The resurgence of platinum-based cancer chemotherapy.

The accidental discovery of the anticancer properties of cisplatin and its clinical introduction in the 1970s represent a major landmark in the history of successful anticancer drugs. Although carboplatin--a second-generation analogue that is safer but shows a similar spectrum of activity to cisplatin--was introduced in the 1980s, the pace of further improvements slowed for many years. However, in the past several years interest in platinum drugs has increased. Key developments include the elucidation of mechanisms of tumour resistance to these drugs, the introduction of new platinum-based agents (oxaliplatin, satraplatin and picoplatin), and clinical combination studies using platinum drugs with resistance modulators or new molecularly targeted drugs.

Design, synthesis and biological evaluation of 6-pyridylmethylaminopurines as CDK inhibitors.

The cyclin-dependent kinase (CDK) inhibitor seliciclib (1, CYC202) is in phase II clinical development for the treatment of cancer. Here we describe the synthesis of novel purines with greater solubility, lower metabolic clearance, and enhanced potency versus CDKs. These compounds exhibit novel selectivity profiles versus CDK isoforms. Compound αSßR-21 inhibits CDK2/cyclin E with IC(50)=30 nM, CDK7-cyclin H with IC(50)=1.3 µM, and CDK9-cyclinT with IC(50)=0.11 µM; it (CCT68127) inhibits growth of HCT116 colon cancer cells in vitro with GI(50)=0.7 µM; and shows antitumour activity when dosed p.o. at 50mg/kg to mice bearing HCT116 solid human tumour xenografts.

Characterization of the biological effects of a novel protein kinase D inhibitor in endothelial cells.

VEGF (vascular endothelial growth factor) plays an essential role in angiogenesis during development and in disease largely mediated by signalling events initiated by binding of VEGF to its receptor, VEGFR2 (VEGF receptor 2)/KDR (kinase insert domain receptor). Recent studies indicate that VEGF activates PKD (protein kinase D) in endothelial cells to regulate a variety of cellular functions, including signalling events, proliferation, migration and angiogenesis. To better understand the role of PKD in VEGF-mediated endothelial function, we characterized the effects of a novel pyrazine benzamide PKD inhibitor CRT5 in HUVECs (human umbilical vein endothelial cells). The activity of the isoforms PKD1 and PKD2 were blocked by this inhibitor as indicated by reduced phosphorylation, at Ser916 and Ser876 respectively, after VEGF stimulation. The VEGF-induced phosphorylation of three PKD substrates, histone deacetylase 5, CREB (cAMP-response-element-binding protein) and HSP27 (heat-shock protein 27) at Ser82, was also inhibited by CRT5. In contrast, CRT6, an inactive analogue of CRT5, had no effect on PKD or HSP27 Ser82 phosphorylation. Furthermore, phosphorylation of HSP27 at Ser78, which occurs solely via the p38 MAPK (mitogen-activated protein kinase) pathway, was also unaffected by CRT5. In vitro kinase assays show that CRT5 did not significantly inhibit several PKC isoforms expressed in endothelial cells. CRT5 also decreased VEGF-induced endothelial migration, proliferation and tubulogenesis, similar to effects seen when the cells were transfected with PKD siRNA (small interfering RNA). CRT5, a novel specific PKD inhibitor, will greatly facilitate the study of the role of PKD signalling mechanisms in angiogenesis.

Pharmacologic characterization of a potent inhibitor of class I phosphatidylinositide 3-kinases.

Extensive evidence implicates activation of the lipid phosphatidylinositide 3-kinase (PI3K) pathway in the genesis and progression of various human cancers. PI3K inhibitors thus have considerable potential as molecular cancer therapeutics. Here, we detail the pharmacologic properties of a prototype of a new series of inhibitors of class I PI3K. PI103 is a potent inhibitor with low IC50 values against recombinant PI3K isoforms p110alpha (2 nmol/L), p110beta (3 nmol/L), p110delta (3 nmol/L), and p110gamma (15 nmol/L). PI103 also inhibited TORC1 by 83.9% at 0.5 micromol/L and exhibited an IC50 of 14 nmol/L against DNA-PK. A high degree of selectivity for the PI3K family was shown by the lack of activity of PI103 in a panel of 70 protein kinases. PI103 potently inhibited proliferation and invasion of a wide variety of human cancer cells in vitro and showed biomarker modulation consistent with inhibition of PI3K signaling. PI103 was extensively metabolized, but distributed rapidly to tissues and tumors. This resulted in tumor growth delay in eight different human cancer xenograft models with various PI3K pathway abnormalities. Decreased phosphorylation of AKT was observed in U87MG gliomas, consistent with drug levels achieved. We also showed inhibition of invasion in orthotopic breast and ovarian cancer xenograft models and obtained evidence that PI103 has antiangiogenic potential. Despite its rapid in vivo metabolism, PI103 is a valuable tool compound for exploring the biological function of class I PI3K and importantly represents a lead for further optimization of this novel class of targeted molecular cancer therapeutic.

Amide-based prodrugs of spermidine-bridged dinuclear platinum. Synthesis, DNA binding, and biological activity.

The chemistry and biology of acetyl-protected spermidine-bridged dinuclear platinum complexes [{ trans-PtCl(NH 3) 2] 2-mu-NH 2(CH 2) 3N(COR)(CH 2) 4NH 2]X 2 (R = H, X = Cl (1,1/t,t-spermidine, BBR3571); R = CH 3 , X = Cl ( 2); R = CH 2 Cl, X = ClO 4 ( 3); R = CF 3 , X = Cl ( 4)) are compared with their carbamate analogues. The compounds are potential prodrugs for the parent compound 1, a highly potent antitumor agent. At pH 6-8 hydrolysis of the blocking group with the release of the "parent" protonated species follows the order 4 > 3 >> 2. For 4, rate constants for the deprotection increase in this pH range. The DNA binding profile of 4 is similar to the Boc derivative, confirming the central influence of charge on DNA binding properties. The differences in cytotoxicity for the protected compounds in ovarian carcinoma cell lines sensitive and resistant to cisplatin cannot completely be explained by spontaneous release of 1,1/t,t-spermidine at physiological pH. Inherent cytotoxicity and cell line specificity may contribute to the observed behavior. The properties of the compounds present them also as possible "second-generation" analogues of the clinically relevant trinuclear complex [{ trans-PtCl(NH 3) 2} 2-mu- trans-Pt(NH 3) 2(NH 2(CH 2) 6NH 2) 2](NO 3) 4, ( 8, BBR3464).

Targeting the limitless replicative potential of cancer: the telomerase/telomere pathway.

The maintenance of telomeric DNA underlies the ability of tumors to possess unlimited replicative potential, one of the hallmarks of cancer. Telomere length and structure are maintained by the reverse transcriptase telomerase and a multiprotein telomere complex termed shelterin. Telomerase activity is elevated in the vast majority of tumors, and telomeres are critically shortened in tumors versus normal tissues, thus providing a compelling rationale to target the telomerase/telomere pathway for broad-spectrum cancer therapy. This strategy is supported by a variety of genetic-based target validation studies. Both telomerase inhibitors and telomere interactive molecules have shown stand-alone antitumor activity at nontoxic doses against a variety of human tumor xenografts in mice. These translational advances have resulted in the first antitelomerase agent, the oligonucleotide-based GRN163L targeting the telomerase RNA template, entering clinical evaluation. Additional translational approaches, such as targeting telomeres using G-quadruplex ligands, should result in antitelomere agents, such as RHPS4, entering the clinic in the near future. These prototype trials will be extremely informative in determining the role of the telomerase/telomere pathway in clinical oncology and, moreover, whether drugs targeting the unlimited replicative potential of cancer will find a place in cancer chemotherapy.

Accumulation, platinum-DNA adduct formation and cytotoxicity of cisplatin, oxaliplatin and satraplatin in sensitive and resistant human osteosarcoma cell lines, characterized by p53 wild-type status.

P53 gene status is implicated in the cytotoxic drug sensitivity and published research has been mostly addressed to cisplatin (CDDP) activity. Previous study in our laboratory considered p53 mutant cell lines A431 (parental) and A431/Pt (CDDP-resistant counterpart, resistance factor R.F.=2.6). For a comparison which contributes to a deeper appreciation of the process that mediates the Pt drug cellular effects, we extended our investigation to the p53 wild-type cell lines U2-OS (human osteosarcoma) and its CDDP-resistant counterpart U2-OS/Pt (R.F.=5). We compared the activity of CDDP, oxaliplatin (L-OHP) and satraplatin (JM216) whose hydrophobicity rank is JM216>L-OHP>CDDP. In U2-OS cells the three drugs accumulated similarly, while in U2-OS/Pt the most hydrophobic drugs were privileged. No significant differences in efflux were observed between sensitive and resistant cell lines. The growing of CDDP resistance seems to be overcome by increasing the hydrophobicity of the Pt agent. An almost linear trend seems to relate R.F. and drug hydrophobicity in U2-OS/Pt and A431/Pt cells. DNA platination in U2-OS as in A431 cells is at the lowest levels for L-OHP. In U2-OS cell line the IC(50) of CDDP (17.6 microM) and JM216 (88.02 microM) do not correlate with their similar levels of Pt-DNA adducts (mean value approximately 0.14 pmol Pt/microg DNA). The presence of a wild-type p53 exalts either CDDP cytotoxicity (two-fold more active in U2-OS than in A431 cells) and CDDP resistance in comparison to a p53 mutant type. The p53 status seems to not improve JM216 or L-OHP cytotoxicity in both cell lines.

Drug evaluation: ADH-1, an N-cadherin antagonist targeting cancer vascularization.

Adherex Technologies Inc, under license from McGill University, is developing ADH-1, an intravenous N-cadherin antagonist that specifically disrupts the disorganized interactions between N-cadherin molecules in tumor blood vessels, as a potential anticancer compound. By May 2005, ADH-1 was in phase Ib/II clinical trials in Europe and the US, and phase II clinical trials in Canada.

Discovery and development of anticancer aptamers.

Aptamers, also termed as decoys or "chemical antibodies," represent an emerging class of therapeutics. They are short DNA or RNA oligonucleotides or peptides that assume a specific and stable three-dimensional shape in vivo, thereby providing specific tight binding to protein targets. In some cases and as opposed to antisense oligonucleotides, effects can be mediated against extracellular targets, thereby preventing a need for intracellular transportation. The first aptamer approved for use in man is a RNA-based molecule (Macugen, pegaptanib) that is administered locally (intravitreally) to treat age-related macular degeneration by targeting vascular endothelial growth factor. The most advanced aptamer in the cancer setting is AS1411, formerly known as AGRO100, which is being administered systemically in clinical trials. AS1411 is a 26-mer unmodified guanosine-rich oligonucleotide, which induces growth inhibition in vitro, and has shown activity against human tumor xenografts in vivo. The mechanism underlying its antiproliferative effects in cancer cells seems to involve initial binding to cell surface nucleolin and internalization, leading to an inhibition of DNA replication. In contrast to other unmodified oligonucleotides, AS1411 is relatively stable in serum-containing medium, probably as a result of the formation of dimers and a quartet structure. In a dose escalation phase I study in patients with advanced solid tumors, doses up to 10 mg/kg/d (using a four or seven continuous infusion regime) have been studied. Promising signs of activity have been reported (multiple cases of stable disease and one near complete response in a patient with renal cancer) in the absence of any significant adverse effects. Further trials are ongoing in renal and non-small cell lung cancers. In preclinical studies, additional aptamers have been described against several cancer targets, such as tenascin-C, the transcription factor signal transducer and activator of transcription 3, and antiapoptotic and Ku proteins.

Synthesis and antimelanoma activity of reversed amide analogues of N-acetyl-4-S-cysteaminylphenol.

The melanin biosynthetic pathway from tyrosine is a potential target for combating malignant melanoma. N-Acetyl-4-S-cysteaminylphenol 1 is a previously synthesized analogue of tyrosine that probably acts by this pathway. It interferes with cell growth and proliferation via selective oxidation in melanocytes to an oquinone that can alkylate cellular nucleophiles. We previously synthesized a range of analogues of the original lead compound 1 most of which displayed greater cytotoxicity than 1. Eighteen new analogues with the amide group reversed have now been synthesized and tested for antimelanoma activity. Most of these reverse amides showed greater cytotoxicity than N-acetyl-4-S-cysteaminylphenol towards five representative melanoma cell lines. The highest cytotoxicity was observed for the piperidine and hexamethyleneimine derivatives 7, 8, 12, 13, and 17 and the catechol 18. The most active compound, 7, had cytotoxicity comparable to cisplatin against the five melanoma cell lines. The moderate activity of 7 and 18 against SK-Mel-24 (non-tyrosinase containing) and an ovarian cell line suggests that interference with the melanin pathway may not be the only mode of action of these compounds. Assays of some of the compounds as substrates for tyrosinase showed that the catechol 18 was the best substrate and that the piperidine derivative 7 was the best substrate of the phenolic compounds synthesized.

Pharmacokinetic-pharmacodynamic relationships for the heat shock protein 90 molecular chaperone inhibitor 17-allylamino, 17-demethoxygeldanamycin in human ovarian cancer xenograft models.

PURPOSE: To establish the pharmacokinetic and pharmacodynamic profile of the heat shock protein 90 (HSP90) inhibitor 17-allylamino, 17-demethoxygeldanamycin (17-AAG) in ovarian cancer xenograft models. EXPERIMENTAL DESIGN: The effects of 17-AAG on growth inhibition and the expression of pharmacodynamic biomarkers c-RAF-1, CDK4, and HSP70 were studied in human ovarian cancer cell lines A2780 and CH1. Corresponding experiments were conducted with established tumor xenografts. The variability and specificity of pharmacodynamic markers in human peripheral blood lymphocytes (PBL) were studied. RESULTS: The IC50 values of 17-AAG in A2780 and CH1 cells were 18.3 nmol/L (SD, 2.3) and 410.1 nmol/L (SD, 9.4), respectively. Pharmacodynamic changes indicative of HSP90 inhibition were demonstrable at greater than or equal the IC50 concentration in both cell lines. Xenograft experiments confirmed tumor growth inhibition in vivo. Peak concentrations of 17-AAG achieved in A2780 and CH1 tumors were 15.6 and 16.5 micromol/L, respectively, and there was no significant difference between day 1 and 11 pharmacokinetic profiles. Reversible changes in pharmacodynamic biomarkers were shown in tumor and murine PBLs in both xenograft models. Expression of pharmacodynamic markers varied between human PBLs from different human volunteers but not within the same individual. Pharmacodynamic biomarker changes consistent with HSP90 inhibition were shown in human PBLs exposed ex vivo to 17-AAG but not to selected cytotoxic drugs. CONCLUSION: Pharmacokinetic-pharmacodynamic relationships were established for 17-AAG. This information formed the basis of a pharmacokinetic-pharmacodynamic-driven phase I trial.

Tumor dose response to the vascular disrupting agent, 5,6-dimethylxanthenone-4-acetic acid, using in vivo magnetic resonance spectroscopy.

PURPOSE: To use (31)P and (1)H magnetic resonance spectroscopy (MRS) to assess changes in tumor metabolic profile in vivo in response to 5,6-dimethylxanthenone-4-acetic acid (DMXAA) with a view to identifying biomarkers associated with tumor dose response. EXPERIMENTAL DESIGN: In vivo (31)P and (1)H MRS measurements of (a) tumor bioenergetics [beta-nucleoside triphosphate/inorganic phosphate (beta-NTP/Pi)], (b) the membrane-associated phosphodiesters and phosphomonoesters (PDE/PME), (c) choline (mmol/L), and (d) lactate/water ratio were made on murine HT29 colon carcinoma xenografts pretreatment and 6 or 24 hours posttreatment with increasing doses of DMXAA. Following in vivo MRS, the tumors were excised and used for high-resolution (31)P and (1)H MRS of extracts to provide validation of the in vivo MRS data, histologic analysis of necrosis, and high-performance liquid chromatography. RESULTS: Both beta-NTP/Pi and PDE/PME decreased in a dose-dependent manner 6 hours posttreatment with DMXAA, with significant decreases in beta-NTP/Pi with 15 mg/kg (P < 0.001) and 21 mg/kg (P < 0.01). A significant decrease in total choline in vivo was found 24 hours posttreatment with 21 mg/kg DMXAA (P < 0.05); this was associated with a significant reduction in the concentration of the membrane degradation products glycerophosphoethanolamine and glycerophosphocholine measured in tissue extracts (P < 0.05). CONCLUSIONS: The reduction in tumor energetics and membrane turnover is consistent with the vascular-disrupting activity of DMXAA. (31)P MRS revealed tumor response to DMXAA at doses below the maximum tolerated dose for mice. Both (31)P and (1)H MRS provide biomarkers of tumor response to DMXAA that could be used in clinical trials.

In vitro and in vivo pharmacokinetic-pharmacodynamic relationships for the trisubstituted aminopurine cyclin-dependent kinase inhibitors olomoucine, bohemine and CYC202.

PURPOSE: To investigate pharmacokinetic-pharmacodynamic relationships for the trisubstituted aminopurine cyclin-dependent kinase inhibitors olomoucine, bohemine, and CYC202 (R-roscovitine; seliciclib) in the HCT116 human colon carcinoma model. EXPERIMENTAL DESIGN: The in vitro activity of the agents was determined in a human tumor panel using the sulforhodamine B assay. The concentration and time dependence was established in HCT116 cells. Molecular biomarkers, including RB phosphorylation and cyclin expression, were assessed by Western blotting. Pharmacokinetic properties were characterized in mice following analysis by liquid chromatography-tandem mass spectrometry. Based on these studies, a dosing regimen was developed for CYC202 that allowed therapeutic exposures in the HCT116 tumor xenograft. RESULTS: The antitumor potency of the agents in vitro was in the order olomoucine (IC50, 56 micromol/L) < bohemine (IC50, 27 micromol/L) < CYC202 (IC50, 15 micromol/L), corresponding to their activities as cyclin-dependent kinase inhibitors. Antitumor activity increased with exposure time up to 16 hours. The agents caused inhibition of RB and RNA polymerase II phosphorylation and depletion of cyclins. They exhibited relatively rapid clearance following administration to mice. CYC202 displayed the slowest clearance from plasma and the highest tumor uptake, with oral bioavailability of 86%. Oral dosing of CYC202 gave active concentrations in the tumor, modulation of pharmacodynamic markers, and inhibition of tumor growth. CONCLUSIONS: CYC202 showed therapeutic activity on human cancer cell lines in vitro and on xenografts. Pharmacodynamic markers are altered in vitro and in vivo, consistent with the inhibition of cyclin-dependent kinases. Such markers may be potentially useful in the clinical development of CYC202 and other cyclin-dependent kinase inhibitors.

SJG-136 (NSC 694501), a novel rationally designed DNA minor groove interstrand cross-linking agent with potent and broad spectrum antitumor activity: part 1: cellular pharmacology, in vitro and initial in vivo antitumor activity.

SJG-136 (NSC 694501) is a rationally designed pyrrolobenzodiazepine dimer that binds in the minor groove of DNA. It spans 6 bp with a preference for binding to purine-GATC-pyrimidine sequences. The agent has potent activity in the National Cancer Institute (NCI) anticancer drug screen with 50% net growth inhibition conferred by 0.14 to 320 nmol/L (7.4 nmol/L mean). Sensitive cell lines exhibit total growth inhibition and 50% lethality after treatment with as little as 0.83 and 7.1 nmol/L SJG-136, respectively. COMPARE and molecular target analysis of SJG-136 data versus that of >60,000 compounds tested in the NCI 60 cell line screen shows that, although the agent has similarity to other DNA binding agents, the pattern of activity for SJG-136 does not fit within the clusters of any known agents, suggesting that SJG-136 possesses a distinct mechanism of action. Testing in the NCI standard hollow fiber assay produced prominent growth inhibition in 20 of 24 i.p. and 7 of 24 s.c. test combinations with 5 of 12 cell lines exhibiting cell kill. In addition, SJG-136 produced antitumor activity in mice bearing CH1 and CH1cisR xenografts, a cisplatin-resistant human ovarian tumor model, and also in mice bearing LS174T xenografts, a human colon tumor model. SJG-136 produces DNA interstrand cross-links between two N-2 guanine positions on opposite strands and separated by 2 bp. In human tumor cell lines, the cross-links form rapidly and persist compared with those produced by conventional cross-linking agents such as nitrogen mustards. In mice bearing the LS174T human colon xenograft, DNA interstrand cross-links can be detected in tumor cells using a modification of the single cell gel electrophoresis (comet) assay after administration of a therapeutic dose. Cross-links in the tumor increase with dose and are clearly detectable at 1 hour after i.v. administration. The level of cross-linking persists over a 24-hour period in this tumor in contrast to cross-links produced by conventional cross-linking agents observed over the same time period.

Phase II study of the efficacy and tolerability of two dosing regimens of the farnesyl transferase inhibitor, R115777, in advanced breast cancer.

PURPOSE: R115777 is an orally active farnesyl transferase inhibitor that specifically blocks farnesylation of proteins involved in growth-factor-dependent cell-signal-transduction pathways. We conducted a phase II study in 76 patients with advanced breast cancer. PATIENTS AND METHODS: Two cohorts of patients were recruited sequentially. The first cohort (n = 41) received a continuous dosing [CD] regimen of R115777 400 or 300 mg bid. The second cohort (n = 35) received 300 mg bid in a cyclical regimen of 21 days of treatment followed by 7 days of rest (intermittent dosing [ID]). RESULTS: In the CD cohort, four patients (10%) had a partial response (PR) and six patients (15%) had stable disease at > or = 24 weeks (SD). In the ID cohort, five patients (14%) had a PR and three patients (9%) had prolonged SD. The first six patients in the CD cohort treated at 400 mg bid all developed grade 3 to 4 neutropenia, so the subsequent 35 patients were treated at 300 mg bid. The incidence of hematologic toxicity was significantly lower in the ID than in the CD (300-mg bid) cohort: grade 3 to 4 neutropenia (14% v 43%; P =.016) and grade 3 to 4 thrombocytopenia (3% v 26%; P =.013). One patient in the ID cohort developed grade 2 to 3 neurotoxicity compared with 15 patients in the CD cohort (3% v 37%; P =.0004). CONCLUSION: The farnesyl transferase inhibitor R115777 has demonstrated clinical activity in patients with metastatic breast cancer, and the ID regimen has a significantly improved therapeutic index compared with the CD regimen.

Overcoming the immortality of tumour cells by telomere and telomerase based cancer therapeutics--current status and future prospects.

A key property of malignant tumours is their immortality or limitless replicative potential. Cell replication is associated with the maintenance of telomeres and in the great majority of cases, through the reactivation of the reverse transcriptase telomerase. Targeting the telomere/telomerase machinery offers a novel and potentially broad-spectrum anticancer therapeutic strategy since telomerase is constitutively overexpressed in the vast majority of human cancers. Telomeres are also critically short in most tumours compared to normal tissues. Strategies that exploit these differences include the direct targeting of components of telomerase: the protein component hTERT or RNA component hTR. Examples of such agents include the small molecule hTERT inhibitor BIBR1532 and GRN163L, a thio-phosphoramidate oligonucleotide targeting the template region of hTR as a "template antagonist". Anti-tumour effects have been observed in both cell lines and, especially for GRN163L, in xenografted human tumours in mice. Effects, however, are largely dependent upon initial telomere length, which can result in a substantial lag before antitumour activity is observed in tumours possessing relatively long telomeres. An alternative approach is to target the telomere itself (Telomere Targeting Agents, TTAs). Several classes of small molecules have been described that induce the G-rich single-stranded overhang of telomeric DNA to fold into 4-stranded G-quadruplex structures. Such folding is incompatible with telomerase function and may induce rapid telomere uncapping. These molecules have shown potent telomerase inhibition in nanomolar concentrations in vitro and the rapid induction of senescence in cancer cells. The trisubstituted acridine based TTA, BRACO19, has demonstrated single agent activity against human tumour xenografts with anti-tumour effects apparent from only 7 days of treatment. In the near future, it is expected that lead examples from both the direct telomerase targeted agents (e.g., GRN163L) and from the distinct class of those targeting telomeres (e.g., AS1410 based on BRACO19) will enter Phase I clinical trial where clinical benefit from this class of novel drugs will be determined.

Enhancement of aqueous solubility and stability employing a trans acetate axis in trans planar amine platinum compounds while maintaining the biological profile.

A general approach to solubilization and possible in vivo activation of the transplatinum geometry is presented. The synthesis and characterization of new water-soluble cytotoxic transplatinum compounds are described. Use of acetate ligands (and carboxylate ligands in general) in trans-[Pt(OAc)(2)(L)(L')] results in significantly enhanced aqueous solubility and chemical stability in comparison to the parent dichlorides. The new compounds are the first cytotoxic transplatinum compounds containing an N(2)O(2) donor set, similar to carboplatin and oxaliplatin.

Emerging drugs for ovarian cancer.

Because most patients presenting with advanced ovarian cancer are not curable by surgery alone, chemotherapy represents an essential component of treatment. The disease may be considered as chemosensitive, as in around three-quarters of patients major (complete) responses are seen to initial treatment with the platinum-containing drugs cisplatin and carboplatin either used alone or in combination with the taxane, paclitaxel. However, only 15-20% of patients experience long-term remission as tumours often become resistant. The probability of achieving a second response depends on the duration of remission after first-line therapy: if this is < 6 months (considered as platinum resistant) second responses are uncommon and usually short-lived; if this is > 6, and especially if > 12 months (platinum sensitive), responses may be seen in about a quarter of patients, to the same drugs as used first line or to drugs such as pegylated liposomal doxorubicin, topotecan and hexamethylmelamine (all three are approved in this setting by the FDA). Gemcitabine, oral etoposide, docetaxel and oxaliplatin also show some activity either in sequential addition to existing approved of first-line therapy (as with gemcitabine) or as second-line therapy. However, there is an urgent unmet clinical need for new drugs capable of prolonging survival either by increasing long-term remission rates and/or duration as first-line treatment or to improve on outcomes of second-line treatment. Strategies currently being exploited in clinical trials include attempts to deliver more killing selectively to tumours (e.g., intraperitoneal administration of cisplatin or radiolabelled monoclonal antibodies), agents designed to target drug resistance mechanisms (e.g., TLK-286 activated by glutathione transferase), agents targeting proteins/receptors shown to be selectively expressed in the disease (e.g., monoclonal antibodies recognising CA-125 or HER1; small molecules targeting HER1 such as gefitinib) and disrupting established tumour vasculature (e.g., 5,6-dimethyl xanthenone 4-acetic acid). At the pre-clinical level, agents being developed to target the phosphatidylinositol 3 kinase/AKT/mTOR pathway, and K-Ras inhibitors, may offer efficacy in the future.

Synthesis and antimelanoma activity of sterically congested tertiary amide analogues of N-acetyl-4-S-cysteaminylphenol.

Interference with the biosynthetic pathway to melanin may be a useful means for developing new chemotherapeutic drugs to combat malignant melanoma. N-Acetyl-4-S-cysteaminylphenol (1) is an analogue of tyrosine that is involved in the pathway to melanin. It is probably oxidized selectively in melanocytes to an o-quinone that can alkylate thiol groups on important cellular enzymes, resulting in interference with cell growth and proliferation. We previously synthesized a range of more lipophilic analogues of 1 by independently varying the acyl portion and introducing substitution alpha to the nitrogen. Most of the new compounds displayed greater cytotoxicity than the original lead compound 1. We also made a series of tertiary amides that again showed higher cytotoxicity than 1. In this work three new acetamides and two new cyclohexanecarboxamides containing 4-S-cysteaminylphenol were prepared incorporating both substitution alpha to the nitrogen and different substituents on the nitrogen of the amide in each compound to increase lipophilicity and to reduce further the possibility of hydrolysis of the amides. Most of the new tertiary amides showed greater cytotoxicity towards five representative melanoma cell lines than the parent secondary amide. The highest cytotoxicity against these five cell lines with IC50 values of 1-15 nicroM, comparable to cisplatin, was observed for N-[2[(4-hydroxyphenyl)thio]-1,1-dimethylethyl]-N-methylcyclohexanecarboxamide (8c). The IC50 values of 14.5 and 5.4 microM for this compound against SK-Mel-24 (not containing tyrosinase) and an ovarian cell line, respectively, suggest that interference with the melanin pathway may not be the only mode of action of this new compound. The cyclohexanecarboxamides were better substrates for mushroom tyrosinase (EC 1.14.18.1) than the acetamides.

Establishment and characterization of acquired resistance to the farnesyl protein transferase inhibitor R115777 in a human colon cancer cell line.

R115777 (Zarnestra) is a farnesyl protein transferase inhibitor currently undergoing worldwide clinical trials. As acquired drug resistance may limit the efficacy of the drug, a model of acquired resistance has been established in vitro by continuous drug exposure of the human colon cancer cell line KM12. A stably resistant cell line possessing 13-fold resistance to R115777 was generated. The resistant cells showed cross-resistance to another, structurally different farnesyl transferase inhibitor-277, but not to GGTI-298. A lack of cross-resistance was observed to a variety of other agents, which included clinically used drugs, such as doxorubicin, etoposide, cisplatin, and paclitaxel, as well as signal transduction blockers, such as the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor UO126, the phosphatidylinositol 3'-kinase inhibitor LY294002, and the epidermal growth factor receptor tyrosine kinase inhibitor PD153035. Resistance did not appear to be related to differences in drug efflux pumps, such as P-glycoprotein or in drug accumulation. Total levels of farnesyl transferase protein subunits were similar in the parent and resistant cells, but, notably, the enzyme activity was markedly reduced in the resistant cell line compared with the parent cells. This was not because of a mutation in the enzyme or a difference in activation of the alpha-subunit of farnesyl transferase by phosphorylation. Hence, resistance to R115777 was generated; the mechanism of resistance in this model may be associated with the enzyme target of the inhibitor. The results suggest that the development of clinical resistance may occur with farnesyl protein transferase inhibitors.