Radha Charan Dash

REV7 is an adaptor protein that mediates protein–protein interactions (PPIs) in DNA damage response and cell cycle control. REV7 functions as a subunit of the translesion synthesis (TLS) DNA polymerase POLζ, which is involved in the replicative bypass of DNA lesions. REV7 is also a component of the shieldin complex, which mediates the choice of pathway for DNA double‐stranded break (DSB) repair. TLS promotes cancer cell survival after DNA damage and serves as a mechanism through which cancers develop acquired chemoresistance. DSB repair helps cancers mitigate DNA breaks induced by radiation; therefore, inhibition of REV7 PPIs has emerged as a therapeutic strategy. We performed a docking‐based virtual screen to identify compounds predicted to disrupt PPIs between REV7 and the REV7‐binding motifs (RBMs) found in the REV3 subunit of POLζ (TLS) and the SHLD3 subunit of shieldin (DSB repair). Biochemical analysis of a promising hit compound and several analogues demonstrated the ability of this scaffold to disrupt the REV7/RBM _REV3 PPI. Several REV7 inhibitors sensitize human cancer cells to radiation treatment, identifying these compounds as a new class of TLS and DSB‐repair targeted anticancer drugs with potential as adjuvant therapies to improve the efficacy of genotoxic cancer therapies.

The enterovirus (EV) genus includes a number of important human and animal pathogens. EV-A71, EV-D68, poliovirus (PV), and coxsackievirus (CV) outbreaks have affected millions worldwide causing a range of upper respiratory, skin, neuromuscular diseases, including acute flaccid myelitis, and hand-foot-and-mouth disease. There are no FDA-approved anti-viral therapeutics for these enteroviruses. In this study, we describe novel broad spectrum anti-viral compounds targeting the conserved non-structural viral protein 2C that have low micro-molar to nanomolar IC ₅₀ values. The selection of resistant mutants resulted in amino acid substitutions in the viral capsid protein, implying a role for 2C in capsid assembly, as has been seen in PV. The assembly and encapsidation stages of the viral life cycle are not fully understood and the inhibitors reported here could be useful probes in understanding these processes.

Translesion synthesis (TLS) is an error-prone DNA damage tolerance mechanism used by actively replicating cells to copy past DNA lesions and extend the primer strand. TLS ensures that cells continue replication in the presence of damaged DNA bases, albeit at the expense of an increased mutation rate. Recent studies have demonstrated a clear role for TLS in rescuing cancer cells treated with first-line genotoxic agents by allowing them to replicate and survive in the presence of chemotherapy-induced DNA lesions. The importance of TLS in both the initial response to chemotherapy and the long-term development of acquired resistance has allowed it to emerge as an interesting target for small molecule drug discovery. Proper TLS function is a complicated process involving a heteroprotein complex that mediates multiple attachment and switching steps through several protein–protein interactions (PPIs). In this review, we briefly describe the importance of TLS in cancer and provide an in-depth analysis of key TLS PPIs, focusing on key structural features at the PPI interface while also exploring the potential druggability of each key PPI.

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance mechanism that replaces the replicative DNA polymerase with a specialized, low-fidelity TLS DNA polymerase that can copy past DNA lesions during active replication. Recent studies have demonstrated a primary role for TLS in replicating past DNA lesions induced by first-line genotoxic agents, resulting in decreased efficacy and acquired chemoresistance. With this in mind, targeting TLS as a combination strategy with first-line genotoxic agents has emerged as a promising approach to develop a new class of anti-cancer adjuvant agents. Areas covered: In this review, we provide a brief background on TLS and its role in cancer. We also discuss the identification and development of inhibitors that target various TLS DNA polymerases or key protein-protein interactions (PPIs) in the TLS machinery. Expert opinion: TLS inhibitors have demonstrated initial promise; however, their continued study is essential to more fully understand the clinical potential of this emerging class of anti-cancer chemotherapeutics. It will be important to determine whether a specific protein involved in TLS is an optimal target. In addition, an expanded understanding of what current genotoxic chemotherapies synergize with TLS inhibitors will guide the clinical strategies for devising combination therapies.

While loss-of-function mutations in the ATRX gene have been implicated as a driving force for a variety of pediatric brain tumors, as well as pancreatic neuroendocrine tumors, the role of ATRX in gene regulation and oncogenic development is not well-characterized. The ADD domain of ATRX (ATRX_ADD) localizes the protein to chromatin by specifically binding to the histone H3 tail. This domain is also a primary region that is mutated in these cancers. The overall goal of our studies was to utilize a variety of techniques (experimental and computational) to probe the H3:ATRX_ADD protein-protein interaction (PPI). We developed two biochemical assays that can be utilized to study the interaction. These assays were utilized to experimentally validate and expand upon our previous computational results. We demonstrated that the three anchor points in the H3 tail (A1, K4, and K9) are all essential for high affinity binding and that disruption of more than one contact region will be required to develop a small molecule that disrupts the PPI. Our approach in this study could be applied to other domains of ATRX, as well as PPIs between other distinct proteins.

SUMMARY: The replication stress response which serves as an anti-cancer barrier is activated not only by DNA damage and replication obstacles, but also oncogenes, mystifying how cancer evolves. Here, we identify that oncogene expression, similar to cancer therapies, induces single stranded DNA (ssDNA) gaps that reduce cell fitness, unless suppressed by translesion synthesis (TLS). DNA fiber analysis and electron microscopy reveal that TLS restricts replication fork slowing, reversal, and fork degradation without inducing replication fork gaps. Evidence that TLS gap suppression is fundamental to cancer, a small molecule inhibitor targeting the TLS factor, REV1, not only disrupts DNA replication and cancer cell fitness, but also synergizes with gap-inducing therapies. This work illuminates that gap suppression during replication is critical for cancer cell fitness and therefore a targetable vulnerability.

Translesion synthesis (TLS) has emerged as a mechanism through which several forms of cancer develop acquired resistance to first‐line genotoxic chemotherapies by allowing replication to continue in the presence of damaged DNA. Small molecules that inhibit TLS hold promise as a novel class of anticancer agents that can serve to enhance the efficacy of these front‐line therapies. We previously used a structure‐based rational design approach to identify the phenazopyridine scaffold as an inhibitor of TLS that functions by disrupting the protein–protein interaction (PPI) between the C‐terminal domain of the TLS DNA polymerase Rev1 (Rev1‐CT) and the Rev1 interacting regions (RIR) of other TLS DNA polymerases. To continue the identification of small molecules that disrupt the Rev1‐CT/RIR PPI, we generated a pharmacophore model based on the phenazopyridine scaffold and used it in a structure‐based virtual screen. In vitro analysis of promising hits identified several new chemotypes with the ability to disrupt this key TLS PPI. In addition, several of these compounds were found to enhance the efficacy of cisplatin in cultured cells, highlighting their anti‐TLS potential.

The Food and Drug Administration-approved antifungal agent, itraconazole (ITZ), has been increasingly studied for its novel biological properties. In particular, ITZ inhibits the hedgehog (Hh) signaling pathway and has the potential to serve as an anticancer chemotherapeutic against several Hh-dependent malignancies. We have extended our studies on ITZ analogues as Hh pathway inhibitors through the design, synthesis, and evaluation of novel des-triazole ITZ analogues that incorporate modifications to the triazolone/side chain region of the scaffold. Our overall results suggest that the triazolone/side chain region can be replaced with various functionalities (hydrazine carboxamides and meta-substituted amides) resulting in improved potency when compared to ITZ. Our studies also indicate that the stereochemical orientation of the dioxolane ring is important for both potent Hh pathway inhibition and compound stability. Finally, our studies suggest that the ITZ scaffold can be successfully modified in terms of functionality and stereochemistry to further improve its anti-Hh potency and physicochemical properties.

An improved and rapid green synthesis of N ‐alkyl/aryl piperazine hydrochlorides using synergistic coupling of hydrated Task Specific Ionic Liquid ([BbIm]OH) and Microwave Irradiation (MWI) has been described. The protocol worked well with good yields for electron withdrawing as well as electron donating groups in aryl amines to provide the respective aryl piperazine hydrochlorides. Presence of other labile groups like hydroxyl and thiol in the aryl amines remained unaffected. The said TSIL could be reused upto five cycles without an appreciable loss of the catalytic activity. It is proposed that [BbIm]OH along with a water molecule is able to catalyse the reaction due to symphoria. The proposed mechanism is supported by DFT and molecular dynamics studies. The use of hydrated TSIL like ([BbIm]OH) as reaction media may open new gates in green organic syntheses.