Hedgehog pathway blockade inhibits melanoma cell growth in vitro and in vivo.

Previous reports have demonstrated a role for hedgehog signaling in melanoma progression, prompting us to explore the therapeutic benefit of targeting this pathway in melanoma. We profiled a panel of human melanoma cell lines and control melanocytes for altered expression of hedgehog pathway members and determined the consequences of both genetic and pharmacological inhibition of the hedgehog pathway activator Smoothened (SMO) in melanoma, both in vitro and in vivo. We also examined the relationship between altered expression of hedgehog pathway mediators and survival in a well-characterized cohort of metastatic melanoma patients with prospectively collected follow up information. Studies revealed that over 40% of the melanoma cell lines examined harbored significantly elevated levels of the hedgehog pathway mediators SMO, GLI2, and PTCH1 compared to melanocytes (p < 0.05). SMO inhibition using siRNA and the small molecule inhibitor, NVP-LDE-225, suppressed melanoma growth in vitro, particularly in those cell lines with moderate SMO and GLI2 expression. NVP-LDE-225 also induced apoptosis in vitro and inhibited melanoma growth in a xenograft model. Gene expression data also revealed evidence of compensatory up-regulation of two other developmental pathways, Notch and WNT, in response to hedgehog pathway inhibition. Pharmacological and genetic SMO inhibition also downregulated genes involved in human embryonic stem cell pluripotency. Finally, increased SMO expression and decreased expression of the hedgehog pathway repressor GLI3 correlated with shorter post recurrence survival in metastatic melanoma patients. Our data demonstrate that hedgehog pathway inhibition might be a promising targeted therapy in appropriately selected metastatic melanoma patients.

Papular variant of annular elastolytic giant-cell granuloma.

A 53-year-old woman presented with a six-month history of non-pruritic, erythematous papules and papular-plaques that were localized to the anterior and lateral aspects of the neck. A biopsy specimen showed elastolysis and granuloma formation, which were consistent with a diagnosis of annular elastolytic giant-cell granuloma. This is one of the few reported cases of this entity that consists predominantly of papular lesions rather than annular plaques.

Chemical leukoderma.

Chemical leukoderma is defined as an acquired, hypopigmented dermatosis that results from repeated cutaneous application of an agent that destroys epidermal melanocytes in genetically susceptible patients. Chemical leukoderma may develop both at the site of contact with the chemical as well as remotely from the exposure. Avoidance of the causative agent may lead to spontaneous repigmentation, but treatments commonly used in vitiligo, such as narrow-band ultraviolet B phototherapy, PUVA photchemotherapy, or topical immunosuppressants, often are necessary. We present a case of chemical leukoderma secondary to pyrethroid insecticides that has progressed despite avoidance of the agent for over ten years.

Phosphorylated 4E-BP1 is associated with poor survival in melanoma.

PURPOSE: Both phosphatidylinositol 3-kinase/AKT and RAS/mitogen-activated protein kinase signal transduction pathways mediate 4E-BP1 phosphorylation, releasing 4E-BP1 from the mRNA cap and permitting translation initiation. Given the prevalence of PTEN and BRAF mutations in melanoma, we first examined translation initiation, as measured by phosphorylated 4E-BP1 (p-4E-BP1), in metastatic melanoma tissues and cell lines. We then tested the association between amounts of total and p-4E-BP1 and patient survival. EXPERIMENTAL DESIGN: Seven human metastatic melanoma cells lines and 72 metastatic melanoma patients with accessible metastatic tumor tissues and extended follow-up information were studied. Expression of 4E-BP1 transcript, total 4E-BP1 protein, and p-4E-BP1 was examined. The relationship between 4E-BP1 transcript and protein expression was assessed in a subset of patient tumors (n = 41). The association between total and p-4E-BP1 levels and survival was examined in the larger cohort of patients (n = 72). RESULTS: 4E-BP1 was hyperphosphorylated in 4 of 7 melanoma cell lines harboring both BRAF and PTEN mutations compared with untransformed melanocytes or RAS/RAF/PTEN wild-type melanoma cells. 4E-BP1 transcript correlated with 4E-BP1 total protein levels as measured by the semiquantitative reverse-phase protein array (P = 0.012). High levels of p-4E-BP1 were associated with worse overall and post-recurrence survival (P = 0.02 and 0.0003, respectively). CONCLUSION: Our data show that translation initiation is a common event in human metastatic melanoma and correlates with worse prognosis. Therefore, effective inhibition of the pathways responsible for 4E-BP1 phosphorylation should be considered to improve the treatment outcome of metastatic melanoma patients.

mTOR inhibition induces upstream receptor tyrosine kinase signaling and activates Akt.

Stimulation of the insulin and insulin-like growth factor I (IGF-I) receptor activates the phosphoinositide-3-kinase/Akt/mTOR pathway causing pleiotropic cellular effects including an mTOR-dependent loss in insulin receptor substrate-1 expression leading to feedback down-regulation of signaling through the pathway. In model systems, tumors exhibiting mutational activation of phosphoinositide-3-kinase/Akt kinase, a common event in cancers, are hypersensitive to mTOR inhibitors, including rapamycin. Despite the activity in model systems, in patients, mTOR inhibitors exhibit more modest antitumor activity. We now show that mTOR inhibition induces insulin receptor substrate-1 expression and abrogates feedback inhibition of the pathway, resulting in Akt activation both in cancer cell lines and in patient tumors treated with the rapamycin derivative, RAD001. IGF-I receptor inhibition prevents rapamycin-induced Akt activation and sensitizes tumor cells to inhibition of mTOR. In contrast, IGF-I reverses the antiproliferative effects of rapamycin in serum-free medium. The data suggest that feedback down-regulation of receptor tyrosine kinase signaling is a frequent event in tumor cells with constitutive mTOR activation. Reversal of this feedback loop by rapamycin may attenuate its therapeutic effects, whereas combination therapy that ablates mTOR function and prevents Akt activation may have improved antitumor activity.

The BAD protein integrates survival signaling by EGFR/MAPK and PI3K/Akt kinase pathways in PTEN-deficient tumor cells.

Tumor cells with mutated PTEN proliferate in an EGFR-independent manner. Induction of PTEN sensitizes cells to EGFR inhibition, and the combination causes synergistic apoptosis. Synergy is due to inhibition of two parallel pathways that phosphorylate the proapoptotic protein BAD at distinct sites. Serine 112 phosphorylation is EGFR/MEK/MAPK dependent, whereas serine 136 phosphorylation is PI3K/Akt dependent. Either phosphorylation is sufficient to sequester BAD to 14-3-3. BAD is released and apoptosis is induced only if both serines are dephosphorylated in response to inhibition of both pathways. Reduction of BAD expression by RNA interference prevents apoptosis in response to pathway inhibition. Thus, BAD integrates the antiapoptotic effects of both pathways. Combined inhibition of EGFR and PI3K signaling may be a useful therapeutic strategy.

Photo-caged agonists of the nuclear receptors RARgamma and TRbeta provide unique time-dependent gene expression profiles for light-activated gene patterning.

Light-activated gene expression systems hold promise as new tools for studying spatial and temporal gene patterning in multicellular systems. Photo-caged forms of nuclear receptor agonists have recently been shown to mediate photo-dependent transcription in mammalian cells, however, because intracellularly released agonists can rapidly diffuse out of cells, the photo-initiated transcription response is only transient and limited to only a few hours in reported examples. Herein we describe a photo-caged thyroid hormone receptor agonist that provides a robust 36 h transcription response to a single irradiation event. These findings are in contrast to a closely related system, which uses a caged retinoic acid receptor agonist, which provides only a short transcription response. Comparison of the two systems, show that the duration of transcription response is not controlled by the rate of diffusion of free ligand out of the cell, but perhaps by the duration of ligand-induced transcription/stability of the active transcription complex.