*Review* **Inhibition of DNA Repair in Cancer Therapy: Toward a Multi-Target Approach**

#### **Samuele Lodovichi <sup>1</sup> , Tiziana Cervelli <sup>2</sup> , Achille Pellicioli 1,\* and Alvaro Galli 2,\***


**\*** Correspondence: achille.pellicioli@unimi.it (A.P.); alvaro.galli@ifc.cnr.it (A.G.)

Received: 4 August 2020; Accepted: 8 September 2020; Published: 12 September 2020

**Abstract:** Alterations in DNA repair pathways are one of the main drivers of cancer insurgence. Nevertheless, cancer cells are more susceptible to DNA damage than normal cells and they rely on specific functional repair pathways to survive. Thanks to advances in genome sequencing, we now have a better idea of which genes are mutated in specific cancers and this prompted the development of inhibitors targeting DNA repair players involved in pathways essential for cancer cells survival. Currently, the pivotal concept is that combining the inhibition of mechanisms on which cancer cells viability depends is the most promising way to treat tumorigenesis. Numerous inhibitors have been developed and for many of them, efficacy has been demonstrated either alone or in combination with chemo or radiotherapy. In this review, we will analyze the principal pathways involved in cell cycle checkpoint and DNA repair focusing on how their alterations could predispose to cancer, then we will explore the inhibitors developed or in development specifically targeting different proteins involved in each pathway, underscoring the rationale behind their usage and how their combination and/or exploitation as adjuvants to classic therapies could help in patients clinical outcome.

**Keywords:** cell cycle checkpoint; DNA repair; cancer therapy; DNA repair inhibitors; synthetic lethality
