Combinatorial nanomedicines for colon cancer therapy.

Colon cancer is one of the major causes of cancer deaths worldwide. Even after surgical resection and aggressive chemotherapy, 50% of colorectal carcinoma patients develop recurrent disease. Thus, the rationale of developing new therapeutic approaches to improve the current chemotherapeutic regimen would be highly recommended. There are reports on the effectiveness of combination chemotherapy in colon cancer and it has been practiced in clinics for long time. These approaches are associated with toxic side effects. Later, the drug delivery research had shown the potential of nanoencapsulation techniques and active targeting as an effective method to improve the effectiveness of chemotherapy with less toxicity. This current focus article provides a brief analysis of the ongoing research in the colon cancer area using the combinatorial nanomedicines and its outcome.

Analysis of factors that affect in vitro chemosensitivity of leukaemic stem and progenitor cells to gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukaemia.

Relapse in acute myeloid leukaemia (AML) is considered to result from the persistence of drug-resistant leukaemic stem and progenitor cells (LSPC) within a bone marrow 'niche' microenvironment. Identifying novel agents that have the potential to target these LSPC in their niche microenvironment will aid in the characterization of candidate agents for post-remission chemotherapy. Using an in vitro model, we found that 48-h culture with gemtuzumab ozogamicin (Mylotarg) resulted in a 34% reduction in CD34(+)CD38(-)CD123(+) LSPC number, whereas normal CD34(+)CD38(-) haemapoietic stem cells were insensitive to this agent. As there was considerable heterogeneity in LSPC response to Mylotarg treatment, various factors potentially underpinning the differential response were assessed. LSPC that overexpressed CD33 (P=0.01), which were P-glycoprotein-negative (P=0.008) and with internal tandem duplication (ITD) of the FLT3 gene (FLT3/ITD) status (P=0.006) responded better to Mylotarg treatment. LSPC from patient samples that have these combined characteristics as well as low LSPC burden showed significantly more chemosensitivity to Mylotarg compared with all other cases (P=0.002). In multivariate analysis, LSPC burden and FLT3 status were found to be predictors of LSPC chemosensitivity to Mylotarg treatment (P<0.0001). In conclusion, we have shown heterogeneity in the LSPC compartment of AML patients underpinning differential in vitro sensitivity to Mylotarg.

Resistance to FLT3 inhibition in an in vitro model of primary AML cells with a stem cell phenotype in a defined microenvironment.

Relapse in acute myeloid leukaemia (AML) is mediated by survival of leukaemic stem cells following remission-induction chemotherapy. It would therefore be useful to identify therapeutic agents that target leukaemic stem cells. We devised a flow cytometric chemosensitivity assay allowing 48 h culture of leukaemic blasts in a defined microenvironment followed by enumeration of viable CD34+CD38-CD123+ leukaemic stem and progenitor cells (LSPC). The assay was used to investigate the LSPC response to cytosine arabinoside (Ara-C) and to the FLT3 inhibitor AG1296. There was a 3.6-fold increase in Ara-C-treated LSPC survival under defined 'niche-like' conditions compared to culture without microenvironmental support. Nine AML samples with internal tandem duplications of FLT3 (FLT3/ITDs) were treated with AG1296. Three samples were very sensitive (>50% kill) and 4 were moderately sensitive (10-50% kill) in bulk suspension culture without microenvironmental support. However, under defined 'niche-like' conditions, the survival of LSPC was enhanced rather than inhibited by AG1296 treatment. We conclude that an interaction between LSPC and a defined in vitro microenvironment models a chemoresistant niche. Our data point to a need to investigate more novel chemotherapeutic agents under these stringent conditions to identify agents that may be suitable to target minimal residual disease in AML.

Effect of lesion characteristics and mineralizing solution type on enamel remineralization in vitro.

The aim was to study the effect of lesion preparation technique and solution composition on remineralization of artificial lesions in vitro. Lesions were prepared with similar total mineral loss, but different mineral distribution, i.e., low (14.0) or high R (34.8) values. Lesions from both groups were remineralized (10 days, 37 degrees C) in two different solutions, with similar supersaturation with respect to hydroxyapatite (St), but calcium:phosphate ratios representing either hydroxyapatite stoichiometry or plaque fluid (PF). Remineralization was quantified microradiographically, mineral distribution was compared with natural white-spot lesions. Mineral loss and depth decreased significantly, and surface-zone mineral content (Zmax) increased significantly, in all lesions. Overall there was a significant relationship of decreasing remineralization with increasing Zmax, but not within either lesion type. PF was significantly more efficient than St in high-R lesions, with lesions remineralizing almost completely in PF. Remineralization was not significantly different in PF or St for low-R lesions but in high-R lesions, PF was more efficient than St, possibly through differences in relative saturations with respect to different calcium phosphates. Differences in area:solution ratios and baseline Zmax values may also have explained the different response to PF. Low-R lesions were similar to natural white-spot lesions in terms of mineral distribution, whereas high-R were not. Concluding, both lesion and remineralizing solution type had a marked influence on remineralization. It is proposed that use of low-R lesions would be more appropriate where more physiologically relevant mineral distribution is required, whereas high-R lesions would be appropriate for studying inherent remineralizing efficiency.

The effect of fluoride at plaque fluid concentrations on enamel de- and remineralisation at low pH.

The aim was to study the effect of fluoride, at concentrations typical of plaque fluid, on de- and remineralisation of subsurface lesions at low pH. Artificial lesions in human enamel were microradiographed to quantify mineral loss and placed in acid-gel systems at pH 4.8, 5.0 and 5.2. Calcium and phosphate were added to give initial Ca and Pi concentrations of either 4.1 and 8.0 mM, or 4.7 and 9.7 mM, at each pH value. Further, at each pH and combination of Ca and Pi, fluoride was added to the gels to give initial concentrations of 1, 2 or 5 ppm, with a non-fluoride control group. The lesions were removed after 10 days and change in mineral content quantified. Those in the non-fluoride control groups had demineralised further. Those exposed to fluoride had remineralised, the amount increasing with increasing fluoride concentration, up to a maximum value of approximately 75%. Calcium activity in the gels was reduced significantly, to levels similar to those reported for plaque fluid at low pH. Fluoride activity was also reduced, though to a lesser extent. These findings contrast with those from studies which have simulated conditions on smooth surface sites and which used experimental solutions composed to reflect salivary fluoride concentrations, where net demineralisation was observed at low pH. This reflects the need for further study of de- and remineralisation under plaque-fluid conditions. In conclusion, subsurface lesions were remineralised at low pH by fluoride at concentrations found in plaque fluid during a cariogenic challenge.