Tubulin/microtubule

Taxanes are a key chemotherapy component for several malignancies, including metastatic breast cancer (MBC), ovarian cancer, and advanced non-small cell lung cancer (NSCLC). Despite the clinical benefit achieved with solvent-based (sb) taxanes, these agents can be associated with significant and severe toxicities. Albumin-bound paclitaxel (Abraxane; nab®-Paclitaxel), a novel solvent-free taxane, has demonstrated higher response rates and improved tolerability when compared with solvent-based formulations in patients with advanced MBC and NSCLC. The technology used to create nab-paclitaxel utilizes albumin to deliver paclitaxel, resulting in an advantageous pharmacokinetic (PK) profile. This review discusses the proposed mechanism of delivery of nab-paclitaxel, including an examination into a hypothesized greater ability to leverage albumin-based transport relative to sb-paclitaxel. An advantageous PK profile and the more efficient use of albumin-based transport may contribute to the preclinical finding that nab-paclitaxel achieves a 33% higher tumor uptake relative to sb-paclitaxel. Another possible contributing factor to the tumor accumulation of nab-paclitaxel is the binding of albumin to secreted protein acidic and rich in cysteine (SPARC), although the data supporting this relationship between SPARC and nab-paclitaxel remain largely correlative at this point. Recent data also suggest that nab-paclitaxel may enhance tumor accumulation of gemcitabine in pancreatic cancer treated with both agents. Additionally, a possible mechanistic synergy between nab-paclitaxel and capecitabine has been cited as the rationale to combine the two agents for MBC treatment. Thus, nab-paclitaxel appears to interact with tumors in a number of interesting, but not fully understood, ways. Continued preclinical and clinical research across a range of tumor types is warranted to answer the questions that remain on the mechanisms of delivery and antitumor activity of nab-paclitaxel[1].

Classic thought on drug distribution holds that the free, or unbound, fraction of drug is the active fraction because drug bound to proteins or other macromolecules might be unable to cross cell membranes. In clinical studies, sb-paclitaxel has been shown to be highly protein bound in plasma, with Cremophor EL further decreasing the free/unbound fraction of drug. To examine the effect that formulation has on the pharmacokinetics (PK) of paclitaxel, a randomized crossover PK study was carried out in patients with cancer receiving either sb-paclitaxel at 175 mg/m2 q3w over a 3-hour infusion or nab-paclitaxel at 260 mg/m2 q3w over a 30-minute infusion. In this study, mass spectrometry was used to identify whether circulating paclitaxel was free/unbound or not. In this report, paclitaxel associated with Cremophor EL would not have been identified as unbound drug. The key finding of the study was that the formulation of nab-paclitaxel allowed a much higher fraction of unbound paclitaxel for nab-paclitaxel vs. sb-paclitaxel (6.3% vs. 2.4%, p < 0.001). Furthermore, the maximal concentration of unbound paclitaxel was about 10-fold higher for nab-paclitaxel (1284 ng/mL vs. 122 ng/mL, p < 0.000001), and the systemic exposure (AUCINF) of unbound paclitaxel was about 3-fold higher for nab-paclitaxel (1159 h*ng/mL vs. 410 h*ng/mL, p < 0.000005). A likely explanation for these differences lies in the entrapment of paclitaxel in Cremophor EL-based micelles in the solvent-based formulation of paclitaxel. Consistent with the effect of micellar entrapment on paclitaxel distribution, Sparreboom et al. found that nab-paclitaxel achieves a higher plasma clearance and a larger volume of distribution vs. sb-paclitaxel in preclinical studies. It has been suggested that micellar entrapment could affect the PK linearity of sb-paclitaxel. Table 3 lists selected PK studies on sb-paclitaxel and nab-paclitaxel and gives the authors' characterizations of PK linearity for the two agents[1].

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Although investigations into the distribution of unbound drug are important, it is also critical to consider that in human blood, paclitaxel is highly bound to proteins and other biomolecules. As stated previously, Kumar et al. demonstrated that when sb-paclitaxel is administered to humans, approximately 95% of paclitaxel binds to other molecules. Albumin and alpha-1-acid glycoprotein contributed equally to this binding, with a minor fraction of paclitaxel bound to lipoproteins. Furthermore, albumin is known to be a ubiquitous carrier of biomolecules in the blood, which prompts the consideration of how albumin may influence the transport of nab-paclitaxel to tumors. Circulating albumin must cross endothelial cells to reach tumors, and albumin has been reported to accomplish this in at least 2 ways (Fig. 1): receptor-mediated transcytosis and the enhanced permeation and retention (EPR) effect. It has been hypothesized that nab-paclitaxel may take advantage of each of these mechanisms to reach the tumor microenvironment[1].

Studies have shown that a large fraction of injected albumin-conjugated molecules accumulate in proximity to tumors. As discussed above, albumin may reach tumors by receptor-mediated transport mechanisms or by the EPR effect. It has been hypothesized that cancer cells may consume albumin from the tumor microenvironment and then metabolize it, possibly enhancing tumor growth. Desai et al. conducted experiments in mice bearing xenograft tumors from injected human breast cancer cells to determine whether formulation played a role in the tumor uptake of paclitaxel. In these experiments, paclitaxel in both formulations was radioactively labeled and the amount of labeled paclitaxel that eventually reached tumors was quantified. When equal amounts were injected, the researchers found that a third more paclitaxel from the nab-paclitaxel formulation was taken up by tumors. The authors suggested that nab-paclitaxel reached a higher tumor accumulation vs. sb-paclitaxel due to both the lack of drug-sequestering solvent micelles and enhanced albumin-mediated transcytosis. A subsequent report of similar experiments suggested that nab-paclitaxel may achieve some degree of tumor selectivity relative to sb-paclitaxel, although the mechanisms responsible for this possibility were not characterized. [1]

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Another molecular mechanism proposed to play a potential role in the tumor accumulation of nab-paclitaxel is the prevalence of albumin-binding proteins such as secreted protein acidic and rich in cysteine (SPARC) in proximity to tumors. According to this theory, proteins such as SPARC may exist at higher-than-normal levels in the tumor interstitium. Thus, these proteins could sequester paclitaxel bound to albumin in tumors at levels higher than those in healthy tissues. High SPARC expression correlates with disease progression across a range of tumor types; however, some clinical data have suggested a correlation between SPARC expression in the tumor and/or tumor microenvironment and positive clinical outcomes in patients receiving nab-paclitaxel. Other studies have failed to show such a correlation. Thus, further studies delineating the molecular relationship between SPARC and nab-paclitaxel are warranted.[1]

[1]. Yardley DA. nab-Paclitaxel mechanisms of action and delivery. J Control Release. 2013 Sep 28;170(3):365-72.

nab-Paclitaxel was initially developed to avoid the toxicities typically associated with Cremophor EL in sb-paclitaxel. In contrast to sb-paclitaxel and docetaxel, nab-paclitaxel does not utilize non-ionic surfactants to solubilize paclitaxel, which are known to contribute to toxicity and entrap paclitaxel within solvent based micelles. nab-Paclitaxel is formulated with human serum albumin at a concentration similar to the concentration of albumin in the blood. Formulation of nab-paclitaxel takes place through high-pressure homogenization in which albumin and paclitaxel are combined to create particles with a mean diameter of 130 nm. This process does not covalently link albumin to paclitaxel. Upon injection, the nab-paclitaxel particles dissolve into soluble albumin–paclitaxel complexes, and paclitaxel may bind and unbind albumin (injected or endogenous) or other biomolecules, or it may exist in a free/unbound state (see Mechanism of Delivery section). Formulation with albumin allows nab-paclitaxel to be reconstituted with a simple saline solution. As such, nab-paclitaxel is administered without steroid or antihistamine prophylaxis for hypersensitivity reactions. Perhaps because nab-paclitaxel delivery is not complicated by solvents, a higher dose can be administered relative to sb-paclitaxel. In a pivotal phase III MBC trial of nab-paclitaxel and sb-paclitaxel at the label-indicated doses as ≥ first-line therapy in patients with MBC, the dose of paclitaxel delivered was 49% higher for patients receiving nab-paclitaxel vs sb-paclitaxel, suggesting that higher dose intensity is feasible with nab-paclitaxel [1].

White to off-white solid powder

Nanoparticle albumin-bound Paclitaxel; Nanoparticle albumin-bound ABI-007

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)