Auger emitting PARPi as a theranostic compound in triple negative breast cancer

Ziel/Aim Poly ADP-ribose polymerase (PARP) inhibition is based on the concept of synthetic lethality where simultaneous loss of two complementary proteins (BRCA mutation and PARP inhibition) leads to cell death. Clinically, PARP inhibitors (PARPi) are approved for ovarian and breast cancer patients harboring germline BRCA mutation (BRCA^mut). In this study, a theranostic approach was investigated by tagging Iod-123/125 to the backbone of the PARPi, Olaparib (Iod-123/125-PARPi-01).

Methodik/Methods In vitro studies comprised four BRCA^wt, four BRCA^mut Triple negative breast cancer (TNBC) cell lines, and a control mammary epithelial breast cell-line (MCF10A). To increase PARP1 expression and its nuclear translocation, the cells were pretreated with combinations of chemotherapeutic drugs and effects were monitored by PARP1 and pH2AX immunostaining. Cell cycle was analysed by staining Iod-125-PARPi-01 (~ 1MBq/1x10⁶ cells) treated cells with propidium iodide followed by flow cytometry. For in vivo biodistribution, Iod-123-PARPi-01 was administered i.v. in MDA-MB-231 xenografted NOD/SCID mice and imaged at 4 and 24 hrs post injection (pi).

Ergebnisse/Results Amongst the chemotherapeutic pretreatments, doxorubicin efficiently induced an overexpression of PARP1 and its translocation into the nucleus, which correlated with an increased intracellular uptake of Iod-125-PARPi-01. Notably, control cells (MCF10A) showed much lower uptake than TNBC cells. Cell cycle analysis of Iod-125-PARPi-01 treated cells showed G2/M arrest in BRCA^wt/BRCA^mut cell lines and pH2AX staining indicated heavy DNA damage. In vivo biodistribution studies showed a high tumor:muscle ratio of 10.4 and a tumor:blood ratio of 2.8, 24 hrs pi.

Schlussfolgerungen/Conclusions Iod-125-PARPi is a promising theranostic agent in both BRCA^wt and BRCA^mut TNBC cell lines. Doxorubicin pretreatment enhances uptake of Iod-125-PARPi in TNBC cell lines. In vivo biodistribution indicated a good tumor uptake and retention which confirms that Iod-125-PARPi is a potent theranostic drug.