Abstract 2877: IKK-mediated signaling controls prostate tumor initiating cells

The heterogeneous nature of prostate cancer tumors is thought to play an important role in the decreased effectiveness of existing therapies. Tumor initiating cells (TICs) are capable of self-renewal and comprise a subset of the tumor mass. These cells are proposed to drive the growth and metastasis of tumors, and are considered to be resistant to traditional cytotoxic and targeted therapies. Several studies have shown that NF-κB signaling is increased in recurrent prostate cancer and enriched in prostate TICs. We sought to determine the potential of an IKK/NF-κB-driven mechanism for inherent or acquired resistance by IKK-mediated control of a subset of prostate tumor initiating cells. These studies were performed by using established prostate cancer cell lines, murine prostate organoids, and a murine prostate cancer animal model. We have found that inhibition of IKKα and IKKβ, upstream regulators of noncanonical and canonical NF-κB signaling, block self-renewal of several PTEN-deficient prostate cancer cell lines. Furthermore, we have also found that IKK is important for tumorigenicity and stemness seen in prostate cancer cells as measured by colony formation and extreme limiting dilution assays. Loss of canonical NF-κB (p65/RelA) decreased stemness while loss of noncanonical did not alter tumorsphere formation. Interestingly, Pten-/- tumors with loss of Ikkα or Ikkβ displayed decreased levels of self-renewing cells as measured by CD49fhigh expression, a known prostate basal cell marker. Isolated murine Pten-/- cells were 2x more efficient than Pten-/-Ikkα-/- or Pten-/-Ikkβ-/- cells in forming prostate organoids suggesting that loss of Ikk decreased the number of self-renewing cells needed for formation. Taken together, we conclude that IKK-mediated signaling is important for maintenance of prostate tumor initiating cells and further studies will address whether IKK-mediated signaling provides a mechanism for evading current therapies.

Note: This abstract was not presented at the meeting.

Citation Format: Sara E. Conard, Aaron Ebbs, Albert S. Baldwin. IKK-mediated signaling controls prostate tumor initiating cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2877. doi:10.1158/1538-7445.AM2017-2877

Akt-dependent activation of mTORC1 complex involves phosphorylation of mTOR (mammalian target of rapamycin) by IκB kinase α (IKKα)

The serine/threonine protein kinase Akt promotes cell survival, growth, and proliferation through phosphorylation of different downstream substrates. A key effector of Akt is the mammalian target of rapamycin (mTOR). Akt is known to stimulate mTORC1 activity through phosphorylation of tuberous sclerosis complex 2 (TSC2) and PRAS40, both negative regulators of mTOR activity. We previously reported that IκB kinase α (IKKα), a component of the kinase complex that leads to NF-κB activation, plays an important role in promoting mTORC1 activity downstream of activated Akt. Here, we demonstrate IKKα-dependent regulation of mTORC1 using multiple PTEN null cancer cell lines and an animal model with deletion of IKKα. Importantly, IKKα is shown to phosphorylate mTOR at serine 1415 in a manner dependent on Akt to promote mTORC1 activity. These results demonstrate that IKKα is an effector of Akt in promoting mTORC1 activity.

IKK is a therapeutic target in KRAS-Induced lung cancer with disrupted p53 activity

Activating mutations in KRAS are prevalent in cancer, but therapies targeted to oncogenic RAS have been ineffective to date. These results argue that targeting downstream effectors of RAS will be an alternative route for blocking RAS-driven oncogenic pathways. We and others have shown that oncogenic RAS activates the NF-κB transcription factor pathway and that KRAS-induced lung tumorigenesis is suppressed by expression of a degradation-resistant form of the IκBα inhibitor or by genetic deletion of IKKβ or the RELA/p65 subunit of NF-κB. Here, genetic and pharmacological approaches were utilized to inactivate IKK in human primary lung epithelial cells transformed by KRAS, as well as KRAS mutant lung cancer cell lines. Administration of the highly specific IKKβ inhibitor Compound A (CmpdA) led to NF-κB inhibition in different KRAS mutant lung cells and siRNA-mediated knockdown of IKKα or IKKβ reduced activity of the NF-κB canonical pathway. Next, we determined that both IKKα and IKKβ contribute to oncogenic properties of KRAS mutant lung cells, particularly when p53 activity is disrupted. Based on these results, CmpdA was tested for potential therapeutic intervention in the Kras-induced lung cancer mouse model (LSL-Kras^G12D) combined with loss of p53 (LSL-Kras^G12D/p53^fl/fl). CmpdA treatment was well tolerated and mice treated with this IKKβ inhibitor presented smaller and lower grade tumors than mice treated with placebo. Additionally, IKKβ inhibition reduced inflammation and angiogenesis. These results support the concept of targeting IKK as a therapeutic approach for oncogenic RAS-driven tumors with altered p53 activity.

Abstract 903: The IKKα kinase is a potential therapeutic target in K-Ras-induced lung cancer

Lung cancer is the leading cause of cancer deaths in the world. In lung cancer, K-Ras oncogenic mutations are widespread, and compounds used to target the biological activity of the Ras proteins failed in clinical trials. Therefore, it is imperative to identify novel therapeutic targets that reduce K-Ras-induced lung tumorigenesis. We have previously shown that K-Ras-induced lung tumorigenesis is potentiated by the subunit p65 of the transcription factor NF-κB; and that K-Ras-induced NF-κB activation in the lung requires IKKα. Therefore, we hypothesized the following: (1) the IKKα kinase promotes K-Ras-induced oncogenesis; and (2) pharmacological inhibition of IKKα activity will be beneficial therapeutically. We used genetic and/or pharmacological approaches to inactivate IKKα in primary lung epithelial cells transformed by K-Ras, as well as K-Ras-positive lung cancer cell lines, and determined that IKKα inhibiton reduces oncogenic properties in vitro. In addition we used a highly specific IKKα inhibitor (CmpdA, Bayer) to treat a K-Ras-induced lung cancer mouse model combined with loss of the tumor suppressor p53 (LSL-K-RasG12D/p53fl/fl). We chose this model for the following reasons: (1) K-Ras activation coupled to p53 loss leads to aggressive lung adenocarcinomas in mice that better resemble human lung tumors; (2) lung cancer patients harboring K-Ras oncogenic mutations frequently display p53 inactivation; and (3) it has been recently demonstrated that p53 loss can enhance NF-κB activation by K-Ras in lung tumors. To induce concomitant K-Ras activation and p53 loss in murine lung epithelial cells, we infected the lungs of LSL-K-RasG12D/p53fl/fl mice by intranasal administration of a Cre-expressing adenovirus (AdCre). Two treatment regimens were used to treat infected animals: CmpdA was either administered daily for 2 weeks immediately following AdCre infection or daily for 4 weeks starting 8 weeks post-infection. In either case, mice treated with CmpdA presented smaller and lower grade tumors than mice treated with placebo. These results show that IKKα promotes lung cancer growth and progression both in vitro and in vivo. In addition, we have shown that pharmacological administration of an IKKα inhibitor slows lung tumor growth and progression in vivo, supporting our hypothesis that IKKα inhibition therapy will have clinical benefits in lung cancer. This research is supported by a FAMRI YCSA Award and a FAPESP Young Investigator Award to DB and a NIH grant (CA73756) to AB.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 903. doi:1538-7445.AM2012-903

Requirement of the NF-kappaB subunit p65/RelA for K-Ras-induced lung tumorigenesis

K-Ras-induced lung cancer is a very common disease, for which there are currently no effective therapies. Because therapy directly targeting the activity of oncogenic Ras has been unsuccessful, a different approach for novel therapy design is to identify critical Ras downstream oncogenic targets. Given that oncogenic Ras proteins activate the transcription factor NF-kappaB, and the importance of NF-kappaB in oncogenesis, we hypothesized that NF-kappaB would be an important K-Ras target in lung cancer. To address this hypothesis, we generated a NF-kappaB-EGFP reporter mouse model of K-Ras-induced lung cancer and determined that K-Ras activates NF-kappaB in lung tumors in situ. Furthermore, a mouse model was generated where activation of oncogenic K-Ras in lung cells was coupled with inactivation of the NF-kappaB subunit p65/RelA. In this model, deletion of p65/RelA reduces the number of K-Ras-induced lung tumors both in the presence and in the absence of the tumor suppressor p53. Lung tumors with loss of p65/RelA have higher numbers of apoptotic cells, reduced spread, and lower grade. Using lung cell lines expressing oncogenic K-Ras, we show that NF-kappaB is activated in these cells in a K-Ras-dependent manner and that NF-kappaB activation by K-Ras requires inhibitor of kappaB kinase beta (IKKbeta) kinase activity. Taken together, these results show the importance of the NF-kappaB subunit p65/RelA in K-Ras-induced lung transformation and identify IKKbeta as a potential therapeutic target for K-Ras-induced lung cancer.

Effects of 4′-Chloro-3α-(diphenylmethoxy)-tropane on Mesostriatal, Mesocortical, and Mesolimbic Dopamine Transmission: Comparison with Effects of Cocaine

Increase in dopamine (DA) neurotransmission resulting from blockade of the DA transporter (DAT) after administration of cocaine is believed to play a major role in mediating its behavioral and reinforcing effects. Since it was hypothesized that drugs that block the DAT have cocaine-like behavioral effects, it was of interest to study in the present article the stimulant effects of cocaine on locomotor activity and on pattern of activation of DA neurotransmission in different DAergic terminal areas in rats and compare these effects with those of 4'-chloro-3alpha-(diphenylmethoxy)-tropane (4-Cl-BZT), a benztropine analog showing higher affinity for the DAT, but reduced behavioral effects compared with cocaine. Administration of cocaine resulted in a dose-dependent stimulation of locomotor activity and DA neurotransmission in the nucleus accumbens shell and core, dorsal caudate, and in the medial prefrontal cortex (PFCX) measured by microdialysis. At comparable doses, the effects of 4-Cl-BZT on DA levels in all brain areas except the PFCX were generally reduced compared with those of cocaine, as were the effects on locomotor activity. The differences in behavioral effects corresponded generally to differences between the drugs with regard to their stimulation of extracellular DA levels, although the mechanism(s) for the differences in extracellular DA may involve effects mediated by sites other than the DAT or differences in the efficiency of the two drugs in blocking DA uptake. Nonetheless, the present results suggest that the differences in behavioral effects between cocaine and 4-Cl-BZT are related to differences in their patterns of activation of DA transmission.

Microarray-based gene expression profiles of allograft rejection and immunosuppression in the rat heart transplantation model

BACKGROUND

Gene expression profiling has the potential to produce new insights into complex biologic systems. To test the value of complement DNA arrays in identifying pathways involved in organ transplant rejection, we examined the gene expression profiles of rat heart allografts from recipients treated with or without immunosuppression to prevent acute allograft rejection.

METHODS

Heterotopic heart transplantation was performed using ACI or Lewis donors and Lewis recipients. Recipients were treated with tacrolimus (Tac) or cyclosporine (CsA) at the equivalent effective doses, and graft hearts were harvested on days 3, 5, and 7. A commercial microarray was used to measure gene expression levels of 588 genes in day 5 grafts. Selected genes were analyzed by reverse transcriptase-polymerase chain reaction.

RESULTS

The expression levels of 118 genes were perturbed in the untreated allograft in comparison with the isograft control, of which 77 genes were categorized as candidate genes for Tac- or CsA-mediated immunosuppression or both, and 41 as genes associated with other pathways. Among the 77 candidate genes, 55 genes shared the same response to suppression by both drugs, including inducible nitric oxide synthase, interferon-gamma, and interferon regulatory factor 1. Drug-specific effects were observed in 22 genes: Fourteen genes were exclusively reversed by Tac and eight by CsA.

CONCLUSIONS

Gene expression profiling reveals a large variety of genes affected during acute rejection, indicating that multiple metabolic pathways, including immune and nonimmune responses, are involved in the local graft rejection events. The differences and similarities of the gene expression profiles relative to the two immunosuppressants may provide more detailed therapeutic approaches for optimal immunosuppression.

FK778, a powerful new immunosuppressant, effectively reduces functional and histologic changes of chronic rejection in rat renal allografts

BACKGROUND

FK778 is a new derivative of the active leflunomide metabolite A77 1726. It effectively prevented acute allograft rejection in several experimental transplant models, and it is currently in phase II trials in human transplant recipients. In this study, we examined the effects of FK778 in a well-established model of chronic renal allograft rejection in the rat.

METHODS

Kidneys of Lewis (LEW) and F344 rats were orthotopically transplanted into bilaterally nephrectomized LEW recipients as the isograft and allograft control, respectively. Allograft recipients were orally administered FK778 at doses of 3 mg/kg per day, 10 mg/kg per day, and 20 mg/kg per day for 10 days. Blood and 24-hr urine samples were collected once a week after grafting for plasma creatinine, allo-specific antibodies, and proteinuria determination. Kidney grafts were harvested on the 90th day after transplantation and subjected to histologic, immunohistologic, and reverse transcriptase-polymerase chain reaction analysis. Histologic sections were semiquantitatively scored using criteria adapted from the Banff' classification for transplant pathologic conditions.

RESULTS

Recipients treated with FK778 for 10 days exhibited a dose-dependent decrease in proteinuria and plasma creatinine for the entire 90-day period after transplantation when compared with the allograft control. FK778, at doses of 10 mg/kg per day and 20 mg/kg per day, remarkably reduced chronic histologic changes, including tubular atrophy, glomerulosclerosis, fibrointimal hyperplasia, and transplant glomerulopathy. In addition, FK778 treatment was associated with decreased intragraft mononuclear cell infiltration, serum allo-specific immunoglobulin (Ig)M and IgG antibody production, and intragraft transforming growth factor beta messenger RNA expression in those recipients surviving 90 days after transplantation when compared with the allograft control.

CONCLUSION

FK778 effectively reduces functional and histologic chronic kidney allograft rejection in the rat.

Tacrolimus and cyclosporine differ in their capacity to overcome ongoing allograft rejection as a result of their differential abilities to inhibit interleukin-10 production

BACKGROUND

Accumulated evidence from clinical transplantation has suggested that tacrolimus-based treatment can reverse ongoing allograft rejection in patients treated with cyclosporine (CsA)-based immunosuppression, even when a high dose of antirejection rescue therapy has failed. This evidence prompted us to investigate whether these two compounds, which share an in vitro mechanism, would differ in their abilities to regulate in situ cellular and molecular events during ongoing allograft rejection.

METHODS

The equivalent effective doses of tacrolimus (3.2 mg/kg/day) and CsA (10 mg/kg/day), when administered orally to Lewis rats for 10 days (day 0-9), were predetermined and defined as the ability of the drug to induce a similar survival of Brown Norway rat heart allografts with an equal suppression of intragraft interleukin (IL)-2 mRNA expression. To investigate the ability of each drug to rescue ongoing allograft rejection, Lewis recipients of Brown Norway rat heart grafts were left untreated for the first 5 days after transplantation. Tacrolimus or CsA was then administered at the equivalent effective dose for 10 days (days 5-14). Heart grafts and blood samples, harvested on days 3, 5, 7, and 10, were analyzed by reverse transcriptase-polymerase chain reaction, real-time quantitative polymerase chain reaction, ELISA, and immunohistology.

RESULTS

Ongoing allograft rejection was found to be rescued by tacrolimus but not by CsA at the equivalent dose (median survival time: untreated, 6 days; tacrolimus, 18 days; and CsA, 7 days). A significant suppression of local intragraft IL-10 mRNA expression and serum protein production along with a dramatic down-regulation of functional CD8+ T and NKR-P1a+ natural killer cell local infiltration by means of decreased of cytotoxic factor release, including granzyme B and perforin 1, was found to be associated with tacrolimus but not CsA treatment. However, both drugs inhibited other immune cells (CD4+ T cell, ED2+ macrophage) and cytokines (IL-1beta, IL-2, IL-4, IL-6, IL-12, interferon-gamma, transforming growth factor-beta, and tumor necrosis factor-alpha) at almost the same levels. The inability of CsA to overcome ongoing allograft rejection could be rescued by cotreating recipients with neutralizing anti-IL-10 antibody on day 5 and day 6 after transplantation: anti-IL-10 antibody alone did not show such an effect.

CONCLUSIONS

Inhibition of IL-10 production is a critical factor in the ability of tacrolimus to reverse ongoing allograft rejection.