comparative prognostic implication of treatment response assessments in mCRPC: PERCIST 1.0, RECIST 1.1, and PSA response criteria

Accurate appraisal of treatment response in metastatic castrate-resistant prostate cancer (mCRPC) is challenging in view of remarkable tumor heterogeneity and the available choices among many established and novel therapeutic approaches. The purpose of this single-center prospective study was to evaluate the comparative prognostic utility of PERCIST 1.0 in predicting overall survival (OS) in patients with mCRPC compared to RECIST 1.1 and prostate-specific antigen (PSA)-based treatment response assessments.

Methods: Patients with mCRPC were prospectively enrolled if they were beginning systemic medical therapy or transitioning to new systemic therapy after not responding to a prior treatment. All patients underwent a baseline ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/ computed tomography (PET/CT) prior to the initiation of treatment and again 4 months after the start of therapy. Patients' responses to treatment at 4 months compared to baseline were evaluated with RECIST 1.1, PERCIST 1.0 and PSA response criteria. The associations between patients' response categories and OS were evaluated. OS was defined as the duration in time between the date of baseline PET/CT to death from any cause. Patients with different response status were compared with logrank tests. Survival probabilities were calculated using the Kaplan-Meier method.

Results: Patients with progressive disease by PSA response criteria at 4 months demonstrated significantly shorter OS (24-month OS probability: 18% ± 11%) compared to patients with stable disease, SD, (44% ± 19%, p=0.03) and complete response, CR, or partial response, PR, (53% ± 11%, p=0.03). RECIST 1.1 response criteria demonstrated a similar trend in OS, however no statistically significant differences were noted between patients with PD (25% ± 15%) compared to SD/non-CR, non-PD (54% ± 13%) and CR/PR (54% ± 14%) (p=0.13). PERCIST 1.0 criteria demonstrated significant differences in OS between responders, CMR/PMR (56% ± 12%), compared to SMD (38% ± 17%, p=0.03) and PMD (21% ± 10%, p=0.01). Patients with progressive disease by both PERICST 1.0 and PSA response criteria demonstrated significantly worse OS (24-month OS: 0%, 12-month OS: 31% ± 14%) compared to patients with progressive disease by either response criteria.

Conclusion: PERCIST 1.0 may provide significant prognostic information for patients with mCRPC undergoing systemic chemotherapy, particularly when incorporated with PSA treatment response criteria.

Molecular characterization of autophagic and apoptotic signaling induced by sorafenib in liver cancer cells

Sorafenib is the unique accepted molecular targeted drug for the treatment of patients in advanced stage of hepatocellular carcinoma. The current study evaluated cell signaling regulation of endoplasmic reticulum (ER) stress, c-Jun-N-terminal kinase (JNK), Akt, and 5'AMP-activated protein kinase (AMPK) leading to autophagy and apoptosis induced by sorafenib. Sorafenib induced early (3-12 hr) ER stress characterized by an increase of Ser51 P-eIF2α/eIF2α, C/EBP homologous protein (CHOP), IRE1α, and sXBP1, but a decrease of activating transcription factor 6 expression, overall temporally associated with the increase of Thr183,Tyr185 P-JNK1/2/JNK1/2, Thr172 P-AMPKα, Ser413 P-Foxo3a, Thr308 P-AKt/AKt and Thr32 P-Foxo3a/Foxo3a ratios, and reduction of Ser2481 P-mammalian target of rapamycin (mTOR)/mTOR and protein translation. This pattern was related to a transient increase of tBid, Bim EL , Beclin-1, Bcl-xL, Bcl-2, autophagy markers, and reduction of myeloid cell leukemia-1 (Mcl-1) expression. The progressive increase of CHOP expression, and reduction of Thr308 P-AKt/AKt and Ser473 P-AKt/AKt ratios were associated with the reduction of autophagic flux and an additional upregulation of Bim EL expression and caspase-3 activity (24 hr). Small interfering-RNA (si-RNA) assays showed that Bim, but not Bak and Bax, was involved in the induction of caspase-3 in sorafenib-treated HepG2 cells. Sorafenib increased autophagic and apoptotic markers in tumor-derived xenograft model. In conclusion, the early sorafenib-induced ER stress and regulation of JNK and AMPK-dependent signaling were related to the induction of survival autophagic process. The sustained drug treatment induced a progressive increase of ER stress and PERK-CHOP-dependent rise of Bim EL , which was associated with the shift from autophagy to apoptosis. The kinetic of Bim EL expression profile might also be related to the tight balance between AKt- and AMPK-related signaling leading to Foxo3a-dependent BIM EL upregulation.

Genitourinary tumours in the targeted therapies era: new advances in clinical practice and future perspectives

Genitourinary cancers represent a heterogeneous group of malignancies arising from genitourinary tract, and are responsible for almost 359 000 newly diagnosed cases and 58 420 related deaths in USA. Continuous advances in cancer genetics and genomics have contributed towards changing the management paradigms of these neoplasms. Neoangiogenesis, through the activation of the tyrosine-kinase receptors signalling pathways, represents the key mediator event in promoting tumour proliferation, differentiation, invasiveness and motility. In the last decade, several treatments have been developed with the specific aim of targeting different cell pathways that have been recognized to drive tumour progression. The following review attempts to provide a comprehensive overview of the literature, focusing on new advances in targeted therapies for genitourinary tumours. Furthermore, the promising results of the latest clinical trials and future perspectives will be discussed.

Targeting androgen-independent pathways: new chances for patients with prostate cancer?

Androgen deprivation therapy (ADT) is the mainstay treatment for advanced prostate cancer (PC). Most patients eventually progress to a condition known as castration-resistant prostate cancer (CRPC), characterized by lack of response to ADT. Although new androgen receptor signaling (ARS) inhibitors and chemotherapeutic agents have been introduced to overcome resistance to ADT, many patients progress because of primary or acquired resistance to these agents. This comprehensive review aims at exploring the mechanisms of resistance and progression of PC, with specific focus on alterations which lead to the activation of androgen receptor (AR)-independent pathways of survival. Our work integrates available clinical and preclinical data on agents which target these pathways, assessing their potential clinical implication in specific settings of patients. Given the rising interest of the scientific community in cancer immunotherapy strategies, further attention is dedicated to the role of immune evasion in PC.

Inefficiencies and Patient Burdens in the Development of the Targeted Cancer Drug Sorafenib: A Systematic Review

Failure in cancer drug development exacts heavy burdens on patients and research systems. To investigate inefficiencies and burdens in targeted drug development in cancer, we conducted a systematic review of all prelicensure trials for the anticancer drug, sorafenib (Bayer/Onyx Pharmaceuticals). We searched Embase and MEDLINE databases on October 14, 2014, for prelicensure clinical trials testing sorafenib against cancers. We measured risk by serious adverse event rates, benefit by objective response rates and survival, and trial success by prespecified primary endpoint attainment with acceptable toxicity. The first two clinically useful applications of sorafenib were discovered in the first 2 efficacy trials, after five drug-related deaths (4.6% of 108 total) and 93 total patient-years of involvement (2.4% of 3,928 total). Thereafter, sorafenib was tested in 26 indications and 67 drug combinations, leading to one additional licensure. Drug developers tested 5 indications in over 5 trials each, comprising 56 drug-related deaths (51.8% of 108 total) and 1,155 patient-years (29.4% of 3,928 total) of burden in unsuccessful attempts to discover utility against these malignancies. Overall, 32 Phase II trials (26% of Phase II activity) were duplicative, lacked appropriate follow-up, or were uninformative because of accrual failure, constituting 1,773 patients (15.6% of 11,355 total) participating in prelicensure sorafenib trials. The clinical utility of sorafenib was established early in development, with low burden on patients and resources. However, these early successes were followed by rapid and exhaustive testing against various malignancies and combination regimens, leading to excess patient burden. Our evaluation of sorafenib development suggests many opportunities for reducing costs and unnecessary patient burden in cancer drug development.

Dissecting major signaling pathways in prostate cancer development and progression: Mechanisms and novel therapeutic targets

Prostate cancer (PCa) is the most frequently diagnosed non-cutaneous malignancy and leading cause of cancer mortality in men. At the initial stages, prostate cancer is dependent upon androgens for their growth and hence effectively combated by androgen deprivation therapy (ADT). However, most patients eventually recur with an androgen deprivation-resistant phenotype, referred to as castration-resistant prostate cancer (CRPC), a more aggressive form for which there is no effective therapy presently available. The current review is an attempt to cover and establish an understanding of some major signaling pathways implicated in prostate cancer development and castration-resistance, besides addressing therapeutic strategies that targets the key signaling mechanisms.

Modulation of Autophagy by Sorafenib: Effects on Treatment Response

The multikinase inhibitor sorafenib is, at present, the only drug approved for the treatment of hepatocellular carcinoma (HCC), one of the most lethal types of cancer worldwide. However, the increase in the number of sorafenib tumor resistant cells reduces efficiency. A better knowledge of the intracellular mechanism of the drug leading to reduced cell survival could help to improve the benefits of sorafenib therapy. Autophagy is a bulk cellular degradation process activated in a broad range of stress situations, which allows cells to degrade misfolded proteins or dysfunctional organelles. This cellular route can induce survival or death, depending on cell status and media signals. Sorafenib, alone or in combination with other drugs is able to induce autophagy, but cell response to the drug depends on the complex integrative crosstalk of different intracellular signals. In cancerous cells, autophagy can be regulated by different cellular pathways (Akt-related mammalian target of rapamycin (mTOR) inhibition, 5′ AMP-activated protein kinase (AMPK) induction, dissociation of B-cell lymphoma 2 (Bcl-2) family proteins from Beclin-1), or effects of some miRNAs. Inhibition of mTOR signaling by sorafenib and diminished interaction between Beclin-1 and myeloid cell leukemia 1 (Mcl-1) have been related to induction of autophagy in HCC. Furthermore, changes in some miRNAs, such as miR-30α, are able to modulate autophagy and modify sensitivity in sorafenib-resistant cells. However, although AMPK phosphorylation by sorafenib seems to play a role in the antiproliferative action of the drug, it does not relate with modulation of autophagy. In this review, we present an updated overview of the effects of sorafenib on autophagy and its related activation pathways, analyzing in detail the involvement of autophagy on sorafenib sensitivity and resistance.

Kinase inhibitors and monoclonal antibodies in oncology: clinical implications

Molecularly targeted cancer therapies, such as small-molecule kinase inhibitors and monoclonal antibodies, constitute a rapidly growing and an important part of the oncology armamentarium. Unlike conventional (cytotoxic) chemotherapeutics, targeted therapies were designed to disrupt cancer cell pathogenesis at specific biological points essential for the development and progression of the tumour. These agents were developed to disrupt specific targets with the aim of minimizing treatment burden compared with conventional chemotherapy. Nevertheless the increasingly common use of targeted therapies has revealed some unanticipated, often clinically significant toxic effects, as well as compromising effective palliative and end-of-life management approaches. Although patients and clinicians welcome improvements in cancer prognosis, these changes can also impact patient quality-of-life. Therefore, as demand for oncology expertise increases, physicians need to apprise themselves of targeted therapies and their clinical implications, including drug-specific side effects, impact on quality of life, and cost issues, especially in relation to end-of-life care. This Review provides a useful summary and guide for professionals treating patients with malignant diseases.

Evaluation of in vivo responses of sorafenib therapy in a preclinical mouse model of PTEN-deficient of prostate cancer

Background

Despite recent advances in the treatment for advanced prostate cancer, outcomes remain poor. This lack of efficacy has prompted the development of alternative treatment strategies. In the present study we investigate the effects of the multikinase inhibitor sorafenib in a genetically engineered mouse model of prostate cancer and explore the rational combination with the mTOR inhibitor everolimus.

Methods

Conditional prostate specific PTEN-deficient knockout mice were utilized to determine the pharmacodynamic and chemopreventive effects of sorafenib. This mouse model was also used to examine the therapeutic efficacy of sorafenib alone or in combination with everolimus. Preclinical efficacy was assessed by comparing the reduction of tumor burden, proliferation, angiogenesis and the induction of apoptosis. Molecular responses were assessed by immunohistochemical, TUNEL and western blot assays.

Results

Pharmacodynamic analysis revealed that a single dose of sorafenib decreased activation of the PI3K/AKT/mTOR signaling axis at doses of 30–60 mg/kg, but activated JAK/STAT3 signaling. Levels of cleaved casapase-3 increased in a dose dependent manner. Chemoprevention studies showed that chronic sorafenib administration was capable of inhibiting tumor progression through the reduction of cancer cell proliferation, angiogenesis and the induction of apoptosis. In intervention models of established castration-naïve and castration-resistant prostate cancer, treatment with sorafenib provided modest but statistically insignificant reduction in tumor burden. However, sorafenib significantly inhibited cancer cell proliferation and MVD but had minimal effects on the induction of apoptosis. Interestingly, the administration of sorafenib increased the expression levels of the androgen receptor, p-GSK3β and p-ERK1/2 in castration-resistant prostate cancers. In both intervention models, combination therapy demonstrated a clear tendency of enhanced antitumor effects over monotherapy. Notably, the treatment combination of sorafenib and everolimus overcame therapeutic escape from single agent therapy in castration-resistant prostate cancers.

Conclusions

In summary, we provide insights into the molecular responses of sorafenib therapy in a clinically relevant model of prostate cancer and present preclinical evidence for the development of targeted treatment strategies based on the use of multikinase inhibitors in combination with mTOR inhibitors for the treatment of advanced prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0509-x) contains supplementary material, which is available to authorized users.

Randomized phase II study of nintedanib in metastatic castration-resistant prostate cancer postdocetaxel

This open-label, phase II trial assessed the efficacy and safety of two doses of nintedanib, a triple angiokinase inhibitor targeting vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor signaling, in patients with metastatic castration-resistant prostate cancer (mCRPC) following progression on docetaxel-based regimens. Patients were randomized to nintedanib 150 mg (arm A, n=40) or 250 mg (arm B, n=41) twice daily for 6 months unless disease progression or adverse events (AEs) led to discontinuation. The primary endpoint was the prostate-specific antigen (PSA) response rate (confirmed PSA decline of ≥20% from baseline). Eighty-one patients were enrolled. The PSA response rate was 0% (0/32) in arm A versus 11.1% (4/36) in arm B (P=0.12); 5.6% of patients (2/36) in arm B showed a PSA reduction of at least 50%. In arm B, the rate of PSA increase was significantly decelerated on treatment versus before treatment (P=0.002). The median progression-free survival was 73.5 and 76.0 days for arm A and arm B, respectively (P=0.3). AEs included gastrointestinal disorders, asthenia, hypertension, and reversible elevated transaminases. The incidence of drug-related serious AEs (no drug-related deaths) was 20.0% (arm A) and 24.4% (arm B). The primary endpoint was not met. Nintedanib (250 mg) showed only modest activity with manageable AEs in patients with mCRPC post-docetaxel.

Incidence and risk of xerosis with targeted anticancer therapies

BACKGROUND

Many targeted therapies used in the treatment of cancer can lead to the development of xerosis, but the incidence and relative risk of xerosis have not been ascertained.

OBJECTIVE

We conducted a systematic review and metaanalysis of clinical trials, to ascertain the incidence and risk of developing xerosis after taking anticancer drugs.

METHODS

The PubMed (1966-October 2013), Web of Science (January 1998-October 2013), and American Society of Clinical Oncology abstracts (2004-2013) databases were searched for clinical trials of 58 targeted agents. Results were calculated using random or fixed effects models.

RESULTS

The incidences of all- and high-grade xerosis were 17.9% (95% confidence interval [CI]: 15.6-20.4%) and 1.0% (95% CI: 0.9-1.5%), respectively. The risk of developing all-grade xerosis was 2.99 (95% CI: 2.0-4.3), and it varied across different drugs (P < .001).

LIMITATIONS

The reporting of xerosis may vary among clinicians and institutions, and the incidence may be affected by age, concomitant medications, comorbidities, and underlying malignancies or skin conditions.

CONCLUSION

Patients receiving targeted therapies have a significant risk of developing xerosis. Patients should be counseled and treated early for this symptom to prevent suboptimal dosing and quality of life impairment.

NSK-01105, a novel sorafenib derivative, inhibits human prostate tumor growth via suppression of VEGFR2/EGFR-mediated angiogenesis

The purpose of this study is to investigate the anti-angiogenic activities of NSK-01105, a novel sorafenib derivative, in in vitro, ex vivo and in vivo models, and explore the potential mechanisms. NSK-01105 significantly inhibited vascular endothelial growth factor (VEGF)-induced migration and tube formation of human umbilical vein endothelial cells at non-cytotoxic concentrations as shown by wound-healing, transwell migration and endothelial cell tube formation assays, respectively. Cell viability and invasion of LNCaP and PC-3 cells were significantly inhibited by cytotoxicity assay and matrigel invasion assay. Furthermore, NSK-01105 also inhibited ex vivo angiogenesis in matrigel plug assay. Western blot analysis showed that NSK-01105 down-regulated VEGF-induced phosphorylation of VEGF receptor 2 (VEGFR2) and the activation of epidermal growth factor receptor (EGFR). Tumor volumes were significantly reduced by NSK-01105 at 60 mg/kg/day in both xenograft models. Immunohistochemical staining demonstrated a close association between inhibition of tumor growth and neovascularization. Collectively, our results suggest a role of NSK-01105 in treatment for human prostate tumors, and one of the potential mechanisms may be attributed to anti-angiogenic activities.

Anti-angiogenesis in prostate cancer: knocked down but not out

Angiogenesis is a very complex physiological process, which involves multiple pathways that are dependent on the homeostatic balance between the growth factors (stimulators and inhibitors). This tightly controlled process is stimulated by angiogenic factors, which are present within the tumor and surrounding tumor-associated stromal cells. The dependence of tumor propagation, invasion and metastasis on angiogenesis makes the inhibitors of new blood vessel formation attractive drugs for treating the malignancies. Angiogenesis can be disrupted by several distinct mechanisms: by inhibiting endothelial cells, by interrupting the signaling pathways or by inhibiting other activators of angiogenesis. This strategy has shown therapeutic benefit in several types of solid tumors, leading to Food and Drug Administration (FDA) approval of anti-angiogenic agents in the treatment of kidney, non-small cell lung, colon and brain cancers. Although no angiogenesis inhibitors have been approved for patients with metastatic prostate cancer, therapies that target new blood vessel formation are still an emerging and promising area of prostate cancer research.

Incidence and risk of sorafenib-induced hypertension: a systematic review and meta-analysis

Hypertension is one of the major side effects of sorafenib, and reported incidences vary substantially among clinical trials. A systematic review was conducted using Medline, PubMed, Embase, and the Cochrane Library for all longitudinal studies to investigate the incidence and risk of hypertension events in cancer patients treated with sorafenib. A total of 14 randomized controlled trials and 39 prospective single-arm trials involving 13,555 patients were selected for the meta-analysis. The relative risk of all-grade and high-grade hypertension associated with sorafenib were 3.07 (95% confidence interval [CI], 2.05–4.60; P<.01) and 3.31 (95% CI, 2.21–4.95; P<.01), respectively. The overall incidence of sorafenib-induced all-grade and high-grade hypertension were 19.1% (95% CI, 15.8%–22.4%) and 4.3% (95% CI, 3.0%–5.5%), respectively. A significantly higher incidence of hypertension was noted in patients with renal cell carcinoma (RCC) compared with those with non-RCC malignancies (all-grade: 24.9% [95% CI, 19.7%–30.1%] vs 15.7%[95% CI, 12.1%–19.3%]; P<.05; high-grade:8.6% [95% CI, 6.0%–11.2%] vs 1.8% [95% CI, 0.9%–2.6%]; P<.05). The trials with median progression-free survival (PFS) longer than 5.3 months (mean PFS) demonstrated a significantly higher incidence of high-grade hypertension than trials with shorter PFS (6.3% [95% CI, 4.1%–8.5%] vs 2.6% [95% CI, 1.4%– 3.8%]; P<.05). Findings of the meta-analysis indicated a significantly high risk of sorafenib-induced hypertension. Patients with RCC have a significantly higher incidence of hypertension and the occurrence of hypertension may be associated with improved prognosis.

Randomized Phase II trial of nintedanib, afatinib and sequential combination in castration-resistant prostate cancer

AIMS

The aim of this article was to evaluate afatinib (BIBW 2992), an ErbB family blocker, and nintedanib (BIBF 1120), a triple angiokinase inhibitor, in castration-resistant prostate cancer patients.

PATIENTS & METHODS

Patients were randomized to receive nintedanib (250 mg twice daily), afatinib (40 mg once daily [q.d.]), or alternating sequential 7-day nintedanib (250 mg twice daily) and afatinib (70 mg q.d. [Combi70]), which was reduced to 40 mg q.d. (Combi40) due to adverse events. The primary end point was progression-free rate at 12 weeks.

RESULTS

Of the 85 patients treated 46, 20, 16 and three received nintedanib, afatinib, Combi40 and Combi70, respectively. At 12 weeks, the progression-free rate was 26% (seven out of 27 patients) for nintedanib, and 0% for afatinib and Combi40 groups. Two patients had a ≥50% decline in PSA (nintedanib and the Combi40 groups). The most common drug-related adverse events were diarrhea, nausea, vomiting and lethargy.

CONCLUSION

Nintedanib and/or afatinib demonstrated limited anti-tumor activity in unselected advanced castration-resistant prostate cancer patients.

A phase II study of GW786034 (pazopanib) with or without bicalutamide in patients with castration-resistant prostate cancer

INTRODUCTION

Pazopanib is an oral vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor. In this randomized, open label phase II study, pazopanib alone or in combination with bicalutamide was evaluated in patients with chemotherapy-naive castration-resistant prostate cancer (CRPC).

PATIENTS AND METHODS

Patients received either pazopanib 800 mg daily (arm A) or pazopanib 800 mg plus bicalutamide 50 mg daily (arm B). A 2-stage study design was used, and the primary endpoint was prostate-specific antigen (PSA) response rate (defined as a confirmed ≥ 50% decline from baseline).

RESULTS

A total of 23 patients (arm A, 10; arm B, 13) were accrued. The main grade 3+ toxicities were hypertension, fatigue, decreased lymphocytes, and increased alanine transaminase. Owing to significant toxicity, the protocol was amended after the first 11 patients and the pazopanib starting dose was reduced to 600 mg daily. In arm A, of 9 evaluable patients, there was 1 patient (11%) with a PSA response, 3 (33%) with stable PSA, and 5 (56%) with PSA progression; in arm B, of 12 evaluable patients, there were 2 patients (17%) with PSA responses, 6 (50%) with stable PSA, and 4 (33%) with PSA progression. Median progression-free survival was similar in both arms at 7.3 months (95% CI, 2.5 months to not reached). Long-term stable disease was seen in 4 patients who remained on treatment for 18 months (arm A), 26 months (arm A), 35 months (arm B), and 52 months (arm B).

CONCLUSION

In this unselected patient population, pazopanib either alone or in combination with bicalutamide failed to show sufficient activity to warrant further evaluation. However, 4 patients had long-term benefit, suggesting that targeting the VEGFR pathway may still be relevant in selected patients and emphasizing the need for improved predictive markers for patients with CRPC.

Targeting metastatic castration-resistant prostate cancer: mechanisms of progression and novel early therapeutic approaches

INTRODUCTION

Advances in clinical research have led to official approval of several new treatments for metastatic prostate cancer in the last three years: sipuleucel-T, cabazitaxel, abiraterone acetate, radium-223 and enzalutamide. Although these agents have all been shown to improve overall survival in randomized Phase III trials, metastatic castration-resistant prostate cancer (mCRPC) remains incurable.

AREAS COVERED

First, the review summarizes the current literature on the biology of mCRPC. The emerging data are increasing our understanding of the mechanisms that underlie the pathogenesis of castrate resistance and where future treatment might be headed. In the second part of the review, the authors assess the future directions in disease therapy. Indeed, novel selected therapeutic approaches, including novel agents and combinatorial therapies, are showing promising early results.

EXPERT OPINION

Targeting different molecular pathways in combination with immunotherapy can be a promising direction in metastatic castration prostate cancer treatment. However, several challenges still exist including elucidating the optimal use and sequencing of these new agents. There are also challenges in both the design and the interpretation of the results from clinical trials.

Randomized, Placebo-Controlled, Phase III Trial of Sunitinib Plus Prednisone Versus Prednisone Alone in Progressive, Metastatic, Castration-Resistant Prostate Cancer

Purpose

We evaluated angiogenesis-targeted sunitinib therapy in a randomized, double-blind trial of metastatic castration-resistant prostate cancer (mCRPC).

Patients and Methods

Men with progressive mCRPC after docetaxel-based chemotherapy were randomly assigned 2:1 to receive sunitinib 37.5 mg/d continuously or placebo. Patients also received oral prednisone 5 mg twice daily. The primary end point was overall survival (OS); secondary end points included progression-free survival (PFS). Two interim analyses were planned.

Results

Overall, 873 patients were randomly assigned to receive sunitinib (n = 584) or placebo (n = 289). The independent data monitoring committee stopped the study for futility after the second interim analysis. After a median overall follow-up of 8.7 months, median OS was 13.1 months and 11.8 months for sunitinib and placebo, respectively (hazard ratio [HR], 0.914; 95% CI, 0.762 to 1.097; stratified log-rank test, P = .168). PFS was significantly improved in the sunitinib arm (median 5.6 v 4.1 months; HR, 0.725; 95% CI, 0.591 to 0.890; stratified log-rank test, P < .001). Toxicity and rates of discontinuations because of adverse events (AEs; 27% v 7%) were greater with sunitinib than placebo. The most common treatment-related grade 3/4 AEs were fatigue (9% v 1%), asthenia (8% v 2%), and hand–foot syndrome (7% v 0%). Frequent treatment-emergent grade 3/4 hematologic abnormalities were lymphopenia (20% v 11%), anemia (9% v 8%), and neutropenia (6% v < 1%).

Conclusion

The addition of sunitinib to prednisone did not improve OS compared with placebo in docetaxel-refractory mCRPC. The role of antiangiogenic therapy in mCRPC remains investigational.

Sorafenib: targeting multiple tyrosine kinases in cancer

Sorafenib (BAY 43-9006, Nexavar®) is an oral multiple tyrosine kinase inhibitor. Main targets are receptor tyrosine kinase pathways frequently deregulated in cancer such as the Raf-Ras pathway, vascular endothelial growth factor (VEGF) pathway, and FMS-like tyrosine kinase 3 (FLT3). Sorafenib was approved by the FDA in fast track for advanced renal cell cancer and hepatocellular cancer and shows good clinical activity in thyroid cancer. Multiple clinical trials are undertaken to further investigate the role of sorafenib alone or in combination for the treatment of various tumor entities.

Role of sorafenib in overcoming resistance of chemotherapy-failure castration-resistant prostate cancer

BACKGROUND

Sorafenib promotes apoptosis through downstream pathways that can be deregulated in CRPC. We hypothesized that sorafenib could overcome chemotherapy resistance in CRPC.

PATIENTS AND METHODS

Eligible patients were those whose disease had progressed during chemotherapy (docetaxel or mitoxantrone) or within 12 weeks of stopping either. Patients then continued or resumed their last chemotherapy regimen with the addition of sorafenib 400 mg twice daily. Patients received a maximum of 6 cycles of chemotherapy/sorafenib followed by sorafenib alone until disease progression. The primary end point was combination safety. Secondary end points were overall response, percentage of SD, and time to progression (TTP).

RESULTS

Twenty-two patients (21 evaluable) were enrolled (16 patients with Gleason score ≥ 7). Median age was 68 years (range, 59-83 years). Median prostate-specific antigen (PSA) was 142 ng/dL (range, 13.6-9584). Visceral and bone disease were present combined in 9 patients (41%). Ten patients (47.6%) showed biochemical response (19% with > 50% PSA decline) and 16 patients (76%) achieved radiographic stability (according to Response Evaluation Criteria for Solid Tumors) after starting sorafenib for a median duration of 6 months (range, 4-12 months). Grade 3/4 nonhematologic toxicities were fatigue (n = 7, 32%), palmar-plantar erythrodysesthesia (n = 4, 18%). Dose reduction of sorafenib occurred at least once in 15 patients (68%) because of palmar-plantar erythrodysesthesia (22%) and fatigue (22%). With a median follow-up of 19 months (range, 3-46 months), median overall survival was 8 months. TTP according to PSA level was 3 months and TTP according to imaging studies and/or clinically was 6 months. Median number of treatment cycles given was 6 (range, 1-10).

CONCLUSION

Sorafenib can be combined safely with chemotherapy and in some patients overcomes chemotherapy resistance.

Pruritus in patients treated with targeted cancer therapies: systematic review and meta-analysis

BACKGROUND

Pruritus has been anecdotally described in association with targeted cancer therapies. The risk of pruritus has not been systematically ascertained.

OBJECTIVE

A systematic review and meta-analysis of the literature was conducted for axitinib, cetuximab, dasatinib, erlotinib, everolimus, gefitinib, imatinib, ipilimumab, lapatinib, nilotinib, panitumumab, pazopanib, rituximab, sorafenib, temsirolimus, tositumomab, vandetanib, and vemurafenib.

METHODS

Databases from PubMed, Web of Science (January 1998 through July 2012), and American Society of Clinical Oncology abstracts (2004 through 2012) were searched. Incidence and relative risk of pruritus were calculated using random- or fixed-effects model.

RESULTS

The incidences of all-grade and high-grade pruritus were 17.4% (95% confidence interval 16.0%-19.0%) and 1.4% (95% confidence interval 1.2%-1.6%), respectively. There was an increased risk of all-grade pruritus (relative risk 2.90 [95% confidence interval 1.76-4.77, P < .001]) and variation among different drugs (P < .001).

LIMITATIONS

The reporting of pruritus may vary, resulting from concomitant medications, comorbidities, and underlying malignancies. We found a higher incidence of pruritus in patients with solid tumors, concordant with those targeted therapies with the highest pruritus incidences.

CONCLUSION

There is a significant risk of developing pruritus in patients receiving targeted therapies. To prevent suboptimal dosing and decreased quality of life, patients should be counseled and treated against this untoward symptom.

Zinc sensitizes prostate cancer cells to sorafenib and regulates the expression of Livin

In prostate carcinogenesis, normal zinc-accumulating epithelial cells are transformed into malignant cells that do not accumulate zinc. Increased levels of zinc have been shown to induce apoptosis through a caspase-dependent mechanism with down-regulated anti-apoptotic proteins in prostate cancer cells. Our previous study showed that, as a member of the inhibitor of apoptosis proteins (IAPs) family, Livin could play an important role in the initiation of human prostate cancer and promote cell proliferation by altering the G1-S cell cycle transition. In the present study, we measured the apoptosis sensitivity of prostate cancer cells to zinc and sorafenib and found that zinc sensitized prostate cancer cells to sorafenib-induced apoptosis. Surprisingly, we also found that, unlike its counterparts Survivin and cIAP2, Livin was not decreased all the time; instead, it was compensatively increased in zinc-mediated apoptosis at 48 h in prostate cancer cells. Our results offer potential treatment combinations that may augment the effect of sorafenib, and also reveal, for the first time, that increased Livin expression may play a role in the early cell death response of prostate cancer cells to zinc.

Evolving landscape and novel treatments in metastatic castrate-resistant prostate cancer

Treatment options for castrate-resistant prostate cancer (CRPC) have advanced in recent years and significantly improved the outlook for patients with this aggressive and lethal disease. Further understanding of the biology of CRPC has led to several new targeted therapies and continues to emphasize the importance of androgen receptor (AR) directed therapy. The treatment landscape is rapidly changing and further biologically rationale, biomarker-based ongoing clinical trials are needed. We review the recent results of major clinical trials in CRPC. New and investigational agents now in clinical evaluation are reviewed including inhibitors of angiogenesis, microtubules, chaperones, AR and intracellular kinases, as well as immunotherapy, radiopharmaceuticals and bone-targeted agents. The recent improvement in prognosis for CRPC brings continued optimism for further improvements. Thoughtful planning of clinical trials and further understanding of the mechanisms of resistance to therapies will allow for continued progress in patient care.

Angiogenesis and anti-angiogenic therapy in prostate cancer

Inhibition of angiogenic pathways has proven an effective strategy for the treatment of several common solid tumors however its role in the management of prostate cancer is yet to be defined. Advances in clinical research have resulted in five new treatments for metastatic prostate cancer in the last two years. The immunotherapy sipuleucel-T, the cytotoxic cabazitaxel, the androgen biosynthesis inhibitor abiraterone acetate, the radioisotope radium-223 and the antiandrogen enzalutamide have all been shown to improve overall survival in randomized phase III studies treatment paradigms are changing rapidly. Angiogenesis is known to play a central role in the progression of advanced prostate cancer however established antiangiogenic therapies including bevacizumab and sunitinib have failed to improve survival in randomized trials to date. Novel treatment combinations and novel agents such as cabozantinib are showing promising early results and it is hoped that further well-designed studies will validate the strong biological hypothesis for the benefit of antiangiogenic therapy to improve outcomes for patients with prostate cancer.

Randomized phase II study of danusertib in patients with metastatic castration-resistant prostate cancer after docetaxel failure

OBJECTIVE

To determine the efficacy and toxicity of danusertib (formerly PHA-739358) administered i.v. over two different dosing schedules with equivalent dose intensity in patients with metastatic castration-resistant prostate cancer with progressive disease after docetaxel-based treatment.

PATIENTS AND METHODS

In this open-label, multicentre phase II trial 88 patients were randomly assigned (1:1 ratio) to receive either danusertib 330 mg/m(2) over 6 h i.v. on days 1, 8 and 15 (arm A, n = 43) or 500 mg/m(2) over 24 h i.v. on days 1 and 15 (arm B, n = 38), every 4 weeks. The primary endpoint chosen for this exploratory study was PSA response rate at 3 months.

RESULTS

Sixty patients (31/43 in arm A and 29/38 in arm B) were evaluable for the primary endpoint. Median progression-free survival was 12 weeks in both arms. PSA response occurred in one patient in each arm; best overall response was stable disease in eight (18.6%) and 13 (34.2%) patients in arms A and B, respectively. Eleven out of 81 (13.6%) treated patients had stable disease for ≥6 months. Danusertib was generally well tolerated; the most common grade 3 and 4 drug-related adverse event was neutropenia which occurred in 37.2% (arm A) and 15.8% (arm B) of the patients.

CONCLUSION

Danusertib monotherapy shows minimal efficacy in patients with castration-resistant prostate cancer. Further studies are required to establish specific biomarkers predictive for either response or prolonged disease stabilization.

Targeting angiogenesis as a promising modality for the treatment of prostate cancer

Antiangiogenic therapy has been successful for the treatment of solid tumors. Several strategies have been used to target angiogenesis in prostate cancer. These strategies include blocking proangiogenic factors via monoclonal antibodies or small molecule inhibitors targeting downstream signaling effector pathways, or using agents with immune-modulatory effects. This review examines the general concepts of tumor angiogenesis and the key clinical trials that have used these agents and other novel biologics in prostate cancer. Targeting angiogenesis is still a promising treatment strategy in prostate cancer with a rational trial design and combination approach.

Effects of sorafenib on C-terminally truncated androgen receptor variants in human prostate cancer cells

Recent evidence suggests that the development of castration resistant prostate cancer (CRPCa) is commonly associated with an aberrant, ligand-independent activation of the androgen receptor (AR). A putative mechanism allowing prostate cancer (PCa) cells to grow under low levels of androgens, is the expression of constitutively active, C-terminally truncated AR lacking the AR-ligand binding domain (LBD). Due to the absence of a LBD, these receptors, termed ARΔLBD, are unable to respond to any form of anti-hormonal therapies. In this study we demonstrate that the multikinase inhibitor sorafenib inhibits AR as well as ARΔLBD-signalling in CRPCa cells. This inhibition was paralleled by proteasomal degradation of the AR- and ARΔLBD-molecules. In line with these observations, maximal antiproliferative effects of sorafenib were achieved in AR and ARΔLBD-positive PCa cells. The present findings warrant further investigations on sorafenib as an option for the treatment of advanced AR-positive PCa.

Medical strategies for treatment of castration resistant prostate cancer (CRPC) docetaxel resistant

Current landscape of treatment of castration-resistant prostate cancer (CRPC) has recently changed. Cabazitaxel, a new taxane with potential antineoplastic activity, has been approved by Food and Drug Administration (FDA) after docetaxel failure. In a phase III trial, cabazitaxel showed increased overall survival (OS) compared with mitoxantrone (15.1 vs. 12.7 mo, HR 0.70, 95% CI 0.59-0.83, p < 0.0001). Furthermore, chemotherapy is not the only strategy available: several studies have shown as CRPC remains dependent on androgen receptor function for growth. Abiraterone acetate, an irreversible inhibitor of CYP17, has also been approved by FDA after docetaxel failure. In a phase III trial comparing abiraterone acetate to placebo, abiraterone showed improvement in OS (14.8 vs. 10.4 mo, HR 0.65, 95% CI 0.54-0.77; p < 0.0001). This review will discuss current options and the ongoing trials for second-line treatment of CRPC including chemotherapy, hormonal therapies, antiangiogenetic and immune strategies.

Phase I study investigating the safety and feasibility of combining imatinib mesylate (Gleevec) with sorafenib in patients with refractory castration-resistant prostate cancer

Background:

Determining the maximum tolerated dose (MTD) and the dose-limiting toxicity (DLT) of sorafenib (S) plus imatinib (IM) in castration-resistant prostate cancer (CRPC) patients.

Methods:

Refractory CRPC patients were enrolled onto this 3+3 dose escalation designed study. Imatinib pharmacokinetics (PK) were determined on day 15, 4 h post dose with a validated LC–MS assay.

Results:

Seventeen patients were enrolled; 10 evaluable (6 at 400 mg S qd with 300 mg IM qd (DL0) and 4 at 400 mg S bid with 300 mg IM qd (DL1)); inevaluable patients received <1 cycle. The median age was 73 (57–89); median prostatic serum antigen was 284 ng ml⁻¹ (11.7–9027). Median number of prior non-hormonal therapies was 3 (1–12). Dose-limiting toxicities were diarrhoea and hand-foot syndrome. Maximum tolerated dose was 400 mg S and 300 mg IM both daily. No biochemical responses were observed. Two patients had stable disease by RECIST. Median time to progression was 2 months (1–5). Median OS was 6 months (1–30+) with 3/17 patients (17%) alive at 21 months median follow-up. Ten patients had PK data suggesting that S reduced IM clearance by 55%, resulting in 77% increased exposure (P=0.005; compared with historical data).

Conclusion:

This is the first report showing that S+IM can be administered in CRPC at a dose of 400 mg S and 300 mg IM, daily.

Sorafenib in progressive castrate-resistant prostate cancer. Can we talk about a new therapeutic option?

Castrate-resistant prostate cancer represents a significant clinical challenge. Currently, the standard treatment for patients with castrate-resistant prostate cancer is chemotherapy, after which patients only receive symptomatic treatment. The available results of phase II clinical trials of sorafenib in patients with hormone-refractory prostate cancer indicate that, despite a relatively short progression-free survival, the treatment may be associated with good outcomes in terms of overall survival and maintenance of a good quality of life. The study presents the authors' critical opinions and observations about the usefulness of sorafenib in patients with prostate cancer.

Phase I study of sorafenib in combination with docetaxel and prednisone in chemo-naïve patients with metastatic castration-resistant prostate cancer

PURPOSE

We performed a dose-escalation study to investigate the safety of sorafenib in combination with docetaxel and prednisone in chemo-naïve patients with metastatic castration-resistant prostate cancer (mCRPC).

METHODS

Six patients were included per dose level. Following docetaxel infusion on day 1 (75 mg/m(2)/q3 weeks), sorafenib was administered at 200 mg BID on days 2-19 (dose level 1), at 200 mg BID on days 1-21 (dose level 2), at 400 mg BID on days 2-19 (dose level 3), at 400 mg BID on days 1-21 (dose level 4). Maximal tolerated dose (MTD) was exceeded if ≥2 patients experienced dose-limiting toxicities (DLT) during cycle 1. The recommended phase 2 dose for sorafenib was defined as one dose level below MTD. If MTD was not reached, the highest feasible dose would be selected to treat an expanded cohort to confirm safety.

RESULTS

Two DLTs were observed during sorafenib dose-escalation consisting of grade 4 febrile neutropenia (dose level 2) and grade 3 hand-foot syndrome (HFS) (dose level 3). Our pharmacokinetic results showed an increased exposure to docetaxel across all dose levels during sorafenib comedication. The main grade ≥3 toxicities were neutropenia (35 %), HFS (27 %), and febrile neutropenia (19 %). The prostate-specific antigen (PSA) response rate was 74 %. Median overall survival was 25.2 months.

CONCLUSION

Three-weekly docetaxel and prednisone could be combined with sorafenib at 400 mg BID on days 1-21 without reaching MTD. However, we observed a pharmacokinetic interaction between sorafenib and docetaxel, associated with significant toxicities, raising concerns about the safety of this combination in mCRPC.

Sorafenib decreases proliferation and induces apoptosis of prostate cancer cells by inhibition of the androgen receptor and Akt signaling pathways

Antihormonal and chemotherapy are standard treatments for nonorgan-confined prostate cancer. The effectivity of these therapies is limited and the development of alternative approaches is necessary. In the present study, we report on the use of the multikinase inhibitor sorafenib in a panel of prostate cancer cell lines and their derivatives which mimic endocrine and chemotherapy resistance. (3)H-thymidine incorporation assays revealed that sorafenib causes a dose-dependent inhibition of proliferation of all cell lines associated with downregulation of cyclin-dependent kinase 2 and cyclin D1 expression. Apoptosis was induced at 2  μM of sorafenib in androgen-sensitive cells, whereas a higher dose of the drug was needed in castration-resistant cell lines. Sorafenib stimulated apoptosis in prostate cancer cell lines through downregulation of myeloid cell leukemia-1 (MCL-1) expression and Akt phosphorylation. Although concentrations of sorafenib required for the antitumor effect in therapy-resistant sublines were higher than those needed in parental cells, the drug showed efficacy in cells which became resistant to bicalutamide and docetaxel respectively. Most interestingly, we show that sorafenib has an inhibitory effect on androgen receptor (AR) and prostate-specific antigen expression. In cells in which AR expression was downregulated by short interfering RNA, the treatment with sorafenib increased apoptosis in an additive manner. In summary, the results of the present study indicate that there is a potential to use sorafenib in prostate cancers as an adjuvant therapy option to current androgen ablation treatments, but also in progressed prostate cancers that become unresponsive to standard therapies.

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.

Castration-resistant prostate cancer: mechanisms, targets, and treatment

Patients with castration-resistant prostate cancer (CRPC), who progress after docetaxel therapy, had until very recently, only a few therapeutic options. Recent advances in this field brought about new perspectives in the treatment of this disease. Molecular, basic, and translational research has given us a better understanding on the mechanisms of CRPC. This great investment has turned into a more rational approach to the development of new drugs. Some of the new treatments are already available to our patients outside clinical trials and may include inhibitors of androgen biosynthesis; new chemotherapy agents; bone-targeted therapy; and immunotherapy. This paper aims to review the mechanisms of prostate cancer resistance, possible therapeutic targets, as well as new options to treat CRPC.

Targeting of distinct signaling cascades and cancer-associated fibroblasts define the efficacy of Sorafenib against prostate cancer cells

Sorafenib, a multi-tyrosine kinase inhibitor, kills more effectively the non-metastatic prostate cancer cell line 22Rv1 than the highly metastatic prostate cancer cell line PC3. In 22Rv1 cells, constitutively active STAT3 and ERK are targeted by sorafenib, contrasting with PC3 cells, in which these kinases are not active. Notably, overexpression of a constitutively active MEK construct in 22Rv1 cells stimulates the sustained phosphorylation of Bad and protects from sorafenib-induced cell death. In PC3 cells, Src and AKT are constitutively activated and targeted by sorafenib, leading to an increase in Bim protein levels. Overexpression of constitutively active AKT or knockdown of Bim protects PC3 cells from sorafenib-induced killing. In both PC3 and 22Rv1 cells, Mcl-1 depletion is required for the induction of cell death by sorafenib as transient overexpression of Mcl-1 is protective. Interestingly, co-culturing of primary cancer-associated fibroblasts (CAFs) with 22Rv1 or PC3 cells protected the cancer cells from sorafenib-induced cell death, and this protection was largely overcome by co-administration of the Bcl-2 antagonist, ABT737. In summary, the differential tyrosine kinase profile of prostate cancer cells defines the cytotoxic efficacy of sorafenib and this profile is modulated by CAFs to promote resistance. The combination of sorafenib with Bcl-2 antagonists, such as ABT737, may constitute a promising therapeutic strategy against prostate cancer.

Progress of molecular targeted therapies for prostate cancers

Prostate cancer remains the most commonly diagnosed malignancy and the second leading cause of cancer-related deaths in men in the United States. The current standard of care consists of prostatectomy and radiation therapy, which may often be supplemented with hormonal therapies. Recurrence is common, and many develop metastatic prostate cancer for which chemotherapy is only moderately effective. It is clear that novel therapies are needed for the treatment of the malignant forms of prostate cancer that recur after initial therapies, such as hormone refractory (HRPC) or castration resistant prostate cancer (CRPC). With advances in understanding of the molecular mechanisms of cancer, we have witnessed unprecedented progress in developing new forms of targeted therapy. Several targeted therapeutic agents have been developed and clinically used for the treatment of solid tumors such as breast cancer, non-small cell lung cancer, and renal cancer. Some of these reagents modulate growth factors and/or their receptors, which are abundant in cancer cells. Other reagents target the downstream signal transduction, survival pathways, and angiogenesis pathways that are abnormally activated in transformed cells or metastatic tumors. We will review current developments in this field, focusing specifically on treatments that can be applied to prostate cancers. Finally we will describe aspects of the future direction of the field with respect to discovering biomarkers to aid in identifying responsive prostate cancer patients.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Phase I study of BIBF 1120 with docetaxel and prednisone in metastatic chemo-naive hormone-refractory prostate cancer patients

Background:

BIBF 1120 is an oral, potent, tyrosine kinase inhibitor that simultaneously targets vascular endothelial growth factor receptors 1–3, platelet-derived growth factor receptors α and β, and fibroblast growth factor receptors 1–3, as well as FLT3 and Src. Currently, the molecule is in phase III development for second-line non-small cell lung cancer and first-line ovarian cancer patients.

Methods:

This phase I dose-escalation study assessed the safety and maximum tolerated dose of continuous daily treatment with BIBF 1120 plus standard-dose docetaxel (75 mg m⁻², every 3 weeks) and prednisone (5 mg BID) in patients with metastatic, chemo-naive, hormone-refractory prostate cancer (HRPC). Secondary objectives were characterisation of BIBF 1120 and docetaxel pharmacokinetics (PK), and preliminary antitumour activity.

Results:

Patients received BIBF 1120 100 mg BID (n=3), 150 mg BID (n=3), 200 mg BID (n=3), and 250 mg BID (n=12). The most frequent drug-related adverse events were diarrhoea (71.4%), asthenia (61.9%), nausea (28.6%), vomiting (28.6%), and alopecia (23.8%). The maximum tolerated dose was 250 mg BID of BIBF 1120. Overall, reversible grade 3/4 liver enzyme elevations occurred in six of twelve patients at this dose level. Among 19 assessable patients, 13 (68.4%) showed a ⩾50% reduction in prostate serum antigen levels from baseline and among 6 evaluable patients with measurable lesions 1 patient experienced a partial response by Response Evaluation Criteria In Solid Tumours criteria. Pharmacokinetic analysis showed no interactions between BIBF 1120 and docetaxel/prednisone.

Conclusion:

Based on the overall safety profile, 200 mg BID was the recommended dose for the combination of BIBF 1120 with the standard dose of 75 mg m⁻² of docetaxel and prednisone that might be further investigated in HRPC patients. This combination was well tolerated, with preliminary signs of efficacy and no indication of PK interaction between BIBF 1120 and docetaxel.

Horizon scanning for novel therapeutics for the treatment of prostate cancer

Treatment options for patients with advanced prostate cancer (PCa) remain limited. Improved understanding of the underlying molecular drivers of PCa pathogenesis, progression and resistance development has provided the fundamental basis for rational targeted drug design. Key findings in recent years include the identification of ETS gene rearrangements, the dissection of PCa molecular heterogeneity and the discovery that castration-resistant prostate cancer (CRPC) remains androgen driven despite the androgen-depleted milieu, thus making androgen receptor (AR) signaling a continued focus of molecularly targeted treatments. AR ligand-independent activation of tyrosine kinase prosurvival signaling cascades and angiogenesis have also been implicated in disease progression. A multitude of new molecularly targeted agents that abrogate AR signaling, inhibit the mitogenic and prosurvival signal transduction pathways, perturb the tumor-bone microenvironment, impair tumor vasculature, facilitate immune modulation and induce apoptosis are in clinical development and are highly likely to change the current treatment paradigm. It is clear that the success of these molecular targeted therapies hinges in part on optimal patient selection based on the molecular disease profile and an improved understanding of the mechanistic basis of acquired resistance. This review outlines the current clinical development of molecular targeted treatments in CRPC, with particular emphasis on agents that are in the later stages of clinical development, and details the challenges and future direction of developing these antitumor agents.

MET and VEGF: synergistic targets in castration-resistant prostate cancer

Recent advances in the treatment of prostate cancer have resulted in improved outcomes, including longer survival, but new options are needed for treating patients with castration-resistant disease, particularly in the presence of bone metastasis. Data from preclinical models and clinical biomarker studies indicate that antiangiogenic agents should be a promising treatment for this patient population, and multiple agents in this class have demonstrated activity in early-stage clinical trials. Pivotal trials in prostate cancer with agents targeting vascular endothelial growth factor (VEGF) signalling have resulted in significant improvements in tumour response and progression-free survival. However, overall survival was not significantly improved. Recent preclinical studies suggest that the limited impact on overall survival may result from the development of evasive resistance after inhibition of angiogenesis, possibly through upregulation of MET (hepatocyte growth factor receptor) signalling. MET plays important roles in angiogenesis, tumour cell invasion and bone metastasis, all of which are key factors in castration-resistant prostate cancer. Inhibition of both the MET and VEGF pathways may improve the efficacy of angiogenesis inhibitors in prostate cancer.