A HER2-specific Modified Fc Fragment (Fcab) Induces Antitumor Effects Through Degradation of HER2 and Apoptosis

FS102 is a HER2-specific Fcab (Fc fragment with antigen binding), which binds HER2 with high affinity and recognizes an epitope that does not overlap with those of trastuzumab or pertuzumab. In tumor cells that express high levels of HER2, FS102 caused profound HER2 internalization and degradation leading to tumor cell apoptosis. The antitumor effect of FS102 in patient-derived xenografts (PDXs) correlated strongly with the HER2 amplification status of the tumors. Superior activity of FS102 over trastuzumab or the combination of trastuzumab and pertuzumab was observed in vitro and in vivo when the gene copy number of HER2 was equal to or exceeded 10 per cell based on quantitative polymerase chain reaction (qPCR). Thus, FS102 induced complete and sustained tumor regression in a significant proportion of HER2-high PDX tumor models. We hypothesize that the unique structure and/or epitope of FS102 enables the Fcab to internalize and degrade cell surface HER2 more efficiently than standard of care antibodies. In turn, increased depletion of HER2 commits the cells to apoptosis as a result of oncogene shock. FS102 has the potential of a biomarker-driven therapeutic that derives superior antitumor effects from a unique mechanism-of-action in tumor cells which are oncogenically addicted to the HER2 pathway due to overexpression.

Abstract B123: Preclinical evaluation of FS102: A HER2-specific Fcab with a novel mechanism of action

HER2 is a validated oncogenic target which is overexpressed in many cancers. Although the approved HER2-specific biologics have improved the standard of care of HER2-positive breast and gastric cancers, a significant unmet medical need exists due to intrinsic or acquired resistance. By randomizing two loops in the CH3 domain of an IgG1 Fc fragment, we generated a HER2-specific Fcab™ (Fc fragment with antigen binding), called FS102, which binds HER2 with high affinity (2 nM), and recognizes an epitope that does not overlap with the epitopes of trastuzumab or pertuzumab. FS102 has a favorable t1/2 of ∼ 60 hours in mice. Biophysical characterization has shown the Fcab to have suitable properties to be developed as a therapeutic. To assess if interactions with the unique HER2 epitope could translate into clinically relevant pharmacological activities, we conducted in vitro and in vivo characterization of FS102 in comparison to trastuzumab monotherapy or trastuzumab-pertuzumab combination therapy. Using the HER2-positive breast cell line SKBr3 as an in vitro model system, we determined the effect of FS102 on HER2 downregulation, cellular proliferation, cell cycle progression, and apoptosis. Both FS102 and trastuzumab were internalized efficiently by SKBr3 cells, but only the former induced profound reduction in cell surface and total HER2 protein levels. Trastuzumab and FS102 both reduced SKBr3 cell proliferation by approximately 50% upon 5 days treatment. However the two agents achieved this inhibition via distinct mechanisms of action (MOA). Consistent with published data, trastuzumab induced G1 cell cycle arrest, while FS102 showed no effect on cell cycle progression. Instead, FS102 significantly induced apoptosis as measured by caspase activity and a loss of membrane integrity, an effect not observed upon exposure to trastuzumab. FS102 displays potent anti-tumor effects in HER2 overexpressing patient-derived xenograft (PDX) murine models, which are positive for a clinically relevant biomarker. Significant tumor inhibition has been observed in gastric, colorectal and breast PDX models. This includes complete tumor regression in 3 out of 8 models evaluated. Moreover, FS102 is significantly more effective than trastuzumab when tested in the biomarker-positive subset of PDX tumors. In one of these PDX model systems, where the tumors were refractory to trastuzumab-pertuzumab combination treatment, subsequent FS102 treatment reversed tumor growth and ultimately led to complete regression of the tumor.

The results indicate that FS102 may have the potential to overcome resistance to conventional HER2 therapy in a biomarker-defined patient subpopulation, and that the Fcab technology is an attractive platform to generate novel biologics with unique antigen recognition and MOA. Additional studies are underway to further elucidate the FS102-induced ErbB receptor degradation pathway.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B123.

Citation Format: Sarah Batey, Kinmei Leung, Robert Rowlands, Samine Isaac, Joana Carvalho, Sarah Weller, Mateusz Wydro, Miguel Gaspar, Melanie Medcalf, Robert Pegram, Vicky Drewett, Mihriban Tuna, John Haurum, Haijun H. Sun. Preclinical evaluation of FS102: A HER2-specific Fcab with a novel mechanism of action. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B123.

Air rifle pellet injury to the middle ear, a very rare occurence

INTRODUCTION

Air rifle pellet injuries are relatively common. These injuries often involve the brain, eyes chest or abdomen. It is rare for ENT surgeons to be involved in the care of these patients.

CASE REPORT

We present the case of a 38 year old man with a history of an air rifle pellet injury to the left ear. Presenting symptoms included bleeding per ear, otoalgia, hearing loss and tinnitus. Imaging and surgical exploration demonstrated a metallic pellet in the left petrous temporal bone, within the middle ear and a fracture of the anterior wall of the external auditory meatus with associated tiny metallic fragments. A further surgical exploration was required to remove a bony sequestrum of the anterior canal wall.

CONCLUSION

The onset of pain and discharge a few months after the injury may imply the formation of a delayed sequestrum. The possibility of an implantation cholesteatoma should also be considered.

Rhabdomyosarcoma of the adult nasopharynx

Rhabdomyosarcoma of the adult head and neck is rare, particularly beyond 40 years of age. In this region, the nasopharynx is an unusual site. Most nasopharyngeal rhabdomyosarcomas are of an alveolar variety. We report a case of embryonal or spindle cell rhabdomyosarcoma in the nasopharynx of a 47-year-old man. The histology of this tumour revealed clear cells that have not been described in embryonal rhabdomyosarcomas occurring in the head and neck. The pathology is discussed and current literature reviewed.