Becatecarin

Enrichment for therapy-resistant cancer stem cells hampers the treatment of triple-negative breast cancer. Targeting these cells via suppression of Notch signalling can be a potential therapeutic strategy. This study aimed to uncover the mode of action of a new indolocarbazole alkaloid loonamycin A against this incurable disease.

The anticancer effects were examined in triple-negative breast cancer cells using in vitro methods, including cell viability and proliferation assays, wound-healing assay, flow cytometry and mammosphere formation assay. RNA-seq technology was used to analyse the gene expression profiles in loonamycin A-treated cells. Real-time RT-PCR and western blot were to evaluate the inhibition of Notch signalling.

Loonamycin A has stronger cytotoxicity than its structural analog rebeccamycin. Besides inhibiting cell proliferation and migration, loonamycin A reduced CD44high/CD24low/− sub-population, mammosphere formation, as well as the expression of stemness-associated genes. Co-administration of loonamycin A enhanced antitumour effects of paclitaxel by inducing apoptosis. RNA sequencing results showed that loonamycin A treatment caused the inhibition of Notch signalling, accompanied by the decreased expression of Notch1 and its targeted genes.

These results reveal a novel bioactivity of indolocarbazole-type alkaloids and provide a promising Notch-inhibiting small molecular candidate for triple-negative breast cancer therapy.

Lentzea aerocolonigenes, as an actinomycete, is a natural producer of the antibiotic and antitumoral drug rebeccamycin. Due to the filamentous cellular morphology handling in cultivations is challenging; therefore, morphology engineering techniques are mandatory to enhance productivity. One promising approach described in the literature is the addition of mineral particles in the micrometer range to precisely adjust cellular morphology and the corresponding product synthesis (microparticle-enhanced cultivation, MPEC). Glass microparticles are introduced in this study as a novel supplementation type for bioprocess intensification in filamentous organisms. Several investigations were conducted to screen for an optimal particle setup, including particle size and concentration regarding their impact and effects on enhanced productivity, microparticle incorporation behavior into the biopellets, the viability of pellets, and morphological changes. Glass microparticles (10 g·L^-1) with a median diameter of 7.9 µm, for instance, induced an up to fourfold increase in product synthesis accompanied by overall enhanced viability of biomass. Furthermore, structural elucidations showed that biopellets isolated from MPEC tend to have lower hyphal density than unsupplemented control pellets. In this context, oxygen microprofiling was conducted to better understand how internal structural changes interwind with oxygen supply into the pellets. Here, the resulting oxygen profiles are of a contradictive trend of steeper oxygen consumption with increasing glass microparticle supplementation. Eventually, MPEC was combined with another promising cultivation strategy, the supplementation of soy lecithin (7.5 g·L^-1), to further increase the cultivation performance. A combination of both techniques in an optimized setup resulted in a rebeccamycin concentration of 213 mg·L^-1 after 10 days of cultivation, the highest value published so far for microparticle-supplemented shake flask cultivations of L. aerocolonigenes.