ADPr-Peptide Synthesis

Immunomodulatory roles of PARPs: Shaping the tumor microenvironment, one ADP-ribose at a time

PARPs encompass a small yet pervasive group of 17 enzymes that catalyze a post-translational modification known as ADP-ribosylation. PARP1, the founding member, has received considerable focus; however, in recent years, the spotlight has shifted to other members within the PARP family. In this opinion piece, we first discuss surprising findings that some FDA-approved PARP1 inhibitors activate innate immune signaling in cancer cells that harbor mutations in the DNA repair pathway. We then discuss hot-off-the-press genetic and pharmacological studies that reveal roles for PARP7, PARP11, and PARP14 in immune signaling in both tumor cells and tumor-associated immune cells. We conclude with thoughts on tuning PARP1-inhibitor-mediated innate immune activation and explore the unrealized potential for small molecule modulators of other PARP family members as next-generation immuno-oncology drugs.

Cytoplasmic ADP-ribosylation levels correlate with markers of patient outcome in distinct human cancers

ADP-ribosylation (ADPR) is a posttranslational modification whose importance in oncology keeps increasing due to frequent use of PARP inhibitors (PARPi) to treat different tumor types. Due to the lack of suitable tools to analyze cellular ADPR levels, ADPR's significance for cancer progression and patient outcome is unclear. In this study, we assessed ADPR levels by immunohistochemistry using a newly developed anti-ADP-ribose (ADPr) antibody, which is able to detect both mono- and poly-ADPR. Tissue microarrays containing brain (n = 103), breast (n = 1108), colon (n = 236), lung (n = 138), ovarian (n = 142), and prostate (n = 328) cancers were used to correlate ADPR staining intensities to clinico-pathological data, including patient overall survival (OS), tumor grade, tumor stage (pT), lymph node status (pN), and the presence of distant metastasis (pM). While nuclear ADPR was detected only in a minority of the samples, cytoplasmic ADPR (cyADPR) staining was observed in most tumor types. Strong cyADPR intensities were significantly associated with better overall survival in invasive ductal breast cancer (p < 0.0001), invasive lobular breast cancer (p < 0.005), and high grade serous ovarian cancer patients (p < 0.01). Furthermore, stronger cytoplasmic ADPR levels significantly correlated with early tumor stage in colorectal and in invasive ductal breast adenocarcinoma (p < 0.0001 and p < 0.01, respectively) and with the absence of regional lymph node metastasis in colorectal adenocarcinoma (p < 0.05). No correlation to cyADPR was found for prostate and lung cancer or brain tumors. In conclusion, our new anti-ADP-ribose antibody revealed heterogeneous ADPR staining patterns with predominant cytoplasmic ADPR staining in most tumor types. Different cyADPR staining patterns could help to better understand variable response rates to PARP inhibitors in the future.