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IntroductionThe Prostate Cancer Foundation (PCF) convened a PCF prostate-specific membrane antigen (PSMA) Theranostics State of the Science Meeting on 18 November 2019, at Weill Cornell Medicine, New York, NY.MethodsThe meeting was attended by 22 basic, translational, and clinical researchers from around the globe, with expertise in PSMA biology, development and use of PSMA theranostics agents, and clinical trials. The goal of this meeting was to discuss the current state of knowledge, the most important biological and clinical questions, and critical next steps for the clinical development of PSMA positron emission tomography (PET) imaging agents and PSMA-targeted radionuclide agents for patients with prostate cancer.ResultsSeveral major topic areas were discussed including the biology of PSMA, the role of PSMA-targeted PET imaging in prostate cancer, the physics and performance of different PSMA-targeted PET imaging agents, the current state of clinical development of PSMA-targeted radionuclide therapy (RNT) agents, the role of dosimetry in PSMA RNT treatment planning, barriers and challenges in PSMA RNT clinical development, optimization of patient selection for PSMA RNT trials, and promising combination treatment approaches with PSMA RNT.DiscussionThis article summarizes the presentations from the meeting for the purpose of globally disseminating this knowledge to advance the use of PSMA-targeted theranostic agents for imaging and treatment of patients with prostate cancer.

Hu11B6 is a monoclonal antibody that internalizes in cells expressing androgen receptor (AR)-regulated prostate-specific enzyme human kallikrein-related peptidase 2 (hK2; KLK2). In multiple rodent models, Actinium-225-labeled hu11B6-IgG1 ([225Ac]hu11B6-IgG1) has shown promising treatment efficacy. In the present study, we investigated options to enhance and optimize [225Ac]hu11B6 treatment. First, we evaluated the possibility of exploiting IgG3, the IgG subclass with superior activation of complement and ability to mediate FC-γ-receptor binding, for immunotherapeutically enhanced hK2 targeted α-radioimmunotherapy. Second, we compared the therapeutic efficacy of a single high activity vs. fractionated activity. Finally, we used RNA sequencing to analyze the genomic signatures of prostate cancer that progressed after targeted α-therapy. [225Ac]hu11B6-IgG3 was a functionally enhanced alternative to [225Ac]hu11B6-IgG1 but offered no improvement of therapeutic efficacy. Progression-free survival was slightly increased with a single high activity compared to fractionated activity. Tumor-free animals succumbing after treatment revealed no evidence of treatment-associated toxicity. In addition to up-regulation of canonical aggressive prostate cancer genes, such as MMP7, ETV1, NTS, and SCHLAP1, we also noted a significant decrease in both KLK3 (prostate-specific antigen ) and FOLH1 (prostate-specific membrane antigen) but not in AR and KLK2, demonstrating efficacy of sequential [225Ac]hu11B6 in a mouse model.

PurposeThe impact of androgen receptor (AR) activity in breast cancer biology is unclear. We characterized and tested a novel therapy to an AR-governed target in breast cancer.Experimental Design: We evaluated the expression of prototypical AR gene products human kallikrein 2 (hK2) and PSA in breast cancer models. We screened 13 well-characterized breast cancer cell lines for hK2 and PSA production upon in vitro hormone stimulation by testosterone [dihydrotestosterone (DHT)]. AR-positive lines were further evaluated by exposure to estrogen (17β-Estradiol) and the synthetic progestin D-Norgestrel. We then evaluated an anti-hK2-targeted radiotherapy platform (hu11B6), labeled with alpha (α)-particle emitting Actinium-225, to specifically treat AR-expressing breast cancer xenografts under hormone stimulation.ResultsD-Norgestrel and DHT activated the AR pathway, while 17β-Estradiol did not. Competitive binding for AR protein showed similar affinity between DHT and D-Norgestrel, indicating direct AR-ligand interaction. In vivo production of hK2 was sufficient to achieve site-specific delivery of therapeutic radionuclide to tumor tissue at >20-fold over background muscle uptake; effecting long-term local tumor control.Conclusions[225Ac]hu11B6 targeted radiotherapy was potentiated by DHT and by D-Norgestrel in murine xenograft models of breast cancer. AR activity in breast cancer correlates with kallikrein-related peptidase-2 and can be activated by D-Norgestrel, a common contraceptive, and AR induction can be harnessed for hK2-targeted breast cancer α-emitter radiotherapy.

Background: Fluorine 18-labelled tetrafluoroborate ([18F]TFB) is a substrate for the sodium/iodide symporter. In thyroid cancer, [18F]TFB-PET/CT may be an alternative to iodine imaging to evaluate the extent of disease, eligibility for radioiodine treatment, and success of redifferentiation therapies. We report the results of a pilot study to determine tumor uptake of [18F]TFB and compare its properties to [124I]IodinePET/CT in patients with metastatic thyroid cancer. Methods: Five patients were included in a prospective study. All patients received PET/CT 1 h after injection of 356 ± 12 MBq [18F]TFB and were given 230 ± 9 MBq [124I]Iodine orally on the same day, followed by PET/CT after 48 h. Before redifferentiation therapy, patients underwent an additional baseline [124I]Iodine PET/CT. Cases were analyzed by two board-certified specialists. Detection rates and Spearman correlation for [18F]TFB and [124I]Iodine were calculated. Results: Three patients had poorly differentiated thyroid cancer and received trametinib in a redifferentiation trial. Two patients had papillary thyroid cancer and did not receive redifferentiation therapy. Of the 33 lesions seen before/without redifferentiation therapy, 19 (58%) were visible on [18F]TFB and 30 (91%) on [124I]Iodine imaging. In the patients who underwent redifferentiation therapy, 48 lesions were newly seen on [124I]Iodine PET/CT with a median SUVmax of 3.3 (range, 0.4–285.0). All of these lesions were [18F]TFB-negative. Conclusion: [18F]TFB failed to predict radioactive iodine uptake in patients with poorly differentiated thyroid cancer who underwent redifferentiation therapy with trametinib. It is unclear whether such discrepancies may also occur in other redifferentiation therapies or may even be encountered in redifferentiation-naïve thyroid cancer. Trial registration number: NCT03196518, registered on June 22, 2017. [ABSTRACT FROM AUTHOR]

Copy number alteration (CNA) profiling of human tumors has revealed recurrent patterns of DNA amplifications and deletions across diverse cancer types. These patterns are suggestive of conserved selection pressures during tumor evolution but cannot be fully explained by known oncogenes and tumor suppressor genes. Using a pan-cancer analysis of CNA data from patient tumors and experimental systems, here we show that principal component analysis-defined CNA signatures are predictive of glycolytic phenotypes, including 18F-fluorodeoxy-glucose (FDG) avidity of patient tumors, and increased proliferation. The primary CNA signature is enriched for p53 mutations and is associated with glycolysis through coordinate amplification of glycolytic genes and other cancer-linked metabolic enzymes. A pan-cancer and cross-species comparison of CNAs highlighted 26 consistently altered DNA regions, containing 11 enzymes in the glycolysis pathway in addition to known cancer-driving genes. Furthermore, exogenous expression of hexokinase and enolase enzymes in an experimental immortalization system altered the subsequent copy number status of the corresponding endogenous loci, supporting the hypothesis that these metabolic genes act as drivers within the conserved CNA amplification regions. Taken together, these results demonstrate that metabolic stress acts as a selective pressure underlying the recurrent CNAs observed in human tumors, and further cast genomic instability as an enabling event in tumorigenesis and metabolic evolution.

Background: PET–CT-based patient metabolic profiling is a novel concept to incorporate patient-specific metabolism into gastric cancer care. Methods: Staging PET–CTs, demographics, and clinicopathologic variables of gastric cancer patients were obtained from a prospectively maintained institutional database. PET–CT avidity was measured in tumor, liver, spleen, four paired muscles, and two paired fat areas in each patient. The liver to rectus femoris (LRF) ratio was defined as the ratio of SUVmean of liver to the average SUVmean of the bilateral rectus femoris muscles. Kaplan–Meier and Cox-proportional hazards models were used to identify the impact of LRF ratio on OS. Results: Two hundred and one patients with distal gastroesophageal (48%) or gastric (52%) adenocarcinoma were included. Median age was 65 years, and 146 (73%) were male. On univariate analysis, rectus femoris PET–CT avidity and LRF ratio were significantly associated with overall survival (p < 0.05). LRF ratio was significantly higher in males, early-stage cancer, patients with an ECOG 0 or 1 performance status, patients with albumin > 3.5 mg/dL, and those with moderately differentiated tumor histology. In multivariable regression, gastric cancer stage, albumin, and LRF ratio were significant independent predictors of overall survival (LRF ratio HR = 0.73 (0.56–0.96); p = 0.024). Survival curves showed that the prognostic impact of LRF was associated with metastatic gastric cancer (p = 0.009). Conclusions: Elevated LRF ratio, a patient-specific PET–CT-based metabolic parameter, was independently associated with an improvement in OS in patients with metastatic gastric cancer. With prospective validation, LRF ratio may be a useful, host-specific metabolic parameter for prognostication in gastric cancer. [ABSTRACT FROM AUTHOR]

PurposeProgression-free survival (PFS) in metastatic castration-resistant prostate cancer (mCRPC) trials has been inconsistently defined and poorly associated with overall survival (OS). A reproducible quantitative definition of radiographic PFS (rPFS) was tested for association with a coprimary end point of OS in a randomized trial of abiraterone in patients with mCRPC.Patients and methodsrPFS was defined as ≥ two new lesions on an 8-week bone scan plus two additional lesions on a confirmatory scan, ≥ two new confirmed lesions on any scan ≥ 12 weeks after random assignment, and/or progression in nodes or viscera on cross-sectional imaging, or death. rPFS was assessed by independent review at 15% of deaths and by investigator review at 15% and 40% of deaths. rPFS and OS association was evaluated by Spearman's correlation.ResultsA total of 1,088 patients were randomly assigned to abiraterone plus prednisone or prednisone alone. At first interim analysis, the hazard ratio (HR) by independent review was 0.43 (95% CI, 0.35 to 0.52; P < .001; abiraterone plus prednisone: median rPFS, not estimable; prednisone: median rPFS, 8.3 months). Similar HRs were obtained by investigator review at the first two interim analyses (HR, 0.49; 95% CI, 0.41 to 0.60; P < .001 and HR, 0.53; 95% CI, 0.45 to 0.62; P < .001, respectively), validating the imaging data assay used. Spearman's correlation coefficient between rPFS and OS was 0.72.ConclusionrPFS was highly consistent and highly associated with OS, providing initial prospective evidence on further developing rPFS as an intermediate end point in mCRPC trials.

PurposeThe PET tracer, (124)I-cG250, directed against carbonic anhydrase IX (CAIX) shows promise for presurgical diagnosis of clear-cell renal cell carcinoma (ccRCC) (Divgi et al. in Lancet Oncol 8:304-310, 2007; Divgi et al. in J Clin Oncol 31:187-194, 2013). The radiometal (89)Zr, however, may offer advantages as a surrogate PET nuclide over (124)I in terms of greater tumor uptake and retention (Rice et al. in Semin Nucl Med 41:265-282, 2011). We have developed a nonlinear immunokinetic model to facilitate a quantitative comparison of absolute uptake and antibody turnover between (124)I-cG250 and (89)Zr-cG250 using a human ccRCC xenograft tumor model in mice. We believe that this unique model better relates quantitative imaging data to the salient biological features of tumor antibody-antigen binding and turnover.MethodsWe conducted experiments with (89)Zr-cG250 and (124)I-cG250 using a human ccRCC cell line (SK-RC-38) to characterize the binding affinity and internalization kinetics of the two tracers in vitro. Serial PET imaging was performed in mice bearing subcutaneous ccRCC tumors to simultaneously detect and quantify time-dependent tumor uptake in vivo. Using the known specific activities of the two tracers, the equilibrium rates of antibody internalization and turnover in the tumors were derived from the PET images using nonlinear compartmental modeling.ResultsThe two tracers demonstrated virtually identical tumor cell binding and internalization but showed markedly different retentions in vitro. Superior PET images were obtained using (89)Zr-cG250, owing to the more prolonged trapping of the radiolabel in the tumor and simultaneous washout from normal tissues. Estimates of cG250/CAIX complex turnover were 1.35 - 5.51 × 10(12) molecules per hour per gram of tumor (20 % of receptors internalized per hour), and the ratio of (124)I/(89)Zr atoms released per unit time by tumor was 17.5.ConclusionPairwise evaluation of (89)Zr-cG250 and (124)I-cG250 provided the basis for a nonlinear immunokinetic model which yielded quantitative information about the binding and internalization of radioantibody bound to CAIX on tumor cells in vivo. (89)Zr-cG250 is likely to provide high-quality PET images and may be a useful tool to quantify CAIX/cG250 receptor turnover and cG250-accessible antigen density noninvasively in humans.