Molecular dissection of effector mechanisms of RAS-mediated resistance to anti-EGFR antibody therapy

Phosphoinositide 3-kinase/Akt and its related signaling pathways in the regulation of tumor-associated macrophages polarization

Tumor-associated macrophages (TAMs) are a type of functionally plastic immune cell population in tumor microenvironment (TME) and mainly polarized into two phenotypes: M2 and M1-like TAMs. The M2-like TAMs could stimulate tumor growth and metastasis, tissue remodeling and immune-suppression, whereas M1-like TAMs could initiate immune response to dampen tumor progression. TAMs with different polarization phenotypes can produce various kinds of cytokines, chemokines and growth factors to regulate immunity and inflammatory responses. It is an effective method to treat cancer through ameliorating TME and modulating TAMs by converting M2 into M1-like phenotype. However, intracellular signaling mechanisms underlying TAMs polarization are largely undefined. Phosphoinositide 3-kinase (PI3K)/Akt is an important signaling pathway participating in M2-like TAMs polarization, survival, growth, proliferation, differentiation, apoptosis and cytoskeleton rearrangement. In the present review, we analyzed the mechanism of TAMs polarization focusing on PI3K/Akt and its downstream mitogen‑activated protein kinase (MAPK) as well as nuclear factor kappa B (NF-κB) signaling pathways, thus provides the first evidence of intracellular targets for cancer immunotherapy.

A phospho-proteomic study of cetuximab resistance in KRAS/NRAS/BRAFV600 wild-type colorectal cancer

PURPOSE

We hypothesised that plasticity in signal transduction may be a mechanism of drug resistance and tested this hypothesis in the setting of cetuximab resistance in patients with KRAS/NRAS/BRAFV600 wild-type colorectal cancer (CRC).

METHODS

A multiplex antibody-based platform was used to study simultaneous changes in signal transduction of 55 phospho-proteins in 12 KRAS/NRAS/BRAFV600 wild-type CRC cell lines (6 cetuximab sensitive versus 6 cetuximab resistant) following 1 and 4 h in vitro cetuximab exposure. We validated our results in CRC patient samples (n = 4) using ex vivo exposure to cetuximab in KRAS/NRAS/BRAFV600 cells that were immunomagnetically separated from the serous effusions of patients with known cetuximab resistance.

RESULTS

Differences in levels of phospho-proteins in cetuximab sensitive and resistant cell lines included reductions in phospho-RPS6 and phospho-PRAS40 in cetuximab sensitive, but not cetuximab resistant cell lines at 1 and 4 h, respectively. In addition, phospho-AKT levels were found to be elevated in 3/4 patient samples following ex vivo incubation with cetuximab for 1 h. We further explored these findings by studying the effects of combinations of cetuximab and two PI3K pathway inhibitors in 3 cetuximab resistant cell lines. The addition of PI3K pathway inhibitors to cetuximab led to a significantly higher reduction in colony formation capacity compared to cetuximab alone.

CONCLUSION

Our findings suggest activation of the PI3K pathway as a mechanism of cetuximab resistance in KRAS/NRAS/BRAFV600 wild-type CRC.

Monoclonal Antibodies in Cancer Therapy

Monoclonal antibody-based immunotherapy is now considered to be a main component of cancer therapy, alongside surgery, radiation, and chemotherapy. Monoclonal antibodies possess a diverse set of clinically relevant mechanisms of action. In addition, antibodies can directly target tumor cells while simultaneously promoting the induction of long-lasting anti-tumor immune responses. The multifaceted properties of antibodies as a therapeutic platform have led to the development of new cancer treatment strategies that will have major impacts on cancer care. This review focuses on the known mechanisms of action, current clinical applications for the treatment of cancer, and mechanisms of resistance of monoclonal antibody therapy. We further discuss how monoclonal antibody-based strategies have moved towards enhancing anti-tumor immune responses by targeting immune cells instead of tumor antigens as well as some of the current combination therapies.

Nanobody Targeting of Epidermal Growth Factor Receptor (EGFR) Ectodomain Variants Overcomes Resistance to Therapeutic EGFR Antibodies

Epidermal growth factor receptor (EGFR) ectodomain variants mediating primary resistance or secondary treatment failure in cancer patients treated with cetuximab or panitumumab support the need for more resistance-preventive or personalized ways of targeting this essential pathway. Here, we tested the hypothesis that the EGFR nanobody 7D12 fused to an IgG1 Fc portion (7D12-hcAb) would overcome EGFR ectodomain-mediated resistance because it targets a very small binding epitope within domain III of EGFR. Indeed, we found that 7D12-hcAb bound and inhibited all tested cell lines expressing common resistance-mediating EGFR ectodomain variants. Moreover, we assessed receptor functionality and binding properties in synthetic mutants of the 7D12-hcAb epitope to model resistance to 7D12-hcAb. Because the 7D12-hcAb epitope almost completely overlaps with the EGF-binding site, only position R377 could be mutated without simultaneous loss of receptor functionality, suggesting a low risk of developing secondary resistance toward 7D12-hcAb. Our binding data indicated that if 7D12-hcAb resistance mutations occurred in position R377, which is located within the cetuximab and panitumumab epitope, cells expressing these receptor variants would retain sensitivity to these antibodies. However, 7D12-hcAb was equally ineffective as cetuximab in killing cells expressing the cetuximab/panitumumab-resistant aberrantly N-glycosylated EGFR R521K variant. Yet, this resistance could be overcome by introducing mutations into the Fc portion of 7D12-hcAb, which enhanced immune effector functions and thereby allowed killing of cells expressing this variant. Taken together, our data demonstrate a broad range of activity of 7D12-hcAb across cells expressing different EGFR variants involved in primary and secondary EGFR antibody resistance.

Serum level of octanoic acid predicts the efficacy of chemotherapy for colorectal cancer

The survival times of patients with advanced colorectal cancer (CRC) have increased due to the introduction of chemotherapy involving irinotecan and cetuximab. However, further studies are required on the effective pretreatment methods for identifying patients with CRC who would respond to particular treatments. The aim of the present study was to identify biomarkers for predicting the efficacy of chemotherapy for CRC. A total of 123 serum samples were collected from 31 patients with CRC just prior to each of the first four rounds of chemotherapy. Serum metabolome analysis was performed using a multiplatform metabolomics system, and univariate Cox regression hazards analysis of the time to disease progression was conducted. Octanoic acid and 1,5-anhydro-D-glucitol were identified as biomarker candidates. In addition, the serum level of octanoic acid was indicated to be significantly associated with the time to disease progression (hazard ratio, 3.3; 95% confidence interval, 1.099–11.840; P=0.033). The serum levels of fatty acids, in particular polyunsaturated fatty acids, tended to be downregulated in the partial response group. The findings of the present study suggest that the serum level of octanoic acid may serve as a useful predictor for the prognosis of CRC.

Phosphorylation of p70 Ribosomal Protein S6 Kinase β-1 is an Independent Prognostic Parameter in Metastatic Colorectal Cancer

BACKGROUND

Deregulation of signal transduction pathways plays a critical role in oncogenesis of colorectal cancer (CRC) and directly affects sensitivity to targeted therapies. Against this background we developed a comprehensive biomarker profiling program including markers of downstream signaling to study their association with clinical outcomes.

PATIENTS AND METHODS

A prospectively studied cohort of 160 patients with metastatic CRC was included. Standard diagnostic workup included mutational analyses of Kirsten rat sarcoma viral oncogene homolog (KRAS), neuroblastoma RAS viral oncogene homolog (NRAS), and v-Raf murine sarcoma viral oncogene homolog B (BRAF). In addition, markers of mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) and mammalian target of rapamycin pathway activation (phosphorylation of extracellular signal-regulated kinase [ERK], AKT, and p70 ribosomal protein S6 kinase β-1 [p70S6K]) were studied using standardized immunohistochemistry.

RESULTS

There was a significant correlation between markers of ERK and AKT activation in the full cohort. In addition, phosphorylation of p70S6K correlated strongly with ERK and AKT phosphorylation and primary tumor localization in the right colon. Subgroup analyses specified these correlations to patients with all-RAS wild type tumors. In contrast, tumors harboring RAS mutations predominantly exhibited ERK phosphorylation. Interestingly, patients with CRC showing high p70S6K phosphorylation (highest quartile) had a significantly inferior overall survival (hazard ratio [HR], 2.4; P = .002) irrespective of RAS mutational status. This effect remained significant in multivariate analysis (P = .002). A patient subgroup characterized by high p70S6K phosphorylation and right-sided primary tumors had a particularly poor prognosis with a dramatically inferior overall survival (HR, 5.2; P < .001). Patients with right-sided primary tumor and low p70S6K phosphorylation had responses to anti-epidermal growth factor receptor antibody-based therapies and overall survival similar to patients with left-sided primary tumors.

CONCLUSION

High phosphorylation of p70S6K is a novel, independent biomarker for poor prognosis, in particular in patients with right-sided primary tumors.