Bharali et al Most chemotherapeutic agents have poor solubility and low bioavailability, and are formulated with toxic solvents.4 Thus, the use of nanocarriers allow for the preparation of low water soluble cancer medications in solid or liquid formula- tions. Doxil and Abraxane are the two well known US Food and Drug Administration (FDA)-approved nanoformulations currently available on market for cancer treatment. Doxil5–7 is a long circulating liposomal formulation of doxorubicin, which has shown signiﬁcant improvements over its counter- part, free doxorubicin. The other FDA-approved nanomedi- cine, Abraxane® (Abraxis Bioscience, Los Angeles, CA), a treatment for metastatic breast cancer, is an albumin- bound nanoparticle formulation of paclitaxel in the ﬁeld of nanotechnology mediated cancer therapy.8–10 Abraxane® for injectable suspension evades the hypersensitivity reaction associated with Cremophor EL, the traditionally used solvent for paclitaxel. This nanoparticle has a size around 100 nm and offers the ability to convert insoluble or poorly soluble drugs, avoiding the need for toxic organic solvents. Having sprouted from a single concept some thirty years ago, nanotechnology has given rise to nanomedicine, among other applications including those associated with physics, biochemistry, and biotechnology, for creating molecular devices able to facilitate therapeutic and diagnostic proce- dures on the nanoscale. Thus, applications of nanotechnology have generated immense interest over past decade in various ﬁelds for diverse applications. This review will discuss the nanotechnological research that has been conducted regarding liposomes, quantum dots (QDs), and especially dendrimers in anticancer therapeutics over the past decade. Liposomes Liposomes are small lipid vesicles within the range of 50 to 1000 nm.11,12 Because of their unique advantages over tradi- tional drug therapy, including their ability to protect the drugs from degradation, targeting the drug to the site of action and reducing the toxicity and side effects of such drugs, liposomes have been studied extensively as drug carriers particularly for cancer therapy.13 Depending upon their size and number of bilayers, liposomes can be classiﬁed into three categories: multi-lamellar vesicles (MLV); large uni-lamellar vesicles (LUV); and small uni-lamellar vesicles (SUV). Liposomes can be classiﬁed in terms of composition and mechanism of intracellular delivery into ﬁve types: conventional liposomes (CL), pH-sensitive liposomes, cationic liposomes, immuno- liposomes, and long-circulating liposomes (LCL). The major problems associated with liposomes are their stability, poor batch to batch reproducibility, difﬁculty in sterilization, and 2 low drug loading capacity. Although liposomes have been extensively studied for last few decades, the only efﬁcient nanoformulation available in the market is Doxil® (ALZA, Moutain View, CA). Quantum dots Semiconductor QDs are rapidly emerging as popular lumines- cence probes for many biological and biomedical applications owing to their extremely small size (approximately 10 nm in diameter), high photostability, tunable optical properties, and multimodality.14–18 Such inorganic–organic composite nano- materials have shown extreme efﬁciency in cancer diagnosis in vivo, with their small size which facilitates unimpeded systemic circulation and attached targeting molecules, allow- ing for speciﬁc ‘honing in’ at neoplastic sites.19–22 Similar to other nanoparticles, QDs can be modiﬁed via conjugation of various surface molecules for targeted delivery.23,24 QDs also provide sufﬁcient surface area to attach therapeutic agents for simultaneous drug delivery and in vivo imaging25 as well as for tissue engineering.26 In vivo cancer targeting and imaging in living animals by QDs was ﬁrst demonstrated by Gao and colleagues,19 where both subcutaneous injection of QD-tagged prostate cancer cells and systemic injection of multifunctional QD probes were used to achieve sensitive and multicolor ﬂuorescence imaging of cancer cells. In a recent a study, Bagalkot and colleagues27 used QD–apatamer (Apt)– doxorubicin (Dox) conjugate for targeted cancer therapy, imaging, and sensing. It was shown that this multifunctional nanoparticle system can deliver doxorubicin to the targeted prostate cancer cells and sense the delivery of doxorubicin by activating the ﬂuorescence of QD, while allowing for simultaneous imaging of the cancer cells. Though most of the major challenges associated with QD to make less toxic optical probes for biological applica- tions have been overcome using different coating materials, under some conditions QDs can become cytotoxic.28 It was discovered that CdSe particles may leak cytotoxic cadmium ions after long-term exposure to ultraviolet (UV) light, while CdTe particles produce reactive oxygen species due to the loss of their protective coating after long-term circulation. In both cases, cytotoxicity and cell death were recorded.29–32 Research is ongoing to ﬁnd suitable biocompatible and stable QD coatings. Nevertheless, QDs also found its application in the near infrared (NIR) imaging (700–1000 nm).33 The use of NIR-QDs can maximize the depth of tissue penetration, allowing for more accurate and sensitive detection of photons in vivo, which is limited by absorption and light scattering in conventional imaging, allowing for more accurate and International Journal of Nanomedicine 2009:4