Immunocytochemical detection and phenotypic characterization of micrometastatic tumour cells in bone marrow of patients with prostate cancer

Liquid biopsy for monitoring of tumor dormancy and early detection of disease recurrence in solid tumors

Cancer is one of the three leading causes of death worldwide. Even after successful therapy and achieving remission, the risk of relapse often remains. In this context, dormant residual cancer cells in secondary organs such as the bone marrow constitute the cellular reservoir from which late tumor recurrences arise. This dilemma leads the term of minimal residual disease, which reflects the presence of tumor cells disseminated from the primary lesion to distant organs in patients who lack any clinical or radiological signs of metastasis or residual tumor cells left behind after therapy that eventually lead to local recurrence. Disseminated tumor cells have the ability to survive in a dormant state following treatment and linger unrecognized for more than a decade before emerging as recurrent disease. They are able to breakup their dormant state and to readopt their proliferation under certain circumstances, which can finally lead to distant relapse and cancer-associated death. In recent years, extensive molecular and genetic characterization of disseminated tumor cells and blood-based biomarker has contributed significantly to our understanding of the frequency and prevalence of tumor dormancy. In this article, we describe the clinical relevance of disseminated tumor cells and highlight how latest advances in different liquid biopsy approaches can be used to detect, characterize, and monitor minimal residual disease in breast cancer, prostate cancer, and melanoma patients.

Printing the Pathway Forward in Bone Metastatic Cancer Research: Applications of 3D Engineered Models and Bioprinted Scaffolds to Recapitulate the Bone-Tumor Niche

Breast cancer commonly metastasizes to bone, resulting in osteolytic lesions and poor patient quality of life. The bone extracellular matrix (ECM) plays a critical role in cancer cell metastasis by means of the physical and biochemical cues it provides to support cellular crosstalk. Current two-dimensional in-vitro models lack the spatial and biochemical complexities of the native ECM and do not fully recapitulate crosstalk that occurs between the tumor and endogenous stromal cells. Engineered models such as bone-on-a-chip, extramedullary bone, and bioreactors are presently used to model cellular crosstalk and bone-tumor cell interactions, but fall short of providing a bone-biomimetic microenvironment. Three-dimensional bioprinting allows for the deposition of biocompatible materials and living cells in complex architectures, as well as provides a means to better replicate biological tissue niches in-vitro. In cancer research specifically, 3D constructs have been instrumental in seminal work modeling cancer cell dissemination to bone and bone-tumor cell crosstalk in the skeleton. Furthermore, the use of biocompatible materials, such as hydroxyapatite, allows for printing of bone-like microenvironments with the ability to be implanted and studied in in-vivo animal models. Moreover, the use of bioprinted models could drive the development of novel cancer therapies and drug delivery vehicles.

Cancer Metastases to Bone: Concepts, Mechanisms, and Interactions with Bone Osteoblasts

The skeleton is a unique structure capable of providing support for the body. Bone resorption and deposition are controlled in a tightly regulated balance between osteoblasts and osteoclasts with no net bone gain or loss. However, under conditions of disease, the balance between bone resorption and deposition is upset. Osteoblasts play an important role in bone homeostasis by depositing new bone osteoid into resorption pits. It is becoming increasingly evident that osteoblasts additionally play key roles in cancer cell dissemination to bone and subsequent metastasis. Our laboratory has evidence that when osteoblasts come into contact with disseminated breast cancer cells, the osteoblasts produce factors that initially reduce breast cancer cell proliferation, yet promote cancer cell survival in bone. Other laboratories have demonstrated that osteoblasts both directly and indirectly contribute to dormant cancer cell reactivation in bone. Moreover, we have demonstrated that osteoblasts undergo an inflammatory stress response in late stages of breast cancer, and produce inflammatory cytokines that are maintenance and survival factors for breast cancer cells and osteoclasts. Advances in understanding interactions between osteoblasts, osteoclasts, and bone metastatic cancer cells will aid in controlling and ultimately preventing cancer cell metastasis to bone.

Single cell transcriptomic analysis of prostate cancer cells

Background

The ability to interrogate circulating tumor cells (CTC) and disseminated tumor cells (DTC) is restricted by the small number detected and isolated (typically <10). To determine if a commercially available technology could provide a transcriptomic profile of a single prostate cancer (PCa) cell, we clonally selected and cultured a single passage of cell cycle synchronized C4-2B PCa cells. Ten sets of single, 5-, or 10-cells were isolated using a micromanipulator under direct visualization with an inverted microscope. Additionally, two groups of 10 individual DTC, each isolated from bone marrow of 2 patients with metastatic PCa were obtained. RNA was amplified using the WT-Ovation™ One-Direct Amplification System. The amplified material was hybridized on a 44K Whole Human Gene Expression Microarray. A high stringency threshold, a mean Alexa Fluor® 3 signal intensity above 300, was used for gene detection. Relative expression levels were validated for select genes using real-time PCR (RT-qPCR).

Results

Using this approach, 22,410, 20,423, and 17,009 probes were positive on the arrays from 10-cell pools, 5-cell pools, and single-cells, respectively. The sensitivity and specificity of gene detection on the single-cell analyses were 0.739 and 0.972 respectively when compared to 10-cell pools, and 0.814 and 0.979 respectively when compared to 5-cell pools, demonstrating a low false positive rate. Among 10,000 randomly selected pairs of genes, the Pearson correlation coefficient was 0.875 between the single-cell and 5-cell pools and 0.783 between the single-cell and 10-cell pools. As expected, abundant transcripts in the 5- and 10-cell samples were detected by RT-qPCR in the single-cell isolates, while lower abundance messages were not. Using the same stringency, 16,039 probes were positive on the patient single-cell arrays. Cluster analysis showed that all 10 DTC grouped together within each patient.

Conclusions

A transcriptomic profile can be reliably obtained from a single cell using commercially available technology. As expected, fewer amplified genes are detected from a single-cell sample than from pooled-cell samples, however this method can be used to reliably obtain a transcriptomic profile from DTC isolated from the bone marrow of patients with PCa.

Urokinase-plasminogen-activator receptor expression in disseminated tumour cells in the bone marrow and peripheral blood of patients with clinically localized prostate cancer

OBJECTIVE To evaluate the expression of urokinase-plasminogen-activator receptor (uPA-R) in disseminated tumour cells (DTC) in bone marrow (BM) and peripheral blood (PB) of patients with clinically localized prostate cancer before radical prostatectomy (RP), and to assess the associations with pathological variables and prognosis. PATIENTS AND METHODS In all, 52 patients (47 with clinically localized cancer and five with benign prostatic hyperplasia, BPH, as controls) were prospectively enrolled. BM and PB samples were drawn before surgery. DTC were enriched using a commercial system, cytokeratin (CK) 8/18 was used to detect DTC, and uPA-R expression was detected by dual-immunostaining of the DTC. The final pathology of the RP specimen was compared with the results of immunostaining. Follow-up was initiated to detect tumour relapse (defined as a prostate-specific antigen (PSA) level of > or =0.2 ng/mL). RESULTS Overall, there was expression of 'CK + uPA-R' in 60% of the BM and in 19% of the PB specimens. Expression of this marker in BM was most significantly increased in those with unfavourable Gleason scores (P = 0.004), followed by high-risk cancer (P = 0.005). The relative risk for CK + uPA-R expression in the BM was 3.1 times higher in high-risk than in low-risk prostate cancer. No relevant expression rates were detected for PB. In the control group, no patient showed CK or uPA-R expression in BM or PB. The PSA-recurrence free survival was significantly lower in patients with CK + uPA-R-positive BM cells (P = 0.01). CONCLUSION In this pilot study, the preoperative detection rate of CK + uPAR expression in BM of patients with prostate cancer increased with Gleason score and in those with high-risk disease. All patients with a later PSA relapse had had uPA-R expression in their DTC from the BM. DTC with uPA-R expression was an adverse prognostic factor for prostate cancer.

Review: Biological relevance of disseminated tumor cells in cancer patients

The prognosis of cancer patients is largely determined by the occurrence of distant metastases. In patients with primary tumors, this relapse is mainly due to clinically occult micrometastasis present in secondary organs at primary diagnosis but not detectable even with high resolution imaging procedures. Sensitive and specific immunocytochemical and molecular assays enable the detection and characterization of disseminated tumor cells (DTC) at the single cell level in bone marrow (BM) as the common homing site of DTC and circulating tumor cells (CTC) in peripheral blood. Because of the high variability of results in DTC and CTC detection, there is an urgent need for standardized methods. In this review, we will focus on BM and present currently available methods for the detection and characterization of DTC. Furthermore, we will discuss data on the biology of DTC and the clinical relevance of DTC detection. While the prognostic impact of DTC in BM has clearly been shown for primary breast cancer patients, less is known about the clinical relevance of DTC in patients with other carcinomas. Current findings suggest that DTC are capable to survive chemotherapy and persist in a dormant nonproliferating state over years. To what extent these DTC have stem cell properties is subject of ongoing investigations. Further characterization is required to understand the biology of DTC and to identify new targets for improved risk prevention and tailoring of therapy. Our review will focus on breast, colon, lung, and prostate cancer as the main tumor entities in Europe and the United States.

Impact of disseminated tumor cells in bone marrow at diagnosis in patients with nonmetastatic prostate cancer treated by definitive radiotherapy

The purpose of this study was to explore whether detection of disseminated tumor cells (DTCs) in bone marrow (BM) of nonmetastatic prostate cancer (PC) was associated with other clinical or histopathological factors at diagnoses or clinical outcome subsequent to definitive radiotherapy (RT). We evaluated BM aspirates from 272 cT(1-4)pN(0)M(0) PC patients by immunocytochemistry employing anticytokeratin antibodies (AE1/AE3). BM-status was compared with clinical and histopathological parameters. Long-term clinical outcome was assessed in 131 of the patients who all had completed definitive RT with or without androgen deprivation (AD), initiating treatment >5 years before cut-off date June 1, 2005. They had at least 1 unfavorable prognostic feature defined as cT(3-4) or Gleason score (GS) >or= 7B or PSA >or= 10 microg/l. Overall death, cause-specific death, distant metastases (DM) as first clinical relapse, local failure as first clinical relapse and biochemical failure were defined as end-points. DTCs were detected in 18% of the patients and were associated with increasing GS (p = 0.04) and percentage of Gleason pattern 4/5 (p = 0.04). The 7-year cumulative risk of DM was 21% for BM-positive patients vs. 6% for BM-negative patients (p = 0.07). In patients receiving RT without AD (n = 75), the 7-year cumulative risk of DM for BM-positive patients was 28% vs. 9% for BM-negative patients (p = 0.03). BM-status did not have impact on other end-points. In conclusion our study shows that presence of DTCs in BM at diagnosis was associated with the histological differentiation of the primary tumor and an increased risk of developing distant metastases after RT.

Clinical approaches to osseous metastases in prostate cancer

BACKGROUND

Prostate cancer is unique among solid tumors in its proclivity to metastasize primarily to bone. Osseous metastases pose a formidable health threat to patients with metastatic disease, putting them at risk for pain, marrow crowding, fracture, and other sequelae. Treatments directed against bone disease have the potential both to palliate pain and to increase survival.

CONCLUSIONS

A number of agents exist that have the potential to palliate the effects of osseous metastases and should be routinely applied in the clinical care of the patient with advanced prostate cancer. These include hormones, bone-seeking radiopharmaceuticals, chemotherapy, and bisphosphonates. Strategies under investigation aim to eradicate bone disease, and not merely palliate symptoms. These approaches combine those listed above with tumor-directed targeting of osseous disease and manipulation of the biology that underlies the cancer's relationship to bone.

From latent disseminated cells to overt metastasis: genetic analysis of systemic breast cancer progression

According to the present view, metastasis marks the end in a sequence of genomic changes underlying the progression of an epithelial cell to a lethal cancer. Here, we aimed to find out at what stage of tumor development transformed cells leave the primary tumor and whether a defined genotype corresponds to metastatic disease. To this end, we isolated single disseminated cancer cells from bone marrow of breast cancer patients and performed single-cell comparative genomic hybridization. We analyzed disseminated tumor cells from patients after curative resection of the primary tumor (stage M0), as presumptive progenitors of manifest metastasis, and from patients with manifest metastasis (stage M1). Their genomic data were compared with those from microdissected areas of matched primary tumors. Disseminated cells from M0-stage patients displayed significantly fewer chromosomal aberrations than primary tumors or cells from M1-stage patients (P < 0.008 and P < 0.0001, respectively), and their aberrations appeared to be randomly generated. In contrast, primary tumors and M1 cells harbored different and characteristic chromosomal imbalances. Moreover, applying machine-learning methods for the classification of the genotypes, we could correctly identify the presence or absence of metastatic disease in a patient on the basis of a single-cell genome. We suggest that in breast cancer, tumor cells may disseminate in a far less progressed genomic state than previously thought, and that they acquire genomic aberrations typical of metastatic cells thereafter. Thus, our data challenge the widely held view that the precursors of metastasis are derived from the most advanced clone within the primary tumor.

From latent disseminated cells to overt metastasis: genetic analysis of systemic breast cancer progression

According to the present view, metastasis marks the end in a sequence of genomic changes underlying the progression of an epithelial cell to a lethal cancer. Here, we aimed to find out at what stage of tumor development transformed cells leave the primary tumor and whether a defined genotype corresponds to metastatic disease. To this end, we isolated single disseminated cancer cells from bone marrow of breast cancer patients and performed single-cell comparative genomic hybridization. We analyzed disseminated tumor cells from patients after curative resection of the primary tumor (stage M0), as presumptive progenitors of manifest metastasis, and from patients with manifest metastasis (stage M1). Their genomic data were compared with those from microdissected areas of matched primary tumors. Disseminated cells from M0-stage patients displayed significantly fewer chromosomal aberrations than primary tumors or cells from M1-stage patients (P < 0.008 and P < 0.0001, respectively), and their aberrations appeared to be randomly generated. In contrast, primary tumors and M1 cells harbored different and characteristic chromosomal imbalances. Moreover, applying machine-learning methods for the classification of the genotypes, we could correctly identify the presence or absence of metastatic disease in a patient on the basis of a single-cell genome. We suggest that in breast cancer, tumor cells may disseminate in a far less progressed genomic state than previously thought, and that they acquire genomic aberrations typical of metastatic cells thereafter. Thus, our data challenge the widely held view that the precursors of metastasis are derived from the most advanced clone within the primary tumor.

Detection of occult metastasis in patients with breast cancer

The most important factor affecting the outcome of patients with invasive cancer is whether the tumor has spread, either regionally (to regional lymph nodes) or systemically. However, a proportion of patients with no evidence of systemic dissemination will develop recurrent disease after primary "curative" therapy. Clearly, these patients had occult systemic spread of disease that was undetectable by routinely employed methods (careful pathological, clinical, biochemical, and radiological evaluation). In addition, the success of adjuvant therapy is assumed to stem from its ability to eradicate occult metastases before they become clinically evident. Therefore, methods for the detection of occult metastases in patients with the earliest stage of cancer, i.e., prior to detection of metastases by any other clinical or pathological analysis, have received a great deal of attention.

Occult metastasis

The most important factor affecting the outcome of patients with invasive cancers is whether the tumor has spread, either regionally (to regional lymph nodes) or systemically. However, a proportion of patients with no evidence of systemic dissemination will develop recurrent disease after primary 'curative' therapy. Clearly, these patients had occult systemic spread of disease that was undetectable by methods routinely employed (careful pathological, clinical, biochemical and radiological evaluation). In addition, the success of adjuvant therapy is assumed to stem from its ability to eradicate occult metastases before they become clinically evident [1]. Therefore, methods for the detection of occult metastases in patients with the earliest stage of cancer, i.e., prior to detection of metastases by any other clinical or pathological analysis, have received a great deal of attention.

Autoantibodies to prostasomes as new markers for prostate cancer

Prostate cancer is one of the leading causes of cancer-related death among men. Given the varying clinical course and the long natural history of the disease, it is important to have good diagnostic and prognostic markers. Prostate specific antigen (PSA) is currently the best marker for the detection of prostate cancer, but in many cases it does not reveal whether metastases have appeared. Since metastases of prostate cancer release prostasomes, which are immunogenic secretory granules of both normal and neoplastic prostate cells, we checked whether anti-prostasome antibodies will appear when the cancer is metastasing. In a pilot study, all 13 patients with serum PSA between 50-500 microg/L had anti-prostasome antibodies, while 39 healthy controls with low PSA values showed background values. There was no overlapping, i.e. the upper range value of controls did not reach the lower range value of patients.

Micrometastases of bone marrow in localized prostate cancer: correlation with established risk factors

PURPOSE

The presence of cytokeratin 18-positive cells in bone marrow correlates with conventional risk factors in many tumors. We examined whether this was also valid for localized or lymphatically spread prostate cancer.

PATIENTS AND METHODS

Immediately before radical prostatectomy, bone marrow aspirates from both sides of the iliac crest were taken from 287 patients. The presence of cells containing cytokeratin 18 was interpreted as micrometastasis.

RESULTS

In patients with negative lymph nodes (n = 219), conventional risk factors (Gleason score, pathologic stage, ploidy, and preoperative prostate-specific antigen) did not correlate with the preoperative detection of cells containing cytokeratin 18. There was also no correlation with lymph node metastases. Furthermore, there was no interdependency between the preoperatively detected number of cells and the established risk factors.

CONCLUSION

We assume the presence of epithelial cells in bone marrow to be an independent parameter, the clinical importance of which must be substantiated by further studies.

Gene expression changes associated with chemically induced rat mammary carcinogenesis

Experimentally induced models of breast carcinogenesis in the rat are widely used for studying the biology of breast cancer and for developing and evaluating cancer prevention and control strategies. However, very little is known about gene expression changes that are associated with experimentally induced mammary carcinogenesis. This paper reports the identification, by differential display of mRNA and molecular cloning, of seven cDNA fragments of gene transcripts overexpressed in mammary carcinomas induced by 1-methyl-1-nitrosourea. These genes included the rat homologues of human galectin-7 gene, the human/mouse melanoma inhibitory activity/bovine chondrocyte-derived retinoic acid sensitive protein gene, the mouse stearoyl-CoA desaturase-2 gene, and the mouse endo B cytokeratin/human cytokeratin-18 gene. Although each of these genes has been implicated in some aspect of carcinogenesis in other organs, this paper is the first report of their overexpression in chemically induced mammary carcinomas. Two previously uncharacterized gene transcripts were also identified. A comparison of the expression levels of several genes in mammary carcinomas with those in the normal mammary gland tissue of virgin rats, mid-stage pregnant rats, and of day 1 postpartum lactating dams indicated that the overexpression of several genes observed in mammary carcinomas could not be accounted for by either a difference in the mammary epithelial content between mammary carcinoma and normal mammary tissue or by mammary epithelium-specific proliferation associated with pregnancy. Several genes were also overexpressed in rat mammary carcinomas induced by 7,12-dimethylbenz[a]anthracene but not in azoxymethane-induced rat colon adenocarcinomas. The genes identified in this study may therefore represent mammary carcinoma-specific molecular markers that may be helpful in investigations of mammary carcinogenesis and its prevention.

Immunocytochemical monitoring of micrometastatic disease: reduction of prostate cancer cells in bone marrow by androgen deprivation

Occult dissemination of tumor cells mainly determines the prognosis of patients with primary prostate cancer. The effect of androgen deprivation on micrometastatic tumor cells in these patients is currently unknown. We therefore used an immunocytochemical assay with monoclonal antibodies (MAbs) directed against epithelial cytoskeleton proteins (i.e., cytokeratins) to monitor the concentration of isolated tumor cells in the bone marrow of 36 prostate cancer patients (stage C), who underwent hormonal androgen deprivation with Flutamide and Leuprorelin acetate. Tumor cells in cytologic bone marrow preparations were detected using an assay that employed the MAb CK2 directed against cytokeratin (CK) 18 and the alkaline anti-alkaline phosphatase staining method. Prior to therapy, we detected between 1 and 38 CK-positive cells per sample of 2 x 10(6) nucleated cells in 21 patients, while the remaining 15 patients displayed tumor-free marrow samples. There was no significant correlation between the concentration of CK-positive cells and the volume of hypo-echogenic lesions as an indicator of the primary tumor volume or the serum level of prostate-specific antigen (PSA). After androgen deprivation, 20 of the 21 initially positive patients either became negative (n = 16) or showed at least a reduction in the concentration of CK-positive cells (n = 4). Moreover, only 2 of the 15 patients with negative pre-treatment findings became positive. All of the 7 patients with remaining tumor cells in the bone marrow after therapy showed no detectable amounts of PSA in their serum. Our findings suggest that serum PSA concentration is no indicator of micrometastatic disease in bone marrow. Neoadjuvant androgen deprivation appears to eliminate disseminated CK-positive tumor cells present in bone marrow, a preferred site of overt metastasis in prostate cancer patients.

Detection of micrometastatic prostate cancer cells in the bone marrow of patients with prostate cancer

Thirty-five patients with prostate cancer were examined for micrometastases to the bone marrow using reverse transcription-polymerase chain reaction (RT-PCR) with primers specific for the prostate-specific antigen (PSA) gene. Of nine patients with bone metastases detectable by bone scan imaging, five patients had PSA mRNA expression in the bone marrow detectable by RT-PCR. Of 26 patients with negative bone scan findings, seven patients had PSA mRNA expression detectable in the bone marrow. RT-PCR could detect micrometastatic prostate cancer cells in the bone marrow that were not detectable by bone scan imaging. Of 16 patients with a serum PSA concentration of 25 ng ml(-1) or greater, only nine (56.3%) had bone metastases detected by bone scans. Of the remaining seven patients, five had micrometastases to the bone marrow detected by RT-PCR. Overall, 14 of 16 patients (87.5%) with a serum PSA concentration of 25 ng ml(-1) or greater had metastatic bone diseases including bone marrow micrometastases. Of 19 patients with a serum PSA concentration of less than 25 ng ml(-1), two (10.5%) had only micrometastatic disease detected by RT-PCR. A significant correlation was observed between the incidence of bone involvement and the serum PSA concentration. This study suggests that RT-PCR will potentially develop into a relevant tool to assess bone involvement including bone marrow micrometastases and establish a precise correlation between serum PSA concentration and metastatic bone disease in patients with prostate cancer.

Detection of minimal disease in patients with solid tumors

The detection and elimination of minimal systemic disease in patients with solid tumors is one of the main current topics in clinical oncology. The present review focuses, therefore, on new diagnostic approaches to identify minimal disease in peripheral blood, bone marrow, and lymph nodes of patients with epithelial cancer as the major type of solid tumors in Western industrialized countries. These approaches may be used to improve tumor staging and monitoring of adjuvant therapies, as well as to detect tumor cell contamination in autologous stem cell grafts. Most investigators have developed either immunocytochemical assays with monoclonal antibodies to a variety of epithelial-specific cytoskeleton and membrane antigens or molecular methods based on the extensive amplification of a specific (c)DNA sequence by the polymerase-chain reaction (PCR). In immunocytochemical assays, antibodies to cytokeratins can be regarded as the most specific and sensitive probes to detect isolated epithelial tumor cells in bone marrow and blood. Molecular methods are based on the detection of either mutations in oncogenes and tumor suppressor genes (e.g., ki-ras and p53 genes) or the mRNA expression of tissue-specific and tumor-associated genes. mRNA species targeted in these assays encode cytokeratins, prostate-specific antigen, prostate-specific membrane antigen, carcinoembryonic antigen, and polymorphic-epithelial mucin. To introduce the available methods into clinical practice, standardized protocols need to be developed and validated in multi-center studies.