Bacterially derived, intact minicells for delivery of therapeutic agents to brain tumors

#Primary brain tumors consist of a diverse group of neoplasms, derived from various different cell lineages. Pursuant to a World Health Organization categorization (Louis et al., 2007), tumors of the central nervous system are classified as astrocytic, oligodendroglial, or mixed (oligoastrocytic). These tumors are further classified by subtypes and are graded, based on histology, from 1 to IV, with grade IV being the most aggressive. Glioblastoma multiforme (GBM), the most aggressive form of primary malignant brain tumor, accounts for approximately 45% to 50% of all primary brain tumors (Wrensch et al., 2002; Behin et al., 2003) and represents the second largest cause of cancer death in adults under 35 years of age (Allard et al., 2009).

#Despite numerous therapeutic efforts, including cytoreductive surgery, radiation therapy and chemotherapy, the prognosis for glioma patients remains very poor (Stewart, 2002; Stupp et al., 2005). A majority eventually develop recurrent and progressive disease, after which the median survival is approximately 6 months (Wong et al., 1999; Lamborn et al., 2008). Median survival for GBM patients is about 12-14 months (Stupp et al., 2005).

#In addition, brain metastasis from primary tumors such as breast, lung, and skin (melanoma) is a significant and growing public health problem. An estimated 250,000 patients in the United States were diagnosed with brain metastases in 2009 (Fox et al., 2011), which is more than 10-fold greater than the incidence of primary brain tumors (Jemal et al., 2009). The prognosis for patients with brain metastases is very poor, and most patients live only 4-6 months after diagnosis. Current treatment regimens provide marginal survival benefits (Eichler and Loeffler, 2007).

#FIG. 1. EGF receptor quantitation on human (U87-MG) and canine brain tumor cells, which were treated with anti-EGFR MAb, followed by R-phycoerythrin conjugated goat anti-mouse IgG. The cells were analyzed using FACS and were compared with fluorescent R-phycoerythrin microbead standards. Control cells were treated in the same manner, except for the primary antibody. EGFR quantitation results revealed an EGFR concentration per cell (in a decreasing order) for BCD-1, U87-MG, BCD-9, BCD-8 and J3T cells was 2,866,854, 1,465,755, 930, 440, 774,352 and 287,622, respectively. Results for each cell line are shown as control (curves with dark border) and anti-EGFR MAb-treated (curves without dark border).

#FIG. 2. Results are shown of a cell proliferation (MTS) assay to determine doxorubicin sensitivity of canine and human (U87-MG) brain cancer cells. Error bars, ±SEM.

#FIG. 3. Representative histograms from FACS analyses show the efficiency of binding of EGFRminicellsDox to canine and human brain cancer cells. >95% of the cells in each case showed significant binding of EGFRminicellsDox. Cells treated with non-specifically targeted gp120minicellsDox did not display any binding to the cells. Anti-gp120 antibody is directed to HIV viral capsid protein gp120, which is not found on any of the tumor cells.

#The present disclosure provides compositions and methods for the treatment of brain tumors. In this respect, the inventors discovered that intact, bacterially derived minicells packaged with one or more anti-neoplastic agents, upon systemic administration, rapidly accumulate in the microenvironment of a brain tumor, in therapeutically significant concentrations. This finding was surprising because the minicells, approximately 400 nm in diameter, are much larger than what conventional understanding sets as the upper limit of 12 nm for a particle that is able to cross the blood brain barrier (BBB). See Sarin et al. (2008) and Laquintana et al. (2009).

#Accordingly, the inventors determined that a wide variety of brain tumors, both primary and metastatic, can be treated by administering systemically a therapeutically effective amount of a composition comprised of a plurality of such minicells, each minicell being a vehicle for an active agent against the tumor.

#Unless defined otherwise, all technical and scientific terms used in this description have the same meaning as commonly understood by those skilled in the relevant art.