Molecular radiotheranostics for neuroendocrine tumours

Gene Abnormalities and Modulated Gene Expression Associated with Radionuclide Treatment: Towards Predictive Biomarkers of Response

Molecular radiotherapy (MRT), also known as radioimmunotherapy or targeted radiotherapy, is the delivery of radionuclides to tumours by targeting receptors overexpressed on the cancer cell. Currently it is used in the treatment of a few cancer types including lymphoma, neuroendocrine, and prostate cancer. Recently reported outcomes demonstrating improvements in patient survival have led to an upsurge in interest in MRT particularly for the treatment of prostate cancer. Unfortunately, between 30% and 40% of patients do not respond. Further normal tissue exposure, especially kidney and salivary gland due to receptor expression, result in toxicity, including dry mouth. Predictive biomarkers to select patients who will benefit from MRT are crucial. Whilst pre-treatment imaging with imaging versions of the therapeutic agents is useful in demonstrating tumour binding and potentially organ toxicity, they do not necessarily predict patient benefit, which is dependent on tumour radiosensitivity. Transcript-based biomarkers have proven useful in tailoring external beam radiotherapy and adjuvant treatment. However, few studies have attempted to derive signatures for MRT response prediction. Here, transcriptomic studies that have identified genes associated with clinical radionuclide exposure have been reviewed. These studies will provide potential features for seeding multi-component biomarkers of MRT response.

Actinium-225 Targeted Agents: Where Are We Now?

α-particle targeted radionuclide therapy has shown promise for optimal cancer management, an exciting new era for brachytherapy. Alpha-emitting nuclides can have significant advantages over gamma- and beta-emitters due to their high linear energy transfer (LET). While their limited path length results in more specific tumor 0kill with less damage to surrounding normal tissues, their high LET can produce substantially more lethal double strand DNA breaks per radiation track than beta particles. Over the last decade, the physical and chemical attributes of Actinium-225 (225Ac) including its half-life, decay schemes, path length, and straightforward chelation ability has peaked interest for brachytherapy agent development. However, this has been met with challenges including source availability, accurate modeling for standardized dosimetry for brachytherapy treatment planning, and laboratory space allocation in the hospital setting for on-demand radiopharmaceuticals production. Current evidence suggests that a simple empirical approach based on 225Ac administered radioactivity may lead to inconsistent outcomes and toxicity. In this review article, we highlight the recent advances in 225Ac source production, dosimetry modeling, and current clinical studies.

Combination of [177Lu]Lu-DOTA-TATE Targeted Radionuclide Therapy and Photothermal Therapy as a Promising Approach for Cancer Treatment: In Vivo Studies in a Human Xenograft Mouse Model

Peptide receptor radionuclide therapy (PRRT) relies on α- and β-emitting radionuclides bound to a peptide that commonly targets somatostatin receptors (SSTRs) for the localized killing of tumors through ionizing radiation. A Lutetium-177 (¹⁷⁷Lu)-based probe linked to the somatostatin analog octreotate ([¹⁷⁷Lu]Lu-DOTA-TATE) is approved for the treatment of certain SSTR-expressing tumors and has been shown to improve survival. However, a limiting factor of PRRT is the potential toxicity derived from the high doses needed to kill the tumor. This could be circumvented by combining PRRT with other treatments for an enhanced anti-tumor effect. Photothermal therapy (PTT) relies on nanoparticle-induced hyperthermia for cancer treatment and could be a useful add-on to PRRT. Here, we investigate a strategy combining [¹⁷⁷Lu]Lu-DOTA-TATE PRRT and nanoshell (NS)-based PTT for the treatment of SSTR-expressing small-cell lung tumors in mice. Our results showed that the combination treatment improved survival compared to PRRT alone, but only when PTT was performed one day after [¹⁷⁷Lu]Lu-DOTA-TATE injection (one of the timepoints examined), showcasing the effect of treatment timing in relation to outcome. Furthermore, the combination treatment was well-tolerated in the mice. This indicates that strategies involving NS-based PTT as an add-on to PRRT could be promising and should be investigated further.

Evaluation of Dosimetric Parameters for Tumor Therapy with 177Lu and 90Y Radionuclides in Gate Monte Carlo Code

BACKGROUND

⁹⁰Y and ¹⁷⁷Lu are two well-known radionuclides used in radionuclide therapy to treat neuroendocrine tumors.

OBJECTIVE

This current study aims to evaluate, compare and optimize tumor therapy with ⁹⁰Y and ¹⁷⁷Lu for different volumes of the tumor using the criterion of self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and dose-volume histogram (DVH) curve using Gate Monte Carlo simulation code.

MATERIAL AND METHODS

In our analytical study, Gate Monte Carlo simulation code has been used to model tumors and simulate particle transport. Spherical tumors were modeled from radius 0.5 to 20 mm. Tumors were uniformly designed from water (soft tissue reagent). The full energy spectrum of each radionuclide of ¹⁷⁷Lu and ⁹⁰Y was used in the total volume of tumors with isotropic radiation, homogeneously. Self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and DVH curve parameters were evaluated.

RESULTS

The absorbed dose for ⁹⁰Y is higher than ¹⁷⁷Lu in all tumors (p-value <5%). The uniformity of the absorbed dose for ¹⁷⁷Lu is much greater than ⁹⁰Y. As the tumor size increases, the DVH graph improves for ⁹⁰Y.

CONCLUSION

Based on self-absorbed dose, cross-absorbed dose, absorbed dose uniformity, and DVH diagram, ¹⁷⁷Lu and ⁹⁰Y are appropriate for smaller and larger tumors, respectively. Next, we can evaluate the appropriate cocktail of these radionuclides, in terms of the type of composition, for the treatment of tumors with a specific size.

Exploring Tumor Heterogeneity Using PET Imaging: The Big Picture

Personalized medicine represents a major goal in oncology. It has its underpinning in the identification of biomarkers with diagnostic, prognostic, or predictive values. Nowadays, the concept of biomarker no longer necessarily corresponds to biological characteristics measured ex vivo but includes complex physiological characteristics acquired by different technologies. Positron-emission-tomography (PET) imaging is an integral part of this approach by enabling the fine characterization of tumor heterogeneity in vivo in a non-invasive way. It can effectively be assessed by exploring the heterogeneous distribution and uptake of a tracer such as 18F-fluoro-deoxyglucose (FDG) or by using multiple radiopharmaceuticals, each providing different information. These two approaches represent two avenues of development for the research of new biomarkers in oncology. In this article, we review the existing evidence that the measurement of tumor heterogeneity with PET imaging provide essential information in clinical practice for treatment decision-making strategy, to better select patients with poor prognosis for more intensive therapy or those eligible for targeted therapy.