The alkaloids obtainable from Vinca rosea, represent one of the most productive areas of chemistry for drugs adversely affecting the growth of experimental malignancies in mammals. Initially, only some of the alkaloids, obtainable from the leaves of the plant by extraction and purifiable by chromatography, were found to be active. These active antineoplastic alkaloids obtained directly from the leaves of the vinca plant included VLB (Vinblastine, vincaleucoblastine), vincristine (leurocristine), leurosine (vinleurosine), leurosidine (vinrosidine), leuroformine (formylleurosine) and deoxy VLB "A" and "B" (4'-deoxy VLB and 4'-deoxyleurosidine). Other less abundant antineoplastic alkaloids have also been formed.
Chemical modification of the Vinca alkaloids started slowly for several reasons. In the first place, the molecular structures involved are extremely complex, and chemists were slow to find reactions which modified one specific functional group of the molecule without affecting other groups. Secondly, dimeric alkaloids lacking desirable chemotherapeutic properties had been recovered or produced from Vinca rosea extracts, and a determination of their structures had led to the conclusion that these inactive compounds were closely related structurally to, and even isomeric with, one or more of the active alkaloids. Thus, it appeared that small chemical changes in the known alkaloids could have a profound effect on antineoplastic activity.
Because of these restrictions, modification of the indole-dihydroindole alkaloids obtained from Vinca rosea has centered around three areas of the molecule: C--3, C--4' and C--4. Considering C--3 modification first, one of the more recent, and more successful modifications of the basic indole-dihydroindole structure has been the preparation of C--3 carboxamide and carboxhydrazide derivatives, most of which have turned out to be active anti-tumor agents. [See Cullinan et al., U.S. Pat. No. 4,203,898, Conrad et al., U.S. Pat. No. 4,191,688, Cullinan and Gerzon, U.S. Pat. No. 4,166,810. Conrad et al. J. Med. Chem., 22, 391 (1979), and Barnett et al., ibid,; 21 88 (1978)]. One of the amides, 4-desacetyl VLB 3-carboxamide (vindesine), is currently being marketed in several European countries as an oncolytic agent. Vindesine is effective in treating some vincristine-resistant leukemias in addition to many common neoplasms including germ-cell tumors. Secondly, reaction of the 3-hydroxy and 3-ester functions of a indole-dihydroindole vinca alkaloid with an isocyanate has produced the corresponnding oxazolidinedione derivatives, one of which, the N-chloroethyl derivative--vinzolidine--is currently undergoing a clinical trial in humans. These oxazolidinedione derivatives are disclosed in Miller and Gutowski, U.S. Pat. No. RE 30,560, reissued Mar. 31, 1981. Trouet et al., U.S. Pat. No. 4,388,305 (same as EPO 41,935) discloses anti-cancer VLB C--3 peptides in which the peptide group contains 1-6 amino acid residues with a terminal free acid or ester group. Amides of this class derived from a single amino acid are also disclosed in Cullinan et al. U.S. Pat. No. 4,203,898 (col. 15, lines 1-16). The hydrazide-azide synthetic procedure of Cullinan et al., is also employed by Trouet et al. to prepare their amides.
A second area of the molecule which has been modified with retention of anti-tumor activity is the C--4' functionality. A majority of these modifications have been based on the 3', 4'-anhydro derivative, makeable both by coupling vindoline and catharanthine via a modified Polonovski reaction--Potier et al. J.C.S. Chem. Comm., 670, (1975)--and by dehydrating VLB or leurosidine--Gutowski and Miller, U.S. Pat. No. 4,029,663. The dehydration reaction produces two exodouble bond isomers in addition to the .DELTA..sup.3',4' -anhydro derivative. Functionalization of any one of these double bonds to form epoxides, diols, etc. has constituted the chief chemical modifications undertaken at C--4'.
The third region of the indole-dihydroindole which has been modified successfully is C--4. In the first place, hydrolysis of the acetoxy group, present in all the naturally-ocurring vinca alkaloids, yields active antineoplastic 4-desacetyl derivatives. (Vindesine, a C--3 carboxamide, is a 4-desacetyl derivative.) Secondly, Hargrove, U.S. Pat. Nos. 3,387,001 and 3,392,173 prepared novel 4-acyl derivatives of 4-desacetyl VLB, 4-desacetyl vincristine, etc. Among these new derivatives was 4-chloroacetyl VLB, an antineoplastic compound which compound could be further reacted with amines; for example, dimethylamine, to yield a potent anticancer drug, vinglycinate, N,N-dimethyl 4-glycinyl VLB. In a different modification, Wright and Neuss, U.S. Pat. No. 4,122,082, oxidized the 4-hydroxyl of 4-desacetyl VLB to a 4-keto compound, and Thompson, U.S. Pat. No. 4,195,022, reduced this ketone to the 4-epihydroxy (4.alpha.-hydroxy) derivative, also a compound with anti-cancer activity.
In addition to the VLB/VCR etc. hydrazide from Cullinan et al, (loc. cit.) and leurosine hydrazide disclosed in Neuss, Gorman, Cone and Huckstep, Tetrahedron Letters 783 (1968) (This article, in Table I, page 785, refers to compound XI as VLB hydrazide, but according to the footnote, the compound is actually an 18'-descarbomethoxy derivative-see also line 2 for the correct name for XI). Derivatives of 4-desacetyl VLB hydrazide are disclosed in Cullinan and Gerzon, U.S. Pat. No. 4,166,810. The named derivatives include mono C.sub.1-3 alkyl, .beta.-hydroxyethyl, .beta.-acetoxyethyl C.sub.2-4 alkanoyl, dichloroacetyl, benzoyl C.sub.1-3 alkylcarbazyl, dimethyl and C.sub.1-3 alkylidine (.dbd.CRR' where R and R.sup.1 are H or methyl or one is ethyl).
Indole-dihydroindole bridged tetramers; i.e., the same or different dimeric alkaloid moieties bridged thru the 3-carboxyl via a bis-amide are described in Conrad and Gerzon, U.S. Pat. No. 4,199.504. Otherwise, indole-dihydroindole vinca alkaloid dimers have not been prepared by bridging through other positions to form vinca tetramers.
VLB and vincristine have been conjugated with proteins to form antigens useful in radioimmune assays 4-Desacetyl VLB 3-carboxazide (4-desacetyl vinblastinoic azide) and the corresponding vincristine compound were the derivatives employed; see Conrad et al., J. Med., Chem., 22, 391 (1979), Root et al, Abstract 182, FACSS, Oct. 6, 1975, and U.S. Pat. No. 4,203,898 Langone et al, Anal. Biochem., 95, 214 (1979) and Teale et al, Brit. J. Clin. Pharm., 4, 169 (1977) for illustrations of this reaction. In some of these instances, the coupling agents were the C--3 carboxazides. In another reference, the alkaloid and protein were coupled via a Mannich reaction involving an unspecified portion of the vinca molecule. The C--3 carboxylic acid has also been used to couple directly to amino groups of a protein via a carbodiimide intermediate.
In testing these conjugates, Johnson et al, Brit. J. Can., 44, 372 (1981) disclose the cytotoxic action vs. human cancer cells of a vindesine-anti-CEA immunoglobulin conjugate prepared from 4-desacetyl VLB azide. This same information is disclosed in Rowland and Simmonds, Ser. No. 332,023 filed Dec. 18, 1981, now abandoned in a continuation-in-part thereof, Ser. No. 528,715, filed Sept. 2, 1983 now abandoned, and in a continuation application thereof, Ser. No. 755,221, filed July 15, 1985. Finally, Rowland, U.S. Pat. No. 4,046,722, claims immunoglobulins with a covalently-bound cytotoxic drug attached thereto.