AMPA receptor and metabotropic glutamate receptor 1 adaptations in the nucleus accumbens core during incubation of methamphetamine craving.

Cue-induced drug craving progressively intensifies after withdrawal from self-administration of cocaine, methamphetamine, and other drugs of abuse, a phenomenon termed incubation of craving. For cocaine and methamphetamine, expression of incubated craving ultimately depends on strengthening of nucleus accumbens (NAc) synapses through an accumulation of high conductance Ca2+-permeable AMPA receptors (CP-AMPARs) that is detectable with electrophysiological approaches. This study sought to further characterize glutamate receptor adaptations in NAc core during methamphetamine incubation. Previous biochemical studies revealed that the CP-AMPARs accumulating after cocaine incubation are mainly homomeric GluA1 receptors and that their accumulation is reflected by increased cell surface GluA1. Here, for methamphetamine, we observed no significant change in surface or total GluA1 (GluA2 and GluA3 were also unchanged). Nonetheless, GluA1 translation was elevated after incubation of methamphetamine craving, as recently found for cocaine. Additionally, for cocaine, we previously observed a withdrawal-dependent decrease in mGlu1 surface expression that precedes and enables CP-AMPAR accumulation and incubation of craving, reflecting weakening of mGlu1-dependent mechanisms that normally limit synaptic CP-AMPAR levels in the NAc core. Here, we observed no change in surface or total mGlu1 protein or its coupling to Homer scaffolding proteins after methamphetamine withdrawal, nor did elevation of mGlu1 tone through repeated injections of an mGlu1-positive allosteric modulator delay incubation of craving. These findings suggest a common role for increased GluA1 translation, but not decreased mGlu1 function, in the incubation of methamphetamine and cocaine craving. We speculate that increased GluA1 translation near synapses may drive formation and synaptic insertion of homomeric GluA1 receptors in the absence of detectable changes in GluA1 protein levels.

AMPA Receptor Plasticity in Accumbens Core Contributes to Incubation of Methamphetamine Craving.

BACKGROUND: The incubation of cue-induced drug craving in rodents provides a model of persistent vulnerability to craving and relapse in human addicts. After prolonged withdrawal, incubated cocaine craving depends on strengthening of nucleus accumbens (NAc) core synapses through incorporation of Ca2+-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (CP-AMPARs). Through metabotropic glutamate receptor 1 (mGluR1)-mediated synaptic depression, mGluR1 positive allosteric modulators remove CP-AMPARs from these synapses and thereby reduce cocaine craving. This study aimed to determine if similar plasticity accompanies incubation of methamphetamine craving. METHODS: Rats self-administered saline or methamphetamine under extended-access conditions. Cue-induced seeking tests demonstrated incubation of methamphetamine craving. After withdrawal periods ranging from 1 to >40 days, rats underwent one of the following procedures: 1) whole-cell patch clamp recordings to characterize AMPAR transmission, 2) intra-NAc core injection of the CP-AMPAR antagonist 1-naphthyl acetyl spermine followed by a seeking test, or 3) systemic administration of a mGluR1 positive allosteric modulator followed by a seeking test. RESULTS: Incubation of methamphetamine craving was associated with CP-AMPAR accumulation in NAc core, and both effects were maximal after ~1 week of withdrawal. Expression of incubated craving was decreased by intra-NAc core 1-naphthyl acetyl spermine injection or systemic mGluR1 positive allosteric modulator administration. CONCLUSIONS: These results are the first to demonstrate a role for the NAc in the incubation of methamphetamine craving and describe adaptations in synaptic transmission associated with this model. They establish that incubation of craving and associated CP-AMPAR plasticity occur much more rapidly during withdrawal from methamphetamine compared with cocaine. However, a common mGluR1-based therapeutic strategy may be helpful for recovering cocaine and methamphetamine addicts.

Non-oncogenic Acute Viral Infections Disrupt Anti-cancer Responses and Lead to Accelerated Cancer-Specific Host Death.

In light of increased cancer prevalence and cancer-specific deaths in patients with infections, we investigated whether infections alter anti-tumor immune responses. We report that acute influenza infection of the lung promotes distal melanoma growth in the dermis and leads to accelerated cancer-specific host death. Furthermore, we show that during influenza infection, anti-melanoma CD8+ T cells are shunted from the tumor to the infection site, where they express high levels of the inhibitory receptor programmed cell death protein 1 (PD-1). Immunotherapy to block PD-1 reverses this loss of anti-tumor CD8+ T cells from the tumor and decreases infection-induced tumor growth. Our findings show that acute non-oncogenic infection can promote cancer growth, raising concerns regarding acute viral illness sequelae. They also suggest an unexpected role for PD-1 blockade in cancer immunotherapy and provide insight into the immune response when faced with concomitant challenges.

NK cells and CD8+ T cells cooperate to improve therapeutic responses in melanoma treated with interleukin-2 (IL-2) and CTLA-4 blockade.

BACKGROUND: Melanoma is one of the few types of cancer with an increasing annual incidence. While a number of immunotherapies for melanoma have been associated with significant clinical benefit, including high-dose IL-2 and cytotoxic T lymphocyte antigen 4 (CTLA-4) blockade, clinical response to either of these single agents has been limited to 11-20% of treated patients. Therefore, in this study, we sought to test the hypothesis that the combination of IL-2 and CTLA-4 blockade could mediate a more profound therapeutic response. METHODS: Here, B6 mice were challenged with poorly immunogenic B16 melanoma on day 0, and treated with CTLA-4 blocking antibody (100 µg/mouse) on days 3, 6, and 9, and IL-2 (100,000 units) twice daily on days 4-8, or both. RESULTS: A highly significant synergistic effect that delayed tumor growth and prolonged survival was demonstrated with the combination immunotherapy compared to either monotherapy alone. The therapeutic effect of combination immunotherapy was dependent on both CD8+ T and NK cells and co-depletion of these subsets (but not either one alone) abrogated the therapeutic effect. CTLA-4 blockade increased immune cell infiltration (including CD8+ T cells and NK cells) in the tumor and IL-2 reduced the proportion of highly differentiated/exhausted tumor-infiltrating NK cells. CONCLUSIONS: These results have implications for the design of clinical trials in patients with metastatic melanoma and provide new insights into how the immune system may be mediating anti-tumor activity with combination IL-2 and CTLA-4 blockade in melanoma.