Phase 2 Study of Cyclophosphamide, Etoposide, and Estramustine in Patients With Castration-Resistant Prostate Cancer

Synthesis and evaluation of 7-(3-aminopropyloxy)-substituted flavone analogue as a topoisomerase IIα catalytic inhibitor and its sensitizing effect to enzalutamide in castration-resistant prostate cancer cells

Prostate cancer patients primarily receive androgen receptor (AR)-targeted drugs as a primary treatment option because prostate cancer is associated with highly activated AR signaling. AR amplification made prostate cancer cells viable under treatment of AR-targeted therapy, leading to castration resistance. AR amplification was more common in enzalutamide-resistant patients. As a strategy to overcome castration resistance and to improve the efficacy of enzalutamide, second-generation nonsteroidal antiandrogen drugs for castration-resistant prostate cancer (CRPC) including topoisomerase II (topo II) poisons such as etoposide and mitoxantrone, have been administered in combination with enzalutamide. In the present study, it was confirmed that amplification of topo IIα, but not I and IIβ, was directly and proportionally associated with poor clinical outcome of Prostate cancer. Among a novel series of newly designed and synthesized 7-(3-aminopropyloxy)-substituted flavone analogues, compound 6, the most potent derivative, was further characterized and identified as a topo IIα catalytic inhibitor that intercalates into DNA and binds to the DNA minor groove with better efficacy and less genotoxicity than etoposide, a topo II poison. Compound 6 showed remarkable efficacy in inhibiting AR-negative CRPC cell growth and sensitizing activity to enzalutamide in AR-positive CRPC cells, thus confirming the potential of topo IIα catalytic inhibitor to overcome resistance to androgen deprivation therapy.

AK-I-190, a New Catalytic Inhibitor of Topoisomerase II with Anti-Proliferative and Pro-Apoptotic Activity on Androgen-Negative Prostate Cancer Cells

Castration-resistant prostate cancer (CRPC) is a clinical challenge in treatment because of its aggressive nature and resistance to androgen deprivation therapy. Topoisomerase II catalytic inhibitors have been suggested as a strategy to overcome these issues. We previously reported AK-I-190 as a novel topoisomerase II inhibitor. In this study, the mechanism of AK-I-190 was clarified using various types of spectroscopic and biological evaluations. AK-I-190 showed potent topoisomerase II inhibitory activity through intercalating into DNA without stabilizing the DNA-enzyme cleavage complex, resulting in significantly less DNA toxicity than etoposide, a clinically used topoisomerase II poison. AK-I-190 induced G1 arrest and effectively inhibited cell proliferation and colony formation in combination with paclitaxel in an androgen receptor–negative CRPC cell line. Our results confirmed that topoisomerase II catalytic inhibition inhibited proliferation and induced apoptosis of AR-independently growing prostate cancer cells. These findings indicate the clinical relevance of topoisomerase II catalytic inhibitors in androgen receptor-negative prostate cancer.

Etoposide Loaded SPION-PNIPAM Nanoparticles Improve the in vitro Therapeutic Outcome on Metastatic Prostate Cancer Cells via Enhanced Apoptosis

Prostate cancer is among the leading causes of death worldwide because its metastatic form is a deadly disease. Therefore, the development of new chemotherapeutics is of immense importance. Nanoparticle technology seems to provide diverse options in this regard. Therefore, poly(N-isopropylacrylamide) (PNIPAM) coated superparamagnetic iron oxide nanoparticles (SPION) loaded with Etoposide were prepared in small sizes (57 nm) and with 3.5 % drug content to improve the efficiency of Etoposide in prostate cancer therapy. Sustained release of the drug was achieved, which found to be sensitive to low pH and high temperature. The anti-growth activity of SPION-PNIPAM-Etoposide formulation against metastatic prostate cancer cells (PC-3, LNCaP) were investigated by SRB assay, then, confirmed by ATP assay. Mode of cell death was evaluated by using flow cytometry analyses. A significant improvement of nanoformulated drug was observed at 5-10 μg/ml doses of the drug in both cell lines. More importantly, this formulation enhanced the cytotoxic effect of Etoposide on PC-3 cells, which is considered more resistant to Etoposide than LNCaP and reduced the IC₅₀ value by 55 % reaching to 4.5 μg drug/ml, which is a very significant improvement in the literature. It was clearly shown that nanoformulated drug provided about 3-fold increases in caspase-dependent early apoptotic cells in PC-3 cells. The novel formulation seems to successfully cause cell death of especially PC-3 metastatic prostate cancer cells. It should therefore be taken into consideration for further animal studies as a novel potent anticancer agent.

A phase I/II study of docetaxel in combination with pegylated liposomal doxorubicin in metastatic castration-resistant prostate cancer

Taxanes and anthracyclines have been among the best-studied chemotherapy classes in castration-resistant prostate cancer (CRPC). Docetaxel (D) 75 mg/m² every 3 weeks has been the standard first line chemotherapy for CRPC. Encapsulation of doxorubicin in polyethylene glycol-coated liposomes (PLD) was developed to enhance the safety and efficacy of conventional doxorubicin. We hypothesize that the combination of weekly low dose-D and PLD would result in a high response rate and low toxicity. Eligibility criteria included metastatic progressive CRPC, no prior D or PLD and good organ function. After a short phase I with no dose-limiting toxicity, D 30 mg/m² was administered on days 1, 8 and 15; and PLD 30 mg/m² on day 1 only, every 28 days. Thirty-seven patients were enrolled. The PSA response rate was 53%. Twenty-two subjects had measurable disease; one (5%) achieved complete response, five (23%) partial response, and twelve (54%) stable disease. Twenty-seven patients (73%) manifested pain relief. The median time to progression was 3.7 months for all patients and 7.9 months for responders. Median overall survival was 16.3 months. Grade 4 neutropenia without infection and anemia occurred in 1 patient each. Grade 3 treatment-related toxicities included: 15% fatigue; 9% neutropenia, anemia and nausea; 6% dehydration and hand-foot syndrome; and 3% infection, febrile neutropenia, thrombosis, stomatitis, headache, vomiting, weight loss and weakness. In this non-comparative study D-PLD demonstrated a higher activity than previously reported with single agent D with favorable side effect profile. A phase 3 study would be needed to evaluate the true benefit of this combination.ClinicalTrials.gov Identifier: NCT00456989.

Dianhydrogalactitol synergizes with topoisomerase poisons to overcome DNA repair activity in tumor cells

1,2:5,6-Dianhydrogalactitol (DAG) is a bi-functional DNA-targeting agent currently in phase II clinical trial for treatment of temozolomide-resistant glioblastoma (GBM). In the present study, we investigated the cytotoxic activity of DAG alone or in combination with common chemotherapy agents in GBM and prostate cancer (PCa) cells, and determined the impact of DNA repair pathways on DAG-induced cytotoxicity. We found that DAG produced replication-dependent DNA lesions decorated with RPA32, RAD51, and γH2AX foci. DAG-induced cytotoxicity was unaffected by MLH1, MSH2, and DNA-PK expression, but was enhanced by knockdown of BRCA1. Acting in S phase, DAG displayed selective synergy with topoisomerase I (camptothecin and irinotecan) and topoisomerase II (etoposide) poisons in GBM, PCa, and lung cancer cells with no synergy observed for docetaxel. Importantly, DAG combined with irinotecan treatment enhanced tumor responses and prolonged survival of tumor-bearing mice. This work provides mechanistic insight into DAG cytotoxicity in GBM and PCa cells and offers a rational for exploring combination regimens with topoisomerase I/II poisons in future clinical trials.