Sym004, a novel anti-EGFR antibody mixture, augments radiation response in human lung and head and neck cancers.

Sym004 represents a novel EGF receptor (EGFR)-targeting approach comprising a mixture of two anti-EGFR antibodies directed against distinct epitopes of EGFR. In contrast with single anti-EGFR antibodies, Sym004 induces rapid and highly efficient degradation of EGFR. In the current study, we examine the capacity of Sym004 to augment radiation response in lung cancer and head and neck cancer model systems. We first examined the antiproliferative effect of Sym004 and confirmed 40% to 60% growth inhibition by Sym004. Using clonogenic survival analysis, we identified that Sym004 potently increased cell kill by up to 10-fold following radiation exposure. A significant increase of γH2AX foci resulting from DNA double-strand breaks was observed in Sym004-treated cells following exposure to radiation. Mechanistic studies further showed that Sym004 enhanced radiation response via induction of cell-cycle arrest followed by induction of apoptosis and cell death, reflecting inhibitory effects on DNA damage repair. The expression of several critical molecules involved in radiation-induced DNA damage repair was significantly inhibited by Sym004, including DNAPK, NBS1, RAD50, and BRCA1. Using single and fractionated radiation in human tumor xenograft models, we confirmed that the combination of Sym004 and radiation resulted in significant tumor regrowth delay and superior antitumor effects compared with treatment with Sym004 or radiation alone. Taken together, these data reveal the strong capacity of Sym004 to augment radiation response in lung and head and neck cancers. The unique action mechanism of Sym004 warrants further investigation as a promising EGFR targeting agent combined with radiotherapy in cancer therapy.

Enhanced radiation sensitivity in HPV-positive head and neck cancer.

Patients with human papillomavirus (HPV+)-associated head and neck cancer (HNC) show significantly improved survival outcome compared with those with HPV-negative (HPV-) tumors. Published data examining this difference offers conflicting results to date. We systematically investigated the radiation sensitivity of all available validated HPV+ HNC cell lines and a series of HPV- HNC cell lines using in vitro and in vivo techniques. HPV+ HNCs exhibited greater intrinsic radiation sensitivity (average SF2 HPV-: 0.59 vs. HPV+: 0.22; P < 0.0001), corresponding with a prolonged G2-M cell-cycle arrest and increased apoptosis following radiation exposure (percent change 0% vs. 85%; P = 0.002). A genome-wide microarray was used to compare gene expression 24 hours following radiation between HPV+ and HPV- cell lines. Multiple genes in TP53 pathway were upregulated in HPV+ cells (Z score 4.90), including a 4.6-fold increase in TP53 (P < 0.0001). Using immortalized human tonsillar epithelial (HTE) cells, increased radiation sensitivity was seen in cell expressing HPV-16 E6 despite the effect of E6 to degrade p53. This suggested that low levels of normally functioning p53 in HPV+ HNC cells could be activated by radiation, leading to cell death. Consistent with this, more complete knockdown of TP53 by siRNA resulted in radiation resistance. These results provide clear evidence, and a supporting mechanism, for increased radiation sensitivity in HPV+ HNC relative to HPV- HNC. This issue is under active investigation in a series of clinical trials attempting to de-escalate radiation (and chemotherapy) in selected patients with HPV+ HNC in light of their favorable overall survival outcome.

Dual targeting of EGFR and HER3 with MEHD7945A overcomes acquired resistance to EGFR inhibitors and radiation.

EGF receptor (EGFR) inhibition is efficacious in cancer therapy, but initially sensitive tumors often develop resistance. In this study, we investigated the potential to overcome acquired resistance to EGFR inhibitors with MEHD7945A, a monoclonal antibody that dually targets EGFR and HER3 (ErbB3). In cancer cells resistant to cetuximab and erlotinib, we found that MEHD7945A, but not single target EGFR inhibitors, could inhibit tumor growth and cell-cycle progression in parallel with EGFR/HER3 signaling pathway modulation. MEHD7945A was more effective than a combination of cetuximab and anti-HER3 antibody at inhibiting both EGFR/HER3 signaling and tumor growth. In human tumor xenograft models, we confirmed the greater antitumor potency of MEHD7945A than cetuximab or erlotinib. MEHD7945A retained potent activity in tumors refractory to EGFR inhibitor alone. Furthermore, MEHD7945A also limited cross-resistance to radiation in EGFR inhibitor-resistant cells by modulating cell-cycle progression and repair processes that control apoptotic cell death. Taken together, our findings confirm an important role of compensatory HER3 signaling in the development of acquired resistance to EGFR inhibitors and offer preclinical proof-of-concept that MEHD7945A can effectively overcome EGFR inhibitor resistance.

Erlotinib is a viable treatment for tumors with acquired resistance to cetuximab.

The epidermal growth factor receptor (EGFR) is a ubiquitously expressed receptor tyrosine kinase (RTK) and is recognized as a key mediator of tumorigenesis in many human tumors. Currently there are five EGFR inhibitors used in oncology, two monoclonal antibodies (panitumumab, and cetuximab) and three tyrosine kinase inhibitors (erlotinib, gefitinib, and lapatinib). Both strategies of EGFR inhibition have demonstrated clinical successes, however many tumors remain non-responsive or acquire resistance during therapy. To explore potential molecular mechanisms of acquired resistance to cetuximab we previously established a series of cetuximab-resistant clones by chronically exposing the NCI-H226 NSCLC cell line to escalating doses of cetuximab. Cetuximab-resistant clones exhibited a dramatic increase in steady-state expression of EGFR, HER2, and HER3 receptors as well as increased signaling through the MAPK and AKT pathways. RNAi studies demonstrated dependence of cetuximab-resistant clones on the EGFR signaling network. These findings prompted investigation on whether or not cells with acquired resistance to cetuximab would be sensitive to the EGFR targeted TKI erlotinib. In vitro, erlotinib was able to decrease signaling through the EGFR axis, decrease cellular proliferation, and induce apoptosis. To determine if erlotinib could have therapeutic benefit in vivo, we established cetuximab-resistant NCI-H226 mouse xenografts, and subsequently treated them with erlotinib. Mice harboring cetuximab-resistant tumors treated with erlotinib exhibited either a tumor regression or growth delay as compared to vehicle controls. Analysis of the erlotinib treated tumors demonstrated a decrease in cell proliferation and increase rates of apoptosis. The work presented herein suggests that 1) cells with acquired resistance to cetuximab maintain their dependence on EGFR and 2) tumors developing resistance to cetuximab can benefit from subsequent treatment with erlotinib, providing rationale for its use in the setting of cetuximab resistance.