RNF43 mutations predict response to anti-BRAF/EGFR combinatory therapies in BRAFV600E metastatic colorectal cancer

Anti-BRAF/EGFR therapy was recently approved for the treatment of metastatic BRAF^V600E colorectal cancer (mCRC^BRAF-V600E). However, a large fraction of patients do not respond, underscoring the need to identify molecular determinants of treatment response. Using whole-exome sequencing in a discovery cohort of patients with mCRC^BRAF-V600E treated with anti-BRAF/EGFR therapy, we found that inactivating mutations in RNF43, a negative regulator of WNT, predict improved response rates and survival outcomes in patients with microsatellite-stable (MSS) tumors. Analysis of an independent validation cohort confirmed the relevance of RNF43 mutations to predicting clinical benefit (72.7% versus 30.8%; P = 0.03), as well as longer progression-free survival (hazard ratio (HR), 0.30; 95% confidence interval (CI), 0.12–0.75; P = 0.01) and overall survival (HR, 0.26; 95% CI, 0.10–0.71; P = 0.008), in patients with MSS-RNF43^mutated versus MSS-RNF43^wild-type tumors. Microsatellite-instable tumors invariably carried a wild-type-like RNF43 genotype encoding p.G659fs and presented an intermediate response profile. We found no association of RNF43 mutations with patient outcomes in a control cohort of patients with MSS-mCRC^BRAF-V600E tumors not exposed to anti-BRAF targeted therapies. Overall, our findings suggest a cross-talk between the MAPK and WNT pathways that may modulate the antitumor activity of anti-BRAF/EGFR therapy and uncover predictive biomarkers to optimize the clinical management of these patients.

The presence of inactivating mutations in RNF43, a negative regulator of WNT, in tumor cells predicts improved response rates and survival outcomes in patients with metastatic BRAF^V600E colorectal cancer treated with anti-BRAF/EGFR therapy.

Abstract P3-12-03: Combined targeting of HER2 and VEGFR2 for effective treatment of HER2-amplified breast cancer brain metastases

Brain metastases remain a serious obstacle in the treatment of patients with human epidermal growth factor receptor-2 (HER2)-amplified breast cancer. Unlike HER2-amplified breast tumors growing in extra-cranial locations, brain metastases do not respond well to HER2 inhibitors and are often the reason for treatment failure. One of the major challenges in studying brain metastases is the lack of preclinical models. We developed a HER2-amplified mouse model of brain metastasis using an orthotopic xenograft of BT474 cells in mice. As seen in patients, the HER2 inhibitors trastuzumab and lapatinib failed to contain brain metastatic tumor growth.

Based on previous findings from our laboratory suggesting a role of vascular endothelial growth factor (VEGF) in the resistance of HER2-overexpressing breast cancer brain metastases to trastuzumab, we combined HER2 inhibitors with the anti-VEGFR2 antibody DC101. The combination of either trastuzumab and DC101 or lapatinib and DC101 significantly slowed metastatic tumor growth in the brain, and resulted in a striking improvement in overall survival. The benefit is due largely to an anti-angiogenic effect. The combination of anti-HER2 and anti-VEGFR2 therapy reduced both the total and functional microvascular density in the brain metastatic tumors. Moreover, tumor tissues under combination therapy showed a marked increase in necrosis.

Preclinical and clinical evidence suggest that the combination of trastuzumab and lapatinib is superior to either agent alone – though this has never been tested in the brain metastatic setting. We consistently observed increased phosphorylation of HER2 in breast tumor cells growing in the brain compared with the mammary fat pad. In addition, while short-term lapatinib treatment significantly reduced HER2 activation in the brain, it could do so only to the level of that observed in the untreated mammary fat pad - and this effect disappeared over time. We hypothesized that more pronounced HER2 inhibition would be beneficial to these brain metastases with increased HER2 activation. We show here a significant growth delay with the combination of the two HER2 inhibitors compared with monotherapy. Moreover, we found a dramatic brain metastatic tumor growth delay in mice treated with both HER2 inhibitors, trastuzumab and lapatinib, and DC101. The triple combination prolonged overall survival 5 times longer than control-treated mice.

Brain metastasis from breast cancer is considered the “final frontier” of breast cancer research and treatment. Our findings support the clinical development of a three-drug regimen of trastuzumab, lapatinib and a VEGF pathway inhibitor for the treatment of HER2-amplified breast cancer brain metastases. While the anti-VEGF antibody bevacizumab in combination with trastuzumab and chemotherapy has shown some promise in HER2-positive metastatic breast cancer patient, there are no data on its efficacy in the context of brain metastases. A clinical trial is now recruiting patients to evaluate the efficacy of bevacizumab in breast cancer patients with active brain metastases, including its combination with trastuzumab in patients with HER2-positive disease. This trial may provide clinical evidence for the approach presented here.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-12-03.

Effect of single-chain antibody targeting of the ligand-binding domain in the anaplastic lymphoma kinase receptor

The tyrosine kinase receptor anaplastic lymphoma kinase (ALK) and its ligand, the growth factor pleiotrophin (PTN), are highly expressed during the development of the nervous system and have been implicated in the malignant progression of different tumor types. Here, we describe human single-chain variable fragment (scFv) antibodies that target the ligand-binding domain (LBD) in ALK and show the effect in vitro and in vivo. The ALK LBD was used as a bait in a yeast two-hybdrid system to select human scFv from a library with randomized complementarity-determining region 3 domains. Surface plasmon resonance showed high-affinity binding of the selected scFv. The anti-ALK scFv competed for binding of PTN to ALK in intact cells and inhibited PTN-dependent signal transduction through endogenous ALK. Invasion of an intact endothelial cell monolayer by U87MG human glioblastoma cells was inhibited by the anti-ALK scFv. In addition, the growth of established tumor xenografts in mice was reversed after the induction of the conditional expression of the anti-ALK scFv. In archival malignant brain tumors expression levels of ALK and PTN were found elevated and appear correlated with poor patient survival. This suggests a rate-limiting function of the PTN/ALK interaction that may be exploited therapeutically.