Christian Thomas

Selection of Tumor-binding Ligands in Cancer Patients with Phage Display Libraries

Phage display has been used extensively in vitro and in animal models to generate ligands and to identify cancer-relevant targets. We report here the use of phage-display libraries in cancer patients to identify tumor-targeting ligands. Eight patients with stage IV cancer, including breast, melanoma, and pancreas, had phage-displayed random peptide or scFv library (1.6 x 10(8)-1 x 10(11) transducing units/kg) administered i.v.; tumors were excised after 30 minutes; and tumor-homing phage were recovered. In three patients, repeat panning was possible using phage recovered and amplified from that same patients tumor. No serious side effects, including allergic reactions, were observed with up to three infusions. Patients developed antiphage antibodies that reached a submaximal level within the 10-day protocol window for serial phage administration. Tumor phage were recoverable from all the patients. Using a filter-based ELISA, several clones from a subset of the patients were identified that bound to a tumor from the same patient in which clones were recovered. The clone-binding to tumor was confirmed by immunostaining, bioassay, and real-time PCR-based methods. Binding studies with noncancer and cancer cell lines of the same histology showed specificity of the tumor-binding clones. Analysis of insert sequences of tumor-homing peptide clones showed several motifs, indicating nonrandom accumulation of clones in human tumors. This is the first reported series of cancer patients to receive phage library for serial panning of tumor targeting ligands. The lack of toxicity and the ability to recover clones with favorable characteristics are a first step for further research with this technology in cancer patients.

Synergistic Targeting of PI3K/AKT Pathway and Androgen Receptor Axis Significantly Delays Castration-Resistant Prostate Cancer Progression In Vivo

The progression to castration-resistant prostate cancer (CRPC) correlates with gain-of-function of the androgen receptor (AR) and activation of AKT. However, as single agents, AR or AKT inhibitors result in a reciprocal feedback loop. Therefore, we hypothesized that combination of an AKT inhibitor with an antiandrogen might result in a more profound, long-lasting remission of CRPC. Here, we report that the AKT inhibitor AZD5363 potently inhibits proliferation and induces apoptosis in prostate cancer cell lines expressing the AR and has anticancer activity in vivo in androgen-sensitive and castration-resistant phases of the LNCaP xenograft model. However, we found that the effect of castration-resistant tumor growth inhibition and prostate-specific antigen (PSA) stabilization is transient and resistance occurs with increasing PSA after approximately 30 days of treatment. Mechanistically, we found that single agent AZD5363 induces increase of AR binding to androgen response element, AR transcriptional activity, and AR-dependent genes such as PSA and NKX3.1 expression. These effects were overcome by the combination of AZD5363 with the antiandrogen bicalutamide, resulting in synergistic inhibition of cell proliferation and induction of apoptosis in vitro, and prolongation of tumor growth inhibition and PSA stabilization in CRPC in vivo. This study provides a preclinical proof-of-concept that combination of an AKT inhibitor with antiandrogen results in prolonged disease stabilization in a model of CRPC. Mol Cancer Ther; 12(11); 2342–55. ©2013 AACR.

A Novel Antiandrogen, Compound 30, Suppresses Castration-Resistant and MDV3100-Resistant Prostate Cancer Growth In Vitro and In Vivo

Resistance to antiandrogen drugs, like MDV3100, occurs in patients with castration-resistant prostate cancer (CRPC). Thus, preventing or treating antiandrogen resistance is a major clinical challenge. We identified a novel antiandrogen, Compound 30, and compared its efficacy with MDV3100. We found that Compound 30 inhibits androgen receptor (AR) activity in LNCaP cells, C4-2 cells, as well as MDV3100-resistant cell lines. Compared with MDV3100, Compound 30 treatment induces greater reduction in AR, prostate-specific antigen (PSA), and AR transcriptional activity, and prevents AR nuclear translocation in AR-sensitive LNCaP cells. Compound 30 has antiproliferative effects in LNCaP cells, in castrate-resistant C4-2 cells, and those resistant to MDV3100. Compound 30 was equally as effective as MDV3100 in reducing tumor volume and PSA in vivo. More importantly, Compound 30 is effective at inhibiting AR activity in MDV3100-resistant cell lines and significantly prevented tumor growth and PSA increases in mice bearing MDV3100-resistant xenografts. Together, our data show that Compound 30 strongly inhibited AR activity and suppressed castration-resistant LNCaP growth as well as MDV3100-resistant cell growth in vitro and in vivo. These data provide a preclinical proof-of-principle that Compound 30 could be a promising next generation anti-AR agent, especially in the context of antiandrogen-resistant tumors. Mol Cancer Ther; 12(5); 567–76. ©2013 AACR.

Transcription Factor Stat5 Knockdown Enhances Androgen Receptor Degradation and Delays Castration-Resistant Prostate Cancer Progression In vivo

Signal transducer and activator of transcription 5 (Stat5) plays an important role in the transition of prostate cancer (PCa) to its castrate-resistant state. Pharmacologic targeting of Stat5 is a rational approach to delay castrate-resistant progression, in part, because Stat5 cooperates with the androgen receptor (AR) to promote PCa progression. Immunostaining of tissue microarrays was used to correlate Stat5 expression with Gleason grade and to characterize changes in treatment-naive and androgen-deprived human PCa. Potency of a Stat5 antisense oligonucleotide (ASO) on Stat5 knockdown, cell growth, and apoptosis was assessed in LNCaP, C4-2, and DU145 cells. Effects of Stat5 knockdown on AR activity and stability was assessed using a PSA transactivation-luciferase assay and cyclohexamide plus MG132 treatment, respectively. LNCaP tumor-bearing mice were castrated and randomly assigned to treatment with Stat5-ASO or controls. Here, we show that the frequency of Stat5 expression is significantly increased in high Gleason grade as well as in hormone-treated PCa. Also, specific knockdown of Stat5 with ASO abrogates androgen-induced AR nuclear translocation and PSA transactivation despite R1881 stimulation. Moreover, Stat5 knockdown destabilizes AR, which leads to AR degradation via the proteasome. Shown for the first time as a preclinical proof-of-principle, Stat5 knockdown with Stat5-ASO significantly delays CRPC tumor progression in vivo. Thereby, we are able to recapitulate our in vitro results by reducing serum PSA and expression levels of target proteins in the xenograft tumors. Mol Cancer Ther; 10(2); 347–59. ©2011 AACR.

Suppression of Heat Shock Protein 27 Using OGX-427 Induces Endoplasmic Reticulum Stress and Potentiates Heat Shock Protein 90 Inhibitors to Delay Castrate-resistant Prostate Cancer

BACKGROUNDnAlthough prostate cancer responds initially to androgen ablation therapies, progression to castration-resistant prostate cancer (CRPC) frequently occurs. Heat shock protein (Hsp) 90 inhibition is a rational therapeutic strategy for CRPC that targets key proteins such as androgen receptor (AR) and protein kinase B (Akt); however, most Hsp90 inhibitors trigger elevation of stress proteins like Hsp27 that confer tumor cell survival and treatment resistance.nnnOBJECTIVEnWe hypothesized that cotargeting the cytoprotective chaperone Hsp27 and Hsp90 would amplify endoplasmic reticulum (ER) stress and treatment-induced cell death in cancer.nnnDESIGN, SETTING, AND PARTICIPANTSnInducible and constitutive Hsp27 and other HSPs were measured by real-time reverse transcription-polymerase chain reaction and immunoblot assays. The combinations of OGX-427 with Hsp90 inhibitors were evaluated in vitro for LNCaP cell growth and apoptosis and in vivo in CRPC LNCaP xenograft models.nnnOUTCOME MEASUREMENTS AND STATISTICAL ANALYSISnTumor volumes were compared using the Kruskal-Wallis test. Overall survival was analyzed using Kaplan-Meier curves, and statistical significance was assessed with the log-rank test.nnnRESULTS AND LIMITATIONSnHsp90 inhibitors induced expression of HSPs in tumor cells and tissues in a dose- and time-dependent manner; in particular, Hsp27 mRNA and protein levels increased threefold. In vitro, OGX-427 synergistically enhanced Hsp90 inhibitor-induced suppression of cell growth and induced apoptosis by 60% as measured by increased sub-G1 fraction and poly(ADP-ribose) polymerase cleavage. These biologic events were accompanied by decreased expression of HSPs, Akt, AR, and prostate-specific antigen, and induction of ER stress markers (cleaved activating transcription factor 6, glucose-regulated protein 78, and DNA-damage-inducible transcript 3). In vivo, OGX-427 potentiated the anticancer effects of Hsp90 inhibitor PF-04929113 (orally, 25mg/kg) to inhibit tumor growth and prolong survival in CRPC LNCaP xenografts.nnnCONCLUSIONSnHSP90 inhibitor-mediated induction of Hsp27 expression can be attenuated by OGX-427, resulting in increased ER stress and apoptosis, and synergistic inhibition of CRPC tumor growth.nnnPATIENT SUMMARYnThis study supports the development of targeted strategies using OGX-427 in combination with Hsp90 inhibitors to improve patient outcome in CRPC.

Carbidopa enhances antitumoral activity of bicalutamide on the androgen receptor‐axis in castration‐resistant prostate tumors

Response to bicalutamide after castration failure is not durable and treatment options at this stage are limited. Carbidopa, an L‐dopa decarboxylase (AR‐coactivator) inhibitor, has been shown to retard prostate tumor growth/PSA production in xenografts. Here, we hypothesize that pharmacological targeting of the AR‐axis by combination treatment with bicalutamide plus carbidopa significantly enhances antitumoral activity in vitro and in vivo compared to monotherapy with either drug.

Abstract A19: Blocking autophagy using lysosomotropic agents sensitizes resistant prostate tumor cells to the novel Akt inhibitor AZD5363

Abstract Introduction and objective: Prostate cancer development is often associated with deletion or silencing of tumor suppressor phosphatase and tensin homologue (PTEN), a negative regulator of the PI3K-Akt pathway, leading to resistance to various therapies in both preclinical and clinical trials. Therefore, the PI3K/Akt pathway plays a central role in various cellular processes promoting survival signaling that can contribute to the malignant phenotype, and, consequently is an attractive pharmacological target. However, as single agents, AKT inhibitors have yet to demonstrate satisfactory results in the treatment of prostate cancer. Although therapeutically relevant concentrations of AKT inhibitors can effectively induce apoptosis as single agents in some prostate cancer cell lines, such as LNCaP, they induce minimal cell death in others, suggesting that there are intrinsic resistance mechanisms that limit their activity in these models. Methods: We investigated the effects of the Akt inhibitor AZD5363 on cell proliferation, cell cycle, apoptosis and Akt downstream pathway. Survival mechanisms induced by AZD5363 were investigated. Then, we examined the impacts of pharmacologic or genetic inhibition of autophagy in combination with AZD5363 on cell proliferation and apoptosis. Furthermore, the anti-cancer activity of combination treatment of a lysosomotropic inhibitor of autophagy (chloroquine) with the Akt inhibitor AZD5363 was evaluated in PC-3 prostate cancer xenograft model. Results: Here, we show that Akt inhibitor AZD5363 affected the Akt downstream pathway by reducing p-mTOR, p-P70S6K and p-S6K protein levels. Moreover, Akt inhibitor AZD5363 alone caused G2 growth arrest failed to induce significant apoptosis and increased autophagy in the PC3 and DU-145 prostate cancer cell lines. Blocking autophagy using pharmacological inhibitors (3-methyladenine, chloroquine and bafilomycin A) or genetic inhibitors (siRNA targeting Atg3 and Atg7) enhanced cell death induced by Akt inhibitor AZD5363 in these tumor prostate cell lines. Importantly, the combination of AZD5363 with chloroquine significantly reduced tumor volume by 84.9% compared with the control group and by 77.5% compared with either drug alone in the PTEN null prostate cancer PC3 xenograft model. Conclusion: Taken together, these data demonstrate that Akt inhibitor AZD5363 synergized with the lysosomotropic inhibitor of autophagy, chloroquine, to induce apoptosis and delay tumor progression in a xenograft model of prostate cancer which was relatively resistant to monotherapy AZD5363. Hence, combination of an AKT inhibitor with an agent that inhibits autophagy provides a novel therapeutic approach which merits further evaluation. Citation Format: Francois Lamoureux, Christian Thomas, Masafumi Kumano, Fan Zhang, Martin Gleave, Amina Zoubeidi. Blocking autophagy using lysosomotropic agents sensitizes resistant prostate tumor cells to the novel Akt inhibitor AZD5363 [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 A19.

Abstract B19: Induction of apoptosis and antitumor activity of the AKT inhibitor AZD5363 is enhanced by combination with hormonal therapies in preclinical models of prostate cancer

Abstract Activation of AKT by mechanisms including loss of the tumor suppressors PTEN and INPP4B is very common in prostate cancer, and has been correlated with poor prognosis and progression to androgen independent disease. Recently, a reciprocal feedback mechanism has been shown to occur between the androgen and AKT signalling axes in prostate cancer models. AZD5363 monotherapy induced apoptosis and inhibited growth of PTEN null, AR+ prostate cancer cell lines including LNCaP, C4-2 and a flutamide resistant variant of PC346C (GI50 10 – 100 nM), and showed moderate anti-proliferative activity in AR amplified, PTEN wild type VCaP cells (GI50 ∼ 1 μM). The PTEN wild type, AR negative DU-145, BPH1 and RWPE1 cell lines were relatively resistant. Monotherapy AZD5363 also caused dosedependent growth inhibition of the PTEN null, AR+ HID28 prostate cancer explant model in vivo. Treatment with AZD5363 increased expression of a panel of androgen regulated genes in LNCaP cells, whereas the same panel of genes was down-regulated when AZD5363 was combined with the novel anti-androgen MDV-3100. Combination of AZD5363 with MDV-3100 resulted in greater inhibition of growth and induction of apoptosis in vitro than monotherapy treatment with these agents, indicating a synergistic interaction. Moreover, combination of AZD5363 and bicalutamide resulted in greater efficacy than AZD5363 monotherapy in LNCaP xenografts in vivo. The data show that whilst AZD5363 has considerable monotherapy activity in AR+/PTEN null prostate cancer models, the combination with anti-androgens merits further evaluation as a possible means to achieve greater anti-tumor activity. AZD5363 is currently in Phase 1 clinical trials. Citation Format: Claire Crafter, Barry R. Davies, Christian Thomas, Francois Lamoureux, Hannah Greenwood, Juan M. Garcia-Martinez, Lorraine Mooney, Sabina Cosulich, Martin Gleave, Amina Zoubeidi. Induction of apoptosis and antitumor activity of the AKT inhibitor AZD5363 is enhanced by combination with hormonal therapies in preclinical models of prostate cancer [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 B19.