Trabectedin—a targeted chemotherapy?

Trabectedin: Supportive care strategies and safety profile

Trabectedin is an approved antineoplastic agent for the treatment of adult patients with advanced soft tissue sarcomas or in combination with pegylated liposomal doxorubicin (PLD) in patients with relapsed platinum sensitive ovarian cancer. The mechanism of action is still not fully understood but many typical side effects seen with other chemotherapy drugs are less common, mild or unreported. Although this apparent favorable safety profile suggests a well-tolerated and manageable therapeutic option in the palliative care setting, trabectedin does have specific adverse side effects which can be hazardous for individual patients. The most commonly observed toxicities with trabectedin include neutropenia, nausea, vomiting, and increases in liver transaminases, anemia, fatigue, thrombocytopenia, anorexia and diarrhea. However, for most patients the appropriate use of supportive care strategies can reduce or overcome these side effects. We present a concise review of the safety data of trabectedin with the corresponding overview of the supportive care strategies.

The intriguing patterns of tumor response to trabectedin

Among soft tissue sarcomas, myxoid liposarcomas are exceedingly sensitive to trabectedin. Obvious tumor shrinkage is seen in some patients, whereas nondimensional changes in tumor tissue are seen in others especially after the first cycles of therapy. These patterns of tumor response are reminiscent of the way in which solid tumors respond to targeted therapies. The finding of trabectedin's ability to target the FUS-CHOP-mediated transcriptional block, restoring adipogenic differentiation within the tumor in myxoid liposarcomas, confirmed a 'targeted' activity that differs from its well-known atypical alkylating mechanism of action. Uterine leiomyosarcoma may show similar patterns of dimensional and nondimensional responses to trabectedin. Unusual cases of delayed response are occasionally seen and suggest other mechanisms of action, including activity on the tumor microenvironment which has recently been reported. An intriguing question is whether the different patterns of response have clinically or therapeutically meaningful correlations.

Phase II study of the mammalian target of rapamycin inhibitor ridaforolimus in patients with advanced bone and soft tissue sarcomas

PURPOSE

Ridaforolimus is an inhibitor of mammalian target of rapamycin, an integral component of the phosphatidyl 3-kinase/AKT signaling pathway, with early evidence of activity in sarcomas. This multicenter, open-label, single-arm, phase II trial was conducted to assess the antitumor activity of ridaforolimus in patients with distinct subtypes of advanced sarcomas.

PATIENTS AND METHODS

Patients with metastatic or unresectable soft tissue or bone sarcomas received ridaforolimus 12.5 mg administered as a 30-minute intravenous infusion once daily for 5 days every 2 weeks. The primary end point was clinical benefit response (CBR) rate (complete response or partial response [PR] or stable disease ≥ 16 weeks). Safety, progression-free survival (PFS), overall survival (OS), time to progression, and duration of response were also evaluated.

RESULTS

A total of 212 patients were treated in four separate histologic cohorts. In this heavily pretreated population, 61 patients (28.8%) achieved CBR. Median PFS was 15.3 weeks; median OS was 40 weeks. Response Evaluation Criteria in Solid Tumors (RECIST) confirmed response rate was 1.9%, with four patients achieving confirmed PR (two with osteosarcoma, one with spindle cell sarcoma, and one with malignant fibrous histiocytoma). Archival tumor protein markers analyzed were not correlated with CBR. Related adverse events were generally mild or moderate and consisted primarily of stomatitis, mucosal inflammation, mouth ulceration, rash, and fatigue.

CONCLUSION

Single-agent ridaforolimus in patients with advanced and pretreated sarcomas led to PFS results that compare favorably with historical metrics. A phase III trial based on these data will further define ridaforolimus activity in sarcomas.

Detection of myxoid liposarcoma-associated FUS-DDIT3 rearrangement variants including a newly identified breakpoint using an optimized RT-PCR assay

Myxoid/round cell liposarcoma is characterized by the recurrent translocations t(12;16)(q13;p11) and, less commonly, t(12;22)(q13;q12), which fuse FUS or EWSR1, respectively, to DDIT3 on chromosome 12. Although a number of different variant breakpoints have been described, greater than 90% of all cases have one of the three different FUS-DDIT3 fusions, which may have clinical significance. To identify the individual breakpoints, a sequence-specific assay such as reverse transcription-PCR (RT-PCR) is needed. In this study, we optimized primer design to develop an RT-PCR assay for the detection of the most common translocations in formalin-fixed paraffin-embedded tissue specimens. We compared our assay with primers previously published for testing formalin-fixed paraffin-embedded specimens and achieved the most consistent results with our primers. We obtained RNA from 32 MLS cases, of which 27 carried one of the three common FUS-DDIT3 chimeric transcript types. Four of the negative cases were from very small biopsies with very low RNA concentration. One case was consistently negative by RT-PCR, but showed a FUS rearrangement by fluorescent in situ hybridization, suggesting that it may harbor one of the rarer FUS-DDIT3 chimeric types. In addition to the common fusions, our assay also identified a novel FUS-DDIT3 fusion between exon 9 of FUS and exon 3 of DDIT3 in one of the cases.

Down-regulation of the nucleotide excision repair gene XPG as a new mechanism of drug resistance in human and murine cancer cells

Background

Drug resistance is one of the major obstacles limiting the activity of anticancer agents. Activation of DNA repair mechanism often accounts for increase resistance to cancer chemotherapy.

Results

We present evidence that nemorubicin, a doxorubicin derivative currently in clinical evaluation, acts through a mechanism of action different from classical anthracyclines, requiring an intact nucleotide excision repair (NER) system to exert its activity. Cells made resistant to nemorubicin show increased sensitivity to UV damage. We have analysed the mechanism of resistance and discovered a previously unknown mechanism resulting from methylation-dependent silencing of the XPG gene. Restoration of NER activity through XPG gene transfer or treatment with demethylating agents restored sensitivity to nemorubicin. Furthermore, we found that a significant proportion of ovarian tumors present methylation of the XPG promoter.

Conclusions

Methylation of a NER gene, as described here, is a completely new mechanism of drug resistance and this is the first evidence that XPG gene expression can be influenced by an epigenetic mechanism. The reported methylation of XPG gene could be an important determinant of the response to platinum based therapy. In addition, the mechanism of resistance reported opens up the possibility of reverting the resistant phenotype using combinations with demethylating agents, molecules already employed in the clinical setting.

[Multidisciplinary treatment for adult soft tissue sarcoma]

The current standard in local treatment of soft tissue sarcomas has shifted from amputation and similar mutilating resections to more organ- and function-preserving surgery. This was possible through multidisciplinary treatment approaches, particularly those including adjuvant radiation therapy. Adjuvant radiation showed significant improvement in local tumour control after resection with tight margins and in high-risk sarcomas. Unfortunately adjuvant radiation failed to improve overall survival. Perioperative chemotherapies also have not contributed to improvement in the overall prognosis worldwide. Progress may occur when the pathogenesis and molecular profile of specific sarcoma subtypes are better understood, allowing more effective new drugs. One example is the treatment of advanced gastrointestinal stromal tumour with imatinib, a small molecular kinase inhibitor of the c-kit receptor. Presently the most effective measure to improve the prognosis with soft tissue sarcomas is early patient referral to expert centres, where diagnostic workup and therapy decisions are made on a multidisciplinary basis and updated according to the newest guidelines and study results.