The Clinical Significance of Circulating Tumor DNA for Minimal Residual Disease Identification in Early-Stage Non-Small Cell Lung Cancer.

Lung cancer (LC) is the deadliest malignancy worldwide. In an operable stage I-III patient setting, the detection of minimal residual disease (MRD) after curative treatment could identify patients at higher risk of relapse. In this context, the study of circulating tumor DNA (ctDNA) is emerging as a useful tool to identify patients who could benefit from an adjuvant treatment, and patients who could avoid adverse events related to a more aggressive clinical management. On the other hand, ctDNA profiling presents technical, biological and standardization challenges before entering clinical practice as a decisional tool. In this paper, we review the latest advances regarding the role of ctDNA in identifying MRD and in predicting patients' prognosis, with a particular focus on clinical trials investigating the potential of ctDNA, the technical challenges to address and the biological parameters that influence the MRD detection.

Comparative Analysis of Free-Circulating and Vesicle-Associated Plasma microRNAs of Healthy Controls and Early-Stage Lung Cancer Patients.

In recent years, circulating extracellular miRNAs have emerged as a useful tool for the molecular characterization and study of tumors' biological functions. However, the high heterogeneity in sample processing, isolation of circulating fraction, RNA extraction, and sequencing hamper the reproducibility and the introduction of these biomarkers in clinical practice. In this paper, we compare the content and the performance of miRNA sequencing in plasma-derived samples processed with different isolation protocols. We tested three different fractions of miRNA from healthy-donor human blood: whole plasma (WP), free-circulating (FC) and EV-associated, isolated by either column (ccEV) or size exclusion chromatography (secEV) miRNAs. An additional cohort of 18 lung cancer patients was analyzed. Protein profiles of ccEV and secEV were compared and miRNA expression profiles were assessed through sequencing. Slight differences were found between ccEV and secEV expressions of typical EV markers. Conversely, sequencing performance and the mirnome profile varied between RNA extracted using different isolation methods. Sequencing performance was better in FC samples. Higher varieties of miRNAs were identified in WP and FC with respect to ccEV and secEV. Analysis of free-circulating and EV-associated miRNA profiles in lung cancer patients demonstrated the reliability of the biomarkers identifiable on plasma with these approaches.

The Role of TP53 Mutations in EGFR-Mutated Non-Small-Cell Lung Cancer: Clinical Significance and Implications for Therapy.

Non-Small-Cell Lung Cancer (NSCLC) is the primary cause of cancer-related death worldwide. Oncogene-addicted patients usually benefit from targeted therapy, but primary and acquired resistance mechanisms inevitably occur. Tumor protein 53 (TP53) gene is the most frequently mutated gene in cancer, including NSCLC. TP53 mutations are able to induce carcinogenesis, tumor development and resistance to therapy, influencing patient prognosis and responsiveness to therapy. TP53 mutants present in different forms, suggesting that different gene alterations confer specific acquired protein functions. In recent years, many associations between different TP53 mutations and responses to Epidermal Growth Factor Receptor (EGFR) targeted therapy in NSCLC patients have been found. In this review, we discuss the current landscape concerning the role of TP53 mutants to guide primary and acquired resistance to Tyrosine-Kinase Inhibitors (TKIs) EGFR-directed, investigating the possible mechanisms of TP53 mutants within the cellular compartments. We also discuss the role of the TP53 mutations in predicting the response to targeted therapy with EGFR-TKIs, as a possible biomarker to guide patient stratification for treatment.

Case Report: The Added Value of Liquid Biopsy in Advanced Colorectal Cancer From Clinical Case Experiences.

Liquid biopsy represents a valid strategy for tumor molecular characterization. It gives the opportunity to bypass tumor heterogeneity, to monitor tumor characteristics during the course of treatment, and to perform the analysis even when tumor tissue is not available or inadequate. In the clinical practice of metastatic colorectal cancer, tumor molecular characterization is crucial for patient management, as RAS and BRAF status could influence the treatment choice. Although for this type of cancer tumor tissue is usually available at diagnosis, liquid biopsy could give complementary information and could permit monitoring of the mutation status during the course of treatment. At present, there are no clinical indications for its use in clinical practice. However, we report four clinical cases for which liquid biopsy analysis gave integrative information with respect to tumor tissue characterization, which permits us to understand the unresponsiveness of patients to treatment, with potential implications in patient's management.

Unveiling mutational dynamics in non-small cell lung cancer patients by quantitative EGFR profiling in vesicular RNA.

The mutational status of the epidermal growth factor receptor (EGFR) guides the stratification of non-small cell lung cancer (NSCLC) patients for treatment with tyrosine kinase inhibitors (TKIs). A liquid biopsy test on cell-free DNA is recommended as a clinical decision-supporting tool, although it has limited sensitivity. Here, we comparatively investigated the extracellular vesicle (EV)-RNA as an independent source for multidimensional and longitudinal EGFR profiling in a cohort of 27 NSCLC patients. We introduced and validated a new rapid, highly specific EV-RNA test with wild-type (WT) and mutant-sensitive probes (E746-A750del, L858R, and T790M). We included a cohort of 20 NSCLC patients with EGFR WT tumor tissues and systematically performed molecular EV-RNA and circulating tumor DNA analyses with clinical data statistics and biophysical profiles of EVs. At the single-patient level, we detected variegated tumor heterogeneity dynamics supported by combinations of driver EGFR mutations. EV-RNA-based mutation analysis showed an unprecedented sensitivity of over 90%. The resistance-associated mutation T790M frequently pre-existed at baseline with a gained EV-transcript copy number at progression, while the general mutational burden was mostly decreasing during the intermediate follow-up. The biophysical profile of EVs and the quantitative assessment of T790M revealed an association with tumor size determined by the sum of the longest diameters in target lesions. Vesicular RNA provides a validated tool suitable for use in clinical practice to investigate the dynamics of common driver EGFR mutations in NSCLC patients receiving TKIs.

Brigatinib in the first-line treatment of ALK+ metastatic NSCLC: safety and efficacy.

Introduction: Among the oncogene-addicted non-small cell lung cancer patients, those bearing ALK rearrangement can be currently treated with next-generation ALK inhibitors. Brigatinib was first used to treat Crizotinib-resistant patients because it can target resistance mutations in ALK fusion protein. Recently, Brigatinib was also studied as upfront treatment of newly diagnosed ALK-positive patients.Areas covered: We outline the drug profile of Brigatinib as first-line treatment and compare it with other ALK inhibitors available. The context of ALK-rearranged non-small cell lung cancer and pharmacological aspects of Brigatinib are reviewed before the analysis of the results from the study ALTA-1 L in terms of efficacy and safety.Expert opinion: The superior efficacy of Brigatinib over Crizotinib as first-line treatment is undoubted. Consequently, Brigatinib is a new option in untreated ALK+ metastatic NSCLC patients, among the other drugs available for this indication, such as Ceritinib and Alectinib. Each of these ALK inhibitors has a specific tolerability profile, so that the choice may be also guided by patient preference according to potential side effects. In the future other factors could impact treatment choice, for instance the kind of resistance ALK mutations develop under treatment could influence the sequence of ALK inhibitors.

Detection of EGFR Mutations in Plasma Cell-Free Tumor DNA of TKI-Treated Advanced-NSCLC Patients by Three Methodologies: Scorpion-ARMS, PNAClamp, and Digital PCR.

Analysis of circulating cell-free tumor DNA (cftDNA) has emerged as a specific and sensitive blood-based approach to detect epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) patients. Still, there is some debate on what should be the preferential clinical method for plasma-derived cftDNA analysis. We tested 31 NSCLC patients treated with anti-EGFR tyrosine kinase inhibitors (TKIs), at baseline and serially during therapy, by comparing three methodologies in detecting EGFR mutations (L858R, exon 19 deletion, and T790M) from plasma: scorpions-amplification refractory mutation system (ARMS) methodology by using EGFR Plasma RGQ PCR Kit-QIAGEN, peptide nucleic acid (PNA) clamp and PANA RealTyper integration by using PNAClamp EGFR-PANAGENE, and digital real time PCR by using QuantStudio 3D Digital PCR System-Thermo Fisher Scientific. Specificity was 100% for all three mutations, independently from the platform used. The sensitivity for L858R (42.86%) and T790M (100%) did not change based on the method, while the sensitivity for Del 19 differed markedly (Scorpion-ARMS 45%, PNAClamp 75%, and Digital PCR 85%). The detection rate was also higher (94.23%) as measured by Digital PCR, and when we monitored the evolution of EGFR mutations over time, it evidenced the extreme inter-patient heterogeneity in terms of levels of circulating mutated copies. In our study, Digital PCR showed the best correlation with tissue biopsy and the highest sensitivity to attain the potential clinical utility of monitoring plasma levels of EGFR mutations.

Instability of Non-Standard Microsatellites in Relation to Prognosis in Metastatic Colorectal Cancer Patients.

Very few data are reported in the literature on the association between elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) and prognosis in advanced colorectal cancer. Moreover, there is no information available in relation to the response to antiangiogenic treatment. We analyzed EMAST and vascular endothelial growth factor-B (VEGF-B) microsatellite status, together with standard microsatellite instability (MSI), in relation to prognosis in 141 patients with metastatic colorectal cancer (mCRC) treated with chemotherapy (CT) alone (n = 51) or chemotherapy with bevacizumab (B) (CT + B; n = 90). High MSI (MSI-H) was detected in 3% of patients and was associated with progression-free survival (PFS; p = 0.005) and overall survival (OS; p < 0.0001). A total of 8% of cases showed EMAST instability, which was associated with worse PFS (p = 0.0006) and OS (p < 0.0001) in patients treated with CT + B. A total of 24.2% of patients showed VEGF-B instability associated with poorer outcome in (p = 0.005) in the CT arm. In conclusion, our analysis indicated that EMAST instability is associated with worse prognosis, particularly evident in patients receiving CT + B.

Extracellular Vesicles in Non-Small-Cell Lung Cancer: Functional Role and Involvement in Resistance to Targeted Treatment and Immunotherapy.

Targeted and immunological therapies have become the gold standard for a large portion of non-small cell lung cancer (NSCLC) patients by improving significantly clinical prognosis. However, resistance mechanisms inevitably develop after a first response, and almost all patients undergo progression. The knowledge of such a resistance mechanism is crucial to improving the efficacy of therapies. So far, monitoring therapy responses through liquid biopsy has been carried out mainly in terms of circulating tumor (ctDNA) analysis. However, other particles of tumor origin, such as extracellular vehicles (EVs) represent an emerging tool for the studying and monitoring of resistance mechanisms. EVs are now considered to be ubiquitous mediators of cell-to-cell communication, allowing cells to exchange biologically active cargoes that vary in response to the microenvironment and include proteins, metabolites, RNA species, and nucleic acids. Novel findings on the biogenesis and fate of these vesicles reveal their fundamental role in cancer progression, with foreseeable and not-far-to-come clinical applications in NSCLC.

Role of liquid biopsy in oncogene-addicted non-small cell lung cancer.

The discovery of actionable oncogene in non-small cell lung cancer (NSCLC) allowed the identification of a subgroup of patients who benefit from targeted tyrosine kinase inhibitors more than others. Mutations in the epidermal growth factor receptor (EGFR), translocations in the anaplastic lymphoma kinase (ALK) and rearrangements in the ROS proto-oncogene 1 (ROS1) must be identified in tumor tissue to guide the proper treatment choice. Liquid biopsy is based on the analysis of tumor materials released in the circulation. Liquid biopsy can be complementary to tissue biopsy, both at baseline and at progression, especially in the detection of somatic gene alterations emerging during the treatment with tyrosine kinase inhibitors (TKIs). Particularly, circulating DNA is used to find mutations in driver oncogenes, while circulating tumor cells, extracellular vesicles (EVs) and cell-free microRNAs (cfmiRNAs) are still under investigation. To help the unbiased use of liquid biopsy in the choice of the appropriate therapy, some recommendations were delivered by expert panels. Currently, analysis of EGFR mutations in cell-free DNA (cfDNA) is recommended at baseline when tissue biopsy harbors scarce tumor cells, and at progression before performing tissue biopsy; liquid biopsy analysis for other oncogenic drivers is not indicated in the clinical practice.

Liquid Biopsy for the Detection of Resistance Mechanisms in NSCLC: Comparison of Different Blood Biomarkers.

The use of targeted agents and immunotherapy for the treatment of advanced non-small-cell lung cancer (NSCLC) has made it mandatory to characterize tumor tissue for patient selection. Moreover, the development of agents that are active against specific resistance mechanisms arising during treatment make it equally important to characterize the tumor tissue at progression by performing tissue re-biopsy. Given that tumor tissue is not always available for molecular characterization due to the paucity of diagnostic specimens or problems relating to the carrying out of invasive procedures, the use of liquid biopsy represents a valid approach to overcoming these difficulties. The most common material used for liquid biopsy in this setting is plasma-derived cell free DNA (cfDNA), which originates from cells undergoing apoptosis or necrosis. However, other sources of tumor material can be considered, such as extracellular vesicle (EV)-derived nucleic acids, which are actively secreted from living cells and closely correspond to tumor dynamics. In this review, we discuss the role of liquid biopsy in the therapeutic management of NSCLC with particular regard to targeted therapy and immunotherapy, and analyze the pros and cons of the different types of samples used in this context.

Ultrasensitive detection of cancer biomarkers by nickel-based isolation of polydisperse extracellular vesicles from blood.

BACKGROUND: Extracellular vesicles (EVs) are secreted membranous particles intensively studied for their potential cargo of diagnostic markers. Efficient and cost-effective isolation methods need to be established for the reproducible and high-throughput study of EVs in the clinical practice. METHODS: We designed the nickel-based isolation (NBI) to rapidly isolate EVs and combined it with newly-designed amplified luminescent proximity homogeneous assay or digital PCR to detect biomarkers of clinical utility. FINDINGS: From plasma of 46 healthy donors, we systematically recovered small EV (~250 nm of mean diameter; ~3 × 1010/ml) and large EV (~560 nm of mean diameter; ~5 × 108/ml) lineages ranging from 50 to 700 nm, which displayed hematopoietic/endothelial cell markers that were also used in spike-in experiments using EVs from tumor cell lines. In retrospective studies, we detected picomolar concentrations of prostate-specific membrane antigen (PSMA) in fractions of EVs isolated from the plasma of prostate cancer patients, discriminating them from control subjects. Directly from oil-encapsulated EVs for digital PCR, we identified somatic BRAF and KRAS mutations circulating in the plasma of metastatic colorectal cancer (CRC) patients, matching 100% of concordance with tissue diagnostics. Importantly, with higher sensitivity and specificity compared with immuno-isolated EVs, we revealed additional somatic alterations in 7% of wild-type CRC cases that were subsequently validated by further inspections in the matched tissue biopsies. INTERPRETATION: We propose NBI-combined approaches as simple, fast, and robust strategies to probe the tumor heterogeneity and contribute to the development of EV-based liquid biopsy studies. FUND: Associazione Italiana per la Ricerca sul Cancro (AIRC), Fondazione Cassa di Risparmio Trento e Rovereto (CARITRO), and the Italian Ministero Istruzione, Università e Ricerca (Miur).

Prognostic Role of Circulating miRNAs in Early-Stage Non-Small Cell Lung Cancer.

Non-small cell lung cancer (NSCLC) is the primary cause of cancer-related death worldwide, with a low 5-year survival rate even in fully resected early-stage disease. Novel biomarkers to identify patients at higher risk of relapse are needed. We studied the prognostic value of 84 circulating microRNAs (miRNAs) in 182 patients with resected early-stage NSCLC (99 adenocarcinoma (ADC), 83 squamous cell carcinoma (SCC)) from whom peripheral blood samples were collected pre-surgery. miRNA expression was analyzed in relation to disease-free survival (DFS) and overall survival (OS). In univariable analyses, five miRNAs (miR-26a-5p, miR-126-3p, miR-130b-3p, miR-205-5p, and miR-21-5p) were significantly associated with DFS in SCC, and four (miR-130b-3p, miR-26a-5p, miR-126-3p, and miR-205-5p) remained significantly associated with OS. In ADC, miR-222-3p, miR-22-3p, and mir-93-5p were significantly associated with DFS, miR-22-3p remaining significant for OS. Given the high-dimensionality of the dataset, multivariable models were obtained using a regularized Cox regression including all miRNAs and clinical covariates. After adjustment for disease stage, only miR-126-3p showed an independent prognostic role, with higher values associated with longer DFS in SCC patients. With regard to ADC and OS, no miRNA remained significant in multivariable analysis. Further investigation into the role of miR-126 as a prognostic marker in early-stage NSCLC is warranted.

A High-Content Screening of Anticancer Compounds Suggests the Multiple Tyrosine Kinase Inhibitor Ponatinib for Repurposing in Neuroblastoma Therapy.

Novel druggable targets have been discovered in neuroblastoma (NB), paving the way for more effective treatments. However, children with high-risk NB still show high mortality rates prompting for a search of novel therapeutic options. Here, we aimed at repurposing FDA-approved drugs for NB treatment by performing a high-content screening of a 349 anticancer compounds library. In the primary screening, we employed three NB cell lines, grown as three-dimensional (3D) multicellular spheroids, which were treated with 10 µmol/L of the library compounds for 72 hours. The viability of 3D spheroids was evaluated using a high-content imaging approach, resulting in a primary hit list of 193 compounds. We selected 60 FDA-approved molecules and prioritized drugs with multi-target activity, discarding those already in use for NB treatment or enrolled in NB clinical trials. Hence, 20 drugs were further tested for their efficacy in inhibiting NB cell viability, both in two-dimensional and 3D models. Dose-response curves were then supplemented with the data on side effects, therapeutic index, and molecular targets, suggesting two multiple tyrosine kinase inhibitors, ponatinib and axitinib, as promising candidates for repositioning in NB. Indeed, both drugs showed induction of cell-cycle block and apoptosis, as well as inhibition of colony formation. However, only ponatinib consistently affected migration and inhibited invasion of NB cells. Finally, ponatinib also proved effective inhibition of tumor growth in orthotopic NB mice, providing the rationale for its repurposing in NB therapy. Mol Cancer Ther; 17(7); 1405-15. ©2018 AACR.

TrkA is amplified in malignant melanoma patients and induces an anti-proliferative response in cell lines.

BACKGROUND: The nerve growth factor (NGF) receptor tyrosine-kinase TrkA is a well-known determinant of the melanocytic lineage, through modulation of the MAPK and AKT cascades. While TrkA gene is frequently rearranged in cancers, its involvement in malignant melanoma (MM) development is still unclear. METHODS: We analyzed a dataset of primary cutaneous MM (n = 31) by array comparative genomic hybridization (aCGH), to identify genomic amplifications associated with tumor progression. The analysis was validated by genomic quantitative PCR (qPCR) on an extended set of cases (n = 64) and the results were correlated with the clinical outcome. To investigate TrkA molecular pathways and cellular function, we generated inducible activation of the NGF-TrkA signaling in human MM cell lines. RESULTS: We identified amplification of 1q23.1, where the TrkA locus resides, as a candidate hotspot implicated in the progression of MM. Across 40 amplicons detected, segmental amplification of 1q23.1 showed the strongest association with tumor thickness. By validation of the analysis, TrkA gene amplification emerged as a frequent event in primary melanomas (50 % of patients), and correlated with worse clinical outcome. However, experiments in cell lines revealed that induction of the NGF-TrkA signaling produced a phenotype of dramatic suppression of cell proliferation through inhibition of cell division and pronounced intracellular vacuolization, in a way straightly dependent on NGF activation of TrkA. These events were triggered via MAPK activity but not via AKT, and involved p21(cip1) protein increase, compatibly with a mechanism of oncogene-induced growth arrest. CONCLUSIONS: Taken together, our findings point to TrkA as a candidate oncogene in MM and support a model in which the NGF-TrkA-MAPK pathway may mediate a trade-off between neoplastic transformation and adaptive anti-proliferative response.

Increased frequency of minimal homozygous deletions is associated with poor prognosis in primary malignant melanoma patients.

Identification of prognostic melanoma-associated copy number alterations (CNAs) is still an area of active research. Here, we investigated by high-resolution array comparative genomic hybridization (aCGH) a cohort of 31 paraffin-preserved primary malignant melanomas (MMs), whose prognosis was not predictable on the basis of conventional histopathological parameters. Although we identified a variety of highly recurrent sites of genomic lesions, the total number of CNAs per patient was not a discriminator of MM outcome. Furthermore, validation of aCGH by quantitative PCR on an extended population of 65 MM samples confirmed the absence of predictive value for the most recurrent CNA loci. Instead, our analysis revealed specific prognostic potential of the frequency of homozygous deletions (representing less than 3% of the total CNAs on average per sample), which was strongly associated with sentinel lymph node (SLN) invasion (P = 0.003), and distant metastasis (P = 0.003). Increased number of homozygous deletions was also indicative of poor patient survival (P = 0.01), both in our samples and in an independent validation of public dataset of primary and metastatic MMs. Moreover, we identified 77 hotspots of minimal common homozygous deletions, enriched in genes involved in cell adhesion processes and cell-communication functions, which preferentially accumulated in primary MMs showing the most severe outcome. Therefore, specific loss of gene loci in regions of minimal homozygous deletion may represent a pivotal type of genomic alteration accumulating during MM progression with potential prognostic implication.

AURA 2: Empowering discovery of post-transcriptional networks.

Post-transcriptional regulation (PTR) of gene expression is now recognized as a major determinant of cell phenotypes. The recent availability of methods to map protein-RNA interactions in entire transcriptomes such as RIP, CLIP and their variants, together with global polysomal and ribosome profiling techniques, are driving the exponential accumulation of vast amounts of data on mRNA contacts in cells, and of corresponding predictions of PTR events. However, this exceptional quantity of information cannot be exploited at its best to reconstruct potential PTR networks, as it still lies scattered throughout several databases and in isolated reports of single interactions. To address this issue, we developed the second and vastly enhanced version of the Atlas of UTR Regulatory Activity (AURA 2), a meta-database centered on mapping interaction of trans-factors with human and mouse UTRs. AURA 2 includes experimentally demonstrated binding sites for RBPs, ncRNAs, thousands of cis-elements, variations, RNA epigenetics data and more. Its user-friendly interface offers various data-mining features including co-regulation search, network generation and regulatory enrichment testing. Gene expression profiles for many tissues and cell lines can be also combined with these analyses to display only the interactions possible in the system under study. AURA 2 aims at becoming a valuable toolbox for PTR studies and at tracing the road for how PTR network-building tools should be designed. AURA 2 is available at http://aura.science.unitn.it.

Melanoma: targeting signaling pathways and RaLP.

BACKGROUND: Metastatic melanoma remains one of the most aggressive forms of cancer, with a survival expectation of above six months only in rare cases. Despite advances in the characterization of the underlying molecular pathways and in the development of specific targeted treatments, available chemo- and immuno-therapy are unable to prolong survival significantly in advanced-stage melanoma. Rai like protein (RaLP) is a newly identified Src homology 2 domain containing (Shc) family member selectively expressed during the transition to metastatic melanoma and thus is a potential melanoma-specific drugable target. OBJECTIVE: To summarize progress in the ongoing therapeutic approaches to metastatic melanoma and discuss RaLP as a potential novel therapeutic target. METHODS: Current understanding of the major signaling pathways involved in melanoma metastatization and of the corresponding pharmacological inhibitors is discussed. CONCLUSION: RaLP might represent a new drugable target for the treatment of metastatic disease.

Regulation of SRC-3 intercompartmental dynamics by estrogen receptor and phosphorylation.

The steroid receptor coactivator 3 gene (SRC-3) (AIB1/ACTR/pCIP/RAC3/TRAM1) is a p160 family transcription coactivator and a known oncogene. Despite its importance, the functional regulation of SRC-3 remains poorly understood within a cellular context. Using a novel combination of live-cell, high-throughput, and fluorescent microscopy, we report SRC-3 to be a nucleocytoplasmic shuttling protein whose intracellular mobility, solubility, and cellular localization are regulated by phosphorylation and estrogen receptor alpha (ERalpha) interactions. We show that both chemical inhibition and small interfering RNA reduction of the mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MEK1/2) pathway induce a cytoplasmic shift in SRC-3 localization, whereas stimulation by epidermal growth factor signaling enhances its nuclear localization by inducing phosphorylation at T24, S857, and S860, known participants in the phosphocode that regulates SRC-3 activity. Accordingly, the cytoplasmic localization of a nonphosphorylatable SRC-3 mutant further supported these results. In the presence of ERalpha, U0126 also dramatically reduces (i) ligand-dependent colocalization of SRC-3 and ERalpha, (ii) the formation of ER-SRC-3 complexes in cell lysates, and (iii) SRC-3 targeting to a visible, ERalpha-occupied and -regulated prolactin promoter array. Taken together, these results indicate that phosphorylation coordinates SRC-3 coactivator function by linking the probabilistic formation of transient nuclear receptor-coactivator complexes with its molecular dynamics and cellular compartmentalization. Technically and conceptually, these findings have a new and broad impact upon evaluating mechanisms of action of gene regulators at a cellular system level.