Subtle Alterations in Microtubule Assembly Dynamics by Br-TMB-Noscapine Strongly Suppress Triple-Negative Breast Cancer Cell Viability Without Mitotic Arrest

9-PAN promotes tubulin- and ROS-mediated cell death in human triple-negative breast cancer cells

OBJECTIVES

To examine the antiproliferative effect of a rationally designed, novel noscapine analogue, 9-((perfluorophenyl)methylene) aminonoscapine, '9-PAN') on MDA-MB-231 breast cancer cell line, and to elucidate the underlying mechanism of action.

METHODS

The rationally designed Schiff base-containing compound, 9-PAN, was characterized using IR, NMR and mass spectra analysis. The effect of the compound on cell viability was studied using an MTT assay. Cell cycle and cell death analyses were performed using flow cytometry. Binding interactions of 9-PAN with tubulin were studied using spectrofluorometry. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were investigated using the probes, DCFDA and rhodamine-123, respectively. Immunofluorescence imaging was used to visualize cellular microtubules.

KEY FINDINGS

9-PAN inhibited cell proliferation (IC₅₀ of 20 ± 0.3 µm) and colony formation (IC₅₀ , 6.2 ± 0.3 µm) by arresting the cells at G₂ /M phase of the cell cycle. It bound to tubulin in a concentration-dependent manner without considerably altering the tertiary conformation of the protein or the polymer mass of the microtubules in vitro. The noscapinoid substantially damaged cellular microtubule network and induced cell death, facilitated by elevated levels of ROS.

CONCLUSIONS

9-PAN exerts its antiproliferative effect by targeting tubulin and elevating ROS level in the cells.

Tubulin- and ROS-dependent antiproliferative mechanism of a potent analogue of noscapine, N-propargyl noscapine

AIM

To rationally-design, synthesize, characterize, biologically evaluate, and to elucidate the anticancer mechanism of action of a novel analogue of noscapine, N-propargyl noscapine (NPN), as a potential drug candidate against triple-negative breast cancer (TNBC).

MATERIALS AND METHODS

After the synthesis and IR, ¹H, ¹³C NMR and mass spectral characterization of NPN, its antiproliferative efficacy against different cancer cell lines was investigated using Sulforhodamine B assay. Cell cycle progression was analysed using flow cytometry. The drug-tubulin interactions were studied using tryptophan-quenching assay, ANS-binding assay, and colchicine-binding assay. Immunofluorescence imaging was used to examine the effect of NPN on cellular microtubules. Levels of reactive oxygen species (ROS), loss of mitochondrial membrane potential (MMP), and cell death were studied by staining the cells with DCFDA, Rhodamine 123, and acridine orange/ethidium bromide, respectively.

KEY FINDINGS

NPN strongly inhibited the viability (IC₅₀, 1.35 ± 0.2 μM) and clonogenicity (IC₅₀, 0.56 ± 0.06 μM) of the TNBC cell line, MDA-MB-231, with robust G₂/M arrest. In vitro, the drug bound to tubulin and disrupted the latter's structural integrity and promoted colchicine binding to tubulin. NPN triggered an unusual form of microtubule disruption in cells, repressed recovery of cold-depolymerized cellular microtubules and suppressed their dynamicity. These effects on microtubules were facilitated by elevated levels of ROS and loss of MMP.

SIGNIFICANCE

NPN can be explored further as a chemotherapeutic agent against TNBC.

Synthesis and Pharmacological Evaluation of Noscapine-Inspired 5-Substituted Tetrahydroisoquinolines as Cytotoxic Agents

A series of 5-substituted tetrahydroisoquinolines was synthesized via a 10-step linear synthesis to assess whether replacement of noscapine's southern isobenzofuranone with other moieties resulted in retained cytotoxic activity. One such molecule, 18g, bearing a para-methoxybenzyl functionality with N-ethylcarbamoyl substitution, produced cell-cycle arrest at the G2/M phase with an EC₅₀ of 2.7 μM in the MCF-7 breast-cancer cell line, a 7-fold increase compared with that of noscapine (5). This molecule had similar activity (EC₅₀ of 2.5 μM) against the resistant NCI/Adr^RES cell line, demonstrating its potential to overcome or avert known resistance mechanisms, unlike current cytotoxic agents. Compound 18g was found to modify the drug-efflux activity of P-gp and, in combination studies, potentiate the antiproliferative activity of vinblastine. These results provide insights into structural modifications to noscapine that will guide future development toward more potent cytotoxic agents that are active against resistant cancer cells.

The potential to treat lung cancer via inhalation of repurposed drugs

Lung cancer is a highly invasive and prevalent disease with ineffective first-line treatment and remains the leading cause of cancer death in men and women. Despite the improvements in diagnosis and therapy, the prognosis and outcome of lung cancer patients is still poor. This could be associated with the lack of effective first-line oncology drugs, formation of resistant tumors and non-optimal administration route. Therefore, the repurposing of existing drugs currently used for different indications and the introduction of a different method of drug administration could be investigated as an alternative to improve lung cancer therapy. This review describes the rationale and development of repositioning of drugs for lung cancer treatment with emphasis on inhalation. The review includes the current progress of repurposing non-cancer drugs, as well as current chemotherapeutics for lung malignancies via inhalation. Several potential non-cancer drugs such as statins, itraconazole and clarithromycin, that have demonstrated preclinical anti-cancer activity, are also presented. Furthermore, the potential challenges and limitations that might hamper the clinical translation of repurposed oncology drugs are described.