**6. Mode of uptake of PABA nanomaterials**

microtubes in the salivary glands and rapidly dividing cells of imaginal discs probably represent the secondary uptake after the microtubes enter into the haemolymph. These findings demonstrate that differential uptake and specificity of live cell targeting by the microtubes depend on the cellular physiology, chemical modification of carrier to travel

Here, several critical questions relevant to biocompatibility and application of p-aminozben‐ zoic containing microstructures are addressed. (1) It determines the parameters of chemi‐ cal and biological modifications suitable for oral administration. However, the impact on specific cellular physiology and efficient uptake of microstructures by carrier molecules based on their chemical modifications cannot be ignored. It is evident that distribution and accumulation is prone to shorter (C=12) alkyl side chain. (2) These organic microtubes overcome cell physiological, pharmacokinetic barriers and show an efficient cellular uptake in animal cultured cells (5,19). (3) It has no adverse effects in physiology, behaviour and growth of insects that shows strong similaries with human at molecular level (3) Finally, modifications in alkyl side chain play an important role in biodistribution. The side chain modifications in BAMT-A and BAMT-B alter the shape of microstructures by changing self assembly properties and discriminate tissue specific distribution specifically in adult eye, its precursor cells, wing imaginal discs and neuronal tissues in larval and adult brain but do not show any conspicuous changes of their biodistribution in cultured insect and human cells. The chemical modifications of self assembled p-aminobenzoic moiety also show a better stability and long self-life before degradation but no short-term toxicity, impaired growth of Drosophila larvae and adults after feeding solely on microtubes containing media. Moreover, no obvious effect on fecundity or impairment of fertility was noticed in the adult female flies. During self assembly, chemical modifications of PABA, and their longer stability in the internal organs provides the microtubes as better-suited and sustainable cargo in live organisms, unlike inorganic nanomaterials that neither accumu‐ late in the live cells nor produce cytotoxicity in the cellular environment. Most logical extension of this work would be the cell specific target delivery in which coupled small molecule on the surface wall have define properties for attachment of specific cell surface and/or stringent proteins for facilitating antigen-antibody reactions. This approach could be used not only to deliver small regulatory RNA and DNA as therapeutic materials but also to optimize pill like properties for oral ingestion with no pharmacokinetic barriers. Though this study used only one structure moiety of drug molecules, it is likely that the method would work with other types organic microstructure as long as three major criteria of orally administered molecule biocompatibility, pharmacokinetics and a capacity for multivalency are considered. Therefore chemical modulations on the surface should be incorporated in the design to attach the multivalency of small ligands. These changes in organic microstructure were described recently. Such attempts for synthesizing tissue or cell guided orally ingested microstructure may favour to make the next generation micropill to deliver biomaterials for effective gene therapy and novel cargo useful for molecular

and enter live cells.

460 Application of Nanotechnology in Drug Delivery

diagnostics.

Broadly, there are two modes of entries, either PABA nano-materials transverse the cell membrane via endocytosis orenergy independent nonendocytotic mechanism. We have carried out a series of investigations on uptake mechanism and cellular internalization for PABA conjugates. Endocytosis is an energy dependent mechanism. The process is hindered at a low temperature (at 4°C instead of 37°C) or in ATP deficient environment. Cells incubated in media containing nanoparticles were either cultured at 4°C or pretreated with NaN3 for inhibiting the production of ATP, thereby hampering the endocytosis process. The level of fluorescent intensity in the cytosol of each cultured cells was reduced dramatically relative to cells cultured in regular standard conditions (Figure 3). This reduction determines that PABA conjugates enter in the sub-cellular compartment of cultured cells via endocytosis. We also sub-categorized the endocytosis pathway including phagocytosis, pinocytosis, clathrin dependent receptor mediated and clathrin independent mechanisms.Internalization often occurs when the clathrin coat on the plasma membrane forms conspicuous invagination in the cell membrane leading to the budding of clathrin-coated vesicles. As a result, extracellular species located on the cell membrane are trapped within the vesicles and invaginated inside the cells. To disrupt the formation of clathrin coated vesicles on the cell membranes, cells were preincubated in sucrose (hypertonic) soluton or K+-depleted media before treatment with all seven nano-particles. Data showed a drastic reduction in PABA nano-particle uptake (Figure 3C), which suggests that a clathrin dependent endocytosis process is involved in entry mechanism.
