Acute Myeloid Leukemia After Radium-223 Therapy: Case Report

Dose estimation after a mixed field exposure: Radium-223 and intensity modulated radiotherapy

INTRODUCTION

Radium-223 dichloride ([²²³Ra]RaCl₂), a radiopharmaceutical that delivers α-particles to regions of bone metastatic disease, has been proven to improve overall survival of men with metastatic castration resistant prostate cancer (mCRPC). mCRPC patients enrolled on the ADRRAD clinical trial are treated with a mixed field exposure comprising radium-223 (²²³Ra) and intensity modulated radiotherapy (IMRT). While absorbed dose estimation is an important step in the characterisation of wider systemic radiation risks in nuclear medicine, uncertainties remain for novel radiopharmaceuticals such as ²²³Ra.

METHODS

24-Colour karyotyping was used to quantify the spectrum of chromosome aberrations in peripheral blood lymphocytes of ADRRAD patients at incremental times during their treatment. Dicentric equivalent frequencies were used in standard models for estimation of absorbed blood dose. To account for the mixed field nature of the treatment, existing models were used to determine the ratio of the component radiation types. Additionally, a new approach (M-FISH_LET), based on the ratio of cells containing damage consistent with high-LET exposure (complex chromosomal exchanges) and low-LET exposure (simple exchanges), was used as a pseudo ratio for ²²³Ra:IMRT dose.

RESULTS

Total IMRT estimated doses delivered to the blood after completion of mixed radiotherapy (after 37 IMRT fractions and two [²²³Ra]RaCl₂ injections) were in the range of 1.167 ± 0.092 and 2.148 ± 0.096 Gy (dose range across all models applied). By the last treatment cycle analysed in this study (four [²²³Ra]RaCl₂ injections), the total absorbed ²²³Ra dose to the blood was estimated to be between 0.024 ± 0.027 and 0.665 ± 0.080 Gy, depending on the model used. Differences between the models were observed, with the observed dose variance coming from inter-model as opposed to inter-patient differences. The M-FISH_LET model potentially overestimates the ²²³Ra absorbed blood dose by accounting for further PBL exposure in the vicinity of metastatic sites.

CONCLUSIONS

The models presented provide initial estimations of cumulative dose received during incremental IMRT fractions and [²²³Ra]RaCl₂ injections, which will enable improved understanding of the doses received by individual patients. While the M-FISH_LET method builds on a well-established technique for external exposures, further consideration is needed to evaluate this method and its use in assessing non-targeted exposure by ²²³Ra after its localization at bone metastatic sites.

The changing role of radium-223 in metastatic castrate-resistant prostate cancer: has the EMA missed the mark with revising the label?

Radium-223 (223Ra) is a life-prolonging treatment in symptomatic men with metastatic castrate-resistant prostate cancer (mCRPC) and bone metastases, but no visceral disease, regardless of prior treatment with docetaxel. Together with four other drugs (i.e. abiraterone, cabazitaxel, docetaxel, enzalutamide), it has been available for clinical use since 2013 and has been shown to also provide benefits in quality-of-life and societal benefits. However, in 2018 the European Medicines Agency ruled to restrict the use of radium-223 to a more advanced disease setting after at least two lines of one or the other life-prolonging agent. This decision was triggered by the results of a safety interim analysis of ERA-223, a trial investigating the combination of 223Ra and abiraterone versus abiraterone alone in patients without prior chemotherapy (with the exception of adjuvant treatment) with asymptomatic bone predominant mCRPC. That safety analysis showed an early increased risk of fracture and deaths with the combination treatment. This review critically appraises the available and emerging data with 223Ra treatment in an attempt to assess the appropriateness of the revised label of radium-223.

Ecotropic viral integration site 1 regulates the progression of acute myeloid leukemia via MS4A3-mediated TGFβ/EMT signaling pathway

Acute myeloid leukemia (AML) is a type of malignant tumor that is caused by malignant clone hematopoietic stem cells. The ecotropic viral integration site 1 (Evi1) is a zinc finger transcription factor, which is highly expressed in AML, and its expression level has been associated with poor prognosis of AML. Previous studies have indicated that Evi1 may regulate cell proliferation, differentiation and apoptosis by inhibiting the membrane-spanning-4-domains subfamily-A member-3 (MS4A3) gene in AML. The aim of the present study was to investigate the role of Evi1 in the progression of AML. The results revealed that Evi1 was overexpressed in leukemia cells compared with normal T lymphocytes. MicroRNAs (miR)-133 and -431 that target Evi1 were investigated, and it was observed that there was a low expression of miR-431 in AML. The transfection of miR-431 was able to decrease the promoter methylation levels of the Evi1 gene in AML cells. The transfection of miR-431 also suppressed the migration and invasion of AML cells. The present study revealed that the transfection of miR-431 mimic was able to downregulate MS4A3 expression in AML cells. Furthermore, the expression levels of transforming growth factor β (TGFβ) and epithelial-to-mesenchymal transition (EMT) markers fibronectin, α-smooth muscle actin, and vimentin were downregulated following the transfection of miR-431 in AML cells. The overexpression of MS4A3 was also able to suppress miR-431-mediated inhibition of the expression of TGFβ and EMT markers in AML cells. The addition of TGFβ inhibited the downregulation of EMT markers by transfection of miR-431 in AML cells. The transfection of miR-431 suppressed the migration and invasion of AML cells, which was also abolished by the addition of TGFβ. In conclusion, the results of the present study indicated that Evi1 may be a potential molecular target of leukemia therapy via MS4A3-mediated TGFβ/EMT signaling pathway.

Hematologic Toxicity From Radium-223 Therapy for Bone Metastases in Castration-Resistant Prostate Cancer: Risk Factors and Practical Considerations

Radium-223 dichloride is an α-emitting radiopharmaceutical that localizes to bone matrix and is approved for the treatment of patients with metastatic castration-resistant prostate cancer (CRPC) and symptomatic bone metastases. The cumulative impact of Ra-223 and other therapeutic agents for metastatic CRPC on myelosuppression in bone marrow is unknown. The phase 3 randomized, double-blind, placebo-controlled ALSYMPCA trial of Ra-223 in patients with CRPC and symptomatic bone metastases demonstrated a significant improvement in overall survival. Of the 571 patients subsequently followed for 3 years, few in either the Ra-223 or placebo arm experienced hematologic adverse events. Little evidence shows secondary malignancies associated with Ra-223 treatment; only 2 cases of secondary leukemia after Ra-223 treatment were found in the literature. The goals of this review were to summarize safety and efficacy results from clinical trials and institutional safety data pertaining to hematologic adverse events occurring with Ra-223, and to discuss practical management issues.