Synthesis and preliminary antitumor evaluation of 5-iminodoxorubicin

Evaluation of PNU-159682 antibody drug conjugates (ADCs)

PNU-159682 is a highly potent secondary metabolite of nemorubicin belonging to the anthracycline class of natural products. Due to its extremely high potency and only partially understood mechanism of action, it was deemed an interesting starting point for the development of a new suite of linker drugs for antibody drug conjugates (ADCs). Structure activity relationships were explored on the small molecule which led to six linker drugs being developed for conjugation to antibodies. Herein we describe the synthesis of novel PNU-159682 derivatives and the subsequent linker drugs as well as the corresponding biological evaluations of the small molecules and ADCs.

Carminomycin-Chitosan: A Conjugated Antituimor Antibiotic

Condensation of the antitumor antibiotic carminomycin with oxidized chitosan in the presence of sodium borohydride provided a new conjugated antibiotic. A ring involving a N atom from the 3′ amino group of the antibiotic sugar moiety and the residue of the oxidized glucosamine ring of chitosan was formed during reductive alkylation. The resultant compound was characterized by IR and UV-VIS spectra which support the conjugate structure. The amount of carminomycin bound to the matrix was 25.2% w/w or 391 carminomycin residues. The biological activity of the carminomycin-chitosan conjugate showed an antibacterial action against Bacillus subtilis on the level of the initial antibiotic. Implanted lymphoid leucosis L1210 and lymphocytic leucosis P388 in hybrid mice BDF1 showed: a T/C = 242.9 (P388) (for free carminomycin T/C = 177.9%) and a T/C = 201.4 (L1210) (for the free drug T/C = 179.85%).

Structural analysis of doxorubicin-polymer conjugates

Synthetic polymers poly(ethylene glycol) (PEG), methoxypoly (ethylene glycol) polyamidoamine (mPEG-PAMAM-G3) and polyamidoamine (PAMAM-G4) dendrimers were used for encapsulation of antibiotic drug doxorubicin (Dox) and its analogue N-(trifluoroacetyl) doxorubicin (FDox) in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize the drug binding process to synthetic polymers. Structural analysis showed that drug-polymer binding occurs via both H-bonding and hydrophobic contacts. The order of binding is PAMAM-G4>mPEG-PAMAM-G3>PEG-6000 with Dox forming more stable conjugate than FDox. Transmission electron microscopy showed significant changes in carrier morphology with major changes in the shape of the polymer aggregate as drug encapsulation occurred. Modeling also showed that drug is located in the surface and in the internal cavities of PAMAM with the free binding energy of -4.14 kcal/mol for Dox and -3.93 kcal/mol for FDox, indicating of spontaneous drug-polymer interaction at room temperature.

Applications of chitosan nanoparticles in drug delivery

We have reviewed the binding affinities of several antitumor drugs doxorubicin (Dox), N-(trifluoroacetyl) doxorubicin (FDox), tamoxifen (Tam), 4-hydroxytamoxifen (4-Hydroxytam), and endoxifen (Endox) with chitosan nanoparticles of different sizes (chitosan-15, chitosan-100, and chitosan-200 KD) in order to evaluate the efficacy of chitosan nanocarriers in drug delivery systems. Spectroscopic and molecular modeling studies showed the binding sites and the stability of drug-polymer complexes. Drug-chitosan complexation occurred via hydrophobic and hydrophilic contacts as well as H-bonding network. Chitosan-100 KD was the more effective drug carrier than the chitosan-15 and chitosan-200 KD.

tRNA binding to antitumor drug doxorubicin and its analogue

The binding sites of antitumor drug doxorubicin (DOX) and its analogue N-(trifluoroacetyl) doxorubicin (FDOX) with tRNA were located, using FTIR, CD, fluorescence spectroscopic methods and molecular modeling. Different binding sites are involved in drug-tRNA adducts with DOX located in the vicinity of A-29, A-31, A-38, C-25, C-27, C-28, G-30 and U-41, while FDOX bindings involved A-23, A-44, C-25, C-27, G-24, G-42, G-53, G-45 and U-41 with similar free binding energy (-4.44 for DOX and -4.41 kcal/mol for FDOX adducts). Spectroscopic results showed that both hydrophilic and hydrophobic contacts are involved in drug-tRNA complexation and FDOX forms more stable complexes than DOX with K DOX-tRNA=4.7 (± 0.5)× 10(4) M(-1) and K FDOX-tRNA=6.3 (± 0.7)× 10(4) M(-1). The number of drug molecules bound per tRNA (n) was 0.6 for DOX and 0.4 for FDOX. No major alterations of tRNA structure were observed and tRNA remained in A-family conformation, while biopolymer aggregation and particle formation occurred at high drug concentrations.

Encapsulation of antitumor drug Doxorubicin and its analogue by chitosan nanoparticles

Biodegradable chitosan of different sizes were used to encapsulate antitumor drug doxorubicin (Dox) and its N-(trifluoroacetyl) doxorubicin (FDox) analogue. The complexation of Dox and FDox with chitosan 15, 100, and 200 KD was investigated in aqueous solution, using FTIR, fluorescence spectroscopic methods, and molecular modeling. The structural analysis showed that Dox and FDox bind chitosan via both hydrophilic and hydrophobic contacts with overall binding constants of K(Dox-ch-15) = 8.4 (±0.6) × 10(3) M(-1), K(Dox-ch-100) = 2.2 (±0.3) × 10(5) M(-1), K(Dox-ch-200) = 3.7 (±0.5) × 10(4) M(-1), K(FDox-ch-15) = 5.5 (±0.5) × 10(3) M(-1), K(FDox-ch-100) = 6.8 (±0.6) × 10(4) M(-1), and K(FDox-ch-200) = 2.9 (±0.5) × 10(4) M(-1), with the number of drug molecules bound per chitosan (n) ranging from 1.2 to 0.5. The order of binding is ch-100 > 200 > 15 KD, with stronger complexes formed with Dox than FDox. The molecular modeling showed the participation of polymer charged NH(2) residues with drug OH and NH(2) groups in the drug-polymer adducts. The presence of the hydrogen-bonding system in FDox-chitosan adducts stabilizes the drug-polymer complexation, with the free binding energy of -3.89 kcal/mol for Dox and -3.76 kcal/mol for FDox complexes. The results show chitosan 100 KD is a more suitable carrier for Dox and FDox delivery.

Antibiotic doxorubicin and its derivative bind milk β-lactoglobulin

β-Lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic molecules such as doxorubicin and its derivatives. We located the binding sites of doxorubicin (DOX) and N-(trifluoroacetyl) doxorubicin (FDOX) with β-lactoglobulin in aqueous solution at physiological conditions, using FTIR, CD and fluorescence spectroscopic methods as well as molecular modeling. Structural analysis showed that DOX and FDOX bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants of K(DOX-)(β)(-LG)=1.0 (± 0.4)× 10(4)M(-1) and K(FDOX-)(β)(-LG)=2.5 (± 0.5)× 10(4)M(-1) and the number of drug molecules bound per protein (n) 1.2 for DOX and 0.6 for FDOX. Molecular modeling showed the participation of several amino acids in the drug-protein complexes with the free binding energy of -8.12 kcal/mol for DOX-β-LG and -7.74 kcal/mol for FDOX-β-LG complexes. DOX and FDOX do not share similar binding sites with β-LG. Protein conformation showed minor alterations with reduction of β-sheet from 58% (free protein) to 57-51% in the drug-β-LG complexes. β-LG can transport doxorubicin and its derivative in vitro.

Probing the binding sites of antibiotic drugs doxorubicin and N-(trifluoroacetyl) doxorubicin with human and bovine serum albumins

We located the binding sites of doxorubicin (DOX) and N-(trifluoroacetyl) doxorubicin (FDOX) with bovine serum albumin (BSA) and human serum albumins (HSA) at physiological conditions, using constant protein concentration and various drug contents. FTIR, CD and fluorescence spectroscopic methods as well as molecular modeling were used to analyse drug binding sites, the binding constant and the effect of drug complexation on BSA and HSA stability and conformations. Structural analysis showed that doxorubicin and N-(trifluoroacetyl) doxorubicin bind strongly to BSA and HSA via hydrophilic and hydrophobic contacts with overall binding constants of K_DOX-BSA = 7.8 (±0.7)×10³ M⁻¹, K_FDOX-BSA = 4.8 (±0.5)×10³ M⁻¹ and K_DOX-HSA = 1.1 (±0.3)×10⁴ M⁻¹, K_FDOX-HSA = 8.3 (±0.6)×10³ M⁻¹. The number of bound drug molecules per protein is 1.5 (DOX-BSA), 1.3 (FDOX-BSA) 1.5 (DOX-HSA), 0.9 (FDOX-HSA) in these drug-protein complexes. Docking studies showed the participation of several amino acids in drug-protein complexation, which stabilized by H-bonding systems. The order of drug-protein binding is DOX-HSA > FDOX-HSA > DOX-BSA > FDOX>BSA. Drug complexation alters protein conformation by a major reduction of α-helix from 63% (free BSA) to 47–44% (drug-complex) and 57% (free HSA) to 51–40% (drug-complex) inducing a partial protein destabilization. Doxorubicin and its derivative can be transported by BSA and HSA in vitro.

Cell photosensitization by 5-iminodaunomycin activated with red light

5-Iminodaunomycin, an anthracycline antitumor drug exhibiting an absorption peak at 595 nm, is shown to photosensitize in vitro cell kill. The photoactivation is performed irradiating the culture dishes during the incubation with the drug for 2 h with 34 mW/cm2 intensity, that is with light doses of up to 245 J/cm2. Long-term effects of administering 50 ng/ml and light for 2 h are studied in terms of growth curves. We show that photoactivation enhances the dark toxicity by a factor of about 10. Immediate cell death is produced by irradiating the cells in the presence of higher drug concentrations (e.g., 1000 ng/ml) which, however, are not toxic in the short term if administered in the dark. The viable cell percentage decreases at increasing light doses, being about 0.6% at the maximum dosage. Administering lower light doses, such as 30 J/cm2, which corresponds to an exposure duration of 15 min, has a short-term effect on the cell survival that strongly depends on the timing of the exposures within the incubation period.

DNA-drug interactions. The crystal structure of d(CGATCG) complexed with daunomycin

The structure of a d(CGATCG)-daunomycin complex has been determined by single crystal X-ray diffraction techniques. Refinement, with the location of 40 solvent molecules, using data up to 1.5 A, converged with a final crystallographic residual, R = 0.25 (RW = 0.22). The tetragonal crystals are in space group P4(1)2(1)2, with cell dimensions of a = 27.98 A and c = 52.87 A. The self-complementary d(CGATCG) forms a distorted right-handed helix with a daunomycin molecule intercalated at each d(CpG) step. The daunomycin aglycon chromophore is oriented at right-angles to the long axis of the DNA base-pairs. This head-on intercalation is stabilized by direct hydrogen bonds and indirectly via solvent-mediated, hydrogen-bonding interactions between the chromophore and its intercalation site base-pairs. The cyclohexene ring and amino sugar substituent lie in the minor groove. The amino sugar N-3' forms a hydrogen bond with O-2 of the next neighbouring thymine. This electrostatic interaction helps position the sugar in a way that results in extensive van der Waals contacts between the drug and the DNA. There is no interaction between daunosamine and the DNA sugar-phosphate backbone. We present full experimental details and all relevant conformational parameters, and use the comparison with a d(CGTACG)-daunomycin complex to rationalize some neighbouring sequence effects involved in daunomycin binding.

Comparison of adriamycin induced immunomodulation with that of the noncardiotoxic anthracycline 5-iminodaunorubicin

Adriamycin (ADM) has been shown to modulate a variety of host immune responses. Although the mechanism(s) for this activity is not known, it has been suggested that free radical compounds generated during ADM metabolism act at the membrane level to alter immune cell function. The generation of free radical metabolites is also believed to be responsible for the cardiotoxic potential of ADM. 5-Iminodaunorubicin (IDM) is a non-cardiotoxic anthracycline analog which undergoes minimal free radical metabolism. In the present study the immunomodulatory capacity of IDM was compared to that of ADM. It was found that IDM and ADM had similar augmenting effects on cytolytic T-cell activity and that this correlated with: (1) Fc-dependent phagocytosis by spleen cells; and (2) the elimination or inhibition of an adherent regulatory cell in the spleen. The natural killer response was either unaffected (fresh NK) or slightly inhibited (cultured NK) by both drugs except moderate dose IDM which resulted in marked augmentation of cultured NK.

Structural requirements for inducing cardiotoxicity by anthracycline antibiotics: studies with neonatal rat cardiac myocytes in culture

Neonatal rat cardiac myocytes maintained in tissue culture were utilized to screen cardiotoxicity induced by a number of adriamycin and daunomycin analogs. Cell toxicity was assessed by leakage of cytoplasmic enzymes and was confirmed by electron microscopy. A number of modifications of structure of adriamycin and daunomycin markedly altered the incidence of toxicity caused by these drugs. Even though some of these structural alterations markedly altered lipid solubility or reactivity of quinone function, these changes did not always account for the differences in the toxicity induced by anthracycline analogs. The cardiomyocyte culture system used in this simple screening technique should be useful in the development of active anthracycline analog with least cardiotoxic potential.

Redox activities of antitumor anthracyclines determined by microsomal oxygen consumption and assays for superoxide anion and hydroxyl radical generation

To explore the structural characteristics of various derivatives of the anticancer drugs, doxorubicin and daunorubicin, for exhibiting redox activities believed to be associated with toxic radical production, we tested over fifty derivatives in a rapid screening procedure for augmenting oxygen consumption by rat liver microsomes. Measurement of parent drug disappearance and of metabolite appearance for fourteen anthracyclines with a broad range of activities for augmenting oxygen consumption indicated that a single reaction, conversion to the 7-deoxyaglycone, occurred. Multiple tests of selected compounds showed that the liver microsome system exhibited saturation kinetics, and calculated values of Vmax/Km gave the same relative order of activities as did the screening test. The liver microsome system was not found to be stereoselective. Measurements of the abilities of a number of the anthracycline derivatives after chemical activation by reduction with sodium borohydride to convert oxygen to superoxide anion, or to the hydroxyl radical, were also made. The reactivities of the anthracyclines in these latter two assays were positively related to the activities obtained in the rat liver microsome screening test, suggesting that all three tests were measuring various steps in the sequence from anthracycline semiquinone radical formation through oxygen activation and radical formation. Superoxide anion generation from chemically reduced anthracyclines was inhibited by the addition of calf thymus DNA, and the extent of inhibition was positively correlated with the measured DNA association constants of the anthracyclines. However, the DNA association constants were unrelated to superoxide anion generation in the absence of DNA or to the augmentation of oxygen consumption in liver microsomes. Half-wave potentials were negatively correlated with both the results of the microsomal oxygen consumption test and the production of superoxide anion in the chemical test system. No relationships were discerned among the DNA association constants, half-wave potentials, or reoxidizabilities of the anthracyclines tested. Comparisons of the relatively low activities of certain of the anthracyclines in the biochemical and chemical tests for oxygen activation with their known high activities against murine tumors in vivo, but low cardiotoxicities in animal model systems, suggest that the separation of the cytotoxic antitumor and cardiotoxic actions of these derivatives may have been achieved.

Structural basis of anthracycline selectivity for unilamellar phosphatidylcholine vesicles: an equilibrium binding study

Fluorescence anisotropy titration was used to determine the equilibrium binding affinities of several anthracycline antitumor antibiotics for sonicated dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) vesicles at 27.5 degrees C. Eight daunomycin analogues, all differing from the parent by one structural change in the aglycon portion of the molecule, as well as four anthracycline congeners modified in the amino sugar were studied. Double-reciprocal plots were used to determine overall binding affinities (K). It was shown that structural changes in both the aglycon and amino sugar portions of the daunomycin molecule strongly modulated K values for DMPC and DPPC bilayers. For modifications in the aglycon portion of an anthracycline, a correlation between drug hydrophobicity and membrane affinity was observed. The number of binding sites per phospholipid molecule (n) and the apparent association constant (Kapp) where K = nKapp, were determined at several temperatures for adriamycin, daunomycin, and carminomycin. The n values were found to be independent of temperature for fluid-phase DMPC or solid-phase DPPC bilayers. The Kapp values (25 degrees C) ranged from (0.82-4.4) X 10(5) M-1 for DMPC vesicles to (4.4-7.3) X 10(5) M-1 for DPPC vesicles. Although the Kapp values for the three drugs were similar for a particular bilayer, major differences were noted in the values of n and, therefore, in the overall vesicle affinities (nKapp). van't Hoff plots showed that anthracycline binding was exothermic; in all cases but one binding was accompanied by a decrease in entropy.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative cytotoxicities of various morpholinyl anthracyclines

A series of quinone- and sugar-modified analogs of adriamycin have been tested for growth inhibition of adriamycin-sensitive (P388/S) and -resistant (P388/ADR) sublines of P388 murine leukemia cells in vitro. P388/ADR is less resistant to analogs of adriamycin containing either a 3'-deamino-3'-(4"-morpholinyl) group, MRA; or a -(3"-cyano-4"-morpholinyl) group, MRA-CN, than to adriamycin. However, MRA-CN was the most potent growth inhibitor of either subline. This potency is reduced by either modification of the quinone unit with a 5-imino substituent or restriction of the cyano-morpholinyl ring by an oxygen bridge to the daunosamine sugar. The calcium antagonist verapamil substantially increases the cytotoxicity of adriamycin to P388/ADR but has no appreciable effect on the cytotoxicity of either MRA or MRA-CN. The results suggest that increased uptake and retention by both MRA and MRA-CN may contribute to their increased cytotoxicity, but that the intense potency of the cyano-morpholinyl analogs must be due to other unique properties of these compounds.