Expression of the platelet-derived growth factor receptor in prostate cancer and treatment implications with tyrosine kinase inhibitors

Role of adenosine deaminase in prostate cancer progression

Prostate cancer (PCa) is the second most common cancer and constitutes about 14.7% of total cancer cases. PCa is highly prevalent and more aggressive in African-American (AA) men than in European-American (EA) men. PCa tends to be highly heterogeneous, and its complex biology is not fully understood. We use metabolomics to better understand the mechanisms behind PCa progression and disparities in its clinical outcome. Adenosine deaminase (ADA) is a key enzyme in the purine metabolic pathway; it was found to be upregulated in PCa and is associated with higher-grade PCa and poor disease-free survival. The inosine-to-adenosine ratio, which is a surrogate for ADA activity was high in PCa patient urine and higher in AA PCa compared to EA PCa. To understand the significance of high ADA in PCa, we established ADA overexpression models and performed various in vitro and in vivo studies. Our studies have revealed that an acute increase in ADA expression during later stages of tumor development enhances in vivo growth in multiple pre-clinical models. Further analysis revealed that mTOR signaling activation could be associated with this tumor growth. Chronic ADA overexpression shows alterations in the cells' adhesion machinery and a decrease in cells' ability to adhere to the extracellular matrix in vitro. Losing cell-matrix interaction is critical for metastatic dissemination which suggests that ADA could potentially be involved in promoting metastasis. This is supported by the association of higher ADA expression with higher-grade tumors and poor patient survival. Overall, our findings suggest that increased ADA expression may promote PCa progression, specifically tumor growth and metastatic dissemination.

Antioxidant, Anti-Inflammatory and Antiproliferative Effects of Osmanthus fragrans (Thunb.) Lour. Flower Extracts

Osmanthus fragrans (Thunb.) Lour. flowers (OF-F) have been traditionally consumed as a functional food and utilized as folk medicine. This study evaluated the antioxidant, anti-inflammatory and cytotoxic effects of OF-F extracts on prostate cancer cells (DU-145) and determined possible protein-ligand interactions of its compounds in silico. The crude OF-F extracts-water (W) and ethanol (E) were tested for phytochemical screening, antioxidant, anti-inflammatory, and anti-cancer. Network and molecular docking analyses of chemical markers were executed to establish their application for anticancer drug development. OF-F-E possessed higher total polyphenols (233.360 ± 3.613 g/kg) and tannin (93.350 ± 1.003 g/kg) contents than OF-F-W. In addition, OF-F-E extract demonstrated effective DPPH scavenging activity (IC50 = 0.173 ± 0.004 kg/L) and contained a high FRAP value (830.620 ± 6.843 g Trolox/kg). In cell culture experiments, OF-F-E significantly reduced NO levels and inhibited cell proliferation of RAW-264.7 and DU-145 cell lines, respectively. Network analysis revealed O. fragrans (Thunb.) Lour. metabolites could affect thirteen molecular functions and thirteen biological processes in four cellular components. These metabolites inhibited key proteins of DU-145 prostate cancer using molecular docking with rutin owning the highest binding affinity with PIKR31 and AR. Hence, this study offered a new rationale for O. fragrans (Thunb.) Lour. metabolites as a medicinal herb for anticancer drug development.

An In Vitro Evaluation and Network Pharmacology Analysis of Prospective Anti-Prostate Cancer Activity from Perilla frutescens

Perilla frutescens (L.) Britt. is extensively cultivated in East Asia as a dietary vegetable, and nutraceuticals are reportedly rich in bioactive compounds, especially with anticancer activities. This study explored the in vitro cytotoxic effects of P. frutescens parts' (stems, leaves, and seeds) extracts on prostate cancer cells (DU-145) and possible interactions of putative metabolites to related prostate cancer targets in silico. The ethanol extract of P. frutescens leaves was the most cytotoxic for the prostate cancer cells. From high-performance liquid chromatography analysis, rosmarinic acid was identified as the major metabolite in the leaf extracts. Network analysis revealed interactions from multiple affected targets and pathways of the metabolites. From gene ontology enrichment analysis, P. frutescens leaf metabolites could significantly affect 14 molecular functions and 12 biological processes in five cellular components. Four (4) KEGG pathways, including for prostate cancer, and six (6) Reactome pathways were shown to be significantly affected. The molecular simulation confirmed the interactions of relevant protein targets with key metabolites, including rosmarinic acid. This study could potentially lead to further exploration of P. frutescens leaves or their metabolites for prostate cancer treatment and prevention.

Establishment of extensive artificial intelligence models for kinase inhibitor prediction: Identification of novel PDGFRB inhibitors

Identifying hit compounds is an important step in drug development. Unfortunately, this process continues to be a challenging task. Several machine learning models have been generated to aid in simplifying and improving the prediction of candidate compounds. Models tuned for predicting kinase inhibitors have been established. However, an effective model can be limited by the size of the chosen training dataset. In this study, we tested several machine learning models to predict potential kinase inhibitors. A dataset was curated from a number of publicly available repositories. This resulted in a comprehensive dataset covering more than half of the human kinome. More than 2,000 kinase models were established using different model approaches. The performances of the models were compared, and the Keras-MLP model was determined to be the best performing model. The model was then used to screen a chemical library for potential inhibitors targeting platelet-derived growth factor receptor-β (PDGFRB). Several PDGFRB candidates were selected, and in vitro assays confirmed four compounds with PDGFRB inhibitory activity and IC₅₀ values in the nanomolar range. These results show the effectiveness of machine learning models trained on the reported dataset. This report would aid in the establishment of machine learning models as well as in the discovery of novel kinase inhibitors.

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.

The role of PDGFRA as a therapeutic target in young colorectal cancer patients

Background

Young patients with colorectal cancer (CRC) exhibit poor prognoses compared to older patients due to the difficulty in early diagnosis and treatment. However, the underlying molecular characteristics are still unclear.

Methods

We conducted a comprehensive analysis of 49 CRC patients without hereditary CRC using the whole-exome and RNA sequencing with tumor and matched normal samples. A total of 594 TCGA samples and 4 patient-derived cells were utilized for validation.

Results

Consensus molecular subtype 4 (CMS4) (53.85%) and CMS2 (38.46%) were enriched in the young (≤ 40 years) and old (> 60 years) age groups, respectively. A CMS4-associated gene, platelet-derived growth factor receptor α (PDGFRA), was significantly upregulated in young patients with CRC (FC = 3.21, p = 0.0001) and was negatively correlated with age (p = 0.0001, R = − 0.526). Moreover, PDGFRA showed a positive co-expression with metastasis-related genes in young CRC patients. In vitro validation confirmed that young patient-derived cells (PDCs) showed an enriched expression of PDGFRA compared to old PDCs and a reduced proliferation rate by knockdown of PDGFRA. Furthermore, young CRC patients were more sensitive to regorafenib, a PDGFRA-targeting drug, than old CRC patients.

Conclusions

Our study suggests that CRC in young patients is associated with CMS4 and PDGFRA. In addition, PDGFRA may serve potential of novel therapeutic strategies and represent a predictive biomarker of response to regorafenib for young CRC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03088-7.

The Use of Normal Stem Cells and Cancer Stem Cells for Potential Anti-Cancer Therapeutic Strategy

BACKGROUND

Despite recent advance in conventional cancer therapies including surgery, radiotherapy, chemotherapy, and immunotherapy to reduce tumor size, unfortunately cancer mortality and metastatic cancer incidence remain high. Along with a deeper understanding of stem cell biology, cancer stem cell (CSC) is important in targeted cancer therapy. Herein, we review representative patents using not only normal stem cells as therapeutics themselves or delivery vehicles, but also CSCs as targets for anti-cancer strategy.

METHODS

Relevant patent literatures published between 2005 and 2017 are discussed to present developmental status and experimental results on using normal stem cells and CSCs for cancer therapy and explore potential future directions in this field.

RESULTS

Stem cells have been considered as important element of regenerative therapy by promoting tissue regeneration. Particularly, there is a growing trend to use stem cells as a target drug-delivery system to reduce undesirable side effects in non-target tissues. Noteworthy, studies on CSC-specific markers for distinguishing CSCs from normal stem cells and mature cancer cells have been conducted as a selective anti-cancer therapy with few side effects. Many researchers have also reported the development of various substances with anticancer effects by targeting CSCs from cancer tissues.

CONCLUSION

There has been a continuing increase in the number of studies on therapeutic stem cells and CSC-specific markers for selective diagnosis and therapy of cancer. This review focuses on the current status in the use of normal stem cells and CSCs for targeted cancer therapy. Future direction is also proposed.

Imatinib Spares cKit-Expressing Prostate Neuroendocrine Tumors, whereas Kills Seminal Vesicle Epithelial-Stromal Tumors by Targeting PDGFR-β

Prostate cancer is a leading cause of cancer-related death in males worldwide. Indeed, advanced and metastatic disease characterized by androgen resistance and often associated with neuroendocrine (NE) differentiation remains incurable. Using the spontaneous prostate cancer TRAMP model, we have shown that mast cells (MCs) support in vivo the growth of prostate adenocarcinoma, whereas their genetic or pharmacologic targeting favors prostate NE cancer arousal. Aiming at simultaneously targeting prostate NE tumor cells and MCs, both expressing the cKit tyrosine kinase receptor, we have tested the therapeutic effect of imatinib in TRAMP mice. Imatinib-treated TRAMP mice experience a partial benefit against prostate adenocarcinoma, because of inhibition of supportive MCs. However, they show an unexpected outgrowth of prostate NE tumors, likely because of defective signaling pathway downstream of cKit receptor. Also unexpected but very effective was the inhibition of epithelial-stromal tumors of the seminal vesicles achieved by imatinib treatment. These tumors normally arise in the seminal vesicles of TRAMP mice, independently of the degree of prostatic glandular lesions, and resemble phyllodes tumors found in human prostate and seminal vesicles, and in breast. In both mice and in patients, these tumors are negative for cKit but express PDGFR-β, another tyrosine kinase receptor specifically inhibited by imatinib. Our results imply a possible detrimental effect of imatinib in prostate cancer patients but suggest a promising therapeutic application of imatinib in the treatment of recurrent or metastatic phyllodes tumors. Mol Cancer Ther; 16(2); 365-75. ©2016 AACR.

Platelet-derived growth factor receptor/platelet-derived growth factor (PDGFR/PDGF) system is a prognostic and treatment response biomarker with multifarious therapeutic targets in cancers

Progress in cancer biology has led to an increasing discovery of oncogenic alterations of the platelet-derived growth factor receptors (PDGFRs) in cancers. In addition, their overexpression in numerous cancers invariably makes PDGFRs and platelet-derived growth factors (PDGFs) prognostic and treatment markers in some cancers. The oncologic alterations of the PDGFR/PDGF system affect the extracellular, transmembrane and tyrosine kinase domains as well as the juxtamembrane segment of the receptor. The receptor is also involved in fusions with intracellular proteins and receptor tyrosine kinase. These discoveries undoubtedly make the system an attractive oncologic therapeutic target. This review covers elementary biology of PDGFR/PDGF system and its role as a prognostic and treatment marker in cancers. In addition, the multifarious therapeutic targets of PDGFR/PDGF system are discussed. Great potential exists in the role of PDGFR/PDGF system as a prognostic and treatment marker and for further exploration of its multifarious therapeutic targets in safe and efficacious management of cancer treatments.

Paradoxical and contradictory effects of imatinib in two cell line models of hormone-refractory prostate cancer

BACKGROUND

Imatinib mesylate is a chemotherapeutic drug that inhibits the tyrosine kinase activity of c-KIT and has been successfully used to treat leukemias and some solid tumors. However, its application for treatment of hormone-refractory prostate cancer (HRPC) has shown modest effectiveness and did not follow the outcomes in cultured cells or animal models. Moreover, the molecular pathways by which imatinib induces cytotoxicity in prostate cancer cells are poorly characterized.

METHODS

Two cell line models of HRPC (DU145 and PC3) were exposed to 20 μM of imatinib for 6-72 hr. MTS assay was used to assess cell viability during the course of experiment. Gene expression analysis of c-KIT, cell-cycle and apoptosis regulators, and angiogenic factors was determined by means of real-time PCR, western blot, and/or immunocytochemistry. The enzymatic activity of the apoptosis effector, caspase-3, was determined by a colorimetric assay.

RESULTS

Imatinib significantly decreased the viability of DU145 cells but paradoxically augmented the viability of PC3 cells. DU145 cells displayed diminished expression of anti-apoptotic Bcl-2 protein and augmented levels of caspase-8 and -9, as well as, increased enzymatic activity of caspase-3 in response to imatinib. No differences existed on the expression levels of apoptosis-related proteins in PC3 cells treated with imatinib, though the activity of caspase-3 was decreased. The mRNA levels of angiogenic factor VEGF were decreased in DU145-treated cells, whereas an opposite effect was seen in PC3. In addition, it was shown that DU145 and PC3 cells present a differential expression of c-KIT protein variants.

CONCLUSION

DU145 and PC3 cells displayed a contradictory behavior in response to imatinib, which was underpinned by a distinct expression pattern (or activity) of target regulators of cell-cycle, apoptosis, and angiogenesis. The paradoxical effect of imatinib in PC3 cells may be related with the differential expression of c-KIT protein variants. Moreover, the present findings helped to understand the discrepancies in the efficacy of imatinib as therapeutic option in HRPC.

The SCF/c-KIT system in the male: Survival strategies in fertility and cancer

Maintaining the delicate balance between cell survival and death is of the utmost importance for the proper development of germ cells and subsequent fertility. On the other hand, the fine regulation of tissue homeostasis by mechanisms that control cell fate is a factor that can prevent carcinogenesis. c-KIT is a type III receptor tyrosine kinase activated by its ligand, stem cell factor (SCF). c-KIT signaling plays a crucial role in cell fate decisions, specifically controlling cell proliferation, differentiation, survival, and apoptosis. Indeed, deregulating the SCF/c-KIT system by attenuation or overactivation of its signaling strength is linked to male infertility and cancer, and rebalancing its activity via c-KIT inhibitors has proven beneficial in treating human tumors that contain gain-of-function mutations or overexpress c-KIT. This review addresses the roles of SCF and c-KIT in the male reproductive tract, and discusses the potential application of c-KIT target therapies in disorders of the reproductive system.

PDGF upregulates Mcl-1 through activation of β-catenin and HIF-1α-dependent signaling in human prostate cancer cells

BACKGROUND

Aberrant platelet derived growth factor (PDGF) signaling has been associated with prostate cancer (PCa) progression. However, its role in the regulation of PCa cell growth and survival has not been well characterized.

METHODOLOGY/PRINCIPAL FINDINGS

Using experimental models that closely mimic clinical pathophysiology of PCa progression, we demonstrated that PDGF is a survival factor in PCa cells through upregulation of myeloid cell leukemia-1 (Mcl-1). PDGF treatment induced rapid nuclear translocation of β-catenin, presumably mediated by c-Abl and p68 signaling. Intriguingly, PDGF promoted formation of a nuclear transcriptional complex consisting of β-catenin and hypoxia-inducible factor (HIF)-1α, and its binding to Mcl-1 promoter. Deletion of a putative hypoxia response element (HRE) within the Mcl-1 promoter attenuated PDGF effects on Mcl-1 expression. Blockade of PDGF receptor (PDGFR) signaling with a pharmacological inhibitor AG-17 abrogated PDGF induction of Mcl-1, and induced apoptosis in metastatic PCa cells.

CONCLUSIONS/SIGNIFICANCE

Our study elucidated a crucial survival mechanism in PCa cells, indicating that interruption of the PDGF-Mcl-1 survival signal may provide a novel strategy for treating PCa metastasis.

Pathways of chemotherapy resistance in castration-resistant prostate cancer

Chemotherapy remains the major treatment option for castration-resistant prostate cancer (CRPC) and limited cytotoxic options are available. Inherent chemotherapy resistance occurs in half of all patients and inevitably develops even in those who initially respond. Docetaxel has been the mainstay of therapy for 6 years, providing a small survival benefit at the cost of significant toxicity. Cabazitaxel is a promising second-line agent; however, it is no less toxic, whereas mitoxantrone provides only symptomatic benefit. Multiple cellular pathways involving apoptosis, inflammation, angiogenesis, signalling intermediaries, drug efflux pumps and tubulin are implicated in the development of chemoresistance. A thorough understanding of these pathways is needed to identify biomarkers that predict chemotherapy resistance with the aim to avoid unwarranted toxicities in patients who will not benefit from treatment. Until recently, the search for predictive biomarkers has been disappointing; however, the recent discovery of macrophage inhibitory cytokine 1 as a marker of chemoresistance may herald a new era of biomarker discovery in CRPC. Understanding the interface between this complex array of chemoresistance pathways rather than their study in isolation will be required to effectively predict response and target the late stages of advanced disease. The pre-clinical evidence for these resistance pathways and their progress through clinical trials as therapeutic targets is reviewed in this study.

Inhibition of prostate cancer using RNA interference-directed knockdown of platelet-derived growth factor receptor

OBJECTIVES

To determine whether platelet-derived growth factor receptor (PDGFR) plays a role in the tumorigenicity of prostate cancer cells.

METHODS

PC3 prostate cancer cells were transfected with small interfering (si)PDGFR-α and siPDGFR-β, constructed according to the conventional small interfering RNA design standard. Reverse transcriptase polymerase chain reaction, Western blot analysis, and cell growth were studied to determine the characteristics of PDGFR-α and PDGFR-β in vitro. The prostate cancer xenograft model was established to investigate whether knockout of PDGFR-α and PDGFR-β decreases prostate cancer tumor growth in vivo. The experimental groups were defined as group 1 (PC3 cells only), group 2 (PC3 cells transfected with small interfering green fluorescent protein), group 3 (PC3 cells transfected with siPDGFR-α), group 4 (PC3 cells transfected with siPDGFR-β), and group 5 (PC3 cells transfected with siPDGFR-α and siPDGFR-β).

RESULTS

Western blot analysis revealed that siPDGFR-α and siPDGFR-β significantly blocked PDGFR-α and PDGFR-β protein expression. After 48 hours of transfection of the PC3 cells with siPDGFR-α and siPDGFR-β, the relative fractions of viable cells were reduced to 47.7% (P = .007) and 38.5% (P = .010). In vivo, mice treated with siPDGFR-α or siPDGFR-β and siPDGFR-α plus siPDGFR-β had significant tumor cell growth arrest compared with the mice in groups 1 and 2 (P = .001). In addition, a significant reduction in the microvessel density was observed in tumors from the mice treated with siPDGFR-α or siPDGFR-β and siPDGFR-α plus siPDGFR-β (P < .001).

CONCLUSIONS

The results of the present study suggest that siPDGFR-α and siPDGFR-β might inhibit prostate cancer cell growth by the suppression of angiogenesis.

Targeting the {alpha} receptor for platelet-derived growth factor as a primary or combination therapy in a preclinical model of prostate cancer skeletal metastasis

PURPOSE

Platelet-derived growth factor α (PDGFRα) is highly expressed in primary prostate cancer and associated skeletal metastases. Here, we tested whether targeting this receptor could impair metastatic colonization and progression, as well as prolong survival, either as primary or as combination therapy.

EXPERIMENTAL DESIGN

We used a preclinical animal model of metastasis in which PC3-ML human prostate cancer cells are inoculated directly in the blood circulation. First, the humanized, monoclonal antibody IMC-3G3 was administered to mice bearing established skeletal metastases. Second, we targeted the stromal PDGFRα with IMC-1E10, an antibody specific for the murine receptor. Third, IMC-3G3 and the bisphosphonate zoledronic acid (ZA), administered separately or in combination, were tested on the progression of skeletal lesions and overall survival. In addition, the ability of IMC-3G3 and ZA to impair initial colonization of the bone marrow by prostate cancer cells was investigated.

RESULTS

The blockade of PDGFRα on prostate cancer cells by IMC-3G3 reduces the size of established skeletal metastases, whereas the IMC-1E10 antibody directed against the stromal PDGFRα fails to inhibit metastatic progression. IMC-3G3 and ZA, either separately or in combination, significantly slow tumor growth and seem to prolong survival. Lastly, the blockade of PDGFRα by IMC-3G3 inhibits the initial phase of bone colonization, whereas ZA is ineffective at this stage.

CONCLUSION

This study presents compelling evidence that targeting PDGFRα with IMC-3G3 delays the progression of early metastatic foci and reduces the size of more established lesions. In addition, IMC-3G3, either alone or in combination with ZA, prolongs survival in animal models.

Sunitinib: a multitargeted receptor tyrosine kinase inhibitor in the era of molecular cancer therapies

Sunitinib is an oral oxindole multitargeted kinase inhibitor that inhibits certain receptor tyrosine kinases (RTKs). These include vascular endothelial growth factor receptors (VEGFR type 1 and 2), platelet-derived growth factor receptors (PDGFR-alpha and PDGFR-beta), stem cell factor receptor (KIT), FMS-like tyrosine kinase-3 (FLT3), glial cell-line derived neurotrophic factor receptor (RET) and the receptor of macrophage-colony stimulating factor (CSF1R). Examination of the antitumor effect of sunitinib in a variety of cell lines in vitro suggested an antiproliferative activity that is dependent on the presence of constitutively active RTK targets. The use of sunitinib as first-line therapy in advanced renal cell carcinoma (RCC) has improved the overall survival compared with that observed after cytokine therapy, while its administration in patients with gastrointestinal stromal tumors (GISTs) after progression or intolerance to imatinib achieved an objective response of 7%. Sunitinib is currently approved for the treatment of GISTs in this setting, and as first-line therapy for the treatment of advanced RCC. The relatively long half-life of sunitinib and its major metabolite allow for a once-daily dosing schedule. An interesting antitumor activity of sunitinib was reported in phase II studies of patients with a variety of malignancies, such as hepatocellular cancer, pancreatic neuroendocrine tumors, and non-small cell lung cancer; results of phase III studies are urgently anticipated. Fatigue is one of the most common adverse effects of sunitinib, as 50-70% of patients with advanced RCC and GIST complained of this adverse effect. Other adverse effects are diarrhea, anorexia, nausea and vomiting, oral changes and bleeding events. Most toxicities are reversible and should not result in discontinuation of sunitinib. If necessary, dose adjustments or interruptions should be made. Hypothyroidism has been described in the first 2 weeks of sunitinib therapy and its incidence increases progressively with the duration of therapy. Sunitinib may exert its hypertensive activity through a direct effect on the vasculature, while its most important cardiac adverse effect is left ventricular dysfunction. A variety of skin adverse effects have been described with the use of sunitinib such as hand-foot syndrome, yellow discoloration of the skin, dry skin, subungual splinter hemorrhages, acral erythema, and generalized skin rashes. Administration of sunitinib in the adjuvant and neoadjuvant setting of patients with RCC and of its combination with chemotherapy and other targeted therapies are currently under intense investigation.

The alpha-receptor for platelet-derived growth factor confers bone-metastatic potential to prostate cancer cells by ligand- and dimerization-independent mechanisms

Prostate adenocarcinoma is the second leading cause of cancer death among men, due primarily to the fact that the majority of prostate cancers will eventually spread to the skeleton. Metastatic dissemination requires a complex series of coordinated events that result in cells that escape from the primary tumor into the circulation and eventually colonize a distant organ. The ability of these cells to evolve into macroscopic metastases depends strongly on their compatibility with, and ability to utilize, this new microenvironment. We previously showed that bone-metastatic prostate cancer cells exposed to human bone marrow respond by activation of cell survival pathways, such as phosphoinositide 3-kinase/Akt, and that these events are mediated by the alpha-receptor for platelet-derived growth factor (PDGFRalpha). Our studies and others have shown that PDGFRalpha may be activated by mechanisms independent of PDGF ligand binding. Here, we provide conclusive evidence that soluble components of human bone marrow can activate PDGFRalpha through a mechanism that does not require the canonical binding of PDGF ligand(s) to the receptor. In particular, we found that dimerization of PDGFRalpha monomers is not induced by human bone marrow, but this does not prevent receptor phosphorylation and downstream signaling from occurring. To establish the relevance of this phenomenon in vivo, we used a PDGFRalpha mutant lacking the extracellular ligand-binding domain. Our studies show that this truncated PDGFRalpha is able to restore bone-metastatic potential of prostate cancer cells as effectively as the full-length form of the receptor.

Promising tumor-associated antigens for future prostate cancer therapy

Prostate cancer (CaP) is one of the most prevalent malignant diseases among men in Western countries. There is currently no cure for metastatic castrate-resistant CaP, and median survival for these patients is about 18 months; the high mortality rate seen is associated with widespread metastases. Progression of CaP from primary to metastatic disease is associated with several molecular and genetic changes that can affect the expression of specific tumor-associated antigens (TAAs) or receptors on the cell surface. Targeting TAAs is emerging as an area of promise for controlling late-stage and recurrent CaP. Several reviews have summarized the progress made in targeting signaling pathways for CaP but will not be discussed here. We describe some important CaP TAAs. These include prostate stem-cell antigen, prostate-specific membrane antigen, MUC1, epidermal growth factor receptor, platelet-derived growth factor and its receptor, urokinase plasminogen activator and its receptor, and extracellular matrix metalloproteinase inducer. We summarize recent advancements in our understanding of their role in CaP metastasis, as well as potential therapeutic options for targeting CaP TAAs. We also discuss the origin, identification, and characterization of prostate cancer stem cells (CSCs) and the potential benefits of targeting prostate CSCs to overcome chemoresistance and CaP recurrence.

Phase II study of dasatinib in patients with metastatic castration-resistant prostate cancer

PURPOSE

Antiproliferative and antiosteoclastic activity from preclinical models show potential for dasatinib, an oral SRC and SRC family kinase inhibitor, as a targeted therapy for patients with prostate cancer. This phase II study investigated the activity of dasatinib in patients with metastatic castration-resistant prostate cancer (CRPC).

EXPERIMENTAL DESIGN

Chemotherapy-naive men with CRPC and increasing prostate-specific antigen were treated with dasatinib 100 or 70 mg twice daily. Endpoints included changes in prostate-specific antigen, bone scans, measurable disease (Response Evaluation Criteria in Solid Tumor), and markers of bone metabolism. Following Prostate Cancer Working Group 2 guidelines, lack of progression according to Response Evaluation Criteria in Solid Tumor and bone scan was determined and reported at 12 and 24 weeks.

RESULTS

Forty-seven patients were enrolled and received dasatinib (initial dose 100 mg twice daily, n = 25; 70 mg twice daily, n = 22), of whom 41 (87%) had bone disease. Lack of progression was achieved in 20 (43%) patients at week 12 and in 9 (19%) patients at week 24. Of 41 evaluable patients, 21 (51%) patients achieved > or =40% reduction in urinary N-telopeptide by week 12, with 33 (80%) achieving some level of reduction anytime on study. Of 15 patients with elevated urinary N-telopeptide at baseline, 8 (53%) normalized on study. Of 40 evaluable patients, 24 (60%) had reduction in bone alkaline phosphatase at week 12 and 25 (63%) achieved some reduction on study. Dasatinib was generally well tolerated and treatment-related adverse events were moderate.

CONCLUSIONS

This study provides encouraging evidence of dasatinib activity in bone and reasonable tolerability in chemotherapy-naive patients with metastatic CRPC.

MP470, a novel receptor tyrosine kinase inhibitor, in combination with Erlotinib inhibits the HER family/PI3K/Akt pathway and tumor growth in prostate cancer

BACKGROUND

Prostate cancer is a common disease in men and at present there is no effective therapy available due to its recurrence despite androgen deprivation therapy. The epidermal growth factor receptor family (EGFR/HER1, HER2/neu and HER3)/PI3K/Akt signaling axis has been implicated in prostate cancer development and progression. However, Erlotinib, an EGFR tyrosine kinase inhibitor, has less effect on proliferation and apoptosis in prostate cancer cell lines. In this study, we evaluate whether MP470, a novel receptor tyrosine kinase inhibitor alone or in combination with Erlotinib has inhibitory effect on prostate cancer in vitro and in vivo.

METHODS

The efficacy of MP470 or MP470 plus Erlotinib was evaluated in vitro using three prostate cancer cell lines by MTS and apoptosis assays. The molecular mechanism study was carried out by phosphorylation antibody array, immunoblotting and immunohistochemistry. A LNCaP mouse xenograft model was also used to determine the tumor growth inhibition by MP470, Erlotinib or the combination treatments.

RESULTS

MP470 exhibits low microM IC50 in prostate cancer cell lines. Additive effects on both cytotoxicity and induction of apoptosis were observed when LNCaP were treated with MP470 in combination with Erlotinib. This combination treatment completely inhibited phosphorylation of the HER family members (HER1, 2, 3), binding of PI3K regulatory unit p85 to HER3 and downstream Akt activity even after androgen depletion. Furthermore, in a LNCaP mouse xenograft model, the MP470-Erlotinib combination produced 30-65% dose-dependent tumor growth inhibition (TGI).

CONCLUSION

We propose that MP470-Erlotinib targets the HER family/PI3K/Akt pathway and may represent a novel therapeutic strategy for prostate cancer.

Grundlagen der systemischen Therapie

Die Einführung sog. »zielgerichteter Medikamente« hat einen Paradigmenwechsel in der Systemtherapic maligner Erkrankungen ausgelöst. Voraussetzung hierfür waren die in den letzten 25 Jahren gesammelten Erkenntnisse der molekularbiologischen, molekulargenetischen und immunologischen Grundlagenforschung, die ein besseres Verständnis der pathogenetischen Prozesse im Rahmen der malignen Transformation und Tumorprogression sowie die Identifikation strategischer Zielstrukturen (»Targets«) ermöglichen. Auf diese Weise wurde ein neuer Ansatz der Entwicklung antineoplastischer Therapeutika angestoßen, der auf die Wirkung an spezifischen Molekülaktivitäten und nicht primär auf zelluläre Endpunkte (Wachstumshemmung, Zelltod) ausgerichtet ist.

Targeted therapy of cancer: new roles for pathologists--prostate cancer

The clinical dilemma today in the management of prostate cancer (PCA) is to distinguish men who need definitive treatment from men who have indolent disease. As demonstrated most recently by the randomized Scandinavian trial evaluating the benefit of prostatectomy over Watchful Waiting, surgery significantly decreased the risk of death from PCA. However, this same study also suggests that 19 men need to be treated to benefit one man. Given the high prevalence of the disease, the aging of the population, and the potential morbidity of treatment, the ability to distinguish aggressive from indolent forms of PCA is critical. Treatment for advanced PCA begins with androgen ablation, but eventually hormone-refractory (HR) PCA emerges. Novel therapies are in various stages of clinical trials, including kinase inhibitors, antisense oligonucleotides, and inhibitors of heat-shock proteins. The discovery of novel therapeutic approaches is an active area of clinical research. Eliminating HR PCA before it advances is a high priority in the biomarker field. Therefore, the development of molecular signatures of lethal PCA are critical. In addition, the recent discovery that a significant percentage of PCAs harbor a TMPRSS2-ETS gene fusion suggests that targeting either the ETS transcription factors or the fusion product may offer a novel approach to therapy. However, in 2007, the mainstay of treatment for advanced PCA remains androgen ablation therapy as originally introduced in the early 1940s.

Characterization of the G-quadruplexes in the duplex nuclease hypersensitive element of the PDGF-A promoter and modulation of PDGF-A promoter activity by TMPyP4

The proximal 5′-flanking region of the human platelet-derived growth factor A (PDGF-A) promoter contains one nuclease hypersensitive element (NHE) that is critical for PDGF-A gene transcription. On the basis of circular dichroism (CD) and electrophoretic mobility shift assay (EMSA), we have shown that the guanine-rich (G-rich) strand of the DNA in this region can form stable intramolecular parallel G-quadruplexes under physiological conditions. A Taq polymerase stop assay has shown that the G-rich strand of the NHE can form two major G-quadruplex structures, which are in dynamic equilibrium and differentially stabilized by three G-quadruplex-interactive drugs. One major parallel G-quadruplex structure of the G-rich strand DNA of NHE was identified by CD and dimethyl sulfate (DMS) footprinting. Surprisingly, CD spectroscopy shows a stable parallel G-quadruplex structure formed within the duplex DNA of the NHE at temperatures up to 100°C. This structure has been characterized by DMS footprinting in the double-stranded DNA of the NHE. In transfection experiments, 10 μM TMPyP4 reduced the activity of the basal promoter of PDGF-A ∼40%, relative to the control. On the basis of these results, we have established that ligand-mediated stabilization of G-quadruplex structures within the PDGF-A NHE can silence PDGF-A expression.

Establishment of the active catalytic domain of human PDGFRβ tyrosine kinase-based ELISA assay for inhibitor screening

Tyrosine kinases are emerging as frequent targets of primary oncogenic events and therefore represent an optimal focus of therapeutic intervention. In an effort towards therapeutic PDGFR inactivation, we expressed the catalytic domain of PDGFRbeta as a soluble active kinase using Bac-to-Bac expression system, and studied the correlations between PDGFRbeta activity and enzyme concentration, ATP concentration, substrate concentration and divalent cation type. And a convenient, effective and non-radioactive ELISA screening model is then established for identification of the potential inhibitors targeting PDGFRbeta kinase. Of 500 RTK target-based compounds, TKI-30 was identified as a small molecule potential inhibitor of PDGFRbeta (IC(50)=0.34 microM). Further studies indicated that TKI-30 blocked PDGF-BB-induced autophosphorylation of PDGFRbeta in a dose-dependent manner in Swiss 3T3 cells and human umbilical vein smooth muscle cells (HUVSMCs). Moreover, it dose-dependently suppressed the PDGF-BB-induced proliferation in HUVSMCs and tube formation of HUVEC. Our data collectively indicated that PDGFRbeta-based ELISA assay is a new method available for screening inhibitors targeting PDGFRbeta kinase and TKI-30 is a potential novel anti-cancer agent worthy of being further investigated.

Phase II study of imatinib mesylate in patients with prostate cancer with evidence of biochemical relapse after definitive radical retropubic prostatectomy or radiotherapy

OBJECTIVES

Patients with biochemical recurrence of prostate cancer after definitive or salvage local therapy in the absence of metastatic disease represent a group well suited to a novel therapeutic intervention. Imatinib mesylate (Gleevec) is a protein-tyrosine kinase inhibitor that has previously been tested in men with androgen-independent and metastatic prostate cancer. This Phase II study was undertaken to determine the safety and efficacy of imatinib mesylate in men with biochemical relapse of nonmetastatic, androgen-sensitive prostate cancer after local therapy.

METHODS

Twenty-seven patients were treated with imatinib mesylate 400 mg twice daily for up to 12 months. Three patients (11%) completed less than 4 weeks of therapy and were included in the intent-to-treat analysis of the response to therapy.

RESULTS

Of the 27 patients treated, 5 (18.5%) had a stable prostate-specific antigen (PSA) during the course of treatment; 2 patients (7.4%) experienced a partial response. The remaining 20 patients (74.1%) demonstrated PSA progression. The median progression-free survival was 3 months. The proportion of patients achieving a partial PSA response during therapy did not significantly differ from the null rate of 5% (P = 0.394). Seven patients (25.9%) discontinued therapy secondary to grade 1 to 3 toxicities. No irreversible National Institutes of Health Common Toxicity Criteria grade 3 or 4 toxicities occurred. Grade 3 and 4 toxicity included leukopenia (3.7%), serum glutamic-oxaloacetic transaminase (3.7%) and serum glutamic-pyruvic transaminase (3.7%) elevation, and rash (18.5%).

CONCLUSIONS

The results of our study have demonstrated that imatinib mesylate delivered at a dose of 400 mg twice daily is associated with a moderate degree of toxicity and a limited PSA response in this patient population.

A phase II trial of imatinib mesylate in patients with biochemical relapse of prostate cancer after definitive local therapy

OBJECTIVE

To determine the biological effects of imatinib mesylate (STI-571, Gleevec; Novartis Pharmaceuticals, Inc., East Hanover, NJ, USA), as measured by prostate-specific antigen (PSA) kinetics in men with biochemical relapse of prostate cancer after definitive local therapy.

PATIENTS AND METHODS

Men with prostate cancer, who had had definitive local therapy, with nonmetastatic recurrent disease as manifested by a rising PSA level, were enrolled on this phase II trial. Men received 400 mg of imatinib mesylate orally twice daily and continuously until disease progression or unacceptable toxicity. The PSA level was measured monthly.

RESULTS

In all, 20 men with biochemically relapsed prostate cancer were treated. The median pretreatment PSA level was 5.4 ng/mL. Of the 19 evaluable men, one achieved a >or= 50% reduction in PSA level and two had decreases of <50%. For the 16 men in whom the on-treatment PSA doubling time (PSADT) could be calculated (those with increasing PSA level) the median PSADT did not increase significantly (5.8 vs 7.2 months, P = 0.64). Eleven of 20 men discontinued therapy due to toxicity and the trial was stopped early due to toxicity.

CONCLUSIONS

Based on the lack of PSA modulation and pronounced toxicities leading to early closure of this trial, further study of single-agent imatinib mesylate at this dose (400 mg twice daily) cannot be recommended in this patient population.

Translation molekularer Zusammenhänge in die klinische Anwendung

For patients with metastatic renal cell cancer (RCC), therapeutic options after cytokine failure are rather limited. There is a considerable need to identify new substances for systemic therapy. Due to upregulation after the loss of a functional von Hippel Lindau gene product, the vascular endothelial growth factor (VEGF) pathway is a promising target for a molecular based therapy. Over the last few years, therapeutic agents have been developed which inhibit this pathway at various levels. Here, we provide an overview of the molecular background and currently used drugs which have entered clinical trials in the setting of metastatic RCC disease. Until now, the results from early clinical trials are very promising, however, the best schedule, dosage, potential combination regimens, as well as long time efficacy, are still to be determined.

PDGFRα, PDGFRβ and KIT expression/activation in conventional chondrosarcoma

Chondrosarcomas represent 20% of all primary bone sarcomas, and many studies have attempted to unravel molecular targets for future development of new therapies. The aim of this study was to investigate the expression/activation of PDGFRalpha, PDGFRbeta and KIT receptor tyrosine kinases (RTKs) as potential therapeutic targets in conventional central primary chondrosarcomas (CCS). The expression of PDGFRalpha, PDGFRbeta and KIT RTKs was detected in 16 CCSs using immunohistochemistry (IHC), and their level of expression and activation status were analysed by immunoprecipitation and western blot experiments. PDGFRalpha, PDGFRbeta and KIT cDNAs were screened to verify the presence of activating mutations and the presence of the cognate ligands was analysed by means of RT-PCR. RTK gene amplification was further studied by means of fluorescence in situ hybridization (FISH) analysis. The immunophenotyping and biochemical analyses showed that the CCSs co-expressed PDGFRalpha and PDGFRbeta, with the latter showing definitively greater protein expression and phosphorylation levels. PDGFRbeta was expressed but not activated in control healthy joint cartilage, in line with no PDGFB detection. Conversely, the KIT gene product did not seem to play a relevant role. These findings, in the absence of activating mutations or an abnormal genomic profile and the presence of PDGFA and PDGFB expression, are consistent with an autocrine/paracrine loop activation of the corresponding receptors. The CCS gene profile described here offers a rationale for the use of RTK inhibitors alone or in combination with chemotherapy, and supports further investigation of RTKs and their downstream signals.

Combined low-dose imatinib mesylate and paclitaxel lack synergy in an experimental model of extra-osseous hormone-refractory prostate cancer

OBJECTIVE

To determine the efficacy of low-dose imatinib mesylate (STI571) alone or combined with a taxane (paclitaxel) in inhibiting the growth of experimental extra-osseous hormone-refractory prostate cancer.

MATERIALS AND METHODS

Orthotopic PC3 prostate tumours were established in male severe combined-immunodeficient mice; on day 3 the mice were randomly assigned to one of four groups: paclitaxel 10 mg/kg intraperitoneally once a week; STI571 50 mg/kg once a day for 6/7 weekdays; combined paclitaxel and STI571; and vehicle-treated controls. On day 40, the primary prostate tumour and metastatic lymphadenopathy were removed and measured. Effects were correlated with tumour cell proliferation and microvessel density.

RESULTS

Paclitaxel reduced the mean tumour weight and volume by 21.3% (not significant) and 73.7% (P < 0.05), respectively, compared to controls, and reduced the number of lymph node metastases by 49.1% (P < 0.05) and mean lymph node size by 13.5% (not significant). Adding low-dose STI571 had a small additive effect on tumour weight and the incidence of lymph node metastases, but this was not significant compared to paclitaxel alone. STI571 alone did not inhibit tumour progression. Antitumour effects were associated with parallel changes in tumour cell proliferation with no significant changes in neo-angiogenesis.

CONCLUSION

Combined low-dose STI571 and paclitaxel had little synergy in this experimental model. Low-dose STI571 monotherapy was not effective in extra-osseous disease, apparently due to a site-specific failure to up-regulate beta-platelet-derived growth factor receptor expression in prostate cancer cells and associated tumour stroma.