A Single-Arm Phase II Trial of Sitravatinib in Advanced Well-Differentiated/Dedifferentiated Liposarcoma

PURPOSE

To evaluate sitravatinib, an inhibitor of multiple receptor tyrosine kinases (RTK), for the treatment of well-differentiated/dedifferentiated liposarcoma (WD/DD LPS).

PATIENTS AND METHODS

This multicenter, open-label, Phase II trial enrolled patients with advanced WD/DD LPS who had received at least one prior systemic regimen and had progression within 12 weeks of enrollment. Patients received sitravatinib 150 mg (later amended to 120 mg) orally daily. A Simon two-stage design was used to evaluate for an improvement in the primary endpoint, progression-free rate at 12 weeks (PFR12), from 20% to 40%. Secondary endpoints included antitumor activity and safety. A subset of patients underwent paired biopsies analyzed using reverse-phase protein array.

RESULTS

Twenty-nine patients enrolled. Median age was 62 years and 31% had received 3 or more prior lines. Most patients (93%) had DDLPS or mixed WD/DD LPS. Overall, 12 of 29 patients (41%) were alive and progression-free at 12 weeks and the study met the primary endpoint. There were no confirmed responses. Median progression-free survival was 11.7 weeks [95% confidence interval (CI): 5.9-35.9] and median overall survival was 31.7 weeks (95% CI: 18.1-90.1). The most common treatment-related adverse events were diarrhea (59%), hypertension (52%), hoarseness (41%), mucositis (31%), and nausea (31%). Baseline expression of phospho-RTKs was not significantly different between patients with and without clinical benefit from sitravatinib, but the number of samples was small.

CONCLUSIONS

Sitravatinib provided a PFR12 of 41% and meaningful disease control in a subset of patients with advanced, progressive WD/DD LPS.

Abstract C071: Keratin 17 excludes CD8-positive T cells and recruits CD163-positive macrophages in pancreatic ductal adenocarcinoma

Background: Keratin 17 (K17) is a negative prognostic biomarker, overexpressed in the biologically most aggressive forms of pancreatic ductal adenocarcinoma (PDAC). In other anatomic sites and disease processes, K17 expression also correlates with immune cell infiltrates and could block T-cell infiltration. Thus, we hypothesized that K17 expression correlates with the inflammatory microenvironment in PDAC. In this study, we aimed to determine the relationship between the stromal immune cell infiltrates and K17 expression, using multiplexed immunohistochemistry (mIHC) and our suite of deep learning tools to quantitatively evaluate the expression of four biomarkers of T-cells and macrophages in PDAC. Methods: mIHC was performed on representative sections of 201 primary PDACs from Stony Brook University Hospital, Thomas Jefferson University Hospital, Cedars Sinai Medical Center, and from a national cohort (KYT, Pancreatic Cancer Action Network, and Perthera). Antibodies for CD4 (helper T-cells), CD8 (cytotoxic T-cells), CD16 (pan-macrophage), CD163 (M2 macrophages), pancytokeratin, and K17 were provided by Roche Diagnostics Corporation through a sponsored research agreement. mIHC was performed on a Discovery Ultra Autostainer (Roche), using horseradish peroxidase (HRP) and alkaline phosphatase (AP)-based protocols with multiple chromogens (Red: CD4, Purple: CD8, Yellow: CD16, Green: CD163, Teal: pancytokeratin, and Brown: K17) to enable multispectral imaging of diverse immune cell populations within the cancer microenvironment. A deep learning analysis workflow was used to detect and classify stromal inflammatory cells, in whole slide images (WSIs), generated using an Olympus VS120 digital microscope (Olympus, Tokyo, Japan). Pixel-wise predictions from a color auto-encoder (ColorAE) union UNET anchor UNET model were combined to create multi-class masks that were further analyzed to perform detection and classification. Results: The analysis of the inflammatory microenvironment focused on defining immune cell infiltrates located within 25 microns of the closest K17-positive versus K17-negative tumor cell in each representative section. Across the sum of K17-positive and negative zones/section, CD4 cell counts ranged from 0-10,617 (mean 2,709), CD8 cell counts ranged from 63-28,596 (mean 6,745), CD16 cell counts ranged from 4-7,797 (mean 3,024), and CD163 cell counts ranged from 35-34,696 (mean 14,968). CD4 T-helper cells, CD8 cytotoxic T cells, and CD16 macrophages were more numerous (respectively, p=0.0012; p=<0.0001; p=<0.0001) in K17-negative tumor zones compared to K17-positive zones. By contrast, the number of CD163 (M2) tumor-promoting macrophages was greater in K17 positive zones (p=0.0019). Conclusion: K17 expression by tumor cells impacts the chronic inflammatory microenvironment, shielding tumor cells from immune cell mediated cytotoxic responses, while recruiting tumor-promoting M2 macrophages, indicating that K17 impacts the immune response as a fundamental hallmark of aggression in PDAC.

Citation Format: Lyanne Oblein, Michael Horowitz, Mahmudul Hasan, Sruthi Babu, Mariana Torrente-Goncalves, Lucia Roa, Jaymie Oentoro, Jason Harper, Xin Yao Zheng, Wei Jiang, Andrew Hendifar, Natalie Moshayedi, Brent Larson, Veronica Placencio-Hickok, Edik Blais, Emmanuel Petricoin, Joel Saltz, Natalia D. Marchenko, Luisa F. Escobar-Hoyos, Kenneth Shroyer. Keratin 17 excludes CD8-positive T cells and recruits CD163-positive macrophages in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C071.

Computational modeling of first responders' willingness to accept radiation exposure during radiological or nuclear events

Since the events of 9/11, a concerted interagency effort has been undertaken to create comprehensive emergency planning and preparedness strategies for the management of a radiological or nuclear event in the US. These planning guides include protective action guidelines, medical countermeasure recommendations, and systems for diagnosing and triaging radiation injury. Yet, key areas such as perception of risk from radiation exposure by first responders have not been addressed. In this study, we identify the need to model and develop new strategies for medical management of large-scale population exposures to radiation and examine the phenomena of radiation dread and its role in emergency response using an agent-based modeling approach. Using the computational modeling platform NetLogo, we developed a series of models examining factors affecting first responders' willingness to work (WTW) in the context of entering areas where radioactive contamination is present or triaging individuals potentially contaminated with radioactive materials. In these models, the presence of radiation subject matter experts (SMEs) was found to increase WTW. Degree of communication was found to be a dynamic variable with either positive or negative effects on WTW dependent on the initial WTW demographics of the test population. Our findings illustrate that radiation dread is a significant confounder for emergency response to radiological or nuclear events and that increasing the presence of radiation SME in the field and communication among first responders when such radiation SMEs are present will help mitigate the effect of radiation dread and improve first responder WTW during future radiological or nuclear events.

Abstract P3-10-02: Identifying breast cancer molecular phenotypes to predict response in a modern treatment landscape: Lessons from ˜1000 patients across 10 arms of the I-SPY 2 TRIAL

Background: The explosion in new treatment options targeting immune checkpoints, HER signaling, DNA repair deficiency, AKT, and other pathways calls for updated breast cancer subtypes beyond HR and HER2 status to predict which patients will respond to which treatments. Here we leverage the I-SPY 2 TRIAL biomarker program over the past 8 years across 10 treatment arms to elucidate a minimal set of biomarkers that may improve response prediction in a modern treatment context, and to investigate which new patient phenotypes are identified by these response-predictive biomarkers.

Methods: 986 patients were considered in this analysis. Treatments included paclitaxel alone (or with trastuzumab (H) in HER2+) or combined with investigational agents: veliparib/carboplatin (VC); neratinib; MK2206; ganitumab; ganetespib; AMG386; TDM1/pertuzumab (P); H/P; and pembrolizumab (Pembro). 24 prospectively defined, mechanism-of-action and pathway-based expression and phospho-protein signatures/biomarkers assayed from pre-treatment biopsies were previously found to be predictive in a particular agent/arm in pre-specified analysis. Here we evaluate these biomarkers in all patients. We assessed association between each biomarker and response in the population as a whole and within each arm and HR/HER2 subtype using a logistic model. To identify optimal dichotomizing thresholds for select biomarkers, 2-fold cross-validation was repeated 500 times. Our analysis is exploratory and does not adjust for multiplicities.

Results: Our initial set of 24 predictive biomarkers reflects DNA repair deficiency (n=2), immune activation (n=7), ER signaling (n=2), HER2 signaling (n=4), proliferation (n=2), phospho-activation of AKT/mTOR (n=2), and ANG/TIE2 (n=1) pathways, among others. Biomarkers reflecting similar biology are correlated and cluster together. We make use of this correlation structure to reduce the dimensionality of the biomarker set to five predictive signals: proliferation, DNA repair deficiency (DRD), immune-engaged (Immune+), luminal/ER (lum), and HER2-activated. These biomarkers, when dichotomized, identify patient groups with differential predicted sensitivities to I-SPY 2 agents and are present at different proportions within receptor subtypes. For instance, in the HER2- subset, Immune+/DRD+ patients are predicted sensitive to both VC and Pembro, and account for 39% of TN, but only 12% of HR+HER2-. On the other end of the spectrum, only 17% of TN are Immune-/DRD-, compared to the majority (56%) of HR+HER2-. There are also subsets of patients positive for only one marker. For the HER2+ subset, 67% are HER2-activated+, and 25% lum+; of these HER2-activated+ patients are more likely to be Immune+ (44%), vs 23% in lum+. HER2-activated+/Immune+ patients have higher predicted sensitivity to HER2-targeted agents than lum+ or Immune- patients.

In all, these molecular phenotypes predict sensitivity to one or more I-SPY 2 investigational agents for 75% of the ˜ 1000 patients.

Conclusion: Molecular phenotypes reflecting proliferation, immune engagement, HER2-activation, luminal/ER-signaling, and DNA repair deficiency may provide a roadmap to guide treatment prioritization for emerging therapeutics.

Citation Format: Wolf DM, Yau C, Wulfkuhle J, Petricoin E, Campbell M, Brown-Swigart L, Hirst G, Asare S, Zhu Z, Lee EP, Delson A, Pohlmann P, I-SPY 2 TRIAL Consortium, Hylton N, Liu MC, Symmans F, DeMichele A, Yee D, Berry D, Esserman L, van 't Veer L. Identifying breast cancer molecular phenotypes to predict response in a modern treatment landscape: Lessons from ˜1000 patients across 10 arms of the I-SPY 2 TRIAL [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-10-02.

Abstract 3610: Synergy between androgen receptor (AR)-targeting agents seviteronel (SEVI) or enzalutamide (ENZA) and mTOR or HER2 pathway-targeting agents in breast cancer

Background: AR is expressed in ~60% of HER2+ and up to 50% of triple negative breast cancer (TNBC) with growing evidence that AR plays a role in BC growth and survival. Next-generation AR-targeting agents including SEVI (selective CYP17-lyase and AR inhibitor) and ENZA (AR inhibitor) have shown promise in preclinical and clinical models of prostate cancer and are currently being evaluated in BC. Approved therapeutics targeting mTOR such as everolimus (EVEROL) and HER2-targeting agents provide significant clinical benefit in some BC patients; however, de novo and acquired resistance remain critical issues that may be partially attributed to compensatory AR action.

Hypothesis: Due to cross-regulation between AR and the HER2/PI3K/mTOR pathway in BC, targeting AR in combination with approved agents for these pathways may improve responses.

Methods: Human BC cell lines HER2+ (BT474, BT474-HR20, SKBR3) and TNBC (MDAMB453, BT549) and an AR+ TNBC mouse mammary carcinoma model (Met-1) were used. Cells were treated with multiple doses of AR-targeting agents SEVI or ENZA and EVEROL, alone or in combination and assayed over time using IncuCyte instrumentation and combination indices calculated using Calcusyn. Anchorage independence was tested by growth on soft agar. Pathway component genes and proteins were measured. In vivo, NOD/SCID mice with HER2+ trastuzumab-resistant BT474-HR20 xenografts were treated with ENZA, EVEROL, or the combination. Similar in vivo experiments with SEVI are ongoing.

Results: Both SEVI and ENZA significantly inhibited proliferation of both HER2+ and TNBC cell lines. Both significantly inhibited growth on soft agar in l Met-1 cells (p=0.0005 for SEVI, p=0.032 for ENZA). Using 9 dose combinations of EVEROL with SEVI or ENZA, synergy was observed in multiple cell lines in vitro, but only in lines containing activating PIK3CA mutations. DHT induced a cell line-specific increase in pHER2 and/or pHER3 that was attenuated by AR inhibition. EVEROL alone caused an increase in total AR, pHER2, and pHER3, and these effects were also abrogated by AR inhibition. In vivo, ENZA inhibited BT474-HR20 xenografts, and combining ENZA with EVEROL decreased tumor viability more than either single agent (p<0.001, repeated measures ANOVA). Similar in vivo studies with SEVI are planned.

Conclusion: Agents targeting AR synergize with EVEROL. Combination therapies targeting AR and the mTOR and HER2/HER3 pathways may provide benefit for HER2+ and TNBC patients. SEVI was a stronger inhibitor of anchorage-independent growth than ENZA and will thus be further investigated in combination with approved HER2/PI3K/mTOR pathway-directed therapeutics in vivo.

This work was funded by DOD BCRP - Clinical Translational Award BC120183 W81XWH-13-1-0090 to JKR and 0091 to AE and R01 CA187733 to JKR

Note: This abstract was not presented at the meeting.

Citation Format: Michael A. Gordon, Nicholas D'Amato, Jessica Christenson, Beatrice Babbs, Haihua Gu, Julia Wulfkuhle, Emmanuel Petricoin, Anthoy Elias, Jennifer K. Richer. Synergy between androgen receptor (AR)-targeting agents seviteronel (SEVI) or enzalutamide (ENZA) and mTOR or HER2 pathway-targeting agents in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3610. doi:10.1158/1538-7445.AM2017-3610

The mRNA-binding protein HuR promotes hypoxia-induced chemoresistance through posttranscriptional regulation of the proto-oncogene PIM1 in pancreatic cancer cells

Previously, it has been shown that pancreatic ductal adenocarcinoma (PDA) tumors exhibit high levels of hypoxia, characterized by low oxygen pressure (pO2) and decreased O2 intracellular perfusion. Chronic hypoxia is strongly associated with resistance to cytotoxic chemotherapy and chemoradiation in an understudied phenomenon known as hypoxia-induced chemoresistance. The hypoxia-inducible, pro-oncogenic, serine-threonine kinase PIM1 (Proviral Integration site for Moloney murine leukemia virus 1) has emerged as a key regulator of hypoxia-induced chemoresistance in PDA and other cancers. Although its role in therapeutic resistance has been described previously, the molecular mechanism behind PIM1 overexpression in PDA is unknown. Here, we demonstrate that cis-acting AU-rich elements (ARE) present within a 38-base pair region of the PIM1 mRNA 3'-untranslated region mediate a regulatory interaction with the mRNA stability factor HuR (Hu antigen R) in the context of tumor hypoxia. Predominantly expressed in the nucleus in PDA cells, HuR translocates to the cytoplasm in response to hypoxic stress and stabilizes the PIM1 mRNA transcript, resulting in PIM1 protein overexpression. A reverse-phase protein array revealed that HuR-mediated regulation of PIM1 protects cells from hypoxic stress through phosphorylation and inactivation of the apoptotic effector BAD and activation of MEK1/2. Importantly, pharmacological inhibition of HuR by MS-444 inhibits HuR homodimerization and its cytoplasmic translocation, abrogates hypoxia-induced PIM1 overexpression and markedly enhances PDA cell sensitivity to oxaliplatin and 5-fluorouracil under physiologic low oxygen conditions. Taken together, these results support the notion that HuR has prosurvival properties in PDA cells by enabling them with growth advantages in stressful tumor microenvironment niches. Accordingly, these studies provide evidence that therapeutic disruption of HuR's regulation of PIM1 may be a key strategy in breaking an elusive chemotherapeutic resistance mechanism acquired by PDA cells that reside in hypoxic PDA microenvironments.

Pilot phase I/II personalized therapy trial for metastatic colorectal cancer: evaluating the feasibility of protein pathway activation mapping for stratifying patients to therapy with imatinib and panitumumab

This nonrandomized phase I/II trial assessed the efficacy/tolerability of imatinib plus panitumumab in patients affected by metastatic colorectal cancer (mCRC) after stratification to treatment by selection of activated imatinib drug targets using reverse-phase protein array (RPPA). mCRC patients presenting with a biopsiable liver metastasis were enrolled. Allocation to the experimental and control arms was established using functional pathway activation mapping of c-Kit, PDGFR, and c-Abl phosphorylation by RPPA. The experimental arm received run-in escalation therapy with imatinib followed by panitumumab. The control arm received panitumumab alone. Seven patients were enrolled in the study. For three of the seven patients, sequential pre- and post-treatment biopsies were used to evaluate the effect of the therapeutic compounds on the drug targets and substrates. A decrease in the activation level of the drug targets and downstream substrates was observed in two of three patients. Combination therapy increased the activation of the AKT-mTOR pathway and several receptor tyrosine kinases. This study proposes a novel methodology for stratifying patients to personalized treatment based on the activation level of the drug targets. This workflow provides the ability to monitor changes in the signaling pathways after the administration of targeted therapies and to identify compensatory mechanisms.

Individualized therapy for metastatic colorectal cancer

Systemic therapeutic efficacy is central to determining the outcome of patients with metastatic colorectal cancer (CRC). In these patients, there is a critical need for predictive biomarkers to optimize efficacy whilst minimizing toxicity. The integration of a new generation of molecularly targeted drugs into the treatment of CRC, coupled with the development of sophisticated technologies for individual tumours as well as patient molecular profiling, underlines the potential for personalized medicine. In this review, we focus on the latest progress made within the genomic and proteomic fields, concerning predictive biomarkers for individualized therapy in metastatic CRC.

P1-06-11: Comparison of Community and Central Her2 Assessment on Outcome of Neoadjuvant Chemotherapy in the I-SPY Trial

Background: Her-2/neu overexpression, by immunohistochemistry (IHC) or fluorescence in-situ hybridization (FISH), is highly correlated with response to trastuzumab and these are currently the gold-standard, FDA-cleared testing methods for assigning treatment to Her-2-directed therapies. However, substantial variability has been documented between community and central laboratory IHC and FISH testing. Biologically, Her-2 overexpression may reflect increased gene copy number, gene expression and/or protein production, and these can be measured by other platforms, including comparative genomic hybridization (CGH), expression arrays and quantitative protein assays, respectively. We sought to determine the degree to which community IHC/FISH results differed from centrally-assessed IHC, FISH, and other assessment platforms within the I-SPY Trial and whether response to neoadjuvant chemotherapy (NAC) differed by platform.

Methods: The I-SPY Trial enrolled 237 women 2002–06 with invasive breast tumors at least 3 cm in clinical/radiographic size who subsequently underwent anthracycline/taxane NAC, serial core biopsies and imaging. Pathologic complete response (pCR) was determined at time of surgery and 3-year follow up has been reached. Trastuzumab was given to Her2+ patients at physician discretion, based upon community IHC/FISH results, and became more widespread after 2005. Central I-SPY laboratories determined Her2 copy number by MIP array, gene expression by Affymetrix and Agilent arrays, and Her2 protein by reverse-phase protein array (RPMA). Unsupervised clustering algorithms were used to evaluate expression patterns. Composite variables were constructed for DNA, RNA and protein positivity as well as for community and central IHC/FISH. Platforms were compared and Kaplan-Meier curves were constructed to compare outcomes by platform.

Results: 222 women were evaluable, though not all patients had results for all platforms. Community composite IHC/FISH was positive in 64/214 (30%) but only 41 of these (64%) were confirmed by central IHC/FISH and 4 additional cases were centrally positive despite negative community testing. Concordance was high among centrally-assessed Her2 platforms, but was lower between community IHC/protein and central RNA (90%), DNA (91%) and protein (91%). Among patients receiving trastuzumab (n=36), the pCR rate was ∼50% regardless of Her2-assessment platform; in contrast, those not receiving trastuzumab had pCR rates below 30%. Among the 64 patients deemed Her2+ by community IHC/FISH, 30 (48%) had pCR and 15 (25%) have had distant relapse. Five distant relapses have occurred despite pCR; all received trastuzumab, all were Her2 positive by multiple central platforms and 3/5 were ER-positive. Sites of distant relapse included brain, bone and viscera; only 1 of 5 had isolated brain relapse.

Conclusions: Community IHC/FISH testing for Her2 expression in the I-SPY Trial overcalled Her2 positivity compared to central testing while central results were highly concordant among DNA, RNA and protein platforms. Despite the high rate of community “false positives”, relapse after pCR occurred only in central Her2 “true positives,” exclusively among those receiving trastuzumab, and was rarely isolated to CNS sanctuary sites.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-06-11.

Chemoresistant colorectal cancer cells and cancer stem cells mediate growth and survival of bystander cells

BACKGROUND

Recent studies suggest that cancer stem cells (CSCs) mediate chemoresistance, but interestingly, only a small percentage of cells in a resistant tumour are CSCs; this suggests that non-CSCs survive by other means. We hypothesised that chemoresistant colorectal cancer (CRC) cells generate soluble factors that enhance survival of chemonaive tumour cells.

METHODS

Chemoresistant CRC cells were generated by serial passage in oxaliplatin (Ox cells). Conditioned media (CM) was collected from parental and oxaliplatin-resistant (OxR) cells. CRC cells were treated with CM and growth and survival were assessed. Tumour growth rates were determined in nude mice after cells were treated with CM. Mass spectrometry (MS) identified proteins in CM. Reverse phase protein microarray assays determined signalling effects of CM in parental cells.

RESULTS

Oxaliplatin-resistant CM increased survival of chemo-naive cells. CSC CM also increased growth of parental cells. Parental and OxR mixed tumours grew larger than tumours composed of parental or OxR cells alone. Mass spectrometry detected unique survival-promoting factors in OxR CM compared with parental CM. Cells treated with OxR CM demonstrated early phosphorylation of EGFR and MEK1, with later upregulation of total Akt .We identified progranulin as a potential mediator of chemoresistance.

CONCLUSION

Chemoresistant tumour cells and CSCs may promote resistance through soluble factors that mediate survival in otherwise chemosensitive tumour cells.

Platform for establishing interlaboratory reproducibility of selected reaction monitoring-based mass spectrometry peptide assays

Mass spectrometry (MS) is an attractive alternative to quantification of proteins by immunoassays, particularly for protein biomarkers of clinical relevance. Reliable quantification requires that the MS-based assays are robust, selective, and reproducible. Thus, the development of standardized protocols is essential to introduce MS into clinical research laboratories. The aim of this study was to establish a complete workflow for assessing the transferability and reproducibility of selected reaction monitoring (SRM) assays between clinical research laboratories. Four independent laboratories in North America, using identical triple-quadrupole mass spectrometers (Quantum Ultra, Thermo), were provided with standard protocols and instrumentation settings to analyze unknown samples and internal standards in a digested plasma matrix to quantify 51 peptides from 39 human proteins using a multiplexed SRM assay. The interlaboratory coefficient of variation (CV) was less than 10% for 25 of 39 peptides quantified (12 peptides were not quantified based upon hydrophobicity) and exhibited CVs less than 20% for the remaining peptides. In this report, we demonstrate that previously developed research platforms for SRM assays can be improved and optimized for deployment in clinical research environments.

Abstract 2276: Proteomic analysis of chemoresistance in colorectal cancer cells: potential paracrine mechanisms of resistance

Background: Chemoresistance occurs in nearly all patients with metastatic colorectal cancer (CRC), and mechanisms to reverse chemoresistance remain elusive. We tested the hypothesis that CRC cells resistant to 5-fluorouracil (5FU-R) and oxaliplatin (Ox-R) exhibit proteomic profiles that may identify previously unrecognized mediators of resistance. In prior studies, we found that conditioned media from oxaliplatin-resistant HT29 cells (Ox-R) could mediate growth and chemoresistance in chemonaive parental HT29 cells in vitro. We sought to identify soluble factors in conditioned media that are potential mediators of the paracrine cell survival mechanisms.

Methods: Parental HT29 (Par) cells were grown in increasing concentrations of 5-FU and oxaliplatin to generate 5FU-R and Ox-R cells. Protein from cell lysates and conditioned media (CM) were analyzed by liquid chromatography-mass spectrometry (LC-MS), and spectral counts were compared. Antibody-conjugated bead technology and ELISAs were used to obtain cytokine profiles of CM. Reverse phase proteomic arrays (RPMA) were used to determine signal transduction pathways activated in cells treated with CM. Ox-R cells were injected into nude mice to determine the paracrine effect on Par cells growing on the opposite flank.

Results: Chemoresistant cells displayed significantly different proteomic profiles. In 5FU-R cells, pathways involving oxidative phosphorylation, inositol metabolism, actin cytoskeleton signaling, regulation of actin-based motility by Rho, and ATM signaling were significantly altered vs Par cells. In Ox-R cells, pathways mediating pyruvate metabolism, integrin signaling, caveolar-mediated endocytosis signaling, and mitochondrial dysfunction were among the most altered vs Par cells. Comparison of 5FU-R and Ox-R cells revealed differences in RNA post-transcriptional modification, ERK/MAPK, RAN, and chemokine signaling. Cytokine profiling demonstrated a significant increase in stem cell factor/c-Kit ligand (p=0.02) and a decrease in TRAIL (p=0.008) and IL-10 (p=0.04). RPPA analysis demonstrated early phosphorylation of EGFR and MEK1 followed by GSK, and mTOR activation. Ox-R tumors growing in vivo induced faster and larger tumor growth of contralateral Par tumors indicating a systemic effect. Conclusions: Chemoresistant CRC cells exhibit proteomes that reflect specific survival pathways, with many previously unrecognized potential mediators of resistance. Analysis of soluble factors from chemoresistant CRC cells demonstrates the presence of numerous potential mediators of cancer cell survival that may act, not only in an autocrine/paracrine manner, but also systemically.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2276.

Breast cancer molecular profiles and tumor response of neoadjuvant doxorubicin and paclitaxel: The I-SPY TRIAL (CALGB 150007/150012, ACRIN 6657)

LBA515

Background: I-SPY is a multi-center trial designed to identify predictive markers of pathological complete response (pCR) and survival of women with locally advanced breast cancers (3cm or greater). Women received neoadjuvant doxorubicin and cyclophosphamide then paclitaxel. Methods: 237 women enrolled, 216 completed serial imaging and core biopsies. Pre-treatment assays include: Agilent expression arrays, MIP aCGH, p53 gene chip and sequencing, IHC and reverse phase protein arrays (RPMA). Response to therapy was measured by serial MRI, pCR and residual cancer burden (RCB). Associations among molecular markers, pCR, RCB and survival were evaluated using chi-square test, Kaplan-Meier curves and log-rank test. Results: Median tumor size was 6cm, % pCR and RCB 0/1 was 27% and 36% for the entire study; % pCR rate for the 144 Agilent arrays was 25%. Distribution, rates of pCR and RCB 0/1 are shown in the Table for molecular and IHC markers. DFS and OS will be presented. Several molecular subtypes, including NKI 70 gene low, luminal A, 21 gene set low and IHC HR+, define 15–28% of patients with 3–10% pCR, yet excellent early survival. Wound healing, most discriminatory for prognosis, is not predictive of chemotherapy response. By RPMA, patients with pCR had increased phosphorylation of 4EBP1, eNOS, cAbl, STAT5, EGFR, AKT (p<0.05). In ER+ patients with poor MR response, pIRS, pIGFR, p706S were activated (p<0.05). RCB is a more refined way to measure pCR and was more predictive of DFS and OS (p=0.01) than pCR alone with a mean follow up of 3.9 years. MR volume is highly predictive of pCR and RCB. For specific subtypes, e.g. basal, RCB is predictive of DFS (p<0.00001). Conclusions: LABC have aggressive biology. Response to therapy and outcome can be predicted by many biomarkers. The I-SPY data set provides a platform to compare, contrast and combine marker signatures to tailor therapy and demonstrates the power of the neoadjuvant setting. Support: ACRIN U01 CA079778 ; CALGB CA31964, CA33601; NCI SPORE CA58207.

[Table: see text]

[Table: see text]

Discovery of a new phospho-HER2+/FISH- molecular subtype of human breast cancer by functional pathway mapping

11009

Background: Effective treatment of breast cancer through the targeting of the HER2 protein in human breast cancer represents a major advance in oncology, yet the identification of responders has relied on non-quantitative methods (IHC) that measure the erbB2 protein or indirect genomic analysis (FISH) of the erbB2 gene that cannot predict protein pathway activation status. We utilized a new quantitative protein microarray assay to measure total and phosphorylated HER2 in the context of broad-scale EGFR signal pathway mapping in order to generate a new molecular characterization scheme for human breast cancer. Methods: Pure tumor epithelium from 149 frozen pre-treatment human breast cancer tissue specimens (from the I-SPY TRIAL: CALGB 150007/150012, ACRIN 6657) were procured via Laser Capture Microdissection and protein pathway mapping was performed using Reverse Phase Protein Microarrays (RPMA) whereby the activation of 40 key signaling proteins was quantitatively measured at once. Results: While phospho-HER2 and total HER2 as measured by RPMA had excellent concordance with FISH (95%) and IHC (94%), of the 63 cases where both clinical FISH and IHC status of c-erbB2 were known, we discovered that 5/45 (11%) of the FISH-/IHC- cases had phosphorylated HER2 levels as high or higher than the FISH+/IHC positive patients. These results were confirmed and validated by independent analysis with quantitative Western Blot using a separate biopsy specimen from the same patients. Conclusions: A new molecular phenotype of human breast cancer has been identified whereby total levels of HER2 are low yet levels of the phosphorlyated receptor are very high. This molecular phenotype is not detectable by FISH analysis nor by measurement of the total HER2 protein itself. Given the central importance of phosphorylation on effective signal transduction of the EGFR family, we are planning to determine the clinical significance of this finding by retrospective analysis of banked material with outcome, and a prospective clinical trial in I-SPY 2. Support: ACRIN U01 CA079778 ; CALGB CA31964, CA33601; NCI SPORE CA58207.

[Table: see text]

Semi-quantitative protein analysis of HER2 and ER levels in human breast cancer reveals broad expression ranges within HER2+ and ER+ phenotypes

11014

Background: ER and HER2 measurements underpin a majority of breast cancer clinical testing, yet determination of ER and HER2 protein levels are routinely performed using subjective approaches. We have developed a semi-quantitative calibrated protein microarray, the Reverse Phase Protein Microarray (RPMA), to more adequately determine accurate and precise protein expression levels in clinical tissue specimens. We utilized this method to determine HER2 and ER expression levels and compared the results to those values reported from the clinical laboratory. Methods: Pure tumor epithelium from 149 frozen pre-treatment human breast cancer tissue specimens (from the I-SPY TRIAL: CALGB 150007/150012, ACRIN 6657) were procured via Laser Capture Microdissection and protein pathway mapping was performed whereby the ER (N=112) and HER2 (N= 118) levels were directly measured and compared with reported IHC values. Results: Overall, RPMA measurements of HER2 had excellent correlation with IHC and FISH HER2 determination with no IHC or FISH false positives (88/88). 7 out of 30 of the FISH/IHC+ cases were found by RPMA to have HER2 values as low or lower than the FISH/IHC- cases with the HER2+ population having RPMA expression levels that varied by as much as 10-fold. There was less concordance between RPMA ER values and IHC ER values. Detailed analysis of a more homogeneous ER+ population (Allred =8) revealed a large dynamic range of expression of ER (10–20 fold) by RPMA. The HER2 and ER RPMA results were independently validated by Western Blot using a separate biopsy. Conclusions: Discreet protein expression values obtained by RPMA for ER and HER2 reveal distinctly broad expression values, with as much as 10–20 fold dynamic range in expression, even in a homogeneous (e.g. Allred score of 8) population. Such dynamic differences in protein expression may produce dramatic effects in therapeutic response rate. These findings, if found to be clinically useful, point to a potential need for more fine-tuned protein expression determination by quantitative high-throughput technologies for patient stratification even for standard-of-care FDA approved therapies.

[Table: see text]

Functional pathway mapping of human glioblastoma multiforme and brain metastases for patient tailored therapy

2076

Background: Genome scanning analysis of human glioblastoma multiforme (GBM) has suggested that this form of cancer is a protein pathway disease. Since genomic analysis cannot directly predict protein activation, analysis of protein pathway activation is required. With the current focus on targeted translational therapeutic modalities, a functional understanding of the GBM signaling repertoire is critical, and yet largely unknown. Methods: Twelve tumors were included in this study: 10 GBMs (9 primary, 1 recurrent) and two brain metastases (1 breast and 1 lung). Pure tumor cell populations were obtained from fixed frozen tissue sections using Laser Capture Microdissection. Protein pathway mapping was performed using Reverse Phase Protein Microarrays (RPMA) whereby the activation of 85 key signaling proteins was quantitatively measured at once. Unsupervised and supervised analysis was used to explore pathway activation. Results: Unsupervised hierarchical clustering of all tumors in the study set revealed largely patient-specific signaling portraits yet also identified distinct pathway subsets. The two metastatic tumors clustered separately and distinctly from the GBMs. The GBM specimens clustered according to pathway activity. Statistical analysis demonstrated significant correlations between certain phosphorylated endpoints detected and overall survival. Phosphorylation of cofilin (S3) was associated with shorter survival time, while Stat1 (Y701) and Shc (Y317) phosphorylation were both positively correlated with longer overall survival. Conclusions: This study represents the most comprehensive proteomic analysis of human GBM pathway mapping to date. Since certain pathway biomarkers are themselves being targeted by current investigational therapies, the ability to map pathway activation and identify critical pathway biomarkers can lead to targeted therapeutics tailored to each patient's tumor. The ability to segregate short from long-term survivors according to protein pathway activation is promising.

[Table: see text]

Use of a prognostic pathway signature for colorectal cancer comprised of EGFR/COX2 and imatinib drug target activation to predict occult metastasis in M0 CRC

4042

Background: Development of distant metastasis is the main cause of death among CRC patients. Approximately 30% of CRC patients initially staged M0-N0 die from tumor recurrence. Previously, we determined that members of EGFR/PDGFR/cAbl/cKit pathways were hyperactivated in hepatic synchronous CRC metastasis compared to primary tumor. In order to determine if this signature was a distinguished repertoire of the early stage primary tumor, we analyzed 58 CRC M0 at the moment of the diagnosis that upon 5 yr follow-up had differing disease progressions. Methods: All tissues were immediately snap frozen after surgery. Reverse phase protein microarray (RPMA) was performed using microdissected material to generate multiplexed pathway profiling. For each sample 75 different endpoints were analyzed. Results: Statistical comparison of the 75 endpoints in 8 M0 patients who progressed to M1 and 50 patients who remained M0 regardless of initial staging, revealed a number of signaling proteins whose activation/phosphorylation were elevated and subsumed in a linked pathway. Specifically COX2 and c-Kit/PDGFR/Notch were highly activated in the 8 patients with occult metastasis. A prognostic pathway signature comprised of 13 interlinked molecules was developed. Univariate, ROC and Kaplan-Meier analysis of this signature revealed a statistically significant prognostic signature with an AUC of 0.87 and a 95% confidence interval. Conclusions: A signaling portrait of 13 interlinked proteins provided a strong prognostic indicator for metastasis regardless of stage. This signature was comprised of the phosphorylation/activation of growth factor receptors, including the entire suite of Gleevec targets. A large number of these prognostic signature components were previously found activated in the metastatic lesions themselves which indicates a potential functional role of this linked protein network in metastatic progression and maintenance. If validated in larger study sets, clinical trials to test Gleevec therapy combined with Cox2 /EGFR inhibitors to prevent/delay development of distant metastasis in patients with M0 should be considered.

[Table: see text]

Breast cancer molecular profiles and tumor response of neoadjuvant doxorubicin and paclitaxel: The I-SPY TRIAL (CALGB 150007/150012, ACRIN 6657)

LBA515

The full, final text of this abstract will be available in Part II of the 2009 ASCO Annual Meeting Proceedings, distributed onsite at the Meeting on May 30, 2009, and as a supplement to the June 20, 2009, issue of the Journal of Clinical Oncology.

[Table: see text]

Genomic and proteomic profiles reveal the association of gelsolin to TP53 status and bladder cancer progression

Bladder cancer transformation and immortalization require the inactivation of key regulatory genes, including TP53. Genotyping of a large cohort of bladder cancer patients (n = 256) using the TP53 GeneChip showed mutations in 103 cases (40.2%), the majority of them mapping to the DNA-binding core domain. TP53 mutation status was significantly associated with tumor stage (P = 0.0001) and overall survival for patients with advanced disease (P = 0.01). Transcript profiling using oligonucleotide arrays was performed on a subset of these cases (n = 46). Supervised analyses identified genes differentially expressed between invasive bladder tumors with wild-type (n = 24) and mutated TP53 (n = 22). Pathway analyses of top-ranked genes supported the central role of TP53 in the functional network of such gene patterns. A proteomic strategy using reverse phase arrays with protein extracts of bladder cancer cell lines validated the association of identified differentially expressed genes, such as gelsolin, to TP53 status. Immunohistochemistry on tissue microarrays (n = 294) revealed that gelsolin was associated with tumor stage and overall survival, correlating positively with TP53 status in a subset of these patients. This study further reveals that TP53 mutations are frequent events in bladder cancer progression and identified gelsolin related to TP53 status, tumor staging, and clinical outcome by independent high-throughput strategies.

Personalized therapy for metastatic colorectal cancer: A closer possibility?

4131

Background: Colorectal cancer (CRC) is the second leading cause of cancer related death in the Western world, and survival rate is closely associated with the development of metastases. Personalized targeted therapies promise to have a dramatic impact on the treatment of cancer over the next decade. The molecular fingerprint of a patient’s tumor is the basis for specific targeted therapy. Most often, we are not measuring what we are treating. If we choose therapy based on the primary tumor, but we are treating the metastasis, we are likely giving the wrong therapy if the two microenvironments are not equivalent. In this study we employed reverse phase protein microarrays (RPPA) to compare the protein kinases signal pathway derangements in the primary CRC and in its synchronous liver metastasis. Methods: Pure cell populations of 34 cases of patient-matched CRC and hepatic metastases (collected at the same surgical time) were isolated through laser capture microdissection and then lysed. The lysed cells were evaluated using RPPA technology that allowed us to analyze the activation status of 80 different kinases. Data analysis was performed using commercially available software. Results: Of the 80 kinases only 20 endpoints were significantly (p< 0.05) altered between the two populations. These endpoints were contained within just a few signaling pathways, including the PI3K-AKT prosurvival pathway and the c-kit/PDGFr/c-abl growth factor pathway. We noted a significant increase in phosphorylation of AKT along with a decrease in phosphorylation of PTEN in the liver metastasis compared to the matched primary tumors. This is in keeping with what is known about AKT since phosphorylation of PTEN serves to destabilize the protein, which serves as a natural upstream suppressor of AKT kinase. Conclusions: Specific cell signaling pathways, such as the PI3K-AKT and the c-kit/PDGFr/c-abl growth factor signaling pathway, are significantly altered and activated in hepatic metastasis compared to the primary colorectal site. Since the data reveals elevation in kinase activity increases on a pathway-wide level, a rational hypothesis can be developed whereby combinations of drugs such as an AKT- mTOR inhibitor and/or Gleevec may be an effective and novel therapeutic strategy for the treatment of metastatic CRC.

No significant financial relationships to disclose.

Accurate diagnosis of acute graft-versus-host disease using serum proteomic pattern analysis

OBJECTIVE

The rapid diagnosis of acute graft-versus-host disease (GVHD) following allogeneic hematopoietic cell transplantation (HCT) is important for optimizing the management of this life-threatening complication. Current diagnostic techniques are time-consuming and require invasive tissue sampling. We investigated serum protein pattern analysis using surface-enhanced laser desorption ionization time-of-flight (SELDI-TOF) mass spectrometry as a tool to diagnose GVHD.

PATIENTS AND METHODS

Eighty-eight serum samples were obtained from 34 patients undergoing HCT either pretransplant (n = 28 samples) or at various time points posttransplant (n = 60 samples), including 22 samples obtained on the day of onset of acute GVHD symptoms. Serum proteomic spectra generated from a "training set" of known samples were used to identify distinct proteomic patterns that best categorized a sample as either pretransplant, posttransplant non-GVHD, or GVHD; these distinct proteomic signatures were subsequently used to classify samples from a masked "test" sample set into the appropriate diagnostic category.

RESULTS

Proteomic pattern analysis accurately distinguished GVHD samples from both posttransplant non-GVHD samples and pretransplant samples (100% specificity and 100% sensitivity in both cases). Furthermore, distinct serum proteomic signatures were identified that distinguished pretransplant from posttransplant non-GVHD samples (100% specificity and 94% sensitivity).

CONCLUSION

These preliminary data suggest a potential application of SELDI-TOF-based proteomic analysis as a rapid and accurate method to diagnose acute GVHD.

Alterations in molecular networks of metastatic colorectal carcinoma reveal organ-specific signatures: Implications for targeted therapy of metastatic disease

3532

Background: Proteomic analysis of aberrant protein kinase activity is poised to provide crucial knowledge that could drive molecular-targeted therapeutics and personalized medicine. Many cancers are detected at late stages when metastasis has already occurred. Knowledge about the molecular derangements in the metastatic lesion is crucial for the rational selection of therapeutics. Very little is known about the signaling networks in the metastatic microenvironment. We employed reverse phase protein microarrays coupled to laser capture microdissection for a multiplexed phosphoproteomic fingerprint of colorectal metastatic disease to begin to understand the molecular functional changes that occur upon metastasis. Methods: 68 frozen cases of patient-matched colorectal cancer and hepatic metastasis, 15 cases of pulmonary metastasis, and 27 cases of hepatic metastasis of other primary cancers including breast, melanoma, pancreatic, ovarian, and stomach cancers (all taken at the same time at surgery), were subjected to laser capture microdissection. Procured tumor epithelia (20,000 cells per sample), were lysed and subjected to reverse phase protein microarray analysis. Using this technique, we measured the phosphorylation state of 75 kinase substrates. Molecular network analysis was performed using commercially available software. Results: Our results indicate that, unlike analysis of gene microarray data, we observe a significant difference between the molecular networks of activated kinase substrates within the metastatic lesion compared to the patient-matched primary tumor. In fact, despite overall patient-specific heterogeneity of the portraits, organ specific signatures that were independent of the primary origin of the tumor were identified. Conculsions: Effective treatment in the new era of personalized targeted therapeutics will require the ability to understand the functional activation of cellular signaling pathways since these are the drug targets themselves. Our results indicate that treatment of metastatic disease, and patient stratification for matching with the appropriate therapy may be organ-specific and not predicated upon the primary site of the disease.

No significant financial relationships to disclose.

CXCR4 heterogeneity in primary cells: possible role of ubiquitination

The chemokine receptor CXCR4 is a primary coreceptor for the HIV-1 virus. The predicted molecular weight (MW) of glycosylated CXCR4 is 45-47 kDa. However, immunoblots of whole cell lysates from human lymphocytes, monocytes, macrophages, and the Jurkat T-lymphocyte line revealed multiple MW isoforms of CXCR4. Three of the bands could be precipitated by anti-CXCR4 monoclonal antibodies (101 and 47 kDa) or coprecipitated with CD4 (62 kDa). Expression of these isoforms was enhanced by infection with a recombinant vaccinia virus encoding CXCR4. In immunoblots of two-dimensional gels, antiubiquitin antibodies reacted with the 62-kDa CXCR4 species from monocytes subsequent to coprecipitation with anti-CD4 antibodies. Culturing of monocytes and lymphocytes with lactacystin enhanced the amount of the 101-kDa CXCR4 isoform in immunoblots by three- to sevenfold. In lymphocytes, lactacystin also increased cell-surface expression of CXCR4, which correlated with enhanced fusion with HIV-1 envelope-expressing cells. Similar increases in the intensity of the 101-kDa isoform were seen after treatment with the lysosomal inhibitors monensin and ammonium chloride. Antiubiquitin antibodies reacted with multiple proteins above 62 kDa, which were precipitated with anti-CXCR4 antibodies. Our data indicate that ubiquitination may contribute to CXCR4 heterogeneity and suggest roles for proteasomes and lysosomes in the constitutive turnover of CXCR4 in primary human cells.

Molecular profiling of human cancer

Traditionally, tumours have been categorized on the basis of histology. However, the staining pattern of cancer cells viewed under the microscope is insufficient to reflect the complicated underlying molecular events that drive the neoplastic process. By surveying thousands of genes at once, using DNA arrays, it is now possible to read the molecular signature of an individual patient's tumour. When the signature is analysed with clustering algorithms, new classes of cancer emerge that transcend distinctions based on histological appearance alone. Using DNA arrays, protein arrays and appropriate experimental models, the ultimate goal is to move beyond correlation and classification to achieve new insights into disease mechanisms and treatment targets.

Divergence of binding, signaling, and biological responses to recombinant human hybrid IFN

Three human IFN-alpha hybrids, HY-1 [IFN-alpha21a(1-75)/alpha2c(76-165)], HY-2 [IFN-alpha21a(1-95)/alpha2c(96-165)], and HY-3 [IFN-alpha2c(1-95)/alpha21a(96-166)], were constructed, cloned, and expressed. The hybrids had comparable specific antiviral activities on Madin-Darby bovine kidney (MDBK) cells but exhibited very different antiproliferative and binding properties on human Daudi and WISH cells and primary human lymphocytes. Our data suggest that a portion of the N-terminal region of the molecule is important for interaction with components involved in binding of IFN-alpha2b while the C-terminal portion of IFN is critical for antiproliferative activity. A domain affecting the antiproliferative activity was found within the C-terminal region from amino acid residues 75-166. The signal transduction properties of HY-2 and HY-3 were evaluated by EMSA and RNase protection assays. Both HY-2 and HY-3 induced activation of STAT1 and 2. However, HY-2 exhibited essentially no antiproliferative effects at concentrations that activated STAT1 and 2. Additionally, at concentrations where no antiproliferative activity was seen, HY-2 induced a variety of IFN-responsive genes to the same degree as HY-3. RNase protection assays also indicate that, at concentrations where no antiproliferative activity was seen for HY-2, this construct retained the ability to induce a variety of IFN-inducible genes. These data suggest that the antiproliferative response may not be solely directed by the activation of the STAT1 and STAT2 pathway in the cells tested.

Inhibition of alpha interferon but not gamma interferon signal transduction by phorbol esters is mediated by a tyrosine phosphatase

Previous studies have indicated that the expression of viral oncoproteins, cell transformation, or phorbol ester treatment of cells can inhibit alpha/beta interferon (IFN-alpha/beta)-induced gene expression. The mechanisms by which these promoters of cell growth exert their inhibitory effects vary, but in most instances they involve a disruption of the IFN-alpha/beta-induced transcription complex ISGF3 such that the DNA-binding component of this complex (the 48-kDa ISGF3gamma protein) does not bind to the interferon-stimulated response element (ISRE). In this report, we demonstrated that phorbol ester treatment of human peripheral blood monocytes dramatically inhibits activation of IFN-alpha/B-stimulated early response genes but by a mechanism which does not involve abrogation of the ISRE binding of ISGF3gamma. Phorbol ester treatment of monocytes inhibited IFN alpha-stimulated tyrosine phosphorylation of the transcription factors Stat1alpha, Stat2, and Stat3 and of the tyrosine kinase Tyk2 but had no effect on IFN-gamma activation of Stat1alpha. IFNalpha-stimulated tyrosine phosphorylation of Jak1 and the alpha subunit of the IFN-alpha receptor were unaffected by phorbol 12-myristate 13-acetate (PMA). Moreover, PMA caused the dephosphorylation of Tyk2 but not of Jak1, which was activated by IFN. Pretreatment of cells with vanadate prevented the effects of PMA with regard to PMA-induced Tyk2 dephosphorylation. These observations suggest that PMA exerts its inhibitory effects by activation of a tyrosine phosphatase which selectively regulates Tyk2 but not Jak1 activity.

Activation of protein kinase A inhibits interferon induction of the Jak/Stat pathway in U266 cells

Activation of early response genes by interferons (IFNs) requires tyrosine phosphorylation of the Stat transcription factors and is mediated by the Jak family of tyrosine kinases. Recent evidence suggests that ERK2 serine/threonine kinase modulates the IFN-stimulated Jak/Stat pathway. In this report we show that in the myeloma cell line U266 protein kinase A specifically interacts with the cytoplasmic domain of the IFNalpha/beta receptor. Treatment of cells with the adenylate cyclase activator forskolin inhibits IFNbeta-, IFNgamma-, and hydrogen peroxide/vanadate-induced formation of complexes that bind to enhancers known to stimulate the expression of IFN-regulated genes. Immunoprecipitations followed by anti-phosphotyrosine immunoblots indicate that tyrosine phosphorylation of the alpha chain of the IFNalpha/beta receptor, Jak1, Tyk2, as well as Stat1 and Stat2 is reduced as a consequence of incubation of cells with forskolin. In contrast, dideoxyforskolin, which fails to activate adenylate cyclase, has no effect on IFN induction of the Jak/Stat pathway. These results indicate a novel regulatory mechanism by which protein kinase A can modulate the Jak/Stat signaling cascade.