Compound B(Biota Europe Ltd.)

In advanced castration resistant prostate cancer (CRPC), mutations in the DNA damage response (DDR) gene ataxia telangiectasia mutated (ATM) are common. While poly(ADP-ribose) polymerase inhibitors are approved in this context, their clinical efficacy remains limited. Thus, there is a compelling need to identify alternative therapeutic avenues for ATM mutant prostate cancer patients. Here, we generated matched ATM-proficient and ATM-deficient CRPC lines to elucidate the impact of ATM loss on DDR in response to DNA damage via irradiation. Through unbiased phosphoproteomic screening, we unveiled that ATM-deficient CRPC lines maintain dependence on downstream ATM targets through activation of ATR and DNA-PKcs kinases. Dual inhibition of ATR and DNA-PKcs effectively inhibited downstream γH2AX foci formation in response to irradiation and radiosensitized ATM-deficient lines to a greater extent than either ATM-proficient controls or single drug treatment. Further, dual inhibition abrogated residual downstream ATM pathway signaling and impaired replication fork dynamics. To circumvent potential toxicity, we leveraged the RUVBL1/2 ATPase inhibitor Compound B, which leads to the degradation of both ATR and DNA-PKcs kinases. Compound B effectively radiosensitized ATM-deficient CRPC in vitro and in vivo, and impacted replication fork dynamics. Overall, dual targeting of both ATR and DNA-PKcs is necessary to block DDR in ATM-deficient CRPC, and Compound B could be utilized as a novel therapy in combination with irradiation in these patients.

Ovarian cancer is the fifth leading cause of cancer related death in the United States. Cisplatin is a platinum-based anti-cancer drug used against ovarian cancer that enters malignant cells and then damages DNA causing cell death. Typically, ovarian cancer cells become resistant to cisplatin making it necessary to increase subsequent dosage, which usually leads to side-effects including irreversible damage to kidney and auditory system tissue. Ovarian cancer resistance is often associated with upregulation of histone deacetylase (HDAC) enzymes that cause DNA to adopt a closed configuration which reduces the ability of cisplatin to target and damage DNA. Compound B, a platinum(IV) complex with two axial phenylbutyrate (PBA) HDAC inhibitor ligands attached to a cisplatin core, can simultaneously inhibit HDAC activity and damage DNA causing decreased cancer cell viability in cisplatin-sensitive (A2780) and -resistant (A2780cis) ovarian cancer cell lines. However, compound B was not previously evaluated in vivo. As simultaneously inhibiting HDAC-mediated resistance with cisplatin treatment could potentiate the platinum drug’s effect, we first confirmed the anti-cancer effect of compound B in the A2780 and A2780cis cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide spectrophotometric assay. Then, we used zebrafish embryo and transgenic animal models to comparatively analyze the effect of cisplatin, compound B, and controls on general organismal, auditory, and renal system toxicity, and cancer metastasis. We found that lower dosages of compound B (0.3 or 0.6 µM) than of cisplatin (2.0 µM) could cause similar or decreased levels of general, auditory, and renal tissue toxicity, and at 0.6 µM, compound B reduces cancer metastasis more than 2.0 µM cisplatin.