This review identifies a timeline to nanomedicine anticancer drug approval using the business model of inventors, innovators and imitators. By evaluating the publication record of nanomedicine cancer therapeutics we identified a trend of very few publications prior to FDA approval. We first enumerated the publications related to cancer involving polymers, liposomes or monoclonal antibodies and determined the number of citations per publication as well as the number of published clinical trials amongst the publications. Combining these data with the development of specific nanomedicines, we are able to identify an invention phase consisting of seminal papers in basic science necessary for the development of a specific nanomedicine. The innovation phase includes the first report, the development and the clinical trials involving that nanomedicine. Finally, the imitation phase begins after approval when others ride the wave of success by using the same formulation for new drugs or using the same drug to validate other nanomedicines. We then focused our analysis on nanomedicines containing camptothecin derivatives, which are not yet approved including two polymers considered innovations and one liposomal formulation in the imitation phase. The conclusion that may be drawn from the analysis of the camptothecins is that approved drugs reformulated in polymeric and liposomal cancer nanomedicines have a more difficult time navigating through the approval process than the parent molecule. This is probably due to the fact that for most currently approved drugs, reformulating them in a nanocarrier provides a small increase in performance that large pharmaceutical companies do not consider being worth the time, effort and expense of development. It also appears that drug carriers have a more difficult path through the clinic than monoclonal antibodies. The added complexity of nanocarriers also deters their use to deliver new molecular entities. Thus, the new drug candidates that might be most improved by drug delivery in nanocarriers are not formulated in this fashion.

This review summarizes the in vivo assessment--preliminary, preclinical, and clinical--of chemotherapeutics derived from camptothecin or a derivative. Camptothecin is a naturally occurring, pentacyclic quinoline alkaloid that possesses high cytotoxic activity in a variety of cell lines. Major limitations of the drug, including poor solubility and inactivity at physiological conditions, prevent full clinical utilization. Camptothecin remains at equilibrium in an active lactone form and inactive hydrolyzed carboxylate form. The active lactone binds to DNA topoisomerase I cleavage complex, believed to be the single site of activity inhibiting DNA religation, resulting in apoptosis. A series of small molecule camptothecin derivatives have been developed that increase solubility, lactone stability and bioavailability to varying levels of success. A number of macromolecular agents have also been described wherein camptothecin(s) are covalently appended or non-covalently associated with the goal of improving solubility and lactone stability, while taking advantage of the tumor physiology to deliver larger doses of drug to the tumor with lower systemic toxicity. With the increasing interest in drug delivery and polymer therapeutics, additional constructs are anticipated. The goal of this review is to summarize the relevant literature for others interested in the field of camptothecin-based therapeutics, specifically in the context of biodistribution, dosing regimens, and pharmacokinetics with the desire of providing a useful source of comparative data. To this end, only constructs where in vivo data is available are reported. The review includes published reports in English through mid-2009.

Dendrimers are an attractive platform for macromolecular imaging due to the presence of multiple terminal groups on the exterior of the molecule. Through application of appropriate metal ion chelates, large numbers of metal ions for imaging (paramagnetic or radioopaque) and therapy (radioactive particle emitters) may be conjugated to the dendrimer in combination with a targeting vector, through classic organic synthetic techniques. Thus, a large amount of these metal ions potentially may be site specifically delivered directly into the body with the dendrimer as the vehicle with the targeting vector directing the modified dendrimer. The development of targeted macromolecular agents with acceptable blood retention times and selective organ uptake then has the potential for various biological applications. A review of comparative studies of dendrimers with various externally appended imaging and targeting agents is presented herein.

A variety of water-soluble polymers, when attached to a liposome, substantially increase liposome circulation half-life in animals. However, in certain conditions, liposomes modified with the most widely used polymer, polyethylene glycol (PEG), induce an IgM response resulting in an accelerated blood clearance (ABC) of the liposome upon the second injection. Modification of liposomes with other water-soluble polymers: HPMA (poly[N-(2-hydroxypropyl) methacrylamide]), PVP (poly(vinylpyrrolidone)), PMOX (poly(2-methyl-2-oxazoline)), PDMA (poly(N,N-dimethyl acrylamide)), and PAcM (poly(N-acryloyl morpholine)), increase circulation times of liposomes; but a precise comparison of their ability to promote long circulation or induce the ABC effect has not been reported. To obtain a more nuanced understanding of the role of polymer structure/MW to promote long circulation, we synthesized a library of polymer diacyl chain lipids with low polydispersity (1.04–1.09), similar polymer molecular weights (2.1–2.5 kDa) and incorporated them into 100 nm liposomes of a narrow polydispersity (0.25–1.3) composed of polymer-lipid/hydrogenated soy phosphatidylcholine/cholesterol/diD: 5.0/54.5/40/0.5. We confirm that HPMA, PVP, PMOX, PDMA and PAcM modified liposome have increased circulation times in rodents and that PVP, PDMA, PAcM do not induce the ABC effect. We demonstrate for the first time, that HPMA does not cause an ABC effect whereas PMOX induces a pronounced ABC effect in rats. We find that a single dose of liposomes coated with PEG and PMOX generate an IgM response in rats towards the respective polymer. Finally, in this homologous polymer series, we observe a positive correlation (R = 0.84 in rats, R = 0.92 in mice) between the circulation time of polymer-modified liposomes and polymer viscosity; PEG and PMOX, the polymers that can initiate an ABC response were the two most viscous polymers. Our findings suggest that that polymers that do not cause an ABC effect such as, HPMA or PVP, deserve further consideration as polymer coatings to improve the circulation of liposomes and other nanoparticles.

For four decades, liposomes composed of both naturally occurring and synthetic lipids have been investigated as delivery vehicles for low molecular weight and macromolecular drugs. These studies paved the way for the clinical and commercial success of a number of liposomal drugs, each of which required a tailored formulation; one liposome size does not fit all drugs! Instead, the physicochemical properties of the liposome must be matched to the pharmacology of the drug. An extensive biophysical literature demonstrates that varying lipid composition can influence the size, membrane stability, in vivo interactions, and drug release properties of a liposome. In this review we focus on recently described synthetic lipid headgroups, linkers and hydrophobic domains that can provide control over the intermolecular forces, phase preference, and macroscopic behavior of liposomes. These synthetic lipids further our understanding of lipid biophysics, promote targeted drug delivery, and improve liposome stability. We further highlight the immune reactivity of novel synthetic headgroups as a key design consideration. For instance it was originally thought that synthetic PEGylated lipids were immunologically inert; however, it’s been observed that under certain conditions PEGylated lipids induce humoral immunity. Such immune activation may be a limitation to the use of other engineered lipid headgroups for drug delivery. In addition to the potential immunogenicity of engineered lipids, future investigations on liposome drugs in vivo should pay particular attention to the location and dynamics of payload release.