Discovery of a potent tubulin polymerization inhibitor: synthesis and evaluation of water-soluble prodrugs of benzophenone analog

Synthesis, biological evaluation and molecular docking investigation of new sulphonamide derivatives bearing naphthalene moiety as potent tubulin polymerisation inhibitors

A new series of sulphonamide derivatives bearing naphthalene moiety were synthesised and evaluated for their antiproliferative and tubulin polymerisation inhibitory activities. These new compounds were evaluated for their in vitro antiproliferative activity against MCF-7 and A549 by using CCK-8 method. Among all the tested compounds, compound 5c with naphthalen-1-yl moiety exhibited the most potent antiproliferative activity against MCF-7 and A549 cell line, with IC₅₀ values of 0.51 ± 0.03 µM and 0.33 ± 0.01 µM, respectively. The results of tubulin polymerisation assay shown that 5c exhibited a significant ability to inhibit tubulin polymerisation with IC₅₀ value of 2.8 μM. Consistent with its antitubulin activity, 5c can significantly arrest the cell cycle at G2/M phase and induce apoptosis in MCF-7 cancer cells. Molecular docking study indicated that compound 5c inhibited tubulin polymerisation through interacting at the colchicine-binding site of tubulin. Furthermore, 5c exhibited low cytotoxic activity on human normal cell line.

A phase 1 dose-escalation and dose-expansion study to assess the safety and efficacy of CKD-516, a novel vascular disrupting agent, in combination with Irinotecan in patients with previously treated metastatic colorectal cancer

Introduction The combination of an anti-angiogenic agent with cytotoxic chemotherapy is a standard treatment strategy for metastatic colorectal cancer. CKD-516 is an oral vascular disrupting agent that was preliminarily shown to be safe and efficacious as a monotherapy in refractory solid cancers. We evaluated the recommended phase 2 dose, safety, and preliminary efficacy of CKD-516 in combination with irinotecan in treatment-refractory metastatic colorectal cancer. Methods This phase 1 dose-escalation and dose-expansion study included patients with treatment-refractory metastatic colorectal cancer. CKD-516 tablets were administered for five consecutive days followed by two days off in combination with intravenous irinotecan (120 mg/m²) administered on day one of each treatment cycle every two weeks. A traditional 3 + 3 dose-escalation design was used. Results In total, 16 and 23 patients were enrolled in the dose-escalation and dose-expansion cohorts, respectively. The most common adverse events included diarrhea (79%), nausea (74%), vomiting (67%), and neutropenia (62%). No dose-limiting toxicity occurred, and the recommended phase 2 dose was determined at CKD-516/irinotecan doses of 11/120 mg/m². No cases of cardiac ischemia, cardiac dysfunction, or thromboembolism were reported. Among the 34 patients with available tumor response assessments, one patient achieved partial response (3%) and 26 patients achieved stable disease (76%). The median progression-free survival and overall survival were 4.1 and 11.6 months, respectively. Conclusion This phase 1 study showed that the combination of oral CKD-516 and irinotecan is safe and tolerable in metastatic, treatment-refractory colorectal patients and showed favorable efficacy outcomes. Further studies to confirm these preliminary findings are warranted. Trial registration number NCT03076957 (Registered at March 10, 2017).

Phase I and pharmacokinetic study of the vascular-disrupting agent CKD-516 (NOV120401) in patients with refractory solid tumors

We report a phase I pharmacological study of an oral formulation of CKD‐516, a vascular‐disrupting agent, in patients with refractory solid tumors. Twenty‐seven patients (16 in the dose‐escalation cohort and 11 in the expansion cohort) received a single daily dose (5‐25 mg) of CKD‐516 five days per week. Nausea (67%) and diarrhea (63%) were the most common treatment‐related adverse events. The recommended phase II dose of oral CKD‐516 was 20 mg/d (15 mg/d with a body surface area (BSA) <1.65 m²). Notably, S‐516 half‐lives in patients receiving 15‐20 mg CKD‐516/d significantly differed between patients with and without splenomegaly that is suggestive of portal hypertension associated with liver cirrhosis (6.1 vs 4.6 hours, respectively). Of 11 patients without splenomegaly who completed at least one cycle of a daily CKD‐516 dose of either 15 or 20 mg, only one patient (9.1%) suffered from any dose‐limiting toxicity. We conclude that a daily oral dose of 15 or 20 mg CKD‐516 five days per week could be tolerable in patients without liver cirrhosis.

Revolutionizing the landscape of colorectal cancer treatment: The potential role of immune checkpoint inhibitors

Colorectal cancer (CRC) represents the third cause of cancer-related mortalities worldwide. The progression of CRC to the metastatic phase significantly compromises the overall survival rates. Despite the advances in the therapeutic protocols, CRC treatment is still challenging. Cancer immunotherapy joined the ranks of surgery, chemotherapy, radiotherapy and targeted therapy as the fifth pillar in the foundation of cancer therapeutics. Interruption of the immunosuppressive signals within the tumor microenvironment and reactivation of antitumor immunity via targeting the molecular immune checkpoints generated promising therapeutic outcomes in several types of hard-to-treat cancers. The year 2017 witnessed the first US Food and Drug Administration (FDA) approval of immune checkpoint inhibitor (ICI) immunotherapy for the management of CRC. The approval was granted to pembrolizumab (anti-PD-1) for the treatment of patients with advanced/metastatic solid malignancies with mismatch-repair deficiency including CRCs. Such natively immunogenic tumors constitute only a minor percentage of all CRCs. Therefore, it is imperative to utilize novel combinatorial regimens to enhance the response of a wider range of CRC tumors to cancer immunotherapy and help in extending the survival rates in patients with advanced/metastatic disease. This review highlights the novel approaches under clinical development to overcome the resistance of CRCs to immunotherapy and improve the therapeutic outcomes.

Involvement of ER stress and reactive oxygen species generation in anti-cancer effect of CKD-516 for lung cancer

PURPOSE

CKD-516 (Valecobulin), a vascular-disrupting agent, inhibits microtubule elongation. We evaluated the effect of CKD-516 on lung cancer cells and the underlying molecular mechanisms.

METHODS

The effects of S516, an active metabolite of CKD-516, were evaluated in HUVECs and three lung cancer cell lines and by a microtubule polymerization assay. Tubulin cross-linking was used to identify the binding site of S516 on tubulin, and Western blotting was performed to identify the intracellular pathways leading to cell death. Subcutaneous lung cancer xenograft models were used to assess the in vivo effect of CKD-516 on tumor growth.

RESULTS

S516 targeted the colchicine binding site on β-tubulin. In lung cancer cells, S516 increased endoplasmic reticulum (ER) stress and induced reactive oxygen species (ROS) generation by mitochondria and the ER. In addition, CKD-516 monotherapy strongly inhibited the growth of lung cancer xenograft tumors and exerted a synergistic effect with carboplatin.

CONCLUSION

The findings suggest that CKD-516 exerts an anticancer effect in company with inducing ER stress and ROS production via microtubule disruption in lung cancer cells. CKD-516 may thus have therapeutic potential for lung cancer.

Application of triazoles as bioisosteres and linkers in the development of microtubule targeting agents

The triazole ring system has emerged as an exciting prospect in the optimization studies of promising lead molecules in the quest for new drugs for clinical usage. Several marketed drugs possess these versatile moieties that are used in a wide range of medical indications. This stems from the unique intrinsic properties of triazoles, which impart stability to the basic pharmacophoric unit with an added advantage of being a bioisostere of different chemical functionalities. In the last decade, the use of triazoles as bioisosteres and linkers in the development of microtubule targeting agents has been extensively investigated. The present review highlights the advances in this promising area of drug discovery and development.

Combretastatin-Inspired Heterocycles as Antitubulin Anticancer Agents

Combretastatin (CA-4) and its analogues are undergoing several clinical trials for treating different types of tumors. In this work, the antiproliferative activity of a series of 2-aminoimidazole-carbonyl analogs of clinically relevant combretastatins A-4 (CA-4) and A-1 was evaluated using a cell-based assay. Among the compounds tested, C-13 and C-21 displayed strong antiproliferative activities against HeLa cells. C-13 inhibited the proliferation of lung carcinoma (A549) cells more potently than combretastatin A-4. C-13 also retarded the migration of A549 cells. Interestingly, C-13 displayed much stronger antiproliferative effects against breast carcinoma and skin melanoma cells compared to noncancerous breast epithelial and skin fibroblast cells. C-13 strongly disassembled cellular microtubules, perturbed the localization of EB1 protein, inhibited mitosis in cultured cells, and bound to tubulin at the colchicine site and inhibited the polymerization of reconstituted microtubules in vitro. C-13 treatment increased the level of reactive oxygen species and induced apoptosis via poly(ADP-ribose) polymerase-cleavage in HeLa cells. The results revealed the importance of the 2-aminoimidazole-carbonyl motif as a double bond replacement in combretastatin and indicated a pharmacodynamically interesting pattern of H-bond acceptors/donors and requisite syn-templated aryls.

Recent advances in trimethoxyphenyl (TMP) based tubulin inhibitors targeting the colchicine binding site

Microtubules (composed of α- and β-tubulin heterodimers) play a pivotal role in mitosis and cell division, and are regarded as an excellent target for chemotherapeutic agents to treat cancer. There are four unique binding sites in tubulin to which taxanes, vinca alkaloids, laulimalide and colchicine bind respectively. While several tubulin inhibitors that bind to the taxane or vinca alkaloid binding sites have been approved by FDA, currently there are no FDA approved tubulin inhibitors targeting the colchicine binding site. Tubulin inhibitors that bind to the colchicine binding site have therapeutic advantages over taxanes and vinca alkaloids, for example, they can be administered orally, have less drug-drug interaction potential, and are less prone to develop multi-drug resistance. Typically, tubulin inhibitors that bind to the colchicine binding site bear the trimethoxyphenyl (TMP) moiety which is essential for interaction with tubulin. Over the last decade, a variety of molecules bearing the TMP moiety have been designed and synthesized as tubulin inhibitors for cancer treatment. In this review, we focus on the TMP analogs that are designed based on CA-4, indole, chalcone, colchicine and natural product scaffolds which are known to interact with the colchicine binding site in tubulin. The challenges and future direction of the TMP based tubulin inhibitors are also discussed in detail.

Enhanced efficacy of radiofrequency ablation for hepatocellular carcinoma using a novel vascular disrupting agent, CKD-516

BACKGROUND

CKD-516 is a novel vascular disrupting agent that shuts down intratumoral blood flow. We therefore hypothesized that concomitant administration of CKD-516 would enhance the therapeutic efficacy of radiofrequency ablation (RFA) by reducing heat sink effects. We assessed the effects of the combination of CKD-516 and RFA in a rat orthotopic hepatocellular carcinoma (HCC) model.

METHODS

Rat HCC cells (N1-S1) were engrafted into the hepatic lobe of Sprague-Dawley (SD) rats. Mice were randomly divided into two groups: RFA-only and CKD-RFA. In the CKD-RFA group, CKD-516 was administered by intraperitoneal injection 2 h before RFA. Ablation zone size was measured on triphenyltetrazolium chloride-stained specimens. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to evaluate the area of apoptosis/necrosis in the ablation zone. Immunohistochemistry with anti-CD31 antibody was performed to evaluate the effect of CKD-516 on tumor vessels.

RESULTS

Ablation zone size was significantly larger in the CKD-RFA group than in the RFA-only group (243.10 ± 74.39 versus 123.30 ± 28.17 mm², p < 0.001). On TUNEL staining, the area of apoptosis/necrosis was also significantly larger in the CKD-RFA group than in the RFA-only group (274.44 ± 140.78 versus 143.74 ± 90.13 mm²; p = 0.006). Immunohistochemistry with anti-CD31 antibody revealed patent tumor vessels in the RFA-only group, while collapsed vessels were seen in the CKD-RFA group, indicating a vascular shutdown effect of CKD-516.

CONCLUSION

Concomitant administration of CKD-516 during RFA can increase the ablation zone of tumors due to its vascular disrupting effect.

Current Advances of Tubulin Inhibitors in Nanoparticle Drug Delivery and Vascular Disruption/Angiogenesis

Extensive research over the last decade has resulted in a number of highly potent tubulin polymerization inhibitors acting either as microtubule stabilizing agents (MSAs) or microtubule destabilizing agents (MDAs). These inhibitors have potent cytotoxicity against a broad spectrum of human tumor cell lines. In addition to cytotoxicity, a number of these tubulin inhibitors have exhibited abilities to inhibit formation of new blood vessels as well as disrupt existing blood vessels. Tubulin inhibitors as a vascular disrupting agents (VDAs), mainly from the MDA family, induce rapid tumor vessel occlusion and massive tumor necrosis. Thus, tubulin inhibitors have become increasingly popular in the field of tumor vasculature. However, their pharmaceutical application is halted by a number of limitations including poor solubility and toxicity. Thus, recently, there has been considerable interests in the nanoparticle drug delivery of tubulin inhibitors to circumvent those limitations. This article reviews recent advances in nanoparticle based drug delivery for tubulin inhibitors as well as their tumor vasculature disruption properties.

Dynamic Contrast-Enhanced MRI Using a Macromolecular MR Contrast Agent (P792): Evaluation of Antivascular Drug Effect in a Rabbit VX2 Liver Tumor Model

Objective

To evaluate the utility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using macromolecular contrast agent (P792) for assessment of vascular disrupting drug effect in rabbit VX2 liver tumor models.

Materials and Methods

This study was approved by our Institutional Animal Care and Use Committee. DCE-MRI was performed with 3-T scanner in 13 VX2 liver tumor-bearing rabbits, before, 4 hours after, and 24 hours after administration of vascular disrupting agent (VDA), using gadomelitol (P792, n = 7) or low molecular weight contrast agent (gadoterate meglumine [Gd-DOTA], n = 6). P792 was injected at a of dose 0.05 mmol/kg, while that of Gd-DOTA was 0.2 mmol/kg. DCE-MRI parameters including volume transfer coefficient (K^trans) and initial area under the gadolinium concentration-time curve until 60 seconds (iAUC) of tumors were compared between the 2 groups at each time point. DCE-MRI parameters were correlated with tumor histopathology. Reproducibility in measurement of DCE-MRI parameters and image quality of source MR were compared between groups.

Results

P792 group showed a more prominent decrease in K^trans and iAUC at 4 hours and 24 hours, as compared to the Gd-DOTA group. Changes in DCE-MRI parameters showed a weak correlation with histologic parameters (necrotic fraction and microvessel density) in both groups. Reproducibility of DCE-MRI parameters and overall image quality was not significantly better in the P792 group, as compared to the Gd-DOTA group.

Conclusion

Dynamic contrast-enhanced magnetic resonance imaging using a macromolecular contrast agent shows changes of hepatic perfusion more clearly after administration of the VDA. Gadolinium was required at smaller doses than a low molecular contrast agent.

Discovery of a potent microtubule-targeting agent: Synthesis and biological evaluation of water-soluble amino acid prodrug of combretastatin A-4 derivatives

Amino acid prodrugs are known to be very useful for improving the aqueous solubility of sparingly water soluble drugs (Drug Discovery Today 2013, 18, 93). Therefore, we synthesized eleven novel combretastatin A-4 amino acid derivatives and evaluated their anti-tumor activities in vitro and in vivo. Among them, compound 15 (valine attached to compound 3, which was shown to be a potent tubulin polymerization inhibitor in our previous study) exhibited high efficacy in tumor-bearing mice, and pharmacokinetic analysis in rats indicated that compound 15 was an effective prodrug as well. Besides, compound 15 significantly inhibited tubulin polymerization in vitro and in vivo by binding to the colchicine binding site. In addition, compound 15 induced cell cycle arrest in the G2/M phase and triggered apoptosis in a caspase-dependent manner. In conclusion, our study showed that compound 15 could have significant anti-tumor activity as a novel microtubule polymerization disrupting agent with improved aqueous solubility.

Phase I Study of CKD-516, a Novel Vascular Disrupting Agent, in Patients with Advanced Solid Tumors

PURPOSE

CKD-516 is a newly developed vascular disrupting agent. This phase I dose-escalation study of CKD-516 was conducted to determine maximum-tolerated dose (MTD), safety, pharmacokinetics, and preliminary antitumor efficacy in patients with advanced solid tumors.

MATERIALS AND METHODS

Patients received CKD-516 intravenously on D1 and D8 every 3 weeks, in a standard 3+3 design. Safety was evaluated by National Cancer Institute Common Terminology Criteria for Adverse Events ver. 4.02 and response was assessed by Response Evaluation Criteria in Solid Tumor ver. 1.1.

RESULTS

Twenty-three patients were treated with CKD-516 at seven dosing levels: 1 mg/m(2)/day (n=3), 2 mg/m(2)/day (n=3), 3.3 mg/m(2)/day (n=3), 5 mg/m(2)/day (n=3), 7 mg/m(2)/day (n=3), 9 mg/m(2)/day (n=6), and 12 mg/m(2)/day (n=2). Mean age was 54 and 56.5% of patients were male. Two dose-limiting toxicities, which were both grade 3 hypertension, were observed in two patients at 12 mg/m(2)/day. The MTD was determined as 12 mg/m(2)/day. Most common adverse events were gastrointestinal adverse events (diarrhea, 34.8% [30.4% grade 1/2, 13.0% grade 3]; nausea, 21.7% [all grade 1/2]; vomiting, 21.7% [all grade 1/2]), myalgia (17.4%, all grade 1/2), and abdominal pain (21.7% [21.7% grade 1/2, 4.3% grade 3]). The pharmacokinetic study showed the dose-linearity of all dosing levels. Among 23 patients, six patients (26.1%) showed stable disease. Median progression-free survival was 39 days (95% confidence interval, 37 to 41 days).

CONCLUSION

This study demonstrates feasibility of CKD-516, novel vascular disrupting agent, in patients with advanced solid tumor. MTD of CKD-516 was defined as 12 mg/m(2)/day on D1 and D8 every 3 weeks.

Early quantification of the therapeutic efficacy of the vascular disrupting agent, CKD-516, using dynamic contrast-enhanced ultrasonography in rabbit VX2 liver tumors

Purpose:

To evaluate the usefulness of dynamic contrast-enhanced ultrasonography (DCE-US) in the early quantification of hemodynamic change following administration of the vascular disrupting agent (VDA) CKD-516 using a rabbit VX2 liver tumor model.

Methods:

This study was approved by our institutional animal care and use committee. Eight VX2 liver-tumor-bearing rabbits were treated with intravenous CKD-516, and all underwent DCE-US using SonoVue before and again 2, 4, 6, and 24 hours following their treatment. The tumor perfusion parameters were obtained from the time-intensity curve of the DCE-US data. Repeated measures analysis of variance was performed to assess any significant change in tumor perfusion over time. Relative changes in the DCE-US parameters between the baseline and follow-up assessments were correlated with the relative changes in tumor size over the course of seven days using Pearson correlation.

Results:

CKD-516 treatment resulted in significant changes in the DCE-US parameters, including the peak intensity, total area under the time-intensity curve (AUC_total), and AUC during wash-out (AUC_out) over time (P<0.05). Pairwise comparison tests revealed that the AUC_total and AUC during wash-in (AUC_in) seen on the two-hour follow-up were significantly lower than the baseline values (P<0.05). However, none of early changes in the DCE-US parameters until 24-hour follow-up showed a significant correlation with the relative changes in tumor size during seven days after CKD-516 treatment.

Conclusion:

Our results suggest that a novel VDA (CKD-516) can cause disruption of tumor perfusion as early as two hours after treatment and that the therapeutic effect of CKD-516 treatment can be effectively quantified using DCE-US.

Vascular disrupting effect of CKD-516: preclinical study using DCE-MRI

Vascular disrupting agents (VDAs) are new class of anti-cancer drugs targeting pre-existing tumor vasculature which lead to tumor ischemia and necrosis. An innovative tubulin polymerization inhibitor, CKD-516, was recently developed as a VDA. We attempted to evaluate its tubulin destabilizing effect using immunofluorescence staining on human endothelial cells (HUVECs) and to ascertain its antivascular effect in a rabbit VX2 tumor model using dynamic contrast-enhanced (DCE) MRI by measuring the changes in kinetic parameters such as K-trans and IAUGC. Immunofluorescence staining using anti-tubulin and anti-actin antibodies on HUVECs showed that CKD-516 selectively disrupted tubulin component of the endothelial cytoskeleton. Serial DCE-MRI showed a significant decrease in K-trans and IAUGC parameters from baseline at 4 h (39.9 % in K-trans; -45.0 % in IAUGC) and at 24 h (-32.2 % in K-trans; -36.5 % in IAUGC), and a significant recovery at 48 h (22.9 % in K-trans; 34.8 % in IAUGC) following administration of CKD-516 at a 0.7-mg/kg dose. When the tumors were stratified according to the initial K-trans value of 0.1, tumors with a high K-trans > 0.1 which was indicative of having well-developed pre-existing vessels, showed greater reduction in K-trans and IAUGC values. On histologic examination, the degree of necrosis of treated tumors was significantly greater than that of untreated tumors. In summary, CKD-516 is an effective VDA which results in rapid vascular shutdown by targeting the tubulin component of tumor vessels and thus leads to necrosis.

Free-breathing dynamic contrast-enhanced MRI of the abdomen and chest using a radial gradient echo sequence with K-space weighted image contrast (KWIC)

OBJECTIVES

To evaluate the feasibility of free-breathing, dynamic contrast-enhanced (DCE) MRI of the abdomen and thorax using the radial-gradient-echo sequence with k-space weighted image contrast (KWIC) reconstruction.

METHODS

Institutional review board approval was obtained. Fourteen patients underwent free-breathing radial DCE-MRI. Radial MRI yielded full-frame images by gridding all k-space data and time-resolved subframe images by using KWIC reconstruction technique. Using subframe KWIC images, voxel-wise perfusion maps were created. For comparison, the breath-hold conventional Cartesian 3D-gradient-echo sequence (VIBE) was also performed during the equilibrium phase. The image qualities of radial and conventional VIBE images were compared quantitatively and qualitatively.

RESULTS

Radial DCE-MRI provided high spatial resolution (1.4 × 1.4 mm) and temporal resolution (4.1 s for subframe images) allowing voxel-wise perfusion mapping with negligible motion or streaking artefacts. There were no significant differences in SNR between full-frame radial images and conventional VIBE images (79.08 vs 74.80, P > 0.05). Overall image quality score of full-frame radial images was slightly lower than that of conventional VIBE images (3.88 ± 0.59 vs. 4.31 ± 0.97, P < 0.05), but provided clinically useful images.

CONCLUSIONS

The free-breathing radial DCE-MRI can provide high spatial and temporal resolution while maintaining reasonably high image quality and thus is a feasible technique for DCE-MRI in the abdomen and thorax.

KEY POINTS

• Dynamic contrast-enhanced magnetic resonance imaging (DCE) MRI is important in oncological imaging • Radial MRI with k-space weighted image contrast (KWIC) reconstruction offers potential improvements • Radial DCE-MRI provides good image quality, reduced artefacts and high spatial/temporal resolution.

A perspective on vascular disrupting agents that interact with tubulin: preclinical tumor imaging and biological assessment

The tumor microenvironment provides a rich source of potential targets for selective therapeutic intervention with properly designed anticancer agents. Significant physiological differences exist between the microvessels that nourish tumors and those that supply healthy tissue. Selective drug-mediated damage of these tortuous and chaotic microvessels starves a tumor of necessary nutrients and oxygen and eventually leads to massive tumor necrosis. Vascular targeting strategies in oncology are divided into two separate groups: angiogenesis inhibiting agents (AIAs) and vascular disrupting agents (VDAs). The mechanisms of action between these two classes of compounds are profoundly distinct. The AIAs inhibit the actual formation of new vessels, while the VDAs damage and/or destroy existing tumor vasculature. One subset of small-molecule VDAs functions by inhibiting the assembly of tubulin into microtubules, thus causing morphology changes to the endothelial cells lining the tumor vasculature, triggered by a cascade of cell signaling events. Ultimately this results in catastrophic damage to the vessels feeding the tumor. The rapid emergence and subsequent development of the VDA field over the past decade has led to the establishment of a synergistic combination of preclinical state-of-the-art tumor imaging and biological evaluation strategies that are often indicative of future clinical efficacy for a given VDA. This review focuses on an integration of the appropriate biochemical and biological tools necessary to assess (preclinically) new small-molecule, tubulin active VDAs for their potential to be clinically effective anticancer agents.

The rationality for using prodrug approach in drug discovery programs for new xenobiotics: opportunities and challenges

The concept of prodrugs has been successfully executed for life cycle management options of several approved drugs and drugs in development. In addition to imparting ideal biopharmaceutical properties, such as solubility, permeability and lipophilicity, some prodrug concepts have also enabled site-specific drug delivery, prolonged the duration of therapeutic effect and improved therapeutic index. The strategic inclusion of prodrug concept during drug discovery and early development process brings in some unique challenges. The communication provides balanced perspectives on the rational use and challenges of prodrug concept during the drug discovery and development process.