Multikinase inhibitors for the treatment of radioiodine refractory thyroid cancer: what have we learned from the 'real-world' experience?

CDK4 phosphorylation status and rational use for combining CDK4/6 and BRAF/MEK inhibition in advanced thyroid carcinomas

Background

CDK4/6 inhibitors (CDK4/6i) have been established as standard treatment against advanced Estrogen Receptor-positive breast cancers. These drugs are being tested against several cancers, including in combinations with other therapies. We identified the T172-phosphorylation of CDK4 as the step determining its activity, retinoblastoma protein (RB) inactivation, cell cycle commitment and sensitivity to CDK4/6i. Poorly differentiated (PDTC) and anaplastic (ATC) thyroid carcinomas, the latter considered one of the most lethal human malignancies, represent major clinical challenges. Several molecular evidence suggest that CDK4/6i could be considered for treating these advanced thyroid cancers.

Methods

We analyzed by two-dimensional gel electrophoresis the CDK4 modification profile and the presence of T172-phosphorylated CDK4 in a collection of 98 fresh-frozen tissues and in 21 cell lines. A sub-cohort of samples was characterized by RNA sequencing and immunohistochemistry. Sensitivity to CDK4/6i (palbociclib and abemaciclib) was assessed by BrdU incorporation/viability assays. Treatment of cell lines with CDK4/6i and combination with BRAF/MEK inhibitors (dabrafenib/trametinib) was comprehensively evaluated by western blot, characterization of immunoprecipitated CDK4 and CDK2 complexes and clonogenic assays.

Results

CDK4 phosphorylation was detected in all well-differentiated thyroid carcinomas (n=29), 19/20 PDTC, 16/23 ATC and 18/21 thyroid cancer cell lines, including 11 ATC-derived ones. Tumors and cell lines without phosphorylated CDK4 presented very high p16CDKN2A levels, which were associated with proliferative activity. Absence of CDK4 phosphorylation in cell lines was associated with CDK4/6i insensitivity. RB1 defects (the primary cause of intrinsic CDK4/6i resistance) were not found in 5/7 tumors without detectable phosphorylated CDK4. A previously developed 11-gene expression signature identified the likely unresponsive tumors, lacking CDK4 phosphorylation. In cell lines, palbociclib synergized with dabrafenib/trametinib by completely and permanently arresting proliferation. These combinations prevented resistance mechanisms induced by palbociclib, most notably Cyclin E1-CDK2 activation and a paradoxical stabilization of phosphorylated CDK4 complexes.

Conclusion

Our study supports further clinical evaluation of CDK4/6i and their combination with anti-BRAF/MEK therapies as a novel effective treatment against advanced thyroid tumors. Moreover, the complementary use of our 11 genes predictor with p16/KI67 evaluation could represent a prompt tool for recognizing the intrinsically CDK4/6i insensitive patients, who are potentially better candidates to immediate chemotherapy.

125I Seed Brachytherapy for Refractory Loco-Regional Recurrence of Non-Anaplastic Thyroid Cancer

Purpose

The purpose of this research was to evaluate the feasibility and efficacy of ¹²⁵I seed brachytherapy as salvage treatment for recurrence from non-anaplastic thyroid cancer refractory to other modalities.

Methods

Between June 2006 and September 2019, fifteen patients with recurrent non-anaplastic thyroid cancer were treated with ¹²⁵I seed brachytherapy. ¹²⁵I seeds were implanted into the tumor under the guidance of CT and/or ultrasound images with the median prescription dose of 120 Gy (range, 100-140 Gy). The median seed number was 80 (range 10-214). Clinical efficacy was evaluated with Response Evaluation Criteria in Solid Tumors.

Findings

Fifteen patients were selected, eleven of whom had papillary carcinoma, two suffered from follicular carcinoma, and two were diagnosed with medullary carcinoma. These patients had twenty-four nodes in total. After they received salvage surgery and/or radioactive iodine (RAI) therapy, local recurrence was detected in all of them. No less than one node was observed in everyone’s cervical or supraclavicular areas, and four patients had lung metastatic. The median follow-up period lasted 48 months (range, 5-93 months). All patients did not develop locoregional recurrence after experiencing ¹²⁵I seed brachytherapy. Only three of them formed new metastases in nontarget regional nodes after brachytherapy, and additional brachytherapy can solve all regional failure problems. No significant adverse events were observed in any patient.

Implications

For the chosen patients, 125I seed brachytherapy is feasible for treating refractory local recurrence from non-anaplastic thyroid cancer. Further studies are required to determine the role of 125I seed brachytherapy in the treatment of thyroid cancer.

Molecular Genetics of Follicular-Derived Thyroid Cancer

Simple Summary

Thyroid tumors that derive from follicular cells are not a homogeneous entity, showing variable morphological appearance and different degrees of differentiation. Molecular markers are useful for both diagnostic purposes and prognostic stratification of patients. In presurgical setting, molecular testing of indeterminate thyroid nodules on aspirates provides useful diagnostic information; the molecular analysis on tumor tissues can also reveal the presence of genetic alterations related to patients’ prognosis. In recent years, the molecular characterization of these tumors has acquired even more importance thanks to the introduction of targeted drugs. This review summarizes the current literature on the molecular landscape of follicular-derived thyroid tumors.

Abstract

Thyroid cancer is the most common type of endocrine-related malignancy, whose incidence rates have increased dramatically in the last few decades. Neoplasms of follicular origin generally have excellent prognosis, with the exception of less differentiated tumors. Follicular-derived thyroid cancer can manifest as a variety of morphologically distinct entities, characterized by various degrees of differentiation and invasiveness. Histological evaluation is thus crucial for the definition of patients’ prognosis. However, within each histological subtype, tumor behavior can be highly variable, and, in this respect, molecular characterization can provide insightful information to refine the risk stratification of tumors. In addition to the importance of its prognostic role, molecular testing can be used to support the differential diagnosis of thyroid nodules in the absence of marked cyto-morphological aberrations. Finally, with the advent of targeted drugs, the presence of molecular alterations will guide the therapeutic strategies for patients with advanced tumors who do not respond to standard treatment. This review aims to describe the genetic landscape of follicular-derived thyroid tumors also highlighting differences across histological subtypes.

A new horizon for the old antibacterial drug clofoctol

The synthetic antibacterial drug clofoctol (CFT) has long been used to treat respiratory tract infections in Europe. In recent years, the drug was found to target two biologically important proteins, the Cdc7/Dbf4 protein kinase complex and the mRNA-binding protein cold shock domain containing E1 (CSDE1), also known as upstream-of-N-Ras protein (UNR). These interactions are at the origin of the antitumor activity of CFT, recently evidenced in prostate cancer and neuroglioma. Drug-protein binding models provide a structural basis to guide the design of more potent anticancer compounds. A renewed interest in CFT can be anticipated for the treatment of cancers, and possibly Coronavirus 2019 (COVID-19).