The Clinically Active PARP Inhibitor AG014699 Ameliorates Cardiotoxicity but Does Not Enhance the Efficacy of Doxorubicin, despite Improving Tumor Perfusion and Radiation Response in Mice

Abstract

AG014699 was the first inhibitor of the DNA repair enzyme PARP-1 to enter clinical trial in cancer patients. In addition to enhancing the cytotoxic effect of DNA-damaging chemotherapies, we have previously shown that AG014699 is vasoactive, thereby having the potential to improve drug biodistribution. The effectiveness of the clinical agent doxorubicin is confounded both by poor tumor penetration and cardiotoxicity elicited via PARP hyperactivation. In this study, we analyzed the impact of AG014699 on doxorubicin tolerance and response in breast (MDA-MB-231) and colorectal (SW620, LoVo) tumor models in vitro and in vivo. As anticipated, AG014699 did not potentiate the response to doxorubicin in vitro. In vivo, AG014699 did not influence the pharmacokinetics of doxorubicin; however, it did ameliorate cardiotoxicity. Both toxicity and extent of amelioration were more pronounced in male than in female mice. AG014699 improved vessel perfusion in both MDA-MB-231 and SW620 tumors; however, this neither led to improved tumor-accumulation of doxorubicin nor enhanced therapeutic response. In contrast, when combined with radiotherapy, AG014699 significantly enhanced response both in vitro and in vivo. Real-time assessment of tumor vessel function and companion histologic studies indicate that doxorubicin causes a profound antivascular effect that counters the positive effect of AG014699 on perfusion. These data indicate that although AG014699 can enhance response to some chemotherapeutic drugs via improved delivery, this does not apply to doxorubicin. PARP inhibitors may still be of use to counter doxorubicin toxicity, and if the gender effect translates from rodents to humans, this would have greater effect in males.

An assay to measure poly(ADP ribose) glycohydrolase (PARG) activity in cells

“…Temozolomide (TMZ) is a DNA alkylating agent and is used as a standard-of-care treatment for patients with glioblastoma 13 . Here we used the colorectal cancer cell line SW620 that we knew was sensitive to alkylating agents ( Figure 5a) and which has been used in xenograft studies in combination with TMZ and the PARP inhibitors olaparib or AG014699 14, 15 . First we used the same assay conditions to determine whether increasing concentrations of TMZ induced PAR chains that could be maintained by inhibiting PARG with a potent inhibitor (compound 8 from Figure 3d).…”

Radiosensitisation by Poly(ADP-ribose) Polymerase Inhibition

“…A number of PARP inhibitors (ABT-888/Veliparib, AZD-2281/Olaparib, AG014699/ Rucaparib, MK-4827/Niraparib, AG14361, GPI-15427, E7016) have been shown to enhance tumour sensitivity to radiation in syngeneic and xenograft models of breast [79,80], colon [81][82][83], lung [79,84,85], nasopharyngeal [86], head and neck [87], and brain tumours [88][89][90][91] (Table 11.1). PARP inhibition combined with Colon carcinoma (SW620, LoVo) AG14361, i.p., 30 min before X-rays (5 or ionising radiation resulted in delayed tumour growth and extended median survival time.…”

Targeting Tumour Hypoxia with PARP Inhibitors: Contextual Synthetic Lethality

“…Nicotinamide is well known to act as a vasodilator [89], suggesting that other PARP inhibitors, which are structurally similar to nicotinamide could also improve vessel perfusion and potentially increase drug delivery to adjacent tumour tissues. Recent studies have demonstrated that PARP inhibitors (AG014699 and Olaparib) significantly increase the cytotoxic effect of radiotherapy in vivo and in vitro [90,91] (Chap. 12).…”