Long-term anatomical and functional outcomes of surgical treatment of retinal complications in children and adolescents with Stickler syndrome between 2004 and 2021.

BACKGROUND: Stickler syndrome (STL) is an inherited progressive connective tissue collagen disorder. STL is the most common hereditary cause of retinal complications, retinal tears, and the development of retinal detachment (RD) in childhood. The aim of the study was to evaluate the long-term anatomical and functional results of surgical treatment of retinal complications in children and adolescents affected by STL. METHODS: A retrospective, single-center study was performed a cohort of children with STL who underwent retinal surgery between 2004 and 2021. RESULTS: The study group consisted of nine children; the mean age at the time of the retinal tear with/without retinal detachment was 7.2 (2-10) years, and the mean follow-up period was 9.6 (5-16) years. Pathogenic variants COL2A1 (5 children) and COL11A1 (3 children) were confirmed in our cohort. In total, we operated on 13 eyes, 11 eyes with complicated RD and two eyes with multiple retinal defects, but without RD. At the end of the follow-up period, an attached retina was achieved 77% (10 eyes) with or without silicone oil tamponade: cryopexy alone was successful in one eye (10%), scleral buckling (EB) in five eyes (50%), and vitrectomy with silicone oil tamponade combined with EB in four eyes (40%). The mean number of surgeries was 2.3 per eye. The resulting best corrected visual acuity ranged from 0.03 to 0.1 in one eye, from 0.16 to 0.4 in two eyes, and from 0.5 to 1.0 in 7 eyes. CONCLUSION: Repair of retinal tears with/without retinal detachment in patients with Stickler syndrome often requires multiple surgeries with combinations of cryopexy, scleral buckling, and/or vitrectomy with silicone oil tamponade. Treatment of the ocular complications arising from STL requires long-term comprehensive care.

Long-term evaluation of pars plana vitrectomy in children with Abusive head trauma.

PURPOSE: To determine the efficacy of pars plana vitrectomy (PPV) in children with intraocular hemorrhage (IOH) secondary to Abusive head trauma (AHT). METHODS: A long-term retrospective analysis evaluating epidemiology, management, safety, anatomical and functional results of PPV for IOH in children with AHT at tertiary referral center for children in the Czech Republic from 2004 to 2017. RESULTS: 18 children were identified with IOH due to AHT during observation period of 14 years. Overall incidence of IOH related to AHT was 29.6/100 000, in children under 1 year 22.2/100 000, in children 1 to 5 years 7.4/100 000. Mean age at the time of diagnosis was 13.7 (SD±20.53) months, median 5 months. IOH resolved in 56% of children, 64% eyes, spontaneously. 44% children, 36% eyes, underwent PPV. PPV was performed 30.5 (SD±16.98) days after established diagnosis on average. Postoperatively, 80% of eyes had anatomical improvement, 20% eyes had preexisting irreversible changes in the posterior pole. Vision of 50% eyes improved after surgery, vision of 20% eyes remained poor, 30% of eyes was not possible to test due to severe neurological impairment. Mean observational period was 33.4 (SD±38.21) months. Mortality rate of AHT in our group was 17%, all victims were younger 4 months. CONCLUSIONS: PPV is a safe and effective procedure to clear IOH in children with AHT. Ophthalmology outcomes are strongly associated with degree of neurological impairment. Best outcomes were achieved with PPV performed between 2 and 5 weeks after trauma. Opportunity to plan surgery within this time frame indicates a good neurological prospect and prevents deprivation amblyopia.

Is ultra low-dose CT with tin filtration useful for examination of SI joints? Can it replace X-ray in diagnostics of sacroiliitis?

OBJECTIVES: The first objective of our study was to determine the radiation exposure received by patients during tin-filtrated ultra-low-dose computed tomography (TFULDCT) of sacroiliac joints and to compare those to conventional X-ray doses. For comparison, we added a cohort examined by low-dose CT (LDCT) without tin filtration. The second objective was to compare the results of TFULDCT and X-ray in the detection of sacroiliitis. METHODS: Our retrospective study covered 45 patients, who were examined for suspected axial spondyloarthritis (AxSpA). The first group underwent TFULDCT as well as conventional radiography (CR); the second group underwent LDCT only without tin filtration. Effective doses of TFULDCT, LDCT and CR were calculated by an experienced medical physicist. TFULDCT and CR were independently evaluated by three investigators, who decided on the presence or absence of rheumatoid inflammatory bone changes. The results were statistically evaluated. RESULTS: In our cohort, the median effective dose for TFULDCT was 0.11 mSv, range (0.06-0.40 mSv), for LDCT 0.5 mSv (0.29-0.89 mSv), and for CR 0.25 mSv (0.06-1.87 mSv). We proved that TFULDCT produces a significantly lower percentage of uncertain results (23.3%; 95% CI: 11.3-41.6%) than CR (66.7%; 95% CI: 48.3-81.1%). CONCLUSIONS: Tin filtration helps to reduce CT radiation exposure to values lower than those resulting from CR. TFULDCT offers better overall diagnostic performance than CR. Our results prove that TFULDCT can replace CR in the diagnosis of sacroiliitis in the radiographical stage of AxSpA.

Expanding the phenotype spectrum associated with pathogenic variants in the COL2A1 and COL11A1 genes.

We report the clinical findings of 26 individuals from 16 unrelated families carrying variants in the COL2A1 or COL11A1 genes. Using Sanger and next-generation sequencing, 11 different COL2A1 variants (seven novel), were identified in 13 families (19 affected individuals), all diagnosed with Stickler syndrome (STL) type 1. In nine families, the COL2A1 disease-causing variant arose de novo. Phenotypically, we observed myopia (95%) and retinal detachment (47%), joint hyperflexibility (92%), midface retrusion (84%), cleft palate (53%), and various degrees of hearing impairment (50%). One patient had a splenic artery aneurysm. One affected individual carrying pathogenic variant in COL2A1 showed no ocular signs including no evidence of membranous vitreous anomaly. In three families (seven affected individuals), three novel COL11A1 variants were found. The propositus with a de novo variant showed an ultrarare Marshall/STL overlap. In the second family, the only common clinical sign was postlingual progressive sensorineural hearing impairment (DFNA37). Affected individuals from the third family had typical STL2 signs. The spectrum of disease phenotypes associated with COL2A1 or COL11A1 variants continues to expand and includes typical STL and various bone dysplasias, but also nonsyndromic hearing impairment, isolated myopia with or without retinal detachment, and STL phenotype without clinically detectable ocular pathology.

Metallacarborane Sulfamides: Unconventional, Specific, and Highly Selective Inhibitors of Carbonic Anhydrase IX.

Carbonic anhydrase IX (CAIX) is a transmembrane enzyme that regulates pH in hypoxic tumors and promotes tumor cell survival. Its expression is associated with the occurrence of metastases and poor prognosis. Here, we present nine derivatives of the cobalt bis(dicarbollide)(1-) anion substituted at the boron or carbon sites by alkysulfamide group(s) as highly specific and selective inhibitors of CAIX. Interactions of these compounds with the active site of CAIX were explored on the atomic level using protein crystallography. Two selected derivatives display subnanomolar or picomolar inhibition constants and high selectivity for the tumor-specific CAIX over cytosolic isoform CAII. Both derivatives had a time-dependent effect on the growth of multicellular spheroids of HT-29 and HCT116 colorectal cancer cells, facilitated penetration and/or accumulation of doxorubicin into spheroids, and displayed low toxicity and showed promising pharmacokinetics and a significant inhibitory effect on tumor growth in syngenic breast 4T1 and colorectal HT-29 cancer xenotransplants.

Preclinical Evaluation of Radiolabeled Peptides for PET Imaging of Glioblastoma Multiforme.

In this study, we have compared four 68Ga-labeled peptides (three Arg-Gly-Asp (RGD) peptides and substance-P) with two 18F-tracers clinically approved for tumor imaging. We have studied in vitro and in vivo characteristics of selected radiolabeled tracers in a glioblastoma multiforme tumor model. The in vitro part of the study was mainly focused on the evaluation of radiotracers stability under various conditions. We have also determined in vivo stability of studied 68Ga-radiotracers by analysis of murine urine collected at various time points after injection. The in vivo behavior of tested 68Ga-peptides was evaluated through ex vivo biodistribution studies and PET/CT imaging. The obtained data were compared with clinically used 18F-tracers. 68Ga-RGD peptides showed better imaging properties compared to 18F-tracers, i.e., higher tumor/background ratios and no accumulation in non-target organs except for excretory organs.

Carbonyl Reduction of Flubendazole in the Human Liver: Strict Stereospecificity, Sex Difference, Low Risk of Drug Interactions.

Flubendazole (FLU), an anthelmintic drug of benzimidazole type, is now considered a promising anti-cancer agent due to its tubulin binding ability and low system toxicity. The present study was aimed at determining more information about FLU reduction in human liver, because this information has been insufficient until now. Subcellular fractions from the liver of 12 human patients (6 male and 6 female patients) were used to study the stereospecificity, cellular localization, coenzyme preference, enzyme kinetics, and possible inter-individual or sex differences in FLU reduction. In addition, the risk of FLU interaction with other drugs was evaluated. Our study showed that FLU is predominantly reduced in cytosol, and the reduced nicotinamide adenine dinucleotide phosphate (NADPH) coenzyme is preferred. The strict stereospecificity of FLU carbonyl reduction was proven, and carbonyl reductase 1 was identified as the main enzyme of FLU reduction in the human liver. A higher reduction of FLU and a higher level of carbonyl reductase 1 protein were found in male patients than in female patients, but overall inter-individual variability was relatively low. Hepatic intrinsic clearance of FLU is very low, and FLU had no effect on doxorubicin carbonyl reduction in the liver and in cancer cells. All these results fill the gaps in the knowledge of FLU metabolism in human.

Long-term results of pars plana vitrectomy as an anti-inflammatory therapy of pediatric intermediate uveitis resistant to standard medical treatment.

PURPOSE: To evaluate the efficacy of pars plana vitrectomy (PPV) as an anti-inflammatory therapy in pediatric recurrent intermediate uveitis. METHODS: A retrospective study evaluated the long-term results of PPV indicated for intermediate uveitis with a mean observation period of 10.3 years (range 7-15.6 years) in 6 children (mean age 8 years, range 6-12 years). Pars plana vitrectomy was performed on 10 eyes in the standard manner and was initiated by vitreous sampling for laboratory examination. Data recorded were perioperative or postoperative vitrectomy complications, anatomic and functional results of PPV, and preoperative and postoperative best-corrected Snellen visual acuity. RESULTS: No perioperative or postoperative complications were observed. Bacteriologic, virologic, mycotic, and cytologic analysis of the vitreous was negative in all tested children. Five eyes were subsequently operated on for posterior subcapsular cataracts. An average preoperative visual acuity of 0.32 improved to an average postoperative visual acuity of 0.8. CONCLUSIONS: In the case of systemic immunosuppressive treatment failure in pediatric uveitis, particularly in eyes with cystoid macular edema, we recommend PPV relatively early.

Photo-induced DNA cleavage and cytotoxicity of a ruthenium(II) arene anticancer complex.

We report DNA cleavage by ruthenium(II) arene anticancer complex [(η(6)-p-terp)Ru(II)(en)Cl](+) (p-terp=para-terphenyl, en=1,2-diaminoethane, complex 1) after its photoactivation by UVA and visible light, and the toxic effects of photoactivated 1 in cancer cells. It was shown in our previous work (T. Bugarcic et al., J. Med. Chem. 51 (2008) 5310-5319) that this complex exhibits promising toxic effects in several human tumor cell lines and concomitantly its DNA binding mode involves combined intercalative and monofunctional (coordination) binding modes. We demonstrate in the present work that when photoactivated by UVA or visible light, 1 efficiently photocleaves DNA, also in hypoxic media. Studies of the mechanism underlying DNA cleavage by photoactivated 1 reveal that the photocleavage reaction does not involve generation of reactive oxygen species (ROS), although contribution of singlet oxygen ((1)O2) to the DNA photocleavage process cannot be entirely excluded. Notably, the mechanism of DNA photocleavage by 1 appears to involve a direct modification of mainly those guanine residues to which 1 is coordinatively bound. As some tumors are oxygen-deficient and cytotoxic effects of photoactivated ruthenium compounds containing {Ru(η(6)-arene)}(2+) do not require the presence of oxygen, this class of ruthenium complexes may be considered potential candidate agents for improved photodynamic anticancer chemotherapy.

New insights into the molecular and epigenetic effects of antitumor Pt(IV)-valproic acid conjugates in human ovarian cancer cells.

Substitutionally inert Pt(IV) prodrugs, combining bioactive axial ligands with Pt(IV) derivatives of antitumor Pt(II) compounds, represent a new generation of anticancer drugs. The rationale behind these prodrugs is to release, by reductive elimination inside the cancer cell, an active Pt(II) drug which binds nuclear DNA as well as bioactive ligands that may potentiate toxic effects of the Pt(II) drugs by an independent pathway. Platinum prodrugs, such as Pt(IV) derivatives of cisplatin containing axial valproic acid (VPA) ligands, destroy cancer cells with greater efficacy than conventional cisplatin. These axial ligands were chosen because VPA inhibits histone deacetylase (HDAC) activity, thereby decondensing chromatin and subsequently increasing the accessibility of DNA within chromatin to DNA-binding agents. We examined the mechanism of cytotoxic activity of Pt(IV) derivatives of cisplatin with VPA axial ligands. Particular attention was paid to the role of the VPA ligand in these Pt(IV) prodrugs in the mechanism underlying their toxic effects in human ovarian tumor cells. We demonstrate that (i) treatment of the cells with these prodrugs resulted in enhanced histone H3 acetylation and decondensation of heterochromatin markedly more effectively than free VPA; (ii) of the total Pt inside the cells, a considerably higher fraction of Pt from the Pt(IV)-VPA conjugates is bound to DNA than from the conjugates with biologically inactive ligands. The results indicate that the enhanced cytotoxicity of the Pt(IV)-VPA conjugates is a consequence of several processes involving enhanced cellular accumulation, downregulation of HDACs and yet other biochemical processes (not involving HDACs) which may potentiate antitumor effects.

Role of tumor hypoxia in acquisition of resistance to microtubule-stabilizing drugs.

Microtubules, an important cytoskeletal protein involved in mitotic and non-mitotic functions of cells, are important targets in cancer therapy. Microtubule-stabilizing drugs like the taxanes are critical adjuvant and palliative first-line therapies for the treatment of early, advanced and metastatic solid tumors of different lineages. Their adverse on- and off-target effects and high susceptibility to multidrug resistance, however, are major challenges encountered in the clinic in the treatment of solid cancers. Although biochemical resistance to microtubule-stabilizing drugs has been well characterized, molecular mechanisms that contribute to clinical resistance to taxanes in solid tumors still remain poorly understood and uncontrolled. The heterogeneous tumor microenvironment leads to greater diversity of resistance mechanisms to taxanes. Tumor hypoxia, a prominent feature of solid tumors, results in a broad range of effects on a number of cellular pathways and is one of the major contributors to the development of resistance to not only microtubule-stabilizing drugs but also other anticancer drugs. In this review, we highlight the potential role of hypoxia in the development of resistance to taxanes through mechanisms that involve altering the cell cycle, changing the properties of microtubules, and inducing the overexpression of gene products that contribute to drug resistance. Hypoxia-induced challenges described in this review are not limited to microtubule-stabilizing drugs alone, but in many cases also impact on treatment with non-microtubule-targeting anticancer drugs.

Antitumor platinum(IV) derivatives of oxaliplatin with axial valproato ligands.

We report new anticancer prodrugs, platinum(IV) derivatives of oxaliplatin conjugated with valproic acid (VPA), a well-known drug having histone deacetylase inhibitory activity. Like most platinum(IV) derivatives, the cytotoxicity of the conjugates was lower in cell culture than that of oxaliplatin, but greater than those of its Pt(IV) derivative containing biologically inactive axial ligands in several cancer cell lines. Notably, these conjugates display activity in both cisplatin sensitive- and resistant tumor cells capable of both markedly enhanced accumulation in tumor cells and acting in a dual threat manner, concurrently targeting histone deacetylase and genomic DNA. These results demonstrate the dual targeting strategy to be a valuable route to pursue in the design of platinum agents which may be more effective in cancer types that are typically resistant to therapy by conventional cisplatin. Moreover, platinum(IV) derivatives containing VPA axial ligands seem to be promising dual-targeting candidates for additional preclinical studies.

A dual-targeting, apoptosis-inducing organometallic half-sandwich iridium anticancer complex.

The cellular mechanism of action of an iridium(III) half-sandwich complex [(η(5)-C5Me4C6H4C6H5)Ir(phen)Cl]PF6 (phen = phenanthroline) (1) is reported. Complex 1 was used to treat several cell lines, including cisplatin-sensitive, cisplatin-resistant (with intrinsic and acquired resistance) carcinoma cells with wild type p53 status as well as the cells with no intact p53 gene, and nontumorigenic cells. Complex 1 preferentially kills cancer cells over nontumorigenic cells and exhibits no cross-resistance with cisplatin. It appears to retain significant activity in human tumor cell lines that are refractory or poorly responsive to cisplatin, and in contrast to cisplatin it displays a high activity in human tumor cell lines that are characterized by both wild type and mutant p53 gene. The mechanism of cell killing was established through detailed cell-based assays. Complex 1 exhibits dual effects in killing cancer cells causing nuclear DNA damage and mitochondrial dysfunction involving ROS production simultaneously. Flow cytometric studies and impedance-based monitoring of cellular responses to 1 demonstrated that 1 acts more quickly than cisplatin to induce cell death and that 1 is a more effective apoptosis inducer than cisplatin in particular in early stages of treatment, when the apoptotic effects predominate over necrosis. Overall, our findings confirm that 1 and its iridium derivatives represent promising candidates for further pre-clinical studies and new additions to the growing family of nonplatinum metal-based anticancer complexes.

Different affinity of nuclear factor-kappa B proteins to DNA modified by antitumor cisplatin and its clinically ineffective trans isomer.

Nuclear factor-kappa B (NF-кB) comprises a family of protein transcription factors that have a regulatory function in numerous cellular processes and are implicated in the cancer cell response to antineoplastic drugs, including cisplatin. We characterized the effects of DNA adducts of cisplatin and ineffective transplatin on the affinity of NF-кB proteins to their consensus DNA sequence (кB site). Although the кB site-NF-κB protein interaction was significantly perturbed by DNA adducts of cisplatin, transplatin adducts were markedly less effective both in cell-free media and in cellulo using a decoy strategy derivatized-approach. Moreover, NF-κB inhibitor JSH-23 [4-methyl-N¹-(3-phenylpropyl)benzene-1,2-diamine] augmented cisplatin cytotoxicity in ovarian cancer cells and the data showed strong synergy with JSH-23 for cisplatin. The distinctive structural features of DNA adducts of the two platinum complexes suggest a unique role for conformational distortions induced in DNA by the adducts of cisplatin with respect to inhibition of the binding of NF-кB to the platinated кB sites. Because thousands of κB sites are present in the DNA, the mechanisms underlying the antitumor efficiency of cisplatin in some tumor cells may involve downstream processes after inhibition of the binding of NF-κB to κB site(s) by DNA adducts of cisplatin, including enhanced programmed cell death in response to drug treatment.

Activation of trans geometry in bifunctional mononuclear platinum complexes by a non-bulky methylamine ligand.

In order to shed light on the mechanism that underlies activity of bifunctional mononuclear Pt(II) analogs of transplatin we examined in the present work a DNA binding mode of the analog of transplatin, namely trans-[Pt(CH3NH2)2Cl2], in which NH3 groups were replaced only by a small, non-bulky methylamine ligand. This choice was made because we were interested to reveal the role of the bulkiness of the amines used to substitute NH3 in transplatin to produce antitumor-active Pt(II) drug. The results indicate that trans-[Pt(CH3NH2)2Cl2] forms a markedly higher amount of more distorting intrastrand cross-links than transplatin which forms in DNA preferentially less distorting and persisting monofunctional adducts. Also importantly, the accumulation of trans-[Pt(CH3NH2)2Cl2] in tumor cells was considerably greater than that of transplatin and cisplatin. In addition, the results of the present work demonstrate that the replacement of ammine groups by the non-bulky methylamine ligand in the molecule of ineffective transplatin results in a radical enhancement of its activity in tumor cell lines including cisplatin-resistant tumor cells. Thus, activation of the trans geometry in bifunctional mononuclear Pt(II) complexes can be also accomplished by replacement of ammine groups in transplatin by non-bulky methylamine ligands so that it is not limited only to the replacement by relatively bulky and stereochemically more demanding amino ligands.

Antitumor carboplatin is more toxic in tumor cells when photoactivated: enhanced DNA binding.

Carboplatin, an analogue of "classical" cis-diamminedichloridoplatinum(II) (cisplatin), is a widely used second-generation platinum anticancer drug. Cytotoxicity of cisplatin and carboplatin is mediated by platinum-DNA adducts. Markedly higher concentrations of carboplatin are required, and the rate of adduct formation is considerably slower. The reduced toxic effects in tumor cells and a more acceptable side-effect profile are attributable to the lower reactivity of carboplatin with nucleophiles, since the cyclobutanedicarboxylate ligand is a poorer leaving group than the chlorides in cisplatin. Recently, platinum complexes were shown to be particularly attractive as potential photochemotherapeutic anticancer agents. Selective photoactivation of platinum complexes by irradiation of cancer cells may avoid enhancement of toxic side-effects, but may increase toxicity selectively in cancer cells and extend the application of photoactivatable platinum complexes to resistant cells and to a wider range of cancer types. Therefore, it was of interest to examine whether carboplatin can be affected by irradiation with light to the extent that its DNA binding and cytotoxic properties are altered. We have found that carboplatin is converted to species capable of enhanced DNA binding by UVA irradiation and consequently its toxicity in cancer cells is markedly enhanced. Recent advances in laser and fiber-optic technologies make it possible to irradiate also internal organs with light of highly defined intensity and wavelength. Thus, carboplatin is a candidate for use in photoactivated cancer chemotherapy.

Interactions of DNA with a new platinum(IV) azide dipyridine complex activated by UVA and visible light: relationship to toxicity in tumor cells.

The Pt(IV) diazido complex trans,trans,trans-[Pt(N(3))(2)(OH)(2)(pyridine)(2)] (1) is unreactive in the dark but is cytotoxic when photoactivated by UVA and visible light. We have shown that 1 when photoactivated accumulates in tumor cells and binds strongly to nuclear DNA under conditions in which it is toxic to tumor cells. The nature of the DNA adducts, including conformational alterations, induced by photoactivated 1 are distinctly different from those produced in DNA by conventional cisplatin or transplatin. In addition, the observation that major DNA adducts of photoactivated 1 are able to efficiently stall RNA polymerase II more efficiently than cisplatin suggests that transcription inhibition may contribute to the cytotoxicity levels observed for photoactivated 1. Hence, DNA adducts of 1 could trigger a number of downstream cellular effects different from those triggered in cancer cells by DNA adducts of cisplatin. This might lead to the therapeutic effects that could radically improve chemotherapy by platinum complexes. The findings of the present work help to explain the different cytotoxic effects of photoactivated 1 and conventional cisplatin and thereby provide new insights into mechanisms associated with the antitumor effects of platinum complexes photoactivated by UVA and visible light.

Replacement of a thiourea with an amidine group in a monofunctional platinum-acridine antitumor agent. Effect on DNA interactions, DNA adduct recognition and repair.

A combination of biophysical, biochemical, and computational techniques was used to delineate mechanistic differences between the platinum-acridine hybrid agent [PtCl(en)(L)](NO(3))(2) (complex 1, en = ethane-1,2-diamine, L = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) and a considerably more potent second-generation analogue containing L' = N-[2-(acridin-9-ylamino)ethyl]-N-methylpropionamidine (complex 2). Calculations at the density functional theory level provide a rationale for the binding preference of both complexes for guanine-N7 and the relatively high level of adenine adducts observed for compound 1. A significant rate enhancement is observed for binding of the amidine-based complex 2 with DNA compared with the thiourea-based prototype 1. Studies conducted with chemical probes and on the bending and unwinding of model duplex DNA suggest that adducts of complex 2 perturb B-form DNA more severely than complex 1, however, without denaturing the double strand and significantly less than cisplatin. Circular and linear dichroism spectroscopies and viscosity measurements suggest that subtle differences exist between the intercalation modes and adduct geometries of the two complexes. The adducts formed by complex 2 most efficiently inhibit transcription of the damaged DNA by RNA polymerase II. Not only do complexes 1 and 2 cause less distortion to DNA than cisplatin, they also do not compromise the thermodynamic stability of the modified duplex. This leads to a decreased or negligible affinity of HMG domain proteins for the adducts formed by either Pt-acridine complex. In a DNA repair synthesis assay the lesions formed by complex 2 were repaired less efficiently than those formed by complex 1. These significant differences in DNA adduct formation, structure, and recognition between the two acridine complexes and cisplatin help to elucidate why compound 2 is highly active in cisplatin-resistant, repair proficient cancer cell lines.

DNA interactions of 2-pyrrolinodoxorubicin, a distinctively more potent daunosamine-modified analogue of doxorubicin.

It was shown earlier that 2-pyrrolinodoxorubicin was 500-1000 times more active towards human and mouse cancer cells in vitro than parental doxorubicin. However, the biochemical factors responsible for such a large difference in potency between doxorubicin and 2-pyrrolinodoxorubicin are not clear at the molecular level. To provide this information, we have investigated in cell-free media by biochemical and biophysical methods interactions of both anthracyclines with DNA, effects of these interactions on activity of human topoisomerase II, human Bloom's syndrome helicase and prokaryotic T7 RNA polymerase, and the capability of these drugs to form DNA interstrand cross-links in formaldehyde-free medium. Experiments aimed at understanding the properties of double-helical DNA in the presence of doxorubicin and 2-pyrrolinodoxorubicin revealed only small differences in DNA modifications by these anthracyclines and resulting conformational alterations in DNA. Similarly, the ability of 2-pyrrolinodoxorubicin modifications of DNA to inhibit catalytic activity of topoisomerase II does not differ significantly from that of doxorubicin. On the other hand, we demonstrate that an important factor responsible for the markedly higher antiproliferative potency of DNA modifications by 2-pyrrolinodoxorubicin is capability of these modifications to inhibit downstream cellular processes which process DNA damaged by this drug and involve separation of complementary strands of DNA, such as DNA unwinding by helicases or RNA polymerases. In addition, the results are also consistent with the hypothesis that in particular the capability of 2-pyrrolinodoxorubicin to readily form DNA interstrand cross-links is responsible for inhibition of these processes in the cells treated with this analogue of doxorubicin.

The contrasting chemistry and cancer cell cytotoxicity of bipyridine and bipyridinediol ruthenium(II) arene complexes.

The synthesis and characterization of ruthenium(II) arene complexes [(eta(6)-arene)Ru(N,N)Cl](0/+), where N,N = 2,2'-bipyridine (bipy), 2,2'-bipyridine-3,3'-diol (bipy(OH)(2)) or deprotonated 2,2'-bipyridine-3,3'-diol (bipy(OH)O) as N,N-chelating ligand, arene = benzene (bz), indan (ind), biphenyl (bip), p-terphenyl (p-terp), tetrahydronaphthalene (thn), tetrahydroanthracene (tha) or dihydroanthracene (dha), are reported, including the X-ray crystal structures of [(eta(6)-tha)Ru(bipy)Cl][PF(6)] (1), [(eta(6)-tha)Ru(bipy(OH)O)Cl] (2) and [(eta(6)-ind)Ru(bipy(OH)(2))Cl][PF(6)] (8). Complexes 1 and 2 exibit CH (arene)/pi (bipy or bipy(OH)O) interactions. In the X-ray structure of protonated complex 8, the pyridine rings are twisted (by 17.31 degrees). In aqueous solution (pH = 2-10), only deprotonated (bipy(OH)O) forms are present. Hydrolysis of the complexes was relatively fast in aqueous solution (t(1/2) = 4-15 min, 310 K). When the arene is biphenyl, initial aquation of the complexes is followed by partial arene loss. Complexes with arene = tha, thn, dha, ind and p-terp, and deprotonated bipyridinediol (bipy(OH)O) as chelating ligands, exhibited significant cytotoxicity toward A2780 human ovarian and A549 human lung cancer cells. Complexes [(eta(6)-bip)Ru(bipy(OH)O)Cl] (7) and [(eta(6)-bz)Ru(bipy(OH)O)Cl] (5) exhibited moderate cytotoxicity toward A2780 cells, but were inactive toward A549 cells. These activity data can be contrasted with those of the parent bipyridine complex [(eta(6)-tha)Ru(bipy)Cl][PF(6)] (1) which is inactive toward both A2780 ovarian and A549 lung cell lines. DFT calculations suggested that hydroxylation and methylation of the bipy ligand have little effect on the charge on Ru. The active complex [(eta(6)-tha)Ru(bipy(OH)O)Cl] (2) binds strongly to 9-ethyl-guanine (9-EtG). The X-ray crystal structure of the adduct [(eta(6)-tha)Ru(bipy(OH)O)(9-EtG-N7)][PF(6)] shows intramolecular CH (arene)/pi (bipy(OH)O) interactions and DFT calculations suggested that these are more stable than arene/9-EtG pi-pi interactions. However [(eta(6)-ind)Ru(bipy(OH)(2))Cl][PF(6)] (8) and [(eta(6)-ind)Ru(bipy)Cl][PF(6)] (16) bind only weakly to DNA. DNA may therefore not be the major target for complexes studied here.