Attenuating Adaptive VEGF-A and IL8 Signaling Restores Durable Tumor Control in AR Antagonist-Treated Prostate Cancers

Inhibiting androgen signaling using androgen signaling inhibitors (ASI) remains the primary treatment for castrate-resistant prostate cancer. Acquired resistance to androgen receptor (AR)-targeted therapy represents a major impediment to durable clinical response. Understanding resistance mechanisms, including the role of AR expressed in other cell types within the tumor microenvironment, will extend the clinical benefit of AR-targeted therapy. Here, we show the ASI enzalutamide induces vascular catastrophe and promotes hypoxia and microenvironment adaptation. We characterize treatment-induced hypoxia, and subsequent induction of angiogenesis, as novel mechanisms of relapse to enzalutamide, highlighting the importance of two hypoxia-regulated cytokines in underpinning relapse. We confirmed AR expression in CD34+ vascular endothelium of biopsy tissue and human vascular endothelial cells (HVEC). Enzalutamide attenuated angiogenic tubule formation and induced cytotoxicity in HVECs in vitro, and rapidly induced sustained hypoxia in LNCaP xenografts. Subsequent reoxygenation, following prolonged enzalutamide treatment, was associated with increased tumor vessel density and accelerated tumor growth. Hypoxia increased AR expression and transcriptional activity in prostate cells in vitro. Coinhibition of IL8 and VEGF-A restored tumor response in the presence of enzalutamide, confirming the functional importance of their elevated expression in enzalutamide-resistant models. Moreover, coinhibition of IL8 and VEGF-A resulted in a durable, effective resolution of enzalutamide-sensitive prostate tumors. We conclude that concurrent inhibition of two hypoxia-induced factors, IL8 and VEGF-A, prolongs tumor sensitivity to enzalutamide in preclinical models and may delay the onset of enzalutamide resistance.

IMPLICATIONS

Targeting hypoxia-induced signaling may extend the therapeutic benefit of enzalutamide, providing an improved treatment strategy for patients with resistant disease.

Targeting nucleotide metabolism enhances the efficacy of anthracyclines and anti-metabolites in triple-negative breast cancer

Triple-negative breast cancer (TNBC) remains the most lethal breast cancer subtype with poor response rates to the current chemotherapies and a lack of additional effective treatment options. We have identified deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) as a critical gatekeeper that protects tumour DNA from the genotoxic misincorporation of uracil during treatment with standard chemotherapeutic agents commonly used in the FEC regimen. dUTPase catalyses the hydrolytic dephosphorylation of deoxyuridine triphosphate (dUTP) to deoxyuridine monophosphate (dUMP), providing dUMP for thymidylate synthase as part of the thymidylate biosynthesis pathway and maintaining low intracellular dUTP concentrations. This is crucial as DNA polymerase cannot distinguish between dUTP and deoxythymidylate triphosphate (dTTP), leading to dUTP misincorporation into DNA. Targeting dUTPase and inducing uracil misincorporation during the repair of DNA damage induced by fluoropyrimidines or anthracyclines represents an effective strategy to induce cell lethality. dUTPase inhibition significantly sensitised TNBC cell lines to fluoropyrimidines and anthracyclines through imbalanced nucleotide pools and increased DNA damage leading to decreased proliferation and increased cell death. These results suggest that repair of treatment-mediated DNA damage requires dUTPase to prevent uracil misincorporation and that inhibition of dUTPase is a promising strategy to enhance the efficacy of TNBC chemotherapy.

Comparison of inhibitory neuromuscular transmission in the Cynomolgus monkey IAS and rectum: special emphasis on differences in purinergic transmission

KEY POINTS

Inhibitory neuromuscular transmission (NMT) was compared in the internal anal sphincter (IAS) and rectum of the Cynomolgus monkey, an animal with high gene sequence identity to humans. Nitrergic NMT was present in both muscles while purinergic NMT was limited to the rectum and VIPergic NMT to the IAS. The profile for monkey IAS more closely resembles humans than rodents. In both muscles, SK3 channels were localized to PDGFRα⁺ cells that were closely associated with nNOS⁺ /VIP⁺ nerves. Gene expression levels of P2RY subtypes were the same in IAS and rectum while KCNN expression levels were very similar. SK3 channel activation and inhibition caused faster/greater changes in contractile activity in rectum than IAS. P2Y1 receptor activation inhibited contraction in rectum while increasing contraction in IAS. The absence of purinergic NMT in the IAS may be due to poor coupling between P2Y1 receptors and SK3 channels on PDGFRα⁺ cells.

ABSTRACT

Inhibitory neuromuscular transmission (NMT) was compared in the internal anal sphincter (IAS) and rectum of the Cynomolgus monkey, an animal with a high gene sequence identity to humans. Electrical field stimulation produced nitric oxide synthase (NOS)-dependent contractile inhibition in both muscles whereas P2Y1-dependent purinergic NMT was restricted to rectum. An additional NOS-independent, α-chymotrypsin-sensitive component was identified in the IAS consistent with vasoactive intestinal peptide-ergic (VIPergic) NMT. Microelectrode recordings revealed slow NOS-dependent inhibitory junction potentials (IJPs) in both muscles and fast P2Y1-dependent IJPs in rectum. The basis for the difference in purinergic NMT was investigated. PDGFRα⁺ /SK3⁺ cells were closely aligned with nNOS⁺ /VIP⁺ neurons in both muscles. Gene expression of P2RY was the same in IAS and rectum (P2RY1>>P2RY2-14) while KCNN3 expression was 32% greater in rectum. The SK channel inhibitor apamin doubled contractile activity in rectum while having minimal effect in the IAS. Contractile inhibition elicited with the SK channel agonist CyPPA was five times faster in rectum than in the IAS. The P2Y1 receptor agonist MRS2365 inhibited contraction in rectum but increased contraction in the IAS. In conclusion, both the IAS and the rectum have nitrergic NMT whereas purinergic NMT is limited to rectum and VIPergic NMT to the IAS. The profile in monkey IAS more closely resembles that of humans than rodents. The lack of purinergic NMT in the IAS cannot be attributed to the absence of PDGFRα⁺ cells, P2Y1 receptors or SK3 channels. Rather, it appears to be due to poor coupling between P2Y1 receptors and SK3 channels on PDGFRα⁺ cells.

Abstract A087: Enzalutamide-induced hypoxia attenuates response and promotes resistance to enzalutamide in preclinical models of prostate cancer

Inhibition of androgen signaling remains the therapeutic mainstay in castrate-resistant prostate cancer. The expression of androgen receptor (AR) splice variants and the retention of active AR signaling have been reported as mechanisms of resistance to the anti-androgen enzalutamide. Other non-AR dependent mechanisms of resistance have also been proposed, including acquisition of a hypoxic tumor microenvironment. We propose that treatment-induced hypoxia and the subsequent induction of angiogenesis may define a novel mechanism of relapse to enzalutamide.

Preclinical experiments were conducted in LNCaP tumors, endothelial cells, and established human prostate cancer cell lines. The effects of enzalutamide on endothelial cells were examined in vivo and in vitro. Tumor growth, intratumoral hypoxia, and blood vessel density were measured in vivo. AR expression, activation, and target gene expression were measured in vitro. The effect of enzalutamide on hypoxia-driven, disease-progressing pathways and genes of interest, and the role of these genes in resistance to enzalutamide, was investigated.

Administration of enzalutamide rapidly induced hypoxia in LNCaP tumors in vivo, followed by angiogenesis-promoted restoration of oxygen tension, increased vessel density, and accelerated tumor growth. In vitro, enzalutamide directly targeted AR-expressing endothelial cells, resulting in decreased growth and tubule formation. Exposure to hypoxia in vitro increased AR expression and transcriptional activity in LNCaP prostate cancer cells and sustained, but did not further potentiate, high basal AR and ARv7 expression and activity in 22Rv1 cells. Enzalutamide failed to attenuate the concurrent hypoxia-induced HIF-1 and NF-κB signaling, resulting in upregulation of disease-progressing genes and pathways. Administration of neutralizing antibodies to two hypoxia-regulated genes, interleukin-8 (IL-8) and VEGF, prolonged enzalutamide-mediated hypoxia over 14 days and LNCaP tumor growth control over 28 days in vivo (p<0.001). Elevated expression of IL-8 and VEGF-A was also detected in MDV3100-resistant models, where neutralization of IL-8 and VEGF-A inhibited tumor angiogenesis and partially reversed resistance to enzalutamide.

We conclude that enzalutamide-induced hypoxia upregulates the expression of VEGF and IL-8, whose multimodel signaling effects, in turn, contribute to microenvironment-promoted resistance in prostate tumors.

Citation Format: Pamela J. Maxwell, Melanie McKechnie, Oisin Duddy, Christopher W. Armstrong, Judith M. Manley, Chee Wee Ong, Jenny Worthington, Elena Deryugina, James P. Quigley, Amina Zoubeidi, David J.J. Waugh, Melissa J. LaBonte. Enzalutamide-induced hypoxia attenuates response and promotes resistance to enzalutamide in preclinical models of prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A087.

Abstract 3836: Imbalanced nucleotide metabolism sensitizes breast cancer cells to anthracyclines

Introduction. Triple negative breast cancer (TNBC) makes up 15% of breast cancers and is associated with poor prognosis. TNBC treatment remains hampered by early visceral metastasis and lymph node involvement at the time of diagnosis and limited effective therapeutic options. Advances in treatment that translate to significant improvements in outcome have been painstakingly incremental, despite advances in research technologies and TNBC subtyping.

We have identified deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) as a critical gatekeeper that protects tumor DNA from the genotoxic misincorporation of uracil during treatment with anthracyclines that are commonly used in the FEC chemotherapy regimen. dUTPase catalyses the hydrolytic dephosphorylation of deoxyuridine triphosphate (dUTP) to deoxyuridine monophosphate (dUMP). This reaction has the dual function of providing dUMP for thymidylate synthase (TS) as part of the thymidylate biosynthesis pathway and of maintaining low intracellular dUTP pools. This is crucial as DNA polymerase cannot distinguish between dUTP and deoxythymidylate triphosphate (dTTP), leading to dUTP misincorporated into DNA. dUTPase is being evaluated as a target in cancer therapy alongside TS-targeted therapies and uracil misincorporation is believed to be a potential mechanism of cytotoxicity. Hypothesis: Targeting dUTPase and inducing uracil misincorporation during the repair of DNA damage induced by anthracyclines represents a novel strategy to induce TNBC cell lethality.

Methods. Inhibition of dUTPase (DUTi) was carried out using SMARTpool siRNA or small molecule inhibition. The effect of DUTi in combination with anthracyclines was determined by growth inhibition and clonogenics assays. DNA damage was assessed by Western blot, immune-fluorescent foci detection, and flow cytometry. Nucleotide metabolites were quantified by LC/MS.

Results. DUTi significantly sensitised TNBC cell lines to doxorubicin and epirubicin. In the MDA-MB-231 cancer cells, loss of dUTPase expression resulted in a synergistic 80% reduction in survival compared to 0.075µM doxorubicin alone at 40%. This decrease in survival correlated with increased activation of proteins involved in DNA damage response, including γ-H2AX(Ser139), a marker for dsDNA breaks. We anticipate that quantification of nucleotides will show an imbalance of dUTP:dTTP, subsequently leading to uracil misincorporation and resulting cell death.

Discussion. These results suggest that repair of anthracycline-induced DNA damage requires dUTPase to prevent uracil misincorporation and that inhibition of dUTPase is a potential novel strategy to enhance the efficacy of anthracyclines. This shows the potential advantage of a dUTPase inhibitor being added to current chemotherapy regimens for TNBC.

Future work will elucidate the mechanism of sensitisation and in vivo translation of combination therapy for TNBC.

Citation Format: Craig Davison, Olivier P. Chevallier, Catherine Knowlson, Melanie McKechnie, Robbie Carson, Jaime Esteve, Richard Wilson, Robert D. Ladner, Melissa J. LaBonte (Wilson). Imbalanced nucleotide metabolism sensitizes breast cancer cells to anthracyclines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3836.

Osteogenic cell response to 3-D hydroxyapatite scaffolds developed via replication of natural marine sponges

Bone tissue engineering may provide an alternative to autograft, however scaffold optimisation is required to maximize bone ingrowth. In designing scaffolds, pore architecture is important and there is evidence that cells prefer a degree of non-uniformity. The aim of this study was to compare scaffolds derived from a natural porous marine sponge (Spongia agaricina) with unique architecture to those derived from a synthetic polyurethane foam. Hydroxyapatite scaffolds of 1 cm(3) were prepared via ceramic infiltration of a marine sponge and a polyurethane (PU) foam. Human foetal osteoblasts (hFOB) were seeded at 1 × 10(5) cells/scaffold for up to 14 days. Cytotoxicity, cell number, morphology and differentiation were investigated. PU-derived scaffolds had 84-91% porosity and 99.99% pore interconnectivity. In comparison marine sponge-derived scaffolds had 56-61% porosity and 99.9% pore interconnectivity. hFOB studies showed that a greater number of cells were found on marine sponge-derived scaffolds at than on the PU scaffold but there was no significant difference in cell differentiation. X-ray diffraction and inductively coupled plasma mass spectrometry showed that Si ions were released from the marine-derived scaffold. In summary, three dimensional porous constructs have been manufactured that support cell attachment, proliferation and differentiation but significantly more cells were seen on marine-derived scaffolds. This could be due both to the chemistry and pore architecture of the scaffolds with an additional biological stimulus from presence of Si ions. Further in vivo tests in orthotopic models are required but this marine-derived scaffold shows promise for applications in bone tissue engineering.

Abstract 2254: Pro-angiogenic CXCL8 signalling underpins microenvironment-induced relapse to anti-androgen therapy of prostate cancer

Introduction and Objectives: Bicalutamide induces a rapid and sustained hypoxia in growing LNCaP prostatic tumors. This treatment-induced hypoxia (>14 days) increases synthesis of the CXC-chemokine Interleukin-8(CXCL8) co-incident with increasing oxygen tension and the restoration of tumor vascularisation1. Consequently, our current hypothesis is that hypoxia induced CXCL8 signalling underpins resistance to bicalutamide-treated tumors and facilitates the adoption of more aggressive cancer cells.

Results: Culturing of LNCaP (PTEN null) and 22Rv1 (PTEN wt) cells under hypoxic conditions (mimicking a bicalutamide-treated tumor microenvironment) increased transcriptional activity of the androgen receptor (AR), Hypoxia-Inducible Factor (HIF-1) and NF-kB, inducing expression of downstream target genes associated with survival, metabolic adaptation and angiogenesis. The magnitude and duration of these responses was greater in PTEN-null LNCaP cells. Experiments were conducted to determine how bicalutamide-mediated inhibition of AR signalling would affect hypoxia-induced potentiation of AR, HIF and NF-kB transcription. Bicalutamide or an AR-targeted siRNA failed to reduce expression of pro-angiogenic, pro-survival and metabolism-associated genes. However, concurrent knockdown of both HIF-1 and NF-kB activity using gene-targeted siRNA's repressed expression of these hypoxia-induced disease-progressing genes. Amongst the genes up-regulated in hypoxic and PTEN-deficient LNCaP cells was expression of CXCL8 and its receptors, CXCR1 and CXCR2, which we have previously shown to be regulated by HIF-1 and NF-kB activity. Potentiation of CXCL8 signalling under hypoxia was found to sustain AR, HIF and NF-kB transcription. Combination of bicalutamide with the proteasome inhibitor bortezomib attenuated hypoxia-induced AR expression and transcriptional activity and decreased HIF-1 activity but failed to reduce NF-kB activity. In contrast, only direct inhibition of CXCL8 signalling was shown to repress activity of AR, HIF-1 and NF-kB in hypoxic LNCaP cells and increased LNCaP cells sensitivity to bicalutamide.

Conclusion: Our data suggests that targeting CXCL8 signalling may therefore be a relevant strategy to enhance tumor response to anti-androgen therapies. Inhibiting signalling of this chemokine attenuates key transcriptional approaches induced in the hypoxic microenvironment of bicalutamide-treated tumors. Moreover, inhibition of CXCL8 signalling may prevent the re-vascularization previously observed in hypoxic LNCaP tumors.

Citation Format: Melanie McKechnie, Pamela J. Maxwell, David J. J. Waugh. Pro-angiogenic CXCL8 signalling underpins microenvironment-induced relapse to anti-androgen therapy of prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2254. doi:10.1158/1538-7445.AM2014-2254

The acceptability of different HIV testing approaches: cross-sectional study among GMSM in Australia

BACKGROUND

We explored the attitudes of Australian gay and other men who have sex with men (GMSM) about the current standard-of-care (non-rapid tests at healthcare settings) and alternative approaches (rapid tests and testing in non-healthcare settings) to better understand the acceptability of alternative testing approaches.

METHODS

The Contemporary Norms in Networks and Communities of GMSM study enrolled GMSM in Sydney, Melbourne and Perth in 2011-2012 using peer referrals. We explored the self-reported preferences for testing: rapid versus non-rapid and in non-healthcare settings (community-based or home-based testing) versus in healthcare settings, and examined factors associated with preferences for these approaches. Analyses of associations used standard univariate and age-adjusted logistic regression models.

RESULTS

Among 827 sexually active non-HIV-positive participants, 89% had been tested for HIV. Most preferred by participants was home rapid testing (46%), followed by standard-of-care (23%) and rapid testing in healthcare (20%) or community settings (7%). About 73% of participants preferred rapid over non-rapid testing, and 56% preferred testing in non-healthcare settings rather than in healthcare settings. Preference for rapid testing was associated with being fully employed (adjusted OR (aOR): 1.81; 95% CI 1.16 to 2.82), managerial/professional occupation (aOR: 2.03; 95% CI 1.19 to 3.46) and engaging in unprotected anal intercourse with casual partners (aOR: 1.89; 95% CI 1.29 to 2.78). The same factors were associated with preference for testing in non-healthcare settings.

CONCLUSIONS

Australian GMSM prefer alternative testing approaches, possibly due to their convenience. The availability of new testing approaches may provide more options for GMSM at risk for HIV infection, improve access to HIV testing and potentially increase HIV testing rates.

Gay men who are not getting tested for HIV

Using data from Australian Gay Community Periodic Surveys 1998-2010, we assessed the prevalence, trends and characteristics of gay men not tested for HIV. In 2010, one in eight Australian gay socially-engaged men were never tested for HIV, most of them sexually active and 56.5 % reporting unprotected anal intercourse. The proportion of not tested men was significantly higher in men younger than 30, of non-European origin and living outside of gay metropolitan areas. Although frequency of testing was associated with sexual practices, significant proportions of men with multiple sex partners and reporting unprotected anal intercourse were not tested as recommended. There were issues with using gay-friendly testing services in gay metropolitan areas. Despite Australia's success in HIV testing, improvement is needed for early detection of HIV infections. Interventions should encourage regular testing, engage with young gay men, improve access and convenience of testing, train service providers and expand testing options.

Potentiation of inflammatory CXCL8 signalling sustains cell survival in PTEN-deficient prostate carcinoma

BACKGROUND

Inflammation and genetic instability are enabling characteristics of prostate carcinoma (PCa). Inactivation of the tumour suppressor gene phosphatase and tensin homolog (PTEN) is prevalent in early PCa. The relationship of PTEN deficiency to inflammatory signalling remains to be characterised.

OBJECTIVE

To determine how loss of PTEN functionality modulates expression and efficacy of clinically relevant, proinflammatory chemokines in PCa.

DESIGN, SETTING, AND PARTICIPANTS

Experiments were performed in established cell-based PCa models, supported by pathologic analysis of chemokine expression in prostate tissue harvested from PTEN heterozygous (Pten(+/-)) mice harbouring inactivation of one PTEN allele.

INTERVENTIONS

Small interfering RNA (siRNA)- or small hairpin RNA (shRNA)-directed strategies were used to repress PTEN expression and resultant interleukin-8 (CXCL8) signalling, determined under normal and hypoxic culture conditions.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Changes in chemokine expression in PCa cells and tissue were analysed by real-time polymerase chain reaction (PCR), immunoblotting, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry; effects of chemokine signalling on cell function were assessed by cell cycle analysis, apoptosis, and survival assays.

RESULTS AND LIMITATIONS

Transient (siRNA) or prolonged (shRNA) PTEN repression increased expression of CXCL8 and its receptors, chemokine (C-X-C motif) receptor (CXCR) 1 and CXCR2, in PCa cells. Hypoxia-induced increases in CXCL8, CXCR1, and CXCR2 expression were greater in magnitude and duration in PTEN-depleted cells. Autocrine CXCL8 signalling was more efficacious in PTEN-depleted cells, inducing hypoxia-inducible factor-1 (HIF-1) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcription and regulating genes involved in survival and angiogenesis. Increased expression of the orthologous chemokine KC was observed in regions displaying atypical cytologic features in Pten(+/-) murine prostate tissue relative to normal epithelium in wild-type PTEN (Pten(WT)) glands. Attenuation of CXCL8 signalling decreased viability of PCa cells harbouring partial or complete PTEN loss through promotion of G1 cell cycle arrest and apoptosis. The current absence of clinical validation is a limitation of the study.

CONCLUSIONS

PTEN loss induces a selective upregulation of CXCL8 signalling that sustains the growth and survival of PTEN-deficient prostate epithelium.

Abstract A70: PTEN loss induces selective upregulation of CXCL8 signaling to modulate survival and resistance to radiation

PTEN is a haplo-insufficient tumor suppressor and the most frequently mutated gene in prostate cancer (CaP). Moreover, loss of PTEN expression arising from allele deletion or promoter methylation is prevalent early disease. The objective of our study was to characterize how the genetic instability and/or stress-induced signaling arising from PTEN loss modulated the expression of clinically-relevant pro-inflammatory chemokines. Transient (siRNA) or prolonged (shRNA) repression of PTEN resulted in increased transcription-mediated increases in expression of CXCL8 and its receptors, CXCR1 and CXCR1 in DU145 and 22Rv1 cells. Stress-induced expression of CXCL8, CXCR1 and CXCR2 was greater in magnitude and duration in PTEN-null PC3 and LNCaP cells, in contrast to the dampened response observed in PTEN-expressing cells. PTEN had no effect on basal or stress-induced expression of CCL2, CXCL12 or their receptors in prostate cancer cells. Moroever, the efficacy of autocrine CXCL8 signaling to induce HIF-1 and NF-κB transcription was also greater in magnitude and duration in PTEN-null prostate cancer cells or following siRNA-mediated PTEN knockdown in DU145 and 22Rv1 cells. Consistent with in vitro data, we observed increased expression of the orthologous murine chemokine KC in atypical cytological features of PTEN+/− prostate tissue relative to normal epithelium in PTENWT glands. Finally, siRNA or shRNA-mediated attenuation of CXCL8 signaling selectively decreased the viability of CaP cells harboring partial or complete PTEN-loss. Furthermore, the knockdown of CXCL8 signaling potentiated the sensitivity of PTEN-depleted prostate cancer cells to clinicallyrelevant doses of ionozing radiation. We conclude that there is a selective upregulation of CXCL8 signaling in PTEN-deficient prostate epithelium, which contributes to the growth, survival and reduced therapeutic sensitivity of these cells.

Citation Format: Jonathan Coulter, Pamela Maxwell, Melanie McKechnie, Jessica Neisen, Richard Kennedy, Manuel Salto-Tellez, Chris Albanese, David Waugh. PTEN loss induces selective upregulation of CXCL8 signaling to modulate survival and resistance to radiation [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A70.

Abstract B200: Selective induction of CXCL8 signaling maintains viability in PTEN-depleted prostate cancer cells

Background: PTEN loss is associated with early prostate cancer progression. We sought to characterize whether PTEN loss regulates pro-inflammatory chemokine signaling and its functional significance to PTEN-depleted prostate cancer cells.

Methods: Chemokine/chemokine receptor expression was assessed in vitro in established cell lines, exhibiting different levels of endogenous PTEN expression. Down-regulation of endogenous PTEN expression in DU145 and 22Rv1 cells was effected using transient siRNA or stable shRNA interventions. Chemokine expression was further evaluated by immunohistochemistry in prostate tissue from wild-type and PTEN+/− mice.

Results: Loss of PTEN induced transcription-mediated increases in expression of CXCL8 and its receptors, CXCR1 and CXCR1 in DU145 and 22Rv1 cells. Stress-induced expression of CXCL8, CXCR1 and CXCR2 was greater in magnitude and duration in PTEN-null PC3 and LNCaP cells, in contrast to the dampened response observed in PTEN-expressing cells. PTEN loss had no effect on basal or stress-induced expression of CCL2, CXCL12 or their receptors CCR2 or CXCR4 in prostate cancer cells. The efficacy of CXCL8 signaling upon HIF-1 and NF-B transcription was also greater in magnitude and duration in PTEN-null prostate cancer cells or following siRNA-mediated PTEN knockdown. Increased expression of the orthologous murine chemokine KC was elevated in atypical cytological features of PTEN+/− prostate tissue relative to normal epithelium in PTENWT glands. Attenuation of CXCL8 signaling using siRNA oligonucleotides or shRNA vectors in cell-based models of partial or complete PTEN-loss significantly decreased cell viability. Furthermore, attenuation of CXCL8 signaling modulates the response of PTEN-depleted prostate cancer cells to clinically-relevant doses of ionizing radiation.

Conclusion: PTEN loss promotes a selective up-regulation of CXCL8 signaling and increases the efficacy of CXCL8 signaling in prostate cancer cells. Functionally, this selective induction of CXCL8 signaling acts to maintain cell viability as an essential adaptation to the genetic instability arising from PTEN loss.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B200.

Tension pneumothorax and the "forbidden CXR"

A case is presented of unilateral tension pneumothorax associated with flail chest and pulmonary contusions in a spontaneously ventilating patient after a fall. The tension element was not suspected until chest x ray was available, nor was immediate needle thoracocentesis performed. No morbidity resulted as a consequence. This case highlights the difficulty in deciding whether or not tension pneumothorax is the predominant cause of respiratory distress in a patient with multiple chest injuries. It provides further evidence challenging some of the doctrine on how to treat suspected tension pneumothorax.