Benchmarking multi-ancestry prostate cancer polygenic risk scores in a real-world cohort

Prostate cancer is a heritable disease with ancestry-biased incidence and mortality. Polygenic risk scores (PRSs) offer promising advancements in predicting disease risk, including prostate cancer. While their accuracy continues to improve, research aimed at enhancing their effectiveness within African and Asian populations remains key for equitable use. Recent algorithmic developments for PRS derivation have resulted in improved pan-ancestral risk prediction for several diseases. In this study, we benchmark the predictive power of six widely used PRS derivation algorithms, including four of which adjust for ancestry, against prostate cancer cases and controls from the UK Biobank and All of Us cohorts. We find modest improvement in discriminatory ability when compared with a simple method that prioritizes variants, clumping, and published polygenic risk scores. Our findings underscore the importance of improving upon risk prediction algorithms and the sampling of diverse cohorts.

Prostate-Specific Membrane Antigen-Targeting Alpha Emitter via Antibody Delivery for Metastatic Castration-Resistant Prostate Cancer: A Phase I Dose-Escalation Study of 225Ac-J591

PURPOSE

Novel therapies are needed to extend survival in metastatic castration-resistant prostate cancer (mCRPC). Prostate-specific membrane antigen (PSMA), a cell surface antigen overexpressed in PC, provides a validated target. This dose-escalation study investigated the safety, efficacy, maximum tolerated dose (MTD), and recommended phase II dose (RP2D) for 225Ac-J591, anti-PSMA monoclonal antibody J591 radiolabeled with the alpha emitter actinium-225.

METHODS

Following investigational new drug-enabling preclinical studies, we enrolled patients with progressive mCRPC that was refractory to or who refused standard treatment options (including androgen receptor pathway inhibitor and had received or been deemed ineligible for taxane chemotherapy). No selection for PSMA was performed. Patients received a single dose of 225Ac-J591 at one of seven dose-escalation levels followed by expansion at the highest dose. Primary end point of dose-escalation cohort was determination of dose-limiting toxicity (DLT) and RP2D.

RESULTS

Radiochemistry and animal studies were favorable. Thirty-two patients received 225Ac-J591 in an accelerated dose-escalation design (22 in dose escalation, 10 in expansion). One patient (1 of 22; 4.5%) experienced DLT in cohort 6 (80 KBq/kg) but none in cohort 7; MTD was not reached, and RP2D was the highest dose level (93.3 KBq/kg). The majority of high-grade adverse events (AEs) were hematologic with an apparent relationship with administered radioactivity. Nonhematologic AEs were generally of low grade. Prostate-specific antigen (PSA) declines and circulating tumor cell (CTC) control were observed: 46.9% had at least 50% PSA decline at any time (34.4% confirmed PSA response), and protocol-defined CTC count response occurred in 13 of 22 (59.1%).

CONCLUSION

To our knowledge, this is the first-in-human phase I dose-escalation trial of a single dose of 225Ac-J591 in 32 patients with pretreated progressive mCRPC demonstrated safety and preliminary efficacy signals. Further investigation is underway.

Prognostic value of neutrophil-to-lymphocyte ratio in patients with metastatic castration-resistant prostate cancer receiving prostate-specific membrane antigen targeted radionuclide therapy

BACKGROUND

Neutrophil count:lymphocyte count ratio (NLR) may be a prognostic factor for men with advanced prostate cancer. We hypothesized that it is associated with prostate-specific antigen (PSA) response and survival in men treated with prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (TRT).

METHODS

Data of 180 men with metastatic castration-resistant prostate cancer (mCRPC) who were treated in sequential prospective radionuclide clinical trials from 2002 to 2021 (utilizing 177Lu-J591, 90Y-J591, 177Lu-PSMA-617, or 225Ac-J591) were retrospectively analyzed. We used a logistic regression to determine the association between NLR and ≥50% PSA decline (PSA50) and a Cox proportional hazards model to investigate the association between NLR and overall survival (OS).

RESULTS

A total of 94 subjects (52.2%) received 177Lu-J591, 51 (28.3%) 177Lu-PSMA-617, 28 (15.6%) 225Ac-J591, and 7 (3.9%) 90Y-J591. The median NLR of 3.75 was used as cut-off (low vs. high NLR; n = 90, respectively). On univariate analysis, NLR was not associated with PSA50 (HR 1.08; 95% confidence interval [CI] 0.99-1.17, p = 0.067). However, it was associated with worse OS (hazard ratio [HR] 1.06, 95% CI 1.02-1.09, p = 0.002), also after controlling for circulating tumor cell count and cancer and leukemia group B risk group (HR 1.05; 95% CI 1.003-1.11, p = 0.036). Men with high NLR were at a higher hazard of death from all causes (HR 1.43, 95% CI 1.05-1.94, p = 0.024).

CONCLUSIONS

NLR provides prognostic information in the setting of patients with mCRPC receiving treatment with PSMA-TRT.

Antibody-drug conjugates for urothelial carcinoma

The standard of care for advanced urothelial carcinoma includes platinum chemotherapy and immunotherapy. Antibody-drug conjugates (ADCs), originally developed for hematologic malignancies, involve potent cytotoxic agents linked to antibodies that recognize tumor-specific antigens; this rational drug design allows for more on-target efficacy, while mitigating systemic toxicity. Herein, we review the emerging landscape of ADCs in urothelial carcinoma. The anti-Nectin-4 ADC enfortumab vedotin has demonstrated efficacy in prospective studies in patients with advanced urothelial carcinoma in several settings either alone or in combination with pembrolizumab. The anti-Trop-2 ADC sacituzumab govitecan has also shown efficacy in single-armed studies. Both conjugates have full or accelerated approval from the Food and Drug Administration. Common adverse events include rash and neuropathy for enfortumab vedotin and myelosuppression and diarrhea for sacituzumab govitecan. Several anti-human epidermal growth factor receptor 2 ADCs are in clinical trials, and in localized bladder cancer, the anti-epithelial cell adhesion molecule ADC oportuzumab monatox is being studied in patients refractory to intravesical bacillus calmette-guerin therapy. Antibody-drug conjugates for urothelial carcinoma are approved and emerging as therapies for patients with advanced urothelial carcinoma, filling a prior void for treatment of progressive disease. Ongoing studies are also evaluating these agents in the neoadjuvant and adjuvant settings.

Long-molecule scars of backup DNA repair in BRCA1- and BRCA2-deficient cancers

Homologous recombination (HR) deficiency is associated with DNA rearrangements and cytogenetic aberrations1. Paradoxically, the types of DNA rearrangements that are specifically associated with HR-deficient cancers only minimally affect chromosomal structure2. Here, to address this apparent contradiction, we combined genome-graph analysis of short-read whole-genome sequencing (WGS) profiles across thousands of tumours with deep linked-read WGS of 46 BRCA1- or BRCA2-mutant breast cancers. These data revealed a distinct class of HR-deficiency-enriched rearrangements called reciprocal pairs. Linked-read WGS showed that reciprocal pairs with identical rearrangement orientations gave rise to one of two distinct chromosomal outcomes, distinguishable only with long-molecule data. Whereas one (cis) outcome corresponded to the copying and pasting of a small segment to a distant site, a second (trans) outcome was a quasi-balanced translocation or multi-megabase inversion with substantial (10 kb) duplications at each junction. We propose an HR-independent replication-restart repair mechanism to explain the full spectrum of reciprocal pair outcomes. Linked-read WGS also identified single-strand annealing as a repair pathway that is specific to BRCA2 deficiency in human cancers. Integrating these features in a classifier improved discrimination between BRCA1- and BRCA2-deficient genomes. In conclusion, our data reveal classes of rearrangements that are specific to BRCA1 or BRCA2 deficiency as a source of cytogenetic aberrations in HR-deficient cells.

Randomized phase II trial of MRI-guided salvage radiotherapy for prostate cancer in 4 weeks versus 2 weeks (SHORTER)

BACKGROUND

Ultra-hypofractionated image-guided stereotactic body radiotherapy (SBRT) is increasingly used for definitive treatment of localized prostate cancer. Magnetic resonance imaging-guided radiotherapy (MRgRT) facilitates improved visualization, real-time tracking of targets and/or organs-at-risk (OAR), and capacity for adaptive planning which may translate to improved targeting and reduced toxicity to surrounding tissues. Given promising results from NRG-GU003 comparing conventional and moderate hypofractionation in the post-operative setting, there is growing interest in exploring ultra-hypofractionated post-operative regimens. It remains unclear whether this can be done safely and whether MRgRT may help mitigate potential toxicity. SHORTER (NCT04422132) is a phase II randomized trial prospectively evaluating whether salvage MRgRT delivered in 5 fractions versus 20 fractions is non-inferior with respect to gastrointestinal (GI) and genitourinary (GU) toxicities at 2-years post-treatment.

METHODS

A total of 136 patients will be randomized in a 1:1 ratio to salvage MRgRT in 5 fractions or 20 fractions using permuted block randomization. Patients will be stratified according to baseline Expanded Prostate Cancer Index Composite (EPIC) bowel and urinary domain scores as well as nodal treatment and androgen deprivation therapy (ADT). Patients undergoing 5 fractions will receive a total of 32.5 Gy over 2 weeks and patients undergoing 20 fractions will receive a total of 55 Gy over 4 weeks, with or without nodal coverage (25.5 Gy over 2 weeks and 42 Gy over 4 weeks) and ADT as per the investigator's discretion. The co-primary endpoints are change scores in the bowel and the urinary domains of the EPIC. The change scores will reflect the 2-year score minus the pre-treatment (baseline) score. The secondary endpoints include safety endpoints, including change in GI and GU symptoms at 3, 6, 12 and 60 months from completion of treatment, and efficacy endpoints, including time to progression, prostate cancer specific survival and overall survival.

DISCUSSION

The SHORTER trial is the first randomized phase II trial comparing toxicity of ultra-hypofractionated and hypofractionated MRgRT in the salvage setting. The primary hypothesis is that salvage MRgRT delivered in 5 fractions will not significantly increase GI and GU toxicities when compared to salvage MRgRT delivered in 20 fractions.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04422132. Date of registration: June 9, 2020.

Complex implementation factors demonstrated when evaluating cost-effectiveness and monitoring racial disparities associated with [18F]DCFPyL PET/CT in prostate cancer men

Prostate cancer (PC) staging with conventional imaging often includes multiparametric magnetic resonance (MR) of the prostate, computed tomography (CT) of the chest, abdomen, and pelvis, and whole-body bone scintigraphy. The recent development of highly sensitive and specific prostate specific membrane antigen (PSMA) positron emission tomography (PET) has suggested that prior imaging techniques may be insufficiently sensitive or specific, particularly when evaluating small pathologic lesions. As PSMA PET/CT is considered to be superior for multiple clinical indications, it is being deployed as the new multidisciplinary standard-of-care. Given this, we performed a cost-effectiveness analysis of [¹⁸F]DCFPyL PSMA PET/CT imaging in the evaluation of PC relative to conventional imaging and anti-3-[¹⁸F]FACBC (¹⁸F-Fluciclovine) PET/CT. We also conducted a single institution review of PSMA PET/CT scans performed primarily for research indications from January 2018 to October 2021. Our snapshot of this period of time in our catchment demonstrated that PSMA PET/CT imaging was disproportionately accessed by men of European ancestry (EA) and those residing in zip codes associated with a higher median household income. The cost-effectiveness analysis demonstrated that [¹⁸F]DCFPyL PET/CT should be considered as an alternative to anti-3-[¹⁸F]FACBC PET/CT and standard of care imaging for prostate cancer staging. [¹⁸F]DCFPyL PET/CT is a new imaging modality to evaluate PC patients with higher sensitivity and specificity in detecting disease than other prostate specific imaging studies. Despite this, access may be inequitable. This discrepancy will need to be addressed proactively as the distribution network of the radiotracer includes both academic and non-academic sites nationwide.

Randomized trial of five or two MRI-guided adaptive radiotherapy treatments for prostate cancer (FORT)

TPS399

Background: The objective of this randomized clinical trial is to demonstrate that 2 treatments of real-time MRI-guided radiotherapy (RT) does not significantly increase patient-reported GI and GU symptoms compared to 5 treatments of RT 2 years after treatment completion (24 months). Methods: Key Eligibility Criteria: Inclusion Criteria 1. Men aged > 18 with histologically confirmed low or intermediate risk prostate cancer per NCCN guidelines. 2. ECOG 0 – 1 3. IPSS < 18 4. Ability to receive MRI-guided radiotherapy. 5. Ability to complete the Expanded Prostate Cancer Index Composite (EPIC) questionnaire. Exclusion Criteria 1. Prior history of receiving pelvic RT. 2. Patient with history of IBD. 3. Hip replacements. 4. History of bladder neck or urethral stricture. 5. TURP < 8 weeks prior to RT 6. Metastatic (pelvic nodal or distant) disease on CT, Bone, and/or PSMA PET scan. Study Design/Endpoints: This is a randomized phase II non-inferiority trial comparing 2 fractions of ultrahypofractionated RT (25 Gy total with optional PSMA/MRI boost to 28 Gy) versus 5 fractions of ultra-hypofractionated RT (37.5 Gy total with optional PSMA/MRI boost to 45 Gy) in the definitive setting for prostate cancer. Subjects will be stratified based on pre-specified stratification factors and randomized 1:1 to receive 2 or 5 fractions using permuted block randomization. The primary endpoint is the change in patient-reported GI and GU symptoms as measured by EPIC at 2 years from end of treatment. Secondary endpoints will include both the safety endpoints including change in GI and GU symptoms at 3, 6, 12 and 60 months from end of treatment, and multiple efficacy endpoints including time to progression, prostate cancer specific survival and overall survival. Sample Size: The sample size is calculated based on a non-inferiority design. The non-inferiority margins are set to be a change score of 6 points for the GI symptoms and 5 points for the GU symptoms. The standard deviations of the change scores are assumed to be 13.2 for the GI symptoms and 10.5 for the GU symptoms based on estimates generated in RTOG 0415 trial. This level of change in scores are deemed as clinically meaningful. For example, 6 points of change score for GI symptoms corresponds to two symptoms worsening by 1 level (i.e., loose stools and frequency of bowel movements change from “no problem” to “very small problem”) or one of the symptoms worsening by 2 levels (i.e., loose stool change from “no problem” to “small problem”). A sample size of 122 with 61 in each arm will ensure 80% power for GI endpoint and 83% power for GU endpoint to detect non-inferiority using a one-sided two-sample t-test at the significance level of 0.05. Adjusting for a projected 10% EPIC/non-compliance rate, 136 patients (68 per arm) will be randomized. Stratification Factors: Patients will be stratified according to baseline EPIC bowel and urinary domain scores and country of treatment. Enrollment: Eleven patients. Clinical trial information: NCT04984343 .

Randomized trial of MRI-guided salvage radiotherapy for prostate cancer in 4 weeks vs. 2 weeks (SHORTER)

TPS400

Background: The objective of this randomized clinical trial is to demonstrate that 2 weeks (5 fractions) of real-time MRI-guided radiotherapy (RT) with an MR Linac does not significantly increase patient-reported GI and GU symptoms compared to 4 weeks (20 fractions) of RT 2 years after treatment completion. Methods: Key Eligibility Criteria: Inclusion Criteria 1. Men aged > 18 with histologically confirmed prostate cancer after prostatectomy with detectable PSA. 2. KPS > 70. 3. Patients with no evidence of distant metastatic disease on PET/CT/MRI/bone scan< 180 days prior to enrollment. 4. Ability to receive MRI-guided radiotherapy. 5. Ability to complete the Expanded Prostate Cancer Index Composite (EPIC) questionnaire. Exclusion Criteria 1. Prior history of receiving pelvic RT. 2. Patient with history of IBD. 3. History of bladder neck or urethral stricture. Study Design/Endpoints: This is a randomized phase II non-inferiority trial comparing 5 fractions of ultrahypofractionated RT (32.5 Gy total with optional PSMA/MRI boost to 40 Gy) versus 20 fractions of hypofractionated RT (55 Gy total with optional PSMA/MRI boost to 60 Gy) in the post-operative setting for prostate cancer. Subjects will be stratified based on pre-specified stratification factors and randomized 1:1 to receive 5 or 20 fractions using permuted block randomization. The primary endpoint is the change in patient-reported GI and GU symptoms as measured by EPIC at 2 years from end of treatment. Secondary endpoints will include both the safety endpoints including change in GI and GU symptoms at 3, 6, 12 and 60 months from end of treatment, and multiple efficacy endpoints including time to progression, prostate cancer specific survival and overall survival. Sample Size: The sample size is calculated based on a non-inferiority design. The non-inferiority margins are set to be a change score of 6 points for the GI symptoms and 5 points for the GU symptoms. The standard deviations of the change scores are assumed to be 13.2 for the GI symptoms and 10.5 for the GU symptoms based on estimates generated in RTOG 0415 trial. This level of change in scores are deemed as clinically meaningful. For example, 6 points of change score for GI symptoms corresponds to two symptoms worsening by 1 level (i.e., loose stools and frequency of bowel movements change from “no problem” to “very small problem”) or one of the symptoms worsening by 2 levels (i.e., loose stool change from “no problem” to “small problem”). A sample size of 122 with 61 in each arm will ensure 80% power for GI endpoint and 83% power for GU endpoint to detect non-inferiority using a one-sided two-sample t-test at the significance level of 0.05. Adjusting for a projected 10% EPIC/non-compliance rate, 136 patients (68 per arm) will be randomized. Stratification Factors: Patients will be stratified according to baseline EPIC bowel and urinary domain scores and use of nodal treatment and ADT. Enrollment: 91 patients. Clinical trial information: NCT04422132 .

A phase I/II dose-escalation study of fractionated 225Ac-J591 for progressive metastatic castration-resistant prostate cancer (mCRPC) in patients with prior treatment with 177Lu-PSMA

TPS288

Background: As prostate-specific membrane antigen targeted radiotherapy (PSMA-TRT) is now an active standard-of-care treatment in mCRPC, ongoing studies with alternative approaches to targeting PSMA will increasingly need to consider the consequences of sequential PSMA-TRT exposure. Our past and ongoing investigations into antibody-based targeting (e.g., J591) and potent alpha emitting payloads (e.g., 225Ac) impact drug kinetics, biodistribution, and resultant clinical toxicities. In a first-in-human phase I dose-escalation study of 225Ac-J591, patients with mCRPC were treated with a single dose of 225Ac-J591 on seven dose levels, up to 93.3 KBq/kg without achievement of maximal tolerated dose (MTD). One patient treated at 80 KBq/kg developed dose-limiting toxicity (DLT) of Gr 4 anemia and thrombocytopenia, but 0 of 6 at 93.3 KBq/Kg had Gr > 3 heme toxicity or Gr > 2 non-heme toxicity. Although not intentionally preselected for prior exposure, 55% (12/22) of patients had 177Lu-PSMA previously. With approval of 177Lu vipivotide tetraxetan, we amended an ongoing phase I dose-escalation study to include a post-177-Lu-PSMA cohort. Methods: Entry criteria include progressive mCRPC by PCWG3 criteria, ECOG PS 0-2, intact organ function, and prior receipt of AR pathway inhibitor and chemotherapy (or refused/ineligible). There is no limit to prior lines of therapy except alpha-emitting therapies (i.e., PSMA-TRT, 223Ra) and in this amended dose-escalation cohort, all patients must have had prior treatment with 177Lu-PSMA. Treatment will be given in a single fractionated cycle of 225Ac-J591 administered on D1 and D15. The phase I component is a 3+3 dose-escalation study design with up to 18 patients, with the goal of identifying MTD. The phase II component will include up to 16-19 patients in a Simon 2-stage design with 90% power to exclude the null hypothesis (35% or fewer patients with PSA50). Eligible men with negative PSMA PET scans will be offered treatment with informed consent in an exploratory subgroup but will not be counted towards phase II efficacy. Secondary outcomes include radiographic response by PCWG3-modified RECIST 1.1 criteria and PSMA PET, biochemical and radiographic progression-free survival, circulating tumor cell counts, and overall survival. Patient reported outcomes, genomic, and immune analyses are exploratory. Enrollment to the post-177Lu-PSMA cohort began in August 2022. Clinical trial information: NCT04506567 .

Increased utilization of prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (PSMA-TRT) in African American (AA) patients at an academic medical center

36

Background: At Weill Cornell Medicine (WCM), we have had a research program utilizing anti-PSMA mAb J591 since the year 2000. With the addition of PSMA ligand-based therapies in 2017, we have enrolled around 300 patients on investigational PSMA-TRT clinical trials. Since the approval of 177Lu-PSMA-617 (Pluvicto; Lu-177 vipivotide tetraxetan), we began standard-of-care (SOC) treatment, co-enrolling willing patients into a research registry. Recognizing the low numbers of AA patients enrolled on therapeutic clinical trials in the U.S., we made a concerted effort to increase the number of AA patients with prostate cancer (PC) enrolled on clinical trials at WCM. We retrospectively assessed the demographic data of patients enrolled on PSMA-TRT clinical trials to determine changing patterns of enrollment, and to determine if our efforts have improved access to these novel treatments for this under-represented, but high-risk population of patients. Methods: We collected demographic data (namely race and ethnicity) on patients with PC from WCM who were included on our PSMA-TRT investigational clinical trial databases or enrolled on our SOC 177Lu-PSMA-617 research registry. We used self-reported race and, when not available (due to patient death or loss of follow-up), demographic information documented in the medical record. Patients were grouped into 5-year cohorts based on either the date of consent for trial enrollment, or the start date of PSMA-TRT treatment (based on available information). Institutional tumor registry data was used as a comparator to assess the total percentage of AA patients with PC seen at WCM. Results: The percentages of patients included on PSMA-TRT clinical trials at WCM who were identified as AA were as follows: 2000-2004: 3.1% (2/65), 2005-2009: 5.1% (3/59), 2010-2014: 6.1% (2/33), and 2015-2019: 5.9% (5/85). The percentage of AA patients on PSMA-TRT studies from 2020 through July 2022 was 18.2% (16/88, inclusive of 8/72 investigational TRT subjects and 8/16 SOC registry participants). The total percentages of AA patients seen at Cornell based upon analysis of our tumor registry data were as follows: 2000-2004: 10.5% (182/1728), 2005-2009: 6.9% (250/3607), 2010-2014: 10% (326/3255), 2015-2019: 11.5% (278/2413), and 2020: 14.1%. Tumor registry data for 2021-present were not yet available. Conclusions: The percentage of AA patients on investigational PSMA-TRT trials at our institution notably increased from 2000-2019 (3.1%-6.1%) to 2020-2022 (11.1%). Moreover, 50% of those treated with 177Lu-PSMA-617 since its FDA approval and co-enrolled on our research registry identified as AA. These data suggest that outreach and increasing access to AA patients for novel PC treatment such as PSMA-TRT can result in increased numbers of underrepresented patients enrolling on clinical trials and receiving the most modern standards of care (i.e., PSMA-TRT).

Phase I results of a phase I/II study of pembrolizumab and AR signaling inhibitor (ARSI) with 225Ac-J591

181

Background: Only a small fraction of patients with PC respond to immunotherapy; radiation increases responses. PSMA targeted radionuclide therapy (PSMA-TRT) radiates multiple sites of disease simultaneously. ARSI can lead to radiosensitization and upregulate PSMA and PD-L1 expression. We hypothesize that the addition of potent alpha-PSMA-TRT (225Ac-J591) will lead to double-stranded DNA breaks, cell death, and subsequent release of neoantigens, thereby increasing the response proportion and duration to pembrolizumab plus ARSI. Here, we present preliminary phase I results of a phase I/II study, including an unexpected cytokine release syndrome (CRS). Methods: Eligibility: Progressive mCRPC by PCWG3 criteria (at least one ARSI, no chemotherapy in the mCRPC setting). Patients received ARSI of physician’s choice, pembrolizumab (400mg every 6 weeks), and single infusion of 225Ac-J591 at two different dose levels (65 or 80 KBq/kg). The primary endpoint for phase I is determination of 225Ac-J591 dose for phase II in a pick-the-winner design. Results: 12 patients were treated (6 at 65 KBq/kg, 6 at 80 KBq/kg). 7 (58%) received enzalutamide, 3 (25%) apalutamide, and 2 (17%) darolutamide. Median age 66.5, median PSA 7.75 ng/mL, 6 (50%) CALGB intermediate risk, 4 (33%) low risk, 11 (92%) with bone metastases, 3 (25%) with nodal metastases. 7 (58%) with prior abiraterone, 6 (50%) prior enzalutamide, 5 (42%) sip-T. All patients experienced PSA decline following therapy, 6 (50%) with >50% decline. With >6 months follow-up, 4 (33%; all at 80 KBq/kg) remain progression-free and on study. Of note, 7 (58%) developed an unexpected CRS 7-14 days following treatment characterized by morbilliform rash, fever >101F, and low blood counts. Inflammatory markers were elevated: IL-6 (2.1-7.7 pg/mL), D-Dimer (306-2378 ng/mL), ferritin (361.3-513.4 ng/mL), fibrinogen (386-461 mg/dL), ESR (16-42 mm/hr). After pausing the ARSI, this reaction improved within 1 week. Thrombocytopenia and/or neutropenia occurred during this syndrome, then typically improved before counts fell again at expected nadir 4 weeks after 225Ac-J591. Overall AEs on study include: 9 (75%) thrombocytopenia (3 with g≥3; 1 g4 with PC marrow infiltration), 7 (58%) neutropenia (none g≥3), 6 (50%) nausea, 7 (58%) g1-2 fatigue, 9 (75%) g1-2 xerostomia, 7 (58%) g1 AST. In contrast to heme AEs with unexpected initial occurrence during CRS followed by typical nadir from TRT, the described non-hematologic AEs were generally independent of CRS. 4 (33%) developed typical irAEs: 2 with rash (D60, D62) and 2 hypothyroidism (D77, D82). Conclusions: Combination therapy with alpha-PSMA-TRT, ARSI, and pembrolizumab demonstrates efficacy in the phase I run-in. A key safety signal that has emerged with triplet therapy is CRS that can be managed supportively. The randomized phase II component is accruing with additional safety visits and sample collection for cytokine analysis. Clinical trial information: NCT04946370 .

Use of a navigable interface for integrated whole genome and transcriptome sequencing as a platform for pursuit of therapeutic targets in advanced prostate cancers

225

Background: Metastatic, castration-resistant prostate cancer (mCRPC) is commonly the deadly form of PC. Among these, a subset of tumors are androgen-indifferent with the most aggressive often manifesting variant histology, including neuroendocrine or small cell changes. Neuroendocrine PC can be de novo (NEPC) or develop in response to therapy as treatment emergent (CRPC-NE). Currently effective durable treatments for NEPC are lacking. Hence, we sought to identify additional targets in CRPC/NEPC using an integrative platform of whole genome (WGS) and transcriptome sequencing (RNAseq). Methods: WGS was performed on55 tumor/normal pairs (CRPC-Ad, n= 32; CRPC-NE, n=13; de novo NEPC, n=7; metastatic hormone naïve, PC n=3) from 48 patients. RNAseq data was available in a subset of 21 samples. We employed the Isabl GxT analytic platform and manually curated single base substitution (SBS, COSMIC v3) molecular signatures and structural variants (SV) that involved tumor suppressor genes and oncogenes. Results: We observed 184 events in cancer-associated genes and targets in 38 cases. Non-canonical ETS fusions were identified in 2 CRPC-Ad patients ( MSMB-ERG and YWHAE-ETV4). Other rare events included SVs affecting ALK ( SLC45A3-ALK) and FGFR1 amplification in 1 patient each. Pathogenic germline alterations in 15% of patients with equal frequency in each clinicopathological state. These variants included genes such as BRCA1, BRCA2, and ATM, and other genes of uncertain relevance for prostate cancer ( e.g., PPM1D and MUTYH). SBS genomic signatures associated with homologous recombination deficiency (HRD) were observed in 15% of the patients (7 cases): 3 harbored germline BRCA1/2mutations, 2 with somatic BRCA2 mutations, and 2 without alteration in BRCA1/2 (1 of these CRPC-Ad had a complex SV disrupting RAD51B) without apparent enrichment for any histology, and a majority of both histologies were enriched in Mismatch repair (MMR)-associated SBS. One subject CRPC-NE and amphicrine character, which displayed a complete response to immune checkpoint blockade, harbored driver mutations in AR and CTNNB1, and homozygous loss of MSH2/6. Further, molecular signatures of potential clinical relevance were detected at varying contributions and included CDK12-type genomic instability (CRPC-Ad, n=2) (4%) and MMR deficiency with POLD1 proofreading (CRPC-Ad) who also experienced a durable response to pembrolizumab. Conclusions: WGS/RNAseq in CRPC and NEPC elucidates genomic signatures associated with HRD and MMR, complex SVs in oncogenes, and non-canonical ETS fusions. Expansion of our analysis is underway with enhanced integration of clinical metadata and RNAseq for rational trial design for aggressive variant CRPC and NEPC.

Abstract CT143: Results of combined targeting of prostate-specific membrane antigen (PSMA) with alpha-radiolabeled antibody 225Ac-J591 and beta-radiolabeled ligand 177Lu-PSMA I&T: preclinical and initial phase 1 clinical data in patients with metastatic castration-resistant prostate cancer (mCRPC)

Background: PSMA is overexpressed by the majority of PC and may be targeted by both antibodies (mAb) and small molecule ligands (SML), each with differing PSMA binding sites, kinetics, and biodistributions. mAbs have long circulating times (exposing organs such a bone marrow) but are too large to target normal tissue luminal PSMA expression in salivary glands, small bowel, and kidney; SMLs rapidly diffuse to all PSMA+ sites and are excreted by the kidneys within hours. Alpha emitters have high potency over a short range whereas beta emitters have lower energy over a significantly longer range. We hypothesized that combining mAb and SML targeting plus combining alpha and beta emitters offered complementary benefits and would be safe and effective.

Methods: A series of cell line and xenograft studies were performed to test mAb vs SML vs combo binding, uptake, and efficacy. A phase I/II clinical trial was initiated, enrolling patients with progressive, PSMA+ (by PSMA PET) mCRPC following potent AR pathway inhibition and chemotherapy (or chemo ineligible/refused)[NCT04886986]. The primary endpoint of phase I is assessment of dose-limiting toxicity (DLT) with secondary endpoints of response, progression-free and overall survival, genomic and imaging correlatives, and patient-reported outcomes.

Results: Binding studies demonstrated that mAb plus SML binding was additive rather than competitive in LNCaP and CWR22Rv1 cell lines. Uptake of 177Lu-mAb plus -SML in LNCaP, CWR22rv1, and PC3/PSMA xenograft models demonstrated synergism, with 44-65% greater tumor radioactivity in combination than the sum of the individual agents. Intracellular tracking studies indicate that the mAb re-directs SML to lysosomes from recycling endosomes, maintains retention of SML in tumor cells, and, therefore, prolongs intra-tumoral radioactivity exposure. Survival was prolonged in animals receiving 225Ac-mAb plus 177Lu-SML vs either drug alone (or control). Nine men with median age 68 (range 55-87), PSA 140 (2.4-9614) have been enrolled in both of 2 planned dose-escalation cohorts. 89% with bone, 44% lymph node, 22% liver, 22% lung metastases; 88% with detectable CTC count (75% unfavorable). All had at least 1 metastatic lesion with PSMA PET SUVmax &gt; liver SUVmean, with SUVmax of the single hottest lesion ranging from 11.6-69.9. For the primary endpoint, 0 of 3 with DLT in cohort 1, and with follow up ongoing, no DLT has occurred to date in 6 patients in cohort 2. Of evaluable patients, 5 of 6 with PSA decline (8-97% decline).

Conclusions: Targeting PSMA with the combination of mAb and SML leads to synergistic radioactivity in preclinical studies. The combination on mAb and SML radiolabeled with alpha and beta emitters appears safe with short-term follow up with phase 2 enrollment planned.

Citation Format: Scott T. Tagawa, Edward Fung, Muhammad O. Niaz, Mahelia Bissassar, Sharon Singh, Amie Patel, Angela Tan, Juana Martinez Zuloaga, Sandra Huicochea Castellanos, Jones T. Nauseef, Ana Molina, Cora Sternberg, David M. Nanus, Joseph Osborne, Neil H. Bander. Results of combined targeting of prostate-specific membrane antigen (PSMA) with alpha-radiolabeled antibody 225Ac-J591 and beta-radiolabeled ligand 177Lu-PSMA I&T: preclinical and initial phase 1 clinical data in patients with metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT143.

Phase I/II study of 225Ac-J591 plus 177Lu-PSMA-I&T for progressive metastatic castration-resistant prostate cancer

TPS5100

Background: PSMA is overexpressed by most prostate cancers and can be successfully targeted by both antibodies (mAb) and small molecule ligands (SML), each with overlapping and distinct binding sites, kinetics, and biodistributions [Kratochwil Sem Nuc Med 2019]. mAbs are larger, with longer circulating times resulting in greater exposure to bone marrow, but lesser access to PSMA expression on luminal tissue ( e.g. salivary glands, small bowel, and kidney). In contrast, SMLs are rapidly excreted via kidneys and readily diffuse to all PSMA-expressing sites. Toxicities of 177Lu vary with these differences in biodistribution ( e.g. more hematologic toxicity with mAb, more xerostomia and nausea with SML, p < 0.001)[Niaz AUA 2020]. Alpha emitting isotopes have shorter ranges but high potency compared to beta emitters which have longer ranges, but lower linear energy transfer. In preclinical models, the combination of mAb plus SML has demonstrated additive binding in LNCaP, CWR22Rv1, and PC3/PSMA PC cell lines, and synergistic uptake of 177Lu-mAb plus 177Lu-SML in xenograft models. We developed a phase I/II study to test our hypothesis that concomitant mAb and SML targeting, plus the combination of alpha (225Ac) and beta emitters (177Lu), may offer complementary benefits in a safe and effective manner. Methods: Key eligibility criteria include progressive mCRPC (PCWG3), at least 1 prior AR pathway inhibitor and taxane chemotherapy (or ineligible/refused), and adequate organ function and performance status. PSMA PET/CT must have at least 1 lesion with SUVmax > liver SUV. Prior PSMA-based therapy with radioisotopes is not allowed. 177Lu-PSMA-I&T (PNT2002) will be administered as in the phase III SPLASH study (6.8 GBq q8w for up to 2 doses). The phase I includes up to two dose-escalation cohorts of concurrent 225Ac-J591 (30 & 40 KBq/Kg q8w x2) in a modified 3+3 schema. All subjects undergo 177Lu SPECT on Day 8 after each dose. The primary objective of the Phase I study is to determine the dose-limiting toxicity and recommended phase II dose (RP2D) for this combination. Primary objective of the Phase II study is to assess the proportion of patients with > 50% PSA decline after treatment. Secondary objectives include radiographic response rate (PCWG3-modified RECIST 1.1), biochemical and radiographic progression-free survival, overall survival, safety (CTCAE 5.0), CTC count changes and conversions, and patient-reported outcomes (FACT-P, BPI-SF, EQ-5D). Exploratory objectives include pre- and post-treatment PSMA-based imaging changes, effects of PSMA radionuclides on the microbiome, relationship between genomic alterations and response, and relationship between PSMA PET/CT results and outcome. The phase I was activated at Weill Cornell Medicine in May 2021. Following determination of the RP2D, a multicenter phase II is planned at Prostate Cancer Clinical Trials Consortium (PCCTC) in 2022. Clinical trial information: 04886986.

Self-reported race and zip code by men with prostate cancer in New York City and association with access to PSMA PET scans

e17007

Background: Prostate-specific membrane antigen (PSMA) is overexpressed on most prostate cancers (PCs), a fact that has been exploited to perform both targeted imaging and treatment. PSMA-based PET imaging allows for more sensitive detection of PC and can be useful even in the context of negative CT and bone scans. Prior to 2021, research protocols using PSMA-PET (PET) were common at large academic centers, but will likely be more commonplace as standard of care (SOC) after recent FDA approval. With a change in SOC imaging, the impact of cost to patients must be examined. We hypothesize that socioeconomic and demographic-based care disparities may widen and access may narrow in the face of these changes. Methods: We collected demographic data on patients with PC from Weill Cornell Medicine (WCM), Brooklyn Methodist Hospital (BMH), and Columbia University Medical Center (CUMC) who received a PSMA PET scan between 1 January 2018 and 31 January 2022. Data collected included age, zip code, primary language, self-reported race and ethnicity, and type of insurance coverage. Zip codes were used to estimate income strata of patients using publicly-available 2018 IRS adjusted gross income (AGIs) as follows ($): < 25k, 25k-50k, 50k-75k, 75k-100k, 100k-200k, and > 200k. Any AGI strata comprising > 20% of population was counted. Patients were divided into four cohorts: those who had a scan (1) as part of therapeutic-based studies for mCRPC, (2) non-therapeutic imaging studies, (3) as a part of a cost-recovery study with an out-of-pocket cost of $1054, and (4) commercial use under post-approval standards of care (SOC) billed to insurance. Proportion of self-reported race in each cohort was compared against overall race distribution for prostate cancer registry from WCM and CUIMC (Table). Results: 896 patients underwent PSMA PET. Approximately half of all scans were in Cohort 4 (49%, n = 368) including all BMH scans. CUMC scans were 90% in Cohort 2 (122/136). In Cohort 1, 2, and 3, > 90% of subjects resided in zip codes with AGI > $100k. In Cohort 4, 84% resided in zip codes with AGI > $100k. Overall 70.4% of subjects identified as White, 8.3% Black or African American, 3.5% Asian, 4.4% Other, and 13.5% were unknown/or declined. African American/Black was most represented on Cohort 4 (11%), and least represented in Cohort 1 (5%). Conclusions: White patients comprise the largest proportion or PET scans whereas non-white groups are underrepresented across all cohorts. Access to PETs has appeared to improve for lower AGI, non-white patients following FDA approval and insurance coverage. It will be critical to assure equitable access across all demographic groups as deployment of PET scanning becomes the new standard of care.[Table: see text]

Genomic instability is enriched in localized prostate cancers from men of African ancestry

270

Background: Whole genome sequencing (WGS) of prostate cancers (PC) from American men of African ancestry (AA) is limited despite AA men having twice the incidence of and mortality from PC as compared to their European ancestry (EA) men. Herein we describe analysis of AA PC WGS to identify genomic contributions to incidence and outcome disparities. Methods: WGS data from AA localized hormone naïve (HN) PCs (n = 23) from our institution were combined with publicly available WGS HNPC datasets (n = 5); quantitative predominant genome-wide ancestry was approximated via RFMix. A comparable EA cohort (n = 224) was similarly assembled. Ancestry groups were compared via regression models correcting for Gleason grade, PSA, and pathologic stage. Results: Analysis of known HNPC driver genes revealed lower frequency of PTEN (2/28 v 70/224, 7% v 31%, p = 0.006) and higher frequency of MYC (5/28 v 13/224, 18% v 5%, p = 0.014) and FOXA1 (7/28 v 24/224, 25% v 11%, p = 0.018) alterations in AA tumors relative to EA. An unbiased search for coding and noncoding drivers uncovered recurrent FOXA1 promoter (n = 8, p = 1.1e-8, RR = 3.92) and gene body protein-coding (n = 5, p = 1.2e-6, RR = 7.83) mutations, as targets of somatic selection and affecting nearly half of AA cases. Despite comparable tumor mutational burdens in each group, analysis of genome-wide mutational signatures revealed an AA-specific enrichment of SNVs in trinucleotide contexts associated with mismatch repair deficiency (SBS6, p = 1.68e-2, RR = 49.1). AA tumors also had significantly more small deletions (sig. ID2) relative to EA samples (p = 2.25e-31, RR = 9.47), implying replication slippage at lagging strands. Finally, AA PC genomes had consistently higher MSI scores relative to EA (median [IQR]: 4.03 [3.8-4.53] v 1.52 [1.21-1.85], p = 2.95e-44), yet lower than MSI-H colon cancers. These associations were independent of tissue preservation method or source, suggesting they reflect an ancestry-specific mutational process. Comparison of germline and somatic variants between AA and EA uncovered candidate DNA damage response genes (DDR) for further functional validation. Conclusions: Analysis of the largest AA cohort to date of WGS HNPC has revealed an ancestry-specific somatic mutational processes resulting in elevated rate of MMR-linked SNVs, replication-slippage associated small deletions, and MSI, relative to EA. The uniformity of these data suggest that AAs may harbor an inherited factor contributing to increased somatic genomic instability in the HNPC context. These results are compatible with published analyses demonstrating lower expression of DDR genes in AA versus EA PCs. Greater MSI and indels (via neoantigen formation) may explain the higher response proportions in AA PC patients treated with immune- and radiotherapies. Studies are ongoing to define mechanisms via associations between germline predisposition, somatic modification, and transcriptional outcome.

Assessment of patient-reported outcomes (PROs) and longer-term adverse events (AEs) in phase I study of 225Ac-J591-PSMA for metastatic castration-resistant prostate cancer (mCRPC)

77

Background: Prostate Specific Membrane Antigen (PSMA) is a conserved cell surface protein in PC and is used for targeted imaging and therapeutics. Antibodies circulate longer than small molecules and are less likely to reach luminal PSMA on normal organs. Here we report PROs and longer-term AEs from the dose-escalation and expansion cohorts of a first-in-human study of combined monoclonal antibody and potent alpha emitter (225Ac-J591). Methods: Eligible subjects with mCPRC were administered 225Ac-J591. Initial to maximum doses were 13.3 to 93.3 KBq/kg). AEs are reporting using CTCAE v5 and PROs, including pain (BPI-SF) and quality of life (QOL, FACT-P), and associations with PSA response were also examined. Results: A total of 32 subjects (one enrolled in both dose-escalation and expansion) were treated with a single dose of 225Ac-J591 across 7 dose levels with expansion at the level (93.3 KBq/kg, n = 16). Median age 69.5 (52-89) and PSA 149.1 (4.8-7168.4). All subjects had at least 1 AE of any grade. Most common were fatigue (31/32, 1 Gr > 2), anorexia (25/32, all Gr 1-2), and thrombocytopenia (25/32, 3 Gr 3, 2 Gr 4). Xerostomia was observed in 14/32 subjects (all Gr 1), 7 of whom had prior 177Lu-PSMA. Pain flare was reported in 43% (17/32) subjects (11 Gr 1, 6 Gr 2). 19 had evaluable PROs at baseline and efficacy visit (week 12). Pain severity (p = 0.8) and interference from pain (p = 0.4) were unchanged from baseline to 12 weeks, yet better PSA response (by percent) was associated with reduced pain severity (r = 0.7, p = 0.0023). Despite at least one AE in each subject, total FACT-P was not significantly changed after treatment (p = 0.2), but emotional well-being declined over time (15 [10.0, 18.0] v 10.0 [7.5, 13.0], p = 0.011). Reduction in median emotional well-being reached clinically important score differences. When stratified by AE, subjects with xerostomia had lower FACT-P total scores, but no difference was observed between those with and without pain. PSA response was not associated with change in QOL or subscales. Conclusions: Pain and quality of life in subjects with mCRPC did not change, on average, from baseline to 12 weeks after treatment with 225Ac-J591. This is despite preliminary evidence of clinical efficacy being accompanied by frequent, treatment emergent AEs. A promising trend toward improved pain in those with PSA response warrants further analysis. Small numbers limited statistical power for testing other subgroup associations. Additional correlations with pretreatment sites of disease, performance status, and adverse event distribution are ongoing. Assessment of changes in PROs in the follow up studies [NCT04506567] are underway. Clinical trial information: NCT03276572.

Quantitative assessment of PSMA imaging before and after 177Lu-PSMA-617 treatment in a Ph I/II trial

37

Background: We have previously reported a dose-intense single-cycle of 177Lu-PSMA-617 was effective in pretreated patients with mCRPC without requiring PSMA-positive imaging for enrollment. Prior post-hoc analyses of these data using approximate quantification of exclusively the most PSMA-positive disease sites have demonstrated associations between PSA response and PFS with pre-treatment 68Ga-PSMA11-PET signal. Greater sophistication in pre- and post-treatment evaluation of PSMA-expression in tumor and normal organs may allow for better patient selection and prediction of toxicities. Methods: A total of 50 patients were treated on a phase I/II study of fractionated-dose (D1, 15) 177Lu-617-PSMA. Quantification using artificial intelligence (AI) were used to measure pre- and post-treatment PSMA signal intensity. Scoring cutoffs with confidence intervals around scan variation were empirically established from a subset of test/re-test of subjects within 24h without intervening therapy. A variety of measurements were performed including SUVmean across all detectable tumor lesions, volume of lesions, and SUVtotal (Total + Volume), as well as select normal organs and changes after treatment. Associations with survival were tested via Cox proportional hazard models in univariate analyses and associations with adverse events (AEs) and PSA responses were via assessed via Wilcoxon rank sum tests. Results: 13 subjects were selected to complete AI-based quantification and associated survival analyses. Among these, 10 (77%) experienced any PSA decline, with 8 (62%) with PSA50 and 3 (23%)with PSA90. Median overall survival (OS) was 17.0 mos (10, NA) via Kaplan-Meier estimates. In univariate analysis, pretreatment SUVmean was associated with improved PFS (HR 0.66, 95% CI 0.49-0.90, p = 0.009) and OS (HR 0.81, 95% CI 0.65-1.00, p = 0.048). The metrics most strongly associated with PSA50 were pretreatment SUVmean (median [IQR]: 7.66 [6.52, 10.54] v 3.50 [3.02, 3.56], p = 0.019) and SUV Total (14982 [11110, 20595] v 1303 [576, 1512], p = 0.019), and change in Volume (-27 [-44, -20] v 145 [38, 154], p = 0.006) and SUVtotal (-57 [-67, -35] v 132 [9, 269], p = 0.030). Subjects with xerostomia had higher salivary gland SUVmax (pretreatment and change in after treatment). Those with pain flare had lower pretreatment SUV scores (Mean, Max, Total) in unaffected portions of bony skeleton. Conclusions: Sophisticated AI-based quantification analysis of PSMA expression on pre- and post-treatment 68Ga-PSMA11-PETs demonstrate associations with treatment efficacy (PSA response, OS), and associations between patient experience (AEs) and PSMA expression in non-tumor tissues. Expansion of this algorithm to a larger patient cohort may improve our ability to anticipate toxicity by body-wide PSMA detection and predict treatment response. Clinical trial information: NCT03042468.

Open label phase II trial of cabozantinib (cabo) in patients with metastatic castrate resistant prostate cancer (mCRPC) and known amplifications or activating mutations in gene targets who have received prior anti-androgen therapy

TPS5095

Background: Despite a variety of therapy classes extending survival in mCRPC – and excepting select population eligible for PARP inhibitors – no molecularly selected drugs are FDA approved in mCRPC. Previously, cabo, an inhibitor of multiple tyrosine kinases ( e.g. MET, VEGFRs 1-3, RET, KIT, TRKB, FLT-3, AXL, TIE-2), was evaluated in phase III trials (COMET-1, COMET-2) in mCRPC. Despite initial promising results, particularly in bone scan responses and rPFS benefit, further application of cabo in mCRPC was halted after improvement in OS was not observed. It is unclear why prolonged rPFS in COMET-1 (vs. prednisone) did not translate into improved OS. Previous failures may reflect inclusion of relatively cabo-insensitive tumors due to an unselected population with regard to presumed cabo activity. Given that mCRPC specimens from our precision medicine cohort have increased expression of target genes MET and KIT, and qualifying genomic alterations (amplifications, activating mutations) are reported in ̃15% of a publicly-available mCRPC cohort, we developed this rationally-designed study. We predict a molecularly-defined mCRPC cohort will identify the population that most benefits from cabo therapy, as reflected by prolonged rPFS and OS, and more frequent PSA declines and CTC conversions. Methods: We have activated a phase II non-randomized, open label trial designed to evaluate treatment response and survival of patients with mCRPC who harbor evidence of increased signaling of the targets of cabo. Study population will have progressed on an ARSI; prior taxane therapy in castration-sensitive PC or CRPC (beyond 12 mos) will be eligible. Molecular eligibility: DNA (tumor or cfDNA) evidence of amplification or activating mutation in selected targets of cabo. Alternatively, IHC confirming high expression (2 or 3+) via CLIA-approved assay is allowed. Overexpression via RNAseq, validated by CLIA-approved IHC, is permitted. All patients will receive 40 mg/d of cabo, with dose-reductions allowed (to 20 mg/d, then 20 mg EOD). Repeat biopsy after 3 weeks on treatment is mandated. Primary endpoint is rPFS. Using median of 5.6 mos (COMET-1) to guide our H0 (50% rPFS rate at 6 mo), the H1 is ≥75% rPFS at 6 mo. Sample size (30) provides 90% power with one-sided alpha of 0.05 via chi-square test. Secondary endpoints include PSA decline by PCWG3, objective radiographic response proportion, OS, and CTC response rate. Exploratory studies will include serial evaluation of cfDNA (via PCF-SELECT); immune tumor microenvironment response via on-treatment biopsy and collection of plasma for circulating immune markers; and exploration of baseline and on-treatment tumor genomic alterations. This trial is multicentered via the Prostate Cancer Clinical Trials Consortium (PCCTC c20-254). Clinical trial information: NCT04631744.

Emerging Prostate-specific Membrane Antigen-based Therapeutics: Small Molecules, Antibodies, and Beyond

Prostate-specific membrane antigen (PSMA) is a clinically validated target for prostate cancer. A variety of PSMA-based therapies, including radionuclide- and cytotoxic drug-conjugated and cellular immune products, are in development, each with variable advantages and disadvantages. Here we briefly describe the landscape of PSMA-based therapies beyond ¹⁷⁷Lu-PSMA-617, which is covered elsewhere. PATIENT SUMMARY: Prostate-specific membrane antigen (PSMA) is a protein expressed on most prostate cancer tumors and on limited other areas in the body. It can be targeted to treat prostate cancer using radioactive particles, drugs, or immune agents.

Baseline and post-treatment circulating tumor cell (CTC) counts with prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (TRT) in men with metastatic castration-resistant prostate cancer (mCRPC)

158

Background: CTC counts are an independent prognostic factor in men with mCRPC; certain changes following treatment (conversion from detectable to undetectable or unfavorable to favorable) are associated with improved overall survival. Most PSMA-TRT efficacy data have focused on PSA or imaging changes. Here, we describe baseline and post-treatment CTC counts from subjects receiving PSMA-TRT. Methods: Men with mCRPC treated on prospective clinical trials of PSMA-TRT and with available CTC counts (CellSearch) were included in our analysis. Depending upon the era of the trial, post-treatment counts were performed at 4-6 (initial era) or 12 weeks (recent era) after a single cycle of PSMA-TRT (individual trial data reported elsewhere). We describe CTC counts at baseline and compare pre-treatment counts to those after PSMA-TRT. Results: 116 men treated with PSMA-TRT had baseline CTC count (90 with both pre- and post-treatment CTC). Forty-four patients (37.9%) received 177Lu-J951, 46 (39.7%) received 177Lu-PSMA-617, and 26 (22.4%) received 225Ac-J591. Median age was 71.5. Fifty-eight patients (50%) had previously received taxane chemotherapy, median PSA was 82.98 ng/mL, and 66 (56.9%) were in the high-risk Halabi (CALGB) prognostic group. Eighty-nine out of one hundred sixteen (76.7%) had detectable baseline CTC and 58/116 (50%) had unfavorable baseline CTC count. Forty-nine out of seventy (70%) had post-treatment CTC count decline, 23/70 (32.9%) converted from detectable to undetectable, and 17/47 (36.2%) converted from unfavorable to favorable. CTC changes stratified by type of PSMA-TRT are reported in the table. Conclusions: This is the largest analysis of CTC changes in patients who have received PSMA-TRT. In addition to PSA changes and other previously reported outcomes, even when low doses of radionuclide therapy as part of dose-escalation studies are included, the majority with detectable CTC counts have post-treatment CTC count decline. A significant portion of patients experience favorable CTC changes. [Table: see text]

The role of androgen deprivation therapy on the clinical course of COVID-19 infection in men with prostate cancer

41

Background: TMPRSS2, a cell surface protease which is commonly upregulated in prostate cancer (PC) and regulated by androgens, is a necessary component for SARS-CoV2 cellular entry into respiratory epithelial cells. PC patients receiving ADT were reported to have a lower risk of SARS-CoV-2 infection. However, whether ADT may have an impact on the severity of COVID-19 illness in this population is poorly understood. Methods: In this study performed across 7 US medical centers, we retrospectively evaluated patients with active PC and SARS-COV-2 viral detection by PCR between 03/01/20 and 05/31/20. We collected information on demographics; medical comorbidities; medications; PC Gleason score at initial diagnosis; presence of active disease, metastases, and castration resistance; ADT use as defined by GnRH analog or antagonist within 3 months or castration levels of testosterone < 50 ng/dL within 6 months of COVID-19 diagnosis, or history of bilateral orchiectomy; active non-ADT systemic therapies including, but not limited to, androgen-receptor-targeted therapies and chemotherapy; and COVID-19-related outcomes including hospitalization, supplemental oxygen use, mechanical ventilation requirement, WHO COVID-19 ordinal scale for clinical improvement, follow-up duration, and vital status. Multivariable mixed-effect logistic regression was performed to evaluate any difference in COVID-19 clinical outcomes between patients on and not on ADT. Survival analysis was done using adjusted Cox proportion-hazards regression model. All tests were two-sided at 0.05 significance level. Results: We identified 465 evaluable patients with median age of 71 (61-81) years. Median duration of follow-up was 60 (12-114.2) days. In this follow up period, there were 195 (41.9%) hospitalizations and 111 (23.9%) deaths. When adjusted for age, BMI, and PC clinical disease state, overall survival (HR 1.28 [95%CI 0.79-2.08], P = 0.32), hospitalization status (HR 1.07 [0.61-1.87], P = 0.82), supplemental oxygen use (HR 1.29 [0.77-2.17], P = 0.34), and use of mechanical ventilation (HR 1.07 [0.51-2.23], P = 0.87) were not statistically different between ADT and non-ADT cohorts. Similarly, in subgroup analysis, no statistical difference in overall survival was found between ADT and non-ADT cohorts for hospitalized patients (HR 1.42 [0.82-2.47], P = 0.21) and those receiving supplemental oxygen (HR 1.10 [0.65-1.85], P = 0.73). Conclusions: In this retrospective cohort of PC patients, use of ADT prior to COVID-19 diagnosis does not protect against severe COVID-19 illness as defined by hospitalization, supplemental oxygen use, or death. Further preclinical work in understanding TMPRSS2 expression and androgen regulation in respiratory epithelial cells is needed. As well, longer clinical follow-up and additional clinical studies inclusive of prospective data are warranted to fully address this question.

Pilot study of anti-prostate-specific membrane antigen (PSMA) antibody J591 for men with metastatic castration-resistant prostate cancer (mCRPC) and unfavorable circulating tumor cell (CTC) count

120

Background: Elevated CTC counts are associated with a poor prognosis in men with mCRPC. PSMA targeted radionuclide therapy has been associated with decline in CTC count, but it remains unclear whether this effect results from radionuclide-induced cytotoxicity. J591 was engineered to have antibody-dependent cytotoxicity. A subset of patients was observed to have CTC count decline following imaging with 111In-J591, so a prospective study was launched to test the hypothesis that “naked” J591 leads to CTC count decline. Methods: In a Simon 2-stage dose de-escalation study, men with progressive mCRPC and unfavorable CTC count (CellSearch > 4) received a single dose of J591. Initial dose cohort 300 mg with de-escalation to 20 mg. CTC count was re-assessed 4, 8, and 12 weeks following therapy along with PSA and standard imaging. An optional PSMA PET was included prior to treatment. The primary endpoint was proportion of subjects with conversion to favorable CTC count ( < 5 CTCs/7.5 mL blood) and/or > 30% decline from baseline within 12 weeks post-treatment. Results: 10 men were enrolled, 9 of whom were evaluable (1 died of progressive mCRPC prior to post-treatment CTC count). Median age was 71.5 years (range 60-81), 78% had prior chemo, ECOG PS 1 in 45% and 2 in 55%. 7 of 9 (78%) evaluable subjects were Halabi CALGB prognostic poor risk category and 2 (22%) intermediate. 6 of 9 had pre-treatment PSMA PET/CT (three 89Zr-J591 and three 68Ga-PSMA11). Though not required, all scans showed > 1 lesion with SUVmax > liver SUV (range 9.12-70.15). 2 of 6 in the 300 mg cohort had CTC count decline; 1 of 6 converted to favorable count (9 to 0 with decrease of 35 to 12 in other). 3 were treated with 20 mg; 1 had CTC count decline of 316 to 112, but 0 converted to favorable count. Across both cohorts, 3 of 9 had a CTC count decline at any point in time, ranging from 65-100% decline. With the pre-specified 2-stage design, enrollment was halted for futility based upon the primary endpoint of 12-week CTC count. PSA values post-treatment increased in 8 (89%) patients and remained unchanged in 1 (11%) patient. Conclusions: Single-agent anti-PSMA antibody J591 may lead to decline in CTC count, though the study did not meet its primary endpoint. A combination or maintenance approach might be preferable and is worthy of exploration.

A phase I/II dose-escalation study of fractionated and multiple dose 225Ac-J591 for progressive metastatic castration-resistant prostate cancer (mCRPC)

TPS188

Background: Prostate-specific membrane antigen (PSMA)-based targeted radionuclide therapy (TRT) is a promising treatment. PSMA-targeting via large antibodies vs small molecules has different kinetics, biodistribution, and resulting clinical toxicities. Using beta-TRT, 177Lu-J591 has more heme toxicity and 177Lu-PSMA-617 more non-heme toxicity (xerostomia and nausea) [Niaz AUA 2020]. Alpha-emitters are more potent than beta radionuclides, and alpha-PSMA-TRT has efficacy even after beta-PSMA-TRT. In a first-in-human phase I dose-escalation study of 225Ac-J591, patients with mCRPC were treated with a single dose of 225Ac-J591 on seven dose levels, up to 93.3 KBq/kg [Tagawa ASCO 2020]. No maximal tolerated dose (MTD) was achieved. One patient treated at 80 KBq/kg developed dose-limiting toxicity (DLT) of grade 4 anemia and thrombocytopenia, but 0 of 6 at 93.3 KBq/Kg had grade > 3 heme toxicity or grade > 2 non-heme toxicity. Preliminary results indicate 64% had any PSA decline and 41% had > 50% PSA decline (PSA50) across all doses, despite lack of selection for PSMA expression and the majority having been previously treated with 177Lu-PSMA. Methods: Entry criteria include progressive mCRPC by PCWG3 criteria, ECOG PS 0-2, intact organ function (including normal neutrophil and platelet counts), and prior receipt of AR pathway inhibitor and chemotherapy (or refuse/ineligible for chemotherapy). There is no limit to prior lines of therapy except alpha-PSMA-TRT. Phase I includes 2 separate parallel dose-escalation cohorts. In the fractionated-dose cohort, men will receive a single cycle of 225Ac-J591 administered on D1 and D15. In the multiple-dose cohort, 225Ac-J591 will be given every 6 weeks for up to 4 cycles. The phase I component is a 3+3 dose-escalation study design, with the goal of identifying MTD. Each phase II component will treat up to 27 men with PSMA+ PET scans in a Simon 2-stage design with 90% power to exclude the null hypothesis (35% or fewer patients with PSA50). Eligible men with negative PSMA PET scans will be offered treatment with informed consent in an exploratory subgroup, but will not be counted towards phase II efficacy. Secondary outcomes include radiographic response by PCWG modified RECIST 1.1 criteria and PSMA PET, biochemical and radiographic progression-free survival, circulating tumor cell counts, and overall survival. Patient reported outcomes, genomic, and immune analyses are exploratory. Enrollment began in August 2020 (NCT04506567). Clinical trial information: NCT04506567.

Phase I trial of apalutamide (Apa) with abiraterone acetate (AA) plus prednisone (P) and docetaxel (Doce) in patients with metastatic castration-resistant prostate cancer (mCRPC)

140

Background: The combination of AR inhibition plus taxane chemotherapy has demonstrated clinical benefit in PC ( i.e. CHAARTED, STAMPEDE), indicating efficacy when targeting the AR signaling pathway at different points. We launched a phase I study to test the hypothesis that the combination of Apa (AR signaling inhibitor), AA (CYP17 inhibitor) + P, and Doce (inhibitor of AR translocation to the nucleus) is safe and effective. Previously we reported that the full doses of all drugs were tolerated in combination and the recommended phase II dose (R2PD). Here we present addition of the expansion cohort and longer follow up. Methods: Men were enrolled with progressive mCRPC, intact organ function, and without prior exposure to Doce (within 3 years) or Apa. In the initial dose-escalation portion, standard doses of AA (1000 mg daily), Doce (75 mg/m2 q3 weeks), and P (5 mg BID) were administered initially with different doses of Apa. Cohort 1 = 120 mg/d, Cohort 2 = 240 mg/d in modified 3+3 design. No GCSF was permitted during dose escalation phase. Following initial combo therapy, men could continue Apa/AA+P without Doce. The expansion cohort added men at full doses of all drugs to narrow confidence intervals around efficacy/toxicity. Results: Sixteen men (4 Apa 120 mg, 12 Apa 240 mg) with mCRPC and median age 70 and median PSA 3.45 ug/mL (range 0.07 – 188.97) were treated. Sites of metastases included bone (50%), lymph node (56%), lung and liver (6% each), and other sites (13%). Seven (44%) were low, 5 (31%) were intermediate, and 4 (25%) were high CALGB (Halabi) risk group. During dose escalation, there was 1 DLT of grade (Gr) 3 hypertension. In the overall study including expansion, non-heme AEs included Gr 3 hypertension (2/16), hyperglycemia (1/16), and rash (1/16), and Gr 2 hypertension (3/16), fatigue (3/16), rash (2/16), neuropathy (2/16), and nausea (1/16). Heme AEs included Gr 3 anemia (1) and Gr 4 neutropenia (10/16, 1 febrile neutropenia). 15/16 (93.8%) of subjects had a PSA50, of whom 12 achieved PSA90 (12/16, 75%) and 4 (25%) had PSA decline > 99%. Of 7 evaluable with measureable disease, all had RECIST response. Median rPFS was not reached with median 22.8 month follow up (range 2.8-46.6 mo). 2-year rPFS was 70.1% (95% CI = 32.3%, 89.5%). 9 of 10 evaluated had undetectable CTCs at 12 weeks; 5 of 5 with baseline detectable CTCs converted to undetectable at 12 weeks. Conclusions: The combination of apa, AA+P, and doce at full doses is tolerable. The combination is associated with a high proportion with PSA decline, measurable disease response, CTC count control, and favorable rPFS. Pre-treatment tumor tissue and pre-and post-treatment plasma ctDNA and CTC characterization are being analyzed. [NCT02913196]. Clinical trial information: NCT02913196.

Successful outcome with eculizumab treatment in a patient with antiphospholipid syndrome presenting with an unusual thrombotic storm

Catastrophic Antiphospholipid Syndrome (CAPS) is a life-threatening complication of APS requiring complex management to optimize patient outcome. We describe a 54-year-old man with APS with history of splanchnic vein thrombosis, a Factor II G20210A heterozygote, autoimmune hemolytic anemia and thrombocytopenia. He developed sudden onset of severe flank pain due to spontaneous bilateral adrenal hemorrhage while on warfarin with a therapeutic INR. Despite unfractionated heparin and initial clinical improvement, severe thrombocytopenia developed requiring dexamethasone, rituximab, and romiplostim. Hospitalization was complicated further by thrombosis of the inferior vena cava, pulmonary embolism, and painful violaceous patches on his neck and ear cartilages. Punch biopsy of lesions revealed C5b-C9 deposition of small vessel thromboses. Although the inciting event for his thrombotic storm remains uncertain, anti-complement therapy with eculizumab provided rapid and durable lesion resolution. Eculizumab was discontinued after 6 months and patient remains in remission without recurrent thrombosis. This case provides insight on the management of CAPS, including the use of eculizumab.

Platinum-Based Chemotherapy in Metastatic Prostate Cancer With DNA Repair Gene Alterations

PURPOSE

Alterations in DNA damage repair (DDR) genes occur in up to 25% of patients with metastatic castration-resistant prostate cancer (mCRPC) and may sensitize to platinum chemotherapy. We aimed to evaluate the efficacy of platinum-based chemotherapy in DDR-mutant (DDRmut) mCRPC.

METHODS

We assessed response to platinum chemotherapy based on DDR gene alteration status in men with mCRPC who underwent tumor and germline genomic profiling. Patients with deleterious alterations in a gene panel that included BRCA2, BRCA1, ATM, PALB2, FANCA, and CDK12 were considered DDRmut.

RESULTS

A total of 109 patients with mCRPC received platinum-based chemotherapy between October 2013 and July 2018. Sixty-four of 109 patients were taxane refractory and poly (ADP-ribose) polymerase inhibitor (PARPi) naïve. Within this subset, DDRmut was found in 16/64 patients (25%) and was associated with an increased likelihood of achieving a prostate-specific antigen (PSA) decline of 50% or more from baseline (PSA50; odds ratio, 7.0; 95% CI, 1.9 to 29.2). Time on platinum chemotherapy tended to be longer in the DDRmut group (median, 3.0 v 1.6 months; hazard ratio, 0.55, 95% CI, 0.29 to 1.24). No difference in survival was detected. Of 8 patients with DDRmut disease who received platinum-based therapy after a PARPi, 3/7 evaluable patients had radiographic partial response or stable disease, and 2/7 had a PSA50 response. None of 4 patients with ATM mutations had platinum responses regardless of prior PARPi exposure.

CONCLUSION

Patients with DDRmut disease had better response to platinum-based chemotherapy, suggesting that DDR status warrants prospective validation as a potential biomarker for patient selection. Responses to platinum chemotherapy were observed in BRCA-altered prostate cancer after PARPi progression. Additional studies are needed to determine the predictive role of individual genes on platinum sensitivity in the context of other clinical and genomic factors.

An evaluation of the efficacy and safety of erdafitinib for the treatment of bladder cancer

INTRODUCTION

Treatment of unresectable or metastatic urothelial carcinoma (UC) has historically relied upon platinum-based chemotherapy and, more recently, immune checkpoint inhibitors. When tumors progress despite those therapies, remaining effective options are limited.

AREAS COVERED

In this review, the authors review the advancement in genomic targets in UC, most notably fibroblast growth factor receptor (FGFR). FGFR has been identified as a target in UC as it is commonly genomically altered (activating mutations or fusions), and may be enriched in UC subtypes that are relatively resistant to immune checkpoint blockade. Erdafitinib, a potent and selective inhibitor of FGFRs, represents the first targeted therapy approved for the treatment of UC by virtue of a confirmed response rate of 40% in an open-label, single-armed phase II trial in molecularly selected tumors. The authors provide their expert opinion of its approval and place it in the context of the current and forthcoming treatment strategies for metastatic UC.

EXPERT OPINION

The approval of erdafitinib provides clinicians with an important new treatment option for patients with metastatic UC and projects forward into an era of enhanced molecular precision in identifying effective therapies in UC.

Alterations in cancer cell mechanical properties after fluid shear stress exposure: a micropipette aspiration study

Over 90% of cancer deaths result not from primary tumor development, but from metastatic tumors that arise after cancer cells circulate to distal sites via the circulatory system. While it is known that metastasis is an inefficient process, the effect of hemodynamic parameters such as fluid shear stress (FSS) on the viability and efficacy of metastasis is not well understood. Recent work has shown that select cancer cells may be able to survive and possibly even adapt to FSS in vitro. The current research seeks to characterize the effect of FSS on the mechanical properties of suspended cancer cells in vitro. Nontransformed prostate epithelial cells (PrEC LH) and transformed prostate cancer cells (PC-3) were used in this study. The Young's modulus was determined using micropipette aspiration. We examined cells in suspension but not exposed to FSS (unsheared) and immediately after exposure to high (6,400 dyn/cm²) and low (510 dyn/cm²) FSS. The PrEC LH cells were ~140% stiffer than the PC-3 cells not exposed to FSS. Post-FSS exposure, there was an increase of ~77% in Young's modulus after exposure to high FSS and a ~47% increase in Young's modulus after exposure to low FSS for the PC-3 cells. There was no significant change in the Young's modulus of PrEC LH cells post-FSS exposure. Our findings indicate that cancer cells adapt to FSS, with an increased Young's modulus being one of the adaptive responses, and that this adaptation is specific only to PC-3 cells and is not seen in PrEC LH cells. Moreover, this adaptation appears to be graded in response to the magnitude of FSS experienced by the cancer cells. This is the first study investigating the effect of FSS on the mechanical properties of cancer cells in suspension, and may provide significant insights into the mechanism by which some select cancer cells may survive in the circulation, ultimately leading to metastasis at distal sites. Our findings suggest that biomechanical analysis of cancer cells could aid in identifying and diagnosing cancer in the future.

Prolyl-4-hydroxylase 3 (PHD3) expression is downregulated during epithelial-to-mesenchymal transition

Prolyl-4-hydroxylation by the intracellular prolyl-4-hydroxylase enzymes (PHD1-3) serves as a master regulator of environmental oxygen sensing. The activity of these enzymes is tightly tied to tumorigenesis, as they regulate cell metabolism and angiogenesis through their control of hypoxia-inducible factor (HIF) stability. PHD3 specifically, is gaining attention for its broad function and rapidly accumulating array of non-HIF target proteins. Data from several recent studies suggest a role for PHD3 in the regulation of cell morphology and cell migration. In this study, we aimed to investigate this role by closely examining the relationship between PHD3 expression and epithelial-to-mesenchymal transition (EMT); a transcriptional program that plays a major role in controlling cell morphology and migratory capacity. Using human pancreatic ductal adenocarcinoma (PDA) cell lines and Madin-Darby Canine Kidney (MDCK) cells, we examined the correlation between several markers of EMT and PHD3 expression. We demonstrated that loss of PHD3 expression in PDA cell lines is highly correlated with a mesenchymal-like morphology and an increase in cell migratory capacity. We also found that induction of EMT in MDCK cells resulted in the specific downregulation of PHD3, whereas the expression of the other HIF-PHD enzymes was not affected. The results of this study clearly support a model by which the basal expression and hypoxic induction of PHD3 is suppressed by the EMT transcriptional program. This may be a novel mechanism by which migratory or metastasizing cells alter signaling through specific pathways that are sensitive to regulation by O2. The identification of downstream pathways that are affected by the suppression of PHD3 expression during EMT may provide important insight into the crosstalk between O2 and the migratory and metastatic potential of tumor cells.

Abstract C30: Resistance to fluid shear stress is a conserved biophysical property of malignant cells

During metastasis, cancer cells enter the circulation in order to gain access to distant tissues, but how this fluid microenvironment influences cancer cell biology is poorly understood. A longstanding view is that circulating cancer cells derived from solid tissues may be susceptible to damage from hemodynamic shear forces, contributing to metastatic inefficiency. However, there have been few efforts to directly test this hypothesis. Here we report that compared to non-transformed epithelial cells, transformed cells are remarkably resistant to fluid shear stress (FSS) in a microfluidic protocol, exhibiting a biphasic decrease in viability when subjected to a series of millisecond pulses of high (750-6,300 dyn/cm2) FSS. We show that magnitude of FSS resistance is influenced by several oncogenes including myc, ras, and PI3K; is an adaptive and transient response triggered by reparable plasma membrane damage; and requires extracellular calcium and actin cytoskeletal dynamics, including the activity of Rho kinase. This novel property of malignant cancer cells may facilitate hematogenous metastasis and indicates, contrary to expectations, that cancer cells are quite resistant to destruction by hemodynamic shear forces.

Citation Format: James Matthew Barnes, Jones T. Nauseef, Michael D. Henry. Resistance to fluid shear stress is a conserved biophysical property of malignant cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C30.

Resistance to fluid shear stress is a conserved biophysical property of malignant cells

During metastasis, cancer cells enter the circulation in order to gain access to distant tissues, but how this fluid microenvironment influences cancer cell biology is poorly understood. A longstanding view is that circulating cancer cells derived from solid tissues may be susceptible to damage from hemodynamic shear forces, contributing to metastatic inefficiency. Here we report that compared to non-transformed epithelial cells, transformed cells are remarkably resistant to fluid shear stress (FSS) in a microfluidic protocol, exhibiting a biphasic decrease in viability when subjected to a series of millisecond pulses of high FSS. We show that magnitude of FSS resistance is influenced by several oncogenes, is an adaptive and transient response triggered by plasma membrane damage and requires extracellular calcium and actin cytoskeletal dynamics. This novel property of malignant cancer cells may facilitate hematogenous metastasis and indicates, contrary to expectations, that cancer cells are quite resistant to destruction by hemodynamic shear forces.

Abstract 436: Resistance to fluid shear stress is a conserved novel biophysical property of malignant cells

During metastasis, cancer cells access distant tissues via the circulation but how this fluid microenvironment influences cancer cell biology is poorly understood. It has been suggested that physical destruction of carcinoma cells due to exposure to hemodynamic forces during circulation is a barrier to metastasis. Here we report that transformed cells are remarkably resistant to fluid shear stress (FSS) in a novel microfluidic protocol. When subjected to a series of millisecond pulses of high FSS, transformed cells exhibit a biphasic decrease in viability. Significantly, human red and white blood cells survived the forces in this protocol. In stark contrast, non-transformed epithelial cells are markedly more susceptible to death under FSS. Accordingly, we show that FSS resistance is a property conferred by oncogenes. We reveal FSS resistance to be a transient and adaptive response triggered by plasma membrane damage and mediated by both extracellular calcium influx and dynamic reorganization of the actin cytoskeleton. This property of malignant cancer cells may facilitate hematogenous metastasis and indicates, contrary to expectations, that cancer cells are quite resistant to FSS. Thus, destruction of circulating cancer cells by hemodynamic shear is not likely to limit metastasis. Our data suggest that FSS resistance is a biophysical biomarker which may be used to rapidly discriminate between malignant and benign cells and, by virtue of representing phenotypic integration of oncogenic transformation, may be more tractable than conventional molecular biomarkers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 436. doi:1538-7445.AM2012-436