Targeted Radionuclide Therapy Using Auger Electron Emitters: The Quest for the Right Vector and the Right Radionuclide

Auger electron emitters (AEEs) are attractive tools in targeted radionuclide therapy to specifically irradiate tumour cells while sparing healthy tissues. However, because of their short range, AEEs need to be brought close to sensitive targets, particularly nuclear DNA, and to a lower extent, cell membrane. Therefore, radioimmunoconjugates (RIC) have been developed for specific tumour cell targeting and transportation to the nucleus. Herein, we assessed, in A-431_CEA-luc and SK-OV-3_1B9 cancer cells that express low and high levels of HER2 receptors, two ¹¹¹In-RIC consisting of the anti-HER2 antibody trastuzumab conjugated to NLS or TAT peptides for nuclear delivery. We found that NLS and TAT peptides improved the nuclear uptake of ¹¹¹In-trastuzumab conjugates, but this effect was limited and non-specific. Moreover, it did not result in a drastic decrease of clonogenic survival. Indium-111 also contributed to non-specific cytotoxicity in vitro due to conversion electrons (30% of the cell killing). Comparison with [¹²⁵I]I-UdR showed that the energy released in the cell nucleus by increasing the RIC’s nuclear uptake or by choosing an AEE that releases more energy per decay should be 5 to 10 times higher to observe a significant therapeutic effect. Therefore, new Auger-based radiopharmaceuticals need to be developed.

A benchmarking study of Geant4 for Auger electrons emitted by medical radioisotopes

Auger emitting radioisotopes are of great interest in targeted radiotherapy because, once internalised in the tumour cells, they can deliver dose locally to the radiation sensitive targets, while not affecting surrounding cells. Geant4 is a Monte Carlo code widely used to characterise the physics mechanism at the basis of targeted radiotherapy. In this work, we benchmarked the modelling of the emission of Auger electrons in Geant4 deriving from the decay of ¹²³I, ¹²⁴I, ¹²⁵I radionuclides against existing theoretical approaches. We also compared Geant4 against reference data in the case of ¹³¹Cs, which is of interest for brachytherapy. In the case of ¹²⁵I and ¹³¹Cs, the simulation results are compared to experimental measurements as well. Good agreement was found between Geant4 and the reference data. As far as we know, this is the first study aimed to benchmark against experimental measurements the emission of Auger electrons in Geant4 for radiotherapy applications.

Micro-elimination of hepatitis C among people with HIV coinfection: declining incidence and prevalence accompanying a multi-center treatment scale-up trial

BACKGROUND

Gay and bisexual men (GBM) are a key population affected by HIV and hepatitis C (HCV) co-infection. Providing HCV treatment scale-up across specialist and non-hepatitis specialist settings may eliminate HCV in this population. We aimed to (1) deliver and measure HCV treatment effectiveness, and (2) determine the population impact of treatment on HCV prevalence and incidence longitudinally.

METHODS

The co-EC Study (Enhancing care and treatment among HCV/HIV co-infected individuals to Eliminate Hepatitis C transmission) was an implementation trial providing HCV direct-acting antiviral treatment in Melbourne, Australia, from 2016-2018. Individuals with HCV/HIV co-infection were prospectively enrolled from primary and tertiary-care services providing care for 85% of GBM with HIV in our jurisdiction. HCV-viraemic prevalence and HCV-antibody/viraemic incidence were measured using a state-wide, individually-linked, electronic surveillance system.

RESULTS

Among 200 participants recruited, 186 initiated treatment during the study period. Sustained virological response among primary care participants (98%, 95%CI:93-100%) was not different to tertiary care (98%, 95%CI:86-100%). From 2012-2019, between 2434 and 3476 GBM with HIV-infection attended our primary-care sites annually providing 13,801 person-years of follow-up; 50-60% received an HCV test annually, 10-14% were anti-HCV positive. Among those anti-HCV positive, viraemic prevalence declined 83% during the study (54% to 9%; 2016 to 2019). HCV incidence decreased 25% annually from 1.7/100 person-years in 2012 to 0.5/100 person-years in 2019 (incidence rate ratio 0.75; CI:0.68-0.83;p<0.001).

CONCLUSION

High treatment effectiveness by non-specialists demonstrates the feasibility of treatment scale-up in this population. Substantial declines in HCV incidence and prevalence among GBM with HIV-infection provides proof-of-concept for HCV micro-elimination.

REGISTRATION

ClinicalTrials.gov (Identifier: NCT02786758).

Nortriptyline plasma levels and therapeutic response

Eighteen depressed outpatients were treated for 6 wk with a mean daily dose of 121 mg of nortriptyline. The mean plasma level was 138 ng/ml during treatment. Therapeutic response was monitored by the Zung Self-Rating Depression Scale and the Hamilton Depression Scale administrered by two psychiatrists blind to the tricyclic used, dose, and plasma levels. Eight patients recovered (Hamilton less than or equal to 6) by the fourth week and 12 by the sixth week. During the steady-state (wk 4 to 6) there was a positive correlation between the weekly Hamilton scores and the weekly nortriptyline levels (p less than 0.01). The 9 patients with mean plasma levels between 50 and 139 ng/ml had a better therapeutic response after 6 wk measured by percent recovered (p less than 0.005). Zung score (p less than 0.05), and Hamilton score (p less than 0.025) than the 9 patients with mean plasma levels between 140 and 260 ng/ml.