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Department of Medical Oncology, Radboud University Medical Center, Nijmegen, the NetherlandsDepartment of Urology, Radboud University Medical Center, Nijmegen, the Netherlands
Department of Medical Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, USADepartment of Medical Oncology, Hospital Moinhos de Vento, Porto Alegre, Brazil
Corresponding author: Department of Medical Oncology, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, the Netherlands. Fax: +31 24 361 5025.
Patients having DNA damage repair (DDR) aberrations showed overall survival benefit.
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Patients harbouring DDR alterations more frequently completed radium-223 therapy.
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Time to subsequent systemic therapy tends to be longer in patients with DDR aberrations.
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These findings support combining radium-223 with agents targeting DNA repair.
Abstract
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.
In this multicenter retrospective cohort study of metastatic castration-resistant prostate cancer patients treated with radium-223, patients harbouring deleterious DNA damage repair aberrations more commonly completed radium-223 therapy and showed a significant overall survival benefit, although biochemical responses to radium-223 did not differ.
1. Introduction
Prostate cancer is the cancer with the highest incidence and the second leading cancer-related cause of death in men worldwide [
]. Since 2004, several new life-prolonging systemic therapies have been registered for treatment of patients with metastatic castration-resistant prostate cancer (mCRPC). However, evidence-based guidelines on sequencing of these therapies are lacking, and biomarkers are needed to help guide clinicians.
Radium-223 is a therapeutic option for mCRPC patients with symptomatic bone metastases and no evidence of visceral metastases [
]. Radium-223 is an alpha emitter, that selectively binds to areas of increased bone turnover in bone metastases and emits high-energy alpha particles of short range (<100 μm), causing double-strand DNA breaks (DSBs) [
DNA damage repair (DDR) genes play a crucial role in protecting the genomic integrity, through detection of DNA damage, signalling to cell-cycle checkpoints, and DNA repair [
]. The repair of DSBs in eukaryotic cells is mediated through homologous recombination, error-prone non-homologous end joining (NHEJ), and microhomology-mediated end joining. The inability to repair DNA damage by NHEJ or other mechanisms can lead to accumulation of deletions and mutations [
]. Germline mutations in selected DDR genes not only result in an increased incidence of prostate cancer but are also associated to a more aggressive disease course [
]. Mutations in homologous recombination genes, such as BRCA1, BRCA2, PALB2 or other genes constituting the DNA damage machinery, such as ATM, ATR, or CHEK2, are candidate predictive biomarkers for targeted therapies like poly-ADP ribose polymerase (PARP) inhibitors.
Following radium-223 treatment, prostate cancer cells with homologous recombination deficiency (HRD) accumulate irreparable DNA damage, which subsequently may result in cellular death through apoptosis. Therefore, cells with mutated homologous recombination genes might be more vulnerable to radionuclides such as radium-223. Mutations in homologous recombination genes have been associated with sensitivity to radium-223 therapy in two small cohort studies [
]. A recent retrospective single-institution study demonstrated that mCRPC patients carrying germline and/or somatic mutations in homologous recombination genes more commonly showed ≥30% alkaline phosphatase (ALP) responses, longer time to ALP progression, and a trend toward longer overall survival (OS) [
]. Another recent retrospective study showed that patients with germline defects in DDR genes appeared to benefit from all standard therapies similarly to the overall population of patients with mCRPC. However, this study included only second-generation androgen signalling inhibitors and taxane-based chemotherapy, but not radium-223 therapy [
]. The present study aimed to strengthen the findings that mCRPC patients with DDR benefit more from radium-223 therapy than patients without DDR.
2. Methods
2.1 Study design and patient population
Metastatic CRPC patients who were treated with radium-223 therapy between February 2013 and June 2019 at Radboud university medical center (Radboudumc) or Johns Hopkins Hospital and had undergone comprehensive analyses of DDR genes through next-generation sequencing (NGS) were consecutively included in this retrospective cohort study. Exclusion criteria were the presence of visceral metastases or prior treatment with radionuclides, PARP inhibitors or platinum chemotherapeutic agents preceding initiation of radium-223 therapy.
The presence or absence of DDR mutations was not a criterium for start of radium-223 administration. All patients gave written informed consent for NGS testing. This study was approved by the institutional review boards and local committees on research involving human subjects at both institutes.
Data from the NGS reports, as well as histopathological, clinical and demographic data were collected and stored in an electronic clinical database. The study population was divided in subgroups based on the presence or absence of (likely) pathogenic somatic and/or germline aberrations in DDR genes (DDR+), or genes (in)directly involved in homologous recombination (HRD+), and mutation-negative (DDR− and HRD−) groups.
2.2 The genetic panel of interest
Tumour samples of all patients were previously sequenced by non-profit institutes (Center for Personalized Cancer Treatment), by fee for service providers (Foundation Medicine [FoundationOne], Personal Genome Diagnostics, Color Genomics, Invitae) and/or by a custom in-house NGS panel using single-molecule molecular inversion probe–based sequencing [
The DDR genetic panel of interest was chosen a priori and stated in the study protocol. The panel defined as DDR+ included ATM, ATR, BAP1, BARD1, BRCA1, BRCA2, BRIP1, CDK12, CHD1, CHEK1, CHEK2, ERCC2, ERCC4, FANCA, FANCC, FANCD2, FANCE, FANCF, FANCG, FANCI, FANCL, FANCM, MRE11A, MUTYH, NBN, NUDT1, PALB2, PARP1, PARP2, PARP3, PPP2R2A, RAD51, RAD51B, RAD51C, RAD51D, RAD52, RAD54L, RPA1, TP53BP1, XRCC2 and XRCC3. The pathogenicity of the alterations was assessed by two clinical molecular biologists within the molecular tumour board, in accodance with the guidelines for the interpretation of sequence variants. Variants that were likely pathogenic or pathogenic in nature were selected for further associations with response and outcome.
In addition to this predefined broad panel, two less inclusive panels of genes directly or indirectly linked to homologous recombination were used for exploratory analysis. One analysis explored the BRCA1 and BRCA2 genes. The other panel, defined as HRD+, consisted of ATM, BRCA1, BRCA2, BRIP1, CDK12, CHEK2, FANCG, FANCI, PALB2, RAD51B and RAD51C.
2.3 Study end points
The primary study end point was OS, defined as time between initiation of radium-223 therapy and date of death from any cause or date of last follow-up. Secondary end points included biochemical (prostate-specific antigen [PSA] and ALP) responses, time to ALP progression (TAP), the number of administered radium-223 injections, time to the first skeletal-related event (TSRE), and time to subsequent treatment (TST) initiation following radium-223 therapy. Changes in PSA and ALP were calculated as maximal decline during therapy from baseline, with cut-offs of 50% and 30%, in accordance with Prostate Cancer Working Group 3 (PCWG3) criteria [
Trial design and objectives for castration-resistant prostate cancer: updated recommendations from the prostate cancer clinical trials working group 3.
]. Biochemical responses were confirmed by a second value. ALP progression was defined as an increase of ≥25% from baseline in patients with no decrease from baseline or as an increase of ≥25% above the nadir, as per the Alpharadin in Symptomatic Prostate Cancer Patients (ALSYMPCA) study criteria [
]. In case a next systemic therapy was started before ≥25% increase of ALP above the nadir, no ALP progression was documented, and patients were censored. According to the institutional upper limit of normal, normalisation of ALP was defined as an ALP level less than 115 U/L in patients with elevated ALP levels at baseline. Skeletal-related events were defined as per PCWG3 criteria [
Trial design and objectives for castration-resistant prostate cancer: updated recommendations from the prostate cancer clinical trials working group 3.
To characterise the cohort, descriptive statistical methods were used. In case of missing data, valid percentages were calculated. Baseline characteristics between the defined DDR+ and DDR− groups were compared using the chi-square test or the Fisher's exact test for categorical variables and the Mann–Whitney U test for continuous variables. Kaplan–Meier curves were used to visualise time-to-event data. Univariate and multivariate Cox proportional hazard models were used to compare time-to-event distributions between subgroups, by calculating hazard ratios (HRs) and 95% confidence intervals (CIs). All statistical tests were two-sided, with P values of <0.05 considered to be statistically significant.
3. Results
3.1 Th patient cohort
In total, 93 patients received radium-223 therapy, underwent somatic and/or germline NGS testing, and were included in this two-centre retrospective study. The 28 patients described previously were included in this cohort study, with updated outcomes and a longer follow-up [
]. Of the 93 included patients, 28 (30.1%) patients were identified with (likely) pathogenic mutations in DDR genes (Fig. 1). Thirty-five different alterations were found, consisting of 27 (77.1%) somatic and eight (22.9%) germline mutations. Mutations were most frequently found in ATM (8.6%), BRCA2 (7.5%) and CDK12 (4.3%) genes.
Fig. 1Next-generation sequencing data of patients with pathogenic DNA damage repair (DDR) alterations.
Between the DDR+ and DDR− subgroups, no statistically significant differences in baseline characteristics were found (Table 1). The median age was 68 years, and 55.9% of the patients underwent prior taxane-based chemotherapy, either upfront in the hormone-sensitive state (30.0%) or in the castration-resistant state (70.0%). Seventy-one percent of the patients had baseline Eastern Cooperative Oncology Group performance status 0. Twelve (12.9%) patients received a concomitant systemic agent during radium-223, of which nine (75.0%) received either abiraterone or enzalutamide, and three (25.0%) received concurrent Sipuleucel-T. The percentage of patients who received concomitant agents was equally distributed across the DDR+ and DDR− subgroup (10.7% versus13.8%) (Supplementary Data).
Table 1Baseline patient demographics and clinical characteristics.
The median OS of the total cohort was 21.0 months (95% CI = 18.3–23.6). DDR+ patients had a statically significant longer median OS than DDR− patients (median 36.3 versus17.0 months; HR = 2.29; 95% CI = 1.21–4.32; P = 0.011) (Fig. 2A).
Fig. 2Kaplan–Meier curves, stratified by DNA damage repair (DDR) mutation status, A. Overall survival, B. Time to alkaline phosphatase (ALP) progression, C. Time to initiation of next systemic therapy. D. Time to first skeletal-related evens (SRE).
Secondary end points TAP and TST favoured the DDR+ group when compared with the DDR− group, although with borderline insignificance. Sixty-eight (73.1%) patients developed ALP progression before initiation of a subsequent systemic therapy. The median TAP was 6.9 months for DDR+ patients, compared with 5.8 months for DDR− patients (HR = 1.48; 95% CI = 0.87–2.50; P = 0.146) (Fig. 2B). At time of evaluation, 71 (76.3%) patients had started a subsequent therapy after radium-223. The median TST in the DDR+ group was 8.9 months, compared with 7.3 months in the DDR− group (P = 0.083; HR = 1.58; 95% CI = 0.94–2.64) (Fig. 2C). No statistically significant difference was found in the TSRE (Fig. 2D).
Patients with DDR alterations more frequently completed all six radium-223 injections than patients without these alterations (78.6% versus 56.9%; P = 0.047; median number of injections = 6 versus 6; P = 0.034) (Table 2 and Supplementary Data).
Despite the longer survival benefit, biochemical responses did not differ significantly between the DDR+ and DDR− groups; PSA response: median = 29.4% versus 34.6% (P = 0.508) and ALP response: median = -33.0% versus -35.0% (P = 0.639). In total, 57 (61.3%) patients showed an ALP decline of ≥30% (Fig. 3).
Fig. 3Waterfall plots of the best biochemical response during therapy, stratified by DNA damage repair (DDR) mutation status. A. Prostate-specific antigen (PSA), B. Alkaline phosphatase (ALP).
DDR+ patients received significantly more subsequent therapies than the DDR− patients, including PARP inhibitors (Supplementary Data). The proportion of patients receiving at least one subsequent therapy after radium-223 was 84.6% in the DDR+ subgroup versus 73.8% in the DDR− subgroup; P = 0.409. A multivariate model included only the DDR mutation status as the prognostic factor of OS (Supplementary Data).
Nine patients (10%) with deleterious aberrations in BRCA1 or BRCA2 were identified. The median OS of these patients was significantly longer when than the OS of patients with wildtype BRCA (median = 36.8 months versus 20.5 months; HR = 2.73; 95% CI = 1.06–7.07; P = 0.038). For all secondary end points no differences were seen.
Results of the exploratory analysis between the HRD subgroups were in line with the differences between the DDR+ and DDR− subgroups (Supplementary Data).
4. Discussion
This retrospective collaborative study investigated in 93 molecularly profiled mCRPC patients whether presence of deleterious aberrations in predefined DDR genes was associated with an improved outcome to radium-223 therapy. We show that patients with pathogenic DDR alterations, including BRCA1 and BRCA2, and additional genes with indirect involvement in homologous recombination, appear to benefit from radium-223 therapy. A remarkable 19-month longer median OS was identified, whilst no clear imbalance was found in baseline characteristics between both groups, nor did subsequent therapies clearly influence the outcome. The proportion of patients that completed six radium-223 injections was higher in the DDR+ compared to the DDR group. Secondary end points favoured the DDR+ group with a numerically longer TAP and TST.
Previous case reports hinted towards a beneficial response to radium-223 in patients with DDR alterations [
] a trend towards an OS benefit was seen in the DDR+ group (median OS = 36.9 versus 19.0 months; HR = 3.3; P = 0.11), which is in line with the OS benefit seen in our study. The recently presented interim analysis of the enrolling prospective PRORADIUM study (NCT02925702) also showed a trend towards prolonged OS in patients with germline homologous recombination mutations (median OS = 14.4 versus 10.6 months, P = 0.066) [
Impact of germline mutations in homologous recombination (HR) genes on the response to Radium-223 for metastatic castration resistant prostate cancer (mCRPC). ESMO Poster 876.
] showed in a metastatic prostate cancer model that radium-223 localises at the bone surface adjacent to the tumour. This suggests indirect mechanisms of action, such as non-immunogenic and immunogenic modulation of the tumour micro-environment (TME) of bone metastases, to explain the beneficial effects of radium-223 [
The OS benefit may also be caused by bystander cytotoxicity, an effect in which cells are damaged by being in close proximity to cells exposed to radiation. Radium-223 treatment leads to a PSA response only in 16% of mCRPC patients, indicating only a limited bystander effect [
]. We could not corroborate that patients with pathogenic DDR alterations are more susceptible to bystander cytotoxicity reflected by a higher proportion of PSA or ALP declines. Therefore, alternative mechanisms may be involved, such as immunogenic modulation. The induction of an effective anti-TME might lead to the release of signals inducing neo-antigen presentation and activation of antigen-specific T cells, described as immunogenic cell death (ICD) [
]. Radium-223-induced DSBs in prostate cancer cells may trigger ICD, leading to an effective antitumour response, reflected by evidence for immunogenic modulation of circulating blood immune subsets, including reduction of PD-1–expressing T-cells, favouring antitumour activity over immunosuppression [
]. The effect of ICD might persist after discontinuation of radium-223 therapy, possibly leading to better responses to other systemic therapies and longer OS. Ongoing studies are examining the combined effect of radium-223 and the checkpoint inhibitors pembrolizumab (NCT03093428) and atezolizumab (NCT02814669).
] reported results from the TOPARP-A study of PARP inhibition in patients with advanced mCRPC, where most responses could be explained by presence of pathogenic DDR defects. These results led to initiation of the TOPARP-B and PROfound trials. Recently the phase-3 PROfound trial demonstrated a significantly improved radiological progression-free survival in mCRPC patients with DDR mutations, when treated with olaparib versus enzalutamide or abiraterone [
]. Moreover, interim OS analysis showed a trend towards prolonged OS for the olaparib cohort of patients with BRCA1, BRCA2 and ATM alterations. Our analyses showed that subsequent PARP inhibitor treatment after radium-223 appeared to have no significant impact on OS in the studied population (Supplementary Data). Clinical trials evaluating combinatory regimens of radium-223 with agents targeting the DNA damage response pathway, including PARP inhibitor olaparib (NCT03317392) and ATR inhibitors, are underway.
Translational studies implementing DDR alterations and other predictive biomarkers are vital to optimise treatment planning, improve outcome and minimise unnecessary toxicity. Baseline genomic testing in mCRPC patients before starting systemic agents will become indispensable to identify patients most likely to benefit from each therapy. Several targeted agents are promising in the treatment of mCRPC patients with DDR and HRD alterations, and our results imply that these patients also appear to derive enhanced benefit from radium-223.
This study has several limitations. Because of the retrospective nature of this study, risk of selection and information bias is present. The sample size of the cohort was based on the number of identified patients and was not determined using predefined statistical testing. Patients were treated at two different large university hospitals, and because of population differences results may not compare to practice in community hospitals. However all patients were treated in accordance with the standard of care of radium-223 therapy as described in the ALSYMPCA trial [
]. NGS testing was carried out by different providers and not primarily initiated for study purposes. The findings in this study require prospective validation in larger cohorts.
5. Conclusions
Metastatic CRPC patients harbouring somatic or germline deleterious DDR aberrations showed significantly longer OS than DDR− patients in our study. Although DDR+ patients more commonly completed radium-223, only a trend towards a longer TAP and TST was seen for DDR+ patients. DDR+ patients received significantly more subsequent therapies, including PARP inhibitors. Whether DDR+ mCRPC patients derive additional benefit form radium-223 needs prospective confirmation. Translational studies are ongoing to more clearly dissect underlying mechanisms, such as immunogenic modulation, that may result in the benefit seen in DDR+ patients.
Role of the funding source
This research was funded by Bayer, The Netherlands. The funding organisation had no role in the design and conduct of the study, the collection, management, analysis and interpretation of the data, and writing of the report.
This publication and the underlying study have been made possible partly on the basis of the data that the Hartwig Medical Foundation and the Center of Personalised Cancer Treatment have made available to the study.
Conflict of interest statement
M.J.v.d.D. discloses grants from Bayer, grants from Janssen-Cilag and personal fees from Astellas.
I.M.v.O. reports grants and personal fees from Astellas, grants and personal fees from Bayer, grants and personal fees from Janssen-Cilag and grants and personal fees from Sanofi.
W.R.G. reports personal fees from Bayer and MSD and reports grants from Astellas, Bayer and Janssen-Cilag.
E.S.A. reports grants and personal fees from Janssen, personal fees from Astellas, grants and personal fees from Sanofi-Genzyme, grants and personal fees from Dendreon, Seal Beach, California, USA, personal fees from Pfizer, grants and personal fees from AstraZeneca, grants and personal fees from Clovis Oncology, Boulder, Colorado, USA, grants and personal fees from Merck, grants from Johnson & Johnson, grants from Genentech, San Francisco, California, USA, grants from Novartis, grants from Bristol Myers Squibb and personal fees from Amgen. In addition E.S.A. reports a patent PCT/US2015/046,806; US20170275673A1 on an AR-V7 biomarker technology licenced to Qiagen. E.S.A. reports partial fund by NIH Cancer Center Support Grant P30 CA006973.
N.M. reports personal fees from Bayer, grants and personal fees from Jansen-Cilag, personal fees from MSD, grants and personal fees from Roche, grants and personal fees from Astellas grants and personal fees from Sanofi.
All remaining authors have declared no conflicts of interest.
P.I.V. reports grants and personal fees from Bayer, grants and personal fees from Astellas, personal fees from AstraZeneca, grants and personal fees from Pfizer, grants and personal fees from Bristol-Myers Squibb, personal fees from Merck.PharmaceuticalsTravel, Accommodations, Expenses: AstraZeneca, Astellas Pharma, Pfizer, Merck Serono, Merck.
Acknowledgements
We thank the Center of Personalised Cancer Treatment and Foundation Medicine for sequencing tissue samples.
Appendix A. Supplementary data
The following is the Supplementary data to this article:
Trial design and objectives for castration-resistant prostate cancer: updated recommendations from the prostate cancer clinical trials working group 3.
Impact of germline mutations in homologous recombination (HR) genes on the response to Radium-223 for metastatic castration resistant prostate cancer (mCRPC). ESMO Poster 876.
We thank colleagues De Vincentis and Frantellizzi [1] for their thoughtful considerations on our recently published manuscript in this journal and their ongoing work on optimising patient selection for radium-223 therapy [1,2].
We were very impressed by the interesting and intriguing work of van der Doelen et al. [1] recently published in your Journal . This inspires some considerations that we would gladly share with the scientific community.
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