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2012 EDUCATIONAL BOOK - American Society of Clinical Oncology

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EARLY ADVANCES IN SCCHN<br />

Fig 1. Targeting epidermal growth<br />

factor resistance in squamous cell carcinoma<br />

<strong>of</strong> the head and neck.<br />

Abbreviations: ERK, extracellular signalregulated<br />

kinase; mTOR, mammalian<br />

target <strong>of</strong> rapamycin; PI3K, phosphoinositide<br />

3-kinase; PTEN, phosphatase and<br />

tensin homolog.<br />

Targeting other<br />

receptor<br />

tyrosine kinases<br />

hibitors with specificities against EGFR, HER2, and HER4<br />

tyrosine kinases. In addition to targeting ErbB/HER family<br />

receptor crosstalk, both <strong>of</strong> these agents have reported activity<br />

against EGFRvIII in preclinical models. In a randomized,<br />

open-label phase II study <strong>of</strong> afatinib compared with cetxuimab<br />

in 124 platinum-refractory patients with recurrent or<br />

metastatic SCCHN, the objective response rate (ORR) favored<br />

afatinib compared with cetuximab (22% vs. 13%,<br />

respectively), as did the median progression-free survival<br />

(PFS; 16 weeks compared with 10 weeks, respectively). The<br />

most common adverse events related to afatinib included<br />

diarrhea and skin toxicity. 10 Afatinib is currently being<br />

evaluated in two phase III trials, including one in the<br />

recurrent or metastatic setting against methotrexate after<br />

progression with platinum-based chemotherapy (NCT-<br />

01345682), and the other in the locally advanced setting<br />

against placebo as maintenance therapy after completion <strong>of</strong><br />

definitive CRT; this latter trial (NCT01345669) is limited to<br />

only those patients whose tumors are HPV negative. Dacomitinib<br />

has undergone single-arm, open-label phase II<br />

evaluation as a first-line therapy in 69 patients with recurrent<br />

or metastatic SCCHN and reported an ORR <strong>of</strong> 11%,<br />

median PFS <strong>of</strong> 2.8 months, and median overall survival (OS)<br />

<strong>of</strong> 7.6 months. Similar to afatinib, diarrhea and skin toxicity<br />

were the most frequent treatment-related adverse events. 11<br />

HER3-targeting agents. HER3 has emerged to become a<br />

key target in the therapeutic strategy to overcome EGFR<br />

resistance. Despite its catalytically inactive tyrosine kinase<br />

domain, HER3 is capable <strong>of</strong> allosterically activating the<br />

kinase domain <strong>of</strong> its heterodimerized partners, preferably<br />

HER2. 12 In addition, phosphorylation <strong>of</strong> the C-terminal tail<br />

<strong>of</strong> HER3 leads to direct recruitment <strong>of</strong> the p85 subunit <strong>of</strong><br />

phosphoinositide 3-kinase (PI3K), rendering it a potent<br />

activator <strong>of</strong> the PI3K-AKT survival pathway. 13,14 Several<br />

HER3 targeting agents are undergoing or completing phase<br />

I development, including MEHD7945A (Genentech, Inc.,<br />

South San Francisco, CA), a humanized, dual-specific, immunoglobulin<br />

(Ig) G1 antibody capable <strong>of</strong> binding to both<br />

PI3K<br />

IRS<br />

Shc<br />

Grb2 Sos<br />

Targeting receptor<br />

tyrosine kinases e.g.<br />

HER family<br />

receptors<br />

TSC2 AKT<br />

PTEN Ras<br />

Targeting<br />

TSC1<br />

multiple<br />

nodes <strong>of</strong> the<br />

Targeting<br />

Raf<br />

same<br />

RHEB<br />

mTOR<br />

multiple<br />

oncogenic<br />

pathways<br />

(horizontal<br />

blockade)<br />

MEK<br />

1/2<br />

ERK<br />

1/2<br />

oncogenic<br />

pathway<br />

(vertical<br />

blockade)<br />

S6K 4E-BP<br />

Transcription<br />

Translation<br />

Growth, Proliferation, Metastasis, Survival<br />

EGFR and HER3 (NCT01207323) 15 ; MM-121/SAR256212<br />

(NCT00734305; Merrimack Pharmaceuticals Inc., Cambridge,<br />

MA and San<strong>of</strong>i <strong>Oncology</strong>, Paris, France) and U3-<br />

1287/AMG 888 (NCT00730470; U3 Pharma, Munich,<br />

Germany and Amgen, Inc., Thousand Oaks, CA), both fully<br />

human monoclonal antibodies directed against HER3;<br />

among others. In a recent report using a mouse monoclonal<br />

antibody (RTJ.2, Santa Cruz Biotechnology, Santa Cruz,<br />

CA; dilution 1:750) against HER3, immunohistochemical<br />

evaluation <strong>of</strong> 387 primary SCCHN specimens showed positive<br />

membranous and cytoplasmic HER3 expression in 34<br />

(8.8%) and 300 (77.5%) cases, respectively. Membranous<br />

HER3 overexpression was significantly associated with<br />

worse OS (p � 0.027) and was an independent prognostic<br />

factor in multivariate analysis. 16 In addition, Wilson and<br />

colleagues demonstrated that a substantial proportion <strong>of</strong><br />

primary SCCHN samples and cell lines have increased<br />

mRNA expression <strong>of</strong> the ligand heregulin, which in turn can<br />

lead to autocrine activation <strong>of</strong> HER3. 17 As such, heregulindriven<br />

tumors with coexpression and activation <strong>of</strong> HER3<br />

may represent a target SCCHN patient population for<br />

HER3-directed therapies.<br />

Targeting EGFR–Mitogen-Activated Protein Kinase and<br />

Other Oncogenic Pathways Concurrently<br />

In many advanced solid tumors, even among molecularly<br />

pr<strong>of</strong>iled patients whose tumors harbor activating mutations,<br />

the activity <strong>of</strong> selective pathway inhibitors administered as<br />

monotherapy appears limited, or in cases <strong>of</strong> initial response,<br />

the duration <strong>of</strong> response is typically short lived. Therapeutic<br />

resistance may occur as a result <strong>of</strong> incomplete pathway<br />

blockade with a single inhibitor, crosstalk and/or upregulation<br />

<strong>of</strong> compensatory escape signaling pathways. A logical<br />

approach to evade such mechanisms <strong>of</strong> resistance is by using<br />

targeted combinations with two agents either interrogating<br />

the same oncogenic signaling pathway (vertical blockade) or<br />

via concurrent modulation <strong>of</strong> two separate signaling pathways<br />

(horizontal blockade). Targeting other receptor ty-<br />

375

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