Prophage induction and mutagenicity of a series of anti-tumour platinum(II) and platinum(IV) co-ordination complexes

11 platinum compounds with nitrogen donor ligands, previously tested for anti-tumour activity, were studied for induction of prophage lambda and for mutagenicity in the Ames assay, with various strains of Salmonella. The compounds included cis and trans isomers of Pt(II) and Pt(IV) complexes and were tested with and without metabolic activation. All the cis compounds elicited prophage induction, whereas the trans compounds were inactive. Mutagenicity was found only in strains containing the R factor, indicating that SOS-type repair processes are required for the conversion of initial DNA lesions into mutations. Mutation induction was also influenced by the excision-repair process. The 2 trans compounds were not, or only slightly, mutagenic; all other compounds were mutagenic in at least one strain, exhibiting a 2-20-fold increase over the spontaneous background level. Addition of liver homogenate had no significant effect on the number of mutants. One compound induced exclusively frameshift mutations. The other mutagenic compounds induced frameshift mutations as well as base-pair substitutions. 7 compounds were more mutagenic for the repair-proficient than for the repair-deficient strains; only one showed the opposite effect. This suggests that for mutagenicity testing of platinum compounds, repair-proficient strains are more sensitive indicators. The differences in response of the various strains are more sensitive indicators. The differences in response of the various strains toward the compounds suggest the formation of different DNA lesions and/or a selective action of repair processes on these lesions. In general, a good qualitative correlation was observed between prophage-inducing capacity, mutagenicity in bacterial and mammalian cells and anti-tumour activity.     

Modifying the properties of platinum (IV) complexes in order to increase biological effectiveness

The preparation of a series of novel Pt(IV) complexes containing the anionic polyfluoroaryl ligands, 2,3,5,6-tetrafluorophenyl (p-HC6F4), 2,3,5,6-tetrafluoro-4-methoxyphenyl (p-MeOC6F4) and pentafluorophenyl (C6F5) are described. The crystal structure of a representative complex, [Pt(p-MeOC6F4)2(O2CEt)2(en)] (en = ethane-1,2-diamine) was determined and confirms the trans arrangement of the carboxylato ligands. Reduction potentials of the series of complexes reveal that replacement of equatorial chloro ligands by polyfluoroaryl ligands makes reduction substantially more difficult. They also confirm previously reported trends in that complexes having axial carboxylato ligands are more readily reduced than those having axial hydroxo ligands. Reduction potentials and in vitro activities showed no obvious correlations. Moderate to high activity was observed for many complexes in the series, including some of those that were very difficult to reduce.     

Synthesis,characterization, cytotoxicity,and DNA binding of some new platinum(II) and platinum(IV) complexes with benzimidazole ligands

In this study, two Pt(II) and three Pt(IV) complexes with the structures of [PtL₂Cl₂] (1), [PtL₂I₂] (2), [PtL₂Cl₂(OH)₂] (3), [PtL₂Cl₂(OCOCH₃)₂] (4), and [PtL₂Cl₄] (5) (L = benzimidazole as carrier ligand) were synthesized and evaluated for their in vitro antiproliferative activities against the human MCF-7, HeLa, and HEp-2 cancer cell lines. The influence of compounds 1–5 on the tertiary structure of DNA was determined by their ability to modify the electrophoretic mobility of the form I and II bands of pBR322 plasmid DNA. The inhibition of BamH1 restriction enzyme activity of compounds 1–5 was also determined. In general, it was found that compounds 1–5 were less active than cisplatin and carboplatin against MCF-7 and HeLa cell lines (except for 1, which was found to be more active than carboplatin against the MCF-7 cell line). Compounds 1 and 3 were found to be significantly more active than cisplatin and carboplatin against the HEp-2 cell line.     

The binding of binuclear platinum(II)-terpyridine complexes to DNA.

The binding of platinum (II)-terpyridine complexes to DNA was studied by using equilibrium dialysis. Optical absorption methods were used to measure the ability of the ligands to aggregate in aqueous buffer. Scatchard plots for the binding of the monomeric [Pt(terpy)SC4H9]+ cation to DNA at I0.01 are curvilinear, concave upwards, suggesting two modes of binding. The association constant decreases at higher ionic strengths, consistent with polyelectrolyte theory, and 1.1 cations are released per bound ligand molecule. The association constants of the binuclear ligands [Pt(terpy)S[CH2]4S(terpy)Pt]2+ and [Pt(terpy)S[CH2]6S(terpy)Pt]2+ are 8 and 23 times larger respectively than the affinity of the monomer. For the latter binuclear derivative the increase may be ascribed to bifunctional reaction. Differential dialysis experiments with DNAs of differing base composition show that [Pt(terpy)SC4H9]+ has a requirement for a single G X C base-pair at the highest-affinity site. However, in the binuclear ligands chromophore specificity is severely compromised. Similar experiments indicate that 9-aminoacridine and selected methylene-linked diacridines show no significant sequence selectivity.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Inhibition of peroxidase, trypsin, and alpha-chymotrypsin by platinum (II) and platinum (IV) complexes

Effects of various complexes of platinum (II) and platinum (IV) on activities of trypsin, alpha-chymotrypsin, and peroxidase were compared. The platinum (II) complexes were found to inhibit these enzymes, though with variable efficiency. The platinum (IV) complexes at concentrations < or = 0.2 mM efficiently inhibited peroxidase but had no effect on the proteases. An enzymatic assay was developed to measure the most effective peroxidase inhibitor (cisplatin) at concentrations of 5-50 microM in the presence of fivefold excess of its isomer (transplatin).     

Synthesis and preliminary evaluation of the new water-soluble radioactive platinum(IV) complexes

A novel class of water-soluble Pt(IV) complexes with histamine (Hist) and radioiodinated histamine ([(125)I/(131)I]Hist) has been synthesised with the goal of potential application for concomitant anticancer radio-chemotherapy of solid tumours. The prepared complex of 1:2 metal:ligand stoichiometry ([Pt(IV)(Hist)(2)(OH)(2)]Cl(2)) was characterised by microanalysis, mass spectrometry, and chromatographic methods. Cytotoxic/cytostatic activities of the complex were examined by flow cytometry method using the MCF-7 cells line. A slightly lower cytotoxicity of the Pt(IV) complex comparing to cisplatin was found (IC(50) 59 and 48 microM, respectively). Both cisplatin and the histamine complex show a cytostatic activity by blocking MCF-7 cells in S-phase of cell cycle. Biodistribution studies in normal rats revealed the highest accumulation of the (131)I-labelled complex in liver and kidneys (41.3% and 12.4% ID after 24 h post-intravenous injection (p.i.v.)). The similar pharmacokinetics was observed in tumour-bearing C3H/W mice, however, a lower accumulation in liver was observed following an intraperitoneal comparing to an intravenous administration. A concentration of the complex in tumour increased with time post-intraperitoneal injection (1.2 and 2.5%ID/g after 2 and 24 h (p.i.), respectively). An increasing tumour/muscle ratio was also observed (2.2 and 4.5 after 2 and 24 h p.i., respectively), and that suggests a penetration of the complex into the tumour cells, and a permanent binding with some cellular components, probably with the DNA.     

A comparative binding of platinum anti-tumour compounds to plasma proteins in the rat (in vivo) and mouse (in vitro).

Plasma protein binding of 195mPt-labelled cisplatin, carboplatin and iproplatin has been studied in vivo in rat and in vitro in mouse, using both electrophoresis and trichloroacetic acid precipitation. After intravenous injection plasma clearance rates were biphasic for all 3 compounds, (t1/2 alpha, 13-17 min) but cisplatin was retained thereafter longer than the others. By 5 min, gel electrophoresis showed protein labelling with all 3 drugs but none involved low mol.wt. proteins (< 16 kDa). At 2 h a notable proportion of the protein bound platinum was associated with the latter components. There was a general resemblance between the distribution patterns of cisplatin and carboplatin whereas iproplatin showed a persistent retention of the label with time to higher mol. wt. proteins. From in vitro incubation with mouse plasma, rates of interaction respectively were cisplatin t1/2 alpha, 35 min, beta 8 h, carboplatin t1/2, 44 h and iproplatin t1/2, 104 h. By electrophoresis the protein bound fraction pattern (1 h) was again similar for cisplatin and carboplatin with virtually no binding to low mol. wt. proteins. After 24 h these were now involved to a high degree (40%). Iproplatin showed relatively marked binding to proteins of higher mol. wt. but no transfer with time to the low mol. wt. protein zone. A possible explanation is the need for in vivo metabolism for this compound as manifest in the rat. It is suggested that the significance of interaction with low mol. wt. proteins merits further investigation in relation to the antitumour and toxicological actions of these drugs.     

Conjugated platinum(IV)-peptide complexes for targeting angiogenic tumor vasculature

The integrins alpha vbeta3 and alpha vbeta5 and the membrane-spanning surface protein aminopeptidase N (APN) are highly expressed in tumor-induced angiogenesis, making them attractive targets for therapeutic intervention. Both integrins and APN recognize a broad range of peptides containing RGD (Arg-Gly-Asp) and NGR (Asn-Gly-Arg) motifs, respectively. Here, we describe the design, synthesis, and characterization of a series of mono- and difunctionalized platinum(IV) complexes in which a conjugated peptide motif, containing RGD, (CRGDC)c, (RGDfK)c, or NGR, is appended as a "tumor-homing device" to target tumor endothelial cells selectively over healthy cells. Platinum(IV)-peptide complexes with nonspecific amino acids or peptide moieties were prepared as controls. Concentration-response curves of these compounds were evaluated against primary proliferating endothelial cells and tumor cell lines and compared to those of cisplatin, a well-described platinum-based chemotherapeutic agent. The Pt(IV)-RGD conjugates were highly and specifically cytotoxic to cell lines containing alpha vbeta3 and alpha vbeta5, approaching the activity of cisplatin. The Pt(IV)-NGR complexes were less active than Pt(IV)-RGD-containing compounds but more active than nonspecific Pt-peptide controls. Integrin alpha vbeta3 mediated, at least in part, the anti-proliferative effect of a Pt(IV)-RGD conjugate, as demonstrated by a decreased inhibitory response when endothelial cells were either (1) incubated with an excess of alpha vbeta3/alpha vbeta5-specific RGD pentapeptides or (2) transfected with RNAi for beta 3, but not beta 1, integrins. These results suggest a rational approach to improved chemotherapy with Pt(IV)-peptide conjugates by selective drug delivery to the tumor compartment.     

Terpyridine platinum(II) complexes inhibit cysteine proteases by binding to active-site cysteine

Platinum(II) complexes have been demonstrated to form covalent bonds with sulfur-donating ligands (in glutathione, metallothionein and other sulfur-containing biomolecules) or coordination bonds with nitrogen-donating ligands (such as histidine and guanine). To investigate how these compounds interact with cysteine proteases, we chose terpyridine platinum(II) (TP-Pt(II)) complexes as a model system. By using X-ray crystallography, we demonstrated that TP-Pt(II) formed a covalent bond with the catalytic cysteine residue in pyroglutamyl peptidase I. Moreover, by using MALDI (matrix-assisted laser desorption/ionization) and TOF-TOF (time of flight) mass spectrometry, we elucidated that the TP-Pt(II) complex formed a covalent bond with the active-site cysteine residue in two other types of cysteine protease. Taken together, the results unequivocally showed that TP-Pt(II) complexes can selectively bind to the active site of most cysteine proteases. Our findings here can be useful in the design of new anti-cancer, anti-parasite or anti-virus platinum(II) compounds.     

Synthesis and cytotoxicity of new platinum(IV) complexes of mixed carboxylates

In order to develop new antitumor platinum(IV) complexes with highly tuned lipophilicity, a series of (diamine)Pt(IV) complexes of the formula [Pt(IV)(dach)L(3)L'] or [Pt(IV)(dach)L(2)L"(2)] (dach=trans-(+/-)-1,2-diaminocyclohexane; L=acetato, propionato; L'=acetato, propionato, valerato or pivalato; L"=trifluoroacetato) have been synthesized by electrophilic substitution of the tris(carboxylato)hydroxoplatinum(IV) complexes, [Pt(IV)(dach)L(3)OH] (L=acetato, propionato), with various carboxylic anhydrides such as acetic, trifluoroacetic, pivalic and valeric anhydrides. The present platinum(IV) complexes were fully characterized by means of elemental analyses, 1H NMR, mass and IR spectroscopies. The complexes 8 and 10, satisfying the appropriate range of lipophilicity (logP=0.18-1.54), exhibited high activity (ED(50), 5.1 and 1.3 microM, respectively) compared with other complexes, which implies that the lipophilicity is an important factor for the antitumor activity of this series of complexes.     

Synthesis, characterization and cytotoxicity of a series of tetrachloridoplatinum(IV) complexes

Two platinum(IV) complexes, [Pt(4bt)Cl₄] (4) and [Pt(dpyam)Cl₄]·DMF (5) (where 4bt is 4,4′-bithiazole and dpyam is 2,2′-dipyridylamine) were prepared from the reaction of H₂PtCl₆·6H₂O with 4,4′-bithiazole and 2,2′-dipyridylamine, respectively, in methanol. Both complexes were fully characterized and their structures were determined by the X-ray diffraction method. These complexes have a bidentate nitrogenous ligand with four chloride anions attached to a Pt(IV) metal in a distorted octahedral environment. These complexes along with three previously reported analogous complexes were used for in vitro cytotoxicity evaluation against four cultures, NIH-3T3, Caco-2, HT-29 and T47D by MTT assay. The methyl group position in the ligand plays an important role in the cytotoxicity of relevant compounds in different cultures. Interestingly, in some cases, the IC₅₀ values of the new complexes were higher for normal cells but lower against cancer cells in comparison with cisplatin, especially in T47D (breast ductal carcinoma).     

The cellular distribution and oxidation state of platinum(II) and platinum(IV) antitumour complexes in cancer cells

The cellular distribution of platinum in A2780 ovarian cancer cells treated with cisplatin and platinum(IV) complexes with a range of reduction potentials has been examined using elemental analysis (synchrotron radiation-induced X-ray emission). The cellular distribution of platinum(IV) drugs after 24 h is similar to that of cisplatin, consistent with the majority of administered platinum(IV) drugs being reduced. Micro-X-ray absorption near-edge spectra of cells treated with cisplatin and platinum(IV) complexes confirmed the reduction of platinum(IV) to platinum(II). In cells treated, the most difficult to reduce complex, cis,trans,cis-[PtCl₂(OH)₂(NH₃)₂], platinum(IV) was detected in the cells along with platinum(II). The observations are in accordance with the relative ease of reduction of the platinum(IV) complexes used and support the requirement of reduction for activation of platinum(IV) complexes.Abbreviations en ethane-1,2-diamine - GM growth medium - PBS phosphate buffered saline - RPMI Roswell Park Memorial Institute - SRIXE synchrotron radiation-induced X-ray emission - XAFS X-ray absorption fine structure - XANES X-ray absorption near-edge spectroscopy     

Photoactive trans ammine/amine diazido platinum(IV) complexes

The synthesis and characterisation of eight new octahedral Pt^IV complexes of the type trans,trans,trans-[Pt(N₃)₂(OH)₂(NH₃)(Am)] where Am = methylamine (2), ethylamine (4), thiazole (6), 2-picoline (8), 3-picoline (10), 4-picoline (12), cyclohexylamine (14), and quinoline (16) are reported, including the X-ray crystal structures of complexes 2, 8, and 14 as well as that of two of the precursor Pt^II complexes (trans-[Pt(N₃)₂(NH₃)(methylamine)] (1) and trans-[Pt(N₃)₂(NH₃)(cyclohexylamine)] (13)). Irradiation with UVA light rapidly induces loss in intensity of the azide-to-Pt^IV charge-transfer bands and gives rise to photoreduction of platinum. These complexes have potential for use as photoactivated anticancer agents.     

Synthesis, characterization, antibacterial and cytotoxic study of platinum (IV) complexes

Platinum (IV) complexes [Pt (L)2Cl2] [where, L= benzyl-N-thiohydrazide (L1), (benzyl-N-thio)-1,3-propanediamine (L2), benzaldehyde-benzyl-N-thiohydrazone (L3) and salicylaldehyde-benzyl-N-thiohydrazone (L4)] have been synthesized. The thiohydrazide, thiodiamine and thiohydrazones can exist as thione-thiol tautomer and coordinate as a bidentate N-S ligand. The ligands were found to act in monobasic bidentate fashion. Analytical data reveal that metal to ligand stoichiometry is 1:2. The complexes have been characterized by elemental analysis, IR, mass, electronic and 1H NMR spectroscopic studies. In vitro antibacterial and cytotoxic studies have been carried out for some complexes. Various kinetic and thermodynamic parameters like order of reaction (n), activation energy (Ea), apparent activation entropy (S#) and heat of reaction (DeltaH) have also been carried out for some complexes.     

Oestriol binding to plasma proteins

Simple diffusion experiments indicated that oestriol was retained by human pregnancy plasma more effectively than by albumin solutions of a corresponding concentration. Oestriol bound (Ka = 6 X 10(6) l/mol at 4 degrees C) to a glycoprotein which had been isolated from plasma by adsorption to Concanavalin A. The free energy of binding at 37 degrees C was -38 kJ/mol. Competition experiments indicated that the oestriol binding glycoprotein had properties expected of sex hormone binding globulin. The distribution of oestriol among the protein fractions of human pregnancy plasma--glycoprotein bound 7.8%, albumin bound 78.6%, unbound 13.6%--suggests that this glycoprotein plays little part in the transport of oestriol.     

Synthesis and characterization of novel platinum(IV) complexes with non-functionalized acetylated carbohydrates

[PtMe3(Me2CO)3]BF4 (1) reacts in acetone with 1,2,3,4-tetraacetyl-beta-D-glucopyranose (C2), pentaacetyl-alpha-D-glucopyranose (C3), pentaacetyl-beta-D-mannopyranose (C4) and pentaacetyl-beta-D-galactopyranose (C5) to give trimethyl(carbohydrate)platinum tetrafluoroborate complexes [PtMe3L]BF4 (2-5) (2, L=C2; 3, L=C3; 4, L=C4; 5, L=C5). The platinum-carbohydrate complexes were isolated as white, air and moisture sensitive powders in moderate to good yields (26-87%), and their identities were confirmed by microanalysis, 1H-, 13C- and 195Pt-NMR spectroscopy and ESI mass spectrometry. The coordination modes of the tridentately bound carbohydrate ligands (2, OH+Oring+Oacetyl; 3, Oring+Oether+Oacetyl; 4,5, Oring+Oether+Oether where Oring is the oxygen of a pyranose ring and Oacetyl/ether is the acetyl and ether oxygen of an acetoxy substituent, respectively) were established by evaluating the chemical shifts and the 2J(Pt,H) coupling constants of the methyl ligands and by 2D-NOE experiments. Evaluation of the 3J(H,H) coupling constants shows that the pyranose rings are present in their 4C1 conformation. The results show that carbohydrates without anchoring groups and even without hydroxyl groups can coordinate to the metal center only through very weak donors such as oxygen atoms of pyranose rings and acetoxy substituents.     

Synthesis,characterization and antitumor activity of a series of N-substituted iminodiacetato(diammine) platinum(II) complexes

A series of water-soluble N-substituted iminodiacetato (diammine)platinum(II) complexes [Pt(NRIDA)(NH₃)₂] have been synthesized and characterized by measurement of physical properties (conductivity and pH) and by various spectroscopic techniques (infrared, ¹H and ¹³C{¹H} nuclear magnetic resonance). The iminodiacetate ligand is coordinated to platinum through an O,N linkage. The results obtained suggest that these complexes are relatively stable for more than 24 h in aqueous solution. Preliminary in vitro and in vivo screening test for antitumor activity of these complexes against L1210 murine leukemia were performed. Many of complexes had acceptable in vitro cytotoxicity, but none displayed a significant level of in vivo antitumor efficacy.     

Quantitative measurement of the reduction of platinum(IV) complexes using X-ray absorption near-edge spectroscopy (XANES)

The platinum(II) drugs cisplatin, carboplatin and oxaliplatin are usefully employed against a range of malignancies, but toxicities and resistance have spurred the search for improved analogs. This has included investigation of the platinum(IV) oxidation state, which provides greater kinetic inertness. It is generally accepted that Pt(IV) complexes must be reduced to Pt(II) for activation. As such, the ability to monitor reduction of Pt(IV) complexes is critical to guiding the design of candidates, and providing mechanistic understanding. Here we report in full that the white line height of X-ray absorption near-edge spectra (XANES) of Pt complexes, normalized to the post-edge minima, can be used to quantitatively determine the proportion of each oxidation state in a mixture. A series of Pt(IV) complexes based on the Pt(II) complexes cisplatin and transplatin were prepared with chlorido, acetato or hydroxido axial ligands, and studies into their reduction potential and cytotoxicity against A2780 human ovarian cancer cells were performed, demonstrating the relationship between reduction potential and cytotoxicity. Analysis of white line height demonstrated a clear and consistent difference between Pt(II) (1.52 ± 0.05) and Pt(IV) (2.43 ± 0.19) complexes. Reduction of Pt(IV) complexes over time in cell growth media and A2780 cells was observed by XANES, and shown to correspond with their reduction potentials and cytotoxicities. We propose that this method is useful for monitoring reduction of metal-based drug candidates in complex biological systems.     

Seminal plasma non-heparin binding proteins (NHBP) reduce the cryoinjury to buffalo cauda epididymal spermatozoa induced by heparin binding proteins (HBP)

Previous cryopreservation studies with buffalo cauda epididymal spermatozoa have reported a deleterious effect of seminal plasma heparin binding protein (HBP). The amount of HBP used in these studies was meager compared to the normal level of HBP in the buffalo ejaculate, still the damage induced upon the spermatozoa was substantial when compared to that incurred to the spermatozoa during routine freezing of ejaculated semen. Thus there might be some factor(s) in the seminal plasma, which reduce the deleterious effect of HBP on spermatozoa during cryopreservation of ejaculated semen. This study was conducted to investigate for the presence of any such factor in buffalo seminal plasma. Seminal plasma proteins were separated on their heparin binding properties as heparin binding (HBP) and non-heparin binding (NHBP). The separated proteins were added to the extender of buffalo cauda epididymal semen for cryopreservation either alone or in combination. The spermatozoa were assessed for progressive motility, viability, acrosomal integrity and response to hypo-osmotic solution test (HOST) at prefreeze and post-thaw stages of cryopreservation. NHBP was found to provide some degree of protection to buffalo spermatozoa against cryopreservation stress as well as the deleterious effect of HBP during cryopreservation.