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A PET imaging agent for evaluating PARP-1 expression in ovarian cancer
Mehran Makvandi, … , Robert H. Mach, Lilie L. Lin
Mehran Makvandi, … , Robert H. Mach, Lilie L. Lin
Published April 16, 2018
Citation Information: J Clin Invest. 2018. https://doi.org/10.1172/JCI97992.
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Categories: Clinical Medicine Oncology Therapeutics

A PET imaging agent for evaluating PARP-1 expression in ovarian cancer

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Abstract

BACKGROUND. Poly(ADP-ribose) polymerase (PARP) inhibitors are effective in a broad population of patients with ovarian cancer; however, resistance caused by low enzyme expression of the drug target PARP-1 remains to be clinically evaluated in this context. We hypothesize that PARP-1 expression is variable in ovarian cancer and can be quantified in primary and metastatic disease using a novel PET imaging agent. METHODS. We used a translational approach to describe the significance of PET imaging of PARP-1 in ovarian cancer. First, we produced PARP1-KO ovarian cancer cell lines using CRISPR/Cas9 gene editing to test the loss of PARP-1 as a resistance mechanism to all clinically used PARP inhibitors. Next, we performed preclinical microPET imaging studies using ovarian cancer patient–derived xenografts in mouse models. Finally, in a phase I PET imaging clinical trial we explored PET imaging as a regional marker of PARP-1 expression in primary and metastatic disease through correlative tissue histology. RESULTS. We found that deletion of PARP1 causes resistance to all PARP inhibitors in vitro, and microPET imaging provides proof of concept as an approach to quantify PARP-1 in vivo. Clinically, we observed a spectrum of standard uptake values (SUVs) ranging from 2–12 for PARP-1 in tumors. In addition, we found a positive correlation between PET SUVs and fluorescent immunohistochemistry for PARP-1 (r2 = 0.60). CONCLUSION. This work confirms the translational potential of a PARP-1 PET imaging agent and supports future clinical trials to test PARP-1 expression as a method to stratify patients for PARP inhibitor therapy. TRIAL REGISTRATION. Clinicaltrials.gov NCT02637934. FUNDING. Research reported in this publication was supported by the Department of Defense OC160269, a Basser Center team science grant, NIH National Cancer Institute R01CA174904, a Department of Energy training grant DE-SC0012476, Abramson Cancer Center Radiation Oncology pilot grants, the Marsha Rivkin Foundation, Kaleidoscope of Hope Foundation, and Paul Calabresi K12 Career Development Award 5K12CA076931.

Authors

Mehran Makvandi, Austin Pantel, Lauren Schwartz, Erin Schubert, Kuiying Xu, Chia-Ju Hsieh, Catherine Hou, Hyoung Kim, Chi-Chang Weng, Harrison Winters, Robert Doot, Michael D. Farwell, Daniel A. Pryma, Roger A. Greenberg, David A. Mankoff, Fiona Simpkins, Robert H. Mach, Lilie L. Lin

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Figure 1

The characterization of PARP1-KO ovarian cancer cell lines and in vitro evaluation of PARP inhibitor efficacy.

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The characterization of PARP1-KO ovarian cancer cell lines and in vitro ...
(A) Immunofluorescence showed PARP-1 was absent in more than 90% of single cells in PARP1-KO polyclonal populations (ANOVA, ****P < 0.0001) and was reduced in BRCA1-restored cells compared with parent control (ANOVA, ****P < 0.0001). (B) Polyclonal populations of PARP1-KO cell lines had reduced PARP-1 by Western blot compared with parent control. (C) [125I]KX1 radioligand binding assays showed a significant reduction in radiotracer binding in PARP1-KO and UWB1.289 BRCA1-restored cell lines compared with parent control (ANOVA, ****P < 0.0001). (D) Immunofluorescence of olaparib-treated UWB1.289 PARP1-KO and UWB1.289 BRCA1-restored cells showed no increase in γH2AX compared with DMSO controls. Olaparib-treated OVCAR8 PARP1-KO G1 and G3 cells showed a 1.3 times increase (ANOVA, **P < 0.01 and ***P < 0.001, respectively) in γH2AX from DMSO controls. This was in contrast to olaparib-treated UWB1.289 and OVCAR8 cells that showed a 2.6 times (ANOVA, ****P < 0.0001) and 2.2 times (ANOVA, ****P < 0.0001) increase in γH2AX from DMSO controls. (E) Cell viability assays showed that PARP1-KO cells were equally resistant to olaparib compared with BRCA1-restored cells and all clinical PARP inhibitors required PARP-1 for maximum efficacy. Loss of PARP1 caused the greatest change in efficacy for niraparib and talazoparib. Cisplatin sensitivity was used as a positive control and remained unchanged after loss of PARP1. All in vitro experiments were completed 3 independent times. Cell lines shown in A–D, from left to right, are: UWB1.289, UWB1.289 BRCA1 restored, UWB1.289 PARP1-KO G1, UWB1.289 PARP1-KO G2, UWB1.289 PARP1-KO G3, OVCAR8, OVCAR8 PARP1-KO G1, OVCAR8 PARP1-KO G2, and OVCAR8 PARP1-KO G3. –, BRCA1 mutant. +, BRCA1 restored.
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ISSN: 0021-9738 (print), 1558-8238 (online)

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