Metabolism and pharmacokinetics of radium-223 in prostate cancer

INTRODUCTION

Prostate cancer metastatic to bone is a cause of significant morbidity and mortality. Bone pain and other skeletal events negatively impact the quality of life in patients who might otherwise be functioning well. As such, there has been intense interest in the development of strategies and pharmaceuticals to address this problem.

AREAS COVERED

The authors reviewed the current literature for articles relevant to metastatic prostate cancer, clinical radiopharmaceuticals, castrate-resistant prostate cancer and development of Radium-223 . The authors have referenced primary literature, clinical trials and relevant review articles that summarize the history, development and current utilization of radiopharmaceuticals for management of bone metastases from prostate cancer.

EXPERT OPINION

Radium-223 is the first radiopharmaceutical with an overall survival benefit approved for the treatment of patients with castration-resistant prostate cancer, symptomatic bone metastasis and no known visceral metastatic disease. The additional benefit of clinically significant improved overall survival should lead to exploration of whether this agent can be used earlier in the treatment algorithm or combined with chemotherapy or androgen deprivation therapy. An individualized approach needs to be tailored to each patient based on their overall symptoms, disease burden, hematologic profile and goals of care.

Tumor-directed PET imaging of metastases in metastatic castration-resistant prostate cancer (mCRPC) using Zr-89 labeled antiprostate-specific membrane antigen (PSMA) antibody J591

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Background: There is no standard imaging (SI) modality that specifically and accurately images prostate cancer (PC) metastases, hampering prognostication and response assessment. J591 is a humanized antibody that targets the external domain of PSMA. We have previously reported on the feasibility, PK and biodistribution properties of 89Zr-J591 in 10 patients (pts) (Pandit-Taskar et al, Eur J Nuc Med Img 2014). We now report on the targeting/accuracy in 50 pts with mCRPC. Methods: Following standard CT/MRI, bone scan (BS), and FDG PET imaging, 5 mCi of 89Zr-J591 was administered IV. 89Zr-J591 was imaged 6-8 days after injection. Positive (pos) scan findings were confirmed, where possible, with biopsies (bxs) in the following preference: concordant 89Zr-J591 and FDG pos, 89Zr-J591 and FDG mismatch, and a mismatch between SI and any PET. Results: Imaging: A total of 703 lesions in 50 pts were identified using all imaging modalities. Bone:538 total bone lesions were detected. 491(91%) lesions were present on J591 of which 99 were only evident by J591. BS identified 339 (63%), CT 301 (56%), and FDG 207 (38%). Soft Tissue: 165 total soft tissue lesions were detected. 90 (55%) were seen on J591 of which 17 were only evident by J591. CT identified 124 (75%) and FDG 88 (53%). Pathology:46 bx’s were evaluable (21 bone, 25 soft tissue) in 34 pts. Of the unique J591 lesions biopsied (bx’d), 5/7 were pos for PC. Bone: We bx’d 19 J591 pos lesions and 2 J591 neg sites. Overall, path concordance with J591 was: 89% true pos, 100% true neg, 11% false pos, and 0% false neg. Soft tissue: We bx’d 16 J591 pos lesions and 9 J591 neg sites. Of these, we found 88% true pos, 11% true neg, 13% false pos, and 89% false neg. Conclusions: J591 PET identifies additional disease in bone not seen using other imaging modalities. These lesions are highly likely to correspond to disease by bx. However, the tracer performed less well in soft tissue, with a high false neg rate. Clinical trial information: NCT01543659.

Pituitary expression of CTLA-4 mediates hypophysitis secondary to administration of CTLA-4 blocking antibody

Hypophysitis is a chronic inflammation of the pituitary gland of unknown (primary forms) or recognizable (secondary forms) etiology, such as the use of ipilimumab in cancer immunotherapy. Ipilimumab, which blocks the T cell inhibitory molecule CTLA-4 (cytotoxic T lymphocyte antigen-4), induces hypophysitis in about 4% of patients through unknown mechanisms. We first established a model of secondary hypophysitis by repeated injections of a CTLA-4 blocking antibody into SJL/J or C57BL/6J mice, and showed that they developed lymphocytic infiltration of the pituitary gland and circulating pituitary antibodies. We next assessed the prevalence of pituitary antibodies in a cohort of 20 patients with advanced melanoma or prostate cancer, 7 with a clinical diagnosis of hypophysitis, before and after ipilimumab administration. Pituitary antibodies, negative at baseline, developed in the 7 patients with hypophysitis but not in the 13 without it; these antibodies predominantly recognized thyrotropin-, follicle-stimulating hormone-, and corticotropin-secreting cells. We then hypothesized that the injected CTLA-4 antibody could cause pituitary toxicity if bound to CTLA-4 antigen expressed "ectopically" on pituitary endocrine cells. Pituitary glands indeed expressed CTLA-4 at both RNA and protein levels, particularly in a subset of prolactin- and thyrotropin-secreting cells. Notably, these cells became the site of complement activation, featuring deposition of C3d and C4d components and an inflammatory cascade akin to that seen in type II hypersensitivity. In summary, the study offers a mechanism to explain the pituitary toxicity observed in patients receiving ipilimumab, and highlights the utility of measuring pituitary antibodies in this form of secondary hypophysitis.

Decision-making Processes among Prostate Cancer Survivors with Rising PSA Levels: Results from a Qualitative Analysis

BACKGROUND

Prostate cancer survivors with a rising prostate-specific antigen (PSA) level have few treatment options, experience a heightened state of uncertainty about their disease trajectory that might include the possibility of cancer metastasis and death, and often experience elevated levels of distress as they have to deal with a disease they thought they had conquered. Guided by self-regulation theory, the present study examined the cognitive and affective processes involved in shared decision making between physicians and patients who experience a rising PSA after definitive treatment for prostate cancer.

METHODS

In-depth interviews were conducted with 34 prostate cancer survivors who had been diagnosed with a rising PSA (i.e., biochemical failure) within the past 12 months. Survivors were asked about their experiences and affective responses after being diagnosed with a rising PSA and while weighing potential treatment options. In addition, patients were asked about their decision-making process for the initial prostate cancer treatment.

RESULTS

Compared with the initial diagnosis, survivors with a rising PSA reported increased negative affect following their diagnosis, concern about the treatability of their disease, increased planning and health behavior change, heightened levels of worry preceding doctor appointments (especially prior to the discussion of PSA testing results), and a strong reliance on physicians' treatment recommendations.

CONCLUSIONS

Prostate cancer survivors' decision-making processes for the treatment of a rising PSA are markedly different from those of the initial diagnosis of prostate cancer. Because patients experience heightened distress and rely more heavily on their physicians' recommendations with a rising PSA, interactions with the health care provider provide an excellent opportunity to address and assist patients with managing the uncertainty and distress inherent with rising PSA levels.

Organoid cultures derived from patients with advanced prostate cancer

The lack of in vitro prostate cancer models that recapitulate the diversity of human prostate cancer has hampered progress in understanding disease pathogenesis and therapy response. Using a 3D organoid system, we report success in long-term culture of prostate cancer from biopsy specimens and circulating tumor cells. The first seven fully characterized organoid lines recapitulate the molecular diversity of prostate cancer subtypes, including TMPRSS2-ERG fusion, SPOP mutation, SPINK1 overexpression, and CHD1 loss. Whole-exome sequencing shows a low mutational burden, consistent with genomics studies, but with mutations in FOXA1 and PIK3R1, as well as in DNA repair and chromatin modifier pathways that have been reported in advanced disease. Loss of p53 and RB tumor suppressor pathway function are the most common feature shared across the organoid lines. The methodology described here should enable the generation of a large repertoire of patient-derived prostate cancer lines amenable to genetic and pharmacologic studies.

Targeting castration-resistant prostate cancer with monoclonal antibodies and constructs

Antibodies administered either alone or in a unique construct that can enhance targeting, immunologic recognition and cell killing, remain an area of active interest for a variety of solid tumors. Prostate cancer has unique characteristics as a target for immune-mediated therapies, particularly since it has not only a wide array of antigens expressed on its cell surface, but also has an associated biomarker, which not only can monitor the disease status but also its response to therapy. A number of unique cell surface antigens, as well as internally mediated cell molecules, have shown their clinical activity and efficacy as prostate cancer treatments. The continued evolution of novel antibody-drug and antibody-imaging constructs will probably offer more efficient ways to deliver a therapeutic to the tumor and enhance imaging of active or treated sites of disease.

American Cancer Society prostate cancer survivorship care guidelines

Prostate cancer survivors approach 2.8 million in number and represent 1 in 5 of all cancer survivors in the United States. While guidelines exist for timely treatment and surveillance for recurrent disease, there is limited availability of guidelines that facilitate the provision of posttreatment clinical follow-up care to address the myriad of long-term and late effects that survivors may face. Based on recommendations set forth by a National Cancer Survivorship Resource Center expert panel, the American Cancer Society developed clinical follow-up care guidelines to facilitate the provision of posttreatment care by primary care clinicians. These guidelines were developed using a combined approach of evidence synthesis and expert consensus. Existing guidelines for health promotion, surveillance, and screening for second primary cancers were referenced when available. To promote comprehensive follow-up care and optimal health and quality of life for the posttreatment survivor, the guidelines address health promotion, surveillance for prostate cancer recurrence, screening for second primary cancers, long-term and late effects assessment and management, psychosocial issues, and care coordination among the oncology team, primary care clinicians, and nononcology specialists. A key challenge to the development of these guidelines was the limited availability of published evidence for management of prostate cancer survivors after treatment. Much of the evidence relies on studies with small sample sizes and retrospective analyses of facility-specific and population databases.

Development of thyroglobulin antibodies after GVAX immunotherapy is associated with prolonged survival

Cancer immunotherapy induces a variety of autoinflammatory responses, including those against the thyroid gland, which can be exploited to predict clinical outcomes. Considering the paucity of information about thyroid autoimmunity in patients receiving cancer vaccines, we designed our study to assess the development of thyroglobulin antibodies (TgAbs) in patients treated with GVAX (vaccine made of a tumor cell type transfected with GM-CSF) and/or ipilimumab and correlated seroconversion with survival. Using both in house and commercial ELISA assays, we measured TgAbs in patients with pancreatic (No. = 53), prostate (No. = 35) or colon (No. = 8) cancer, before and after treatment with GVAX only (No. = 34), GVAX plus ipilimumab (No. = 42) or ipilimumab (No. = 20), and correlated their levels with patient's survival, disease status and T-cell surface markers. Antibodies to thyroperoxidase, myeloperoxidase, proteinase 3, insulin and actin were also measured. TgAbs specifically developed after GVAX, independent of the underlying cancer (81% in prostate, 75% colon cancer and 76% pancreatic cancer) and co-administration of ipilimumab (75% in GVAX only and 78% in GVAX plus ipilimumab). This TgAbs seroconversion could be detected mainly by the in house assay, suggesting that the thyroglobulin epitopes recognized by the antibodies induced by GVAX are different from the epitopes seen in the classic form of Hashimoto thyroiditis. Notably, TgAbs seroconversion was associated with significantly prolonged survival (p = 0.01 for pancreas and p = 0.005 for prostate cancer). In conclusion, GVAX immunotherapy induces the appearance of TgAbs that recognize a unique antigenic repertoire and associate with prolonged survival.

Evaluating 18F-16β-fluoro-5α-dihydrotestosterone (FDHT) and FDG PET as prognostic biomarkers for patients (pts) treated with abiraterone acetate (AA)

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Background: There are no available imaging biomarkers that can prognosticate for clinical outcomes for patients treated with AA. FDG and FDHT PET demonstrate glucose metabolism and androgen receptor expression, respectively. This is the first study of FDG and FDHT PET as a prognostic biomarker for pts treated with AA. Methods: Pts with progressive metastatic castration resistant prostate cancer (mCRPC) starting AA underwent FDG and FDHT PET scans on an imaging clinical trial. PSA, SUVmax (hottest slice of hottest lesion), and SUVmaxavg (average SUVmax of 5 index lesions) were collected. An SUV value of 1 was imputed for calculating SUVmaxavg in the absence of 5 index lesions. Imaging characteristics were compared to PFS, defined as time to radiographic progression, biochemical relapse or death. The Cox proportional hazards model was used to determine the association between the PET measurements and PFS. The statistics used to measure the association was the concordance probability estimate (CPE). Results: 24 scans sets were obtained. Median pt characteristics were: age 70 (48-85), Gleason score 8 (range 6-10), PSA 85 (2-459). Radiographic and PSA progression occurred in 15/24 (63%), radiographic only 4/24 (17%), and biochemical only 2/24 (9%). 1 pt died on study, 1 elected to discontinue tx, and 1 remains on AA. 16/24 (67%) and 18/24 (75%) of FDG and FDHT PET scans respectively had ≥ 5 hypermetabolic lesions. Median FDG SUVmax was 8 (2-15), FDG SUVmaxavg 5 (1-11), FDHT SUVmax 11 (3-28) and FDHT SUVmaxavg 7 (1-16). The correlation between PET measurements and PFS is described (Table). Conclusions: Preliminarily, baseline FDG SUVmax and SUVmaxavg appear to be prognostic for PFS in pts treated with AA. Higher SUV values prognosticate for a shorter time to progression. Further evaluations of FDG/FDHT PET in mCRPC are underway to better define the role each modality has as a prognostic and response biomarker for AA. Clinical trial information: NCT00588185. [Table: see text]

Emerging treatments in management of prostate cancer: biomarker validation and endpoints for immunotherapy clinical trial design

The rapidly emerging field of immunotherapy and the development of novel immunologic agents that have been approved in melanoma and successfully studied in lung cancer, kidney cancer, and prostate cancer have mandated that there be uniformity in clinical trial analysis beyond conventional survival endpoints and imaging. This includes some measure of determining whether the immunologic target is hit and how the treatment has impacted on the immune system in toto. While melanoma is leading the field towards these ends, there is some doubt that not all of the recent successes with immune therapies, for example, checkpoint inhibitors, will be effective for every cancer, and that the toxicities may also be different depending on the malignancy. This review serves to elucidate the current issues facing clinical investigators who perform immunologic trials targeted at patients with prostate cancer and discusses the challenges in assessing the right immunologic endpoints to demonstrate biologic/immunologic targeting leading to clinical benefit.

Phase I study of ARN-509, a novel antiandrogen, in the treatment of castration-resistant prostate cancer

PURPOSE

ARN-509 is a novel androgen receptor (AR) antagonist for the treatment of castration-resistant prostate cancer (CRPC). ARN-509 inhibits AR nuclear translocation and AR binding to androgen response elements and, unlike bicalutamide, does not exhibit agonist properties in the context of AR overexpression. This first-in-human phase I study assessed safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor activity of ARN-509 in men with metastatic CRPC.

PATIENTS AND METHODS

Thirty patients with progressive CRPC received continuous daily oral ARN-509 at doses between 30 and 480 mg, preceded by administration of a single dose followed by a 1-week observation period with pharmacokinetic sampling. Positron emission tomography/computed tomography imaging was conducted to monitor [(18)F]fluoro-α-dihydrotestosterone (FDHT) binding to AR in tumors before and during treatment. Primary objective was to determine pharmacokinetics, safety, and recommended phase II dose.

RESULTS

Pharmacokinetics were linear and dose proportional. Prostate-specific antigen declines at 12 weeks (≥ 50% reduction from baseline) were observed in 46.7% of patients. Reduction in FDHT uptake was observed at all doses, with a plateau in response at ≥ 120-mg dose, consistent with saturation of AR binding. The most frequently reported adverse event was grade 1/2 fatigue (47%). One dose-limiting toxicity event (grade 3 abdominal pain) occurred at the 300-mg dose. Dose escalation to 480 mg did not identify a maximum-tolerated dose.

CONCLUSION

ARN-509 was safe and well tolerated, displayed dose-proportional pharmacokinetics, and demonstrated pharmacodynamic and antitumor activity across all dose levels tested. A maximum efficacious dose of 240 mg daily was selected for phase II exploration based on integration of preclinical and clinical data.

Perspectives on immunotherapy in prostate cancer and solid tumors: where is the future?

The goals of any cancer therapy are to improve disease control, palliate pain and improve overall survival. We are fortunate to have in our cancer armamentarium two new immune-directed therapies which not only impact on disease control but also on overall survival. The first, sipuleucel-T, a cellular-based vaccine, was approved for prostate cancer and was shown to be safe with minimal toxicity. The second, ipilimumab, a monoclonal antibody directed to an immunologic checkpoint molecule, showed a survival benefit in patients with advanced melanoma. Benefit appeared to correlate in some cases with the development of autoimmune events, signaling that the immune system is in overdrive against the cancer. Where we are and where we will likely go are the topics to be discussed in this review.

Ipilimumab alone or in combination with radiotherapy in metastatic castration-resistant prostate cancer: results from an open-label, multicenter phase I/II study

BACKGROUND

This phase I/II study in patients with metastatic castration-resistant prostate cancer (mCRPC) explored ipilimumab as monotherapy and in combination with radiotherapy, based on the preclinical evidence of synergistic antitumor activity between anti-CTLA-4 antibody and radiotherapy.

PATIENTS AND METHODS

In dose escalation, 33 patients (≥6/cohort) received ipilimumab every 3 weeks × 4 doses at 3, 5, or 10 mg/kg or at 3 or 10 mg/kg + radiotherapy (8 Gy/lesion). The 10-mg/kg cohorts were expanded to 50 patients (ipilimumab monotherapy, 16; ipilimumab + radiotherapy, 34). Evaluations included adverse events (AEs), prostate-specific antigen (PSA) decline, and tumor response.

RESULTS

Common immune-related AEs (irAEs) among the 50 patients receiving 10 mg/kg ± radiotherapy were diarrhea (54%), colitis (22%), rash (32%), and pruritus (20%); grade 3/4 irAEs included colitis (16%) and hepatitis (10%). One treatment-related death (5 mg/kg group) occurred. Among patients receiving 10 mg/kg ± radiotherapy, eight had PSA declines of ≥50% (duration: 3-13+ months), one had complete response (duration: 11.3+ months), and six had stable disease (duration: 2.8-6.1 months).

CONCLUSIONS

In mCRPC patients, ipilimumab 10 mg/kg ± radiotherapy suggested clinical antitumor activity with disease control and manageable AEs. Two phase III trials in mCRPC patients evaluating ipilimumab 10 mg/kg ± radiotherapy are ongoing. ClinicalTrials.gov identifier: NCT00323882.

Repetitively dosed docetaxel and ¹⁵³samarium-EDTMP as an antitumor strategy for metastatic castration-resistant prostate cancer

BACKGROUND

β-emitting bone-seeking radiopharmaceuticals have historically been administered for pain palliation whereas docetaxel prolongs life in patients with metastatic castration-resistant prostate cancer (mCRPC). In combination, these agents simultaneously target the bone stroma and cancer cell to optimize antitumor effects. The toxicity and efficacy when each agent is combined at full, recommended doses, in a repetitive fashion is not well established.

METHODS

Patients with progressive mCRPC and ≥ 3 bone lesions received (153) Sm-EDTMP (samarium-153 ethylene diamine tetramethylene phosphonate) at a dose of 1.0 mCi/kg every 9 weeks and docetaxel at a dose of 75 mg/m(2) every 3 weeks. In the absence of unacceptable toxicity, patients were allowed to continue additional cycles, defined by 9 weeks of treatment, until intolerance or biochemical/radiographic disease progression.

RESULTS

Of the 30 patients treated, approximately 50% were considered to be taxane-naive, 36.7% were taxane-refractory, and 13.3% had previously been exposed to taxanes but were not considered refractory. Patients received on average 2.5 cycles of treatment (6.5 doses of docetaxel and 2.5 doses of (153) Sm-EDTMP). Twelve patients (40%) demonstrated a decline in their prostate-specific antigen level of ≥ 50%. The median progression-free survival (biochemical or radiographic) was 7.0 months and the overall survival was 14.3 months. Nine patients (30%) did not recover platelet counts >100 K/mm(3) after a median of 3 cycles to allow for additional treatment, with 4 patients experiencing prolonged thrombocytopenia. The most common reasons for trial discontinuation were progressive disease and hematologic toxicity.

CONCLUSIONS

The results of the current study indicate that (153) Sm-EDTMP can be safely combined with docetaxel at full doses on an ongoing basis in patients with mCRPC. Although thrombocytopenia limited therapy for some patients, preliminary efficacy supports the strategy of combining a radiopharmaceutical with chemotherapy, which is an appealing strategy given the anticipated availability of α emitters that can prolong survival.

Evaluating 18F-16B-fluoro-5α-dihydrotestosterone (FDHT) and FDG-PET as a measure of disease progression in metastatic castration resistant prostate cancer (mCRPC)

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Background: Prostate Cancer Working Group 2 defines radiographic progression as new lesions on bone scan. Molecular imaging has potential as a biomarker that reflects both alterations in disease burden and tumor biology. FDG and FDHT PET capture glycolytic activity and androgen receptor (AR) expression and tracer binding, respectively. We examined these tracers in mCRPC patients (pts) at progression (POD) to determine patterns of relapse. Methods: mCRPC pts simultaneously enrolled in imaging and therapeutic clinical trials had FDG and/or FDHT PET scans performed at baseline (BL) and within 4 weeks of treatment (rx) discontinuation for protocol-defined POD. BL characteristics, rx, SUVmax, SUVmaxavg (average of 5 index lesions), and presence of new lesion(s) at POD were collected. ΔSUV was calculated relative to BL. Results: 44 mCRPC pts (86 BL PET scans, 84 scans at POD) receiving novel anti-androgens (eg, enzalutamide) (n=18), abiraterone (abi) (n=10), chemotherapy-based rx (n=5), prednisone (n=4), or other targeted rx (n=7) were included. Of those with PET POD, 75% (24/32) had > 1 new lesion on FDG-PET and 96% (25/26) had > 1 new lesion on FDHT. New lesions on FDHT were seen in 33% (6/18) of pts on novel anti-androgens as compared with 100% (10/10) on abi. Presence of a new FDG avid lesion was similar for both anti-androgens and abi (56% vs 60%). Conclusions: POD on FDG/FDHT is more frequently detected by a new lesion rather than ΔSUV in existing index lesions. This is possibly an underestimate of change as the BL scan and not the post-rx nadir scan were used as a comparator. AR and glycolytic activity at POD may be dependent on individual and treatment factors. Notably, a third of pts on anti-androgens had a new FDHT avid lesion at POD. Full lesional analysis of metastases may enhance our understanding of tumor biology at POD. Clinical trial information: NCT00588185. [Table: see text]

Chimeric antigen receptor (CAR+) modified T cells targeting prostate specific membrane antigen (PSMA) in patients (pts) with castrate metastatic prostate cancer (CMPC)

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Background: A phase I dose-escalating study to assess safety, dose and targeting efficiency of genetically modified autologous human T cells targeted to PSMA was initiated. Preclinical models demonstrated anti-tumor activity and accumulation, migration, and persistence of these cells to tumor. The autologous PSMA-targeted T cells utilizes the P28z second generation chimeric antigen receptor following iv cyclophosphamide (Cy). For safety, the herpes simplex virus-1 thymidine kinase (hsvtk) gene is co-expressed with the P28z receptor, rendering T cells sensitive to ganciclovir for immediate T cell elimination. The expression of hsvtk enables PET imaging using radiolabeled FIAU to localize these T cells Methods: Autologous T cells are activated from a leukapheresis product using anti-CD3/CD28 Dynabeads. Release criteria include mean vector copy number by Q-PCR and vector identity by Southern blot, absence of Replication Competent Retrovirus and residual Dynabeads. Pts were dosed from 107 to 3 x 107 CAR+ T cells/kg.All 7 pts received 300mg/m2 of Cy one day before infusion. Baseline and post treatment imaging included FDG, FDHT and 18F-FIAU PET scans. Results: Three pts in cohort 1 received 1 x 107 CAR+ T cells/kg safely. A fourth pt received the same dose with a modified vector with higher copy number. One pt had stable disease for > 6 months; a second pt has stable scans for > 20 months; the third and fourth patients progressed. Of 3 pts in cohort 2, one received 1.5 x 107 CAR+ T cells/kg and 2 received 3 x 107 CAR+ cell/kg. All 3 had intermittent fever spikes up to 39oC associated with increased levels of IL-4, IL-8, IP-10, sIL-2ra and IL-6 suggesting T cell activation. CAR+ cells persisted in the circulation for up to 2 weeks. Scans with 18F-FIAU labeling suggests that imaging may be cell dose dependent. Conclusions: We have shown that pts can be safely treated with an ex vivo transduction, expansion and therapeutic protocol for the generation of PSMA targeted T cells. Cytokine production suggests in vivo activation and persistence of T cells in blood for up to 2 weeks. Ongoing imaging with 18F may be suboptimal; a second cohort of pts will be studied with 124I-FIAU. Clinical trial information: NCTO1140373.

Chimeric antigen receptor (CAR+) modified T cells targeting prostate-specific membrane antigen (PSMA) in patients (pts) with castrate metastatic prostate cancer (CMPC)

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Background: A phase I dose-escalating study to assess safety, dose and targeting efficiency of genetically modified autologous human T cells targeted to PSMA was initiated. Preclinical models demonstrated anti-tumor activity and accumulation, migration, and persistence of these cells to tumor. The autologous PSMA-targeted T cells utilizes the P28z second generation chimeric antigen receptor following iv cyclophosphamide (Cy). For safety, the herpes simplex virus-1 thymidine kinase (hsvtk) gene is co-expressed with the P28z receptor, rendering T cells sensitive to ganciclovir for immediate T cell elimination. The expression of hsvtk enables PET imaging using radiolabeled FIAU to localize these T cells. Methods: Autologous T cells are activated from a leukapheresis product using anti-CD3/CD28 Dynabeads. Release criteria include mean vector copy number by Q-PCR and vector identity by Southern blot, absence of Replication Competent Retrovirus and residual Dynabeads. Pts were dosed from 107 to 3 x 107 CAR+ T cells/kg. All 7 pts received 300mg/m2 of Cy one day before infusion. Baseline and post treatment imaging included FDG, FDHT and 18F-FIAU PET scans. Results: Three pts in cohort 1 received 1 x 107 CAR+ T cells/kg safely. A fourth pt received the same dose with a modified vector with higher copy number. One pt had stable disease for > 6 months; a second pt has stable scans for > 16 months; the third and fourth patients progressed. Of 3 pts in cohort 2, one received 1.5 x 107 CAR+ T cells/kg and 2 received 3 x 107 CAR+ cell/kg. All 3 had intermittent fever spikes up to 39oC associated with increased levels of IL-4, IL-8, IP-10, sIL-2ra and IL-6 suggesting T cell activation. CAR+ cells persisted in the circulation for up to 2 weeks. Scans with 18F-FIAU labeling suggests that imaging may be cell dose dependent. Conclusions: We have shown that pts can be safetly treated with an ex vivo transduction, expansion and therapeutic protocol for the generation of PSMA targeted T cells. Cytokine production suggests activation of these T cells with their persistence in blood for up to 2 weeks. If imaging with FIAU is suboptimal, a second cohort of pts will be studied with 124I- FIAU. Clinical trial information: NCT01140373.

A phase I dose escalation trial of vaccine replicon particles (VRP) expressing prostate-specific membrane antigen (PSMA) in subjects with prostate cancer

PSMA-VRP is a propagation defective, viral replicon vector system encoding PSMA under phase I evaluation for patients with castration resistant metastatic prostate cancer (CRPC). The product is derived from an attenuated strain of the alphavirus, Venezuelan Equine Encephalitis (VEE) virus, and incorporates multiple redundant safety features. In this first in human trial, two cohorts of 3 patients with CRPC metastatic to bone were treated with up to five doses of either 0.9×10(7)IU or 0.36×10(8)IU of PSMA-VRP at weeks 1, 4, 7, 10 and 18, followed by an expansion cohort of 6 patients treated with 0.36×10(8)IU of PSMA-VRP at weeks 1, 4, 7, 10 and 18. No toxicities were observed. In the first dose cohort, no PSMA specific cellular immune responses were seen but weak PSMA-specific signals were observed by ELISA. The remaining 9 patients, which included the higher cohort and the extension cohort, had no PSMA specific cellular responses. PSMA-VRP was well-tolerated at both doses. While there did not appear to be clinical benefit nor robust immune signals at the two doses studied, neutralizing antibodies were produced by both cohorts suggesting that dosing was suboptimal.

A phase I/IIA study of AGS-PSCA for castration-resistant prostate cancer

BACKGROUND

This first-in-human phase I/IIA study was designed to evaluate the safety and pharmacokinetics (PKs) of AGS-PSCA a fully human monoclonal antibody directed to prostate stem cell antigen (PSCA) in progressive castration-resistant prostate cancer.

PATIENTS AND METHODS

Twenty-nine patients were administered infusions of AGS-PSCA (1-40 mg/kg) every 3 weeks for 12 weeks; 18 final patients received a 40-mg/kg loading dose followed by 20-mg/kg repeat doses. Primary end points were safety and PK. Immunogenicity, antitumor activity and circulating tumor cells were also evaluated.

RESULTS

No drug-related serious adverse events were noted. Dose escalation stopped before reaching the maximum tolerated dose as target concentrations were achieved. Drug levels accumulated linearly with dose and the mean terminal half-life was 2-3 weeks across dose levels. The 40-mg/kg loading dose followed by repeated 20-mg/kg doses yielded serum drug concentrations above the projected minimum therapeutic threshold after two to three doses without excessive drug accumulation or toxicity. Significant antitumor effects were not seen.

CONCLUSIONS

A 40-mg/kg loading dose followed by 20-mg/kg infusions every 3 weeks is the recommended phase II dose of AGS-PSCA. PSCA is a promising drug target and studies in prostate and other relevant solid tumors are planned.

A phase I study of the androgen signaling inhibitor ARN-509 in patients with metastatic castration-resistant prostate cancer (mCRPC)

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Background: ARN-509 is a novel small molecule AR antagonist that impairs AR nuclear translocation and binding to DNA, inhibiting tumor growth and promoting apoptosis, with no partial agonist activity. (Clegg et al., 2012) We conducted a phase I trial to assess safety, pharmacokinetics (PK), and determine the recommended phase II dose (RP2D). Methods: Eligible patients with mCRPC received ARN-509 orally on a continuous daily dosing schedule. Seven doses (30, 60, 90, 120, 180, 240, and 300 mg) were tested using standard 3x3 dose escalation criteria. Once drug concentrations were achieved that met or exceeded optimal levels predicted preclinically, an additional 2 dose levels were tested to further confirm the safety margin of ARN-509 (390 and 480 mg). Anti-tumor activity was assessed by PSA, radiographic responses, and FDHT-PET imaging. Results: Thirty patients were enrolled. The most common grades 1-2 treatment-related adverse events were fatigue (38%), nausea (29%), and pain (24%). There was only 1 treatment-related grade 3 adverse event (abdominal pain) at 300 mg, possibly related to a higher pill burden. PK was shown to be linear and dose-dependent. At 12 weeks, 42% of patients have had ≥ 50% PSA declines. Eleven (37%) patients have discontinued the study due to progression, with the longest patient still on study for more than 16 months. FDHT-PET imaging demonstrated AR blockade at 4 weeks across multiple dose levels. Conclusions: In this phase I study, ARN-509 was shown to be safe and well tolerated with linear PK. Based on promising activity across all dose levels and pharmacodynamic evidence of AR antagonism, an optimal biologic dose of 240 mg daily was selected for phase II investigation. DOD/PCF PCCTC trial sponsored by Aragon Pharmaceuticals.