Verteporfin: a milestone in opthalmology and photodynamic therapy.

During the past year, a photosensitiser named benzoporphyrin derivative (BPD) has been approved in 26 countries under the generic name verteporfin (Visudynetrade mark, Novartis), for the treatment of patients with a certain type of the wet form of age-related macular degeneration (AMD) by photodynamic therapy (PDT). AMD is the leading cause of blindness in the developed world, with approximately half a million new cases of the wet form per year. The approval of Visudynetrade mark therapy represents a major milestone in ophthalmology since AMD was previously untreatable by any modality which would preserve existing vision. It was also a milestone in the development of PDT, not only because it represented the first breakthrough in the use of PDT to treat an otherwise untreatable condition, but also because it represented the first mass market for a PDT treatment where prospects of a substantial financial return on many years of investment appear to be likely. In this article, we look at the background to the development of BPD, primarily for its use in AMD, but also in other applications.

Effect of geometric isomerism in dinuclear platinum antitumour complexes on the rate of formation and structure of intrastrand adducts with oligonucleotides.

The dinuclear platinum complexes [[trans -PtCl (NH3)2]2[mu]-[NH2(CH2) n NH2]](NO3)2[1,1/t,t ( n = 4,6)] and [[cis-PtCl(NH3)2]2[mu];-[NH2(CH2) n NH2](NO3) 2[1,1/c,c ( n = 4,6)] exhibit antitumour activity comparable with cisplatin. 1,1/c,c complexes do not form 1,2 GG intrastrand adducts, the major adduct of cisplatin, with double-stranded DNA. This 1H NMR spectroscopy study shows that, in the absence of a complementary strand, 1,1/c,c ( n = 4,6) form a 1,2 GG (N7, N7) intrastrand adduct with r(GpG), d(GpG) and d(TGGT). Initial binding to r(GpG) (and also reaction with GMP) at 37 degrees C was slower for 1,1/c,c compared with 1,1/t,t, whereas the second binding step (adduct closure) was faster for 1,1/c,c. However, the 1H NMR spectra of the 1,1/c,c adducts at 37 degrees C show two H8 signals, one of which is broad and becomes sharper on increasing the temperature, indicating restricted rotation around the Pt-N7 bond. For the d(GpG)-1,1/c,c ( n = 4) adduct, 2D NMR spectroscopy assigned the broad H8 signal to the 3' G, which has syn base orientation and 60% S-type/40% N-type sugar conformation. The 5' G has anti base orientation and S-type sugar conformation. Apart from the restricted rotation around the 3' G, the structure is similar to that of 1,2 GG intrastrand adducts of 1,1/t,t. This steric hindrance may explain the inability of 1,1/c,c complexes to form 1,2 GG intrastrand adducts with sterically more demanding double-stranded DNA.

Site-specific d(GpG) intrastrand cross-links formed by dinuclear platinum complexes. Bending and NMR studies.

The novel platinum drugs [{trans-PtCl(NH3)2}2H2N(CH2)nNH2]2+ (1,1/t,t) are currently undergoing preclinical development. The bifunctional DNA binding of these agents allows comparison with that of cisplatin [Farrell et al. (1995) Biochemistry, 34, 15480]. The major DNA lesion of cisplatin, the 1,2-d(GpG) intrastrand adduct, produces a rigid, directed bend 30-35 degrees into the major groove of DNA. We have now completed a structural analysis of the corresponding adduct formed with the dinuclear complexes. Gel retardation assays on 15-22 bp oligonucleotides containing a central d(TG*G*T) site show that the (Pt,Pt)-intrastrand adducts result in a flexible nondirectional bend. This bend is essentially independent of chain length (n = 2, 4, 6). Chemical reactivity assays indicated a hypersensitivity of the thymine 5' to the adduct and an enhanced sensitivity of the 3'-thymine to OsO4. 2D 1H NMR studies on a d(TG1G2T) adduct of [{trans-PtCl(NH3)2}2H2N(CH2)6NH2]2+ have delineated the structural features responsible for these observations. In contrast to the cisplatin adduct, which displays a 100% N-type sugar of the 5'-G and an anti base conformation of the platinated bases in both solid state and solution, the dinuclear adduct does not display the typical N-type sugar pucker. The base orientations are anti (5'-T), anti (G1), anti/syn (G2), and anti (3'-T) while the sugar conformations are N, S/N, N, and S, respectively. The 5'-T remains stacked with its guanine neighbor while the 3'-T becomes unstacked, a reverse of the situation observed for cis-DDP.

DNA-binding properties of novel cis- and trans platinum-based anticancer agents in 2 human ovarian carcinoma cell lines.

We have investigated the comparative initial DNA binding properties of 7 platinum-based anticancer drugs: 5 cis-oriented compounds, cisplatin, tetraplatin (Ormaplatin), JM118 [cis ammine dichloro (cyclohexylamine) platinum (II)], JM216 [bisacetato cis ammine dichloro (cyclohexylamine) platinum (IV)] and JM149 [cis ammine dichloro (cyclohexylamine) trans dihydroxo platinum (IV)], and 2 trans-oriented compounds, transplatin and JM335 [trans ammine dichloro (cyclohexylamine) dihydroxo platinum (IV)] in SKOV-3 and CHI human ovarian carcinoma cells. Unlike transplatin, the trans complex JM335 was comparably cytotoxic to its cis isomer JM149 and cisplatin. No significant correlation was observed between levels of total platinum bound to DNA after exposure to the 7 drugs and cytotoxicity in either cell line. Using a competitive enzyme-linked immunoabsorbent assay, DNA extracted from CH1 cells exposed to the 5 cis platinum drugs was recognized by the monoclonal antibody ICR4 (raised against DNA platinated by cisplatin) in the order JM118 > cisplatin > JM216 > tetraplatin > JM149; a strong positive correlation which just attained statistical significance was observed between recognition by ICR4 and cytotoxicity. In contrast, DNA extracted from CH1 cells exposed to the trans platinum drugs transplatin and JM335 was no more immunoreactive than control DNA. Using alkaline elution, interstrand cross-link levels after exposure to drug did not correlate with cytotoxicity in either cell line. The 5 cis drugs formed interstrand cross-links in both cell lines, whereas transplatin formed very low levels in SKOV-3 and undetectable levels in CH1. JM335 was efficient at forming interstrand cross-links in SKOV-3 but, notably, none were observed in CH1. In contrast, in the CH1 cells, single-strand breaks were observed with JM335 (but not with any other drug). The novel trans complex JM335 was unique, among the platinum drugs studied, in its ability to form both DNA interstrand cross-links and single strand breaks (DNA lesion formation being cell line dependent), a property which may account for its cytotoxicity.

Mechanisms of acquired resistance to the orally active platinum-based anticancer drug bis-acetato-ammine-dichloro-cyclohexylamine platinum (i.v.) (JM216) in two human ovarian carcinoma cell lines.

Acquired resistance to the p.o. active lipophilic platinum drug bis-acetato-ammine-dichloro-cyclohexylamine platinum (i.v.) (JM216) was generated in the 41M and CH1 human ovarian carcinoma cell lines, and their resistance mechanisms were compared to parallel cisplatin-resistant (cisR) cell lines. Intracellular platinum accumulation was not reduced in either 41M/JM216R or CH1/JM216R compared to the parent lines after JM216 exposure (1-100 microM for 2 h), and neither 41M/JM216R nor CH1/JM216R was cross-resistant to cadmium chloride, suggesting that metallothionein levels are not elevated. Resistance in 41M/JM216R (resistance factor, 1.9) appeared to be mainly due to elevated glutathione levels; levels were 1.6- and 1.8-fold higher in 41M/JM216R compared to 41M when expressed in terms of protein content and cell number respectively, reflected by a 1.7-fold reduction in total platinum bound to DNA in 41M/JM216R after JM216 exposure (10-100 microM for 2 h). This is in contrast to 41McisR, in which the major resistance mechanism was reduced intracellular accumulation. There was no difference between CH1 and CH1/JM216R in glutathione levels or levels of total platinum bound to DNA and DNA interstrand cross-links immediately after JM216 exposure (10-100 microM for 2 h or 25 microM for 2 h, respectively). In common with CH1cisR, increased DNA repair appeared to be the major resistance mechanism in CH1/JM216R (resistance factor, 6.2). Half times of removal of total platinum from DNA after JM216 exposure (25 microM for 2 h) were 20 h in CH1 and 11 h in CH1JM216R; at 24 h after JM216 exposure (25 microM for 2 h), no removal of DNA interstrand cross-links was observed in CH1, while in CH1/JM216R 20% of cross-links had been removed. These results suggest that compared to cisplatin, acquired resistance to JM216 is less likely to occur through reduced accumulation. However, resistance can result from elevated glutathione levels or increased DNA repair, mechanisms also shown to be involved in cisplatin resistance.

A novel trans-platinum coordination complex possessing in vitro and in vivo antitumor activity.

As part of a drug discovery program to discover more effective platinum-based anticancer drugs, a series of platinum complexes of trans coordination geometry centered on trans-ammine(cyclohexylaminedichlorodihydroxo)platinum(IV) (JM335) has been evaluated in vitro against a panel of cisplatin-sensitive and cisplatin-resistant human tumor cell lines (predominantly ovarian). In vitro, against 5 human ovarian carcinoma cell lines, JM335 was comparably cytotoxic to cisplatin itself and over 50-fold more potent than transplatin (mean 50% inhibitory concentrations: JM335, 3.1 microM; cisplatin, 4.1 microM; transplatin, 162 microM). With the use of seven pairs of human tumor cell lines (parent and subline with acquired resistance to cisplatin and encompassing all of the known major mechanisms of resistance to cisplatin) JM335 exhibited a different cross-resistance pattern to that of its cis isomer (JM149). JM335 showed non-cross-resistance in six of the seven resistant lines, cross-resistance in the A2780cisR line possibly being associated with high levels of glutathione. Preliminary intracellular DNA binding studies showed that in contrast to transplatin, JM335 was efficient at forming DNA-DNA interstrand cross-links. In vivo, JM335 produced growth delays in excess of 15 days against 4 of 6 human ovarian carcinoma xenografts and was unique among the complexes studied in retaining some efficacy against a cisplatin-resistant subline of the murine ADJ/PC6 plasmacytoma. JM335 is the first trans-platinum complex to demonstrate marked antitumor efficacy against both murine and human s.c. tumor models and represents a significant structural lead to complexes capable of circumventing cross-resistance to cisplatin.

Circumvention of acquired tetraplatin resistance in a human ovarian carcinoma cell line by a novel trans platinum complex, JM335 [trans ammine (cyclohexylamine) dichloro dihydroxo platinum (IV)].

Acquired resistance to tetraplatin [d,1-trans-1,2-diaminocy-clohexane tetrachloroplatinum (IV)] has been generated in vitro in the human ovarian carcinoma cell line PXN94; the derived line, PXN94tetR, was 24-fold resistant to tetraplatin. Intracellular tetraplatin accumulation was reduced in PXN94tetR compared with PXN94 by an average of 1.3-fold across the concentration range 1-100 microM (2 hr exposure). There was no significant difference in glutathione levels between the 2 cell lines. PXN94tetR was 1.6-fold more resistant to cadmium chloride than PXN94, suggesting that metallothionein levels may be elevated. However, no significant difference was observed between PXN94 and PXN94tetR in the levels of total platinum bound to DNA or DNA interstrand cross-links immediately after tetraplatin exposure (10-100 microM x 2 hr). There was also no significant difference between the 2 cell lines in the rate of removal of total platinum or interstrand cross-links from DNA following 2 hr exposure to 25 microM tetraplatin. Hence the major mechanism of acquired tetraplatin resistance in PXN94tetR appears to be increased tolerance of platinum-DNA adducts. PXN94tetR was partially cross-resistant to the bifunctional alkylating agents melphalan, chlorambucil and mitomycin C. Partial cross-resistance was also observed to Adriamycin, bleomycin, etoposide, 5-fluorouracil and vinblastine; however, no elevation in P-glycoprotein levels was apparent in PXN94tetR. No cross-resistance was observed to taxotere. PXN94tetR was partially cross-resistant to cisplatin, carboplatin and several novel cis platinum complexes. In contrast, resistance was completely circumvented by the novel trans platinum complex JM335 [trans ammine (cyclohexylamine) dichloro dihydroxo platinum (IV)].

In vitro platinum drug chemosensitivity of human cervical squamous cell carcinoma cell lines with intrinsic and acquired resistance to cisplatin.

The platinum drug chemosensitivity of five human cervical squamous cell carcinoma cell lines (HX/151, HX/155, HX/156, HX/160 and HX/171) derived from previously untreated patients has been determined. Compared to our data obtained previously using human ovarian carcinoma cell lines, all five lines were relatively resistant to cisplatin, carboplatin, iproplatin and tetraplatin. One of the lines (HX/156) was exceptionally sensitive to the novel platinum (IV) ammine/amine dicarboxylates JM216 [bis-acetatoammine dichloro (cyclohexylamine) platinum (IV)] and JM221 [ammine dibutyrato dichloro (cyclohexylamine) platinum (IV)]. The range in IC50 values across the five lines was approximately 2.5-fold for cisplatin, carboplatin and iproplatin, 13-fold for tetraplatin and JM216, and 25-fold for JM221. No significant correlation (P > 0.05) was observed between platinum drug chemosensitivity and either glutathione levels or cadmium chloride sensitivity, an indicator of metallothionein levels. In addition, there was no significant correlation (P > 0.05) between cisplatin cytotoxicity and intracellular cisplatin accumulation or JM216 cytotoxicity and intracellular JM216 accumulation over the dose range 5-100 microM (2 h exposure). The exceptional sensitivity of HX/156 to JM216 appears, at least partially, to be a result of enhanced accumulation of JM216. An 8.6-fold acquired cisplatin resistant stable variant of HX/155 has been generated in vitro. Intracellular cisplatin accumulation was reduced by 2.4 +/- 0.3-fold (mean +/- s.d.) in HX/155cisR across the dose range 1-100 microM (2 h exposure). Glutathione levels in HX/155cisR were elevated by 1.3-fold in terms of protein content and by 1.6-fold in terms of cell number. HX/155cisR was 1.9-fold resistant to cadmium chloride. Total platinum bound to DNA after cisplatin exposure (10, 25, 50 or 100 microM for 2 h) was 3.6 +/- 0.6-fold (mean +/- s.d.) lower in HX/155cisR. Hence the mechanism of acquired cisplatin resistance in HX/155cisR appears to be multifocal, with reduced intracellular drug accumulation and elevated glutathione and metallothionein levels combining to reduce DNA platination levels. While HX/155cisR was cross-resistant to tetraplatin and carboplatin, novel platinum (II) and (IV) ammine/amine complexes, including JM216 and JM221, partially circumvented resistance (resistance factors of 1.5-2). Non cross-resistance was observed to iproplatin and nine non-platinum anticancer agents. Intracellular tetraplatin accumulation was reduced by 1.8 +/- 0.1-fold (mean +/- s.d.) in HX/155cisR across the dose range 1-100 microM (2 h exposure). In contrast, after JM216 exposure (1-100 microM for 2 h), no significant difference in intracellular platinum levels between HX/155 and HX/155cisR was observed.(ABSTRACT TRUNCATED AT 400 WORDS)