Randomized Phase II Trial of Sipuleucel-T with or without Radium-223 in Men with Bone-metastatic Castration-resistant Prostate Cancer

PURPOSE

To investigate whether radium-223 increases peripheral immune responses to sipuleucel-T in men with bone-predominant, minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

A total of 32 patients were randomized 1:1 in this open-label, phase II multicenter trial. Patients in the control arm received three sipuleucel-T treatments, 2 weeks apart. Those in the combination arm received six doses of radium-223 monthly, with sipuleucel-T intercalated between the second and fourth doses of radium-223. The primary endpoint was a comparison of peripheral antigen PA2024-specific T-cell responses (measured by proliferation index). Secondary endpoints were progression-free survival (PFS), overall survival (OS), and PSA responses.

RESULTS

We enrolled 32 patients, followed for a median of 1.6 years. Six weeks after the first sipuleucel-T dose, participants in the control arm had a 3.2-fold greater change in PA2024-specific T-cell responses compared with those who received combination treatment (P = 0.036). Patients in the combination arm were more likely to have a >50% PSA decline [5 (31%) vs. 0 patients; P = 0.04], and also demonstrated longer PFS [39 vs. 12 weeks; HR, 0.32; 95% confidence interval (CI), 0.14-0.76] and OS (not reached vs. 2.6 years; HR, 0.32; 95% CI, 0.08-1.23).

CONCLUSIONS

Our data raise the possibility of greater clinical activity with the combination of sipuleucel-T and radium-223 in men with asymptomatic bone mCRPC, despite the paradoxically lower immune responses observed. Additional study to confirm these findings in a larger trial is warranted.

Quantitative and Qualitative Analysis of Blood-based Liquid Biopsies to Inform Clinical Decision-making in Prostate Cancer

CONTEXT

Genomic stratification can impact prostate cancer (PC) care through diagnostic, prognostic, and predictive biomarkers that aid in clinical decision-making. The temporal and spatial genomic heterogeneity of PC together with the challenges of acquiring metastatic tissue biopsies hinder implementation of tissue-based molecular profiling in routine clinical practice. Blood-based liquid biopsies are an attractive, minimally invasive alternative.

OBJECTIVE

To review the clinical value of blood-based liquid biopsy assays in PC and identify potential applications to accelerate the development of precision medicine.

EVIDENCE ACQUISITION

A systematic review of PubMed/MEDLINE was performed to identify relevant literature on blood-based circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), and extracellular vesicles (EVs) in PC.

EVIDENCE SYNTHESIS

Liquid biopsy has emerged as a practical tool to profile tumor dynamics over time, elucidating features that evolve (genome, epigenome, transcriptome, and proteome) with tumor progression. Liquid biopsy tests encompass analysis of DNA, RNA, and proteins that can be detected in CTCs, ctDNA, or EVs. Blood-based liquid biopsies have demonstrated promise in the context of localized tumors (diagnostic signatures, risk stratification, and disease monitoring) and advanced disease (response/resistance biomarkers and prognostic markers).

CONCLUSIONS

Liquid biopsies have value as a source of prognostic, predictive, and response biomarkers in PC. Most clinical applications have been developed in the advanced metastatic setting, where CTC and ctDNA yields are significantly higher. However, standardization of assays and analytical/clinical validation is necessary prior to clinical implementation.

PATIENT SUMMARY

Traces of tumors can be isolated from blood samples from patients with prostate cancer either as whole cells or as DNA fragments. These traces provide information on tumor features. These minimally invasive tests can guide diagnosis and treatment selection.

COVID-19 and androgen-targeted therapy for prostate cancer patients

The current pandemic (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global health challenge with active development of antiviral drugs and vaccines seeking to reduce its significant disease burden. Early reports have confirmed that transmembrane serine protease 2 (TMPRSS2) and angiotensin converting enzyme 2 (ACE2) are critical targets of SARS-CoV-2 that facilitate viral entry into host cells. TMPRSS2 and ACE2 are expressed in multiple human tissues beyond the lung including the testes where predisposition to SARS-CoV-2 infection may exist. TMPRSS2 is an androgen-responsive gene and its fusion represents one of the most frequent alterations in prostate cancer. Androgen suppression by androgen deprivation therapy and androgen receptor signaling inhibitors form the foundation of prostate cancer treatment. In this review, we highlight the growing evidence in support of androgen regulation of TMPRSS2 and ACE2 and the potential clinical implications of using androgen suppression to downregulate TMPRSS2 to target SARS-CoV-2. We also discuss the future directions and controversies that need to be addressed in order to establish the viability of targeting TMPRSS2 and/or ACE2 through androgen signaling regulation for COVID-19 treatment, particularly its relevance in the context of prostate cancer management.

Abstract 5436: Purification and mRNA profiling of extracellular vesicles for early detection of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the 4th most common cause of cancer-related deaths worldwide. The poor prognosis of HCC is due to the fact that diagnosis is often made at an advanced stage in disease development. It is crucial to develop a non-invasive liquid biopsy-based diagnostic solution for early detection of HCC. In this study, we developed a covalent chemistry-based nanostructured silicon substrate (“EV Click Chip”) for the isolation of HCC extracellular vesicles (EVs). The EV Click Chip leverages specific click chemistry reactions and sensitive multi-marker cocktail antibody identification of the HCC EVs. The EV Click Chip also allows for the subsequent release of the captured HCC EVs and is optimal for the downstream molecular analysis. A well-validated 10 liver-specific genes were quantified using reverse transcription droplet digital PCR (RT-ddPCR) in HCC EVs purified by the optimized EV Click Chips for the detection of HCC. Our EV Click Chip-based HCC-EV Assay is able to differentiate HCC from non-HCC controls (chronic liver diseases, healthy donors and other cancers) and outperformed clinical AFP test for distinguishing early-stage HCC from at-risk cirrhotic patients.

Citation Format: Yi-Te Lee, Na Sun, Ryan Y. Zhang, Rueihung Kao, Pin-Jung Chen, Pai-Chi Teng, Jasmine J. Wang, Yingying Yang, Minhyung Kim, Edwin M. Posadas, Sungyong You, Ju Dong Yang, Vatche G. Agopian, Hsian-Rong Tseng, Yazhen Zhu. Purification and mRNA profiling of extracellular vesicles for early detection of hepatocellular carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5436.

Abstract 4331: Nuclear size of circulating tumor cells is associated with prognosis in metastatic, castration-resistant prostate cancer

Background: Current risk stratification models in prostate cancer (PC) have been based on clinical and pathological variables. Beyond serum prostate-specific antigen (PSA) concentration measurements, there remain few new biomarkers to help identify patients at risk for poor clinical outcomes. Morphological analyses using Gleason scoring along with cell nuclear size and shape remains to be a fundamental pathological practice of PC that have been utilized to identify aggressive diseases and to associate with aggressive metastasis. In particular, changes in nuclear shape and composition have been associated with outcome in early stage disease. Circulating tumor cells (CTCs) have arisen as contemporary noninvasive prognostic biomarkers for PC. Previously, a subgroup of PC CTCs, with prominently small nuclei (< 8.5 μm), were found to be correlated with the presence of visceral metastases. This subgroup was named very-small-nuclear CTCs (vsnCTCs). We proposed vsnCTCs as a putative biomarker of a lethal subtype in metastatic castration resistant PC (mCRPC).

Methods: In this study, 76 patients with mCRPC were recruited for overall survival (OS) analysis. Of the 76 patients, 50 had available pre-treatment blood specimens prior to the initiation of androgen receptor signaling inhibitor (ARSI, e.g. abiraterone and enzalutamide) or taxane or tyrosine kinase inhibitor therapy. Using the NanoVelcro CTC Enumeration Assay, CTCs were captured and subjected to immunofluorescence staining. CTCs were identified as DAPI+/CK+/CD45- with a round or oval nucleus. Additionally, CTC nuclear size was measured and defined as the square root of the product of the long axis and the short axis. Kaplan-Meier analysis and Cox proportional hazards model were conducted.

Results: Patients with vsnCTC (i.e., vsnCTC+) had a significantly shortened OS compared with patients without vsnCTC (i.e., vsnCTC-). The median OS was 34 (vsnCTC+, n=49) vs. 149 (vsnCTC-, n=27) weeks (log-rank HR=2.6 with 95% CI 1.5 to 4.5, p=0.0006). Progression free survival (PFS) analysis was performed for the 50 patients with pre-treatment blood samples. The median PFS was 12 (vsnCTC+, n=32) vs. 26 (vsnCTC-, n=18) weeks (log-rank HR=2.2 with 95% CI 1.3 to 4.0, p=0.0038). We also found that the hazard ratio of overall survival increased significantly as the CTC nuclear size decreased using the p-spline plot.

Conclusions: Our study showed that nuclear size reduction has importance in CTCs in a fashion similar to its utility in tissue. This study points toward the importance of the vsnCTC in patients with mCRPC, as vsnCTC+ patients represented a group at risk for faster clinical progression who are at the highest risk for morality. We posit that the vsnCTC represents a new hallmark of an aggressive subtype of mCRPC. This has potential importance in optimizing therapeutic choices.

Citation Format: JASMINE J. WANG, Pai-Chi Teng, Yu Jen Jan, Jie-Fu Chen, Galen Cook-Wiens, Nu Yao, Gina C. Chu, Pin-Jung Chen, Yingying Yang, Yee Hui Yeo, Yi-Te Lee, Leland W. Chung, Sungyong You, Yazhen Zhu, Michael R. Freeman, Andre Rogatko, Ju Dong Yang, Hsian-Rong Tseng, Edwin M. Posadas. Nuclear size of circulating tumor cells is associated with prognosis in metastatic, castration-resistant prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4331.

Abstract 5447: Gene expression of circulating tumor cells is predictive of treatment response in patients with advanced prostate cancer

Background: Genome and transcriptome-based analysis has begun to reshape the approach to prostate cancer (PC). Two different gene expression signatures have shown that PC can be divided into 3 subclasses reflecting luminal-basal biology. These subtypes point toward biological drivers that may strongly influence how care should be personalized including optimization of androgen receptor targeted therapy. The majority of work done in this area has been based on tissue-based gene expression. With the advent of newer nanotechnology platforms for isolation of circulating tumor cells (CTCs), profiling of PC gene expression from blood is now possible.

Methods: We recruited 34 patients with metastatic castration resistant PC who had available blood specimens prior to initiation of androgen receptor signaling inhibitor (ARSI, e.g. abiraterone, enzalutamide and apalutamide) therapy. We combined variations of the NanoVelcro Assays (thermoresponsive, click-chemistry) allowing for capture and release of CTCs with intact mRNA. Gene sets from the PCS and PAM50 signatures were re-reviewed to optimize signal detection in the blood and enriched for genes upregulated in PC. The NanoString nCounter platform was applied to profile the resulting genes. A pilot study was conducted using banked samples available through the Urologic Oncology Program Blood and Biospecimen Bank at Cedars-Sinai Medical Center.

Results: The final assay was tested in banked blood samples and provided classifications of patients that associated with clinical responsiveness to therapy. Validation was conducted to examine the performance of the CTC-specific PCS/PAM50 panel in public databases (including Prostate Cancer Transcriptome Atlas and GenomeDx). Our pilot study showed that the median overall survival was significantly worse in PCS1 patients.

Conclusions: This study shows initial proof of principle that genomic classification in blood is possible using contemporary tool for blood component isolation and RNA profiling. Additional technical and clinical validations are needed prior to widespread implementation, but these methods may make it possible to increase the utilization of genomic classifiers in clinical studies and in practice.

Citation Format: PAI-CHI TENG, Minhyung Kim, Yu Jen Jan, Jie-Fu Chen, Nu Yao, Gina C. Chu, Pin-Jung Chen, Jasmine J. Wang, Yi-Te Lee, Yazhen Zhu, Leland W. Chung, Felix Y. Feng, Michael R. Freeman, Sungyong You, Hsian-Rong Tseng, Edwin M. Posadas. Gene expression of circulating tumor cells is predictive of treatment response in patients with advanced prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5447.

Pharmacokinetics, Safety, and Antitumor Effect of Apalutamide with Abiraterone Acetate plus Prednisone in Metastatic Castration-Resistant Prostate Cancer: Phase Ib Study

PURPOSE

Apalutamide is a next-generation androgen receptor (AR) inhibitor approved for patients with nonmetastatic castration-resistant prostate cancer (CRPC) and metastatic castration-sensitive prostate cancer. We evaluated the pharmacokinetics, safety, and antitumor activity of apalutamide combined with abiraterone acetate plus prednisone (AA-P) in patients with metastatic CRPC (mCRPC).

PATIENTS AND METHODS

Multicenter, open-label, phase Ib drug-drug interaction study conducted in 57 patients with mCRPC treated with 1,000 mg abiraterone acetate plus 10 mg prednisone daily beginning on cycle 1 day 1 (C1D1) and 240 mg apalutamide daily starting on C1D8 in 28-day cycles. Serial blood samples for pharmacokinetic analysis were collected on C1D7 and C2D8.

RESULTS

Systemic exposure to abiraterone, prednisone, and prednisolone decreased 14%, 61%, and 42%, respectively, when apalutamide was coadministered with AA-P. No increase in mineralocorticoid excess-related adverse events was observed. Patients without prior exposure to AR signaling inhibitors had longer median treatment duration and greater mean decrease in prostate-specific antigen (PSA) from baseline compared with those who had received prior therapy. Confirmed PSA reductions of ≥50% from baseline at any time were observed in 80% (12/15) of AR signaling inhibitor-naïve patients and 14% (6/42) of AR signaling inhibitor-treated patients.

CONCLUSIONS

Treatment with apalutamide plus AA-P was well tolerated and showed evidence of antitumor activity in patients with mCRPC, including those with disease progression on AR signaling inhibitors. No clinically significant pharmacokinetic interaction was observed between abiraterone and apalutamide; however, apalutamide decreased exposure to prednisone. These data support development of 1,000 mg abiraterone acetate plus 10 mg prednisone daily with 240 mg apalutamide daily in patients with mCRPC.

SUN-739 Next Generation AR Antagonists Increase Systemic Active Glucocorticoid Exposure by Altering Glucocorticoid Metabolism

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Despite the increased survival benefits of these agents, resistance normally occurs and the disease transitions to its lethal form. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations and increased ratio of active to inactive glucocorticoids. We measured cortisol and cortisol/cortisone ratio (substrate/product of 11β-HSD2) in serum using mass spectrometry before and 1 month on-treatment in 3 clinical trials: 1) neoadjuvant apalutamide + leuprolide (n=25) 2) enzalutamide +/- PROSTVAC for metastatic castration-resistant prostate cancer (n=54) and 3) enzalutamide +/- PROSTVAC for non-metastatic castration-sensitive prostate cancer (n=38 patients). Progression-free survival (PFS) was determined in the metastatic CRPC study of enzalutamide +/- PROSTVAC for those with glucocorticoid changes above and below the median. A statistically significant rise in cortisol concentration and cortisol/cortisone ratio with AR antagonist treatment occurred uniformly across all 3 clinical trials. For example, a rise in cortisol/cortisone ratio occurred in 23/25 (92%) patients (p < 0.001), 36/54 (67%) patients (p < 0.001), and 30/38 (79%) patients (p = 0.051), in the 3 respective trials. In the trial of enzalutamide +/- PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved PSA progression-free survival and radiographic progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed. In conclusion, treatment with enzalutamide or apalutamide increases systemic exposure to active glucocorticoids. These findings have potential consequences for immune suppression and the efficacy of treatment combinations using next-generation AR antagonists. On-treatment, glucocorticoid changes might serve as a pharmacodynamic biomarker.

Loss of testosterone impairs anti-tumor neutrophil function

In men, the incidence of melanoma rises rapidly after age 50, and nearly two thirds of melanoma deaths are male. The immune system is known to play a key role in controlling the growth and spread of malignancies, but whether age- and sex-dependent changes in immune cell function account for this effect remains unknown. Here, we show that in castrated male mice, neutrophil maturation and function are impaired, leading to elevated metastatic burden in two models of melanoma. Replacement of testosterone effectively normalized the tumor burden in castrated male mice. Further, the aberrant neutrophil phenotype was also observed in prostate cancer patients receiving androgen deprivation therapy, highlighting the evolutionary conservation and clinical relevance of the phenotype. Taken together, these results provide a better understanding of the role of androgen signaling in neutrophil function and the impact of this biology on immune control of malignancies.

It is known that there are sex differences in the incidence and prognosis of certain cancers, including melanoma. In this study, the authors utilize a melanoma model to reveal that castrated mice have a higher metastatic burden associated with androgen dependent impaired neutrophil function.

Randomized phase II study of sipuleucel-T (SipT) with or without radium-223 (Ra223) in men with asymptomatic bone-metastatic castrate-resistant prostate cancer (mCRPC)

130

Background: SipT-induced antigen-specific immune responses in mCRPC patients correlate with survival. Due to the immunomodulatory effects of radiopharmaceutical agents (e.g. enhancing tumor-antigen display), we hypothesized that combined use of Ra223 and SipT would augment SipT-related immune response and improve outcomes compared to SipT alone. Methods: Patients with asymptomatic mCRPC and bone-predominant mets, without visceral mets >1.0 cm, were randomized (1:1) to standard SipT alone or combined with 6 doses of Ra223 (NCT02463799). Men in the SipT+Ra223 arm received SipT between the 2nd and 3rd dose of Ra223. Clinical endpoints were radiographic/clinical PFS, PSA response (≥50% decline), AlkPhos response (≥30% decline), and safety. Immunologic endpoints were PA2024-specific T-cell proliferation 6 wks after the first SipT infusion, PA2024-specific ELISPOT response, PAP-specific proliferation and ELISPOT, humoral responses against both antigens, and antigen spread. Results: 32 men were randomized, 16 per arm. Baseline characteristics in SipT and SipT+Ra223 arms were matched with respect to age (median 70 vs 71 yrs), Gleason (8-10: 69% vs 69%), PSA (median 82 vs 72 ng/mL), AlkPhos (median 125 vs 125 U/L) and ECOG scores (≥1: 19% vs 31%). After median follow up of 5.3 (range 2.8–26.6) mo, median PFS was longer in the SipT+Ra223 arm (10.7 vs 3.1 mo; HR 0.35, 95% CI 0.15–0.81; P=0.02). Outcomes were also better in the SipT+Ra223 arm with respect to PSA responses (5/15=33% vs 0/14=0%; P=0.04) and AlkPhos responses (9/15=60% vs 1/15=7%; P=0.01). No safety concerns were observed with the combination (grade 3 AEs shown in the Table). Conclusions: SipT combined with Ra223 was associated with improved clinical outcomes compared to SipT alone. Since neither agent reliably induces PSA responses alone, these data suggest a synergistic effect of the combination. Immunologic endpoints will be presented at the meeting. Larger randomized studies of this combination are warranted. Clinical trial information: NCT02463799. [Table: see text]

Phase Ib study of niraparib plus androgen receptor-targeted therapy (ART) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

122

Background: Poly ADP-ribose polymerase (PARP) inhibitor and abiraterone acetate + prednisone (AA+P) has activity in pts with mCRPC regardless of DNA repair gene defects (DRD). Methods: This phase 1b study (Bedivere; NCT02924766) began with a 3+3 dose escalation of niraparib (Part 1), followed by expansion (Part 2) of the recommended phase 2 dose (RP2D) of nira + AA+P. Pts with mCRPC received nira 200 or 300 mg/day with AA+P. Dose-limiting toxicities (DLTs) were evaluated the first 28 days. Serial PK for nira were collected on cycle 1 day 1 (C1D1) over 24 h; PK for nira and abiraterone were collected on C2D1 over 10 h. Results: Nira 200 mg + 1000 mg AA+P was selected as the RP2D dose. 4 pts in 200 mg cohort and 8 pts in 300 mg cohort were enrolled in Part 1. During Part 1, 1 patient in the 300 mg cohort had two DLTs: Gr 3 fatigue and Gr 4 increased gamma glutamyltransferase. Therefore, the 200 mg dose was evaluated in 15 pts in Part 2. In 19 total pts treated with 200 mg niraparib, 12 (63%) pts had Gr 3-4 AEs, 5 (26%) pts had an AE with outcome of drug discontinuation and 1 (5%) patient had an AE with outcome of death (general physical health deterioration; unrelated). AEs of special interest were: 6 pts (32%) thrombocytopenia, 6 pts (32%) hypertension, 5 pts (26%) anemia and 3 pts (16%) neutropenia of any grade. 21% pts in 200 mg cohort had treatment emergent serious AE (TESAE) while 50% treated with 300 mg had TESAE. The exposure (AUC24h) on Day 1 of Cycle 2 for 200 mg niraparib with 1000 mg of AA were 17745±9380 ng.h/mL and 712±140 ng.h/mL, respectively. These exposures are consistent with single agent PK. Summaries of all responses will be provided, including a patient with primarily bone disease and carrying an ATM mutation who had a circulating tumor cell conversion and was on study treatment for 22.1 mo. Conclusions: The safety and PK findings support the choice of nira 200 mg in combination with AA+P in pts with mCRPC. The efficacy of nira + AA+P is being evaluated in an ongoing phase 3 MAGNITUDE study (NCT03748641). Clinical trial information: NCT02924766.

Prostate cancer CTC-RNA Assay: A new method for contemporary genomics and precision medicine via liquid biopsy

170

Background: Transcriptome-based analysis has begun to reshape the approach to prostate cancer (PC). Two different gene expression signatures have shown that PC can be divided into 3 subclasses reflecting luminal-basal biology. These subtypes point toward biological drivers that may strongly influence how care should be personalized including optimization of androgen receptor targeted therapy. The majority of work done in this area has been based on tissue-based gene expression. With the advent of newer nanotechnology platforms for isolation of circulating tumor cells (CTCs), profiling of PC gene expression from blood is now possible. Methods: We recruited 34 patients with metastatic castration resistant PC at Cedars-Sinai Medical Center who had available blood specimens prior to initiation of androgen receptor signaling inhibitor (ARSI, e.g. abiraterone, enzalutamide and apalutamide) therapy.We utilized the NanoVelcro Assays which allow for capture and release of CTCs with intact mRNA. Gene sets from the PCS and PAM50 signatures were re-reviewed to optimize signal detection in the blood and enriched for genes upregulated in PC. The NanoString nCounter platform was used for RNA profiling. Results: The final assay was tested in banked blood samples and provided classifications of patients that associated with clinical responsiveness to therapy. Validation was conducted to examine the performance of the CTC-specific PCS/PAM50 panel in public databases (including Prostate Cancer Transcriptome Atlas and GenomeDx). Our pilot study showed that the median overall survival was significantly worse in PCS1 patients. Conclusions: This study shows initial proof of principle that genomic classification in blood is possible using contemporary tool for blood component isolation and RNA profiling. Additional technical and clinical validations are needed prior to widespread implementation, but these methods may make it possible to increase the utilization of genomic classifiers in clinical studies and in practice.

The effect of deep AR suppression with enzalutamide or apalutamide on endogenous glucocorticoids: Implications for adverse effects and development of combination therapies

17

Background: Metabolic consequences of potent AR suppression with enzalutamide and apalutamide are unresolved. Endocrine perturbations induced by potent AR antagonists may promote adverse effects and impinge on the potential efficacy of combination therapies, including for example, immunotherapies. We hypothesized that enzalutamide and apalutamide will block 11β-HSD2, the major enzyme that inactivates cortisol in peripheral tissues and results in increased systemic exposure to endogenous active glucocorticoids. We further hypothesized that AR is co-expressed with 11β-HSD2, suggesting a mechanism of suppression. Methods: Cortisol and cortisol/cortisone ratio (substrate/product of 11β-HSD2) were measured in serum using mass spectrometry before and on-treatment in 3 clinical trials: 1) neoadjuvant apalutamide + leuprolide 2) enzalutamide +/- PROSTVAC for metastatic castration-resistant prostate cancer 3) enzalutamide +/- PROSTVAC for non-metastatic castration-sensitive prostate cancer. AR and 11β-HSD2 expression were assessed in kidneys of 13 men and 9 women. Results: A rise in cortisol concentration and cortisol/cortisone ratio occurs uniformly across all 3 trials of potent AR antagonists. For example, a rise in cortisol/cortisone ratio occurred in 23/25 (92%) patients (p<0.001), 30/38 (79%) patients (p=0.051), and 36/64 (67%) patients (p<0.001), in the 3 respective trials. AR is only expressed alongside 11β-HSD2 in the kidneys of men but not women. Conclusions: Treatment with enzalutamide or apalutamide increases systemic exposure to active glucocorticoids. This effect is likely mediated by AR suppression of 11β-HSD2 in the kidney. These findings have potential consequences for immune suppression, the efficacy of treatment combinations using next-generation AR antagonists, and adverse effects of these drugs.

Association of very small nuclear circulating tumor cell (vsnCTC) with clinical outcomes in metastatic castration-resistant prostate cancer

168

Background: Circulating tumor cells (CTCs) have arisen as contemporary noninvasive prognostic biomarkers for prostate cancer (PC). Previously, a subgroup of PC CTCs, with particularly small nuclei (<8.5 μm), were found to be correlated with the presence of visceral metastases. This subgroup was named very-small-nuclear CTCs (vsnCTCs). We proposed vsnCTCs as a putative biomarker of a lethal subtype in metastatic castration resistant PC (mCRPC). Methods: In this study, 76 patients with mCRPC were recruited for overall survival (OS) analysis. Of the 76 patients, 47 had available pre-treatment blood specimens prior to the initiation of androgen receptor signaling inhibitor (ARSI, e.g. abiraterone and enzalutamide) or taxane therapy. Using the NanoVelcro CTC Assay, CTCs were captured and subjected to immunofluorescence staining. CTCs were identified as DAPI+/CK+/CD45- with a round or oval nucleus. Additionally, CTC nuclear size was measured and defined as the square root of the product of the long axis and the short axis. Kaplan-Meier analysis and Cox proportional hazards model were conducted. Results: Patients with vsnCTC (i.e., vsnCTC+) had a significantly shortened OS compared with patients without vsnCTC (i.e., vsnCTC-). The median OS was 34 (vsnCTC+, n=49) vs. 149 (vsnCTC-, n=27) weeks (log-rank HR=2.6 with 95% CI 1.5 to 4.5, p=0.0006). Progression free survival (PFS) analysis was performed for the 47 patients with pre-treatment blood samples. The median PFS was 14 (vsnCTC+, n=29) vs. 26 (vsnCTC-, n=18) weeks (log-rank HR=2.2 with 95% CI 1.2 to 3.9, p=0.0069). We also found that the hazard ratio of overall survival increased significantly as the CTC nuclear size decreased using the p spline plot. Conclusions: Our study showed that nuclear size reduction has importance in CTCs in a fashion similar to its utility in tissue. This study points toward the importance of the vsnCTC in patients with mCRPC, as vsnCTC+ patients represented a group at risk for faster clinical progression who are at the highest risk for morality. We posit that the vsnCTC represents a new hallmark of an aggressive subtype of mCRPC. This has potential importance in optimizing therapeutic choices.

Defining the monocyte subset transcriptional signature associated with progression during androgen-target therapy in prostate cancer patients

157

Background: Myeloid-derived circulating monocytes are emerging as cells of interest in cancer biology. The role of circulating monocytes in human Prostate Cancer (PCa) is poorly understood. Here we asked what is the association of monocyte-specific subsets and their transcriptional signatures with PCa progression during (AR)-target therapy. Methods: Single-cell RNAseq analysis were performed in blood monocytes from 4 patients at two specific time points over their clinical, course: T1)responding to next generation androgen receptor signaling inhibitors (e.g. abiraterone or enzalutamide) as reflected by a decline in serum PSA and/or radiographic response, and T2)progressing through treatment as detected by increases in the serum PSA concentration and/or radiographic signs of progression .PBMC were subjected to Ficoll-purification, and FACS sorted to exclude dead cells and cells expressing B- and T- lineage markers. Samples were then pooled using a BD™ Single-Cell Multiplexing Kit. The samples for scRNA-seq analysis included monocytes defined as classical CD14++CD16−, intermediate CD14+CD16+, and non-classical CD14low/-CD16+++. Results: We have observed nine (9) transcriptionally-defined clusters.Clusters 0, 1, 4, 5, and 8 mapped closely to that of classical monocytes with high expression of CD14and low expression of FCG3RA (CD16). Clusters 2 and 3 mapped closely to that of NK cells with high expression of FCG3RA(CD16) and KLRB1(CD161), and clusters 6 and 7 corresponded to CD14low FCG3RAhigh SIGLEC10+ monocytes. Importantly, our preliminary data revealed a decrease in the percentage of cells in clusters 2 and 6 and an increase in the percentage of cells in cluster 4 in progressing patients (T2). At the transcriptional level, the three main clusters (classical, non-classical, NK-like) were distinguished by 32, 33, and 72 genes, respectively. Our preliminary findings show that progression was associated with several innate immune transcripts while cytotoxic genes were associated with response to Enzalutamide. Conclusions: These data suggest that monocytes transcriptional signature may be reshaped by PCa. Further study of monocytes in PCa progression are warranted.

Deep androgen receptor suppression in prostate cancer exploits sexually dimorphic renal expression for systemic glucocorticoid exposure

BACKGROUND

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Metabolic, hormonal and immunologic effects of deep AR suppression are unknown. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations, increased ratio of active to inactive glucocorticoids and possibly suboptimal response to immunotherapy. On-treatment glucocorticoid changes might serve as an indicator of active glucocorticoid exposure and resultant adverse consequences.

PATIENTS AND METHODS

Human kidney tissues were stained for AR and 11β-HSD2 expression. Patients in three trials [neoadjuvant apalutamide plus leuprolide, enzalutamide ± PROSTVAC (recombinant poxvirus prostate-specific antigen vaccine) for metastatic castration-resistant prostate cancer (CRPC) and enzalutamide ± PROSTVAC for non-metastatic castration-sensitive prostate cancer] were analyzed for cortisol and its metabolites using liquid chromatography-mass spectrometry (LC-MS/MS). Progression-free survival was determined in the metastatic CRPC study of enzalutamide ± PROSTVAC for those with glucocorticoid changes above and below the median.

RESULTS

Concurrent AR and 11β-HSD2 expression occurs only in the kidneys of men. A statistically significant rise in cortisol concentration, cortisol/cortisone ratio and tetrahydrocortisol/tetrahydrocortisone ratio with AR antagonist treatment occurred uniformly across all three trials. In the trial of enzalutamide ± PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed.

CONCLUSION

Enzalutamide and apalutamide treatment toggles renal 11β-HSD2 and significantly increases indicators of and exposure to biologically active glucocorticoids, which is associated with clinical outcomes.

Safety and Efficacy of BIND-014, a Docetaxel Nanoparticle Targeting Prostate-Specific Membrane Antigen for Patients With Metastatic Castration-Resistant Prostate Cancer: A Phase 2 Clinical Trial

Importance

Preferential delivery of docetaxel to tumors by prostate-specific membrane antigen (PSMA)-targeted nanoparticles is clinically effective, and the selective reduction of PSMA-positive circulating tumor cells (CTCs) after treatment has implications for patient selection and disease monitoring.

Objective

To determine the safety and efficacy of BIND-014, a PSMA-directed docetaxel-containing nanoparticle, in patients with metastatic castration-resistant prostate cancer (mCRPC).

Design, Setting, and Participants

A multicenter open-label, phase 2 clinical trial of 42 chemotherapy-naive patients with progressing mCRPC after treatment with abiraterone acetate and/or enzalutamide was conducted from June 24, 2013, to June 10, 2016.

Intervention

Treatment with BIND-014 at a dosage of 60 mg/m2 was given intravenously on day 1 of 21-day cycles in combination with prednisone until disease progression or unacceptable toxic effects occurred.

Main Outcomes and Measures

The primary end point was radiographic progression-free survival according to Prostate Cancer Working Group 2 recommendations and Response Evaluation Criteria in Solid Tumors, version 1.1. Secondary end points included prostate-specific antigen (PSA) response (≥50% reduction from baseline) and changes in CTC number (from ≥5 to <5 cells per 7.5 mL of blood) (CellSearch). Changes in CTC number based on PSMA expression levels on CTCs were also evaluated (Epic Sciences).

Results

Among the 42 patients (81% white), the median age was 66 (range, 50-85) years, and median number of doses received was 6 (range, 1-21). A PSA response was observed in 12 of 40 patients (30%; 95% CI, 18%-45%), measurable disease response in 6 of 19 (32% [95% CI, 15%-54%]), and CTC conversions in 13 of 26 (50%; 95% CI, 32%-68%). Median radiographic progression-free survival was 9.9 (95% CI, 7.1-12.6) months. With use of the Epic Sciences non-EPCAM-based CTC detection platform, CTCs were detected in 16 of 18 patients (89%); 11 of 18 (61%) had CTCs with PSMA expression above the analytical threshold level (PSMA positive) at baseline (range, 0.4-72.4 CTCs/mL). After treatment, PSMA-positive CTCs were preferentially reduced. Treatment-related adverse events included grade 1 or 2 fatigue (29 of 42 patients [69%]), nausea (23 [55%]), neuropathy (14 [33%]), and neutropenic fever (1 [2%]).

Conclusions and Relevance

These findings suggest that treatment with BIND-014 is active and well tolerated in patients with chemotherapy-naive mCRPC. Antitumor activity may be related to PSMA expression levels on CTCs, which suggests that patients who are likely to benefit from this treatment can be identified before treatment is initiated.

Trial Registration

ClinicalTrials.gov Identifier: NCT01812746.

Abstract 453: A circulating tumor cell assay for dynamic assessment of drug sensitivity in metastatic castration-resistant prostate cancer

Background: Tissue-based gene signatures can predict clinical behavior in prostate cancer (PC). Our objective was to extend their application to circulating tumor cells (CTCs) and to show that changes in the signature were associated with changes in clinical behavior.

Methods: Our approach combined the Thermoresponsive(TR)-NanoVelcro CTC purification system with the Nanostring nCounter system for cellular purification and transcriptomic analysis. The Prostate Cancer Classification System (PCS) panel was modified for use in CTCs. We selected 31 blood samples from 23 PC patients receiving androgen receptor signaling inhibitors (ARSI) and measured the PCS1 Z score (probability). These findings were compared with clinical outcome data (responsiveness/resistance).

Results: A modified, 16-gene PCS1 signature was established and validated through a rigorous bioinformatics process. We performed analytical validation of our combined CTC-RNA system to ensure reproducibility and specificity. In patient bloods, ARSI-resistant samples (ARSI-R, n=14) had significantly higher PCS1 Z scores as compared with ARSI-sensitive samples (ARSI-S, n=17) (Rank-sum test, P=0.003). The analyzed bloods contained samples from 8 patients who developed resistance to an ARSI allowing for dynamic measurement of gene expression. Our analysis found that the PCS1 Z score increased at the time that ARSI-resistance emerged (Pairwise T-test, P=0.016).

Conclusions:Using this new methodology, contemporary, clinically-relevant gene signatures such as PCS could be measured non-invasively in CTCs. These findings can be used to relate gene expression to clinical drug response. This approach also allowed for measurement of dynamic variations of gene expression in individual patients over time that correlated to ARSI sensitivity.

Citation Format: Pai-Chi Teng, Yu Jen Jan, Junhee Yoon, Jie-Fu Chen, Pin-Jung Chen, Nu Yao, Shirley Cheng, Amber Lozano, Michael R. Freeman, Sungyong You, Hsian-Rong Tseng, Edwin M. Posadas. A circulating tumor cell assay for dynamic assessment of drug sensitivity in metastatic castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 453.

Covalent chemistry on nanostructured substrates enables noninvasive quantification of gene rearrangements in circulating tumor cells

Well-preserved mRNA in circulating tumor cells (CTCs) offers an ideal material for conducting molecular profiling of tumors, thereby providing a noninvasive diagnostic solution for guiding treatment intervention and monitoring disease progression. However, it is technically challenging to purify CTCs while retaining high-quality mRNA.Here, we demonstrate a covalent chemistry-based nanostructured silicon substrate ("Click Chip") for CTC purification that leverages bioorthogonal ligation-mediated CTC capture and disulfide cleavage-driven CTC release. This platform is ideal for CTC mRNA assays because of its efficient, specific, and rapid purification of pooled CTCs, enabling downstream molecular quantification using reverse transcription Droplet Digital polymerase chain reaction. Rearrangements of ALK/ROS1 were quantified using CTC mRNA and matched with those identified in biopsy specimens from 12 patients with late-stage non-small cell lung cancer. Moreover, CTC counts and copy numbers of ALK/ROS1 rearrangements could be used together for evaluating treatment responses and disease progression.

A circulating tumor cell specific RNA assay for assessment of androgen receptor signaling inhibitor sensitivity in metastatic castration-resistant prostate cancer

5059

Background: Our objective is to develop a circulating tumor cell (CTC)-RNA assay for characterizing clinically relevant RNA signatures for the assessment of androgen receptor signaling inhibitors (ARSIs) sensitivity in metastatic castration-resistant prostate cancer (mCRPC) patients. Methods: We developed NanoVelcro CTC-RNA Assay by combining Thermoresponsive(TR)-NanoVelcro CTC purification system with NanoString nCounter platform for CTC purification and RNA analysis. Based on the well-validated, tissue-based Prostate Cancer Classification System (PCS), we selected the most aggressive and ARSI-resistant subtype- the PCS1, for CTC analysis. We applied a rigorous bioinformatic process to develop a CTC-PCS1 panel that is specific to PC CTCs. We validated NanoVelcro CTC-RNA Assay and CTC-PCS1 panel with PC cell lines to demonstrate sensitivity and specificity of the PCS1 Z score (the likelihood estimate of the PCS1 subtype) for identifying PCS1 subtype and ARSI resistance. We then selected 31 blood samples from 23 PC patients receiving ARSIs to test in our assay. The PCS1 Z score of each sample was computed and compared with ARSI treatment sensitivity. Results: We established a 16-gene CTC-PCS1 panel that consists of CTC-specific RNA signatures. The validation studies using PC cell lines showed that the assay can detect the RNA transcripts with high sensitivity and scalability in the range of 1-100 cells. We also showed that the genes in CTC-PCS1 panel is highly expressed in PC cells. We further demonstrated that the CTC-PCS1 panel is highly specific in identifying PCS1-like samples, and the high PCS1 Z score is associated with ARSI resistance. In patient bloods, ARSI-resistant samples (ARSI-R, n=14) had significantly higher PCS1 Z scores as compared with ARSI-sensitive samples (ARSI-S, n=17) (Rank-sum test, P=0.003). In 8 patients who were initially sensitive to ARSI (ARSI-S) and later developed resistance (ARSI-R), we found that the PCS1 Z score increased from the time of ARSI-S to the time of ARSI-R (Pairwise T-test, P=0.016). Conclusions: Using our new methodology, we developed a first-in-class CTC-RNA assay and demonstrated the feasibility of transforming clinically-relevant tissue-based RNA profiling into CTC tests. This approach allows for detecting RNA expression relevant to clinical drug resistance in a non-invasive fashion, which can facilitate patient-specific treatment selection and early detection of drug resistance- a goal in precision oncology.

Digitally captured step counts for evaluating performance status in advanced cancer patients: A single cohort, prospective trial (Digi-STEPS)

TPS6651

Background: Advanced cancer patients undergo dynamic changes in their functionality and physical activity over the course of their treatment. Monitoring patient function is important because it can inform treatment decisions and allow for timely and appropriate intervention. Current scales that assess patient function, such as the ECOG Performance Status (PS), are limited in their ability to capture the wide range in activity that cancer patients can experience on a daily basis outside of the clinic setting. Given recent technological advances in wearable activity monitors, we can collect real-time, objective information about a patient’s daily activity including steps, stairs, heart rate, sleep, and activity intensity. Thus, the primary objective of this study is to determine whether longitudinal changes in objectively-assessed activity are associated with change in physician-rated ECOG PS. Methods: This is a prospective, single cohort trial being conducted at Cedars-Sinai Medical Center. Stage 3/4 cancer patients who are English or Spanish-speaking, ambulatory (assistive walking devices are allowed) and expected to be seen for treatment or follow-up with their oncologist at least every 8 weeks are eligible for study. Consenting patients will be asked to wear a Fitbit Charge HR continuously for 8 weeks during the study period and for one week prior to the 6 month and 1 year follow-up visits. Primary outcomes are change in average daily step counts and ECOG PS at 8 weeks from baseline. Secondary outcomes include: 1) Change in NIH PROMIS patient-reported outcomes (physical function, pain, sleep, emotional distress, and fatigue), 2) Change in frailty status at 8 weeks, 3) Occurrence of adverse events, and 4) 6-month and 1-year survival outcomes. Baseline assessments include a physical exam, medical history, and frailty assessment. The attending oncologist will rate the patient's ECOG PS at baseline and at the end-of-study visit. Weekly NIH PROMIS questionnaires will be administered online over the 8-week study and again at 6 months and 1 year follow-up. The occurrence of serious cancer-related adverse events, chemotherapy-associated toxicities, and hospitalizations will be documented up to 12 weeks from baseline. Survival will be assessed at 6 months and 1 year. Accrual is ongoing with 20 patients currently enrolled of a target sample size of 60 patients. Clinical trial information: NCT03757182.

A Circulating Tumor Cell-RNA Assay for Assessment of Androgen Receptor Signaling Inhibitor Sensitivity in Metastatic Castration-Resistant Prostate Cancer

Rationale: Our objective was to develop a circulating tumor cell (CTC)-RNA assay for characterizing clinically relevant RNA signatures for the assessment of androgen receptor signaling inhibitor (ARSI) sensitivity in metastatic castration-resistant prostate cancer (mCRPC) patients. Methods: We developed the NanoVelcro CTC-RNA assay by combining the Thermoresponsive (TR)-NanoVelcro CTC purification system with the NanoString nCounter platform for cellular purification and RNA analysis. Based on the well-validated, tissue-based Prostate Cancer Classification System (PCS), we focus on the most aggressive and ARSI-resistant PCS subtype, i.e., PCS1, for CTC analysis. We applied a rigorous bioinformatic process to develop the CTC-PCS1 panel that consists of prostate cancer (PCa) CTC-specific RNA signature with minimal expression in background white blood cells (WBCs). We validated the NanoVelcro CTC-RNA assay and the CTC-PCS1 panel with well-characterized PCa cell lines to demonstrate the sensitivity and dynamic range of the assay, as well as the specificity of the PCS1 Z score (the likelihood estimate of the PCS1 subtype) for identifying PCS1 subtype and ARSI resistance. We then selected 31 blood samples from 23 PCa patients receiving ARSIs to test in our assay. The PCS1 Z scores of each sample were computed and compared with ARSI treatment sensitivity. Results: The validation studies using PCa cell line samples showed that the NanoVelcro CTC-RNA assay can detect the RNA transcripts in the CTC-PCS1 panel with high sensitivity and linearity in the dynamic range of 5-100 cells. We also showed that the genes in CTC-PCS1 panel are highly expressed in PCa cell lines and lowly expressed in background WBCs. Using the artificial CTC samples simulating the blood sample conditions, we further demonstrated that the CTC-PCS1 panel is highly specific in identifying PCS1-like samples, and the high PCS1 Z score is associated with ARSI resistance samples. In patient bloods, ARSI-resistant samples (ARSI-R, n=14) had significantly higher PCS1 Z scores as compared with ARSI-sensitive samples (ARSI-S, n=17) (Rank-sum test, P=0.003). In the analysis of 8 patients who were initially sensitive to ARSI (ARSI-S) and later developed resistance (ARSI-R), we found that the PCS1 Z score increased from the time of ARSI-S to the time of ARSI-R (Pairwise T-test, P=0.016). Conclusions: Using our new methodology, we developed a first-in-class CTC-RNA assay and demonstrated the feasibility of transforming clinically-relevant tissue-based RNA profiling such as PCS into CTC tests. This approach allows for detecting RNA expression relevant to clinical drug resistance in a non-invasive fashion, which can facilitate patient-specific treatment selection and early detection of drug resistance, a goal in precision oncology.

A noninvasive prognostic biomarker for metastatic castration-resistant prostate cancer: Very small nuclear circulating tumor cells

179

Background: Circulating tumor cells (CTCs) have arisen as a contemporary biomarker for prostate cancer (PC). A subgroup of PC CTCs, with particularly small nuclei ( < 8.54 μm), were found to be correlated with poor prognosis and the emergence of visceral metastases (VM). This subgroup was named very-small nuclear CTCs (vsnCTCs). The findings led us to explore vsnCTCs as an aggressive biomarker in metastatic castration-resistant PC (mCRPC). We also explored a biological pathway that potentially drives this morphologic phenomenon. Studies showed that the disruption of the linker of nucleoskeleton and cytoskeleton (LINC) complex proteins, such as emerin, results in nuclear envelope instability and drives cancer cells to an amoeboid phenotype with increasing capacity of migration and invasion. We hypothesized that emerin mislocalization is associated with vsnCTC formation and may be a critical step of metastasis. Methods: Using our NanoVelcro CTC assay, we are able to capture and enumerate CTCs from patients' blood and correlate this data with clinical outcomes. We collected samples from 35 mCRPC patients who failed first-line androgen deprivation therapy and started treatment with abiraterone, enzalutamide, or taxane-based chemotherapy. Survival analyses were performed to exam the correlation between vsnCTC counts and patients’ prognosis. Concurrently, emerin staining was performed and the distribution and expression levels were analyzed in selected vsnCTC samples. Results: The presence of one or more vsnCTCs correlated with worse overall survival (P = 0.00013), progression free survival (PSA progression: P = 0.012; radiographic progression: P = 0.0015), and faster time to VM (P = 0.024). We also observed lower emerin content in vsnCTCs compared to WBC, and more prominent emerin mislocalization in vsnCTCs compared to CTCs with larger nuclei. Conclusions: Our study demonstrated the importance of morphologic characterization of CTCs and suggested that vsnCTCs is a putative biomarker for prediction of worse outcome. Additionally, our findings of emerin mislocalization in vsnCTCs suggested a potential biological pathway behind this nuclear morphologic phenomenon.

A circulating tumor cell RNA assay for dynamic assessment of androgen receptor signaling inhibitors sensitivity in metastatic castration-resistant prostate cancer

157

Background: Tissue-based gene signatures can predict clinical behavior in prostate cancer (PC). Our objective was to extend their application to circulating tumor cells (CTCs) and to show that changes in the signature were associated with changes in clinical behavior. Methods: Our approach combined the Thermoresponsive(TR)-NanoVelcro CTC purification system with the Nanostring nCounter system for cellular purification and transcriptomic analysis. The Prostate Cancer Classification System (PCS) panel was modified for use in CTCs. We selected 31 blood samples from 23 PC patients receiving androgen receptor signaling inhibitors (ARSI) and measured the PCS1 Z score (probability). These findings were compared with clinical outcome data (responsiveness/resistance). Results: A modified, 16-gene PCS1 signature was established and validated through a rigorous bioinformatics process. We performed analytical validation of our combined CTC-RNA system to ensure reproducibility and specificity. In patient bloods, ARSI-resistant samples (ARSI-R, n = 14) had significantly higher PCS1 Z scores as compared with ARSI-sensitive samples (ARSI-S, n = 17) (Rank-sum test, P = 0.003). The analyzed bloods contained samples from 8 patients who developed resistance to an ARSI allowing for dynamic measurement of gene expression. Our analysis found that the PCS1 Z score increased at the time that ARSI-resistance emerged (Pairwise T-test, P = 0.016). Conclusions: Using this new methodology, contemporary, clinically-relevant gene signatures such as PCS could be measured non-invasively in CTCs. These findings can be used to relate gene expression to clinical drug response. This approach also allowed for measurement of dynamic variations of gene expression in individual patients over time that correlated to ARSI sensitivity.