Abstract LB242: Characterizing the fate&lt;tissue distribution and excretion route&gt; of cancer vaccine lipoplex-RNA following intravenous injection of 14C-DOTMA-lipoplex-mRNA in mice
Authors: Yip Victor , Roth Gillie , Torres Elizabeth , Wichner Sara , Blanchette Craig , Kamath Amrita , Shen Ben-Quan 
Published: April 2023

Abstract
Messenger RNA (mRNA) has emerged as a new class of therapeutic agent delivered by a carrier lipoplex (LPX) to elicit an immune-response for treating various diseases, including cancers. However, the PK and tissue distribution of the components is not well characterized given its therapeutic novelty and structural complexity. As such, this study aimed to characterize the distribution and metabolic fate of LPX-mRNA using a radiolabeled DOTMA, a component of the LPX-mRNA therapeutic, to aid the development of this anti-cancer agent. To track the fate of LPX-mRNA, DOTMA was first radiolabeled with [14C] through chemical synthesis (14C-DOTMA, and then mixed with DOPE and mRNA at a specific ratio to form 14C-DOTMA-LPX-mRNA (14C-LPX-mRNA)). The plasma protein binding and blood cell partitioning for both 14C-LPX-mRNA and 14C-DOTMA alone were assessed in vitro. Moreover, the in vivo biodistribution and elimination of both 14C-molecules were characterized following a single intravenous (IV) injection in mice up to 12 weeks.The in-vitro assays showed the 14C-DOTMA and the 14C-LPX-mRNA were highly associated with plasma proteins and blood cell as the complexes were spun down at a much higher level as compared to in PBS solution (~5% and ~60% plasma proteins bound and ~60% and ~80% blood cell partitioned in 14C-DOTMA and the 14C-LPX-mRNA, respectively). Following in-vivo dosing in mice, plasma radioactivity of both test molecules showed a biphasic elimination profile with a rapid phase of decrease during the first 3 days followed by a prolonged exposure phase. The radioactivity in the whole blood and plasma displayed similar profiles but had minimal partitioning to blood cells, differing from the in-vitro data. We hypothesized that, both drug substances began to associate with plasma proteins/blood cells, then quickly distributed to the tissues and eliminated from the systemic circulation. Among all tissues analyzed, the liver and spleen showed the highest radioactivity levels where the 14C-LPX-mRNA peaked within the day while 14C-DOTMA peaked at 3-weeks-after-dose, followed by a long persistency. Lower levels of distribution and persistence of radioactivity were also observed in other tissues. The route of elimination is mainly through the biliary-fecal route with minimal contribution from the renal route for 14C-LPX-mRNA. 14C-LPX-mRNA achieved mass balance at 8-weeks after dose where ~70% was eliminated through feces, 3% through urine and ~20% remaining in tissues. 14C-DOTMA animals have an under-recovery of about 40-50% in radioactivity due to animals’ low intake of food and water which caused a severe reduction in animals’ weight. In summary, this study fully characterized the fate of the 14C-DOTMA and the 14C-LPX-mRNA in vitro and in vivo in mice. Our data demonstrated that the LPX-mRNA (by tracking DOTMA) mainly distributed to the spleen and liver with a long persistency, consistent with previous study showing the spleen as the major tissue for mRNA distribution. However, the LPX’s elimination profile (duration/persistency) is likely very different from that of mRNA. The ongoing work is to track the fate of mRNA component in LPX-mRNA, which could provide more insight on the correlation of DOTMA and mRNA, and help the development of this novel therapeutic modality.
Citation Format: Victor Yip, Gillie Roth, Elizabeth Torres, Sara Wichner, Craig Blanchette, Amrita Kamath, Ben-Quan Shen. Characterizing the fate&lt;tissue distribution and excretion route&gt; of cancer vaccine lipoplex-RNA following intravenous injection of 14C-DOTMA-lipoplex-mRNA in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB242.