Enhancing the anti-tumor response by combining DNA damage repair inhibitors in the treatment of solid tumors

The anti-cancer efficacy of anti-malignancy therapies is related to DNA damage. However, DNA damage-response mechanisms can repair DNA damage, failing anti-tumor therapy. The resistance to chemotherapy, radiotherapy, and immunotherapy remains a clinical challenge. Thus, new strategies to overcome these therapeutic resistance mechanisms are needed. DNA damage repair inhibitors (DDRis) continue to be investigated, with polyadenosine diphosphate ribose polymerase inhibitors being the most studied inhibitors. Evidence of their clinical benefits and therapeutic potential in preclinical studies is growing. In addition to their potential as a monotherapy, DDRis may play an important synergistic role with other anti-cancer therapies or in reversing acquired treatment resistance. Here we review the impact of DDRis on solid tumors and the potential value of combinations of different treatment modalities with DDRis for solid tumors.

The developing landscape of combinatorial therapies of immune checkpoint blockade with DNA damage repair inhibitors for the treatment of breast and ovarian cancers

The use of immune checkpoint blockade (ICB) using antibodies against programmed death receptor (PD)-1, PD ligand (PD-L)-1, and cytotoxic T-lymphocyte antigen 4 (CTLA-4) has redefined the therapeutic landscape in solid tumors, including skin, lung, bladder, liver, renal, and breast tumors. However, overall response rates to ICB therapy remain limited in PD-L1-negative patients. Thus, rational and effective combination therapies will be needed to address ICB treatment resistance in these patients, as well as in PD-L1-positive patients who have progressed under ICB treatment. DNA damage repair inhibitors (DDRis) may activate T-cell responses and trigger inflammatory cytokines release and eventually immunogenic cancer cell death by amplifying DNA damage and generating immunogenic neoantigens, especially in DDR-defective tumors. DDRi may also lead to adaptive PD-L1 upregulation, providing a rationale for PD-L1/PD-1 blockade. Thus, based on preclinical evidence of efficacy and no significant overlapping toxicity, some ICB/DDRi combinations have rapidly progressed to clinical testing in breast and ovarian cancers. Here, we summarize the available clinical data on the combination of ICB with DDRi agents for treating breast and ovarian cancers and discuss the mechanisms of action and other lessons learned from translational studies conducted to date. We also review potential biomarkers to select patients most likely to respond to ICB/DDRi combination therapy.

CONCORDE: A phase I platform study of novel agents in combination with conventional radiotherapy in non-small-cell lung cancer

Lung cancer is the leading cause of cancer mortality worldwide and most patients are unsuitable for 'gold standard' treatment, which is concurrent chemoradiotherapy. CONCORDE is a platform study seeking to establish the toxicity profiles of multiple novel radiosensitisers targeting DNA repair proteins in patients treated with sequential chemoradiotherapy. Time-to-event continual reassessment will facilitate efficient dose-finding.

Improving radio-chemotherapy efficacy of prostate cancer by co-deliverying docetaxel and dbait with biodegradable nanoparticles

Combining DNA damage repair inhibitors and chemotherapeutic agents is an emerging strategy in cancer treatment. In this study, we engineered the polycation nanoparticle (NP), which co-encapsulated DNA damage repair inhibitor Dbait and chemotherapeutic drug Docetaxel (Dtxl), using H1 nanopolymer (folate--polyethylenimine600-cyclodextrin), and the size of H1/Dbait/Dtxl was about 117 nm. We demonstrated that H1/Dbait/Dtxl enhanced the efficiency of radio-chemotherapy in prostate cancer cells by CCK-8 assay and colony-forming assay. Importantly, the improvement of radio-chemotherapy of H1/Dbait/Dtxl in prostate cancer was also validated in vivo, and the NP did not have a high toxicity profile. The results of immunohistochemistry and western blot supported that the improved therapeutic efficacy was through inhibiting DNA damage repair signalling pathway. Our study supports further investigations using NP to co-deliver DNA damage repair inhibitors and chemotherapeutics to improve the therapeutic efficacy of cancer.