We describe evidence for a novel mechanism of monoclonal antibody (MAb)-directed nanoparticle (immunoliposome) targeting to solid tumors in vivo. Long-circulating immunoliposomes targeted to HER2 (ErbB2, Neu) were prepared by the conjugation of anti-HER2 MAb fragments (Fab ¶ or single chain Fv) to liposome-grafted polyethylene glycol chains. MAb fragment conjugation did not affect the biodistribution or long-circulating properties of i.v.-administered liposomes. However, antibody-directed targeting also did not increase the tumor localization of immunoliposomes, as both targeted and nontargeted liposomes achieved similarly high levels (7-8% injected dose/g tumor tissue) of tumor tissue accumulation in HER2-overexpressing breast cancer xenografts (BT-474). Studies using colloidal gold-labeled liposomes showed the accumulation of anti-HER2 immunoliposomes within cancer cells, whereas matched nontargeted liposomes were located predominantly in extracellular stroma or within macrophages. A similar pattern of stromal accumulation without cancer cell internalization was observed for anti-HER2 immunoliposomes in non-HER2-overexpressing breast cancer xenografts (MCF-7). Flow cytometry of disaggregated tumors posttreatment with either liposomes or immunoliposomes showed up to 6-fold greater intracellular uptake in cancer cells due to targeting. Thus, in contrast to nontargeted liposomes, anti-HER2 immunoliposomes achieved intracellular drug delivery via MAb-mediated endocytosis, and this, rather than increased uptake in tumor tissue, was correlated with superior antitumor activity. Immunoliposomes capable of selective internalization in cancer cells in vivo may provide new opportunities for drug delivery.

Acetylation is a key posttranslational modification of many proteins responsible for regulating critical intracellular pathways. Although histones are the most thoroughly studied of acetylated protein substrates, histone acetyltransferases (HATs) and deacetylases (HDACs) are also responsible for modifying the activity of diverse types of nonhistone proteins, including transcription factors and signal transduction mediators. HDACs have emerged as uncredentialed molecular targets for the development of enzymatic inhibitors to treat human cancer, and six structurally distinct drug classes have been identified with in vivo bioavailability and intracellular capability to inhibit many of the known mammalian members representing the two general types of NAD+-independent yeast HDACs, Rpd3 (HDACs 1, 2, 3, 8) and Hda1 (HDACs 4, 5, 6, 7, 9a, 9b, 10). Initial clinical trials indicate that HDAC inhibitors from several different structural classes are very well tolerated and exhibit clinical activity against a variety of human malignancies; however, the molecular basis for their anticancer selectivity remains largely unknown. HDAC inhibitors have also shown preclinical promise when combined with other therapeutic agents, and innovative drug delivery strategies, including liposome encapsulation, may further enhance their clinical development and anticancer potential. An improved understanding of the mechanistic role of specific HDACs in human tumorigenesis, as well as the identification of more specific HDAC inhibitors, will likely accelerate the clinical development and broaden the future scope and utility of HDAC inhibitors for cancer treatment.

Graphical AbstractHighlights d Ligand-receptor interactions in tumors were investigated using single-cell RNA-seq d Identified interactions were regressed against phenotypic measurements of tumors d The approach provides a tool for studying cell-cell interactions and their variability In BriefTumors are composed of cancer cells and many non-malignant cell types, such as immune and stromal cells. To better understand how all cell types in a tumor cooperate to facilitate malignant growth, Kumar et al. studied communication between cells via ligand and receptor interactions using single-cell data and computational modeling. SUMMARYTumor ecosystems are composed of multiple cell types that communicate by ligand-receptor interactions. Targeting ligand-receptor interactions (for instance, with immune checkpoint inhibitors) can provide significant benefits for patients. However, our knowledge of which interactions occur in a tumor and how these interactions affect outcome is still limited. We present an approach to characterize communication by ligand-receptor interactions across all cell types in a microenvironment using single-cell RNA sequencing. We apply this approach to identify and compare the ligand-receptor interactions present in six syngeneic mouse tumor models. To identify interactions potentially associated with outcome, we regress interactions against phenotypic measurements of tumor growth rate. In addition, we quantify ligand-receptor interactions between T cell subsets and their relation to immune infiltration using a publicly available human melanoma dataset. Overall, this approach provides a tool for studying cell-cell interactions, their variability across tumors, and their relationship to outcome.We thank Merrimack Pharmaceuticals, Inc. for sponsoring the research and supporting publication of the results and the internal review team for reviewing the article prior to submission. We also acknowledge the NIGMS Interdisciplinary Biotechnology Training Program (T32-GM008334) and NCI (U01-CA215798) for funding (to M.P.K. and D.A.L.). K. performed all computational analyses. J.D. and Y.J. processed the mouse syngeneic tumor samples, performed the flow cytometry analysis, and obtained the scRNA-seq data. A.S. provided the tumor growth data. M.P.K., A.R., and G.L. helped design the computational analysis. D.C.

No abstract

Liposome formulations of camptothecins have been actively pursued because of the potential for significant pharmacologic advantages from successful drug delivery of this important class of anticancer drugs. We describe nanoliposomal CPT-11, a novel nanoparticle/liposome construct containing CPT-11 (irinotecan) with unprecedented drug loading efficiency and in vivo drug retention. Using a modified gradient loading method featuring a sterically hindered amine with highly charged, multivalent anionic trapping agents, either polymeric (polyphosphate) or nonpolymeric (sucrose octasulfate), liposomes were capable of entrapping CPT-11 at extremely high drug-to-lipid ratios (>800 g CPT-11/mol phospholipid) and retaining encapsulated drug in vivo with a half-life of drug release in the circulation of 56.8 hours. CPT-11 was also protected from hydrolysis to the inactive carboxylate form and from metabolic conversion to SN-38 while circulating. The maximum tolerated dose in normal mice was determined to be 80 mg/kg for free CPT-11 and >320 mg/kg for nanoliposomal CPT-11. Nanoliposomal CPT-11 showed markedly superior efficacy when compared with free CPT-11 in human breast (BT474) and colon (HT29) cancer xenograft models. This study shows that intraliposomal stabilization of CPT-11 using a polymeric or highly charged, nonpolymeric polyanionic trapping agent results in a markedly active antitumor agent with low toxicity. (Cancer Res 2006; 66(6): 3271-7)

We previously reported the development of epidermal growth factor receptor (EGFR)-targeted immunoliposomes that bind and internalize in tumor cells which overexpress EGFR and/or mutant EGFR variant III (EGFRvIII), enabling intracellular delivery of potent anticancer agents in vitro. We now describe in vivo proof-of-concept for this approach for the delivery of multiple anticancer drugs in EGFR-overexpressing tumor models. Anti-EGFR immunoliposomes were constructed modularly with FabVfragments of cetuximab (IMC-C225), covalently linked to liposomes containing probes and/or anticancer drugs. Pharmacokinetic and biodistribution studies confirmed long circulation times (t 1/2 = 21 hours) and efficient accumulation in tumors (up to 15% ID/g) irrespective of the presence of the targeting ligand. Although total accumulations of anti-EGFR immunoliposomes and nontargeted liposomes in EGFR-overexpressing tumors were comparable, only immunoliposomes internalized extensively within tumor cells (92% of analyzed cells versus <5% for nontargeted liposomes), indicating different mechanisms of delivery at the cellular level. In vivo therapy studies in a series of xenograft models featuring overexpression of EGFR and/or EGFRvIII showed the superiority of immunoliposomal delivery of encapsulated drugs, which included doxorubicin, epirubicin, and vinorelbine. For each of these drugs, anti-EGFR immunoliposome delivery showed significant antitumor effects and was significantly superior to all other treatments, including the corresponding free or liposomal drug (P < 0.001-0.003). We conclude that anti-EGFR immunoliposomes provide efficient and targeted drug delivery of anticancer compounds and may represent a useful new treatment approach for tumors that overexpress the EGFR. (Cancer Res 2005; 65(24): 11631-8)

No abstract

Targeted drug delivery systems that combine imaging and therapeutic modalities in a single macromolecular construct may offer advantages in the development and application of nanomedicines. To incorporate the unique optical properties of luminescent quantum dots (QDs) into immunoliposomes for cancer diagnosis and treatment, we describe the synthesis, biophysical characterization, tumor cell-selective internalization, and anticancer drug delivery of QD-conjugated immunoliposome-based nanoparticles (QD-ILs). Pharmacokinetic properties and in vivo imaging capability of QD-ILs were also investigated. Freeze-fracture electron microscopy was used to visualize naked QDs, liposome controls, nontargeted QD-conjugated liposomes (QD-Ls), and QD-ILs. QD-ILs prepared by insertion of anti-HER2 scFv exhibited efficient receptor-mediated endocytosis in HER2-overexpressing SK-BR-3 and MCF-7/HER2 cells but not in control MCF-7 cells as analyzed by flow cytometry and confocal microscopy. In contrast, nontargeted QD-Ls showed minimal binding and uptake in these cells. Doxorubicin-loaded QD-ILs showed efficient anticancer activity, while no cytotoxicity was observed for QD-ILs without chemotherapeutic payload. In athymic mice, QD-ILs significantly prolonged circulation of QDs, exhibiting a plasma terminal half-life ( t 1/2) of approximately 2.9 h as compared to free QDs with t 1/2 < 10 min. In MCF-7/HER2 xenograft models, localization of QD-ILs at tumor sites was confirmed by in vivo fluorescence imaging.