Course Content
Developing a Diffuse Large B-Cell Lymphoma PET probe, including radiofluorination, in vitro and in vivo biological assessments
0/2
Design and in vivo evaluation of an antibody-radio-drug conjugate (ArDC) for click-to-release conversion from a SPECT probe state to a cytotoxic state in a mouse lung cancer model
0/2
Evaluating the Pharmacokinetic Properties of 225Ac-labeled Macropa Chelators for Targeted Alpha Therapy in a DLL3-Expressing Small-Cell Lung Cancer Model
0/2
Targeting ALDH1A1 for the identification and treatment of therapy resistant cancers
0/2
[18F]F-AraG uptake in the vertebral bone marrow predicts survival in immunotherapy treated non-small cell lung cancer patients
0/2
Comparing total-body metabolic PET imaging signatures of lung cancer cachexia to other wasting conditions
0/2
ChoKα-targeted NIR fluorophore for intraoperative NSCLC imaging in clinical companion canines
0/2
Prognostic Power and Therapeutic Precision in Lymphoma and Lung Cancer Management
About Lesson
Abstract Body:

Introduction: Measuring drug payload biodistribution in preclinical models can provide mechanistic insights into antibody drug conjugate (ADC) efficacy and tolerability but often requires the use of 3H/14C labels or mass spectrometric methods to maintain drug structure and function.1 Noninvasive imaging of radioimmunoconjugates by PET or SPECT is seldom a faithful surrogate for ADC biodistribution as the fate of the radiolabeled probe does not necessarily mirror that of the drug payload.2 Such efforts are further confounded by the risk that radiolabeling drug-modified antibodies can lead to over-modification and altered disposition.3 Inspired by the concept of theranostics, we designed an antibody-conjugatable ADC payload that serves as a conventional SPECT probe in one state but with the potential to be converted on demand to a conventional cytotoxic ADC payload – a therapeutic state – by administration of a bioorthogonal switch, effectively enabling imaging and therapy from a single molecular entity we term an antibody radio-drug conjugate (ArDC). Importantly, this work is distinct from previous click-to-release approaches for ADCs4,5 in that payload activation can be achieved for intracellular ArDC catabolites through use of cell permeable tetrazines.

Methods: An ArDC was designed to incorporate a potent DNA-damaging agent, pyrrolobenzodiazepine (PBD) dimer, masked by a novel transcyclooctene-para-aminobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (TCO-PAB-DOTA), which served as a site of radiolabeling and to attenuate drug activity (Figure 1a). All in vivo studies were conducted in mice bearing HCC1569X2 xenografts expressing the internalizing human lung cancer antigen, Ly6E.6 After confirming stability, an in vivo SPECT imaging study with 111In-labeled ArDC – alongside the 111In-DOTA-labeled parent antibody as a control – confirmed the ability to noninvasively image the in vivo disposition of the ArDC payload. In a separate non-radioactive study, tumor growth inhibition was measured for a single 0.5 mg/kg dose of the parent ADC, the ArDC alone, or the ArDC followed 6 days later by a single dose (10, 30 or 100 umol/kg) of tetrazine. Traceless, on-demand conversion from the TCO-PAB-DOTA-masked state to the cytotoxic state was accomplished via the bond-breaking variant of the tetrazine/trans-cyclooctene (Tz/TCO) inverse-electron demand Diels-Alder (IEDDA) click reaction.

Results: Live animal SPECT-CT imaging of tumor-bearing mice dosed with the radiolabeled conjugate showed steady accumulation of 111In signal in the tumor over 6 days for [111In]ArDC, which was comparable to that of the control, [111In]αLy6E (Figure 1b). The tetrazine ultimately proved highly effective at switching the ArDC to a cytotoxic form in vivo, inducing tumor growth inhibition in mice whereas the tetrazine or ArDC alone was inactive (Figure 1c).

Conclusions: The efforts herein lay the groundwork for directly characterizing ADC payload distribution/efficacy and distribution/toxicity relationships in living subjects, which may accelerate engineering efforts to achieve more tumor-selective delivery of ADCs. The ArDC approach may eventually offer the possibility of selecting and treating patients with a single active pharmaceutical agent while gating payload activation on maximization of delivery – measured by noninvasive imaging – to tumor versus normal tissues. Despite this potential, several challenges lie ahead of implementing such an effort including the overall complexity of the approach and optimizing payload biodistribution.

Image/Figure:

Click to view full size

Image/Figure Caption:

Figure 1. A) Structural diagram of antibody-radio-drug conjugate (ArDC). The payload is a pyrrolobenzodiazepine (PBD) dimer (red) labeled and attenuated in potency by a TCO-PAB-DOTA group (yellow-black-green) attached to the N10 nitrogen; the DOTA can chelate a radioactive metal isotope to enable tracking in vivo of both conjugated and released payload. Reaction of the TCO with a tetrazine prompts click/release of the TCO-PAB-DOTA and free drug payload from the ArDC or downstream catabolites (even intracellular), effectively resulting in the fully-cytotoxic and unlabeled ADC or free PBD dimer. B) SPECT-CT imaging (111In) of the anti-Ly6E targeted antibody-radio-drug conjugate labeled through DOTA within the radio-drug (ArDC, upper) versus conventional antibody-drug conjugate labeled through DOTA conjugated via lysines (ADC, lower). C) Tumor growth inhibition observed following tetrazine-induced switching of ArDC in the HCC1569X2 mouse xenograft model. SCID mice were inoculated with HCC1569X2 tumor cells and tumors were allowed to grow for ~7 days to a volume of 200-300 mm3 (Day 0), at which time the ArDC was administered intravenously in the tail vein at a dose of 0.5 mg/kg. Six days later, a single dose of tetrazine was administered IV in the tail vein at 100, 30 or 10 mmol/kg. Controls with ArDC only (1 mg/kg), ADC only (0.5 mg/kg) or tetrazine only (100 mmol/kg) are also shown.

Author

Charles Andrew Boswell
Genentech
0% Complete