Novel therapies in urothelial carcinoma: a biomarker-driven approach

Urothelial malignancies, including carcinomas of the bladder, ureters, and renal pelvis comprised ∼8% of new cancer cases in the USA in 2016. In the metastatic setting, 15% of patients exhibit long-term survival following cisplatin-based chemotherapy and in patients with recurrent disease, response rates to second-line chemotherapy are generally 15%-20% with a 3-month progression-free survival. However, recent advances in immunotherapy represent an opportunity to significantly improve patient outcomes. Moreover, the advent of next-generation sequencing has resulted in both an improved understanding of the fundamental genetic changes that characterize urothelial carcinoma (UC) and identification of several candidate biomarkers of response to various therapies. Incorporation of prospective genotyping into clinical trials will allow for the identification and enrichment of patients most likely to respond to specific targeted therapies and chemotherapy. Combining different therapeutic classes to enhance outcomes is also an area of active research in UC.

Enhanced Radiosensitivity in Solid Tumors using a Tumor-selective Alkyl Phospholipid Ether Analog

Antitumor alkyl phospholipid (APL) analogs comprise a group of structurally related molecules with remarkable tumor selectivity. Some of these compounds have shown radiosensitizing capabilities. CLR127 is a novel, clinical-grade antitumor APL ether analog, a subtype of synthetic APL broadly targeting cancer cells with limited uptake in normal tissues. The purpose of this study was to investigate the effect of CLR127 to modulate radiation response across several adult and pediatric cancer types in vitro as well as in murine xenograft models of human prostate adenocarcinoma, neuroblastoma, Ewing sarcoma, and rhabdomyosarcoma. In vitro, CLR127 demonstrated selective uptake in cancer cells compared to normal cells. In cancer cells, CLR127 treatment prior to radiation significantly decreased clonogenic survival in vitro, and led to increased radiation-induced double-stranded DNA (dsDNA) breakage compared with radiation alone, which was not observed in normal controls. In animal models, CLR127 effectively increased the antitumor response to fractionated radiotherapy and led to delayed tumor regrowth at potentially clinically achievable doses. In conclusion, our study highlights the ability of CLR127 to increase radiation response in several cancer types. Given almost universal uptake of CLR127 in malignant cells, future research should test whether the observed effects can be extended to other tumor types. Our data provide a strong rationale for clinical testing of CLR127 as a tumor-targeted radiosensitizing agent. Mol Cancer Ther; 17(11); 2320-8. ©2018 AACR.

Abstract 3946: Androgen receptor drives differential gene expression in KRAS-mediated non-small cell lung cancer

The Cancer Genome Atlas (TCGA) has identified alterations such as amplification, deletion, or mutation of androgen receptor (AR) in about 5% of human lung squamous cell carcinoma and adenocarcinoma. The expression of AR in human lung appears to play a crucial role in lung development and type II pneumocytes (PTII) maturation, but unlike in prostate cancer, the role of AR is not well known in non-small cell lung cancer (NSCLC). In our study, we demonstrated AR in NSCLC cell lines translocated into the nucleus over time when stimulated with synthetic androgen R1881, while addition of enzalutamide (MDV3100) or AR siRNA reduced AR nuclear localization. Using an NSCLC human tissue microarray also revealed that 10 out of 88 patients (11%) have positive AR immunohistochemical staining. Preliminary data from clonogenic assay indicated that enzalutamide might have radiosensitizing effect on certain NSCLC cells at 2 Gy, further suggesting the involvement of AR in lung cancer and its potential therapeutic value as a target. With the induction of R1881 for 30 minutes to 24 hours, certain NSCLC cells display decreased AR mRNA (0.5-0.8 fold), while others show modest increase (up to 1.5 fold), suggesting that AR regulation in these cells might be different due to their mutational landscapes. We then used predesigned 384 well panels from Bio-Rad to survey the effects of R1881, enzalutamide, and AR siRNA on mRNA expression levels of selected NSCLC cells. Distinct expression profiles were observed between cells that have wild-type and mutated KRAS. Taken together, these findings suggest that the AR signaling could be different based on KRAS mutational profiles of NSCLCs, and further work is required to reveal the underlying mechanism. Chromatin immunoprecipitation (ChIP) assay and RNA sequencing will be utilized to investigate AR interactions with androgen response elements and differential expressions in KRAS-driven NSCLC cells, respectively.

Citation Format: Albert Roy Wang, Hope Beyer, Sean Brennan, Shannon Stiles, Dylan Wiese, Darya Buehler, Anwaar Saeed, Andrew M. Baschnagel, Gopal Iyer. Androgen receptor drives differential gene expression in KRAS-mediated non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3946.

Abstract 5796: Modulation of transcription factor landscape through BET family protein inhibition is dependent on specific driver mutations in pancreatic cancer

Targeting of bromodomain and extra-terminal domain (BET) family protein activity has the potential to reduce proliferation in many cancers. However, changes in transcription factor (TF) landscape can be influenced by different mutational profiles of specific cancers. Within this mutational background, BET proteins can target these TFs and create an oncogenic phenotype. To exploit these altered TF readouts, we tested the hypothesis that inhibition of BET activity in different genetic mutations of pancreatic cancer will lead to antiproliferative effects. Towards this, we treated pancreatic cancer cell lines that had mutations in KRAS, CDKN1A, SMAD4 and TP53 with a bromodomain inhibitor. We showed that cell lines with CDKN1A deletion and wild-type SMAD4 were highly resistant to BET inhibition and had a high nanomolar IC50 concentration. Through targeted transcription factor gene expression profiling of over 400 TFs, we discovered that LMO2, GTF2B, ID1, and CREB1 were upregulated, while SALL4, TCF4, and TP63 were downregulated in these cell lines. This suggests that these TFs may be partly responsible for resistance to BET inhibition. Furthermore, we showed dramatic changes in TF landscapes in pancreatic cancer cells sensitive to BET treatment compared to the resistant cells. This indicates that for antiproliferative effects in pancreatic cancer cells, modulating BET activity may be necessary to switch on or off specific TFs. Together, these results suggest that BET inhibitors may be useful in pancreatic cancer treatment and that mutation-specific differences in TF targets of BETs may dictate the progression of pancreatic cancer.

Citation Format: Mikele G. Weldon, Albert R. Wang, Hope A. Beyer, Shannon G. Stiles, Gopal Iyer. Modulation of transcription factor landscape through BET family protein inhibition is dependent on specific driver mutations in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5796.

Commentary on "DNA damage response and repair gene alterations are associated with improved survival in patients with platinum-treated advanced urothelial carcinoma."

PURPOSE

Platinum-based chemotherapy remains the standard treatment for advanced urothelial carcinoma by inducing DNA damage. We hypothesize that somatic alterations in DNA damage response and repair (DDR) genes are associated with improved sensitivity to platinum-based chemotherapy.

EXPERIMENTAL DESIGN

Patients with diagnosis of locally advanced and metastatic urothelial carcinoma treated with platinum-based chemotherapy who had exon sequencing with the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) assay were identified. Patients were dichotomized based on the presence/absence of alterations in a panel of 34 DDR genes. DDR alteration status was correlated with clinical outcomes and disease features.

RESULTS

One hundred patients were identified, of which 47 harbored alterations in DDR genes. Patients with DDR alterations had improved progression-free survival (9.3 vs. 6.0 months, log-rank P = 0.007) and overall survival (23.7 vs. 13.0 months, log-rank P = 0.006). DDR alterations were also associated with higher number mutations and copy-number alterations. A trend toward positive correlation between DDR status and nodal metastases and inverse correlation with visceral metastases were observed. Different DDR pathways also suggested variable effect on clinical outcomes.

CONCLUSIONS

Somatic DDR alteration is associated with improved clinical outcomes in platinum-treated patients with advanced urothelial carcinoma. Once validated, it can improve patient selection for clinical practice and future study enrollment.

Abstract 827: Statistical analyses of stable housekeeping gene expression in cancer post-irradiation

Ionizing radiation (IR) can induce DNA damage in human cells and result in changes in gene expression. The changes could also include some of the commonly used housekeeping genes (HKG), and thus making them unstable over the time period after being exposed to radiation. Normalization of housekeeping genes is critical for understanding gene expression post-irradiation. Toward the validation of stable HKGs, cancer cell lines from head and neck, non-small cell lung and pancreas were irradiated to 2, 4 and 6 Gy IR doses. Statistical analysis of RNA expression of fourteen HKGs measured at 5 min to 48hrs post-irradiation reveal tradition HKGs such as beta-actin (ACTB) and glucose-6-phosphate-dehydrogenase (G6PD) to be unstable, while TATA-Box Binding Protein (TBP) and Importin 8 (IPO8) was identified as stable HKGs in non-small lung and pancreas cell across all IR doses and time. Interestingly in head and neck cancer, TBP is also found stable across all IR doses and time. The statistical framework used for identification and validation of HKGs can serve as a reliable metric for quantifying gene expression post-irradiation.

Citation Format: Albert R. Wang, Gopal Iyer, Sean Brennan, Shay Bourgeois, Eric Armstrong, Pari Shah, Paul M. Harari. Statistical analyses of stable housekeeping gene expression in cancer post-irradiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 827. doi:10.1158/1538-7445.AM2017-827

Abstract 4121: Androgen receptor as a potential target in non-small cell lung cancer

The cancer genome atlas (TCGA) has identified androgen receptor (AR) to be mutated, deleted and amplified across human lung squamous cell carcinoma and adenocarcinoma. Expression of AR is critical for early lung development. However, the intriguing expression of AR in non-small cell lung cancer (NSCLC) opens up an alternative treatment paradigm in the event of onset of clinical resistance to lung cancer drugs. To investigate this potential, a) 10 NSCLC cell lines and 3 control prostate cancer cell lines were stimulated with synthetic AR agonist, R1881 at 24, 48 and 72 hours. 0.5-4-fold RNA and protein expression was found across these lung cancer cell lines when compared to unstimulated cells. b) droplet digital PCR revealed varying copies of AR DNA when benchmarked to prostate AR. c) cell proliferation assays of these cell lines with enzalutamide (MVD3100) treatment resulted in 50-65% cell survival at concentrations ranging from 10 - 25 µM. d) Immunohistochemical staining of AR in a NSCLC human tissue microarray (TMA) revealed 10 out of 88 patients (11%) to have AR positive staining in their tumor. This included 6 adenocarcinomas and 2 squamous cell carcinomas. 8 patients had focal while 2 had diffuse staining. Validation of the TMA performed with whole mount slides confirmed diffuse staining in these 11 samples. Taken together, these findings suggest AR is a potential therapeutic target in NSCLC and further work is underway to test these observations in drug resistant lung cancer cell lines and pre-clinical mouse models.

Citation Format: Sean Brennan, Albert R. Wang, Hope Beyer, Dylan Wiese, Darya Buehler, Anwaar Saeed, Andrew M. Baschnagel, Gopal Iyer. Androgen receptor as a potential target in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4121. doi:10.1158/1538-7445.AM2017-4121

Insulin-like growth factor 1 receptor mediated tyrosine 845 phosphorylation of epidermal growth factor receptor in the presence of monoclonal antibody cetuximab

BACKGROUND

The epidermal growth factor receptor (EGFR) is frequently overexpressed in head and neck squamous cell carcinoma (HNSCC) and several other human cancers. Monoclonal antibodies, such as cetuximab that block EGFR signaling, have emerged as valuable molecular targeting agents in clinical cancer therapy. Prolonged exposure to cetuximab can result in cells acquiring resistance by a process that remains incompletely understood.

METHODS

In this study, we analyzed the immediate early molecular response of cetuximab on physical interactions between EGFR and Insulin growth factor 1 like receptor (IGF-1R) in head and neck cancer cells that are resistant to cetuximab. Co-immunoprecipitation, small molecule inhibitors against phospho-Src and IGF-1R, quantitative western blot of EGFR and Src phosphorylation, cell proliferation assays were used to suggest the role of IGF-1R mediated phosphorylation of specific tyrosine Y845 on EGFR via increased heterodimerization of EGFR and IGF-1R in cetuximab resistant cells.

RESULTS

Heterodimerization of EGFR with IGF-1R was increased in cetuximab resistant HNSCC cell line UMSCC6. Basal levels of phosphorylated EGFR Y845 showed significant increase in the presence of cetuximab. Surprisingly, this activated Y845 level was not inhibited in the presence of Src inhibitor PP1. Instead, inhibition of IGF-1R by picropodophyllin (PPP) reduced the EGFR Y845 levels. Taken together, these results suggest that heterodimerization of EGFR with IGF-1R can lead to increased activity of EGFR and may be an important platform for cetuximab mediated signaling in head and neck tumors that have become resistant to anti-EGFR therapy.

CONCLUSIONS

EGFR-IGF-1R interaction has a functional consequence of phosphorylation of EGFR Y845 in cetuximab resistant HNSCC cells and dual targeting of EGFR and IGF-1R is a promising therapeutic strategy.

Microfluidic enrichment for the single cell analysis of circulating tumor cells

Resistance to drug therapy is a major concern in cancer treatment. To probe clones resistant to chemotherapy, the current approach is to conduct pooled cell analysis. However, this can yield false negative outcomes, especially when we are analyzing a rare number of circulating tumor cells (CTCs) among an abundance of other cell types. Here, we develop a microfluidic device that is able to perform high throughput, selective picking and isolation of single CTC to 100% purity from a larger population of other cells. This microfluidic device can effectively separate the very rare CTCs from blood samples from as few as 1 in 20,000 white blood cells. We first demonstrate isolation of pure tumor cells from a mixed population and track variations of acquired T790M mutations before and after drug treatment using a model PC9 cell line. With clinical CTC samples, we then show that the isolated single CTCs are representative of dominant EGFR mutations such as T790M and L858R found in the primary tumor. With this single cell recovery device, we can potentially implement personalized treatment not only through detecting genetic aberrations at the single cell level, but also through tracking such changes during an anticancer therapy.

Small Molecule Inhibition of MDM2-p53 Interaction Augments Radiation Response in Human Tumors

MDM2-p53 interaction and downstream signaling affect cellular response to DNA damage. AMG 232 is a potent small molecule inhibitor that blocks the interaction of MDM2 and p53. We examined the capacity of AMG 232 to augment radiation response across a spectrum of human tumor cell lines and xenografts. AMG 232 effectively inhibited proliferation and enhanced radiosensitivity via inhibition of damage repair signaling. Combined AMG 232 and radiation treatment resulted in the accumulation of γH2AX-related DNA damage and induction of senescence with promotion of apoptotic and/or autophagic cell death. Several molecules involved in senescence, autophagy, and apoptosis were specifically modulated following the combined AMG 232/radiation treatment, including FoxM1, ULK-1, DRAM, and BAX. In vivo xenograft studies confirmed more potent antitumor and antiangiogenesis efficacy with combined AMG 232/radiation treatment than treatment with drug or radiation alone. Taken together, these data identify the capacity of AMG 232 to augment radiation response across a variety of tumor types harboring functional p53.

Abstract 4660: Temporal interrogation of EGFR signaling in head and neck cancer reveals highly distinct phosphorylation waves for individual EGFR inhibitors

Targeting the epidermal growth factor receptor (EGFR/HER) family is an effective target for cancer therapeutics with thousands of cancer patients treated annually with EGFR inhibitors. However, we are only beginning to appreciate the rapid and dynamic signaling impact of various EGFR inhibitors on cancer cell phosphorylation events. The purpose of this study was to characterize the temporal phosphoprotein kinetics in head and neck cancer cells treated with the anti-EGFR antibodies cetuximab and Sym004. For the first time, perturbation data were generated using reverse phase protein array probed with 183 phosphorylated proteins involved in various signaling pathways at 11 different time points starting as early as 5 min and up to 24 hours. A novel signaling module comprised of phospho-ATM at Ser-1981, p-53(Ser15), p-IkB-α (Ser32/36) and p-Bad (Ser112) was found to be highly upregulated following exposure to Sym004. Concomitantly, high resolution imaging also revealed rapid EGFR degradation and increased endosomal trafficking with Sym004 treatment. Correlation matrix on a temporal scale revealed distinct network topologies suggesting that phosphorylation occurs in distinct waves over time. These response patterns were highly distinct when comparing cetuximab with Sym004. Using this platform, we are able to quantify the strength of various signaling networks triggered by EGFR inhibition and are able to model new pathways. These findings may have significant implications for developing more personalized treatment strategies including logical combination with other molecular target inhibitors.

Note: This abstract was not presented at the meeting.

Citation Format: Gopal Iyer. Temporal interrogation of EGFR signaling in head and neck cancer reveals highly distinct phosphorylation waves for individual EGFR inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4660. doi:10.1158/1538-7445.AM2014-4660

Germline single nucleotide polymorphisms associated with response of urothelial carcinoma to platinum-based therapy: the role of the host

BACKGROUND

Variations in urothelial carcinoma (UC) response to platinum chemotherapy are common and frequently attributed to genetic and epigenetic variations of somatic DNA. We hypothesized that variations in germline DNA may contribute to UC chemosensitivity.

PATIENTS AND METHODS

DNA from 210 UC patients treated with platinum-based chemotherapy was genotyped for 80 single nucleotide polymorphisms (SNPs). Logistic regression was used to examine the association between SNPs and response, and a multivariable predictive model was created. Significant SNPs were combined to form a SNP score predicting response. Eleven UC cell lines were genotyped as validation.

RESULTS

Six SNPs were significantly associated with 101 complete or partial responses (48%). Four SNPs retained independence association and were incorporated into a response prediction model. Each additional risk allele was associated with a nearly 50% decrease in odds of response [odds ratio (OR) = 0.51, 95% confidence interval 0.39-0.65, P = 1.05 × 10(-7)). The bootstrap-adjusted area under the curves of this model was greater than clinical prognostic factors alone (0.78 versus 0.64). The SNP score showed a positive trend with chemosensitivity in cell lines (P = 0.115).

CONCLUSIONS

Genetic variants associated with response of UC to platinum-based therapy were identified in germline DNA. A model using these genetic variants may predict response to chemotherapy better than clinical factors alone.

A phase Ib safety and tolerability study of a pan class I PI3K inhibitor buparlisib (BKM120) and gefitinib (gef) in EGFR TKI-resistant NSCLC

8107

Background: Overcoming EGFR TKI resistance (R) is a major clinical challenge; reported mechanisms include EGFR T790M mutation (mt), MET amplification (amp) and PIK3CA mt. As the PI3K pathway is a central convergent signaling node, we hypothesized that addition of buparlisib (BKM) could overcome EGFR TKI-R. Methods: Patients (pt) resistant to EGFR TKI (Jackman JCO 2010) were enrolled to determine safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of BKM-gef. Using a “3+3” design, escalating doses of BKM were added to pt progressing on gef (Gp A). Pt not on gef preceding enrolment received a 2 wk run in (Gp B). Given the favorable CNS penetration of BKM, a CNS gp with brain metastases only was included. Pt had pretreatment biopsies and sequential PET-CT scans (baseline & d28). Results: 15 pt have been treated at 3 dose levels: BKM 80 mg/d (n=6), 100 mg/d (n=6), 80 mg 5d on 2d off (5/2, n=3), with gef 250 mg/d. Gp A (n=9, 1 CNS), B (n=6, 1 CNS), F:M (9:6), median age 63 (47-73) and majority >3 lines of therapy. DLT was G3 diarrhea observed in 2/6 pt at BKM100. Common adverse events (AE, all grades) include rash (80%), diarrhea (73%), fatigue (60%), anorexia (47%), mucositis (40%). Notably, 40% of pt had late (beyond DLT period) G3 toxicities such as rash and diarrhea. MTD is BKM 80/d and gef 250/d. To improve the overall safety profile, an intermittent schedule of BKM80 5/2 was also found to be feasible. In gp B, PET-CT done after 2 wk run-in of gef, 3/4 evaluable pt demonstrated reduction in SUVmax of which 1 had PR. With addition of BKM, reduction in SUVmax (>25%) was seen in 4/10 pt (gp A & B). Median PFS 2.8 m (95%CI 2.3 – 8.1), two pt in CNS gp had PFS of 2.8 and 10.7 m. Molecular analyses revealed 6/12 (50%) harbored T790M mt, 2/5 (40%) MET amp, 0/12 PI3KCA mt. In gp A, 4/9 pt (2 T790M; 1 MET amp) had clinical responses, including slight tumor shrinkage and reduced pleural effusion, but required dose reductions due to AE. PK profiles are being analyzed. Conclusions: MTD is gef 250-BKM 80/d. Antitumor activity has been observed with addition of BKM in EGFR TKI-R pt. In view of late toxicities and long t½ of BKM, exploring alternative schedules is warranted. A dose expansion cohort at MTD is currently ongoing. Clinical trial information: NCT01570296.

Aromatic aldehyde and hydrazine activated peptide coated quantum dots for easy bioconjugation and live cell imaging

We present a robust scheme for preparation of semiconductor quantum dots (QDs) and cognate partners in a conjugation ready format. Our approach is based on bis-aryl hydrazone bond formation mediated by aromatic aldehyde and hydrazinonicotinate acetone hydrazone (HyNic) activated peptide coated quantum dots. We demonstrate controlled preparation of antibody--QD bioconjugates for specific targeting of endogenous epidermal growth factor receptors in breast cancer cells and for single QD tracking of transmembrane proteins via an extracellular epitope. The same approach was also used for optical mapping of RNA polymerases bound to combed genomic DNA in vitro.

Alterations in genes regulating cell cycle and apoptosis in high-grade urothelial carcinoma

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Background: Dysregulations of cell cycle and inhibition of apoptosis are crucial factors in tumorigenesis of multiple malignancies, including urothelial carcinoma (UC). Deletions of TP53 and CDKN2A and amplification of MDM2 have been observed in UC, but their exact frequency and functional consequence is less known. We sought to determine the frequency of copy number alteration (CNA) and mutations of genes that regulate cell cycle or apoptosis in a panel of 96 cases of high-grade UC (HGUC) of bladder.

Methods: 96 frozen cases of HGUC were studied, including 11 bladder small cell carcinomas. DNA was isolated and analyzed for CNA by comparative genomic hybridization (CGH) using a one million oligonucleotide probe array from Agilent. The targeted genes included TP53, MDM2, CCND1, CCNE1, CDKN2A/B, E2F3 and Rb1. Traditional Sanger sequencing for mutations within TP53, Rb1, and CDKN2A was also performed.

Results: The frequency of CNA and mutations are listed in the table. Overall, 54 of 96 cases (56%) showed CNA (45) or mutation (13). Deletion of CDKN2A/B and amplification of E2F3 were the most common alterations in cell cycle regulatory genes (13 cases each, 14%), followed by amplification of CCND1 (11 cases, 11%). There was no co-amplification of CCND1 and CCNE1 in any sample. Rb1 deletion was present in five cases. CNA in E2F3 and Rb1 were mutually exclusive in 14 of 16 cases (88%) and were both present in two cases only. Mutations in TP53 were noted in 13 cases and deletions in nine. Amplification of MDM2 was noted in four cases, none of which overlapped with TP53 deletions or mutations. Overexpression of E2F3 was significantly more common in small cell carcinoma (5/11) compared to conventional UC (8/85, p = 0.006).

Conclusions: Regulators of cell cycle and apoptosis are amplified, deleted or mutated in more than half of cases (56%) of high-grade urothelial carcinoma. The overwhelming majority of these abnormalities are nonoverlapping. Amplification of E2F3 seems to be overrepresented in small cell carcinoma of bladder.

[Table: see text]

No significant financial relationships to disclose.

Single-step conjugation of antibodies to quantum dots for labeling cell surface receptors in mammalian cells

Labeling of cell surface receptors in living cells can be achieved using antibody-conjugated semiconductor quantum dots (QDs). The inherent photostable property of QDs can be exploited for understanding the arrangement and distribution of receptors in the plasma membrane. We describe herein methods that allow conjugation of antibodies to QDs in a single step without the formation of side products. This protocol can be adapted universally for any type of QD structure with a coating of free amino groups.