Abstract 1668: Effective targeting of colorectal cancer with a recombinant antibody mixture against EGFR, HER3 and IGF1R

The epidermal growth factor receptor (EGFR) plays an important role in the development and maintenance of the malignant phenotype of several human cancers. Therefore, it is a frequently pursued therapeutic target and several antibodies targeting EGFR have been clinically approved. However, the clinical responses to current anti-EGFR agents are often modest, indicating a need for improved therapeutics. Resistance mechanisms to anti-EGFR antibodies include ligand up-regulation, receptor tyrosine kinase plasticity, and mutations in downstream signaling molecules such as KRAS, BRAF, and PIK3CA.

Here, we present data showing that a mixture of antibodies targeting HER3, EGFR, and IGF1R (HEI mixture) with high affinity ligand-blocking antibodies induced growth inhibition in a large panel of cancer cell lines. Synergies of simultaneous inhibition of the three targets were frequently seen in cell lines and xenograft tumor models. In particular, colorectal cancer cell lines were sensitive to the HEI mixture and superiority to cetuximab was seen in several cell lines. Surprisingly, the HEI mixture was effective at inhibiting the growth of KRAS and BRAF mutated cell lines, suggesting that the three receptor tyrosine kinases may still contribute to the malignant phenotype of tumors with these genomic alterations. Colorectal cancer is thought to be a ligand driven disease and hence the inhibitory activity of the HEI mixture was tested in the presence of EGFR, HER3 and IGF1R ligands and compared with the activity of cetuximab. As expected, the HEI mixture was able to block growth stimulation induced by all ligands, whereas heregulin and IGF1/IGF2 caused resistance to cetuximab.

A clinically relevant subpopulation of colorectal cancer harbors amplification of IGF2, a major ligand for IGF1R, and hence should display sensitivity to IGF1R targeting. The HEI mixture was tested in three metastatic colorectal PDX models with IGF2 overexpression and induced tumor regression in all three models.

In conclusion, our data indicate that simultaneous targeting of EGFR, HER3 and IGFR1 provides a broader efficacy than targeting a single receptor, and thereby provides a rationale for simultaneous targeting of the three receptors with a recombinant antibody mixture.

Citation Format: Christina Egebjerg, Camilla Fröhlich, Karsten Wessel Eriksen, Thomas Tuxen Poulsen, Klaus Kofoed, Thomas Bouquin, Andrea Bretotti, Livio Trusolino, Ivan David Horak, Michael Kragh, Mikkel Wandahl Pedersen. Effective targeting of colorectal cancer with a recombinant antibody mixture against EGFR, HER3 and IGF1R. [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 1668. doi:10.1158/1538-7445.AM2015-1668

Abstract 5455: Surface accumulation of receptor tyrosine kinases upon treatment with tyrosine kinase inhibitors and resulting enhancement of activity upon treatment cessation

Receptor tyrosine kinases (RTKs) constitute the largest family of structurally related oncogenes and are often involved in the initiation, maintenance and/or metastasis of various human cancers. The genes encoding RTKs are frequently amplified, fused, mutated, or the ligands are expressed at high levels, causing abnormal activation and downstream signaling. Two major types of drugs have been used with success to treat cancers with abnormal RTK activation, recombinant monoclonal antibodies (mAbs) and small molecule inhibitors of the tyrosine kinases (TKIs). TKIs have proven most successful against cancers driven by gene fusions or mutations, whereas mAbs dominate in cancers driven by gene amplifications or ligand-mediated RTK activation. Recent studies show that the two types of treatment modalities may often be synergistic, but the reason for this is not well characterized.

Here, we demonstrate that surface levels of various RTKs increase in cancer cell lines upon treatment with TKIs specific for the individual RTKs. The effect was most pronounced in cell lines with amplification or autocrine ligand production and occurred at inhibitor concentrations suboptimal for inhibition of growth. Removal of the TKIs resulted in an increase in RTK activity and cancer cell proliferation as a result of the increased RTK levels.

MAbs, especially mAb mixtures, when given in combination with the TKIs were found to prevent RTK accumulation and led to enhanced efficacy. Due to the increased number of receptors, the combination also resulted in enhancement of secondary effector functions, such as ADCC.

In conclusion, our results demonstrate that in certain contexts TKI treatment leads to RTK accumulation and that this accumulation has the potential to enhance tumor growth. Antibody mixtures, when given together with the TKIs, can prevent RTK accumulation and even enhance the TKI activity.

Citation Format: Anne-Mette Bjerregaard, Michael V. Grandal, Camilla Frohlich, Trine Lindsted, Christina Egebjerg, Ivan D. Horac, Michael Kragh, Mikkel W. Pedersen. Surface accumulation of receptor tyrosine kinases upon treatment with tyrosine kinase inhibitors and resulting enhancement of activity upon treatment cessation. [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 5455. doi:10.1158/1538-7445.AM2015-5455

ErbB2-driven breast cancer cell invasion depends on a complex signaling network activating myeloid zinc finger-1-dependent cathepsin B expression

Aberrant ErbB2 receptor tyrosine kinase activation in breast cancer is strongly linked to an invasive disease. The molecular basis of ErbB2-driven invasion is largely unknown. We show that cysteine cathepsins B and L are elevated in ErbB2 positive primary human breast cancer and function as effectors of ErbB2-induced invasion in vitro. We identify Cdc42-binding protein kinase beta, extracellular regulated kinase 2, p21-activated protein kinase 4, and protein kinase C alpha as essential mediators of ErbB2-induced cysteine cathepsin expression and breast cancer cell invasiveness. The identified signaling network activates the transcription of cathepsin B gene (CTSB) via myeloid zinc finger-1 transcription factor that binds to an ErbB2-responsive enhancer element in the first intron of CTSB. This work provides a model system for ErbB2-induced breast cancer cell invasiveness, reveals a signaling network that is crucial for invasion in vitro, and defines a specific role and targets for the identified serine-threonine kinases.

Identification of a c-Jun N-terminal kinase-2-dependent signal amplification cascade that regulates c-Myc levels in ras transformation

Ras is one of the most frequently activated oncogenes in cancer. Two mitogen-activated protein kinases (MAPKs) are important for ras transformation: extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase 2 (JNK2). Here we present a downstream signal amplification cascade that is critical for ras transformation in murine embryonic fibroblasts. This cascade is coordinated by ERK and JNK2 MAPKs, whose Ras-mediated activation leads to the enhanced levels of three oncogenic transcription factors, namely, c-Myc, activating transcription factor 2 (ATF2) and ATF3, all of which are essential for ras transformation. Previous studies show that ERK-mediated serine 62 phosphorylation protects c-Myc from proteasomal degradation. ERK is, however, not alone sufficient to stabilize c-Myc but requires the cooperation of cancerous inhibitor of protein phosphatase 2A (CIP2A), an oncogene that counteracts protein phosphatase 2A-mediated dephosphorylation of c-Myc. Here we show that JNK2 regulates Cip2a transcription via ATF2. ATF2 and c-Myc cooperate to activate the transcription of ATF3. Remarkably, not only ectopic JNK2, but also ectopic ATF2, CIP2A, c-Myc and ATF3 are sufficient to rescue the defective ras transformation of JNK2-deficient cells. Thus, these data identify the key signal converging point of JNK2 and ERK pathways and underline the central role of CIP2A in ras transformation.