Exposure-toxicity relationship of cabozantinib in patients with renal cell cancer and salivary gland cancer

Exposure-response relationship of cabozantinib in patients with metastatic renal cell carcinoma treated in routine care

BACKGROUND

Interindividual pharmacokinetic variability may influence the clinical benefit or toxicity of cabozantinib in metastatic renal cell carcinoma (mRCC). We aimed to investigate the exposure-toxicity and exposure-response relationship of cabozantinib in unselected mRCC patients treated in routine care.

METHODS

This ambispective multicenter study enrolled consecutive patients receiving cabozantinib in monotherapy. Steady-state trough concentration (Cmin,ss) within the first 3 months after treatment initiation was used for the PK/PD analysis with dose-limiting toxicity (DLT) and survival outcomes. Logistic regression and Cox proportional-hazards models were used to identify the risk factors of DLT and inefficacy in patients, respectively.

RESULTS

Seventy-eight mRCC patients were eligible for the statistical analysis. Fifty-two patients (67%) experienced DLT with a median onset of 2.1 months (95%CI 0.7-8.2). In multivariate analysis, Cmin,ss was identified as an independent risk factor of DLT (OR 1.46, 95%CI [1.04-2.04]; p = 0.029). PFS and OS were not statistically associated with the starting dose (p = 0.81 and p = 0.98, respectively). In the multivariate analysis of PFS, Cmin, ss > 336 ng/mL resulted in a hazard ratio of 0.28 (95%CI, 0.10-0.77, p = 0.014). By contrast, Cmin, ss > 336 ng/mL was not statistically associated with longer OS.

CONCLUSION

Early plasma drug monitoring may be useful to optimise cabozantinib treatment in mRCC patients treated in monotherapy, especially in frail patients starting at a lower than standard dose.

Therapeutic Drug Monitoring for Tyrosine Kinase Inhibitors in Metastatic Renal Cell Carcinoma

Inter-individual variability in drug response pose significant challenges to treatment with tyrosine kinase inhibitors (TKIs) in patients with metastatic renal cell carcinoma (mRCC). TKIs meet traditional criteria for using therapeutic drug monitoring (TDM), but research is still limited. Understanding the role of TDM in individualizing treatment strategies could help optimize treatment. Here we review the state of knowledge of TDM for TKIs in mRCC treatment. A comprehensive literature review of original research studies focusing on TDM of TKIs in mRCC treatment, clinical in vivo studies reporting on pharmacokinetics-pharmacodynamics, therapeutic ranges, drug concentrations, dose adjustments, clinical outcomes, or other relevant aspects related to TDM. We reviewed studies involving human subjects published in peer-reviewed journals. A narrative synthesis approach was employed to summarize the findings. Key themes and trends related to TDM of TKIs in mRCC treatment were identified and synthesized to provide a comprehensive overview of the current state of knowledge. Our search yielded 25 articles. Most were observational. The most consistently reported association between plasma concentration and effect was pazopanib Ctrough >20 µg/mL, but this concentration was not significant across all studies. We found inconsistent evidence for sunitinib and cabozantinib. For axitinib, we found a clear exposure-response relationship, but research was too diverse to conclude on a therapeutic window to use for TDM. We found much heterogeneity between recommended time of measurement (minimum plasma concentration [Cmin], maximal plasma concentration [Cmax], area under the curve [AUC]) and large variation in plasma concentration associated with clinical outcomes, which makes it difficult to recommend specific concentration intervals based on 1 or more of these measurements. Results were more consistent with TKIs continuously administered. Further research is needed to elucidate the long-term impact of TDM to possibly establish standardized therapeutic intervals. Prospective studies are suggested. The application of TDM in TKI-combination therapy is warranted in future research.

Results of the first international quality control programme for oral targeted oncolytics

AIMS

With the rising number of oral targeted oncolytics and growing awareness of the benefits of therapeutic drug monitoring (TDM) within the field of oncology, it is expected that the requests for quantifying concentrations of these drugs will increase. It is important to (cross-)validate available assays and ensure its quality, as results may lead to altered dosing recommendations. Therefore, we aimed to evaluate the performance of laboratories measuring concentrations of targeted oral oncolytics in a one-time international quality control (QC) programme.

METHODS

Participating laboratories received a set of plasma samples containing low, medium and high concentrations of imatinib, sunitinib, desethylsunitinib, pazopanib, cabozantinib, olaparib, enzalutamide, desmethylenzalutamide and abiraterone, with the request to report their results back within five weeks after shipment. Accuracy was defined acceptable if measurements where within 85%-115% from the weighed-in reference concentrations. Besides descriptive statistics, an exploratory ANOVA was performed.

RESULTS

Seventeen laboratories from six countries reported 243 results. Overall, 80.7% of all measurements were within the predefined range of acceptable accuracy. Laboratories performed best in quantifying imatinib and poorest in quantifying desethylsunitinib (median absolute inaccuracy respectively 4.0% (interquartile range (IQR) 1.8%-6.5%) and 15.5% (IQR 8.8%-34.9%)). The poorest performance of desethylsunitinib might be caused by using the stable-isotope-labelled sunitinib instead of desethylsunitinib as an internal standard, or due to the light-induced cis(Z)/trans(E) isomerization of (desethyl)sunitinib. Overall, drug substance and performing laboratory seemed to influence the absolute inaccuracy (F = 16.4; p < 0.001 and F = 35.5; p < 0.001, respectively).

CONCLUSION

Considering this is the first evaluation of an international QC programme for oral targeted oncolytics, an impressive high percentage of measurements were within the predefined range of accuracy. Cross-validation of assays that are used for dose optimization of oncolytics will secure the performance and will protect patients from incorrect advices.

Phase I Trial of the Multi-kinase Inhibitor Cabozantinib, a CYP3A4 Substrate, plus CYP3A4-Interacting Antiretroviral Therapy in People Living with HIV and Cancer (AMC-087)

PURPOSE

To evaluate the safety, pharmacokinetics, and pharmacodynamic effects of cabozantinib, a CYP3A4 substrate, in people living with human immunodeficiency virus and cancer receiving antiretrovirals (ARV).

PATIENTS AND METHODS

Patients received a reduced dose of cabozantinib (20 mg orally daily) with strong CYP3A4 inhibitors (ARV ritonavir or non-ARV cobicistat, stratum A), or a standard 60 mg dose with ARVs that are CYP3A4 inducers (efavirenz or etravirine, stratum B) or noninteracting ARVs (stratum C). Initial dose escalation in stratum A and stratum B was performed on the basis of tolerability.

RESULTS

36 patients received cabozantinib plus ARVs, including 20 in stratum A, 9 in B, and 7 in C. The recommended initial cabozantinib doses for stratum A, B, and C were 20, 60, and 60 mg, respectively. Doses of 40 or 60 mg plus CYP3A4 inhibitors in stratum A and 100 mg plus CYP3A4 inducers in stratum B were associated with excessive toxicity, whereas 60 mg with noninteracting ARVs was not. The steady state minimal concentrations were lower at 20 mg in stratum A or 60 mg in stratum B compared with 60 mg in stratum C, while total exposure was only lower in 60 mg in stratum B compared with 60 mg in stratum C. Activity was observed in Kaposi sarcoma and an AXL-amplified sarcoma.

CONCLUSIONS

Cabozantinib as a single agent should be initiated at 20 mg daily and 60 mg daily when taken concurrently with ARVs that are strong CYP3A4 inhibitors and inducers, respectively, with consideration for subsequent escalation per current cabozantinib guidelines. See related commentary by Eisenmann and Sparreboom, p. 4999.

Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors in the Treatment of Advanced Renal Cancer

Seven tyrosine kinase inhibitor compounds with anti-angiogenic properties remain key drugs to treat advanced renal cell carcinoma. There is a strong rationale to develop therapeutic drug monitoring for these drugs. General considerations of such monitoring of the several groups of anticancer drugs are given, with a focus on oral therapy. Pharmacokinetics and the factors of inter- and intraindividual variabilities of these tyrosine kinase inhibitors are described together with an exhaustive presentation of their pharmacokinetic/pharmacodynamic relationships. The latter was observed in studies where every patient was treated with the same dose, and the results of several prospective studies based on dose individualization support the practice of increasing individual dosage in case of low observed plasma drug concentrations. Finally, the benefits and limits of therapeutic drug monitoring as a routine practice are discussed.

Impact of Cabozantinib Exposure on Proteinuria and Muscle Toxicity in Patients with Unresectable Hepatocellular Carcinoma

This prospective study investigated the impact of cabozantinib exposure on proteinuria and muscle toxicity, in a cohort of 14 Japanese patients with unresectable hepatocellular carcinoma (uHCC). We measured the trough concentration of cabozantinib (Ctrough) weekly for 6 weeks after starting treatment. Although the initial dose was less than 60 mg in most cases, dose interruption occurred in 79%, primarily because of proteinuria and/or malaise. The median and coefficient of variation of maximum Ctrough at 7−42 d were 929.0 ng/mL and 59.2%, respectively. The urinary protein-to-creatinine ratio (UPCR), serum creatine kinase, and serum aldolase values were all significantly elevated following treatment. Moreover, maximum changes in serum creatine kinase and aldolase were significantly associated with maximum Ctrough (r = 0.736, p < 0.01; r = 0.798, p < 0.001; respectively). Receiver operating characteristic (ROC) curve analysis showed that changes in serum creatine kinase ≥70.5 U/L and aldolase ≥6.1 U/L from baseline relatively accurately predicted inclusion in the high-maximum Ctrough (≥929.0 ng/mL) group, with an area under the ROC of 0.929 and 0.833, respectively. Measurement of serum creatine kinase and aldolase may increase the clinical usefulness of cabozantinib treatment for uHCC and help alleviate difficulties with dose adjustments.

Reassessing vascular endothelial growth factor (VEGF) in anti-angiogenic cancer therapy

Vascularization is fundamental to the growth and spread of tumor cells to distant sites. As a consequence, angiogenesis, the sprouting of new blood vessels from existing ones, is a characteristic trait of cancer. In 1971, Judah Folkman postulated that tumour growth is angiogenesis dependent and that by cutting off blood supply, a neoplastic lesion could be potentially starved into remission. Decades of research have been devoted to understanding the role that vascular endothelial growth factor (VEGF) plays in tumor angiogenesis, and it has been identified as a significant pro-angiogenic factor that is frequently overexpressed within a tumor mass. Today, anti-VEGF drugs such as Sunitinib, Sorafenib, Axitinib, Tanibirumab, and Ramucirumab have been approved for the treatment of advanced and metastatic cancers. However, anti-angiogenic therapy has turned out to be more complex than originally thought. The failure of this therapeutic option calls for a reevaluation of VEGF as the major target in anti-angiogenic cancer therapy. The call for reassessment is based on two rationales: first, tumour blood vessels are abnormal, disorganized, and leaky; this not only prevents optimal drug delivery but it also promotes hypoxia and metastasis; secondly, tumour growth or regrowth might be blood vessel dependent and not angiogenesis dependent as tumour cells can acquire blood vessels via non-angiogenic mechanisms. Therefore, a critical assessment of VEGF, VEGFRs, and their inhibitors could glean newer options such as repurposing anti-VEGF drugs as vascular normalizing agents to enhance drug delivery of immune checkpoint inhibitors.