A. DNCT and its Prior Uses
The goal of cancer therapy is to achieve a degree of selectivity that spares normal cells and destroys all malignant ones, since even a small number of remaining malignant cells can lead to recurrence, metastasis, and death. A two-component or binary system comprised of constituents that alone are nonlethal and largely confined to malignant cells, and which when combined are lethal to the neoplastic cells yet innocuous to normal cells is an ideal modality. One advantage of this type of binary system is that each component can be manipulated independently to maximize selectivity.
Boron neutron capture therapy (BNCT, see FIG. 1) is a binary system which combines two separately nonlethal constituents, a radiosensitizing compound that contains a stable boron-10(.sup.10 B) isotope, and nonionizing neutron radiation. When boron-10 is irradiated with neutrons, a nuclear reaction occurs that yields helium nuclei (.alpha.-particle), lithium nuclei, and about 100 million times more energy than the initial irradiated energy. The generated radiation destroys malignant cells containing the boron compound. Selectivity is achieved through the use of compounds which accumulate primarily in malignant cells and/or by aiming the neutron beam at the tumor mass which contains the boron carrier.
BNCT has historically been used or attempted primarily for brain cancers, and specifically, for glioblastoma multiform, an aggressive malignant brain tumor.
It would be of great benefit to be able to extend the use of BNCT to urogenital tumors, including cancer of the prostate, kidney, and bladder.
Prostate cancer is the most frequently diagnosed carcinoma in the U.S. male population. In 1994 the expected incidence is 200,000 new cases with 40,000 fatalities. Cure is limited to those with early localized disease. Therapeutic modalities include radical surgery, radiotherapy, androgen deprivation, cryotherapy, and observation. Patients presenting with organ confined cancer are candidates for curative surgery or radiotherapy. However, only approximately one third of patients present with truly curable prostate cancer, while the rest have advanced disease which is incurable. Early detection and screening may increase the proportion of patients with curable disease. However, new more effective therapies are necessary for patients with advanced disease.
Deaths attributable to kidney, or renal, cancer has risen in the United States from approximately 5,000 in 1960 to over 10,000 in 1990. It is estimated that there has been a 35% increase in renal cancer in men and a 16% increase in renal cancer in women in that timeframe. There were approximately 10,000 deaths attributable to bladder cancer in 1994, and an estimated 51,200 new bladder cancer cases reported in that year. The rate of bladder cancer is four times greater among men than women. When detected at an early stage, the 5-year survival rate for bladder cancer is 91%. However, for regional and distant disease, the survival rates are 46% and 9%, respectively. Surgery, alone or in combination with other treatments is currently used in over 90% of bladder cancer. Preoperative chemotherapy alone or with radiation before cystecomy has improved some treatment results.
B. Boron-containing Compounds Reported for Use in BNCT
Many classes of compounds have been synthesized for BNCT. For example, see Barth, R. F.; Soloway, A. H.; Fairchild, R. G.; Brugger, R. M., Cancer, 70:2995-3008 (1992); Fairchild, R. G.; Kahl, S. B.; Laster, B. H.; Kalef-Ezra, J.; Popenoe, E. A., Cancer Res., 50:4860-4865 (1990); and Zamenhof, R. G.; Kalend, A. M.; and Bloomer, W. D., J. Nat'l Cancer Inst., 84:1290-1291 (1992).
Examples of boron-containing compounds include Na.sub.2 B.sub.12 H.sub.11 SH (sodium borocaptate or BSH), p-carboxybenzeneboronic acid, sodium decahydrodecaborate, B.sub.12 H.sub.11 SH.sup.2-, B.sub.10 Cl.sub.9 (SH).sub.2.sup.2-, p-boronophenylalanine, boronated amino and polyamino acids, including boronated polylysine; N-succinimidyl-3-(undecahydrododeca-boranyldithio)propionate, and carborane-containing amino acids, carborane-containing promazine, carborane-containing porphyrins, and other polyhedral boranes. See Barth, et al., Cancer, 70:2995-3008 (1992), and Hawthorne, Angew. Chem. Int. Ed. Engl. 1993, 32, 950-984.
The first boron-containing nucleoside, 5-dihydroxyboryl-2'-deoxyuridine, was synthesized by Schinazi and Prusoff in 1978. Schinazi, R. F., Prusoff, W. H., Tetrahedron Lett., 4981-4984 (1978); and Schinazi, R. F.; Prusoff, W. H., J. Org. Chem., 50:841-847 (1985).
Sood, et al. have reported the synthesis of a series of cyanoborane adducts of 2'-deoxynucleosides, specifically 2'-deoxyguanosine-N.sup.7 cyanoborane, 2'-deoxyinosine-N.sup.7 cyanoborane, 2'-deoxyadenosine-N.sup.1 -cyanoborane, and 2'-deoxycytidine-N.sup.3 cyanoborane. Sood, A.; Spielvogel, B. F.; Shaw, B. R., J. Am. Chem. Soc., 111:9234-9235 (1989).
Sood, et al. have also reported the synthesis of oligonucleotides with a boronated internucleotide backbone, in the form of boranophosphates and boranophosphate methyl esters. The borane (BH.sub.3) group in these boronated oligonucleotides is isoelectronic and isostructural with normal O-oligonucleotides and oligonucleotide methylphosphonates. Sood, A.; Shaw, B. R.; Spielvogel, B. F., J. Am. Chem. Soc., 112:9000-9001 (1990). The Sood compounds in general have a low boron content and some have lower than desired lipophilicity.
U.S. Pat. No. 5,130,302 to Spielvogel, et al., discloses a novel class of boronated nucleosides, nucleotides and oligonucleotides for use as antineoplastic, antiinflammatory, and antihypertensive agents. The nucleosides, nucleotides and oligonucleotides are covalently attached to either BH.sub.2 CN, BH.sub.3, or BH.sub.2 CO.sub.2 R moieties, wherein R is C.sub.1 to C.sub.18 alkyl.
A number of carboranyl pyrimidines have been prepared for use in boron neutron capture therapy. Examples of carboranyl pyrimidines include 5-(3-O-carboranylpropyl-6-methyl-2-thiouracil (compound A) (Wilson, J. G., Pigment Cell Res., 2:297-303 (1989)), 2,4-dichloro-5-(1-o-carboranylmethyl)-6-methylpyrimidine; (compound B) (Reynolds, R. C.; Trask, T. W.; Sedwick, W. D. J. Org. Chem., 56:2391-2395 (1991)); and 5-carboranyluracil (compound C) (Goudgaon, N. M.; El-Kattan, Y.; Fulcrand, G.; Liotta, D. C.; Schinazi, R. F., IMEBORON VIII, Knoxville, Tenn.; p72 (1993)).
Purine and pyrimidine nucleosides that contain a carboranyl group attached to the purine or pyrimidine base have also been reported. Yamamoto, Y.; Seko, T.; Nakamura, H., Heteroatom Chem., 3:239-244 (1992); and Schinazi, R. F.; Goudgaon, N. M.; Soria, J.; Liotta, D. C., 5th International Symposium on Neutron Capture Therapy, Columbus, Ohio; p11 (1992); Schinazi, R. F.; Goudgaon, N.; Soria, J.; Liotta, D. C., Tenth International Roundtable: Nucleosides and Nucleotides, Park City, Utah; p28 (1992). These compounds are lipophilic and some are readily phosphorylated by cellular kinases, and in certain cells can incorporate into DNA as analogues of natural 2'-deoxypyrimidine nucleosides. Examples include 5-carboranyl-2'-deoxyuridine (compound D, CDU), 5-carboranyluridine (compound E, CU), 5-(1-hydroxymethyl)carboranyluridine, and 5-(1-hydroxymethyl)carboranyluridine (compound F, HMCU). ##STR1##
PCT WO 93/17028 filed by Raymond F. Schinazi and Dennis C. Liotta discloses a number of synthetic nucleosides that contain a carboranyl moiety covalently attached to a purine or pyrimidine base, wherein the sugar moiety optionally contains a second heteroatom in the 3'-position of the ring. Preferred compounds are 2-hydroxymethyl-5-(5-carboranylcytosin-1-yl)-1,3-oxathiolane (compound G) and 2-hydroxymethyl-5-(5-carboranyluridin-1-yl)-1,3-oxathiolane (compound H).
Powell, et al., recently reported the synthesis of oligonucleotides that contain 3',5'-nido-o-carboranyl-phosphoramidate linkages (compound I). While the oligonucleotide could reportedly localize in the cell nucleus, the boron moiety is acid labile because it is linked to the phosphorus atom through an amide-type bond.
C. Antisense Oligonucleotide Therapy
The requirements for efficient BNCT with oligonucleotides, which include cell selectivity (ability to accumulate preferentially in diseased cells), stability of the chemotherapeutic agent in vivo (resistance against digestion by cellular nucleases and chemical stability), and transportability (ability of the chemotherapeutic agent to pass easily through cellular membranes), are very similar to the requirements for Antisense Oligonucleotide Technology (AOT), another recently developed therapy for cancer as well as other diseases. Uhlmann, "Antisense Oligonucleotides: A New Therapeutic Approach" Chemical Reviews, 90(4) (June 1990). Antisense technology refers in general to the modulation of gene expression through a process wherein a synthetic oligonucleotide is hybridized to a complementary nucleic acid sequence to inhibit transcription or replication (if the target sequence is DNA), inhibit translation (if the target sequence is RNA) or to inhibit processing (if the target sequence is pre-RNA). A wide variety of cellular activities can be modulated using this technique. A simple example is the inhibition of protein biosynthesis by an antisense oligonucleotide bound to mRNA. In another embodiment, a synthetic oligonucleotide is hybridized to a specific gene sequence in double stranded DNA, forming a triple stranded complex (triplex) that inhibits the expression of that gene sequence. Antisense oligonucleotides can be also used to activate gene expression indirectly by suppressing the biosynthesis of a natural repressor or directly by reducing termination of transcription. AOT can be used to inhibit the expression of pathogenic genes, for example, those that facilitate the replication of viruses, including human immunodeficiency virus (HIV), hepatitis B virus (HBV), and herpes viruses, and cancers, particularly solid tumor masses such as urogenital cancers, gliomas, breast cancer, and melanomas.
An attractive approach to the treatment of urogenital tumors may be to combine aspects of AOT and BCNT using oligonucleotides that will selectively localize in target urogenital cancer cells.
It is therefore an object of the present invention to provide a method for the treatment of urogenital tumors, and in particulars cancer of the prostate, bladder, and kidney, using BNCT.
It is another object of the present invention to provide a method for the treatment of urogenital cancer that includes the combined approaches of AOT and BNCT.