Central Hypothyroidism is Frequent During Mitotane Therapy in Adrenocortical Cancer Patients: Prevalence and Timeline

CONTEXT

Central hypothyroidism was described previously in mitotane-treated patients but data on its prevalence and time of occurrence are limited.

OBJECTIVE

To better characterize thyroid hormone insufficiency in patients exposed to mitotane.

METHODS

We reviewed medical records of patients from 2 academic centers in Montreal (Canada) and Toulouse (France) with exposure to mitotane therapy for adrenocortical cancer between 1995 and 2020. We analyzed the thyroid function parameters during and after treatment.

RESULTS

In our cohort of 83 patients, 17 were excluded because of preexisting primary hypothyroidism or drug-induced hypothyroidism. During follow-up, 3/66 patients maintained a normal thyroid function and 63/66 developed central hypothyroidism. Among those 63 patients, 56 presented with an inappropriately normal or low TSH and 7 with a mildly elevated TSH. The onset of hypothyroidism was: <3 months in 33.3%, 3 to 6 months in 19.1%, 6 to 9 months in 14.3%, and 9 to 12 months in 9.5%. At least 14.3% of cases occurred after 12 months of exposure, and 6 patients had an undetermined time of occurrence. Over time, 27 patients stopped mitotane and partial (42.3%) or complete (23.1%) recovery from hypothyroidism was observed, mainly in the first 2 years after mitotane discontinuation.

CONCLUSION

Mitotane therapy is frequently associated with new onset of central hypothyroidism with a prevalence of 95.5%. Most cases occurred in the first year of treatment. Partial or full recovery of thyroid function occurs in 65.4% of cases. This study supports the importance of systematic monitoring of TSH and free T4 levels during and following discontinuation of mitotane therapy.

RF21 | PSUN07 Germline Genetic Testing in a Cohort of Adults with Adrenocortical Carcinoma : Insights From a Clinical Care Setting

Context

About 5-10% of adrenocortical cancer (ACC) arise in patients with genetic predisposition syndromes, including Li-Fraumeni, Lynch, MEN1, or Familial Adenomatous Polyposis (APC). Recent European (2018) and American guidelines (2020) recommend that all adults with ACC should be offered clinical genetic counseling. There is a paucity of data regarding systematic germline testing in adults with ACC and the extent of the genetic evaluation is unclear.

Objective

To describe the germline genetic characteristics in a cohort of adult patients with ACC evaluated in a tertiary clinical care center.

Methods

Data including demographics, personal and family history of neoplasia, pathology reports, clinical features and genetic testing were retrospectively collected from charts of patients treated at Centre hospitalier de l'Université de Montréal (CHUM). After genetic counseling, genetic testing was proposed to patients with a pathologic diagnosis of ACC. From 2005 to 2015, TP53 gene analysis was performed using direct sequencing and MLPA. Since 2016, multigene testing was performed for a progressively increasing number of oncogenic genes using a custom next-generation panel for germline leucocyte DNA including at least the TP53, MSH2, MSH6, MLH1,PMS2, EPCAM, MEN1, BRCA1 and BRCA2 genes (Invitae, CA). An extended panel, based on past medical and familial history, was performed at the discretion of the geneticist. Patient data was retrospectively investigated.

Results

We analyzed data from 44 patients with available germline genetic results. Median age of the patients was 46 years (ranging from 22 to 79 years), including 11 males (25.0%) and 33 females (75.0%). Ten patients (22.7%) underwent only TP53 gene analysis and 32 patients (72.7%) were studied using the larger oncogenic genetic panel.

Germline pathogenic or likely pathogenic variants were identified in 5 of the 44 patients (11.4%) while genetic variants of unknown significance (VUS) were found in 7 of the 44 patients (15.9%). Among patients with pathogenic variants, one had a family history and known germline mutation in the BRCA2 gene (8765delAG, p.Glu2846GlyfsX23). One patient had a personal and familial medical history suggesting a MEN1 syndrome that was confirmed with the finding of a germline MEN1 mutation (c.1556delC, p.Pro519Leu fs40). Unsuspected germline pathogenic variants were found in three patients: 1) TP53 (c.425delC, p.Pro142fs), 2) MUTYH (c.536A&gt;G, p.Tyr179Cys) and 3) MSH6 (c.3649-3655, p.Arg1217Leu fs9) genes. Variants of unknown significance (VUS) were found in the following genes: POT1, MSH3, PALB2, RAD51d, APC, ATM and BRCA2.

Conclusions

Germline pathogenic variants were found in 11.4% of our cohort of patients with ACC. VUS were found in 15.9% of patients but their significance remains to be determined. Genetic counseling and germline genetic testing should be offered to all patients with ACC; however the optimal use and extent of oncogenic gene panels need to be better defined.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m., Sunday, June 12, 2022 12:48 p.m. - 12:53 p.m.

Cerebral investigation of healthy siblings of schizophrenics

Computed tomography (CT) studies have demonstrated that lateral ventricular size measured by ventricular brain ratio (VBR), as well as third ventricle width, is statistically enlarged in schizophrenics. Moreover, these cerebral abnormalities differ according to symptomatology evaluated with a positive and negative symptom scale. The aim of this study was to investigate, using CT scans, healthy siblings of schizophrenics, and relate the results to their ill siblings. Nineteen healthy siblings of 12 previously studied schizophrenics underwent CT scans, which were compared to those of their related schizophrenic sibling and to 17 unrelated control subjects. The results showed that in ten of 12 families, schizophrenics have larger ventricles (lateral and third ventricles) than their healthy siblings. Ventricular enlargement of healthy siblings was correlated with severity of negative symptoms of their ill sibling. Implications of a familial contribution for ventricular size and negative symptoms are discussed.

Social interactions impact on the dopaminergic system and drive individuality

Individuality is a striking feature of animal behavior. Individual animals differ in traits and preferences which shape their interactions and their prospects for survival. However, the mechanisms underlying behavioral individuation are poorly understood and are generally considered to be genetic-based. Here, we devised a large environment, Souris City, in which mice live continuously in large groups. We observed the emergence of individual differences in social behavior, activity levels, and cognitive traits, even though the animals had low genetic diversity (inbred C57BL/6J strain). We further show that the phenotypic divergence in individual behaviors was mirrored by developing differences in midbrain dopamine neuron firing properties. Strikingly, modifying the social environment resulted in a fast re-adaptation of both the animal's traits and its dopamine firing pattern. Individuality can rapidly change upon social challenges, and does not just depend on the genetic status or the accumulation of small differences throughout development.

Allosteric nature of P2X receptor activation probed by photoaffinity labelling

BACKGROUND AND PURPOSE

In P2X receptors, agonist binding at the interface between neighbouring subunits is efficiently transduced to ion channel gating. However, the relationship between binding and gating is difficult to study because agonists continuously bind and unbind. Here, we covalently incorporated agonists in the binding pocket of P2X receptors and examined how binding site occupancy affects the ability of the channel to gate.

EXPERIMENTAL APPROACH

We used a strategy for tethering agonists to their ATP-binding pocket, while simultaneously probing ion channel gating using electrophysiology. The agonist 2',3'-O-(4-benzoylbenzoyl)-ATP (BzATP), a photoaffinity analogue of ATP, enabled us to trap rat homomeric P2X2 receptor and a P2X2/1 receptor chimera in different agonist-bound states. UV light was used to control the degree of covalent occupancy of the receptors.

KEY RESULTS

Irradiation of the P2X2/1 receptor chimera - BzATP complex resulted in a persistent current that lasted even after extensive washout, consistent with photochemical tethering of the agonist BzATP and trapping of the receptors in an open state. Partial labelling with BzATP primed subsequent agonist binding and modulated gating efficiency for both full and partial agonists.

CONCLUSIONS AND IMPLICATIONS

Our photolabelling strategy provides new molecular insights into the activation mechanism of the P2X receptor. We show here that priming with full agonist molecules leads to an increase in gating efficiency after subsequent agonist binding.

Mutagenicity of malachite green and leucomalachite green in in vitro tests

The genotoxic potential of the fungicide malachite green (MG) and its reduced derivative leucomalachite green (LMG) was assessed in bacteria and mammalian cells using the standard Salmonella typhimurium/Ames and CHO/HGPRT tests. In vitro potential DNA damaging effects of MG and LMG were tested using the single-cell gel electrophoresis (Comet) assay on CHO cells. Malachite green was found to be extremely cytotoxic to bacteria and mammalian cells. It did not have any mutagenic activity, in any bacterial strains, in the presence or absence of metabolic activation for doses up to 10 microg per plate. In the CHO/HGPRT test, the mutagenic potential of MG could be evaluated only for very low concentrations ranging from 0.001 to 0.05 microg ml(-1) medium. When S9 fraction was added to the medium, the highest tested dose could be increased to 1 microg ml(-1). In these experimental conditions, MG did not increase the number of thioguanine-resistant mutants. Leucomalachite green was less toxic than MG to Salmonella typhimurium and did not have mutagenic activity in the Ames' test for doses up to 2000 microg per plate. It was also less cytotoxic than MG to CHO cells and was tested at doses ranging from 5 to 100 microg ml(-1). Overall results indicated that LMG was not mutagenic in the HGPRT test. In the Comet assay, MG induced DNA damage only at cytotoxic doses. Loss of cell viability was observed for doses of > or = 3 microg ml(-1), with parallel increase in DNA alterations as measured by the tail moment. After metabolic activation, however, DNA damage was observed at doses (15-20 microg ml(-1)) inducing only low cytotoxicity. In this case, the direct genotoxicity of MG metabolites could not be excluded. In the absence or presence of metabolic activation, LMG did not have any effect on cell viability or DNA damage for doses up to 500 microg ml(-1). This study indicates that LMG, which is the main residue found in fish tissues after treatment with MG, did not have any mutagenic or clastogenic effects in the experimental conditions used.

Comparative in vitro and in vivo assessment of genotoxic effects of etoposide and chlorothalonil by the comet assay

The alkaline single cell gel electrophoresis (comet) assay was used to assess in vitro and in vivo genotoxicity of etoposide, a topoisomerase II inhibitor known to induce DNA strand breaks, and chlorothalonil, a fungicide widely used in agriculture. For in vivo studies, rats were sacrificed at various times after treatment and the induction of DNA strand breaks was assessed in whole blood, bone marrow, thymus, liver, kidney cortex and in the distal part of the intestine. One hour after injection, etoposide induced DNA damage in all organs studied except kidney, especially in bone marrow, thymus (presence of HDC) and whole blood. As observed during in vitro comet assay on Chinese hamster ovary (CHO) cells, dose- and time-dependent DNA effects occurred in vivo with a complete disappearance of damage 24 h after administration. Even though apoptotic cells were detected in vitro 48 h after cell exposure to etoposide, such a result was not found in vivo. After chlorothalonil treatment, no DNA strand breaks were observed in rat organs whereas a clear dose-related DNA damage was observed in vitro. The discrepancy between in vivo and in vitro models could be explained by metabolic and mechanistic reasons. Our results show that the in vivo comet assay is able to detect the target organs of etoposide and suggest that chlorothalonil is devoid of appreciable in vivo genotoxic activity under the protocol used.

Mutagenicity of bithionol sulfoxide and its metabolites in the salmonella/mammalian microsome test

The mutagenic effects of bithionol sulfoxide and its two major metabolites, bithionol and bithionol sulfone, on 4 Salmonella typhimurium strains (TA97, TA98, TA100 and TA102) were investigated. Bithionol sulfoxide was found to be mutagenic to TA98 and TA100. However, mutagenicity was abolished in the presence of rat-liver S9 fractions.