It is essential to complete palate closure at the correct time during fetal development, otherwise a serious malformation, cleft palate, will ensue. The steps in palate formation in humans take place between the 7th and 12th week and consist of outgrowth of palatal shelves from the paired maxillary prominences, reorientation of the shelves from vertical to horizontal, apposition of the medial surfaces, formation of a bilayered seam, degradation of the seam and bridging of mesenchyme. However, in the soft palate, the mechanism of closure is unclear. In previous studies it is possible to find support for both fusion and the alternative mechanism of merging. Here we densely sample the late embryonic-early fetal period between 54 and 74 days post-conception to determine the timing and mechanism of soft palate closure. We found the epithelial seam extends throughout the soft palates of 57-day specimens. Cytokeratin antibody staining detected the medial edge epithelium and distinguished clearly that cells in the midline retained their epithelial character. Compared with the hard palate, the epithelium is more rapidly degraded in the soft palate and only persists in the most posterior regions at 64 days. Our results are consistent with the soft palate following a developmentally more rapid program of fusion than the hard palate. Importantly, the two regions of the palate appear to be independently regulated and have their own internal clocks regulating the timing of seam removal. Considering data from human genetic and mouse studies, distinct anterior-posterior signaling mechanisms are likely to be at play in the human fetal palate.

Epidemiologic and experimental evidence suggest that a subset of breast cancer is insulin responsive, but it is unclear whether safe and effective therapies that target the insulin receptor (IR), which is homologous to oncogenes of the tyrosine kinase class, can be developed. We demonstrate that both pharmacologic inhibition of IR family tyrosine kinase activity and insulin deficiency have antineoplastic activity in a model of insulin-responsive breast cancer. Unexpectedly, in contrast to insulin deficiency, pharmacologic IR family inhibition does not lead to significant hyperglycemia and is well tolerated. We show that pharmacokinetic factors explain the tolerability of receptor inhibition relative to insulin deficiency, as the small molecule receptor kinase inhibitor BMS-536924 does not accumulate in muscle at levels sufficient to block insulin-stimulated glucose uptake. Metformin, which lowers insulin levels only in settings of hyperinsulinemia, had minimal activity in this normoinsulinemic model. These findings highlight the importance of tissue-specific drug accumulation as a determinant of efficacy and toxicity of tyrosine kinase inhibitors and suggest that therapeutic targeting of the IR family for cancer treatment is practical.

Epidemiologic and experimental evidence suggest that a subset of breast cancer is insulin-responsive, but it is unclear if safe and effective therapies that target the insulin receptor can be developed. We demonstrate that both insulin receptor family tyrosine kinase inhibition and insulin deficiency have anti-neoplastic activity in a model of insulin-responsive breast cancer in mice metabolically normal at baseline. In contrast to insulin deficiency, insulin receptor inhibition does not lead to hyperglycemia and is well-tolerated. We show that pharmacokinetic factors explain the safety of receptor inhibition relative to ligand deficiency, as BMS-536924 does not accumulate in muscle at levels sufficient to block insulin-stimulated glucose uptake. Metformin, which lowers the elevated insulin levels present in settings of insulin resistance, had minimal activity in this model. The findings highlight the importance of tissue-specific drug accumulation as a determinant of efficacy and toxicity of tyrosine kinase inhibitors, and suggest that therapeutic targeting of the insulin receptor family for cancer treatment is practical. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2300. doi:10.1158/1538-7445.AM2011-2300

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In view of accumulating evidence that links hyperinsulinemia to aggressive cancer behavior, the insulin receptor tyrosine kinase has been viewed as a potentially important molecular target for certain cancers. To study the effects of attenuation of insulin signaling on the growth of the mouse 4T1 breast cancer model in vivo, we compared the effects of alloxan‐induced insulin deficiency to those of BMS‐536924, an inhibitor of the insulin and IGF‐I receptor kinases. Both interventions reduced AktSer473 phosphorylation in neoplastic tissue and significantly reduced tumor growth. Insulin deficiency led to reduced muscle AktSer473 phosphorylation, while BMS‐536924 led to hyperinsulinemia and increased muscle AktSer473 phosphorylation, a finding which correlated with significantly lower drug accumulation in muscle than in neoplastic tissue. We measured glucose uptake and utilization in muscle to determine if BMS‐536924 abolished insulin‐dependent glucose uptake. Our data indicate that insulin dependent glucose uptake by muscle remained intact. Thus, tissue‐specific distribution of BMS‐536924 may account for antineoplastic activity without severe metabolic toxicity, indicating that pharmacologic targeting of the insulin receptor in neoplastic disease may be practical. This work is supported by the McGill Integrated Cancer Research Training Program (MICRTP).