Erwin van Puijenbroek

Increasing the efficacy of CD20 antibody therapy through the engineering of a new type II anti-CD20 antibody with enhanced direct and immune effector cell-mediated B-cell cytotoxicity

CD20 is an important target for the treatment of B-cell malignancies, including non-Hodgkin lymphoma as well as autoimmune disorders. B-cell depletion therapy using monoclonal antibodies against CD20, such as rituximab, has revolutionized the treatment of these disorders, greatly improving overall survival in patients. Here, we report the development of GA101 as the first Fc-engineered, type II humanized IgG1 antibody against CD20. Relative to rituximab, GA101 has increased direct and immune effector cell-mediated cytotoxicity and exhibits superior activity in cellular assays and whole blood B-cell depletion assays. In human lymphoma xenograft models, GA101 exhibits superior antitumor activity, resulting in the induction of complete tumor remission and increased overall survival. In nonhuman primates, GA101 demonstrates superior B cell-depleting activity in lymphoid tissue, including in lymph nodes and spleen. Taken together, these results provide compelling evidence for the development of GA101 as a promising new therapy for the treatment of B-cell disorders.

Preclinical Activity of the Type II CD20 Antibody GA101 (Obinutuzumab) Compared with Rituximab and Ofatumumab In Vitro and in Xenograft Models

We report the first preclinical in vitro and in vivo comparison of GA101 (obinutuzumab), a novel glycoengineered type II CD20 monoclonal antibody, with rituximab and ofatumumab, the two currently approved type I CD20 antibodies. The three antibodies were compared in assays measuring direct cell death (AnnexinV/PI staining and time-lapse microscopy), complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cell-mediated phagocytosis (ADCP), and internalization. The models used for the comparison of their activity in vivo were SU-DHL4 and RL xenografts. GA101 was found to be superior to rituximab and ofatumumab in the induction of direct cell death (independent of mechanical manipulation required for cell aggregate disruption formed by antibody treatment), whereas it was 10 to 1,000 times less potent in mediating CDC. GA101 showed superior activity to rituximab and ofatumumab in ADCC and whole-blood B-cell depletion assays, and was comparable with these two in ADCP. GA101 also showed slower internalization rate upon binding to CD20 than rituximab and ofatumumab. In vivo, GA101 induced a strong antitumor effect, including complete tumor remission in the SU-DHL4 model and overall superior efficacy compared with both rituximab and ofatumumab. When rituximab-pretreated animals were used, second-line treatment with GA101 was still able to control tumor progression, whereas tumors escaped rituximab treatment. Taken together, the preclinical data show that the glyoengineered type II CD20 antibody GA101 is differentiated from the two approved type I CD20 antibodies rituximab and ofatumumab by its overall preclinical activity, further supporting its clinical investigation. Mol Cancer Ther; 12(10); 2031–42. ©2013 AACR.

GA201 (RG7160): A Novel, Humanized, Glycoengineered Anti-EGFR Antibody with Enhanced ADCC and Superior In Vivo Efficacy Compared with Cetuximab

Purpose: Anti-EGF receptor (EGFR) antibodies and small-molecule tyrosine kinase inhibitors have shown activity in epithelial tumors; however, agents that work by blocking the EGFR growth signal are ineffective when the oncogenic stimulus arises downstream, such as in tumors with KRAS mutations. Antibodies of the IgG1 subclass can also kill tumor cells directly through antibody-dependent cell-mediated cytotoxicity (ADCC), and the efficacy of this is determined by the interaction of the Fc portion of the target cell–bound antibody and Fc receptors present on immune effector cells. Experimental Design: We report the development of GA201, a novel anti-EGFR monoclonal antibody with enhanced ADCC properties. GA201 was derived by humanization of the rat ICR62 antibody. The Fc region of GA201 was glycoengineered to contain bisected, afucosylated carbohydrates for enhanced binding to FcγRIIIA. Results: In vitro binding of GA201 to EGFR inhibited EGF ligand binding, EGFR/HER2 heterodimerization, downstream signaling, and cell proliferation to a similar extent as cetuximab. However, GA201 exhibited superior binding to both the low- and high-affinity variants of FcγRIIIA. This resulted in significantly enhanced induction of ADCC compared with cetuximab against both KRAS-wild-type and -mutant tumor cells lines. This enhanced ADCC translated into superior in vivo efficacy in a series of mouse xenograft models. Efficacy of GA201 was further increased when administered in combination with chemotherapy (irinotecan). Conclusions: These data suggest that GA201 may be more effective than cetuximab in patients with EGFR-positive solid tumors and may also represent a first-in-class treatment of patients with KRAS-mutated tumors. Clin Cancer Res; 19(5); 1126–38. ©2012 AACR.

Cergutuzumab amunaleukin (CEA-IL2v), a CEA-targeted IL-2 variant-based immunocytokine for combination cancer immunotherapy: Overcoming limitations of aldesleukin and conventional IL-2-based immunocytokines

ABSTRACT We developed cergutuzumab amunaleukin (CEA-IL2v, RG7813), a novel monomeric CEA-targeted immunocytokine, that comprises a single IL-2 variant (IL2v) moiety with abolished CD25 binding, fused to the C-terminus of a high affinity, bivalent carcinoembryonic antigen (CEA)-specific antibody devoid of Fc-mediated effector functions. Its molecular design aims to (i) avoid preferential activation of regulatory T-cells vs. immune effector cells by removing CD25 binding; (ii) increase the therapeutic index of IL-2 therapy by (a) preferential retention at the tumor by having a lower dissociation rate from CEA-expressing cancer cells vs. IL-2R-expressing cells, (b) avoiding any FcγR-binding and Fc effector functions and (c) reduced binding to endothelial cells expressing CD25; and (iii) improve the pharmacokinetics, and thus convenience of administration, of IL-2. The crystal structure of the IL2v-IL-2Rβγ complex was determined and CEA-IL2v activity was assessed using human immune effector cells. Tumor targeting was investigated in tumor-bearing mice using 89Zr-labeled CEA-IL2v. Efficacy studies were performed in (a) syngeneic mouse models as monotherapy and combined with anti-PD-L1, and in (b) xenograft mouse models in combination with ADCC-mediating antibodies. CEA-IL2v binds to CEA with pM avidity but not to CD25, and consequently did not preferentially activate Tregs. In vivo, CEA-IL2v demonstrated superior pharmacokinetics and tumor targeting compared with a wild-type IL-2-based CEA immunocytokine (CEA-IL2wt). CEA-IL2v strongly expanded NK and CD8+ T cells, skewing the CD8+:CD4+ ratio toward CD8+ T cells both in the periphery and in the tumor, and mediated single agent efficacy in syngeneic MC38-CEA and PancO2-CEA models. Combination with trastuzumab, cetuximab and imgatuzumab, all of human IgG1 isotype, resulted in superior efficacy compared with the monotherapies alone. Combined with anti-PD-L1, CEA-IL2v mediated superior efficacy over the respective monotherapies, and over the combination with an untargeted control immunocytokine. These preclinical data support the ongoing clinical investigation of the cergutuzumab amunaleukin immunocytokine with abolished CD25 binding for the treatment of CEA-positive solid tumors in combination with PD-L1 checkpoint blockade and ADCC competent antibodies.

Premedication and chemotherapy agents do not impair imgatuzumab- (GA201) mediated antibody-dependent cellular cytotoxicity and combination therapies enhance efficacy

Purpose: Imgatuzumab (GA201) is a novel anti-EGFR mAb that is glycoengineered for enhanced antibody-dependent cellular cytotoxicity (ADCC). Future treatment schedules for imgatuzumab will likely involve the use of potentially immunosuppressive drugs, such as premedication therapies, to mitigate infusion reactions characteristic of mAb therapy and chemotherapy combination partners. Because of the strong immunologic component of mode of action of imgatuzumab, it is important to understand whether these drugs influence imgatuzumab-mediated ADCC and impact efficacy. Experimental Design: We performed a series of ADCC assays using human peripheral blood mononuclear cells that were first preincubated in physiologically relevant concentrations of commonly used premedication drugs and cancer chemotherapies. The ability of common chemotherapy agents to enhance the efficacy of imgatuzumab in vivo was then examined using orthotopic xenograft models of human cancer. Results: A majority of premedication and chemotherapy drugs investigated had no significant effect on the ADCC activity of imgatuzumab in vitro. Furthermore, enhanced in vivo efficacy was seen with imgatuzumab combination regimens compared with single-agent imgatuzumab, single-agent chemotherapy, or cetuximab combinations. Conclusions: These data indicate that medications currently coadministered with anti-EGFR therapies are unlikely to diminish the ADCC capabilities of imgatuzumab. Further studies using syngeneic models with functional adaptive T-cell responses are now required to fully understand how chemotherapy agents will influence a long-term response to imgatuzumab therapy. Thus, this study and future ones can provide a framework for designing imgatuzumab combination regimens with enhanced efficacy for investigation in phase II trials. Clin Cancer Res; 22(10); 2453–61. ©2015 AACR.

Abstract 486: Tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for the immunotherapy of cancer.

IL-2 therapy can lead to durable responses in cancer patients, but is associated with significant toxicity. None of the described IL-2-based immunocytokines has progressed beyond Phase II trials due to various constraints in their design: 1) pM affinity for IL-2Rαβγ on immune cells and pulmonary vascular endothelium compromising tumor targeting due to the fusion of two wildtype IL-2 moieties to the antibody, together with FcγR binding on the same cells; 2) Rapid systemic clearance and short half-life due to high affinity IL-2Rαβγ binding; 3) Preferential activation of Tregs over immune effectors by wt IL-2. Here, we describe a novel monomeric tumor-targeted immunocytokine where a single, engineered IL-2 variant (IL-2v) with abolished IL-2Rα (CD25) binding is fused to the C-terminus of an antibody with a heterodimeric Fc-part. FcγR and C1q binding is completely abolished by a novel Fc mutation. For targeting, human(-ized) high affinity antibodies against CEA (GA504, CEA-IL2v) or FAP (GA501, FAP-IL2v) were selected. CEA- and FAP-IL2v were recombinantly produced and induction of P-STAT5, proliferation, activation induced cell death (AICD), activation markers and cytokines were determined on effector cells. Safety, pharmacokinetics (PK), tumor targeting, pharmacodynamics and anti-tumor efficacy were analyzed in SCID and immunocompetent C57Bl/6 mice. FAP- and CEA-IL-2v completely lack binding to CD25, but retain IL-Rβγ binding. They do not bind to CD25 or preferentially activate Tregs, and induce lower degree of AICD. However, IL-2Rβγ bioactivity is retained and they activate NK, CD4+ and CD8+ T cells as shown by induction of activation markers and proliferation. In particular, CEA- and FAP-IL2v expand and activate NK cells and skew the CD4:CD8 ratio towards CD8+ T cells in vivo. In C57Bl/6 mice, CEA- and FAP-IL2v demonstrate improved safety despite of higher exposure and circulatory half-life than the corresponding wt IL-2 immunocytokine. MicroSPECT/CT imaging revealed FAP-mediated tumor targeting of FAP-IL2v with low normal tissue uptake with FAP-IL2v tumor targeting being similar to the parental FAP antibody with low accumulation in lymphoid tissues and clearly superior to an FAP-targeted wt IL-2 immunocytokine that shows preferential spleen targeting. Studies in tumor-bearing mice showed dose dependent anti-tumor efficacy of CEA- and FAP-IL2v in established xenograft and syngeneic mouse models. Thus, CEA- and FAP-IL2v demonstrate superior safety, PK and tumor targeting, while lacking preferential induction of Tregs due to abolished CD25 and FcγR binding, monovalency and high-affinity tumor-targeting as compared to classical immunocytokines. They retain capacity to activate NK and T‐effector cells through IL‐2Rβγ; in particular once targeted to the tumor microenvironment. These data support their investigation for the immunotherapy of CEA/FAP-positive tumors. Citation Format: Christian Klein, Inja Waldhauer, Valeria Nicolini, Claire Dunn, Anne Freimoser-Grundschober, Sylvia Herter, Edwin Geven, Otto Boerman, Tapan Nayak, Erwin van Puijenbroek, David Wittig, Samuel Moser, Oliver Ast, Peter Bruenker, Ralf Hosse, Sabine Lang, Sebastian Neumann, Hubert Kettenberger, Adelbert Grossmann, Ingo Gorr, Stefan Evers, Pavel Pisa, Jennifer Fretland, Victor Levitsky, Christian Gerdes, Marina Bacac, Ekkehard Moessner, Pablo Umana. Tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for the immunotherapy 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 486. doi:10.1158/1538-7445.AM2013-486

GA101 P329G LALA, a variant of obinutuzumab with abolished ADCC, ADCP and CDC function but retained cell death induction, is as efficient as rituximab in B cell depletion and antitumor activity

CD20-antibodies are believed to mediate three different mechanisms of action (MOA): 1) direct cell death (DCD)/apoptosis, 2) antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP), 3) complement-dependent cytotoxicity (CDC). The relative contribution of these MOAs to the clinical

Abstract 3629: Engineering a novel asymmetric head-to-tail 2+1 T-cell bispecific (2+1 TCB) IgG antibody platform with superior T-cell killing compared to 1+1 asymmetric TCBs

T cell bispecific antibodies that recruit and engage T cells for tumor cell killing through binding to the T cell receptor (TCR) upon binding to a tumor antigen (TA) and subsequent crosslinking have attracted broad interest. Here, we describe a novel asymmetric head-to-tail 2+1 T cell bispecific antibody (2+1 TCB) platform characterized by the fusion of a flexible Fab fragment to the N-terminus of the CD3e Fab of a heterodimeric asymmetric bispecific TA-CD3e IgG1 antibody in head-to-tail geometry via a flexible linker. The resulting TCB is monovalent for CD3e (KD 70-100 nM) and binds bivalently with avidity to the TA on the target cell. Correct heavy chain pairing is enabled by knob-into-holes technology, correct light chain pairing by CrossMAb technology or using a common light chain. This enables production with standard processes in CHO cells. To exclude FcgR-mediated unspecific TCR and FcgR co-activation resulting in unspecific cytokine release, Fc- effector functions (ADCC, ADCP, CDC) are abolished by introduction of P329G LALA mutations while FcRn binding and IgG-like pharmacokinetic properties are retained as shown in mouse and Cynomolgus. For comparative profiling, the following TCBs were generated with specificity for the tumor antigens MCSP/CSPG4, FOLR1/FRalpha, CD19 and CD20: 2+1 TCBCD3-inside, 2+1 TCBCD3-outside, one-armed 1+1 TCBCD3-inside and a classical asymmetric 1+1 IgG TCB. In vitro Jurkat-NFAT, T cell killing, activation and proliferation assays show that both 2+1 TCB formats mediate superior potency of killing (for CSPG4, FOLR1, CD19, CD20) and superior absolute killing (for CSPG4, CD19) compared to the respective classical asymmetric 1+1 IgG TCB. Surprisingly, the 2+1 TCBCD3-inside format was found to be superior in potency compared to the 2+1 TCBCD3-outside format, although its binding affinity for CD3e is reduced. These data confirm that TCBs mediate extremely potent T cell killing with fM-pM EC50 values based on CD3e antibodies with affinities of only 70-100 nM. Notably, for CD19 both, 2+1 TCBCD3-inside and one-armed 1+1 TCBCD3-inside, mediate comparable potency and overall killing, and both were superior compared to the asymmetric 1+1 IgG TCB. These data underline the importance of the head-to-tail geometry with two Fabs on one arm attached to each other via a flexible G4S-linker. Finally, using 2+1 and 1+1 FOLR1 TCBs we demonstrate that bivalent binding allows better differentiation in killing of cells with high vs. low FOLR1 expression as compared to monovalent binding. Taken together, we demonstrate that the 2+1 TCBCD3-inside is the most potent, efficacious and versatile TCB design. Due to its orientation with the CD3e Fab inside, it allows the conversion of existing antibodies into potent TCBs without format restriction. Based on this platform, CEA CD3 TCB (RG7802, Phase I/Ib) and CD20 CD3 TCB (RG6026, Phase I) have entered clinical trials. Citation Format: Christian Klein, Christiane Neumann, Tanja Fauti, Tina Weinzierl, Anne Freimoser-Grundschober, Inja Waldhauer, Linda Fahrni, Sylvia Herter, Erwin van Puijenbroek, Sara Colombetti, Johannes Sam, Sabine Lang, Sherri Dudal, Wolfgang Schafer, Jorg T. Regula, Samuel Moser, Oliver Ast, Ralf Hosse, Ekkehard Mossner, Peter Brunker, Marina Bacac, Pablo Umana. Engineering a novel asymmetric head-to-tail 2+1 T-cell bispecific (2+1 TCB) IgG antibody platform with superior T-cell killing compared to 1+1 asymmetric TCBs [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 3629. doi:10.1158/1538-7445.AM2017-3629

Abstract PR8: Novel tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for immunotherapy of cancer.

Introduction: IL-2 therapy can lead to durable responses in a modest proportion of cancer patients, but the treatment is associated with significant toxicity. Over the last decades, various IL-2-based immunocytokines have been generated by fusing IL-2 to tumor-targeting antibodies. However, none of these molecules have progressed beyond Phase II trials and they are hampered by various liabilities: 1) High functional affinity (low pM) for IL-2Rabg on immune cells and on pulmonary vascular endothelium (Krieg et al., PNAS, 2010) compromising preferential tumor targeting due to fusion of two IL-2 moieties to the antibody. This is further compounded when the immunocytokine binds to FcgRs on the same cells. 2) Rapid systemic clearance and short half-life due to high affinity IL-2Rabg binding. 3) Preferential activation of Tregs over immune effectors due to use of wildtype IL-2. Here, we describe a novel monomeric tumor-targeted immunocytokine where a single, engineered IL-2 variant (IL-2v) with abolished IL-2Ra (CD25) binding is fused to the C-terminus of a tumor-specific hIgG1 antibody with a heterodimeric Fc-part. FcgR and C1q binding is completely abolished by a novel Fc mutation. For targeting, human(-ized) high affinity antibodies against CEA (GA504, CEA-IL2v) or FAP (GA501, FAP-IL2v) were chosen. Experimental procedures: CEA- and FAP-IL2v were recombinantly produced and characterized by surface plasmon resonance. Induction of P-STAT5, proliferation, activation induced cell death (AICD), various activation markers and cytokine release were determined on effector cells. Safety, pharmacokinetics (PK), tumor targeting by imaging, immune-pharmacodynamics and anti-tumor efficacy were analyzed in immunocompromised Scid and immunocompetent C57BL/6 mice. Results: IL-2v completely lacks binding to CD25, but retains IL-Rbg binding. In line with this, FAP- and CEA-IL2v do not bind to CD25 or preferentially activate Tregs, and do not cause AICD. However, IL-2Rbg bioactivity is retained and they are still able to activate NK, CD4 and CD8 T cells as shown by concentration dependent increase in activation markers and induction of proliferation. In particular, CEA- and FAP-IL2v expand and activate NK cells and skew the CD4:CD8 ratio towards activated CD8 T cells in vivo. In C57BL/6 mice CEA- and FAP-IL2v demonstrate improved safety despite of ca. 2-fold higher exposure and t1/2 than a wildtype IL-2-based IgG immunocytokine. SPECT/CT imaging revealed FAP-mediated tumor targeting and accumulation of FAP-IL2v with low normal tissue uptake. Notably, FAP-IL2v tumor targeting was similar to the parental FAP antibody with low accumulation in lymphoid tissues; clearly superior to an FAP-targeted wt IL-2 immunocytokine that showed preferential homing to the spleen. Studies in tumor bearing mice showed dose dependent efficacy of CEA- and FAP-IL2v in established xenograft and immunocompetent syngeneic mouse models in terms of survival. Conclusion: CEA- and FAP-IL2v demonstrate superior safety, PK and tumor targeting, while lacking preferential induction of Tregs due to abolished CD25 and FcgR binding, monovalency and high-affinity tumor-targeting as compared to conventional immunocytokines. They retain the capacity to activate NK and T effector cells through IL 2Rbg; in particular once targeted and immobilized in the tumor microenvironment. These preclinical properties support further investigation for the immunotherapy of CEA/FAP-positive tumors. This abstract is also presented as Poster A23. Citation Format: Christian Klein, Waldhauer Inja, Valeria Nicolini, Dunn Claire, Anne Freimoser, Anne Freimoser, Sylvia Herter, Edwin Geven, Otto Boerman, Erwin van Puijenbroek, David Wittig, Samuel Moser, Oliver Ast, Ralf Hosse, Sabine Lang, Sebastian Neumann, Adelbert Grossmann, Ingo Gorr, Stefan Evers, Pavel Pisa, Jennifer Fretland, Victor Levitsky, Christian Gerdes, Marina Bacac, Ekkehard Moessner, Ekkehard Moessner, Pablo Umana. Novel tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for immunotherapy of cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr PR8.

Abstract LB-236: M4-3-ML2, a novel glycoengineered humanized IgG1 antibody, targeting a membrane-proximal epitope of MCSP/CSPG4 exhibits potent ADCC induction in vitro and in vivo anti-tumoral efficacy in disseminated melanoma models

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL MCSP/CSPG4 is a large transmembrane proteoglycan identified in melanomas as HMW-MAA. In the mouse it is known as neurite growth factor 2 (NG2), a marker of pericyte recruitment. MCSP has been used as a target for clinical imaging of (uveal) melanomas by immunoscintigraphy. MCSP shows uniform and abundant expression in ca. 60-80% of melanoma, and was described in lobular breast carcinoma, glioblastoma, osteo- & chondrosarcoma, and basal cell carcinoma. It is present at high levels on pericytes of tumor neovasculature, but down-regulated as vessels mature. Normal tissue expression is low and it is not detected on PBMCs. We have generated human/Cynomolgus cross-reactive antibodies against a membrane-proximal MCSP epitope by mouse immunization with a linear peptide derived from the membrane proximal D3 domain followed by boosting with melanoma cells. The mouse antibody LC007 was selected for humanization due to its potent induction of ADCC as a chimeric antibody, compared to antibodies to membrane distal epitopes of MCSP. LC007 as chimeric IgG1 and its humanized IgG1 derivative M4-3-ML2 are characterized by the following properties: i) Specific binding to the native epitope on MCSP+ melanoma cells, but no induction of internalization; ii) Specific IHC staining of MCSP+ cells in FFPET samples; iii) ca 10 nM monovalent affinity for hMCSP D3 domain. Moreover, glycoengineering of LC007 and M4-3-ML2 antibodies using GlycoMab technology resulted in increased binding affinity for hFcgRIIIa and enhanced ADCC potency and absolute killing of melanoma cell lines. As expected, neither up to 10 ug/mL wildtype, nor glycoengineered M4-3-ML2 induced relevant cytokine (IL-6, TNF-α, IFN-γ) release in human whole blood supporting that MCSP is not expressed there. Subsequently, we studied anti-tumoral efficacy of the chimeric antibody LC007 and the humanized antibody M4-3-ML2 in disseminated models of MV3 and MDA-MB435 melanoma after i.v. injection of tumor cells in hCD16 transgenic Scid mice, which express the functional human high affinity FcgRIIIa receptor on NK cells. Both, glycoengineered LC007 and M4-3-ML2 mediated efficacy in terms of enhanced median and overall survival in both disseminated xenograft models, and were superior to the respective non-glycoengineered antibodies. Taken together, our studies support MCSP/CSPG4 as an attractive target for antibody-based cancer immunotherapy. Further studies investigating the anti-angiogenic effect of MCSP antibodies via their action on pericytes/vascular smooth muscle cells are ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-236. doi:1538-7445.AM2012-LB-236