Mechanisms of acquired resistance to rapalogs in metastatic renal cell carcinoma.

The mechanistic target of rapamycin (mTOR) is an established therapeutic target in renal cell carcinoma (RCC). Mechanisms of secondary resistance to rapalog therapy in RCC have not been studied previously. We identified six patients with metastatic RCC who initially responded to mTOR inhibitor therapy and then progressed, and had pre-treatment and post-treatment tumor samples available for analysis. We performed deep whole exome sequencing on the paired tumor samples and a blood sample. Sequence data was analyzed using Mutect, CapSeg, Absolute, and Phylogic to identify mutations, copy number changes, and their changes over time. We also performed in vitro functional assays on PBRM1 in RCC cell lines. Five patients had clear cell and one had chromophobe RCC. 434 somatic mutations in 416 genes were identified in the 12 tumor samples. 201 (46%) of mutations were clonal in both samples while 129 (30%) were acquired in the post-treatment samples. Tumor heterogeneity or sampling issues are likely to account for some mutations that were acquired in the post-treatment samples. Three samples had mutations in TSC1; one in PTEN; and none in MTOR. PBRM1 was the only gene in which mutations were acquired in more than one post-treatment sample. We examined the effect of PBRM1 loss in multiple RCC cell lines, and could not identify any effect on rapalog sensitivity in in vitro culture assays. We conclude that mTOR pathway gene mutations did not contribute to rapalog resistance development in these six patients with advanced RCC. Furthermore, mechanisms of resistance to rapalogs in RCC remain unclear and our results suggest that PBRM1 loss may contribute to sensitivity through complex transcriptional effects.

p63-expressing cells are the stem cells of developing prostate, bladder, and colorectal epithelia.

The tumor protein p63 (p63), and more specifically the NH2-terminal truncated (ΔN) p63 isoform, is a marker of basal epithelial cells and is required for normal development of several epithelial tissues, including the bladder and prostate glands. Although p63-expressing cells are proposed to be the stem cells of the developing prostate epithelium and bladder urothelium, cell lineages in these endoderm-derived epithelia remain highly controversial, and rigorous lineage tracing studies are warranted. Here, we generated knock-in mice expressing Cre recombinase (Cre) under the control of the endogenous ΔNp63 promoter. Heterozygote ΔNp63(+/Cre) mice were phenotypically normal and fertile. Cre-mediated recombination in ΔNp63(+/Cre);ROSA26(EYFP) reporter mice faithfully recapitulated the pattern of ΔNp63 expression and were useful for genetic lineage tracing of ΔNp63-expressing cells of the caudal endoderm in vivo. We found that ΔNp63-positive cells of the urogenital sinus generated all epithelial lineages of the prostate and bladder, indicating that these cells represent the stem/progenitor cells of those epithelia during development. We also observed ΔNp63 expression in caudal gut endoderm and the contribution of ΔNp63-positive cells to the stem/progenitor compartment of adult colorectal epithelium. Because p63 is a master regulator of stratified epithelial development, this finding provides a unique developmental insight into the cell of origin of squamous cell metaplasia and squamous cell carcinoma of the colon.

Transcriptomic Correlates of Tumor Cell PD-L1 Expression and Response to Nivolumab Monotherapy in Metastatic Clear Cell Renal Cell Carcinoma.

PURPOSE: PD-L1 expression on tumor cells (TC) is associated with response to anti-PD-1-based therapies in some tumor types, but its significance in clear cell renal cell carcinoma (ccRCC) is uncertain. We leveraged tumor heterogeneity to identify molecular correlates of TC PD-L1 expression in ccRCC and assessed their role in predicting response to anti-PD-1 monotherapy. EXPERIMENTAL DESIGN: RNA sequencing was performed on paired TC PD-L1 positive and negative areas isolated from eight ccRCC tumors and transcriptomic features associated with PD-L1 status were identified. A cohort of 232 patients with metastatic ccRCC from the randomized CheckMate-025 (CM-025) trial was used to confirm the findings and correlate transcriptomic profiles with clinical outcomes. RESULTS: In both the paired samples and the CM-025 cohort, TC PD-L1 expression was associated with combined overexpression of immune- and cell proliferation-related pathways, upregulation of T-cell activation signatures, and increased tumor-infiltrating immune cells. In the CM-025 cohort, TC PD-L1 expression was not associated with clinical outcomes. A molecular RCC subtype characterized by combined overexpression of immune- and cell proliferation-related pathways (previously defined by unsupervised clustering of transcriptomic data) was enriched in TC PD-L1 positive tumors and displayed longer progression-free survival (HR, 0.32; 95% confidence interval, 0.13-0.83) and higher objective response rate (30% vs. 0%, P = 0.04) on nivolumab compared with everolimus. CONCLUSIONS: Both TC-extrinsic (immune-related) and TC-intrinsic (cell proliferation-related) mechanisms are likely intertwined in the regulation of TC PD-L1 expression in ccRCC. The quantitation of these transcriptional programs may better predict benefit from anti-PD-1-based therapy compared with TC PD-L1 expression alone in ccRCC.

Expression of T-Cell Exhaustion Molecules and Human Endogenous Retroviruses as Predictive Biomarkers for Response to Nivolumab in Metastatic Clear Cell Renal Cell Carcinoma.

PURPOSE: We sought to validate levels of CD8+ tumor-infiltrating cells (TIC) expressing PD-1 but not TIM-3 and LAG-3 (IF biomarker; Pignon and colleagues, 2019) and to investigate human endogenous retroviruses (hERV) as predictors of response to anti-PD-1 in a randomized trial of nivolumab (nivo) versus everolimus (evero) in patients with metastatic clear cell renal cell carcinoma (mccRCC; CheckMate-025). EXPERIMENTAL DESIGN: Tumor tissues (nivo: n = 116, evero: n = 107) were analyzed by multiparametric immunofluorescence (IF) and qRT-PCR. Genomic/transcriptomic analyses were performed in a subset of samples. Clinical endpoints included objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and durable response rate (DRR, defined as complete response or partial response with a PFS ≥ 12 months). RESULTS: In the nivo (but not evero) arm, patients with high-IF biomarker density (24/116, 20.7%) had higher ORR (45.8% vs. 19.6%, P = 0.01) and DRR (33.3% vs. 14.1%, P = 0.03) and longer median PFS (9.6 vs. 3.7 months, P = 0.03) than patients with low-IF biomarker. By RNA sequencing, several inflammatory pathways (q < 0.1) and immune-related gene signature scores (q < 0.05) were enriched in the high-IF biomarker group. When combined with the IF biomarker, tumor cell (TC) PD-L1 expression (≥1%) further separated clinical outcomes in the nivo arm. ERVE-4 expression was associated with increased DRR and longer PFS in nivo-treated patients. CONCLUSIONS: High levels of CD8+ TIC expressing PD-1 but not TIM-3 and LAG-3 and ERVE-4 expression predicted response to nivo (but not to evero) in patients with mccRCC. Combination of the IF biomarker with TC PD-L1 improved its predictive value, confirming our previous findings.

KIR3DL3 Is an Inhibitory Receptor for HHLA2 that Mediates an Alternative Immunoinhibitory Pathway to PD1.

Blockade of the PD1 pathway is a broadly effective cancer therapy, but additional immune-inhibitory pathways contribute to tumor immune evasion. HERV-H LTR-associating 2 (HHLA2; also known as B7H5 and B7H7) is a member of the B7 family of immunoregulatory ligands that mediates costimulatory effects through its interaction with the CD28 family member transmembrane and immunoglobulin domain containing 2 (TMIGD2). However, HHLA2 has also been known to have inhibitory effects on T cells. Here, we report that we have identified killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) as an inhibitory receptor for HHLA2 in T cells and natural killer (NK) cells and have generated HHLA2 and KIR3DL3 antibodies that block the immune-inhibitory activity of HHLA2, preserving the costimulatory signal. It is known that HHLA2 is frequently expressed in several tumor types, including clear cell renal cell carcinoma (ccRCC). We found that HHLA2 expression was nonoverlapping with PDL1 expression in ccRCC, suggesting that HHLA2 mediates a mechanism of tumor immune evasion that is independent from PDL1. Blockade of both the PD1 and KIR3DL3 pathways may be a more effective way to reverse tumor immune evasion.See related Spotlight on p. 128.

Efficacy and Safety of Nivolumab Plus Ipilimumab versus Sunitinib in First-line Treatment of Patients with Advanced Sarcomatoid Renal Cell Carcinoma.

PURPOSE: Patients with advanced renal cell carcinoma with sarcomatoid features (sRCC) have poor prognoses and suboptimal outcomes with targeted therapy. This post hoc analysis of the phase III CheckMate 214 trial analyzed the efficacy of nivolumab plus ipilimumab (NIVO+IPI) versus sunitinib in patients with sRCC. PATIENTS AND METHODS: Patients with sRCC were identified via independent central pathology review of archival tumor tissue or histologic classification per local pathology report. Patients were randomized 1:1 to receive nivolumab (3 mg/kg) plus ipilimumab (1 mg/kg) every 3 weeks (four doses) then nivolumab 3 mg/kg every 2 weeks, or sunitinib 50 mg orally every day (4 weeks; 6-week cycles). Outcomes in patients with sRCC were not prespecified. Endpoints in patients with sRCC and International Metastatic Renal Cell Carcinoma Database Consortium intermediate/poor-risk disease included overall survival (OS), progression-free survival (PFS) per independent radiology review, and objective response rate (ORR) per RECIST v1.1. Safety outcomes used descriptive statistics. RESULTS: Of 1,096 randomized patients in CheckMate 214, 139 patients with sRCC and intermediate/poor-risk disease and six with favorable-risk disease were identified. With 42 months' minimum follow-up in patients with sRCC and intermediate/poor-risk disease, median OS [95% confidence interval (CI)] favored NIVO+IPI [not reached (NR) (25.2-not estimable [NE]); n = 74] versus sunitinib [14.2 months (9.3-22.9); n = 65; HR, 0.45 (95% CI, 0.3-0.7; P = 0.0004)]; PFS benefits with NIVO+IPI were similarly observed [median 26.5 vs. 5.1 months; HR, 0.54 (95% CI, 0.33-0.86; P = 0.0093)]. Confirmed ORR was 60.8% with NIVO+IPI versus 23.1% with sunitinib, with complete response rates of 18.9% versus 3.1%, respectively. No new safety signals emerged. CONCLUSIONS: NIVO+IPI showed unprecedented long-term survival, response, and complete response benefits versus sunitinib in previously untreated patients with sRCC and intermediate/poor-risk disease, supporting the use of first-line NIVO+IPI for this population.See related commentary by Hwang et al., p. 5.

Interplay of somatic alterations and immune infiltration modulates response to PD-1 blockade in advanced clear cell renal cell carcinoma.

PD-1 blockade has transformed the management of advanced clear cell renal cell carcinoma (ccRCC), but the drivers and resistors of the PD-1 response remain incompletely elucidated. Here, we analyzed 592 tumors from patients with advanced ccRCC enrolled in prospective clinical trials of treatment with PD-1 blockade by whole-exome and RNA sequencing, integrated with immunofluorescence analysis, to uncover the immunogenomic determinants of the therapeutic response. Although conventional genomic markers (such as tumor mutation burden and neoantigen load) and the degree of CD8+ T cell infiltration were not associated with clinical response, we discovered numerous chromosomal alterations associated with response or resistance to PD-1 blockade. These advanced ccRCC tumors were highly CD8+ T cell infiltrated, with only 27% having a non-infiltrated phenotype. Our analysis revealed that infiltrated tumors are depleted of favorable PBRM1 mutations and enriched for unfavorable chromosomal losses of 9p21.3, as compared with non-infiltrated tumors, demonstrating how the potential interplay of immunophenotypes with somatic alterations impacts therapeutic efficacy.

Ku proteins interact with activator protein-2 transcription factors and contribute to ERBB2 overexpression in breast cancer cell lines.

INTRODUCTION: Activator protein-2 (AP-2) alpha and AP-2gamma transcription factors contribute to ERBB2 gene overexpression in breast cancer. In order to understand the mechanism by which the ERBB2 gene is overexpressed we searched for novel AP-2 interacting factors that contribute to its activity. METHODS: Ku proteins were identified as AP-2alpha interacting proteins by glutathione serine transferase (GST)-pull down followed by mass spectrometry. Transfection of the cells with siRNA, expression vectors and reporter vectors as well as chromatin immunoprecipitation (ChIP) assay were used to ascertain the implication of Ku proteins on ERBB2 expression. RESULTS: Nuclear proteins from BT-474 cells overexpressing AP-2alpha and AP-2gamma were incubated with GST-AP2 or GST coated beads. Among the proteins retained specifically on GST-AP2 coated beads Ku70 and Ku80 proteins were identified by mass spectrometry. The contribution of Ku proteins to ERBB2 gene expression in BT-474 and SKBR3 cell lines was investigated by downregulating Ku proteins through the use of specific siRNAs. Depletion of Ku proteins led to downregulation of ERBB2 mRNA and protein levels. Furthermore, reduction of Ku80 in HCT116 cell line decreased the AP-2alpha activity on a reporter vector containing an AP-2 binding site linked to the ERBB2 core promoter, and transfection of Ku80 increased the activity of AP-2alpha on this promoter. Ku siRNAs also inhibited the activity of this reporter vector in BT-474 and SKBR3 cell lines and the activity of the ERBB2 promoter was further reduced by combining Ku siRNAs with AP-2alpha and AP-2gamma siRNAs. ChIP experiments with chromatin extracted from wild type or AP-2alpha and AP-2gamma or Ku70 siRNA transfected BT-474 cells demonstrated Ku70 recruitment to the ERBB2 proximal promoter in association with AP-2alpha and AP-2gamma. Moreover, Ku70 siRNA like AP-2 siRNAs, greatly reduced PolII recruitment to the ERBB2 proximal promoter. CONCLUSIONS: Ku proteins in interaction with AP-2 (alpha and gamma) contribute to increased ERBB2 mRNA and protein levels in breast cancer cells.

irRECIST for the Evaluation of Candidate Biomarkers of Response to Nivolumab in Metastatic Clear Cell Renal Cell Carcinoma: Analysis of a Phase II Prospective Clinical Trial.

PURPOSE: Immune-related RECIST (irRECIST) were designed to capture atypical responses seen with immunotherapy. We hypothesized that, in patients with metastatic clear cell renal cell carcinoma (mccRCC), candidate biomarkers for nivolumab response would show improved association with clinical endpoints capturing atypical responders (irRECIST) compared with standard clinical endpoints (RECISTv1.1). EXPERIMENTAL DESIGN: Endpoints based on RECISTv1.1 [objective response rate (ORR)/progression-free survival (PFS)] or irRECIST [immune-related ORR (irORR)/immune-related PFS (irPFS)] were compared in patients enrolled in the CheckMate-010 trial. Pretreatment tumors were analyzed by PD-L1 and PD-L2 IHC, and by multiplex immunofluorescence for CD8, PD-1, TIM-3, and LAG-3. T-cell activation signatures were assessed by RNA sequencing. RESULTS: Median irPFS was significantly longer than median PFS. irORR was not significantly different from ORR, but immune-related progressive disease (irPD) rate was significantly lower than progressive disease (PD) rate. Tumor cell (TC) PD-L1 expression was not associated with PFS or ORR, but patients with TC PD-L1 ≥1% had longer median irPFS and higher irORR. High percentage of CD8+ tumor-infiltrating cells (TIC) that are PD-1+TIM-3-LAG-3- (% CD8+PD-1+TIM-3-LAG-3- TIC) correlated with high levels of T-cell activation and was associated with longer median irPFS and higher irORR. Notably, combination of TC PD-L1 expression with % CD8+PD-1+TIM-3-LAG-3- TIC identified three groups of patients for which irPFS and irORR were significantly different. CONCLUSIONS: Atypical responders to nivolumab were identified in the CheckMate-010 trial. We observed improved association of candidate biomarkers for nivolumab response with endpoints defined by irRECIST compared with RECISTv1.1. TC PD-L1 expression in combination with PD-1 expression on CD8+ TIC may predict outcome on nivolumab in mccRCC.

p63+ ureteric bud tip cells are progenitors of intercalated cells.

During renal branching morphogenesis, ureteric bud tip cells (UBTC) serve as the progenitor epithelium for all cell types of the collecting duct. While the transcriptional circuitry of ureteric bud (UB) branching has been intensively studied, the transcriptional control of UBTC differentiation has been difficult to ascertain. This is partly due to limited knowledge of UBTC-specific transcription factors that mark the progenitor state. Here, we identify the transcription factor p63 (also known as TP63), a master regulator of basal stem cells in stratified epithelia, as a specific marker of mouse and human UBTC. Nuclear p63 marks Ret+ UBTC transiently and is silenced by the end of nephrogenesis. Lineage tracing revealed that a subset of UBTC expressing the ΔNp63 isoform (N-terminus truncated p63) is dedicated to generating cortical intercalated cells. Germline targeting of ΔNp63 in mice caused a marked reduction in intercalated cells near the time of birth, indicating that p63 not only marks UBTC, but also is essential for their differentiation. We conclude that the choice of UBTC progenitors to differentiate is determined earlier than previously recognized and that UBTC progenitors are prepatterned and fate restricted. These findings prompt the rethinking of current paradigms of collecting duct differentiation and may have implications for regenerative renal medicine.

Differential expression of c-Met between primary and metastatic sites in clear-cell renal cell carcinoma and its association with PD-L1 expression.

In preclinical models, c-Met promotes survival of renal cancer cells through the regulation of programmed death-ligand 1 (PD-L1). However, this relationship in human clear cell renal cell carcinoma (ccRCC) is not well characterized. We evaluated c-Met expression in ccRCC patients using paired primary and metastatic samples and assessed the association with PD-L1 expression and other clinical features. Areas with predominant and highest Fuhrman nuclear grade (FNG) were selected. c-Met expression was evaluated by IHC using an anti-Met monoclonal antibody (MET4 Ab) and calculated by a combined score (CS, 0-300): intensity of c-Met staining (0-3) x % of positive cells (0-100). PD-L1 expression in tumor cells was previously assessed by IHC and PD-L1+ was defined as PD-L1 > 0% positive cells. Our cohort consisted of 45 pairs of primary and metastatic ccRCC samples. Overall, c-Met expression was higher in metastatic sites compared to primary sites (average c-Met CS: 55 vs. 28, p = 0.0003). Higher c-Met expression was associated with higher FNG (4 vs. 3) in primary tumors (average c-Met CS: 52 vs. 20, p = 0.04). c-Met expression was numerically greater in PD-L1+ vs. PD-L1- tumors. Higher c-Met expression in metastatic sites compared to primary tumors suggests that testing for biomarkers of response to c-Met inhibitors should be conducted in metastases. While higher c-Met expression in PD-L1+ tumors requires further investigation, it supports exploring these targets in combination clinical trials.

Landscape of tumor-infiltrating T cell repertoire of human cancers.

We developed a computational method to infer the complementarity-determining region 3 (CDR3) sequences of tumor-infiltrating T cells in 9,142 RNA-seq samples across 29 cancer types. We identified over 600,000 CDR3 sequences, including 15% that were full length. CDR3 sequence length distribution and amino acid conservation, as well as variable gene usage, for infiltrating T cells in many tumors, except in brain and kidney cancers, resembled those for peripheral blood cells from healthy donors. We observed a strong association between T cell diversity and tumor mutation load, and we predicted SPAG5 and TSSK6 as putative immunogenic cancer/testis antigens in multiple cancers. Finally, we identified three potential immunogenic somatic mutations on the basis of their co-occurrence with CDR3 sequences. One of them, a PRAMEF4 mutation encoding p.Phe300Val, was predicted to result in peptide binding strongly to both MHC class I and class II molecules, with matched HLA types in its carriers. Our analyses have the potential to simultaneously identify immunogenic neoantigens and tumor-reactive T cell clonotypes.

Comprehensive analyses of tumor immunity: implications for cancer immunotherapy.

BACKGROUND: Understanding the interactions between tumor and the host immune system is critical to finding prognostic biomarkers, reducing drug resistance, and developing new therapies. Novel computational methods are needed to estimate tumor-infiltrating immune cells and understand tumor-immune interactions in cancers. RESULTS: We analyze tumor-infiltrating immune cells in over 10,000 RNA-seq samples across 23 cancer types from The Cancer Genome Atlas (TCGA). Our computationally inferred immune infiltrates associate much more strongly with patient clinical features, viral infection status, and cancer genetic alterations than other computational approaches. Analysis of cancer/testis antigen expression and CD8 T-cell abundance suggests that MAGEA3 is a potential immune target in melanoma, but not in non-small cell lung cancer, and implicates SPAG5 as an alternative cancer vaccine target in multiple cancers. We find that melanomas expressing high levels of CTLA4 separate into two distinct groups with respect to CD8 T-cell infiltration, which might influence clinical responses to anti-CTLA4 agents. We observe similar dichotomy of TIM3 expression with respect to CD8 T cells in kidney cancer and validate it experimentally. The abundance of immune infiltration, together with our downstream analyses and findings, are accessible through TIMER, a public resource at http://cistrome.org/TIMER . CONCLUSIONS: We develop a computational approach to study tumor-infiltrating immune cells and their interactions with cancer cells. Our resource of immune-infiltrate levels, clinical associations, as well as predicted therapeutic markers may inform effective cancer vaccine and checkpoint blockade therapies.

Mutations in TSC1, TSC2, and MTOR Are Associated with Response to Rapalogs in Patients with Metastatic Renal Cell Carcinoma.

PURPOSE: We examined the hypothesis that mutations in mTOR pathway genes are associated with response to rapalogs in metastatic renal cell carcinoma (mRCC). EXPERIMENTAL DESIGN: We studied a cohort of mRCC patients who were treated with mTOR inhibitors with distinct clinical outcomes. Tumor DNA from 79 subjects was successfully analyzed for mutations using targeted next-generation sequencing of 560 cancer genes. Responders were defined as those with partial response (PR) by RECIST v1.0 or stable disease with any tumor shrinkage for 6 months or longer. Nonresponders were defined as those with disease progression during the first 3 months of therapy. Fisher exact test assessed the association between mutation status in mTOR pathway genes and treatment response. RESULTS: Mutations in MTOR, TSC1, or TSC2 were more common in responders, 12 (28%) of 43, than nonresponders, 4 (11%) of 36 (P = 0.06). Mutations in TSC1 or TSC2 alone were also more common in responders, 9 (21%), than nonresponders, 2(6%), (P = 0.05). Furthermore, 5 (42%) of 12 subjects with PR had mutations in MTOR, TSC1, or TSC2 compared with 4 (11%) of 36 nonresponders (P = 0.03). Eight additional non-mTOR pathway genes were found to be mutated in at least 4 of 79 tumors (5%); none were associated positively with response. CONCLUSIONS: In this cohort of mRCC patients, mutations in MTOR, TSC1, or TSC2 were more common in patients who experienced clinical benefit from rapalogs than in those who progressed. However, a substantial fraction of responders (24 of 43, 56%) had no mTOR pathway mutation identified. Clin Cancer Res; 22(10); 2445-52. ©2016 AACRSee related commentary by Voss and Hsieh, p. 2320.

Cell kinetic studies fail to identify sequentially proliferating progenitors as the major source of epithelial renewal in the adult murine prostate.

There is evidence that stem cells and their progeny play a role in the development of the prostate. Although stem cells are also considered to give rise to differentiated progeny in the adult prostate epithelium ex vivo, the cohort of adult prostate stem cells in vivo as well as the mechanisms by which the adult prostate epithelium is maintained and regenerated remain highly controversial. We have attempted to resolve this conundrum by performing in vivo tracing of serially replicating cells after the sequential administration of two thymidine analogues to mice. Our results show that, during normal prostate homeostasis, sequentially proliferating cells are detected at a rate that is consistent with a stochastic process. These findings indicate that in vivo, under steady-state conditions, most adult prostate epithelial cells do not represent the progeny of a small number of specialized progenitors that generate sequentially replicating transit-amplifying (TA) cells but are formed by stochastic cell division. Similarly, no rapidly cycling TA cells were detected during regeneration following one cycle of androgen-mediated involution/regeneration of the prostate epithelium. These findings greatly enhance our understanding of the mechanisms regulating prostate epithelial cell renewal and may have significant implications in defining the cell of origin of proliferative prostatic diseases.

Young investigator challenge: Application of cytologic techniques to circulating tumor cell specimens: Detecting activation of the oncogenic transcription factor STAT3.

BACKGROUND: The circulating tumor cell (CTC) field is rapidly advancing with the advent of continuously improving technologies for enriching these rare neoplastic cells from blood. CTC enumeration provides prognostic information, and CTC characterization has the potential to provide more useful information for the clinical decision-making process in this era of personalized medicine and targeted therapeutics. Proof-of-principle studies have shown that CTC samples can be characterized with a variety of techniques in the research laboratory environment. The goal of the current study was to validate routine cytologic techniques and immunohistochemical markers in CTC samples in a clinical cytology laboratory, using inducible phosphorylated signal transducer and activator of transcription 3 (pSTAT3) as a clinically important example and Ki-67 as a positive control. METHODS: Whole blood from noncancer patients was spiked with breast cancer cell lines with constitutive or inducible pSTAT3 expression and underwent CTC processing in the CellSearch system. The resulting CTC samples were subjected to various cytologic/immunocytochemical techniques and were compared with non-CTC-processed cultured cell controls. RESULTS: CTC-processed samples showed a morphology comparable to that of controls in cytospin, ThinPrep, and cell block preparations. Immunocytochemistry for Ki-67 and pSTAT3 provided biological information from CTC samples, showing uniform Ki-67 staining across all samples, pSTAT3 positivity in the constitutive and induced cells, and an absence of pSTAT3 expression in the noninduced cells, as expected. CONCLUSIONS: CTC samples can be processed in the cytology laboratory with routine methods. CTC morphologic and immunophenotypic analysis can be easily integrated into the existing clinical workflow, moving the field closer to a true peripheral blood liquid biopsy for cancer patients.

ΔNp63 (p40) expression in prostatic adenocarcinoma with diffuse p63 positivity.

Basal cells of benign prostate glands are typically p63 positive, whereas malignant glands are usually p63 negative. A rare subset of prostatic adenocarcinoma (PCa) demonstrates aberrant diffuse p63 expression but is negative for high-molecular-weight cytokeratin. Strong p63 staining of the tumor cells can obscure the loss of high-molecular-weight cytokeratin when using a cocktail of basal cell markers and create a diagnostic pitfall. The p63 protein has 6 major isoforms; of these, TAp63 and ΔNp63 (p40) are the best characterized N-terminal variants. In an attempt to aid in the diagnosis of p63-positive PCas, we studied ΔNp63 expression in tumors with aberrant p63. Immunohistochemistry was performed on 31 cores of aberrant p63-positive PCas from 24 patients and on a tissue microarray containing 125 cores of conventional PCas from 40 radical prostatectomy cases using a ΔNp63-specific polyclonal (p40) antibody and a TAp63-specific monoclonal antibody (p63, clone 4A4) that recognizes both TAp63 and ΔNp63. Most of the aberrant p63-positive tumors showed diffuse positivity for p40 (29/31 cores, 93.5%; 23/24 cases, 96%). All 40 conventional PCa (125 cores) were negative for p40 and p63 in the tumor cells. In summary, p40 is expressed in most p63-positive PCas but negative in p63-negative conventional PCas. From a diagnostic perspective, the use of immunohistochemistry for ΔNp63/p40 provides only a small advantage over the more widely used p63 assays. Our 1 ΔNp63-negative p63-positive case may represent expression of the TAp63 isoform in the tumor.

Androgen receptor controls EGFR and ERBB2 gene expression at different levels in prostate cancer cell lines.

EGFR or ERBB2 contributes to prostate cancer (PCa) progression by activating the androgen receptor (AR) in hormone-poor conditions. Here, we investigated the mechanisms by which androgens regulate EGFR and ERBB2 expression in PCa cells. In steroid-depleted medium (SDM), EGFR protein was less abundant in androgen-sensitive LNCaP than in androgen ablation-resistant 22Rv1 cells, whereas transcript levels were similar. Dihydrotestosterone (DHT) treatment increased both EGFR mRNA and protein levels and stimulated RNA polymerase II recruitment to the EGFR gene promoter, whereas it decreased ERBB2 transcript and protein levels in LNCaP cells. DHT altered neither EGFR or ERBB2 levels nor the abundance of prostate-specific antigen (PSA), TMEPA1, or TMPRSS2 mRNAs in 22Rv1 cells, which express the full-length and a shorter AR isoform deleted from the COOH-terminal domain (ARDeltaCTD). The contribution of both AR isoforms to the expression of these genes was assessed by small interfering RNAs targeting only the full-length or both AR isoforms. Silencing of both isoforms strongly reduced PSA, TMEPA1, and TMPRSS2 transcript levels. Inhibition of both AR isoforms did not affect EGFR and ERBB2 transcript levels but decreased EGFR and increased ERBB2 protein levels. Proliferation of 22Rv1 cells in SDM was inhibited in the absence of AR and ARDeltaCTD. A further decrease was obtained with PKI166, an EGFR/ERBB2 kinase inhibitor. Overall, we showed that ARDeltaCTD is responsible for constitutive EGFR expression and ERBB2 repression in 22Rv1 cells and that ARDeltaCTD and tyrosine kinase receptors are necessary for sustained 22Rv1 cell growth.