Repurposing Drugs for Cancer Radiotherapy: Early Successes and Emerging Opportunities

Inorganic Nanoparticles as Radiosensitizers for Cancer Treatment

Nanotechnology has expanded what can be achieved in our approach to cancer treatment. The ability to produce and engineer functional nanoparticle formulations to elicit higher incidences of tumor cell radiolysis has resulted in substantial improvements in cancer cell eradication while also permitting multi-modal biomedical functionalities. These radiosensitive nanomaterials utilize material characteristics, such as radio-blocking/absorbing high-Z atomic number elements, to mediate localized effects from therapeutic irradiation. These materials thereby allow subsequent scattered or emitted radiation to produce direct (e.g., damage to genetic materials) or indirect (e.g., protein oxidation, reactive oxygen species formation) damage to tumor cells. Using nanomaterials that activate under certain physiologic conditions, such as the tumor microenvironment, can selectively target tumor cells. These characteristics, combined with biological interactions that can target the tumor environment, allow for localized radio-sensitization while mitigating damage to healthy cells. This review explores the various nanomaterial formulations utilized in cancer radiosensitivity research. Emphasis on inorganic nanomaterials showcases the specific material characteristics that enable higher incidences of radiation while ensuring localized cancer targeting based on tumor microenvironment activation. The aim of this review is to guide future research in cancer radiosensitization using nanomaterial formulations and to detail common approaches to its treatment, as well as their relations to commonly implemented radiotherapy techniques.

The role of bacteria and its derived biomaterials in cancer radiotherapy

Bacteria-mediated anti-tumor therapy has received widespread attention due to its natural tumor-targeting ability and specific immune-activation characteristics. It has made significant progress in breaking the limitations of monotherapy and effectively eradicating tumors, especially when combined with traditional therapy, such as radiotherapy. According to their different biological characteristics, bacteria and their derivatives can not only improve the sensitivity of tumor radiotherapy but also protect normal tissues. Moreover, genetically engineered bacteria and bacteria-based biomaterials have further expanded the scope of their applications in radiotherapy. In this review, we have summarized relevant researches on the application of bacteria and its derivatives in radiotherapy in recent years, expounding that the bacteria, bacterial derivatives and bacteria-based biomaterials can not only directly enhance radiotherapy but also improve the anti-tumor effect by improving the tumor microenvironment (TME) and immune effects. Furthermore, some probiotics can also protect normal tissues and organs such as intestines from radiation via anti-inflammatory, anti-oxidation and apoptosis inhibition. In conclusion, the prospect of bacteria in radiotherapy will be very extensive, but its biological safety and mechanism need to be further evaluated and studied.

Aspirin Inhibits Fibronectin Expression and Reverses Fibronectin-Mediated Cell Invasiveness by Activating Akt Signaling in Preeclampsia

Preeclampsia is a severe gestational hypertensive disorder that may lead to maternal multiple organ dysfunction and adverse fetal outcomes. Aspirin provides a protective effect by reducing the risk of preeclampsia; however, its mechanism of action is unclear. Fibronectin (FN) is a key factor in cell motility and is associated with preeclampsia. Here, we demonstrated that cellular FN expression was elevated in the placenta of preeclamptic patients. The functional roles of plasma and cellular FN in trophoblasts were investigated by treating HTR-8/SVneo cells with exogenous recombinant human FN protein (rhFN) and siRNA, respectively. Trophoblast migration and invasion were inhibited by rhFN and facilitated by FN knockdown. Moreover, rhFN activated ERK and Akt signaling in trophoblasts, and FN-suppressed cell motility was rescued by ERK and/or Akt inhibitors. In this study, aspirin suppressed trophoblast cellular FN expression and reversed FN-mediated cell functions, including cell migration, invasion, and ERK/Akt signal changes. Taken together, the results of this study revealed the effects of FN on trophoblast motility and signaling; aspirin inhibits FN expression and reverses FN-mediated trophoblast biology. These results provide a drug mechanism for disease prevention and a target for preeclampsia intervention.

Aspirin Restores Radiosensitivity in Cervical Cancer Cells by Inducing Mitotic Catastrophe through Downregulating G2/M Effectors

BACKGROUND/AIM

Compromised cell-cycle checkpoint is a major obstacle for rendering radiotherapeutic success of radioresistant cells. Aspirin (ASA), an anti-inflammatory agent was repurposed previously for improving radiotherapy by limiting radiation toxicity. However, the underlying mechanism was unclear. The present study aimed to identify the mechanism of ASA mediated reversal of radioresistance in cervical cancer cells.

METHODS

Radioresistant subline SiHa/RR was developed from parental cervical squamous carcinoma cell line SiHa by chronic fractionated irradiation (IR). The radioresistance property of SiHa/RR was confirmed by clonogenic assay. Alteration in cell-cycle by ASA was determined by flow cytometry. ASA induced nuclear damage as consequence of mitotic catastrophe was confirmed by microscopic observation. The interaction between ASA and G2/M regulators was explored through in silico docking analysis and expressional change of them was affirmed by western blotting. Immunofluorescence study to examine Aurora Kinase A localization in presence and absence of ASA treatment was conducted. Finally the radiosensitizing ability of ASA was verified by apoptotic parameters (flow cytometrically and by western blotting).

RESULT

Higher colony forming ability of SiHa/RR compared to SiHa became restrained upon ASA (5μM) treatment prior to IR. Flow cytometric analysis of ASA treated cells showed increased G2/M population followed by enlargement of cells displaying giant multinucleated morphology; typical characteristics of mitotic catastrophe. Underlying noteworthy mechanisms involved decreased expressions of G2/M regulatory proteins (Cyclin B1, CDK1, Aurora A Kinase, pAurora A Kinase) in IR/ASA along with inhibiting nuclear localization of Aurora Kinase A in SiHa/RR. Docking results also supported the findings. Prolonged treatment (12 h) with ASA led to apoptosis by altering expressions of Bcl2, Bax and Cytochrome C; which was achieved through the event of mitotic catastrophe.

CONCLUSION

This work established that G2/M arrest and mitotic catastrophe can be considered as the principle mechanism of restoration of radiosensitivity in SiHa/RR by ASA pretreatment.

Repurposing Pharmaceuticals Previously Approved by Regulatory Agencies to Medically Counter Injuries Arising Either Early or Late Following Radiation Exposure

The increasing risks of radiological or nuclear attacks or associated accidents have served to renew interest in developing radiation medical countermeasures. The development of prospective countermeasures and the subsequent gain of Food and Drug Administration (FDA) approval are invariably time consuming and expensive processes, especially in terms of generating essential human data. Due to the limited resources for drug development and the need for expedited drug approval, drug developers have turned, in part, to the strategy of repurposing agents for which safety and clinical data are already available. Approval of drugs that are already in clinical use for one indication and are being repurposed for another indication is inherently faster and more cost effective than for new agents that lack regulatory approval of any sort. There are four known growth factors which have been repurposed in the recent past as radiomitigators following the FDA Animal Rule: Neupogen, Neulasta, Leukine, and Nplate. These four drugs were in clinic for several decades for other indications and were repurposed. A large number of additional agents approved by various regulatory authorities for given indications are currently under investigation for dual use for acute radiation syndrome or for delayed pathological effects of acute radiation exposure. The process of drug repurposing, however, is not without its own set of challenges and limitations.

Melanoma Cell Intrinsic GABAA Receptor Enhancement Potentiates Radiation and Immune Checkpoint Inhibitor Response by Promoting Direct and T Cell-Mediated Antitumor Activity

PURPOSE

Most patients with metastatic melanoma show variable responses to radiation therapy and do not benefit from immune checkpoint inhibitors. Improved strategies for combination therapy that leverage potential benefits from radiation therapy and immune checkpoint inhibitors are critical.

METHODS AND MATERIALS

We analyzed metastatic melanoma tumors in the TCGA cohort for expression of genes coding for subunits of type A γ-aminobutyric acid (GABA) receptor (GABA_AR), a chloride ion channel and major inhibitory neurotransmitter receptor. Electrophysiology was used to determine whether melanoma cells possess intrinsic GABA_AR activity. Melanoma cell viability studies were conducted to test whether enhancing GABA_AR mediated chloride transport using benzodiazepine-impaired viability. A syngeneic melanoma mouse model was used to assay the effect of benzodiazepine on tumor volume and its ability to potentiate radiation therapy or immunotherapy. Treated tumors were analyzed for changes in gene expression by RNA sequencing and presence of tumor-infiltrating lymphocytes by flow cytometry.

RESULTS

Genes coding for subunits of GABA_ARs express functional GABA_ARs in melanoma cells. By enhancing GABA_AR-mediated anion transport, benzodiazepines depolarize melanoma cells and impair their viability. In vivo, benzodiazepine alone reduces tumor growth and potentiates radiation therapy and α-PD-L1 antitumor activity. The combination of benzodiazepine, radiation therapy, and α-PD-L1 results in near complete regression of treated tumors and a potent abscopal effect, mediated by increased infiltration of polyfunctional CD8⁺ T cells. Treated tumors show expression of cytokine-cytokine receptor interactions and overrepresentation of p53 signaling.

CONCLUSIONS

This study identifies an antitumor strategy combining radiation and/or an immune checkpoint inhibitor with modulation of GABA_ARs in melanoma using benzodiazepine.

Adrenergic stress constrains the development of anti-tumor immunity and abscopal responses following local radiation

The abscopal effect following ionizing radiation therapy (RT) is considered to be a rare event. This effect does occur more frequently when combined with other therapies, including immunotherapy. Here we demonstrate that the frequency of abscopal events following RT alone is highly dependent upon the degree of adrenergic stress in the tumor-bearing host. Using a combination of physiologic, pharmacologic and genetic strategies, we observe improvements in the control of both irradiated and non-irradiated distant tumors, including metastatic tumors, when adrenergic stress or signaling through β-adrenergic receptor is reduced. Further, we observe cellular and molecular evidence of improved, antigen-specific, anti-tumor immune responses which also depend upon T cell egress from draining lymph nodes. These data suggest that blockade of β2 adrenergic stress signaling could be a useful, safe, and feasible strategy to improve efficacy in cancer patients undergoing radiation therapy.

Redirecting extracellular proteases to molecularly guide radiosensitizing drugs to tumors

Patients with advanced cancers are treated with combined radiotherapy and chemotherapy, however curability is poor and treatment side effects severe. Drugs sensitizing tumors to radiotherapy have been developed to improve cell kill, but tumor specificity remains challenging. To achieve tumor selectivity of small molecule radiosensitizers, we tested as a strategy active tumor targeting using peptide-based drug conjugates. We attached an inhibitor of the DNA damage response to antibody or cell penetrating peptides. Antibody drug conjugates honed in on tumor overexpressed cell surface receptors with high specificity but lacked efficacy when conjugated to the DNA damage checkpoint kinase inhibitor AZD7762. As an alternative approach, we synthesized activatable cell penetrating peptide scaffolds that accumulated within tumors based on matrix metalloproteinase cleavage. While matrix metalloproteinases are integral to tumor progression, they have proven therapeutically elusive. We harnessed these pro-tumorigenic extracellular proteases to spatially guide radiosensitizer drug delivery using cleavable activatable cell penetrating peptides. Here, we tested the potential of these two drug delivery platforms targeting distinct tumor compartments in combination with radiotherapy and demonstrate the advantages of protease triggered cell penetrating peptide scaffolds over antibody drug conjugates to deliver small molecule amine radiosensitizers.