Metastasis and drug resistance are the major causes of mortality in patients with non-small cell lung cancer (NSCLC). Several receptor tyrosine kinases (RTKs), including AXL, are involved in the progression of NSCLC. The AXL/MER/SKY subfamily is involved in cell adhesion, motility, angiogenesis, and signal transduction and may play a significant role in the invasiveness of cancer cells. Notably, no specific inhibitors of AXL have been described. A series of CL1 sublines with progressive invasiveness established from a patient with NSCLC has been identified that positively correlates with AXL expression and resistance to chemotherapeutic drugs. The ectopic overexpression of AXL results in elevated cell invasiveness and drug resistance. Nuclear factor-KB (NF-KB) signaling activity is associated with AXL expression and may play an important role in the enhancement of invasiveness and doxorubicin resistance, as shown by using the NF-KB inhibitor, sulfasalazine, and IKB dominant-negative transfectants. In the current study, sulfasalazine exerted a synergistic anticancer effect with doxorubicin and suppressed cancer cell invasiveness in parallel in CL1 sublines and various AXL-expressing cancer cell lines. Phosphorylation of AXL and other RTKs (ErbB2 and epidermal growth factor receptor) was abolished by sulfasalazine within 15 min, suggesting that the inhibition of NF-KB and the kinase activity of RTKs are involved in the pharmacologic effects of sulfasalazine. Our study suggests that AXL is involved in NSCLC metastasis and drug resistance and may therefore provide a molecular basis for RTK-targeted therapy using sulfasalazine to enhance the efficacy of chemotherapy in NSCLC. [Cancer Res 2007;67(8):3878-87]

The complexity of chronic pain and the challenges of pharmacotherapy highlight the importance of development of new approaches to pain management. Gene therapy approaches may be complementary to pharmacotherapy for several advantages. Gene therapy strategies may target specific chronic pain mechanisms in a tissue-specific manner. The present collection of articles features distinct gene therapy approaches targeting specific mechanisms identified as important in the specific pain conditions. Dr. Fairbanks group describes commonly used gene therapeutics (herpes simplex viral vector (HSV) and adeno-associated viral vector (AAV)), and addresses biodistribution and potential neurotoxicity in pre-clinical models of vector delivery. Dr. Tao group addresses that downregulation of a voltage-gated potassium channel (Kv1.2) contributes to the maintenance of neuropathic pain. Alleviation of chronic pain through restoring Kv1.2 expression in sensory neurons is presented in this review. Drs Goins and Kinchington group describes a strategy to use the replication defective HSV vector to deliver two different gene products (enkephalin and TNF soluble receptor) for the treatment of post-herpetic neuralgia. Dr. Hao group addresses the observation that the pro-inflammatory cytokines are an important shared mechanism underlying both neuropathic pain and the development of opioid analgesic tolerance and withdrawal. The use of gene therapy strategies to enhance expression of the anti-pro-inflammatory cytokines is summarized. Development of multiple gene therapy strategies may have the benefit of targeting specific pathologies associated with distinct chronic pain conditions (by Guest Editors, Drs. C. Fairbanks and S. Hao).

Chronic pain is increasingly recognized as an important comorbidity of HIV-infected patients, however, the exact molecular mechanisms of HIV-related pain are still elusive. CCAAT/enhancer binding proteins (C/EBPs) are expressed in various tissues, including the CNS. C/EBPβ, one of the C/EBPs, is involved in the progression of HIV/AIDS, but the exact role of C/EBPβ and its upstream factors are not clear in HIV pain state. Here, we used a neuropathic pain model of perineural HIV envelope glycoprotein gp120 application onto the rat sciatic nerve to test the role of phosphorylated C/EBPβ (pC/EBPβ) and its upstream pathway in the spinal cord dorsal horn (SCDH). HIV gp120 induced overexpression of pC/EBPβ in the ipsilateral SCDH compared with contralateral SCDH. Inhibition of C/EBPβ using siRNA against C/EBPβ reduced mechanical allodynia. HIV gp120 also increased TNFα, TNFRI, mitochondrial superoxide (mtO), and pCREB in the ipsilateral SCDH. ChIP-qPCR assay showed that pCREB enrichment on the C/EBPβ gene promoter regions in rats with gp120 was higher than that in sham rats. Intrathecal TNF soluble receptor I (functionally blocking TNFα bioactivity) or knockdown of TNFRI using antisense oligodeoxynucleotide against TNFRI reduced mechanical allodynia, and decreased mtO, pCREB and pC/EBPβ. Intrathecal Mito-tempol (a mitochondria-targeted Oscavenger) reduced mechanical allodynia and decreased pCREB and pC/EBPβ. Knockdown of CREB with antisense oligodeoxynucleotide against CREB reduced mechanical allodynia and lowered pC/EBPβ. These results suggested that the pathway of TNFα/TNFRI-mtO-pCREB triggers pC/EBPβ in the HIV gp120-induced neuropathic pain state. Furthermore, we confirmed the pathway using both cultured neurons treated with recombinant TNFα and repeated intrathecal injection of recombinant TNFα in naive rats. This finding provides new insights in the understanding of the HIV neuropathic pain mechanisms and treatment. Painful HIV-associated sensory neuropathy is a neurological complication of HIV infection. Phosphorylated C/EBPβ (pC/EBPβ) influences AIDS progression, but it is still not clear about the exact role of pC/EBPβ and the detailed upstream factors of pC/EBPβ in HIV-related pain. In a neuropathic pain model of perineural HIV gp120 application onto the sciatic nerve, we found that pC/EBPβ was triggered by TNFα/TNFRI-mtO-pCREB signaling pathway. The pathway was confirmed by using cultured neurons treated with recombinant TNFα , and by repeated intrathecal injection of recombinant TNFα in naive rats. The present results revealed the functional significance of TNFα/TNFRI-mtO-pCREB-pC/EBPβ signaling in HIV neuropathic pain, and should help in the development of more specific treatments for neuropathic pain.

The symptoms of HIV-sensory neuropathy are dominated by neuropathic pain. Recent data show that repeated use of opiates enhances the chronic pain states in HIV patients. Limited attention has so far been devoted to exploring the exact pathogenesis of HIV painful disorder and opiate abuse in vivo, for which there is no effective treatment. Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal domain protein (BET) family and functions as a chromatin 'reader' that binds acetylated lysines in histones in brain neurons to mediate the transcriptional regulation underlying learning and memory. Here, we established a neuropathic pain model of interaction of intrathecal HIV envelope glycoprotein 120 (gp120) and chronic morphine in rats. The combination of gp120 and morphine (gp120/M, for 5 days) induced persistent mechanical allodynia compared with either gp120 or morphine alone. Mechanical allodynia reached the lowest values at day 10 from gp120/M application, beginning to recover from day 21. In the model, gp120/M induced overexpression of Brd4 mRNA and protein at day 10 using RT-qPCR and western blots, respectively. Immunohistochemical studies showed that Brd4 at day 10 was expressed in the neurons of spinal cord dorsal horn. BET inhibitor I-BET762 dose-dependently increased the mechanical threshold in the gp120/M pain state. The present study provides preclinical evidence for treating HIV neuropathic pain with opioids using the BET inhibitor.