Patient-derived Prostate Cancer Xenograft Models Research Articles

Preclinical Efficacy of a PSMA-Targeted Actinium-225 Conjugate (225Ac-Macropa-Pelgifatamab): A Targeted Alpha Therapy for Prostate Cancer.

Initially, prostate cancer responds to hormone therapy, but eventually resistance develops. Beta emitter-based prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs. The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide. Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi; all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models. These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase I study has been initiated (NCT06052306).

Darolutamide Potentiates the Antitumor Efficacy of a PSMA-targeted Thorium-227 Conjugate by a Dual Mode of Action in Prostate Cancer Models.

Androgen receptor (AR) inhibitors are well established in the treatment of castration-resistant prostate cancer and have recently shown efficacy also in castration-sensitive prostate cancer. Although most patients respond well to initial therapy, resistance eventually develops, and thus, more effective therapeutic approaches are needed. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and presents an attractive target for radionuclide therapy. Here, we evaluated the efficacy and explored the mode of action of the PSMA-targeted thorium-227 conjugate (PSMA-TTC) BAY 2315497, an antibody-based targeted alpha-therapy, in combination with the AR inhibitor darolutamide. The in vitro and in vivo antitumor efficacy and mode of action of the combination treatment were investigated in preclinical cell line-derived and patient-derived prostate cancer xenograft models with different levels of PSMA expression. Darolutamide induced the expression of PSMA in androgen-sensitive VCaP and LNCaP cells in vitro, and the efficacy of darolutamide in combination with PSMA-TTC was synergistic in these cells. In vivo, the combination treatment showed synergistic antitumor efficacy in the low PSMA-expressing VCaP and in the high PSMA-expressing ST1273 prostate cancer models, and enhanced efficacy in the enzalutamide-resistant KUCaP-1 model. The treatments were well tolerated. Mode-of-action studies revealed that darolutamide induced PSMA expression, resulting in higher tumor uptake of PSMA-TTC, and consequently, higher antitumor efficacy, and impaired PSMA-TTC-mediated induction of DNA damage repair genes, potentially contributing to increased DNA damage. These results provide a strong rationale to investigate PSMA-TTC in combination with AR inhibitors in patients with prostate cancer.

Targeting castration-resistant prostate cancer with a novel RORγ antagonist elaiophylin

Prostate cancer (PCa) patients who progress to metastatic castration-resistant PCa (mCRPC) mostly have poor outcomes due to the lack of effective therapies. Our recent study established the orphan nuclear receptor RORγ as a novel therapeutic target for CRPC. Here, we reveal that elaiophylin (Elai), an antibiotic from Actinomycete streptomyces, is a novel RORγ antagonist and showed potent antitumor activity against CRPC in vitro and in vivo. We demonstrated that Elai selectively binded to RORγ protein and potently blocked RORγ transcriptional regulation activities. Structure–activity relationship studies showed that Elai occupied the binding pocket with several key interactions. Furthermore, Elai markedly reduced the recruitment of RORγ to its genomic DNA response element (RORE), suppressed the expression of RORγ target genes AR and AR variants, and significantly inhibited PCa cell growth. Importantly, Elai strongly suppressed tumor growth in both cell line based and patient-derived PCa xenograft models. Taken together, these results suggest that Elai is novel therapeutic RORγ inhibitor that can be used as a drug candidate for the treatment of human CRPC.

Abstract A009: Evaluation of hormonal therapy in a panel of prostate patient-derived xenograft models and comparison to standard cell line models

Abstract Background: Prostate cancer is the second most common cancer worldwide for males, and the fourth most common cancer overall, with more than 1 million new cases diagnosed. However, progress toward understanding the biology of prostate cancer and the development of new therapies has been hampered by the lack of in vivo models that adequately represent the spectrum of benign, latent, aggressive, and metastatic forms of the human disease. Here we report the validation of a panel of patient-derived xenograft (PDX) models and their utilization in preclinical studies alongside cell line models of prostate cancer that are routinely used. Methods: Prostate cancer samples obtained from patients undergoing surgery were collected with ethical consent, disaggregated, and established subcutaneously in Rag-2 knockout mice (The Jackson Laboratory) to generate PDX models. Tumor material was diagnosed on the basis of operative histology and immunohistochemistry (IHC for PSA, androgen receptor expression). Subcutaneous tumor growth of prostate models was evaluated 3 times a week by measuring the tumor in two dimensions using electronic calipers for the duration of the study, and tumor volumes were estimated. For orthotopic PC3M, tumor growth was checked once weekly by bioluminescent imaging (BLI). Briefly, the mice were injected (s.c.) with 150mg/kg D-Luciferin prior to imaging, anesthetized following administration of D-Luciferin, and placed into the imaging chamber (Spectrum CT) and imaged for luminescence (ventral view). Results: We have established a bank of transplantable prostate cancer PDX. Two models were reported to be hormone sensitive and 2 models represented castrate-resistant prostate cancer (CRPC), one of which has a TMPRSS-ETS fusion. In comparison, cell-derived LNCaP requires testosterone to grow whereas the bioluminescent PC3M CRPC orthotopic model develops metastasis in the liver, lungs, lumbar lymph nodes, fore limbs, and hind limbs, representing the late stage of cancer. The tumor response to standard-of-care agents such as docetaxel, abiraterone, and enzalutamide will be reported. Conclusions: We have characterized both cell- and patient-derived prostate cancer xenograft models that will provide a clinically relevant platform spanning the different stages of the disease for preclinical drug evaluation. Citation Format: Nektaria Papadopoulou, Louise Woolley, Louise Wainwright, Lucy Harris, Jane Wrigley, Jason King, Anne Collins, Rajendra Kumari. Evaluation of hormonal therapy in a panel of prostate patient-derived xenograft models and comparison to standard cell line models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A009.

Abstract 2824: Validation of a panel of patient-derived xenograft models for prostate caner and cell line models for preclinical drug evaluation

Abstract Background: Prostate cancer is the second most common cancer worldwide for males, and the fourth most common cancer overall, with more than a million new cases diagnosed. However, progress toward understanding the biology of prostate cancer and the development of new therapies has been hampered by the lack of in vivo models that adequately represent the spectrum of benign, latent, aggressive, and metastatic forms of the human disease. Here we report the validation of a panel of patient-derived xenograft (PDX) models and their utilization in preclinical studies alongside cell line models of prostate cancer. Methods: Prostate cancer samples obtained from patients undergoing surgery were collected with ethical consent, disaggregated and established subcutaneously in Rag2-/-γC-/- mice (The Jackson Laboratory) to generate PDX models. Tumor material was diagnosed on the basis of operative histology and immunohistochemistry (IHC for PSA, androgen receptor expression). Tumor growth in both Rag2-/-γC-/- and NSG mice was evaluated in comparison to cell line models such LNCaP and PC3M. Briefly tumours were measured 3 times a week and tumour volumes were estimated using the formula 0.5 (LxW2) by measuring the tumour in two dimensions using electronic callipers for the duration of the study. For orthotopic PC3M, tumour growth was checked once weekly by bioluminescent imaging (BLI). Briefly, the mice were injected (s.c.) with 150mg/kg D-Luciferin prior to imaging, anaesthetised following administration of D-Luciferin and placed into the imaging chamber (Spectrum CT) and imaged for luminescence (ventral view). Results: We have established a bank of transplantable prostate cancer PDX and stocks are maintained in liquid nitrogen which can be resuscitated in in both Rag2-/-γC-/- and NSG mice. Two models were reported to be hormone sensitive and 2 models represented castrate resistant prostate cancer (CRPC) one of which has a TMPRSS-ETS fusion. In comparison cell-derived LNCaP requires testosterone to grow whereas the bioluminescent PC3M CRPC orthotopic model develops metastasis in the liver, lungs, lumbar lymph nodes, fore limbs and hind limbs representing the late stage of cancer. Conclusions: We have characterised both cell and patient-derived prostate cancer xenograft models which will provide a clinically relevant platform spanning the different stages of the disease for preclinical drug evaluation. Citation Format: Nektaria Papadopoulou, Jane Wrigley, Andrew McKenzie, Jason King, Louise Wainwright, Kelly Jones, Anne Collins, Rajendra Kumari. Validation of a panel of patient-derived xenograft models for prostate caner and cell line models for preclinical drug evaluation [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 2824. doi:10.1158/1538-7445.AM2017-2824

Abstract 4981: Extracellular spacer and co-stimulatory domains define target sensitivity and persistence of CAR T cells for the treatment of PSCA+ bone metastatic prostate cancer

Abstract Advancing chimeric antigen receptor (CAR)-engineered adoptive T cells for the treatment of solid cancers is a major focus in the field of immunotherapy, given impressive recent clinical responses in hematological malignancies. Prostate cancer should be amenable to CAR-based immunotherapy given that several tumor antigens, including prostate stem-cell antigen (PSCA), are widely over-expressed in metastatic disease. The selectivity of CARs for solid cancers is crucial, however, due to the absence of truly restricted tumor antigen expression and potential safety concerns with “on-target off-tumor” activity. Here, we show that optimized co-stimulatory signaling and extracellular spacer domains are essential in defining a CAR’s selectivity towards tumor cells that over-express the target antigen. The 4-1BB co-stimulatory domain in PSCA-CARs confers enhanced tumor selectivity with dampened yet dose-responsive cytokine production, reduced T cell exhaustion phenotype, and equivalent tumor killing ability compared to PSCA-CARs containing the CD28 co-stimulatory domain. CARs containing a short extracellular spacer demonstrate the most selective killing of high PSCA-expressing tumors but are unable to produce the inflammatory cytokines important for a complete anti-tumor response. We show that longer extracellular spacers in PSCA-CARs are necessary for both tumor killing and cytokine production. PSCA-CARs exhibit robust in vivo anti-tumor activity in subcutaneous and orthotopic bone-metastatic patient-derived prostate cancer xenograft models, and 4-1BB-containing CARs show superior persistence in controlling metastatic disease compared with CD28-containing CARs. Our study demonstrates the critical impact of CAR components in defining an optimized tumor-selective CAR T cell, and also highlights the importance of clinically relevant animal models in developing effective solid cancer CAR T cell therapies. Citation Format: Kelly Kennewick, Dileshni Tilakawardane, Ethan Gerdts, John Murad, Anthony Park, Brook Jeang, Yukiko Yamaguchi, Stephen J. Forman, Saul Priceman. Extracellular spacer and co-stimulatory domains define target sensitivity and persistence of CAR T cells for the treatment of PSCA+ bone metastatic prostate cancer [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 4981. doi:10.1158/1538-7445.AM2017-4981

Next generation patient-derived prostate cancer xenograft models

There is a critical need for more effective therapeutic approaches for prostate cancer. Research in this area, however, has been seriously hampered by a lack of clinically relevant, experimental in vivo models of the disease. This review particularly focuses on the development of prostate cancer xenograft models based on subrenal capsule grafting of patients’ tumor tissue into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. This technique allows successful development of transplantable, patient-derived cancer tissue xenograft lines not only from aggressive metastatic, but also from localized prostate cancer tissues. The xenografts have been found to retain key biological properties of the original malignancies, including histopathological and molecular characteristics, tumor heterogeneity, response to androgen ablation and metastatic ability. As such, they are highly clinically relevant and provide valuable tools for studies of prostate cancer progression at cellular and molecular levels, drug screening for personalized cancer therapy and preclinical drug efficacy testing; especially when a panel of models is used to cover a broader spectrum of the disease. These xenograft models could therefore be viewed as next-generation models of prostate cancer.

Abstract 316: Cabazitaxel antitumor activity in docetaxel-resistant patient-derived prostate cancer xenograft models.

Abstract Introduction: The first line of chemotherapy for castration resistant prostate cancer (CRPC) patients is docetaxel treatment. Continued treatment after progression on docetaxel with cabazitaxel can be very strenuous for patients. Clearly, selection of patients that will benefit from either docetaxel or cabazitaxel treatment would be an essential asset to the management of CRPC. Therefore docetaxel-resistant, CRPC xenografts PC339-DOC and PC346C-DOC were developed. These xenografts were tested for sensitivity to cabazitaxel as an initial step to develop a biomarker gene expression profile of docetaxel resistance and cabazitaxel sensitivity in CRPC. Materials and Methods: PC339 (low sensitivity to docetaxel, log cell kill 0.7) and PC346C (moderate sensitivity to docetaxel, log cell kill 1.0) bearing mice were treated with bolus injections of docetaxel (33 mg/kg) every two weeks until the tumor became resistant. Cabazitaxel efficacy was tested in the resistant xenografts by treating PC339-DOC and PC346C-DOC bearing mice with a single bolus injection cabazitaxel (33 mg/kg). Body weight and tumor volume (TV) were monitored up to 160 days post-treatment. Log cell kill was calculated as measure of antitumor activity, taken into account the tumor growth delay induced by the treatment and the tumor doubling time of the tumor (log cell kill= tumor growth delay / tumor doubling time x 3,32). Log cell kill values of < 0.7 reflect no antitumor activity. Importantly, both naïve and resistant xenografts are lacking expression of docetaxel transporter P-glycoprotein (P-gp/ABCB1/MDR1). Results: PC339-DOC was generated within 4 months after start of docetaxel treatment suggesting some intrinsic resistance against docetaxel. In contrast, PC346C-DOC could be classified as acquired resistance as it took more than one year to develop docetaxel resistance in the naïve PC346C. Cabazitaxel was highly active in PC339-DOC, causing complete regression in 4 out of 5 mice (log cell kill > 2.8) while cabazitaxel lacked antitumor activity in PC346C-DOC (log cell kill 0.20). Conclusion: Cabazitaxel was highly active in a docetaxel-resistant PC339DOC xenograft. Low antitumor activity in PC346C-DOC suggests different mechanisms of resistance in both resistant models and potential cross-resistance between taxanes. The differences between PC339-DOC and PC346C-DOC will allow the development of a biomarker profile to specifically select CRPC patients that could benefit from continued treatment with taxanes. Citation Format: Ellen S. de Morree, Corrina M.A. de Ridder, Herman Burger, Erik A.C. Wiemer, Ron H.J. Mathijssen, Ronald de Wit, Wytske M. van Weerden. Cabazitaxel antitumor activity in docetaxel-resistant patient-derived prostate cancer xenograft models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 316. doi:10.1158/1538-7445.AM2013-316

Kava Components Down-Regulate Expression of AR and AR Splice Variants and Reduce Growth in Patient-Derived Prostate Cancer Xenografts in Mice

Men living in Fiji and drinking kava have low incidence of prostate cancer (PCa). However, the PCa incidence among Fijian men who had migrated to Australia, increased by 5.1-fold. We therefore examined the potential effects of kava root extracts and its active components (kavalactones and flavokawains) on PCa growth and androgen receptor (AR) expression. PCa cell lines (LNCaP, LAPC-4, 22Rv1, C4-2B, DU145 and PC-3) with different AR expression, and a transformed prostate myofibroblast cell line (WPMY-1), were treated with a commercial kava extract, kavalactones (kawain, 5′6′-dehydrokawain, yangonin, methysticin) and flavokawain B. Expression of AR and its target genes (PSA and TMPRSS2) was examined. Two novel patient-derived PCa xenograft models from high grade PCa specimens were established by implanting the specimens into nude mice and passing tumor pieces through subcutaneous injection in nude mice, and then treated with kava extract and flavokawain B to examine their effects on tumor growth, AR expression and serum PSA levels. The kava extract and flavokawain B effectively down-regulated the expression of both the full-length AR and AR splice variants. The kava extract and kavalactones accelerated AR protein degradation, while flavokawain B inhibited AR mRNA transcription via decreasing Sp1 expression and the binding of Sp1 to the AR promoter. The kava root extract and flavokawain B reduce tumor growth, AR expression in tumor tissues and levels of serum PSA in the patient-derived PCa xenograft models. These results suggest a potential usefulness of a safe kava product or its active components for prevention and treatment of advanced PCa by targeting AR.