Cancer immunotherapy: a paradigm shift for prostate cancer treatment

Long-range gene regulation in hormone-dependent cancer

The human genome is organized into multiple structural layers, ranging from chromosome territories to progressively smaller substructures, such as topologically associating domains (TADs) and chromatin loops. These substructures, collectively referred to as long-range chromatin interactions (LRIs), have a significant role in regulating gene expression. TADs are regions of the genome that harbour groups of genes and regulatory elements that frequently interact with each other and are insulated from other regions, thereby preventing widespread uncontrolled DNA contacts. Chromatin loops formed within TADs through enhancer and promoter interactions are elastic, allowing transcriptional heterogeneity and stochasticity. Over the past decade, it has become evident that the 3D genome structure, also referred to as the chromatin architecture, is central to many transcriptional cellular decisions. In this Review, we delve into the intricate relationship between steroid receptors and LRIs, discussing how steroid receptors interact with and modulate these chromatin interactions. Genetic alterations in the many processes involved in organizing the nuclear architecture are often associated with the development of hormone-dependent cancers. A better understanding of the interplay between architectural proteins and hormone regulatory networks can ultimately be exploited to develop improved approaches for cancer treatment.

Graphdiyne Oxide-Mediated Photodynamic Therapy Boosts Enhancive T-Cell Immune Responses by Increasing Cellular Stiffness

Purpose

Nanomaterial-based photodynamic therapy (PDT) has been commonly used for the treatment of cancerous tumors. Despite significant achievements made in this field, the intrinsic impact of nanomaterials-based PDT on the mechanical properties of oral squamous cell carcinoma (OSCC) cells is not entirely understood. Here, we used atomic force microscopy (AFM) to measure the stiffness of OSCC cells subjected to PDT in co-culture systems to evaluate the T cell-mediated cancer cell-killing effects.

Methods

In this study, AFM was used to assess the stiffness of PDT-subjected cells. The phototoxicity of graphdiyne oxide (GDYO) was assessed using confocal laser scanning microscopy (CLSM), measurements of membrane cholesterol levels, and assessments of the F-actin cytoskeleton. A co-culture system was used to evaluate the effects of CD8⁺ T cells (cytotoxic T lymphocytes), demonstrating how PDT modulates the mechanical properties of cancer cells and activates T cell responses. The antitumor immunotherapeutic effect of GDYO was further evaluated in a murine xenograft model.

Results

GDYO increased the mechanical stiffness of tumor cells and augmented T-cell cytotoxicity and inflammatory cytokine secretion (IFN-γ and TNF-α) under laser in vitro. Furthermore, GDYO-based PDT exerted inhibitory effects on OSCC models and elicited antitumor immune responses via specific cytotoxic T cells.

Conclusion

These results highlight that GDYO is a promising candidate for OSCC therapy, shifting the mechanical forces of OSCC cells and breaking through the barriers of the immunosuppressive tumor microenvironment. Our study provides a novel perspective on nanomaterial-based antitumor therapies.

mRNA-From COVID-19 Treatment to Cancer Immunotherapy

This review provides an overview covering mRNA from its use in the COVID-19 pandemic to cancer immunotherapy, starting from the selection of appropriate antigens, tumor-associated and tumor-specific antigens, neoantigens, the basics of optimizing the mRNA molecule in terms of stability, efficacy, and tolerability, choosing the best formulation and the optimal route of administration, to summarizing current clinical trials of mRNA vaccines in tumor therapy.

Exploiting Ca2+ signaling in T cells to advance cancer immunotherapy

Decades of basic research has established the importance of Ca²⁺ to various T cell functions, such as cytotoxicity, proliferation, differentiation and cytokine secretion. We now have a good understanding of how proximal TCR signaling initiates Ca²⁺ influx and how this influx subsequently changes transcriptional activities in T cells. As chimeric antigen receptor (CAR)-T therapy has achieved great clinical success, is it possible to harness Ca²⁺ signaling to further advance CAR-T research? How is CAR signaling different from TCR signaling? How can functional CARs be identified in a high-throughput way? Quantification of various Ca²⁺ signals downstream of CAR/TCR activation might help answer these questions. Here we first summarized recent studies that used Ca²⁺ dye, genetically-encoded Ca²⁺ indicators (GECI) or transcriptional activity reporters to understand CAR activation in vitro and in vivo. We next reviewed several proof-of-concept reports that manipulate Ca²⁺ signaling by light or ultrasound to achieve precise spatiotemporal control of T cell functions. These efforts, though preliminary, opened up new avenues to solve the on-target/off-tumor problem of therapeutic T cells. Other modalities to regulate Ca²⁺ signaling, such as radio wave and electrical pulse, were also discussed. Thus, monitoring or manipulating Ca²⁺ signaling in T cells provides us many opportunities to advance cancer immunotherapy.

Immunodiagnostics and Immunotherapy Possibilities for Prostate Cancer

Despite significant progress in early detection and improved treatment modalities prostate cancer remains the second leading cause of cancer death in American men which results in about 30,000 deaths per year in the USA. An aggressive phenotype leading to 2.58% risk of dying from prostate cancer still exists and immunotherapy has offered new possibilities to treat metastatic prostate cancer that cannot be treated by other modalities. Cancer immunotherapy is a rapidly growing field of research aimed at identifying biomarkers in immunodiagnosis and to develop new therapies by enabling the immune system to detect and destroy cancer cells. Immunotherapy falls into three different broad categories which are checkpoint inhibitors, cytokines, and vaccine immunotherapy. While immunotherapy to treat prostate cancer is still limited progress has been made; for treatment of advanced prostate cancer sipuleucel-T has been administered to patients in personalized doses to destroy prostate cancer cells which is promising and invites further research to determine immunotherapies for advanced prostate cancer. Antibody-based targeted immunotherapy and dendritic-cell-based vaccination are among the therapies that are currently being evaluated as promising approaches to treat prostate cancer. Combination immunotherapies include prostate cancer vaccines and radiotherapy for castration resistant prostate cancer. Microbial vectors for prostate cancer immunotherapy have been developed and bacterial strains have been engineered to express cancer-specific antigens, cytokines, and prodrug-converting cytokines. These approaches are addressed in the present review.

Elimination of CD4lowHLA-G+ T cells overcomes castration-resistance in prostate cancer therapy

Androgen deprivation therapy (ADT) is a main treatment for prostate cancer (PCa) but the disease often recurs and becomes castration-resistant in nearly all patients. Recent data implicate the involvement of immune cells in the development of this castration-resistant prostate cancer (CRPC). In particular, T cells have been found to be expanded in both PCa patients and mouse models shortly after androgen deprivation. However, whether or which of the T cell subtypes play an important role during the development of CRPC is unknown. Here we identified a novel population of CD4^lowHLA-G⁺ T cells that undergo significant expansion in PCa patients after ADT. In mouse PCa models, a similar CD4^low T cell population expands during the early stages of CRPC onset. These cells are identified as IL-4-expressing T_H17 cells, and are shown to be associated with CRPC onset in patients and essential for the development of CRPC in mouse models. Mechanistically, CD4^lowHLA-G⁺ T cells drive androgen-independent growth of prostate cancer cells by modulating the activity and migration of CD11b^lowF4/80^hi macrophages. Furthermore, following androgen deprivation, elevated PGE₂-EP2 signaling inhibited the expression of CD4 in thymocytes, and subsequently induced the polarization of CD4^low naïve T cells towards the IL-4-expressing T_H17 phenotype via up-regulation of IL23R. Therapeutically, inactivating PGE₂ signaling with celecoxib at a time when CD4^lowHLA-G⁺ T cells appeared, but not immediately following androgen deprivation, dramatically suppressed the onset of CRPC. Collectively, our results indicate that an unusual population of CD4^lowHLA-G⁺ T cells is essential for the development of CRPC and point to a new therapeutic avenue of combining ADT with PGE₂ inhibition for the treatment of prostate cancer.

Potentiating prostate cancer immunotherapy with oncolytic viruses

The clinical effectiveness of immunotherapies for prostate cancer remains subpar compared with that for other cancers. The goal of most immunotherapies is the activation of immune effectors, such as T cells and natural killer cells, as the presence of these activated mediators positively correlates with patient outcomes. Clinical evidence shows that prostate cancer is immunogenic, accessible to the immune system, and can be targeted by antitumour immune responses. However, owing to the detrimental effects of prostate-cancer-associated immunosuppression, even the newest immunotherapeutic approaches fail to initiate the clinically desired antitumour immune reaction. Oncolytic viruses, originally used for their preferential cancer-killing activity, are now being recognized for their ability to overturn cancer-associated immune evasion and promote otherwise absent antitumour immunity. This oncolytic-virus-induced subversion of tumour-associated immunosuppression can potentiate the effectiveness of current immunotherapeutics, including immune checkpoint inhibitors (for example, antibodies against programmed cell death protein 1 (PD1), programmed cell death 1 ligand 1 (PDL1), and cytotoxic T lymphocyte antigen 4 (CTLA4)) and chemotherapeutics that induce immunogenic cell death (for example, doxorubicin and oxaliplatin). Importantly, oncolytic-virus-induced antitumour immunity targets existing prostate cancer cells and also establishes long-term protection against future relapse. Hence, the strategic use of oncolytic viruses as monotherapies or in combination with current immunotherapies might result in the next breakthrough in prostate cancer immunotherapy.

Formulation of the bivalent prostate cancer vaccine with surgifoam elicits antigen-specific effector T cells in PSA-transgenic mice

We previously developed and characterized an adenoviral-based prostate cancer vaccine for simultaneous targeting of prostate-specific antigen (PSA) and prostate stem cell antigen (PSCA). We also demonstrated that immunization of mice with the bivalent vaccine (Ad₅-PSA+PSCA) inhibited the growth of established prostate tumors. However, there are multiple challenges hindering the success of immunological therapies in the clinic. One of the prime concerns has been to overcome the immunological tolerance and maintenance of long-term effector T cells. In this study, we further characterized the use of the bivalent vaccine (Ad₅-PSA+PSCA) in a transgenic mouse model expressing human PSA in the mouse prostate. We demonstrated the expression of PSA analyzed at the mRNA level (by RT-PCR) and protein level (by immunohistochemistry) in the prostate lobes harvested from the PSA-transgenic (PSA-Tg) mice. We established that the administration of the bivalent vaccine in surgifoam to the PSA-Tg mice induces strong PSA-specific effector CD8⁺ T cells as measured by IFN-γ secretion and in vitro cytotoxic T-cell assay. Furthermore, the use of surgifoam with Ad₅-PSA+PSCA vaccine allows multiple boosting vaccinations with a significant increase in antigen-specific CD8⁺ T cells. These observations suggest that the formulation of the bivalent prostate cancer vaccine (Ad₅-PSA+PSCA) with surgifoam bypasses the neutralizing antibody response, thus allowing multiple boosting. This formulation is also helpful for inducing an antigen-specific immune response in the presence of self-antigen, and maintains long-term effector CD8⁺ T cells.

The Toll-like receptor 5 agonist entolimod suppresses hepatic metastases in a murine model of ocular melanoma via an NK cell-dependent mechanism

Uveal melanoma (UM) is the most common primary cancer of the eye in adults and progresses to metastatic disease predominantly of the liver in ∼50% of patients. In these cases, life expectancy averages just 9 months due to the lack of effective treatment options. The Toll-like receptor 5 (TLR5) agonist entolimod (former name CBLB502) rapidly activates TLR5-NF-κB signaling in hepatocytes and suppresses growth of both TLR5-expressing and non-expressing tumors in the liver through mobilization and activation of innate and adaptive immune mechanisms. The goal of this study was to explore the potential of entolimod as an immunotherapeutic agent against hepatic metastasis of UM using the TLR5-positive B16LS9 mouse model of ocular melanoma. Mice were given seven subcutaneous injections of vehicle or entolimod given 72 h apart started one day before, on the same day or three days after intraocular injection of B16LS9 cells. All tested regimens of entolimod treatment resulted in significantly reduced B16LS9 metastasis to the liver. Entolimod induced mobilization of natural killer (NK) cells to the liver and stimulated their maturation, differentiation and activation. Antibody-mediated depletion of NK cells from mice abrogated entolimod's antimetastatic activity in the liver and eliminated the entolimod-elicited in vitro cytotoxic activity of hepatic lymphocytes against B16LS9 cells. These results provide pre-clinical evidence of entolimod's efficacy against hepatometastasis of UM and support its further development as an anticancer immunotherapeutic drug.

Kallikrein-related peptidases (KLKs) as emerging therapeutic targets: focus on prostate cancer and skin pathologies

INTRODUCTION

Tissue kallikrein and the kallikrein-related peptidases (KLKs) constitute a family of 15 homologous secreted serine proteases with trypsin- or chymotrypsin-like activities, which participate in a broad spectrum of physiological procedures. Deregulated expression and/or activation of the majority of the family members have been reported in several human diseases, thereby making KLKs ideal targets for therapeutic intervention.

AREAS COVERED

In the present review, we summarize the role of KLKs in normal human physiology and pathology, focusing on prostate cancer and skin diseases. Furthermore, we discuss the recent advances in the development of KLK-based therapies. A great number of diverse engineered KLKs inhibitors with improved potency, selectivity and immunogenicity have been synthesized by redesigning examples that are endogenous and naturally occurring. Moreover, encouraging results have been documented using KLKs-based vaccines and immunotherapies, as well as KLKs-mediated activation of pro-drugs. Finally, KLKs-targeting aptamers and KLKs-based imaging tools represent novel approaches towards the exploitation of KLKs' therapeutic value.

EXPERT OPINION

The central/critical roles of KLK family in several human pathologies highlight KLKs as attractive molecular targets for developing novel therapeutics.

Anti-tumor effect of the alphavirus-based virus-like particle vector expressing prostate-specific antigen in a HLA-DR transgenic mouse model of prostate cancer

The goal of this study was to determine if an alphavirus-based vaccine encoding human Prostate-Specific Antigen (PSA) could generate an effective anti-tumor immune response in a stringent mouse model of prostate cancer. DR2bxPSA F1 male mice expressing human PSA and HLA-DRB1(*)1501 transgenes were vaccinated with virus-like particle vector encoding PSA (VLPV-PSA) followed by the challenge with Transgenic Adenocarcinoma of Mouse Prostate cells engineered to express PSA (TRAMP-PSA). PSA-specific cellular and humoral immune responses were measured before and after tumor challenge. PSA and CD8 reactivity in the tumors was detected by immunohistochemistry. Tumor growth was compared in vaccinated and control groups. We found that VLPV-PSA could infect mouse dendritic cells in vitro and induce a robust PSA-specific immune response in vivo. A substantial proportion of splenic CD8 T cells (19.6 ± 7.4%) produced IFNγ in response to the immunodominant peptide PSA(65-73). In the blood of vaccinated mice, 18.4 ± 4.1% of CD8 T cells were PSA-specific as determined by the staining with H-2D(b)/PSA(65-73) dextramers. VLPV-PSA vaccination also strongly stimulated production of IgG2a/b anti-PSA antibodies. Tumors in vaccinated mice showed low levels of PSA expression and significant CD8+ T cell infiltration. Tumor growth in VLPV-PSA vaccinated mice was significantly delayed at early time points (p=0.002, Gehan-Breslow test). Our data suggest that TC-83-based VLPV-PSA vaccine can efficiently overcome immune tolerance to PSA, mediate rapid clearance of PSA-expressing tumor cells and delay tumor growth. The VLPV-PSA vaccine will undergo further testing for the immunotherapy of prostate cancer.

Beyond PSA: managing modern therapeutic options in metastatic castration-resistant prostate cancer

Prostate cancer remains a significant cause of cancer-related deaths in men in the United States. Significant advances in the treatment of metastatic castration-resistant prostate cancer have been made in recent years with the arrival of new therapeutic targets and options. The definition of progression of disease must be thought of in the context of clinical symptoms and radiographic evidence rather than as changes in prostate-specific antigen (PSA). Ultimately, the use of PSA criteria alone should not be used to determine the progression of disease; instead, PSA should be evaluated in combination with other clinical data.

Targeting the interleukin-11 receptor α in metastatic prostate cancer: A first-in-man study

BACKGROUND

Receptors in tumor blood vessels are attractive targets for ligand-directed drug discovery and development. The authors have worked systematically to map human endothelial receptors (“vascular zip codes”) within tumors through direct peptide library selection in cancer patients. Previously, they selected a ligand-binding motif to the interleukin-11 receptor alpha (IL-11Rα) in the human vasculature.

METHODS

The authors generated a ligand-directed, peptidomimetic drug (bone metastasis-targeting peptidomimetic-11 [BMTP-11]) for IL-11Rα–based human tumor vascular targeting. Preclinical studies (efficacy/toxicity) included evaluating BMTP-11 in prostate cancer xenograft models, drug localization, targeted apoptotic effects, pharmacokinetic/pharmacodynamic analyses, and dose-range determination, including formal (good laboratory practice) toxicity across rodent and nonhuman primate species. The initial BMTP-11 clinical development also is reported based on a single-institution, open-label, first-in-class, first-in-man trial (National Clinical Trials number NCT00872157) in patients with metastatic, castrate-resistant prostate cancer.

RESULTS

BMTP-11 was preclinically promising and, thus, was chosen for clinical development in patients. Limited numbers of patients who had castrate-resistant prostate cancer with osteoblastic bone metastases were enrolled into a phase 0 trial with biology-driven endpoints. The authors demonstrated biopsy-verified localization of BMTP-11 to tumors in the bone marrow and drug-induced apoptosis in all patients. Moreover, the maximum tolerated dose was identified on a weekly schedule (20-30 mg/m²). Finally, a renal dose-limiting toxicity was determined, namely, dose-dependent, reversible nephrotoxicity with proteinuria and casts involving increased serum creatinine.

CONCLUSIONS

These biologic endpoints establish BMTP-11 as a targeted drug candidate in metastatic, castrate-resistant prostate cancer. Within a larger discovery context, the current findings indicate that functional tumor vascular ligand-receptor targeting systems may be identified through direct combinatorial selection of peptide libraries in cancer patients. Cancer 2015;121:2411–2421. © 2015 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.

The authors report on the development of a new ligand-directed peptidomimetic (termed bone metastasis-targeting peptidomimetic-11) for interleukin-11 receptor-based human vascular targeting, including the translation from preclinical studies to a first-in-class, first-in-man clinical trial in patients with metastatic, castrate-resistant prostate cancer.

Tumor stroma-derived factors skew monocyte to dendritic cell differentiation toward a suppressive CD14+ PD-L1+ phenotype in prostate cancer

Tumor-associated stromal myofibroblasts are essential for the progression and metastatic spread of solid tumors. Corresponding myeloid cell infiltration into primary tumors is a negative prognostic factor in some malignancies. The aim of this study was to define the exact role of stromal myofibroblasts and stromal factors in early prostate carcinoma (PCa) regulating monocyte infiltration and differentiation into dendritic cells (DCs). Epithelial and stromal primary cultures were generated from PCa biopsies and their purity confirmed. Stromal cells produced significantly more of the (C-C) motif chemokine ligand 2 (CCL2), interleukin 6 (IL-6) and transforming growth factor β (TGFβ) than epithelial cells. Monocyte chemoattraction was predominantly due to stromal-derived factors, mainly CCL2. DCs generated in the presence of stromal (but not epithelial) factors upregulated CD209, but failed to downregulate the monocyte marker CD14 in a signal transducer and activator of transcription 3 (STAT3)-dependent manner. Monocytes exposed to stromal factors did not produce detectable amounts of IL-10, however, upon lipopolysaccharide stimulation, stromal factor generated dendritic cells (sDC) produced significantly more IL-10 and less IL-12 than their conventional DC counterparts. sDC failed to cross-present tumor-antigen to CD8⁺ T cells and suppressed T-cell proliferation. Most importantly, sDC expressed significantly elevated levels of programmed cell death ligand-1 (PD-L1) in a primarily STAT3 and IL-6-dependent manner. In parallel with our findings in vitro, tumor-infiltrating CD14⁺ cells in situ were found to express both PD-L1 and CD209, and a higher percentage of tumor-associated CD3⁺ T cells expressed programmed cell death-1 (PD-1) molecules compared to T cells in blood. These results demonstrate a hitherto undescribed, fundamental contribution of tumor-associated stromal myofibroblasts to the development of an immunosuppressive microenvironment in early PCa.

Novel method to characterize immune cells from human prostate tissue

BACKGROUND

Benign prostatic hyperplasia (BPH) is the most common benign adenoma and prostate cancer is the most frequent malignancy in men over 50 years of age in the Western world, where it remains a significant health problem. Prostate lesions are known to contain immune cells, which may contribute to the immune control of tumor progression. However, due to their low numbers and restricted access to necessary material it is difficult to isolate immune cells from prostate tissue to characterize their immunological features.

METHODS

An efficient and robust method was developed to process prostate tissue and isolate immune cells for phenotypic analysis by multicolor flow cytometry as downstream application. Fresh prostate tissue from 11 patients undergoing surgery for bladder outlet obstruction due to BPH was processed to evaluate the number, viability, yield, and frequency of various immune cell types.

RESULTS

The presented method does not include enzymatic digestion nor incubation steps at 37 °C, increasing cellular viability and avoiding possible phenotypic modification. Various immune cell populations were detected in all patient samples and the median cellular viability was 90%. The number of detected events of individual cell populations varied between patients. The median frequency of different immune cell populations also varied, being 87% for the CD3- and 15% for the CD3+ cell population.

CONCLUSIONS

This novel method will allow the phenotypic characterization of immune cell populations present in tumor tissue of prostate cancer patients and promote development of novel approaches to immunotherapy of the disease.

PSMA-targeted stably linked "dendrimer-glutamate urea-methotrexate" as a prostate cancer therapeutic

One of the important criteria for achieving efficient nanoparticle-based targeted drug delivery is that the drug is not prematurely released at off-target sites. Here we report the preclinical evaluation of a serum-stable dendrimer-based drug conjugate capable of actively targeting into prostate cancer (PC) cells, delivered through the prostate-specific membrane antigen (PSMA). Multiple molecules of PSMA-binding small molecule glutamate urea (GLA; targeting agent) and the drug methotrexate (MTX) were conjugated to generation 5 PAMAM dendrimer (G5) through Cu-free "click" chemistry. The GLA was conjugated through a stable amide bond, and the MTX was conjugated either through ester (Es)- or amide (Am)-coupling, to generate G5-GLA(m)-(Es)MTX(n) and G5-GLA(m)-(Am)MTX(n), respectively. In serum-containing medium, free MTX was slowly released from "G5-GLA(m)-(Es)MTX(n)", with ~8% MTX released from the dendrimer in 72 h, whereas the MTX on G5-GLA(m)-(Am)MTX(n) was completely stable. The G5-GLA(m)-(Am)MTX(n) bound and internalized into PSMA-expressing LNCaP cells, but not into PSMA-negative PC3 cells. The conjugate-inhibited recombinant dihydrofolate reductase and induced potent cytotoxicity in the LNCaP cells, but not in the PC3 cells. Similar to the action of free GLA, stable amide-linked dendrimer-GLA was capable of inhibiting the enzyme N-acetylated α-linked acidic dipeptidase (NAALADase) activity of PSMA. The G5-GLA(m)-MTX(n) may serve as a serum-stable nanoparticle conjugate to specifically and effectively target and treat PSMA-overexpressing prostate tumors.

CTLA-4 blockade and the renaissance of cancer immunotherapy

Cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) plays a key role in restraining the adaptive immune response of T-cells towards a variety of antigens including tumor associated antigens (TAAs). The blockade of this immune checkpoint elicits an effective anticancer immune response in a range of preclinical models, suggesting that naturally occurring (or therapeutically induced) TAA specific lymphocytes need to be "unleashed" in order to properly fight against malignant cells. Therefore, investigators have tested this therapeutic hypothesis also in humans: the favorable results obtained with this strategy in patients with advanced cutaneous melanoma are revolutionizing the management of this highly aggressive disease and are fueling new enthusiasm on cancer immunotherapy in general. Here we summarize the biology of CTLA-4, overview the experimental data supporting the rational for targeting CTLA-4 to treat cancer and review the main clinical findings on this novel anticancer approach. Moreover, we critically discuss the current challenges and potential developments of this promising field of cancer immunotherapy.

Endocytosis of gene delivery vectors: from clathrin-dependent to lipid raft-mediated endocytosis

The ideal nonviral vector delivers its nucleic acid cargo to a specific intracellular target. Vectors enter cells mainly through endocytosis and are distributed to various intracellular organelles. Recent advances in microscopy, lipidomics, and proteomics confirm that the cell membrane is composed of clusters of lipids, organized in the form of lipid raft domains, together with non-raft domains that comprise a generally disordered lipid milieu. The binding of a nonviral vector to either region can determine the pathway for its endocytic uptake and subsequent intracellular itinerary. Given this model of the cell membrane structure, endocytic pathways should be reclassified in relation to lipid rafts. In this review, we attempt to assess the currently recognized endocytic pathways in mammalian cells. The endocytic pathways are classified in relation to the membrane regions that make up the primary endocytic vesicles. This review covers the well-recognized clathrin-mediated endocytosis (CME), phagocytosis, and macropinocytosis in addition to the less addressed pathways that take place in lipid rafts. These include caveolae-mediated, flotillin-dependent, GTPase regulator associated with focal adhesion kinase-1 (GRAF1)-dependent, adenosine diphosphate-ribosylation factor 6 (Arf6)-dependent, and RhoA-dependent endocytic pathways. We summarize the regulators associated with each uptake pathway and methods for interfering with these regulators are discussed. The fate of endocytic vesicles resulting from each endocytic uptake pathway is highlighted.

Proposed mechanisms of action for prostate cancer vaccines

Prostate cancer is responsible for the deaths of more than 33,000 American men every year. Once this disease has become metastatic, there is no curative treatment. Alternative therapies to chemotherapy and radical prostatectomy are being increasingly explored. Prostate cancer vaccines--which trigger a tumour-specific cytotoxic-T-lymphocyte-mediated immune attack by the patient's immune system--have been investigated in clinical trials with modest, yet encouraging, results. When developing and administering prostate cancer vaccines, it is critical to consider how vital parameters, such as the stage of disease progression and the nature of adjuvant therapies, could influence treatment outcome. Of particular interest are current and future strategies for diminishing the activity of regulatory T lymphocytes.

Combining T-cell immunotherapy and anti-androgen therapy for prostate cancer

BACKGROUND

Prostate cancer remains a significant health problem for men in the Western world. Although treatment modalities are available, these do not confer long-term benefit and are accompanied by substantial side effects. Adoptive immunotherapy represents an attractive alternative to conventional treatments as a means to control tumor growth.

METHODS

To selectively target the tumor-expressed form of Muc1 we constructed a retroviral vector encoding a chimeric antigen receptor (CAR) directed against the aberrantly-expressed extracellular portion of Muc1 called the 'variable number of tandem repeats'.

RESULTS

We now demonstrate that T cells can be genetically engineered to express a CAR targeting the tumor-associated antigen Muc1. CAR-Muc1 T cells were able to selectively kill Muc1-expressing human prostate cancer cells. However, we noted that heterogeneous expression of the Muc1 antigen on tumor cells facilitated immune escape and the outgrowth of target-antigen loss variants of the tumor. Given the importance of androgen ablation therapy in the management of metastatic prostate cancer, we therefore also tested the value of combining conventional (anti-androgen) and experimental (CAR-Muc1 T cells) approaches. We show that CAR-Muc1 T cells were not adversely impacted by anti-androgen therapy and subsequently demonstrate the feasibility of combining the approaches to produce additive anti-tumor effects in vitro.

CONCLUSIONS

Adoptive transfer of CAR-Muc1 T cells alone or in combination with other luteinizing hormone-releasing hormone analogs or antagonists should be tested in human clinical trials.