HER2 is a transmembrane oncoprotein encoded by the HER2/neu gene and is overexpressed in approximately 20 to 25% of invasive breast cancers. It can be therapeutically targeted by trastuzumab, a humanized IgG1 kappa light chain monoclonal antibody. Although trastuzumab is currently considered one of the most effective treatments in oncology, a significant number of patients with HER2-overexpressing breast cancer do not benefit from it. Understanding the mechanisms of action and resistance to trastuzumab is therefore crucial for the development of new therapeutic strategies. This review discusses proposed trastuzumab mode of action as well as proposed mechanisms for resistance. Mechanisms for resistance are grouped into four main categories: (1) obstacles preventing trastuzumab binding to HER2; (2) upregulation of HER2 downstream signaling pathways; (3) signaling through alternate pathways; and (4) failure to trigger an immune-mediated mechanism to destroy tumor cells. These potential mechanisms through which trastuzumab resistance may arise have been used as a guide to develop drugs, presently in clinical trials, to overcome resistance. The mechanisms conferring trastuzumab resistance, when completely understood, will provide insight on how best to treat HER2-overexpressing breast cancer. The understanding of each mechanism of resistance is therefore critical for the educated development of strategies to overcome it, as well as for the development of tools that would allow definitive and efficient patient selection for each therapy. (Clin Cancer Res 2009;15(24):7479–91)

We hypothesized that chronic inhibition of epidermal growth factor receptor (EGFR) by cetuximab, a monoclonal anti-EGFR antibody, induces up-regulation of its ligands resulting in resistance and that microRNAs (miRs) play an important role in the ligand regulation in head and neck squamous cell carcinoma (HNSCC). Genome-wide changes in gene and miR expression were determined in cetuximab-sensitive cell line, SCC1, and its resistant derivative 1Cc8 using DNA microarrays and RT-PCR. The effects of differentially expressed EGFR ligands and miRs were examined by MTS, colony formation, ELISA, and western blot assays. Heparin-binding EGF-like growth factor (HB-EGF) and its regulator, miR-212, were differentially expressed with statistical significance when SCC1 and 1Cc8 were compared for gene and miR expression. Stimulation with HB-EGF induced cetuximab resistance in sensitive cell lines. Inhibition of HB-EGF and the addition of miR-212 mimic induced cetuximab sensitivity in resistant cell lines. MicroRNA-212 and HB-EGF expression were inversely correlated in an additional 33 HNSCC and keratinocyte cell lines. Six tumors and 46 plasma samples from HNSCC patients were examined for HB-EGF levels. HB-EGF plasma levels were lower in newly diagnosed HNSCC patients when compared to patients with recurrent disease. Increased expression of HB-EGF due to down-regulation of miR-212 is a possible mechanism of cetuximab resistance. The combination of EGFR ligand inhibitors or miR modulators with cetuximab may improve the clinical outcome of cetuximab therapy in HNSCC.

Optical metabolic imaging measures fluorescence intensity and lifetimes from metabolic cofactors nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). These molecular level measurements provide unique biomarkers for early cellular responses to cancer treatments. Head and neck squamous cell carcinoma (HNSCC) is an attractive target for optical imaging because of easy access to the site using fiber optic probes. Two HNSCC cell lines, SCC25 and SCC61, were treated with Cetuximab (anti-EGFR antibody), BGT226 (PI3K/mTOR inhibitor), or cisplatin (chemotherapy) for 24 hours. Results show increased redox ratio, NADH α₁ (contribution from free NADH), and FAD α₁ (contribution from protein-bound FAD) for malignant cells compared with the nonmalignant cell line OKF6 (p<0.05). In SCC25 and SCC61 cells, the redox ratio is unaffected by cetuximab treatment and decreases with BGT226 and cisplatin treatment (p<0.05), and these results agree with standard measurements of proliferation rates after treatment. For SCC25, NADH α₁ is reduced with BGT226 and cisplatin treatment. For SCC61, NADH α₁ is reduced with cetuximab, BGT226, and cisplatin treatment. Trends in NADH α₁ are statistically similar to changes in standard measurements of glycolytic rates after treatment. FAD α₁ is reduced with cisplatin treatment (p<0.05). These shifts in optical endpoints reflect early metabolic changes induced by drug treatment. Overall, these results indicate that optical metabolic imaging has potential to detect early response to cancer treatment in HNSCC, enabling optimal treatment regimens and improved patient outcomes.

On the basis of the demonstrated single-agent activity of cisplatin in patients with advanced cervical cancer and the observation of in vitro synergism between this agent and decitabine, a new DNA hypomethylating agent, we designed a phase II trial in which the combined use of the two agents are used as first-line therapy in patients with recurrent and/or metastatic disease. Eligible patients were those with histopathologically proven diagnosis of squamous cell carcinoma of the cervix, which was not considered suitable for curative surgery and/or irradiation, having measurable disease, leukocyte counts more than or equal to 4,000/μl, thrombocyte counts more than or equal to 100,000/μl, serum creatinine more than or equal to 1.5 mg/dl, and normal liver function tests. Initial dose of cisplatin was 40 mg/m2, whereas decitabine was 50 mg/m2for 3 consecutive days every 21 days. Because of toxicity, the dose of cisplatin was reduced to 30 mg/m2. Twenty-five patients were included in the study; 24 of them were eligible for the evaluation of toxicity, whereas 21 of them were eligible for the evaluation of tumor responses. Nineteen (79.2%) patients had received prior radiotherapy. A total of 75 cycles of chemotherapy were administered to the patients, with a median of 3 cycles (range: 1–8) per patient. The most frequently observed side effect was neutropenia, which was National Cancer Institute- Common Toxicity Criteria grades III and IV in 68.0% of cases. One patient died of complications caused by drug-related neutropenic sepsis. The most common nonhematologic grades III and IV toxicities were nausea and vomiting, which occurred in 17.3% and 9.3% of the cycles, respectively. Of a total of 21 patients evaluable for tumor response, 8 (38.1%) achieved a partial response, whereas stable disease was documented in 5 cases (23.8%). Median progression-free interval (PFI) was 16 weeks, and median survival was 19 weeks (95% CI 7.9–31.2). Objective responses were more frequent in patients with metastatic lesions in nonirradiated sites. Cisplatin- decitabine combination was moderately active in patients with advanced squamous cell carcinoma of the cervix, mainly in patients presenting with metastatic disease at previously nonirradiated sites. However, this regimen produced significant hematologic toxicity. Further studies with this combination including a larger patient population, preferably with the concomitant administration of hematopoietic growth factors, are warranted.