Nanotechnology, in silico and endocrine-based strategy for delivering paclitaxel and miRNA: Prospects for the therapeutic management of breast cancer.

Breast cancer is one of the most prevalent and reoccurring cancers and the second most common reason of death in women. Despite advancements in therapeutic strategies for breast cancer, early tumor recurrence and metastasis in patients indicate resistance to chemotherapeutic medicines, such as paclitaxel due to the abnormal expression of ER and EGF2 in breast cancer cells. Therefore, the development of alternatives to paclitaxel is urgently needed to overcome challenges involving drug resistance. An increasing number of studies has revealed miRNAs as novel natural alternative substances that play a crucial role in regulating several physiological processes and have a close, adverse association with several diseases, including breast cancer. Due to the therapeutic potential of miRNA and paclitaxel in cancer research, the current review focuses on the differential roles of various miRNAs in breast cancer development and treatment. miRNA delivery to a specific target site, the development of paclitaxel and miRNA formulations, and nanotechnological strategies for the delivery of nanopaclitaxel in the management of breast cancer are discussed. These strategies involve improving the cellular uptake and bioavailability and reducing the toxicity of free paclitaxel to achieve accumulation tumor site. Furthermore, a molecular docking study was performed to ascertain the enhanced anticancer activity of the nanoformulation of ANG1005 and Abraxane. An in silico analysis revealed that ANG1005 and Abraxane nanoformulations have superior and significantly enhanced interactions with the proteins α-tubulin and Bcl-2. Therefore, ANG1005 and Abraxane may be more suitable in the therapeutic management of breast cancer than the existing free paclitaxel. miRNAs can revert abnormal gene expression to normalcy; since miRNAs serve as tumor suppressors. Therefore, restoration of particular miRNAs levels as a replacement therapy may be an effective endocrine potential strategy for treating ER positive/ negative breast cancers.

Selective and Marked Blockade of Endothelial Sprouting Behavior Using Paclitaxel and Related Pharmacologic Agents.

Whether alterations in the microtubule cytoskeleton affect the ability of endothelial cells (ECs) to sprout and form branching networks of tubes was investigated in this study. Bioassays of human EC tubulogenesis, where both sprouting behavior and lumen formation can be rigorously evaluated, were used to demonstrate that addition of the microtubule-stabilizing drugs, paclitaxel, docetaxel, ixabepilone, and epothilone B, completely interferes with EC tip cells and sprouting behavior, while allowing for EC lumen formation. In bioassays mimicking vasculogenesis using single or aggregated ECs, these drugs induce ring-like lumens from single cells or cyst-like spherical lumens from multicellular aggregates with no evidence of EC sprouting behavior. Remarkably, treatment of these cultures with a low dose of the microtubule-destabilizing drug, vinblastine, led to an identical result, with complete blockade of EC sprouting, but allowing for EC lumen formation. Administration of paclitaxel in vivo markedly interfered with angiogenic sprouting behavior in developing mouse retina, providing corroboration. These findings reveal novel biological activities for pharmacologic agents that are widely utilized in multidrug chemotherapeutic regimens for the treatment of human malignant cancers. Overall, this work demonstrates that manipulation of microtubule stability selectively interferes with the ability of ECs to sprout, a necessary step to initiate and form branched capillary tube networks.

Synthesis and Biological Investigation of Bile Acid-Paclitaxel Hybrids.

Chenodeoxycholic acid and ursodeoxycholic acid (CDCA and UDCA, respectively) have been conjugated with paclitaxel (PTX) anticancer drugs through a high-yield condensation reaction. Bile acid-PTX hybrids (BA-PTX) have been investigated for their pro-apoptotic activity towards a selection of cancer cell lines as well as healthy fibroblast cells. Chenodeoxycholic-PTX hybrid (CDC-PTX) displayed cytotoxicity and cytoselectivity similar to PTX, whereas ursodeoxycholic-PTX hybrid (UDC-PTX) displayed some anticancer activity only towards HCT116 colon carcinoma cells. Pacific Blue (PB) conjugated derivatives of CDC-PTX and UDC-PTX (CDC-PTX-PB and UDC-PTX-PB, respectively) were also prepared via a multistep synthesis for evaluating their ability to enter tumor cells. CDC-PTX-PB and UDC-PTX-PB flow cytometry clearly showed that both CDCA and UDCA conjugation to PTX improved its incoming into HCT116 cells, allowing the derivatives to enter the cells up to 99.9%, respect to 35% in the case of PTX. Mean fluorescence intensity analysis of cell populations treated with CDC-PTX-PB and UDC-PTX-PB also suggested that CDC-PTX-PB could have a greater ability to pass the plasmatic membrane than UDC-PTX-PB. Both hybrids showed significant lower toxicity with respect to PTX on the NIH-3T3 cell line.

Supramolecular Organization of Polymer Prodrug Nanoparticles Revealed by Coarse-Grained Simulations.

Drug-polymer conjugates that can self-assemble into nanoparticles are promising drug delivery systems that improve the drug bioavailability and allow their controlled release. However, despite the possibility of reaching high drug loadings, the efficiency of the drug release, mediated by cleavage of the drug-polymer linker, is a key parameter to obtain significant anticancer activity. To overcome the limitations of experimental characterizations and to gain a better understanding of such systems, we conducted a coarse-grained molecular dynamics simulation study on four representative drug-polymer conjugates obtained by the "drug-initiated" method and studied their supramolecular organization upon self-assembly. The prodrugs were composed of either a gemcitabine or a paclitaxel anticancer drug, either a propanoate or a diglycolate linker, and a polyisoprene chain. Our simulations gave crucial information concerning the spatial organization of the different components (e.g., drug, linker, polymer, etc.) into the nanoparticles and revealed that the linkers are not fully accessible to the solvent. Notably, some cleavage sites were either poorly hydrated or partially solvated. These observations might account for the low efficiency of drug release from the nanoparticles, particularly when the linker is too short and/or not hydrophilic/solvated enough. We believe that our theoretical study could be adapted to other types of polymer prodrugs and could guide the design of new polymer prodrug nanoparticles with improved drug release efficiency.

Taccalonolide C-6 Analogues, Including Paclitaxel Hybrids, Demonstrate Improved Microtubule Polymerizing Activities.

The C-22,23-epoxy taccalonolides are microtubule stabilizers that bind covalently to ß-tubulin with a high degree of specificity. We semisynthesized and performed biochemical and cellular evaluations on 20 taccalonolide analogues designed to improve target engagement. Most notably, modification of C-6 on the taccalonolide backbone with the C-13 N-acyl-ß-phenylisoserine side chain of paclitaxel provided compounds with 10-fold improved potency for biochemical tubulin polymerization as compared to that of the unmodified epoxy taccalonolide AJ. Covalent docking demonstrated that the C-13 paclitaxel side chain occupied a binding pocket adjacent to the core taccalonolide pocket near the M-loop of ß-tubulin. Although paclitaxel-taccalonolide hybrids demonstrated improved in vitro biochemical potency, they retained features of the taccalonolide chemotype, including a lag in tubulin polymerization and high degree of cellular persistence after drug washout associated with covalent binding. Together, these data demonstrate that C-6 modifications can improve the target engagement of this covalent class of microtubule drugs without substantively changing their mechanism of action.

CoA recycling by a benzoate coenzyme A ligase in cascade reactions with aroyltransferases to biocatalyze paclitaxel analogs.

A Pseudomonas CoA ligase (BadA) biocatalyzed aroyl CoA thioesters used by a downstream N-benzoyltransferase (NDTNBT) in a cascade reaction made aroyl analogs of the anticancer drug paclitaxel. BadA kept the high-cost aroyl CoA substrates at saturation for the downstream NDTNBT by recycling CoA when it was added as the limiting reactant. A deacylated taxane substrate N-debenzoyl-2'-deoxypaclitaxel was converted to its benzoylated product at a higher yield, compared to the converted yield in assays in which the BadA ligase chemistry was omitted, and benzoyl CoA was added as a cosubstrate. The resulting benzoylated product 2'-deoxypaclitaxel was made at 196% over the theoretical yield of product that could be made from the CoA added at 50 µM, and the cosubstrates benzoic acid (100 µM), and N-debenzoyl-2'-deoxypaclitaxel (500 µM) added in excess. In addition, a 2-O-benzoyltransferase (mTBT) was incubated with BadA, aroyl acids, CoA, a 2-O-debenzoylated taxane substrate, and cofactors under the CoA-recycling conditions established for the NDTNBT/BadA cascade. The mTBT/BadA combination also made various 2-O-aroylated products that could potentially function as next-generation baccatin III compounds. These ligase/benzoyltransferase cascade reactions show the feasibility of recycling aroyl CoA thioesters in vitro to make bioactive acyl analogs of paclitaxel precursors.

An effective method to produce 7-epitaxol from taxol in HCO3.

It is known that 7-epitaxol has much stronger cytotoxicity than taxol does. However, the content of 7-epitaxol in yew is much less than taxol, which makes it more costly to obtain. We describe here a method to effectively convert taxol to 7-epitaxol. The key condition for reaction needs NaHCO3 in solvent acetonitrile (ACN). The conversion rate can be over 82%.

Cloning and characterization of the ß-xylosidase from Dictyoglomus turgidum for high efficient biotransformation of 10-deacetyl-7-xylosltaxol.

With the aim of finding an extracellular biocatalyst that can efficiently remove the C-7 xylose group from 10-deacetyl-7-xylosltaxol, a Dictyoglomus turgidum ß-xylosidase was cloned and expressed in Escherichia coli BL21 (DE3). The molecular mass of purified Dt-Xyl3 was approximately 84 kDa. The recombinant Dt-Xyl3 was most active at pH 5.0 and 75 °C, retaining 88% activity at 65 °C for 1 h, and displaying excellent stability over pH 4.0-7.5 for 24 h. In terms of kinetic parameters, the Km and Vmax values for pNPX were 0.8316 mM and 5.0178 µmol/mL·min, respectively. Moreover, Dt-Xyl3 was activated by Mn2+ and Ba2+ and inhibited by Cu2+, Ni+ and Al3+. In particular, it displayed high tolerance to salts with 60.8% activity in 20% (w/v) NaCl. Ethanol and methanol at 5-15% showed little effect on the enzymatic activity. Dt-Xyl3 demonstrated multifunctional activities followed by pNPX, pNPAraf and pNPG and had a high selectivity for cleaving the outer xylose moieties of 10-deacetyl-7-xylosltaxol with Kcat/Km 110.87 s-1/mM, which produced 10-deacetyl-taxol to semi-synthesize paclitaxel. Under the optimized conditions (60 °C, pH 4.5, enzyme dosage of 0.5 U/mL), 1 g of 10-deacetyl-7-xylosltaxol was transformed to its corresponding aglycone 10-deacetyl-taxol within 30 min, with a molar conversion of 98%. This is the first report that Dictyoglomus turgidum can produce extracellular GH3 ß-xylosidase with highly specific activity for 10-deacetyl-7-xylosltaxol biotransformation, thus leading to the application of ß-xylosidase Dt-Xyl3 as a biocatalyst in biopharmaceutics.

A multi-national, randomised, open-label, parallel, phase III non-inferiority study comparing NK105 and paclitaxel in metastatic or recurrent breast cancer patients.

BACKGROUND: NK105 is a novel nanoparticle drug delivery formulation that encapsulates paclitaxel (PTX) in polymeric micelles. We conducted an open-label phase III non-inferiority trial to compare the efficacy and safety of NK105 and PTX in metastatic or recurrent breast cancer. METHODS: Patients were randomly assigned in a 1:1 ratio to receive either NK105 (65 mg/m2) or PTX (80 mg/m2) on days 1, 8 and 15 of a 28-day cycle. The primary endpoint was progression-free survival (PFS), with a non-inferiority margin of 1.215. RESULTS: A total of 436 patients were randomised and 211 patients in each group were included in the efficacy analysis. The median PFS was 8.4 and 8.5 months for NK105 and PTX, respectively (adjusted hazard ratio: 1.255; 95% confidence interval: 0.989-1.592). The median overall survival and overall response rates were 31.2 vs. 36.2 months and 31.6% vs. 39.0%, respectively. The two groups exhibited similar safety profiles. The incidence of peripheral sensory neuropathy (PSN) was 1.4% vs. 7.5% (≥Grade 3) for NK105 and PTX, respectively. The patient-reported outcomes of PSN were significantly favourable for NK105 (P < 0.0001). CONCLUSIONS: The primary endpoint was not met, but NK105 had a better PSN toxicity profile than PTX. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov: NCT01644890.

A Phase II Study of Genexol-PM and Cisplatin as Induction Chemotherapy in Locally Advanced Head and Neck Squamous Cell Carcinoma.

LESSONS LEARNED: Induction chemotherapy with Genexol-PM and cisplatin demonstrated modest tumor response in locally advanced head and neck squamous cell carcinoma.Considering favorable toxicity profiles and promising survival data, further studies on this regimen are warranted in patients with head and neck squamous cell carcinoma. BACKGROUND: Genexol-PM is a polymeric micellar formulation of paclitaxel without Cremophor EL. We investigated the efficacy and safety of Genexol-PM plus cisplatin as induction chemotherapy (IC) in patients with locally advanced head and neck squamous cell carcinoma (LA-HNSCC). METHODS: Patients received Genexol-PM (230 mg/m2) and cisplatin (60 mg/m2) every 3 weeks as IC. After three cycles of IC, definitive treatment of either concurrent chemoradiotherapy (CCRT) with weekly cisplatin (30 mg/m2) or surgery was performed. The primary endpoint was overall response rate (ORR) after IC. RESULTS: Of 52 patients enrolled, 47 completed three cycles of IC, and the ORR was 55.8% (95% confidence interval, 42.3-69.3). Although there was one treatment-related death, toxicity profiles to Genexol-PM and cisplatin were generally favorable, and the most common grade 3 or 4 toxicities were neutropenia (15.4%), anorexia (7.7%), and general weakness (7.7%). Fifty-one patients received definitive treatment (CCRT [n = 44] or radical surgery [n = 7]). The rate of complete response following CCRT was 81.8% (36/44). After a median follow-up of 39 months, estimates of progression-free survival (PFS) and overall survival (OS) at 3 years were 54.3% and 71.3%, respectively. CONCLUSION: IC with Genexol-PM and cisplatin demonstrated modest tumor response with well-tolerated toxicity profiles for patients with LA-HNSCC.

Optimised approach to albumin-drug conjugates using monobromomaleimide-C-2 linkers.

Conjugation of therapeutics to human serum albumin (HSA) using bromomaleimides represents a promising platform for half-life extension. We show here that the Cys-34 crevice substantially reduces the rate of serum stabilising maleimide hydrolysis in these conjugates, necessitating reagent optimisation. This improved reagent design is applied to the construction of an HSA-paclitaxel conjugate, preventing drug loss during maleimide hydrolysis.

Active learning strategies with COMBINE analysis: new tricks for an old dog.

The COMBINE method was designed to study congeneric series of compounds including structural information of ligand-protein complexes. Although very successful, the method has not received the same level of attention than other alternatives to study Quantitative Structure Active Relationships (QSAR) mainly because lack of ways to measure the uncertainty of the predictions and the need for large datasets. Active learning, a semi-supervised learning approach that makes use of uncertainty to enhance models' performance while reducing the size of the training sets, has been used in this work to address both problems. We propose two estimators of uncertainty: the pool of regressors and the distance to the training set. The performance of the methods has been evaluated by testing the resulting active learning workflows in 3 diverse datasets: HIV-1 protease inhibitors, Taxol-derivatives and BRD4 inhibitors. The proposed strategies were successful in 80% of the cases for the taxol-derivatives and BRD4 inhibitors, while outperformed random selection in the case of the HIV-1 protease inhibitors time-split. Our results suggest that AL-COMBINE might be an effective way of producing consistently superior QSAR models with a limited number of samples.

Effect of XlogP and Hansen Solubility Parameters on Small Molecule Modified Paclitaxel Anticancer Drug Conjugates Self-Assembled into Nanoparticles.

Small molecule modified anticancer drug conjugates (SMMDCs) can self-assemble into nanoparticles (NPs) as therapeutic NP platforms for cancer treatment. Here we demonstrate that the XlogP and Hansen solubility parameters of paclitaxel (PTX) SMMDCs is essential for SMMDCs self-assembling into NPs. The amorphous state of PTX SMMDCs will also affect SMMDCs self-assembling into NPs. However, the antitumor activity of these PTX SMMDCs NPs decreased along with their XlogP values, indicating that a suitable XlogP value for designing the SMMDCs is important for self-assembling into NPs and for possessing antitumor activity. For higher level XlogP SMMDCs, a degradable linker should be considered in the design of SMMDCs to overcome the problem of lower antitumor activity. It is preferable that the hydrophilic groups in the SMMDCs should be present on the surface of self-assembling NPs.

Species of family Promicromonosporaceae and family Cellulomonadeceae that produce cellulosome-like multiprotein complexes.

OBJECTIVES: To screen the phylogenetically-nearest members of Cellulosimicrobium cellulans for the production of cellulosome-like multienzyme complexes and extracellular ß-xylosidase activity against 7-xylosyltaxanes and to get corresponding molecular insights. RESULTS: Cellulosimicrobium (family Promicromonosporaceae) and all genera of the family Cellulomonadeceaec produced both cellulosome-like multienzyme complexes and extracellular ß-xylosidase activity, while the other genera of the family Promicromonosporaceae did not. Multiple sequence alignments further indicated that hypothetic protein M768_06655 might be a possible key subunit. CONCLUSION: This is the first report that many actinobacteria species can produce cellulosome-like multienzyme complexes. The production of cellulosome-like complexes and the extracellular ß-xylosidase activity against 7-xylosyltaxanes might be used to differentiate the genus Cellulosimicrobium from other genera of the family Promicromonosporaceae.

Biocatalysis of a Paclitaxel Analogue: Conversion of Baccatin III to N-Debenzoyl-N-(2-furoyl)paclitaxel and Characterization of an Amino Phenylpropanoyl CoA Transferase.

In this study, we demonstrate an enzyme cascade reaction using a benzoate CoA ligase (BadA), a modified nonribosomal peptide synthase (PheAT), a phenylpropanoyltransferase (BAPT), and a benzoyltransferase (NDTNBT) to produce an anticancer paclitaxel analogue and its precursor from the commercially available biosynthetic intermediate baccatin III. BAPT and NDTNBT are acyltransferases on the biosynthetic pathway to the antineoplastic drug paclitaxel in Taxus plants. For this study, we addressed the recalcitrant expression of BAPT by expressing it as a soluble maltose binding protein fusion (MBP-BAPT). Further, the preparative-scale in vitro biocatalysis of phenylisoserinyl CoA using PheAT enabled thorough kinetic analysis of MBP-BAPT, for the first time, with the cosubstrate baccatin III. The turnover rate of MBP-BAPT was calculated for the product N-debenzoylpaclitaxel, a key intermediate to various bioactive paclitaxel analogues. MBP-BAPT also converted, albeit more slowly, 10-deacetylbaccatin III to N-deacyldocetaxel, a precursor of the pharmaceutical docetaxel. With PheAT available to make phenylisoserinyl CoA and kinetic characterization of MBP-BAPT, we used Michaelis-Menten parameters of the four enzymes to adjust catalyst and substrate loads in a 200-µL one-pot reaction. This multienzyme network produced a paclitaxel analogue N-debenzoyl-N-(2-furoyl)paclitaxel (230 ng) that is more cytotoxic than paclitaxel against certain macrophage cell types. Also in this pilot reaction, the versatile N-debenzoylpaclitaxel intermediate was made at an amount 20-fold greater than the N-(2-furoyl) product. This reaction network has great potential for optimization to scale-up production and is attractive in its regioselective O- and N-acylation steps that remove protecting group manipulations used in paclitaxel analogue synthesis.

Erythrocyte Membrane-Wrapped pH Sensitive Polymeric Nanoparticles for Non-Small Cell Lung Cancer Therapy.

The application of nano drug delivery systems (NDDSs) may enhance the effectiveness of chemotherapeutic drugs in vivo. However, the short blood circulation time and poor drug release profile in vivo are still two problems with them. Herein, by using red blood cell membrane (RBCm) wrapping and pH sensitive technology, we prepared RBCm wrapped pH sensitive poly(l-γ-glutamylcarbocistein)-paclitaxel (PGSC-PTX) nanoparticles (PGSC-PTX@RBCm NPs), to prolong the circulation time in blood and release PTX timely and adequately in acidic tumor environment. The PGSC-PTX NPs and PGSC-PTX@RBCm NPs showed spherical morphology with average sizes about 50 and 100 nm, respectively. The cytotoxicity of PGSC-PTX@RBCm NPs was considerably decreased compared with that of PGSC-PTX NPs. PTX release from PGSC-PTX and PGSC-PTX@RBCm NPs at pH 6.5 was remarkably higher than those at pH 7.4, respectively. The PGSC-PTX@RBCm NPs exhibited remarkably decreased uptake by macrophages than PGSC-PTX NPs. The area under the curve within 72 h (AUC0-72h) for is significantly higher than PGSC-PTX NPs. The PGSC-PTX@RBCm NPs also showed significantly stronger growth-inhibiting effect on tumor than PGSC-PTX NPs. These results indicated that PGSC-PTX@RBCm NPs have acidic drug release sensitivity, the characteristics of long circulation, and remarkable tumor growth inhibiting effect. This study may provide an effective strategy for improving the antitumor effect of NDDS.

Self-Assembled Tumor-Penetrating Peptide-Modified Poly(l-γ-glutamylglutamine)-Paclitaxel Nanoparticles Based on Hydrophobic Interaction for the Treatment of Glioblastoma.

To enhance the tumor-penetrating ability and targeting therapeutic effect of polymer-drug conjugates (PDCs), tumor-penetrating peptide RGERPPR (RGE) modified and PEGylated poly(l-γ-glutamylglutamine)-paclitaxel (PGG-PTX) nanoparticles (RGE-PEG/PGG-PTX NPs) were prepared by using a so-called "modular" design strategy. In brief, a RGERPPR-conjugated targeting material, DSPE-PEG-RGERPPR, was first synthesized and assembled with PGG-PTX into RGE-PEG/PGG-PTX NPs based on the hydrophobic interaction between the groups of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) and PTX. The NPs exhibited a uniform spherical morphology with particle size of around 90 nm, as shown by the dynamic light scattering and transmission electron microscopy results. The NPs showed good in vitro stability at 4 °C for over 3 weeks, sustained drug release within 120 h, and good hemocompatibility. The cellular-uptake study displayed that the NPs showed increased uptake by U87 MG cells and human umbilical vein endothelial cells (HUVECs) compared to the unmodified PGG-PTX. The cytotoxicity test demonstrated that RGE-PEG/PGG-PTX NPs produced a stronger growth inhibitory effect against U87 MG cells and HUVECs than PGG-PTX, which was consistent with the cellular uptake results. Finally, the pharmacodynamic study proved that RGE-PEG/PGG-PTX NPs significantly prolonged the median survival time of nude mice bearing intracranial glioblastoma. The results indicated the effectiveness of RGE-PEG/PGG-PTX NPs in the treatment of glioblastoma as well as the feasibility of the "modular" design strategy in the preparation of active-targeting PDCs.

Synthesis and anti-inflammatory evaluation of novel paclitaxel analogs.

A series of paclitaxel analogs modified at C-3'-N and C-7 positions were synthesized from baccatin III and their structures were confirmed by 1H-NMR, 13C-NMR, HR-MS. Compound 7e exhibited potent ability to decrease TNFα (tumor necrosis factor α) in the LPS-activated RAW264.7 murine macrophage-like cell line. The preliminary data indicated that the anti-inflammatory effects may be related to MD-2 and Toll-like receptor 4 (TLR4), rather than Toll-like receptor 2 (TLR2).

Taxol®: The First Microtubule Stabilizing Agent.

Taxol®, an antitumor drug with significant activity, is the first microtubule stabilizing agent described in the literature. This short review of the mechanism of action of Taxol® emphasizes the research done in the Horwitz' laboratory. It discusses the contribution of photoaffinity labeled analogues of Taxol® toward our understanding of the binding site of the drug on the microtubule. The importance of hydrogen/deuterium exchange experiments to further our insights into the stabilization of microtubules by Taxol® is addressed. The development of drug resistance, a major problem that arises in the clinic, is discussed. Studies describing differential drug binding to distinct ß-tubulin isotypes are presented. Looking forward, it is suggested that the ß-tubulin isotype content of a tumor may influence its responses to Taxol®.

Co-administration of tLyp-1 with polymeric paclitaxel conjugates: Enhanced intratumoral accumulation and anti-tumor efficacy.

BACKGROUND: It has been previously demonstrated that conjugation of paclitaxel to a linear poly(l-γ-glutamylglutamine) backbone can enhance water solubility of paclitaxel. However, intratumoral penetration of the nanoscale poly(l-γ-glutamylglutamine)-paclitaxel conjugate (PGG-PTX) was still limited due to dysfunctional tumor blood vessels as well as high interstitial pressure in the tumor microenvironment. PURPOSE: The objective of the present research was to investigate the feasibility of co-administration of a tumor penetration enhancing peptide tLyp-1 for improving intratumoral accumulation and consequent anti-tumor efficacy of PGG-PTX. METHODS: The influence of co-administration of tLyP-1 with PGG-PTX on intratumoral accumulation (via HPLC-MS/MS) and anti-tumor efficacy (by monitoring the change in the tumor volume) was investigated using a breast cancer (4T1) tumor-bearing mouse model. In addition, the systemic toxicity of co-administration of tLyP-1 with PGG-PTX was assessed by monitoring the change in the animal body weight. RESULTS: It was observed that co-administration of tLyP-1 with PGG-PTX dramatically improved PGG-PTX accumulation in the tumors, resulting in improved inhibition efficiency against tumor growth. Moreover, co-administration of tLyP-1 with PGG-PTX did not change the systemic toxicity profile of PGG-PTX. CONCLUSION: Co-administration of tLyp-1 may be a promising strategy for improving the passive tumortargeting performance of polymeric drug conjugates.