Inhibition of CXCR7 extends survival following irradiation of brain tumours in mice and rats.

BACKGROUND: In experimental models of glioblastoma multiforme (GBM), irradiation (IR) induces local expression of the chemokine CXCL12/SDF-1, which promotes tumour recurrence. The role of CXCR7, the high-affinity receptor for CXCL12, in the tumour's response to IR has not been addressed. METHODS: We tested CXCR7 inhibitors for their effects on tumour growth and/or animal survival post IR in three rodent GBM models. We used immunohistochemistry to determine where CXCR7 protein is expressed in the tumours and in human GBM samples. We used neurosphere formation assays with human GBM xenografts to determine whether CXCR7 is required for cancer stem cell (CSC) activity in vitro. RESULTS: CXCR7 was detected on tumour cells and/or tumour-associated vasculature in the rodent models and in human GBM. In human GBM, CXCR7 expression increased with glioma grade and was spatially associated with CXCL12 and CXCL11/I-TAC. In the rodent GBM models, pharmacological inhibition of CXCR7 post IR caused tumour regression, blocked tumour recurrence, and/or substantially prolonged survival. CXCR7 expression levels on human GBM xenograft cells correlated with neurosphere-forming activity, and a CXCR7 inhibitor blocked sphere formation by sorted CSCs. CONCLUSIONS: These results indicate that CXCR7 inhibitors could block GBM tumour recurrence after IR, perhaps by interfering with CSCs.

Evidence that cyclic AMP phosphodiesterase inhibitors suppress TNF alpha generation from human monocytes by interacting with a 'low-affinity' phosphodiesterase 4 conformer.

1. We have investigated the inhibitory effects of RP 73401 (piclamilast) and rolipram against human monocyte cyclic AMP-specific phosphodiesterase (PDE4) in relation to their effects on prostaglandin (PG)E2-induced cyclic AMP accumulation and lipopolysaccharide (LPS)-induced TNF alpha production and TNF alpha mRNA expression. 2. PDE4 was found to be the predominant PDE isoenzyme in the cytosolic fraction of human monocytes. Cyclic GMP-inhibited PDE (PDE3) was also detected in the cytosolic and particulate fractions. Reverse transcription polymerase chain reaction (RT-PCR) of human monocyte poly (A+) mRNA revealed amplified products corresponding to PDE4 subtypes A and B of which the former was most highly expressed. A faint band corresponding in size to PDE4D was also observed. 3. RP 73401 was a potent inhibitor of cytosolic PDE4 (IC50: 1.5 +/- 0.6 nM, n = 3). (+/-)-Rolipram (IC50: 313 +/- 6.7 nM, n = 3) was at least 200 fold less potent than RP 73401. R-(-)-rolipram was approximately 3 fold more potent than S-(+)-rolipram against cytosolic PDE4. 4. RP 73401 (IC50: 9.2 +/- 2.1 nM, n = 6) was over 50 fold more potent than (+/-)-rolipram (IC50: 503 +/- 134 nM, n = 6) ) in potentiating PGE2-induced cyclic AMP accumulation. R-(-)-rolipram (IC50: 289 +/- 121 nM, n = 5) was 4.7 fold more potent than its S-(+)-enantiomer (IC50: 1356 +/- 314 nM, n = 5). A strong and highly-significant, linear correlation (r = 0.95, P < 0.01, n = 13) was observed between the inhibitory potencies of a range of structurally distinct PDE4 inhibitors against monocyte PDE4 and their ED50 values in enhancing monocyte cyclic AMP accumulation. A poorer, though still significant, linear correlation (r = 0.67, P < 0.01, n = 13) was observed between the potencies of the same compounds in potentiating PGE2-induced monocyte cyclic AMP accumulation and their abilities to displace [3H]-rolipram binding to brain membranes. 5. RP 73401 (IC50: 6.9 +/- 3.3 nM, n = 5) was 71 fold more potent than (+/-)-rolipram (IC50: 490 +/- 260 nM, n = 4) in inhibiting LPS-induced TNF alpha release from monocytes. R-(-)-rolipram (IC50: 397 +/- 178 nM, n = 3) was 5.2-fold more potent than its S-(+)- enantiomer (IC50: 2067 +/- 659 nM, n = 3). As with cyclic AMP, accumulation a closer, linear correlation existed between the potency of structurally distinct compounds in suppressing TNF alpha with PDE4 inhibition (r = 0.93, P < 0.01, n = 13) than with displacement of [3H]-rolipram binding (r = 0.65, P < 0.01, n = 13). 6. RP 73401 (IC50: 2 nM) was 180 fold more potent than rolipram (IC50: 360 nM) in suppressing LPS (10 ng ml-1)-induced TNF alpha mRNA. 7. The results demonstrate that RP 73401 is a very potent inhibitor of TNF alpha release from human monocytes suggesting that it may have therapeutic potential in the many pathological conditions associated with over-production of this pro-inflammatory cytokine. Furthermore, PDE inhibitor actions on functional responses are better correlated with inhibition of PDE4 catalytic activity than displacement of [3H]-rolipram from its high-affinity binding site, suggesting that the native PDE4 in human monocytes exists predominantly in a 'low-affinity' state.