Morris Cyril Berenbaum

In vivo biological activity of the components of haematoporphyrin derivative.

The in vivo biological activity of various fractions and components of haematoporphyrin derivative (HpD) have been determined by measuring the depth of necrosis of implanted tumours in mice exposed to light after the administration of standard doses of porphyrins dissolved in alkali. In this assay, haematoporphyrin, hydroxyethylvinyldeuteroporphyrin and protoporphyrin are inactive, but the mono- and di-acetates of haematoporphyrin (which are major components of HpD) and acetoxyethylvinyldeuteroporphyrin are active. However, the situation appears to be more complex than this. The normal method for preparing HpD for injection involves an alkali treatment which causes hydrolysis and elimination of the acetoxy functions, and the only recognized products (haematoporphyrin, hydroxyethylvinyldeuteroporphyrin and protoporphyrin) are inactive in the in vivo assay. It is concluded that the active component here is a porphyrin, possibly a dimer or oligomer, which is retained on the column during the normal separation by HPLC. This conclusion is supported by the observations that (i) the crude material obtained from the spent column is active without further alkali treatment, and (ii) activity develops over 30 min, when HpD or the mono- or diacetates of haematoporphyrin are treated with sodium bicarbonate in aqueous DMSO. The advantages of working with a pure substance (e.g. haematoporphyrin diacetate) rather than a mixture (HpD) are stressed.

On the nature of ‘haematoporphyrin derivative’

The components of haematoporphyrin derivative (a preparation used as a photosensitiser in clinical applications, and made by treating haematoporphyrin with sulphuric acid–acetic acid) have been separated by preparative h.p.l.c. and identified by comparison with authentic porphyrindicarboxylic acids. The composition of the mixture is some-what variable but the main components are O,O′-diacetylhaematoporphyrin (6) and O-acetylhaematoporphyrin (2)/(3) with smaller amounts of the 8(3)-(1-acetoxyethyl)-3(8)-vinyldeuteroporphyrin isomers (7) and (8) and the corresponding alcohols (4) and (5).

Second generation tumour photosensitisers: the synthesis and biological activity of octaalkyl chlorins and bacteriochlorins with graded amphiphilic character

Routes to hydroxychlorin derivatives of two distinct categories (nuclear hydroxy substituent; side-chain hydroxy substituent) are developed. Such substances, covering a range of amphiphilic character depending on the number of hydroxy groups, are seen as potential sensitisers for photodynamic therapy. Osmylation of octaethylporphyrin gives the dihydroxyoctaethylchlorin 2 and the tetrahydroxybacteriochlorin 3. Pinacol–pinacolone rearrangement of 2 gives the octaethyl-β-oxochlorin 4, borohydride reduction of which gives the secondary alcohol 6. This is converted via the bromochlorin 7(prepared using 50% HBr/HOAc at room temperature) into a series of ethers, including those, 10, 11, 12, derived from glycerol, D-glucose, and D-mannitol respectively. Alkylation of these unprotected polyols with the highly hindered bromide 7 occurs preferentially at the primary alcohol functions in each case. Some of these hydroxychlorins are found in animal assays to be highly effective sensitisers of tumour photonecrosis. In this respect the most effective compounds in each category are the most highly hydroxylated. However, the D-glucose derivative 11 proves also to be an effective sensitiser of skin and muscle, i.e. it does not show the selectivity shown by 5,10,15,20-tetra(m-hydroxyphenyl)chlorin.

Second generation tumour photosensitisers: the synthesis of octa-alkyl chlorins and bacteriochlorins with graded amphiphilic character

Two series of polyhydroxy derivatives of hydroporphyrins are synthesised which have the hydroxy substituents at β-positions, or in a side chain: these amphiphilic systems are tested in vivo as tumour photosensitisers, and some are found to be very effective.