Probing the Mechanism of Action of Cry41Aa on HepG2 through the Establishment of a Resistant Subline

Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after being proteolytically activated. To better understand the mechanism of action of Cry41Aa, we evolved resistance in HepG2 cells through repeated exposure to increasing doses of the toxin. Concentrations of Cry41Aa that killed over 50% of the parental HepG2 cells had no significant effect on the viability of the resistant cells and did not induce either pore formation or p38 phosphorylation (both characteristic features of pore-forming toxins). Preliminary RNA sequencing data identified AQP9 as a potential mediator of resistance, but extensive investigations failed to show a causal link and did not support an enhanced cell repair process as the resistance mechanism.

The role of membrane-bound metal ions in toxicity of a human cancer cell-active pore-forming toxin Cry41Aa from Bacillus thuringiensis

Bacillus thuringiensis crystal (Cry) proteins, used for decades as insecticidal toxins, are well known to be toxic to certain insects, but not to mammals. A novel group of Cry toxins called parasporins possess a strong cytocidal activity against some human cancer cells. Cry41Aa, or parasporin3, closely resembles commercially used insecticidal toxins and yet is toxic to the human hepatic cancer cell line HepG2, disrupting membranes of susceptible cells, similar to its insecticidal counterparts. In this study, we explore the protective effect that the common divalent metal chelator EGTA exerts on Cry41Aa's activity on HepG2 cells. Our results indicate that rather than interfering with a signalling pathway as a result of chelating cations in the medium, the chelator prevented the toxin's interaction with the membrane, and thus the subsequent steps of membrane damage and p38 phosphorylation, by removing cations bound to plasma membrane components. BAPTA and DTPA also inhibited Cry41Aa toxicity but at higher concentrations. We also show for the first time that Cry41Aa induces pore formation in planar lipid bilayers. This activity is not altered by EGTA, consistent with a biological context of chelation. Salt supplementation assays identified Ca²⁺, Mn²⁺ and Zn²⁺ as being able to reinstate Cry41Aa activity. Our data suggest the existence of one or more metal cation-dependent receptors in the Cry41Aa mechanism of action.

The effect of a new syringe design on the ability of rheumatoid arthritis patients to inject a biological medication

Self-administration of new biological medications can be difficult for Rheumatoid Arthritis patients with functional impairment and hand and dexterity limitation. Twenty-three Rheumatoid Arthritis (RA) patients participated in this study to compare preferences and injection forces using a conventional syringe and a new ergonomically designed syringe. Injection force measurements were collected in two ways: a) isometric forces, with the syringes' plungers in fixed positions (depressed halfway and fully depressed), and b) forces exerted during injection of the medication. Subjects' grip and pinch strengths were measured. A perception questionnaire gauged subjects' impressions and preferences. Subjects were capable of exerting significantly higher isometric forces using the new syringe with the plunger fixed both halfway and fully depressed. During injection of the medication, peak and mean injection forces were significantly higher, and duration was shorter, when using the new syringe. Subjects rated the new syringe higher on all twenty attributes on preference and performance. Therefore, it is expected that the new syringe will benefit self-administration of medication injection for RA patients.