Phase I and pharmacokinetic study of karenitecin in patients with recurrent malignant gliomas

Natural product inspired leads in the discovery of anticancer agents: an update

Natural products have emerged as major leads for the discovery and development of new anti-cancer drugs. The plant-derived anti-cancer drugs account for approximately 60% and the quest for new anti-cancer agents is in progress. Anti-cancer leads have been isolated from plants, animals, marine organisms, and microorganisms from time immemorial. The process of semisynthetic modifications of the parent lead has led to the generation of new anti-cancer agents with improved therapeutic efficacy and minimal side effects. The various chemo-informatics tools, bioinformatics, high-throughput screening, and combinatorial synthesis are able to deliver the new natural product lead molecules. Plant-derived anticancer agents in either late preclinical development or early clinical trials include taxol, vincristine, vinblastine, topotecan, irinotecan, etoposide, paclitaxel, and docetaxel. Similarly, anti-cancer agents from microbial sources include dactinomycin, bleomycin, mitomycin C, and doxorubicin. In this review, we highlighted the importance of natural products leads in the discovery and development of novel anti-cancer agents. The semisynthetic modifications of the parent lead to the new anti-cancer agent are also presented. Further, the leads in the preclinical settings with the potential to become effective anticancer agents are also reviewed.Communicated by Ramaswamy H. Sarma.

New Visions on Natural Products and Cancer Therapy: Autophagy and Related Regulatory Pathways

Macroautophagy (autophagy) has been a highly conserved process throughout evolution and allows cells to degrade aggregated/misfolded proteins, dysfunctional or superfluous organelles and damaged macromolecules, in order to recycle them for biosynthetic and/or energetic purposes to preserve cellular homeostasis and health. Changes in autophagy are indeed correlated with several pathological disorders such as neurodegenerative and cardiovascular diseases, infections, cancer and inflammatory diseases. Conversely, autophagy controls both apoptosis and the unfolded protein response (UPR) in the cells. Therefore, any changes in the autophagy pathway will affect both the UPR and apoptosis. Recent evidence has shown that several natural products can modulate (induce or inhibit) the autophagy pathway. Natural products may target different regulatory components of the autophagy pathway, including specific kinases or phosphatases. In this review, we evaluated ~100 natural compounds and plant species and their impact on different types of cancers via the autophagy pathway. We also discuss the impact of these compounds on the UPR and apoptosis via the autophagy pathway. A multitude of preclinical findings have shown the function of botanicals in regulating cell autophagy and its potential impact on cancer therapy; however, the number of related clinical trials to date remains low. In this regard, further pre-clinical and clinical studies are warranted to better clarify the utility of natural compounds and their modulatory effects on autophagy, as fine-tuning of autophagy could be translated into therapeutic applications for several cancers.

Molecular Engineering of Curcumin, an Active Constituent of Curcuma longa L. (Turmeric) of the Family Zingiberaceae with Improved Antiproliferative Activity

Cancer is the world’s second leading cause of death, accounting for nearly 10 million deaths and 19.3 million new cases in 2020. Curcumin analogs are gaining popularity as anticancer agents currently. We reported herein the isolation, molecular engineering, molecular docking, antiproliferative, and anti-epidermal growth factor receptor (anti-EGFR) activities of curcumin analogs. Three curcumin analogs were prepared and docked against the epidermal growth factor receptor (EGFR), revealing efficient binding. Antiproliferative activity against 60 NCI cancer cell lines was assessed using National Cancer Institute (NCI US) protocols. The compound 3b,c demonstrated promising antiproliferative activity in single dose (at 10 µM) as well as five dose (0.01, 0.10, 1.00, 10, and 100 µM). Compound 3c inhibited leukemia cancer panel better than other cancer panels with growth inhibition of 50% (GI₅₀) values ranging from 1.48 to 2.73 µM, and the most promising inhibition with GI₅₀ of 1.25 µM was observed against leukemia cell line SR, while the least inhibition was found against non-small lung cancer cell line NCI-H226 with GI₅₀ value of 7.29 µM. Compounds 3b,c demonstrated superior antiproliferative activity than curcumin and gefitinib. In molecular docking, compound 3c had the most significant interaction with four H-bonds and three π–π stacking, and compound 3c was found to moderately inhibit EGFR. The curcumin analogs discovered in this study have the potential to accelerate the anticancer drug discovery program.

Is more better? An analysis of toxicity and response outcomes from dose-finding clinical trials in cancer

BACKGROUND

The overwhelming majority of dose-escalation clinical trials use methods that seek a maximum tolerable dose, including rule-based methods like the 3+3, and model-based methods like CRM and EWOC. These methods assume that the incidences of efficacy and toxicity always increase as dose is increased. This assumption is widely accepted with cytotoxic therapies. In recent decades, however, the search for novel cancer treatments has broadened, increasingly focusing on inhibitors and antibodies. The rationale that higher doses are always associated with superior efficacy is less clear for these types of therapies.

METHODS

We extracted dose-level efficacy and toxicity outcomes from 115 manuscripts reporting dose-finding clinical trials in cancer between 2008 and 2014. We analysed the outcomes from each manuscript using flexible non-linear regression models to investigate the evidence supporting the monotonic efficacy and toxicity assumptions.

RESULTS

We found that the monotonic toxicity assumption was well-supported across most treatment classes and disease areas. In contrast, we found very little evidence supporting the monotonic efficacy assumption.

CONCLUSIONS

Our conclusion is that dose-escalation trials routinely use methods whose assumptions are violated by the outcomes observed. As a consequence, dose-finding trials risk recommending unjustifiably high doses that may be harmful to patients. We recommend that trialists consider experimental designs that allow toxicity and efficacy outcomes to jointly determine the doses given to patients and recommended for further study.

Population pharmacokinetic analysis of AR-67, a lactone stable camptothecin analogue, in cancer patients with solid tumors

Background AR-67 is a novel camptothecin analogue at early stages of drug development. The phase 1 clinical trial in cancer patients with solid tumors was completed and a population pharmacokinetic model (POP PK) was developed to facilitate further development of this investigational agent. Methods Pharmacokinetic data collected in the phase 1 clinical trial were utilized for the development of a population POP PK by implementing the non-linear mixed effects approach. Patient characteristics at study entry were evaluated as covariates in the model. Subjects (N = 26) were treated at nine dosage levels (1.2-12.4 mg/m²/day) on a daily × 5 schedule. Hematological toxicity data were modeled against exposure metrics. Results A two-compartment POP PK model best described the disposition of AR-67 by fitting a total of 328 PK observations from 25 subjects. Following covariate model selection, age remained as a significant covariate on central volume. The final model provided a good fit for the concentration versus time data and PK parameters were estimated with good precision. Clearance, inter-compartmental clearance, central volume and peripheral volume were estimated to be 32.2 L/h, 28.6 L/h, 6.83 L and 25.0 L, respectively. Finally, exposure-pharmacodynamic analysis using E_max models showed that plasma drug concentration versus time profiles are better predictors of AR-67-related hematologic toxicity were better predictors of leukopenia and thrombocytopenia, as compared to total dose. Conclusions A POP PK model was developed to characterize AR-67 pharmacokinetics and identified age as a significant covariate. Exposure PK metrics C_max and AUC were shown to predict hematological toxicity. Further efforts to identify clinically relevant determinants of AR-67 disposition and effects in a larger patient population are warranted.

Topoisomerase 1B poisons: Over a half-century of drug leads, clinical candidates, and serendipitous discoveries

Topoisomerases are DNA processing enzymes that relieve supercoiling (torsional strain) in DNA, are necessary for normal cellular division, and act by nicking (and then religating) DNA strands. Type 1B topoisomerase (Top1) is overexpressed in certain tumors, and the enzyme has been extensively investigated as a target for cancer chemotherapy. Various chemical agents can act as "poisons" of the enzyme's religation step, leading to Top1-DNA lesions, DNA breakage, and eventual cellular death. In this review, agents that poison Top1 (and have thus been investigated for their anticancer properties) are surveyed, including natural products (such as camptothecins and indolocarbazoles), semisynthetic camptothecin and luotonin derivatives, and synthetic compounds (such as benzonaphthyridines, aromathecins, and indenoisoquinolines), as well as targeted therapies and conjugates. Top1 has also been investigated as a therapeutic target in certain viral and parasitic infections, as well as autoimmune, inflammatory, and neurological disorders, and a summary of literature describing alternative indications is also provided. This review should provide both a reference for the medicinal chemist and potentially offer clues to aid in the development of new Top1 poisons.

Silicon-containing analogs of camptothecin as anticancer agents

The plant pentacyclic alkaloid camptothecin and its structural analogs were extensively studied. These compounds are interesting due to the antitumor activity associated with their ability to inhibit topoisomerase I in tumor cells. During the last decades of the 20th century, a large number of the silicon-containing camptothecins (silatecans) were synthesized. 7-tert-Butyldimethylsilyl-10-hydroxy-camptothecin (DB-67 or AR-67) has enhanced lipophilicity and demonstrates a antitumor activity superior to its carbon analog. To date, certain silatecans are under clinical trials and their ultimate role in cancer therapy appears promising. In this review, we present chemical methodologies for the synthesis of silicon-containing camptothecins, their chemical properties, biological activity, and results of clinical trials.

Camptothecin (CPT) and its derivatives are known to target topoisomerase I (Top1) as their mechanism of action: did we miss something in CPT analogue molecular targets for treating human disease such as cancer?

Camptothecin (CPT) was discovered from plant extracts more than 60 years ago. Since then, only two CPT analogues (irinotecan and topotecan) have been approved for cancer treatment, although several thousand CPT derivatives have been synthesized and many of them were actively studied in our research community over the past 6+ decades. In this review article, we briefly summarize: (1) the discovery and early development of CPTs, (2) the recognized CPT mechanism of action (MOA), (3) the synthesis of CPT and CPT analogues, and (4) the structure-activity relationship (SAR) of CPT and its analogues. Next, we provide evidence that certain CPT analogues can exert improved efficacy with low toxicity independently of topoisomerase I (Top1) inhibition; instead, these CPT analogues use novel MOAs by targeting important cancer survival-associated oncogenic proteins and/or by bypassing various treatment-resistant mechanisms. We then present a comprehensive review of the most advanced CPT analogues in clinical development, with the goal of resolving why no new CPTs have been FDA approved for cancer treatment, beyond irinotecan and topotecan. We argue that new CPT Top1 inhibitor drugs are unlikely being found to be significantly better than irinotecan and/or topotecan in terms of the overall antitumor activity and toxicity. The significance of CPT analogues that possess novel MOAs has not been sufficiently recognized so far. In our opinion, this is a research area with great potential to make a breakthrough for development of the next generation of CPT analogues that possess high efficacy (due to novel targets) and low toxicity (due to low inhibition of Top1 activity/function) for effective treatment of human disease, including cancer.

Dose-finding designs for trials of molecularly targeted agents and immunotherapies

Recently, there has been a surge of early phase trials of molecularly targeted agents (MTAs) and immunotherapies. These new therapies have different toxicity profiles compared to cytotoxic therapies. MTAs can benefit from new trial designs that allow inclusion of low-grade toxicities, late-onset toxicities, addition of an efficacy endpoint, and flexibility in the specification of a target toxicity probability. To study the degree of adoption of these methods, we conducted a Web of Science search of articles published between 2008 and 2014 that describe phase 1 oncology trials. Trials were categorized based on the dose-finding design used and the type of drug studied. Out of 1,712 dose-finding trials that met our criteria, 1,591 (92.9%) utilized a rule-based design, and 92 (5.4%; range 2.3% in 2009 to 9.7% in 2014) utilized a model-based or novel design. Over half of the trials tested an MTA or immunotherapy. Among the MTA and immunotherapy trials, 5.8% used model-based methods, compared to 3.9% and 8.3% of the chemotherapy or radiotherapy trials, respectively. While the percentage of trials using novel dose-finding designs has tripled since 2007, the adoption of these designs continues to remain low.

Karenitecin (bnp1350) and flavopridol as radiosensitizers in malignant glioma

The poor prognosis of malignant glioma patients highlights the need to develop low toxicity, tumor specific agents with the ability to synergize with proven efficacious treatment modalities, e.g., ionizing irradiation. This paper investigates the potential of BNP1350 (karenitecin), a topoisomerase I-targeting anticancer agent, and flavopridol a cyclin-dependent kinase inhibitor as radiosensitizers at clinically relevant doses in glioblastoma cell lines. A clonogenic survival and apoptosis assays were performed to test the effect of karenitecin (0.1 nM to 10 nM), flavopridol, (50 nM to 500 nM), radiation (1 Gy to 5.5 Gy) and a combination of radiation and karenitecin or radiation and flavopridol on the glioma cell lines T986 and M059K. Cells were stained for cyclins B and D using antibodies followed by flow cytometry. Propidium Iodide staining was used to reveal the various phases of the cell cycle; cyclin staining in the G0/G1 and G2/M phase of the cell cycle was estimated as the Mean Fluorescence Intensity (MFI) after subtracting the MFI recorded by the isotype controls. Results demonstrated that in irradiated cells, pretreatment with karenitecin induced apoptosis, a transient arrest in the G2/M phase of the cell cycle and increased the expression of cyclin B1. Flavopridol treatment also induced apoptosis and a transient block in the G2/M phase of the cell cycle. The combined effects of karenitecin and flavopridol displayed synergistic effects. The unique radiosensitizing activity of orally administrable karenitecin and flavopridol is consistent with continued investigation of these compounds preclinically, as well as in the clinical setting.

Phase I study of iniparib concurrent with monthly or continuous temozolomide dosing schedules in patients with newly diagnosed malignant gliomas

Iniparib is a prodrug that converts to highly reactive cytotoxic metabolites intracellularly with activity in preclinical glioma models. We investigated the maximum tolerated dose (MTD) of iniparib with monthly (m) and continuous (c) temozolomide (TMZ) dosing schedules in patients with malignant gliomas (MG). Adults with newly diagnosed MG who had successfully completed ≥80% of radiation (RT) and TMZ without toxicity received mTMZ dosing (150-200 mg/m(2) days 1-5/28 days) or cTMZ dosing (75 mg/m(2)/days × 6 weeks) in conjunction with iniparib (i.v. 2 days/week) in the adjuvant setting. Iniparib was dose escalated using a modified continual reassessment method (mCRM). 43 patients (32 male; 34 GBM, 8 AA, 1 gliosarcoma; median age 54 years; median KPS 90) were enrolled across 4 dose levels. In the mTMZ group, 2/4 patients had dose limiting toxicities (DLT) at 19 mg/kg/week (rash/hypersensitivity). At 17.2 mg/kg/week, 1/9 patients had a DLT (grade 3 fatigue). Additional grade 3 toxicities were neutropenia, lymphopenia, and nausea. In the cTMZ group, one DLT (thromboembolic event) occurred at 10.2 mg/kg/week. Dose escalation stopped at 16 mg/kg/week based on mCRM. The mean maximum plasma concentration of iniparib increased with dose. Concentration of the two major circulating metabolites, 4-iodo-3-aminobenzamide and 4-iodo-3-aminobenzoic acid, was ≤5% of the corresponding iniparib concentration. Iniparib is well tolerated, at doses higher than previously investigated, in combination with TMZ after completion of RT + TMZ in patients with MG. Recommended phase 2 dosing of iniparib based on mCRM is 17.2 mg/kg/week with mTMZ and 16 mg/kg/week with cTMZ. An efficacy study of TMZ/RT + iniparib followed by TMZ + iniparib in newly diagnosed GBM using these doses has completed enrollment. Survival assessment is ongoing.

Evaluation of the Safety and Benefit of Phase I Oncology Trials for Patients With Primary CNS Tumors

PURPOSE

Patients with high-grade gliomas (HGG) are frequently excluded from first-in-human solid tumor trials because of perceived poor prognosis, excessive toxicities, concomitant drug interactions, and poor efficacy. We conducted an analysis of outcomes from select, single-agent phase I studies in patients with HGG. We compared outcomes to pooled analysis of published studies in solid tumors with various molecular and cytotoxic drugs evaluated as single agents or as combinations.

PATIENT AND METHODS

Individual records of patients with recurrent HGG enrolled onto Adult Brain Tumor Consortium trials of single-agent, cytotoxic or molecular agents from 2000 to 2008 were analyzed for baseline characteristics, toxicities, responses, and survival.

RESULTS

Our analysis included 327 patients with advanced, refractory HGG who were enrolled onto eight trials involving targeted molecular (n=5) and cytotoxic (n=3) therapies. At enrollment, patients had a median Karnofsky performance score of 90 and median age of 52 years; 62% were men, 63% had glioblastoma, and the median number of prior systemic chemotherapies was one. Baseline laboratory values were in an acceptable range to meet eligibility criteria. Patients were on the study for a median of two cycles (range, <one to 56 cycles), and 96% were evaluable for primary end points. During cycle 1, grade≥3 nonhematologic and grade≥4 hematologic toxicities were 5% (28 of 565 adverse events) and 0.9% (five of 565 adverse events), respectively, and 66% of these occurred at the highest dose level. There was one death attributed to drug. Overall response rate (complete and partial response) was 5.5%. Median progression-free and overall survival times were 1.8 and 6 months, respectively.

CONCLUSION

Patients with HGG who meet standard eligibility criteria may be good candidates for solid tumor phase I studies with single-agent molecular or cytotoxic drugs with favorable preclinical rationale and pharmacokinetic properties in this population.

Natural small-molecule enhancers of autophagy induce autophagic cell death in apoptosis-defective cells

Resistance of cancer cells to chemotherapy is a significant problem in oncology, and the development of sensitising agents or small-molecules with new mechanisms of action to kill these cells is needed. Autophagy is a cellular process responsible for the turnover of misfolded proteins or damaged organelles, and it also recycles nutrients to maintain energy levels for cell survival. In some apoptosis-resistant cancer cells, autophagy can also enhance the efficacy of anti-cancer drugs through autophagy-mediated mechanisms of cell death. Because the modulation of autophagic processes can be therapeutically useful to circumvent chemoresistance and enhance the effects of cancer treatment, the identification of novel autophagic enhancers for use in oncology is highly desirable. Many novel anti-cancer compounds have been isolated from natural products; therefore, we worked to discover natural, anti-cancer small-molecule enhancers of autophagy. Here, we have identified a group of natural alkaloid small-molecules that function as novel autophagic enhancers. These alkaloids, including liensinine, isoliensinine, dauricine and cepharanthine, stimulated AMPK-mTOR dependent induction of autophagy and autophagic cell death in a panel of apoptosis-resistant cells. Taken together, our work provides novel insights into the biological functions, mechanisms and potential therapeutic values of alkaloids for the induction of autophagy.

Adaptive dose-finding studies: a review of model-guided phase I clinical trials

PURPOSE

We provide a comprehensive review of adaptive phase I clinical trials in oncology that used a statistical model to guide dose escalation to identify the maximum-tolerated dose (MTD). We describe the clinical setting, practical implications, and safety of such applications, with the aim of understanding how these designs work in practice.

METHODS

We identified 53 phase I trials published between January 2003 and September 2013 that used the continual reassessment method (CRM), CRM using escalation with overdose control, or time-to-event CRM for late-onset toxicities. Study characteristics, design parameters, dose-limiting toxicity (DLT) definition, DLT rate, patient-dose allocation, overdose, underdose, sample size, and trial duration were abstracted from each study. In addition, we examined all studies in terms of safety, and we outlined the reasons why escalations occur and under what circumstances.

RESULTS

On average, trials accrued 25 to 35 patients over a 2-year period and tested five dose levels. The average DLT rate was 18%, which is lower than in previous reports, whereas all levels above the MTD had an average DLT rate of 36%. On average, 39% of patients were treated at the MTD, and 74% were treated at either the MTD or an adjacent level (one level above or below).

CONCLUSION

This review of completed phase I studies confirms the safety and generalizability of model-guided, adaptive dose-escalation designs, and it provides an approach for using, interpreting, and understanding such designs to guide dose escalation in phase I trials.

Protective role of humanin on bortezomib-induced bone growth impairment in anticancer treatment

BACKGROUND

Bortezomib is a proteasome inhibitor currently studied in clinical trials of childhood cancers. So far, no side effects on bone growth have been reported in treated children. However, bortezomib was recently found to induce apoptosis in growth plate chondrocytes and impair linear bone growth in treated mice. We hypothesize that [Gly(14)]-humanin (HNG), a 24-amino acid synthetic antiapoptotic peptide, can prevent bortezomib-induced bone growth impairment.

METHODS

Mice with human neuroblastoma or medulloblastoma tumor xenografts (9-13 animals/group) received one 2-week cycle (2 injections/week) of bortezomib (0.8 mg/kg or 1.0mg/kg), or HNG (1 µg/mouse), or the combination of HNG/bortezomib, or vehicle. Cultures of human growth plate cartilage, chondrogenic- and cancer cell lines, and immunohistochemistry for detection of proapoptotic proteins were also used. Statistical significance was evaluated by two-sided Mann-Whitney U test or by parametric or nonparametric analysis of variance.

RESULTS

Bortezomib efficiently blocked the proteasome and induced pronounced impairment of linear bone growth from day 0 to day 13 (0.09 mm/day, 95% confidence interval [CI] = 0.07 to 0.11 mm/day; vs 0.19 mm/day, 95% CI = 0.15 to 0.23 mm/day in vehicle; P < .001), an effect significantly prevented by the addition of HNG (0.15 mm growth/day, 95% CI = 0.14 to 0.16 mm/day; P < .001 vs bortezomib only; P = 0.03 vs vehicle). Bortezomib was highly toxic when added to cultures of human growth plate cartilage, with markedly increased apoptosis compared with control (P < .001). However, when combining with HNG, bortezomib-induced apoptosis was entirely prevented, as was Bax and PARP activation. Bortezomib delayed tumor growth, and HNG did not interfere with the anticancer effect when studied in human tumor xenografts or cell lines.

CONCLUSIONS

HNG prevents bortezomib-induced bone growth impairment without interfering with bortezomib's desired anticancer effects.

Preclinical and clinical activity of the topoisomerase I inhibitor, karenitecin, in melanoma

INTRODUCTION

This review covers the preclinical and clinical activity of the novel camptothecin analog, karenitecin, in melanoma.

AREAS COVERED

While the camptothecins are widely used antitumor agents that inhibit topoisomerase I, their utility is limited by instability, high interpatient variability and the development of drug resistance. Karenitecin was rationally designed to overcome these limitations. The authors review the data on karenitecin in preclinical models and in clinical trials in melanoma using studies published in Medline and reports presented at AACR and ASCO.

EXPERT OPINION

Karenitecin shows activity in melanoma, both as a single agent and in combination. In adverse prognostic factor melanoma, karenitecin showed prolonged disease stabilization in 34% of patients. Because preclinical studies suggested a synergistic interaction between karenitecin and HDAC inhibitors, a schedule-specific combination Phase I-II trial of valproic acid and karenitecin was carried out in heavily pretreated melanoma patients which showed a benefit rate in 47% patients with acceptable toxicity. The treatment for melanoma is in rapid transition and genomic profiling is now an integral part, and hence the optimal use of karenitecin in melanoma should be re-evaluated with regard to specific mutational status.

Phase 1 clinical trial of bortezomib in adults with recurrent malignant glioma

Bortezomib selectively binds and inhibits the 20S proteasome enzyme's active sites. This study was conducted to determine the side effects and maximum tolerated dose (MTD) of bortezomib in patients with recurrent malignant glioma. Separate dose escalations were conducted in patients taking or not taking enzyme-inducing anti-seizure drugs (+/-EIASD). The starting dose in both groups was 0.9 mg/m(2) intravenously twice weekly for the first three of each 4 week cycle. Imaging assessment of response was carried out and Plasma 20S proteasome activity inhibition and imaging was conducted to monitor efficacy. The 66 patients enrolled had a median age of 51 years, median KPS of 90%, and 77% had glioblastoma multiforme. The MTD in the -EIASD group was 1.70 mg/m(2) based on grade 3 thrombocytopenia, sensory neuropathy and fatigue. In the +EIASD group escalation was terminated at 2.5 mg/m(2) without meeting meet the MTD criteria. However, proteasome inhibition in this group did not change at doses above 1.90 mg/m(2) suggesting that further escalations would be unlikely to increase a biologic effect. Mean proteasome inhibition plateaued in +EIASD patients receiving 2.1 mg/m(2) of bortezomib at 77 ± 12% and in -EIASD patients treated with a dose of 1.7 mg/m(2) at 79 ± 6%. Two partial responses were observed. This study determined that EIASDs effect the MTD of bortezomib and the dose required for maximal inhibition of whole blood 20S proteasome. Some evidence of clinical activity was noted in this phase I study in patients with recurrent high grade gliomas.

Further studies toward the stereocontrolled synthesis of silicon-containing peptide mimics

Further studies are reported on the utilization of the versatile reaction between chiral sulfinimines and alkyldiphenylsilyl lithium reagents with the goal of preparing a wide range of silanediol-based protease inhibitors. In particular, focus has been placed to demonstrate how a number of genetically encoded amino acid side chains such as serine, threonine, tyrosine, lysine, proline, arginine, aspartate and asparagine might be incorporated into the overall approach. Efforts to apply this synthetic methodology for accessing biologically relevant silanediol dipeptide mimics are also described. This includes the synthesis of a potential inhibitor of the human neutrophil elastase, as well as a diphenylsilane mimic of a hexapeptide fragment of the human islet amyloid polypeptide.