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Selected Parenteral Lipid Nanoemulsions Under Clinical Study
Chapter 20
Selected Parenteral Lipid Nanoemulsions Under Clinical Study: Comparison Concerning Passive Accumulation in Tumors, Active Targeting of Tumors, and Validation Status Past lipid-based dispersion systems such as simple emulsions, micellar systems, and liposomes have been utilized for parenteral administration of lipophilic drugs for several decades [804–806]. [Parenteral administration, as used below, will refer specifically to injection into the bloodstream.] As pointed out by Constantinides and Wasan (in their preface to the 2004 theme issue on “Advances in lipid-based drug solubilization and targeting” [804]), there has been a renewed interest to expand the array of targetable lipid-based drug-delivery systems, to solubilize a wide variety of (lipophilic) drugs, which provide the required stability and cost-effectiveness as well as ease of processing and manufacture in sterile form. In addition, these drug-delivery systems are expected to be at least as efficacious and less toxic than the earlier developed systems [804]. In particular, the lipid emulsions have significant potential as an intravenous vehicle for lipophilic drugs because of their high solubilization capacity. Accordingly, lipid emulsions have higher drug-loading capacity than liposomes; emulsions are also easier to process and manufacture in a sterile form [807]. For intravenous administration, however, one limitation with lipid emulsions (for delivery of drugs which are poorly soluble in water) is the need for biocompatibility of the oil phase and surfactants used [807]. A good example of a challenging drug, with the above formulation drawbacks, is paclitaxel (cf. Section 13.2). (Paclitaxel has been identified as one of the best antineoplastic drugs found in nature in the past decades, and has demonstrated a wide spectrum of activity against solid tumors including ovarian, breast, head, Studies in Interface Science, Vol. 25. DOI: 10.1016/B978-0-444-53798-0.00022-5 # 2011 Elsevier B.V. All rights reserved.
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neck, colon, nonsmall cell lung, and prostatic cancers and AIDS-related Kaposi’s sarcoma [807–809]. Paclitaxel has proven to be one of the most broadly effective, and by far the most commercially successful, anticancer agents ever introduced into the marketplace [807].) The first commercially available formulation containing paclitaxel, TaxolÒ (Bristol-Myers Squibb), was approved by the FDA in 1992. The marketed formulation is based on an ethanol-surfactant mixture, where the surfactant utilized is cremophor [806,807]. Although a commonly used surfactant for lipophilic compounds, cremophor has unfortunately been associated with a wide spectrum of adverse reactions, including bronchospasm, hypotension, and other hypersensitivity-type reactions ([807]; see also Section 13.2 and Refs. [602,603,806]). Other serious side effects, for which cremophor has been found responsible, are nephrotoxicity, cardiotoxicity, and neurotoxicity [809]. Constantinides et al. further point out that long infusion times after 10-fold dilution of the cremophor:ethanol solution as well as premedication are, therefore, required to reduce the severity or incidence of these adverse effects. In addition to the safety issues, there are a number of formulationrelated concerns that substantiate the need for an improved formulation, such as precipitation after dilution thus requiring administration through a filter and the requirement for nonplasticized infusion sets [807]. While several generic paclitaxel products have recently been approved for clinical use, a considerable need still exists for a new formulation of paclitaxel that retains efficacy, improves tolerability, and provides advantages with respect to preparation and administration ([807]; see also Refs. [806,809,810]).
20.1 TOCOL NANOEMULSIONS FOR SOLUBILIZING, AND DRUG DELIVERY, OF PACLITAXEL: PASSIVE ACCUMULATION IN TUMORS Studies by Constantinides and coworkers [807,811,812] have shown that, unlike several other paclitaxel formulations in various stages of development, the use of tocol-based nanoemulsions enables formulation of the active component without altering any chemical bonds or the molecular structure of paclitaxel. (A commonly employed tocol in the food industry is a-tocopherol, also known as vitamin E.) A tocol emulsion was used to provide a safe, lipophilic component to solubilize the highly water-insoluble molecule, paclitaxel, without the use of any toxic organic solvents ([811,812]; cf. Ref. [810]). The use of vitamin E (a-tocopherol) to dissolve paclitaxel, with the addition of surfactants, enables the production of a stable (cremophor-free) nanoemulsion of paclitaxel at high drug loading [807,811]. After emulsification, this nanoemulsion contains paclitaxel at a concentration of 10 mg/ml, and the mean particle size is 100 nm which enables final sterilization by filtration [807]. In addition to these physicochemical and manufacturing advantages, the above small-particle emulsion formulation of paclitaxel (named “TocosolÒ-
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paclitaxel”) has the capability for passive accumulation in tumors via the enhanced permeability and retention (EPR) effect [807]. The EPR effect results from the known leakiness of tumor vasculature (e.g., Refs. [565–568]) that allows nanoparticles to easily permeate and accumulate in cancer tissues. In addition, the lymphatic drainage system does not operate effectively in tumor tissue. As a consequence, leaked polymer molecules or nanoparticles are retained for a prolonged period of time in the tumor interstitium [606,807]. When nanoemulsion particles contain anticancer drugs, the EPR effect can lead to greater drug efficacy ([807]; see also below). TocosolÒ-paclitaxel has successfully completed Phase I and Phase II clinical trials [807,812], and a Phase III clinical trial has been initiated [812]. This tocol nanoemulsion of paclitaxel displays several advantages over the existing cremophor:ethanol formulation, including a ready-to-use product that incorporates high drug loading of paclitaxel (10 mg/ml), smaller dose volumes, and shorter infusion periods. The tocol-nanoemulsion formulation may provide a superior safety profile while allowing for delivery of a greater “dose density,” thus potentially resulting in greater antitumor efficacy [807]. As reviewed by Constantinides et al., clinical studies reported (as of 2004) with TocosolÒ-paclitaxel include a dose escalation Phase I study in 37 patients, and four separate Phase IIA studies in patients with ovarian cancer, colorectal cancer, nonsmall cell lung cancer, or bladder cancer [807]. In addition, a 2006 industry newsletter article (dated 11-10-06 in Pharmaceutical Business Review Online) on the TocosolÒ-paclitaxel agent (by Sonus Pharmaceuticals) provides a summarization of some further results: Sonus’s TocosolÒ-paclitaxel allows a dose of paclitaxel to be delivered via a 15-min infusion compared to the 3-h TaxolÒ administration. Based on Phase IIB data, this tocol nanoemulsion is described as showing a marked reduction in overall incidence of neuropathy compared to other paclitaxel formulations (37% for Tocosol compared to 71% for AbraxaneÒ [i.e., albumin-bound paclitaxel (by Abraxis Biosciences)] and 60% for TaxolÒ). This pharmaceutical industry newsletter further recounts that historically, paclitaxel formulations, including AbraxaneÒ, have been associated with high incidence of neuropathy and, hence, often patients are forced to discontinue therapy. Accordingly, if TocosolÒ-paclitaxel is again able to demonstrate an improved neuropathy profile in the current Phase III trial, this would represent a major benefit (see industry newsletter article, dated 11-10-06, online at www.pharmaceutical-business-review.com).
20.2 CHOLESTEROL-RICH/PHOSPHOLIPID NANOEMULSIONS CONTAINING DERIVATIZED PACLITAXEL: ACTIVE UPTAKE INTO TUMORS VIA LDL RECEPTORS Besides the capability of nanoemulsion particles in general to passively accumulate in tumors via the EPR effect (cf. Section 20.1), a small fraction of such lipid-nanoemulsion types are also capable of participating in a process of
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active uptake into tumors (see below). Specifically, these select types of lipid nanoemulsions are able to actively target tumors via the process of receptormediated endocytosis. An even smaller number of these select lipid nanoemulsions, capable of active tumor targeting, are under clinical study—one example of which follows. Maranhao and coworkers [808,813–815] have developed a cholesterol-rich nanoemulsion, which they have termed “LDE,” that undergoes active uptake into cancer tissues after injection into the bloodstream (see below). (Besides cholesterol compounds, LDE contains a substantial concentration of phospholipid. In brief, LDE was prepared from a lipid mixture composed of 40 mg cholesteryl oleate, 20 mg egg phosphatidylcholine, 1 mg triolein, and 0.5 mg cholesterol [808,816].) These authors have demonstrated in various studies that their (cremophor-free) nanoemulsion, LDE, is taken up by the low-density lipoprotein, or LDL, receptors [808,813–816]. LDE is manufactured without protein, but when in contact with blood plasma it acquires apolipoprotein E (apo E) which is also recognized by the LDL receptors, thus allowing endocytosis of the nanoemulsion. LDE can therefore be used to target antineoplastic drugs against cancer cells that overexpress LDL receptors ([808]; cf. Section 14.1). It has already been demonstrated in patients that after intravenous injection, LDE can concentrate in leukemia cells or in solid tumors such as ovarian and breast carcinomas that overexpress those receptors [815,817,818]. Accordingly, the association of paclitaxel to LDE was tested. It was observed that the LDE–paclitaxel complex tends to dissociate in the bloodstream after injection into mice [816]. Derivatization with oleic acid (i.e., covalently attaching an oleoyl chain to paclitaxel) was used as a strategy to improve the association yield and the stability of the drug when complexed with LDE. Compared with commercial paclitaxel (TaxolÒ, i.e., paclitaxel-cremophor), the resulting LDE–paclitaxel oleate complex showed higher therapeutic index (in mice) that was achieved by diminution of the toxicity and increase of the anticancer action [808,816]. In a recent clinical study by Dias et al. [808], the pharmacokinetics of LDE–paclitaxel oleate and the ability of LDE to concentrate the drug in the tumor were investigated in patients with gynecologic cancers. Either LDE– paclitaxel oleate complex, doubly labeled with [14C]-cholesteryl oleate and [3H]-paclitaxel oleate, or [3H]-paclitaxel-cremophor was intravenously injected into eight patients. (Blood samples were then collected over 24 h to determine the plasma decay curves. Fractional clearance rate (FCR) and pharmacokinetic parameters were calculated by means of compartmental analysis. In addition, specimens from tumors and the corresponding normal tissues were excised, during surgery, for radioactivity measurements and histological analysis [808].) Plasma decay curves were first obtained after the injection of the doubly labeled LDE–paclitaxel oleate in five patients. It was found that the decay
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curves of the LDE’s [14C]-cholesteryl oleate did not substantially differ from that of [3H]-paclitaxel oleate [808]. Next, plasma decay curves of [3H]-paclitaxel oleate associated to LDE injected in five patients and [3H]-paclitaxelcremophor injected in three patients were both obtained. The curve of paclitaxel oleate is slower than that of paclitaxel-cremophor; accordingly, the FCR of paclitaxel oleate is smaller than that of paclitaxel-cremophor (0.069 0.027 and 0.231 0.128 h 1, respectively, P ¼ 0.028) [808]. Dias et al. also measured tissue uptake of the labels [14C]-cholesteryl oleate and [3H]-paclitaxel oleate of the LDE–paclitaxel oleate association. It was found that the uptake of both cholesteryl oleate and paclitaxel oleate by the tumor was greater than that of the normal tissues. The (mean) tumor uptake/ normal tissue uptake ratio of cholesteryl oleate was very similar to that of paclitaxel oleate (3.5 1.7 and 3.6 2.1, P ¼ 0.936) [808]. These authors state that the above experiments, in which LDE uptake by the tumor (where the LDL receptors are upregulated) is measured comparatively to the uptake of normal tissues, strongly support the assumption that LDE–paclitaxel oleate complex retains the ability of this lipid nanoemulsion to bind to receptors and concentrate in the tumor tissues with LDL-receptor upregulation. This reasoning is suggested by the 3.6 times greater uptake measured in the tumor compared to normal tissues [808]. Dias et al. conclude that this clinical study shows that the association of paclitaxel oleate to the cholesterol-rich nanoemulsion, LDE, is stable in the bloodstream of cancer patients and markedly alters the pharmacokinetic profile of paclitaxel oleate when compared to the commercial paclitaxel-cremophor formulation. These authors further point out that a clear-cut demonstration that LDE indeed performs as a drug targeting vehicle is given by the finding of a 3.6 times greater uptake of paclitaxel oleate, associated to the nanoemulsion, into the tumor compared to normal tissues. This figure is practically equal to the 3.5 times concentration ratio of the LDE-radioactive cholesterol ester, which these authors argue is a convincing counterproof to the decay curves of the plasma pharmacokinetics of the LDE–paclitaxel oleate complex. Accordingly, these authors assert that when taken together, both the plasma and tissue data demonstrate that LDE carries the paclitaxel derivative in the blood plasma and delivers the drug derivative to the tumor tissue without substantial dissociation [808].
20.3 STABLE (NONPHOSPHOLIPID, NONPROTEIN) LIPID NANOEMULSIONS FOR TARGETING TUMORS: ACTIVE UPTAKE OF (UNMODIFIED) PACLITAXEL VIA ENDOCYTOSIS Another type of parenteral lipid nanoemulsion, which is capable of active targeting of tumors via the process of receptor-mediated endocytosis (cf. Chapters 12–18), is the “LCM/nanoparticle-derived” drug-delivery agent
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described extensively in Chapter 19. As explained therein, a commercial-scale pharmaceutical-grade manufacturing method, which includes a modified FilmixÒ chemical formulation (see Sections 17.1 and 19.1), to produce this type of nanoemulsion drug-delivery agent has been developed and recently patented (in 2007) by Shorr and Rodriguez [803] of Cornerstone Pharmaceuticals for use in clinical work. [As per S.E.C. filings, Cornerstone Pharmaceuticals has been granted (since 2000) a worldwide license to all of the FilmixÒ technology’s underlying intellectual property (e.g., Refs. [538–546]) in the field of cancer drug-delivery therapy (as noted in www.sec.gov: S.E.C. public record “Form SB-2” filed 2-12-07 (re: CIK #0001166509), “Exhibit #10-4.htm”). In addition, as recorded before (cf. first paragraph of Chapter 19), CAV-CON Inc. itself is not a subsidiary of Cornerstone Pharmaceuticals, Inc. (nor does Cornerstone endorse, either explicitly or implicitly, any CAV-CON product).] Consistent with marked similarities of the documented lipid composition employed by Shorr and Rodriguez [803], in relation to the FilmixÒ lipid formulation (see Section 17.1 vs. Section 19.1; see also below), they report that their patented manufacturing method produces a (cremophor-free) lipid nanoemulsion comprising “nongas containing nanoparticles” [803]—which display the same active targeting of tumors (see Section 19.3) as already described for the “dispersed LMN” within the original (cremophor-free) FilmixÒ nanoemulsion (cf. Chapters 16–18). The marked, documented similarities in the targeting behavior of the two (differently named) nanoparticles, as well as further corroborating data (see Section 19.3 for details), provide forceful evidence that “nongas containing nanoparticles” and “dispersed LMN” are most likely structured essentially the same (see Chapter 19 for a detailed discussion). This conclusion is not surprising since a review of published documents (see formulation instructions in Refs. [538–546] vs. Ref. [803]; cf. Section 19.3) makes clear that the lipid nanoparticles in all cases were formed from mostly, or entirely, the same key lipid types and in very similar, or the same, weight ratios (see Sections 17.1 and 19.1 for discussion)—despite differences in the two manufacturing methodologies. Other structural features which are actually fully identical for both the nongas containing nanoparticles (in the nanoemulsion produced by the patented manufacturing method of Cornerstone Pharmaceuticals ([803]; cf. Ref. [819])) and the dispersed LMN (within the stable FilmixÒ nanoemulsion (cf. Sections 12.1, 15.2, and 16.2.2)) are as follows: (1) both targeted drugdelivery agents do not contain any phospholipids (of human or other origin); (2) both agents do not contain any proteins (of human or other origin); and (3) for effective, (actively) targeted drug-delivery of paclitaxel to tumors there is no chemical modification or derivatization, of the paclitaxel molecule, at all required [538–546,803,819]. These features in common for this category of parenteral lipid nanoemulsion further simplify, that is, remove some potential complications (cf. below) to, the process of parenteral drug delivery in patients. In view of such advantages, a clinical trial is reported as in
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preparation, by Cornerstone Pharmaceuticals (e.g., Ref. [820]), for targeted drug-delivery of paclitaxel to tumors in patients using this drug-delivery agent (manufactured in accord with their recently patented method [803]). [The “tradename” for their proprietary drug-delivery vehicle, as expressed in the Cornerstone Pharmaceuticals company website (www.cornerstonepharma. com) and in a 2007 A.A.P.S. Workshop [819], is “EmulsiphanTM.” In addition, when the EmulsiphanTM drug-delivery vehicle (a.k.a. nanoemulsion delivery-technology platform) is utilized for targeted drug-delivery of paclitaxel, this Emulsiphan-based product candidate is referred to as “EmPACTM” [819,820].] The above-described structural features for this category of parenteral lipid nanoemulsion (i.e., based upon a “LCM/nanoparticle-derived” formulation) avoid various past problems reported for earlier versions of (actively) targeted drug-delivery agents utilizing the LDL receptor-mediated endocytic pathway (see below). As explained in a literature review by Firestone [821], numerous published studies have shown that many types of cancer cells have unusually great LDL requirements (see also Section 14.1). Thus, if LDL could be made to carry antineoplastic drugs, it would serve as a targeting vehicle; this concept was proposed in 1981–1982 [642,822] and has been reviewed several times since then [613,823–826]. Drugs have been associated with LDL by reconstituting LDL particles with the result that all or part of the core is replaced by drug [827,828]. The method fails unless the drug is compatible with the phospholipid coat [829]; LDL anchoring molecules, covalently attached to the drug, such as oleoyl, retinyl, and cholesteryl facilitate reconstitution [830]. These complications can now be avoided since the above-described “LCM/nanoparticle-derived” formulation contains no phospholipids, and no chemical modification of paclitaxel is required (unlike the cholesterol-rich/ phospholipid nanoemulsion described in Section 20.2). In addition, the lipid composition of this “LCM/nanoparticle-derived” nanoemulsion consists of cholesterol esters, free cholesterol, and glycerides (cf. Sections 17.1 and 19.1) and is, therefore, similar to the lipid composition of both LDL particles (cf. Section 14.1) and chylomicron remnant particles (cf. Section 14.2.1).The “LCM/nanoparticle-derived” drug-delivery agent is manufactured without protein, but when its lipid nanoparticles are in contact with blood plasma they likely acquire (i.e., bind) apolipoprotein E (cf. Section 14.2.1) and/or apolipoprotein B (cf. Section 14.1). Both of these apolipoproteins (apo E and apo B) are recognized by the LDL receptors, thus allowing receptor-mediated endocytosis of this parenteral lipid nanoemulsion. This “LCM/nanoparticlederived” drug-delivery agent can therefore be used to actively target antineoplastic drug (e.g., paclitaxel) against tumor cells that overexpress LDL receptors (see Chapters 13 and 14). In conclusion, the grounds for pursuing the above cancer-chemotherapy approach, utilizing the LDL receptor-mediated endocytic pathway, have been
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well summarized by Firestone and coworkers earlier [821,829]. Briefly, high LDL requirements have been documented for the following human malignancies: acute myeloid leukemia [624]; monocytic (FAB-M5) and myelomonocytic (FAB-M4) leukemias, chronic myeloid leukemia in blast crisis [626]; epidermoid cervical cancer EC-50, endometrial adenocarcinoma AC-258 [642] and four other gynecological cancers [831]; gastric carcinoma, parotid adenoma [832]; medulloblastoma, oligodendroma, malignant meningioma [627]; glioma V-251MG [630]; G2 hepatoma [833,834]; squamous lung tumor [835]; and choriocarcinoma [836]. Firestone also states that most human tumors have not yet been surveyed, so it is reasonable to suppose that many more tumors will be found to have exceptionally high LDL requirements. This expectation is hinted at and corroborated by the frequent finding of depletion of LDL in the blood of cancer patients [821].
Selected Parenteral Lipid Nanoemulsions Under Clinical Study: Comparison Concerning Passive Accumulation in Tumors, Active Targeting of Tumors, and Validation Status Past lipid-based dispersion systems such as simple emulsions, micellar systems, and liposomes have been utilized for parenteral administration of lipophilic drugs for several decades [804–806]. [Parenteral administration, as used below, will refer specifically to injection into the bloodstream.] As pointed out by Constantinides and Wasan (in their preface to the 2004 theme issue on “Advances in lipid-based drug solubilization and targeting” [804]), there has been a renewed interest to expand the array of targetable lipid-based drug-delivery systems, to solubilize a wide variety of (lipophilic) drugs, which provide the required stability and cost-effectiveness as well as ease of processing and manufacture in sterile form. In addition, these drug-delivery systems are expected to be at least as efficacious and less toxic than the earlier developed systems [804]. In particular, the lipid emulsions have significant potential as an intravenous vehicle for lipophilic drugs because of their high solubilization capacity. Accordingly, lipid emulsions have higher drug-loading capacity than liposomes; emulsions are also easier to process and manufacture in a sterile form [807]. For intravenous administration, however, one limitation with lipid emulsions (for delivery of drugs which are poorly soluble in water) is the need for biocompatibility of the oil phase and surfactants used [807]. A good example of a challenging drug, with the above formulation drawbacks, is paclitaxel (cf. Section 13.2). (Paclitaxel has been identified as one of the best antineoplastic drugs found in nature in the past decades, and has demonstrated a wide spectrum of activity against solid tumors including ovarian, breast, head, Studies in Interface Science, Vol. 25. DOI: 10.1016/B978-0-444-53798-0.00022-5 # 2011 Elsevier B.V. All rights reserved.
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neck, colon, nonsmall cell lung, and prostatic cancers and AIDS-related Kaposi’s sarcoma [807–809]. Paclitaxel has proven to be one of the most broadly effective, and by far the most commercially successful, anticancer agents ever introduced into the marketplace [807].) The first commercially available formulation containing paclitaxel, TaxolÒ (Bristol-Myers Squibb), was approved by the FDA in 1992. The marketed formulation is based on an ethanol-surfactant mixture, where the surfactant utilized is cremophor [806,807]. Although a commonly used surfactant for lipophilic compounds, cremophor has unfortunately been associated with a wide spectrum of adverse reactions, including bronchospasm, hypotension, and other hypersensitivity-type reactions ([807]; see also Section 13.2 and Refs. [602,603,806]). Other serious side effects, for which cremophor has been found responsible, are nephrotoxicity, cardiotoxicity, and neurotoxicity [809]. Constantinides et al. further point out that long infusion times after 10-fold dilution of the cremophor:ethanol solution as well as premedication are, therefore, required to reduce the severity or incidence of these adverse effects. In addition to the safety issues, there are a number of formulationrelated concerns that substantiate the need for an improved formulation, such as precipitation after dilution thus requiring administration through a filter and the requirement for nonplasticized infusion sets [807]. While several generic paclitaxel products have recently been approved for clinical use, a considerable need still exists for a new formulation of paclitaxel that retains efficacy, improves tolerability, and provides advantages with respect to preparation and administration ([807]; see also Refs. [806,809,810]).
20.1 TOCOL NANOEMULSIONS FOR SOLUBILIZING, AND DRUG DELIVERY, OF PACLITAXEL: PASSIVE ACCUMULATION IN TUMORS Studies by Constantinides and coworkers [807,811,812] have shown that, unlike several other paclitaxel formulations in various stages of development, the use of tocol-based nanoemulsions enables formulation of the active component without altering any chemical bonds or the molecular structure of paclitaxel. (A commonly employed tocol in the food industry is a-tocopherol, also known as vitamin E.) A tocol emulsion was used to provide a safe, lipophilic component to solubilize the highly water-insoluble molecule, paclitaxel, without the use of any toxic organic solvents ([811,812]; cf. Ref. [810]). The use of vitamin E (a-tocopherol) to dissolve paclitaxel, with the addition of surfactants, enables the production of a stable (cremophor-free) nanoemulsion of paclitaxel at high drug loading [807,811]. After emulsification, this nanoemulsion contains paclitaxel at a concentration of 10 mg/ml, and the mean particle size is 100 nm which enables final sterilization by filtration [807]. In addition to these physicochemical and manufacturing advantages, the above small-particle emulsion formulation of paclitaxel (named “TocosolÒ-
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paclitaxel”) has the capability for passive accumulation in tumors via the enhanced permeability and retention (EPR) effect [807]. The EPR effect results from the known leakiness of tumor vasculature (e.g., Refs. [565–568]) that allows nanoparticles to easily permeate and accumulate in cancer tissues. In addition, the lymphatic drainage system does not operate effectively in tumor tissue. As a consequence, leaked polymer molecules or nanoparticles are retained for a prolonged period of time in the tumor interstitium [606,807]. When nanoemulsion particles contain anticancer drugs, the EPR effect can lead to greater drug efficacy ([807]; see also below). TocosolÒ-paclitaxel has successfully completed Phase I and Phase II clinical trials [807,812], and a Phase III clinical trial has been initiated [812]. This tocol nanoemulsion of paclitaxel displays several advantages over the existing cremophor:ethanol formulation, including a ready-to-use product that incorporates high drug loading of paclitaxel (10 mg/ml), smaller dose volumes, and shorter infusion periods. The tocol-nanoemulsion formulation may provide a superior safety profile while allowing for delivery of a greater “dose density,” thus potentially resulting in greater antitumor efficacy [807]. As reviewed by Constantinides et al., clinical studies reported (as of 2004) with TocosolÒ-paclitaxel include a dose escalation Phase I study in 37 patients, and four separate Phase IIA studies in patients with ovarian cancer, colorectal cancer, nonsmall cell lung cancer, or bladder cancer [807]. In addition, a 2006 industry newsletter article (dated 11-10-06 in Pharmaceutical Business Review Online) on the TocosolÒ-paclitaxel agent (by Sonus Pharmaceuticals) provides a summarization of some further results: Sonus’s TocosolÒ-paclitaxel allows a dose of paclitaxel to be delivered via a 15-min infusion compared to the 3-h TaxolÒ administration. Based on Phase IIB data, this tocol nanoemulsion is described as showing a marked reduction in overall incidence of neuropathy compared to other paclitaxel formulations (37% for Tocosol compared to 71% for AbraxaneÒ [i.e., albumin-bound paclitaxel (by Abraxis Biosciences)] and 60% for TaxolÒ). This pharmaceutical industry newsletter further recounts that historically, paclitaxel formulations, including AbraxaneÒ, have been associated with high incidence of neuropathy and, hence, often patients are forced to discontinue therapy. Accordingly, if TocosolÒ-paclitaxel is again able to demonstrate an improved neuropathy profile in the current Phase III trial, this would represent a major benefit (see industry newsletter article, dated 11-10-06, online at www.pharmaceutical-business-review.com).
20.2 CHOLESTEROL-RICH/PHOSPHOLIPID NANOEMULSIONS CONTAINING DERIVATIZED PACLITAXEL: ACTIVE UPTAKE INTO TUMORS VIA LDL RECEPTORS Besides the capability of nanoemulsion particles in general to passively accumulate in tumors via the EPR effect (cf. Section 20.1), a small fraction of such lipid-nanoemulsion types are also capable of participating in a process of
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active uptake into tumors (see below). Specifically, these select types of lipid nanoemulsions are able to actively target tumors via the process of receptormediated endocytosis. An even smaller number of these select lipid nanoemulsions, capable of active tumor targeting, are under clinical study—one example of which follows. Maranhao and coworkers [808,813–815] have developed a cholesterol-rich nanoemulsion, which they have termed “LDE,” that undergoes active uptake into cancer tissues after injection into the bloodstream (see below). (Besides cholesterol compounds, LDE contains a substantial concentration of phospholipid. In brief, LDE was prepared from a lipid mixture composed of 40 mg cholesteryl oleate, 20 mg egg phosphatidylcholine, 1 mg triolein, and 0.5 mg cholesterol [808,816].) These authors have demonstrated in various studies that their (cremophor-free) nanoemulsion, LDE, is taken up by the low-density lipoprotein, or LDL, receptors [808,813–816]. LDE is manufactured without protein, but when in contact with blood plasma it acquires apolipoprotein E (apo E) which is also recognized by the LDL receptors, thus allowing endocytosis of the nanoemulsion. LDE can therefore be used to target antineoplastic drugs against cancer cells that overexpress LDL receptors ([808]; cf. Section 14.1). It has already been demonstrated in patients that after intravenous injection, LDE can concentrate in leukemia cells or in solid tumors such as ovarian and breast carcinomas that overexpress those receptors [815,817,818]. Accordingly, the association of paclitaxel to LDE was tested. It was observed that the LDE–paclitaxel complex tends to dissociate in the bloodstream after injection into mice [816]. Derivatization with oleic acid (i.e., covalently attaching an oleoyl chain to paclitaxel) was used as a strategy to improve the association yield and the stability of the drug when complexed with LDE. Compared with commercial paclitaxel (TaxolÒ, i.e., paclitaxel-cremophor), the resulting LDE–paclitaxel oleate complex showed higher therapeutic index (in mice) that was achieved by diminution of the toxicity and increase of the anticancer action [808,816]. In a recent clinical study by Dias et al. [808], the pharmacokinetics of LDE–paclitaxel oleate and the ability of LDE to concentrate the drug in the tumor were investigated in patients with gynecologic cancers. Either LDE– paclitaxel oleate complex, doubly labeled with [14C]-cholesteryl oleate and [3H]-paclitaxel oleate, or [3H]-paclitaxel-cremophor was intravenously injected into eight patients. (Blood samples were then collected over 24 h to determine the plasma decay curves. Fractional clearance rate (FCR) and pharmacokinetic parameters were calculated by means of compartmental analysis. In addition, specimens from tumors and the corresponding normal tissues were excised, during surgery, for radioactivity measurements and histological analysis [808].) Plasma decay curves were first obtained after the injection of the doubly labeled LDE–paclitaxel oleate in five patients. It was found that the decay
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curves of the LDE’s [14C]-cholesteryl oleate did not substantially differ from that of [3H]-paclitaxel oleate [808]. Next, plasma decay curves of [3H]-paclitaxel oleate associated to LDE injected in five patients and [3H]-paclitaxelcremophor injected in three patients were both obtained. The curve of paclitaxel oleate is slower than that of paclitaxel-cremophor; accordingly, the FCR of paclitaxel oleate is smaller than that of paclitaxel-cremophor (0.069 0.027 and 0.231 0.128 h 1, respectively, P ¼ 0.028) [808]. Dias et al. also measured tissue uptake of the labels [14C]-cholesteryl oleate and [3H]-paclitaxel oleate of the LDE–paclitaxel oleate association. It was found that the uptake of both cholesteryl oleate and paclitaxel oleate by the tumor was greater than that of the normal tissues. The (mean) tumor uptake/ normal tissue uptake ratio of cholesteryl oleate was very similar to that of paclitaxel oleate (3.5 1.7 and 3.6 2.1, P ¼ 0.936) [808]. These authors state that the above experiments, in which LDE uptake by the tumor (where the LDL receptors are upregulated) is measured comparatively to the uptake of normal tissues, strongly support the assumption that LDE–paclitaxel oleate complex retains the ability of this lipid nanoemulsion to bind to receptors and concentrate in the tumor tissues with LDL-receptor upregulation. This reasoning is suggested by the 3.6 times greater uptake measured in the tumor compared to normal tissues [808]. Dias et al. conclude that this clinical study shows that the association of paclitaxel oleate to the cholesterol-rich nanoemulsion, LDE, is stable in the bloodstream of cancer patients and markedly alters the pharmacokinetic profile of paclitaxel oleate when compared to the commercial paclitaxel-cremophor formulation. These authors further point out that a clear-cut demonstration that LDE indeed performs as a drug targeting vehicle is given by the finding of a 3.6 times greater uptake of paclitaxel oleate, associated to the nanoemulsion, into the tumor compared to normal tissues. This figure is practically equal to the 3.5 times concentration ratio of the LDE-radioactive cholesterol ester, which these authors argue is a convincing counterproof to the decay curves of the plasma pharmacokinetics of the LDE–paclitaxel oleate complex. Accordingly, these authors assert that when taken together, both the plasma and tissue data demonstrate that LDE carries the paclitaxel derivative in the blood plasma and delivers the drug derivative to the tumor tissue without substantial dissociation [808].
20.3 STABLE (NONPHOSPHOLIPID, NONPROTEIN) LIPID NANOEMULSIONS FOR TARGETING TUMORS: ACTIVE UPTAKE OF (UNMODIFIED) PACLITAXEL VIA ENDOCYTOSIS Another type of parenteral lipid nanoemulsion, which is capable of active targeting of tumors via the process of receptor-mediated endocytosis (cf. Chapters 12–18), is the “LCM/nanoparticle-derived” drug-delivery agent
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described extensively in Chapter 19. As explained therein, a commercial-scale pharmaceutical-grade manufacturing method, which includes a modified FilmixÒ chemical formulation (see Sections 17.1 and 19.1), to produce this type of nanoemulsion drug-delivery agent has been developed and recently patented (in 2007) by Shorr and Rodriguez [803] of Cornerstone Pharmaceuticals for use in clinical work. [As per S.E.C. filings, Cornerstone Pharmaceuticals has been granted (since 2000) a worldwide license to all of the FilmixÒ technology’s underlying intellectual property (e.g., Refs. [538–546]) in the field of cancer drug-delivery therapy (as noted in www.sec.gov: S.E.C. public record “Form SB-2” filed 2-12-07 (re: CIK #0001166509), “Exhibit #10-4.htm”). In addition, as recorded before (cf. first paragraph of Chapter 19), CAV-CON Inc. itself is not a subsidiary of Cornerstone Pharmaceuticals, Inc. (nor does Cornerstone endorse, either explicitly or implicitly, any CAV-CON product).] Consistent with marked similarities of the documented lipid composition employed by Shorr and Rodriguez [803], in relation to the FilmixÒ lipid formulation (see Section 17.1 vs. Section 19.1; see also below), they report that their patented manufacturing method produces a (cremophor-free) lipid nanoemulsion comprising “nongas containing nanoparticles” [803]—which display the same active targeting of tumors (see Section 19.3) as already described for the “dispersed LMN” within the original (cremophor-free) FilmixÒ nanoemulsion (cf. Chapters 16–18). The marked, documented similarities in the targeting behavior of the two (differently named) nanoparticles, as well as further corroborating data (see Section 19.3 for details), provide forceful evidence that “nongas containing nanoparticles” and “dispersed LMN” are most likely structured essentially the same (see Chapter 19 for a detailed discussion). This conclusion is not surprising since a review of published documents (see formulation instructions in Refs. [538–546] vs. Ref. [803]; cf. Section 19.3) makes clear that the lipid nanoparticles in all cases were formed from mostly, or entirely, the same key lipid types and in very similar, or the same, weight ratios (see Sections 17.1 and 19.1 for discussion)—despite differences in the two manufacturing methodologies. Other structural features which are actually fully identical for both the nongas containing nanoparticles (in the nanoemulsion produced by the patented manufacturing method of Cornerstone Pharmaceuticals ([803]; cf. Ref. [819])) and the dispersed LMN (within the stable FilmixÒ nanoemulsion (cf. Sections 12.1, 15.2, and 16.2.2)) are as follows: (1) both targeted drugdelivery agents do not contain any phospholipids (of human or other origin); (2) both agents do not contain any proteins (of human or other origin); and (3) for effective, (actively) targeted drug-delivery of paclitaxel to tumors there is no chemical modification or derivatization, of the paclitaxel molecule, at all required [538–546,803,819]. These features in common for this category of parenteral lipid nanoemulsion further simplify, that is, remove some potential complications (cf. below) to, the process of parenteral drug delivery in patients. In view of such advantages, a clinical trial is reported as in
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preparation, by Cornerstone Pharmaceuticals (e.g., Ref. [820]), for targeted drug-delivery of paclitaxel to tumors in patients using this drug-delivery agent (manufactured in accord with their recently patented method [803]). [The “tradename” for their proprietary drug-delivery vehicle, as expressed in the Cornerstone Pharmaceuticals company website (www.cornerstonepharma. com) and in a 2007 A.A.P.S. Workshop [819], is “EmulsiphanTM.” In addition, when the EmulsiphanTM drug-delivery vehicle (a.k.a. nanoemulsion delivery-technology platform) is utilized for targeted drug-delivery of paclitaxel, this Emulsiphan-based product candidate is referred to as “EmPACTM” [819,820].] The above-described structural features for this category of parenteral lipid nanoemulsion (i.e., based upon a “LCM/nanoparticle-derived” formulation) avoid various past problems reported for earlier versions of (actively) targeted drug-delivery agents utilizing the LDL receptor-mediated endocytic pathway (see below). As explained in a literature review by Firestone [821], numerous published studies have shown that many types of cancer cells have unusually great LDL requirements (see also Section 14.1). Thus, if LDL could be made to carry antineoplastic drugs, it would serve as a targeting vehicle; this concept was proposed in 1981–1982 [642,822] and has been reviewed several times since then [613,823–826]. Drugs have been associated with LDL by reconstituting LDL particles with the result that all or part of the core is replaced by drug [827,828]. The method fails unless the drug is compatible with the phospholipid coat [829]; LDL anchoring molecules, covalently attached to the drug, such as oleoyl, retinyl, and cholesteryl facilitate reconstitution [830]. These complications can now be avoided since the above-described “LCM/nanoparticle-derived” formulation contains no phospholipids, and no chemical modification of paclitaxel is required (unlike the cholesterol-rich/ phospholipid nanoemulsion described in Section 20.2). In addition, the lipid composition of this “LCM/nanoparticle-derived” nanoemulsion consists of cholesterol esters, free cholesterol, and glycerides (cf. Sections 17.1 and 19.1) and is, therefore, similar to the lipid composition of both LDL particles (cf. Section 14.1) and chylomicron remnant particles (cf. Section 14.2.1).The “LCM/nanoparticle-derived” drug-delivery agent is manufactured without protein, but when its lipid nanoparticles are in contact with blood plasma they likely acquire (i.e., bind) apolipoprotein E (cf. Section 14.2.1) and/or apolipoprotein B (cf. Section 14.1). Both of these apolipoproteins (apo E and apo B) are recognized by the LDL receptors, thus allowing receptor-mediated endocytosis of this parenteral lipid nanoemulsion. This “LCM/nanoparticlederived” drug-delivery agent can therefore be used to actively target antineoplastic drug (e.g., paclitaxel) against tumor cells that overexpress LDL receptors (see Chapters 13 and 14). In conclusion, the grounds for pursuing the above cancer-chemotherapy approach, utilizing the LDL receptor-mediated endocytic pathway, have been
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well summarized by Firestone and coworkers earlier [821,829]. Briefly, high LDL requirements have been documented for the following human malignancies: acute myeloid leukemia [624]; monocytic (FAB-M5) and myelomonocytic (FAB-M4) leukemias, chronic myeloid leukemia in blast crisis [626]; epidermoid cervical cancer EC-50, endometrial adenocarcinoma AC-258 [642] and four other gynecological cancers [831]; gastric carcinoma, parotid adenoma [832]; medulloblastoma, oligodendroma, malignant meningioma [627]; glioma V-251MG [630]; G2 hepatoma [833,834]; squamous lung tumor [835]; and choriocarcinoma [836]. Firestone also states that most human tumors have not yet been surveyed, so it is reasonable to suppose that many more tumors will be found to have exceptionally high LDL requirements. This expectation is hinted at and corroborated by the frequent finding of depletion of LDL in the blood of cancer patients [821].