Olfactory neuroblastoma mimics molecular heterogeneity and lineage trajectories of small-cell lung cancer

The olfactory epithelium undergoes neuronal regeneration from basal stem cells and is susceptible to olfactory neuroblastoma (ONB), a rare tumor of unclear origins. Employing alterations in Rb1/Trp53/Myc (RPM), we establish a genetically engineered mouse model of high-grade metastatic ONB exhibiting a NEUROD1+ immature neuronal phenotype. We demonstrate that globose basal cells (GBCs) are a permissive cell of origin for ONB and that ONBs exhibit cell fate heterogeneity that mimics normal GBC developmental trajectories. ASCL1 loss in RPM ONB leads to emergence of non-neuronal histopathologies, including a POU2F3+ microvillar-like state. Similar to small-cell lung cancer (SCLC), mouse and human ONBs exhibit mutually exclusive NEUROD1 and POU2F3-like states, an immune-cold tumor microenvironment, intratumoral cell fate heterogeneity comprising neuronal and non-neuronal lineages, and cell fate plasticity-evidenced by barcode-based lineage tracing and single-cell transcriptomics. Collectively, our findings highlight conserved similarities between ONB and neuroendocrine tumors with significant implications for ONB classification and treatment.

Single Cell Analysis of Treatment-Resistant Prostate Cancer: Implications of Cell State Changes for Cell Surface Antigen Targeted Therapies

Targeting cell surface molecules using radioligand and antibody-based therapies has yielded considerable success across cancers. However, it remains unclear how the expression of putative lineage markers, particularly cell surface molecules, varies in the process of lineage plasticity, wherein tumor cells alter their identity and acquire new oncogenic properties. A notable example of lineage plasticity is the transformation of prostate adenocarcinoma (PRAD) to neuroendocrine prostate cancer (NEPC)--a growing resistance mechanism that results in the loss of responsiveness to androgen blockade and portends dismal patient survival. To understand how lineage markers vary across the evolution of lineage plasticity in prostate cancer, we applied single cell analyses to 21 human prostate tumor biopsies and two genetically engineered mouse models, together with tissue microarray analysis (TMA) on 131 tumor samples. Not only did we observe a higher degree of phenotypic heterogeneity in castrate-resistant PRAD and NEPC than previously anticipated, but also found that the expression of molecules targeted therapeutically, namely PSMA, STEAP1, STEAP2, TROP2, CEACAM5, and DLL3, varied within a subset of gene-regulatory networks (GRNs). We also noted that NEPC and small cell lung cancer (SCLC) subtypes shared a set of GRNs, indicative of conserved biologic pathways that may be exploited therapeutically across tumor types. While this extreme level of transcriptional heterogeneity, particularly in cell surface marker expression, may mitigate the durability of clinical responses to novel antigen-directed therapies, its delineation may yield signatures for patient selection in clinical trials, potentially across distinct cancer types.

Role of CD38 in anti-tumor immunity of small cell lung cancer

Introduction

Immune checkpoint blockade (ICB) with or without chemotherapy has a very modest benefit in patients with small cell lung cancer (SCLC). SCLC tumors are characterized by high tumor mutation burden (TMB) and low PD-L1 expression. Therefore, TMB and PD-L1 do not serve as biomarkers of ICB response in SCLC. CD38, a transmembrane glycoprotein, mediates immunosuppression in non-small cell lung cancer (NSCLC). In this brief report, we highlight the potential role of CD38 as a probable biomarker of immunotherapy response in SCLC.

Methods

We evaluated the role of CD38 as a determinant of tumor immune microenvironment in SCLC with bulk and single-cell transcriptomic analyses and protein assessments of clinical samples and preclinical models, including CD38 in vivo blockade.

Results

In SCLC clinical samples, CD38 levels were significantly correlated with the gene expression of the immunosuppressive markers FOXP3, PD-1 and CTLA-4. CD38 expression was significantly enhanced after chemotherapy and ICB treatment in SCLC preclinical models and clinical samples. A combination of cisplatin/etoposide, ICB, and CD38 blockade delayed tumor growth compared to cisplatin/etoposide.

Conclusion

Our study provides a preliminary but important direction toward exploring CD38 as a potential biomarker of ICB response and CD38 blockade as a combination strategy for chemo-immunotherapy in SCLC.

Immune heterogeneity in small-cell lung cancer and vulnerability to immune checkpoint blockade

Atezolizumab (anti-PD-L1), combined with carboplatin and etoposide (CE), is now a standard of care for extensive-stage small-cell lung cancer (ES-SCLC). A clearer understanding of therapeutically relevant SCLC subsets could identify rational combination strategies and improve outcomes. We conduct transcriptomic analyses and non-negative matrix factorization on 271 pre-treatment patient tumor samples from IMpower133 and identify four subsets with general concordance to previously reported SCLC subtypes (SCLC-A, -N, -P, and -I). Deeper investigation into the immune heterogeneity uncovers two subsets with differing neuroendocrine (NE) versus non-neuroendocrine (non-NE) phenotypes, demonstrating immune cell infiltration hallmarks. The NE tumors with low tumor-associated macrophage (TAM) but high T-effector signals demonstrate longer overall survival with PD-L1 blockade and CE versus CE alone than non-NE tumors with high TAM and high T-effector signal. Our study offers a clinically relevant approach to discriminate SCLC patients likely benefitting most from immunotherapies and highlights the complex mechanisms underlying immunotherapy responses.

CRACD loss promotes small cell lung cancer tumorigenesis via EZH2-mediated immune evasion

The mechanisms underlying immune evasion and immunotherapy resistance in small cell lung cancer (SCLC) remain unclear. Herein, we investigate the role of CRACD tumor suppressor in SCLC. We found that CRACD is frequently inactivated in SCLC, and Cracd knockout (KO) significantly accelerates SCLC development driven by loss of Rb1, Trp53, and Rbl2. Notably, the Cracd-deficient SCLC tumors display CD8+ T cell depletion and suppression of antigen presentation pathway. Mechanistically, CRACD loss silences the MHC-I pathway through EZH2. EZH2 blockade is sufficient to restore the MHC-I pathway and inhibit CRACD loss-associated SCLC tumorigenesis. Unsupervised single-cell transcriptomic analysis identifies SCLC patient tumors with concomitant inactivation of CRACD, impairment of tumor antigen presentation, and downregulation of EZH2 target genes. Our findings define CRACD loss as a new molecular signature associated with immune evasion of SCLC cells and proposed EZH2 blockade as a viable option for CRACD-negative SCLC treatment.

Lineage tracing reveals clonal progenitors and long-term persistence of tumor-specific T cells during immune checkpoint blockade

Paired single-cell RNA and T cell receptor sequencing (scRNA/TCR-seq) has allowed for enhanced resolution of clonal T cell dynamics in cancer. Here, we report a scRNA/TCR-seq analysis of 187,650 T cells from 31 tissue regions, including tumor, adjacent normal tissues, and lymph nodes (LN), from three patients with non-small cell lung cancer after immune checkpoint blockade (ICB). Regions with viable cancer cells are enriched for exhausted CD8+ T cells, regulatory CD4+ T cells (Treg), and follicular helper CD4+ T cells (TFH). Tracking T cell clonotypes across tissues, combined with neoantigen specificity assays, reveals that TFH and tumor-specific exhausted CD8+ T cells are clonally linked to TCF7+SELL+ progenitors in tumor draining LNs, and progressive exhaustion trajectories of CD8+ T, Treg, and TFH cells with proximity to the tumor microenvironment. Finally, longitudinal tracking of tumor-specific CD8+ and CD4+ T cell clones reveals persistence in the peripheral blood for years after ICB therapy.

Abstract NG05: Multi-omic approaches to study the role of plasticity in therapy resistance and metastasis in lung cancer

Lineage plasticity, the ability of cells to transdifferentiate between committed developmental pathways, has been proposed as a source of intratumoral heterogeneity and as a mechanism for tumor adaptation to stringent environmental conditions. Lineage plasticity is increasingly recognized as a contributor to both drug resistance and metastasis, as recently highlighted by our team (Quintanal-Villalonga et al., Nat Rev Clin Oncol 2020), thus representing a biological phenomenon with high clinical relevance. Leveraging bulk and single-cell multi-omic approaches in clinical specimens, we aimed to perform a comprehensive molecular characterization of lung cancer cellular plasticity in the settings of (1) histological transdifferentiation as a mechanism of resistance to targeted therapy, and (2) disease progression. In lung adenocarcinomas (LUADs), lineage plasticity drives small cell (SCLC) and squamous cell (LUSC) transdifferentiation in the context of acquired resistance to targeted inhibitors. In the EGFR -mutant cancers, transformation to SCLC and to LUSC as a mechanism of acquired TKI resistance has been reported in 14% and 9% of cases, respectively. Transdifferentiated tumors portend poorer prognosis than non-transformed tumors. To date, no preventative therapies for transformation are available, although tumor subsets at high risk of transformation (concomitant TP53/RB1 inactivation in the case of SCLC transdifferentiation) have been identified. Defining molecular mechanisms of histological transformation in lung cancer has been challenging due in part to a paucity of well-annotated pre- and post-transformation clinical samples. We hypothesized that mixed histology tumors (LUAD/SCLC and LUAD/LUSC), containing different histological components and sharing common driver mutations, may represent an intermediate step of transdifferentiation, and an ideal substrate to study lineage plasticity, with both histological components sharing location, time, and treatment influence. By selecting mixed histology specimens amenable for clean microdissection of each histological component (10 LUAD/LUSC and 11 LUAD/SCLC), as well as pre- and post-transdifferentiated samples (N=17), we performed comprehensive genomic, epigenomic, transcriptomic, and protein characterization. Our data supports that histological transdifferentiation from LUAD to LUSC or SCLC tumors is driven by epigenetic remodeling rather than by mutational events, and indicates that transdifferentiated tumors retain epigenomic features of their previous LUAD state. Integrative epigenomic, transcriptomic, and protein analysis revealed divergent biological pathways dysregulated for each histological outcome, such as upregulation of genes involved in Hedgehog and Notch signaling and MYC targets in LUSC-transdifferentiated tumors. Most interestingly, these analyses identified commonly dysregulated pathways in both SCLC- and LUSC-transdifferentiating tumors, including remarkable downregulation of a variety of immune-related pathways and upregulation of genes involved in the PRC2 epigenetic remodeling complex and AKT signaling. To validate drivers of transdifferentiation from our multi-omic data, preclinical in vivo experiments indicated that concurrent activation of AKT and MYC overexpression induced a LUSC phenotype with increased P40 and CK5/6 expression in EGFR -mutant LUAD patient-derived models. LUSC features in these models were further accentuated by the EGFR inhibitor osimertinib, which enriched for transdifferentiated LUSC cells. With the aim to validate potential therapeutic targets to prevent transdifferentiation from our multi-omic data, we tested the efficacy of EZH2 (the catalytic subunit of PRC2) or AKT pharmacological inhibitors in combination with osimertinib in an EGFR -mutant patient-derived xenograft model of LUAD-to-LUSC transdifferentiation and observed that inhibition of either pathway dramatically delayed relapse and prevented emergence of LUSC phenotypic markers. Additionally, pharmacological targeting of AKT and EGFR delayed relapse in a mixed LUAD/SCLC patient-derived xenograft model representing an intermediate step of LUAD-to-SCLC transdifferentiation. Interestingly, AKT inhibition selectively targeted the SCLC compartment of the tumor and prevented full SCLC transformation.

This work was published in two manuscripts, of which I am the first and co-corresponding author (Quintanal-Villalonga et al., Cancer Discov 2021; Quintanal-Villalonga et al., J Hematol Oncol 2021) and defines a novel landscape of potential drivers and therapeutic vulnerabilities of histological transdifferentiation in lung cancer. Both transformed and de novo SCLCs are aggressive and rapidly metastatic lung tumors. Limited treatment options and transient responses translate to poor prognosis for patients with SCLC; 5-year survival rates are <1% for extensive disease, and SCLC accounts for >200,000 annual deaths worldwide. Metastasis is the main cause of mortality among patients with SCLC. To characterize SCLC metastasis, we combined single-cell RNA sequencing (scRNA-seq) and multiplexed ion beam imaging (MIBI) technologies to study intratumoral heterogeneity and the surrounding tumor microenvironment (TME). Efforts to apply these technologies to human SCLC tumors have been limited, as surgical resections of primary tumors are performed in <5% of patients with SCLC, and scRNA-seq processing of biopsied samples is extremely challenging. Additionally, since resection is only clinically indicated for exceptionally early stage de novo disease, these samples fail to capture the spectrum of disease progression. Through the optimization of protocols allowing single cell profiling of difficult samples such as small tissue biopsies, pleural effusions, and fine needle aspirations, along with larger volume resections, we constructed a single-cell atlas of SCLC patient tumors, with 155,098 transcriptomes, including 54,523 transcriptomes from 21 SCLC clinical specimens. Despite substantial heterogeneity among SCLC tumors, we detected a minor cell subpopulation that was shared among tumors across subtypes, treatments, and tissue locations, pointing to a potentially universal characteristic of this malignancy. This subpopulation demonstrated a pro-metastatic, highly plastic (stem-like) phenotype and exhibited profound PLCG2 overexpression. Direct genetic manipulation validated that PLCG2 expression promotes metastatic features and induced plasticity in vitro and in vivo. Consistently, we found that higher representation of this subpopulation in clinical samples, as well as PLCG2 expression itself, are strong predictors of shorter overall survival in patients with SCLC. Additionally, we found that SCLC is enriched for a profibrotic, immunosuppressive monocyte/macrophage population associated with the recurrent pro-metastatic PLCG2-high subpopulation, with potential implications in the metastatic process. I am the co-first author of this work published in Cancer Cell (Chan JM*, Quintanal-Villalonga* et al., Cancer Cell 2021) defining a novel mechanism of plasticity-mediated metastasis in SCLC. These works highlight the key role of plasticity in disease progression and therapy resistance in lung cancer, and describe molecular events occurring during fate reprogramming, thus nominating potential drivers and therapeutic vulnerabilities in plasticity-driven clinically relevant biological processes.

Citation Format: Alvaro Quintanal-Villalonga, Joseph M. Chan, Vianne R. Gao, Yubin Xie, Dana Pe’er, Charles M. Rudin. Multi-omic approaches to study the role of plasticity in therapy resistance and metastasis in lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG05.

The ectonucleotidase CD39 identifies tumor-reactive CD8+ T cells predictive of immune checkpoint blockade efficacy in human lung cancer

Improved identification of anti-tumor T cells is needed to advance cancer immunotherapies. CD39 expression is a promising surrogate of tumor-reactive CD8+ T cells. Here, we comprehensively profiled CD39 expression in human lung cancer. CD39 expression enriched for CD8+ T cells with features of exhaustion, tumor reactivity, and clonal expansion. Flow cytometry of 440 lung cancer biospecimens revealed weak association between CD39+ CD8+ T cells and tumoral features, such as programmed death-ligand 1 (PD-L1), tumor mutation burden, and driver mutations. Immune checkpoint blockade (ICB), but not cytotoxic chemotherapy, increased intratumoral CD39+ CD8+ T cells. Higher baseline frequency of CD39+ CD8+ T cells conferred improved clinical outcomes from ICB therapy. Furthermore, a gene signature of CD39+ CD8+ T cells predicted benefit from ICB, but not chemotherapy, in a phase III clinical trial of non-small cell lung cancer. These findings highlight CD39 as a proxy of tumor-reactive CD8+ T cells in human lung cancer.

Protocol to dissociate, process, and analyze the human lung tissue using single-cell RNA-seq

We report a protocol for obtaining high-quality single-cell transcriptomics data from human lung biospecimens acquired from core needle biopsies, fine-needle aspirates, surgical resection, and pleural effusions. The protocol relies upon the brief mechanical and enzymatic disruption of tissue, enrichment of live cells by fluorescence-activated cell sorting (FACS), and droplet-based single-cell RNA sequencing (scRNA-seq). The protocol also details a procedure for analyzing the scRNA-seq data. For complete details on the use and execution of this protocol, please refer to Chan et al. (2021).

Lineage plasticity in prostate cancer depends on JAK/STAT inflammatory signaling

Drug resistance in cancer is often linked to changes in tumor cell state or lineage, but the molecular mechanisms driving this plasticity remain unclear. Using murine organoid and genetically engineered mouse models, we investigated the causes of lineage plasticity in prostate cancer and its relationship to antiandrogen resistance. We found that plasticity initiates in an epithelial population defined by mixed luminal-basal phenotype and that it depends on increased Janus kinase (JAK) and fibroblast growth factor receptor (FGFR) activity. Organoid cultures from patients with castration-resistant disease harboring mixed-lineage cells reproduce the dependency observed in mice by up-regulating luminal gene expression upon JAK and FGFR inhibitor treatment. Single-cell analysis confirms the presence of mixed-lineage cells with increased JAK/STAT (signal transducer and activator of transcription) and FGFR signaling in a subset of patients with metastatic disease, with implications for stratifying patients for clinical trials.

Abstract 1594: Reversal of lineage plasticity in RB1/TP53-deleted prostate cancer through FGFR and Janus kinase inhibition

The inherent plasticity of tumor cells provides a mechanism of resistance to many molecularly targeted therapies, exemplified by adeno-to-neuroendocrine lineage transitions seen in prostate and lung cancer. Here we investigate the root cause of this lineage plasticity in a primary murine prostate organoid model that mirrors the lineage transition seen in patients. These cells lose luminal identity within weeks following deletion of Trp53 and Rb1, ultimately acquiring an Ar-negative, Syp+ phenotype after orthotopic in vivo transplantation. We performed single-cell transcriptomic analysis of a time-course experiment on the prostate organoid following Trp53 and Rb1 deletion. Critical to this study, we developed SEACells, a method that enumerates distinct, highly granular cell states, allowing for robust transcriptomic quantification. Leveraging the SEACell platform, we developed several graph-based computational approaches based on Markov absorption, diffusion maps, and attributed stochastic block models to quantify dynamic changes in plasticity. These quantitative models independently confirmed rapid collapse of cell-type fidelity in the form of a mixed luminal-basal phenotype following tumor suppressor gene deletion. These methods compute metrics for plasticity that we correlated to candidate driver gene programs. Among the strongest plasticity correlates, Jak-Stat and Fgfr signaling stood out as gene programs activated early in the time-course prior to any corresponding morphological changes. We further developed a regression-based approach to nominate ligand-receptor interactions that activate downstream Jak-Stat signaling, which identified Fgf-Fgfr interactions that were functionally validated with growth factor addition and pharmacological inhibition. Most strikingly, genetic or pharmacologic inhibition of Jak1/2 in combination with Fgfr blockade not only reversed the plastic state and restored organoids to their wild-type morphology, but also re-sensitized drug-resistant cells to antiandrogen therapy in models with residual AR expression. We additionally confirm early activation of Jak/Stat transcriptional programs in an Rb1/Trp53/Pten-deleted genetically engineered mouse model undergoing substantial cell-type diversification under plasticity in the context of the tumor microenvironment. Collectively, we show that lineage plasticity initiates quickly as a largely cell-autonomous process that is further increased in the in vivo setting, and through newly developed computational approaches, we identify a pharmacological strategy that restores lineage identity using clinical grade inhibitors.

Citation Format: Joseph M. Chan, Wouter R. Karthaus, Manu Setty, Jillian R. Love, Samir Zaidi, Jimmy Zhao, Zi-ning Choo, Sitara Persad, Justin LaClair, Kayla E. Lawrence, Ojasvi Chaudhary, Ignas Masilionis, Linas Mazutis, Ronan Chaligne, Dana Pe'er, Charles Sawyers. Reversal of lineage plasticity in RB1/TP53-deleted prostate cancer through FGFR and Janus kinase inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1594.

Targeting Lysine-Specific Demethylase 1 Rescues Major Histocompatibility Complex Class I Antigen Presentation and Overcomes Programmed Death-Ligand 1 Blockade Resistance in SCLC

INTRODUCTION

SCLC is a highly aggressive neuroendocrine tumor that is characterized by early acquired therapeutic resistance and modest benefit from immune checkpoint blockade (ICB). Repression of the major histocompatibility complex class I (MHC-I) represents a key mechanism driving resistance to T cell-based immunotherapies.

METHODS

We evaluated the role of the lysine-specific demethylase 1 (LSD1) as a determinant of MHC-I expression, functional antigen presentation, and immune activation in SCLC in vitro and in vivo through evaluation of both human SCLC cell lines and immunocompetent mouse models.

RESULTS

We found that targeted inhibition of LSD1 in SCLC restores MHC-I cell surface expression and transcriptionally activates genes encoding the antigen presentation pathway. LSD1 inhibition further activates interferon signaling, induces tumor-intrinsic immunogenicity, and sensitizes SCLC cells to MHC-I-restricted T cell cytolysis. Combination of LSD1 inhibitor with ICB augments the antitumor immune response in refractory SCLC models. Together, these data define a role for LSD1 as a potent regulator of MHC-I antigen presentation and provide rationale for combinatory use of LSD1 inhibitors with ICB to improve therapeutic response in SCLC.

CONCLUSIONS

Epigenetic silencing of MHC-I in SCLC contributes to its poor response to ICB. Our study identifies a previously uncharacterized role for LSD1 as a regulator of MHC-I antigen presentation in SCLC. LSD1 inhibition enables MHC-I-restricted T cell cytolysis, induces immune activation, and augments the antitumor immune response to ICB in SCLC.

Inhibition of XPO1 Sensitizes Small Cell Lung Cancer to First- and Second-Line Chemotherapy

Small cell lung cancer (SCLC) is an aggressive malignancy characterized by early metastasis and extreme lethality. The backbone of SCLC treatment over the past several decades has been platinum-based doublet chemotherapy, with the recent addition of immunotherapy providing modest benefits in a subset of patients. However, nearly all patients treated with systemic therapy quickly develop resistant disease, and there is an absence of effective therapies for recurrent and progressive disease. Here we conducted CRISPR-Cas9 screens using a druggable genome library in multiple SCLC cell lines representing distinct molecular subtypes. This screen nominated exportin-1, encoded by XPO1, as a therapeutic target. XPO1 was highly and ubiquitously expressed in SCLC relative to other lung cancer histologies and other tumor types. XPO1 knockout enhanced chemosensitivity, and exportin-1 inhibition demonstrated synergy with both first- and second-line chemotherapy. The small molecule exportin-1 inhibitor selinexor in combination with cisplatin or irinotecan dramatically inhibited tumor growth in chemonaïve and chemorelapsed SCLC patient-derived xenografts, respectively. Together these data identify exportin-1 as a promising therapeutic target in SCLC, with the potential to markedly augment the efficacy of cytotoxic agents commonly used in treating this disease. SIGNIFICANCE: CRISPR-Cas9 screening nominates exportin-1 as a therapeutic target in SCLC, and exportin-1 inhibition enhances chemotherapy efficacy in patient-derived xenografts, providing a novel therapeutic opportunity in this disease.

Signatures of plasticity, metastasis, and immunosuppression in an atlas of human small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive malignancy that includes subtypes defined by differential expression of ASCL1, NEUROD1, and POU2F3 (SCLC-A, -N, and -P, respectively). To define the heterogeneity of tumors and their associated microenvironments across subtypes, we sequenced 155,098 transcriptomes from 21 human biospecimens, including 54,523 SCLC transcriptomes. We observe greater tumor diversity in SCLC than lung adenocarcinoma, driven by canonical, intermediate, and admixed subtypes. We discover a PLCG2-high SCLC phenotype with stem-like, pro-metastatic features that recurs across subtypes and predicts worse overall survival. SCLC exhibits greater immune sequestration and less immune infiltration than lung adenocarcinoma, and SCLC-N shows less immune infiltrate and greater T cell dysfunction than SCLC-A. We identify a profibrotic, immunosuppressive monocyte/macrophage population in SCLC tumors that is particularly associated with the recurrent, PLCG2-high subpopulation.

Comprehensive molecular characterization of lung tumors implicates AKT and MYC signaling in adenocarcinoma to squamous cell transdifferentiation

BACKGROUND

Lineage plasticity, the ability to transdifferentiate among distinct phenotypic identities, facilitates therapeutic resistance in cancer. In lung adenocarcinomas (LUADs), this phenomenon includes small cell and squamous cell (LUSC) histologic transformation in the context of acquired resistance to targeted inhibition of driver mutations. LUAD-to-LUSC transdifferentiation, occurring in up to 9% of EGFR-mutant patients relapsed on osimertinib, is associated with notably poor prognosis. We hypothesized that multi-parameter profiling of the components of mixed histology (LUAD/LUSC) tumors could provide insight into factors licensing lineage plasticity between these histologies.

METHODS

We performed genomic, epigenomics, transcriptomics and protein analyses of microdissected LUAD and LUSC components from mixed histology tumors, pre-/post-transformation tumors and reference non-transformed LUAD and LUSC samples. We validated our findings through genetic manipulation of preclinical models in vitro and in vivo and performed patient-derived xenograft (PDX) treatments to validate potential therapeutic targets in a LUAD PDX model acquiring LUSC features after osimertinib treatment.

RESULTS

Our data suggest that LUSC transdifferentiation is primarily driven by transcriptional reprogramming rather than mutational events. We observed consistent relative upregulation of PI3K/AKT, MYC and PRC2 pathway genes. Concurrent activation of PI3K/AKT and MYC induced squamous features in EGFR-mutant LUAD preclinical models. Pharmacologic inhibition of EZH1/2 in combination with osimertinib prevented relapse with squamous-features in an EGFR-mutant patient-derived xenograft model, and inhibition of EZH1/2 or PI3K/AKT signaling re-sensitized resistant squamous-like tumors to osimertinib.

CONCLUSIONS

Our findings provide the first comprehensive molecular characterization of LUSC transdifferentiation, suggesting putative drivers and potential therapeutic targets to constrain or prevent lineage plasticity.

Multi-omic analysis of lung tumors defines pathways activated in neuroendocrine transformation

Lineage plasticity is implicated in treatment resistance in multiple cancers. In lung adenocarcinomas (LUADs) amenable to targeted therapy, transformation to small cell lung cancer (SCLC) is a recognized resistance mechanism. Defining molecular mechanisms of neuroendocrine (NE) transformation in lung cancer has been limited by a paucity of pre-/post-transformation clinical samples. Detailed genomic, epigenomic, transcriptomic, and protein characterization of combined LUAD/SCLC tumors, as well as pre-/post-transformation samples, support that NE transformation is primarily driven by transcriptional reprogramming rather than mutational events. We identify genomic contexts in which NE transformation is favored, including frequent loss of the 3p chromosome arm. We observed enhanced expression of genes involved in PRC2 complex and PI3K/AKT and NOTCH pathways. Pharmacological inhibition of the PI3K/AKT pathway delayed tumor growth and NE transformation in an EGFR-mutant patient-derived xenograft model. Our findings define a novel landscape of potential drivers and therapeutic vulnerabilities of neuroendocrine transformation in lung cancer.

Publisher Correction: Lineage plasticity in cancer: a shared pathway of therapeutic resistance

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Tumor Analyses Reveal Squamous Transformation and Off-Target Alterations As Early Resistance Mechanisms to First-line Osimertinib in EGFR-Mutant Lung Cancer

PURPOSE

Patterns of resistance to first-line osimertinib are not well-established and have primarily been evaluated using plasma assays, which cannot detect histologic transformation and have differential sensitivity for copy number changes and chromosomal rearrangements.

EXPERIMENTAL DESIGN

To characterize mechanisms of resistance to osimertinib, patients with metastatic EGFR-mutant lung cancers who received osimertinib at Memorial Sloan Kettering Cancer Center and had next-generation sequencing performed on tumor tissue before osimertinib initiation and after progression were identified.

RESULTS

Among 62 patients who met eligibility criteria, histologic transformation, primarily squamous transformation, was identified in 15% of first-line osimertinib cases and 14% of later-line cases. Nineteen percent (5/27) of patients treated with first-line osimertinib had off-target genetic resistance (2 MET amplification, 1 KRAS mutation, 1 RET fusion, and 1 BRAF fusion) whereas 4% (1/27) had an acquired EGFR mutation (EGFR G724S). Patients with squamous transformation exhibited considerable genomic complexity; acquired PIK3CA mutation, chromosome 3q amplification, and FGF amplification were all seen. Patients with transformation had shorter time on osimertinib and shorter survival compared with patients with on-target resistance. Initial EGFR sensitizing mutation, time on osimertinib treatment, and line of therapy also influenced resistance mechanism that emerged. The compound mutation EGFR S768 + V769L and the mutation MET H1094Y were identified and validated as resistance mechanisms with potential treatment options.

CONCLUSIONS

Histologic transformation and other off-target molecular alterations are frequent early emerging resistance mechanisms to osimertinib and are associated with poor clinical outcomes.See related commentary by Piotrowska and Hata, p. 2441.

Monocyte cell membrane-derived nanoghosts for targeted cancer therapy

Core-shell type 'nanoghosts' were synthesized with a drug-loaded biodegradable PLGA core and a monocyte cell membrane-derived shell. The nanoghosts were monodisperse with an average size <200 nm, and showed good serum stability for 120 h. Doxorubicin-loaded nanoghosts showed greater cellular uptake and cytotoxicity compared to non-coated nanoparticle controls in metastatic MCF-7 breast cancer cell lines.

Immediate versus deferred initiation of androgen deprivation therapy in prostate cancer patients with PSA-only relapse. An observational follow-up study

BACKGROUND

The optimal timing to start androgen deprivation therapy (ADT) in prostate cancer patients with rising prostate-specific antigen (PSA) as the only sign of relapse is unknown.

METHODS

We identified men with prostate cancer in the Cancer of the Prostate Strategic Urologic Research Endeavour (CaPSURE) study who would have been eligible (⩽ cT3aN0M0, primary radical prostatectomy or radiotherapy, PSA relapse as the only evidence of recurrence) for a randomised trial comparing 'immediate' versus 'deferred' ADT initiation. We emulated such trial by assigning patients to the 'immediate' strategy if they initiated ADT within 3 months of PSA relapse and to the 'deferred' strategy if they initiated ADT when they presented with metastasis, symptoms or a short PSA doubling time. We censored patients when they deviated from the assigned strategy and adjusted for this censoring via inverse probability weighting.

RESULTS

Of 2096 eligible patients (median age 69, interquartile range 63-75 years), 88% were white, 35% had a Gleason score ⩾ 7, 69% were treated with radical prostatectomy and 31% received radiotherapy only as primary treatment. The mean time from primary treatment to PSA relapse was 37.4 (standard deviation [SD] 34.2) months. Mean follow-up from primary treatment was 91.4 (SD 48.4) months. The adjusted mortality hazard ratio for immediate versus deferred ADT was 0.91 (95% confidence interval (CI), 0.52-1.60), which would be translated into a similar 5-year survival (difference between groups: -2.0% (95% CI: -10.0 to 5.9%).

CONCLUSION

Our analysis suggests that prostate cancer patients undergoing immediate ADT initiation within three months after PSA-only relapse had similar survival to those who deferred ADT initiation within 3 months after clinical progression.

Active surveillance: does serial prostate biopsy increase histological inflammation?

BACKGROUND

Active surveillance (AS) is an appropriate management strategy for men with low-risk prostate cancer. Most protocols recommend repeated prostate biopsy every 12-24 months. The purpose of this paper is to describe histological inflammation patterns in men on AS who underwent serial prostate biopsy for disease monitoring.

METHODS

We reviewed records of men on AS from January 1999 through February 2011 who had a diagnostic plus ≥1 repeat transrectal ultrasound-guided biopsies performed at our institution. The type and degree of inflammatory infiltrate were grossly reviewed and scored for each patient's biopsy by a single pathologist. Relationship of inflammation severity and number of serial biopsies was assessed using a repeated measures mixed model. Unpaired t-test and χ(2)-square analysis assessed variance in degree of inflammation and location of inflammation relative to cancer grade progression defined as Gleason sum increase.

RESULTS

Fifty-six men met study inclusion criteria. Mean age was 62.1 (6.5) years, 71% were stage cT1c, 79% had a PSA level <10 ng ml(-1), and 98% had diagnostic Gleason sum ≤6. A small, statistically significant increase in maximum chronic inflammation (CI) scores with greater number of repeat biopsies was observed. CI scores were not associated with number of biopsies based on upgrade status. The main limitation to our study is our small sample size. Potential unmeasured confounders, such as unreported antibiotic use or symptomatic prostatitis, may have also affected our findings.

CONCLUSIONS

In this pilot study of 56 men on AS for localized prostate cancer, degree of chronic histological inflammation increased with greater number of prostate biopsies, but was not associated with subsequent risk of grade progression.

PSA screening: determinants of primary-care physician practice patterns

BACKGROUND

The effect of practice guidelines and the European Randomised Screening for Prostate Cancer (ERSPC) and Prostate, Lung, Colorectal and Ovarian (PLCO) trials on PSA screening practices of primary-care physicians (PCPs) is unknown.

METHODS

We conducted a national cross-sectional on-line survey of a random sample of 3010 PCPs from July to August 2010. Participants were queried about their knowledge of prostate cancer, PSA screening guidelines, the ERSPC and PLCO trials, and about their PSA screening practices. Factors associated with PSA screening were identified using multivariable linear regression.

RESULTS

A total of 152 (5%) participants opened and 89 completed the on-line survey, yielding a response rate of 58% for those that viewed the invitation. Eighty percent of respondents correctly identified prostate cancer risk factors. In all, 51% and 64% reported that they discuss and order PSA screening for men aged 50-75 years, respectively. Fifty-four percent were most influenced by the US Preventative Services Task Force (USPSTF) guidelines. Also, 21% and 28% of respondents stated that their PSA screening practices were influenced by the ERSPC and PLCO trials, respectively. Medical specialty was the only variable associated with propensity to screen, with family medicine physicians more likely to use PSA screening than internists (β=0.21, P=0.02).

CONCLUSIONS

Half of the physicians surveyed did not routinely discuss PSA screening with eligible patients. The impact of the ERSPC and PLCO trials on PSA screening practices was low among US PCPs. USPSTF recommendations for PSA screening continue to be the strongest influence on PCPs' propensity to use PSA screening.

Coplanar and coaxial orientations of RNA bases and helices

Electrostatic interactions, base-pairing, and especially base-stacking dominate RNA three-dimensional structures. In an A-form RNA helix, base-stacking results in nearly perfect parallel orientations of all bases in the helix. Interestingly, when an RNA structure containing multiple helices is visualized at the atomic level, it is often possible to find an orientation such that only the edges of most bases are visible. This suggests that a general aspect of higher level RNA structure is a coplanar arrangement of base-normal vectors. We have analyzed all solved RNA crystal structures to determine the degree to which RNA base-normal vectors are globally coplanar. Using a statistical test based on the Watson-Girdle distribution, we determined that 330 out of 331 known RNA structures show statistically significant (p < 0.05; false discovery rate [FDR] = 0.05) coplanar normal vector orientations. Not surprisingly, 94% of the helices in RNA show bipolar arrangements of their base-normal vectors (p < 0.05). This allows us to compute a mean axis for each helix and compare their orientations within an RNA structure. This analysis revealed that 62% (208/331) of the RNA structures exhibit statistically significant coaxial packing of helices (p < 0.05, FDR = 0.08). Further analysis reveals that the bases in hairpin loops and junctions are also generally planar. This work demonstrates coplanar base orientation and coaxial helix packing as an emergent behavior of RNA structure and may be useful as a structural modeling constraint.

Demographic factors associated with the diet quality of older US men: baseline data from the Osteoporotic Fractures in Men (MrOS) study

OBJECTIVE

Throughout the world, the proportion of the male population aged 65 years and older is increasing. Yet, we have limited information regarding diet quality and predictors of diet quality in this segment of the population. The objectives of the current analyses are to describe the diet quality of a cohort of men >65 years of age, and identify lifestyle factors associated with poor diet quality.

METHODS

We present a cross-sectional analysis of the diet quality of 5928 men, aged 65-100 years, who are participants in the Osteoporotic Fractures in Men (MrOS) cohort study. Dietary intake was determined using a modified Block 98 food-frequency questionnaire. Diet quality was calculated using the previously validated Diet Quality Index-Revised (DQI-R). Univariate and multivariate modelling was used to estimate the variance in diet quality predicted by a number of sociodemographic factors, including age, race/ethnicity, body mass index (BMI), marital status, education, smoking status, physical activity, self-perceived health and nutritional supplement use.

RESULTS

Overall, we found that in this geographically diverse group of older men, diet quality was low, with a mean modified DQI-R for the entire study population of 62.5 (standard deviation 13.1) out of an ideal of 100. Further, younger age, very low total calorie intake (< or = 1187 kcal day- 1), higher BMI, residence in a North or Southeast community, being of African-American or Hispanic race, being less educated, not using dietary supplements and smoking were each significant independent predictors of a poorer diet.

CONCLUSION

These data may prove useful in both understanding the dietary intake of older US men as it relates to published dietary guidelines, and for targeting future dietary intervention programmes.

Highly elevated PSA and dietary PhIP intake in a prospective clinic-based study among African Americans

African-American men die from prostate cancer (PC) nearly twice as often as white US men and consume about twice as much of the predominant US dietary heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a genotoxic rat-prostate carcinogen found primarily in well-cooked chicken and beef. To investigate the hypothesis that PhIP exposure increases PC risk, an ongoing prospective clinic-based study compared PC screening outcomes with survey-based estimates of dietary PhIP intake among 40-70-year-old African-American men with no prior PC in Oakland, CA. They completed food-frequency and meat-cooking/consumption questionnaires and had a prostate-specific antigen (PSA) test and digital-rectal exam. Results for 392 men indicated a 17 (+/-17) ng/kg day mean (+/-1 s.d.) daily intake of PhIP, about twice that of white US men of similar age. PhIP intake was attributable mostly to chicken (61%) and positively associated (R(2)=0.32, P<0.0001) with saturated fat intake. An odds ratio (95% confidence interval) of 31 (3.1-690) for highly elevated PSA > or =20 ng/ml was observed in the highest 15% vs lowest 50% of estimated daily PhIP intake (> or =30 vs < or =10 ng/kg day) among men 50+ years old (P=0.0002 for trend) and remained significant after adjustment for self-reported family history of (brother or father) PC, saturated fat intake and total energy intake. PSA measures were higher in African-American men with positive family history (P=0.007 all men, P<0.0001 highest PSA quartile). These preliminary results are consistent with a positive association between PhIP intake and highly elevated PSA, supporting the hypothesis that dietary intervention may help reduce PC risk.

History of diabetes, clinical features of prostate cancer, and prostate cancer recurrence-data from CaPSURE (United States)

OBJECTIVES

There is a growing epidemiologic literature suggesting an inverse association between history of diabetes and risk of incident prostate cancer. To our knowledge, the relationship between diabetes and tumor features and risk of recurrence among men with prostate cancer has not been examined previously. We hypothesized that men with diabetes would present with more favorable prostate cancer and experience lower risk of recurrence.

METHODS

We identified 691 men with diabetes at the time of prostate cancer diagnosis, among 6722 men diagnosed with prostate cancer in 1989 to 2002 within CaPSURE(TM), a community-based prostate cancer registry study. We compared clinical and socio-demographic variables by diabetes status, using chi2 tests, t-tests, and multinomial logistic regression. We examined recurrence rates for prostate cancer among patients with and without diabetes using Kaplan-Meier log-rank tests and Cox proportional hazard models.

RESULTS

In multivariate analyses, history of diabetes was not associated with any diagnostic clinical parameter, and treatment-specific recurrence rates for prostate cancer generally did not differ by diabetes history. Among men with low-prognostic risk or who were younger at prostate cancer diagnosis, being diabetic (versus not) was associated with an elevated risk of recurrence after radiation therapy, in multivariate analyses.

CONCLUSIONS

Contrary to data suggesting that diabetes may be modestly protective against risk of incident prostate cancer, we did not observe any evidence of an inverse association between history of diabetes and aggressiveness at diagnosis or risk of recurrence, in this population of men with prostate cancer.

Total and specific complementary and alternative medicine use in a large cohort of men with prostate cancer

OBJECTIVES

To assess specific complementary and alternative medicine (CAM) use in the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE), a large, community-based national registry of men with prostate cancer.

METHODS

We examined more than 50 types of CAM use in a large, national, community-based registry of men with prostate cancer (CaPSURE). Participants completed biannual surveys within 2 years of diagnosis and treatment. We analyzed associations of CAM use with sociodemographic and clinical features, using chi-square tests and multivariate logistic regression.

RESULTS

One third of 2582 respondents reported using CAM. Common practices included vitamin and mineral supplements (26%), herbs (16%), antioxidants (13%), and CAM for prostate health (12%; eg, saw palmetto, selenium, vitamin E, lycopene). In multivariate analyses, users were more likely to have other comorbid conditions, worse cancer grade at diagnosis, higher incomes, more education, and to live in the West.

CONCLUSIONS

Complementary and alternative medicine use was associated with sociodemographic and clinical characteristics in this large sample of men with prostate cancer. These results should be considered by health care professionals counseling men with prostate cancer regarding diet and secondary prevention.

Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study

BACKGROUND

A high calcium intake, mainly from dairy products, may increase prostate cancer risk by lowering concentrations of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], a hormone thought to protect against prostate cancer. The results of epidemiologic studies of this hypothesis are inconclusive.

OBJECTIVE

We investigated the association between dairy product and calcium intakes and prostate cancer risk in the Physicians' Health Study, a cohort of male US physicians.

DESIGN

At baseline, the men answered abbreviated dietary questionnaires. During 11 y of follow-up, we documented 1012 incident cases of prostate cancer among 20885 men. We estimated dairy calcium intake on the basis of consumption of 5 major dairy products and used logistic regression to estimate relative risk.

RESULTS

At baseline, men who consumed >600 mg Ca/d from skim milk had lower plasma 1,25(OH)(2)D(3) concentrations than did those consuming < or =150 mg Ca/d [71 compared with 85 pmol/L (30.06 compared with 35.64 pg/mL); P = 0.005]. Compared with men consuming < or =0.5 daily servings of dairy products, those consuming >2.5 servings had a multivariate relative risk of prostate cancer of 1.34 (95% CI: 1.04, 1.71) after adjustment for baseline age, body mass index, smoking, exercise, and randomized treatment assignment in the original placebo-controlled trial. Compared with men consuming < or =150 mg Ca/d from dairy products, men consuming >600 mg/d had a 32% higher risk of prostate cancer (95% CI: 1.08, 1.63).

CONCLUSIONS

These results support the hypothesis that dairy products and calcium are associated with a greater risk of prostate cancer.

Milk intake, circulating levels of insulin-like growth factor-I, and risk of colorectal cancer in men

BACKGROUND

Milk and dietary calcium may have antiproliferative effects against colorectal cancer, but milk intake also raises serum levels of insulin-like growth factor-I (IGF-I). A high ratio of IGF-I to IGF-binding protein-3 (IGFBP-3) has been linked to an increased risk of colorectal cancer.

METHODS

In a case-control study nested in the Physicians' Health Study, plasma samples were collected from the period 1982 through 1983 from 14 916 men, aged 40-84 years, who also answered dietary questionnaires. Circulating levels of IGF-I and IGFBP-3 were assayed among 193 men who developed colorectal cancer during 13 years of follow-up and 318 age- and smoking-matched cancer-free control men. Conditional logistic regression was used to assess relative risks (RRs) of colorectal cancer for tertiles of IGF-I/IGFBP-3 and dietary factors. Statistical tests were two-sided.

RESULTS

Overall, there was a moderate but statistically nonsignificant inverse association between intake of low-fat milk or calcium from dairy food and colorectal cancer risk. Intake of dairy food (especially low-fat milk) was also positively and moderately associated with plasma levels of IGF-I, IGFBP-3, and IGF-I/IGFBP-3 among control men. We observed a statistically significant interaction between low-fat milk intake and IGF-I/IGFBP-3 in association with risk of colorectal cancer (P(interaction) =.03). Nondrinkers with IGF-I/IGFBP-3 in the highest tertile had a threefold higher risk than nondrinkers with IGF-I/IGFBP-3 in the lowest tertile (RR = 3.05; 95% confidence interval [CI] = 1.29 to 7.24), but no such increase was seen among frequent low-fat milk drinkers (RR = 1.05; 95% CI = 0.41 to 2.69). Conversely, among men with high IGF-I/IGFBP-3, frequent low-fat milk drinkers had a 60% lower risk (95% CI = 0.17 to 0.87; P(trend) =.02) than nondrinkers.

CONCLUSION

Intake of dairy products was associated with a modest increase in circulating IGF-I levels, but intake of low-fat milk was associated with lower risk of colorectal cancer, particularly among individuals with high IGF-I/IGFBP-3. This subpopulation, which is at increased risk of colorectal cancer, might benefit the most from specific dietary intervention.

Diet and prostate cancer risk in a cohort of smokers, with a specific focus on calcium and phosphorus (Finland)

BACKGROUND

Calcium, phosphorus, fructose, and animal protein are hypothesized to be associated with prostate cancer risk, potentially via their influence on 1,25-dihydroxyvitamin D3. We examined these nutrients and overall diet and prostate cancer risk in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study (ATBC Study).

MATERIALS AND METHODS

The ATBC Study was a randomized 2 x 2 trial of alpha-tocopherol and beta-carotene on lung cancer incidence conducted among Finnish male smokers; 27,062 of the men completed a food-use questionnaire at baseline, and comprise the current study population. There were 184 incident clinical (stage 2-4) prostate cancer cases diagnosed between 1985 and 1993. We used Cox proportional hazards models to examine associations between dietary intakes and prostate cancer.

RESULTS

We did not observe significant independent associations for calcium and phosphorus and prostate cancer risk. However, men with lower calcium and higher phosphorus intake had a multivariate relative risk of 0.6 (95% CI 0.3-1.0) compared to men with lower intakes of both nutrients, adjusting for age, smoking, body mass index, total energy, education, and supplementation group. Of the other foods and nutrients examined, none was significantly associated with risk.

DISCUSSION

This study provides, at best, only weak evidence for the hypothesis that calcium and phosphorus are independently associated with prostate cancer risk, but suggests that there may be an interaction between these nutrients.

The role of the MoFe protein alpha-125Phe and beta-125Phe residues in Azotobacter vinelandii MoFe protein-Fe protein interaction

Site-directed mutagenesis and gene-replacement techniques were used to substitute alanine for the MoFe protein alpha- and beta-subunit phenylalanine-125 residues both separately and in combination. These residues are located on the surface of the MoFe protein near the pseudosymmetric axis of symmetry between the alpha- and beta-subunits. Altered MoFe proteins that contain an alanine substitution at only one of the respective positions exhibit proton reduction activities of about 25-50% when compared to that of the wild-type protein. The lower level of proton reduction also corresponds with decreases in the rates of MgATP hydrolysis. The MoFe protein which contains alanine substitutions in both the alpha- and beta- subunits did not exhibit any proton reduction activity or MgATP hydrolysis. Stopped flow spectrophotometry of the singly substituted MoFe proteins indicate primary electron transfer rate constants approximately an order of magnitude slower than what is observed for wild-type MoFe protein, while no primary electron transfer is observed for the doubly substituted MoFe protein. The doubly substituted MoFe protein is able to interact with the Fe protein as shown by chemical crosslinking experiments. However, this protein does not form a tight complex with the Fe protein when treated with MgADP-AlF4- or when using the altered 127delta Fe protein. Stopped flow spectrophotometry was also used to quantitate the first-order dissociation rate constants for the two component proteins. These results suggest that the 125Phe residues are involved in an early event(s) that occurs upon component protein docking and could be involved in eliciting MgATP hydrolysis.

Construction and characterization of a heterodimeric iron protein: defining roles for adenosine triphosphate in nitrogenase catalysis

One molecule of MgATP binds to each subunit of the homodimeric Fe protein component of nitrogenase. Both MgATP molecules are hydrolyzed to MgADP and P(i) in reactions coupled to the transfer of one electron into the MoFe protein component. As an approach to assess the contributions of individual ATP binding sites, a heterodimeric Fe protein was produced that has an Asn substituted for residue 39 in the ATP binding domain in one subunit, while the normal Asp(39) residue within the other subunit remains unchanged. Separation of the heterodimeric Fe protein from a mixed population with homodimeric Fe proteins contained in crude extracts was accomplished by construction of a seven His tag on one subunit and a differential immobilized-metal-affinity chromatography technique. Three forms of the Fe protein (wild-type homodimeric Fe protein [Asp(39)/Asp(39)], altered homodimeric Fe protein [Asn(39)/Asn(39)], and heterodimeric Fe protein [Asp(39)/Asn(39)]) were compared on the basis of the biochemical and biophysical changes elicited by nucleotide binding. Among those features examined were the MgATP- and MgADP-induced protein conformational changes that are manifested by the susceptibility of the [4Fe-4S] cluster to chelation and by alterations in the electron paramagnetic resonance, circular dichroism, and midpoint potential of the [4Fe-4S] cluster. The results indicate that changes in the [4Fe-4S] cluster caused by nucleotide binding are the result of additive conformational changes contributed by the individual subunits. The [Asp(39)/Asn(39)] Fe protein did not support substrate reduction activity but did hydrolyze MgATP and showed MgATP-dependent primary electron transfer to the MoFe protein. These results support a model where each MgATP site contributes to the rate acceleration of primary electron transfer, but both MgATP sites must be functioning properly for substrate reduction. Like the altered homodimeric [Asn(39)/Asn(39)] Fe protein, the heterodimeric [Asp(39)/Asn(39)] Fe protein was found to form a high affinity complex with the MoFe protein, revealing that alteration on one subunit is sufficient to create a tight complex.

Supplemental vitamin E intake and prostate cancer risk in a large cohort of men in the United States

A clinical trial of vitamin E and beta-carotene supplementation for lung cancer prevention among male smokers in Finland recently reported an unexpected, strong protective effect of vitamin E against prostate cancer incidence and mortality. Our objective was to prospectively examine supplemental vitamin E intake and prostate cancer risk in a distinct U.S. population. In 1986, we identified 47,780 U.S. male health professionals, free from diagnosed cancer, who completed a dietary and lifestyle questionnaire; supplemental vitamin E and prostate cancer incidence were updated biennially through 1996. We estimated relative risks (RRs) from multivariate pooled logistic regression models. There were 1896 total (non-stage A1), 522 extraprostatic, and 232 metastatic or fatal incident prostate cancer cases diagnosed between 1986-1996. Men consuming at least 100 IU of supplemental vitamin E daily had multivariate RRs of 1.07 (95% confidence interval [CI], 0.95-1.20) for total and 1.14 (95% CI, 0.82-1.59) for metastatic or fatal prostate cancer compared with those consuming none. Current use, dosage, and total duration of use of specific vitamin E supplements or multivitamins were not associated with risk. However, among current smokers and recent quitters, those who consumed at least 100 IU of supplemental vitamin E per day had a RR of 0.44 (95% CI, 0.18-1.07) for metastatic or fatal prostate cancer compared with nonusers. Thus, supplemental vitamin E was not associated with prostate cancer risk generally, but a suggestive inverse association between supplemental vitamin E and risk of metastatic or fatal prostate cancer among current smokers and recent quitters was consistent with the Finnish trial among smokers and warrants further investigation.

Evidence that MgATP accelerates primary electron transfer in a Clostridium pasteurianum Fe protein-Azotobacter vinelandii MoFe protein nitrogenase tight complex

The nitrogenase catalytic cycle involves binding of the iron (Fe) protein to the molybdenum-iron (MoFe) protein, transfer of a single electron from the Fe protein to the MoFe protein concomitant with the hydrolysis of at least two MgATP molecules, followed by dissociation of the two proteins. Earlier studies found that combining the Fe protein isolated from the bacterium Clostridium pasteurianum with the MoFe protein isolated from the bacterium Azotobacter vinelandii resulted in an inactive, nondissociating Fe protein-MoFe protein complex. In the present work, it is demonstrated that primary electron transfer occurs within this nitrogenase tight complex in the absence of MgATP (apparent first-order rate constant k = 0.007 s-1) and that MgATP accelerates this electron transfer reaction by more than 10,000-fold to rates comparable to those observed within homologous nitrogenase complexes (k = 100 s-1). Electron transfer reactions were confirmed by EPR spectroscopy. Finally, the midpoint potentials (Em) for the Fe protein [4Fe-4S]2+/+ cluster and the MoFe protein P2+/N cluster were determined for both the uncomplexed and complexed proteins and with or without MgADP. Calculations from electron transfer theory indicate that the measured changes in Em are not likely to be sufficient to account for the observed nucleotide-dependent rate accelerations for electron transfer.

Spectroscopic evidence for changes in the redox state of the nitrogenase P-cluster during turnover

Biological nitrogen fixation catalyzed by nitrogenase requires the participation of two component proteins called the Fe protein and the MoFe protein. Each alphabeta catalytic unit of the MoFe protein contains an [8Fe-7S] cluster and a [7Fe-9S-Mo-homocitrate] cluster, respectively designated the P-cluster and FeMo-cofactor. FeMo-cofactor is known to provide the site of substrate reduction whereas the P-cluster has been suggested to function in nitrogenase catalysis by providing an intermediate electron-transfer site. In the present work, evidence is presented for redox changes of the P-cluster during the nitrogenase catalytic cycle from examination of an altered MoFe protein that has the beta-subunit serine-188 residue substituted by cysteine. This residue was targeted for substitution because it provides a reversible redox-dependent ligand to one of the P-cluster Fe atoms. The altered beta-188(Cys) MoFe protein was found to reduce protons, acetylene, and nitrogen at rates approximately 30% of that supported by the wild-type MoFe protein. In the dithionite-reduced state, the beta-188(Cys) MoFe protein exhibited unusual electron paramagnetic resonance (EPR) signals arising from a mixed spin state system (S = 5/2, 1/2) that integrated to 0.6 spin/alphabeta-unit. These EPR signals were assigned to the P-cluster because they were also present in an apo-form of the beta-188(Cys) MoFe protein that does not contain FeMo-cofactor. Mediated voltammetry was used to show that the intensity of the EPR signals was maximal near -475 mV at pH 8.0 and that the P-cluster could be reversibly oxidized or reduced with concomitant loss in intensity of the EPR signals. A midpoint potential (Em) of -390 mV was approximated for the oxidized/resting state couple at pH 8.0, which was observed to be pH dependent. Finally, the EPR signals exhibited by the beta-188(Cys) MoFe protein greatly diminished in intensity under nitrogenase turnover conditions and reappeared to the original intensity when the MoFe protein returned to the resting state.

Prospective study of colorectal cancer risk in men and plasma levels of insulin-like growth factor (IGF)-I and IGF-binding protein-3

BACKGROUND

Insulin-like growth factor-I (IGF-I) is a potent mitogen for normal and neoplastic cells, whereas IGF-binding protein-3 (IGFBP-3) inhibits cell growth in many experimental systems. Acromegalics, who have abnormally high levels of growth hormone and IGF-I, have higher rates of colorectal cancer. We therefore examined associations of plasma levels of IGF-I and IGFBP-3 with the risk of colorectal cancer in a prospective case-control study nested in the Physicians' Health Study.

METHODS

Plasma samples were collected at baseline from 14916 men without diagnosed cancer. IGF-I, IGF-II, and IGFBP-3 were assayed among 193 men later diagnosed with colorectal cancer during 14 years of follow-up and among 318 age- and smoking-matched control subjects. All P values are two-sided.

RESULTS

IGFBP-3 levels correlated with IGF-I levels (r=.64) and with IGF-II levels (r=.90). After controlling for IGFBP-3, age, smoking, body mass index (weight in kg/[height in m]2), and alcohol intake, men in the highest quintile for IGF-I had an increased risk of colorectal cancer compared with men in the lowest quintile (relative risk [RR]=2.51; 95% confidence interval [CI]=1.15-5.46; P for trend = .02). After controlling for IGF-I and other covariates, men with higher IGFBP-3 had a lower risk (RR=0.28; 95% CI=0.12-0.66; P for trend = .005, comparing extreme quintiles). The associations were consistent during the first and the second 7-year follow-up intervals and among younger and older men. IGF-II was not associated with risk.

CONCLUSIONS

Our findings suggest that circulating IGF-I and IGFBP-3 are related to future risk of colorectal cancer.

Dairy products, calcium, phosphorous, vitamin D, and risk of prostate cancer (Sweden)

OBJECTIVES

Dairy products consistently have been associated with an increased risk of prostate cancer, yet the mechanism of this relationship remains unknown. Recent hypotheses propose that 1,25 dihydroxyvitamin D (1,25 D) is protective for prostate cancer. One study in the United States found that calcium consumption, which can lower circulating 1,25 D, was associated with higher risk of advanced prostate cancer, and we sought to address this hypothesis in a distinct population.

METHODS

We analyzed data from a population-based case-control study of prostate cancer conducted in Orebro, Sweden, with 526 cases and 536 controls. Using unconditional logistic regression models, we examined the relationship of dairy products, dietary calcium, phosphorous, and vitamin D with risk of total, extraprostatic, and metastatic prostate cancer.

RESULTS

Calcium intake was an independent predictor of prostate cancer (relative risk (RR) = 1.91, 95 percent confidence interval (CI) 1.23-2.97 for intake > or = 1183 vs. < 825 mg/day), especially for metastatic tumors (RR = 2.64, 95 percent CI 1.24-5.61), controlling for age, family history of prostate cancer, smoking, and total energy and phosphorous intakes. High consumption of dairy products was associated with a 50 percent increased risk of prostate cancer.

CONCLUSIONS

Our results support the hypothesis that high calcium intake may increase risk of prostate cancer, and this relation may underlie previously observed associations between dairy products and prostate cancer.

What causes prostate cancer? A brief summary of the epidemiology

In recent decades, prostate cancer has emerged as one of the most common diseases among older men, particularly in Western society. Several years ago, only age, race, and family history were known risk factors for this disease. However, today, much progress has been made towards discovering nutritional and hormonal risk factors for prostate cancer. Biomarkers, including testosterone and insulin-like growth factor, and nutritional factors, especially meat, fat, and dairy intake, have been linked to greater risk of disease. Higher consumption of selenium and vitamin E, fructose/fruits, and tomatoes all have been associated with reduced occurrence of prostate cancer, but as yet their efficacy for prevention remains unproven. The challenge of understanding the enigmas of this disease will continue into future decades, as we convert current knowledge into preventive and therapeutic recommendations.

Plasma insulin-like growth factor-I and prostate cancer risk: a prospective study

Insulin-like growth factor-I (IGF-I) is a mitogen for prostate epithelial cells. To investigate associations between plasma IGF levels and prostate cancer risk, a nested case-control study within the Physicians' Health Study was conducted on prospectively collected plasma from 152 cases and 152 controls. A strong positive association was observed between IGF-I levels and prostate cancer risk. Men in the highest quartile of IGF-I levels had a relative risk of 4.3 (95 percent confidence interval 1.8 to 10.6) compared with men in the lowest quartile. This association was independent of baseline prostate-specific antigen levels. Identification of plasma IGF-I as a predictor of prostate cancer risk may have implications for risk reduction and treatment.

Obesity, fat distribution, and weight gain as risk factors for clinical diabetes in men

OBJECTIVE

To investigate the relation between obesity, fat distribution, and weight gain through adulthood and the risk of non-insulin-dependent diabetes mellitus (NIDDM).

RESEARCH DESIGN AND METHODS

We analyzed data from a cohort of 51,529 U.S. male health professionals, 40-75 years of age in 1986, who completed biennial questionnaires sent out in 1986, 1988, 1990, and 1992. During 5 years of follow-up (1987-1992), 272 cases of NIDDM were diagnosed among men without a history of diabetes, heart disease, and cancer in 1986 and who provided complete health information. Relative risks (RRs) associated with different anthropometric measures were calculated controlling for age, and multivariate RRs were calculated controlling for smoking, family history of diabetes, and age.

RESULTS

We found a strong positive association between overall obesity as measured by body mass index (BMI) and risk of diabetes. Men with a BMI of > or = 35 kg/m2 had a multivariate RR of 42.1 (95% confidence interval [CI] 22.0-80.6) compared with men with a BMI < 23.0 kg/m2. BMI at age 21 and absolute weight gain throughout adulthood were also significant independent risk factors for diabetes. Fat distribution, measured by waist-to-hip ratio (WHR), was a good predictor of diabetes only among the top 5%, while waist circumference was positively associated with the risk of diabetes among the top 20% of the cohort.

CONCLUSIONS

These data suggest that waist circumference may be a better indicator than WHR of the relationship between abdominal adiposity and risk of diabetes. Although early obesity, absolute weight gain throughout adulthood, and waist circumference were good predictors of diabetes, attained BMI was the dominant risk factor for NIDDM; even men of average relative weight had significantly elevated RRs.

Self-understanding and reaching out to sick children and their families: an ongoing professional challenge

Health care professionals face a series of taxing, emotionally wrenching, painful experiences as they begin to care for frightened, ill children and their families. Loss, grief, overidentification with patients, and overwhelming anxiety are among their "occupational hazards." Open, frank discussion of intense feelings and reactions and mutual support are essential elements in helping caregivers to cope in ways that do not result in withdrawal from children and families. By developing strategies that reach out to patients and their families, professionals enhance their own personal professional gratification and self-esteem. The insights of parents are used extensively both to illustrate concepts and to emphasize the critical role parents can play as "resources" for professionals and "partners in care."