Latent hematopoietic stem cell toxicity associated with protracted drug administration

Harnessing small extracellular vesicles for pro-oxidant delivery: novel approach for drug-sensitive and resistant cancer therapy

Multidrug resistance (MDR) is an inevitable clinical problem in chemotherapy due to the activation of abundant P-glycoprotein (P-gp) that can efflux drugs. Limitations of current cancer therapy highlight the need for the development of a comprehensive cancer treatment strategy, including drug-resistant cancers. Small extracellular vesicles (sEVs) possess significant potential in surmounting drug resistance as they can effectively evade the efflux mechanism and transport small molecules directly to MDR cancer cells. One mechanism mediating MDR in cancer cells is sustaining increased levels of reactive oxygen species (ROS) and maintenance of the redox balance with antioxidants, including glutathione (GSH). Herein, we developed GSH-depleting benzoyloxy dibenzyl carbonate (B2C)-encapsulated sEVs (BsEVs), which overcome the efflux system to exert highly potent anticancer activity against human MDR ovarian cancer cells (OVCAR-8/MDR) by depleting GSH to induce oxidative stress and, in turn, apoptotic cell death in both OVCAR-8/MDR and OVCAR-8 cancer cells. BsEVs restore drug responsiveness by inhibiting ATP production through the oxidation of nicotinamide adenine dinucleotide with hydrogen (NADH) and inducing mitochondrial dysfunction, leading to the dysfunction of efflux pumps responsible for drug resistance. In vivo studies showed that BsEV treatment significantly inhibited the growth of OVCAR-8/MDR and OVCAR-8 tumors. Additionally, OVCAR-8/MDR tumors showed a trend towards a greater sensitivity to BsEVs compared to OVCAR tumors. In summary, this study demonstrates that BsEVs hold tremendous potential for cancer treatment, especially against MDR cancer cells.

Toxicity testing using hematopoietic stem cell assays

For over 40 years, in vitro assays have been used to understand the complex system of hematopoiesis. Now, several of these assays are undergoing resurgence as scientists in academia and industry are discovering how these assays can be utilized in drug discovery and development. These assays use primary cells from various hematopoietic tissues in multiple species to provide high content information. While conditions in the human body cannot be completely reproduced in vitro, hematopoietic colony-forming cell assays are proving to be a clinically relevant tool to evaluate potential toxic effects of new compounds. The ability to use these assays as a replacement of, or in conjunction with, high-throughput screening assays and high priced in vivo assays can improve the success of the decision-making process, saving time and costs during drug development.

A New Approach to Evaluate the Total Reserve of Hematopoietic Progenitors after Acute Irradiation

Based on the capacity of certain hematopoietic growth factors to mobilize the hematopoietic progenitors from bone marrow to peripheral blood, we have investigated whether the number of progenitors that can be mobilized to peripheral blood after irradiation correlates with the radiation dose and reflects the total reserve of bone marrow progenitors that survive the exposure. In three different mouse strains, a close relationship was observed between the number of G-CSF mobilized progenitors and the radiation dose received by the animals. When G-CSF was replaced by one single injection of SD01 plus thrombopoietin, a similar relationship between the two parameters was observed, which fitted to the multitarget theoretical model. This treatment also promoted 50% survival in mice receiving a lethal dose of 9 Gy. The estimation of the total number of CFU-GM progenitors in the irradiated mice also allowed us to establish a good relationship between the number of progenitors that were mobilized to peripheral blood with respect to the global reserve of surviving progenitors. These results suggest that the quantification of mobilized hematopoietic progenitors would predict the severity and reversibility of the hematopoietic syndrome of irradiated victims, based on direct estimations of their global reserve of hematopoietic progenitors and stem cells.

In vitro and in vivo effects of acetyldinaline on murine megakaryocytopoiesis

PURPOSE

Acetyldinaline (CI-994) has shown preclinical efficacy in vitro and in vivo against solid tumor and leukemia cell lines. Since myelosuppression was the dose-limiting toxicity for acetyldinaline in preclinical and clinical studies, experiments were conducted to examine the in vitro and in vivo effects of acetyldinaline on murine megakaryocytic (CFU-meg) progenitor cells.

METHODS

Bone marrow and spleen cells from untreated mice were continuously exposed in vitro to acetyldinaline or dinaline in clonal assays. For the in vivo study, BDF(1) mice were dosed orally with 50 mg/kg acetyldinaline every day for 14 days.

RESULTS

Both acetyldinaline and dinaline induced an in vitro dose-dependent decrease in CFU-meg colonies derived from either the spleen or bone marrow. Splenic CFU-meg were more sensitive in vitro to acetyldinaline and dinaline than their marrow counterparts. In the in vivo experiments, platelet counts decreased throughout the 14-day dosing period and had returned to normal by day 18. Marrow and spleen CFU-meg declined after the first dose but had recovered by days 4 and 7, respectively. Elevated splenic CFU-meg counts were observed through day 20, 6 days after dosing ended. Recovery of platelet counts in treated mice was associated with increases in both marrow and splenic CFU-meg.

CONCLUSIONS

There was differential in vitro toxicity of acetyldinaline to murine CFU-meg derived from the bone marrow versus spleen. The in vitro assay predicted the more severe effect of acetyldinaline on splenic progenitors than on their marrow counterparts that was observed in the in vivo phase. In addition, megakaryocytopoiesis in the marrow showed evidence of recovery from drug toxicity in the face of continuing daily acetyldinaline treatments.