The sonic hedgehog (Shh) signaling pathway is a major regulator of cell differentiation, cell proliferation, and tissue polarity. Aberrant activation of the Shh pathway has been shown in a variety of human cancers, including, basal cell carcinoma, malignant gliomas, medulloblastoma, leukemias, and cancers of the breast, lung, pancreas, and prostate. Tumorigenesis, tumor progression and therapeutic response have all been shown to be impacted by the Shh signaling pathway. Downstream effectors of the Shh pathway include smoothened (SMO) and glioma-associated oncogene homolog (GLI) family of zinc finger transcription factors. Both are regarded as important targets for cancer therapeutics. While most efforts have been devoted towards pharmacologically targeting SMO, developing GLI-targeted approach has its merit because of the fact that GLI proteins can be activated by both Shh ligand-dependent and -independent mechanisms. To date, two SMO inhibitors (LDE225/Sonidegib and GDC-0449/Vismodegib) have received FDA approval for treating basal cell carcinoma while many clinical trials are being conducted to evaluate the efficacy of this exciting class of targeted therapy in a variety of cancers. In this review, we provide an overview of the biology of the Shh pathway and then detail the current landscape of the Shh-SMO-GLI pathway inhibitors including those in preclinical studies and clinical trials.

Approximately 100,000 primary and metastatic brain tumor patients/year in the US survive long enough (>6 months) to experience radiation-induced brain injury. Prior to 1970, the human brain was thought to be highly radioresistant; the acute CNS syndrome occurs after single doses >30 Gy; white matter necrosis occurs at fractionated doses >60 Gy. Although white matter necrosis is uncommon with modern techniques, functional deficits, including progressive impairments in memory, attention, and executive function have become important, because they have profound effects on quality of life. Preclinical studies have provided valuable insights into the pathogenesis of radiation-induced cognitive impairment. Given its central role in memory and neurogenesis, the majority of these studies have focused on the hippocampus. Irradiating pediatric and young adult rodent brains leads to several hippocampal changes including neuroinflammation and a marked reduction in neurogenesis. These data have been interpreted to suggest that shielding the hippocampus will prevent clinical radiation-induced cognitive impairment. However, this interpretation may be overly simplistic. Studies using older rodents, that more closely match the adult human brain tumor population, indicate that, unlike pediatric and young adult rats, older rats fail to show a radiation-induced decrease in neurogenesis or a loss of mature neurons. Nevertheless, older rats still exhibit cognitive impairment. This occurs in the absence of demyelination and/or white matter necrosis similar to what is observed clinically, suggesting that more subtle molecular, cellular and/or microanatomic modifications are involved in this radiation-induced brain injury. Given that radiation-induced cognitive impairment likely reflects damage to both hippocampal- and non-hippocampal-dependent domains, there is a critical need to investigate the microanatomic and functional effects of radiation in various brain regions as well as their integration at clinically relevant doses and schedules. Recently developed techniques in neuroscience and neuroimaging provide not only an opportunity to accomplish this, but they also offer the opportunity to identify new biomarkers and new targets for interventions to prevent or ameliorate these late effects.

Up to 30% of patients with metastatic breast cancer eventually develop brain metastasis, yet the pathologic mechanism behind this development remains poorly understood. Here, we profiled long noncoding RNAs in brain metastatic tumors from patients with breast cancer and found that the X-inactive-specific transcript (XIST) was significantly downregulated in these tissues. XIST expression levels inversely correlated with brain metastasis, but not with bone metastasis in patients. Silencing of XIST preferentially promoted brain metastatic growth of XIST cells in our xenograft models. Moreover, knockout of XIST in mice mammary glands accelerated primary tumor growth as well as metastases in the brain. Decreased expression of XIST stimulated epithelial-mesenchymal transition and activated c-Met via MSN-mediated protein stabilization, which resulted in the promotion of stemness in the tumor cells. Loss of XIST also augmented secretion of exosomal miRNA-503, which triggered M1-M2 polarization of microglia. This M1-M2 conversion upregulated immune suppressive cytokines in microglia that suppressed T-cell proliferation. Furthermore, we screened an FDA-approved drug library and identified fludarabine as a synthetic lethal drug for XIST breast tumor cells and found that fludarabine blocked brain metastasis in our animal model. Our results indicate that XIST plays a critical role in brain metastasis in breast cancer by affecting both tumor cells and the tumor microenvironment and that the XIST-mediated pathway may serve as an effective target for treating brain metastasis. These findings describe mechanisms of how loss of the lncRNA XIST promotes brain metastasis in breast cancer and identify fludarabine as a potential therapeutic agent that specifically eliminates XIST tumor cells in the brain. .

Activation of toll-like receptors (TLRs) on cells of the innate immune system initiates, amplifies, and directs the antigen-specific acquired immune response. Ligands that stimulate TLRs, therefore, represent potential immune adjuvants. In this study, a potent TLR7 agonist was conjugated to phospholipids, poly(ethylene glycol) (PEG), or phospholipid-PEG via a versatile benzoic acid functional group. Compared to the unmodified TLR7 agonist, each conjugate displayed a distinctive immunological profile in vitro and in vivo. In mouse macrophages and human peripheral blood mononuclear cells, the phospholipid TLR7 agonist conjugate was at least 100-fold more potent than the free TLR7 ligands, while the potency of PEG−phospholipid conjugate was similar to that of the unmodified TLR7 agonist. When administered systemically in mice, the phospholipid and phospholipid−PEG TLR7 conjugates induced prolonged increases in the levels of proinflammatory cytokines in serum, compared to the unmodified TLR7 activator. When the conjugates were used as adjuvants during vaccination, only the phospholipid TLR7 agonist conjugates induced both Th1 and Th2 antigen-specific immune responses. These data show that the immunostimulatory activity of a TLR7 ligand can be amplified and focused by conjugation, thus broadening the potential therapeutic application of these agents.

inosine monophosphate dehydrogenase ͉ IFN regulatory factor