The events of cell reproduction are governed by oscillations in the activities of cyclin-dependent kinases (Cdks). Cdks control the cell cycle by catalysing the transfer of phosphate from ATP to specific protein substrates. Despite their importance in cell-cycle control, few Cdk substrates have been identified. Here, we screened a budding yeast proteomic library for proteins that are directly phosphorylated by Cdk1 in whole-cell extracts. We identified about 200 Cdk1 substrates, several of which are phosphorylated in vivo in a Cdk1-dependent manner. The identities of these substrates reveal that Cdk1 employs a global regulatory strategy involving phosphorylation of other regulatory molecules as well as phosphorylation of the molecular machines that drive cell-cycle events. Detailed analysis of these substrates is likely to yield important insights into cell-cycle regulation.

In this study, we investigated the role of the peripheral endothelin-1 (ET-1) concentration in a cancer pain model. To test the hypothesis that the concentration of ET-1 in the tumor microenvironment is important in determining the level of cancer pain we used two cancer pain mouse models that differed significantly in production of ET-1. The two mouse cancer models were produced by injection of cells derived from a human oral squamous cell carcinoma (SCC) and melanoma into the hind paw of female mice. Pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, was significantly greater in the SCC group than the melanoma group. The peripheral concentration of ET-1 within the cancer microenvironment was significantly greater in the SCC group. Intra-tumor expression of both ET-1 mRNA and ET-1 protein were significantly higher in the SCC model compared to the melanoma model. ET receptor antagonism was effective as an analgesic for cancer pain in the SCC model only. To address the potential confounding factor of tumor volume we evaluated the contribution of tumor volume to cancer pain in the two models. The mean volumes of the tumors in the melanoma group were significantly greater than the tumors in the SCC group. In both groups, the pain level correlated with tumor volume, but the correlation was stronger in the melanoma group. We conclude that ET-1 concentration is a determinant of the level of pain in a cancer pain mouse model and it is a more important factor than tumor volume in producing cancer pain. These results suggest that future treatment regimens for cancer pain directed at ET-1 receptor antagonism show promise and may be tumor type specific.

In this study we investigated the role of endothelin-1 (ET-1) and its peripheral receptor (ET-A) in carcinoma-induced pain in a mouse cancer pain model. Tumors were induced in the hind paw of female mice by local injection of cells derived from a human oral squamous cell carcinoma (SCC). Significant pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, began at four days after SCC inoculation and lasted to 28 days, the last day of measurement. Intra-tumor expression of both ET-1 mRNA and ET-1 protein were significantly upregulated compared to normal tissue, and local administration of the ET-A receptor selective antagonist, BQ-123 (100 microM) significantly elevated withdrawal thresholds, indicating the induction of an antinociceptive effect. These findings support the suggestion that ET-1 and ET-A receptors contribute to the severity of carcinoma-induced soft tissue cancer pain.

We investigated the cannabinoid receptor (CBr) agonists Win55,212-2 (non-selective) and AM1241 (CBr2 selective) and the peripheral receptor (CBr1) in carcinoma-induced pain using a mouse model. Tumors were induced in the hind paw of female mice by local injection of a human oral squamous cell carcinoma (SCC). Significant pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, began at four days after SCC inoculation and lasted to 18 days. Local administration of Win55,212-2 (10 mg/kg) and AM1241 (10 mg/kg) significantly elevated withdrawal thresholds, indicating an antinociceptive effect. Ipsilateral expression of CBr1 protein in L5 DRG was significantly upregulated compared to ipsilateral L4 DRG and in normal tissue. These findings support the suggestion that cannabinoids are capable of producing antinociception in carcinoma-induced pain.

We previously reported that endothelin A (ET-A) receptor antagonism attenuates carcinoma-induced pain in a cancer pain mouse model. In this study, we investigated the mechanism of ET-A receptor-mediated antinociception and evaluated the role of endogenous opioid analgesia. Squamous cell carcinoma (SCC) cell culture treated with the ET-A receptor antagonist (BQ-123) at 10−6 M and 10−5 M significantly increased production and secretion of β-endorphin and leu-enkephalin, respectively. Behavioral studies were performed by inducing tumors in the hind paw of female nude mice with local injection of cells derived from a human oral SCC. Significant pain, as indicated by reduction in withdrawal thresholds in response to mechanical stimulation, began at four days after SCC inoculation and lasted to 18 days, the last day of measurement. Local administration of either naloxone methiodide (500 µg/kg), selective antagonists for µ-opioid receptor (CTOP, 500 µg/kg) or δ-opioid receptor (naltrindole, 11 mg/kg), but not κ-opioid receptor (nor-BNI, 2.5 mg/kg), significantly reversed antinociception observed from ET-A receptor antagonism (BQ-123, 92 mg/kg) in cancer animals. These results demonstrate that antagonism of peripheral endothelin-A receptor attenuates carcinoma pain by modulating release of endogenous opioids to act on opioid receptors in the cancer microenvironment.