Efficacy of Radium-223 in Bone-metastatic Castration-resistant Prostate Cancer with and Without Homologous Repair Gene Defects

Synergistic Activity of DNA Damage Response Inhibitors in Combination with Radium-223 in Prostate Cancer

Radium-223 (223Ra) and Lutetium-177-labelled-PSMA-617 (177Lu-PSMA) are currently the only radiopharmaceutical treatments to prolong survival for patients with metastatic-castration-resistant prostate cancer (mCRPC); however, mCRPC remains an aggressive disease. Recent clinical evidence suggests patients with mutations in DNA repair genes associated with homologous recombination have a greater clinical benefit from 223Ra. In this study, we aimed to determine the utility of combining DNA damage response (DDR) inhibitors to increase the therapeutic efficacy of X-rays, or 223Ra. Radiobiological responses were characterised by in vitro assessment of clonogenic survival, repair of double strand breaks, cell cycle distribution, and apoptosis via PARP-1 cleavage. Here, we show that DDR inhibitors increase the therapeutic efficacy of both radiation qualities examined, which is associated with greater levels of residual DNA damage. Co-treatment of ATM or PARP inhibition with 223Ra increased cell cycle arrest in the G2/M phase. In comparison, combined ATR inhibition and radiation qualities caused G2/M checkpoint abrogation. Additionally, greater levels of apoptosis were observed after the combination of DDR inhibitors with 223Ra. This study identified the ATR inhibitor as the most synergistic inhibitor for both radiation qualities, supporting further pre-clinical evaluation of DDR inhibitors in combination with 223Ra for the treatment of prostate cancer.

Genomic Correlates of Prostate-Specific Membrane Antigen Expression and Response to 177Lu-PSMA-617: A Retrospective Multicenter Cohort Study

PURPOSE

While 177Lu-PSMA-617 (LuPSMA) is an effective therapy for many patients with metastatic castration-resistant prostate cancer (mCRPC), biomarkers associated with outcomes are not well defined. We hypothesized that prostate cancer mutational profile may associate with clinical activity of LuPSMA. We devised a study to evaluate associations between mCRPC mutational profile with LuPSMA clinical outcomes.

METHODS

This was a multicenter retrospective analysis of patients with mCRPC with next-generation sequencing (NGS) who received LuPSMA. PSA50 response (ie, ≥50% decline in prostate-specific antigen [PSA]) rate, PSA progression free survival (PSA PFS), and overall survival (OS) were compared between genetically defined subgroups.

RESULTS

One hundred twenty-six patients with NGS results who received at least one cycle of LuPSMA were identified. The median age was 73 (IQR, 68-78) years, 124 (98.4%) received ≥1 prior androgen receptor-signaling inhibitor, and 121 (96%) received ≥1 taxane-based chemotherapy regimen. Fifty-eight (46%) patients with a DNA damage repair gene mutation (DNA damage response group) and 59 (46.8%) with a mutation in TP53, RB1, or PTEN tumor suppressor genes (TSG group) were identified. After adjusting for relevant confounders, the presence of ≥1 TSG mutation was associated with shorter PSA PFS (hazard ratio [HR], 1.93 [95% CI, 1.05 to 3.54]; P = .034) and OS (HR, 2.65 [95% CI, 1.15 to 6.11]; P = .023). There was improved OS favoring the DNA damage response group (HR, 0.37 [95% CI, 0.14 to 0.97]; P = .044) on multivariable analysis. Univariate analysis of patients with ATM mutations had significantly higher rates of PSA50 response, PSA PFS, and OS.

CONCLUSION

Outcomes on LuPSMA varied on the basis of mutational profile. Prospective studies to define the clinical activity of LuPSMA in predefined genomic subgroups are justified.

Case report: Exceptional and durable response to Radium-223 and suspension of androgen deprivation therapy in a metastatic castration-resistant prostate cancer patient

Despite the development of new therapies in the last few years, metastatic prostate cancer (PCa) is still a lethal disease. Radium-223 (Ra-223) is approved for patients with advanced castration-resistant prostate cancer (CRPC) with bone metastases and no visceral disease. However, patients' outcomes are heterogenous, and there is lack of validated predictive biomarkers of response, while biomarkers for early identification of patients who benefit from treatment are limited. This case report describes a remarkable and durable response to Ra-223 in a CRPC patient with bone metastases who had rapidly progressed to many previous therapies; this response is now lasting for 5 years even after having stopped backbone androgen deprivation therapy (ADT). Here, we present the clinical course of this exceptional response, as well as comprehensive genomic and histopathology analyses on sequential biopsies acquired before and after therapy. Additionally, we review current knowledge on predictive and response biomarkers to Ra-223 in metastatic prostate cancer.

Radiotheranostics in advanced prostate cancer: Current and future directions

The discovery of small molecules that target the extracellular domain of prostate-specific membrane antigen (PSMA) has led to advancements in diagnostic imaging and the development of precision radiopharmaceutical therapies. In this review, we present the available existing data and highlight the key ongoing clinical evaluations of PSMA-based imaging in the management of primary, biochemically recurrent, and metastatic prostate cancer. We also discuss clinical studies that explore the use of PSMA-based radiopharmaceutical therapy (RPT) in metastatic prostate cancer and forthcoming trials that investigate PSMA RPT in earlier disease states. Multidisciplinary collaboration in clinical trial design and therapeutic administration is critical to the continued progress of this evolving radiotheranostics field.

A potential biomarker of radiosensitivity in metastatic hormone sensitive prostate cancer patients treated with combination external beam radiotherapy and radium-223

PURPOSE

The ADRRAD trial reported the safety and feasibility of the combination of external beam radiotherapy and radium-223 in the treatment of de novo bone metastatic prostate. This study aimed to determine if any biomarkers predictive of response to these treatments could be identified.

EXPERIMENTAL DESIGN

30 patients with newly diagnosed bone metastatic hormone sensitive prostate cancer were recruited to the ADRRAD trial. Blood samples were taken pre-treatment, before cycles 2 to 6 of radium-223, and 8 weeks and 6 months after treatment. Mononuclear cells were isolated and DNA damage was assessed at all timepoints.

RESULTS

DNA damage was increased in all patients during treatment, with bigger increases in foci observed in patients who relapsed late compared to those who relapsed early. Increases in DNA damage during the radium-223 only cycles of treatment were specifically related to response in these patients. Analysis of hematology counts also showed bigger decreases in red blood cell and hemoglobin counts in patients who experienced later biochemical relapse.

CONCLUSIONS

While some patients responded to this combination treatment, others relapsed within one year of treatment initiation. This study identifies a biomarker based approach that may be useful in predicting which patients will respond to treatment, by monitoring both increases in DNA damage above baseline levels in circulating lymphocytes and decreases in red blood cell and hemoglobin counts during treatment.

DNA Damage by Radiopharmaceuticals and Mechanisms of Cellular Repair

DNA is an organic molecule that is highly vulnerable to chemical alterations and breaks caused by both internal and external factors. Cells possess complex and advanced mechanisms, including DNA repair, damage tolerance, cell cycle checkpoints, and cell death pathways, which together minimize the potentially harmful effects of DNA damage. However, in cancer cells, the normal DNA damage tolerance and response processes are disrupted or deregulated. This results in increased mutagenesis and genomic instability within the cancer cells, a known driver of cancer progression and therapeutic resistance. On the other hand, the inherent instability of the genome in rapidly dividing cancer cells can be exploited as a tool to kill by imposing DNA damage with radiopharmaceuticals. As the field of targeted radiopharmaceutical therapy (RPT) is rapidly growing in oncology, it is crucial to have a deep understanding of the impact of systemic radiation delivery by radiopharmaceuticals on the DNA of tumors and healthy tissues. The distribution and activation of DNA damage and repair pathways caused by RPT can be different based on the characteristics of the radioisotope and molecular target. Here we provide a comprehensive discussion of the biological effects of RPTs, with the main focus on the role of varying radioisotopes in inducing direct and indirect DNA damage and activating DNA repair pathways.

High-LET radiation induces large amounts of rapidly-repaired sublethal damage

There is agreement that high-LET radiation has a high Relative Biological Effectiveness (RBE) when delivered as a single treatment, but how it interacts with radiations of different qualities, such as X-rays, is less clear. We sought to clarify these effects by quantifying and modelling responses to X-ray and alpha particle combinations. Cells were exposed to X-rays, alpha particles, or combinations, with different doses and temporal separations. DNA damage was assessed by 53BP1 immunofluorescence, and radiosensitivity assessed using the clonogenic assay. Mechanistic models were then applied to understand trends in repair and survival. 53BP1 foci yields were significantly reduced in alpha particle exposures compared to X-rays, but these foci were slow to repair. Although alpha particles alone showed no inter-track interactions, substantial interactions were seen between X-rays and alpha particles. Mechanistic modelling suggested that sublethal damage (SLD) repair was independent of radiation quality, but that alpha particles generated substantially more sublethal damage than a similar dose of X-rays, [Formula: see text]. This high RBE may lead to unexpected synergies for combinations of different radiation qualities which must be taken into account in treatment design, and the rapid repair of this damage may impact on mechanistic modelling of radiation responses to high LETs.

Determinants of outcome following PSMA-based radioligand therapy and mechanisms of resistance in patients with metastatic castration-resistant prostate cancer

[177Lu]Lu-PSMA has recently been approved for use in the post-taxane, post-novel hormonal-agent setting in patients with metastatic castration-resistant prostate cancer. As a beta-emitting radioligand targeting prostate-specific membrane antigen (PSMA), it delivers radiation to cells expressing PSMA on their surface. In pivotal clinical trials, patients were selected for this treatment based on positron emission tomography (PET)/CT imaging, requiring PSMA-avid disease with no evidence of discordant disease on 2-[18F]fluoro-2-deoxy-D-glucose PET/CT or contrast CT scan. Despite exhibiting an optimal imaging phenotype, the response for many patients is not durable, and a minority do not respond to [177Lu]Lu-PSMA at all. Disease progression is inevitable even for those who achieve an exceptional initial response. Reasons for both primary and acquired resistance are largely unknown; however, they are likely due to the presence of underlying PSMA-negative disease not identified on imaging, molecular factors conferring radioresistance, and inadequate delivery of lethal radiation, particularly to sites of micrometastatic disease. Biomarkers are urgently needed to optimize patient selection for treatment with [177Lu]Lu-PSMA by identifying those who are most and least likely to respond. Retrospective data support using several prognostic and predictive baseline patient- and disease-related parameters; however, robust prospective data is required before these can be translated into widespread use. Further, early on-treatment clinical parameters (in addition to serial prostate-specific antigen [PSA] levels and conventional restaging imaging) may serve as surrogates for predicting treatment response. With little known about the efficacy of treatments given after [177Lu]Lu-PSMA, optimal treatment sequencing is paramount, and biomarker-driven patient selection will hopefully improve treatment and survival outcomes.

Urinary DNA as a Tool for Germline and Somatic Mutation Detection in Castration-Resistant Prostate Cancer Patients

(1) Background: DNA damage response (DDR) pathway gene mutations are detectable in a significant number of patients with metastatic castration-resistant prostate cancer (mCRPC). The study aimed at identification of germline and/or somatic DDR mutations in blood and urine samples from patients with mCRPC for correlation with responses to entire sequence of systemic treatment and survival outcomes. (2) Methods: DDR gene mutations were assessed prospectively in DNA samples from leukocytes and urine sediments from 149 mCRPC patients using five-gene panel targeted sequencing. The impact of DDR status on progression-free survival, as well as treatment-specific and overall survival, was evaluated using Kaplan–Meier curves and Cox regression. (3) Results: DDR mutations were detected in 16.6% of urine and 15.4% of blood samples. BRCA1, BRCA2, CHEK2, ATM and NBN mutations were associated with significantly shorter PFS in response to conventional androgen deprivation therapy and first-line mCRPC therapy with abiraterone acetate. Additionally, BRCA1 and BRCA2 mutation-bearing patients had a significantly worse response to radium-223. However, DDR mutation status was predictive for the favourable effect of second-line abiraterone acetate after previous taxane-based chemotherapy. (4) Conclusions: Our data confirm the benefit of non-invasive urine-based genetic testing for timely identification of high-risk prostate cancer cases for treatment personalization.

Genomic characterization of metastatic castration-resistant prostate cancer patients undergoing PSMA radioligand therapy: A single-center experience

BACKGROUND

Genomic defects in DNA-damage repair (DDR) mechanisms have been proposed to affect the radiosensitivity of prostate cancers. In this study, we intended to evaluate the prevalence of genetic alterations in a cohort of metastatic castration-resistant prostate cancer (mCRPC) patients undergoing radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-inhibitors as well as the impact of such mutations on treatment outcomes.

METHODS

Data of consecutive mCRPC patients from 2017 to 2021 who were treated with PSMA-RLT and underwent next-generation sequencing (NGS) were collected and analyzed for response and survival outcomes.

RESULTS

In 95 patients of mCRPC treated with PSMA-RLT, 15 patients (median age: 66 years, range: 50-73 years; [¹⁷⁷ Lu]Lu-PSMA-617, n = 12; [²²⁵ Ac]Ac-PSMA-617, n = 3) underwent NGS. The median progression-free survival (PFS) of this cohort was 3 months (95% confidence interval: 1.6-4.4 months). On NGS, 21 genetic alterations were reported in 10/15 (67%) patients, of which 13 were DDR-associated alterations involving the genes: ATM (n = 3), BRCA2 (n = 3), TP53 (n = 2), PTEN (n = 2), FANCD2 (n = 1), FANCM (n = 1), and NBN (n = 1). Overall, 5/15 (33%) patients harbored six pathogenic variants (BRCA2, n = 2; ATM, n = 1; TP53, n = 1; PTEN, n = 2). No significant difference was noted for the biochemical response, radiological response, PFS, and overall survival between the patients with and without genetic alterations.

CONCLUSIONS

Patients of mCRPC undergoing PSMA-RLT were frequently seen to harbor DDR-associated aberrations, albeit with no significant impact on treatment outcomes. Large prospective trials comparing PSMA-RLT-related outcomes in DDR-deficient and -proficient patients are required to bring out the differences, if any, in a more observable manner.

Radium-223 dichloride treatment in metastatic castration-resistant prostate cancer in Finland: A real-world evidence multicenter study

BACKGROUND

Radium-233 dichloride is an alpha emitter that specifically targets bone metastases in prostate cancer. Results of a previously reported phase III randomized trial showed survival benefit for radium-223 compared to best supportive care in castration-resistant prostate cancer (CRPC) with bone metastases. However, real-world data are also needed with wider inclusion criteria.

METHODS

We report results of a retrospective multicenter study including all patients with metastatic CRPC treated with radium-223 in all five university hospitals in Finland since the introduction of the treatment. We identified 160 patients who had received radium-223 in Finland in 2014-2019.

RESULTS

The median overall survival (OS) was 13.8 months (range 0.5-57 months), and the median real-world progression-free survival (rwPFS) was 4.9 months (range 0.5-29.8 months). Alkaline phosphatase (ALP) values within the normal range before and during the radium-223 treatment or the reduction of elevated ALP to normal range during treatment were associated with better OS when compared to elevated ALP values before and during treatment (p < 0.0001). High prostate-specific antigen (PSA) level (≥100 μg/L) before radium-223 treatment was associated with poor OS compared to low PSA level (<20 μg/L) (p = 0.0001). Most patients (57%) experienced pain relief. Pain relief indicated better OS (p = 0.002). Radium-223 treatment was well tolerated. Toxicity was mostly low grade. Only 12.5% of the patients had grade III-IV adverse events, most commonly anemia, neutropenia, leucopenia, and thrombocytopenia.

CONCLUSION

Radium-223 was well tolerated in routine clinical practice, and most patients achieved pain relief. Pain relief, ALP normalization, lower baseline PSA, and PSA decrease during radium-223 treatment were prognostic for better survival. The efficacy of radium-223 in mCRPC as estimated using OS was comparable to earlier randomized trial in this retrospective real-world study. Our results support using radium-223 for mCRPC patients with symptomatic bone metastases even in the era of new-generation androgen receptor-targeted agents.

Phase I Study of Niraparib in Combination with Radium-223 for the Treatment of Metastatic Castrate-Resistant Prostate Cancer

PURPOSE

To identify the safety of niraparib, a PARP inhibitor, in combination with Radium-223 for the treatment of metastatic castrate-resistant prostate cancer (mCRPC) in men without known BRCA mutations.

PATIENTS AND METHODS

Men with progressive mCPRC following ≥1 line of androgen receptor (AR)-targeted therapy and bone metastases but no documented BRCA-1 or BRCA-2 alterations or bulky visceral disease were included. Niraparib dose was escalated in combination with standard dosing of Radium-223 using a time-to-event continual reassessment method. The highest dose level with a DLT probability <20% was defined as MTD. Secondary endpoints included PSA change and progression-free survival. Exploratory analyses included assessing DNA mutations found in ctDNA as well as gene expression changes assessed in whole blood samples.

RESULTS

Thirty patients were treated with niraparib and radium-223: 13 patients received 100 mg, 12 received 200 mg, and 5 patients received 300 mg of niraparib. There were six DLT events: two (13%) for neutropenia, two (13%) for thrombocytopenia, whereas fatigue and nausea each occurred once (3%). Anemia (2/13%) and neutropenia (2/13%) were the most common grade 3 adverse events. For patients with prior chemotherapy exposure, the MTD was 100 mg, whereas the MTD for chemotherapy naïve patients was 200 mg. Whole blood gene expression of PAX5 and CD19 was higher in responders and ARG-1, IL2R, and FLT3 expression was higher in nonresponders.

CONCLUSIONS

Combining niraparib with Radium-223 in patients with mCRPC was safe; however, further studies incorporating biomarkers will better elucidate the role of combinations of PARP inhibitors with DNA damaging and other agents.

DNA Damage Repair Defects and Targeted Radionuclide Therapies for Prostate Cancer: Does Mutation Really Matter? A Systematic Review

The aim of the present review was to assess the impact of DNA damage repair (DDR) mutations on response and outcome of patients (pts) affected by advanced prostate cancer (PCa) submitted to radionuclide therapies with [223Ra]RaCl2 (223Ra-therapy) or prostate specific membrane antigen (PSMA) ligands. A systematic literature search according to PRISMA criteria was made by using two main databases. Only studies published up until to October 2022 in the English language with ≥10 enrolled patients were selected. Seven studies including 326 pts, of whom 201 (61.6%) harboring DDR defects, were selected. The majority of selected papers were retrospective and four out of seven (57.1%) had small sample size (<50 pts). Three out of seven (42.8%) studies reported a more favorable outcome (overall or progression free survival) after therapy with alpha emitters (223Ra-therapy or [225Ac]Ac-PSMA-617) in subjects with DDR defects with respect to those without mutations. In two studies employing alpha or beta emitters ([177Lu]/[225Ac]-PMSA), no significant benefit was registered in pts harboring DDR defects. In all but one paper, no significant difference in response rate was reported among pts with or without DDR mutations. Although preliminary and biased by the retrospective design, preliminary data suggest a trend towards a longer survival in PCa pts harboring DDR defects submitted to radionuclide targeted therapy with alpha emitters.

Prognostic factors in metastatic castration resistant prostate cancer patients treated with radium-223: a retrospective study

BACKGROUND

Our study aims to identify baseline prognostic factors in metastatic castration resistant prostate cancer (mCRPC) patients treated with radium-223.

METHODS

Data about demographics, ECOG performance status, lymph node (LN) involvement, local treatment for prostate cancer, previous systemic treatments, cells blood count, PSA, ALP, albumin, LDH, bone protecting agents use (BPA), analgesic use and survival were collected. Univariable and multivariable analyses were performed.

RESULTS

Seventy-five men received radium-223 between September 2013 and December 2019. Median age was 73 years. Thirty-four (45.3%) had ECOG PS 0, 41 (54.7%) PS 1-2. In univariable analysis, LN involvement (HR 1.68, 95% CI 1.01-2.80, P=0.047), absence of local treatment on primary tumor (HR 1.93, 95% CI 1.13-3.29, P=0.016), baseline strong opioidsuse (HR 1.82, 95% CI 1.08-3.06, P=0.024), high platelets to lymphocyte ratio (PLR) (HR 1.91, 95% CI 1.06-3.45, P=0.03), high baseline ALP (HR 1.81, 95% CI 1.10-2.99, P=0.019) and high baseline LDH (HR 3.86,95% CI 2.01-7.41, P<0.001) were significantly associated with worst OS. At multivariable analysis, LN involvement, strong opioids use, baseline ALP, LDH and PLR levels were significantly associated with outcome.

CONCLUSIONS

In mCRPC patients treated with Radium-223, baseline ALP, LDH, strong opioid use, PLR, LN involvement and treatment on primary site are associated with different OS.

DNA damage repair gene germline profiling for metastatic prostate cancer patients of different ancestries

BACKGROUND

Germline and somatic mutations in DNA damage repair genes (DDRg) are now recognized as new biomarkers for the management of metastatic prostate cancers (mPC). We evaluate the frequency of germline DDRg mutations among French mPC patients of European and African ancestries.

METHODS

Targeted next-generation sequencing of 21 DDRg was performed on germline DNA from 557 mPC patients, including 15.1% of cases with an African origin.

RESULTS

Forty-seven germline mutations in 11 DDR genes were identified in 46 patients of the total cohort (8.3%). BRCA2 (4.1%) and ATM (2.0%) were the most frequently mutated genes. There was no difference in DDRg mutation frequency between mPC patients of European ancestry and those of African origin. Germline mutations of BRCA2 were associated with a positive family history of breast cancer (p = 0.02). The mean age at metastatic stage (59.7 vs. 67.0; p = 0.0003) and the mean age at death (65.2 vs. 73.9; p = 0.0003) were significantly earlier for carriers of BRCA2 mutation than for non-carriers. Moreover, the Cox model showed that BRCA2 positive status was statistically associated with poorer survival (hazard ratio: 0.29; 95% confidence interval 0.18-0.48; p < 0.0001).

CONCLUSION

We showed that, in France, BRCA2 and ATM are the main predisposing DDR genes in mPC patients, with a particular aggressiveness for BRCA2 leading to early metastatic stage and death.

The impact of genetic aberrations on response to radium-223 treatment for castration-resistant prostate cancer with bone metastases

BACKGROUND

Radium (Ra)-223 is an established treatment option for patients with metastatic castrate-resistant prostate cancer (mCRPC) who have symptomatic bone metastases without soft tissue disease. Studies have indicated genetic aberrations that regulate DNA damage response (DDR) in prostate cancer can increase susceptibility to treatments such as poly ADP-ribose polymerase inhibitors and platinum-based therapies. This study aims to evaluate mCRPC response to Ra-223 stratified by tumor genomics.

METHODS

This is a retrospective study of mCRPC patients who received Ra-223 and genetic testing within the Mayo Clinic database (Arizona, Florida, and Minnesota) and Tulane Cancer Center. Patient demographics, genetic aberrations, treatment responses in terms of alkaline phosphatase (ALP) and prostate-specific antigen (PSA), and survival were assessed. Primary end points were ALP and PSA response. Secondary end points were progression-free survival (PFS) and overall survival (OS) from time of first radium treatment.

RESULTS

One hundred and twenty-seven mCRPC patients treated with Ra-223 had germline and/or somatic genetic sequencing. The median age at time of diagnosis and Ra-223 treatment was 61.0 and 68.6 years, respectively. Seventy-nine (62.2%) had Gleason score ≥ 8 at time of diagnosis. 50.4% received prior docetaxel, and 12.6% received prior cabazitaxel. Notable alterations include TP53 (51.7%), BRCA 1/2 (15.0%), PTEN (13.4%), ATM (11.7%), TMPRSS2-ERG (8.2%), RB deletion (3.4%), and CDK12 (1.9%). There was no significant difference in ALP or PSA response among the different genetic aberrations. Patients with a TMPRSS2-ERG mutation exhibited a trend toward lower OS 15.4 months (95% confidence interval [CI] 10.0-NR) versus 26.8 months (95% CI 20.9-35.1). Patients with an RB deletion had a lower PFS 6.0 months (95% CI 1.28-NR) versus 9.0 months (95% CI 7.3-11.1) and a lower OS 13.9 months (95% CI 5.2-NR) versus 26.5 months (95% CI 19.8-33.8).

CONCLUSIONS

Among mCRPC patients treated with Ra-223 at Mayo Clinic and Tulane Cancer Center, we did not find any clear negative predictors of biochemical response or survival to treatment. TMPRSS2-ERG and RB mutations were associated with a worse OS. Prospective studies and larger sample sizes are needed to determine the impact of genetic aberrations in response to Ra-223.

Role of Olaparib in the Management of Metastatic Castration-Resistant Prostate Cancer: A Japanese Clinician's Perspective

Several studies have identified various targetable genomic alterations in prostate cancer, which accumulate during carcinogenesis and cancer progression. Genomic alterations in genes involved in DNA damage repair by homologous recombination repair may predict increased sensitivity to poly-ADP ribose polymerase (PARP) inhibitors. The Phase 3 PROfound trial has shown that treatment with the PARP inhibitor olaparib was associated with an improved radiographic progression-free survival and overall survival among patients with homologous recombination repair-deficient metastatic castration-resistant prostate cancer (mCRPC) after the treatment with androgen receptor targeting therapy, especially in men with BRCA1 or BRCA2 mutation. In Japan, olaparib was approved in December 2020 for the treatment of mCRPC with BRCA1 or BRCA2 mutation. In addition, genetic tests to detect BRCA1 or BRCA2 mutation to select patients who are likely to benefit from olaparib were also approved. This review summarizes the status of olaparib treatment for mCRPC, focusing on the situation in Japan.

Comprehensive circular RNA expression profile of lung adenocarcinoma with bone metastasis: Identification of potential biomarkers

Background: Lung adenocarcinoma (LUAD) has a significant tendency to metastasize to the bone, with severe comorbidities. Recent studies have reported that circular RNAs (circRNAs) are involved in various cancer metastasis-related physiological cellular processes. However, their role in LUAD with bone metastasis (LUAD-BM) remains unknown.

Methods: Bone metastasis (BM) circRNAs were identified using high-throughput sequencing and validated by quantitative reverse transcription-PCR (qRT-PCR). Bioinformatic analyses were used to predict the potential functions of the differentially expressed circRNAs. The effects of circ_0096442 on the growth and metastasis of A549 cells were detected in a co-culture system of A549 and bone marrow-derived cells.

Results: There were 598 (238 upregulated and 360 downregulated) 390 (187 upregulated and 203 downregulated) and 644 (336 upregulated and 308 downregulated) differentially expressed circRNAs between LUAD-BM and LUAD, LUAD-BM and healthy individuals, and LUAD and healthy individuals, respectively. These differentially expressed circRNAs play important roles in cellular components, biological processes, and molecular functions. Moreover, they map several pathways related to BM, including DNA repair, DNA damage, and osteoclast differentiation. The results validated by qRT-PCR for the five most dysregulated circRNAs are consistent with the sequencing data. Additionally, circ_0096442 was found to promote the growth and metastasis of LUAD in a bone microenvironment.

Conclusion: Our findings provide a novel and important circRNA expression profile of LUAD-BM and suggest that circ_0096442 may be a biomarker for LUAD-BM.

Prostate cancer immunotherapy: a review of recent advancements with novel treatment methods and efficacy

Immunotherapy remains to be an appealing treatment option for prostate cancer with some documented promise. Prostate cancer is traditionally considered as an immunologically "cold" tumor with low tumor mutation burden, low expression of PD-L1, sparse T-cell infiltration, and a immunosuppressive tumor microenvironment (TME). Sipuleucel-T (Provenge) is the first FDA approved immunotherapeutic agent for the treatment of asymptomatic or minimally symptomatic metastatic castrate resistant prostate cancer (mCRPC); demonstrating a benefit in overall survival. However various clinical trials by immune checkpoint inhibitors (ICIs) and their combinations with other drugs have shown limited responses in mCRPC. Up to now, only a small subset of patients with mismatch repair deficiency/microsatellite instability high and CDK12 mutations can clinically benefit from ICIs and/or their combinations with other agents, such as DNA damage agents. The existence of a large heterogeneity in genomic alterations and a complex TME in prostate cancer suggests the need for identifying new immunotherapeutic targets. As well as designing personalized immunotherapy strategies based on patient-specific molecular signatures. There is also a need to adjust strategies to overcome histologic barriers such as tissue hypoxia and dense stroma. The racial differences of immunological responses between men of diverse ethnicities also merit further investigation to improve the efficacy of immunotherapy and better patient selection in prostate cancer.

Genomic biomarkers to guide precision radiotherapy in prostate cancer

Our ability to prognosticate the clinical course of patients with cancer has historically been limited to clinical, histopathological, and radiographic features. It has long been clear however, that these data alone do not adequately capture the heterogeneity and breadth of disease trajectories experienced by patients. The advent of efficient genomic sequencing has led to a revolution in cancer care as we try to understand and personalize treatment specific to patient clinico-genomic phenotypes. Within prostate cancer, emerging evidence suggests that tumor genomics (e.g., DNA, RNA, and epigenetics) can be utilized to inform clinical decision making. In addition to providing discriminatory information about prognosis, it is likely tumor genomics also hold a key in predicting response to oncologic therapies which could be used to further tailor treatment recommendations. Herein we review select literature surrounding the use of tumor genomics within the management of prostate cancer, specifically leaning toward analytically validated and clinically tested genomic biomarkers utilized in radiotherapy and/or adjunctive therapies given with radiotherapy.

[18F]-Labeled PARP-1 PET imaging of PSMA targeted alpha particle radiotherapy response

The growing interest and clinical translation of alpha particle (α) therapies brings with it new challenges to assess target cell engagement and to monitor therapeutic effect. Noninvasive imaging has great potential to guide α-treatment and to harness the potential of these agents in the complex environment of disseminated disease. Poly(ADP) ribose polymerase 1 (PARP-1) is among the most abundantly expressed DNA repair enzymes with key roles in multiple repair pathways-such as those induced by irradiation. Here, we used a third-generation PARP1-specific radiotracer, [18F]-PARPZ, to delineate castrate resistant prostate cancer xenografts. Following treatment with the clinically applied [225Ac]-PSMA-617, positron emission tomography was performed and correlative autoradiography and histology acquired. [18F]-PARPZ was able to distinguish treated from control (saline) xenografts by increased uptake. Kinetic analysis of tracer accumulation also suggests that the localization of the agent to sites of increased PARP-1 expression is a consequence of DNA damage response. Together, these data support expanded investigation of [18F]-PARPZ to facilitate clinical translation in the ⍺-therapy space.

Stereotactic Radiotherapy for Lesions Detected via 68Ga-Prostate-specific Membrane Antigen and 18F-Fluorodexyglucose Positron Emission Tomography/Computed Tomography in Patients with Nonmetastatic Prostate Cancer with Early Prostate-specific Antigen Progression on Androgen Deprivation Therapy: A Prospective Single-center Study

BACKGROUND

Dual-tracer positron emission tomography/computed tomography (PET/CT) with a ⁶⁸Ga-labelled prostate-specific membrane antigen (PSMA) ligand and ¹⁸F-fluorodeoxyglucose (FDG) improves detection of metastatic heterogeneity and burden in patients with nonmetastatic prostate cancer (nmPCa). However, there is limited prospective evidence regarding its impact on the efficacy of stereotactic body radiotherapy (SBRT).

OBJECTIVE

To evaluate metastasis-free survival (MFS) and toxicity after SBRT to dual-tracer PET/CT-detected metastases in patients with nmPCa and early prostate-specific antigen (PSA) progression on androgen deprivation therapy (ADT; PSA ≤2 ng/ml).

DESIGN, SETTING, AND PARTICIPANTS

Patients were prospectively screened using dual-tracer PET/CT between April 2019 and October 2020. SBRT was recommended for patients with five or fewer nonvisceral metastases (SBRT group). Patients without detectable metastases (N-/M- group) and those who refused SBRT (ADT group) continued to receive ADT. Patients were followed with conventional imaging.

INTERVENTION

SBRT to each PET/CT-detected metastasis.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Kaplan-Meier methods were used to determine MFS. Toxicity was evaluated using Common Terminology Criteria for Adverse Event v4.0.

RESULTS AND LIMITATIONS

Seventy-four consecutive patients were screened. The median PSA and PSA doubling time were 0.59 ng/ml and 4.56 mo, respectively. Overall, 54 patients had metastases and 17 had PSMA-/FDG+ disease. Seven patients were excluded from the MFS analysis, including two with a history of abiraterone treatment and five with more than five metastases. The median follow-up was 21.4 mo. The ADT group had shorter MFS than the SBRT group (11.0 mo vs not reached; hazard ratio [HR] 4.69, 95% confidence interval [CI] 2.92-25.0; p < 0.001) and the N-/M- group (11.0 mo vs not reached; HR 8.78, 95% CI 4.04-40.30; p < 0.001). There was no significant difference in median MFS between the SBRT group and the N-/M- group (p = 0.261). A PSA response >90% was achieved by 86% of patients in the SBRT group. There were no grade ≥3 adverse events after SBRT. The nonrandomized design is the major study limitation.

CONCLUSIONS

Dual-tracer PET/CT-guided SBRT delivered superior local control rates in comparison to ADT alone and had minimal toxicity.

PATIENT SUMMARY

We investigated metastasis-targeted radiotherapy for patients with up to five prostate cancer metastases detected with two different radioisotope scans. Our results show that this approach yields promising metastasis-free survival and low toxicity.

Impact of DNA damage repair defects on response to PSMA radioligand therapy in metastatic castration-resistant prostate cancer

PURPOSE

Prostate-specific membrane antigen radioligand therapy (PSMA-RLT) is a novel treatment for castration-resistant prostate cancer (mCRPC). While the majority of patients responds to PSMA-RLT, with 10-15% having an exceptional response, approximately 30% of patients is unresponsive to PSMA-RLT. The molecular underpinning may in part explain these varying responses. This study investigated alterations in DNA damage repair (DDR) genes in tumour biopsies and their association with response to PSMA-RLT.

METHODS

A predefined retrospective cohort study was performed in mCRPC patients of whom the tumours had undergone next-generation sequencing of 40 DDR genes and received Lu-177-PSMA and/or Ac-225-PSMA-RLT. The primary outcome of this study was to compare the progression free survival (PFS) after PSMA-RLT for patients with and without pathogenic DDR aberrations in their tumour. Secondary outcomes were prostate-specific antigen (PSA) response and overall survival (OS).

RESULTS

A total of 40 patients were included of which seventeen had a tumour with a pathogenic DDR aberration (DDR+), of which eight had defects in BRCA1/2. DDR+ patients had an equal varying response to PSMA-RLT compared to those without pathological DDR anomalies (DDR-) in terms of PFS (5.9 vs. 6.4 months, respectively; HR 1.14; 95% CI 0.58-2.25; p = 0.71), ≥50% PSA response (59% vs. 65%, respectively; p = 0.75) or OS (11.1 vs. 10.7 months, respectively; HR 1.40; 95% CI: 0.68-2.91; p = 0.36).

CONCLUSION

In this study of a selected cohort, pathogenic DDR aberrations were not associated with exceptional responsiveness to PSMA-RLT. Translational studies in larger prospective cohorts are warranted to associate DDR gene defects with differential responses to PSMA-RLT.

FANCI may serve as a prognostic biomarker for cervical cancer: A systematic review and meta-analysis

BACKGROUND

DNA damage is a fundamental process that plays a considerable role in generating protein diversity. FANCI, loaded on the altered chromatin, plays a vital role in DNA damage. Abnormal FANCI expression is potentially associated with carcinogenesis.However, the biological role of FANCI in cervical cancer is yet to be determined.

METHODS

We analyzed FANCI expression via multiple gene expression databases. Genes co-expressed with FANCI and its regulators were identified using LinkedOmics. The correlations between FANCI and cancer immune infiltrates were investigated via Tumor Immune Estimation Resource (TIMER).

RESULTS

FANCI was found upregulated with amplification in tumor tissues of multiple cervical cancer cohorts. High FANCI expression was associated with poorer overall survival (OS). Functional network analysis suggested that FANCI regulates spliceosome, DNA replication, and cell cycle signaling via pathways involving several cancer-related kinases and the E2F family. In additional, FANCI expression was positively correlated with infiltrating levels of CD4+ T and CD8+ T cells, and neutrophils. FANCI expression also showed strong correlations with diverse immune marker sets in cervical cancer.

CONCLUSION

These findings suggested that FANCI is correlated with prognosis of and immune infiltration in cervical cancer, laying a foundation for further study of the immune regulatory role of FANCI in cervical cancer.

A functionally impaired missense variant identified in French Canadian families implicates FANCI as a candidate ovarian cancer-predisposing gene

Background

Familial ovarian cancer (OC) cases not harbouring pathogenic variants in either of the BRCA1 and BRCA2 OC-predisposing genes, which function in homologous recombination (HR) of DNA, could involve pathogenic variants in other DNA repair pathway genes.

Methods

Whole exome sequencing was used to identify rare variants in HR genes in a BRCA1 and BRCA2 pathogenic variant negative OC family of French Canadian (FC) ancestry, a population exhibiting genetic drift. OC cases and cancer-free individuals from FC and non-FC populations were investigated for carrier frequency of FANCI c.1813C>T; p.L605F, the top-ranking candidate. Gene and protein expression were investigated in cancer cell lines and tissue microarrays, respectively.

Results

In FC subjects, c.1813C>T was more common in familial (7.1%, 3/42) than sporadic (1.6%, 7/439) OC cases (P = 0.048). Carriers were detected in 2.5% (74/2950) of cancer-free females though female/male carriers were more likely to have a first-degree relative with OC (121/5249, 2.3%; Spearman correlation = 0.037; P = 0.011), suggesting a role in risk. Many of the cancer-free females had host factors known to reduce risk to OC which could influence cancer risk in this population. There was an increased carrier frequency of FANCI c.1813C>T in BRCA1 and BRCA2 pathogenic variant negative OC families, when including the discovery family, compared to cancer-free females (3/23, 13%; OR = 5.8; 95%CI = 1.7–19; P = 0.005). In non-FC subjects, 10 candidate FANCI variants were identified in 4.1% (21/516) of Australian OC cases negative for pathogenic variants in BRCA1 and BRCA2, including 10 carriers of FANCI c.1813C>T. Candidate variants were significantly more common in familial OC than in sporadic OC (P = 0.04). Localization of FANCD2, part of the FANCI-FANCD2 (ID2) binding complex in the Fanconi anaemia (FA) pathway, to sites of induced DNA damage was severely impeded in cells expressing the p.L605F isoform. This isoform was expressed at a reduced level, destabilized by DNA damaging agent treatment in both HeLa and OC cell lines, and exhibited sensitivity to cisplatin but not to a poly (ADP-ribose) polymerase inhibitor. By tissue microarray analyses, FANCI protein was consistently expressed in fallopian tube epithelial cells and only expressed at low-to-moderate levels in 88% (83/94) of OC samples.

Conclusions

This is the first study to describe candidate OC variants in FANCI, a member of the ID2 complex of the FA DNA repair pathway. Our data suggest that pathogenic FANCI variants may modify OC risk in cancer families.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-021-00998-5.

Cabazitaxel activity in men with metastatic castration-resistant prostate cancer with and without DNA damage repair defects

BACKGROUND

Cabazitaxel was shown to improve overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) after abiraterone/enzalutamine and docetaxel failure, though benefit by the presence of DNA damage repair (DDR) defects is unknown. With the advent of poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) in partially overlapping indications with cabazitaxel, we aimed to determine cabazitaxel activity in men with mCRPC according to their DDR status.

METHODS

This is a retrospective multicenter study that enrolled patients with mCRPC treated with cabazitaxel who had undergone DDR tumour tissue profiling. Patients with at least one deleterious germline or somatic alterations were considered DDR positive (DDR+). Each DDR + patient has been matched with a DDR negative (DDR-) from the same institution who underwent the same test. An exploratory cohort of patients found to be DDR + by liquid biopsy was also included. Prostate specific antigen (PSA) decline≥50% (PSA50), PSA progression-free survival (PFS, PSA-PFS), radiographic PFS (rPFS), clinical PFS or radiographic PFS (c/rPFS) and OS were evaluated.

RESULTS

Among 190 men (95 DDR+, 95 DDR-) with tissue sequencing, PSA50 was achieved with cabazitaxel in 29/92 (32%) and 33/92 (36%) in patients with DDR+ and DDR- (P = 0.64). The median rPFS was 5.33 months [95%CI 4.34-7.04] versus 5.75 months [95%CI 4.67-7.27] (P = 0.55). The median OS was 15.4 months [95%CI 12.16-26.6] and 11.5 months [95%CI 9.76-14.4] (P = 0.036), respectively. No PSA50 responses on cabazitaxel were observed in BRCA1/2 patients previously treated with PARPi (n = 10). Similar outcomes with cabazitaxel were observed in the liquid biopsy cohort (n = 63 DDR+).

CONCLUSIONS

Our study suggests that cabazitaxel is active in patients with mCRPC regardless of their DDR status, although its activity in men pretreated with a PARPi may be lower.

Radium-223 Treatment of Patients with Metastatic Castration Resistant Prostate Cancer: Biomarkers for Stratification and Response Evaluation

Simple Summary

Radium-223 dichloride ([²²³Ra]RaCl₂; Ra-223) is an alpha-emitting radiopharmaceutical treatment for patients with metastatic castration resistant prostate cancer (mCRPC) with predominantly bone metastases. While responses to chemotherapeutic and antihormonal mCRPC treatments can be assessed by serum PSA levels, a decrease of serum PSA levels is not expected during Ra-223 therapy. Moreover, radiographic evaluation of bone metastases response is challenging. Therefore, novel biomarkers to select patients for Ra-223 treatment and monitoring response are urgently needed. In this review, we discuss the currently used and exploratory biomarkers for this purpose, including soluble and cellular factors detected in the peripheral blood, genetic defects and radiographic assessments. We conclude that some biomarkers, including metabolic products of collagen degradation and novel PET scan techniques, might hold promise as predictors of response to Ra-223 treatment. However, these biomarkers have not been extensively studied. Consequently, currently, no biomarker has established a place in patient stratification and response evaluation.

Abstract

Radium-223 dichloride ([²²³Ra]RaCl₂; Ra-223) is a targeted alpha-emitting radiopharmaceutical which results in an overall survival and health related quality of life (HRQoL) benefit in symptomatic patients with metastatic castration resistant prostate cancer (mCRPC) and predominantly bone metastasis. Although effective, options to select patients who will derive treatment benefit and to monitor and predict treatment outcomes are limited. PSA response and radiographic evaluation are commonly used in mCRPC treatment assessment but are not informative in Ra-223 treated patients. Consequently, there is a clear need for predictive and prognostic tools. In this review, we discuss the physiology of bone metastases and the mechanism of action and efficacy of Ra-223 treatment, as well as offering an outline of current innovative prognostic and predictive biomarkers.

Clinical outcomes, management, and treatment patterns in patients with metastatic castration-resistant prostate cancer treated with radium-223 in community compared to academic settings

BACKGROUND

The most common site of disease in metastatic castration-resistant prostate cancer (mCRPC) is the bone. The ALSYMPCA study demonstrated that radium-223 significantly improved overall survival (OS) in mCRPC patients with symptomatic bone metastases and without visceral metastases. However, administration requires a multidisciplinary approach and an infrastructure that supports coordination of care, which may differ by practice site. We aimed to evaluate practice patterns and treatment outcomes in patients with mCRPC treated at a community practice (CP) compared with those treated at an academic center (AC).

METHODS

This retrospective review included 200 adult mCRPC patients receiving radium-223 between January 2014 and June 2017. The primary endpoint, OS, was estimated from the date of radium-223 initiation. Secondary outcomes included a comparison of baseline characteristics, reasons for initiation and discontinuation of radium-223, and treatment sequencing. A subset analysis of OS based on the number of radium-223 doses and on sequencing of radium-223 either before or after chemotherapy was also conducted.

RESULTS

Most patients were treated at a CP (57%). Patients treated at CP sites were significantly older (74.9 vs. 71.9 years; p = .031) and had more comorbidities (Klabunde score 1.1 vs. 0.7; p = .020) than those in an AC but initiated treatment within a shorter period of time from diagnosis of mCRPC (1.3 vs. 1.9 years; p < .001) and received a greater mean number of radium-223 doses (5.4 vs. 4.8; p = .001). There were no observed differences in OS between CPs versus ACs (21.6 vs. 20.7 months; p = .306). Overall, patients who received 5-6 doses versus 1-4 doses of radium-223 had a longer median OS (23.3 vs. 6.4 months; p < .001). The most common reason for discontinuation in patients who did not complete treatment was disease progression. Overall, 43% of patients received radium-223 monotherapy and 57% concurrently with other agents.

CONCLUSIONS

Most patients received radium-223 concurrently with abiraterone acetate or enzalutamide and were able to complete 5-6 doses of radium-223. Despite differences in the populations and treatment patterns, no survival differences between patients treated in ACs versus CPs were observed. Additional real-world data are needed to validate these findings.

Basic Science and Molecular Genetics of Prostate Cancer Aggressiveness

Androgen receptor function, tumor cell plasticity, loss of tumor suppressors, and defects in DNA repair genes affect aggressive features of prostate cancer. Prostate cancer development, progression, and aggressive behavior are often attributable to function of the androgen receptor. Tumor cell plasticity, neuroendocrine features, and loss of tumor suppressors lend aggressive behavior to prostate cancer cells. DNA repair defects have ramifications for prostate cancer cell behavior.

Genetic Contribution to Metastatic Prostate Cancer

Recent studies show that the prevalence of germline pathogenic and likely pathogenic variants (also known as mutations) in DNA repair genes in metastatic prostate cancer is higher than previously recognized and higher than in unaffected men. Specific gene dysfunction is important in prostate cancer initiation and/or evolution to metastases. This article reviews key literature on individual genes, recognizing BRCA2 as the gene most commonly altered in the metastatic setting. This article discusses the importance of representative and diverse inclusion, and efforts to advance management for at-risk carrier populations to maximize clinical benefit.

Efficacy and safety of Prostate stereotactic body radiotherapy for metastatic castration-resistant prostate cancer: A prospective cohort study

BACKGROUND

The efficacy and safety of prostate SBRT in men with mCRPC is unknown.

MATERIALS AND METHODS

A prospective cohort study was conducted with 125 men diagnosed with mCRPC. All patients received ADT plus chemotherapy. Patients were randomly assigned to receive daily prostate SBRT (36-48 Gy in 6-8 fractions). Patients who did not receive SBRT served as controls.

RESULTS

The primary endpoints were PFS and OS. After 89 months of total follow-up, the median PFS was 13.8 months in the SBRT group (n = 61) and 12.0 months in the control group (n = 64) (HR, 0.87; 95% CI, 0.61-1.24; P = 0.249). The OS was 25.7 months in the SBRT group and 23.8 months in the control group (HR, 0.93; 95% CI, 0.65-1.33; P = 0.230). A non-significant increase in the PSA response rate (50.8% vs. 43.7%) and time to PSA progression (8.3 months vs. 7.0 months) was observed in the SBRT group compared to the control group; however, the time to symptomatic progression was significantly prolonged in the SBRT group (11.3 months) compared to the control group (8.5 months) (HR, 0.76; 95% CI, 0.53-1.08; P = 0.019). There was an 11.5% incidence of radiation cystitis and radiation rectitis in the SBRT group, and the degree and incidence of hormone-related and chemotherapy-related adverse events were similar between the two groups.

CONCLUSION

Adding prostate SBRT significantly prolonged the time to symptomatic progression and non-significantly prolonged PFS and OS among men with mCRPC compared to treatment with ADT plus chemotherapy alone.

Radium-223 Treatment Increases Immune Checkpoint Expression in Extracellular Vesicles from the Metastatic Prostate Cancer Bone Microenvironment

PURPOSE

Radium-223 prolongs survival in a fraction of men with bone metastatic prostate cancer (PCa). However, there are no markers for monitoring response and resistance to Radium-223 treatment. Exosomes are mediators of intercellular communication and may reflect response of the bone microenvironment to Radium-223 treatment. We performed molecular profiling of exosomes and compared the molecular profile in patients with favorable and unfavorable overall survival.

EXPERIMENTAL DESIGN

We performed exosomal transcriptome analysis in plasma derived from our preclinical models (MDA-PCa 118b tumors, TRAMP-C2/BMP4 PCa) and from the plasma of 25 patients (paired baseline and end of treatment) treated with Radium-223. All samples were run in duplicate, and array data analyzed with fold changes +2 to -2 and P < 0.05.

RESULTS

We utilized the preclinical models to establish that genes derived from the tumor and the tumor-associated bone microenvironment (bTME) are differentially enriched in plasma exosomes upon Radium-223 treatment. The mouse transcriptome analysis revealed changes in bone-related and DNA damage repair-related pathways. Similar findings were observed in plasma-derived exosomes from patients treated with Radium-223 detected changes. In addition, exosomal transcripts detected immune-suppressors (e.g., PD-L1) that were associated with shorter survival to Radium-223. Treatment of the Myc-CaP mouse model with a combination of Radium-223 and immune checkpoint therapy (ICT) resulted in greater efficacy than monotherapy.

CONCLUSIONS

These clinical and coclinical analyses showed that RNA profiling of plasma exosomes may be used for monitoring the bTME in response to treatment and that ICT may be used to increase the efficacy of Radium-223.

Targeting treatment options for castration-resistant prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed solid tumor and the second leading cause of cancer-related deaths in U.S. men in 2020. Androgen-deprivation therapy (ADT) is the standard of care for metastatic PCa. Unfortunately, PCa relapse often occurs one to two years after initiation of ADT, resulting in the development of castration-resistant PCa (CRPCa), a lethal disease. While several anticancer agents such as docetaxel, abiraterone acetate, and enzalutamide are currently utilized to extend a patient's life after development of CRPCa, patients will eventually succumb to the disease. Hence, while targeting androgen signaling and utilization of docetaxel remain the most crucial agents for many of these combinations, many studies are attempting to exploit other vulnerabilities of PCa cells, such as inhibition of key survival proteins, anti-angiogenesis agents, and immunotherapies. This review will focus on discussing recent advances on targeting therapy. Several novel small molecules will also be discussed.

The Mutational Landscape of Metastatic Castration-sensitive Prostate Cancer: The Spectrum Theory Revisited

BACKGROUND

Emerging data suggest that metastasis is a spectrum of disease burden rather than a binary state, and local therapies, such as radiation, might improve outcomes in oligometastasis. However, current definitions of oligometastasis are solely numerical.

OBJECTIVE

To characterize the somatic mutational landscape across the disease spectrum of metastatic castration-sensitive prostate cancer (mCSPC) to elucidate a biological definition of oligometastatic CSPC.

DESIGN, SETTING, AND PARTICIPANTS

This was a retrospective study of men with mCSPC who underwent clinical-grade sequencing of their tumors (269 primary tumor, 25 metastatic sites). Patients were classified as having biochemically recurrent (ie, micrometastatic), metachronous oligometastatic (≤5 lesions), metachronous polymetastatic (>5 lesions), or de novo metastatic (metastasis at diagnosis) disease.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We measured the frequency of driver mutations across metastatic classifications and the genomic associations with radiographic progression-free survival (rPFS) and time to castrate-resistant prostate cancer (CRPC).

RESULTS AND LIMITATIONS

The frequency of driver mutations in TP53 (p =  0.01), WNT (p =  0.08), and cell cycle (p =  0.04) genes increased across the mCSPC spectrum. TP53 mutation was associated with shorter rPFS (26.7 vs 48.6 mo; p =  0.002), and time to CRPC (95.6 vs 155.8 mo; p =  0.02) in men with oligometastasis, and identified men with polymetastasis with better rPFS (TP53 wild-type, 42.7 mo; TP53 mutated, 18.5 mo; p =  0.01). Mutations in TP53 (incidence rate ratio [IRR] 1.45; p =  0.004) and DNA double-strand break repair (IRR 1.61; p <  0.001) were associated with a higher number of metastases. Mutations in TP53 were also independently associated with shorter rPFS (hazard ratio [HR] 1.59; p =  0.03) and the development of CRPC (HR 1.71; p =  0.01) on multivariable analysis. This study was limited by its retrospective nature, sample size, and the use of commercially available sequencing platforms, resulting in a limited predefined set of genes examined.

CONCLUSIONS

Somatic mutational profiles reveal a spectrum of metastatic biology that helps in redefining oligometastasis beyond a simple binary state of lesion enumeration.

PATIENT SUMMARY

Oligometastatic prostate cancer is typically defined as less than three to five metastatic lesions and evidence suggests that using radiation or surgery to treat these sites improves clinical outcomes. As of now, treatment decisions for oligometastasis are solely defined according to the number of lesions. However, this study suggests that tumor mutational profiles can provide a biological definition of oligometastasis and complement currently used numerical definitions.

Clinical outcomes and molecular profiling of advanced metastatic castration-resistant prostate cancer patients treated with 225Ac-PSMA-617 targeted alpha-radiation therapy

INTRODUCTION

Targeted alpha-radiation therapy (TAT) with ²²⁵Ac-labeled prostate-specific membrane antigen (PSMA) ligands is a promising novel treatment option for metastatic castration-resistant prostate cancer (mCRPC) patients. However, limited data are available on efficacy, quality of life (QoL), and pretherapeutic biomarkers. The aim of this study was to evaluate the efficacy of ²²⁵Ac-PSMA TAT and impact on QoL in advanced mCRPC, and to explore predictive biomarkers on pretherapeutic metastatic tissue biopsies.

METHODS

Observational cohort study including consecutive patients treated with ²²⁵Ac-PSMA TAT between February 2016 and July 2018. Primary endpoint was overall survival (OS). Furthermore, prostate-specific antigen (PSA) changes, radiological response, safety, QoL, and xerostomia were evaluated. Biopsies were analyzed with immunohistochemistry and next-generation sequencing.

RESULTS

Thirteen patients were included. Median OS was 8.5 months for the total cohort and 12.6 months for PSMA radioligand therapy-naïve patients. PSA declines of ≥90% and ≥50% were observed in 46% and 69% of patients, respectively. Six patients were radiologically evaluable; 50% showed partial response. All patients showed >90% total tumor volume reduction on PET imaging. Patients experienced clinically relevant decrease of pain and QoL improvement in physical and role functioning domains. Xerostomia persisted during follow-up. Patients with high baseline immunohistochemical PSMA expression or DNA damage repair alterations tended to have longer OS.

CONCLUSIONS

TAT with ²²⁵Ac-PSMA resulted in remarkable survival and biochemical responses in advanced mCRPC patients. Patients experienced clinically relevant QoL improvement, although xerostomia was found to be nontransient. Baseline immunohistochemical PSMA expression and DNA damage repair status are potential predictive biomarkers of response to ²²⁵Ac-PSMA TAT.

Interactions between androgen receptor signaling and other molecular pathways in prostate cancer progression: Current and future clinical implications

In last years several improvements have been made in the management of prostate cancer (PCa). Androgen receptor (AR) is considered the main driver in PCa growth and progression and most drugs are directed against AR pathway. Once PCa spreads outside the prostate, androgen deprivation therapy (ADT) represents the cornerstone of treatment in hormone-sensitive prostate cancer (HSPC). Unfortunately, the response is only transient and most patients eventually develop castration-resistant prostate cancer (CRPC). Most resistance mechanisms depend on maintenance of AR signalling in castration environment. Recent discoveries of multiple growth-promoting and survival pathways in PCa suggest the importance of alternative mechanisms involved in disease progression, such as DNA damage response pathway, PTEN/PI3K/AKT/mTOR pathway, cell cycle pathway, WNT pathway, TMPRSS2/ETS fusion, neuroendocrine pattern and immune system response. In this review, we discuss the interplay between AR signaling and other molecular pathways involved in PCa pathogenesis and their therapeutic implication in advanced disease.

Targeting DNA Damage Response in Prostate and Breast Cancer

Steroid hormone signaling induces vast gene expression programs which necessitate the local formation of transcription factories at regulatory regions and large-scale alterations of the genome architecture to allow communication among distantly related cis-acting regions. This involves major stress at the genomic DNA level. Transcriptionally active regions are generally instable and prone to breakage due to the torsional stress and local depletion of nucleosomes that make DNA more accessible to damaging agents. A dedicated DNA damage response (DDR) is therefore essential to maintain genome integrity at these exposed regions. The DDR is a complex network involving DNA damage sensor proteins, such as the poly(ADP-ribose) polymerase 1 (PARP-1), the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), the ataxia-telangiectasia-mutated (ATM) kinase and the ATM and Rad3-related (ATR) kinase, as central regulators. The tight interplay between the DDR and steroid hormone receptors has been unraveled recently. Several DNA repair factors interact with the androgen and estrogen receptors and support their transcriptional functions. Conversely, both receptors directly control the expression of agents involved in the DDR. Impaired DDR is also exploited by tumors to acquire advantageous mutations. Cancer cells often harbor germline or somatic alterations in DDR genes, and their association with disease outcome and treatment response led to intensive efforts towards identifying selective inhibitors targeting the major players in this process. The PARP-1 inhibitors are now approved for ovarian, breast, and prostate cancer with specific genomic alterations. Additional DDR-targeting agents are being evaluated in clinical studies either as single agents or in combination with treatments eliciting DNA damage (e.g., radiation therapy, including targeted radiotherapy, and chemotherapy) or addressing targets involved in maintenance of genome integrity. Recent preclinical and clinical findings made in addressing DNA repair dysfunction in hormone-dependent and -independent prostate and breast tumors are presented. Importantly, the combination of anti-hormonal therapy with DDR inhibition or with radiation has the potential to enhance efficacy but still needs further investigation.

Clinical implications of genomic evaluations for prostate cancer risk stratification, screening, and treatment: a narrative review

New classification systems based on molecular features have been introduced to improve precision medicine for prostate cancer (PCa). This review covers the increasing risk of PCa and the differences in response to targeted therapy that are related to specific gene variations. We believe that genomic evaluations will be useful for guiding PCa risk stratification, screening, and treatment. We searched the PubMed and MEDLINE databases for articles related to genomic testing for PCa that were published in 2020 or earlier. There is increasing evidence that germline mutations in DNA repair genes, such as BRCA1/2 or ATM, are closely related to the development and aggressiveness of PCa. Targeted prostate-specific antigen screening based on the presence of germline alterations in DNA repair genes is recommend to achieve an early diagnosis of PCa. In cases of localized PCa, even if it has a favorable risk classification, patients under active surveillance with these gene alterations are likely to develop aggressive PCa. Thus, active treatment may be preferable to active surveillance for these patients. In cases of metastatic castration–resistant PCa, BRCA1/2 and DNA mismatch repair genes may be useful biomarkers for predicting the response to androgen receptor–targeting agents, poly (ADP-ribose) polymerase inhibitors, platinum chemotherapy, prostate-specific membrane antigen–targeted therapy, immunotherapy, and radium-223. Genomic evaluations may allow for risk stratification of patients with PCa based on their molecular features, which may help guide precision medicine for treating PCa.

Genomic and Clinicopathologic Characterization of ATM-deficient Prostate Cancer

PURPOSE

The ATM (ataxia telangiectasia mutated) gene is mutated in a subset of prostate cancers, and ATM mutation may confer specific therapeutic vulnerabilities, although ATM-deficient prostate cancers have not been well-characterized.

EXPERIMENTAL DESIGN

We genetically validated a clinical grade IHC assay to detect ATM protein loss and examined the frequency of ATM loss among tumors with pathogenic germline ATM mutations and genetically unselected primary prostate carcinomas using tissue microarrays (TMAs). Immunostaining results were correlated with targeted somatic genomic sequencing and clinical outcomes.

RESULTS

ATM protein loss was found in 13% (7/52) of primary Gleason pattern 5 cancers with available sequencing data and was 100% sensitive for biallelic ATM inactivation. In a separate cohort with pathogenic germline ATM mutations, 74% (14/19) had ATM protein loss of which 70% (7/10) of evaluable cases had genomic evidence of biallelic inactivation, compared with zero of four of cases with intact ATM expression. By TMA screening, ATM loss was identified in 3% (25/831) of evaluable primary tumors, more commonly in grade group 5 (17/181; 9%) compared with all other grades (8/650; 1%; P < 0.0001). Of those with available sequencing, 80% (4/5) with homogeneous ATM protein loss and 50% (6/12) with heterogeneous ATM protein loss had detectable pathogenic ATM alterations. In surgically treated patients, ATM loss was not significantly associated with clinical outcomes in random-effects Cox models after adjusting for clinicopathologic variables.

CONCLUSIONS

ATM loss is enriched among high-grade prostate cancers. Optimal evaluation of ATM status requires both genomic and IHC studies and will guide development of molecularly targeted therapies.

Impact of DNA damage repair defects on response to radium-223 and overall survival in metastatic castration-resistant prostate cancer

PURPOSE

Radium-223 is a targeted alpha radiation therapy for metastatic castration-resistant prostate cancer. DNA damage repair (DDR) defective prostate cancers, specifically genetic aberrations leading to homologous recombination deficiency (HRD), accumulate irreparable DNA damage following genotoxic treatment. This retrospective study assessed DDR mutation status in patients treated with radium-223, investigating their association with efficacy and overall survival (OS).

PATIENTS AND METHODS

Included patients were treated with radium-223 and had results from primary or metastatic tumour tissue of a comprehensive next-generation sequencing panel of DDR genes, including canonical HRD genes. Patients were grouped by presence (DDR+) or absence (DDR-) of pathogenic somatic or germline aberrations in DDR genes. We evaluated OS, time to ALP progression (TAP), time to initiation of subsequent systemic therapy (TST) and biochemical responses between DDR groups.

RESULTS

Ninety-three patients were included. Twenty-eight (30%) patients had DDR mutations, most frequently in ATM (8.6%), BRCA2 (7.5%) and CDK12 (4.3%) genes. DDR+ patients showed prolonged OS (median 36.3 versus 17.0 months; HR 2.29; P = 0.01). Median TAP and TST in the DDR+ and DDR- patients was 6.9 versus5.8 months (HR = 1.48; P = 0.15), and 8.9 versus7.3 months (HR = 1.58; P = 0.08), respectively. DDR+ patients more frequently completed radium-223 therapy (79% versus 47%; P = 0.05). No difference in biochemical responses were seen.

CONCLUSION

Patients harbouring DDR aberrations showed significant OS benefit, and more commonly completed radium-223 therapy. These findings need prospective confirmation and support strategies of genotoxic agents such as radium-223 in patients harbouring DDR defects.

Radium 223-Mediated Zonal Cytotoxicity of Prostate Cancer in Bone

BACKGROUND

Bone-targeting radiotherapy with Radium-223 (Rad-223), a radioisotope emitting genotoxic alpha-radiation with limited tissue penetrance (∼100 µm), prolongs the survival of patients with metastatic prostate cancer (PCa). Confoundingly, the clinical response to Rad-223 is often followed by detrimental relapse and progression, and whether Rad-223 causes tumor-cell directed cytotoxicity in vivo remains unclear. We hypothesized that limited radiation penetrance in situ defines outcome.

METHODS

We tested Rad-223 overall response by PC3 and C4-2B human PCa cell lines in mouse bones (n = 5-18 tibiae per group). Rad-223 efficacy at subcellular resolution was determined by intravital microscopy analysis of dual-color fluorescent PC3 cells (n = 3-4 mice per group) in tissue-engineered bone constructs. In vivo data were fed into an in silico model to predict Rad-223 effectiveness in lesions of different sizes (1-27, 306 initial cells; n = 10-100 simulations) and the predictions validated in vivo by treating PCa tumors of varying sizes in bones (n = 10-14 tibiae per group). Statistical tests were performed by two-sided Student t test or by one-way ANOVA followed by Tukey's post-hoc test.

RESULTS

Rad-223 (385 kBq/kg) delayed the growth (means [SD]; comparison with control-treated mice) of PC3 (6.7 × 105[4.2 × 105] vs 2.8 × 106 [2.2 × 106], P = .01) and C4-2B tumors in bone (7.7 × 105 [4.0 × 105] vs 3.5 × 106 [1.3 × 106], P < .001). Cancer cell lethality in response to Rad-223 (385 kBq/kg) was profound but zonally confined along the bone interface compared with the more distant tumor core, which remained unperturbed (day 4; 13.1 [2.3%] apoptotic cells, 0-100 µm distance from bone vs 3.6 [0.2%], >300 µm distance; P = .01).In silico simulations predicted greater efficacy of Rad-223 on single-cell lesions (eradication rate: 88.0%) and minimal effects on larger tumors (no eradication, 16.2% growth reduction in tumors of 27 306 cells), as further confirmed in vivo for PC3 and C4-2B tumors.

CONCLUSIONS

Micro-tumors showed severe growth delay or eradication in response to Rad-223, whereas macro-tumors persisted and expanded. The relative inefficacy in controlling large tumors points to application of Rad-223 in secondary prevention of early bone-metastatic disease and regimens co-targeting the tumor core.

α-Particle-Emitter Radiopharmaceutical Therapy: Resistance Is Futile

Alpha-emitter radiopharmaceutical therapy (α-RPT) is a treatment modality that is impervious to conventional cellular resistance mechanisms because of the unique properties of the α-particle. Radiobiological studies of α-particle emitters have been few as they require detailed consideration of both biology and physics. Clinical studies of this radiation delivery modality have shown highly promising results in cancers that are resistant to other treatments. The work by Yard and colleagues published in this issue introduces an innovative approach to radiobiological investigations of α-RPT and highlights the specific physics considerations required to properly investigate this multidisciplinary treatment modality.See related article by Yard et al., p. 5640.

PARP inhibitor combinations in prostate cancer

Polyadenosine-diphosphate-ribose polymerase (PARP) inhibitors cause deoxyribonucleic acid (DNA) damage that can be lethal to cells with deficient repair mechanisms. A number of PARP inhibitors are being tested as treatments for men with prostate cancer, both as monotherapies and in combinations that are based on purported synergies in treatment effect. While the initial single-agent development focused on men with identified deficiencies in DNA-repair pathways, broader patient populations are being considered for combination approaches. This review summarizes the current clinical development of PARP inhibitors and explores the rationale for novel combination strategies.

Harnessing cell-free DNA: plasma circulating tumour DNA for liquid biopsy in genitourinary cancers

In the era of precision oncology, liquid biopsy techniques, especially the use of plasma circulating tumour DNA (ctDNA) analysis, represent a paradigm shift in the use of genomic biomarkers with considerable implications for clinical practice. Compared with tissue-based tumour DNA analysis, plasma ctDNA is more convenient to test, more readily accessible, faster to obtain and less invasive, minimizing procedure-related risks and offering the opportunity to perform serial monitoring. Additionally, genomic profiles of ctDNA have been shown to reflect tumour heterogeneity, which has important implications for the identification of resistant clones and selection of targeted therapy well before clinical and radiographic changes occur. Moreover, plasma ctDNA testing can also be applied to cancer screening, risk stratification and quantification of minimal residual disease. These features provide an unprecedented opportunity for early treatment of patients, improving the chances of treatment success.

Radium-223 as an Approved Modality for Treatment of Bone Metastases

Radium-223 dichloride (²²³Ra) is an α-emitter radionuclide approved for treatment of osteoblastic metastases in castrate-resistant prostate cancer (mCRPC) patients. ²²³Ra increases overall survival, improves bone pain, increases the median time to the first skeletal-related event, reduces the use of external beam radiation therapy for bone pain palliation, reduces the rates of spinal cord compression, and hospitalization. ²²³Ra therapy has minimal side effects; the most common hematological side effects are anemia, thrombocytopenia and neutropenia while the nonhematological side effects that may occur are bone pain flare, nausea, fatigue, and diarrhea. Alongside ²²³Ra therapy there are currently a variety of first-line therapeutic options available to treat mCRPC patients and much debate regarding the appropriate treatment algorithm for these patients and the possible combination of therapies among the ones available. In this article, we review the rationale behind ²²³Ra therapy as well as ²²³Ra mechanisms of action, biodistribution and dosimetry, optimal timing possibilities to initiate ²²³Ra in contrast to other treatments available, the association of ²²³Ra with other therapies and the means of evaluating patients in order to properly deliver to ²²³Ra therapy. Furthermore, we will discuss ²²³Ra dose administration possibilities, patient and dose preparation and the challenges of treatment response evaluation during and after ²²³Ra.

Dosimetry, Radiobiology and Synthetic Lethality: Radiopharmaceutical Therapy (RPT) With Alpha-Particle-Emitters

As a treatment modality that is fundamentally different from other therapies against cancer, radiopharmaceutical therapy with alpha-particle emitters has drawn the attention of the therapy community and also the biopharmaceutical industry. Alpha-particles cause a preponderance of complex DNA double-strand breaks (DSBs). This provides an opportunity to either enhance cell kill by using DNA DSB repair inhibitors or identify patients who are likely to be high responders to alpha-emitter RPT. The short-range and high potency of alpha-particles requires special dosimetry considerations. These are reviewed in light of recent updates to the phantoms and associated dosimetric quantities used for dosimetry calculations. A formalism for obtaining the necessary microscale pharmacokinetic information from patient nuclear medicine imaging is presented. Alpha-emitter based radiopharmaceutical therapy is an exciting cancer therapy modality that is being revisited. Further development of imaging and dosimetric methods specific to alpha-particle emitters, coupled with standardization of the methods and rigorous evidence that dosimetry applied to alphaRPT improves patient care are needed moving forward.