Serum oxylipin profiles in IgA nephropathy patients reflect kidney functional alterations

Immunoglobulin A nephropathy (IgAN) is a leading cause of chronic kidney disease, frequently associated with hypertension and renal inflammation. ω-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fish oil (FO) improve kidney function in animal models, but have inconsistent metabolic effects in humans. Oxylipin profiles in serum from IgAN patients supplemented with either FO or corn oil (CO) placebo were analyzed by liquid chromatography coupled to tandem mass spectrometry. EPA cyclooxygenase and lipoxygenase metabolites, and EPA and DHA epoxides and diols were increased in response to FO supplementation, as were total epoxides and epoxide/diol ratios. Several of these metabolites were drivers of separation as assessed by multivariate analysis of FO patients pre- vs. post-supplementation, including 17,18-dihydroxyeicosatrienoic acid, prostaglandin D₃, prostagalandin E₃, Resolvin E1, 12-hydroxyeicosapentaenoic acid, and 10(11)-epoxydocosapentaenoic acid. In patients whose proteinuria improved, plasma total oxylipins as well as several hydroxyoctadecadienoic acids, hydroxyeicosatetraenoic acids, and leukotriene B₄ metabolites were among the metabolites that were significantly lower than in patients whose proteinuria either did not improve or worsened. These data support the involvement of oxylipins in the inflammatory component of IgAN as well as the potential use of oxylipin profiles as biomarkers and for assessing responsiveness to ω-3 fatty acid supplementation in IgAN patients.

New opportunities from the cancer metabolome

BACKGROUND

Metabolomics, the study of all metabolites produced in the body, which often includes flora and drug metabolites, is the omics approach that can be considered most closely related to a patient's phenotype. Metabolomics has a great and largely untapped potential in the field of oncology, and the analysis of the cancer metabolome to identify biofluid markers and novel druggable targets can now be undertaken in many research laboratories.

CONTENT

The cancer metabolome has been used to identify and begin to evaluate potential biomarkers and therapeutic targets in a variety of malignancies, including breast, prostate, and kidney cancer. We discuss the several standard techniques for metabolite separation and identification, with their potential problems and drawbacks. Validation of biomarkers and targets may entail intensive use of labor and technology and generally requires a large number of study participants as well as laboratory validation studies. The field of pharmacometabolomics, in which specific therapies are chosen on the basis of a patient's metabolomic profile, has shown some promise in the translation of metabolomics into the arena of personalized medicine.

SUMMARY

The relatively new approach using metabolomics has just begun to enter the mainstream of cancer diagnostics and therapeutics. As this field advances, metabolomics will take its well-deserved place next to genomics, transcriptomics, and proteomics in both clinical and basic research in oncology.

Urine dipstick analysis for identification of runners susceptible to acute kidney injury following an ultramarathon

This study examined whether urine dipstick testing might be useful to predict the development of acute kidney injury after an ultramarathon. Participants in the 2011 161-km Western States Endurance Run underwent post-race blood and urine dipstick analyses. Of the 310 race finishers, post-race urine dipstick testing was completed on 152 (49%) and post-race blood also was obtained from 150 of those runners. Based on "injury" and "risk" criteria for acute kidney injury of blood creatinine 2.0 and 1.5 times estimated baseline, respectively, 4% met the criteria for injury and an additional 29-30% met the criteria for risk of injury. Those meeting the injury criteria had higher creatine kinase concentrations (P < 0.001) than those not meeting the criteria. Urine dipstick tests that read positive for at least 1+ protein, 3+ blood, and specific gravity ≥ 1.025 predicted those meeting the injury criteria with sensitivity of 1.00 (95% confidence interval [CI] 0.54-1.00), specificity of 0.76 (95% CI 0.69-0.83), positive predictive value of 0.15 (95% CI 0.06-0.30), negative predictive value of 1.00 (95% CI 0.97-1.00), and likelihood ratio for a positive test of 4.2. We conclude that urine dipstick testing was successfully able to identify those individuals meeting injury criteria for acute kidney injury with excellent sensitivity and specificity.

Kidney tumor biomarkers revealed by simultaneous multiple matrix metabolomics analysis

Metabolomics is increasingly being used in cancer biology for biomarker discovery and identification of potential novel therapeutic targets. However, a systematic metabolomics study of multiple biofluids to determine their interrelationships and to describe their use as tumor proxies is lacking. Using a mouse xenograft model of kidney cancer, characterized by subcapsular implantation of Caki-1 clear cell human kidney cancer cells, we examined tissue, serum, and urine all obtained simultaneously at baseline (urine) and at, or close to, animal sacrifice (urine, tissue, and plasma). Uniform metabolomics analysis of all three "matrices" was accomplished using gas chromatography- and liquid chromatography-mass spectrometry. Of all the metabolites identified (267 in tissue, 246 in serum, and 267 in urine), 89 were detected in all 3 matrices, and the majority was altered in the same direction. Heat maps of individual metabolites showed that alterations in serum were more closely related to tissue than was urine. Two metabolites, cinnamoylglycine and nicotinamide, were concordantly and significantly (when corrected for multiple testing) altered in tissue and serum, and cysteine-glutathione disulfide showed the highest change (232.4-fold in tissue) of any metabolite. On the basis of these and other considerations, three pathways were chosen for biologic validation of the metabolomic data, resulting in potential therapeutic target identification. These data show that serum metabolomics analysis is a more accurate proxy for tissue changes than urine and that tryptophan degradation (yielding anti-inflammatory metabolites) is highly represented in renal cell carcinoma, and support the concept that PPAR-α antagonism may be a potential therapeutic approach for this disease.

Evaluation of selective inhibitors of nuclear export (SINE) CRM1 inhibitors for the treatment of renal cell carcinoma (RCC)

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Background: For the ~30% of patients who present with RCC at the metastatic stage, multi-kinase inhibitors have been used with moderate success: progression-free survival remains at only one to two years, and thus it is imperative to discover novel therapeutic approaches for metastatic disease. We asked whether (1) SINE inhibitors of chromosome region maintenance protein 1 (CRM1) attenuate key cell cycle regulatory and apoptotic molecules and whether these compounds exert salutary effects in a human RCC xenograft mouse model. Methods: Four RCC cell lines (ACHN, Caki-1, 786-O, and A498) with distinct genotypes, and primary normal human kidney (NHK) cell lines, were used in this study. The cells were treated with the chemically related SINE CRM1 inhibitors KPT-185 or 251 and MTT assays were performed. In addition, cell cycle analyses, immunofluorescence for p53 and p21, and immunoblotting for CRM1, p53, p21, p27, and p-MDM2 were performed for all cell lines. RCC mice with Caki-1 xenografts were treated with vehicle, the orally-available CRM1 inhibitor KPT-251, or sorafenib for 26 days. Tumor volume was measured over several days. Results: Both KPT185 and 251 specifically reduced CRM1 protein levels in RCC cells. KPT-185 caused dose-dependent cytotoxicity in RCC cells, which was greater than sorafenib in RCC cell lines but less in NHK cells, suggesting a possible clinical advantage of KPT-185 over sorafenib. By FACS analysis, we showed that KPT-185 arrests the cell cycle in both G2/M and G1, and increased the sub-G0 cell population. KPT-185 and 251 both increased p53 and p21 in RCC cells, and KPT-185 confined these proteins to the nucleus. In vivo, KPT-251 inhibited Caki-1 xenografts in mice compared to both vehicle and sorafenib without obvious systemic adverse effects. Conclusions: We introduce a completely novel therapeutic approach to the treatment of RCC based on inhibition of the nuclear export of key cell cycle regulatory proteins. Inhibition of CRM1 leads to forced nuclear retention, and thereby activation, of several key p53-pathway proteins, leading to cell cycle arrest and apoptosis in RCC cell lines in vitro and tumor growth inhibition in vivo.

Sorafenib attenuates p21 in kidney cancer cells and augments cell death in combination with DNA-damaging chemotherapy

There are few effective therapeutic options for metastatic renal cell carcinoma (RCC). Conventional chemotherapeutic agents are ineffective since these tumors are unusually resistant to DNA damage, likely due to an exuberant DNA repair response. Sorafenib, as one of the few available effective therapeutic options for metastatic RCC, has been shown to inhibit cell proliferation by inhibition of tyrosine kinases. We have recently shown that sorafenib inhibits soluble epoxide hydrolase, which catalyzes metabolism of the anti-inflammatory epoxyeicosatrienoic acids. Given previous work demonstrating the anti-apoptotic role of p21 in RCC as a potential mechanism for its drug resistance, we asked whether sorafenib signals through this pathway. We now show that sorafenib markedly decreases p21 levels in several RCC and hepatocellular carcinoma cells. Neither the MEK inhibitor PD98059 nor the sEH inhibitor t-AUCB, which represent known sorafenib-targeted signaling pathways, alter p21 levels, demonstrating that the p21 inhibitory effect of sorafenib is independent of these signaling cascades. In cells treated with doxorubicin to augment p21, sorafenib markedly decreases this protein, and the combinations of paclitaxel or doxorubicin with sorafenib show additive cytotoxicity as a function of the VHL status of the cells, suggesting that lower doses of each agent could be used in the clinical setting. In summary, we show a novel signaling pathway by which sorafenib exerts its salutary effects in RCC; future work will focus on the use of these drug combinations in the context of conventional therapeutics, and novel compounds and protocols targeting p21 in conjunction with sorafenib should be pursued.

Urinary acylcarnitines are altered in human kidney cancer

Kidney cancer often diagnosed at late stages when treatment options are severely limited. Thus, greater understanding of tumor metabolism leading ultimately to novel approaches to diagnosis is needed. Our laboratory has been utilizing metabolomics to evaluate compounds appearing in kidney cancer patients' biofluids at concentrations different from control patients. Here, we collected urine samples from kidney cancer patients and analyzed them by chromatography coupled to mass spectrometry. Once normalized to control for urinary concentration, samples were analyzed by two independent laboratories. After technical validation, we now show differential urinary concentrations of several acylcarnitines as a function of both cancer status and kidney cancer grade, with most acylcarnitines being increased in the urine of cancer patients and in those patients with high cancer grades. This finding was validated in a mouse xenograft model of human kidney cancer. Biological validation shows carbon chain length-dependent effects of the acylcarnitines on cytotoxicity in vitro, and higher chain length acylcarnitines demonstrated inhibitory effects on NF-κB activation, suggesting an immune modulatory effect of these compounds. Thus, acylcarnitines in the kidney cancer urine may reflect alterations in metabolism, cell component synthesis and/or immune surveillance, and may help explain the profound chemotherapy resistance seen with this cancer. This study shows for the first time the value of a novel class of metabolites which may lead to new therapeutic approaches for cancer and may prove useful in cancer biomarker studies. Furthermore, these findings open up a new area of investigation into the metabolic basis of kidney cancer.

Urine metabolomics for kidney cancer detection and biomarker discovery

Renal cell carcinoma (RCC) is one of the few human cancers whose incidence is increasing. The disease regularly progresses asymptomatically and is frequently metastatic upon presentation, thereby necessitating the development of an early method of detection. A metabolomic approach for biomarker detection using urine as a biofluid is appropriate since the tumor is located in close proximity to the urinary space. By comparing the composition of urine from individuals with RCC to control individuals, differences in metabolite composition of this biofluid can be identified, and these data can be utilized to create a clinically applicable and, possibly, bedside assay. Recent studies have shown that sample handling and processing greatly influences the variability seen in the urinary metabolome of both cancer and control patients. Once a standard method of collection is developed, identifying metabolic derangements associated with RCC will also lead to the investigation of novel targets for therapeutic intervention. The objective of this review is to discuss existing methods for sample collection, processing, data analysis, and recent findings in this emerging field.

CD4+ T cells from elite controllers resist HIV-1 infection by selective upregulation of p21

Elite controllers represent a unique group of HIV-1-infected persons with undetectable HIV-1 replication in the absence of antiretroviral therapy. However, the mechanisms contributing to effective viral immune defense in these patients remain unclear. Here, we show that compared with HIV-1 progressors and HIV-1-negative persons, CD4+ T cells from elite controllers are less susceptible to HIV-1 infection. This partial resistance to HIV-1 infection involved less effective reverse transcription and mRNA transcription from proviral DNA and was associated with strong and selective upregulation of the cyclin-dependent kinase inhibitor p21 (also known as cip-1 and waf-1). Experimental blockade of p21 in CD4+ T cells from elite controllers resulted in a marked increase of viral reverse transcripts and mRNA production and led to higher enzymatic activities of cyclin-dependent kinase 9 (CDK9), which serves as a transcriptional coactivator of HIV-1 gene expression. This suggests that p21 acts as a barrier against HIV-1 infection in CD4+ T cells from elite controllers by inhibiting a cyclin-dependent kinase required for effective HIV-1 replication. These data demonstrate a mechanism of host resistance to HIV-1 in elite controllers and may open novel perspectives for clinical strategies to prevent or treat HIV-1 infection.

Urine metabolomic analysis identifies potential biomarkers and pathogenic pathways in kidney cancer

Kidney cancer is the seventh most common cancer in the Western world, its incidence is increasing, and it is frequently metastatic at presentation, at which stage patient survival statistics are grim. In addition, there are no useful biofluid markers for this disease, such that diagnosis is dependent on imaging techniques that are not generally used for screening. In the present study, we use metabolomics techniques to identify metabolites in kidney cancer patients' urine, which appear at different levels (when normalized to account for urine volume and concentration) from the same metabolites in nonkidney cancer patients. We found that quinolinate, 4-hydroxybenzoate, and gentisate are differentially expressed at a false discovery rate of 0.26, and these metabolites are involved in common pathways of specific amino acid and energetic metabolism, consistent with high tumor protein breakdown and utilization, and the Warburg effect. When added to four different (three kidney cancer-derived and one "normal") cell lines, several of the significantly altered metabolites, quinolinate, α-ketoglutarate, and gentisate, showed increased or unchanged cell proliferation that was cell line-dependent. Further evaluation of the global metabolomics analysis, as well as confirmation of the specific potential biomarkers using a larger sample size, will lead to new avenues of kidney cancer diagnosis and therapy.

A metabolomics approach using juvenile cystic mice to identify urinary biomarkers and altered pathways in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and affects 1 in 1,000 individuals. Ultrasound is most often used to diagnose ADPKD; such a modality is only useful late in the disease after macroscopic cysts are present. There is accumulating evidence suggesting that there are common cellular and molecular mechanisms responsible for cystogenesis in human and murine PKD regardless of the genes mutated, and, in the case of complex metabolomic analysis, the use of a mouse model has distinct advantages for proof of principle over a human study. Therefore, in this study we utilized a urinary metabolomics-based investigation using gas chromatography-time of flight mass spectrometry to demonstrate that the cystic mouse can be discriminated from its wild-type counterpart by urine analysis alone. At day 26 of life, before there is serological evidence of kidney dysfunction, affected mice are distinguishable by urine metabolomic analysis; this finding persists through 45 days until 64 days, at which time body weight differences confound the results. Using functional score analysis and the KEGG pathway database, we identify several biologically relevant metabolic pathways which are altered very early in this disease, the most highly represented being the purine and galactose metabolism pathways. In addition, we identify several specific candidate biomarkers, including allantoic acid and adenosine, which are augmented in the urine of young cystic mice. These markers and pathway components, once extended to human disease, may prove useful as a noninvasive means of diagnosing cystic kidney diseases and to suggest novel therapeutic approaches. Thus, urine metabolomics has great diagnostic potential for cystic renal disorders and deserves further study.

Sorafenib has soluble epoxide hydrolase inhibitory activity, which contributes to its effect profile in vivo

The advent of multikinase inhibitors targeting the vascular endothelial growth factor (VEGF) receptor has revolutionized the treatment of highly angiogenic malignancies such as renal cell carcinoma. Interestingly, several such inhibitors are commercially available, and they each possess diverse specific beneficial and adverse effect profiles. In examining the structure of sorafenib, it was hypothesized that this compound would possess inhibitory effects on the soluble epoxide hydrolase, an enzyme with pleiotropic effects on inflammation and vascular disease. We now show that sorafenib but not another VEGF receptor targeted inhibitor sunitinib is a potent inhibitor of the human soluble epoxide hydrolase in vitro (K(I) = 17 +/- 4 nmol/L). Furthermore, sorafenib causes the expected in vivo shift in oxylipid profile resulting from soluble epoxide hydrolase inhibition, evidence of a reduction in the acute inflammatory response. Lipopolysaccharide-induced hypotension was reversed with sorafenib but not sunitinib treatment, suggesting that soluble epoxide hydrolase inhibition accounts for at least part of the anti-inflammatory effect of sorafenib. The pharmacokinetic studies presented here in light of the known potency of sorafenib as a soluble epoxide hydrolase inhibitor indicate that the soluble epoxide hydrolase will be largely inhibited at therapeutic doses of sorafenib. Thus, it is likely that soluble epoxide hydrolase inhibition contributes to the beneficial effects from the inhibition of the VEGF receptor and other kinases during treatment with sorafenib.

Grade-dependent proteomics characterization of kidney cancer

Kidney cancer is frequently metastatic on presentation at which point the disease is associated with a 95% mortality. Assessment of tumor grade on pathological examination is the most powerful means for prognostication as well as for stratification of patients into those who might respond to conventional or targeted therapy. Although there exist several grading systems in common use, all suffer from significant disparity among observers. In an attempt to objectify this process as well as to acquire grade-specific mechanistic information, we performed LC-MS/MS-based proteomics analysis on 50 clear cell kidney cancers equally distributed among normal tissues and Fuhrman grades 1-4. Initial experiments confirmed the utility of using archived formalin-fixed paraffin-embedded samples for LC-MS/MS-based proteomics analysis, and the LC-MS/MS findings were validated by extensive immunoblotting. We now show that changes among many biochemical processes and pathways are strongly grade-dependent with the glycolytic and amino acid synthetic pathways highly represented. In addition, proteins relating to acute phase and xenobiotic metabolism signaling are highly represented. Self-organized mapping of proteins with similar patterns of expression led to the creation of a heat map that will be useful in grade characterization as well as in future research relating to oncogenic mechanisms and targeted therapies for kidney cancer.

High throughput screening of a small molecule one-bead-one-compound combinatorial library to identify attenuators of p21 as chemotherapy sensitizers

Kidney cancer is notoriously difficult to treat when metastatic due to its resistance to conventional chemotherapy. p21 is a cyclin kinase inhibitor which, in many tumor cell lines, conveys an antiapoptotic function through its induction by the DNA damage responsive p53 pathway, such that attenuation of p21 sensitizes several disparate cancer cell lines to DNA-damaging chemotherapy. Since clinical applications with therapeutic antisense and siRNA approaches are problematic, we sought to discover other methods to inhibit p21 which are more readily translatable to the clinic. Utilizing an on-bead enzyme-linked colorimetric binding assay, we screened a diverse one-bead-one-compound combinatorial small molecule library and identified 12 candidate compounds which bind p21. Each of the 12 candidate compounds was synthesized and tested individually and three ligands were found which had the highest p21 binding affinity and yielded similar chemical structure. These three compounds caused dose-dependent cytotoxicity as well as apoptosis when exposed to two RCC cell lines. In addition, these compounds sensitized cells to apoptosis when incubated with doxorubicin such that a lower dose of doxorubicin was required in the presence of the compounds for equivalent cell killing. Interestingly, a representative of the three compounds decreased p21 levels by specific induction of ubiquitin-dependent proteosome degradation. Thus, by high throughput screening of thousands of candidate small molecules, we have identified compounds which attenuate p21, cause RCC cell apoptosis and sensitize RCC cells to DNA-damaging chemotherapy. These compounds are currently being evaluated in in vivo assays as potential novel therapeutic for RCC.

Disparate effects of roscovitine on renal tubular epithelial cell apoptosis and senescence: implications for autosomal dominant polycystic kidney disease

BACKGROUND/AIMS

Control of apoptosis in autosomal dominant polycystic kidney disease (ADPKD) and in at least some cancers is likely regulated by the endogenous cyclin kinase inhibitor p21, levels of this protein being decreased in ADPKD and increased in many malignancies. The cyclin kinase inhibitor roscovitine has shown efficacy in treatment of murine PKD. We asked how a single agent can be efficacious in both PKD and cancer.

METHODS

Renal tubular epithelial cells were incubated at diverse roscovitine concentrations; apoptosis and senescence were measured. Subsequently, levels of pro- and antiapoptotic proteins were evaluated.

RESULTS

Renal tubular epithelial cells exposed to 'low' concentrations of roscovitine showed minimal apoptosis in association with markedly increased levels of the antiapoptotic protein p21, and these cells became senescent. Conversely, cells exposed to 'high' levels of roscovitine became apoptotic. The mechanism of antiapoptosis and senescence with 'low'-dose roscovitine involves augmentation of the antiapoptotic proteins.

CONCLUSIONS

Data in this study provide a mechanistic explanation of how roscovitine is effective in PKD, and suggest that further study of this agent should focus on assessment of dose response. Furthermore, our discovery of senescence induced by a PKD effective drug suggests a new area of therapeutic investigation in this disease.

Urine metabolomics analysis for kidney cancer detection and biomarker discovery

Renal cell carcinoma (RCC) accounts for 11,000 deaths per year in the United States. When detected early, generally serendipitously by imaging conducted for other reasons, long term survival is generally excellent. When detected with symptoms, prognosis is poor. Under these circumstances, a screening biomarker has the potential for substantial public health benefit. The purpose of this study was to evaluate the utility of urine metabolomics analysis for metabolomic profiling, identification of biomarkers, and ultimately for devising a urine screening test for RCC. Fifty urine samples were obtained from RCC and control patients from two institutions, and in a separate study, urine samples were taken from 13 normal individuals. Hydrophilic interaction chromatography-mass spectrometry was performed to identify small molecule metabolites present in each sample. Cluster analysis, principal components analysis, linear discriminant analysis, differential analysis, and variance component analysis were used to analyze the data. Previous work is extended to confirm the effectiveness of urine metabolomics analysis using a larger and more diverse patient cohort. It is now shown that the utility of this technique is dependent on the site of urine collection and that there exist substantial sources of variation of the urinary metabolomic profile, although group variation is sufficient to yield viable biomarkers. Surprisingly there is a small degree of variation in the urinary metabolomic profile in normal patients due to time since the last meal, and there is little difference in the urinary metabolomic profile in a cohort of pre- and postnephrectomy (partial or radical) renal cell carcinoma patients, suggesting that metabolic changes associated with RCC persist after removal of the primary tumor. After further investigations relating to the discovery and identity of individual biomarkers and attenuation of residual sources of variation, our work shows that urine metabolomics analysis has potential to lead to a diagnostic assay for RCC.

Antisense attenuation of p21 sensitizes kidney cancer to apoptosis in response to conventional DNA damaging chemotherapy associated with enhancement of phospho-p53

PURPOSE

Kidney cancer is notoriously difficult to treat when metastatic due to its resistance to conventional chemotherapy. Thus, the 5-year survival rate in patients with metastatic renal cell carcinoma is less than 10% and novel approaches to treatment are needed. The cyclin kinase inhibitor p21 generally conveys an anti-apoptotic function through its induction by the DNA damage responsive p53 pathway. We capitalized on this function of p21 and used an antisense approach to sensitize p53-wt renal cell carcinoma cells to chemotherapy induced apoptosis by attenuating p21 protein levels.

MATERIALS AND METHODS

The human renal cell carcinoma cell lines ACHN and SN12C were transfected with antisense and control oligodeoxynucleotides. Assessment of p21 and apoptosis relevant protein levels as well as apoptosis was performed using standard techniques.

RESULTS

Pre-incubation of ACHN and SN12C cells with phosphorothioate antisense p21 oligodeoxynucleotide markedly attenuated p21 and sensitized cells to the apoptosis induced by doxorubicin and cisplatin, such that an order of magnitude less of doxorubicin or cisplatin could be used in the presence of antisense to achieve equivalent or greater cell death. In addition, the mechanism of ACHN cell death associated with p21 attenuation involved decreases in the levels of anti-apoptotic proteins as well as an increase in the active form of the pro-apoptotic protein p53.

CONCLUSIONS

Since phosphorothioate antisense oligodeoxynucleotides accumulate to a higher degree in the kidney and liver than in any other organ, our findings suggest a reevaluation of conventional chemotherapy in kidney cancer in association with antisense p21 oligodeoxynucleotide.

p21 is decreased in polycystic kidney disease and leads to increased epithelial cell cycle progression: roscovitine augments p21 levels

Background

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease with few treatment options other than renal replacement therapy. p21, a cyclin kinase inhibitor which has pleiotropic effects on the cell cycle, in many cases acts to suppress cell cycle progression and to prevent apoptosis. Because defects in cell cycle arrest and apoptosis of renal tubular epithelial cells occur in PKD, and in light of earlier reports that polycystin-1 upregulates p21 and that the cyclin-dependent kinase inhibitor roscovitine arrests progression in a mouse model, we asked whether (1) p21 deficiency might underlie ADPKD and (2) the mechanism of the salutary roscovitine effect on PKD involves p21.

Methods

p21 levels in human and animal tissue samples as well as cell lines were examined by immunoblotting and/or immunohistochemisty. Apoptosis was assessed by PARP cleavage. p21 expression was attenuated in a renal tubular epithelial cell line by antisense methods, and proliferation in response to p21 attenuation and to roscovitine was assessed by the MTT assay.

Results

We show that p21 is decreased in human as well as a non-transgenic rat model of ADPKD. In addition, hepatocyte growth factor, which induces transition from a cystic to a tubular phenotype, increases p21 levels. Furthermore, attenuation of p21 results in augmentation of cell cycle transit in vitro. Thus, levels of p21 are inversely correlated with renal tubular epithelial cell proliferation. Roscovitine, which has been shown to arrest progression in a murine model of PKD, increases p21 levels and decreases renal tubular epithelial cell proliferation, with no affect on apoptosis.

Conclusion

The novelty of our study is the demonstration in vivo in humans and rat models of a decrement of p21 in cystic kidneys as compared to non-cystic kidneys. Validation of a potential pathogenetic model of increased cyst formation due to enhanced epithelial proliferation and apoptosis mediated by p21 suggests a mechanism for the salutary effect of roscovitine in ADPKD and supports further investigation of p21 as a target for future therapy.

Targeting the PI3K-Akt pathway in kidney cancer

Kidney cancer, or renal cell carcinoma, is a relatively rare malignancy but is metastatic at diagnosis in a third of patients; metastatic disease has a dismal prognosis. Conventional chemotherapy has been woefully inadequate, thus novel targets for 'designer' therapies are being actively evaluated. The PI3K-Akt signaling cascade, owing to its dual role in both survival and mitogenic signaling, is in theory an ideal therapeutic target for this disease, but may also represent its fatal flaw. Thus, largely due to toxicity issues, no PI3K or Akt inhibitors are currently ready for clinical application. In this review, we discuss PI3K-Akt inhibitors as well as inhibitors of pathways and targets both immediately up- and downstream of this cascade, many of which show promise in the clinic.

Attenuation of PTEN increases p21 stability and cytosolic localization in kidney cancer cells: a potential mechanism of apoptosis resistance

BACKGROUND

The PTEN (Phosphatase and Tensin homolog deleted on chromosome Ten) tumor suppressor gene is frequently mutated or deleted in a wide variety of solid tumors, and these cancers are generally more aggressive and difficult to treat than those possessing wild type PTEN. While PTEN lies upstream of the phosphoinositide-3 kinase signaling pathway, the mechanisms that mediate its effects on tumor survival remain incompletely understood. Renal cell carcinoma (RCC) is associated with frequent treatment failures (approximately 90% in metastatic cases), and these tumors frequently contain PTEN abnormalities.

RESULTS

Using the ACHN cell line containing wild type PTEN, we generated a stable PTEN knockdown RCC cell line using RNA interference. We then used this PTEN knockdown cell line to show that PTEN attenuation increases resistance to cisplatin-induced apoptosis, a finding associated with increased levels of the cyclin kinase inhibitor p21. Elevated levels of p21 result from stabilization of the protein, and they are dependent on the activities of phosphoinositide-3 kinase and Akt. More specifically, the accumulation of p21 occurs preferentially in the cytosolic compartment, which likely contributes to both cell cycle progression and resistance to apoptosis.

CONCLUSION

Since p21 regulates a decision point between repair and apoptosis after DNA damage, our data suggest that p21 plays a key role in mechanisms used by PTEN-deficient tumors to escape chemotherapy. This in turn raises the possibility to use p21 attenuators as chemotherapy sensitizers, an area under active continuing investigation in our laboratories.

A comprehensive urinary metabolomic approach for identifying kidney cancerr

The diagnosis of cancer by examination of the urine has the potential to improve patient outcomes by means of earlier detection. Due to the fact that the urine contains metabolic signatures of many biochemical pathways, this biofluid is ideally suited for metabolomic analysis, especially involving diseases of the kidney and urinary system. In this pilot study, we test three independent analytical techniques for suitability for detection of renal cell carcinoma (RCC) in urine of affected patients. Hydrophilic interaction chromatography (HILIC-LC-MS), reversed-phase ultra performance liquid chromatography (RP-UPLC-MS), and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) all were used as complementary separation techniques. The combination of these techniques is best suited to cover a very large part of the urine metabolome by enabling the detection of both lipophilic and hydrophilic metabolites present therein. In this study, it is demonstrated that sample pretreatment with urease dramatically alters the metabolome composition apart from removal of urea. Two new freely available peak alignment methods, MZmine and XCMS, are used for peak detection and retention time alignment. The results are analyzed by a feature selection algorithm with subsequent univariate analysis of variance (ANOVA) and a multivariate partial least squares (PLS) approach. From more than 2000 mass spectral features detected in the urine, we identify several significant components that lead to discrimination between RCC patients and controls despite the relatively small sample size. A feature selection process condensed the significant features to less than 30 components in each of the data sets. In future work, these potential biomarkers will be further validated with a larger patient cohort. Such investigation will likely lead to clinically applicable assays for earlier diagnosis of RCC, as well as other malignancies, and thereby improved patient prognosis.