Nanotherapy Targeting the Tumor Microenvironment.

Cancer is characterized by high mortality and low curability. Recent studies have shown that the mechanism of tumor resistance involves not only endogenous changes to tumor cells, but also to the tumor microenvironment (TME), which provides the necessary conditions for the growth, invasion, and metastasis of cancer cells, akin to Stephen Paget's hypothesis of "seed and soil." Hence, the TME is a significant target for cancer therapy via nanoparticles, which can carry different kinds of drugs targeting different types or stages of tumors. The key step of nanotherapy is the achievement of accurate active or passive targeting to trigger drugs precisely at tumor cells, with less toxicity and fewer side effects. With deepened understanding of the tumor microenvironment and rapid development of the nanomaterial industry, the mechanisms of nanotherapy could be individualized according to the specific TME characteristics, including low pH, cancer-associated fibroblasts (CAFs), and increased expression of metalloproteinase. However, some abnormal features of the TME limit drugs from reaching all tumor cells in lethal concentrations, and the characteristics of tumors vary in numerous ways, resulting in great challenges for the clinical application of nanotherapy. In this review, we discuss the essential role of the tumor microenvironment in the genesis and development of tumors, as well as the measures required to improve the therapeutic effects of tumor microenvironment-targeting nanoparticles and ways to reduce damage to normal tissue.

Low ketolytic enzyme levels in tumors predict ketogenic diet responses in cancer cell lines in vitro and in vivo.

The ketogenic diet (KD) is a high-fat, very-low-carbohydrate diet that triggers a fasting state by decreasing glucose and increasing ketone bodies, such as ß-hydroxybutyrate (ßHB). In experimental models and clinical trials, the KD has shown anti-tumor effects, possibly by reducing energy supplies to cells, which damage the tumor microenvironment and inhibit tumor growth. Here, we determined expression levels of genes encoding the ketolytic enzymes 3-hydroxybutyrate dehydrogenase 1 (BDH1) and succinyl-CoA: 3-oxoacid CoA transferase 1 (OXCT1) in 33 human cancer cell lines. We then selected two representative lines, HeLa and PANC-1, for in vivo examination of KD sensitivity in tumors with high or low expression, respectively, of these two enzymes. In mice with HeLa xenografts, the KD increased tumor growth and mouse survival decreased, possibly because these tumors actively consumed ketone bodies as an energy source. Conversely, the KD significantly inhibited growth of PANC-1 xenograft tumors. ßHB added to each cell culture significantly increased proliferation of HeLa cells, but not PANCI-1 cells. Downregulation of both BDH1 and OXCT1 rendered HeLa cells sensitive to the KD in vitro and in vivo. Tumors with low ketolytic enzyme expression may be unable to metabolize ketone bodies, thus predicting a better response to KD therapy.

Mitochondrial ultrastructure & release of proteins during liver regeneration.

BACKGROUND & OBJECTIVES: It has been reported that some proteins are released from mitochondria during liver regeneration after partial hepatectomy (PH), but the relationship between proteins release and mitochondrial permeability transition (MPT) remains unclear. We undertook this study to demonstrate the changes of mitochondrial ultrastructure and proteins release during liver regeneration and to determine the relationship between proteins release and MPT in liver regeneration in rats. METHODS: After PH and administration of cyclosporin-A (CsA, a specific inhibitor of MPT), ultrastructural morphology of mitochondria in the remnant liver were determined by electron microscopy. Catalytic activity of mitochondrial and cytosolic proteins including aspartate aminotransferase (AST) and glutamic acid dehydrogenase (GDH) was measured. RESULTS: The liver mitochondria at 24 and 72 h were quite variable in morphology and ultrastructure. The enzyme activities of AST and GDH in cytosol released from mitochondrial matrix changed significantly at 24 and 72 h. CsA can inhibit the permeability of mitochondria partly at the same time. INTERPRETATION & CONCLUSIONS: The changes of mitochondria in ultrastructure reflected the feature of MPT, and the changes of enzymes activities released from mitochondrial matrix were consistent with those of mitochondrial ultrastructure. CsA can inhibit these changes to some extent. There was a close relationship of MPT with mitochondrial ultrastructure and proteins release during liver regeneration.

[Effect of opening of neuronal mitochondrial permeability transition pore on respiratory function after cardiopulmonary resuscitation in rats].

OBJECTIVE: To investigate the effect of opening of neuronal mitochondrial permeability transition pore (MPTP) on respiratory function after cardiopulmonary resuscitation (CPR) in rats and its possible mechanism. METHODS: Cardiac arrest (CA)/CPR rat model was reproduced by asphyxiation and ice-cold KCl followed resuscitation and restoration of spontaneous circulation (ROSC). The rats were sacrificed by decapitation at 3, 6, 12, 24, 48 and 72 hours. Isolation of brain cortex neuronal mitochondria was processed. MPTP opening degree was examined by spectrophotometer. Clark oxygen electrode was used to measure mitochondrial respiratory function: the mitochondrial ultra structure was examined with transmission electron microscope (TEM). RESULTS: Mitochondrial respiratory function was severely injured after CA/CPR. Mitochondrial respiratory state III (R3) was decreased. Neural cell MPTP opened persistently after ROSC. The opening degree of MPTP did not reach the peak instantly, and its change depended on time. It remained at a low level within 6 hours after ROSC, then rapidly opened, reaching the maximal degree at 12 hours, but it became smaller at 24 hours. At 48 hours the degree of opening became larger again, but shrank once more at 72 hours. However, it did not reach the normal level (all P<0.05). Although R3 was decreased, mitochondrial respiratory state IV (R4) was increased, meanwhile the respiratory control rate (RCR) and P/O ratio descended markedly. They maintained at low levels along with the elapse of time (P<0.05 or P<0.01). TEM revealed obvious injury to neurons. Correlation analysis showed that the MPTP opening degree and RCR was obviously positively correlated (r=0.025, P<0.05). CONCLUSION: The opening of MPTP is the main cause of aggravation of energy metabolism disturbance of neural cells after CPR. To take measures to inhibit the opening of MPTP within 12 hours after ROSC may promote improvement of neuronal mitochondrial function, and it might help win the chances for neural function to recover.

Detection of mitochondrial DNA deletion by a modified PCR method in a 60Co radiation-exposed patient.

A new PCR based method was developed to detect deleted mitochondrial DNA (mtDNA). Peripheral blood cell DNA was obtained from a victim who was accidently exposed to a 60Co radiation source in 1990. Using the DNA as template, first PCR was performed to generate multiple products including true deletions and artifacts. The full length product was recovered and used as template of secondary PCR. The suspicious deletion product of mtDNA could be confirmed only if it was yielded by first PCR. Using either original primers or their nested primers, the suspicious deletion product was amplified and authenticated as a true deletion product. The template was recovered and determined to be a deletion by sequencing directly. The results show that a new mtDNA deletion, which spans 889 bp from nt 11688 to nt 12576, was detected in the peripheral blood cells of the victim. It indicates that this new PCR-based method was more efficient at detecting small populations of mtDNA deletion than other routine methods. MtDNA deletion was found in the victim, suggesting the relationship between the deletion and phenotypes of the disease.

Search for difference in aminoacylation of mitochondrial DNA-encoded wild-type and mutant human tRNALeu (UUR).

The pathogenetic mechanism of the most extensively investigated A3243G mutated tRNALeu(UUR) gene, which causes the MELAS encephalomyopathy, maternally inherited diabetes, or chronic progressive external ophlthalmoplegia, is still unresolved, despite the numerous investigations on the topic. Previous evidences presented in published work suggested that the mitochondrial DNA harboring A3243G mutation result decreases in the rates of mitochondrial protein synthesis. To search for differences in aminoacylation of mitochondrial DNA-encoded wild-type and mutant human tRNALeu(UUR), we have expressed and purified the two kinds of tRNAsLeu(UUR), and have expressed human mitochondrial leucyl-tRNA synthetase for in vitro assays of aminoacylation of wild-type and mutant human tRNALeu(UUR). The results indicate human mitochondrial tRNALeu(UUR) gene A3243G point mutant can remarkably reduce its aminoacylation, suggesting it could be one of the mechanisms that the mutation can produce in such clinical phenotypes.

[Effects of A3243G point mutation on aminoacylation of human mitochondrial tRNALeu(UUR)].

The wild-type and mutant-type human mitochondrial tRNALeu(UUR) genes were synthesized and transcribed in vitro with T7 RNA polymerase. The kinetic parameters of human mitochondrial leucyl-tRNA synthetase(mtLeuRS) were determined with wild-type and mutant-type human mitochondrial tRNALeu(UUR) respectively. The results show that the value of Km/Kcat of mtLeuRS for the mutant-type tRNALeu(UUR) is 63.9% as compared with the wild-type. Human mitochondrial tRNALeu(UUR) gene A3243G point mutant can remarkably reduce it's aminoacylation activity, suggesting it would be one of the mechanisms that the mutation could produce such clinical phenotypes.