Phase I and pharmacological study of the farnesyltransferase inhibitor tipifarnib (Zarnestra, R115777) in combination with gemcitabine and cisplatin in patients with advanced solid tumours

RAS: Circuitry and therapeutic targeting

Cancer has affected the lives of millions worldwide and is truly regarded as a devastating disease process. Despite advanced understanding of the genomic underpinning of cancer development and progression, therapeutic challenges are still persistent. Among all the human cancers, around 33% are attributed to mutations in RAS oncogene, a crucial component of the signaling pathways. With time, our understanding of RAS circuitry has improved and now the fact that it activates several downstream effectors, depending on the type and grades of cancer has been established. The circuitry is controlled via post-transcriptional mechanisms and frequent distortions in these mechanisms lead to important metabolic as well as immunological states that favor cancer cells' growth, survival, plasticity and metastasis. Therefore, understanding RAS circuitry can help researchers/clinicians to develop novel and potent therapeutics that, in turn, can save the lives of patients suffering from RAS-mutant cancers. There are many challenges presented by resistance and the potential strategies with a particular focus on novel combinations for overcoming these, that could move beyond transitory responses in the direction of treatment. Here in this review, we will look at how understanding the circuitry of RAS can be put to use in making strategies for developing therapeutics against RAS- driven malignancies.

CRISPR/Cas9 genome-wide loss-of-function screening identifies druggable cellular factors involved in sunitinib resistance in renal cell carcinoma

BACKGROUND

Multi-targeted tyrosine kinase inhibitors (TKIs) are the standard of care for patients with advanced clear cell renal cell carcinoma (ccRCC). However, a significant number of ccRCC patients are primarily refractory to targeted therapeutics, showing neither disease stabilisation nor clinical benefits.

METHODS

We used CRISPR/Cas9-based high-throughput loss of function (LOF) screening to identify cellular factors involved in the resistance to sunitinib. Next, we validated druggable molecular factors that are synthetically lethal with sunitinib treatment using cell and animal models of ccRCC.

RESULTS

Our screening identified farnesyltransferase among the top hits contributing to sunitinib resistance in ccRCC. Combined treatment with farnesyltransferase inhibitor lonafarnib potently augmented the anti-tumour efficacy of sunitinib both in vitro and in vivo.

CONCLUSION

CRISPR/Cas9 LOF screening presents a promising approach to identify and target cellular factors involved in the resistance to anti-cancer therapeutics.

RAS: Striking at the Core of the Oncogenic Circuitry

Cancer is a devastating disease process that touches the lives of millions worldwide. Despite advances in our understanding of the genomic architecture of cancers and the mechanisms that underlie cancer development, a great therapeutic challenge remains. Here, we revisit the birthplace of cancer biology and review how one of the first discovered oncogenes, RAS, drives cancers in new and unexpected ways. As our understanding of oncogenic signaling has evolved, it is clear that RAS signaling is not homogenous, but activates distinct downstream effectors in different cancer types and grades. RAS signaling is tightly controlled through a series of post-transcriptional mechanisms, which are frequently distorted in the context of cancer, and establish key metabolic and immunologic states that support cancer growth, migration, survival, metastasis, and plasticity. While targeting RAS has been fiercely pursued for decades, new strategies have recently emerged with the potential for therapeutic efficacy. Thus, understanding the complexities of RAS biology may translate into improved therapies for patients with RAS-driven cancers.

A phase II study of tipifarnib and gemcitabine in metastatic breast cancer

Background Tipifarnib is an orally active, competitive inhibitor of farnesyltransferase which has shown encouraging signs of activity either alone or when combined with other agents. Clinical studies of tipifarnib in combination with anti-estrogen therapy have yielded disappointing results. In contrast, tipifarnib appears to be synergistic in combination with anthracycline based chemotherapy. Here we report the results of the first prospective phase II trial evaluating the efficacy of the novel combination of tipifarnib and gemcitabine in the treatment of metastatic breast cancer. Patients and Methods 30 postmenopausal women with metastatic breast cancer were treated on a 21-day cycle with tipifarnib 300 mg PO twice daily from days 1 through 14. Gemcitabine was administered intravenously at a dose of 1000 mg/m² on days 1 and 8. Patients were treated until disease progression or unacceptable toxicity. Results There was one complete response and four partial responses yielding an objective response rate of 16.7%. Median progression-free survival and overall survival was 2.5 months (95% confidence interval: 1.6-5.7 months) and 13.1 months (95% confidence interval: 9.1-20.6 months), respectively. 40% of patients experienced grade 4 neutropenia in this study. Conclusion The combination of tipifarnib and gemcitabine is not well tolerated with high rates of myelosuppression and is not more effective than gemcitabine monotherapy in the treatment of metastatic breast cancer.

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

Simvastatin interacts synergistically with tipifarnib to induce apoptosis in leukemia cells through the disruption of RAS membrane localization and ERK pathway inhibition

Tipifarnib, a farnesyltransferase inhibitor (FTI), was initially designed to disrupt RAS farnesylation and membrane localization necessary for RAS function. However, alternative geranylgeranylation has been postulated as an escape mechanism by which RAS bypasses the effect of FTI treatment. In this study, we demonstrate that simvastatin, an HMG-CoA reductase inhibitor, augments the cytotoxic effect of tipifarnib by blocking the alternative geranylgeranylation of RAS. Notably, this effect was accompanied by disruption of RAS membrane localization and ERK downregulation. In addition, the apoptotic effect of this combination was associated with downregulation of the antiapoptotic Mcl-1 protein and activation of the caspase cascade. These findings demonstrate that combining tipifarnib and simvastatin was successful in targeting RAS/ERK signaling and inducing apoptosis in leukemia cells. Both simvastatin and tipifarnib were used at clinically achievable doses, which make the combination promising for future clinical studies.

A phase I multicenter study of continuous oral administration of lonafarnib (SCH 66336) and intravenous gemcitabine in patients with advanced cancer

We conducted a phase I study to assess safety, pharmacokinetics, pharmacodynamics, and activity of lonafarnib plus gemcitabine. Subjects received oral lonafarnib twice daily and gemcitabine on days 1, 8, and 15 every 28 days; multiple dose levels were explored. Lonafarnib had no apparent effect on gemcitabine PK. Mean lonafarnib half-life ranged from 4 to 7 hr; median T(max) values ranged from 4 to 8 hr. Two patients had partial response; seven patients had stable disease at least 6 months. Oral lonafarnib at 150 mg a.m./100 mg p.m. plus gemcitabine at 1,000 mg/m(2) is the maximum tolerated dose with acceptable safety and tolerability.

Targeting protein prenylation for cancer therapy

Protein farnesylation and geranylgeranylation, together referred to as prenylation, are lipid post-translational modifications that are required for the transforming activity of many oncogenic proteins, including some RAS family members. This observation prompted the development of inhibitors of farnesyltransferase (FT) and geranylgeranyl-transferase 1 (GGT1) as potential anticancer drugs. In this Review, we discuss the mechanisms by which FT and GGT1 inhibitors (FTIs and GGTIs, respectively) affect signal transduction pathways, cell cycle progression, proliferation and cell survival. In contrast to their preclinical efficacy, only a small subset of patients responds to FTIs. Identifying tumours that depend on farnesylation for survival remains a challenge, and strategies to overcome this are discussed. One GGTI has recently entered the clinic, and the safety and efficacy of GGTIs await results from clinical trials.

In vitro sensitivity testing of minimally passaged and uncultured gliomas with TRAIL and/or chemotherapy drugs

TRAIL/Apo-2L has shown promise as an anti-glioma drug, based on investigations of TRAIL sensitivity in established glioma cell lines, but it is not known how accurately TRAIL signalling pathways of glioma cells in vivo are reproduced in these cell lines in vitro. To replicate as closely as possible the in vivo behaviour of malignant glioma cells, 17 early passage glioma cell lines and 5 freshly resected gliomas were exposed to TRAIL-based agents and/or chemotherapeutic drugs. Normal human hepatocytes and astrocytes and established glioma cell lines were also tested. Cross-linked TRAIL, but not soluble TRAIL, killed both normal cell types and cells from three tumours. Cells from only one glioma were killed by soluble TRAIL, although only inefficiently. High concentrations of cisplatin were lethal to glioma cells, hepatocytes and astrocytes. Isolated combinations of TRAIL and chemotherapy drugs were more toxic to particular gliomas than normal cells, but no combination was generally selective for glioma cells. This study highlights the widespread resistance of glioma cells to TRAIL-based agents, but suggests that a minority of high-grade glioma patients may benefit from particular combinations of TRAIL and chemotherapy drugs. In vitro sensitivity assays may help identify effective drug combinations for individual glioma patients.

Development of farnesyltransferase inhibitors for clinical cancer therapy: focus on hematologic malignancies

Farnesyltransferase inhibitors (FTIs) target and inhibit the peptide prenylating enzyme farnesyltransferase. This new class of signal transduction inhibitors is being tested clinically in diverse malignancies, with encouraging results in hematololgic malignancies and breast cancer in particuarl. Critical questions have yet to be answered, for example, optimal dose and schedule, disease subgroups most likely to respond, and appropriate combinations with standard cytotoxics and new biologics. Gene profiling studies of malignant target cells obtained during FTI clinical trials will help to identify patients who are likely to respond to FTIs and to develop mechanisms for overcoming FTI resistance. Clinical trials and correlative laboratory studies in progress and under development will define the optimal roles of FTIs in cancer patients.

Phase I Trial of Tipifarnib (R115777) Concurrent With Radiotherapy in Patients with Glioblastoma Multiforme

PURPOSE

To conduct a Phase I trial to determine the maximally tolerated dose (MTD) of tipifarnib in combination with conventional three-dimensional conformal radiotherapy (RT) for patients with glioblastoma multiforme.

METHODS AND MATERIALS

After resection or biopsy, tipifarnib was given 1 week before and then continuously during RT (60 Gy), followed by adjuvant administration until progression. The tipifarnib dose during RT was escalated in cohorts of 3 starting at 200 mg/day.

RESULTS

Thirteen patients were enrolled, and 12 were evaluable for MTD. Of these patients, 7 had undergone biopsy, 4 had partial resection, and 1 had gross total resection. No dose-limiting toxicity (DLT) was observed during the concomitant treatment at 200 mg. All 3 patients at 300 mg experienced DLT during the concomitant treatment: 1 with sudden death and 2 with acute pneumonitis. The MTD was reached at 300 mg. The adjuvant treatment was suppressed from the protocol after a case of pneumonitis during this treatment. Six additional patients were included at 200 mg/day of the new protocol, confirming the safety of this treatment. Of the 9 evaluable patients, 1 had partial response, 4 had stable disease, and 3 had rapid progression; the patient with gross total resection was relapse-free after 21 months. Median survival of the evaluable patients was 12 months (range, 5.2-21 months).

CONCLUSION

Tipifarnib (200 mg/day) concurrent with standard radiotherapy is well tolerated in patients with glioblastoma. Preliminary efficacy results are encouraging.

Sensitisation for cisplatin-induced apoptosis by isothiocyanate E-4IB leads to signalling pathways alterations

A new synthetic isothiocyanate (ITC) derivative, ethyl 4-isothiocyanatobutanoate (E-4IB), appeared to be an effective modulator of cellular proliferation and potent inducer of apoptosis. In cooperation with cisplatin, this compound exerted synergistic effects in human ovarian carcinoma A2780 cells. In the present study we investigated in more detail E4IB-sensitisation for cisplatin-induced apoptosis. Sequential administration of both cytostatic agents led to increased intracellular platinum accumulation, glutathione level depletion and mitochondrial membrane potential dissipation. These events were accompanied with poly (ADP-ribosyl) polymerase cleavage, stimulation of caspase-3 activity, upregulation of p53, FasL and Gadd45alpha, cyclin B1 downregulation and an increase in mitogen-activated protein kinases JNK, ERK and p38 phosphorylation as well as PI3K level alterations. The presented results might have implications for developing new strategies aimed at therapeutic benefit of natural or synthetic ITCs in cooperation with various anticancer drugs.

Linking oncogenic pathways with therapeutic opportunities

The accumulation of multiple mutations and alterations in the cancer genome underlies the complexity of cancer phenotypes. A consequence of these alterations is the deregulation of various cell-signalling pathways that control cell function. Molecular-profiling studies, particularly DNA microarray analyses, have the potential to describe this complexity. These studies also provide an opportunity to link pathway deregulation with potential therapeutic strategies. This approach, when coupled with other methods for identifying pathway activation, provides an opportunity to both match individual patients with the most appropriate therapeutic strategy and identify potential options for combination therapy.

Side effects of anti-cancer molecular-targeted therapies (not monoclonal antibodies)

PURPOSE OF REVIEW

Major advances have been achieved in the field of biologically based therapies for cancer in the last few years, and some of the recently approved 'molecular-targeted therapies' are now being used in daily clinical practice. We aim to review some aspects of the toxicity and safety of small-molecule anti-cancer molecular-targeted therapies, with some insights into the physiopathology and predictive factors of toxicity, its correlation with response, and how to prevent and overcome it.

RECENT FINDINGS

As a whole, small-molecule molecular-targeted therapies are well tolerated. Their toxic profile is favorable, but during the drug development process some severe (sometimes lethal) toxicities have been observed, such as interstitial lung disease in patients treated with drugs targeting the epidermal growth factor receptor. Pharmacogenomic studies can help us to identify those patients with well characterized polymorphisms, and to define the best-tolerated and most effective treatments.

SUMMARY

Molecular-targeted therapies have a good toxicity profile in general; however, some patients are exquisitely sensitive to developing particular and severe toxicities related to these drugs.