Microtubule-Interfering Drugs: Current and Future Roles in Epithelial Ovarian Cancer Treatment

Taxanes and epothilones are chemotherapeutic agents that ultimately lead to cell death through inhibition of normal microtubular function. This review summarizes the literature demonstrating their current use and potential promise as therapeutic agents in the treatment of epithelial ovarian cancer (EOC), as well as putative mechanisms of resistance. Historically, taxanes have become the standard of care in the front-line and recurrent treatment of epithelial ovarian cancer. In the past few years, epothilones (i.e., ixabepilone) have become of interest as they may retain activity in taxane-treated patients since they harbor several features that may overcome mechanisms of taxane resistance. Clinical data now support the use of ixabepilone in the treatment of platinum-resistant or refractory ovarian cancer. Clinical data strongly support the use of microtubule-interfering drugs alone or in combination in the treatment of epithelial ovarian cancer. Ongoing clinical trials will shed further light into the potential of making these drugs part of current standard practice.

WILD-seq: Clonal deconvolution of transcriptomic signatures of sensitivity and resistance to cancer therapeutics in vivo.

Tumour heterogeneity is thought to be a major barrier to successful cancer treatment due to the presence of drug resistant clonal lineages. However, identifying the characteristics of such lineages that underpin resistance to therapy has remained challenging. Here we present WILD-seq; Wholistic Interrogation of Lineage Dynamics by sequencing, a platform that leverages expressed barcodes to simultaneously map clonal identities and transcriptional states at single cell resolution. Our optimised pipeline ensures recurrent representation of clonal lineages across animals and samples, facilitating analysis of clonal dynamics under perturbation. Application of WILD-seq to two triple negative mammary carcinoma mouse models, identified changes in clonal abundance, gene expression and microenvironment in response to JQ1 or taxane chemotherapy. WILD-seq reveals oxidative stress protection as a major mechanism of taxane resistance that renders our tumour models collaterally sensitive to non-essential amino acid deprivation. In summary, WILD-seq enables facile coupling of lineage and gene expression in vivo to elucidate clone-specific pathways of resistance to cancer therapies.

Dual Targeting of EGFR with PLK1 Exerts Therapeutic Synergism in Taxane-Resistant Lung Adenocarcinoma by Suppressing ABC Transporters

To overcome the limitations of chemoresistance, combination therapies using druggable targets have been investigated. Our previous studies led us to hypothesize that the downregulation of PLK1 expression or activity can be one strategy to overcome the hurdles of taxane resistance by the downregulation of ABC transporters. To explore this, various versions of PLK1 including a constitutively active version, kinase-dead form, and polo-box domain mutant were expressed in paclitaxel-resistant lung adenocarcinoma (LUADTXR). Targeting PLK1 using shRNA or non-functional mutants downregulated ABCB1, ABCC9, and ABCG2 in LUADTXR cells, which was similar to the downregulation effects from treatment with PLK1 inhibitors. The high expression of EGFR in LUAD led us to administer gefitinib, showing a markedly reduced EGFR level in LUADTXR cells. When gefitinib and PLK1 inhibitors were combined, LUADTXR cells tended to undergo apoptosis more effectively than parental cells, showing a synergistic effect on the downregulation of ABC transporters through c-Myc and AP-1. Clinical data provide evidence for the relevance between survival rates and expressions of PLK1 and EGFR in LUAD patients. Based on these results, we suggest that a combination of gefitinib and PLK1 inhibitors exerts strong synergism in LUADTXR, which helps to overcome the limitations associated with taxanes.

Circulating Cell-Free DNA as Biomarker of Taxane Resistance in Metastatic Castration-Resistant Prostate Cancer

There are no biomarkers predictive of resistance to docetaxel or cabazitaxel validated for patients with metastatic castration-resistant prostate cancer (mCRPC). We assessed the association between ABCB1 amplification and primary resistance to docetaxel or cabazitaxel for patients with mCRPC, using circulating cell-free DNA (cfDNA). Patients with ≥1 plasma sample drawn within 12 months before starting docetaxel (cohort A) or cabazitaxel (cohort B) for mCRPC were identified from the Dana–Farber Cancer Institute IRB approved database. Sparse whole genome sequencing was performed on the selected cfDNA samples and tumor fractions were estimated using the computational tool ichorCNA. We evaluated the association between ABCB1 amplification or other copy number alterations and primary resistance to docetaxel or cabazitaxel. Of the selected 176 patients, 45 samples in cohort A and 21 samples in cohort B had sufficient tumor content. No significant association was found between ABCB1 amplification and primary resistance to docetaxel (p = 0.58; odds ratio (OR) = 1.49) or cabazitaxel (p = 0.97; OR = 1.06). No significant association was found between exploratory biomarkers and primary resistance to docetaxel or cabazitaxel. In this study, ABCB1 amplification did not predict primary resistance to docetaxel or cabazitaxel for mCRPC. Future studies including ABCB1 amplification in a suite of putative biomarkers and a larger cohort may aid in drawing definitive conclusions.

Targeting tumor-macrophage interaction via the Notch2-Jag1 axis reverses tumor resistance to paclitaxel

Taxanes are widely used in chemotherapy, but intrinsic and acquired resistance limit the clinical outcomes. Studies showed tumor interaction with suppressive macrophages plays a key role in taxane resistance, yet therapeutic strategies that deplete or repolarize macrophages are challenging. Here we uncovered a novel tumor-macrophage interaction via Notch2-Jag1 justacrine signaling that can be targeted to sensitize paclitaxel response without affecting the broad macrophage functions. Using translatome profiling, we identified Notch2 upregulation during taxol-induced prolonged mitosis. Notch2 was subsequently activated in the post-mitotic G1 phase by Jag1 expressed on neighboring macrophages, which promoted tumor cell survival by upregulating p38 and anti-apoptotic proteins. Notch2 also upregulated cytokines that further recruited Jag1-expressing macrophages. By targeting this Notch2-Jag1 interaction with a pan-Notch inhibitor, RO4929097, taxol resistance was significantly attenuated in multiple mouse tumor models. Our results point to combining Notch inhibitor with taxane as an effective strategy to selectively disrupt tumor-macrophage interaction underlying chemoresistance.

Final results of phase 1 evaluation of the safety and clinical activity of sapanisertib in combination with serabelisib and paclitaxel in patients with advanced ovarian, endometrial, or breast cancer.

5569 Background: Evidence suggests that activation of the PI3K/AKT/mTOR pathway by paclitaxel may play a role in the development of taxane resistance. Conversely, PI3K inhibitors have been shown to sensitize tumors to the effects of paclitaxel. Therefore, the link between taxane resistance and activation of the PI3K/AKT/mTOR signaling pathway suggests inhibition of this pathway in combination with antimitotic drugs like paclitaxel may improve treatment outcomes in many malignancies. To further investigate this hypothesis we combined the TORC 1/2 inhibitor sapanisertib (TAK-228), the PI3Kα isoform inhibitor serabelisib (TAK-117), and paclitaxel in a phase I trial of heavily pretreated patients to determine the safety, efficacy, and RP2D. Methods: This is an open label, cohort study of sapanisertib (TAK-228) and serabelisib (TAK-117) given on days 2-4, 9-11, 16-18, and 23-25 with paclitaxel on days 1, 8, and 15 of a 28-day cycle. A traditional 3+3 dose escalation design with a maximum of 5 dosing cohorts was used. All 5 cohorts plus an expansion cohort are presented. Results: Enrollment has been completed and the overall results are summarized. Nineteen patients were enrolled; the majority were heavily pretreated with the average number of prior regimens exceeding 4. Based upon ITT, the ORR is 37%. The ORR is 47% in patients that completed at least 3 cycles. The clinical benefit rate is 73% and the PFS currently stands at approximately 11 months. Two patients with endometrioid endometrial adenocarcinoma achieved a complete response. All patients received comprehensive genomic profiling and 7 patients received prior mTOR inhibitor. Overall, the combination was well tolerated, except by patients in cohort 5. One DLT occurred in the last patient enrolled. The most common non-laboratory AEs were nausea (6%), fatigue (5%), and mucositis (5%). There were 45 (9%) grade 3 or 4 events, and the most common were decreased WBC and non-febrile neutropenia. Hyperglycemia was common in patients with a history of diabetes mellitus. Conclusions: Overall, the combination of sapanisertib, serabelisib, and paclitaxel was safe and efficacious throughout the first 4 cohorts. There were few serious adverse events, and most side effects were managed with routine supportive care interventions. Preliminary clinical results appear very promising, especially for patients with PI3K/AKT/mTOR pathway mutations. The positive effects of the combination were routinely seen in the lowest dosing cohorts and clinical benefit was even seen in patients that had previously failed everolimus or temsirolimus. All patients were either resistant or refractory to paclitaxel at time of enrollment, so further exploration of this combination to elucidate the mechanism of benefit is warranted. Clinical trial information: NCT03154294.