Intracellular labeling method for chip-based capillary electrophoresis fluorimetric single cell analysis using liposomes

Microfluidic single-cell analysis of oxidative stress in Dictyostelium discoideum

Microfluidic chemical cytometry is a powerful technique for examining chemical contents of individual cells, but applications have focused on cells from multicellular organisms, especially mammals. We demonstrate the first use of microfluidic chemical cytometry to examine a unicellular organism, the social amoeba Dictyostelium discoideum. We used the reactive oxygen species indicator dichlorodihydrofluorescein diacetate to report on oxidative stress and controlled for variations in indicator loading and retention using carboxyfluorescein diacetate as an internal standard. After optimizing indicator concentration, we investigated the effect of peroxide treatment through single-cell measurements of 353 individual cells. The peak area ratio of dichlorofluorescein to carboxyfluorescein increased from 1.69 ± 0.89 for untreated cells to 5.19 ± 2.72 for cells treated with 40 mM hydrogen peroxide. Interestingly, the variance of the data also increased with oxidative stress. While preliminary, these results are consistent with the hypothesis that heterogeneous stress responses in unicellular organisms may be adaptive.

Response of single leukemic cells to peptidase inhibitor therapy across time and dose using a microfluidic device

Single-cell methodologies are revealing cellular heterogeneity in numerous biological processes and pathologies. For example, cancer cells are characterized by substantial heterogeneity in basal signaling and in response to perturbations, such as drug treatment. In this work, we examined the response of 678 individual U937 (human acute myeloid leukemia) cells to an aminopeptidase-inhibiting chemotherapeutic drug (Tosedostat) over the course of 95 days. Using a fluorescent reporter peptide and a microfluidic device, we quantified the rate of reporter degradation as a function of dose. While the single-cell measurements reflected ensemble results, they added a layer of detail by revealing unique degradation patterns and outliers within the larger population. Regression modeling of the data allowed us to quantitatively explore the relationships between reporter loading, incubation time, and drug dose on peptidase activity in individual cells. Incubation time was negatively correlated with the number of peptide fragment peaks observed, while peak area (which was proportional to reporter loading) was positively correlated with both the number of fragment peaks observed and the degradation rate. Notably, a statistically significant change in the number of peaks observed was identified as dose increased from 2 to 4 μM. Similarly, a significant difference in degradation rate as a function of reporter loading was observed for doses ≥2 μM compared to the 1 μM dose. These results suggest that additional enzymes may become inhibited at doses >1 μM and >2 μM, demonstrating the utility of single-cell data to yield novel biological hypotheses.

A novel rapamycin-polymer conjugate based on a new poly(ethylene glycol) multiblock copolymer

PURPOSE

Rapamycin has demonstrated potent anti-tumor activity in preclinical and clinical studies. However, the clinical development of its formulations was hampered due to its poor solubility and undesirable distribution in vivo. Chemical modification of rapamycin presents an opportunity for overcoming the obstacles and improving its therapeutic index. The objective of this study is to develop a drug-polymer conjugate to increase the solubility and cellular uptake of rapamycin.

METHODS

We developed the rapamycin-polymer conjugate using a novel, linear, poly(ethylene glycol) (PEG) based multiblock copolymer. Cytotoxicity and cellular uptake of the rapamycin-polymer conjugate were evaluated in various cancer cells.

RESULTS

The rapamycin-polymer conjugate provides enhanced solubility in water compared with free rapamycin and shows profound activity against a panel of human cancer cell lines. The rapamycin-polymer conjugate also presents high drug loading capacity (wt% ~ 26%) when GlyGlyGly is used as a linker. Cellular uptake of the conjugate was confirmed by confocal microscopic examination of PC-3 cells that were cultured in the presence of FITC-labled polymer (FITC-polymer).

CONCLUSION

This study suggests that the rapamycin-polymer conjugate is a novel anti-cancer agent that may provide an attractive strategy for treatment of a wide variety of tumors.

Microfluidic chemical cytometry of peptide degradation in single drug-treated acute myeloid leukemia cells

Microfluidic systems show great promise for single-cell analysis; however, as these technologies mature, their utility must be validated by studies of biologically relevant processes. An important biomedical application of these systems is characterization of tumor cell heterogeneity. In this work, we used a robust microfluidic platform to explore the heterogeneity of enzyme activity in single cells treated with a chemotherapeutic drug. Using chemical cytometry, we measured peptide degradation in the U937 acute myeloid leukemia (AML) cell line in the presence and absence of the aminopeptidase inhibitor Tosedostat (CHR-2797). The analysis of 99 untreated cells revealed rapid and consistent degradation of the peptide reporter within 20 min of loading. Results from drug-treated cells showed inhibited, but ongoing degradation of the reporter. Because the device operates at an average sustained throughput of 37 ± 7 cells/h, we were able to sample cells over the course of this time-dependent degradation. In data from 498 individual drug-treated cells, we found a linear dependence of degradation rate on amount of substrate loaded superimposed upon substantial heterogeneity in peptide processing in response to inhibitor treatment. Importantly, these data demonstrated the potential of microfluidic systems to sample biologically relevant analytes and time-dependent processes in large numbers of single cells.

Microchip electrophoresis with chemiluminescence detection for assaying ascorbic acid and amino acids in single cells

A method based on microchip electrophoresis (MCE) with chemiluminescence (CL) detection was developed for the determination of ascorbic acid (AA) and amino acids including tryptophan (Trp), glycine (Gly) and alanine (Ala) present in single cells. Cell injection, loading, lysing, electrophoretic separation and CL detection were integrated onto a simple cross microfluidic chip. A single cell was loaded in the cross intersection by electrophoretic means through applying a set of potentials at the reservoirs. The docked cell was lysed rapidly under a direct electric field. The intracellular contents were MCE separated within 130 s. CL detection was based on the enhancing effects of AA and amino acids on the CL reaction of luminol with K(3)[Fe(CN)(6)]. Rat hepatocytes were prepared and analyzed as the test cellular model. The average intracellular contents of AA, Trp, Gly and Ala in single rat hepatocytes were found to be 38.3, 5.15, 3.78 and 3.84 fmol (n=12), respectively.

Determination of ascorbic acid in individual rat hepatocyte cells based on capillary electrophoresis with electrochemiluminescence detection

A novel method to detect ascorbic acid (AA) in individual rat hepatocyte cells was developed by combining CE with electrochemiluminescence (ECL) based on tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)(3)2+). A single cell, followed by 0.1% SDS as cell lysis solution, was injected into the inlet of the separation capillary by electromigration. After optimizing the analytical conditions, the RSDs of migration time and peak height were 0.38% and 2.6% for 1.0x10(-5) M AA (n=10), respectively. The linear range of AA was from 1.0x10(-8) to 5.0x10(-5) M with a correlation coefficient of 0.9979 and the LOD (S/N=3) was estimated to be 1.0x10(-8) M. This method has been successfully applied to determine AA in single rat hepatocytes and the amount of AA in seven rat hepatocytes ranged from 16 to 62 fmol. The above results demonstrated that CE coupled with ECL is convenient, sensitive, and will become an attractive alternative method for single-cell analysis.