Phase 1 study of Z-endoxifen in patients with advanced gynecologic, desmoid, and hormone receptor-positive solid tumors

Background: Differential responses to tamoxifen may be due to inter-patient variability in tamoxifen metabolism into pharmacologically active Z-endoxifen. Z-endoxifen administration was anticipated to bypass these variations, increasing active drug levels, and potentially benefitting patients responding sub-optimally to tamoxifen.

Materials and Methods: Patients with treatment-refractory gynecologic malignancies, desmoid tumors, or hormone receptor-positive solid tumors took oral Z-endoxifen daily with a 3+3 phase 1 dose escalation format over 8 dose levels (DLs). Safety, pharmacokinetics/pharmacodynamics, and clinical outcomes were evaluated.

Results: Thirty-four of 40 patients were evaluable. No maximum tolerated dose was established. DL8, 360 mg/day, was used for the expansion phase and is higher than doses administered in any previous study; it also yielded higher plasma Z-endoxifen concentrations. Three patients had partial responses and 8 had prolonged stable disease (≥ 6 cycles); 44.4% (8/18) of patients at dose levels 6–8 achieved one of these outcomes. Six patients who progressed after tamoxifen therapy experienced partial response or stable disease for ≥ 6 cycles with Z-endoxifen; one with desmoid tumor remains on study after 62 cycles (nearly 5 years).

Conclusions: Evidence of antitumor activity and prolonged stable disease are achieved with Z-endoxifen despite prior tamoxifen therapy, supporting further study of Z-endoxifen, particularly in patients with desmoid tumors.

Biodistribution, Tumor Detection, and Radiation Dosimetry of 18F-5-Fluoro-2'-Deoxycytidine with Tetrahydrouridine in Solid Tumors

In preclinical studies, 5-fluoro-2'-deoxycytidine (FdCyd), an inhibitor of DNA methyltransferase and DNA hypermethylation, has shown treatment efficacy against multiple malignancies by suppressing epigenetic hypermethylation in tumor cells. Several ongoing clinical trials are using FdCyd, and although some patients may respond to this drug, in most patients it is ineffective. Thus, establishing a noninvasive imaging modality to evaluate the distribution of the drug may provide insight into the variable responses. A novel experimental radiopharmaceutical, ¹⁸F-labeled FdCyd, was developed as a companion imaging agent to the nonradioactive form of the drug, FdCyd. We present the first-in-humans radiation dosimetry results and biodistribution of ¹⁸F-FdCyd, administered along with tetrahydrouridine, an inhibitor of cytidine/deoxycytidine deaminase, in patients with a variety of solid tumors undergoing FdCyd therapy. Methods: This phase 0 imaging trial examined the ¹⁸F-FdCyd biodistribution and radiation dosimetry in 5 human subjects enrolled in companion therapy trials. In each subject, 4 sequential PET scans were acquired to estimate whole-body and individual organ effective dose, using OLINDA/EXM, version 1.0. Tumor-to-background ratios were also calculated for the tumor sites visualized on PET/CT imaging. Results: The average whole-body effective dose for the experimental radiopharmaceutical ¹⁸F-FdCyd administered in conjunction with tetrahydrouridine was 2.12E-02 ± 4.15E-03 mSv/MBq. This is similar to the radiation dose estimates for ¹⁸F-FDG PET. The critical organ, with the highest absorbed radiation dose, was the urinary bladder wall at 7.96E-02 mSv/MBq. Other organ doses of note were the liver (6.02E-02mSv/MBq), kidneys (5.26E-02 mSv/MBq), and gallbladder (4.05E-02 mSv/MBq). Tumor target-to-background ratios ranged from 2.4 to 1.4, which potentially enable tumor visualization in static PET images. Conclusion: This phase 0 imaging clinical trial provides evidence that ¹⁸F-FdCyd administered in conjunction with tetrahydrouridine yields acceptable individual organ and whole-body effective doses, as well as modest tumor-to-background ratios that potentially enable tumor visualization. Dose estimates for ¹⁸F-FdCyd are comparable to those for other PET radiopharmaceuticals, such as ¹⁸F-FDG. Further studies with larger study populations are warranted to assess ¹⁸F-FdCyd imaging as a predictor of FdCyd treatment effectiveness.

Abstract 3671: Phenotypic heterogeneity within prostate cancer bone metastases measured by 18F-DCFBC PET/CT and 18F-NaF PET/CT

Purpose: The purpose of this study was to compare the spatial colocalization of prostate-specific membrane antigen (PSMA) targeting agent 18F-DCFBC PET/CT, a marker which demonstrates correlation with tumor aggressiveness, and 18F-NaF PET/CT, a marker of osteoblastic activity, within bone lesions of patients with metastatic prostate cancer. Methods: Twenty-eight metastatic prostate cancer patients received 18F-DCFBC PET/CT and 18F-NaF PET/CT scans (median interval 7 days, range 1-57). Tracer-specific regions of interest (ROI) were derived from threshold containing 80% of maximum SUV (SUV80%). Lesion detection and uptake was compared across the two PET/CT agents using non-parametric testing (Spearman correlation, Wilcoxon rank sum) accounting for intra-patient correlation. Lesion-specific registration was completed by global alignment of skeletal segments followed by local neighborhood optimization of area surrounding lesion. Spatial concordance was evaluated using overlap volume (OV), calculated as the volume of ROI intersection (shared volume) relative to the minimum volume of NaF-ROI or PSMA-ROI to account for differences in ROI volumes. Differences in uptake and CT Hounsfield units (HU) were compared within concordant (overlapping) and discordant (NaF-only, PSMA-only) regions of the same lesion using Wilcoxon signed rank test accounting for intra-patient correlation. Results: Twenty-six patients had positive NaF or DCFBC PET/CT scans, with a total of 241 metastatic sites identified. Lesion-level NaF SUV80% and DCFBC-2hr SUV80% were not significantly correlated at baseline (ρ=0.41, p>0.1). Lesion-level NaF-SUV80% was lower in bone lesions detected only by NaF (N=96) compared to NaF-SUV80% in bone lesions detected by both tracers (N=82), nearing significance (p=0.065). This pattern was not observed in DCFBC-SUV80% (p=0.5). To avoid bias from motion artifacts, only lesions in pelvis and spine were considered for voxel-based analysis (N=42). NaF and PSMA ROIs showing varying levels of spatial concordance (OV mean=0.26, range=0-1), which was modestly associated with higher sclerosis (ρ=0.4, p=0.01) and weakly associated with lower PSMA activity (ρ=0.3, p=0.07). Intra-lesion PSMA-only regions were significantly less sclerotic compared to concordant (p=0.04) and NaF-only (p=0.03) regions, indicating regions of active tumor seeding extend beyond regions of active bone remodeling within the tumor. Conclusions: Metastatic seeding and growth of prostate cancer in bone is biologically complex and dependent on bone microenvironment. We find regions of aggressive cellular activity (PSMA-targeting PET/CT) show heterogeneous colocalization with regions of rapid bone remodeling (NaF PET/CT) within sites of metastatic bone disease. These preliminary findings are important for consideration of targeted radionuclide therapies in metastatic prostate cancer.

Citation Format: Stephanie A. Harmon, Esther Mena, Joanna Shih, Ethan Bergvall, Stephen Adler, Sherif Mehralivand, Ravi A. Madan, James L. Gulley, William L. Dahut, Baris Turkbey, Peter L. Choyke, M Liza Lindenberg. Phenotypic heterogeneity within prostate cancer bone metastases measured by 18F-DCFBC PET/CT and 18F-NaF PET/CT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3671.

A Prospective Comparison of 18F-Sodium Fluoride PET/CT and PSMA-Targeted 18F-DCFBC PET/CT in Metastatic Prostate Cancer

The purpose of this study was to compare the diagnostic performance of ¹⁸F-DCFBC PET/CT, a first-generation ¹⁸F-labeled prostate-specific membrane antigen (PSMA)-targeted agent, and ¹⁸F-NaF PET/CT, a sensitive marker of osteoblastic activity, in a prospective cohort of patients with metastatic prostate cancer. Methods: Twenty-eight prostate cancer patients with metastatic disease on conventional imaging prospectively received up to 4 PET/CT scans. All patients completed baseline ¹⁸F-DCFBC PET/CT and ¹⁸F-NaF PET/CT scans, and 23 patients completed follow-up imaging, with a median follow-up interval of 5.7 mo (range, 4.2-12.6 mo). Lesion detection was compared across the 2 PET/CT agents at each time point. Detection and SUV characteristics of each PET/CT agent were compared with serum prostate-specific antigen (PSA) levels and treatment status at the time of baseline imaging using nonparametric statistical testing (Spearman correlation, Wilcoxon rank). Results: Twenty-six patients had metastatic disease detected on ¹⁸F-NaF or ¹⁸F-DCFBC at baseline, and 2 patients were negative on both scans. Three patients demonstrated soft tissue-only disease. Of 241 lesions detected at baseline, 56 were soft-tissue lesions identified by ¹⁸F-DCFBC only and 185 bone lesions detected on ¹⁸F-NaF or ¹⁸F-DCFBC. ¹⁸F-NaF detected significantly more bone lesions than ¹⁸F-DCFBC (P < 0.001). Correlation of PSA with patient-level SUV metrics was strong in ¹⁸F-DCFBC (ρ > 0.5, P < 0.01) and poor in ¹⁸F-NaF (ρ < 0.3, P > 0.1). When PSA levels were combined with treatment status, patients with below-median levels of PSA (<2 ng/mL) on androgen deprivation therapy (n = 11) demonstrated more lesions on ¹⁸F-NaF than ¹⁸F-DCFBC (P = 0.02). In PSA greater than 2 ng/mL, patients on androgen deprivation therapy (n = 8) showed equal to or more lesions on ¹⁸F-DCFBC than on ¹⁸F-NaF. Conclusion: The utility of PSMA-targeting imaging in metastatic prostate cancer appears to depend on patient disease course and treatment status. Compared with ¹⁸F-NaF PET/CT, ¹⁸F-DCFBC PET/CT detected significantly fewer bone lesions in the setting of early or metastatic castrate-sensitive disease on treatment. However, in advanced metastatic castrate-resistant prostate cancer, ¹⁸F-DCFBC PET/CT shows good concordance with NaF PET/CT.

Utility of 18F-fluoroestradiol (18F-FES) PET/CT imaging as a pharmacodynamic marker in patients with refractory estrogen receptor-positive solid tumors receiving Z-endoxifen therapy

BACKGROUND

Z-endoxifen is the most potent of the metabolites of tamoxifen, and has the potential to be more effective than tamoxifen because it bypasses potential drug resistance mechanisms attributable to patient variability in the expression of the hepatic microsomal enzyme CYP2D6. ¹⁸F-FES is a positron emission tomography (PET) imaging agent which selectively binds to estrogen receptor alpha (ER-α) and has been used for non-invasive in vivo assessment of ER activity in tumors. This study utilizes ¹⁸F-FES PET imaging as a pharmacodynamic biomarker in patients with ER+ tumors treated with Z-endoxifen.

METHODS

Fifteen patients were recruited from a parent therapeutic trial of Z-endoxifen and underwent imaging with ¹⁸F-FES PET at baseline. Eight had positive lesions on the baseline scan and underwent follow-up imaging with ¹⁸F-FES 1-5 days post administration of Z-endoxifen.

RESULTS

Statistically significant changes (p = 0.0078) in standard uptake value (SUV)-Max were observed between the baseline and follow-up scans as early as 1 day post drug administration.

CONCLUSION

F-FES PET imaging could serve as a pharmacodynamic biomarker for patients treated with ER-directed therapy.

Abstract P4-01-09: 18F-FLT-PET/CT for the prediction of response to ANG-1005 therapy in patients with brain metastases from breast cancer

Background: ANG1005 (formerly called GRN1005) is a peptide-drug conjugate being developed for targeted treatment of brain metastases. It consists of 3 molecules of paclitaxel covalently linked to Angiopep-2 designed to cross the blood brain barrier (BBB) via the low density lipoprotein (LDL) receptor-related protein-1 (LRP1)-mediated trancytosis. This drug was evaluated in a multi-center, open-label single-arm study (GRABMB study). An interim analysis determined that the agent met the futility endpoint based on MRI assessment (SABC 2012). However, centrally confirmed responses were achieved in the study, and a biomarker substudy enrolling patients (pts) to evaluate the utility of FLT-PET in assessing response to treatment with ANG1005 suggested sufficient activity of the agent to allow continuation of the study. 18F-FLT (3’-Fluoro-3’ deoxythymidine)-PET imaging is a novel imaging modality which provides a tool for measuring in vivo tumor cell proliferation. FLT is an analog of thymidine; cellular retention of FLT reflects DNA synthesis.

Methods: Adult pts with measurable BMBC were eligible with or without history of prior WBRT. We compared 18F-FLT-PET/CT with MRI-gadolinium contrast images for brain metastases detection and for assessment of whether treatment with ANG1005 was associated with significant change in intracranial tumor uptake of 18F-FLT.

ANG1005 therapy was administered intravenously at 550 mg/m2 q 21d until progression of intra-cranial disease or unacceptable toxicity. All pts underwent 18F-FLT PET/CT imaging before and after 1 cycle of therapy with ANG1005. Pts were scanned dynamically over 30 min followed by a static whole body PET image at 1 hour post-injection. We calculated the% of change before and after therapy, with change &gt; 20% considered significant.

Results: 5/10 planned pts have been accrued to the substudy to date, and 12 metastatic brain lesions have been analyzed. The maximum standard uptake value (SUVmax) ranged from 0.8 to 4.0, mean 1.8 for baseline scans. Tumor to normal brain background ratios ranged from 3.2 to 22.3, mean 9.4. 7/12 lesions showed &gt;20% change between pre and post therapy. The average% change was (-) 42.39% ± 12.77, range: 29.2 to 66.8% (using SUVmax), and (-) 38.7% ± 14.3, range: 20.12 to 57.10% (using tumor to normal ratios). Based on brain MRI evaluation per RECIST 1.1 criteria, 1 pt had intra-cranial partial response (PR) and 3 patients had stable disease (SD). These pts remained on therapy for an average of 7 cycles, range: 5 to 9 cycles. 1 pt withdrew consent after 2 cycles of therapy and opted to receive whole brain radiation therapy. 5/42 pts achieved a confirmed investigator-assessed PR by MRI at 550 mg/m2, and 4/13 pts achieved a PR at 650 mg/m2, a dose not progressed due to toxicity.

Conclusion: This pilot study using 18F-FLT-PET imaging of brain metastases suggests that it is a promising tool for detection and measurement of CNS disease. Given that contrast-enhanced MRI detection of brain metastases represent gadolinium leakage through the BBB rather than actual tumor volume measurements, better approaches are needed to assess efficacy of therapies. Accrual to this study is ongoing. Updated results with ANG1005 will be presented during the meeting.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-09.