Optimization of Weight Ratio for DSPE-PEG/TPGS Hybrid Micelles to Improve Drug Retention and Tumor Penetration.

PURPOSE: To enhance therapeutic efficacy and prevent phlebitis caused by Asulacrine (ASL) precipitation post intravenous injection, ASL-loaded hybrid micelles with size below 40 nm were developed to improve drug retention and tumor penetration. METHODS: ASL-micelles were prepared using different weight ratios of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethyleneglycol-2000 (DSPE-PEG2000) and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) polymers. Stability of micelles was optimized in terms of critical micelle concentration (CMC) and drug release properties. The encapsulation efficiency (EE) and drug loading were determined using an established dialysis-mathematic fitting method. Multicellular spheroids (MCTS) penetration and cytotoxicity were investigated on MCF-7 cell line. Pharmacokinetics of ASL-micelles was evaluated in rats with ASL-solution as control. RESULTS: The ASL-micelles prepared with DSPE-PEG2000 and TPGS (1:1, w/w) exhibited small size (~18.5 nm), higher EE (~94.12%), better sustained in vitro drug release with lower CMC which may be ascribed to the interaction between drug and carriers. Compared to free ASL, ASL-micelles showed better MCTS penetration capacity and more potent cytotoxicity. Pharmacokinetic studies demonstrated that the half-life and AUC values of ASL-micelles were approximately 1.37-fold and 3.49-fold greater than that of free ASL. CONCLUSIONS: The optimized DSPE-PEG2000/TPGS micelles could serve as a promising vehicle to improve drug retention and penetration in tumor.

Quantitative determination of intracellular Asulacrine in MCF-7 breast cancer cells by liquid chromatography-mass spectrometry and its application to cellular pharmacokinetic studies of P188 modified liposomes.

Asulacrine (ASL), an analogue of amsacrine, has shown higher anti-breast and anti-lung cancer activity. Hereby, a new sensitive and selective liquid chromatography-mass spectrometry (LC/MS) method was developed to determine intracellular asulacrine. The chromatographic separation was performed on an Agilent Zorbax Extend-C18 column (2.1 mm i.d. × 50 mm, 5 µm) using gradient elution with water (2 mmol/L ammonium acetate and 0.1% acetic acid) and acetonitrile as the mobile phase. The detection was achieved with selected ion monitoring mode using electrospray ionization in positive mode with target ions at m/z 465.3 and m/z 326.1 for asulacrine and midazolam, respectively. The standard curve showed a good linearity with the lower limit of quantification of 1 ng/mL, as a result of which, the trace concentration of ASL in cell suspension could be quantified. The intra- and inter-day accuracy ranged from -5.28 to 6.5% and from -6.32 to 1.05%, and the intra- and inter-day precisions were no more than 7.65% and 11.71%, respectively. Additionally, no degradation of asulacrine was observed during stability evaluation. The method was proved to be powerful and practical to determine and compare the intracellular distribution and kinetics of ASL under different formulations in MCF-7 breast cancer cells.

Strategies to maximize liposomal drug loading for a poorly water-soluble anticancer drug.

PURPOSE: To develop a liposomal system with high drug loading (DL) for intravenous (i.v.) delivery of a poorly water-soluble basic drug, asulacrine (ASL). METHODS: A thin-film hydration and extrusion method was used to fabricate the PEGylated liposomal membranes followed by a freeze and thaw process. A novel active drug loading method was developed using ammonium sulphate gradient as an influx driving force of ASL solubilized with sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD). DL was maximized by optimizing liposomal preparation and loading conditions. Pharmacokinetics was evaluated following i.v. infusion in rabbits. RESULTS: Freeze-thaw resulted in unilamellar liposome formation (180 nm) free of micelles. Higher DL was obtained when dialysis was used to remove the untrapped ammonium sulphate compared to ultracentrifuge. The pH and SBE-ß-CD level in the loading solution played key roles in enhancing DL. High DL ASL-liposomes (8.9%w/w, drug-to-lipid mole ratio 26%) were obtained with some drug "bundles" in the liposomal cores and were stable in a 5% glucose solution for >80 days with minimal leakage (<2%). Surprisingly, following administration of ASL-liposomes prepared with or without SBE-ß-CD, the half-lives were similar to the drug solution despite an increased area under the curve, indicating drug leakage from the carriers. CONCLUSIONS: High liposomal DL was achieved with multiple strategies for a poorly-water soluble weak base. However, the liposomal permeability needed to be tailored to improve drug retention.

Polymer conjugates of acridine-type anticancer drugs with pH-controlled activation.

Acridines are potent DNA-intercalating anticancer agents with high in vivo anticancer effectiveness, but also severe side effects. We synthesized five 9-anilinoacridine-type drugs and their conjugates with biocompatible water-soluble hydrazide polymer carrier. All of the synthesized acridine drugs retained their in vitro antiproliferative properties. Their polymer conjugates were sufficiently stable at pH 7.4 (model of pH in blood plasma) while releasing free drugs at pH 5.0 (model of pH in endosomes). After internalization of the conjugates, the free drugs were released and are visible in cell nuclei by fluorescence microscopy. Their intercalation ability was proven using a competitive ethidium bromide displacement assay.

Pyrazole Substituted 9-Anilinoacridines as HER2 Inhibitors Targeting Breast Cancer - An in-silico approach.

BACKGROUND: Breast cancer is one of the malignant tumours which mainly affect the female population. 20% of the cases of breast cancer are due to the over-expression of Human epidermal growth factor receptor-2 (HER2), which is the dominant tyrosine kinase receptor. In general, 9-anilinoacridine derivatives play an important role in antitumor activity due to their DNA-intercalating properties. OBJECTIVE: Some novel 9-anilinoacridines substituted with pyrazole moiety (1a-z) were designed and their HER2enzyme (PDB id-3PP0) inhibition activity was performed by molecular docking studies using the Glide module of Schrodinger suite 2019-4. METHODS: Glide module of the Schrodinger suite was used to perform docking studies; qikprop module was used for in-silico ADMET screening and the Prime-MMGBSA module was used for free binding energy calculations. Based on GLIDE scoring functions, we can determine the binding affinity of ligands (1a-z) towards HER2. RESULTS: The inhibitory activity of ligands against HER2 was mainly due to the strong hydrophobic and hydrogen bonding interactions. Almost all the compounds 1a-z exhibited a good binding affinity with Glide scores in the range of -4.9 to -9.75, when compared with the standard drugs CK0403 (-4.105) and Tamoxifen (-3.78). From the results of in-silico ADMET properties, it was evident that most of the compounds fell within the recommended values. MM-GBSA binding calculations of the most potent inhibitors were found to be more favourable. CONCLUSION: The results of in-silico studies provide strong evidence for the potential of valuable ligands in pyrazole substituted 9-anilinoacridines as HER2 inhibitors, and the compounds, 1v,s,r,d,a,o with significant Glide scores may produce significant anti-breast cancer activity.

Synthesis and Anticancer Evaluation of Sulfur Containing 9-anilinoacridines.

BACKGROUND: DNA topoisomerases are a class of enzymes that play a critical role in fundamental biological processes of replication, transcription, recombination, repair and chromatin remodeling. Amsacrine (m-AMSA), the best-known compound of 9-anilinoacridines series, was one of the first DNA-intercalating agents to be considered a Topoisomerase II inhibitor. OBJECTIVES: A series of sulfur-containing 9-anilinoacridines related to amsacrine were synthesized and evaluated for their anticancer activity. METHODS: Cell viability was assessed by the MTT assay. The topoisomerase II inhibitory assay was performed using the Human topoisomerase II Assay kit, and flow cytometry was used to evaluate the effects on the cell cycle of K562 cells. Molecular docking was performed using the Schrödinger Maestro program. RESULTS: Compound 36 was found to be the most cytotoxic of the sulfide series against SW620, K562, and MCF-7. The limited SAR suggested the importance of the methansulfonamidoacetamide side chain functionality, the lipophilicity, and the relative metabolic stability of 36 in contributing to the cytotoxicity. Topoisomerase II α inhibitory activity appeared to be involved in the cytotoxicity of 36 through the inhibition of decatenation of kinetoplast DNA (kDNA) in a concentration- dependent manner. Cell cycle analysis further showed Topo II inhibition through the accumulation of K562 cells in the G2/M phase of the cell cycle. The docking of 36 into the Topo II α-DNA complex suggested that it may be an allosteric inhibitor of Topo II α. CONCLUSION: Compound 36 exhibits anticancer activity by inhibiting topoisomerase II, and it could further be evaluated in in vivo models.

Benzoquinazoline derivatives as new agents affecting DNA processing.

A new series of benzo[h]quinazoline and benzo[f]quinazoline derivatives was prepared and studied for the biological activity. The compounds carrying a dimethylaminoethyl side chain (6c, 8c and 12) inhibit cell growth. The ability to form a molecular complex with DNA and to interfere with topoII and topoI relaxation activity was evidenced for the most active 6c and 8c, along with the capacity to induce apoptosis on HeLa cells.

Identification of some novel oxazine substituted 9-anilinoacridines as SARS-CoV-2 inhibitors for COVID-19 by molecular docking, free energy calculation and molecular dynamics studies.

Coronavirus disease (COVID-19), a life-threatening disease, is caused by SARS-CoV-2. The targeted therapeutics of small molecules helps the scientific community to fight against SARS-CoV-2. In this article, some oxazine substituted 9-anilinoacridines (A1-A48) was designed by docking, MM-GBSA and molecular dynamics (MD) simulation studies for their COVID-19 inhibitory activity. The docking of ligands A1-A48 against SARS-CoV-2 (PDB ID: 5R82) are performed by using Glide module, in silico ADMET screening by QikProp module, binding energy using Prime MM-GB/SA module, MD simulation by Desmond module and atomic charges were derived by Jaguar module of Schrodinger suit 2019-4. Compound A38 has the highest G-score (-7.83) when compared to all the standard compounds which are proposed for COVID-19 treatment such as ritonavir (-7.48), lopinavir (-6.94), nelfinavir (-5.93), hydroxychloroquine (-5.47) and mataquine (-5.37). Compounds A13, A23, A18, A7, A48, A46, A32, A20, A1 and A47 are significantly active against SARS-CoV-2 main protease when compared with hydroxychloroquine and mataquine. The residues GLN19, THR24, THR25, THR26, LEU27, HIE41, SER46, MET49, ASN119, ASN142, HIE164, MET165, ASP187, ARG188 and GLN189 of SARS-CoV-2 main protease play a crucial role in binding with ligands. The in silico ADMET properties of the molecules are within the recommended values. The binding free energy was calculated using PRIME MM-GB/SA studies. From the ligands A38, A13, A23, A18, A7, A48 and A46 with significant Glide scores may produce significant COVID-19 activity for further development. Compound A38 was subjected to MD simulation at 100 ns to study the dynamic behaviour of protein-ligand complex.Communicated by Ramaswamy H. Sarma.

Expedient synthesis and anticancer evaluation of dual-action 9-anilinoacridine methyl triazene chimeras.

The efficient synthesis of molecular hybrids including a DNA-intercalating 9-anilinoacridine (9-AnA) core and a methyl triazene DNA-methylating moiety is described. Nucleophilic aromatic substitution (SN Ar) and electrophilic aromatic substitution (EAS) reactions using readily accessible starting materials provide a quick entry to novel bifunctional anticancer molecules. The chimeras were evaluated for their anticancer activity. Chimera 7b presented the highest antitumor activity at low micromolar IC50 values in antiproliferative assays performed with various cancer cell lines. In comparison, compound 7b outperformed DNA-intercalating drugs like amsacrine and AHMA. Mechanistic studies of chimera 7b suggest a dual mechanism of action: methylation of the DNA-repairing protein MGMT associated with the triazene structural portion and Topo II inhibition by intercalation of the acridine core.

Synthesis of 9-anilinoacridine triazines as new class of hybrid antimalarial agents.

There is challenge and urgency to synthesize cost-effective chemotherapeutic agents for treatment of malaria after the widespread development of resistance to CQ. In the present study, we synthesized a new series of hybrid 9-anilinoacridine triazines using the cheap chemicals 6,9-dichloro-2-methoxy acridine and cyanuric chloride. The series of new hybrid 9-anilinoacridine triazines were evaluated in vitro for their antimalarial activity against CQ-sensitive 3D7 strain of Plasmodium falciparum and their cytotoxicity were determined on VERO cell line. Of the evaluated compounds, two compounds 17 (IC(50)=4.21 nM) and 22 (IC(50)=4.27 nM) displayed two times higher potency than CQ (IC(50)=8.15 nM). Most of the compounds showed fairly high selectivity index. The compounds 13 and 29 displayed >96.59% and 98.73% suppression, respectively, orally against N-67 strain of Plasmodium yoelii in swiss mice at dose 100 mg/kg for four days.

Synthesis and antitumor activity of novel amsacrine analogs: the critical role of the acridine moiety in determining their biological activity.

A new series of N-[4-(2'-oxo-2H-pyrano[2,3-b]quinolin-5'-ylamino)-phenyl]-methanesulfonamides was prepared and analyzed as novel amsacrine-like derivatives. Our preliminary biological evaluation has shown that the replacement of the acridine moiety with the analogous 2-oxo-2H-pyrano[2,3-b]quinoline system drastically reduced both their anticancer activity and their propency to intercalate into double stranded DNA.

In-silico Design, ADMET Screening, MM-GBSA Binding Free Energy of Some Novel Isoxazole Substituted 9-Anilinoacridines as HER2 Inhibitors Targeting Breast Cancer.

BACKGROUND: Human Epidermal development factor Receptor-2 (HER2) is a membrane tyrosine kinase which is overexpressed and gene amplified in human breast cancers. HER2 amplification and overexpression have been linked to important tumor cell proliferation and survival pathways for 20% of instances of breast cancer. 9-aminoacridines are significant DNA-intercalating agents because of their antiproliferative properties. OBJECTIVE: Some novel isoxazole substituted 9-anilinoacridines(1a-z) were designed by in-silico technique for their HER2 inhibitory activity. Docking investigations of compounds 1a-z are performed against HER2 (PDB id-3PP0) by using Schrodinger suit 2016-2. METHODS: Molecular docking study for the designed molecules 1a-z are performed by Glide module, in-silico ADMET screening by QikProp module and binding free energy by Prime-MMGBSA module of Schrodinger suit. The binding affinity of designed molecules 1a-z towards HER2 was chosen based on GLIDE score. RESULTS: Many compounds showed good hydrophobic communications and hydrogen bonding associations to hinder HER2. The compounds 1a-z, aside from 1z have significant Glide scores in the scope of - 4.91 to - 10.59 when compared with the standard Ethacridine (- 4.23) and Tamoxifen (- 3.78). The in-silico ADMET properties are inside the suggested about drug likeness. MM-GBSA binding of the most intense inhibitor is positive. CONCLUSION: The outcomes reveal that this study provides evidence for the consideration of isoxazole substituted 9-aminoacridine derivatives as potential HER2 inhibitors. The compounds, 1s,x,v,a,j,r with significant Glide scores may produce significant anti breast cancer activity and further in vitro and in vivo investigations may prove their therapeutic potential.

Novel Thiazine Substituted 9-Anilinoacridines: Synthesis, Antitumour Activity and Structure Activity Relationships.

BACKGROUND: 9-anilinoacridines are acting as DNA-intercalating agents which plays an important role as antitumor drugs, due to their anti-proliferative properties. Some anticancer agents contain 9- anilinoacridines such as amsacrine (m-AMSA), and nitracrine (Ledakrine) have been already developed. METHODS: In this study, novel 9-anilinoacridines substituted with thiazines 4a-r were designed, synthesized, characterized by physical and spectral data and their cytotoxic activities against DLA cell lines were evaluated. RESULTS: Among those compounds, 4b, c, e, g, i, j, k, m, o, p, q, r exhibited significant short term in vitro cytotoxic activity against Daltons lymphoma ascites (DLA) cells with CTC50 value of 0.18 to 0.31µM. The compounds 4b, c, e, g, i, j, k, m, o, p, q, r are also exhibited significant long term in vitro anti-tumour activity against human tumor cell lines, HEp-2 (laryngeal epithelial carcinoma) by Sulforhodamine B assay with CTC50 value of 0.20 to 0.39µM. The compounds 4b, i, j exhibited significant in vivo antitumor activity with % Increase in Life Span (ILS) 48-82%. CONCLUSION: Results obtained in this study clearly demonstrated that many of the thiazine substituted 9- anilinoacridines exert interesting anti-tumour activity. The compounds 4b, i, j have significant anti-tumour activity and useful drugs after further refinement. The above derivatives will encourage to design future antitumor agents with high therapeutic potentials.

Anticancer compounds as leishmanicidal drugs: challenges in chemotherapy and future perspectives.

Leishmaniasis comprises a spectrum of parasitic illnesses caused by several species of the protozoan kinetoplastid parasite, Leishmania spp. The disease affects 12 million people around the world with an annual death rate of approximately 80,000 people. Several drugs are available for treating leishmaniasis. For example, pentavalent antimonial compounds, such as sodium stibogluconate and meglumine antimonite are the drugs used in first-line chemotherapy. As second-line drugs, amphotericin B and pentamidine are used. However, current treatments against leishmaniasis are usually unsatisfactory due to some limitations including the route of administration of the drugs, their unaffordable cost and toxicity. Efforts have been made to develop new leishmanicidal drugs and to find new strategies of drug design. Hence, it is interesting to point out that the effectiveness of certain molecules as both anticancer drugs and antiprotozoal agents suggested that this class of compounds and their derivatives might be useful as antileishmanial agents. This review summarizes the anticancer compounds that have been investigated against leishmaniasis. Some of such agents include: compounds with in vitro antileishmanial activities, molecules tested in clinical trials and registered patents. We finally discuss challenges in chemotherapy and future prospects in the treatment of leishmaniasis.

Synthesis and biological activity of stable and potent antitumor agents, aniline nitrogen mustards linked to 9-anilinoacridines via a urea linkage.

To improve the chemical stability and therapeutic efficacy of N-mustard, a series of phenyl N-mustard linked to DNA-affinic 9-anilinoacridines and acridine via a urea linker were synthesized and evaluated for antitumor studies. The new N-mustard derivatives were prepared by the reaction of 4-bis(2-chloroethyl)aminophenyl isocyanate with a variety of 9-anilinoacridines or 9-aminoacridine. The antitumor studies revealed that these agents exhibited potent cytotoxicity in vitro without cross-resistance to taxol or vinblastine and showed potent antitumor therapeutic efficacy in nude mice against human tumor xenografts. It also showed that 24d was capable of inducing marked dose-dependent levels of DNA cross-linking by comet assay and has long half-life in rat plasma.

Detecting genotoxic effects of potential clastogens: an in vivo study using the transgenic lacZ plasmid and the MutaMouse model.

In the present paper the capacity of the pUR288 plasmid mouse model and the MutaMouse model to detect the clastogens bleomycin, m-AMSA, o-AMSA and camptothecin, was investigated. Ethylnitrosourea (ENU) served as a positive control, methylcellulose as a negative control. Only bleomycin induced a slight but significant increase in lacZ mutant frequency (MF) in bone marrow of pUR288 plasmid mice. Exposure to the other compounds did not result in an increase in the MF in bone marrow and liver in both mouse models. For the MutaMouse this result was expected, for the plasmid mouse an increase in MF after clastogen exposure was expected. The positive control ENU induced statistically significant increases in MF compared with the negative control in both models and in both tissues analyzed. Hybridisation of DNA of mutant colonies derived from plasmid mice with labelled total mouse DNA (Hybridisation Assay) demonstrated an increase in the percentage of colonies hybridised with total mouse DNA as compared with the negative control, which suggests that there was indeed a biological response associated with treatment. The latter results indicate that the plasmid mouse assay may still be a promising model for the detection of clastogens.

Development and validation of bioanalytical method for the determination of asulacrine in plasma by liquid chromatography.

Asulacrine (9-[(2-methoxy-4-methylsulphonylamino)phenylamino]-N,5-dimethyl-4-acridinecarboxamide), an analogue of the antileukaemia drug amsacrine, has high antitumour activity in mice and has also shown clinical activity. A simple method is described for the quantitation of asulacrine in plasma by liquid chromatography. Chromatographic separation was achieved on a reversed phase C 18 column (250 mm x 4.6mm, particle size 5 microm, Gemini) using isocratic elution (acetonitrile and 0.01 M sodium acetate buffer pH 4.0, 45/55, v/v) at a flow rate of 1 ml/min. Asulacrine and internal standard (the ethylsulphonanilide analogue) were measured using UV detection at 254 nm. The total chromatographic run-time was 8 min with asulacrine and internal standard eluting at approximately 4.7 and approximately 6.5 min, respectively. Limit of quantification was 0.1microg/ml. The linearity range of the method was 0.1-10 microg/ml (r2=0.9995). Mean recoveries from plasma were 100-105%. Intra-batch and inter-batch precision was 7.1 and 7.8%, respectively, and intra-batch and inter-batch accuracy (relative error) was 4.9 and 8.4%, respectively (n=8 in all cases). The bench top, freeze thaw, short-term storage and stock solution stability evaluation indicated no evidence of degradation of asulacrine. The validated method is simple, selective and rapid and can be used for pharmacokinetic studies in mice.

Multiseed liposomal drug delivery system using micelle gradient as driving force to improve amphiphilic drug retention and its anti-tumor efficacy.

To improve drug retention in carriers for amphiphilic asulacrine (ASL), a novel active loading method using micelle gradient was developed to fabricate the ASL-loaded multiseed liposomes (ASL-ML). The empty ML were prepared by hydrating a thin film with empty micelles. Then the micelles in liposomal compartment acting as 'micelle pool' drove the drug to be loaded after the outer micelles were removed. Some reasoning studies including critical micelle concentration (CMC) determination, influencing factors tests on entrapment efficiency (EE), structure visualization, and drug release were carried out to explore the mechanism of active loading, ASL location, and the structure of ASL-ML. Comparisons were made between pre-loading and active loading method. Finally, the extended drug retention capacity of ML was evaluated through pharmacokinetic, drug tissue irritancy, and in vivo anti-tumor activity studies. Comprehensive results from fluorescent and transmission electron microscope (TEM) observation, encapsulation efficiency (EE) comparison, and release studies demonstrated the formation of ML-shell structure for ASL-ML without inter-carrier fusion. The location of drug mainly in inner micelles as well as the superiority of post-loading to the pre-loading method , in which drug in micelles shifted onto the bilayer membrane was an additional positive of this delivery system. It was observed that the drug amphiphilicity and interaction of micelles with drug were the two prerequisites for this active loading method. The extended retention capacity of ML has been verified through the prolonged half-life, reduced paw-lick responses in rats, and enhanced tumor inhibition in model mice. In conclusion, ASL-ML prepared by active loading method can effectively load drug into micelles with expected structure and improve drug retention.

Interactions between antiplasmodial 3,6-diamino-1'-dimethyl-9-anilinoacridine and hematin and concanamycin A.

Antiplasmodial 9-anilinoacridine derivatives exert their effects either by inhibiting DNA topoisomerase (topo) II or by interfering with heme crystallization within the parasite acidic food vacuole. Previous studies have shown that analogs of 9-anilinoacridine containing 3,6-diamino substitutions (in the acridine ring) inhibit Plasmodium falciparum DNA topo II in situ, whereas those with a 3,6-diCl substitution act by inhibiting beta-hematin formation, a property also seen with 3,6-diamino-1'-dimethyl-9-anilinoacridine (DDAA). To understand this seemingly anomalous property of DDAA, studies of its interaction with hematin and localization within the parasite food vacuole were undertaken. A weak interaction with hematin was demonstrated spectroscopically. Antagonism of DDAA inhibition of Plasmodium falciparum growth in culture by concanamycin A, a macrolide antibiotic inhibitor of vacuolar H(+)-ATPase derived from Streptomyces sp, was equivocal.

Derivatives of amsacrine: determinants required for high activity against Lewis lung carcinoma.

Antitumor activity against the Lewis lung carcinoma in mice is reported for the series of 36 acridine-substituted derivatives of the antileukemia agent amsacrine. This series is the one from which the analogue N,5-dimethyl-9-[(2-methoxysulfonylamino)phenylamino]-4-acridinecarboxamide (CI-921), presently in clinical trial, was chosen. The analogues also were tested in vitro by comparing growth inhibition data [IC50 values (concentration required to reduce growth of cultured cells to 50% of that of untreated cultures)], using L1210 murine leukemia cells and HCT-8 human colon carcinoma cells. Determined IC50 values were highly dependent on the culture medium used, and it was found that the presence of ascorbate in the medium had a major effect on the stability of compounds to oxidation. A survey of 115 analogues of amsacrine indicates that a low ratio of IC50 values (HCT-8/L1210) is necessary but not sufficient for good antitumor activity against the solid tumor. DNA binding constants did not in themselves predict activity, although they were related to dose potency. Other factors, such as drug lipophilicity, acridine base strength, and drug solubility, also are involved, probably in providing effective drug distribution. It is concluded that in vitro assay data provide information useful for drug design but that other factors also are important for in vivo activity.