NOTCH3-targeted antibody drug conjugates regress tumors by inducing apoptosis in receptor cells and through transendocytosis into ligand cells

Aberrant NOTCH3 signaling and overexpression is oncogenic, associated with cancer stem cells and drug resistance, yet therapeutic targeting remains elusive. Here, we develop NOTCH3-targeted antibody drug conjugates (NOTCH3-ADCs) by bioconjugation of an auristatin microtubule inhibitor through a protease cleavable linker to two antibodies with differential abilities to inhibit signaling. The signaling inhibitory antibody rapidly induces ligand-independent receptor clustering and internalization through both caveolin and clathrin-mediated pathways. The non-inhibitory antibody also efficiently endocytoses via clathrin without inducing receptor clustering but with slower lysosomal co-localization kinetics. In addition, DLL4 ligand binding to the NOTCH3 receptor mediates transendocytosis of NOTCH3-ADCs into ligand-expressing cells. NOTCH3-ADCs internalize into receptor and ligand cells independent of signaling and induce cell death in both cell types representing an atypical mechanism of ADC cytotoxicity. Treatment of xenografts with NOTCH3-ADCs leads to sustained tumor regressions, outperforms standard-of-care chemotherapy, and allows targeting of tumors that overexpress NOTCH3 independent of signaling inhibition.

NOTCH3 receptor is overexpressed in breast, lung, and ovarian tumors

Newly generated NOTCH3-targeted antibody drug conjugates are efficacious and safe

NOTCH3 antibodies internalize through different routes depending on signaling status

NOTCH3 antibody intercellular trafficking occurs by transendocytosis into ligand cells

Abstract 935: Generation and preclinical characterization of CD123-CPI antibody-drug conjugate (ADC)

CD123 is expressed on cancer cells in a variety of hematologic malignancies including acute myeloid leukemia (AML). CD123 is frequently expressed on leukemic blasts and leukemic stem cells (LSCs), a cell population associated with relapse in patients, but there is minimal or no expression on most normal hematopoietic cells and solid tissues. Thus, CD123 is a promising target for AML. We have generated an anti-CD123 ADC that carries cyclopropylpyrroloindoline (CPI) payload that crosslinks DNA. A drug loading of 2 molecules of CPI per molecule of antibody was achieved by site-specific conjugation using our transglutaminase methodology. Upon binding to the CD123 antigen, CD123-ADC is internalized and delivered to the endosomal-lysosomal pathway whereupon the CPI payload is released from the antibody by proteolysis of the linker. The released CPI alkylates DNA, which activates ATR/ATM, CHK1, CHK2 and FANCD2, ultimately resulting in cell death. In vitro, CD123–CPI elicited cytotoxicity in a dose-dependent manner against several CD123-positive, but not against CD123-negative cell lines. Cell lines with higher CD123 expression level were more sensitive to the ADC. Long-Term Culture-Initiating Cells in vitro assay showed that AML patient bone marrow samples that naturally have high percentage of LSCs yielded substantially fewer colonies in CD123-ADC treated cells compared to control ADC. Importantly, CD123-ADC had no adverse effects in healthy donor bone marrow cells experimentally enriched in CD34+ primitive stem cells. This result suggests that CD123-ADC specifically inhibits the growth potential of leukemic blasts and progenitor cells. In vivo, robust antileukemic activity was observed in CD123-positive AML cell line-derived xenograft models. Low doses of CD123-ADC effectively regressed tumors whereas the tumor progressed in mice that received control ADC. Efficacy was also evaluated in disseminated AML PDX models (n≥7) established with patient samples of various cytogenetics and molecular abnormalities, and relapse/refractory. Flow cytometry analyses of leukemic load in peripheral blood and in bone marrow samples of mice showed that CD123-ADC was efficacious in reducing tumor burden even at the suboptimal doses. In summary, our data demonstrate that our CD123-ADC is highly active in a broad panel of primary AML samples. Currently, CD123-ADC in combination with other AML therapies is being tested in vivo. All these attributes of CD123-ADC make it an attractive agent to evaluate in clinical trials.

Citation Format: Yoon-Chi Han, Fan Jiang, Nicole Piche-Nicholas, Madan Katragadda, Nadira Prashad, Manoj Charati, Wendy Hu, Mauricio Leal, Nathan Tumey, Andreas Maderna, Russell Dushin, Kenny Kim, LuAnna Lemon, Marc Damelin, HP Gerber, Lioudmila Tchistiakova, Frank Loganza, Chris O'Donnell, Puja Sapra. Generation and preclinical characterization of CD123-CPI antibody-drug conjugate (ADC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 935.

Abstract 818: NG-HER2 ADC (PF-06804103) is superior to trastuzumab emtansine in a mouse 'avatar' head-to-head clinical trial

Patient-derived xenografts (PDXs) are resected human tumors engrafted into mice and represent personalized murine ‘avatars' of those tumors. PDXs are valuable tumor models for drug development since they recapitulate the complexity of the human tumor microenvironment more extensively than cell line xenografts (CLXs). Unlike CLXs, PDXs are never passaged in vitro, and therefore they more faithfully recapitulate native tumor biology and response to therapeutics. Thus, PDXs may more accurately predict clinical activity of therapeutic compounds than traditional CLXs. We are developing a next generation (NG)-HER2 antibody-drug conjugate (ADC), PF-06804103, that employs a proprietary site-specific conjugation technology that chemically links the clinically-validated linker-payload “ValCit-Aur0101” to an anti-HER2 antibody. The site-specific conjugation enables enhanced exposures and reduced off-target toxicities as previously described. We utilized our PDX collection to evaluate the breadth-of-efficacy of PF-06804103 versus trastuzumab emtansine (T-DM1), an FDA-approved ADC for metastatic breast cancer patients with high HER2 expression. Efficient cleavage of the ‘ValCit' linker and payload release in the early endosome is not impacted by the rapid recycling properties of the HER2 receptor, unlike T-DM1 which requires catabolism in the within the lysosomal milieu to efficiently release its payload. To date, we have enrolled >20 HER2-expressing breast, gastric and non-small cell lung cancer PDXs, with varying low to high HER2 expression levels, in a head-to-head ‘mouse avatar clinical trial' comparing activity of a single cycle of T-DM1 (6 mg/kg) to PF-06804103 (3 mg/kg). Impressively, PF-06804103 had more durable complete responses and a higher objective response rate (ORR) than T-DM1 (84% vs. 4%), including in low-moderate HER2 expressers. PF-06804103 prolonged median overall survival (OS) of mice with HER2-expressing tumors compared to T-DM1 (100 vs 45 days). Biomarker analysis showed that tumors at all levels of HER2 expression were more likely to receive more benefit with PF-06804103 than T-DM1 (HR < 0.45). By leveraging our novel PDX ‘avatar' clinic, we were able to demonstrate that PF-06804103 displays superior in vivo breadth-of-efficacy compared to T-DM1.

Citation Format: Matthew S. Sung, Christine Hopf, Erik Upeslacis, Jonathon Golas, Mark Kaplan, Kiran Khandke, Manoj Charati, Frank Kotch, Frank Loganzo, Ken Geles, Judy Lucas, Hans-Peter Gerber, Puja Sapra, Edward Rosfjord. NG-HER2 ADC (PF-06804103) is superior to trastuzumab emtansine in a mouse 'avatar' head-to-head clinical trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 818.

Abstract 1220: A novel PTK7-targeted antibody-drug conjugate eliminates tumor-initiating cells and induces sustained tumor regressions

Disease relapse after treatment is common in triple-negative breast cancer (TNBC), ovarian cancer and non-small cell lung cancer (NSCLC). Therapies that target tumor-initiating cells (TICs) should improve patient survival by eliminating the cells that can drive tumor regrowth and metastasis. Here we identify Protein Tyrosine Kinase 7 (PTK7), a highly conserved but catalytically inactive receptor tyrosine kinase, as an antigen that is enriched on TICs in low-passage patient-derived xenografts (PDX) of TNBC, NSCLC and other tumor types. An anti-PTK7 antibody-drug conjugate (ADC) was generated from a humanized anti-PTK7 monoclonal antibody, a cleavable valine-citrulline-based linker and the Aur0101 auristatin microtubule inhibitor. The anti-PTK7 ADC induced sustained regressions of TNBC, NSCLC and ovarian cancer PDX, with improved activity over standard-of-care chemotherapy, and reduced the frequency of TICs as determined by serial transplantation experiments. Moreover, the ADC may have additional mechanisms of action, including an anti-angiogenic effect, that promote anti-tumor immune responses. Together these preclinical results indicate the potential of the anti-PTK7 ADC to improve the long-term survival of cancer patients. The ADC is currently being tested in a Phase 1 clinical trial, from which interim results will be presented.

Citation Format: Marc Isaac Damelin, Alex Bankovich, Jeff Bernstein, Justin Lucas, Liang Chen, Sam Williams, Albert Park, Jorge Aguilar, Elana Ernstoff, Manoj Charati, Russell Dushin, Amy Jackson-Fisher, Monette Aujay, Christina Lee, Hanna Ramoth, Milly Milton, Johannes Hampl, Sasha Lazetic, Virginia Pulito, Douglas Armellino, Edward Rosfjord, Magali Guffroy, Hadi Falahatpisheh, Lindsay King, Frank Barletta, Robert Stull, Marybeth Pysz, Paul Escarpe, David Liu, Orit Foord, Brenda Gibson, Eric Powell, Christopher O’Donnell, Xiaohua Xin, Hans Peter Gerber, Puja Sapra, Scott Dylla. A novel PTK7-targeted antibody-drug conjugate eliminates tumor-initiating cells and induces sustained tumor regressions. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1220.

Abstract 868: Creating a superior, site-specific anti-HER2 antibody-drug conjugate (NG-HER2 ADC) for treatment of solid tumors

Antibody-drug conjugates (ADCs) have emerged as an important class of cancer therapeutics. The FDA approval of Kadcyla (T-DM1), a single agent for treatment of HER2-positive advanced metastatic breast cancer, was a significant milestone in the field of targeted therapy, as the first and only ADC for treatment of solid tumors. Despite the 3-month improvement over standard of care in the median survival, almost all the patients eventually became refractory to T-DM1. We have identified several possible areas for improvement: 1) The potency of T-DM1 as confirmed by the Phase III clinical data is restricted to high HER2 tumors which leaves moderate or low HER2 expressing patients without access to T-DM1 treatment; 2) The 48% overall response rate is indicative of intrinsic resistance to T-DM1 and all T-DM1 treated patients eventually relapse. 3) The randomized lysine conjugation in T-DM1 generates heterogeneity of the product. We have developed a novel, site-specific anti-HER2 ADC (NG-HER2 ADC) and evaluated it in comparative preclinical studies with T-DM1. The results show that the NG-HER2 ADC is ∼ 10 fold more potent than T-DM1 in HER2 3+ xenograft models of breast and gastric cancers. Our proprietary cleavable and permeable linker-payload can mediate bystander effect and this enables potent anti-tumor activity in non-HER2 amplified breast cancer and heterogeneous low HER2 NSCLC PDX models, where T-DM1 is ineffective. Our ADC can overcome T-DM1 resistance in in vitro and in vivo models.. Our site-specific ADC at HNSTD of 9 mg/kg in cynomolgus monkeys showed high AUC, long half-life and had normal clinical observations with no marked neutropenia. On the contrary, conventional conjugates with cleavable linker payloads typically have severe bone marrow toxicity as DLT above 5 mg/kg. The therapeutic index for NG-HER2 ADC is significantly greater than T-DM1 in all models tested. NG-HER2 ADC has a projected clinical efficacious dose of ∼1 mg/kg, compared to 3-5 mg/kg for T-DM1, based on PK/PD modeling. In addition, the activity of the NG-HER2 ADC shows increased infiltration of CD8 positive effector cells, an essential component for immuno-oncology (IO) efficacy, in a syngeneic HER2 overexpressing model. This property potentially allows the combination of the ADC with IO drugs to improve the long-term, overall survival. Our data provides preclinical proof of concept for NG-HER2 ADC with best-in-class potential and is currently being tested in preparation for clinical trials for treatment of HER2 solid tumors.

Citation Format: Dangshe Ma, Bitha Narayanan, Kim Marquette, Edmund Graziani, Frank Loganzo, Manoj Charati, Nadira Prashad, Nathan Tumey, Jon Golas, Christine Hosselet, George Hu, Frank Barletta, Alison Betts, Judy Lucas, Chris O’Donnell, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Creating a superior, site-specific anti-HER2 antibody-drug conjugate (NG-HER2 ADC) for treatment of solid tumors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 868.

Abstract 1697: Therapeutic targeting the NOTCH3 receptor with antibody drug conjugates

Activation and mutation of the NOTCH signaling pathway is oncogenic in many tissue types and the target of multiple anti-cancer therapies currently in clinical development. Initial therapeutic strategies designed to target the NOTCH pathway have focused on inhibition of aberrant signaling, but can have undesirable side-effects or insufficient anti-tumor activity. Antibody drug conjugates (ADCs) are an emerging therapeutic modality that equips antibodies with potent cytotoxic payloads that can be directly delivered to tumor cells. We have developed and compared anti-NOTCH3 ADCs using two different classes of therapeutic anti-NOTCH3 antibodies that target the juxtamembrane Negative Regulatory Region (NRR). The first class is unable to stabilize the NOTCH3-NRR in an auto-inhibitory conformation in the presence of ligand and does not block ADAM protease cleavage of the receptor. The second class contains an antibody that exhibits potent signaling inhibition by stabilizing the NRR in an inactive state. Despite antagonizing NOTCH3 signaling, the inhibitory anti-NOTCH3 antibody was unable to regress preclinical tumor xenografts with active NOTCH3 signaling. To enhance their potency, both classes of anti-NOTCH3 antibodies were conjugated to an auristatin-based microtubule inhibitor through a cleavable linker. Unexpectedly, the inhibitory anti-NOTCH3 antibody demonstrated more rapid trafficking to the lysosome than the non-inhibitory antibody suggesting that the two antibodies have distinct internalization routes with important implications for NOTCH3-ADC pharmacology. Pharmacodynamic biomarker analysis demonstrated anti-NOTCH3 ADCs disrupted the mitotic spindle apparatus, induced cell cycle arrest and triggered apoptosis. Anti-NOTCH3 ADCs exhibited robust anti-tumor activity and induce prolonged tumor regressions in preclinical models of breast, lung and ovarian cancer regardless of their ability to block signaling. Furthermore, anti-NOTCH3 ADC treatment was able to regress OVCAR3 ovarian tumor xenografts that were refractory to a platinum-based agent or relapsed anti-VEGF therapy. Our studies demonstrate that anti-NOTCH3 ADCs had enhanced efficacy compared to other NOTCH signaling inhibitors and also allowed targeting of tumors that over-expressed NOTCH3 but were not necessarily addicted to its signaling. The safety and efficacy of the non-inhibitory anti-NOTCH3 ADC, PF-06650808, is currently being examined in a Ph1 clinical trial (Protocol B7501001).

Citation Format: Kenneth G. Geles, Yijie Gao, Latha Sridharan, Andreas Giannakou, Ting-Ting Yamin, Jonathan Golas, Judy Lucas, Manoj Charati, Xiantang Li, Magali Guffroy, Tim Nichols, Kai Wang, Max Follettie, Andreas Maderna, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Therapeutic targeting the NOTCH3 receptor with antibody drug conjugates. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1697. doi:10.1158/1538-7445.AM2015-1697

Mild method for succinimide hydrolysis on ADCs: impact on ADC potency, stability, exposure, and efficacy

The stability of the connection between the antibody and the toxin can have a profound impact on ADC safety and efficacy. There has been increasing evidence in recent years that maleimide-based ADCs are prone to payload loss via a retro-Michael type reaction. Herein, we report a mild method for the hydrolysis of the succinimide-thioether ring which results in a "ring-opened" linker. ADCs containing this hydrolyzed succinimide linker show equivalent cytotoxicity, improved in vitro stability, improved PK exposure, and improved efficacy as compared to their nonhydrolyzed counterparts. This method offers a simple way to improve the stability, exposure, and efficacy of maleimide-based ADCs.

Abstract 2059: In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer

Antibody drug conjugates (ADCs) are clinically validated as a modality for targeted therapy of solid and hematological cancer due to advancements in target selection, conjugation chemistry and linker technology. However, much about mechanism of action (MoA) is yet to be fully understood. Our goal was to interrogate ADC pharmacokinetics and pharmacodynamics establishing proof of mechanism (PoM) of drug action with a diverse panel of ADCs. Herein, we describe the development of novel immunohistochemical (IHC) methods for in situ visualization of ADCs binding to target expressing cells and their cognate downstream biomarkers of response in formalin fixed paraffin embedded cells/tissues. We demonstrate specific binding of 4 different ADCs spanning 2 solid tumor targets and an endothelial cell target using IHC with anti-human IgG in human tumor xenograft models expressing the respective targets. ADC binding to target is observed as early as 20 minutes after a single dose of ADC at 3 mg/kg. Utilizing an anti-microtubule inhibitor (MTI) payload-specific antibody we additionally detect ADC binding to tumor cells by monitoring the cytotoxic payload. The cell type where the antibodies and payload localized was identified by double and triple IHC. Pharmacodynamic biomarkers of response for two payload classes (DNA damaging agents and MTIs) were detected with antibodies against phospho-Histone H2AX and phospho-Histone H3, respectively - confirming the expected ADC MoAs. Downstream apoptosis of target cells was detected with cleaved caspase 3 IHC. The kinetics of biomarker response and downstream cellular impact was quantified via image analysis with biomarkers evident as early as 24 hours after a single dose for both tumor cell and vascular targets. Furthermore, we observed a correlation between biomarkers of response and efficacy of the ADCs as measured by statistically significant tumor growth inhibition for the 4 ADCs we studied. These data suggest that IHC interrogations of drug action should be used to further the clinical development of ADCs via demonstration of pharmacodynamic activities at the cellular level, establishing PoM data, and enabling predictive preclinical oncology models in order to reduce clinical attrition of ADCs.

Citation Format: Jonathon Golas, Andrea T. Hooper, Justin Lucas, Heather Jones, Timothy Nichols, Kiran Khandke, Manoj Charati, Roger Conant, Michael Cinque, Judy Lucas, Marc Damelin, Ken Geles, Caiazzo Teresa, Frank Loganzo, Puja Sapra, Hans-Peter Gerber, Chad May. In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2059. doi:10.1158/1538-7445.AM2014-2059

Abstract 1241: Targeting the IL-13 receptor alpha 2 with novel antibody-drug conjugates for the treatment of cancer

The IL-13 receptor alpha 2 (IL-13Rα2) is a transmembrane protein that is highly expressed on several cancers including glioblastoma, ovarian, pancreatic cancers. It can internalize after binding to its ligand IL-13 or in response to ligation with an antibody. In addition, we have discovered that IL-13Rα2 is up-regulated in tumor cell lines that are resistant to chemotherapeutic drugs. These properties make IL-13Rα2 an attractive target for antibody-drug conjugate (ADC), an emerging modality of molecularly targeted cancer therapies. A humanized monoclonal antibody, hAB08 with an affinity of 0.17 nM to the soluble recombined hIL-13Rα2, was conjugated with two novel microtubule inhibitors (MTIs), MTI1 and MTI2, developed by Pfizer. In vitro cytotoxicity of the conjugates was tested against IL-13Rα2 positive and negative cell lines. These conjugates were effective against the IL-13Rα2 positive cell lines (PC3MM2 and A375), having an IC50 ranging from 1.1 to 3.8 ng Ab/mL. However, both of the ADCs were not active against the IL-13Rα2 negative H460 cell line. When treating mice with established human PC3MM2 and A375 tumors, these conjugates were efficacious at 3 mg/kg in reducing tumor growth. In the PC3MM2 model, treatment with hAB08-MTI1 and hAB08-MTI2 resulted in 5 out of 8 or 3 out of 8 animals without measurable tumors at Day 76, respectively. In contrast, the vehicle control group and control ADC (hIgG8.8-MTI1 and hIgG8.8-MTI2) groups were terminated at Day 15, 15, 19 due to the large size of tumors, respectively. These in vitro and in vivo results demonstrate potent antitumor activities of hAB08-MTI1 and hAB08-MTI2 against IL-13Rα2 positive tumors. The findings support the development of novel hAB08-MTI1 or hAB08-MTI2 ADCs as a molecularly targeted therapy for cancer patients that are resistant to standard chemotherapy.

Citation Format: Dangshe Ma, Haige Zhang, Fang Jin, Manoj Charati, Kiran Khandke, Judy Lucas, Max Follettie, L. Nathan Tumey, Hans-Peter Gerber, Lioudmila Tchistiakova, Puja Sapra. Targeting the IL-13 receptor alpha 2 with novel antibody-drug conjugates for the treatment of cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1241. doi:10.1158/1538-7445.AM2013-1241

Abstract 5471: Notch-antibody drug conjugates have a different mechanism of action than Notch signaling inhibitors and induce tumor regression

There are four different Notch receptors in mammalian cells that have overlapping patterns of expression in embryonic and adult tissues, but fulfill non-redundant roles during hematopoietic stem cell specification, T cell development, intestinal crypt cell specification and vascular development. Notch receptors are over-expressed or amplified in certain human tumors and regulate cell proliferation, differentiation, and survival through an intracellular domain that functions as a transcriptional activator. Several strategies are in development to block Notch signaling for therapeutic purposes in cancer, including gamma-secretase inhibitors that block all Notch signaling and antibody-based targeting of individual receptors. However, blocking pathway activation with inhibitory antibodies has proven to be less efficacious than originally anticipated. Therefore, we have targeted Notch with antibody-drug conjugates (ADCs) that combine the specificity of high affinity anti-Notch antibodies with the cytotoxicity of microtubule inhibitors. These ADCs enhance efficacy and also allow targeting in tumors that overexpress Notch but are not driven by its signaling. Notch antibodies were conjugated though cleavable and non-cleavable linkers to novel tubulin inhibitor-based payloads. Notch-ADCs inhibited the in vitro growth of lung, breast and ovarian cancer cell lines in the low ng/ml range and in vivo regressed the growth of established human tumor xenografts. Our data demonstrate that Notch-ADCs are more potent than small molecule inhibitors and unconjugated antibodies, and induce sustained tumor regression in pre-clinical models.

Citation Format: Kenneth G. Geles, Yijie Gao, Latha Sridharan, Andreas Giannakou, Ting-Ting Yamin, Jonathan Golas, Manoj Charati, Kiran Khandke, Judy Lucas, Andreas Maderna, Christopher J. O'Donnell, Lioudmila Tchistiakova, Hans-Peter Gerber, Puja Sapra. Notch-antibody drug conjugates have a different mechanism of action than Notch signaling inhibitors and induce tumor regression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5471. doi:10.1158/1538-7445.AM2013-5471