Effects of PHA-665752 and vemurafenib combination treatment on in vitro and murine xenograft growth of human colorectal cancer cells with BRAFV600E mutations

Effectiveness of 225Ac-Labeled Anti-EGFR Radioimmunoconjugate in EGFR-Positive Kirsten Rat Sarcoma Viral Oncogene and BRAF Mutant Colorectal Cancer Models

Eighty percent of colorectal cancers (CRCs) overexpress epidermal growth factor receptor (EGFR). Kirsten rat sarcoma viral oncogene (KRAS) mutations are present in 40% of CRCs and drive de novo resistance to anti-EGFR drugs. BRAF oncogene is mutated in 7%-10% of CRCs, with even worse prognosis. We have evaluated the effectiveness of [225Ac]Ac-macropa-nimotuzumab in KRAS mutant and in KRAS wild-type and BRAFV600E mutant EGFR-positive CRC cells in vitro and in vivo. Anti-CD20 [225Ac]Ac-macropa-rituximab was developed and used as a nonspecific radioimmunoconjugate. Methods: Anti-EGFR antibody nimotuzumab was radiolabeled with 225Ac via an 18-membered macrocyclic chelator p-SCN-macropa. The immunoconjugate was characterized using flow cytometry, radioligand binding assay, and high-performance liquid chromatography, and internalization was studied using live-cell imaging. In vitro cytotoxicity was evaluated in 2-dimensional monolayer EGFR-positive KRAS mutant DLD-1, SW620, and SNU-C2B; in KRAS wild-type and BRAFV600E mutant HT-29 CRC cell lines; and in 3-dimensional spheroids. Dosimetry was studied in healthy mice. The in vivo efficacy of [225Ac]Ac-macropa-nimotuzumab was evaluated in mice bearing DLD-1, SW620, and HT-29 xenografts after treatment with 3 doses of 13 kBq/dose administered 10 d apart. Results: In all cell lines, in vitro studies showed enhanced cytotoxicity of [225Ac]Ac-macropa-nimotuzumab compared with nimotuzumab and controls. The inhibitory concentration of 50% in the DLD-1 cell line was 1.8 nM for [225Ac]Ac-macropa-nimotuzumab versus 84.1 nM for nimotuzumab. Similarly, the inhibitory concentration of 50% was up to 79-fold lower for [225Ac]Ac-macropa-nimotuzumab than for nimotuzumab in KRAS mutant SNU-C2B and SW620 and in KRAS wild-type and BRAFV600E mutant HT-29 CRC cell lines. A similar trend was observed for 3-dimensional spheroids. Internalization peaked 24-48 h after incubation and depended on EGFR expression. In the [225Ac]Ac-macropa-nimotuzumab group, 3 of 7 mice bearing DLD-1 tumors had complete remission. Median survival was 40 and 34 d for mice treated with phosphate-buffered saline and [225Ac]Ac-macropa-rituximab (control), respectively, whereas it was not reached for the [225Ac]Ac-macropa-nimotuzumab group (>90 d). Similarly, median survival of mice bearing HT-29 xenografts was 16 and 12.5 d for those treated with [225Ac]Ac-macropa-rituximab and phosphate-buffered saline, respectively, and was not reached for those treated with [225Ac]Ac-macropa-nimotuzumab (>90 d). One of 7 mice bearing HT-29 xenografts and treated using [225Ac]Ac-macropa-nimotuzumab had complete remission. Compared with untreated mice, [225Ac]Ac-macropa-nimotuzumab more than doubled (16 vs. 41 d) the median survival of mice bearing SW620 xenografts. Conclusion: [225Ac]Ac-macropa-nimotuzumab is effective against KRAS mutant and BRAFV600E mutant CRC models.

Cetuximab resistance induced by hepatocyte growth factor is overcome by MET inhibition in KRAS, NRAS, and BRAF wild-type colorectal cancers

PURPOSE

Recent evidence has highlighted the role of hepatocyte growth factor (HGF) as a putative biomarker to predict EGFR inhibitor resistance. This study investigated the impact of plasma HGF levels on EGFR inhibition and the counter effect of MET inhibition in KRAS, NRAS, and BRAF (RAS/RAF) wild-type colorectal cancers (CRCs).

METHODS

Plasma HGF levels were analyzed with clinical outcomes of patients with metastatic CRC (mCRC) receiving palliative first-line chemotherapy. Then, in vitro experiments were conducted to validate the clinical findings and to establish pre-clinical evidence of MET inhibition by capmatinib.

RESULTS

A total of 80 patients were included: cetuximab + FOLFIRI (n = 35) and bevacizumab + FOLFIRI (n = 45). Both progression-free survival (PFS) and overall survival (OS) were significantly lesser in the high vs low HGF group: median 11.8 vs. 24.7 months, respectively, for PFS (p = 0.009), and median 21.1 months vs. not reached, respectively, for OS (p = 0.018). The difference was significantly evident in the cetuximab group. In five RAS/RAF wild-type CRC cells, the addition of HGF activated ERK1/2 and AKT via MET phosphorylation, resulting in cetuximab resistance in vitro. In cetuximab-sensitive Caco-2 and SNU-C4 cells, capmatinib overcame cetuximab resistance in the presence of HGF by attenuating HGF-induced MET signaling activation.

CONCLUSION

Patients with mCRC receiving cetuximab + FOLFIRI who presented with high plasma HGF levels had significantly worse PFS and OS. Cetuximab resistance induced by HGF was mediated by AKT and ERK activation and overcome by MET inhibition in vitro.

Analysis of erythrocyte signalling pathways during Plasmodium falciparum infection identifies targets for host-directed antimalarial intervention

Intracellular pathogens mobilize host signaling pathways of their host cell to promote their own survival. Evidence is emerging that signal transduction elements are activated in a-nucleated erythrocytes in response to infection with malaria parasites, but the extent of this phenomenon remains unknown. Here, we fill this knowledge gap through a comprehensive and dynamic assessment of host erythrocyte signaling during infection with Plasmodium falciparum. We used arrays of 878 antibodies directed against human signaling proteins to interrogate the activation status of host erythrocyte phospho-signaling pathways at three blood stages of parasite asexual development. This analysis reveals a dynamic modulation of many host signalling proteins across parasite development. Here we focus on the hepatocyte growth factor receptor (c-MET) and the MAP kinase pathway component B-Raf, providing a proof of concept that human signaling kinases identified as activated by malaria infection represent attractive targets for antimalarial intervention.

Plasmodium infection activates signaling pathways in a-nucleated erythrocytes. Here, Adderley et al. use a comprehensive antibody microarray to show that infection extensively modulates host cell signalling and that the host receptor tyrosine kinase c-MET supports Plasmodium falciparum proliferation.

Targeting Colon Cancers with Mutated BRAF and Microsatellite Instability

The subgroup of colon cancer (CRC) characterized by mutation in the BRAF gene and high mutation rate in the genomic DNA sequence, known as the microsatellite instability (MSI) phenotype, accounts for roughly 10% of the patients and derives from polyps with a serrated morphology. In this review, both features are discussed with regard to therapeutic opportunities. The most prevalent cancer-associated BRAF mutation is BRAF V600E that causes constitutive activation of the pro-proliferative MAPK pathway. Unfortunately, the available BRAF-specific inhibitors had little clinical benefit for metastatic CRC patients due to adaptive MAPK reactivation. Recent contributions for the development of new combination therapy approaches to pathway inhibition will be highlighted. In addition, we review the promising role of the recently developed immune checkpoint therapy for the treatment of this CRC subtype. The MSI phenotype of this subgroup results from an inactivated DNA mismatch repair system and leads to frameshift mutations with translation of new amino acid stretches and the generation of neo-antigens. This most likely explains the observed high degree of infiltration by tumour-associated lymphocytes. As cytotoxic lymphocytes are already part of the tumour environment, their activation by immune checkpoint therapy approaches is highly promising.