Utilizing CD44v6 and V600EBRAF-mutation for in vitro targeted combination therapy of thyroid carcinomas.

Aim: The aim of this study was to assess the feasibility of targeted therapy of thyroid carcinoma, first exploring potential targets BRAF, EGFR and CD44v6 in patient material through immunohistochemistry and mutation analysis. Materials and methods: A patient cohort (n = 22) consisting of seven papillary (PTC), eight anaplastic (ATC) and seven follicular (FTC) thyroid carcinomas were evaluated. Additionally, eight thyroid carcinoma cells lines were analyzed for CD44v6-expression and sensitivity to the multi-kinase inhibitor sorafenib (Nexavar®), which targets numerous serine/threonine and tyrosine kinases, including the Raf family kinases. Targeted therapy using 131I-AbN44v6, a novel anti-CD44v6 antibody, and/or sorafenib was evaluated in 3D multicellular tumor spheroids. Results: Of the two cell surface proteins, EGFR and CD44v6, the latter was overexpressed in >80 % of samples, while EGFR-expression levels were moderate at best in only a few samples. BRAF mutations were more common in PTC patient samples than in ATC samples, while FTC samples did not harbor BRAF mutations. CD44v6-expression levels in the thyroid carcinoma cell lines were more heterogenous compared to patient samples, while BRAF mutational status was in line with the original tumor type. Monotherapy in 3D multicellular ATC tumor spheroids with either 131I-AbN44v6 or sorafenib resulted in delayed spheroid growth. The combination of 131I-AbN44v6 and sorafenib was the most potent and resulted in significantly impaired spheroid growth. Conclusion: This "proof of concept" targeted therapy study in the in vitro ATC 3D multicellular tumor spheroids indicated applicability of utilizing CD44v6 for molecular radiotherapy both as a monotherapy and in combination with sorafenib.

Characterization of CD44 variant expression in head and neck squamous cell carcinomas.

CD44 is a complex family of molecules, associated with aggressive malignancies and cancer stem cells. However, the role of CD44 variants in tumor progression and treatment resistance is not clear. In this study, the expression of CD44 and its variants was assessed in head and neck squamous cell carcinomas (HNSCC). Furthermore, subpopulations of cells expressing high amounts of CD44 variants were identified and characterized, for e.g., cell cycle phase and radioresistance. Results revealed high and homogenous CD44 and CD44v7 expression in four cell lines and CD44v4 and CD44v6 in three cell lines. CD44v3 was highly expressed in two cell lines, whereas CD44v5, CD44v7/8, CD44v10, CD133, and CD24 demonstrated no or moderate expression. Moreover, a subpopulation of very high CD44v4 expression was identified, which is independent of cell phase, demonstrating increased proliferation and radioresistance. In cell starvation experiments designed to enrich for cancer stem cells, a large population with dramatically increased expression of CD44, CD44v3, CD44v6, and CD44v7 was formed. Expression was independent of cell phase, and cells demonstrated increased radioresistance and migration rate. Our results demonstrate that the heterogeneity of tumor cells has important clinical implications for the treatment of HNSCC and that some of the CD44 variants may be associated with increased radioresistance. Highly expressed CD44 variants could make interesting candidates for selective cancer targeting.

A novel CD44v6 targeting antibody fragment with improved tumor-to-blood ratio.

The chimeric monoclonal antibody U36 (cMAb U36) recognizes the CD44v6 antigen. Its potential as a radioimmunotargeting agent, as well as its safety, has been shown in previous studies in head and neck cancer patients. However, intact MAbs have long circulation time in the blood and tumor targeting may also be hampered due to the slow and incomplete diffusion into solid tumors. In comparison, smaller monovalent Fab' and divalent F(ab')2 fragments are expected to exhibit shorter circulating half-lives, better tumor penetration and are thus more likely to yield better imaging results. In this study, novel F(ab')2 and Fab' fragments from cMAb U36 were radiolabeled with 125I and the characteristics of the conjugates in vitro were examined. The biodistribution of the conjugates were then evaluated in nude mice bearing CD44v6-expressing xenograft tumors. Furthermore, the penetration depth and distribution in tumor tissue was assessed by autoradiography in selected tumor samples. The in vitro experiments showed that the conjugates were stable and had intact affinity to CD44v6. The biodistribution study demonstrated superior tumor-to-blood ratio for the novel cMAb U36 fragment 125I-F(ab')2 compared with both the intact MAb and the monovalent fragment form. Autoradiography also revealed better tumor penetration for 125I-F(ab')2. This study demonstrates that the use of antibody fragments may improve radioimmunotargeting and possibly improve the management of head and neck malignancies.