Assessment of Phenylboronic Acid Nitrogen Mustards as Potent and Selective Drug Candidates for Triple-Negative Breast Cancer

Dual-responsive probe and DNA interstrand crosslink precursor target the unique redox status of cancer cells

Elevated GSH and H2O2 in cancer cells is sometimes doubted due to their contrary reactivities. Here, we construct a dual-responsive fluorescent probe to confirm the conclusion, and employ this to exploit a redox-inducible DNA interstrand crosslink (ICL) precursor. It crosslinks DNA upon activation by GSH and H2O2, affording an alternative dual-responsive strategy.

H2 O2 -Inducible DNA Cross-linking Agents Capable of Releasing Multiple DNA Alkylators as Anticancer Prodrugs

Three compounds with arylboronate esters conjugated with two equivalent nitrogen mustards [bis(2-chloroethyl)methylamine, HN2] have been synthesized and characterized. These inactive small molecules selectively react with H2 O2 to produce multiple DNA cross-linkers, such as two HN2 molecules alongside a bisquinone methide (bisQM), leading to efficient DNA ICL formation. In comparison to other amine functional groups, using HN2 as a leaving group greatly improves the DNA cross-linking efficiency of these arylboronate esters as well as cellular activity. The introduction of HN2 in these arylboronate ester analogues favored the generation of bisQM that can directly cross-link DNA. Two equivalents of HN2 are also generated from these compounds upon treatment with H2 O2 , which directly produces DNA ICL products. The cumulative effects of HN2 and bisQM on DNA cross-linking makes these molecules highly effective H2 O2 -inducible DNA ICL agents. The three compounds with HN2 as a leaving group showed greatly enhanced cytotoxicity towards cancer cells in comparison to those containing trimethyl amine as a leaving group. This provides an effective strategy for further design of novel potential ROS-activated anticancer prodrugs.

Hydrogen Peroxide-Inducible PROTACs for Targeted Protein Degradation in Cancer Cells

Proteolysis-targeting chimeras (PROTACs) provide a powerful technique to degrade targeted proteins utilizing the cellular ubiquitin-proteasome system. The major concern is the host toxicity resulting from their poor selectivity. Inducible PROTACs responding to exogenous stimulus, such as light, improve their specificity, but it is difficult for photo-activation in deep tissues. Herein, we develop H2 O2 -inducible PROTAC precursors 2/5, which can be activated by endogenous H2 O2 in cancer cells to release the active PROTACs 1/4 to effectively degrade targeted proteins. This results in the intended cytotoxicity towards cancer cells while targeted protein in normal cells remains almost unaffected. The higher Bromodomain-containing protein 4 (BRD4) degradation activity and cytotoxicity of 2 towards cancer cells is mainly due to the higher endogenous concentration of H2 O2 in cancer cells (A549 and H1299), characterized by H2 O2 -responsive fluorescence probe 3. Western blot assays and cytotoxicity experiments demonstrate that 2 degrades BRD4 more effectively and is more cytotoxic in H2 O2 -rich cancer cells than in H2 O2 -deficient normal cells. This method is also extended to estrogen receptor (ER)-PROTAC precursor 5, showing H2 O2 -dependent ER degradation ability. Thus, we establish a novel strategy to induce targeted protein degradation in a H2 O2 -dependent way, which has the potential to improve the selectivity of PROTACs.

Boron- and phosphorus-containing molecular/nano platforms: exploiting pathological redox imbalance to fight cancer

Cancer is currently the second leading cause of death globally. Despite multidisciplinary efforts, therapies to fight various types of cancer still remain inefficient. Reducing high recurrence rates and mortality is thus a major challenge to tackle. In this context, redox imbalance is an undervalued characteristic of cancer. However, it may be targeted by boron- and phosphorus-containing materials to selectively or systemically fight cancer. In particular, boron and phosphorus derivatives are attractive building blocks for rational drug discovery due to their unique and wide regioselective chemistry, high degree of tuneability and chemical stability. Thus, they can be meticulously employed to access tunable molecular platforms to selectively exploit the redox imbalance of cancer cells towards necrosis/apoptosis. This field of research holds a remarkable potential; nevertheless, it is still in its infancy. In this mini-review, we underline recent advances in the development of boron- or phosphorus-derivatives as molecular/nano platforms for rational anticancer drug design. Our goal is to provide comprehensive information on different methodologies that bear an outstanding potential to further develop this very promising field of research.

Recent Advances in Hydrogen Peroxide Responsive Organoborons for Biological and Biomedical Applications

Hydrogen peroxide is the most stable reactive oxygen species generated endogenously, participating in numerous physiological processes and abnormal pathological conditions. Mounting evidence suggests that a higher level of H₂ O₂ exists in various disease conditions. Thus, H₂ O₂ functions as an ideal target for site-specific bioimaging and therapeutic targeting. The unique reactivity of organoborons with H₂ O₂ provides a method for developing chemoselective molecules for biological and biomedical applications. This review highlights the design and application of boron-derived molecules for H₂ O₂ detection, and the utility of boron moieties toward masking reactive compounds leading to the development of metal prochelators and prodrugs for selectively delivering an active species at the target sites with elevated H₂ O₂ levels. Additionally, the emergence of H₂ O₂ -responsive theranostic agents consisting of both therapeutic and diagnostic moieties in one integrated system are discussed. The purpose of this review is to provide a better understanding of the role of boron-derived molecules toward biological and pharmacological applications.