Experimental antitumor activity of taxotere (RP 56976, NSC 628503), a taxol analogue.

Taxotere (RP 56976; NSC 628503; N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl taxol) is a new microtubule stabilizing agent. It is obtained by semisynthesis from a noncytotoxic precursor extracted from the needles of the tree, Taxus baccata L. Taxotere was evaluated for antitumor activity against a variety of transplantable tumors of mice. Taxotere had no marked schedule dependency and was found active by the i.v. and the i.p. routes. Upon i.v. administration, 9 of 11 tumor models tested responded to Taxotere. B16 melanoma was found highly sensitive to Taxotere, with a tumor growth inhibition of 0% and a 3.0 log10 tumor cell kill at the maximum tolerated dose. In the same trial, taxol produced only a 1.1 log10 tumor cell kill at the maximum tolerated dose. Taxotere cured early stage pancreatic ductal adenocarcinoma 03 (6 of 6 cures) and colon adenocarcinoma 38 (7 of 7 cures). It also effected greater than 80% complete regressions of advanced stage disease with both tumors. Taxotere was active against early and advanced stage colon adenocarcinoma 51, with 2.3 and 1.7 log10 cell kill, respectively. Four other tumors responded to a lesser extent: Lewis lung (5.5% tumor growth inhibition), Glasgow osteogenic sarcoma (27.2% tumor growth inhibition), L1210 and P388 leukemias (70 and 54% increase in life span, respectively). Because of its good preclinical activity and its unique mechanism of action, Taxotere has entered Phase I clinical trials.

Molecular and cellular interactions between intoplicine, DNA, and topoisomerase II studied by surface-enhanced Raman scattering spectroscopy.

The surface-enhanced Raman scattering spectra of the new antitumoral agent, intoplicine (RP 60475, NSC 645008), and those of its complexes with DNA and topoisomerase II in vitro and in K562 cancer cells were obtained. Intoplicine was found to unwind DNA and to inhibit purified calf thymus topoisomerase II via a stabilization of the ternary cleavable complex. The intensity of the surface-enhanced Raman scattering spectrum of intoplicine was not modified by the addition of plasmid pBR322 or calf thymus DNA. In the complex of this antitumor agent with topoisomerase II, the signal of intoplicine was completely abolished, indicating that at least some portion of intoplicine binds to an internal part of the enzyme. During the formation of the ternary complex, intoplicine was released from the interior of the protein and formed hydrogen bonds via its hydroxyl and/or amino groups. Similar modifications of the intoplicine spectra were found by microsurface-enhanced Raman scattering spectroscopy of the compound in the nucleus of treated K562 cells. In contrast, intoplicine was found to be in a free form in the cytoplasm.

Experimental antitumor activity against murine tumor model systems of 8-carbamoyl-3-(2-chloroethyl)imidazo[5,1-d]-1,2,3,5-tetrazin-4(3 H)-one (mitozolomide), a novel broad-spectrum agent.

8-Carbamoyl-3-(2-chloroethyl)imidazo[5,1-d]-1,2,3,5-tetrazin-4(3H) -one (mitozolomide) demonstrates curative action against a range of murine tumor model systems. At single doses of between 20 and 40 mg/kg, the latter of which approximates the 10% lethal dose value in mice, the compound elicited cures against the L1210 and P388 leukemias irrespective of the route of tumor and/or drug administration; in these tests, animals receiving 10(5) cells i.p. survived greater than 60 days after treatment. Potent effects were also observed against the TLX5 lymphoma (s.c.) and B16 melanoma (i.p.). In other experiments, 7 of 10 animals implanted with 2 X 10(5) Lewis lung carcinoma cells survived greater than 60 days while 10 of 10 animals survived greater than 60 days after implantation of the Colon 26 tumor. Potent inhibition of the solid tumor models was also observed with complete cures of the Colon 38, M5076 sarcoma, and ADJ/PC6A plasmacytoma. In cross-resistance studies, the compound was ineffective against an L1210 leukemia made resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea and against a TLX5 lymphoma resistant to dimethyltriazenes but cured animals bearing the L1210 leukemia with derived resistance to cyclophosphamide.

Intoplicine (RP 60475) and its derivatives, a new class of antitumor agents inhibiting both topoisomerase I and II activities.

Intoplicine (RP 60475, NSC 645008) is an antitumor derivative in the 7H-benzo[e]pyrido[4,3-b]indole series which is now being tested in clinical trials. Intoplicine strongly binds DNA (KA = 2 x 10(5) M-1) and thereby increases the length of linear DNA. These properties are consistent with DNA unwinding by intoplicine. Intoplicine was found to be a dual topoisomerase I and II inhibitor, with DNA sites of enzyme inhibition being different for these two enzymes. In this study, 22 analogues of intoplicine were evaluated for their effects on topoisomerase I- and II-mediated DNA cleavage reactions by using enzymes purified from calf thymus. Site-specific DNA cleavage mediated by topoisomerase I was observed with 7H-benzo[e]pyrido[4,3-b]indole derivatives but not with 11H-benzo[g]-pyrido[4,3-b]indole derivatives. Site-specific DNA cleavage mediated by topoisomerase II occurred with derivatives having hydroxyl groups at the 3-position on the 7H-benzo[e]pyrido[4,3-b]indole ring or at the 4-position on the 11H-benzo[g]pyrido[4,3-b]indole ring. Study of the relationships between the in vivo antitumor activity on P388 leukemia and the topoisomerase I- and/or II-mediated DNA cleavage activity revealed that the most highly active antitumor compounds possessed both topoisomerase I-and II-inhibitory properties. Compounds selectively inhibiting either topoisomerase I or II were less active. These results suggest that dual topoisomerase I and II inhibition is critical for the antitumor activity of this new series of antitumor compounds.

Thyroid pathologies in transgenic mice expressing a human activated Ras gene driven by a thyroglobulin promoter.

Four transgenic mice carrying the human activated c-Ha-Ras gene, the expression of which was driven into the thyroid gland by a bovine thyroglobulin promoter, have been produced. The M1 and M2 mice developed papillary thyroid carcinomas and the M2 mouse also developed a lung carcinoma, however none of them transmitted the transgene. Both the M3 and the M4 mice gave rise to transgenic lines. M3 progeny mice develop a goitre with morphological aspects of hyperplasia as well as a thymus hyperplasia. M4 developed a papillary thyroid carcinoma and a lung carcinoma. Lung tumors but not thyroid tumors were observed in M4 adult transgenic progeny. In this M4 line, thyroid dysgenesis leading to growth retardation and premature death was observed upon serial backcross that enhanced the DBA/2J genetic background. The development of thyroid tumors in M1, M2, M4 transgenic mice demonstrates the oncogenic potential of activated Ras gene in the thyroid gland. The M4 line raises interesting questions relative to the interference between the Ras-mediated signal transduction pathway and thyroid morphogenesis.

Telomerase: a therapeutic target for the third millennium?

Telomerase offers the potential opportunity to control cell proliferation by interfering with a totally new and unique biological process which is cell senescence. The aim of this review is to impartially present the state of the art in telomerase with the pros and the cons of the current scientific situation of this fast-growing and fascinating topic for answering the key question asked by experimental and medical oncologists: Will telomerase be a therapeutic target for the third millenium? The most convincing argument (which is a scientifically documented one) for going ahead with this target is obviously the strong correlation existing between the level and frequency of telomerase expression and the malignant properties of tumors. This has been now largely documented in established tumor cell lines and fresh tumor samples obtained from patients. Noteworthy is the very important difference of telomerase expression between malignant and normal tissues. This difference is much higher than those observed for classical enzymatic targets of chemotherapy such as thymidylate synthetase, dihydrofolate reductase and topoisomerases. If this translates to the clinical situation, telomerase inhibitors might display a good selectivity for tumor cells with a minimal toxicity for normal tissues. The most appealing criticism (which is still purely speculative) is obviously the clinical relevance of inhibiting telomerase in cancer patients. According to the paradigm currently proposed for telomeres and telomerases, it can be predicted that telomerase inhibition will not affect a tumor until its telomeres reach the critical size for entering senescence. This means that during anti-telomerase therapy, the tumor cells will continue grow undergoing 20-30 divisions until the telomeres reach a critical size leading to tumor senescence. Does this make sense, especially in patients with advanced tumors at the beginning of the therapy? Ultimately, the definitive answer to the question will not come from intellectual speculation but from the properties of telomerase inhibitors, first in tumor bearing animals, then finally in cancer patients! Several institutions are very active in the development of telomerase inhibitors. Different stategies are used: direct inhibition of telomerase, interference with telomeres (G quartets), interaction with other proteins involved in the regulation of telomerase and telomeres.

Differential sensitivity to pertussis toxin of 3T3 cells transformed with different oncogenes.

Pertussis toxin (PT), which blocks the activity of several G-proteins, has been found to exert a marked inhibitory effect on the DNA synthesis induced in 3T3 cells by serum or growth factors. 3T3 cells transformed with human c-ras oncogenes (Ha-ras, Ki-ras, N-ras) or with src, an oncogene coding for a protein kinase, have lost sensitivity to growth control by PT, even though substrates for PT can still be ADP-ribosylated in vivo. In contrast, 3T3 cells transformed with the SV40 virus behave like normal untransformed cells with respect to the ability of PT to decrease their growth rate. Oncogenes can thus likely be classified either as 'responders' or 'non-responders' to PT.

Combination of the novel farnesyltransferase inhibitor RPR130401 and the geranylgeranyltransferase-1 inhibitor GGTI-298 disrupts MAP kinase activation and G(1)-S transition in Ki-Ras-overexpressing transformed adrenocortical cells.

To test the Kirsten-Ras (Ki-Ras) alternative prenylation hypothesis in malignant transformation, we used a novel farnesyltransferase inhibitor competitive to farnesyl-pyrophosphate, RPR130401, and a CaaX peptidomimetic geranylgeranyltransferase-1 inhibitor GGTI-298. In Ki-Ras-overexpressing transformed adrenocortical cells, RPR130401 at 1-10 microM inhibited very efficiently the [(3)H]farnesyl but not [(3)H]geranylgeranyl transfer to Ras. However, proliferation of these cells was only slightly sensitive to RPR130401 (IC(50)=30 microM). GGTI-298 inhibited the growth of these cells with an IC(50) of 11 microM but cell lysis was observed at 15 microM. The combination of 10 microM RPR130401 and 10 microM GGTI-298 inhibited efficiently (80%) cell proliferation. These combined inhibitors but not each inhibitor alone blocked the cell cycle in G(0)/G(1) and disrupted MAP kinase activation. Thus, combination of two inhibitors, at non-cytotoxic concentrations, acting on the farnesyl-pyrophosphate binding site of the farnesyltransferase and the CaaX binding site of the geranylgeranyltransferase-1 respectively is an efficient strategy for disrupting Ki-Ras tumorigenic cell proliferation.

Ultrastructure of HRP-identified sympathetic preganglionic neurons in cats.

Electron microscopic studies were conducted on cat sympathetic preganglionic neurons which were labeled using retrograde transport of horseradish peroxidase from the injection site in the stellate ganglion to somas in the thoracic spinal cord. Based on size, the identified somas were divided into two groups: large multipolar somas (25-35 micron), usually having three dendrites with a mean diameter of 8 micron, and small fusiform somas (12-24 micron), with two primary dendrites with a mean diameter of about 4 micron. The ultrastructures of the perikarya and dendrites were similar to other spinal neurons. Three types of terminals were identified: 1) round asymmetric terminals, 2) pleomorphic symmetric terminals, and 3) round symmetric terminals. On the soma, pleomorphic terminals were more numerous than round asymmetric terminals. On the dendrites, the density of round asymmetric terminals was similar to pleomorphic symmetric terminals. Round symmetric terminals represent only a small percent on either the soma or dendrites. Because of the greater total density of terminals on the dendrites than soma, pleomorphic symmetric and round asymmetric terminals are primarily located on the dendrites. Very few dense-core vesicles characteristic of monomamine terminals were observed, perhaps due to the fixative used.

Sympathetic neurons in the cat spinal cord projecting to the stellate ganglion.

Horseradish peroxidase (HRP) was injected into the stellate ganglia of anesthetized cats. After a 2-day survival time the spinal cord was processed for the HRP reaction to study the distribution of the preganglionic neurons which project to the stellate ganglia. HRP-labeled neurons in the cord were located exclusively on the side ipsilateral to the injected stellate ganglia and were concentrated in four distinct areas: (1) intermediolateral cell column (78.2%), (2) lateral funiculus (18.5%), (3) intercalated area and (4) central autonomic area (3.3%) for the latter 2 areas). Their distribution pattern in the very rostral pole of the thoracic sympathetic preganglionic cell column was different from the typical thoracic pattern in that a greater proportion of the cells were located in the lateral funiculus, and a few labeled cells were observed in the ventral horn. Longitudinally, a wide range (C8-T8) of spinal cord levels projected to the stellate ganglia, with a peak at the T2 level. These observations infer that a large population of axonal processes of sympathetic preganglionic neurons traveled several segments of the spinal cord through an intraspinal pathway before exiting a particular ventral root.

[Purification and study of two superoxide dismutases of the mushroom Pleurotus olearius]. / Purification et étude des deux superoxyde dismutases du champignon Pleurotus olearius

Two different superoxide dismutases have been purified from the luminous fungus Pleurotus olearius. The second enzyme SODm presents structural differences with the first enzyme SODc previously described [5]: it has a molecular weight of 78,000 and is composed of identical subunits (20,000); it contains also two functional Mn atoms. Using an antiserum prepared against SODc, we have shown that there is no cross-reaction between these two proteins. Spectral studies of the first enzyme SODc suggest that the active center contains trivalent manganese Mn-III.

Preclinical profile of docetaxel (taxotere): efficacy as a single agent and in combination.

Docetaxel (Taxotere; Rhône-Poulenc Rorer, Antony, France) is a new taxoid currently being studied in phase II and III clinical trials worldwide, with promising activity in breast cancer. Docetaxel was evaluated as a single agent against against seven mammary tumors, five from mice and two of human origin. Six of the seven models were found to be sensitive to docetaxel, exhibiting regressions of advanced-stage disease in murine models (MA16/C, MA13/C), and long tumor growth delays (Calc18) and cures (MX-1) in human tumor xenografts. In combination studies in tumor-bearing mice, synergism with docetaxel was observed with cyclophosphamide, 5-fluorouracil, etoposide, vinorelbine (Navelbine; Pierre Fabre Oncologie, Boulogne, France), and methotrexate. A similar level of efficacy was obtained in the cases of docetaxel/vincristine and docetaxel/mitomycin C, compared with the activity of the best single agent. Good activity was obtained with the docetaxel/doxorubicin, docetaxel/vinblastine, and docetaxel/cisplatin combinations; however, the activity of these combinations was lower than that of the best agent in the combination when tested in monotherapy. In terms of tolerance, 60% to 70% of the highest nontoxic dose of each agent could be administered in combination, except for vinca alkaloids, in which 80% to 100% of the maximum tolerated dose did not cause additional toxicity. Although docetaxel is a very potent agent when used in monotherapy, the above results suggest that it also will have a key role in clinical combination chemotherapy.

Preclinical evaluation of docetaxel (Taxotere).

Progress in cancer chemotherapy has been made owing to the discovery and development of drugs that have new structures, new mechanisms of action, and high levels of experimental antitumor activity. Docetaxel (Taxotere; Rhône-Poulenc Rorer, Antony, France) is prepared by semisynthesis from 10-deacetyl baccatin III, an inactive taxoid precursor extracted from the needles of the European yew Taxus baccata. Docetaxel has been found to promote tubulin assembly in microtubules and to inhibit their depolymerization. As predicted by its unique biochemical mechanism of action, docetaxel acts as a mitotic spindle poison and induces a mitotic block in proliferating cells. In vitro, the docetaxel concentrations required to reduce murine and human cell survival by 50% range from 4 to 35 ng/mL, and the cytotoxic effects are greater on proliferating cells than on nonproliferating cells. Docetaxel also is cytotoxic at clinically relevant concentrations against fresh human tumor biopsy specimens (breast, lung, ovarian, colorectal cancer, melanoma) in a soft agar cloning system. Docetaxel has significant in vivo antitumor activity in the different models generally used for the preclinical evaluation of drugs. Eleven of 12 murine transplantable tumors in syngeneic mice have been found to be sensitive to intravenous docetaxel with complete regressions of advanced-stage tumors. Activity also has been observed with human tumor xenografts in nude mice at an advanced stage. In combination studies, synergism has been observed in vivo with 5-fluorouracil, cyclophosphamide, etoposide, vinorelbine, and methotrexate. Preclinical toxicity in mice and dogs has been evaluated by using one and five daily intravenous doses, respectively. The dog was found to be the more sensitive species. The dose-limiting toxicities are hematologic and gastrointestinal in both species. Neurotoxicity also has been observed at high dosages in mice.

Preclinical evaluation of CPT-11 and its active metabolite SN-38.

CPT-11 (irinotecan) is a water-soluble analogue of camptothecin (CPT), an antitumor drug extracted from the Chinese tree Camptotheca acuminata. SN-38 is an active metabolite of CPT-11 that contributes significantly to its activity. The antitumor effects of CPT-11 and SN-38 are exerted through a novel mechanism of action; inhibition of DNA topoisomerase I. CPT-11 and its metabolite have demonstrated potent inhibitory activity against a variety of cancer cell lines in vitro and against several murine and human tumors grafted in mice in vivo, including those that express multidrug resistance. CPT-11 has also shown synergistic activity in combination with 5-fluorouracil and cisplatin in vitro. No irreversible or unusual toxicities were observed with CPT-11 in animal toxicity studies. In summary, the preclinical profile of CPT-11 confirmed this drug to be an attractive candidate for clinical development.

Domain-structured N1,N2-derivatized hydrazines as inhibitors of ribonucleoside diphosphate reductase: redox-cycling considerations.

Eight analogues of 1-[5-halogenosalicylidene]-2-[2'-pyridinoyl]hydrazine and -[2'-pyridyl]hydrazine, four of 1-[pyridoxylidene]-2-[2'-pyridinoyl]hydrazine, seven of 1-[pyridoxylidene]-2-[2'-pyridyl]hydrazine, and one each of 1, 2-bis[pyridoxylidene]diaminoethane and bis[pyridoxylidenehydrazino]phthalazine were synthesized. Their solutions in DMF were assayed for activity against the metalloenzyme ribonucleoside diphosphate reductase (RdR), prepared from a subcutaneously growing murine tumor (sarcoma 180) implanted in B6D2F3 male mice. The 14C-labeled CDP reductase was assayed by the modified method of Takeda and Weber, in which [14C]cytidine was separated from deoxycytidine by thin-layer chromatography (TLC) on cellulose foil. Distribution of radioactivity was assessed with an automatic TLC linear analyzer. Of the 31 compounds tested, 13 were essentially inactive, 7 were highly active against RdR, and the remaining 20 were slightly more active than hydroxyurea (used as a reference compound). The mechanism of inhibition is discussed in terms of three alternative pathways, initiated by sequestration of iron embedded in the R1 subunit of the metalloenzyme to form a C-centered chelate radical (via redox cycling). Alternatively, the latter could either reduce the tyrosyl radical or intercept radicals generated in the reduction process.

Relationships between the structure of taxol analogues and their antimitotic activity.

A variety of synthetic analogues of taxol, a naturally occurring antitumor diterpene, were examined for their potency to inhibit microtubule disassembly. For some of the compounds, the in vitro cytotoxic properties showed a good correlation with the tubulin assay. This structure-activity relationship study shows that inhibition of microtubule disassembly is quite sensitive to the configuration at C-2' and C-3'. A correlation between the conformation of the side chain at C-13 and the activity is suggested. Of all the compounds examined, one of the most potent in inhibiting microtubule disassembly and in inhibiting murine P388 leukemic cells, N-debenzoyl-N-tert-(butoxycarbonyl)-10-deacetyltaxol, named taxotere, was selected for evaluation as a potential anticancer agent.

Multivariate data analysis using D-optimal designs, partial least squares, and response surface modeling: A directional approach for the analysis of farnesyltransferase inhibitors.

We have investigated the combined use of partial least squares (PLS) and statistical design principles in principal property space (PP-space), derived from principal component analysis (PCA), to analyze farnesyltransferase inhibitors in order to identify "activity trends" (an approach we call a "directional" approach) and quantitative structure-activity relationships (QSAR) for a congeneric series of inhibitors: the benzo[f]perhydroisoindole (BPHI) series. Trends observed in the PCA showed that the descriptors used were relevant to describe our structural data set by clearly identifying two well-defined structural subclasses of inhibitors. D-Optimal design techniques allowed us to define a training set for PLS study in PP-space. Models were derived for each biological assay under evaluation: the in vitro Ki-Ras and cellular HCT116 tests. Each of these assay-based sets was subdivided once more into two subsets according to two structural classes in this BPHI series as revealed by the PCA model. The response surface modeling (RSM) methodology was used for each subset, and the corresponding RSM plots helped us identify "activity trends" exploited to guide further analogue design. For more precise activity predictions more refined PLS models on constrained PP-spaces were developed for each subset. This approach was validated with predicted sets and demonstrates that useful information can be extracted from just a few very informative and representative compounds. Finally, we also showed the potential use of such a strategy at an early stage of an optimization process to extract the first "activity trends" that might support decision making and guide medicinal chemists in the initial design of new analogues and/or lead followup libraries.

Synthesis and antitumor activity of 1-[[(dialkylamino)alkyl]amino]-4-methyl-5H-pyrido[4,3-b]benzo[e]- and -benzo[g])indoles. A new class of antineoplastic agents.

The thermal Fischer indolization of hydrazones resulting from 4-hydrazino-5-methyl-1H-pyridin-2-one and various beta- and alpha-tetralones led to 4-methyl-6,7-dihydro-2H,5H-pyrido[4,3- b]benzo[e]indol-1-ones and 4-methyl-11-dihydro-2H,5H-pyrido[4,3- b]benzo[g]indol-1-ones, respectively. After aromatization, these compounds were transformed by phosphorus oxychloride, giving 1-chloro-4-methyl-5H-pyrido[4,3- b]benzo[e]- and -benzo[g]indoles which were substituted by [(dialkylamino)alkyl]amines. The resulting 1-[[(dialkylamino)alkyl]amino]-4-methyl-5H-pyrido- [4,3-b]benzo[e]- and -benzo[g]indoles, as well as hydroxy derivatives obtained by demethylation of methoxylated compounds with hydrobromic acid, were tested for antitumor activity in vitro (leukemic and solid tumor cells) and in vivo on various experimental tumor models using the standard NCI protocols. 1-[[3-(Dialkylamino)propyl]-amino]-4-methyl-9-hydroxy-5H-pyrido[4,3- b]benzo[e]indoles appeared as a promising new class of antineoplastic agents.

Heterocyclic quinones. 17. A new in vivo active antineoplastic drug: 6,7-bis(1-aziridinyl)-4-[[3-(N,N-dimethylamino)propyl]amino]-5,8- quinazolinedione.

A series of heterocyclic quinones, 6-substituted and 6,7-disubstituted 4-(alkylamino)-5,8-quinazolinediones, have been synthesized in order to evaluate their in vitro cytotoxicity on L1210 leukemia cells. Among 14 derivatives that have been prepared and studied for the structure-activity relationship, the most potent cytotoxic compound on L1210 leukemia cells was the 6,7-bis(1-aziridinyl)-4-[[3-(N,N-dimethylamino)propyl]amino]-5,8- quinazolinedione (24). This compound has been tested with the use of a cell-image processor on MCF-7 human mammary and HBL human melanoma cell lines. The results show that compound 24 influences cell proliferation and blocks both cells lines in the S phase. In vivo antineoplastic activity of compound 24 has been demonstrated on a broad spectrum of murine experimental models, but it was found highly toxic and produced long-delayed deaths.

Synthesis and structure-activity relationships of new antitumor taxoids. Effects of cyclohexyl substitution at the C-3' and/or C-2 of taxotere (docetaxel).

Synthesis and cytotoxicity of the new analogs (11-13) of docetaxel possessing cyclohexyl groups instead of phenyl groups at the C-3' and/or C-2 benzoate positions are described. The C-2 cyclohexanecarboxylate analog of paclitaxel (15) is also synthesized for comparison. The potency of these new taxoids were examined for their inhibitory activity for microtubule disassembly and also for their cytotoxicity against murine P388 leukemia cell line as well as doxorubicin-resistant P388 leukemia cell line (P388/Dox). It is found that 3'-dephenyl-3'-cyclohexyldocetaxel (11) (0.72T) and 2-(hexahydro)docetaxel (12) (0.85T) possess strong inhibitory activity for microtubule disassembly equivalent to docetaxel (0.7T), which is more potent than paclitaxel (1.0T). The results clearly indicate that phenyl or an aromatic group at C-3' or C-2 is not a requisite for strong binding to the microtubules. This finding has opened an avenue for development of new nonaromatic analogs of docetaxel and paclitaxel. 3'-Dephenyl-3'-cyclohexyl-2-(hexahydro)docetaxel (13) (2T) turns out to be a substantially weaker inhibitor. The cytotoxicities of 11-13 against P388 are, however, in the same range that is 8-12 times weaker than docetaxel and 4-6 times weaker than paclitaxel, i.e., 13 shows equivalent cytotoxicity to that of 11 or 12 in spite of much lower microtubule disassembly inhibitory activity. The cytotoxicities of these new taxoids against the P388/Dox cell line are only 2-2.5 times lower than that of docetaxel. The potency of 2-(hexahydro)paclitaxel (15) for these assays is much lower than the docetaxel counterpart 12. The significant loss of activity in vivo against B16 melanoma is observed for 11-13, i.e., 11 is only marginal (T/C = 38% at 20 mg/kg/day), and 12 and 13 are inactive (T/C = 76% and 79%, respectively). This could be ascribed to faster metabolism, faster excretion or other bioavailability problems.