Sunitinib therapy is currently a standard of care in advanced GIST and RCC, but has failed to show a benefit for advanced HCC in a phase III trial versus sorafenib, primarily due to its adverse effects in this population. With the approval of sorafenib for HCC in many countries, and the development of other anti-VEGFR TKIs, there is an increased appreciation of their toxicity profile and the challenge of effectively managing these toxicities. Furthermore, the mechanism mediating TKI-induced toxicities in HCC remains unknown and the association of toxicities with clinical outcomes remains an open question. Many other antiangiogenic agents are under active development in HCC. Therefore, understanding the impact of toxicities associated with antiangiogenic therapy on outcome and exploring the potential mechanism mediating these toxicities have become priorities.
Therapy with sunitinib––similar to other TKIs––has been frequently associated with hematologic toxicities. Indeed, in this exploratory study we found significant and rapid decreases in all myeloid and lymphoid populations in advanced HCC patients. This may be particularly relevant in HCC. a tumor which typically develops and progresses in a setting of chronic inflammation and cirrhosis, driven by inflammatory cytokines (e.g., IL-6, TNF-α) that can influence inflammatory cell function (22
). However, whether modulation of inflammatory pathways is related to response to antiangiogenic therapy and/or inflammatory pathways drive tumor growth in the face of antiangiogenic therapy remains unclear.
We previously found that sunitinib substantially decreases CPCs in HCC patients (6
). This effect appeared to be more specific to sunitinib than other antiangiogenic agents such as bevacizumab or cediranib, which reduce the number of CPCs only transiently and more subtly (23
). CPCs are likely early hematopoietic cell precursors. Thus, the inhibitory activity of sunitinib against c-KIT and FLT3 – in addition to inhibition of VEGFRs – might explain this myelosuppressive effect (24
). Here, we show that sunitinib at an intermittent dose of 37.5 mg appears to decrease all circulating hematopoietic cell populations in advanced HCC patients. This finding is consistent with observations with sunitinib at the 50 mg dose in GIST patients (25
), and with direct evidence from preclinical studies (26
To account for the known heterogeneity of HCCs, we stratified patients both on their BCLC stage and CLIP score. We conducted correlation analyses for OS as well as TTP, which may be a more meaningful endpoint in HCC phase II trials (27
). Irrespective of the stratification and the progression endpoint, the extent of the decrease in neutrophil, monocyte or platelet counts was associated with more favorable outcomes. This is in line with the correlations seen between the changes in circulating cytokine level (e.g., soluble c-KIT, IL-6) and survival outcome in these patients (6
). On the other hand, higher lymphocyte count (at day 42) and blood circulating CD34+
cells (at any time-point) during sunitinib treatment were associated with superior survival in advanced HCC patients in univariate and multivariate analyses. These results point to the potential role for sunitinib in modulating anti-tumor immune responses, as suggested in metastatic RCC patients treated with sunitinib (28
). Furthermore, these data are consistent with the additive effects seen after depletion of tumor-associated inflammatory cells in HCC in mice treated with sorafenib (30
). The hypothesis that controlling inflammation and immune responses with sunitinib or sorafenib may benefit advanced HCC patients by delaying disease progression should be evaluated in future studies.
As expected, inflammatory cell changes correlate with changes in certain cytokines (IL-1β, IL-6, IL-8, TNF-α). However, surprisingly, we also detected associations between inflammatory cell changes and growth factors and their soluble receptors. Decreases in sVEGFR2 (a protein significantly reduced in circulation by most anti-VEGFR TKIs (31
)) associated with drops in neutrophils and WBCs. This may be due to potential pharmacodynamic marker value of sVEGFR2 changes after treatment (31
), or may indicate a direct modulation of myelopoiesis by VEGF-VEGFR2 pathway. The drop in the number of platelets was associated with decreases in plasma levels of VEGF-C (a VEGF family member that can bind to both VEGFR2 and VEGFR3) and increases in sVEGFR3. Platelets express VEGFR3, and store and release VEGF-C from their α-granules (32
), but a role for the VEGF-C-VEGFR3 pathway in thrombopoiesis remains to be identified. Finally, we detected an association between changes in plasma sVEGFR1 (an endogenous blocker of VEGF and placental growth factor, PlGF) and lymphocyte counts. VEGF and PlGF are thought to be involved in myeloid cell trafficking and dendritic cell differentiation (33
). The potential significance of endogenous modulation of VEGF pathway after sunitinib treatment on changes in lymphocyte numbers in circulation remains to be established by future studies (Supplementary Table S8
). Of interest, we confirmed in this HCC cohort that sunitinib could transiently induce a mild increase in erythropoiesis, which is reversible after treatment breaks. Since VEGF has been shown to suppress erythropoiesis in mouse models by suppressing EPO expression in the liver (17
), these data provide clinical evidence that early Hgb measurements might be useful as a pharmacodynamic marker in patients receiving anti-VEGF therapy. The clinical relevance of this clinically measurable but transient stimulation of erythropoiesis remains to be established in future studies.
Finally, several non-hematologic toxicities occur frequently in the HCC patients treated with sunitinib, and some of them associated with survival outcomes in our study. We observed an association of fatigue with improved TTP. In addition, skin toxicities were associated with prolonged OS and TTP. Despite the well-known association of skin toxicities and clinical outcomes in patients receiving anti-EGFR therapies in other malignancies including colon and pancreatic cancers, the significance of skin toxicities associated with sorafenib and sunitinib in predicting clinical outcome has only recently started to be appreciated (13
). In our study, nausea and vomiting correlated with higher risk of death (but not of disease progression), and no association was observed with diarrhea. Although the effect size for non-hematologic toxicities appears smaller than for hematologic toxicities, they may both be informative. For example, one patient in this study experienced a severe non-hematologic toxicity (Grade 4 toxic peripheral vestibulopathy) whose onset and resolution closely followed the onset and resolution of his hematologic toxicity (Grade 3 neutropenia, Grade 2 anemia and Grade 1 thrombocytopenia at nadir)(34
). Further characterization of the potential association of GI toxicities with clinical outcomes should be explored and the potential mechanism mediating this association remains to be elucidated in future large studies.
Hypertension is often used as a pharmacodynamic endpoint for antiangiogenic therapy. However, its value as a predictive marker for clinical outcomes remains unclear. Two studies have proposed that the degree of hypertension is a potential predictive biomarker of survival in cancer patients receiving bevacizumab or axitinib treatment (12
). However, other studies failed to observe this association. In our study, hypertension was not associated with OS or TTP. The lower frequency of hypertension (12%) and other adverse events in our study may limit the power of analysis of these associations.
In conclusion, sunitinib appears to induce a decrease in all mature myeloid and lymphoid cell populations. A more favorable progression and survival outcome was seen in patients with greater decreases in inflammatory cells, as well as in those with skin toxicities and fatigue. However, it is the high incidence of serious adverse effects––seen with continuous dosing of sunitinib––that led to the early stoppage of a recent phase III trial in advanced HCC. Therefore, as further development of sunitinib in HCC appears unlikely, this exploratory, hypothesis-generating study should inform future trials. Further investigations in larger studies are needed to confirm and validate the value of these biomarkers and potential immunomodulation of sorafenib and other anti-VEGFR TKIs in patients with HCC.
Statement of Translational Relevance
The anti-vascular endothelial growth factor receptor tyrosine kinase inhibitor (VEGFR TKI) sorafenib has been the first systemic agent to show overall survival benefits in advanced hepatocellular carcinoma (HCC) and is a current standard of care. The recent failure of sunitinib (a more potent anti-VEGFR TKI) in a phase III trial versus sorafenib was due, in part, to its toxicity. Therefore, understanding the mechanisms of action of TKIs in HCC has become even more critical for further progress in HCC therapy. However, there are no confirmed mechanisms of action or biomarkers of efficacy and toxicity for any anti-VEGFR TKI. The results of our analysis strongly support the hypothesis that the effect of sunitinib on the immune system is related to its activity in HCC patients. Moreover, this exploratory study suggests that early hematopoietic toxicities may predict progression and survival outcomes in advanced HCC after sunitinib treatment. While translation of this concept in clinical practice will require further understanding of these effects and validation in large studies of sorafenib and other TKIs, these results open new avenues for clinical and preclinical research in this area.