Tumor penetration and epidermal growth factor receptor saturation by panitumumab correlate with antitumor activity in a preclinical model of human cancer.

BACKGROUND: Successful treatment of solid tumors relies on the ability of drugs to penetrate into the tumor tissue. METHODS: We examined the correlation of panitumumab (an anti-epidermal growth factor [EGFR] antibody) tumor penetration and EGFR saturation, a potential obstacle in large molecule drug delivery, using pharmacokinetics, pharmacodynamics, and tumor growth rate in an A431 epidermoid carcinoma xenograft model of human cancer. To determine receptor saturation, receptor occupancy, and levels of proliferation markers, immunohistochemical and flow cytometric methods were used. Pharmacokinetic data and modeling were used to calculate growth characteristics of panitumumab-treated tumors. RESULTS: Treatment with panitumumab in vivo inhibited pEGFR, Ki67 and pMAPK levels vs control. Tumor penetration and receptor saturation were dose- and time-dependent, reaching 100% and 78%, respectively. Significant tumor inhibition and eradication (p < 0.05) were observed; plasma concentration associated with tumor eradication was estimated to be 0.2 µg/ml. The tumor inhibition model was able to describe the mean tumor growth and death rates. CONCLUSIONS: These data demonstrate that the antitumor activity of panitumumab correlates with its ability to penetrate into tumor tissue, occupy and inhibit activation of EGFR, and inhibit markers of proliferation and MAPK signaling.

Activity of panitumumab alone or with chemotherapy in non-small cell lung carcinoma cell lines expressing mutant epidermal growth factor receptor.

Epidermal growth factor receptor (EGFR) kinase domain mutations cause hyperresponsiveness to ligand and hypersensitivity to small-molecule tyrosine kinase inhibitors. However, little is known about how these mutations respond to antibodies against EGFR. We investigated the activity of panitumumab, a fully human anti-EGFR monoclonal antibody, in vitro in mutant EGFR-expressing non-small cell lung carcinoma (NSCLC) cells and in vivo with chemotherapy in xenograft models. Mutant EGFR-expressing NSCLC cells (NCI-H1975 [L858R+T790M] and NCI-H1650 [Delta746-750]) and CHO cells were treated with panitumumab before EGF stimulation to assess the inhibition of EGFR autophosphorylation. Established tumors were treated with panitumumab (25, 100, or 500 mug/mouse twice a week) alone or with docetaxel (10 or 20 mg/kg once a week) or cisplatin (7.5 mg/kg once a week). Antitumor activity and levels of proliferation markers were analyzed. Treatment of mutant EGFR-expressing CHO and NSCLC cells with panitumumab inhibited ligand-dependent autophosphorylation. In NCI-H1975 and NCI-H1650 xenografts, treatment with panitumumab alone or with cisplatin inhibited tumor growth compared with control (P < 0.0003). With panitumumab plus docetaxel, enhanced antitumor activity was seen in both xenografts versus panitumumab alone. Panitumumab treatment alone decreased Ki-67 and phospho- mitogen-activated protein kinase (pMAPK) staining in both xenografts compared with control. Docetaxel enhanced panitumumab activity in NCI-H1650 xenografts (decreased Ki-67 and pMAPK staining by >60%) when compared with either agent alone. Panitumumab inhibits ligand-induced EGFR phosphorylation, tumor growth, and markers of proliferation alone or with docetaxel in NSCLC cell lines that express clinically observed EGFR kinase domain mutations, including the small-molecule tyrosine kinase inhibitor-resistant T790M mutation.

Securin is overexpressed in breast cancer.

Securin regulates sister chromatid separation during mitosis, induces bFGF-mediated angiogenesis, and securin overexpression causes in vitro transformation and in vivo tumor formation in nude mice. As estrogen administration to oophorectomized rats increased pituitary securin expression, we used immunohistochemistry to examine securin and estrogen receptor alpha (ER-alpha) expression in 90 breast tumors and 18 normal breast tissues. Breast tumor securin and ER-alpha expression were quantitated by image analysis and expressed as fold difference relative to securin expression in normal breast tissue. Low cytoplasmic securin expression was seen in the normal breast epithelium, whereas abundant cytoplasmic and nuclear securin expression was demonstrated in all 90 breast tumors. Highest securin expression was seen in brain metastatic breast tumors (4.3-fold, P<0.01), cells derived from metastatic breast cancers (6.5-fold, P<0.001), and in invasive ductal carcinoma (mean+/-s.e.: 3.8-fold, P<0.001). Highly pleomorphic (4.1-fold) or highly proliferative breast tumors (1.6-fold) exhibited high immunohistochemical securin expression compared to low-grade breast tumors (P<0.05). Northern blot analysis in 12 of the breast tumors confirmed the immunohistochemical findings demonstrating increased securin mRNA expression compared to normal breast mucosa (2.5-fold, P=0.03), with highest securin evident in invasive (3.5-fold) vs noninvasive tumors (1.9-fold, P=0.03). In addition, some tumors that exhibited high securin expression also expressed high ER-alpha levels (P<0.0001). These results demonstrate that the estrogen-induced transforming gene, securin is abundantly expressed in breast carcinoma, and is associated with the presence of metastatic spread, and lymph node invasion. We propose immunohistochemical tumor securin expression as a potential invasive marker, and novel therapeutic target in breast cancer.