Alpha and Beta Radiation for Theragnostics

Targeted radionuclide therapy (TRT) has significantly evolved from its beginnings with iodine-131 to employing carrier molecules with beta emitting isotopes like lutetium-177. With the success of Lu-177-DOTATATE for neuroendocrine tumors and Lu-177-PSMA-617 for prostate cancer, several other beta emitting radioisotopes, such as Cu-67 and Tb-161, are being explored for TRT. The field has also expanded into targeted alpha therapy (TAT) with agents like radium-223 for bone metastases in prostate cancer, and several other alpha emitter radioisotopes with carrier molecules, such as Ac-225, and Pb-212 under clinical trials. Despite these advancements, the scope of TRT in treating diverse solid tumors and integration with other therapies like immunotherapy remains under investigation. The success of antibody-drug conjugates further complements treatments with TRT, though challenges in treatment optimization continue.

A Panel-Based Mutational Signature of Mismatch Repair Deficiency is Associated With Durable Response to Pembrolizumab in Metastatic Castration-Resistant Prostate Cancer

INTRODUCTION/BACKGROUND

Immune checkpoint inhibitors (ICIs) have limited efficacy in prostate cancer (PCa). Better biomarkers are needed to predict responses to ICIs. We sought to demonstrate that a panel-based mutational signature identifies mismatch repair (MMR) deficient (MMRd) PCa and is a biomarker of response to pembrolizumab.

PATIENTS AND METHODS

Clinico-genomic data was obtained for 2664 patients with PCa sequenced at Dana-Farber Cancer Institute (DFCI) and Memorial Sloan Kettering (MSK). Clinical outcomes were collected for patients with metastatic castration-resistant PCa (mCRPC) treated with pembrolizumab at DFCI. SigMA was used to characterize tumors as MMRd or MMR proficient (MMRp). The concordance between MMRd with microsatellite instability (MSI-H) was assessed. Radiographic progression-free survival (rPFS) and overall survival (OS) were collected for patients treated with pembrolizumab. Event-time distributions were estimated using Kaplan-Meier methodology.

RESULTS

Across both cohorts, 100% (DFCI: 12/12; MSK: 43/43) of MSI-H tumors were MMRd. However, 14% (2/14) and 9.1% (6/66) of MMRd tumors in the DFCI and MSK cohorts respectively were microsatellite stable (MSS), and 26% (17/66) were MSI-indeterminate in the MSK cohort. Among patients treated with pembrolizumab, those with MMRd (n = 5) versus MMRp (n = 14) mCRPC experienced markedly improved rPFS (HR = 0.088, 95% CI: 0.011-0.70; P = .0064) and OS (HR = 0.11, 95% CI: 0.014-0.80; P = .010) from start of treatment. Four patients with MMRd experienced remissions of >= 2.5 years.

CONCLUSION

SigMA detects additional cases of MMRd as compared to MSI testing in PCa and identifies patients likely to experience durable response to pembrolizumab.

Developments in Combining Targeted Radionuclide Therapies and Immunotherapies for Cancer Treatment

Targeted radionuclide therapy (TRT) and immunotherapy are rapidly growing classes of cancer treatments. Basic, translational, and clinical research are now investigating therapeutic combinations of these agents. In comparison to external beam radiation therapy (EBRT), TRT has the unique advantage of treating all disease sites following intravenous injection and selective tumor uptake and retention-a particularly beneficial property in metastatic disease settings. The therapeutic value of combining radiation therapy with immune checkpoint blockade to treat metastases has been demonstrated in preclinical studies, whereas results of clinical studies have been mixed. Several clinical trials combining TRT and immune checkpoint blockade have been initiated based on preclinical studies combining these with EBRT and/or TRT. Despite the interest in translation of TRT and immunotherapy combinations, many questions remain surrounding the mechanisms of interaction and the optimal approach to clinical implementation of these combinations. This review highlights the mechanisms of interaction between anti-tumor immunity and radiation therapy and the status of basic and translational research and clinical trials investigating combinations of TRT and immunotherapies.