Sensitivity and resistance to EGF-R inhibitors: approaches to enhance the efficacy of EGF-R antibodies

EGFR expression levels affect the mode of action of EGFR-targeting monoclonal antibodies

Epidermal growth factor receptor (EGFR) expression levels appear to modulate the efficacy of EGFR-targeting monoclonal antibodies. More specifically, we observed that high EGFR densities negatively affect the effects of EGFR-specific antibodies on EGFR phosphorylation yet exacerbate Fc-mediated tumor-cell killing. These results suggest that the predominant mode of action of EGFR-targeting antibodies depend on EGFR expression levels.

Antibody-dependent cellular cytotoxicity in patients on chronic hemodialysis

BACKGROUND

Antibody (Ab)-dependent cellular cytotoxicity (ADCC) is considered to be a relevant mechanism of action of Ab-based tumor therapies. However, knowledge about ADCC capacity of dialysis patients (DP) is limited. The aim of our study was to investigate if ADCC capacity of effector cells obtained from DP differed from those of healthy individuals (HI).

METHODS

First, we performed ADCC assays with isolated polymorphonuclear cells (PMN) and peripheral blood mononuclear cells (PBMC), mediated by the epidermal growth factor receptor Ab cetuximab or panitumumab. As cetuximab is of human IgG1 and panitumumab of human IgG2 isotype, both Abs differ in their affinity to Fcγ receptors and effector cell recruitment.

RESULTS

Using PMN as effectors, ADCC levels via panitumumab proved to be higher than via cetuximab, but did not differ between DP and HI. In contrast, IgG2-mediated ADCC with PBMC from DP was significantly enhanced compared to HI. IgG2 Abs predominantly bind to FcγRIIa. Within the PBMC, monocytes are the only cytotoxic cells physiologically expressing this receptor. ADCC experiments with isolated monocytes confirmed them to be the pivotal cells for the observed effect. Analysis of monocytes' Fc receptor expression demonstrated no difference between DP and HI, but monocytes of DP proved to be numerically increased and appeared preactivated.

CONCLUSION

Our studies implicate that ADCC capacity is not impaired in DP and that it might particularly be reasonable to apply human IgG2 Abs as therapeutics for these patients.

7th annual European Antibody Congress 2011: November 29-December 1, 2011, Geneva, Switzerland

The 7th European Antibody Congress (EAC), organized by Terrapin Ltd., was again held in Geneva, Switzerland, following on the tradition established with the 4th EAC. The 2011 version of the EAC was attended by nearly 250 delegates who learned of the latest advances and trends in the global development of antibody-based therapeutics. The first day focused on advances in understanding structure-function relationships, choosing the best format, glycoengineering biobetter antibodies, improving the efficacy and drugability of mAbs and epitope mapping. On the second day, the discovery of novel targets for mAb therapy, clinical pipeline updates, use of antibody combinations to address resistance, generation and identification of mAbs against new targets and biosimilar mAb development were discussed. Antibody-drug conjugates, domain antibodies and new scaffolds and bispecific antibodies were the topics of the third day. In total, nearly 50 speakers provided updates of programs related to antibody research and development on-going in the academic, government and commercial sectors.

Fc-engineered EGF-R antibodies mediate improved antibody-dependent cellular cytotoxicity (ADCC) against KRAS-mutated tumor cells

Oncogenic mutations of the KRAS gene have emerged as a common mechanism of resistance against epidermal growth factor receptor (EGF-R)-directed tumor therapy. Mutated KRAS leads to ligand-independent activation of signaling pathways downstream of EGF-R. Thereby, direct effector mechanisms of EGF-R antibodies, such as blockade of ligand binding and inhibition of signaling, are bypassed. Thus, a humanized variant of the approved EGF-R antibody Cetuximab inhibited growth of wild-type KRAS-expressing A431 cells, but did not inhibit KRAS-mutated A549 tumor cells. We then investigated whether killing of tumor cells harboring mutated KRAS can be improved by enhancing antibody-dependent cellular cytotoxicity (ADCC). Protein- and glyco-engineering of antibodies' Fc region are established technologies to enhance ADCC by increasing antibodies' affinity to activating Fcgamma receptors. Thus, EGF-R antibody variants with increased affinity for the natural killer (NK) cell-expressed FcgammaRIIIa (CD16) were generated and analyzed. These variants triggered significantly enhanced mononuclear cell (MNC)-mediated killing of KRAS-mutated tumor cells compared to wild-type antibodies. Additionally, cells transfected with mutated KRAS were killed as effectively by ADCC as vector-transfected control cells. Together, these data demonstrate that KRAS mutations are not sufficient to render tumor cells resistant to ADCC. Consequently Fc-engineered EGF-R antibodies may prove effective against KRAS-mutated tumors, which are not susceptible to signaling inhibition by EGF-R antibodies.